Actuators doi: 10.3390/act15110592

Authors: Said Bencherifi Azzeddine Dekhane Mohamed Faouzi Rachedi Habib Benbouhenni Riyadh Bouddou Jun-Jiat Tiang

Artificial intelligence (AI)-based control is gaining increasing attention in electrical-machine drives as a means of approximating nonlinear control laws through data-driven learning. Neural behavioral cloning provides a practical framework for reproducing an existing analytical controller while retaining the established control architecture. However, neural controllers are typically selected according to supervised validation loss, despite the fact that its ability to predict closed-loop control performance remains unclear. This paper systematically investigates the relationship between supervised learning accuracy and closed-loop performance through neural behavioral cloning of an integral sliding-mode speed controller for a 2.2 kW field-oriented induction motor drive. A bias-free, odd-symmetric neural network is trained to approximate the analytical control law, while the integral state, state-update law, anti-windup mechanism, actuator saturation, execution sequence, and controller lifecycle are kept identical in the analytical and neural implementations, thereby isolating the effect of the learned approximation on closed-loop behavior. The controllers are evaluated under ten benchmark conditions comprising nominal operation, six individual parameter perturbations, and a combined worst-case condition, with the sliding-surface coefficient selected equal to the PI design bandwidth parameter. Across five trained networks, whose validation mean-squared errors span a factor of 2.4, supervised validation accuracy exhibits only a weak relationship with closed-loop performance. The largest ITAE variation among the five networks within any benchmark cell is 1.60% of the corresponding cell median, while the network with the highest validation error yields the lowest ITAE in nine of the ten benchmark cells. Nevertheless, all neural controllers closely reproduce the analytical controller and achieve a 39–68% reduction in ITAE relative to a conventional proportional–integral controller, with a median reduction of 49% across the ten benchmark cells. These results indicate that, within the investigated setting, supervised validation loss is not a reliable criterion for ranking behaviorally cloned controllers according to their closed-loop performance. The findings are limited to a single induction motor drive, one teacher controller, one network architecture (H = 16), and five trained networks representing two distinct validation-error groups; broader conclusions require systematic evaluation across architectures, teacher controllers, drive conditions, and training configurations.

Actuators doi: 10.3390/act15110591

Authors: Byron Ricardo Zapata Chancusig Jaime Rolando Heredia Velastegui Víctor Ruiz-Díez José Luis Sánchez-Rojas

This work presents the functional enhancement of a previously developed miniature robot actuated by 3D-printed piezoelectric resonators through the integration of environmental and spatial sensors and the experimental comparison of proportional-derivative (PD) and sliding mode control (SMC) strategies. The platform integrates an inertial measurement unit, a time-of-flight distance sensor, and a total volatile organic compound (TVOC) sensor, enabling the robot to execute a predefined route while acquiring environmental and spatial information. Two control strategies, PD and SMC, were experimentally compared using yaw-angle feedback and differential adjustment of the excitation frequencies. For a 0° reference, the PD and SMC controllers achieved mean absolute errors of 0.515° and 0.652°, respectively. During a transition from 0° to 90°, both controllers exhibited similar transient responses; however, during the return transition from 90° to 0°, only the PD controller successfully completed the rotation. In addition, the PD controller achieved a 12.27% higher linear velocity and a 5.44% higher counterclockwise angular velocity. The VL53L0X sensor exhibited a mean absolute error of 9 mm and a mean percentage error of 8.22%, while the SGP30 successfully detected an increase in TVOC during exposure to isopropyl alcohol, followed by a decrease during the dissipation phase.

Actuators doi: 10.3390/act15110590

Authors: Peng Hang Zihao Zhao Yiru Liu Jian Sun Xiaocong Zhao

Surrounding vehicles may misjudge an autonomous vehicle’s intended motion and yield or merge at the wrong time. These conflicts are difficult to test systematically when surrounding vehicles’ expectations cannot be varied separately from the autonomous vehicle’s planned motion. This paper proposes an intention-misjudgment-oriented background-traffic generator for autonomous-vehicle testing. A speed-intention perturbation mechanism separates the nominal speed plan of the vehicle under test (VUT) from the estimate supplied to surrounding vehicles, enabling controlled underestimation and overestimation. A Transformer-based interaction encoder relates the perturbed estimate to traffic context and 50-step guiding-lane references to generate context-dependent responses. Multimodal decoding represents alternative responses, while learned affine state updates couple their evolution to inter-vehicle interactions and VUT control inputs. In highway-merging simulations, the best-matching generated trajectories have lower average and endpoint position errors than those of the Mixtures of Affine Time-varying Systems (MATS) baseline trajectory-prediction model at all three comparison speeds. Across 2353 matched initial scenarios, underestimating the VUT’s future speed by 25% yields an observed collision rate of 11.3%, compared with 6.7% under accurate estimation. The generated cases illustrate conflicts associated with delayed lane changes and altered passing order. These results characterize controlled, simulator-based stress-test outcomes in the IDM–MOBIL highway-merging setting; they do not constitute empirical validation of human-driver responses to intention misjudgment.

Actuators doi: 10.3390/act15110589

Authors: Chuang Wu Chongjing Cao

Dielectric elastomer actuator (DEA)-driven capsule robots convert periodic excitations into net translation through passive constraints, yet a systematic study on optimal constraint design remains largely unexplored. To address this gap, we present a comparative numerical study of six passive constraint families that range from linear and bistable springs to limit stops and polynomial shapes and encompass 2447 configurations under a reference condition. The best configuration of each family spans more than an order of magnitude in speed, from 2.62 mm/s (linear spring) to 33.86 mm/s (asymmetric bistable). We find that the sign of the constraint-force derivative at the rest position separates every family with negative rest-position stiffness from every family with positive stiffness, whereas the second derivative (curvature) shows no correlation with speed. Building on this observation, we formulate a library-based inverse-design framework that treats velocity as a specification and minimizes the peak driving force. The comparisons reported here are made under one reference condition, and the ranking is therefore a property of the library as sampled rather than a general design rule. For example, relaxing the target velocity from 25 mm/s to 23 mm/s reduces the peak force from 0.31 N to 0.19 N. These results move passive-constraint design from empirical trial-and-error toward a requirement-driven methodology for future soft capsule robots.

Actuators doi: 10.3390/act15110588

Authors: Mingchao Geng Yanfeng Han Jinfeng Wang Jingjun Zhou Erwei Li

Traditional 3-RRS and 3-RPS mechanisms adopt open-chain limbs, where R, P, and S denote revolute, prismatic, and spherical joints, respectively. Although these mechanisms are widely used, they suffer from insufficient stiffness and accuracy under heavy-load and high-precision operating conditions. By contrast, existing configurations equipped with closed-loop sub-chains can offer improved stiffness yet suffer from complex structures. To address these issues, a novel closed-loop actuated 3-(RRRPR)S parallel mechanism is proposed. The configuration consists of a moving platform, a fixed platform, and three identical (RRRPR)S closed-loop actuated limbs. Each limb contains a closed-loop sub-chain composed of a planar five-bar mechanism (RRRPR), in which the prismatic joint P is the actuated joint. The design of the closed-loop actuated limb effectively shortens the transmission chain length of the limb, reduces the overall height of the mechanism, and improves its stiffness and dynamic characteristics. To address the complex constraint relationship imposed by the closed-loop sub-chain (RRRPR) on the moving platform, the equivalent motion screw theory is used to systematically analyze the rationality of the actuated joint selection, thereby ensuring the correctness of the configuration design. Through the analysis of the motion characteristics of the closed-loop sub-chain, the motion mapping relationship between the serial open-chain limb and the closed-loop actuated limb is established. By combining the influence coefficient theory with the Newton–Euler equations in screw form, the kinematic and dynamic models of the mechanism are established in a concise and compact form. A prototype of the 3-(RRRPR)S closed-loop actuated parallel mechanism was developed. Experimental results show that the mechanism can achieve continuous and stable motion under the tested motion groups, providing a practical basis for the engineering application of similar parallel mechanisms.

Actuators doi: 10.3390/act15110587

Authors: Young T. Choi Norman M. Wereley

This study presents analytical modeling and numerical simulation of a double-adjustable magnetorheological (MR) recoil damper combining a field-controlled inner valve, an effectively field-free bypass, and a pressure-actuated lid. A quasi-steady hydraulic model coupled to lid dynamics describes lock-up, open-lid, and closed-lid states. For the baseline geometry and a prescribed yield stress of 40 kPa, the dynamic force range is approximately three to four below passive closure. After seating, nearly all flow passes through the bypass, and field control becomes negligible. Under the nominal firing pulse of a 20 mm cartridge, constant-field operation gives the shortest predicted stroke and lowest counter-recoil velocity among the three double-adjustable operating modes, with a transmitted-force peak close to the conventional-spring value. Velocity-triggered on–off operation retains most of the rebound reduction while applying the field only during counter-recoil; relative to the spring, it reduces stroke by nearly 40% and battery-stop kinetic energy by about 91%. Two fixed linear viscous dampers provide soft and hard reference levels, and the hard reference closely reproduces the constant-field response over the examined load-amplitude range. At reduced loads below passive lid seating, on–off operation lowers the transmitted-force peak relative to the 40 kPa constant-field case at the cost of a longer stroke; this trade-off does not establish superiority over lower constant-field settings. These results describe conditional performance trade-offs; the early closure transient and the coupled device response remain experimentally unvalidated.

Actuators doi: 10.3390/act15110586

Authors: Gaofeng Che Jinchun Deng

This paper addresses the asymptotic tracking control problem for a class of nonaffine pure-feedback nonlinear systems with partially unknown internal dynamics. Traditional backstepping control is plagued by the notorious complexity explosion arising from repeated differentiation of virtual control signals. Dynamic surface control (DSC) alleviates the computational burden by introducing low-pass filters; nevertheless, it can only guarantee semi-global uniformly ultimately bounded stability instead of exact asymptotic tracking, and its control performance is highly sensitive to filter parameter tuning. Conventional recursive gain control (RGC) eliminates the reliance on filters, yet it merely ensures uniform ultimate boundedness of tracking errors without asymptotic convergence. To overcome these limitations, this paper develops a novel adaptive recursive gain tracking control (ARGTC) scheme. By seamlessly integrating recursive gain construction and online adaptive parameter update laws, the proposed filter-free controller avoids the complexity explosion of backstepping and completely removes the auxiliary low-pass filters indispensable to DSC. Rigorous Lyapunov stability analysis together with Barbálat’s lemma mathematically proves that the closed-loop tracking error converges asymptotically to zero while all closed-loop signals remain uniformly bounded. The designed adaptive update laws obviate the requirement for prior knowledge of the upper bounds of nonlinear uncertainties, thereby reducing design conservatism. Comprehensive comparative numerical simulations are carried out under various operating conditions, including sinusoidal, square-wave and multi-frequency reference tracking, measurement noise disturbances, time-varying parameter perturbations, actuator saturation constraints, multiple initial-condition tests, and filter parameter sensitivity analysis. Quantitative performance metrics and diverse visual results consistently verify that the proposed ARGTC achieves superior transient response, steady-state accuracy, low computational cost, and strong robustness in comparison with backstepping, RGC, DSC, adaptive DSC, approximation-free prescribed performance control approaches and adaptive sliding-mode control (ASMC).

Actuators doi: 10.3390/act15110585

Authors: Yechun Ma Jing Yang Kailei Liu Shaopeng Kang Hongbin Qiang Xiaolong Zhao

To address the challenges of non-smooth reference force commands, uncertain nonlinear dynamics, and external load disturbances in electro-hydraulic servo systems (EHSSs), this study proposes an adaptive nonsingular terminal sliding mode control (ANTSMC) method combined with a nonlinear tracking differentiator (NTD) and a radial basis function neural network (RBFNN) to improve the tracking performance of the loading force. First, the NTD is adopted to generate smooth reference force signals and their corresponding derivatives. Subsequently, an RBFNN is developed to approximate the unknown lumped uncertainty online, and its estimate is incorporated into the control law for adaptive uncertainty compensation. On this basis, an ANTSMC law is designed to improve force tracking performance and attenuate residual approximation errors. Furthermore, the closed-loop boundedness and convergence properties are investigated through Lyapunov stability analysis. Finally, simulation and experimental results demonstrate the effectiveness of the proposed method.

Actuators doi: 10.3390/act15110584

Authors: Jiewei Zeng Wentao Xia

Levitation control of high-speed maglev trains requires accurate state perception and effective suppression of composite disturbances. This paper proposes a composite levitation control strategy combining multi-sensor fusion, intelligent parameter optimization and active feedforward compensation. A dynamic Jacobian extended Kalman filter (EKF) fuses eddy current displacement and accelerometer data to estimate the gap and acceleration in real time, with an equilibrium-point linearized Kalman filter as the baseline. The dynamic EKF achieves lower gap and acceleration RMSEs than the baseline, with an acceleration variance reduction rate of 82.46% versus 64.03%. On a single-degree-of-freedom platform, the residual against the pre-processed observation is at the micrometre level, a consistency indicator rather than an absolute accuracy. Particle swarm optimization reduces the step-response overshoot of a cascade PID controller from 10.02% to 3.39%. A Hall sensor array is proposed to measure the normal component of the traction field, and the feedforward compensation reduces the maximum gap deviation under a 1180 N pulse from 0.14 mm to 0.01 mm, within 0.03 mm under 20% parameter mismatch. The cascade and feedforward modules were validated together under composite disturbance, and the estimator was validated on the measurement channels; a fully integrated vehicle-level test remains to be carried out.

Actuators doi: 10.3390/act15110583

Authors: Pengfei Chen Xiaohao Chen Weidong Jiao Yonghua Jiang

To statically reproduce the continuously distributed centrifugal load on metallic blades of rotating machinery, an electromagnetic loading method using a non-uniform double-sided linear induction motor is proposed. The method utilizes eddy currents induced in a stationary conductive specimen by a time-varying traveling magnetic field and the resulting Lorentz forces to generate an equivalent distributed load. A mapping relationship is established among the target centrifugal line load, the period-averaged electromagnetic line load, the local wavenumber, and the spatial phase. The non-uniform traveling magnetic field is realized through segmented phase discretization and phase assignment to winding slots. A two-dimensional time-domain finite element model is developed for verification. The normalized spatial profile of the normal magnetic flux density at the specimen midplane has a correlation coefficient of 0.942 with the target profile. Within the main evaluation region, the period-averaged electromagnetic line load reproduces the increasing target distribution with normalized root mean square and mean absolute errors of 12.06% and 9.82%, respectively. The total electromagnetic load over the full specimen length is 8.01% below the target centrifugal load. The proposed method provides a new approach for non-contact static reconstruction of centrifugal loads.

Actuators doi: 10.3390/act15110582

Authors: Jing Nie Yong Li

Speed ripple attenuation in geared flexible drives requires control of synchronous components and residual fluctuations within an existing embedded control architecture. This paper develops a five-state delay-coordinate predictive damping controller (D5–PD) that adds auxiliary q-axis current to a proportional–integral (PI)-regulated drive. Direction-specific models are identified from drive speed history and auxiliary current records with exact delay shifts. A three-step output-weighted design is solved offline and deployed as five-coefficient feedback with scalar scheduling and current limits, at a 1 ms auxiliary update period on an F28379D. Experiments compare PI, six-branch multi-resonant control (MR), and D5–PD under six conditions with three runs per controller. At +300 r/min and +1 A, D5–PD reduces mean speed ripple root mean square (RMS) by 38.83% relative to PI and 5.61% relative to MR at nearly equal auxiliary command alternating-current (AC) RMS. Its load current-normalized responses at 2 and 8 Hz are 37.39% and 60.17% lower than MR without disturbance-specific retuning. Total ripple is lower than PI in all six conditions and MR in five; residual RMS is lower than MR throughout. A separate 0.20 A benchmark with six records per method gives 2.12% lower total ripple and 7.68% lower command RMS than proportional ripple damping. These results demonstrate an embedded auxiliary damping implementation and characterize its tradeoffs with frequency-selective and proportional feedback in terms of total ripple, residual fluctuations and command demand.

Actuators doi: 10.3390/act15110581

Authors: Jiuyi Wang Hongen Ge Xin Zhang

To characterize the dynamic behavior of the hydraulic system of a ground coal-bunker cleaning device under variable operating conditions, a mechanical–hydraulic co-simulation model was established by coupling ADAMS and AMESim. A pipeline pressure-drop model accounting for distributed frictional, local, and coiling-induced losses was developed based on the Darcy–Weisbach equation. The effects of the number of rod sections, hydraulic-hose length, valve-group actuation interval, and the equivalent hose-coiling state were evaluated. Increasing the rod sections from 1 to 30 raised the steady-state pressure of the lead-screw lifting motor by 42.0%, reduced its flow rate by 26.9%, and increased the pressure settling time by 167.2%. Increasing the hose length from 5 to 20 m reduced cylinder pressure from 25.20 to 11.30 bar and the pressure synchronization coefficient from 0.966 to 0.775. A 0.5 s valve-group interval reduced the composite disturbance by approximately 54%. At the representative flow rate of 22.59 L/min, the calculated total pressure loss increased from 0.664 MPa for the one-layer state to 0.742 MPa for the nine-layer state, an increase of approximately 11.7%, while frictional loss remained the dominant component. For different working conditions, finite-range sensitivity comparisons identified reflected inertia and load torque, hydraulic capacitance and distributed flow resistance, temporal overlap of branch flow demand, and distributed pipeline friction as the response-specific drivers of the four investigated operating scenarios. The model and results can provide a basis for optimizing actuation timing, hose layout, and operating strategies for coal-bunker cleaning devices.

Actuators doi: 10.3390/act15110580

Authors: Tao Zhao Hengfa Wu Xin Dong Xiaojun Ding Yang Gao Sen Qian

To address the problems of cable slackness and non-smooth cable-tension variation curves during the motion of an antagonistic cable-driven parallel robot (CDPR), this paper focuses on a three-degree-of-freedom (DOF) redundantly constrained CDPR. First, an inverse kinematics model of the robot is established using the vector closed-loop principle. Second, a dynamics model of the robot is established using the Newton–Euler method. Linear programming, quadratic programming, and nonlinear programming are respectively adopted to optimize the cable tensions. Through numerical simulation and comparative analysis, the nonlinear programming method, which produces the smallest cable tension fluctuations and the smoothest cable tension variation curves, is selected as the optimal approach among the three tested methods. Finally, numerical simulations and experiments verify the correctness of the inverse kinematic and dynamic models of the robot, as well as the effectiveness of the proposed cable tension optimization method. The results provide a theoretical reference for dynamic modeling and cable tension optimization of similar redundantly constrained CDPRs.

Actuators doi: 10.3390/act15110579

Authors: Yuchao Fang Peiyi Wang Kang Wang Yutong Yue

The azimuth axis of a two-gimbal electro-optical stabilized platform is susceptible to nonlinear friction torque, external disturbances, and parameter variations during line-of-sight stabilization. To address these issues, an improved Twin Delayed Deep Deterministic Policy Gradient (TD3) algorithm incorporating multi-step returns and fuzzy dynamic action limiting, termed MSF-TD3, is proposed. In practical control, insufficient sensitivity to long-term control effects and pronounced steady-state output fluctuations may limit convergence and stability. A multi-step return mechanism is introduced to enhance the utilization of future reward information, while fuzzy adaptive action limiting constrains the control output according to the operating state. Simulation results show that, in variable-amplitude and variable-frequency target tracking, the root-mean-square error (RMSE) of MSF-TD3 is reduced by approximately 15.2%, 88.6%, and 87.2% compared with standard TD3, proportional-integral-derivative (PID) control, and extended sliding-mode disturbance observer (ESMO)-based control, respectively. In stepped target switching under compound disturbances, the corresponding reductions are approximately 1.7%, 16.1%, and 8.3%. Moreover, the root-mean-square (RMS) control input is reduced by approximately 69.7% relative to TD3. The results demonstrate the effectiveness of the proposed method in improving tracking accuracy, disturbance rejection, and control smoothness.

Actuators doi: 10.3390/act15110578

Authors: Giulia Petrucci Valentina Di Meo Fabio Cappelli Martina Baldini Augusto Nascetti Domenico Caputo Nicola Lovecchio

Point-of-care electroanalytical platforms for viable bacteria detection require local incubation and temperature control while maintaining compatibility with microfluidic handling and optical detection. This work presents a thin-film MEMS-based System-on-Glass (SoG) designed as a thermo-optical module for a four-site electrochemical bacterial-sensing platform. The SoG integrates a microfabricated double-spiral metal heater on one side of the glass substrate and six hydrogenated amorphous silicon (a-Si:H) temperature sensors along with eight complementary photosensors on the opposite side. The heater geometry was optimized through electrothermal simulations, which also established a linear relationship between the sensor and water temperature used to define the closed-loop setpoint. Infrared thermography on fabricated prototypes confirmed the simulated thermal distribution, yielding a mean temperature of 37.0 °C and a spatial variation from 36.4 to 37.7 °C across the active region. The temperature sensors showed a linear, reproducible response of approximately −4 mV/°C in two prototypes, while the photosensors exhibited dark currents in the 10−13 A range and a peak responsivity of 0.27–0.28 A/W at approximately 540–550 nm. Dedicated control software closed the loop between integrated sensing and actuation, regulating the temperature at 37 °C with an overshoot of 0.7 °C, a settling time of 140 s, and steady-state fluctuations confined within a single quantization step of the acquisition electronics. These results demonstrate the suitability of the SoG as a compact, controllable microscale thermo-optical platform for incubation, actuation, and complementary optical monitoring in point-of-care electroanalytical bacterial sensing.

Actuators doi: 10.3390/act15110577

Authors: Yanhong Peng

Although soft actuators offer compliance and adaptability, their nonlinear multiphysics dynamics, hysteresis, and material-dependent behavior create substantial challenges for accurate modeling and control [...]

Actuators doi: 10.3390/act15110576

Authors: Yapeng Xu Zhaole Ma Yufei Ma Kaishun Hao Caidong Wang Wenming Wang

Robotic physical interaction tasks require both compliance and load-bearing capacity. This review surveys variable stiffness method (VSM) based on mechanical and non-mechanical adjustment, with direct modulation of the equivalent physical stiffness at the output. Mechanical approaches are classified into independent and antagonistic configurations, and their principles are summarized in terms of variable transmission ratio, variable spring pretension, and variable physical properties of springs. Non-mechanical approaches are then reviewed from the smart materials, structural reconfiguration, jamming effects, and multi-mechanism synergy. Representative applications in humanoid robot, exoskeletons and prostheses, soft robots, and special robots are compared in terms of stiffness range, adjustment speed, load capacity, energy consumption, control complexity, and reliability. Mechanical approaches provide higher stiffness, load capacity, and predictability, whereas non-mechanical approaches offer greater potential for lightweight design, compliant integration, and adaptation to large deformation. The two categories involve distinct trade-offs in response speed, energy consumption, hysteresis, lifetime, and system integration. Future research should pursue task oriented integration of mechanisms, materials, and structures, establish unified testing protocols that include auxiliary actuation systems, and strengthen coupled motion stiffness sensing, low-power stiffness retention, and lifecycle reliability validation.

Actuators doi: 10.3390/act15110575

Authors: Fatma Lajmi Hassene Seddik Bilel Neji Hedi Dhouibi Ilyes Boulkaibet

The reliability and safety of modern industrial applications demand efficient fault detection and isolation (FDI) systems. Unfortunately, traditional diagnostic techniques are often highly sensitive to measurement noise, leading to frequent false alarms. Additionally, many contemporary methods require exhaustive training datasets, limiting their practical applicability. To address these challenges, this paper proposes a novel hybrid diagnostic framework applied to a continuous fluid mixing and filling process. The presented framework combines continuous residual analysis with discrete-event temporal reasoning. A timed diagnoser, implemented using Stateflow, represents bounded time intervals as active behavioral guards to continuously monitor the system against nominal timelines. When a temporal violation is detected, a Fuzzy Inference System (FIS) is triggered to isolate the root cause. The FIS effectively resolves diagnostic ambiguities—particularly masking effects caused by concurrent actuator and sensor malfunctions by correlating continuous fluid levels with discrete temporal deviations. Extensive simulations under noisy conditions demonstrate that the proposed hybrid architecture achieves a 100% detection rate and a 99.0% fault localization accuracy, while completely eliminating false alarms (0% false alarm rate). These quantitative results significantly outperform classical observer-based techniques and standard discrete Petri net methodologies, confirming the robustness and superiority of the proposed framework.

Actuators doi: 10.3390/act15110574

Authors: Jinyuan Cui Zhenxing Guo Min Liu Chuncheng Zhao Zhiqi Liu Yunxiao Hao Zepeng Li

Excavator swing systems typically suffer from significant throttling losses and braking energy waste during frequent acceleration and deceleration, resulting in low energy efficiency. To address these issues, an electro-hydraulic hybrid drive swing system for excavators (E-HHDSS) combining electric and hydraulic drives is proposed. The E-HHDSS employs a permanent magnet synchronous motor (PMSM) and a hydraulic pump/motor in parallel to drive the swing system. The PMSM provides fast response and precise motion control, while the pump/motor cooperates with a hydraulic accumulator to regulate system power and recover braking energy. During braking, the braking energy is converted into hydraulic energy and stored in the accumulator. During subsequent acceleration, the stored energy is released to assist the PMSM, thereby reducing electrical power demand. Furthermore, a speed control strategy based on operating condition identification is developed to coordinate the two power sources. The strategy integrates adaptive PMSM control with hydraulic system operation to achieve stable speed tracking and effective braking energy recovery under different operating conditions. Experimental results demonstrate satisfactory dynamic performance, with a maximum braking energy recovery efficiency of 57.6% and a 40.8% reduction in overall energy consumption.

Actuators doi: 10.3390/act15110573

Authors: Yichang Wang Yicheng Wang He Zhang

This paper investigates a strongly nonlinear system with coupled time-varying parameters related to vehicle speed and adhesion coefficient, as well as repetitive disturbances under practical industrial operating conditions. A fuzzy tracking control system framework is proposed, which consists of a Takagi–Sugeno (T-S) fuzzy observer with proportional-derivative (PD)-type iterative learning disturbance estimation and a T-S fuzzy P controller with disturbance compensation. Using the sector nonlinearity approach with properly selected premise variables, an exact T-S fuzzy representation of four-wheel-steering (4WS) vehicle dynamics is constructed. The T-S fuzzy observer is designed based on a common Lyapunov function and the linear matrix inequality (LMI) technique. Furthermore, an iterative learning law is developed to suppress repetitive disturbances across successive iterations. By employing a T-S fuzzy proportional controller together with disturbance compensation, the proposed scheme realizes high-precision path tracking. Joint time- and iteration-domain Lyapunov analysis derives LMI-based co-design conditions for all control gains, ensuring that tracking and observation errors converge to bounded regions. Simulation results demonstrate fast error convergence and satisfactory tracking performance of the proposed method under various operating conditions.

Actuators doi: 10.3390/act15110572

Authors: Kaiyu Dai Haohua Dai Jikang Zhou Wanshun Zang

In electrohydraulic operation benches (EHOB), one of the significant challenges of advancing toward intelligent control is ensuring operational safety under time-varying constraints, where excessive position or velocity may cause mechanical damage or environmental hazards. The inherent model uncertainties and high-order differential dynamics of electrohydraulic systems make it difficult to directly apply various safety mechanisms. Therefore, a modified state equation is constructed by consolidating matched and mismatched disturbances into a unified input channel. Then, a parallel safety mechanism based on Control Barrier Function (CBF) is introduced without disrupting the underlying ESO-backstepping control framework, which facilitates time-varying constraints to be enforced with merely position measurement. The CBF-based safety approach proactively modifies the intermediate virtual control laws when the actual trajectory approaches the constraint boundary, preserving a sufficient safety margin before violation occurs. Furthermore, a multiplicative disturbance induced by the modified state formulation is handled through an adaptive safety estimation scheme, avoiding velocity-constraint violations and reducing tracking error. Rigorous Lyapunov stability analysis proves that all closed-loop signals are uniformly ultimately bounded and the system states remain within the expanded safe set. Comparative experiments across multiple scenarios, including sinusoidal tracking and arbitrary joystick manipulation, demonstrate that the proposed controller can achieve high-precision position-tracking performance under position and velocity constraints.

Actuators doi: 10.3390/act15110571

Authors: Minhui Shen Jiwei Wen

To address the problems of inferior-quality data and excessive PSF post-corrections in practical LPV safety control, this paper proposes a safe Q-learning control method integrated with influence function and PSF correction feedback. First, an influence function is introduced to quantify the impact of individual samples on Q-function updates. By evaluating the variation in loss functions before and after removing each sample, samples with adverse effects on policy updates are identified and eliminated so as to mitigate the negative impacts of low-quality data on Q-function estimation and controller updating. Second, the PSF correction term is incorporated into the cost function as a penalty to guide the learning of nominal control actions with reduced reliance on PSF intervention. In summary, the proposed method improves the nominal control policy from two perspectives: learning-data cleaning and safety-correction feedback. While optimizing LPV system performance and reducing PSF correction times, it still guarantees the satisfaction of system safety constraints. Simulation results show that the proposed method can effectively improve learning-data quality, reduce PSF corrections, and ensure the safety and stability of the closed-loop system. The turbofan engine case study further demonstrates that the proposed method can achieve stable regulation while satisfying the prescribed safety constraints, verifying its applicability to practical LPV systems.

Actuators doi: 10.3390/act15110570

Authors: Zhaokai Li Yuli Hu Pu Guo

PID control is widely adopted in fast-forging press hydraulic systems. However, it often fails to deliver satisfactory performance under variable operating conditions due to its fixed control parameters. To tackle this problem, this paper proposes a control strategy that combines digital twin (DT) technology with cascaded particle swarm optimization (PSO). In the outer-layer optimization, a twin model is first built in MATLAB/Simulink. By combining real-time sensor data with PSO, the outer-layer optimization identifies the optimal effective bulk modulus of the hydraulic oil. This procedure updates the twin model and enables real-time mapping between the twin model and the physical system. Based on the updated twin model, the inner-layer optimization employs PSO to tune the fractional-order PID (FOPID) controller parameters (Kp, Ki, Kd, λ, and μ) online. The optimal parameters are then applied to the physical system to enhance control performance. Experimental results show that, compared with single-layer PSO-FOPID control, the proposed strategy reduces settling time by 9.36% and overshoot by 2.216 percentage points under no-load conditions. Under loaded forging conditions, it reduces settling time by 12.7% and overshoot by 0.2 percentage points, thereby improving the system’s response speed and position-tracking accuracy.

Actuators doi: 10.3390/act15110569

Authors: Daeji Kim Hyune-Jun Park Joo-Young Oh Jung-Woo Cho Changheon Song

A tilt-rotator increases the reachable workspace of a hydraulic excavator, but its configuration also changes structural load paths. This study developed a structural-load-aware work-path planner for a 14-ton excavator using nominal analytical soil loads and an experimentally correlated multibody dynamics model. A full-factorial combination of five tilt angles, five rotation angles, and nine excavation positions yielded 225 candidate motions. The 147 retained motions had predicted peak stresses of 98.5–149.0 MPa. These stresses informed action features and reward penalties in an action-conditioned dueling deep Q-network. Excavated cells became non-traversable holes; the planner incorporated in-place turning and conditional posture-repeat constraints. In the 9 × 9 obstacle environment, the stress-informed agent’s selected route required 44 actions and 452 s of simulated time, compared with 47 actions and 458 s for its stress-uninformed counterpart; cumulative peak-stress indices were 3158.0 and 3361.8 MPa, respectively. In the 5 × 5 environment, its route required one additional action and had a 4.2% higher index. A 21 × 28 site-derived numerical environment was completed in 453 actions, including 280 excavations. The method supports comparative structural-load assessment for construction-machinery safety and future integration with machine-stability criteria. These single-seed comparisons neither establish statistical superiority nor validate machine stability.

Actuators doi: 10.3390/act15110568

Authors: Zhenhua Zhu Peng Wang Yucheng Zhang

Electric wheel-drive actuators offer rapid and precise torque regulation, yet translating motor torque into commanded ground traction force remains challenging under deformable terrain interactions and wheel-slip constraints. This study proposes an observer-based traction-force control architecture for an electric agricultural tractor, formulating traction tracking as a constrained actuator-control problem. To avoid fragile and expensive wheel-force transducers, a causal physics-informed ridge observer estimates dynamic longitudinal wheel–soil interaction forces online using standard onboard kinematic and actuator signals. The observed force is then integrated into a feedback PI regulator coupled with a dynamic anti-windup slip limiter to prevent excessive soil shear failure. Evaluated on a high-fidelity single-wheel testbed in the Genesis physics engine across contrasting tilled and compacted soils, the causal observer achieves accurate dynamic force estimation with normalized RMSE below 0.15%. Under nominal tillage operations across 1.0 and 2.0 m/s forward speeds, the closed-loop controller achieves sub-1.5% steady-state force tracking. Under excessive traction demands near the terrain adhesion limit, the dynamic slip limiter actively intervenes to prevent runaway wheel spin-out, strictly bounding peak slip below 18.2% and sustaining stable traction at the physical boundary. This framework provides a sensor-efficient and robust solution for precise traction regulation in electric off-road vehicles.

Actuators doi: 10.3390/act15110567

Authors: Meryem Lagoune Samia Latreche Habib Benbouhanni Mabrouk Khemliche Badreddine Babes Hamza Khemliche Mihai Oproescu Nicu Bizon

Reliable operation of photovoltaic (PV)-powered water pumping systems is essential for sustainable irrigation and water supply, particularly in remote areas where maintenance and continuous monitoring are challenging. This paper proposes a Super-Twisting Observer (STO)-assisted hierarchical LSTM–CNN Fault-Tolerant Control (FTC) framework (LC-FTC) for fault diagnosis and fault-tolerant operation of PV-powered brushless DC (BLDC) water-pumping systems. The study investigates the diagnostic usefulness of residual signals generated by an STO and evaluates their ability to support data-driven fault detection and classification within a simulation framework. The proposed framework integrates model-based state estimation with data-driven fault diagnosis and signal substitution. A dataset is generated using a MATLAB/Simulink model under four operating conditions and multiple single and combined measurement-fault scenarios involving DC-link voltage and current measurements, the speed sensor, and the current sensor. The STO generates residual signals for fault diagnosis and estimated signals for subsequent signal substitution. The diagnostic architecture operates hierarchically: a Long Short-Term Memory (LSTM) network analyzes the temporal evolution of the residual signals to detect and localize fault-related events, after which the corresponding signal segments are classified using a one-dimensional Convolutional Neural Network (1D-CNN). The diagnostic decision is subsequently used by the FTC stage to select either measured or STO-estimated signals. On the continuous blind C1 detection evaluation, the LSTM detector achieved 99.98% accuracy, 99.97% precision, 100% recall, and a 99.99% F1-score. On the fault-containing candidate segments generated by the LSTM-guided procedure, the CNN achieved an Exact Match of 80.10% and a Macro-F1 of 93.36%. However, grouped three-fold cross-validation yielded an Exact Match accuracy of 63.33 ± 16.20%, indicating variability in performance across folds. The LSTM-guided segmentation procedure reduced the number of candidate segments forwarded to the CNN by 67.07% relative to the fixed-window procedure under the evaluated C1 condition. The STO-assisted FTC stage reduced the RMSE relative to the fault-injected measurements by approximately 98.6–100% under the investigated noise-free simulation conditions. Additional simulation-based analyses examined measurement noise, parameter variation, fault severity, and temporal-sequence settings. Overall, the results indicate the feasibility of using STO-generated residual signals for hierarchical data-driven fault diagnosis and subsequent fault-tolerant signal substitution under the investigated simulation conditions. All results were obtained in simulation; experimental and hardware-in-the-loop validation remain future work.

Actuators doi: 10.3390/act15110566

Authors: Hongtao Yu Fan Xiao Fanglei Fan Huilin Xu Zhiying Zhu Zhifang Zhu Quanguo Lu

To address the limited grasping stroke (GS) of piezoelectric-actuated microgrippers, this paper proposes a novel symmetric microgripper configuration integrating reversed Scott Russell (S–R) mechanisms and differential lever amplification mechanisms (DLAMs). Four reversed S–R mechanisms are arranged in parallel and connected via a central linkage, which is actuated by a piezoelectric stack actuator (PSA). The tension–compression deformation of the parallel S–R units generates two pairs of displacements with equal magnitudes and opposite directions, which are further transmitted to the DLAM to amplify the GS. A semi-analytical mechanical model of the microgripper is established, incorporating a simplified PSA model to describe the mechanical behavior of the actuator. Based on the analytical model, the displacement amplification ratio (DAR) and first-order natural frequency (FNF) are selected as dual optimization objectives to optimize the structural geometric parameters. The static and dynamic performances of the proposed microgripper are preliminarily validated via finite element simulations and experiments. Experimental results show that the microgripper achieves a GS of 857 μm, a bilateral DAR of 68, and an FNF of 265 Hz. Although the modeling error is relatively large, the established model can still provide guidance for the integrated design of the microgripper. Finally, grasping tests further demonstrate that the developed microgripper can be applied to micromanipulation and microassembly tasks.

Actuators doi: 10.3390/act15110565

Authors: Pei Deng Qiang Chen Qi Liu Yuxin Jin Shijie Gu Jie Li

Sensorless position and speed estimation methods for permanent magnet synchronous motors (PMSMs) eliminate the need for mechanical sensors, thereby reducing costs, enhancing reliability, minimizing system volume, and enabling maintenance-free operation. Furthermore, these approaches achieve high-precision control and exhibit strong adaptability to harsh environments. Particularly in medium- and high-speed operations, sensorless schemes based on the nonsingular fast terminal sliding mode observer (NFTSMO) offer strong robustness and rapid convergence. However, inherent speed chattering increases speed fluctuation and introduces adverse harmonic distortions in the estimation system. To address this, this paper proposes an improved observer strategy based on complex-vector reconstruction. This method formulates a reduced-order system model in the complex domain and constructs an isotropic sliding-mode surface, effectively suppressing the odd harmonics induced by the algorithmic structure. Additionally, a nonlinear tracking differentiator (TD) is introduced to filter out high-frequency noise from the estimated position and speed signals. Simulation and experimental results demonstrate that, compared to the conventional NFTSMO, the proposed method mitigates high-frequency chattering and improves speed estimation accuracy in medium- and high-speed sensorless operations, while maintaining comparable position tracking accuracy and convergence speed.

Actuators doi: 10.3390/act15110564

Authors: Weiwei Li Heyong Han Chuiyi Liu Yunzhong Jiang

Asymmetric valve-controlled asymmetric cylinder systems (AVCACSs) are key actuation components in mechatronic drive systems such as hydraulic rolling shears, yet conventional models treat hydraulic damping as a constant and neglect valve geometric asymmetry, resulting in considerable errors under bidirectional flow conditions. This paper develops a direction-dependent damping model based on the power-matching principle, in which the valve-geometry asymmetry is described by a piecewise transfer function. Directional load pressures and flows are redefined for forward extension and reverse retraction, and separate damping-ratio models are derived for the two motions. The analysis shows that the valve-port area-gradient ratio (VPAGR) and the rod-to-cap area ratio (RTCAR) affect the forward and reverse damping ratios in opposite ways: as the matching value i increases, the forward ratio rises while the reverse ratio falls, and the reverse ratio remains higher throughout. Even under perfect matching (i = m = n, 0 < i ≤ 1), the minimum forward and reverse ratios still differ; at i = 0.5 the gap reaches 0.14, quantifying the bidirectional asymmetry in flow gain and response speed, while at i = 1 the two ratios converge to the symmetric case, confirming the generality of the model. The model is validated by Simulink simulations and experiments on a hydraulic double-sided rolling shear, providing a quantitative basis for component matching and control design of hydraulic actuation systems.

Actuators doi: 10.3390/act15110563

Authors: Xuyang Shang Yiqi Qin Shuman Xu Liangzhu Wang Zengzhi Zhang

Soft pneumatic actuators (SPAs) are widely applied in soft robots for their good compliance and environmental adaptability. However, conventional SPAs with a single prescribed deformation mode provide limited dexterity for tasks requiring reconfigurable motion. To address this limitation, this paper proposes a four-chamber circumferentially symmetric SPA with a dual-channel architecture for large-angle bending. Finite-element simulations, using a third-order Ogden hyperelastic model, are employed to investigate the effects of chamber height, chamber spacing, and actuation pressure on bending performance. The simulations indicate that contact between adjacent chambers provides a passive constraint that suppresses out-of-plane distortion at moderate pressures, whereas loss of this constraint at higher pressures leads to out-of-plane distortion. A prototype is fabricated via the water-soluble sacrificial template method, and bending experiments are conducted to verify design effectiveness. For the geometry with the optimal comprehensive performance within the simulation parameter range (8 mm chamber height and 2 mm chamber spacing), a bending angle of 350.1° is achieved at 35 kPa, approaching a full-circular fold. The simulations further indicate that, for the modeled configuration, planar bending is maintained below 35 kPa; above 40 kPa, out-of-plane distortion and local stress concentrations become pronounced. The fabricated prototype exhibits deformation consistent with the simulations. The proposed architecture exhibits large-angle bending at low pressure under the single-chamber inflation mode, and its circumferentially symmetric layout provides a structural basis for multidirectional pneumatic actuation, serving as a potential building block for soft grippers, manipulators, and miniature inspection devices.

Actuators doi: 10.3390/act15110562

Authors: Naixuan Zhu Junjie Luo Yuedong Pan Yifan Geng Haodong Cui Zhengcai Yang

Last-mile delivery robots frequently navigate pedestrian-rich local corridors, where sensing, tracking, communication, and computation delays can make pedestrian observations stale and degrade collision-risk estimation. This paper develops a delay-aware risk-adaptive model predictive control (MPC) pipeline that coordinates observation-age compensation and continuous multi-parameter adaptation in a common candidate-based planner. A normalized interaction-risk score jointly schedules the reference speed, pedestrian-avoidance weight, and motion-smoothness weight, enabling efficient motion in low-risk situations and progressively more conservative behavior as predicted risk increases. The method is evaluated through 800 performance simulations, including a 480-run main study over three pedestrian densities, four observation delays, and ten random seeds, a 240-run ablation study, and an 80-run 40 m extended-route evaluation. In the main study, the proposed method achieves a 100% goal-reaching rate, compared with 81.7% for the efficiency-oriented baseline, while reducing average collision count and collision duration by 61.5% and 74.8%, respectively, and increasing minimum robot–human distance by 55.9%. The corresponding collision-free run rate reaches 69.2%. Among successful runs, its mean completion time is 15.32 s, only 6.9% longer than the efficiency-oriented baseline. At a 1.0 s observation delay, the proposed method reduces collision count by 70.2% relative to the efficiency-oriented controller and by 49.9% relative to rule-based switching, while reducing absolute clearance-estimation error to 0.056 m under the tested prescribed pedestrian-motion model. Ablation results confirm that both delay compensation and adaptive weighting contribute to the improvement. On the 40 m extended route, the proposed controller retains a 100% goal-reaching rate and a 70% collision-free run rate. Its mean decision time and average run-wise 95th-percentile decision time are 58.28 ms and 74.21 ms, respectively, both below the 100 ms control period, indicating real-time potential without a measurable average computational penalty.

Actuators doi: 10.3390/act15110561

Authors: Koharu Takebayashi Zizhen An Mingcong Deng

In this paper, an operator- and observer-based nonlinear tracking control scheme is proposed. Initially, the error-based extended state observer (eESO) is employed on the objective nonlinear plant, which addresses the compensation for perturbations like modeling uncertainty, unknown dynamics and external disturbance. Moreover, an additional feedback loop is constructed following the principle of the operator-based robust right coprime factorization (RRCF) feedback framework, which aims at further guaranteeing the robust stability of the proposed overall tracking scheme. Specifically, by interpreting each component as an operator and designing the controllers to satisfy the robust stability condition, the proposed scheme can be shown to be bounded-input bounded-output (BIBO) stable, while the satisfactory tracking performance is achieved simultaneously. The proposed nonlinear tracking control scheme is then applied into a flexible arm system that is driven by the shape memory alloy (SMA) actuator. Experimental validation demonstrates that the proposed method outperforms the selected benchmark methods in terms of mean RMSE, achieving values of 0.0692, 0.0653, and 0.0781 across three experimental scenarios, respectively. These findings confirm the effectiveness and practical feasibility of the proposed tracking control scheme.

Actuators doi: 10.3390/act15110560

Authors: Ali Al-Ghanimi Jinchuan Zheng

Constant-slope sliding surfaces require a trade-off: steep slopes improve regulation under sustained disturbance but increase transient control effort, while shallow slopes reduce effort at the expense of accuracy. We investigate a surface whose slope is scheduled by a weighted phase-space measure of the tracking error. Because the schedule depends on error rate, differentiation introduces a state-dependent coefficient on the error acceleration; if it vanishes, the equivalent control becomes singular, and if it changes sign, the effective input gain reverses. We show that the coefficient’s deviation from unity is bounded by one quarter of the coupling gain times the square root of the velocity weight, independently of the energy scale. A single inequality therefore guarantees a well-posed control law and a uniquely solvable manifold. Finite-time reaching and exponential convergence follow, with practical stability under a boundary layer. In six-degree-of-freedom quadrotor simulations with exact kinematics, attitude-upset recovery, hover disturbance, and inertia uncertainty, evaluated over 20 held-out disturbance phases, the reference PSEC configuration reduces peak commanded torque by 51.7% at e0=0.3rad compared with c=24 at matched steady-state accuracy. However, the peak increases by 32.6% at e0=0.1rad. A procedure-selected PSEC configuration (origin slope 25.35) reduces the peak by 67–77% over e0=0.1–0.5rad. A tuned capped terminal surface is more accurate.

Actuators doi: 10.3390/act15110559

Authors: Wenjie Wang Hanshu Rao Tian Zhang Xiongding Liu Chenxi Wu Xiaodan Zhao Wu Wei Huixin Feng

This paper investigates the asymptotic formation tracking control problem for heterogeneous multi-agent systems (HMASs) subject to external disturbances and time-varying actuator faults. A comprehensive model incorporating these uncertainties is formulated to capture realistic engineering scenarios. To ensure robustness and adaptability, an integral sliding surface is constructed, followed by a rigorous analysis of the formation tracking error dynamics. A variable-gain disturbance observer is proposed to estimate the lumped disturbance and fault-induced input error using measured velocity and commanded input effectively. Leveraging information from neighboring agents and the leader, a distributed adaptive sliding mode fault-tolerant controller is synthesized. By utilizing the Lyapunov stability theorem, sufficient conditions for asymptotic tracking under smooth feedback are rigorously derived. Theoretical analysis demonstrates that under the proposed adaptive fault-tolerant control protocol, all follower agents asymptotically achieve the desired formation as t→∞. Numerical simulations are provided to validate the effectiveness and robustness of the proposed approach.

Actuators doi: 10.3390/act15110558

Authors: Zaidi Elyazid Habib Benbouhenni Abdelhakim Mabrek Khoudir Marouani Alin Gheorghita Mazare Laurentiu Mihai Ionescu Nicu Bizon

This paper proposes a fault-robust backstepping-based control strategy for induction motor (IM) drives fed by parallel-connected voltage-source inverters (VSIs). The developed control scheme is engineered to achieve precise speed tracking, optimal current sharing among parallel inverter legs, and effective suppression of zero-sequence circulating currents (ZSCCs) under both normal operation and inverter fault scenarios. Initially, a comprehensive mathematical model of the parallel inverter-fed IM drive is formulated in the synchronous reference frame, rigorously incorporating the inter-inverter coupling dynamics. Utilizing Lyapunov stability theory, a nonlinear backstepping controller is subsequently synthesized to guarantee closed-loop stability and the asymptotic convergence of tracking errors. To evaluate the robustness and fault-tolerance of the proposed method, open-circuit faults in the inverter power switches are investigated. The dynamic impacts of these faults on motor speed, electromagnetic torque, stator currents, current distribution, and ZSCCs are thoroughly analyzed through both simulation and experimental validations. The experimental findings indicate that the proposed controller successfully sustains stable speed regulation, enhances current sharing, and significantly mitigates circulating currents and torque ripples during fault conditions. Furthermore, comparative evaluations against conventional proportional–integral controllers highlight the superior transient response and enhanced fault resilience of the suggested approach. Ultimately, these results substantiate the efficacy of the proposed backstepping-based control framework in ensuring highly reliable operation of parallel inverter-fed IM drives across diverse operating states.

Actuators doi: 10.3390/act15110557

Authors: Yuan-Ming Cheng Po-Wei Wu Kuan-Yu Hsu

Accurate platform-orientation feedback is important for trajectory tracking in parallel motion platforms, but high-precision measurement systems can be costly. This study develops a low-cost inertial measurement unit (IMU)-based feedback compensation framework for a three-axis parallel motion platform. A GY-9250 IMU integrated with an STM32 microcontroller provides roll and pitch estimates through Kalman filtering of gyroscope and accelerometer measurements. Inverse kinematics maps the estimated orientation into actuator coordinates to formulate posture-derived displacement errors. The hybrid controller combines proportional control based on encoder-derived actuator tracking errors with single-input fuzzy compensation based on the posture-derived displacement errors. The framework is implemented using an NI CompactRIO controller (National Instruments Corporation, Austin, TX, USA) and evaluated through circular orientation trajectories with different periods and angular amplitudes. Relative to proportional control at the same gain of Kp = 2, the hybrid controller reduces RMS angular tracking error by 0.6%, 30.0%, and 62.3% in three tested conditions, but increases it by 34.4% in the fourth condition. These results demonstrate condition-dependent benefits rather than consistent superiority over proportional control. Independent dynamic attitude validation, between-run variability, and end-to-end execution timing remain unquantified. The study provides a practical implementation of low-cost orientation-feedback compensation and identifies the need for further validation of its accuracy, repeatability, and timing characteristics.

Actuators doi: 10.3390/act15110556

Authors: Ali Jnadi Sergei Savin Yaroslav Kholodov

This work presents a sampling-based Quadratic Stability Control (QSC) framework for nonlinear mechanical systems with parametric uncertainty and compares it with a nominal Linear Quadratic Regulator (LQR). The proposed method synthesizes a single state-feedback gain by enforcing a common quadratic Lyapunov condition over a finite set of locally linearized models sampled in state and parameter space. A systematic numerical study evaluates the effects of the number of sampled models, state sampling radius, parameter uncertainty, and actuator configuration. Performance is assessed using trajectory mean-squared error, final position error, and offline controller-synthesis time. The results show that QSC has higher position error than nominal LQR at 5% uncertainty but lower error at 10% and 15% across five independently sampled designs, with greater force effort while maintaining comparable nominal performance. The common quadratic certificate covers the sampled models and their convex hull, not the full continuous nonlinear domain. These benefits are obtained at the cost of higher offline semidefinite-programming complexity.

Actuators doi: 10.3390/act15110555

Authors: Jiawei Lu Jinsheng Song Zihao Qiu Xin Wen Shiqi Wang

This study presents a planar particle image velocimetry (PIV) investigation of near-wall velocity deficit mitigation in a compact curved channel using sweeping jet actuation. A compact sweeping jet oscillator was developed based on a simplified fluidic oscillator configuration and integrated into the curved wall region of the channel. The effects of jet incidence angle, actuator placement, array layout, and jet-to-freestream velocity ratio were examined within a fixed streamwise measurement window near the curved wall. The analysis focuses on time-averaged in-plane velocity fields and representative streamwise velocity profiles, with emphasis on changes in the near-wall low-speed region and local streamwise velocity recovery. The results show that sweeping jet actuation can weaken the measured near-wall low-speed region and promote local streamwise velocity recovery within the planar PIV window. Among the tested cases, a jet incidence angle of 60° and actuator placement at the beginning of the bend produced a more balanced local recovery response. The comparison between different array layouts indicates that the observed recovery is affected by the combined influence of actuator spacing, actuator number, and total actuation input; therefore, it should not be interpreted as an isolated spacing effect. The present results provide a systematic low-speed experimental basis for selecting sweeping jet incidence angle, actuator placement, array configuration, and equivalent actuation input in compact curved channel flow control applications. The findings clarify how different actuation parameters affect local near-wall velocity deficit mitigation and streamwise velocity recovery within a controlled optical access configuration.

Actuators doi: 10.3390/act15110554

Authors: Saad F. Almokmesh Bashar B. Alzuwayer Talal E. Alotaibi

Self-powered sensor nodes need vibration harvesters that work over a band of frequencies, but the arrays and graded metamaterials that provide such bandwidth need many separately clamped resonators. This numerical study presents a kirigami-graded metabeam in which U-shaped slits in one 250 × 16 × 0.5 mm aluminum sheet release four tabs of graded length (44–62 mm); the sheet is folded and clamped at both ends, and a PZT-5A patch straddling each root feeds its own resistive load. A distributed-parameter cell model is verified against a three-dimensional coupled-field finite-element model within 1% in frequency and 2% in power. In the finite-element model, each cell mode is confined to one tab (off-diagonal amplitudes ≤ 0.09) and the cells deliver 0.59–1.44 µW per (m s−2)2 at 130–274 Hz; their band-mean power is 3.6 times that of a single clamped tab and 0.9 times that of four separately clamped tabs, with two clamps instead of four. Interleaving the cells so that frequency-adjacent cells are not spatial neighbors keeps the modes localized on an 18 Hz grid and gives a continuous 212–284 Hz band with 1.1 times the four-tab power. One root-compliance parameter places 18 cell frequencies within 2–3%, and the sensitivity of the results to the assumed damping is quantified. No measurement is reported; the experimental characterization of the prototype is left to a separate study.

Actuators doi: 10.3390/act15100553

Authors: Zhiqiang Wang Yunpeng Zhang Weinong Fu Zhenyang Qiao

The rapidly exploring random tree star (RRT*) algorithm is widely used for path planning, but finding an initial feasible path can require substantial sampling. Learning-based enhancements commonly predict promising sampling regions from grid maps. This paper presents a model that combines a Tree Long Short-Term Memory encoder with a Transformer decoder to predict an ordered sequence of keypoints from a hierarchical map representation. The resulting TLT-RRT* planner checks the predicted segments, repairs infeasible connections, and continues path optimization using RRT*. The multi-branch tree representation avoids explicitly storing a full high-dimensional grid when the environment admits a compact hierarchical representation. Two- and three-dimensional experiments show shorter initial-path times than the selected RRT-based baselines in the evaluated settings. Six-dimensional manipulator examples and resource benchmarks further characterize the implementation and its computational limits.

Actuators doi: 10.3390/act15100552

Authors: Jinyang Li Jianzhen Li Xianju Fang Changjiang Li

This paper addresses the optimal affine formation control problem for second-order multi-agent systems (MASs). The control objective is to steer the formation with stress matrix constraints while minimizing the sum of all the local time-varying cost functions. The key challenge is the tight coupling between position tracking, velocity regulation, and time-varying cost minimization. We develop a distributed estimator–controller framework that decouples these dynamics via three local estimators. For each agent, these estimators can track the global optimization variables using only local information from its neighbors. On this basis, a distributed optimizer is designed for the agents. Theoretical analysis shows that, using the proposed optimizer, all agents’ trajectories converge to the optimal solution by a prescribed time, and affine formation is simultaneously achieved within that horizon. Simulation results further illustrate the superior tracking performance of our algorithm in multi-robot scenarios.

Actuators doi: 10.3390/act15100551

Authors: Jian Xu Zihao Li Chenguang Guo Jiuqing An

This paper investigates fault-tolerant tracking for continuous-time nonlinear systems subject to input nonaffinity and prescribed state inequality constraints. A slack-function-based transformation and a dynamic precompensator are adopted to handle state constraints and input nonaffinity, respectively. The fault model applies to redundant auxiliary-drive channels of the precompensator and includes stuck, outage, bias, and loss-of-effectiveness modes. Under fault-free operation, an off-policy integral Bellman equation is formed from measured data, and the critic and actor weights are computed by regularized projected least squares. Online, the learned actor is embedded in an adaptive fault-tolerant controller. The stability analysis gives a local forward-invariance condition and retains policy-approximation, regression, and derivative-filter errors in the ultimate bound. Direct closed-loop simulations of a nonaffine continuous stirred tank reactor include single-drive outage, repeated fault switching, and measurement noise. The supplied code and raw trajectories reproduce all comparisons and quantify the regression conditioning and iteration residuals.

Actuators doi: 10.3390/act15100550

Authors: Hongjun Meng Lin Wang Wenjie Du Zebo Wu

Quadruped robots are used in various scenarios, but their rigid structure limits their applications. In contrast, soft structures offer greater flexibility, adaptability, and lower costs but struggle with motion modeling and control stability. This paper proposes a novel design for a quadruped robot that uses pneumatic soft actuators for joint movement. Firstly, kinematic principles are applied to model single-leg movements; subsequently, a data-driven approach is proposed to model the soft actuator by integrating the control principle with the single-leg structure. Furthermore, a system identification-based approach is proposed for parameter estimation. Ultimately, the model predictive control method is effectively employed to track the predefined gait during locomotion. Experimental results demonstrate that the designed robot can walk smoothly and follow the preset gait accurately.

Actuators doi: 10.3390/act15100549

Authors: Hailin Hu Wei Guo Fu Feng Yuquan Chen Yuhui Chen

Traditional cascade control structures for surface-mounted permanent magnet synchronous motors (SPMSMs) suffer from strong coupling between the speed and current loops and high sensitivity to parameter variations. To address these issues, this paper proposes a model-free predictive direct speed control (MFPDSC) method based on an ultra-local model. The core innovation lies in constructing a direct speed ultra-local model that mathematically merges the q-axis current dynamics with the motion equation via integration, directly relating the rotor speed to the q-axis voltage. This eliminates the dependence on cascade structures and consolidates the disturbances of both loops into a single lumped perturbation for estimation. Compared with existing model-free predictive direct speed control schemes, the proposed method requires fewer control parameters. The d-axis adopts model-free predictive current control (MFPCC), and disturbances are compensated in real time by a data-driven observer and a reduced-order extended state observer (RESO). The d-axis current control and direct speed control act simultaneously to generate the voltage vector. Finally, experiments on a physical platform demonstrate that the proposed method offers advantages in speed tracking, load disturbance rejection, and robustness against parameter variations, thereby verifying the effectiveness of the proposed control strategy.

Actuators doi: 10.3390/act15100548

Authors: Tianyi Yao Mengyao Chen Li Sun Zhaocheng Shi Hongfei Yu Jiantao Wu Renhao Ge Boyan Zhang

Adolescent lower-limb postural abnormalities encompass physiological alignment variation, impaired dynamic motor control, and structural deformity, which require different intervention goals and standards of evidence. This review classifies flexible wearable lower-limb systems into motor-cable, pneumatic artificial muscle, elastic-element, and smart-material technologies, and compares the assisted joints, mass boundaries, power supply, sensing and control, and human-subject findings. Direct evidence in children and adolescents is distinguished from mixed-age evidence and technology transferred from adult populations. Current studies mainly support gait assistance, improved walking economy, and rehabilitation training. A small number of systems have been tested in children with cerebral palsy, but the evidence is insufficient to show that flexible external traction can produce sustained correction of the osseous alignment associated with adolescent genu varum or genu valgum. Motor-cable systems facilitate force-feedback control, pneumatic systems are constrained by their air supply and response characteristics, elastic assistance depends on stiffness and gait-phase matching, and smart materials still present thermal, electrical, and durability challenges. Future adolescent-oriented systems should prioritize growth-adjustable sizing, low distal mass, measurable interaction forces, and fail-safe unloading. Their effectiveness should be evaluated through off-device retention of functional gains and long-term follow-up.

Actuators doi: 10.3390/act15100547

Authors: Wumian Zhao Xinbo Chen Chunjie Wei Kunming Zhu Jiantao Yao

Soft robots adapt to object shapes through structural compliance; wrapping actuators generate gripping force through continuous enveloping contact. This study presents a vacuum-driven pneumatic helical spring (PHS) actuator and a simplified analytical model linking manufacturing constraints, free shape, gripping force, and axial load capacity. Under quasi-static, uniform-helix, and equivalent linear-stiffness assumptions, angle mapping, geometric compatibility, and incremental energy relate constraint-tube angle, vacuum pressure, and target radius to free shape, contact onset, and total normal gripping force under cylindrical constraints. Friction and target weight provide a simplified axial-load estimate under the assumed Coulomb relation, rather than a strict physical upper bound. Tests on a single prototype show that the model captures shape-tightening and gripping-force trends over the tested range, with a root mean square error of 2.19 N between predictions and indirect estimates of total normal gripping force. Grasping and towing demonstrations show the prototype’s ability to conform to the tested target shapes. The model supports actuator design and operating-condition selection for a given target within the investigated range.

Actuators doi: 10.3390/act15100546

Authors: Hui Yang Long Bai Zhongjie Long Wen Shi

For the automated perfusion of thermal protection layers on large-scale spherical-crown honeycomb structures of spacecraft, path planning and simulation studies are carried out for a five-degree-of-freedom (5-DOF) 5PRR+5PUS-PRPU hybrid perfusion manipulator. According to the manufacturing characteristics of honeycomb perfusion, three perfusion trajectories (circular, square and 5-shaped) are designed for the moving platform, and analytical path planning is implemented for these predefined paths. A simulation control framework based on conventional PID position correction is established for this 5-DOF hybrid manipulator, and comprehensive trajectory tracking simulations are performed under purely kinematic assumptions. The driving simulation of the hybrid manipulator is conducted using the theoretical displacement profiles of driving sliders. Simulated displacement, velocity and acceleration curves of each slider are obtained for different perfusion paths. Meanwhile, the comparisons and tracking error curves between simulated and desired end-effector trajectories are presented. This work verifies the kinematic feasibility of the hybrid manipulator for the perfusion task under ideal conditions and provides theoretical support for its potential aerospace manufacturing application.

Actuators doi: 10.3390/act15100545

Authors: Helmut Kogler Bernhard Manhartsgruber Markus Schöberl

Lumped parameter models are widely used as approximations of reality for system design and dynamic simulation due to their often simple and intuitive physical principles. This is particularly convenient, if the modeling is confined to one single physical domain, for instance, dynamic models of electronic circuits. Hydraulic drive technology is an interaction of physical effects from multiple domains such as mechanics, fluid dynamics and thermodynamics, which in turn makes the development of lumped parameter models more involved. In order to get simple models certain assumptions result in approximations that sometimes leave the correct physical context to some extent, which may lead to unexpected dynamic behaviour of certain models, like closed hydraulic systems. In this paper the problems of conventional hydraulic lumped parameter modeling regarding mass and energy conservation are addressed. The deficiencies of the established models from literature are investigated by simulations and analysed with an energy-based modeling framework from systems theory, which in turn enables the development of a simple strategy to adapt the original models in order to achieve a mass-conservative and energy-consistent behaviour under stated assumptions, even with existing simulation tools. Furthermore, the approximation of wave propagation effects in transmission lines by lumped parameter models is investigated by simulations.

Actuators doi: 10.3390/act15100544

Authors: Chen Yue Honghai Shen Yongsen Xu Rui Xu Chao Liang Hairong Chu

During periodic scanning, friction-dominated disturbances near motion reversals cause velocity fluctuations in an inertially stabilized platform (ISP). This paper proposes a disturbance rejection control method based on an iterative-learning-embedded finite-time extended state observer (IL-FTESO). Unlike conventional external iterative learning control (ILC), which learns directly from the tracking error, the proposed method embeds ILC in the disturbance estimation channel. Within each scanning cycle, a finite-time extended state observer (FTESO) accelerates disturbance estimation, and the resulting estimate serves as the learning signal for updating the repetitive disturbance compensation in the next cycle. This structure integrates real-time disturbance estimation within each cycle with cycle-to-cycle iterative compensation. Theoretical analysis establishes convergence of the FTESO observation error and ultimate boundedness of both the learning and closed-loop tracking errors. Experiments on a physical ISP with fiber-optic gyroscope feedback show that the proposed method improves overall angular-rate tracking accuracy and suppresses error peaks near motion reversals. Compared with conventional external ILC, it reduces the root–mean–square error by 58.8% and 61.0%, the maximum absolute error by 45.4% and 48.1%, and the mean absolute error by 53.6% and 68.5% under the 20∘/s, 0.5 Hz and 5∘/s, 2 Hz periodic commands, respectively.

Actuators doi: 10.3390/act15100543

Authors: Jangwon Lee Ho Seon Choi

Backpack load carriage can alter gait mechanics and dynamic stability, while existing assistive backpacks have primarily targeted load transmission and metabolic cost. This study investigated whether active vertical repositioning of a moving mass within a backpack could influence gait-stability-related outcomes. A frontal-plane double inverted pendulum model was combined with inertial measurement unit (IMU)-derived motion states to calculate a model-estimated mediolateral extrapolated center of mass (XCoM), and model predictive control (MPC) regulated a 5 kg moving mass in real time. Six participants walked on a treadmill at 1.2 m/s under a Normal condition, three fixed-mass conditions (Low, Mid, and High), and a Powered condition with XCoM-based moving-mass control. Short-term largest Lyapunov exponent (LLE), kinematic variability (KV), and trunk sway were evaluated as gait-stability-related outcomes. In the Powered condition, short-term LLE was 19.0%, 15.7%, and 24.4% lower than in the Low, Mid, and High conditions, respectively, with all six participants showing lower LLE in each comparison. However, no pairwise comparison of LLE, KV, or trunk sway remained statistically significant after Bonferroni correction. The model-estimated XCoM and filtered moving-mass velocity command were negatively correlated (r=−0.3310). These findings support the feasibility of state-dependent moving-mass control during load carriage and indicate the need for further evaluation of its effects on gait stability in a larger cohort.

Actuators doi: 10.3390/act15100542

Authors: Shih-Feng Chen Bo-Xuan Wu Sin-Wei Chen Chung-Chen Tsao Ting-Hsueh Chuang

Deep learning has achieved high accuracy in machining condition monitoring, yet accuracy alone cannot reveal whether a model relies on physically meaningful evidence or on dataset shortcuts. The difficulty is that common tasks such as tool-wear and surface-roughness estimation lack a known ground-truth basis for discrimination, so attribution outputs cannot be validated. This study therefore constructs a benchmark task—three-class cutting-speed classification (Vc = 60, 80, 100 m/min)—in which, for a fixed tool diameter, the spindle-speed-dependent spectral content is an a priori known correct basis, enabling the reliability of explainable AI (XAI) methods to be examined under controlled conditions; the task is deliberately simple and serves as a validation framework for attribution methods rather than as a demanding monitoring problem. Cutting force signals were acquired from 3 × 3 full-factorial milling experiments on 17-4PH stainless steel using a Kistler 9170A rotating dynamometer; the torque Mz and resultant force Fa were segmented by sliding windows into 2970 single-channel samples (15 records × 99 windows × 2 channels), each represented by 50 time segments × 6 amplitude-independent statistics. A 1D-CNN, an LSTM, and a fully connected network (NN) were evaluated under five-fold StratifiedGroupKFold cross-validation. The 1D-CNN achieved 93.97% accuracy with roughly one-seventh of the parameters (NN 90.24%, LSTM 89.12%), the smallest fold-to-fold standard deviation, and 84.5% on the most difficult fold; as a single random seed was used, performance conclusions are descriptive only. Holding out whole cutting conditions reduced the mean accuracy to 83–86% (one feed level: 54–57%), so the accuracies describe generalization across records of the studied conditions, not to unseen conditions. Fold-wise application of LRP, LIME, and SHAP showed that the 1D-CNN and NN distributed importance across the entire signal (normalized entropy ≥ 0.97), whereas for the LSTM the gradient × input attribution used as the LRP implementation placed 9.4 times the uniform share on the final time segment, consistently across all five folds, a concentration that SHAP (expected gradients referenced to background training samples) and the perturbation-based LIME did not reproduce. Gradient-free occlusion and resampling reproduced it, and retraining showed that it follows the last input position while removing the final segments did not reduce accuracy; it therefore reflects positional sensitivity rather than reliance on the sequence end. In this run, cross-fold Spearman correlations of LIME rankings lay within −0.05 to 0.05, versus 0.20–0.70 for LRP and SHAP; because exploratory recalculations with alternative aggregation choices gave markedly different LIME correlations, this is reported as a run-specific observation rather than as a property of LIME. All three architectures relied predominantly on frequency-domain features; because the tooth-passing frequencies (159.2–265.3 Hz) exceed the 100 Hz Nyquist frequency of the 200 Hz sampling rate yet lie below the 300 Hz low-pass cutoff of the signal conditioner, they are aliased into the analyzed band, and the dominant-frequency feature reflects the spindle rotation frequency and aliased tooth-passing components, both proportional to spindle speed and hence consistent with the physical definition of cutting speed. The contributions are: a controlled validation framework that cross-validates attribution credibility through importance concentration, inter-method agreement, and cross-fold reproducibility; and the observation that the end-of-sequence concentration of the LSTM, revealed by gradient × input but not by SHAP or LIME, reflects positional sensitivity rather than the basis of classification, highlighting the need to verify attribution concentration with independent analyses rather than relying on a single attribution method.

Actuators doi: 10.3390/act15100541

Authors: Steven Nicolalde Luis Morales David Pozo-Espín

This work presents the design and experimental validation of two interval type-2 fuzzy controllers for the angular regulation of a one-degree-of-freedom QNET VTOL plant: a fuzzy controller with a PD+I structure (IT2FL) and a hybrid fuzzy sliding-mode controller (IT2FL-SMC). Both run in a cascade scheme, with the outer loop handling angular position and an inner loop handling motor current. In the IT2FL-SMC, the discontinuous switching term of a conventional sliding-mode controller is replaced by an interval type-2 fuzzy reaching action, while the continuous term is derived from a second-order model of the plant identified experimentally. The footprint of uncertainty is tuned on the platform, and both controllers are compared against PID, conventional SMC, type-1 fuzzy, and type-1 fuzzy sliding-mode controllers under the same conditions. The tests include step-reference changes and physical eccentric-load disturbances applied in both directions. In reference tracking, the IT2FL gives the smoothest actuation, with the lowest total variation of the control input and the shortest settling time. Under both disturbances, the IT2FL-SMC gives the lowest integral absolute and squared errors, though with a more active control signal. The two controllers turn out to be complementary: one favors smooth actuation, the other favors disturbance rejection.

Actuators doi: 10.3390/act15100540

Authors: Batın Demircan Tuğçe Tepebaşi Sabri Biçakçi Ersin Akyüz

The traditional control approach for piston-type wave makers is reduced to a piston position tracking problem based on open-loop wave-maker theory; however, due to hydrodynamic loading, nonlinear effects, and propagation delays, the target wave condition at the measurement section cannot be guaranteed. This experimental study involves controllers tuned offline through numerical simulations and validated in real time on a 24 m wave channel. The novelty of this work is a two-layer field-programmable gate array (FPGA) cascade that regulates the measured wave height in closed loop, not just the piston position. In the inner layer, the hydraulic servo cylinder position is controlled within a 1 ms cycle using a proportional–integral (PI) or a Takagi–Sugeno (T–S) fuzzy controller; the outer layer, in a 20 ms cycle, updates the position reference via real-time wave height feedback. Controller parameters were tuned using three meta-heuristic algorithms under the integral of time-weighted absolute error criterion, and a similarity-based rule reduction reduced the T–S consequent parameters from 27 to 9, yielding 66.7% and 62.5% reductions in FPGA execution time and digital signal processing slice usage with tracking-error changes of only 2.2–2.3%. Experiments confirm high-accuracy position tracking and steady-state wave height regulation, verified by fast Fourier transform analysis.

Actuators doi: 10.3390/act15100539

Authors: Alessandro Mazzone Gianpietro Di Rito Marco Lucarini

The increase in reliability and safety levels of electrical power devices is key to the transition toward aviation electrification. Safety-critical equipment, such as propulsion motors, must comply with stringent requirements to obtain airworthiness certification. Permanent Magnet Synchronous Motors (PMSMs) have emerged as a suitable solution for high-performance flight control actuation, with promising extension to propulsive functions. Nevertheless, the reliability of PMSM power electronics converters remains below certification requirements, so fault-tolerant capabilities are essential for flightworthiness, making prompt and effective Fault Detection and Isolation (FDI) algorithms essential. This paper presents the Model-in-the-Loop (MIL) validation of a Neural Network (NN) algorithm for the detection and isolation of MOSFET faults and open-phase faults in PMSM power drives. The approach combines a feedforward NN, trained on simulation-generated data for a multi-class classification problem, with a counter-based decision logic ensuring fast and robust isolation, using a compact architecture. A feature selection analysis reduces the network size at a modest accuracy cost. For MIL validation, the NN-based algorithm is integrated within a high-fidelity dynamic model of an electrically driven UAV propeller, comprising a three-phase PMSM with Field-Oriented Control (FOC), digital signal processing, and aerodynamic loads derived from Blade Element Momentum Theory (BEMT). Faults are injected at different operating speeds, during speed transients, and under combined parametric uncertainty to evaluate the FDI performance in terms of detection latency, isolation capability, and robustness. The results demonstrate the effectiveness of the approach, which can be extended to other fault categories and support the development of fault-tolerant PMSM control.

Actuators doi: 10.3390/act15100538

Authors: Qihong Duan Jin Wu Nat Hsu Harrison Teng Emily Joseph Fangzhou Xia

Magnetically driven microrobots have shown significant potential in biomedical applications, including endovascular intervention, targeted therapy, and drug delivery, particularly in the treatment of cardiovascular diseases. Conventional vascular interventional procedures typically rely on physicians to manually manipulate guidewires under medical imaging guidance, which often suffer from strong dependence on operator experience, prolonged procedure time, and increased patient discomfort. To address these limitations, this study proposes a magnetic vascular robotic navigation method based on path planning and reinforcement learning. By controlling a robotic manipulator to regulate the external magnetic field, the proposed method enables motion control of a magnetic guidewire during vascular interventions. In the proposed framework, the robotic manipulator serves as the actuation platform, where the path planning algorithm provides global navigation guidance, while the reinforcement learning strategy performs local motion control. In addition, a simplified two-dimensional virtual vascular environment was constructed for algorithm training, and the proposed method was deployed on a robotic manipulator system for experimental validation in a real vascular phantom. Experimental results demonstrate that the proposed method achieves stable guidewire navigation within vascular environments and outperforms conventional control methods in key metrics such as procedure time, thereby validating its feasibility and potential for endovascular intervention applications.

Actuators doi: 10.3390/act15100537

Authors: Cun Wang Xiaojun Zhang Lingyu Sun Minglu Zhang Jidong Jia

To address the limitations of traditional wall-climbing robots in ferromagnetic wall operation scenarios, such as poor surface adaptability, insufficient motion stability, and difficulties in negotiating complex surface transitions, this paper proposes a four-wheel permanent magnet wall-climbing robot and systematically investigates its stability. First, the center of gravity (CoG) of the robot was determined based on a 3D prototype model developed in SolidWorks2020. To ensure reliable adhesion, the anti-slip and anti-overturning stability criteria under various operating conditions were derived. Furthermore, combining the mechanical characteristics, a magnetic field simulation model for the magnetically adsorbed wheels was established. Electromagnetic simulations of the permanent magnets were conducted using Ansoft Maxwell, followed by adhesion force experiments. Finally, the robot prototype was assembled, and a test system was constructed to evaluate its overall performance. The experimental results demonstrate that the designed robot can smoothly negotiate inner right-angle corners. This validates the effectiveness of the proposed structural design and stability analysis, providing a feasible technical solution for wall-climbing robots in complex scenarios and exhibiting significant potential for engineering applications.

Actuators doi: 10.3390/act15100536

Authors: Leandro Iorio Alice Proietti Dounia Noqra Fabrizio Quadrini Loredana Santo

Telecommunication, energy generation, defense and research are just a few of the sectors that need to deploy structures in the space environment. Traditional systems are complex and expensive and, as a result, there is a critical need for new solutions. Shape memory polymer composites (SMPCs) have the potential to be used in such systems, since they can provide an actuation load during shape recovery. In this paper, an SMPC device with an embedded heat source, used to trigger the shape change, was manufactured by hand lamination and autoclave molding. A thermo-mechanical cycle was applied to investigate the SM ability. Tests were performed by powering the heat source from 20 V to 24 V. Recovery angle and recovery speed were evaluated at 24 V. Microscopy showed that a good level of agglomeration was reached thanks to autoclave molding, with the functional interlayer being uniformly distributed. SM tests underlined that the recovery load was not affected by the memory temperature and, regardless of the activation temperature, it always reached the same plateau value. Finally, the SMPC device was integrated into a 1U CubeSat and used to deploy one of its sides; an opening of 28 deg was obtained in only 45 s.

Actuators doi: 10.3390/act15100535

Authors: Yuming Fan Jian Wang

This paper considers the stable tracking problem of high-speed train control systems based on event-triggered control. With the aid of external auxiliary dynamics and the integral signal of the controlled system state, an integral event-triggering condition was designed. The stability of the closed-loop system is obtained through a Lyapunov function by extending the dimension and decaying it at the triggering time point. At the same time, Zeno-like phenomena are also excluded from the closed-loop system. The cooperative control problem of designing separate event-triggering conditions for each train is also considered in this paper. Finally, numerical examples are provided to illustrate the efficiency and feasibility of the theoretical results.

Actuators doi: 10.3390/act15100534

Authors: Yoshiki Tanaka Yuya Nishida Kazuo Ishii

Long-term and repeated observation of shallow seafloor environments is required to evaluate temporal changes in seagrass meadows and other coastal ecosystems. In this study, we propose a cable-restricted observation system consisting of an underwater vehicle, a tether cable, and a seafloor station equipped with a reel. The vehicle can repeatedly cruise over a designated area along nearly the same trajectory using the cable constraint. A design flow was developed to determine system parameters, including the reel radius, the number of cable turns, and the thrust required for the vehicle. In addition, a vehicle position model based on an involute curve and a motion model considering cable deflection were introduced. To evaluate the proposed system and trajectory model, water tank test and a sea trial were conducted using a 2.5 m tether cable. The radii of reels were 0.084 m and 0.775 m in the water tank test and sea trial, respectively. The experimental results confirmed that the vehicle could repeatedly cruise along approximately the same trajectory by winding and unwinding the cable. In the sea trial, the maximum differences between the measured and estimated positions were 0.541 m in the x-direction and 0.643 m in the y-direction. These results demonstrate the feasibility of the proposed system for repeated observation of a specified seafloor.

Actuators doi: 10.3390/act15100533

Authors: Jonah Vennemann Niklas König Rudolf Gerlich Matthias Nienhaus

Methods for self-sensing position determination in active magnetic bearings enable a reduction in system costs and complexity. Many well-known methods rely on current measurements or their derivatives to estimate the rotor’s displacement relative to the centre. However, measuring voltage often yields a better signal-to-noise ratio compared to current measurements, especially considering smaller machines where the current is often sensed using a shunt. Nevertheless, star-connected active magnetic bearings and the associated star-point voltage are rarely addressed in research. The star-point voltage provides valuable information for self-sensing position determination in other types of electric machines, such as permanent magnet synchronous motors. The goal of this research is to exploit the star-point voltage of an active magnetic bearing to estimate the rotor position. This study presents an analytical derivation of the star-point voltage for a four-phase active magnetic bearing, followed by a description of a differential measurement method for the star-point voltage. It is shown that, under the selected operating conditions, the resulting measured values depend exclusively on the coil inductance and the known DC supply voltage. To extract the position information from the obtained signal, the system was characterized at a standstill. The resulting measured values were used for polynomial fits, which were implemented on the microcontroller. Finally, the proposed method was experimentally validated inside the control loop under quasi static conditions. Experiments conducted on a laboratory prototype with a large air gap of 2 mm showed an RMS value of the estimation error ranging from 9.2 μm to 36.9 μm and a signal-to-noise ratio of approximately 70 dB.

Actuators doi: 10.3390/act15100532

Authors: Wei Zou Lei Wang Weiwei Shao

For a class of discrete systems with polytopic uncertainties and actuator faults, a robust PD-type iterative learning fault-tolerant control scheme is investigated in this article. By providing a two-dimensional analysis of the learning process, the fault system of a repetitive nature is equivalently converted into an uncertain linear repetitive process. Additionally, employing repetitive process stability theory, new sufficient conditions with less conservatism for the robust stability of the designed fault-tolerant controller are derived in terms of linear matrix inequality constraints. The controller gain matrices are exactly given as well. Finally, simulation results of an industrial SCARA robot demonstrate the efficiency and feasibility of the proposed strategy in comparison to the developed robust P-type iterative learning fault-tolerant control strategy.

Actuators doi: 10.3390/act15100531

Authors: Lin Li Yaqi Mi Xinqin Gao Xupeng Wang Youzhi Lu Zizhuo Wang

During downhill walking, the human knee joint is subjected to a relatively high transient flexion velocity and impact load during the initial foot-contact phase, whereas low motion resistance is required during the subsequent knee-extension recovery phase. To address the difficulty that conventional bidirectional-damping knee exoskeletons have in simultaneously providing effective impact attenuation and preserving freedom of knee extension, an asymmetric-damping knee exoskeleton is proposed in this study. The proposed exoskeleton is based on the coaxial series integration of a magnetorheological (MR) damper and a one-way bearing. The mechanical characteristics of the one-way bearing, which locks in the knee-flexion direction and overruns freely in the knee-extension direction, are exploited so that direction-selective damping is enabled, characterized by high resistance for impact attenuation during knee flexion and low resistance during knee-extension recovery. In addition, an event-triggered control strategy based on the jerk signal measured by a shank-mounted inertial measurement unit (IMU) is employed so that the MR damper is driven into a high-damping state only after a landing impact is detected; thus, dependence on complete gait-phase recognition is reduced. Based on a single-degree-of-freedom human–exoskeleton coupled dynamic model and a Bingham constitutive model, MATLAB R2024a simulations were conducted under three conditions: without an exoskeleton, with a symmetric-damping exoskeleton, and with the proposed asymmetric-damping exoskeleton. In addition, finite element analysis of the magnetic-field distribution within the damper was performed using COMSOL 5.6. The results indicate that, under the representative operating conditions considered in this study, the peak angular velocity of the knee joint is reduced by the asymmetric-damping configuration compared with the condition without an exoskeleton. Although the peak-suppression performance of the proposed configuration is slightly lower than that of the symmetric-damping configuration, the sustained resistance during the knee-extension recovery phase is substantially reduced, and a trade-off between impact attenuation and freedom of motion is demonstrated. These findings indicate that direction-selective impact attenuation can be enabled by partially transferring damping-direction selection from the control layer to the mechanical structure, without reliance on accurate and complete gait-phase recognition, while the risk of sustained damping during knee extension caused by control delays or misclassification is reduced. This structure–control collaborative approach provides a new design pathway for semi-active exoskeletons to reduce control complexity, improve the determinacy of the damping direction, and support the development of lightweight and low-power assistive technologies for downhill walking.

Actuators doi: 10.3390/act15100530

Authors: Xuelian Xie Lieyu Tian Huiyin Zhang Wu Guo Qiankun Huang Xuguang Ren Junguo Cui Fuyuan Li

The increasing demand for deep-sea drilling and the exploration of rock-hosted marine mineral resources has driven the development of seabed drilling systems with active control capabilities. A direct drive permanent magnet synchronous motor (PMSM) for seabed coring was designed to achieve low-speed high-torque operation, high efficiency, and low torque ripple. First, considering the limited installation space and operation requirements, six structural parameters, including stator slot depth, slot opening height, stator tooth width, air gap length, total effective core length, and pole arc coefficient, were selected as initial design variables. A fractional factorial design was employed to screen the significant design variables affecting motor efficiency and cogging torque. Subsequently, second-order response surface models were constructed to establish the nonlinear relationships between the design variables and optimization objectives. An NSGA-II algorithm with reference points is proposed to simultaneously maximize motor efficiency and minimize cogging torque. The optimization results demonstrate that the proposed method effectively improves the overall electromagnetic performance of the motor. Compared with the initial design, the motor efficiency was increased from 84.4583% to 86.7692%, while the cogging torque was reduced from 0.4952 N·m to 0.1711 N·m. A prototype motor was fabricated, and no-load, load, and torque ripple tests were performed to validate the optimized design.

Actuators doi: 10.3390/act15100529

Authors: Sun Ho Jang Hyeong Rae Cho Hyung Gil Hong Bo-Kyu Kwon

Cross-embodiment human-to-robot motion retargeting requires transferring human motion to robot-feasible actions despite differences in kinematic structure, reachable workspace, and sensing-to-control latency. This paper proposes Cross-Embodiment Motion Retargeting (CE-MR), a lightweight Physical AI framework that combines two wearable inertial measurement units (IMUs), a robot-independent canonical motion representation, residual Deep Koopman (RDK) prediction, and posture-aware inverse kinematics (IK). Upper-arm and forearm orientations are used to reconstruct shoulder-relative wrist motion and arm configuration without acceleration integration or direct human-to-robot joint correspondence. Human motion is represented by a 14-dimensional state and predicted over a 200-ms receding horizon using a constant-velocity prior corrected by a compact RDK model with 2270 trainable parameters. Using 100 human-arm demonstrations across five motion categories, RDK reduced canonical-position RMSE from 0.04506 to 0.03183 at 200 ms, corresponding to a 29.36% improvement over constant-velocity prediction, while reducing full-state normalized RMSE by 28.63%. Online evaluation using the official Gazebo simulation model of the ROBOTIS OpenMANIPULATOR-X showed 100% final-target IK success for all four ablation modes. In a representative single-operator Gazebo ablation, the complete CE-MR configuration showed a mean normalized human–robot posture discrepancy of 0.0708 compared with 0.1375 in the independently performed RDK trial, while maintaining a mean Cartesian IK residual of 0.728 mm. Stable integrated execution further demonstrated operation near 20 Hz under favorable IK conditions. These results support CE-MR as a compact proof-of-concept framework for predictive human-to-robot cross-embodiment motion transfer from wearable human sensing to online simulated robot execution.

Actuators doi: 10.3390/act15100528

Authors: Claudio Domenico Cobisi Carmelo Burgio Federico Nasca Mariazzurra Carlino Mathav Vignesh Giuseppe Rovere Francesco Bosco Ferdinando Granata

Background: Robotic-assisted total hip arthroplasty (RA-THA) may improve component positioning but adds workflow demands during adoption. We evaluated the learning curve for total operative and robotic workflow time during the initial implementation of a CT-based robotic system. Methods: We retrospectively analyzed 108 consecutive adults undergoing primary RA-THA between January 2024 and June 2025. We recorded skin-to-skin and robotic workflow times for each procedure. Segmented regression was fitted to individual procedure times, with model selection by Bayesian information criterion. We used CUSUM sensitivity analyses and LOESS smoothing to describe time trends. Results: For both endpoints, a one-breakpoint model was favored, with the estimated change in slope at case 12. Mean skin-to-skin time was 80.8 ± 24.9 min in cases 1–12 and 48.1 ± 12.7 min in cases 13–108. Corresponding robotic workflow times were 46.3 ± 18.8 and 28.2 ± 9.7 min. The CUSUM peak varied with the reference value, and the analysis of individual times did not support a distinct late optimization phase. Conclusions: Operative times decreased most markedly during the first approximately 12 cases and more gradually thereafter. These findings describe operative efficiency in a single-surgeon cohort; further studies should examine clinical outcomes and component-positioning accuracy alongside time trends.

Actuators doi: 10.3390/act15100527

Authors: Yong Peng Jie Li Yiqiu Tan Pengxiang Zhu Yuexin Li Qiang Chen Lianchun Wang Danfeng Zhou

In electrodynamic suspension (EDS) maglev systems, the time-varying magnetic fields experienced by onboard superconducting magnets can induce excessive AC losses and elevate the risk of quench, posing a critical threat to operational reliability. Conventional three-dimensional finite element analysis, though accurate, requires hours per frequency point and cannot support real-time quench assessment or parametric design optimization. This paper proposes an efficient magnetic shielding analysis method based on a reflection–absorption decoupled lumped-parameter framework. The three-dimensional eddy current field is reduced to a low-order coupled system by decomposing the eddy currents into plate-surface modes, a global circulation loop, and side-wall contributions, all coupled through a unified series magnetic circuit, while the field penetration through the cavity wall is captured via a finite impulse response (FIR) diffusion kernel with a high-frequency correction. The proposed method achieves a simulation time of 3–5 s per frequency point, a speedup of approximately 103∼104 over finite element analysis, with a root-mean-square shielding effectiveness deviation of 2.03 dB over 10–3000 Hz. The efficiency of the proposed method enables co-optimization of the outer dewar and superconducting magnets, offering a practical analysis tool for quench mitigation and electromagnetic compatibility design in EDS maglev systems.

Actuators doi: 10.3390/act15100526

Authors: Ting Chen Qian Xu Fei Shao Xingkun Xie Yiwei Gao

Eight-track vehicles feature large grounding areas, low ground contact pressure, and high load-bearing capacity, and are widely adopted for heavy-duty engineering transportation and large special-purpose operation platforms. Accurate characterization of their steady-state steering forces is essential for tracked-chassis parameter matching and structural optimization. Nevertheless, existing steering dynamic models mainly focus on double-track, four-track, and six-track configurations, ignoring slip distribution differences induced by the parallel dual-track and multi-segment grounding structure of eight-track vehicles. To fill this gap, this paper establishes a steady-state steering dynamic model for large-scale eight-track vehicles. Lateral force, traction force, and steering resistance moment of each track group are derived via grounding micro-element integration, and vehicle static equilibrium equations are constructed. The damped Newton iteration algorithm is employed to solve the transcendental equations numerically, followed by key-parameter sensitivity analysis. A RecurDyn-based virtual prototype is further developed for multi-body dynamic simulation verification. Quantitative comparison shows that the maximum relative error of track driving force is within the engineering acceptable range, validating the correctness and engineering applicability of the presented model. Track gauge and grounding length are identified as dominant factors for steering driving force, whereas track width and the spacing between homolateral parallel tracks exert limited influence. This model can provide theoretical support for multi-track vehicle chassis optimization.

Actuators doi: 10.3390/act15100525

Authors: Duy-Tinh Hoang Manh-Dung Nguyen Yong-Joo Kim Kyung-Hun Shin Jang-Young Choi

This paper presents an analytical model for predicting electromagnetic forces in an 8-pole/12-slot surface-mounted permanent magnet synchronous machine considering static rotor eccentricity and magnetic saturation. The eccentric air gap is represented by an equivalent concentric region with circumferentially varying magnetic permeability, allowing the harmonic analytical formulation to be retained. Magnetic saturation is incorporated through an iterative permeability update. The calculated radial and tangential air-gap flux-density components are used to evaluate the Maxwell-stress distributions, integrated electromagnetic loads, and unbalanced magnetic force under no-load and on-load conditions. The analytical results agree well with nonlinear finite-element analysis. No-load experiments using three stationary axial conductors are further conducted to validate the predicted redistribution of the radial air-gap flux density at different stator positions and eccentricity levels. The results show that rotor eccentricity mainly redistributes the Maxwell-stress distribution, whereas magnetic saturation limits its magnitude under heavy-load operation. Both effects, therefore, need to be considered for accurate analytical force prediction under eccentric operating conditions.

Actuators doi: 10.3390/act15100524

Authors: Dongning Liu Jiangtao Li Feng Sun Chuan Zhao Hanwen Zhang

Material removal rate and material removal per unit energy are key indicators for evaluating EDM efficiency. By studying the relationship between these indicators and EDM discharge parameters, it is possible to improve machining efficiency and material removal performance. Taking the EDM structure with magnetic-levitation micro-motion compensation as the research object, this paper combines the dynamic levitation position of the moving electrode with the formula of the gap between electrodes and establishes a mathematical model among the macroscopic feed position of the spindle, the dynamic compensation position of the moving electrode, the pulse energy and the heat flux density of the workpiece. It also analyzes the conversion process of single-pulse energy and the Gaussian heat flux density on the workpiece surface. By combining the response surface method, the mapping relationship between electrode discharge parameters and material removal rate, as well as the material removal amount per unit energy, was obtained. Finite-element simulations and single-factor continuous machining experiments show that the MRR is more sensitive to the low-voltage current and pulse interval, whereas the material removal per unit energy exhibits a non-monotonic dependence on the discharge parameters. Specifically, it shows a decreasing trend followed by an increasing trend with increasing low-voltage current and pulse width, whereas the opposite trend is observed with increasing high-voltage current and pulse interval. These results suggest that a moderate low-voltage current, a relatively high-voltage current, a short pulse width, and an appropriate pulse interval are favorable for magnetic-levitation micro-motion-compensated EDM to achieve both high MRR and high material removal per unit energy.

Actuators doi: 10.3390/act15100523

Authors: Jaewook Lee Jeongwoo Lee

This study develops a design procedure for electromechanical regenerative dampers using recorded damper stroke, velocity, and force from city, highway, country, and rough-road driving. The signals are converted into directional force, mechanical-power, energy-coverage, and operating-duty requirements. Motor size, gear ratio, lever ratio, power-network limits, packaging, and reflected inertia are screened, and 12 V and 48 V configurations are selected separately. Force tracking is checked with a prescribed-motion actuator model, and the selected designs are compared with a hydraulic reference in a quarter-car model under paired ISO Class B/80, C/60, and D/40 km/h inputs. The design points include 0.4 kW at 0.30 m/s, 0.6 kW for continuous-load screening, and 2.3 kW for 95% mechanical-energy coverage per damper. On the selected Class D/40 km/h input, the interface-force NRMSE is 52.3% for the 12 V configuration and 23.5% for the 48 V configuration. This is a comparison of two complete system designs, and prototype validation remains necessary.

Actuators doi: 10.3390/act15100522

Authors: Zhilong Zhang Wenxiang Deng

Achieving high-precision and highly adaptive leg joint control is a formidable challenge for hydraulic quadruped robots, owing to their dynamic uncertainties, nonlinearities, and frequent contact events. This paper proposes an event-based active compliance control strategy for hydraulic quadruped robots, which integrates the extended state observer (ESO) based robust integral of the sign of the error (RISE) inner-loop joint trajectory tracking controller and the event-based admittance outer-loop force controller with no contact force measurement. In the inner loop, ESOs are employed to estimate and compensate for the difficult-to-model dynamic coupling characteristics of the joints, while the RISE controller suppresses the residual disturbance compensation errors, thereby achieving asymptotic tracking performance. In the outer loop, a generalized momentum observer (GMO) compensated by neural networks is adopted to estimate contact forces, avoiding the installation of end-effector force sensors. Meanwhile, a contact detection mechanism is introduced to trigger admittance control upon unintended contact, thereby buffering the contact forces. Demonstrated through simulations, the proposed algorithm enhances joint position tracking accuracy, effectively mitigates impact forces from unintended contact, and improves the stability of robot locomotion.

Actuators doi: 10.3390/act15100521

Authors: Ti Deng Haichao Liu Jinjun Wu Tianfeng Zhou Liang Li Qi Zhao

Rapid pressure unloading is essential for the back pressure assembly of injector test systems. In this study, a high-speed unloading valve was developed for the back pressure assembly of an injector test system, and its pressure unloading characteristics were investigated through coupled numerical simulation and experimental testing. An electromagnetic–mechanical–fluid coupled dynamic model was established to describe the interactions among electromagnetic actuation, valve core motion, and hydraulic forces. Three-dimensional CFD simulations were performed to investigate the steady flow and hydraulic-force characteristics, followed by a two-dimensional transient model for analyzing the hydraulic force during valve closure. A coupled Simulink–AMESim model was then established to evaluate the system-level pressure unloading response and compared with experimental measurements under several initial pressure conditions. The CFD results reproduced the variation in flow rate with pressure differential, while sensitivity and uncertainty analyses showed that the quantified factors could not fully account for the discrepancy in absolute flow rate. Three-dimensional CFD revealed both axial and radial hydraulic forces, while 2D–3D comparison supported the use of the two-dimensional model for transient axial-force analysis. The system-level simulation and experimental results exhibited comparable pressure unloading characteristics within the investigated operating range.

Actuators doi: 10.3390/act15100520

Authors: Feng Xiong Wenhao Xu Hang Yin Yan Li Neng Zhang Tianqi Yin

This paper addresses the vibration response produced at the supporting foundation by multiple low-frequency tonal components transmitted through magnetic bearing supports. A composite active magnetic bearing (AMB) control method is proposed in which the measured foundation vibration serves as the direct control objective. With a PID feedback loop maintaining five-degree-of-freedom (5-DOF) stable levitation of the rotor, the complex frequency-response matrices from the control currents to the foundation accelerations at the target frequencies are identified in the closed loop by simultaneous multi-channel excitation, with random initial phases combined with correlation integration. The conjugate transpose of the pseudo-inverse of each matrix forms a decoupling matrix, which is embedded in the reconstruction of the filtered reference signals to build a narrowband MIMO FxLMS feedforward loop; together with the PID feedback loop, this constitutes the composite control system. MATLAB/Simulink simulations show that the controller converges stably under 15% amplitude mismatch, 5° phase mismatch and broadband background noise. In experiments on a 5-DOF AMB test rig, the average attenuations of the three target tonal components at 34.5, 37 and 41.5 Hz over five foundation measurement points reach 18.1, 18.0 and 18.36 dB, respectively, with a maximum attenuation of 32.8 dB, and no pronounced amplification is observed outside the target frequencies. After the feedforward loop is engaged, the rotor displacement peaks at approximately ±0.08 mm during the transient and then settles within ±0.05 mm, far below the 0.3 mm working air gap. The results indicate that, with PID feedback maintaining stable levitation, the compensating electromagnetic forces of the AMBs can suppress the foundation vibration response formed by multiple non-synchronous low-frequency tonal components, achieving coordinated control over multi-tonal vibration suppression and stable rotor levitation.

Actuators doi: 10.3390/act15100519

Authors: Wenye Wu Wangwei Li Lili Fan Haimin Zhu

A piezoelectric shunt damping ring comprising six circumferential stack–frame units is proposed for vibration suppression in shaft–support systems. Bow-shaped protective frames transfer radial motion into axial deformation of piezoelectric stacks connected to independent passive series-RL circuits. A complete-ring electromechanical model incorporates deformation transfer, directional coupling, and the combined feedback of the shunt branches. A coupling-corrected analytical relation predicts a common inductance of approximately 0.1936 H, within about 0.3% of the numerical optimum. With all six branches active, joint inductance–resistance optimization yields approximately 0.19301 H and 144 Ω, reducing the predicted peak force transmissibility from 4.35 to 2.14, a reduction of 50.8%. Two branches aligned with the excitation direction provide most of the attainable attenuation, with diminishing returns from additional branches. Parameter studies show a non-monotonic resistance effect and greater sensitivity to inductance detuning than to resistance variation. Harmonic frequency-sweep tests on a shaft–support assembly show that activating all six branches reduces the peak transmitted force from 35.8 to 24.3 N under constant input-force excitation, corresponding to 32.1% attenuation. These results support the configuration’s vibration-suppression capability and provide guidance for circuit tuning and branch selection.

Actuators doi: 10.3390/act15100518

Authors: Yuxin Jin Shijie Gu Mingxin Liu Pei Deng Jie Li

Electromagnetic sleds require high-performance sensorless control for linear synchronous motor (LSM) propulsion systems, yet model-based methods suffer from position estimation errors caused by parameter mismatches due to temperature rise and stator segment transitions. This paper proposes an integrated sensorless control scheme with online parameter identification based on the model reference adaptive system (MRAS). First, the position estimation errors induced by both uniform parameter deviation and inter-phase asymmetry are theoretically quantified, revealing that resistance deviation causes errors inversely proportional to speed, while inductance deviation introduces speed-independent errors. Subsequently, adaptive laws for online stator resistance and inductance identification are designed using Popov’s hyperstability theory, ensuring global asymptotic stability. The identified parameters are fed back to the back-EMF observer in real time. Simulation and experimental results demonstrate that the MRAS algorithm maintains uniform ultimate boundedness under initial parameter mismatches and ensures accurate tracking during 3 g acceleration. Under full closed-loop sensorless control with parameter adaptation, the position error is confined within 9.3% of the pole pitch. The proposed scheme satisfies the operational requirements of the electromagnetic sled and provides an effective solution for sensorless control.

Actuators doi: 10.3390/act15100517

Authors: Hasti Gharavi Farshid Taban Soroush Korivand Nader Jalili

This study examines physically interpretable PZT signal features for concrete curing in two independent campaigns using rebound-hammer impact and controlled burst-sine actuation. Spearman correlations tracked feature medians across common Days 3, 7, 14, and 21 using campaign-specific compressive strengths as curing-progress references. Differences in batch, replication, and measurement configuration prevent isolation of excitation-method effects. Under impact excitation, PZT-B/Extra gave coefficients of 0.95, −1.00, 0.40, and 0.80 for peak count, time of maximum response, zero-crossing rate, and relative 2–4 kHz energy. Under controlled actuation, the side-actuation–Middle-sensor layout led screening across 70–110 kHz: RMS amplitude had a median coefficient of −0.80, meeting the criterion at three frequencies, while two-bin Fourier entropy had +0.87 and met it at all four. Additional within-method analyses showed Method 1 peak-count and response-timing directions persisted with Day 28, while zero-crossing-rate and relative-energy associations weakened; for Method 2, negative RMS persisted whereas Fourier entropy and layout ordering were age-set sensitive. The 120 kHz condition was retained for sensitivity analysis. These exploratory associations track curing-related mechanical development, not the complete curing state, and do not establish strength-specific sensitivity. PZT sensing complements standardized strength testing; no predictive or explainable-AI model was evaluated.

Actuators doi: 10.3390/act15100516

Authors: Feng Jiao Kai Li Xiaolong Tong Ruihe Cao Rongxin Zhu

Aiming at nonlinearity, time-varying parameters, variable surrounding rock conditions and complex external disturbances of the rotary system of hydraulic rock bolters in underground coal mines, traditional control methods suffer from low rotational speed tracking accuracy, weak anti-disturbance capacity, frequent sticking and drill bit damage. This paper investigates high-precision adaptive rotational speed control for rock bolters. First, a drill bit optimal rotational speed calculation model is established by integrating the rock hardness coefficient and drill bit wear characteristics with a wear correction coefficient. Considering the nonlinear friction of the rotary system and the dead-zone nonlinearity of the electro-hydraulic proportional valves, a valve-controlled motor rotary system model with nonlinear compensation is constructed. A smooth adaptive nonlinear function is designed, and a reduced-order adaptive nonlinear observer is built to accurately estimate unmodeled system states and lumped disturbances. A composite disturbance rejection predictive control strategy based on the adaptive observer is proposed. The simulation results show that the proposed adaptive observer achieves significantly improved disturbance observation accuracy and stability compared with conventional observers. The comparative simulations verify that the composite control strategy realizes fast and accurate tracking of the rotational speed of the rock bolters. This research provides the theoretical support for the adaptive high-precision rotational speed control of hydraulic rock bolters under complex working conditions, delivers critical engineering value for improving the efficiency and safety of roadway support construction, and promotes the intelligent upgrading of underground support equipment.

Actuators doi: 10.3390/act15100515

Authors: Szabolcs Lazar Mircea-Viorel Dragoi

Bioinspired actuators have attracted increasing attention because of their adaptability, compliance, energy efficiency, and potential for integration into advanced mechanical and robotic systems. However, existing reviews predominantly focus on particular material families, actuation principles, or robotic applications, without providing a unified assessment of their industrial relevance. This review addresses this gap by examining the applications, design, modelling, optimization, and manufacturing of bioinspired actuators from an industrial perspective. A broad bibliometric analysis based on the Web of Science Core Collection was complemented by a harmonized IEEE Xplore search. The investigation began with an analysis of 21 relevant review papers to identify the principal research orientations and insufficiently explored areas. Subsequently, 74 primary studies, including nine additional publications identified through IEEE Xplore, were selected for qualitative analysis using explicitly defined screening and eligibility criteria. The reviewed systems were classified according to their application areas and development approaches, with particular attention paid to robotics, grippers, clamping and positioning devices, modelling and optimization, and manufacturing technologies. Their validation conditions and technological maturity were also examined to distinguish demonstrated industrial applications from industrial-oriented prototypes and potential industrial applications. The results show that most reported solutions remain at the prototype stage, with limited evidence of continuous operation under realistic production conditions. The main barriers to industrial adoption include insufficient durability, limited manufacturing repeatability and scalability, control complexity, and the absence of standardized performance-assessment procedures. Based on these findings, future research directions are proposed for industrial validation, health monitoring, scalable manufacturing, integrated sensing and adaptive control, and modular multifunctional systems.

Actuators doi: 10.3390/act15100514

Authors: Xu Liu Hao Zhang Minfeng Zhang

Running a dense neuro-fuzzy sliding mode controller (SMC) on a resource-constrained UAV edge platform forces a three-way trade-off between compute, formal stability guarantees, and robustness to uncertainty. We recast the extended Kalman filter (EKF) from state estimation into weight-space prediction, which lets the controller drop inactive fuzzy rules on the fly while retaining stability proofs built on martingale theory. The framework couples four ideas. EKF weight-space compression treats the innovation sequence as an approximate martingale difference sequence. A graph attention network (GAT) learns time-varying inter-channel coupling and feeds it straight into the SMC equivalent-control term. Reinforcement learning with Lyapunov post-regularization, wrapped in a Wasserstein distributional-robustness constraint, is shown to form a supermartingale. Finally, INT8 quantization-aware training prepares the whole stack for edge deployment. These pieces rest on a common martingale foundation that yields finite-sample pruning-error bounds (Azuma–Hoeffding), worst-case tracking bounds (Doob), stochastic stability via supermartingale Lyapunov functions, and a minimum dwell-time theorem for switching rule sets. Across 10,000 high-fidelity PyBullet simulation runs, the framework cuts active fuzzy rules by 73% on average at the cost of 0.3–0.5 cm of simulated tracking error, and the INT8-compiled inference stack attains 4.2 ms mean latency and 0.93 W measured on a Jetson Orin Nano in a bench-top (non-flight) benchmark. The hardware experiments reported here are the edge-inference benchmarks; closed-loop control results are simulation-based, and flight validation on the physical platform is left to future work.

Actuators doi: 10.3390/act15100513

Authors: Andrew J. Hildreth Reza Rashidi Maryam Nasri Nikta Amiri Olivia C. Manley Dan DeFord Danny Tantalo Dylan Albicker Joe Clement

Steel structures operating in demanding environments require instrumentation capable of detecting structural damage and supporting timely intervention. This paper presents a compact wireless system that integrates piezoelectric sensing, decision-making, and localized on-demand repair. A surface-mounted piezoelectric transducer (PZT) transmitter–receiver pair is bonded to a steel plate, while an Arduino controller drives the transmitter with a 5 V, 10 kHz signal and acquires the sampled receiver response. Damage is identified through relative changes from a baseline established for the intact plate. Upon detection, a motor-driven miniature valve releases low-viscosity adhesive from an internal reservoir through a silicone tube for gravity-fed delivery to the damaged region. The system also logs and transmits data for MATLAB R2025b-based post-processing. A 3D-printed PLA/TPU housing integrates the sensing, control, power, and repair components while mechanically separating sensing and actuation functions. Coupled-field harmonic simulations in ANSYS were used to evaluate the electromechanical response of the bonded PZT pair and support the experimental design. Experimental frequency sweeps characterized the intact-system response, while controlled slot-width tests at 10 kHz showed a systematic decrease in the sampled receiver-response index with increasing defect width. Repair performance was further supported by partial recovery of the sampled response, together with morphology and bond-strength evidence showing continuous adhesive filling and mechanically meaningful bonding. The results demonstrate the feasibility of integrating piezoelectric sensing, decision-making, and localized on-demand repair within a single portable system for steel structures.

Actuators doi: 10.3390/act15100512

Authors: Shunshun Zhang Zilei Ji Yudong Xie Yi Wan Chuanying Wang Fujian Chen Xiangqian Zhu Shuai Ji Dong Wang Xiao Han Shawuti Yingming Geyu Zhu

Improving energy efficiency while maintaining accurate force and displacement control is a key requirement for servo deep-drawing die-cushion systems. Electro-hydraulic actuators (EHAs), which combine the high power density of hydraulic transmission with the controllability of electric drives, provide an effective approach for improving the dynamic performance and energy efficiency of metal-forming equipment. This paper investigates the control and energy-efficiency characteristics of an EHA applied to a servo deep-drawing die-cushion system, with particular emphasis on the working mechanism of its hydraulic system, the AMESim-Simulink co-simulation control strategy, and the energy-efficiency distribution characteristics. Firstly, an electro-hydrostatic actuator (EHA) model composed of a permanent magnet synchronous motor, a fixed-displacement pump, valve block unit, accumulator, and single-rod double-acting hydraulic cylinder is established. The power flow relationship of the system in the four-quadrant working condition is analyzed, and the flow distribution characteristics of the main oil circuit, supplementary oil circuit, and bypass branch are studied. Secondly, a joint simulation platform is built based on AMESim and Simulink to achieve bidirectional coupling between the hydraulic actuator and the motor drive control system. In the speed control loop, the traditional PI and fuzzy PI control strategies are compared; in the position control loop, the PID control and sliding mode control strategies are simulated and analyzed. The results show that the fuzzy PI control has better dynamic regulation ability under load torque and speed step change conditions, which can reduce speed overshoot and shorten the regulation process; the position-control results under a step-displacement command show that the sliding-mode controller improves the transient response and steady-state tracking accuracy compared with the conventional PID controller. Finally, the system’s four-quadrant energy efficiency, motor efficiency, pump volumetric efficiency, and mechanical efficiency are analyzed from the perspective of energy conversion. The results show that the system efficiency is affected by load, actuator speed, motor speed, and pump pressure difference, and the efficient working area is mainly distributed in the medium-high speed and moderate load range.

Actuators doi: 10.3390/act15100511

Authors: Robert Braun Magnus Landberg Petter Krus

The Hydraulic Infinite Linear Actuator with Multiple Rods (HILA-MR) enables multiple outputs to share a common hydraulic piston through independently controlled clamping mechanisms. This architecture has the potential to reduce actuation-system mass, volume, sensor count, and complexity in medium-heavy unmanned aerial vehicles (UAVs). However, because multiple control surfaces compete for a shared actuation resource, actuator performance depends strongly on the scheduling strategy used to allocate piston motion. This work investigates the feasibility of using HILA-MR for primary flight-control applications and evaluates three scheduling algorithms: time-division multiplexing (TDM), round-robin (RR), and multi-grip (MG). Simulation results were validated experimentally using a three-rod HILA-MR test rig. The algorithms were assessed using representative flight control commands and subsequently evaluated in coupled flight dynamics simulations. Results show good agreement between simulation and experiments. Compared with TDM, the RR and MG algorithms significantly improve tracking performance through adaptive allocation of actuation effort. Flight-dynamics simulations further demonstrate that the HILA-MR actuator achieved acceptable tracking performance during representative climb and turning maneuvers. The results indicate that HILA-MR is a promising actuation concept for future UAV flight-control systems.

Actuators doi: 10.3390/act15100510

Authors: Jinjie Jiang Chenyu Wang Haoyu Cheng Aixi Wu Xiaodong Sun

Small unmanned surface vehicles operating in confined, vegetation-rich, or ecologically sensitive waters require compact propulsion systems that minimize entanglement and unintended contact. Here, we present a 178 mm biomimetic surface robot propelled by bilateral flexible fins actuated by piezoelectric bimorphs. A differential high-voltage circuit drives each bimorph, while compliant fin structures transmit local bending into distributed deformation. We characterized static and dynamic fin kinematics, blocked thrust, and untethered swimming performance. Static fin-tip deflection increased nearly linearly with voltage, with similar spatial deformation profiles across the tested voltages. In dry-bench tests, fin-tip velocity reached a local maximum near 142 Hz. Under water-loaded conditions, both mean blocked thrust and path-averaged swimming speed were highest at 134 Hz, consistent with a shift in the preferred operating frequency following fluid loading and system integration. At 100 V under this condition, the robot produced a mean blocked thrust of approximately 15.3 mN and achieved a path-averaged speed of 43.68 ± 3.46 mm/s (mean ± SD, n = 5). At a differential peak voltage of 100 V and a drive frequency of 134 Hz, full-system battery-side input power was approximately 2.0 W; the blocked-thrust-to-power ratio was approximately 7.8 mN W−1, and the system-level electrical cost of transport (COT) was approximately 17.2. These results show that local piezoelectric bending can be transmitted through compliant fins to generate measurable thrust and repeatable untethered motion, providing a blade-free propulsion approach for compact surface robots.

Actuators doi: 10.3390/act15100509

Authors: Monserrat Stephania Martínez-Álvarez Alan Francisco Pérez-Vidal Felipe de Jesús Sorcia-Vázquez Gerardo Ortiz-Torres Jesse Yoe Rumbo-Morales Jorge Aurelio Brizuela-Mendoza Julio César Rodríguez-Cerda Carmen Elvira Hernández-Magaña María Dolores Figueroa-Jiménez

Population aging has contributed to an increased prevalence of conditions that impair lower-limb mobility in older adults, resulting in reduced functional independence and a greater risk of falls. In this context, assistive and rehabilitation exoskeletons have emerged as a technological approach to maintaining and restoring mobility. This study reviews 135 publications from 2016 to 2026 on lower-limb exoskeletons for older adults. The studies were classified according to design, actuation method, assisted joint, application, and evaluation evidence. The results of this analysis show that, within the reviewed literature, multi-joint and ankle exoskeletons are the most frequently represented systems. Among the studies reporting the actuation method, active electric systems and passive unpowered mechanisms are the most common, whereas pneumatic and hybrid solutions are reported less frequently. The reviewed developments also emphasize lightweight design and portability, together with control strategies intended to adapt assistance to the user’s needs. Gait assistance and motor rehabilitation account for the largest body of evidence, whereas sit-to-stand transitions, stair locomotion, and fall prevention remain underexplored. The reported evaluations employ functional, metabolic, spatiotemporal, and electromyographic metrics, with several studies reporting improvements in mobility-related outcomes. However, further clinical validation and more standardized assessments of safety, stability, and long-term performance are needed. Additional progress in regulatory guidance may also facilitate the clinical and everyday use of these technologies.

Actuators doi: 10.3390/act15100508

Authors: Hui Cao Zhiping Xie Bingyan Chen Fengshou Gu

The longitudinal non-uniformities in mass and stiffness distributions of railway vehicle carbodies, caused by doors, windows, and equipment compartments, significantly affect elastic vibrations and ride comfort. This paper establishes a vertical elastic vibration model based on the Euler–Bernoulli beam theory for variable cross-section carbodies, using piecewise uniform beam segments to represent actual cross-sectional properties. The transfer matrix method combined with the Newton–Raphson iteration is employed to solve natural frequencies and mode shapes. A hybrid active control strategy integrating secondary vertical electro-hydraulic actuators and distributed piezoelectric actuators is proposed. Based on a decentralised control architecture, a H∞ robust optimal controller is designed to suppress both rigid-body motions and the first two elastic modes. Simulation results at 250 km/h with a 20% centre-mass proportion show that the combined control reduces the vertical acceleration power spectral density (PSD) at the first vertical bending frequency to 5% of the passive suspension level, and to 35% at bounce and pitch frequencies. The Sperling ride index increases monotonically with speed, with the 20% mass proportion of the middle sub-beam yielding the best performance. The piezoelectric actuator voltage PSD reaches a peak of approximately 4000 V2·Hz−1 near the first bending frequency (0–15 Hz), demonstrating effective elastic vibration suppression, while the secondary actuator force PSD at the second bending frequency remains at around 103 N2·Hz−1, indicating limited contribution. The proposed variable cross-section beam model combined with hybrid control provides a theoretical foundation and engineering reference for lightweight design and active vibration reduction of high-speed trains.

Actuators doi: 10.3390/act15100507

Authors: Jin Peng Yu Han Tan Jun Yangyi Zhang Xinyi He Ping Jin

Permanent-magnet brushless DC motors (PMBLDCMs) are widely used in various industrial applications. This paper proposed a fully analytical dynamic model of PMBLDCMs based on the armature reaction and subsequent commutation phenomenon. First, it introduced the PMBLDCM prototype, including the stator currents, electromagnetic torque, and rotor position calculated via electromotive force balance equations, the Maxwell stress tensor method, and motion formulas. Then, it employed the subdomain method under load conditions to analyze magnetic flux densities in the airgaps and the stator slots. Finally, it established a field-circuit coupling finite-element model (FEM) to verify magnetic flux densities, back-EMF, torque and rotor-position predictions. A 1.5 kW PMBLDCM prototype was built with back-EMF and stator-phase currents validated through experiments. In addition, torque and rotor-position results are validated against FEM instead of physical experiments.

Actuators doi: 10.3390/act15100506

Authors: Liheng Wang Ming Zhuang Tenghui Dong Haibo Long Chuanshi Liu Qiyang Wu

Clean and reliable integrated air refrigerators are essential for the cryogenic systems of Tokamak devices. However, the high-speed drive motors in these systems are subjected to severe axial asymmetric temperature span boundaries. The axial temperature difference between the compressor and expander ends can reach a maximum value of 180 °C. To mitigate the risk of localized thermal accumulation under such extreme conditions, this paper proposes a switchable cooperative thermal management strategy. The approach integrates internal cooling using self-produced cryogenic air from the expander with a dynamically switchable multi-channel water-cooling network. A segmented switching logic is implemented for the water-cooling channel and the cold-air channel at the bearing near the expander to adapt to variable thermal boundaries. A multi-source thermal network (MSTN) model was established, and the cooling parameters were optimized using a genetic algorithm (GA). Experimental results at 35,000 rpm under a −85.4 °C deep-cooling condition demonstrate that the strategy successfully maintains the peak motor temperature at 126.2 °C. The measured system cooling capacity of 17 kW surpasses the initial design target (15 kW), confirming the engineering feasibility and robustness of the proposed strategy for clean cryogenic cooling in fusion engineering applications.

Actuators doi: 10.3390/act15100505

Authors: Pengfei Song Xiang Chen Yunsong Xu Zhiqiang Long

A train network control system is a cyber–physical system (CPS) whose safe operation depends on the integrity and timeliness of on-board sensor data. As such systems migrate towards networked and wireless architectures, the measurement link becomes exposed to replay, denial-of-service (DoS) and false data injection attacks (FDIA), against which single-dimensional detectors are no longer sufficient. This paper proposes a unified sensor-attack detection framework based on multidimensional consistency checking. A linear discrete-time state-space model and an explicit threat model are established first, and each attack is mapped component by component onto the system architecture and onto the network-level countermeasures that remain applicable. Three complementary layers then extract attack features from the algebraic, temporal-statistical and physical dimensions: analytical-redundancy parity-space detection, improved Transformer-based temporal prediction, and a physics-informed neural network (PINN) observer. For the PINN layer, a sufficient FDIA detectability condition is derived. The attack enters the physical residual through an explicitly computed attack-to-residual gain, which yields a non-centrality parameter and a closed-form bound on the attack magnitude; the gain predicted by the theory agrees with the measured gain to within 14%. Every distributional assumption behind these statistics is verified rather than taken for granted. The three statistics are then combined by a likelihood-ratio rule built from empirically estimated class-conditional densities of probability-integral-transformed statistics. This rule requires no conditional-independence assumption and additionally returns a coarse attack-type estimate whose reliability is quantified experimentally. On a single-car maglev experimental platform, the fused rule attains the highest average area under the curve (AUC, 0.943) and the highest F1 score, and it gives the shortest detection delay of all methods in every scenario (0.06–1.18 s, against 1.04–10.20 s for the individual layer). In a closed-loop Monte Carlo study it reaches an AUC of 0.996 under complete channel blocking, a regime in which the algebraic and physical layers collapse to 0.001.

Actuators doi: 10.3390/act15100504

Authors: Wenxuan Wu Yaoyao Lu Xiangzhong Yan Ziqian Li Yuan Liu Xinyu Liu Feiyan Min

Series Elastic Actuators (SEAs) have been widely adopted in collaborative robots, rehabilitation robots, and other compliant robotic systems owing to their excellent compliance and force-control performance. However, the introduction of elastic elements also increases dynamic complexity, giving rise to nonlinearities, parameter uncertainties, and oscillations. To address these issues, this paper proposes a Transformer-based temporal reinforcement learning control method for SEAs within the Proximal Policy Optimization (PPO) framework. First, a Transformer replaces the conventional Multi-Layer Perceptron (MLP) policy network to extract temporal dependency features from observation sequences via the self-attention mechanism. Second, a fixed-length historical state window is incorporated into the policy input to mitigate the performance degradation caused by partial observability (POMDP). Both simulation and hardware experiments validate the proposed method. In simulation, it achieves superior transient performance (a 10–90% rise time of 0.111 s and an overshoot of 3.68%) together with stable sinusoidal tracking. Real-world tests on a physical SEA platform further confirm its practical feasibility: multi-target step tracking attains a 10–90% rise time of approximately 0.15 s with overshoot below 2.3%, whereas long-duration sinusoidal tracking (60° amplitude, 0.1 Hz) maintains an RMS error of approximately 2.3° and smooth, chatter-free control actions. Comparative studies against MLP, LSTM, and CNN architectures reveal that the Transformer policy offers significant advantages in suppressing elastic oscillations and generating smooth control commands, confirming the efficacy of temporal modeling for the complex dynamics of SEA systems. An ablation study over the historical window length (L = 1–8) shows that at least four history steps are required to suppress elastic oscillations under fast target switching, while the mean inference time remains below 0.81 ms for L ≤ 8. In hardware payload experiments (0–1200 g), the tracking RMSE increases monotonically from 7.70° to 8.55° and the peak overshoot from 2.50% to 8.53%, while all runs remain stable without controller fault or divergence; the complete control task, including Transformer inference, executes within 0.61 ms on the real-time controller.

Actuators doi: 10.3390/act15100503

Authors: Yuchao Fang Xinyi Peng Peiyi Wang

This paper proposes a composite control method integrating frequency-domain precompensation (FDP) with a bandwidth-separated cascaded extended state observer (BSCESO), hereafter termed FDP-BSCESO, for high-precision line-of-sight trajectory tracking of an electro-optical stabilized platform. First, the reference trajectory is reconstructed offline using the identified closed-loop frequency response. Within the effective closed-loop bandwidth, inverse magnitude and phase compensation is applied to reduce amplitude attenuation and phase lag without increasing the feedback bandwidth. Second, the BSCESO employs a low-bandwidth first-stage observer and a higher-bandwidth residual observer to hierarchically estimate and compensate disturbance components with different temporal characteristics. The boundedness of the observer errors and the input-to-state stability of the closed-loop tracking error dynamics are analyzed. Comparative simulations against PID, ADRC, and SMC under disturbance-free, band-limited random-disturbance, and multi-frequency deterministic disturbance conditions show improved tracking and disturbance-rejection performance. Across the tested external-disturbance cases, the root mean square tracking error is reduced by 38.83–65.11% relative to the best-performing benchmark in the corresponding cases.

Actuators doi: 10.3390/act15100502

Authors: Kiyoshi Hoshino

In this study, the author proposes a swordsmanship training robot that evades attacks from human opponents by actively moving its target areas (or designated striking targets) on its body. Similar to a human practitioner wearing protective armor in Kendo, the robot is equipped with three target areas corresponding to the head, throat, and torso. They are independently actuated by three AC servo motors mounted in the central or lower parts of the body, which also house the control hardware responsible for motion control. Each target area is driven by a toothed pulley and timing belt mechanism. This transmission system enables precise position control while enhancing operational safety by absorbing excessive loads when large external forces are applied to the robot or when accidental collisions with human users occur. A high-speed camera is installed beneath the robot’s eye. Using visual information captured by the camera, the robot can estimate the likely attack type that an opponent is about to initiate and execute an appropriate defensive maneuver. In addition, a set of push-button switches corresponding to different defensive actions is provided. By observing the opponent’s movement, a human operator can manually trigger the most suitable defensive maneuver through these switches.

Actuators doi: 10.3390/act15100501

Authors: Fei Wang Lin Song Shijia Wang Jiaqiu Zheng Pengfei Wang

The rapid expansion of the low-altitude economy places unprecedented demands on the safety and reliability of unmanned aerial vehicles (UAVs). To address the limitations of single-modal feature extraction in capturing heterogeneous complementary information, this paper proposes a temporal and time–frequency dual-modality weighted fusion network (TTF-DWFNet) for UAV fault diagnosis. The proposed framework employs a parallel dual-branch architecture: a temporal modality branch utilizes a one-dimensional Transformer with a broadcast self-attention mechanism to model global temporal dependencies from raw vibration data, while a time–frequency modality branch transforms the data into spectrograms and leverages a two-dimensional convolutional neural network (CNN) to extract local texture features. Furthermore, an adaptive weighted fusion module is designed to automatically learn the discriminative contribution weights of the heterogeneous features at the channel level, enabling effective feature integration. Extensive experiments on two public datasets show that TTF-DWFNet achieves state-of-the-art accuracy of 96.47% and 92.76%, outperforming existing CNN-based and Transformer-based methods. The proposed TTF-DWFNet architecture has great practical application potential.

Actuators doi: 10.3390/act15100500

Authors: Xiaoxiong Zhou Hui Shen Shanshan Huang Zhihan Shi Guangming Zhang

This paper studies distributed leader–follower consensus for heterogeneous nonlinear multi-agent systems with different physical orders and channel-dependent matched and mismatched disturbances. A channel-wise fixed-time extended-state observer estimates the lumped disturbance in each state equation, while a finite-terminal-time performance function constrains neighborhood errors during the transient and steady-state stages. Order-dependent composite surfaces and controllers are designed without augmenting lower-order followers to a common order. Sufficient conditions are derived for fixed-time observer convergence, practical fixed-time convergence of the composite surfaces, boundedness of the complete closed loop, and invariance of the prescribed-performance funnels. Simulations with followers of orders [2,3,2,3] demonstrate disturbance reconstruction, prescribed-performance satisfaction, bounded control effort, and reduced sensitivity of the dominant observer–surface convergence phase to the initial condition.

Actuators doi: 10.3390/act15100499

Authors: Di Zhao Zhe Yue Wensong Zhang Jianping Yuan Weihua Ma Haofei Ban Sen Li Weiwei Lei

This paper presents a vision-guided nonlinear model predictive control (MPC) framework for coordinated dual-manipulator pre-contact acquisition of tumbling targets. Temporal monocular estimation supplies pose, motion, and uncertainty; rigid-body prediction generates fixture trajectories; and model-based or diffusion candidates initialize exact Denavit–Hartenberg (DH) refinement before clearance-checked execution. Synthetic tests give mean position and attitude errors of 0.0170–0.0182 m and 1.05–1.19°. With initial-state uncertainty and ±6% inertia mismatch, 3 s fixture-prediction root-mean-square error is 0.0822 m with 94.5% covariance coverage. In 30 paired stress scenarios, original-criterion safe capture is 19/30 for exact-DH MPC versus 14/30 for linearized MPC (exact McNemar p=0.180). A separate reviewer-motivated post hoc sensitivity imposes three-step angular-rate matching uniformly across five methods: safe capture is 19/30 versus 8/30 (Holm-adjusted p=0.0171). Diffusion and uncertainty inflation add no safe captures. Actual-cycle analysis finds a small 1.15% iteration reduction with diffusion, without an end-to-end timing benefit. Sequential mean update times are 1.234 s without diffusion and 1.392 s with diffusion, exceeding the 0.10 s simulated update interval. The evidence concerns delay-free, fixed-base kinematic supervisory planning with target-specific synthetic vision, not real-time hardware control or flight readiness.

Actuators doi: 10.3390/act15100498

Authors: Seokkan Ki Jun Yeong Lee Jung Gi Choi Gyu Hyeon Song Duri Han Jeongyun Kim Jeyeong Kim Wonkyeong Son Miseon Shim Changsoon Choi Seon Jeong Kim Shi Hyeong Kim Hyeon Jun Sim

Thermal comfort is a key determinant of human health and requires adaptive responses to dynamic environments. Here, we report a temperature-adaptive textile enabled by a tensile stress mismatch-driven poly(N-isopropylacrylamide) (PNIPAM) actuator operating within a human-friendly temperature range of 18–38 °C. A pre-stretched polyurethane core fiber integrated within a PNIPAM sheath in a noncoaxial configuration induces programmable bending through tensile-stress mismatch between elastic recovery and hydrogel swelling. Unlike conventional bilayer hydrogel actuators based on differential swelling between laminated layers, this pre-stretching strategy amplifies structural deformation through elastic restoring stress. When extended to a two-dimensional textile architecture, this strategy enables reversible, dynamic pore modulation with an approximately 400% increase in pore area. This study provides a promising platform for smart adaptive textiles, wearable healthcare, and soft robotics.

Actuators doi: 10.3390/act15090497

Authors: Cagdas Hisar Güven Balta Necmi Altın

Sliding mode control (SMC) is widely used for permanent magnet synchronous motor (PMSM) drives because of its robustness against disturbances and parameter uncertainties. However, the reaching law still faces a trade-off between fast convergence and chattering suppression. Reaching laws based on the signum function usually provide rapid convergence but induce severe high-frequency oscillations, whereas smooth or exponential modifications may reduce discontinuity at the expense of slower transient response or excessively large control gains. To address these limitations, this paper proposes a novel sine-logarithmic reaching law combined with a power-rate term for PMSM sliding mode control. The proposed structure avoids both the conventional smooth and exponential approximations commonly used in the literature. A theoretical analysis is presented, and the convergence behavior is characterized in terms of practical finite-time stability. The effectiveness of the proposed reaching law is evaluated in MATLAB/Simulink through comparative PMSM simulation studies, including start-up, steady-state, load-disturbance, parameter-variation, and total harmonic distortion (THD) tests against representative reaching laws from the literature. The simulation results indicate that the proposed method provides a favorable trade-off among rapid reaching, chattering attenuation, steady-state accuracy, and harmonic performance. These findings suggest that the proposed reaching law is a competitive alternative for PMSM sliding mode control.

Actuators doi: 10.3390/act15090496

Authors: Helin Wang Liwen Cao Huanrui Zhang

With the rapid development of autonomous systems, there is a growing need for versatile yet low-cost platforms that integrate perception, decision-making, and control in real-time environments. This study presents the design and implementation of a multi-functional intelligent car system based on the STM32F103C8T6 microcontroller. The system integrates an OPENMV camera for visual recognition, a DY-SV8F voice module, a dual 4-channel grayscale sensor array for high-precision path tracking, and a PS2 remote controller. A hierarchical control architecture is adopted. The core role of the actuators, which drives the vehicle’s motion in response to visual and sensory feedback, is emphasized through a tightly coupled control loop that translates perceptual data into precise PWM signals for motor speed and direction regulation. The core contribution lies in the design of a novel path tracking algorithm featuring Gaussian-weighted sensor fusion, a finite-state machine for path feature recognition, and an adaptive PID controller with curvature-based feedforward compensation. Furthermore, this paper provides a detailed exposition of a lightweight color marker recognition algorithm operating in the hue, saturation, value (HSV) color space, including its mathematical formulation and system-level integration with the motion control loop for event-triggered multi-modal task execution. Experimental results demonstrate that the proposed system achieves a mean absolute path tracking deviation of 2.1 mm, a color detection accuracy of 100% under controlled lighting, and flawless execution of complex, event-driven task sequences.

Actuators doi: 10.3390/act15090495

Authors: Wang Chen Mengke Xiong Xiaojie Zhou Wen Sun

To address the limited candidate voltage vectors, insufficient voltage-tracking capability, and parameter sensitivity of conventional model predictive voltage control (MPVC) for permanent magnet synchronous motor (PMSM) drives, this paper proposes an improved dual-vector incremental model predictive voltage control strategy with adaptive forgetting factor recursive least squares (IDV-IMPVC-AFFRLS). First, an incremental voltage prediction model is developed to eliminate the explicit dependence on permanent-magnet flux linkage and reduce parameter dependence to stator resistance and inductance. Second, six virtual voltage vectors are synthesized to expand the candidate set from eight to 14, and a Lagrange-multiplier-based dual-vector duty-cycle optimization is employed to improve reference-voltage approximation. Third, an adaptive forgetting factor recursive least squares (AFFRLS) algorithm based on the prediction-error norm is introduced to identify and update the stator resistance and inductance online. Experimental results show that, under nominal parameters, IDV-IMPVC reduces phase-current THD from 16.57% to 8.45% and torque ripple from 0.10 N·m to 0.04 N·m, corresponding to reductions of 49.0% and 60.0%, respectively. Under resistance and inductance mismatches, IDV-IMPVC-AFFRLS limits THD to 9.15% and torque ripple to 0.04 N·m, demonstrating improved steady-state performance and parameter robustness.

Actuators doi: 10.3390/act15090494

Authors: Erik Prada Jaroslav Romančík Peter Jan Sincak Ľubica Miková Martin Varga Michal Kelemen

Soft robotic actuators exploit structural compliance to produce adaptive motion, but their response depends strongly on the interaction between geometry, material distribution, specific reinforcement, and actuation. This manuscript presents a bio-inspired hybrid soft actuator based on the elongated, continuously deformable morphology of the arrow worm and evaluates whether its bending response can be programmed through structural morphology. Four force-controlled nonlinear static finite element studies were performed in SOLIDWORKS Simulation using a hyperelastic Ogden model for the EcoflexTM 00-50 body and orthotropic models for the Thermoplastic Polyurethane (TPU) 68D reinforcement spine and Acrylonitrile styrene acrylate (ASA) pressure pad. Across the analysed force activation levels, maximum resultant displacement increased from 0.948 mm to 17.88 mm, equivalent strain from 0.005268 to 0.06833, and maximum von Mises stress from 0.596 MPa to 5.447 MPa. Simultaneously, effective-average incremental stiffness decreased from 0.21097 N/mm to 0.04846 N/mm, corresponding to a 77.03% reduction. These findings demonstrate progressive nonlinear softening and the transformation of mechanical input into a guided global shape change. A representative comparison with existing measurements of the fabricated actuator was additionally used to quantitatively cross-check the predicted bending response. The result of the morphological calculation was also the creation of a morphological map for quantitative and qualitative assessment of normalized morphological descriptors of the actuator.

Actuators doi: 10.3390/act15090493

Authors: Heeseok Shin Myeongjun Kim Heechang Moon Jeonghoon Kwak

Reverse path tracking of multi-trailer systems is challenging because tractor steering affects the following bodies only through passive hitch joints, causing tracking-error propagation and increasing the risk of jackknifing. This paper proposes a backstepping-based recursive virtual-heading (BS-RVH) controller that converts the path-tracking error of the final trailer into a desired heading rate and recursively generates the desired hitch angles, preceding-body heading rates, and tractor steering command. Desired hitch-angle saturation is included, and local boundedness and the effect of saturation residuals are analyzed. For a tractor–two-trailer system, BS-RVH achieves lateral root-mean-square errors of 0.015 m, 0.021 m, and 0.013 m on the S-curve, circular, and figure-eight paths, respectively. These values represent reductions of 93.0–93.4% compared with the curvature-based controller. The maximum absolute hitch angles remain below 12°, and all paths reach the predefined 99.5% completion threshold without jackknifing. An additional tractor–three-trailer evaluation completes the same paths without jackknifing, with lateral root-mean-square errors ranging from 0.073 m to 0.112 m. These results demonstrate the effectiveness and stage-wise extensibility of BS-RVH under low-speed kinematic conditions.