Search Results (54)

This study presents a phenomenological model for predicting the thermomechanical behaviour of spring-type actuators made of shape memory alloys (SMAs). The model incorporates the kinetics of martensite–austenite phase transitions as a function of temperature and applied stress. The primary innovation is the inclusion of a scalar internal variable that represents the evolution of the phase transformation within a phenomenological macroscopic model. This approach enables the deformation–force–temperature behaviour of SMA-based spring elements under cyclic loading to be accurately described. A set of constitutive equations was derived to describe reversible and residual strains, along with transformation start and finish conditions. Model parameters were calibrated using experimental data from VSP-1 and TN-1K SMA springs that were subjected to thermal cycling. The validation results show a high correlation between the theoretical predictions and the experimental data, with deviation margins of less than 6.5%. The model was then applied to designing and analysing thermosensitive actuator mechanisms for temperature control systems. This yielded accurate deformation–force characteristics, demonstrating low inertia and high repeatability. This approach enables the efficient prediction and improvement of the performance of SMA-based spring elements in actuators, making it relevant for adaptive systems in marine and aerospace applications. Full article

The construction of high-rise buildings necessitates efficient and reliable material transport systems to improve productivity and reduce labor-intensive tasks. Traditional methods such as cranes and elevators are widely used but are often constrained by high costs and spatial limitations. Manipulator-based robotic systems have been explored as alternatives; however, they require complex control algorithms and struggle with confined construction environments. To address these challenges, we propose a lifting robot designed for repetitive inter-floor material transport in construction sites. The proposed system integrates a gear-connected double parallelogram linkage with a crank-rocker mechanism, enabling one-degree of freedom (1-DOF) operation for simplified control and precise positioning. Additionally, a spring-cable-based gravity compensation mechanism is implemented to reduce actuator torque, enhancing energy efficiency and structural stability. A prototype was fabricated, and experimental validation was conducted to evaluate torque reduction, positioning accuracy, and structural performance. Results demonstrate that the proposed system effectively minimizes driving torque, improves load-handling stability, and enhances overall operational efficiency. This study provides a foundation for developing automated lifting solutions in construction, contributing to reduced worker strain and increased productivity. Full article

This paper aims to solve the problems of poor mobility, passability, and stability in heavy-duty vehicles, and proposes an active suspension system control strategy based on position–force feedback optimal control to coordinately enhance vehicle passability and wheel grounding performance. Firstly, a two-degrees-of-freedom one-sixth vehicle active suspension model and a valve-controlled hydraulic actuator system model are constructed, and the advantages of impedance control in robot compliance control are integrated to analyze their applicability in hydraulic active suspension. Next, a position feedback controller and force feedback LQG optimal controller for fuzzy PID control are designed, the fuzzy PID-LQG (FPL) integrated method is applied to the hydraulic active suspension system, and the dynamic load of the wheel is tracked by impedance control to obtain the spring mass displacement correction. Then, a suspension system model under the excitation of a C-class road surface and a 0.11 m raised road surface is constructed, and the dynamic simulation and comparison of active/passive suspension systems are carried out. The results show that, compared with PS and LQR control, the body vertical acceleration, suspension dynamic deflection, and wheel dynamic load root-mean-square value of the proposed FPL integrated control active suspension are reduced, which can effectively reduce the body vibration and wheel dynamic load and meet the design objectives proposed in this paper, effectively improving vehicle ride comfort, handling stability, passability, and wheel grounding performance. Full article

Historically, a large fraction of fatigue testing of both components and structures has been performed using hydraulic actuators. These are typically driven by servo-valves, which are in themselves very inefficient. But, as most tests involve elastically stressing mechanical components, a lot of stored energy could be recovered. Unfortunately, servo-valves are not regenerative—simply metering out fluid in order to relax the system prior to the start of the next cycle. There is much to be gained with a more intelligently controlled system. The FastBlade facility in Scotland uses a new type of regenerative test hydraulics. Digital displacement pump/motors (DDPMs), originated by Artemis Intelligent Power, now Danfoss Scotland, are used to load and unload the test structure directly via hydraulic rams. The DDPMs are driven by induction motors supplied by three-phase frequency converters, each with a very loose speed correction target, such that they can speed up or slow down according to the instantaneous torque exerted by the load. The rotating assembly of the induction motor and DDPM is designed to have sufficient inertia so as to function as a kinetic energy storage flywheel. The loading energy is then cyclically transferred between the rotating inertia of the motor/DDPM and the spring energy in the test structure. The electric motor provides sufficient energy to maintain the target average cyclical shaft speed of the DDPM whilst the bulk of the system energy oscillates between the two storage mechanisms. Initial tests (at low load) suggest that this technique requires only 30% of the energy previously needed. FastBlade is a unique facility built by the University of Edinburgh and Babcock, with support from the UK EPSRC, conceived as a means of testing and certifying turbine blades for marine current turbines. However, this approach can be used in any cyclical application where elastic energy is stored. Full article

Most trunk-like robots are designed with distributed actuators to mimic the envelope-grasping behavior of elephant trunks in nature, leading to a complex actuation system. In this paper, a modular underactuated elephant trunk-imitating robot based on the combined drive of the cable and shape memory alloy (SMA) springs is designed. Unlike the traditional underactuated structure that can only passively adapt to the envelope of the object contour, the proposed elephant trunk robot can control the cable tension and the equivalent stiffness of the SMA springs to achieve active control of the envelope morphology for different target objects. The overall structure of the elephant trunk robot is designed and the principle of deformation envelope is elucidated. Based on the static model of the robot under load, the mapping relationship between the tension force and the tension angle between modules is derived. The positive kinematic model of the elephant trunk robot is established based on the Debavit–Hartenberg (D–H) method, the spatial position of the elephant trunk robot is obtained, and the Monte Carlo method is used to derive the robot’s working space. The active bending envelope grasping performance is further verified by building the prototype to perform grasping experiments on objects of various shapes. Full article

Continuously rotating gimbals for scanning purposes are widely used in space applications. For high-precision gimbals, it is essential to lock the gimbal before launch and unlock it on orbit. This kind of gimbal puts forward the need for hold down release mechanisms that are able to clear the gap between the rotating and fixed parts at release. Existing technologies either lack the function of gap avoidance after separation or rely more or less on the elastic deformation of the structure or limited spring forces for unlocking, which are either unreliable or complicated. To address this problem, this paper presents the design of a novel non-pyrotechnic heavy-load hold down release mechanism (HDRM) based on shape memory alloy actuator. The proposed HDRM is shock-free and capable of clearing an axial gap of 8 mm for safe rotating at release. The structure and operational principle of the proposed design are straightforward. Detailed tests show the proposed HDRM may withstand a maximum external force of 50 KN with relatively high stiffness under 15 KN of preload, indicating a better performance than existing products. The HDRM demonstrates its promising usage as an alternative to traditional pyrotechnic and non-pyrotechnic HDRMs. Full article

With the advancement of manufacturing, the precision requirements for various high-precision processing equipment and instruments have further increased. Due to its noncontact nature, simple structure, and controllable performance, electromagnetic levitation has broad application prospects in ultra-precision instruments and ground testing of aerospace equipment. Research on vibration isolation technology using electromagnetic levitation is imperative. This paper reviews the latest research achievements of three types of passive isolators and five active isolation actuators. It also summarizes the current research status of analytical methods for passive isolators and the impact of isolator layout. This study explores current isolators’ achievements, such as the development of passive isolators that generate negative stiffness and require mechanical springs for uniaxial translational vibrations, single-function actuators, and control systems focused on position and motion vibration control. Based on the current isolators’ characteristics, this review highlights future developments, including focusing on passive isolators for heavy loads and multi-axis isolation, addressing complex vibrations, including rotational ones, and developing methods to calculate forces and torques for arbitrary six-DOF movements while improving speed. Additionally, it emphasizes the importance of multifunctional actuators to simplify system structures and comprehensive control systems that consider more environmental factors. This provides significant reference value for vibration isolation technology using electromagnetic levitation. Full article

To improve the vibration performance of oil-lubricated tilting pad bearing systems, this paper investigates the impact of different structural parameters on the vibration reduction effect of piezoelectric actuators on flexible tilting pad bearings. Four sets of flexible tilting pad bearings were designed and manufactured, including a flexible hinge tilting pad bearing and three sets of double-layer spring-supported flexible tilting pad bearings with different parameters. The radial displacement of the bearing load pad was controlled to varying degrees using a piezoelectric actuator, and semi-active control experiments were conducted on the flexible tilting pad bearings. The experimental results show that appropriately reducing the radial clearance and the stiffness of the bearing’s flexible structure can effectively suppress vibrations, enhance the vibration reduction effect of the piezoelectric actuation, and increase the stability of the bearing-rotor system. This study is of significant importance for the design of flexible tilting pad bearings and the vibration suppression of rotor systems. Full article

SMA actuators are a group of lightweight actuators that offer advantages over conventional technology and allow for simple and compact solutions to the increasing demand for electrical actuation. In particular, an increasing number of SMA torsional actuator applications have been published recently due to their ability to supply rotational motion under load, resulting in advantages such as module simplification and the reduction of overall product weight. This paper presents the conceptual design, operating principle, experimental characterization and working performance of torsional actuators applicable in active rudder in aeronautics. The proposed application comprises a pair of SMA torsion springs, which bi-directionally actuate the actuator by Joule heating and natural cooling. The experimental results confirm the functionality of the torsion springs actuated device and show the rotation angle of the developed active rudder was about 30° at a heating current of 5 A. After the design and experiment, one of their chief drawbacks is their relatively slow operating speed in rudder positioning, but this can be improved by control strategy and small modifications to the actuator mechanism described in this work. Full article

Pneumatic artificial muscles (PAMs) possess compliant properties desirable for certain applications such as prosthetics and robotic structures. However, this compliance along with their inherent nonlinear dynamics make them difficult to accurately model and as such accurately control under certain control architectures. Common approaches to this problem include measuring the actuator’s physical properties and approximating a model based on these parameters or using deep learning methods to train a model with the actuator’s behaviours. This paper introduces an optimisation-based modelling approach based on a particle swarm optimisation (PSO) algorithm using a mass–spring–damper approximation for the PAM, as well as a piecewise modelling method that accounts for nonlinear dynamics. The use of optimisation to estimate model parameters removes the need to measure physical properties, and the three-element approximation allows for fast model generation with low computational complexity and training data requirements. Through multiple tests comparing model behaviour with real PAM motion, the accuracy of these models is confirmed to be promising for future work. Dynamic nonlinearities are properly accounted for using the piecewise modelling method, including both hysteresis and disproportionate input/output relationship across the stroke length of the actuator. Compared with other PAM modelling techniques, this method has improved generation time, lower computational load requirements, and complexity and can be applied to actuators for which the phenomenological mass–spring–damper model is a good approximation. Full article

Dynamic stiffness is a parameter of great importance for the assessment of the sound insulation properties of resilient materials commonly used under floating floors in dwellings. This work proposes a simplified approach that relies on an electro-mechanical circuit model for the determination of this parameter using a two-degree-of-freedom system of masses and springs. Unlike the method described in the standard ISO 9052-1, the proposed approach uses a single electrodynamic actuator both as an impulser and vibration sensor, thus reducing the instrumental requirements and yielding a more stable arrangement. By measuring the input electrical impedance of the mass-loaded actuator when coupled to a slab–material system it was possible to retrieve the mechanical mobility function thereof and thus obtain the dynamic stiffness of the material. Several materials were tested following the proposed approach, with results showing good agreement when compared to those obtained following the standardized procedure. In general, the preliminary research encourages the use of the proposed approach for characterization purposes. Full article

This paper illustrates an experimental activity for the closed-loop position control of an actuator made using shape memory alloy (SMA) wire. A solution with the self-sensing effect was implemented to miniaturize the systems, i.e., without external sensors. A proportional control algorithm was initially used, demonstrating the idea’s feasibility; the wire can behave simultaneously as an actuator and sensor. An experimental investigation was subsequently conducted for the optimization of the developed actuator. As for the material, a Flexinol wire, Ni-Ti alloy, with a diameter of 0.150 mm and a length of 200 mm, was used. Preliminarily, characterization of the SMA wire at constant and variable loads was carried out; the characteristics detected were elongation vs. electric current and elongation vs. electrical resistance. The control system is PC based with a data acquisition card (DAQ). A drive board was designed and built to read the wire’s electrical resistance and power it by pulse width modulation (PWM). A notable result is that the actuator works with good precision and in dynamic conditions, even when it is called to support a load up to 65% different from that for which the electrical resistance–length correlation has previously been experimentally obtained, on which the control is based. This opens up the possibility of using the actuator in a counteracting configuration with a spring, which makes hardware implementation and control management simple. Full article

This study introduces an approach for modeling an arm of a Stewart platform to analyze the location of sections with a high deflection among the arms. Given the dynamic nature of the Stewart platform, its arms experience static and dynamic loads. The static loads originate from the platform’s own weight components, while the dynamic loads arise from the movement or holding of equipment in a specific position using the end-effector. These loads are distributed among the platform arms. The arm encompasses various design categories, including spring-mass, spring-mass-damper, mass-actuator, and spring-mass-actuator. In accordance with these designs, joint points should be strategically placed away from critical sections where maximum buckling or deformation is prominent. The current study presents a novel model employing Euler’s formula, a fundamental concept in buckling analysis, to propose this approach. The results align with experimental and numerical reports in the literature that prove the internal force of the platform arm is affecting the arm stiffness. The equal stiffness of an arm is related to its internal force and its deflection. The study demonstrates how higher levels of dynamic loading influence the dynamic platform, causing variations in the maximum arm’s buckling deflection, its precise location, and the associated deflection slope. Notably, in platform arms capable of adjusting their tilt angles relative to the vertical axis, the angle of inclination directly correlates with deflection and its gradient. The assumption of linearity in Euler’s formula seems to reveal distinctive behavior in deflection gradients concerning dynamic mechanisms. Full article

The integration of a passive elastic element in series between a motor and its load is popular in many human–robot interaction scenarios. By virtually imposing elastic behavior on the motor, an impedance control can act as a second stiffness to such an actuator. In this study, we investigated how participants perceived the different stiffness settings in a series elastic actuator by measuring the Just Noticeable Difference (JND) of the real stiffness of the elastic element and the virtual stiffness introduced by impedance control. We conducted a user study during which participants interacted with an impedance-controlled Series Elastic Actuator through a lever. During the user study, we varied the real stiffness of the elastic element and the virtual stiffness. We found that participants seem to perceive both the virtual stiffness and the real stiffness in the same way and in accordance to Weber’s law, which states that the stiffness JND is always equal to a fraction of the initial stiffness. Following these findings, we concluded that the impedance controller can implement an effective virtual stiffness with a behavior comparable to a real torsional spring. Therefore, a system combining real and virtual stiffness can simulate a single combined stiffness for a user interacting with it. Full article

Shape memory alloys (SMAs) are gaining popularity in the fields of automotive and aerospace engineering due to their unique thermomechanical properties. This paper proposes a numerical implementation of a comprehensive constitutive model for simulating the thermomechanical behavior of shape memory alloys, with temperature and strain as control variables to adjust the shape memory effect and super elasticity effect of the material. By implementing this model as a user subroutine in the FE code Abaqus/Standard, it becomes possible to account for variations in material properties in complex components made of shape memory alloys. To demonstrate the potential of the proposed model, a skid plate system design is presented. The system uses bistable actuators with shape memory alloy springs to trigger plate movement. The kinematics and dynamics of the system are simulated, and effective loads are generated by the shape memory alloy state change due to the real temperature distribution in the material, which depends on the springs’ geometrical parameters. Finally, the performance of the actuator in switching between different configurations and maintaining stability in a specific configuration is assessed. The study highlights the promising potential of shape memory alloys in engineering applications and demonstrates the ability to use them in complex systems with accurate simulations. Full article