Feature Papers to Celebrate the SCIE Coverage

The lower limb exoskeleton investigated in this work actively supports the knee and hip and is intended to provide full motion support during gait. Parallel elastic actuators are integrated into the hip joints to improve the energy efficiency in gait. The prototype was tested in sit-to-stand and gait trials, in which the actuators were cascade-controlled with position trajectories. The compliant actuation of the hip in gait experiments proved to be more efficient; the peak torque was reduced by up to 31% and the RMS power was reduced by up to 36%. Full article

Twisted coiled actuators (TCAs) are a type of soft actuator made from polymer fibres such as nylon sewing thread. As they provide motion in a compact, lightweight, and flexible package, they provide a solution to the actuation of wearable mechatronic devices for motion assistance. Their limitation is that they provide low total force, requiring them to actuate in parallel with multiple units. Previous literature has shown that the force and stroke production can be improved by incorporating them into fabric meshes. A fabric mesh could also improve the contraction efficiency, strain rate, and user comfort. Therefore, this study focused on measuring these performance metrics for a set of TCAs embedded into a woven fabric mesh. The experimental results show that the stroke of the actuators scaled linearly with the number of activated TCAs, achieving a maximum applied force of 11.28 N, a maximum stroke of 12.23%, and an efficiency of 1.8%. Additionally, two control methods were developed and evaluated, resulting in low overshoot and steady-state error. These results indicate that the designed actuators are viable for use in wearable mechatronic devices, since they can scale to meet different requirements, while being able to be accurately controlled with minimal additional components. Full article

The ionic polymer metal composite (IPMC) actuator is a kind of soft actuator that can work for underwater applications. However, IPMC actuator control suffers from high nonlinearity due to the existence of inherent creep and hysteresis phenomena. Furthermore, for underwater applications, they are highly exposed to parametric uncertainties and external disturbances due to the inherent characteristics and working environment. Those factors significantly affect the positioning accuracy and reliability of IPMC actuators. Hence, feedback control techniques are vital in the control of IPMC actuators for suppressing the system uncertainty and external disturbance. In this paper, for the first time an adaptive full-order recursive terminal sliding-mode (AFORTSM) controller is proposed for the IPMC actuator to enhance the positioning accuracy and robustness against parametric uncertainties and external disturbances. The proposed controller incorporates an adaptive algorithm with terminal sliding mode method to release the need for any prerequisite bound of the disturbance. In addition, stability analysis proves that it can guarantee the tracking error to converge to zero in finite time in the presence of uncertainty and disturbance. Experiments are carried out on the IPMC actuator to verify the practical effectiveness of the AFORTSM controller in comparison with a conventional nonsingular terminal sliding mode (NTSM) controller in terms of smaller tracking error and faster disturbance rejection. Full article

In this work, we address the simulation and testing of MEMS micromirrors with hardening and softening behaviour excited with patches of piezoelectric materials. The forces exerted by the piezoelectric patches are modelled by means of the theory of ferroelectrics developed by Landau–Devonshire and are based on the experimentally measured polarisation hysteresis loops. The large rotations experienced by the mirrors also induce geometrical nonlinearities in the formulation up to cubic order. The solution of the proposed model is performed by discretising the device geometry using the Finite Element Method, and the resulting large system of coupled differential equations is solved by means of the Harmonic Balance Method. Numerical results were validated with experimental data collected on the devices. Full article

This paper discusses the design and manufacturing of a thin polymer spherical adaptive reflector of diameter $D=200$ mm, controlled by an array of 25 independent electrodes arranged in a keystone configuration actuating a thin film of PVDF-TrFE in $d_{31}$-mode. The 5 $\mathsf{\mu }$m layer of electrostrictive material is spray-coated. The results of the present study confirm that the active material can be modelled by a unidirectional quadratic model and that excellent properties can be achieved if the material is properly annealed. The experimental influence functions of the control electrodes are determined by a quasi-static harmonic technique; they are in good agreement with the numerical simulations and their better circular symmetry indicates a clear improvement in the manufacturing process, as compared to a previous study. The low order optical modes can be reconstructed by combining the 25 influence functions; a regularization technique is used to alleviate the ill-conditioning of the Jacobian and allow to approximate the optical modes with reasonable voltages. Full article

This paper presents a magneto-rheological (MR) actuator that can be easily inserted into haptic shoes and can haptically simulate the material properties of the ground. To increase the resistive force of the proposed actuator, we designed a movable piston having multiple operation modes of MR fluids. Further, the design of a solenoid coil was optimized to maximize the resistive force in a limited-sized MR actuator. Simulations were conducted to predict the actuation performance and to show that the magnetic flux flows well by forming a closed loop in the proposed actuator. The quantitative evaluation of the proposed actuator was investigated by measuring the resistive force as a function of the input current and its pressed depth. From the result, we found that the proposed actuator can create over 600 N by adjusting the input current. Full article

The work reported here was aimed at improving the practical efficiency of the model-based development and integration of electromechanical actuators. Models are proposed to serve as preliminary design, virtual prototyping, and validation. The first part focuses on the early phases of a project in order to facilitate the identification of modelling needs and constraints, and to build a top-level electromechanical actuator model for preliminary studies and sub-specification. Detailed modelling and simulation are then addressed with a mixed view on the control, power capability, and thermal balance. Models for the power chain are firstly considered by focusing on the key practical issues in modelling the electric motor, power electronics, and mechanical power transmission. The same logic is applied to the signal and control chain with practical considerations concerning the parameters of the controller, its digital implementation, the sensors, and their signal conditioning. Numerous orders of magnitude are provided to justify the choices made and to facilitate decision-making for and through simulation activities. Full article

This paper shows the construction of a low-cost, open-source mechanical ventilator. The motivation for constructing this kind of ventilator comes from the worldwide shortage of mechanical ventilators for treating COVID-19 patients—the COVID-19 pandemic has been striking hard in some regions, especially the deprived ones. Constructing a low-cost, open-source mechanical ventilator aims to mitigate the effects of this shortage on those regions. The equipment documented here employs commercial spare parts only. This paper also shows a numerical method for monitoring the patients’ pulmonary condition. The method considers pressure measurements from the inspiratory limb and alerts clinicians in real-time whether the patient is under a healthy or unhealthy situation. Experiments carried out in the laboratory that had emulated healthy and unhealthy patients illustrate the potential benefits of the derived mechanical ventilator. Full article

In the current clinical practice, the diagnosis of Rheumatoid Arthritis (RA) draws on the qualitative evaluation of pain sensitivity thresholds which is affected by several source of uncertainties, due to an operator-dependent diagnostic protocol. Taking our cue from the diagnostic shortcomings, we have explored the possibility of automating the measurement of mechanical nociceptive thresholds through the adoption of soft pneumatic actuators controlled by an embedded control unit. In this work, we want to show that a purpose-made biomechatronic device actuated by soft and pneumatic actuators is potentially a boon both for rheumatologists and biomedical researchers involved in nociception and physicophysical studies. In the full breadth and scope of the objective diagnosis of RA, the first prototype of a novel biomechatronic device for quantitative and automatic measurement of mechanical nociceptive thresholds has been designed and tested through nociception experiments on 10 subjects. The experimental results show that the designed device can reliably generate the controllable and repeatable nociceptive stimuli needed for the objective diagnosis of RA. Full article

$H_{\infty }$ surge control in centrifugal compressors by using active magnetic bearings (AMBs) has been successfully designed and implemented. However, the structure and design process of $H_{\infty }$ surge control are quite complex. This paper reports on the design and implementation of fractional-order proportional-derivative control (FOPD) that results in the required specifications of surge control with a simple controller structure. To validate its effectiveness, the proposed FOPD surge controller has been implemented on a centrifugal compressor test rig equipped with AMBs. Simulation and experimental results show that the FOPD surge controller outperforms integer-order PD (IOPD) control in extending the surge limit in terms of the mass flow and provides similar performance as the $H_{\infty }$ controller. Full article

The actuation of silicone/ethanol soft composite material-actuators is based on the phase change of ethanol upon heating, followed by the expansion of the whole composite, exhibiting high actuation stress and strain. However, the low thermal conductivity of silicone rubber hinders uniform heating throughout the material, creating overheated damaged areas in the silicone matrix and accelerating ethanol evaporation. This limits the actuation speed and the total number of operation cycles of these thermally-driven soft actuators. In this paper, we showed that adding 8 wt.% of diamond nanoparticle-based thermally conductive filler increases the thermal conductivity (from 0.190 W/mK to 0.212 W/mK), actuation speed and amount of operation cycles of silicone/ethanol actuators, while not affecting the mechanical properties. We performed multi-cyclic actuation tests and showed that the faster and longer operation of 8 wt.% filler material-actuators allows collecting enough reliable data for computational methods to model further actuation behavior. We successfully implemented a long short-term memory (LSTM) neural network model to predict the actuation force exerted in a uniform multi-cyclic actuation experiment. This work paves the way for a broader implementation of soft thermally-driven actuators in various robotic applications. Full article

This research explores a new ATE (Automatic Testing Equipment) method for Micro Electro Mechanical Systems (MEMS) devices. In this method, microscale aerodynamic drag force is generated on a movable part of a MEMS sensor from a micronozzle hole located a specific distance above the chip that will result in a measurable change in output. This approach has the potential to be generalized for the characterization of every MEMS device in mass production lines to test the functionality of devices rapidly and characterize important mechanical properties. The most important testing properties include the simultaneous application of controllable and non-invasive manipulative force, a single handler for multi-sensor, and non-contact characterization, which are relatively difficult to find with other contemporary approaches. Here we propose a custom-made sensing platform consisting of a microcantilever array interconnected to a data acquisition device to read the capacitive effects of each cantilever’s deflection caused by air drag force. This platform allows us to empirically prove the functionality and applicability of the proposed characterization method using airflow force stimuli. The results, stimulatingly, exhibited that air force from a hole of 5 µm radii located 25 µm above a 200 × 200 µm² surface could be focused on a circular spot with radii of approximately 5 µm with surface sweep accuracy of <8 µm. This micro-size airflow jet can be specifically designed to apply airflow force on the MEMS movable component surface. Furthermore, it was shown that the generated air force range could be controlled from 20 nN to 60 nN, approximately, with a linear dependency on airflow ranging from 5 m/s to 20 m/s, which is from a 5 µm radius microhole air jet placed 400 µm above the chip. In this case-study chip, for a microcantilever with a length of 400 µm, the capacitance curve increased linearly from 28.2 pF to 30.5 pF with airflow variation from 5 m/s to 21 m/s from a hole. The resultant curve is representative of a standard curve for testing of the further similar die. Based on these results, this paper paves the way towards the development of a new non-contact, non-invasive, easy-to-operate, reliable, and relatively cheap air-based method for characterizing and testing MEMS sensors. Full article