Actuators, Volume 11, Issue 7 (July 2022) – 32 articles

Teleoperation, in which humans and robots work together to improve work performance, is growing explosively. However, the work performance of teleoperation is not yet excellent. Master–slave systems with different kinematics and workspaces need space-transformation control techniques. These techniques cause psychological fatigue to an operator with poor manipulation skills. In this study, we propose an intuitive master design that focuses on fatigue. Large workspaces reduce mental fatigue; however, they lead to physical fatigue problems. To solve this problem, we reflect the role of actuators in the design, through functional separation using movement and gravity compensation. This study proposes the design and prototype fabrication of an intuitive master K-handler to improve remote-work performance. The K-handler features six degrees of freedom (DoF), an anthropomorphic structure, and a lightweight nature. It has a reach long enough to cover the workspace of the human arm to reduce mental fatigue. In addition, gravity compensation, which can reduce the operator’s physical fatigue during operation, is possible in all workspace areas. Full article

Low-frequency oscillations are a primary issue for integrating a renewable source into the grid. The objective of this study was to find sensitive parameters that cause low-frequency oscillations and design a Twin Delayed Deep Deterministic Policy Gradient (TD3) agent controller to damp the oscillations without requiring an accurate system model. In this work, a Q-learning (QL)-based model-free wind speed DFIG was designed on the rotor-side converter (RSC), and a QL-based model-free DC-link voltage regulator was designed on the grid-side converter (GSC) to enhance the stability of the system. In the next step, the TD3 agent was trained to learn the system dynamics by replacing the inner current controllers of the RSC, which replaced the QL-based model. In the first stage, the conventional PSS and Proportional–Integral (PI) controllers were introduced to both the RSC and GSC. Then, the system was trained to become model-free by replacing the PSS and the PI controller with a QL algorithm under very small wind speed variations. In the second stage, the QL algorithm was replaced with the TD3 agent by introducing large variations in wind speed. The results reveal that the TD3 agent can sustain the stability of the DFIG system under large variations in wind speed without assuming a detailed control structure beforehand, while QL-based controllers can stabilize the doubly fed induction generator (DFIG)-equipped wind energy conversion system (WECS) under small variations in wind speed. Full article

In this paper, the calculation method of dynamic stress concentration around piezoelectric ceramics containing regular n-sided holes under the action of electroelastic coupling wave was studied, and it was applied to promising barium calcium zirconate titanate material. First, electroelastic governing equations were decomposed by using the auxiliary function method, and the solution forms of the elastic wave field and electric field were obtained by using the wave function expansion method. Then, the triangular boundary was simplified to a circular boundary using the mapping function, and the corresponding modal coefficients were determined according to simplified boundary conditions. Finally, the dynamic stress-concentration factor was calculated to characterize the dynamic stress concentration. We performed numerical simulations with a correlation coefficient of (1 − x)[(Ba_0.94Ca_0.06) (Ti_0.92Sn_0.08)]-xSm₂O₃-0.06 mol% GeO₂ (abbreviated as (1 − x)BCTS-xSm-0.06G). The numerical calculation results show that the incident wave number, piezoelectric properties, shape parameters of the hole, and deflection angle have a great influence on the dynamic stress around the defect, and some significant laws are summarized through analysis. Full article

This paper combines a synthetic jet actuator (SJA) and a leeward porous coating to alter the aerodynamic forces on a cylinder in crossflow at $Re$ = 4.2 × 10${}^4$. While SJAs and porous coatings are known to be effective flow control methods in isolation, their combined effect has not been studied. A 2D numerical model was created of a cylinder with a SJA at 90° and 100° leeward porous coating. The model was validated using accompanying water tunnel tests. The combined model was tested for dimensionless frequencies 0.15 $<f^{+}<$ 4 and compared to reference models. For $f^{+}<$ 1, using only the SJA increases the cylinder drag coefficient ($C_d$). Combining a porous coating with the SJA in that regime lowers the $C_d$ values by 15–21%, and causes an overall reduction in $C_d$ compared to the smooth cylinder baseline case. However, using only the porous coating causes a superior 35% reduction in $C_d$. For $f^{+}>$ 1, the combined SJA and porous coating configuration did not differ from the SJA only configuration, achieving the largest drag reduction of 45% at $f^{+}$ = 4. The flow control mechanisms of the SJA and porous coating do not combine constructively in this current setup. However, the porous coating is beneficial for $f^{+}<$ 1, causing an overall drag reduction even when the active SJA tends to increase drag. Full article

A procedure for 3D printing of silicone elastomers with a direct ink writing (DIW) process has demonstrated great potential in areas as diverse as flexible electronics, medical devices, and soft robotics. In this report, we propose a comprehensive guide for printing highly stretchable silicones in response to material, equipment and process dilemmas. Specifically, we first tested the material properties of Dow Corning 737, then modeled and simulated two commonly used needles to select a suitable needle, followed by parameter optimization experiments using the built DIW printer to find out the appropriate printing speed and layer height with a defined air pressure and needle diameter. Finally, the optimal combination of parameters was obtained. For further demonstration, artificial muscles and structurally complex soft grippers were also printed directly to verify the feasibility of high-precision 3D printing of soft actuators with soft materials. We believe that this work could provide a guide for further work using the DIW process to print soft matter in a wide range of application scenarios. Full article

This experimental research focuses on the impacts of submerged synthetic jets on a fully-developed turbulent boundary layer (TBL) under a drag reduction working case. Two-dimensional velocity vectors in the flow field are captured with the aid of a particle image velocimetry (PIV) system. Proper orthogonal decomposition (POD) analyses provide evidence that synthetic jets notably attenuate the induction effect of prograde vortex on the low-speed fluid in large-scale fluctuation velocity field, thereby weakening the bursting process of near-wall turbulent events. Furthermore, the introduced perturbance redistributes the turbulent kinetic energy (TKE) and concentrates the TKE onto small-scale coherent structures. Modal time coefficients in various orders of POD are divided into components of multiple frequency bands by virtue of complementary ensemble empirical mode decomposition (CEEMD). It is found that the turbulence signals are shifted from low-frequency to high-frequency bands thanks to synthetic jets, thus revealing the relationship between scales and frequency bands. One further method of scale decomposition is proposed, that is, the large-scale fluctuating flow field will be obtained after removing the high-frequency noise data with the help of continuous mean square error (CMSE) criterion. Full article

This paper begins with a quick survey of potential space applications and a brief review of previous experiments on the shape control of a spherical shell reflector with a thin film of PVDF-TrFE. Next, the problem of thermal sensitivity is addressed numerically; it is found that, because of the large thermal expansion of the active material, the surface figure error generated by a linear thermal gradient on a unimorph reflector is considerable and its correction requires large control voltages. The surface figure accuracy can be greatly improved by a balanced design (i.e., adding a passive layer symmetrical to the PVDF-TrFE layer) and using a low CTE substrate. Finally, the paper considers a petal reflector; the unimorph design is even more sensitive than the full reflector to the thermal gradient, but the balanced design turns out to be better than the full reflector, both from the point of view of the surface figure error and the control voltages. Full article

Lane detection is one of the most basic and essential tasks for autonomous vehicles. Therefore, the fast and accurate recognition of lanes has become a hot topic in industry and academia. Deep learning based on a neural network is also a common method for lane detection. However, due to the huge computational burden of the neural network, its real-time performance is often difficult to meet the requirements in the fast-changing actual driving scenes. A lightweight network combining the Squeeze-and-Excitation block and the Self-Attention Distillation module is proposed in this paper, which is based on the existing deeplabv3plus network and specifically improves its real-time performance. After experimental verification, the proposed network achieved 97.49% accuracy and 60.0% MIOU at a run time of 8.7 ms, so the network structure achieves a good trade-off between real-time performance and accuracy. Full article

In this paper, a novel asymmetrical bistable short mover permanent magnet actuator is presented. The comparisons between the presented machine and the asymmetrical structure bistable permanent magnet actuator are introduced. The static and dynamic characteristics of the high-voltage circuit breaker with the presented machine are calculated and discussed. The influences of the length of the mover and the initial mover position in the presented machine are studied and researched. The merits of the presented machine, such as less permanent magnet volume, low cost, small mover mass, and high starting speed, are researched and discussed. The Genetic Algorithm is used to optimize the presented machine. Finally, a conventional permanent magnet actuator prototype is created and tested on account of the limited experimental conditions. The characteristic curves of position versus retaining force are acquired to confirm the proposed design. Full article

To maintain the safe operation and acceptable performance of robot manipulators when faults occur inside the system, fault-tolerant control must deal differently uncertainties and disturbances, especially with the occurrence of loss-effective faults. Therefore, in this paper, an active fault-tolerant control for robot manipulators based on the combination of a novel finite-time synchronous fast terminal sliding mode control and extended state observer is proposed. Due to the internal constraints of the synchronization technique, the position error at each actuator simultaneously approaches zero and tends to be equal. Therefore, the proposed controller can suppress the effects of faults and guarantee the acceptable performance of robot manipulators when faults occur. First, an extended state observer is designed to estimate the lumped uncertainties, disturbance and faults. Then, the information from the observer is used to combine with the main novel synchronous fast terminal sliding mode controller as a compensator. By combining the merits of the observer compensation, sliding mode and synchronization technique, the proposed fault-tolerant controller is able to deal with uncertainties and disturbances in normal operation mode and reduce the effects of faults in case faults occur, especially in the occurrence of loss-effective faults. Finally, the enhanced safety, reality and effectiveness of the proposed fault-tolerant control are evaluated through the control of a 3-DOF robot manipulator in both a simulated environment and experiment. Full article

This paper presents the dynamic formulation of an artificial-muscle-driven and computed-muscle–force control for the planar locomotion of a snake robot. The snake robot uses a series of antagonistic pneumatic artificial muscles, assembled at the joints, to generate the locomotion. Kinematics of the artificial-muscle-driven robot in the joint and Cartesian spaces was derived with respect to the muscles’ motion. The Lagrangian mechanics was employed for the formulation of the dynamic model of the robot and deriving the equations of motion. A model-based computed-muscle-force control was designed to track the desired paths/trajectories in Cartesian space. The feedback linearization method based on a change of coordinate was utilized to determine an equivalent linear (input-to-state) system. Then, a full state feedback control law was designed, which satisfies the stability and tracking problems. The performance of the dynamic model and the controller were successfully demonstrated in simulation studies for tracking a circle-shape path and a square-shape path with a constant linear velocity while generating the lateral undulation gait. The results indicate a low magnitude of tracking errors where the controlled muscle force are bounded to the actual pneumatic artificial muscle’s limitations. Full article

In recent years, with the upgrading of the attack technology, stealthy DoS jamming attacks have become the primary factor to threaten the security of Industrial Cyber-Physical Systems (ICPS). Considering the complex industrial scenarios of ICPS, which are influenced by a variety of external and internal interference, a $H_{\infty }$ controller designing problem is studied in this paper for an ICPS which deploys a hybrid-triggered mechanism (HTM) in the wireless channel encountering stealthy DoS jamming attacks. By employing a compensation mechanism which is employed in the controller to mitigate the impacts of attacks, external disturbance, limited channel capacity, wireless channel noise, we establish a closed-loop system and prove the closed-loop system is mean square exponentially stable and can achieve the desired $H_{\infty }$ disturbance rejection level theoretically. Finally, simulation examples are used to demonstrate effectiveness of the proposed $H_{\infty }$ controller. Full article

This paper addressed the optimal policy selection problem of attacker and sensor in cyber-physical systems (CPSs) under denial of service (DoS) attacks. Since the sensor and the attacker have opposite goals, a two-player zero-sum game is introduced to describe the game between the sensor and the attacker, and the Nash equilibrium strategies are studied to obtain the optimal actions. In order to effectively evaluate and quantify the gains, a reinforcement learning algorithm is proposed to dynamically adjust the corresponding strategies. Furthermore, security state estimation is introduced to evaluate the impact of offensive and defensive strategies on CPSs. In the algorithm, the $\epsilon$-greedy policy is improved to make optimal choices based on sufficient learning, achieving a balance of exploration and exploitation. It is worth noting that the channel reliability factor is considered in order to study CPSs with multiple reasons for packet loss. The reinforcement learning algorithm is designed in two scenarios: reliable channel (that is, the reason for packet loss is only DoS attacks) and unreliable channel (the reason for packet loss is not entirely from DoS attacks). The simulation results of the two scenarios show that the proposed reinforcement learning algorithm can quickly converge to the Nash equilibrium policies of both sides, proving the availability and effectiveness of the algorithm. Full article

Weight-on-Wheels (WoW) systems are aimed at indicating if the aircraft weight is loading onto the landing gear and its wheels, even partially. These systems are an integral part of the actuation system for safety-critical applications and shall provide reliable information on the actual operational status of the LG. That information reveals if the vehicle is in flight or on the ground. In this way, several kinds of accidents may be prevented, relating for instance, to the incorrect deployment of the landing gear, or even manoeuvres to a certain extent, therefore protecting the aircraft from dangerous damage. There are different architectures that have been proposed in the bibliography, some of them based on strain gauges deployed on the structure, or on proximity sensors installed on the wheels. Being this device and considered critical for safety, it is convenient to couple it with complementary measurements, recorded and processed by different sources. In general, it can be stated that such an intelligent sensor network may be seen as a fundamental support for proper landing gear deployment. The presented paper reports the results of a preliminary investigation performed by the authors to evaluate the possibility of deploying fibre optics on the landing gear structure as part of a WoW system to retrieve the required information. This choice would have a remarkable effect in terms of significant cabling reduction (a single array of sensing elements could be deployed over a single line), and cost abatement from both a manufacturing and operational point of view. There are many other benefits also when referring to an optical instead of a standard electrical sensor system. Due to its small size and ease of integration into different families of materials, it could be considered a system for monitoring the operating status of most actuators on board modern aircraft. Full article

In this paper, dual RRT optimization is proposed to solve the formation shape generation problem for a large number of MUVs. Since large numbers of MUVs are prone to collision during formation shape generation, this paper considers the use of path planning algorithms to solve the collision avoidance problem. Additionally, RRT as a commonly used path planning algorithm has non-optimal solutions and strong randomness. Therefore, this paper proposes a dual RRT optimization to improve the drawbacks of RRT, which is applicable to the formation shape generation of MUVs. First, an initial global path can be obtained quickly by taking advantage of RRT-connect. After that, RRT* is used to optimize the initial global path locally. After finding the section that needs to be optimized, RRT* performs a new path search on the section and replaces the original path. Due to its asymptotic optimality, the path obtained by RRT* is shorter and smoother than the initial path. Finally, the algorithm can further optimize the path results by introducing a path evaluation function to determine the results of multiple runs. The experimental results show that the dual RRT operation optimization can greatly reduce the running time while avoiding obstacles and obtaining better path results than the RRT* algorithm. Moreover, multiple runs still ensure stable path results. The formation shape generation of MUVs can be completed in the shortest time using dual RRT optimization. Full article

A ball screw type energy regenerative active suspension under fractional order PID control is proposed and studied in order to improve the vibration damping performance of the suspension. A mathematical model of the energy regenerative actuator is established, the energy recovery power at different frequencies is measured through experiments, and then the electromagnetic torque constant, representing the proportional relationship between the output torque and current of the motor, is calculated according to the experimental results. A mathematical model of the control circuit is established and the feasibility and the superiority of the fractional order PID control are verified by simulation and experiments. To achieve a better damping effect, the fractional order PID controller of the whole vehicle suspension system is parameterized using the Beetle Antenna Search (BAS) algorithm. The results showed that the mean energy recovery power of the actuator was about 3.5091 W at a vibration frequency of 11/6 Hz, and the electromagnetic torque constant of the motor was about 0.2885. The actuator control circuit was feasible, and the root mean square value of current deviation under fractional order PID control was 1.1158 mA, which was optimized by 9.40%, compared to the PID control. The BAS algorithm effectively realized the parameter tuning of the controller, and both the tuned PID and fractional order PID controllers, achieved optimization of suspension damping performance. The optimal value of the damping performance objective function under fractional order PID control was 0.3270, which was optimized by 62.93%, compared to the PID control. In addition, all suspension performance indices under fractional order PID control were optimized to a certain extent, compared with the PID control. Full article

The uncertainty of emissivity has a major effect on the accuracy of a pyrometer in billet temperature measurement. In order to eliminate the influence of emissivity, we place a reflector with two apertures at the front of a pyrometer. The two apertures on the reflector are used to measure intrinsic radiation and approximate blackbody radiation of the billet. The radiation is collected by two infrared dual-band detectors in the pyrometer. Then, the real-time emissivity of the billet can be measured with no assumptions, so the influence of emissivity is eliminated. In addition, the measurement uncertainty is analyzed based on the ray-tracing method. The pyrometer is developed and the accuracy verification of emissivity is implemented. Compared with the reference material at the same temperature, the measurement errors of the emissivity are 0.021 and 0.005 at two wavelengths. Then, we install the pyrometer in the medium plate rolling process for measurement. Compared with a thermal imager used in the rolling process, the measurement fluctuation is reduced obviously. It indicates that the method of emissivity measurement is very effective for billet temperature measurement. Full article

Patients who have an implantable cardiac pacemaker that survive beyond the operational life of the device require replacement surgeries that increase healthcare costs and may possibly introduce post-operative complications such as infection. In this paper, we propose a piezoelectric energy harvester design for powering pacemakers to extend their operational life. The design uses a thin strip of piezoelectric PVDF that captures energy from bending of the lead wire. We assemble a prototype to validate a finite element model, and then use the finite element model to characterize the power output of the design based on a cantilever beam loading condition, where displacement at the cantilever tip simulated heart motion. The voltage output from the prototype was compared to the output from the finite element simulation and the finite element simulation provided a good estimate of the voltage output. Further finite element analysis showed that for a 10 cm long section of the proposed design, a 9.1 mm tip displacement provided a power output of 1 μW and a voltage output of ±1.4 V during each cycle. Full article

The design and control of baby chairs have attracted great interest due to children’s increasing consumption market. As a human-robot interface, the features of baby chairs, such as their flexibility, comfortableness, safety, etc., are important factors that should be considered. Therefore, in this paper, to provide competent assistance to parents in taking care of their children, we propose a novel design and control scheme for improving children’s living goods and easing parents’ burden. Firstly, a novel modularization design method is introduced to redesign the shape and structure of the baby chair to cater to multifunctional demands. Flexible materials are chosen to adapt to different body shapes for the sake of safety and comfortableness. Moreover, a Cartesian impedance controller enhanced by a radial basis function neural network (RBFNN) is proposed to achieve a safe, smooth and accurate control of the baby chair with children sitting on it in various uncertain situations using integrated actuators. Both target posture control and periodic control of the chair are implemented to meet different practical requirements. The feasibility of both the chair design and its control is verified in the MATLAB simulation environment through reference tracking tasks. The experimental results demonstrate that our controller can achieve satisfactory performance by controlling the position error in a reasonable range and keeping the manipulation stable and smooth. With the increasing demand for baby chairs in the global children’s consumption market, we believe that the methodology proposed in this paper will attract more research and industry interest. Full article

Evaluating the impact of morphing devices in terms of actuation energy is a promising approach to quantify, from the earliest stages of wing design, the convenience of active camber morphing compared to the use of conventional control surfaces. A morphing wing device consists of an adaptive structure coupled with an actuation system. The starting point for the design of the adaptive structure is a three-dimensional parametric-geometry-representation technique working on the definition of the external morphing shape. The morphing shape is defined to be feasible from the structural point of view and able to meet the aerodynamic design requirements. The new method presented here enables the computation of the actuation energy as a combination of strain energy and external aerodynamic work. The former is the energy required to deform the skin and can be computed in an analytical way, based on the same quantities used by the parameterization technique. The latter is used to compute the energy needed to counteract the external aerodynamic loads during the deformation. This method is applied to the design optimization of a morphing aileron which is installed on a 24 m span wing, starts at 65% of both the chord and the semi-span and extends for one third of the span. A parametric study shows the superiority of the morphing aileron, compared with an equivalent hinged aileron, in terms of energy saving, weight penalty reduction and ease of on-board installation. The morphing aileron is more compact and requires a lower actuation energy combined with a lower deflection, while providing the same roll moment. Full article

Billions of people are using smartphones and computers with poor posture. A careless attitude towards spinal posture could be dangerous for long-term spinal health, leading eventually to curvature of the spine. Ignoring this fact and its treatment at the early stage will significantly deteriorate spinal health and force surgical intervention. Instead of developing an automated posture-correcting system, the existing research mostly focused on a posture-monitoring system to inform the users via a human interface, e.g., Bluetooth-based devices. Therefore, this paper proposes a novel posture-correction method to automatically prevent spinal disease by facilitating proper posture habits. Specifically, we develop a fluid-driven wearable posture corrector, whose skeleton can be fabricated simply using a 3D printer, to estimate angular posture deviation using sensors and provide appropriate assistance to correct the posture habit of the user. Mounted sensors provide the degree of postural bending, and a controller regulates the appropriate signals to provide a friendly pulling force as a reminder to the user through a fluid-driven actuator. The skeleton with a fluid-driven tool is designed to mimic the motion of the spinal posture by activating the actuator, which injects (or releases) the fluid into (or from) the skeleton frame and regulates forces to reduce the angular deviation of the skeleton. The 3D-printed skeleton with a flexible rubber tube has been experimentally evaluated to ensure proper actuating mechanism through the adjustment of air pressure. It is found that, by applying air pressure in the range of 0 to 101.4 kPa, the skeleton is pulled back approximately 1 N to 7 N forces, minimizing the angle up to 12.44${}^{\circ }$ with respect to the initial steady stage, which leads to a maximum posture correction of 32.55% angle ($\theta$) of poor posture. From the above experiments, we ensure the functionality of the proposed posture corrector in producing backward forces to correct the posture automatically. Full article

Recently, cost-effective ionic polymer metal composite (IPMC) membranes coated with novel metals (viz., Ag, Au, or Pt) have exhibited excellent bending actuation performance, which was electrically stimulated. Herein, we have developed an IPMC membrane of highly cost-effective Kraton (KR) fabricated by incorporating Copper nanoparticles (CuNPs). It was then coated with Pt-metal using a solution casting process. The developed IPMC membrane (KR-CuNPs-Pt) was characterized using Fourier-transform infrared (FTIR) spectroscopy, Transmission electron microscopy (TEM), and X-ray diffraction (XRD) techniques. Further, ionic exchange capacity (IEC), the proton conductivity (PC), and water uptake/loss studies have also been performed. Actuation performance was measured using the electromechanical techniques. The actuation force of ca. 0.343 mN and displacement of ca. 18 mm at 4 VDC indicate that the developed membrane may serve as an alternative to the highly expensive commercialized IPMC actuators based on perfluorinated polymers. A soft bending actuator in the form of a micro-gripper was also developed. Full article

Detecting the faults in hydraulic systems in advance is difficult owing to the complexity associated with such systems. Hence, it is necessary to investigate the different fault modes and analyze the system reliability in order to establish a method for improving the reliability and security of hydraulic systems. To this end, this paper proposes a novel one-dimensional multichannel convolution neural network (1DMCCNN) for diagnosing fault modes. In this work, a landing gear hydraulic system was constructed with a normal model and a fault model; five types of faults were considered. Pressure signals were extracted from this hydraulic system, and the extracted signals were subsequently input into the convolution neural network (CNN) as multichannel data. Thereafter, the data were subjected to a one-dimensional convolution filter. The differences between channels were used to enhance features. The features obtained in this manner were compared for fault diagnoses. Furthermore, this proposed method was verified via simulations; the simulation results indicated that the precision of the 1DMCCNN was considerably higher than that of conventional machine learning algorithms. Full article

Stereo garage technology can effectively alleviate the problem of parking difficulties, but the safety problems of its actuators, via which the core of stereo parking function can be realized, seriously affect its promotion and further development. In this paper, a two degrees of freedom (2-DOF) parallel lifting actuator for a stereo parking robot is designed by researching the type synthesis of the mechanism based on the screw theory. The limb constrained triangle method, the flexibility of limb constrained triangle, and the failure probability are proposed to determine the final configuration of the parallel lifting actuator. Then, this paper completes the dimensional optimization of the parallel lifting actuator based on the multi-motion performance indexes and kinematic analysis, which improves the safety and stability of the actuator. Finally, this paper verifies the validity of the parallel lifting actuator by establishing a parallel lifting actuator verification model system. By verifying the dynamic characteristics of the model mobile platform under different load conditions, it is proven that the kinematic stability of the mobile platform decreases with the increase of load mass under load conditions. Additionally, through practical application experiment, it is proven that the parallel lifting mechanism can effectively alleviate the parking difficulty problem. Full article

In this study, we developed a superconducting magnetic bearing using a permanent repulsive magnet. A repulsive magnetic levitation system with a permanent magnet can generate a strong levitation force in the absence of a power supply. However, it is unstable, except in the direction of repulsion. In contrast, superconducting magnetic bearings can generate a restoring force in all directions by utilizing the magnetic flux pinning property of the superconductors. Therefore, we constructed a superconducting magnetic bearing (SMB), which is stable along all axes without control, and has a strong axial levitation force, by combining a repulsive-type magnetic levitation system and a superconducting magnetic levitation system. We also reduced the amount of HTS used for the SMB and proposed an efficient method of using HTS. Furthermore, a driving test of the flywheel incorporating the SMB was conducted to verify the characteristics of the SMB. The experiment confirmed that the flywheel could overcome the resonance and drive the flywheel. In the drive experiment, the flywheel was driven up to 10,000 rpm. Full article

A scheme for modelling and controlling a two-dimensional positioning system with a topology-optimized compliant mechanism is presented. The system is designed to ensure a relatively large workspace and exhibit robustness against system nonlinearities. A detailed design procedure based on topology optimization is presented, and a nonlinear description of the designed mechanism is developed as a starting point for further precise position control. The theoretical model is shown to be suitable for a considerably larger working range without losing consistency. A backstepping controller is employed to manipulate the nonlinearities in the model resulting from the geometrical and material nonlinearity of the mechanical structure. The hysteresis of the piezoelectric actuator is also taken into consideration. An experimental verification of the controller demonstrates that the proposed design approach improves the performance of compliant mechanism and satisfies the needs for precision positioning. Full article

This paper mainly studies the data-based security fault tolerant iterative learning control (SFTILC) problem of nonlinear networked control systems (NCSs) under sensor failures and denial-of-service (DoS) attacks. Firstly, the radial basis function neural network (RBFNN) is used to approximate the sensor failure function and a DoS attack compensation mechanism is proposed in the iterative domain to lessen the impact of DoS attacks. Then, using the dynamic linearization technology, the nonlinear system considering failures and network attacks is transformed into a linear data model. Further, based on the designed linearization model, a new data-based SFTILC algorithm is designed to ensure the satisfactory tracking performance of the system. This process only uses the input and output data of the system, and the stability of the system is proved by using the compression mapping principle. Finally, a digital simulation is used to demonstrate the effectiveness of the proposed SFTILC algorithm. Full article

As a core component of the X-ray absorption fine structure spectroscopy (XAFS) system, the multi-channel double-crystal monochromator (DCM) can improve the time resolution of the system significantly. In contrast to the conventional single-channel DCM, the multi-channel DCM includes more pairs of crystals that are located separately in the master and slave motor axis with the same driving direction. However, a mismatched parallelism in the pitch direction, which can result from the manual mounting operation between the two separated crystals, directly affects the performance of the flux and the angular stability of the monochromatic beam. This poses a significant challenge to the precision position tracking of this system. In this paper, the mounting errors were translated into repetitive errors in the slave motor when the master motor was rotated at a constant velocity. Therefore, the iterative learning control (ILC) was considered in order to improve the tracking accuracy of the slave motor motion. The zero-magnitude error controller (ZMETC) was used to calculate the learning function to accelerate the convergence of the control inputs, and the convergence conditions of the control signal and error were also given. To validate the effectiveness of the proposed method, comparative experiments were performed on the motor motion platform. Experimental results indicated that the ILC effectively decreased the parallelism errors of the multi-channel DCM under various trajectories by comparing them with feedback controllers and the ZMETC, respectively. Full article

In this study, synergetic-based adaptive control design is developed for trajectory tracking control of joint position in knee-rehabilitation system. This system is often utilized for rehabilitation of patients with lower-limb disabilities. However, this knee-assistive system is subject to uncertainties when applied to different persons undertaking exercises. This is due to the different masses and inertias of different persons. In order to cope with these uncertainties, an adaptive scheme has been proposed. In this study, an adaptive synergetic control scheme is established, and control laws are developed to ensure stable knee exoskeleton system subjected to uncertainties in parameters. Based on Lyapunov stability analysis, the developed adaptive synergetic laws are used to estimate the potential uncertainties in the coefficients of the knee-assistive system. These developed control laws guarantee the stability of the knee rehabilitation system controlled by the adaptive synergetic controller. In this study, particle swarm optimization (PSO) algorithm is introduced to tune the design parameters of adaptive and non-adaptive synergetic controllers, in order to optimize their tracking performances by minimizing an error-cost function. Numerical simulations are conducted to show the effectiveness of the proposed synergetic controllers for tracking control of the exoskeleton knee system. The results show that compared to classical synergetic controllers, the adaptive synergetic controller can guarantee the boundedness of the estimated parameters and hence avoid drifting, which in turn ensures the stability of the controlled system in the presence of parameter uncertainties. Full article

Piezoelectric flags have functions of both classic flags and energy harvesting, and are becoming a new research focus. Interface circuits that convert wind energy to electrical energy are the key component of piezoelectric flags. A new structure for piezoelectric flags was designed to generate vibration by wind induction. After theoretical analysis, only SEH (standard energy harvesting) and SSHC (synchronized switch-harvesting-on capacitors) interface circuits were found suitable for piezoelectric flags. Simulation in Multisim was performed to compare SEH and SSHC in different load resistance. Experiments were carried out using different wind speeds. The on-time and delay-time of each switch were controlled by the proposed control algorithm. Both simulation and experimental results indicate that the output voltage with SSHC is higher than the output voltage with SEH. When the resistance is 1700 kΩ and the wind speed is 24 m/s, the output power of SSHC can be increased by 45.63% compared with the SEH circuit. Full article