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Actuators, Volume 11, Issue 11 (November 2022) – 37 articles

Cover Story (view full-size image): In this work, an inverse dynamics-based whole-body controller is presented for a torque-controlled quadrupedal manipulator capable of performing locomotion while executing manipulation tasks. Unlike existing methods that deal with locomotion and manipulation separately, the proposed controller can handle them uniformly, which can take into account the coupling effects between the base, the limbs, and the manipulated object. The controller tracks the desired task-space motion references based on a hierarchical optimization algorithm, given a set of hierarchies that define strict priorities and the importance of weighting each task within a hierarchy. Several simulations have been performed to demonstrate the effectiveness of the proposed controller. View this paper
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15 pages, 5841 KiB  
Article
Comparison between Density and Velocity Fields in Burst Modulation of a Dielectric-Barrier-Discharge Plasma Actuator
by Kenta Emori, Yutaka Kaneko and Hiroyuki Nishida
Actuators 2022, 11(11), 340; https://doi.org/10.3390/act11110340 - 21 Nov 2022
Cited by 2 | Viewed by 1370
Abstract
The flow field produced by a dielectric-barrier-discharge plasma actuator using burst modulation was experimentally investigated in quiescent air from two viewpoints: density and vorticity fields. A wide range of burst signal parameters were evaluated using particle-image velocimetry and background-oriented schlieren measurements. Four types [...] Read more.
The flow field produced by a dielectric-barrier-discharge plasma actuator using burst modulation was experimentally investigated in quiescent air from two viewpoints: density and vorticity fields. A wide range of burst signal parameters were evaluated using particle-image velocimetry and background-oriented schlieren measurements. Four types of flow-field patterns were found: Type 1 was a wall jet, similar to continuous operation; Type 2 was a periodical, independent vortex moving along the wall surface; Types 3 and 4 demonstrated a feature wherein the periodic shedding of the vortex pair (primary and secondary vortices) occurred while moving over the surface. While Types 3 and 4 demonstrated a shared feature, they had different density and vorticity structures. The change of the flow-field pattern from Type 1 to Type 4 was triggered by a lower burst frequency and ratio, as well as a higher base frequency. In addition, the vorticity strength and density were strongly negatively correlated and depended on the rate of power consumption to generate one vortex. Full article
(This article belongs to the Special Issue Dielectric Barrier Discharge Plasma Actuator for Active Flow Control)
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18 pages, 5686 KiB  
Article
Robust Stabilization of Underactuated Two-Wheeled Balancing Vehicles on Uncertain Terrains with Nonlinear-Model-Based Disturbance Compensation
by Yongkuk Kim and SangJoo Kwon
Actuators 2022, 11(11), 339; https://doi.org/10.3390/act11110339 - 21 Nov 2022
Cited by 4 | Viewed by 2143
Abstract
Two-wheeled inverted pendulum (TWIP) vehicles are prone to lose their mobility and postural stability owing to their inherently unstable and underactuated dynamic characteristics, specifically when they encounter abruptly changed slopes or ground friction. Overcoming such environmental disturbances is essential to realize an agile [...] Read more.
Two-wheeled inverted pendulum (TWIP) vehicles are prone to lose their mobility and postural stability owing to their inherently unstable and underactuated dynamic characteristics, specifically when they encounter abruptly changed slopes or ground friction. Overcoming such environmental disturbances is essential to realize an agile TWIP-based mobile platform. In this paper, we suggest a disturbance compensation method that is compatible with unmanned TWIP systems in terms of the nonlinear-model-based disturbance observer, where the underactuated dynamic model is transformed to a fully actuated form by regarding the gravitational moment of the inverted pendulum as a supplementary pseudo-actuator to counteract the pitch-directional disturbances. Consequently, it enables us to intuitively determine the disturbance compensation input of the two wheels and the pitch reference input accommodating to uncertain terrains in real time. Through simulation and experimental results, the effectiveness of the proposed method is validated. Full article
(This article belongs to the Special Issue Modeling, Optimization and Control of Robotic Systems)
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14 pages, 3527 KiB  
Article
Improvement of Adaptive Motion Performance in a Flexible Actuator, Based on Electrically Induced Deformation
by Haiqiang Liu, Chen Yang, Zhengyun Xu, Ming Lv and Rougang Zhou
Actuators 2022, 11(11), 338; https://doi.org/10.3390/act11110338 - 21 Nov 2022
Cited by 1 | Viewed by 2089
Abstract
An actuator built with flexible material has the advantage of smaller size and can withstand certain collisions better than actuators with rigid material. This paper proposes a crawling actuator model driven by dielectric elastomer (DE), which uses the electrically induced deformation of the [...] Read more.
An actuator built with flexible material has the advantage of smaller size and can withstand certain collisions better than actuators with rigid material. This paper proposes a crawling actuator model driven by dielectric elastomer (DE), which uses the electrically induced deformation of the DE membrane to drive the motion of the actuator. When the dielectric elastomer in the actuator is at higher voltage, the DE material produces higher deformation, and the deformation is transmitted to the ground through the friction foot thus driving the motion of the actuator. An interpolation fitting estimation algorithm (IFEA) was constructed based on the relevant material properties and principles. The pre-stretch length of the DE membrane was determined and verified through experiment; the verified results showed that the actuator has better driving performance when the membrane pre-stretching ratio is equal to 3. The crawling actuator can achieve a speed of about 50 mm/s at 4 kv and can reach 11 mm/s when loaded with four times its weight. The new crawling actuator achieved an excellent turning ability of 8.2°/s at 60% duty cycle and 32 Hz frequency. Compared with other types of crawling actuators, the actuator presented in this work has better load capacity and crawling performance. Full article
(This article belongs to the Section Actuator Materials)
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23 pages, 7882 KiB  
Article
PSO-Based Variable Parameter Linear Quadratic Regulator for Articulated Vehicles Snaking Oscillation Yaw Motion Control
by Tianlong Lei, Xiaochao Gu, Kanghua Zhang, Xiang Li and Jixin Wang
Actuators 2022, 11(11), 337; https://doi.org/10.3390/act11110337 - 18 Nov 2022
Cited by 2 | Viewed by 1367
Abstract
In this paper, the seven degrees of freedom (DOF) nonlinear system model of articulated vehicles, including the vehicle dynamics model, tire and hydraulic steering system model, and the linearized ideal reference model, is constructed. A layered stability controller for the articulated vehicle is [...] Read more.
In this paper, the seven degrees of freedom (DOF) nonlinear system model of articulated vehicles, including the vehicle dynamics model, tire and hydraulic steering system model, and the linearized ideal reference model, is constructed. A layered stability controller for the articulated vehicle is built. The particle swarm optimization (PSO)-based variable parameter linear quadratic regulator (LQR) for the upper-level yaw torque controller and the lower-level torque distributor based on the principle of the minimum tire utilization are established. The effectiveness of the LQR upper-level yaw torque controller for an articulated vehicle at different speeds and control references are compared and analyzed through feedforward and feedback control. We optimize the parameters in the LQR controller using PSO and verify the improvement in the controller’s performance with optimized parameters. Overall, the effect of front and rear-integrated control is best, followed by rear-based and front-based control. The PSO algorithm to optimize the LQR controller parameters for snaking oscillation control is effective. Full article
(This article belongs to the Section Actuators for Land Transport)
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13 pages, 565 KiB  
Article
Adaptive Neural Control of a 2DOF Helicopter with Input Saturation and Time-Varying Output Constraint
by Bing Wu, Jiale Wu, Jian Zhang, Guojian Tang and Zhijia Zhao
Actuators 2022, 11(11), 336; https://doi.org/10.3390/act11110336 - 18 Nov 2022
Cited by 6 | Viewed by 1569
Abstract
An adaptive neural control for uncertain 2DOF helicopter systems with input saturation and time-varying output constraints is provided. A radial basis function neural network is used to estimate the uncertainty terms present in the system. The saturation error and the external disturbance are [...] Read more.
An adaptive neural control for uncertain 2DOF helicopter systems with input saturation and time-varying output constraints is provided. A radial basis function neural network is used to estimate the uncertainty terms present in the system. The saturation error and the external disturbance are considered as a composite disturbance, and an adaptive auxiliary parameter is introduced to compensate it. An asymmetric barrier Lyapunov function is employed to address the constraint violation of the system output. The closed-loop stability of the system is then demonstrated by Lyapunov theory analysis. Simulation results demonstrate the effectiveness of the control strategy. Full article
(This article belongs to the Special Issue Intelligent Control of Flexible Manipulator Systems and Robotics)
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12 pages, 4914 KiB  
Communication
Analytical Modeling of Density and Young’s Modulus Identification of Adsorbate with Microcantilever Resonator
by Yue Yang, Yanling Tian, Xianping Liu, Yumeng Song and Hui Tang
Actuators 2022, 11(11), 335; https://doi.org/10.3390/act11110335 - 18 Nov 2022
Cited by 1 | Viewed by 1190
Abstract
Density and Young’s modulus are critical parameters in biological research, which can be used to characterize molecules, cells, or tissues in the diagnosis of severe diseases. Microcantilever resonators are ideal tools to measure the physical parameters of small objects at the micro/nanoscale. In [...] Read more.
Density and Young’s modulus are critical parameters in biological research, which can be used to characterize molecules, cells, or tissues in the diagnosis of severe diseases. Microcantilever resonators are ideal tools to measure the physical parameters of small objects at the micro/nanoscale. In this study, a mathematical model was built based on the Rayleigh–Ritz method with the consideration of the first five-order bending natural frequencies. The mathematical model can be used to detect the density and Young’s modulus of an adsorbate on a cantilever resonator with a single measurement. The influence of different order natural frequencies and the adsorbate position on the measurement accuracy and reliability was analyzed. This study revealed that the frequency pairs and the relative position of the adsorbate on the cantilever are two important factors that affect the accuracy and reliability of the measurement. Choosing appropriate frequency pairs can help to improve the accuracy and reliability of measurement. Finally, the results of finite element analysis verified the proposed method. Full article
(This article belongs to the Special Issue Actuating, Sensing, Control, and Instrumentation for Ultra Precision Engineering)
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20 pages, 7850 KiB  
Article
Performance Assessment of a Low-Cost Miniature Electrohydrostatic Actuator
by Brendan Deibert and Travis Wiens
Actuators 2022, 11(11), 334; https://doi.org/10.3390/act11110334 - 18 Nov 2022
Viewed by 1631
Abstract
Low-cost small-scale (<100 W) electrohydrostatic actuators (EHAs) are not available on the market, largely due to a lack of suitable components. Utilizing plastic 3D printing, a novel inverse shuttle valve has been produced which, when assembled with emerging small-scale hydraulic pumps and cylinders [...] Read more.
Low-cost small-scale (<100 W) electrohydrostatic actuators (EHAs) are not available on the market, largely due to a lack of suitable components. Utilizing plastic 3D printing, a novel inverse shuttle valve has been produced which, when assembled with emerging small-scale hydraulic pumps and cylinders from the radio-controlled hobby industry, forms a low-cost and high-performance miniature EHA. This paper presents experimental test results that characterize such a system and highlight its steady, dynamic, and thermal performance capabilities. The results indicate that the constructed EHA has good hydraulic efficiency downstream of the pump and good dynamic response but is limited by the efficiency of the pump and the associated heat generated from the pump’s losses. The findings presented in this paper validate the use of a 3D printed plastic inverse shuttle valve in the construction of a low-cost miniature EHA system. Full article
(This article belongs to the Special Issue 10th Anniversary of Actuators)
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11 pages, 3022 KiB  
Article
The Effect of SiC-MOSFET Characteristics on the Performance of Dielectric Barrier Discharge Plasma Actuators with Two-Stroke Charge Cycle Operation
by Shintaro Sato, Tomoki Yoshikawa and Naofumi Ohnishi
Actuators 2022, 11(11), 333; https://doi.org/10.3390/act11110333 - 17 Nov 2022
Cited by 1 | Viewed by 1706
Abstract
The low-voltage operation of a dielectric-barrier-discharge (DBD) plasma actuator with a simple electric circuit has the potential to put it into industrial applications. However, there is an issue that the efficiency of the low-voltage operated DBD plasma actuator is lower than that of [...] Read more.
The low-voltage operation of a dielectric-barrier-discharge (DBD) plasma actuator with a simple electric circuit has the potential to put it into industrial applications. However, there is an issue that the efficiency of the low-voltage operated DBD plasma actuator is lower than that of the high-voltage operated one. In this study, the characteristics of silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs), which are used in the electric circuit, are investigated with a focus on the on-state resistance. The on-state resistance of the SiC-MOSFET affects the rise time of the applied voltage in our experimental condition. The energy consumption by applying a pulse voltage to the DBD plasma actuator increases with increasing the on-state resistance. Flow visualization with particle image velocimetry measurement reveals that a DBD plasma actuator with the SiC-MOSFET whose on-state resistance is the lowest induces the highest velocity of the ionic wind. Also, low on-state resistance is preferable in terms of the thrust-to-power ratio. These findings contribute to the development of an optimal power supply for DBD plasma actuators for industrial applications. Full article
(This article belongs to the Special Issue Dielectric Barrier Discharge Plasma Actuator for Active Flow Control)
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24 pages, 7546 KiB  
Article
Time-Optimal Trajectory Planning of 6-DOF Manipulator Based on Fuzzy Control
by Feifan He and Qingjiu Huang
Actuators 2022, 11(11), 332; https://doi.org/10.3390/act11110332 - 16 Nov 2022
Cited by 5 | Viewed by 1784
Abstract
Currently, the teaching programming or offline programming used by an industrial manipulator can manually set the running speed of the manipulator. In this paper, to consider the running speed and stability of the manipulator, the time-optimal trajectory planning (TOTP) of the manipulator is [...] Read more.
Currently, the teaching programming or offline programming used by an industrial manipulator can manually set the running speed of the manipulator. In this paper, to consider the running speed and stability of the manipulator, the time-optimal trajectory planning (TOTP) of the manipulator is transformed into a nonlinear optimal value search problem under multiple constraints, and a time-search algorithm based on fuzzy control is proposed, so that the end of the manipulator can run along the given path in Cartesian space for the shortest time, and the angular velocity and angular acceleration of each joint is within a limited range. In addition, a simulation model of a 6-DOF manipulator is established in MATLAB, taking a straight-line trajectory of the end of the manipulator in Cartesian space as an example, and the effectiveness and efficiency of the algorithm proposed in this paper are proved by comparing the execution time with the bisection algorithm and the traditional gradient descent method. Full article
(This article belongs to the Special Issue Modeling, Optimization and Control of Robotic Systems)
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25 pages, 5304 KiB  
Review
A Review of Soft Actuator Motion: Actuation, Design, Manufacturing and Applications
by Xianzhi Tang, Huaqiang Li, Teng Ma, Yang Yang, Ji Luo, Haidan Wang and Pei Jiang
Actuators 2022, 11(11), 331; https://doi.org/10.3390/act11110331 - 14 Nov 2022
Cited by 16 | Viewed by 6767
Abstract
Compared with traditional rigid robots, soft robots have high flexibility, low stiffness, and adaptability to unstructured environments, and as such have great application potential in scenarios such as fragile object grasping and human machine interaction. Similar to biological muscles, the soft actuator is [...] Read more.
Compared with traditional rigid robots, soft robots have high flexibility, low stiffness, and adaptability to unstructured environments, and as such have great application potential in scenarios such as fragile object grasping and human machine interaction. Similar to biological muscles, the soft actuator is one of the most important parts in soft robots, and can be activated by fluid, thermal, electricity, magnet, light, humidity, and chemical reaction. In this paper, existing principles and methods for actuation are reviewed. We summarize the preprogrammed and reprogrammed structures under different stimuli to achieve motions such as bending, linear, torsional, spiral. and composite motions, which could provide a guideline for new soft actuator designs. In addition, predominant manufacturing methods and application fields are introduced, and the challenges and future directions of soft actuators are discussed. Full article
(This article belongs to the Special Issue Soft Actuators and Robotics)
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14 pages, 46301 KiB  
Article
Design and Implementation of an Asynchronous Finite State Controller for Wheeled Mobile Robots
by Alessandro Bozzi, Simone Graffione, Roberto Sacile and Enrico Zero
Actuators 2022, 11(11), 330; https://doi.org/10.3390/act11110330 - 13 Nov 2022
Cited by 3 | Viewed by 1459
Abstract
Wheeled mobile robots (WMRs) can navigate in uncontrolled environments with the assistance of electronic or physical devices. Several works have been conducted on the control and management of the path-tracking of a vehicle in different road scenarios. This paper aims to create an [...] Read more.
Wheeled mobile robots (WMRs) can navigate in uncontrolled environments with the assistance of electronic or physical devices. Several works have been conducted on the control and management of the path-tracking of a vehicle in different road scenarios. This paper aims to create an asynchronous finite state control law for a WMR. The control law is based on a proportional–integral–derivative controller, and the performance of the proposed model is evaluated in virtual and real environments in two different scenarios. In the first one, the WMR must perform a zig-zag maneuver between obstacles, while the second one involves a double left lane change. In the proposed scenarios, the WMR drives along a path until an obstacle is detected at less than 50 cm, causing the WMR to check whether the first lane is free to go and move on. These scenarios and the related required engineering approaches seem particularly suitable for system engineering in a student’s laboratory for the design and implementation of automated guidance system modeling. Full article
(This article belongs to the Special Issue Advanced Technologies and Applications in Robotics)
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15 pages, 2575 KiB  
Article
Brake Pressure Estimation of the Integrated Braking System Considering Vehicle Dynamics
by Haichao Liu, Lingtao Wei, Hongqi Liu, Jinjun Wu and Liang Li
Actuators 2022, 11(11), 329; https://doi.org/10.3390/act11110329 - 10 Nov 2022
Cited by 2 | Viewed by 1724
Abstract
The integrated braking control system (IBC) has become one of the most popular brake-by-wire (BBW) solutions due to its compactness and versatility. Accurate monitoring of wheel cylinder pressure in real time is the basis for brake pressure control, and pressure estimation is a [...] Read more.
The integrated braking control system (IBC) has become one of the most popular brake-by-wire (BBW) solutions due to its compactness and versatility. Accurate monitoring of wheel cylinder pressure in real time is the basis for brake pressure control, and pressure estimation is a low-cost and reliable method. However, the IBC is an electromechanical hydraulic coupling system that has significant nonlinear behaviors; moreover, vehicle dynamics also have a critical impact on the accuracy of pressure estimation. To solve this problem, this paper proposes a novel adaptive extended Kalman filter (EKF) approach that combines a hydraulic model and a single-wheel model. This novel strategy has better estimation than the hydraulic model when the pressure is accurately estimated by the single-wheel model, while when the single-wheel model is not accurate, the EKF degrades to the hydraulic model. Finally, vehicle experimental data under high- and low-mu braking are collected. The pressure estimation error of the EKF is within 0.4 MPa in the low-mu road and 2 MPa in the high-mu road. It is proven that the proposed pressure estimation strategy is highly effective. Full article
(This article belongs to the Section Actuators for Land Transport)
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26 pages, 4597 KiB  
Review
The Research on Soft Pneumatic Actuators in Italy: Design Solutions and Applications
by Maria Paterna, Carlo De Benedictis and Carlo Ferraresi
Actuators 2022, 11(11), 328; https://doi.org/10.3390/act11110328 - 10 Nov 2022
Cited by 4 | Viewed by 3261
Abstract
Interest in soft actuators has increased enormously in the last 10 years. Thanks to their compliance and flexibility, they are suitable to be employed to actuate devices that must safely interact with humans or delicate objects or to actuate bio-inspired robots able to [...] Read more.
Interest in soft actuators has increased enormously in the last 10 years. Thanks to their compliance and flexibility, they are suitable to be employed to actuate devices that must safely interact with humans or delicate objects or to actuate bio-inspired robots able to move in hostile environments. This paper reviews the research on soft pneumatic actuators conducted in Italy, focusing on mechanical design, analytical modeling, and possible application. A classification based on the geometry is proposed, since a wide set of architectures and manufacturing solutions are available. This aspect is confirmed by the extent of scenarios in which researchers take advantage of such systems’ improved flexibility and functionality. Several applications regarding bio-robotics, bioengineering, wearable devices, and more are presented and discussed. Full article
(This article belongs to the Special Issue Artificial Muscles for Biorobotics: Study, Application and Future Perspectives)
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15 pages, 5789 KiB  
Article
Design and Analysis of a High Power Density Permanent Magnet Linear Generator for Direct-Drive Wave Power Generation
by Xinyu Fan, Changkun Wang, Zhibing Zhu and Hao Meng
Actuators 2022, 11(11), 327; https://doi.org/10.3390/act11110327 - 10 Nov 2022
Cited by 2 | Viewed by 1913
Abstract
Wave energy is a new type of clean energy. Aiming at a low wave energy density and small wave height in China’s coastal areas, a tubular permanent magnet linear generator (PMLG) with a short stroke, small volume, and high power density is designed [...] Read more.
Wave energy is a new type of clean energy. Aiming at a low wave energy density and small wave height in China’s coastal areas, a tubular permanent magnet linear generator (PMLG) with a short stroke, small volume, and high power density is designed for wave power generation. Firstly, the generator’s electromagnetic parameters are analyzed by the analytical method, and the magnetic circuit topology and basic structure of the generator are analyzed by the equivalent magnetic circuit method (EMCM). Then, the finite element method (FEM) is used to analyze the influence law of the generator’s basic structural parameters on the output electromotive force (EMF) and its sinusoidal characteristics. The multi-factor and multi-level analysis is carried out based on the orthogonal test method to study the size parameters of the above analysis, and the optimal structure parameter combination for the generator is obtained. Finally, the prototype is trial-produced and tested for steady-state and transient performance to confirm the accuracy of the simulation calculations, and the output performance under no-load and load conditions is examined. The results show that both the optimized prototype’s power density and the output EMF’s sinusoidal properties have been improved under the proposed scheme. Full article
(This article belongs to the Special Issue Linear Motors and Direct-Drive Technology)
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15 pages, 3668 KiB  
Article
Design of Piezopolymer Interdigital Transducers with Scaled Electrode Geometries Based on FEM Analysis
by Lorenzo Capineri, Luca Bergamaschi and Andrea Bulletti
Actuators 2022, 11(11), 326; https://doi.org/10.3390/act11110326 - 08 Nov 2022
Viewed by 1554
Abstract
The design of interdigital transducers (IDT) for active structural health monitoring (SHM) systems often requires a tuning of their characteristics for specific applications. IDTs are generally preferred for the selectivity of Lamb’s guided modes, but the directivity of the radiation pattern is a [...] Read more.
The design of interdigital transducers (IDT) for active structural health monitoring (SHM) systems often requires a tuning of their characteristics for specific applications. IDTs are generally preferred for the selectivity of Lamb’s guided modes, but the directivity of the radiation pattern is a design parameter that is often difficult to customize for complex mechanical structures. This work proposes a comprehensive experimental study of the IDT with regular geometry, highlighting the dimensional parameters that can optimize the overall performance. From this study, a scaled electrode geometry emerged as a possible solution to shape the directivity diagram while maintaining the selectivity of the guided wave modes. This study based on FEM simulators led to a more versatile design of IDTs built with piezopolymer films of polyvinylidene fluoride (PVDF). The experimental validation showed the directivity diagrams and the ultrasonic guided mode selection were in very good agreement with the simulations. Another outcome of the investigation was the off axis propagation due to the contribution of the bus bars for connecting the IDT fingers to the excitation electronic circuit. Full article
(This article belongs to the Topic Advances in Piezoelectric/Ultrasonic Sensors and Actuators)
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17 pages, 429 KiB  
Article
A Precise Stabilization Method for Linear Stochastic Time-Delay Systems
by Huasheng Zhang, Changan Shao, Han Geng and Tingting Zhang
Actuators 2022, 11(11), 325; https://doi.org/10.3390/act11110325 - 07 Nov 2022
Viewed by 1113
Abstract
Based on ensuring the steady-state performance of the system, some dynamic performance indicators that have not yet been realized in linear stochastic systems with time-delay are discussed in this paper. First, in view of the relationship between system eigenvalues and system performances, the [...] Read more.
Based on ensuring the steady-state performance of the system, some dynamic performance indicators that have not yet been realized in linear stochastic systems with time-delay are discussed in this paper. First, in view of the relationship between system eigenvalues and system performances, the region stability is provided, which can reflect the dynamic performance of the systems. Second, the design scheme of the region stabilization controller is given based on the region stability, so that the closed-loop system has the corresponding dynamic performance. Third, this paper also designs an algorithm to deal with the situation in which the eigenvalues are located in the non-connected region in order to obtain more accurate control system dynamic performance. Finally, an example shows how the precise control method dominates the dynamic performance of the system. Full article
(This article belongs to the Section Control Systems)
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23 pages, 9967 KiB  
Article
Robust Tracking Control of Piezo-Actuated Nanopositioning Stage Using Improved Inverse LSSVM Hysteresis Model and RST Controller
by Ayad G. Baziyad, Irfan Ahmad, Yasser Bin Salamah and Abdulaziz Alkuhayli
Actuators 2022, 11(11), 324; https://doi.org/10.3390/act11110324 - 07 Nov 2022
Cited by 7 | Viewed by 1866
Abstract
Nanopositioning technology is widely used in high-resolution applications. It often uses piezoelectric actuators due to their superior characteristics. However, piezoelectric actuators exhibit a hysteresis phenomenon that limits their positioning accuracy. To compensate for the hysteresis effect, developing an accurate hysteresis model of piezoelectric [...] Read more.
Nanopositioning technology is widely used in high-resolution applications. It often uses piezoelectric actuators due to their superior characteristics. However, piezoelectric actuators exhibit a hysteresis phenomenon that limits their positioning accuracy. To compensate for the hysteresis effect, developing an accurate hysteresis model of piezoelectric actuators is very important. This task is challenging, requiring some considerations of the multivalued mapping of hysteresis loops and the generalization capabilities of the model. This challenge can be dealt with by developing a machine learning-based model, whose inverse model can be used to efficiently design an accurate feedforward controller for hysteresis compensation. However, this approach depends on model accuracy and the type of data used to train the model. Thus, accurate prediction of the hysteresis behavior may not be guaranteed in the presence of disturbances. In this paper, a machine learning-based model is used to design a hysteresis compensator and then combined with a robust feedback controller to enhance the robustness of a nanopositioning control system. The proposed model is based on hysteresis operators, the least square support vector machine (LSSVM) method, and particle swarm optimization (PSO) algorithm. The inverse model is used to design the feedforward controller, and the RST controller is employed to develop feedback control. Our main contribution is the introduction of a hybrid controller capable of compensating for the hysteresis effect, and at the same time, eliminating remaining modeling errors and rejecting disturbances. The performance of the proposed approach is evaluated through MATLAB simulation, as well as through real-time experiments. The experimental results of our approach demonstrate superior tracking performance compared with the PID-LSSVM controller. Full article
(This article belongs to the Special Issue Piezoelectric Actuators and Transducers: Materials, Design, Control and Applications)
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11 pages, 842 KiB  
Article
A Weak SNR Signal Extraction Method for Near-Bit Attitude Parameters Based on DWT
by Yanhui Mao, Yongmin Zhong, Yi Gao and Yuelong Wang
Actuators 2022, 11(11), 323; https://doi.org/10.3390/act11110323 - 07 Nov 2022
Cited by 2 | Viewed by 1155
Abstract
In practice, the near-bit signals are usually accompanied by noises generated by drilling tool vibration and high-speed rotary. This study introduces discrete wavelet transform to a well drilling area and presents a new weal signal extraction algorithm, which can eliminate the vibration and [...] Read more.
In practice, the near-bit signals are usually accompanied by noises generated by drilling tool vibration and high-speed rotary. This study introduces discrete wavelet transform to a well drilling area and presents a new weal signal extraction algorithm, which can eliminate the vibration and rotary noises effectively and obtain the useful gravity attitude signals based on the discrete wavelet transform through a hard threshold method. The effectiveness and usefulness of our method are verified via Matlab simulation and actual drilling data. Full article
(This article belongs to the Special Issue Designing, Sensing, Instrumentation, Diagnosis, Controlling, and Integration of Actuators in Digital Manufacturing Especially in Aerospace Engineering)
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18 pages, 9202 KiB  
Article
Experimental Study on the Working Characteristics of Tri-Electrode Plasma Actuator Utilizing a Combination of Corona and Barrier Discharges
by Asami Hatamoto, Kumi Nakai and Hiroyuki Nishida
Actuators 2022, 11(11), 322; https://doi.org/10.3390/act11110322 - 07 Nov 2022
Cited by 3 | Viewed by 1689
Abstract
A tri-electrode plasma actuator (TED-PA), which has an additional electrode with a DC voltage, induces jets from two facing electrodes and achieves larger thrust and higher efficiency than a conventional dielectric barrier discharge plasma actuator. However, there are problems such as the large [...] Read more.
A tri-electrode plasma actuator (TED-PA), which has an additional electrode with a DC voltage, induces jets from two facing electrodes and achieves larger thrust and higher efficiency than a conventional dielectric barrier discharge plasma actuator. However, there are problems such as the large potential difference between the exposed electrodes, which can cause sparks and device destruction. Therefore, it is necessary to clarify the working mechanism of TED-PAs and optimize their configuration and applied voltage. In this study, we obtained the discharge photograph, the thrust, and the flow velocity field and investigated the characteristics of the DC voltage and the frequency of the AC voltage. To isolate the effects of the discharge from the potential variation, a corona discharge plasma actuator and a TED-PA were compared. As a result, increasing the frequency of the AC voltage induced stronger jets from the AC and DC electrodes. This result indicates that the barrier discharge enhances the jet from the DC electrode without changing the potential difference between the electrodes. Full article
(This article belongs to the Special Issue Dielectric Barrier Discharge Plasma Actuator for Active Flow Control)
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20 pages, 3500 KiB  
Article
Multi-Disturbance Observers-Based Nonlinear Control Scheme for Wire Rope Tension Control of Hoisting Systems with Backstepping
by Wanshun Zang, Xiao Chen and Jun Zhao
Actuators 2022, 11(11), 321; https://doi.org/10.3390/act11110321 - 06 Nov 2022
Cited by 4 | Viewed by 1317
Abstract
The objective of this paper is to pursue a wire rope control methodology for reducing the tension difference between two wire ropes of a hoisting system. As we know, complicated disturbances exist in the complex electro-hydraulic hoisting system, notably, some of these disturbances [...] Read more.
The objective of this paper is to pursue a wire rope control methodology for reducing the tension difference between two wire ropes of a hoisting system. As we know, complicated disturbances exist in the complex electro-hydraulic hoisting system, notably, some of these disturbances are coupled, such as high-speed airflow disturbances, structure vibrations and vibrations in flexible wire ropes. Furthermore, there are model errors in force modeling due to the Coulomb friction between two wire ropes and two moveable head sheaves in the real physical hoisting systems. To eliminate disturbances, two types of disturbance observers (DOs) are employed: a traditional disturbance observer (TDO) and a coupled disturbance observer (CDO), both of which are utilized to estimate and compensate for the Coulomb friction and coupled disturbances online. As a result, a nonlinear backstepping control scheme is presented with estimation values from the TDO and the CDO. The experiment’s results demonstrate the effectiveness of the proposed control methodology. Full article
(This article belongs to the Section Control Systems)
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21 pages, 5737 KiB  
Article
Driving Torque Control of Dual-Motor Powertrain for Electric Vehicles
by Jinglai Wu, Bing Wang and Xianqian Hong
Actuators 2022, 11(11), 320; https://doi.org/10.3390/act11110320 - 03 Nov 2022
Cited by 5 | Viewed by 2434
Abstract
This paper investigates the driving torque control method for the dual-motor powertrain in electric vehicles (EVs) to achieve the performance of accurate vehicle speed tracking, seamless driving mode shift, and high energy efficiency. The configuration of the dual-motor powertrain is based on the [...] Read more.
This paper investigates the driving torque control method for the dual-motor powertrain in electric vehicles (EVs) to achieve the performance of accurate vehicle speed tracking, seamless driving mode shift, and high energy efficiency. The configuration of the dual-motor powertrain is based on the parallel axle transmission structure, which does not contain any clutch or synchronizer. The powertrain provides three driving modes that are two single-motor driving modes and one dual-motor combined driving mode. A detailed dynamic model of the dual-motor powertrain is built to simulate the dynamic response of an EV. An energy management strategy (EMS) is used to select the driving mode and determine the ideal driving torque of two motors. The dynamic control strategy tries to track the ideal vehicle speed when uncertain parameters existed and avoid power interruption or impact during the mode shift. Three dynamic control strategies are proposed, which are the backward dynamic control strategy (BDCS), combined forward and backward dynamic control strategy (CFBDCS), and nested forward and backward dynamic control strategy (NFBDCS). The simulation results demonstrate that the NFBDCS has the best comprehensive performance in vehicle speed tracking, seamless mode shift, and good system energy efficiency. Full article
(This article belongs to the Special Issue Design, Control, and Optimization of Powertrain for New Energy Vehicles)
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18 pages, 5878 KiB  
Article
Efficient Spatiotemporal Graph Search for Local Trajectory Planning on Oval Race Tracks
by Matthias Rowold, Levent Ögretmen, Tobias Kerbl and Boris Lohmann
Actuators 2022, 11(11), 319; https://doi.org/10.3390/act11110319 - 03 Nov 2022
Cited by 8 | Viewed by 2054
Abstract
Autonomous racing has increasingly become a research subject as it provides insights into dynamic, high-speed situations. One crucial aspect of handling these situations, especially in the presence of dynamic obstacles, is the generation of a collision-free trajectory that represents a safe behavior and [...] Read more.
Autonomous racing has increasingly become a research subject as it provides insights into dynamic, high-speed situations. One crucial aspect of handling these situations, especially in the presence of dynamic obstacles, is the generation of a collision-free trajectory that represents a safe behavior and is also competitive in the case of racing. We propose a local planning approach that generates such trajectories for a racing car on an oval race track by searching a spatiotemporal graph. A considerable challenge of search-based methods in a spatiotemporal domain is the curse of dimensionality. Therefore, we propose how a previously presented graph structure that is based on intervals instead of discrete values can be searched more efficiently without losing optimality by using a uniform-cost search strategy. We extend the search method to make it anytime-capable so that it can provide a suboptimal trajectory even if the search has to be terminated early. The graph-based planning approach allows us to apply a flexible cost function so that our approach can operate fully autonomously on an oval race track, including the pit lane. We present a cost function for oval racing and explain how the terms contribute to the desired behaviors. This is supported by results with a full-scale prototype. Full article
(This article belongs to the Special Issue Intelligent Control and Robotic System in Path Planning)
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17 pages, 11434 KiB  
Article
Smooth Trajectory Planning at the Handling Limits for Oval Racing
by Levent Ögretmen, Matthias Rowold, Marvin Ochsenius and Boris Lohmann
Actuators 2022, 11(11), 318; https://doi.org/10.3390/act11110318 - 03 Nov 2022
Cited by 7 | Viewed by 1879
Abstract
In motion planning for autonomous racing, the challenge arises in planning smooth trajectories close to the handling limits of the vehicle with a sufficient planning horizon. Graph-based trajectory planning methods can find the global discrete-optimal solution, but they suffer from the curse of [...] Read more.
In motion planning for autonomous racing, the challenge arises in planning smooth trajectories close to the handling limits of the vehicle with a sufficient planning horizon. Graph-based trajectory planning methods can find the global discrete-optimal solution, but they suffer from the curse of dimensionality. Therefore, to achieve low computation times despite a long planning horizon, coarse discretization and simple edges that are efficient to generate must be used. However, the resulting rough trajectories cannot reach the handling limits of the vehicle and are also difficult to track by the controller, which can lead to unstable driving behavior. In this paper, we show that the initial edges connecting the vehicle’s estimated state with the actual graph are crucial for vehicle stability and race performance. We therefore propose a sampling-based approach that relies on jerk-optimal curves to generate these initial edges. The concept is introduced using a layer-based graph, but it can be applied to other graph structures as well. We describe the integration of the curves within the graph and the required adaptation to racing scenarios. Our approach enables stable driving at the handling limits and fully autonomous operation on the race track. While simulations show the comparison of our concept with an alternative approach based on uniform acceleration, we also present experimental results of a dynamic overtake with speeds up to 74 m/s on a full-size vehicle. Full article
(This article belongs to the Special Issue Intelligent Control and Robotic System in Path Planning)
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19 pages, 6442 KiB  
Article
Sensorless Control Analysis of Electric Motor Drives Based on High-Frequency Signal Injection and Its Simulation Verification
by Michal Duhancik, Tomas Coranic, Stefan Gaspar and Vladimir Lipovsky
Actuators 2022, 11(11), 317; https://doi.org/10.3390/act11110317 - 01 Nov 2022
Cited by 2 | Viewed by 1518
Abstract
The subject of this research is the sensorless control method verification of an asynchronous motor by a simulation in the area of low speed (up to 5 Hz) via the high-frequency analog signal injection method. The implementation of the continuous signal injection method [...] Read more.
The subject of this research is the sensorless control method verification of an asynchronous motor by a simulation in the area of low speed (up to 5 Hz) via the high-frequency analog signal injection method. The implementation of the continuous signal injection method is simpler when compared with the discrete signal injection; however, the discrete signal injection method has more advantages in signal processing. The injected analog signal will be superimposed on the main stator voltage. The response to this signal will be manifested mainly based on the asymmetries of the asynchronous motor, which are given by the design of the motor. The influence of the stator inductance LS will be suppressed by a suitable elimination method since this asymmetry is undesirable for the rotor position detection. The asymmetry caused by the rotor slotting will be used to detect the rotor position. The less the rotor slots are inclined, the stronger the asymmetry. Therefore, to verify the given estimation method as realistically as possible, a mathematical model of an asynchronous motor, including asymmetries due to magnetic core saturation and asymmetries due to rotor slotting, has been designed in order to get as close as possible to the real condition. Thus, the chapter “Asymmetry Creation due to Rotor Slotting” describes the given phenomenon in more detail. Subsequently, the INFORM method the rotor position detection is implemented and defined in the chapter: “Rotor Position Estimation Based on HF Signal Injection.” Given the fact that the asymmetries caused by magnetic core saturation are undesirable, he estimation error reaches up to 10%; therefore, saturations are suppressed by a convenient method. After filtering out these asymmetries, the control accuracy is achieved with the maximum rotor position estimation error of 0.05 rad, representing 1%. The inaccuracy is directly proportional to the rotor rotation speed, and it is also caused by the computing power, the processing frequency, and the complexity of the computing algorithm. The present research paper serves essentially to verify the sensorless method based on a high-frequency signal injection and as a basis for effectiveness and efficiency compared with other control methods. Full article
(This article belongs to the Special Issue Designing, Sensing, Instrumentation, Diagnosis, Controlling, and Integration of Actuators in Digital Manufacturing Especially in Aerospace Engineering)
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17 pages, 5899 KiB  
Article
A Pneumatic Control Method for Commercial Vehicle Electronic Brake System Based on EPV Module
by Lanjiang Zhang, Yang Yan, Qingwei Zhu, Gang Zhao, Deying Feng and Jian Wu
Actuators 2022, 11(11), 316; https://doi.org/10.3390/act11110316 - 31 Oct 2022
Cited by 4 | Viewed by 2153
Abstract
The traditional electronic braking system (EBS) of a commercial vehicle has the problems of sluggish pressure response, large dynamic error and unsatisfactory braking effect during braking. First, a novel EBS system based on electronic pneumatic valves (EPV) module is designed, which integrated the [...] Read more.
The traditional electronic braking system (EBS) of a commercial vehicle has the problems of sluggish pressure response, large dynamic error and unsatisfactory braking effect during braking. First, a novel EBS system based on electronic pneumatic valves (EPV) module is designed, which integrated the control of each pneumatic valve. Secondly, the hardware of the EBS bottom controller and the air pressure closed-loop control are carried out. A kind of similar to PWM (SPWM) air pressure control method is proposed. By controlling the opening and closing time of the solenoid valves, the brake air pressure could be precisely regulated, and the dynamic response characteristics of the system are improved. Eventually, commercial vehicle air brake hardware in the loop (HIL) test platform based on LabVIEW and NI-PXI system is built to verify the effectiveness of the EBS dynamic response characteristics. The experimental results showed that the continuous control of EBS solenoid valves is realized by using the SPWM control method, and the fine dynamic response characteristics of EBS air pressure closed-loop control are ensured. Full article
(This article belongs to the Section Actuators for Land Transport)
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21 pages, 4913 KiB  
Article
Research on Optimal Oil Filling Control Strategy of Wet Clutch in Agricultural Machinery
by Yu Qian, Lin Wang, Zhun Cheng, Yirong Zhao, Xingwei Wang and Zhixiong Lu
Actuators 2022, 11(11), 315; https://doi.org/10.3390/act11110315 - 30 Oct 2022
Cited by 1 | Viewed by 1633
Abstract
To improve the wet clutch engagement quality, which is widely used in agricultural machinery, the oil filling control strategy of a wet clutch is studied based on the method of simulation and experiment in detail in this paper. Firstly, this paper carries out [...] Read more.
To improve the wet clutch engagement quality, which is widely used in agricultural machinery, the oil filling control strategy of a wet clutch is studied based on the method of simulation and experiment in detail in this paper. Firstly, this paper carries out the dynamic analysis of the wet clutch engagement process, establishes the mathematical model of the mechanical domain and the hydraulic domain of the hydraulic execution system, and designs the backstepping oil pressure controller. The controllability of the output oil pressure of the clutch hydraulic actuator is verified on the joint simulation platform of Matlab/Simulink (Version R2017b, MathWorks, Natick, MA, USA) and AMESim (Version 2019.1, Simcenter Amesim, Siemens Digital Industries Softwares, Berlin&Munuch, Germany). Then, this paper analyzes the clutch engagement process, extracts five factors affecting the oil filling process, and selects four clutch engagement quality evaluation indexes. An amount of 50 groups of experiments are carried out on the wet clutch oil filling test simulation platform built by SimulationX (Version 3.8, ESI ITI GmbH, Dresden, Germany). The response surface method (RSM) and stepwise regression analysis method are used to explore the mathematical models of the quality evaluation index and influencing factors of the oil filling process. Through 15 groups of random tests, the prediction accuracy of the stepwise regression model and the RSM model of each index is compared, and the models with high accuracy are selected to establish the comprehensive prediction mathematical model of clutch engagement quality, combined with the variance weight method. Finally, according to the working condition of the 3 MPa oil filling pressure studied in this paper, the optimal oil filling control strategy is obtained by the proposed clutch engagement quality prediction model. Under the target condition, when the oil filling rate of stage 1 is the highest and the proportion of phase 1’s duration to the total oil filling time is 69.65%, the oil filling rate of stage 2 is the lowest and the proportion of phase 2’s duration to the total oil filling time is 21.85%, and the proportion of phase 3’s duration to the total oil filling time is 8.51%, the engagement quality of wet clutch is the best. The research method of wet clutch optimal oil filling control strategy proposed in this paper provides a reliable method for the ride comfort research of agricultural machinery and clutch control. Full article
(This article belongs to the Section Actuators for Land Transport)
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14 pages, 6170 KiB  
Article
Theoretical and Numerical Study on Dynamic Response of Propellant Actuator
by Pengzhao Xu, Ning Zhao, Kunlin Shi, Shaokang Cui, Chi Chen and Jun Liu
Actuators 2022, 11(11), 314; https://doi.org/10.3390/act11110314 - 28 Oct 2022
Viewed by 1475
Abstract
In order to solve the complexity of the structure, assembly process, component contact state and working process of the propellant actuator by conventional methods, a novel design method based on theoretical and numerical analysis was proposed. The internal ballistic model of the propellant [...] Read more.
In order to solve the complexity of the structure, assembly process, component contact state and working process of the propellant actuator by conventional methods, a novel design method based on theoretical and numerical analysis was proposed. The internal ballistic model of the propellant actuator was established based on the classical internal ballistic theory, and the pressure–time characteristic curve of the propellant gas was then obtained. According to the characteristic curve, the dynamic characteristics of the piston under different design conditions of the shear slice were calculated by numerical simulation. The results show that the pressure–time characteristics of the internal ballistic model were in good agreement with the experimental data, indicating that the the internal ballistic model of the propellant actuator is reasonable. Additionally, the structure optimization design and drop safety of the propellant actuator were carried out using the finite element method. It was found that with increasing the propellant charge, the movement time of the piston decreases and the maximum velocity increases. Moreover, the critical values of the propellant charge are 5 mg, 6 mg, 7 mg for the thickness of the shear slice of 0.2 mm, 0.3 mm and 0.4 mm, respectively. Full article
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23 pages, 8682 KiB  
Article
Experimental Study on the Snowfall Flow Control of Backward-Facing Steps Using a High-Durability Designed Plasma Electrode
by Tasuku Tanaka, Hisashi Matsuda, Toshiki Takahashi, Takahiro Chiba, Nobuyoshi Watanabe, Hideaki Sato and Masafumi Takeyama
Actuators 2022, 11(11), 313; https://doi.org/10.3390/act11110313 - 27 Oct 2022
Cited by 2 | Viewed by 2535
Abstract
Using a high-durability designed plasma electrode (PA), the plasma actuation effect on both a two-dimensional backward-facing step flow (standard model) and an arc-shaped three-dimensional backward-facing step flow (arc model) was investigated experimentally. First, we searched for plasma operation control conditions suitable for the [...] Read more.
Using a high-durability designed plasma electrode (PA), the plasma actuation effect on both a two-dimensional backward-facing step flow (standard model) and an arc-shaped three-dimensional backward-facing step flow (arc model) was investigated experimentally. First, we searched for plasma operation control conditions suitable for the two-dimensional backward-facing step flow by carrying out experiments using a medium-sized circulating wind tunnel. Next, using the natural-snow wind tunnel of the Hokkaido University of Science, we examined whether an AC-driven PA can control snowfall flow. It became clear for the first time that the amount of snow accumulation can be reduced by more than 20% when the PA is driven at a dimensionless frequency of fH/U = 0.32, where f is the pulsed modulation frequency, H is the step height, and U is the mainstream velocity, and the duty ratio D (the time ratio of PA_ON to the total time when controlled by the pulsed modulation frequency) is equal to 1.0%. It was also confirmed that by masking the arc-shaped electrode parallel to the mainstream and using only the part perpendicular to the mainstream of the PA electrode, the amount of accumulated snow could be reduced by up to 20%. It has become clear that high-durability designed plasma electrodes can control the snowfall flow and reduce the amount of accumulated snow. Full article
(This article belongs to the Special Issue Dielectric Barrier Discharge Plasma Actuator for Active Flow Control)
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13 pages, 5125 KiB  
Article
Analysis of Trajectory Tracking Characteristics of a Magnetically Driven Oil-Free Scroll Compressor
by Ce Shi, Feng Sun, Fangchao Xu, Junjie Jin, Ling Tong, Qing Zhou and Koichi Oka
Actuators 2022, 11(11), 312; https://doi.org/10.3390/act11110312 - 27 Oct 2022
Viewed by 1353
Abstract
The conventional scroll compressor cannot run oil-free because of wear and tear and lubrication problems during operation due to some parts, such as anti-rotation devices. The magnetic drive oil-free scroll compressor (MDOFSC) uses a contactless drive method to avoid this drawback. In order [...] Read more.
The conventional scroll compressor cannot run oil-free because of wear and tear and lubrication problems during operation due to some parts, such as anti-rotation devices. The magnetic drive oil-free scroll compressor (MDOFSC) uses a contactless drive method to avoid this drawback. In order to solve the swing problem of the orbiting scroll during the operation of the MDOFSC, decentralized control and centralized control are used to study the trajectory tracking characteristics. Firstly, the structure and working principle of the MDOFSC are introduced, and the system’s magnetic circuit and differential control principle are analyzed. Then, the dynamic model of the MDOFSC under the condition of non-compressed gas is established, and the coordinate matrix decoupling method is used to analyze the relationship between the degree of freedom of the system and the measurement distance of the displacement sensor. Finally, the system is simulated and experimentally studied under centralized PID control, and the experimental comparison study between decentralized control and centralized control is conducted. The results show that centralized control dramatically improves the trajectory control ability of the system. Full article
(This article belongs to the Special Issue Advanced Theory and Application of Magnetic Actuators)
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16 pages, 5828 KiB  
Article
Design and Test of an Active Pneumatic Soft Wrist for Soft Grippers
by Guangming Chen, Tao Lin, Shi Ding, Shuang Chen, Aihong Ji and Gabriel Lodewijks
Actuators 2022, 11(11), 311; https://doi.org/10.3390/act11110311 - 27 Oct 2022
Cited by 4 | Viewed by 1857
Abstract
An active wrist can deliver both bending and twisting motions that are essential for soft grippers to perform dexterous manipulations capable of producing a wide range movements. Currently, the versions of gripper wrists are relatively heavy due to the bending and twisting motions [...] Read more.
An active wrist can deliver both bending and twisting motions that are essential for soft grippers to perform dexterous manipulations capable of producing a wide range movements. Currently, the versions of gripper wrists are relatively heavy due to the bending and twisting motions performed by the motors. Pneumatic soft actuators can generate multiple motions with lightweight drives. This research evaluates a pneumatic soft wrist based on four parallel soft helical actuators. The kinematics models for predicting bending and twisting motions of this soft wrist are developed. Finite element method simulations are conducted to verify the functions of bending and twisting of this wrist. In addition, the active motions of the soft pneumatic wrist are experimentally demonstrated. Based on sensitivity studies of geometric parameters, a set of parameter values are identified for obtaining maximum bending and twisting angles for a bionic human wrist. Through simulation and experimental tests of the soft wrist for a soft gripper, the desired bending and twisting motions as those of a real human hand wrist are established. Full article
(This article belongs to the Special Issue Soft Actuators and Robotics)
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