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Actuators, Volume 12, Issue 2 (February 2023) – 47 articles

Cover Story (view full-size image): We propose and demonstrate a haptic device with liquid-pouch motors that can simulate a handshake. Because handshakes involve contact of the palms or soft skin, handshake simulation requires the haptic device to provide pressure onto specific areas of the palm with soft contact. This can be achieved with thermally driven liquid-pouch motors, which inflate and deflate when a low-boiling-point liquid, here Novec ™ 7000, evaporates and condenses, respectively. Due to the simplicity of the soft actuator system, this haptic glove is lightweight and conformable. To design the haptic glove, we experimentally investigated the contact region and strength in handshakes, which led to an optimal number, size and position for the liquid-pouch motors. Sensory experiments verified that the designed haptic glove successfully simulated handshakes. View this paper
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16 pages, 8416 KiB  
Article
A Novel Field-Oriented Control Algorithm for Permanent Magnet Synchronous Motors in 60° Coordinate Systems
by Xiao Tang, Zhi Zhang, Xueliang Liu, Chang Liu, Ming Jiang and Yue Song
Actuators 2023, 12(2), 92; https://doi.org/10.3390/act12020092 - 18 Feb 2023
Cited by 10 | Viewed by 1890
Abstract
In this study, a novel field-oriented control (FOC) algorithm was proposed in a 60° coordinate system for controlling the speed of permanent magnet synchronous motors. The FOC algorithm consists of several parts in which the reference currents and feedback currents are transformed into [...] Read more.
In this study, a novel field-oriented control (FOC) algorithm was proposed in a 60° coordinate system for controlling the speed of permanent magnet synchronous motors. The FOC algorithm consists of several parts in which the reference currents and feedback currents are transformed into the representation form in a 60° coordinate system. Current regulators are typically used in a 60° coordinate system to directly obtain the reference voltage vector. The proposed FOC structure was established by incorporating the space vector pulse width modulation algorithm in a 60° coordinate system. The proposed FOC structure simplified the FOC algorithm and reduced its computational burden. The feasibility of the proposed method was verified through simulations and experiments. Full article
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14 pages, 4711 KiB  
Article
A Deep Trajectory Controller for a Mechanical Linear Stage Using Digital Twin Concept
by Kantawatchr Chaiprabha and Ratchatin Chancharoen
Actuators 2023, 12(2), 91; https://doi.org/10.3390/act12020091 - 17 Feb 2023
Cited by 4 | Viewed by 2023
Abstract
An industrial linear stage is a device that is commonly used in robotics. To be precise, an industrial linear stage is an electro-mechanical system that includes a motor, electronics, flexible coupling, gear, ball screw, and precision linear bearing. A tight fit can provide [...] Read more.
An industrial linear stage is a device that is commonly used in robotics. To be precise, an industrial linear stage is an electro-mechanical system that includes a motor, electronics, flexible coupling, gear, ball screw, and precision linear bearing. A tight fit can provide better precision but also generates a difficult-to-model friction that is highly nonlinear and asymmetrical. Herein, this paper proposes an advanced trajectory controller based on a digital twin framework incorporated with artificial intelligence (AI), which can effectively control a precision linear stage. This framework offers several advantages: detection of abnormalities, estimation of performance, and selective control over any situation. The digital twin is developed via Matlab’s Simscape and runs concurrently having a real-time controller. Full article
(This article belongs to the Special Issue New Control Schemes for Actuators)
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19 pages, 6571 KiB  
Article
A Study of a Bistable Reciprocating Piston Pump Driven by Shape Memory Alloys and Recuperative Springs
by Mihail Kostov, Todor Todorov, Rosen Mitrev, Konstantin Kamberov and Rumen Nikolov
Actuators 2023, 12(2), 90; https://doi.org/10.3390/act12020090 - 17 Feb 2023
Cited by 3 | Viewed by 1614
Abstract
This paper presents and examines a new design concept for a bistable reciprocating piston pump. The bistable pump mechanism belongs to the bistable mechanisms, which have two stable positions at the end of the suction and discharge strokes. The transition between the stable [...] Read more.
This paper presents and examines a new design concept for a bistable reciprocating piston pump. The bistable pump mechanism belongs to the bistable mechanisms, which have two stable positions at the end of the suction and discharge strokes. The transition between the stable positions is achieved by using triggering force at each beginning of suction and discharge and subsequent movement using a recuperative spring. In this mechanism, the triggering forces are created by two Shape Memory Alloy (SMA) wires. Geometric and force expressions for the pump suction and discharge strokes are derived. Additional equations are obtained for the balance of moments for the two stable equilibrium positions and the unstable position in the middle of the stroke. Numerical studies have been conducted for the suction and discharge strokes, considering the force exerted by the gas on the piston, which is modelled by an indicator diagram assuming a polytropic process. It was found that the load on the mechanism has significant non-uniformity. The diagrams illustrating the distribution of total moments showed that the cold SMA wire shifted the point of instability. The numerical example shows how to choose the right spring stiffness to obtain energy recovery. In this way, the triggering SMA forces act only at the beginning of the two strokes and, after that, the recuperative forces substitute the action of the SMA forces. The theoretical relationships and methods presented here are suitable for synthesizing new pumps or analyzing similar mechanisms. Full article
(This article belongs to the Special Issue Innovative Actuators Based on Shape Memory Alloys)
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15 pages, 4700 KiB  
Article
Development of a Contact Force Model Suited for Spherical Contact Event
by Siyuan Wang and Peng Gao
Actuators 2023, 12(2), 89; https://doi.org/10.3390/act12020089 - 17 Feb 2023
Cited by 1 | Viewed by 1548
Abstract
The stiffness coefficient suited for a spherical contact body is developed by means of a contact semi-angle based on Steuermann’s theory. The new static contact force model is close to the results of FEM when the index of the polynomial is equal to [...] Read more.
The stiffness coefficient suited for a spherical contact body is developed by means of a contact semi-angle based on Steuermann’s theory. The new static contact force model is close to the results of FEM when the index of the polynomial is equal to 2. The strain energy is derived according to the contact stiffness coefficient. Taylor expansion is used in the dissipated energy integration process to obtain a more accurate hysteresis damping factor. The new dynamic contact force model consists of the new stiffness coefficient and new hysteresis damping factor, which is suitable for the spherical-contact event with a high coefficient of restitution. Full article
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0 pages, 163 KiB  
Retraction
RETRACTED: Lv et al. A Closed-Loop Control Mathematical Model for Photovoltaic-Electrostatic Hybrid Actuator with a Slant Lower Electrode Based on PLZT Ceramic. Actuators 2021, 10, 285
by Zhen Lv, Muhammad Uzair, Xinjie Wang and Yafeng Liu
Actuators 2023, 12(2), 88; https://doi.org/10.3390/act12020088 - 16 Feb 2023
Cited by 1 | Viewed by 1208
Abstract
The journal retracts the article, A Closed-Loop Control Mathematical Model for Photovoltaic-Electrostatic Hybrid Actuator with a Slant Lower Electrode Based on PLZT Ceramic [...] Full article
17 pages, 6409 KiB  
Article
A Novel Ultra-Low Power Consumption Electromagnetic Actuator Based on Potential Magnetic Energy: Theoretical and Finite Element Analysis
by M. Albertos-Cabanas, D. Lopez-Pascual, I. Valiente-Blanco, G. Villalba-Alumbreros and M. Fernandez-Munoz
Actuators 2023, 12(2), 87; https://doi.org/10.3390/act12020087 - 16 Feb 2023
Viewed by 1901
Abstract
A novel concept of a rotary electromagnetic actuator for positioning with ultra-low power consumption is presented. The device is based on harnessing potential magnetic energy stored between permanent magnets facing each other with opposing magnetization polarities. When combined with an active electromagnetic control [...] Read more.
A novel concept of a rotary electromagnetic actuator for positioning with ultra-low power consumption is presented. The device is based on harnessing potential magnetic energy stored between permanent magnets facing each other with opposing magnetization polarities. When combined with an active electromagnetic control and passive stabilization system, the rotor of the device can switch between stable equilibrium positions in a fast way with a minimal fraction of the power and energy consumption of a traditional electromagnetic actuator. In this paper, a theoretical model, supported by finite element analysis results, is presented. The actuator has been designed in detail to operate as an optical filter wheel actuator. Calculations demonstrate that the device has the potential to provide a power-consumption saving of up to 86.6% and an energy consumption reduction of up to 58.6% with respect to a traditional filter wheel actuator. Full article
(This article belongs to the Special Issue Electromagnetic Actuators)
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14 pages, 7278 KiB  
Article
Numerical Study on Unbalance Response of Dual-Rotor System Based on Nonlinear Bearing Characteristics of Active Magnetic Bearings
by Nianxian Wang, Mingzheng Liu, Junfu Yao, Pingping Ge and Huachun Wu
Actuators 2023, 12(2), 86; https://doi.org/10.3390/act12020086 - 16 Feb 2023
Cited by 4 | Viewed by 1385
Abstract
The magnetic suspended dual-rotor system (MSDS) has the advantage of a high power density. The system can be used in high-speed rotating machinery. The major purpose of this study is to predict the unbalance response of the MSDS considering the nonlinear bearing characteristics [...] Read more.
The magnetic suspended dual-rotor system (MSDS) has the advantage of a high power density. The system can be used in high-speed rotating machinery. The major purpose of this study is to predict the unbalance response of the MSDS considering the nonlinear bearing characteristics of active magnetic bearings (AMBs). Firstly, the nonlinear bearing model was established by a non-linear magnetic circuit method (NMCM). The model considers magnetic flux leakage, magnetic saturation, and working position flotation accurately. Then, the dynamic model of the system was established by using the finite element method and solved by the Newmark-β method. Finally, the effects of external load, rotational speeds, and control parameters were studied. Axial trajectory diagrams, stability zone diagrams, and waterfall diagrams were employed to analyze the dynamic behaviors of the MSDS. The results indicate that the external load, rotational speeds, and control parameters have a significant impact on the unbalance response of the system. Super harmonics of rotational frequencies and their combined frequencies may be excited by heavy load conditions. Appropriate control parameters can suppress the nonlinear phenomena. The obtained results of this research will contribute to the design and fault diagnosis of MSDSs. Full article
(This article belongs to the Special Issue Advanced Theory and Application of Magnetic Actuators)
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14 pages, 1548 KiB  
Article
Optimal Voltage Distribution on PZT Actuator Pairs for Vibration Damping in Beams with Different Boundary Conditions
by Andrea Rossi and Fabio Botta
Actuators 2023, 12(2), 85; https://doi.org/10.3390/act12020085 - 16 Feb 2023
Viewed by 1719
Abstract
In recent decades, many studies have been conducted on the use of smart materials in order to dampen and control vibrations. Lead zirconate titanate piezoceramics (PZT) are very attractive for such applications due to their ability of delivering high energy strain in the [...] Read more.
In recent decades, many studies have been conducted on the use of smart materials in order to dampen and control vibrations. Lead zirconate titanate piezoceramics (PZT) are very attractive for such applications due to their ability of delivering high energy strain in the structure. A pair of piezoelectric actuators can actively dampen the resonances of the structure, but the damping effectiveness strongly relies on its location. Damping effectiveness can be substantially increased if the structure is fully covered with PZT actuator pairs and the voltage distribution on each pair is optimized. In this way, each actuator pair contributes to the vibration attenuation and only the driving voltage’s sign, distributed on each actuator pair, needs to be identified for each resonance. This approach is here applied to the case of Euler–Bernoulli beams with constant cross-section and the optimal voltage distribution is investigated for several boundary conditions. The theoretical model results were corroborated with finite element simulations, which were carried out considering beams covered by ten PZT actuator pairs. The numerical results agree remarkably well with the theoretical predictions for each examined case (i.e., free-free, pinned-pinned, and fixed-fixed). Full article
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20 pages, 7426 KiB  
Article
Research on the Residual Vibration Suppression of Delta Robots Based on the Dual-Modal Input Shaping Method
by Zhongfeng Guo, Jianqiang Zhang and Peisen Zhang
Actuators 2023, 12(2), 84; https://doi.org/10.3390/act12020084 - 15 Feb 2023
Cited by 3 | Viewed by 2371
Abstract
The Delta robot is a high-speed and high-precision parallel robot. When it is in function, the end effector generates residual vibration, which reduces the repeat positioning accuracy and positioning efficiency. The input shaping method has previously been shown to suppress the residual vibration [...] Read more.
The Delta robot is a high-speed and high-precision parallel robot. When it is in function, the end effector generates residual vibration, which reduces the repeat positioning accuracy and positioning efficiency. The input shaping method has previously been shown to suppress the residual vibration of the robot, but the vibration suppression effect of the single-modal input shaper is not good for the delta robot, which has multiple dominant modes for the residual vibration. To solve this problem, this paper proposes an effective method for residual vibration suppression of Delta robots based on dual-modal input shaping technology. Firstly, the modal analysis of the Delta robot is performed using finite element software, and the dominant modal of its residual vibration is determined. Secondly, six dual-modal input shapers are designed according to the obtained modal parameters. Finally, Simulink is used for simulation analysis to verify the robustness and vibration suppression performance of the designed six dual-modal input shapers and traditional single-modal input shapers. The simulation results show that the designed ZVD-EI dual-modal input shaper has good robustness, can effectively suppress the residual vibration of the Delta robot, and can effectively improve the repetitive positioning accuracy and work efficiency of the Delta robot when it is running at high speed. Full article
(This article belongs to the Special Issue Advanced Theory and Application of Magnetic Actuators)
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12 pages, 3005 KiB  
Article
Dynamic Response Analysis of an Immersed Electrothermally Actuated MEMS Mirror
by Tailong Liu, Teng Pan, Shuijie Qin, Hui Zhao and Huikai Xie
Actuators 2023, 12(2), 83; https://doi.org/10.3390/act12020083 - 15 Feb 2023
Cited by 1 | Viewed by 1683
Abstract
MEMS mirrors have a wide range of applications, most of which require large field-of-view (FOV). Immersing MEMS mirrors in liquid is an effective way to improve the FOV. However, the increased viscosity, convective heat transfer and thermal conductivity in liquid greatly affect the [...] Read more.
MEMS mirrors have a wide range of applications, most of which require large field-of-view (FOV). Immersing MEMS mirrors in liquid is an effective way to improve the FOV. However, the increased viscosity, convective heat transfer and thermal conductivity in liquid greatly affect the dynamic behaviors of electrothermally actuated micromirrors. In this paper, the complex interactions among the multiple energy domains, including electrical, thermal, mechanical and fluidic, are studied in an immersed electrothermally actuated MEMS mirror. A damping model of the immersed MEMS mirror is built and dimensional analysis is applied to reduce the number of variables and thus significantly simplify the model. The solution of the fluid damping model is solved by using regression analysis. The dynamic response of the MEMS mirror can be calculated easily by using the damping model. The experimental results verify the effectiveness and accuracy of these models. The difference between the model prediction and the measurement is within 4%. The FOV scanned in a liquid is also increased by a factor of 1.6. The model developed in this work can be applied to study the dynamic behaviors of various immersed MEMS actuators. Full article
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10 pages, 25468 KiB  
Article
Power Optimization of TiNiHf/Si Shape Memory Microactuators
by Gowtham Arivanandhan, Zixiong Li, Sabrina M. Curtis, Lisa Hanke, Eckhard Quandt and Manfred Kohl
Actuators 2023, 12(2), 82; https://doi.org/10.3390/act12020082 - 15 Feb 2023
Cited by 3 | Viewed by 1773
Abstract
We present a novel design approach for the power optimization of cantilever-based shape memory alloy (SMA)/Si bimorph microactuators as well as their microfabrication and in situ characterization. A major concern upon the miniaturization of SMA/Si bimorph microactuators in conventional double-beam cantilever designs is [...] Read more.
We present a novel design approach for the power optimization of cantilever-based shape memory alloy (SMA)/Si bimorph microactuators as well as their microfabrication and in situ characterization. A major concern upon the miniaturization of SMA/Si bimorph microactuators in conventional double-beam cantilever designs is that direct Joule heating generates a large size-dependent temperature gradient along the length of the cantilevers, which significantly enhances the critical electrical power required to complete phase transformation. We demonstrate that this disadvantage can be mitigated by the finite element simulation-assisted design of additional folded beams in the perpendicular direction to the active cantilever beams, resulting in temperature homogenization. This approach is investigated for TiNiHf/Si microactuators with a film thickness ratio of 440 nm/2 µm, cantilever beam length of 75–100 µm and widths of 3–5 µm. Temperature-homogenized SMA/Si microactuators show a reduction in power consumption of up to 48% compared to the conventional double-beam cantilever design. Full article
(This article belongs to the Special Issue Cooperative Microactuator Systems)
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18 pages, 6705 KiB  
Article
Design of Farm Irrigation Control System Based on the Composite Controller
by Xue Li, Zhiqiang Li, Dongbo Xie, Minxue Wang, Guoan Zhou and Liqing Chen
Actuators 2023, 12(2), 81; https://doi.org/10.3390/act12020081 - 14 Feb 2023
Cited by 2 | Viewed by 5138
Abstract
Farmland irrigation is an essential foundation for good crop growth, while traditional farmland irrigation techniques cannot fully consider the impact of factors such as natural precipitation and crop transpiration on crop growth, which can, to a certain extent, result in poor irrigation decisions [...] Read more.
Farmland irrigation is an essential foundation for good crop growth, while traditional farmland irrigation techniques cannot fully consider the impact of factors such as natural precipitation and crop transpiration on crop growth, which can, to a certain extent, result in poor irrigation decisions and a complex farmland environment that cannot be monitored promptly, thereby reducing farmland production efficiency. This study designs a farmland irrigation control system based on a composite controller. Firstly, an irrigation control method is proposed to establish a prediction model for future rainfall and crop transpiration using historical meteorological data. The composite controller is designed based on the prediction model to realize an irrigation control operation with an irrigation value as the control quantity, a water and fertilizer machine, and a solenoid valve as the actuators. Secondly, an intelligent irrigation control cloud platform based on Java language is designed to monitor farm information and irrigation operation records in real-time to facilitate visual management. Finally, the prediction accuracy is high, based on the prediction model results, which can provide a specific reference basis. The superiority of the proposed controller is verified by simulation using MATLAB/Simulink. The results show that the proposed controller can be well suited for nonlinear control systems and has good control performance while ensuring high tracking accuracy, strong robustness, and fast convergence. Full article
(This article belongs to the Section Control Systems)
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20 pages, 3809 KiB  
Article
Analysis and Validation of Sensitivity in Torque-Sensitive Actuators
by Minh Tran, Lukas Gabert and Tommaso Lenzi
Actuators 2023, 12(2), 80; https://doi.org/10.3390/act12020080 - 14 Feb 2023
Cited by 2 | Viewed by 2256
Abstract
Across different fields within robotics, there is a great need for lightweight, efficient actuators with human-like performance. Linkage-based passive variable transmissions and torque-sensitive transmissions have emerged as promising solutions to meet this need by significantly increasing actuator efficiency and power density, but their [...] Read more.
Across different fields within robotics, there is a great need for lightweight, efficient actuators with human-like performance. Linkage-based passive variable transmissions and torque-sensitive transmissions have emerged as promising solutions to meet this need by significantly increasing actuator efficiency and power density, but their modeling and analysis remain an open research topic. In this paper, we introduce the sensitivity between input displacement and output torque as a key metric to analyze the performance of these complex mechanisms in dynamic tasks. We present the analytical model of sensitivity in the context of two different torque-sensitive transmission designs, and used this sensitivity metric to analyze the differences in their performance. Experiments with these designs implemented within a powered knee prosthesis were conducted, and results validated the sensitivity model as well as its role in predicting actuators’ dynamic performance. Together with other design methods, sensitivity analysis is a valuable tool for designers to systematically analyze and create transmission systems capable of human-like physical behavior. Full article
(This article belongs to the Special Issue Actuators in Assistive and Rehabilitation Robotics)
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1 pages, 523 KiB  
Correction
Correction: Duan, E.; Bryant, M. Implications of Spatially Constrained Bipennate Topology on Fluidic Artificial Muscle Bundle Actuation. Actuators 2022, 11, 82
by Emily Duan and Matthew Bryant
Actuators 2023, 12(2), 79; https://doi.org/10.3390/act12020079 - 13 Feb 2023
Viewed by 847
Abstract
The authors wish to make the following corrections in Section 3 [...] Full article
21 pages, 8372 KiB  
Article
On a Vision-Based Manipulator Simulator
by Shuwen Yu and Guangbo Hao
Actuators 2023, 12(2), 78; https://doi.org/10.3390/act12020078 - 12 Feb 2023
Cited by 1 | Viewed by 1395
Abstract
This paper presents a typical grasp–hold–release micromanipulation simulator based on MATLAB and Simulink. Closed-loop force and position control were implemented only based on a camera. The work was mainly focused on control performance improvements and GUI design. Different types of control strategies were [...] Read more.
This paper presents a typical grasp–hold–release micromanipulation simulator based on MATLAB and Simulink. Closed-loop force and position control were implemented only based on a camera. The work was mainly focused on control performance improvements and GUI design. Different types of control strategies were investigated in both the position and force control processes. Finally, incremental PID and positional PID were adopted in the gripper position control and force control processes, respectively. The best performance of the gripper position control was the fast response of 0.3 s without overshoot and steady-state errors in the range of 10–40 Hz. The new camera control algorithm kept a big motion range (4.48 × 4.48 mm) and a high position resolution of 0.56 µm, with a high force resolution of 1.56 µN in the force control stage. The maximum error between the measured force and the real force was maintained below 4 µN. The steady-state error and the setting time were less than 1.2% and less than 1.5 s, respectively. A separate app, the Image Generation Simulator app, was developed to assist users in getting suitable initial coordinates, camera parameters, desired position resolutions, and force resolutions, which are packed as a standalone executable file. The main app can run the simulation model, debug, playback, and report simulation results, and calculate the calibration equation. Different initial coordinates, camera parameters, sample frequencies, controller parameters, and even controller types can be adjusted from this app. Full article
(This article belongs to the Section Control Systems)
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11 pages, 4683 KiB  
Communication
Design of a Single-Sided, Coreless, Flat-Type Linear Voice Coil Motor
by Wei Zhang, He Zhang, Junren Mu and Song Wang
Actuators 2023, 12(2), 77; https://doi.org/10.3390/act12020077 - 11 Feb 2023
Cited by 1 | Viewed by 1993
Abstract
A voice coil motor is a type of permanent magnet linear motor, which is based on the Ampere force theorem. It has the following advantages: a simple structure, a small size, no cogging force, and a fast response time. In this study, a [...] Read more.
A voice coil motor is a type of permanent magnet linear motor, which is based on the Ampere force theorem. It has the following advantages: a simple structure, a small size, no cogging force, and a fast response time. In this study, a voice coil motor was designed to provide x-directional thrust in the magnetically levitated cable table of a lithography machine. The voice coil motor designed in this study was based on the Halbach permanent magnet array, and adopted a single-sided, coreless, flat-type structure. First, the magnetic field distribution was analyzed based on the magnetic charge method to obtain an expression for the magnetic field and the thrust. The results of this analysis agreed very well with the finite element simulation results. Next, the main parameters of the motor, including the number of turns made by the coil, the size of the wire, and the size of the permanent magnets, were selected and optimized to increase the force density. Finally, two double-layer, serpentine waterway water-cooling plate configurations were designed for this voice coil motor. The validity of this water-cooling structure was verified for two different winding equivalent models. This provided feasibility to further upgrade the windings’ current density. Full article
(This article belongs to the Section Actuators for Medical Instruments)
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14 pages, 4027 KiB  
Article
Parameter Identification of Displacement Model for Giant Magnetostrictive Actuator Using Differential Evolution Algorithm
by Xiaojun Ju, Jili Lu, Bosong Rong and Hongyan Jin
Actuators 2023, 12(2), 76; https://doi.org/10.3390/act12020076 - 10 Feb 2023
Cited by 4 | Viewed by 1371
Abstract
Based on Jiles–Atherton theory and the quadratic law, a displacement model for giant magnetostrictive actuators (GMA) has been developed. The Runge–Kutta method is used to solve the nonlinear differential equation of the hysteresis model in a segmented magnetic field. Aiming at the problem [...] Read more.
Based on Jiles–Atherton theory and the quadratic law, a displacement model for giant magnetostrictive actuators (GMA) has been developed. The Runge–Kutta method is used to solve the nonlinear differential equation of the hysteresis model in a segmented magnetic field. Aiming at the problem that the model parameters are coupled with each other and difficult to estimate, a heuristic intelligent search algorithm-differential evolution algorithm (DE) is employed to implement parameter identification. In order to verify the effectiveness of the algorithm, comparative studies with the genetic algorithm (GA) and the particle swarm optimization (PSO) applied in parameter identification are performed. The simulation results demonstrate that the algorithm has the advantages of requiring few control variables, fast convergence speed, stable identified results, and excellent repeatability. Furthermore, the experimental results demonstrate that the output displacements calculated from the identified model are in great agreement with the measured values. Accordingly, the DE can identify the parameters of a displacement model for giant magnetostrictive actuators with satisfactory accuracy and reliability. Full article
(This article belongs to the Section Miniaturized and Micro Actuators)
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15 pages, 3609 KiB  
Essay
Adaptive Gait Generation for Hexapod Robots Based on Reinforcement Learning and Hierarchical Framework
by Zhiying Qiu, Wu Wei and Xiongding Liu
Actuators 2023, 12(2), 75; https://doi.org/10.3390/act12020075 - 9 Feb 2023
Cited by 4 | Viewed by 2830
Abstract
Gait plays a decisive role in the performance of hexapod robot walking; this paper focuses on adaptive gait generation with reinforcement learning for a hexapod robot. Moreover, the hexapod robot has a high-dimensional action space and therefore it is a great challenge to [...] Read more.
Gait plays a decisive role in the performance of hexapod robot walking; this paper focuses on adaptive gait generation with reinforcement learning for a hexapod robot. Moreover, the hexapod robot has a high-dimensional action space and therefore it is a great challenge to use reinforcement learning to directly train the robot’s joint angles. As a result, a hierarchical and modular framework and learning details are proposed in this paper, using only seven-dimensional vectors to denote the agent actions. In addition, we conduct experiments and deploy the proposed framework using a real hexapod robot. The experimental results show that superior reinforcement learning algorithms can converge in our framework, such as SAC, PPO, DDPG and TD3. Specifically, the gait policy trained in our framework can generate new adaptive hexapod gait on flat terrain, which is stable and has lower transportation cost than rhythmic gaits. Full article
(This article belongs to the Special Issue Applications of Intelligent Control in Actuators Systems)
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24 pages, 5031 KiB  
Review
Strain Characteristics of PLZT-Based Ceramics for Actuator Applications
by Apichart Limpichaipanit and Athipong Ngamjarurojana
Actuators 2023, 12(2), 74; https://doi.org/10.3390/act12020074 - 9 Feb 2023
Cited by 1 | Viewed by 2085
Abstract
Lead lanthanum zirconate titanate (PLZT) ceramics exhibit excellent dielectric, ferroelectric and piezoelectric properties, and they can be used in many applications, including actuators. In this review, the processing and properties of PLZT-based ceramics will be the main focus of the first part. An [...] Read more.
Lead lanthanum zirconate titanate (PLZT) ceramics exhibit excellent dielectric, ferroelectric and piezoelectric properties, and they can be used in many applications, including actuators. In this review, the processing and properties of PLZT-based ceramics will be the main focus of the first part. An introduction to PLZT ceramics is given and the methods to improve processing of PLZT-based ceramics are explained in terms of the addition of sintering aids, fabrication in the form of composites, and the application of dopants. The second part will be related to strain measurement to investigate converse piezoelectric properties (actuating effect). Strain measurement techniques by Michelson interferometry and case studies in PLZT-based ceramics (aging effect, temperature dependence and magnetic field effect) are included. Full article
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16 pages, 4127 KiB  
Article
Position Control of a Cost-Effective Bellow Pneumatic Actuator Using an LQR Approach
by Goran Gregov, Samuel Pincin, Antonio Šoljić and Ervin Kamenar
Actuators 2023, 12(2), 73; https://doi.org/10.3390/act12020073 - 9 Feb 2023
Cited by 3 | Viewed by 1884
Abstract
Today, we are witnessing an increasing trend in the number of soft pneumatic actuator solutions in industrial environments, especially due to their human-safe interaction capabilities. An interesting solution in this frame is a vacuum pneumatic muscle actuator (PMA) with a bellow structure, which [...] Read more.
Today, we are witnessing an increasing trend in the number of soft pneumatic actuator solutions in industrial environments, especially due to their human-safe interaction capabilities. An interesting solution in this frame is a vacuum pneumatic muscle actuator (PMA) with a bellow structure, which is characterized by a high contraction ratio and the ability to generate high forces considering its relatively small dimensions. Moreover, such a solution is generally very cost-effective since can be developed by using easily accessible, off-the-shelf components combined with additive manufacturing procedures. The presented research analyzes the precision positioning performances of a newly developed cost-effective bellow PMA in a closed-loop setting, by utilizing a Proportional-Integral-Derivative (PID) controller and a Linear Quadratic Regulator (LQR). In a first instance, the system identification was performed and a numerical model of the PMA was developed. It was experimentally shown that the actuator is characterized by nonlinear dynamical behavior. Based on the numerical model, a PID controller was developed as a benchmark. In the next phase, an LQR that involves a nonlinear pregain term was built. The point-to-point positioning experimental results showed that both controllers allow fast responses without overshoot within the whole working range. On the other hand, it was discovered that the LQR with the corresponding nonlinear pregain term allows an error of a few tens of micrometers to be achieved across the entire working range of the muscle. Additionally, two different experimental pneumatic solutions for indirect and direct vacuum control were analyzed with the aim of investigating the PMA response time and comparing their energy consumption. This research contributes to the future development of the pneumatically driven mechatronics systems used for precise position control. Full article
(This article belongs to the Special Issue 10th Anniversary of Actuators)
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14 pages, 3702 KiB  
Article
Origami-Inspired Soft Pneumatic Actuators: Generalization and Design Optimization
by Abdelrahman Zaghloul and Gary M. Bone
Actuators 2023, 12(2), 72; https://doi.org/10.3390/act12020072 - 9 Feb 2023
Cited by 10 | Viewed by 3266
Abstract
Soft actuators are essential to soft robots and can also be used with rigid-bodied robots. This paper is focused on methods for improving the applicability of origami-inspired soft pneumatic actuators (OSPA). Our method for rapidly fabricating OSPA is shown to be capable of [...] Read more.
Soft actuators are essential to soft robots and can also be used with rigid-bodied robots. This paper is focused on methods for improving the applicability of origami-inspired soft pneumatic actuators (OSPA). Our method for rapidly fabricating OSPA is shown to be capable of making a range of actuator sizes out of different materials. The largest OSPA has a force-to-weight ratio of 124, and can lift a 44 kg mass using a −85 kPa supply pressure. Experiments with a smaller OSPA demonstrate that it can perform 150,000 contraction/extension cycles while carrying a 2 kg mass with minimal degradation due to its materials and design. Compared to other OSPAs for which fatigue tests were reported, our accordion pattern OSPA has the best values of work-to-mass ratio, max. force, and fatigue life. A computationally efficient FEA-based constrained optimization method for maximizing an OSPA’s work output is then proposed. A 55% improvement in the work output was predicted, while validation experiments with OSPA prototypes showed a 53% improvement. While these improvement percentages are very similar, the values of the predicted stroke and work output are about 16% larger than the experimental values. The optimization requires only ~5 h to run on a common laptop. Full article
(This article belongs to the Special Issue Recent Advances in Pneumatic Soft Actuators)
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15 pages, 1717 KiB  
Article
Optimised Voltage Distribution on Piezoelectric Actuators for Modal Excitations Damping in Tapered Beams
by Andrea Rossi and Fabio Botta
Actuators 2023, 12(2), 71; https://doi.org/10.3390/act12020071 - 9 Feb 2023
Cited by 1 | Viewed by 1339
Abstract
Vibration mitigation is a prominent matter in several engineering fields. Several adverse phenomena are related to vibrations, such as fatigue, noise, etc. The availability of smart materials increases the solutions for both vibration damping and energy harvesting applications. Piezoelectric materials seem to be [...] Read more.
Vibration mitigation is a prominent matter in several engineering fields. Several adverse phenomena are related to vibrations, such as fatigue, noise, etc. The availability of smart materials increases the solutions for both vibration damping and energy harvesting applications. Piezoelectric materials seem to be the most promising for these applications. However, their positioning significantly affects their efficiency. Several studies were performed on the positioning of piezoelectric actuators to dampen a target resonance in cantilever beams with constant cross-sections. Here, an analytical model for the optimal voltage distribution on an array of piezoceramic (PZT) actuator pairs is proposed in the case of tapered beams. The effect of tapering on the optimal voltage distribution was investigated for several eigenmode excitations and tapering ratios. The model outcomes were corroborated via FEM simulations and a fair agreement was found for each considered case. Full article
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20 pages, 1604 KiB  
Article
A Novel State Estimation Approach for Suspension System with Time-Varying and Unknown Noise Covariance
by Qiangqiang Li, Zhiyong Chen and Wenku Shi
Actuators 2023, 12(2), 70; https://doi.org/10.3390/act12020070 - 8 Feb 2023
Cited by 1 | Viewed by 1691
Abstract
In this paper, a novel state estimation approach based on the variational Bayesian adaptive Kalman filter (VBAKF) and road classification is proposed for a suspension system with time-varying and unknown noise covariance. Using the VB approach, the time-varying noise covariance can be inferred [...] Read more.
In this paper, a novel state estimation approach based on the variational Bayesian adaptive Kalman filter (VBAKF) and road classification is proposed for a suspension system with time-varying and unknown noise covariance. Using the VB approach, the time-varying noise covariance can be inferred from the inverse-Wishart distribution and then optimized state estimation by the finite sampling posterior probability distribution function (PDF) of noise covariance and backward Kalman smoothing. In addition, a new road classification algorithm based on multi-objective optimization and the linear classifier is proposed to identify the unknown noise covariance. Simulation results for a suspension model with time-varying and unknown noise covariance show that the proposed approach has a higher performance in state estimation accuracy than other filters. Full article
(This article belongs to the Section Actuators for Land Transport)
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23 pages, 1739 KiB  
Article
An Obstacle-Avoidance Motion Planning Method for Redundant Space Robot via Reinforcement Learning
by Zeyuan Huang, Gang Chen, Yue Shen, Ruiquan Wang, Chuankai Liu and Long Zhang
Actuators 2023, 12(2), 69; https://doi.org/10.3390/act12020069 - 8 Feb 2023
Cited by 3 | Viewed by 2442
Abstract
On-orbit operation tasks require the space robot to work in an unstructured dynamic environment, where the end-effector’s trajectory and obstacle avoidance need to be guaranteed simultaneously. To ensure the completability and safety of the tasks, this paper proposes a new obstacle-avoidance motion planning [...] Read more.
On-orbit operation tasks require the space robot to work in an unstructured dynamic environment, where the end-effector’s trajectory and obstacle avoidance need to be guaranteed simultaneously. To ensure the completability and safety of the tasks, this paper proposes a new obstacle-avoidance motion planning method for redundant space robots via reinforcement learning (RL). First, the motion planning framework, which combines RL with the null-space motion for redundant space robots, is proposed according to the decomposition of joint motion. Second, the RL model for null-space obstacle avoidance is constructed, where the RL agent’s state and reward function are defined independent of the specific information of obstacles so that it can adapt to dynamic environmental changes. Finally, a curriculum learning-based training strategy for RL agents is designed to improve sample efficiency, training stability, and obstacle-avoidance performance. The simulation shows that the proposed method realizes reactive obstacle avoidance while maintaining the end-effector’s predetermined trajectory, as well as the adaptability to unstructured dynamic environments and robustness to the space robot’s dynamic parameters. Full article
(This article belongs to the Special Issue Advanced Spacecraft Structural Dynamics and Actuation Control)
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18 pages, 2000 KiB  
Article
Data-Driven Nonlinear Iterative Inversion Suspension Control
by Tao Wen, Xu Zhou, Xiaolong Li and Zhiqiang Long
Actuators 2023, 12(2), 68; https://doi.org/10.3390/act12020068 - 7 Feb 2023
Cited by 2 | Viewed by 1167
Abstract
The commercial operation of the maglev train has strict requirements for the reliability and safety of the suspension control system. However, due to a large number of unmodeled dynamics of the suspension system, it is difficult to obtain the precise mathematical model of [...] Read more.
The commercial operation of the maglev train has strict requirements for the reliability and safety of the suspension control system. However, due to a large number of unmodeled dynamics of the suspension system, it is difficult to obtain the precise mathematical model of the suspension system. After the suspension system has been operated for a long time with high load, the system model will change due to the wear, aging and failure of components, as well as the settlement of the line and track. The control performance is degraded. Therefore, this paper proposes a data-driven nonlinear iterative inversion suspension control algorithm, which can achieve high-precision tracking performance recovery control after control performance degradation without depending on the suspension system model. The control performance of the suspension system is improved by learning the measured data of the historical suspension system, and the fast convergence of the tracking error and high-precision stable suspension control are realized in the presence of unmodeled dynamics and external noise interference. Based on the historical suspension data of the maglev train suspension control system, the inverse dynamics model of the suspension system is identified by iterative inversion learning based on data drive, and the suspension control framework based on iterative inversion is designed. Then, the nonlinear input update strategy is used to realize the rapid convergence of the learning process. Finally, the simulation experiment of the maglev train suspension system and the physical experiment of the maglev system experimental platform are combined. It is verified that the proposed levitation control algorithm can achieve high-precision fast tracking performance recovery control after the system control performance degrades under noise environment. Full article
(This article belongs to the Section Actuators for Land Transport)
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20 pages, 6645 KiB  
Article
Attitude Control of Vehicle Based on Series Active Suspensions
by Weiwei Jia, Weizhou Zhang, Fangwu Ma and Liang Wu
Actuators 2023, 12(2), 67; https://doi.org/10.3390/act12020067 - 5 Feb 2023
Cited by 3 | Viewed by 2080
Abstract
When vehicles with traditional passive suspension systems are driving in complex terrain, large swing and vibrations of the car body make passengers and goods uncomfortable and unstable, even at very low-speed conditions. Considering the actual need for intelligent resource exploration in the sustainable [...] Read more.
When vehicles with traditional passive suspension systems are driving in complex terrain, large swing and vibrations of the car body make passengers and goods uncomfortable and unstable, even at very low-speed conditions. Considering the actual need for intelligent resource exploration in the sustainable economy, visual-based perception and localization systems of unmanned vehicles still cannot handle the sensor noise coursed by large body motions. In order to improve the stability and safety of vehicles in complex terrain, an attitude control system is proposed for mainly eliminating the external body motions of the vehicle by using series active suspensions. A model predictive control method considered the differences between the simulated and real vehicle, and the performance restrictions of actuators are used to design the attitude controller for reducing the heaving, pitching, and rolling motions of the vehicle. After simulations and real car tests, the results show that the proposed attitude controller can significantly improve the attitude stability of vehicles in harsh terrain. Full article
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15 pages, 4720 KiB  
Article
Effect of the Crystal Structure on the Piezoelectricity of [001]-Textured (Na, K)(Nb, Sb)O3-SrZrO3-(Bi, Ag)ZrO3 Lead-Free Piezoelectric Thick Film
by Su-Hwan Go, Dae-Su Kim, Yeon-Gyeong Chae, Seok-June Chae, Eun-Ji Kim, Hyeon-Min Yu, Bum-Joo Kim, Seok-Jung Park, Joun-Ho Lee and Sahn Nahm
Actuators 2023, 12(2), 66; https://doi.org/10.3390/act12020066 - 3 Feb 2023
Cited by 7 | Viewed by 1549
Abstract
An amount of 3.0 mol% NaNbO3 seeds was used to align the grains of 0.96(Na0.5K0.5)(Nb0.93Sb0.07)O3-(0.04−x)SrZrO3-x(Bi0.5Ag0.5)ZrO3 [NKNS-(0.04−x)SZ-xBAZ] thick films (0.0 ≤ x ≤ 0.04) along the [...] Read more.
An amount of 3.0 mol% NaNbO3 seeds was used to align the grains of 0.96(Na0.5K0.5)(Nb0.93Sb0.07)O3-(0.04−x)SrZrO3-x(Bi0.5Ag0.5)ZrO3 [NKNS-(0.04−x)SZ-xBAZ] thick films (0.0 ≤ x ≤ 0.04) along the [001] direction. All the textured thick films had large Lotgering factors (>95%). The textured NKNS-0.02SZ-0.02BAZ thick film has a rhombohedral-orthorhombic-tetragonal (R-O-T) structure with a large proportion of the R-O structure (>80%) and nanodomains (0.7 nm in width and 6 nm in length). This thick film exhibited a large d33 value (760 ± 20 pC/N), kp value (0.58) and strain (0.16% at 4.0 kV/mm), with good temperature stability and fatigue properties. The high piezoelectricity of this thick film can be attributed to its high degree of texturing, optimized domain configuration, and the presence of nanodomains. The piezoelectric ceramic with a large d15/d33 value showed a large d33 value after [001] texturing because of the easy rotation of the spontaneous polarizations. Hence, the d15/d33 value can be used to select piezoelectric ceramics with large d33 values after [001] texturing. Full article
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20 pages, 5758 KiB  
Article
Improved Craig–Bampton Method Implemented into Durability Analysis of Flexible Multibody Systems
by Gengxiang Wang, Zepeng Niu and Ying Feng
Actuators 2023, 12(2), 65; https://doi.org/10.3390/act12020065 - 2 Feb 2023
Viewed by 2567
Abstract
The Craig–Bampton method is frequently applied in most commercial multibody dynamic software. Nevertheless, the Craig–Bampton modes only represent the free-free modes in flexible multibody systems. However, the free-free modes are incapable of all engineering applications. Hence, a rational set of reference conditions must [...] Read more.
The Craig–Bampton method is frequently applied in most commercial multibody dynamic software. Nevertheless, the Craig–Bampton modes only represent the free-free modes in flexible multibody systems. However, the free-free modes are incapable of all engineering applications. Hence, a rational set of reference conditions must be correctly chosen to define a unique displacement field. Firstly, a simple 2D beam with two revolute joints is taken as an example to prove that the free-free modes are not suitable for all engineering applications, and the results are validated by ANSYS and the analytical solution. Secondly, the Craig–Bampton method is improved by two different methods: (i) the reference conditions are added to the original Craig–Bampton matrix and (ii) the reference conditions are applied to the shape functions to redefine the mass and stiffness matrices before constructing the original Craig–Bampton matrix. This implementation illustrates that the improved Craig–Bampton matrix can not only generate the free-free modes but is also suitable for the non-free-free modes. Finally, two discrepant reference conditions are imposed to obtain the dynamic response of the flexible connecting rod based on the improved Craig–Bampton method, which is validated using the normal mode approach. Simulations show that the improved Craig–Bampton method can be used as a general-purpose method in durability analysis. Full article
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15 pages, 10358 KiB  
Article
Fractional Derivative Viscosity of ANCF Cable Element
by Yaqi Gu, Zuqing Yu, Peng Lan and Nianli Lu
Actuators 2023, 12(2), 64; https://doi.org/10.3390/act12020064 - 2 Feb 2023
Cited by 2 | Viewed by 1613
Abstract
Typical engineering cable structures, such as high-voltage wire and wire rope, usually bring a damping effect which cannot be ignored due to the technological problems of manufacturing. For such problems, especially the damping of cable structures undergoing large displacement and severe deformation, few [...] Read more.
Typical engineering cable structures, such as high-voltage wire and wire rope, usually bring a damping effect which cannot be ignored due to the technological problems of manufacturing. For such problems, especially the damping of cable structures undergoing large displacement and severe deformation, few studies have been reported in the past. In this work, the fractional derivative viscosity model is introduced into the cables described by the absolute nodal coordinate formulation. The computer implementation algorithm of the proposed cable damping model is given based on the three-parameter fractional derivative model. Two numerical examples demonstrate the effectiveness and convergence property of the proposed cable damping model. An experiment is proposed in which a wire is tensioned and released. Configurations are captured by the high-speed camera and compared with the results obtained from the numerical simulation. The agreement of the simulation and experimental results validates the proposed cable damping in application. Full article
(This article belongs to the Special Issue Advanced Spacecraft Structural Dynamics and Actuation Control)
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22 pages, 3021 KiB  
Review
Gelatin Soft Actuators: Benefits and Opportunities
by Sandra Edward and Holly M. Golecki
Actuators 2023, 12(2), 63; https://doi.org/10.3390/act12020063 - 31 Jan 2023
Cited by 2 | Viewed by 2804
Abstract
Soft robots are being developed as implantable devices and surgical tools with increasing frequency. As this happens, new attention needs to be directed at the materials used to engineer these devices that interface with biological tissues. Biocompatibility will increase if traditional materials are [...] Read more.
Soft robots are being developed as implantable devices and surgical tools with increasing frequency. As this happens, new attention needs to be directed at the materials used to engineer these devices that interface with biological tissues. Biocompatibility will increase if traditional materials are replaced with biopolymers or proteins. Gelatin-based actuators are biocompatible, biodegradable, versatile, and tunable, making them ideal for biomedical and biomechanical applications. While building devices from protein-based materials will improve biocompatibility, these new materials also bring unique challenges. The properties of gelatin can be tuned with the addition of several additives, crosslinkers, and plasticizers to improve mechanical properties while altering the characteristic fluid absorption and cell proliferation. Here, we discuss a variety of different gelatin actuators that allow for a range of actuation motions including swelling, bending, folding, and twisting, with various actuation stimulants such as solvent, temperature, pneumatic pressure, electric field, magnetic field, or light. In this review, we examine the fabrication methods and applications of such materials for building soft robots. We also highlight some ways to further extend the use of gelatin for biomedical actuators including using fiber-reinforced gelatin, gelatin cellular solids, and gelatin coatings. The understanding of the current state-of-the-art of gelatin actuators and the methods to expand their usage may expand the scope and opportunities for implantable devices using soft hydrogel robotics. Full article
(This article belongs to the Special Issue 10th Anniversary of Actuators)
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