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Actuators, Volume 11, Issue 5 (May 2022) – 26 articles

Cover Story (view full-size image): Axial flow turbines operate over a wide range of Reynolds numbers. However, at low Reynolds numbers below 1 × 105, the aerodynamic characteristics deteriorate greatly. In this study, an experiment to reduce the passage vortex was conducted using a dielectric barrier discharge plasma actuator. The plasma actuator was installed on the endwall of a linear turbine cascade. From the velocity distribution measured using particle image velocimetry, the secondary flow vector, turbulence intensity, and vorticity were analyzed. It was found that the optimum location of the plasma actuator was immediately before the blade leading edge. This is because the inlet boundary layer can be accelerated near the blade leading edge, weakening the horseshoe vortex which initially causes the passage vortex. View this paper
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Article
Body Calibration: Automatic Inter-Task Mapping between Multi-Legged Robots with Different Embodiments in Transfer Reinforcement Learning
Actuators 2022, 11(5), 140; https://doi.org/10.3390/act11050140 - 21 May 2022
Viewed by 636
Abstract
Machine learning algorithms are effective in realizing the programming of robots that behave autonomously for various tasks. For example, reinforcement learning (RL) does not require supervision or data sets; the RL agent explores solutions by itself. However, RL requires a long learning time, [...] Read more.
Machine learning algorithms are effective in realizing the programming of robots that behave autonomously for various tasks. For example, reinforcement learning (RL) does not require supervision or data sets; the RL agent explores solutions by itself. However, RL requires a long learning time, particularly for actual robot learning situations. Transfer learning (TL) in RL has been proposed to address this limitation. TL realizes fast adaptation and decreases the problem-solving time by utilizing the knowledge of the policy, value function, and Q-function from RL. Taylor proposed TL using inter-task mapping that defines the correspondence between the state and action between the source and target domains. Inter-task mapping is defined based on human intuition and experience; therefore, the effect of TL may not be obtained. The difference in robot shapes for TL is similar to the cognition in the modification of human body composition, and automatic inter-task mapping can be performed by referring to the body representation that is assumed to be stored in the human brain. In this paper, body calibration is proposed, which refers to the physical expression in the human brain. It realizes automatic inter-task mapping by acquiring data modeled on a body diagram that illustrates human body composition and posture. The proposed method is evaluated in a TL situation from a computer simulation of RL to actual robot control with a multi-legged robot. Full article
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Communication
A Finite-Time Trajectory-Tracking Method for State-Constrained Flexible Manipulators Based on Improved Back-Stepping Control
Actuators 2022, 11(5), 139; https://doi.org/10.3390/act11050139 - 19 May 2022
Viewed by 476
Abstract
In order to solve the trajectory-tracking-control problem of the state-constrained flexible manipulator systems, a finite-time back-stepping control method based on command filtering is presented in this paper. Considering that the virtual signal requires integration in each step, which will lead to high computational [...] Read more.
In order to solve the trajectory-tracking-control problem of the state-constrained flexible manipulator systems, a finite-time back-stepping control method based on command filtering is presented in this paper. Considering that the virtual signal requires integration in each step, which will lead to high computational complexity in the traditional back-stepping, the finite-time command filter is used to filter the virtual signal and to obtain the intermediate signal in finite time, to thus reduce the computational complexity. The compensation mechanism is used to eliminate the error generated by the command filter. Furthermore, the adaptive estimation method is introduced to approach the uncertainty of the state-constrained flexible manipulator system. Then, the Lyapunov function is used to prove that the tracking error of the system can be stabilized in a sufficiently small origin neighborhood within a finite time. The simulation of a single rod flexible manipulator system demonstrates the effect of the proposed approach. Full article
(This article belongs to the Special Issue Dynamics and Control of Robot Manipulators)
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Article
Flexible Control Strategy for Upper-Limb Rehabilitation Exoskeleton Based on Virtual Spring Damper Hypothesis
Actuators 2022, 11(5), 138; https://doi.org/10.3390/act11050138 - 19 May 2022
Viewed by 506
Abstract
The focus of this work is to design a control strategy with the dynamic characteristics of spring damping to realize the virtual flexibility and softness of a rigid-joint exoskeleton without installing real, physical elastic devices. The basic idea of a “virtual softening control [...] Read more.
The focus of this work is to design a control strategy with the dynamic characteristics of spring damping to realize the virtual flexibility and softness of a rigid-joint exoskeleton without installing real, physical elastic devices. The basic idea of a “virtual softening control strategy” for a single rigid joint is that a virtual spring damper (VSD) is installed between the motor and the output shaft. By designing the control signal of the motor, the torque output of the joint actuator is softened so that the output has the characteristics of elasticity and variable stiffness. The transfer velocity profile of human limbs reaching from one posture to another always presents as bell-shaped. According to this characteristic, we constructed a trajectory planning method for a point-to-point position-tracking controller based on a normal distribution function, and it was successfully applied to the control of 5-DoF upper-limb rehabilitation exoskeleton. A multi-joint cooperative flexible controller based on the virtual spring damper hypothesis (VSDH) was successfully applied to solve the constrained control problem of the exoskeletons and the self-motion problem caused by redundant degrees of freedom (DoFs). The stability of the closed-loop controlled system is theoretically proven by use of the scalar energy function gradient method and the Riemann metric convergence analysis method. Full article
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Article
Dynamic Performance Analysis and Design of Vortex Array Grippers
Actuators 2022, 11(5), 137; https://doi.org/10.3390/act11050137 - 17 May 2022
Viewed by 475
Abstract
In this study, the performance of a vortex array gripper was numerically investigated based on the pressure distribution on the surface of a gripped object and the resulting suction force. An analysis of the suction force generated by a single-vortex gripper was performed [...] Read more.
In this study, the performance of a vortex array gripper was numerically investigated based on the pressure distribution on the surface of a gripped object and the resulting suction force. An analysis of the suction force generated by a single-vortex gripper was performed to determine the geometric parameters for providing a good suction force and subsequently, for the vortex array gripper configuration. Array grippers consisting of two- and four-vortex grippers were studied. For dual-vortex grippers, the generated suction forces of various inlet air configurations with different vortex gripper distances are illustrated. The pros and cons of all types of air supply and the influence of positive pressure formed by outlet airflow interaction were examined. The analysis of quad-vortex grippers also revealed that the suction force could be increased by reducing the outlet flow interaction between the grippers using the placement of exhaust vents. Thus, the installation of array grippers can be arranged in a more compact form to increase the total suction force per unit operation area with uniformity. Full article
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Article
Development of a Parallel Dual-Stage Compliant Nanopositioning System
Actuators 2022, 11(5), 136; https://doi.org/10.3390/act11050136 - 13 May 2022
Viewed by 617
Abstract
This paper presents a novel parallel dual-stage compliant nanopositioning system (PDCNS), aimed at nanoscale positioning for microscale manipulation. In the developed PDCNS, the coarse stage actuated by the voice coil motor and the fine stage driven by the piezoelectric actuator are integrated in [...] Read more.
This paper presents a novel parallel dual-stage compliant nanopositioning system (PDCNS), aimed at nanoscale positioning for microscale manipulation. In the developed PDCNS, the coarse stage actuated by the voice coil motor and the fine stage driven by the piezoelectric actuator are integrated in a parallel manner by a specially devised A-shaped compliant mechanism, which leads to many excellent performances, such as good resolution and large stroke and broadband. To enhance the closed-loop-positioning capability of the proposed PDCNS, a double-servo cooperative control (DSCC) strategy is specially constructed. The performance of the proposed PDCNS is evaluated by analytical model, finite element analysis, and experimental research. Results show that the first-order resonance frequency of the designed A-shaped compliant mechanism can reach 99.7 Hz. Combined with the designed DSCC, the developed PDCNS prototype is demonstrated to provide a stroke of 1.49 mm and a positioning resolution of ≤50 nm. Full article
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Article
Single Actuator with Versatile Controllability of 2-DOF Assistance for Exosuits via a Novel Moving-Gear Mechanism
Actuators 2022, 11(5), 135; https://doi.org/10.3390/act11050135 - 13 May 2022
Viewed by 628
Abstract
Decreasing the system weight while maintaining the assistance performance can help reduce the metabolic penalty in exosuits. Various researchers have proposed a bi-directional cable-driven actuator that can provide two degrees of freedom (2-DOF) assistance by using a single motor. However, such systems face [...] Read more.
Decreasing the system weight while maintaining the assistance performance can help reduce the metabolic penalty in exosuits. Various researchers have proposed a bi-directional cable-driven actuator that can provide two degrees of freedom (2-DOF) assistance by using a single motor. However, such systems face limitations associated with the controllability of the assistance force. This study proposes a novel cable-driven system, that is, a dual pulley drive, that can provide versatile controllability of 2-DOF cable actuation by using a single motor via a novel moving gear mechanism. The moving gear winds the cable by switching both the side pulleys, which are then used for 2-DOF cable actuation. The spiral springs embedded between the pulley and base shaft work to release the cable. Results of experiments demonstrate that the dual pulley drive provides a versatile range of motion. The proposed system can provide 34.1% of overlapping motion per cable round trip time and support the non-overlapping motion. The preliminary integration of the dual pulley drive to the exosuit confirms that the novel exosuit is considerably lighter than the state-of-the-art exosuit. The calculations indicate that the operating cable speed and force generated using the proposed design are higher than the existing exosuit. Full article
(This article belongs to the Special Issue Actuation Solutions for Wearable Robots)
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Article
Enhancing Dynamic Bandwidth of Amplified Piezoelectric Actuators by a Hybrid Lever and Bridge-Type Compliant Mechanism
Actuators 2022, 11(5), 134; https://doi.org/10.3390/act11050134 - 12 May 2022
Viewed by 580
Abstract
Ongoing interests in high-speed precision actuation continuously sparks great attention on developing fast amplified piezoelectric actuators (APAs) with compliant mechanisms. A new type of APA with enhanced resonance frequency is herein reported based on a hybrid compliant amplifying mechanism. A two-stage displacement flexure [...] Read more.
Ongoing interests in high-speed precision actuation continuously sparks great attention on developing fast amplified piezoelectric actuators (APAs) with compliant mechanisms. A new type of APA with enhanced resonance frequency is herein reported based on a hybrid compliant amplifying mechanism. A two-stage displacement flexure amplifier is proposed by synthesizing the lever-type and semi bridge-type compliant mechanisms in a compact configuration, promising to a well tradeoff between the displacement amplification ratio and dynamic bandwidth. The static and dynamic performances are experimentally evaluated. The resonance frequency of 2.1 kHz, displacement amplification ratio of 6, and step response time of around 0.4 ms are realized with a compact size of 50 mm × 44 mm × 7 mm. Another contribution of this paper is to develop a comprehensive two-port dynamic stiffness model to predict the static and dynamic behaviors of the compliant amplifier. The modeling approach presented here differs from previous studies in that it enables the traditional transfer matrix method to formulate both the kinetostatics and dynamics of compliant mechanisms including serial-parallel branches and rigid bodies. Full article
(This article belongs to the Special Issue Design and Control of Compliant Manipulators: Volume II)
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Article
Influences of Parameter Deviation on the Vibration Isolation System of an End Effector
Actuators 2022, 11(5), 133; https://doi.org/10.3390/act11050133 - 09 May 2022
Viewed by 630
Abstract
The vibration problem influences the precision of the equipment. However, some vibration isolation systems (VISs) with the perfect theoretical and simulation results are still unable to suppress the vibration well, resulting in the damage during the operation, such as the phenomenon of fragments [...] Read more.
The vibration problem influences the precision of the equipment. However, some vibration isolation systems (VISs) with the perfect theoretical and simulation results are still unable to suppress the vibration well, resulting in the damage during the operation, such as the phenomenon of fragments for the end effector of a glass substrate handling robot. Therefore, this paper focuses on the glass substrate handling robot in actual production and simplifies the VIS into a 2D (2 degree) system. From the analysis of the deviation of material parameters and installation deviations between vibration isolators, this paper concludes that, as long as there is a deviation, the vibration isolation performance of the system will be reduced. Through the mutually verified theory, simulation, and experimental structure, this paper also presents that the resonance frequency increase factor of the vibration isolation system is approximately the deviation. As for the end effector, the distance of the two vibration isolations is 579.4 mm. The change of the load does not change the isolation frequency of the same system, but the resonance amplitude will increase. The results of this study can supervise the installation and selection of vibration isolators in VISs. At the same time, the reasons for the weak vibration isolation performance of some systems are explained. Full article
(This article belongs to the Special Issue Piezoelectric Ultrasonic Actuators and Motors)
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Article
Pressure Fluctuation Characteristics Analysis of Centrifugal Pump as Turbine in Its Start-Up Process
Actuators 2022, 11(5), 132; https://doi.org/10.3390/act11050132 - 07 May 2022
Viewed by 549
Abstract
In order to study pressure fluctuation characteristics of a centrifugal pump as turbine (PAT) in its start-up process, Fluent was used to do numerical simulation of the PAT start-up process. Time and frequency domain analyses were performed on the data acquired at different [...] Read more.
In order to study pressure fluctuation characteristics of a centrifugal pump as turbine (PAT) in its start-up process, Fluent was used to do numerical simulation of the PAT start-up process. Time and frequency domain analyses were performed on the data acquired at different positions and different heads. The results show that a large number of low-pressure areas and strong vortexes are formed within the impeller at the initial time of start-up. With the increase in rotating speed, the vortexes rapidly decrease and are concentrated on the blade non-working face. The pressure fluctuation amplitude is the maximum at the start-up initial instant; with increase in rotating speed, it reduces rapidly at the volute spiral part. The pressure fluctuation number within one impeller rotation cycle is consistent with blade number, and the dominant frequency of pressure fluctuation is 6 times the impeller rotational frequency. The dominant frequency amplitude of radial pressure fluctuation increases with decrease in radial size in the volute. The pressure fluctuation in the impeller is much more intensive than that in the volute, and its maximum dominant frequency amplitude occurs in the middle of the impeller towards the inner edge. With the increase in head, the number of pressure fluctuation and the amplitude of dominant frequency increase at the same time during the start-up process. Full article
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Article
Structural Design and Experiments of a Dynamically Balanced Inverted Four-Bar Linkage as Manipulator Arm for High Acceleration Applications
Actuators 2022, 11(5), 131; https://doi.org/10.3390/act11050131 - 05 May 2022
Viewed by 644
Abstract
Industrial robotic manipulators in pick-and-place applications require short settling times to achieve high productivity. The fluctuating reaction forces and moments on the base of a dynamically unbalanced manipulator, however, cause base vibrations, leading to increased settling times. These base vibrations can be eliminated [...] Read more.
Industrial robotic manipulators in pick-and-place applications require short settling times to achieve high productivity. The fluctuating reaction forces and moments on the base of a dynamically unbalanced manipulator, however, cause base vibrations, leading to increased settling times. These base vibrations can be eliminated with dynamic balancing, which is achieved, in general, with the addition of counter-masses and counter-inertias. Adding these elements, however, comes at the cost of increased moving mass and inertia, resulting in lower natural frequencies and again higher settling times. For a minimal settling time it is therefore essential that a balanced mechanism has high natural frequencies with an optimal mass distribution. A dynamically balanced inverted four-bar linkage architecture is therefore favoured over architectures which depend on counter-masses and counter-rotating flywheels. The goal of this paper is to present and experimentally verify a structural design of a manipulator arm with high natural frequencies that is based on a dynamically balanced inverted four-bar linkage. The dynamical properties and the robustness to manufacturing tolerances are both verified with simulations and experiments. Experiments for 5.2 G tip accelerations show, when fully balanced, a reduction of 99.3% in reaction forces and 97.8% in reaction moments as compared to the unbalanced mechanism. The manipulator reached 21 G tip accelerations and a first natural frequency of 212 Hz was measured, which is significantly high and more than adequate for implementation in high acceleration applications. Full article
(This article belongs to the Special Issue Dynamics and Control of Robot Manipulators)
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Article
A Novel Resolution Scheme of Time-Energy Optimal Trajectory for Precise Acceleration Controlled Industrial Robot Using Neural Networks
Actuators 2022, 11(5), 130; https://doi.org/10.3390/act11050130 - 03 May 2022
Viewed by 658
Abstract
The surging popularity of adopting industrial robots in smart manufacturing has led to an increasing trend in the simultaneous improvement of the energy costs and operational efficiency of motion trajectory. Motivated by this, multi-objective trajectory planning subject to kinematic and dynamic constraints at [...] Read more.
The surging popularity of adopting industrial robots in smart manufacturing has led to an increasing trend in the simultaneous improvement of the energy costs and operational efficiency of motion trajectory. Motivated by this, multi-objective trajectory planning subject to kinematic and dynamic constraints at multiple levels has been considered as a promising paradigm to achieve the improvement. However, most existing model-based multi-objective optimization algorithms tend to come out with infeasible solutions, which results in non-zero initial and final acceleration. Popular commercial software toolkits applied to solve multi-objective optimization problems in actual situations are mostly based on the fussy conversion of the original objective and constraints into strict convex functions or linear functions, which could induce a failure of duality and obtain results exceeding limits. To address the problem, this paper proposes a time-energy optimization model in a phase plane based on the Riemann approximation method and a solution scheme using an iterative learning algorithm with neural networks. We present forward-substitution interpolation functions as basic functions to calculate indirect kinematic and dynamic expressions introduced in a discrete optimization model with coupled constraints. Moreover, we develop a solution scheme of the complex trajectory optimization problem based on artificial neural networks to generate candidate solutions for each iteration without any conversion into a strict convex function, until minimum optimization objectives are achieved. Experiments were carried out to verify the effectiveness of the proposed optimization solution scheme by comparing it with state-of-the-art trajectory optimization methods using Yalmip software. The proposed method was observed to improve the acceleration control performance of the solved robot trajectory by reducing accelerations exceeding values of joints 2, 3 and 5 by 3.277 rad/s2, 26.674 rad/s2, and 7.620 rad/s2, respectively. Full article
(This article belongs to the Special Issue Design and Control of High-Precision Motion Systems)
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Article
Effects of the Installation Location of a Dielectric Barrier Discharge Plasma Actuator on the Active Passage Vortex Control of a Turbine Cascade at Low Reynolds Numbers
Actuators 2022, 11(5), 129; https://doi.org/10.3390/act11050129 - 02 May 2022
Viewed by 805
Abstract
Because axial flow turbines are widely used as the main components of jet engines and industrial gas turbines, their energy reduction effect is significant, even with a slight performance improvement. These turbines operate over a wide range of Reynolds numbers. However, at low [...] Read more.
Because axial flow turbines are widely used as the main components of jet engines and industrial gas turbines, their energy reduction effect is significant, even with a slight performance improvement. These turbines operate over a wide range of Reynolds numbers. However, at low Reynolds numbers below 1 × 105, the aerodynamic characteristics deteriorate greatly, due to the flow separation of the boundary layer on the blade suction surface and an increase in the secondary flow. In this study, an experiment to reduce the passage vortex was conducted using a dielectric barrier discharge plasma actuator, which is expected to operate with a new innovative active flow control technology. The plasma actuator was installed on the endwall of a linear turbine cascade in the test section of a wind tunnel. From the velocity distribution measured using particle image velocimetry, the secondary flow vector, turbulence intensity, and vorticity were analyzed. The input voltage and frequency of the plasma actuator were fixed at 12 kVp-p and 10 kHz, respectively. In particular, the optimum installation location of the plasma actuator was examined from upstream to mid-passage positions of the turbine cascade (normalized axial location of Z/Cax = −0.35 to 0.51). In addition, the effect of the Reynolds number was examined by varying it between Reout = 1.8 × 104 and 3.7 × 104. From the experimental results, it was found that the optimum location of the plasma actuator was immediately before the blade leading edge (Z/Cax = −0.20 to −0.06). This is because the inlet boundary layer can be accelerated near the blade leading edge, weakening the horseshoe vortex which initially causes the passage vortex. At a higher Reynolds number, the passage vortex suppression effect of the plasma actuator is weakened, because the flow induced by the plasma actuators becomes relatively weaker as the mainstream velocity increases with an increase in the Reynolds number. Full article
(This article belongs to the Special Issue Dielectric Barrier Discharge Plasma Actuator for Active Flow Control)
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Article
Disturbance Observer-Based Tracking Controller for Uncertain Marine Surface Vessel
Actuators 2022, 11(5), 128; https://doi.org/10.3390/act11050128 - 02 May 2022
Viewed by 695
Abstract
In this study, a novel control framework is proposed to improve the tracking performance of uncertain marine vessels which work in enhanced sea states. The proposed control strategy is based on incorporating a fixed-time nonlinear disturbance observer (FTNDO) in a fixed-time convergent backstepping [...] Read more.
In this study, a novel control framework is proposed to improve the tracking performance of uncertain marine vessels which work in enhanced sea states. The proposed control strategy is based on incorporating a fixed-time nonlinear disturbance observer (FTNDO) in a fixed-time convergent backstepping control. More specifically, the FTNDO is developed to reconstruct the total uncertainties due to the system uncertainty and unknown time-varying exterior disturbances. In comparison with the existing disturbance observers, the FTNDO guarantees that the estimation errors will converge to the origin within a predefined time even if the initial estimation errors tend toward infinity. This feature is quite important in the closed-loop system stability analysis as the separation principle does not hold in nonlinear systems. Besides, it does not require the restricting assumption that the upper bound of the lumped uncertainty or its time derivative has to be bounded or known. A backstepping control with a compensation control part is then designed to make the tracking errors converge to the origin within a finite time regardless of initial tracking errors. The compensation control is developed by means of the estimated signal and applied to totally reject the total uncertainty. The global fixed-time stabilization of the closed-loop system is investigated through the Lyapunov stability criterion. Numerical simulation results conducted on an uncertain marine surface vessel confirm the superior control performance and efficiency of the planned method in comparison with the existing disturbance observer-based tracking control strategies. Full article
(This article belongs to the Special Issue Finite-Time/Fixed-Time Control for Mechanical Systems)
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Article
Smooth-Switching Gain Based Adaptive Neural Network Control of n-Joint Manipulator with Multiple Constraints
Actuators 2022, 11(5), 127; https://doi.org/10.3390/act11050127 - 29 Apr 2022
Viewed by 639
Abstract
Modeling errors, external loads and output constraints will affect the tracking control of the n-joint manipulator driven by the permanent magnet synchronous motor. To solve the above problems, the smooth-switching for backstepping gain control strategy based on the Barrier Lyapunov Function and adaptive [...] Read more.
Modeling errors, external loads and output constraints will affect the tracking control of the n-joint manipulator driven by the permanent magnet synchronous motor. To solve the above problems, the smooth-switching for backstepping gain control strategy based on the Barrier Lyapunov Function and adaptive neural network (BLF-ANBG) is proposed. First, the adaptive neural network method is established to approximate modeling errors, unknown loads and unenforced inputs. Then, the gain functions based on the error and error rate of change are designed, respectively. The two gain functions can respectively provide faster response speed and better tracking stability. The smooth-switching for backstepping gain strategy based on the Barrier Lyapunov Function is proposed to combine the advantages of both gain functions. According to the above strategy, the BLF-ANBG strategy is proposed, which not only solves the influence of multiple constraints, unknown loads and modeling errors, but also enables the manipulator system to have better dynamic and steady-state performances at the same time. Finally, the proposed controller is applied to a 2-DOF manipulator and compared with other commonly used methods. The simulation results show that the BLF-ANBG strategy has good tracking performance under multiple constraints and model errors. Full article
(This article belongs to the Special Issue Dynamics and Control of Robot Manipulators)
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Article
Model-Independent Observer-Based Current Sensorless Speed Servo Systems with Adaptive Feedback Gain
Actuators 2022, 11(5), 126; https://doi.org/10.3390/act11050126 - 29 Apr 2022
Viewed by 612
Abstract
This study proposes a solution to the speed control problem of servo machines in the form of multi-loop current sensorless control with a reduction in the system model dependence level and the number of feedback loops, which provides the two contributions: first, a [...] Read more.
This study proposes a solution to the speed control problem of servo machines in the form of multi-loop current sensorless control with a reduction in the system model dependence level and the number of feedback loops, which provides the two contributions: first, a model-independent observer estimates speed and acceleration using only the position measurement, thereby ensuring the first-order estimation error dynamics; second, the active damping acceleration stabilizes the inner loop with the adaptive feedback gain increasing and decreasing automatically according to the transient and steady-state operation modes. The experimental study highlighted the effectiveness of the acceleration loop adaptation technique, which used an actual servo system comprising the QUBE-servo2 and myRIO-1900. Full article
(This article belongs to the Special Issue Robotics and Control: State of the Art)
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Article
Development and Analysis of Key Components of a Multi Motion Mode Soft-Bodied Pipe Robot
Actuators 2022, 11(5), 125; https://doi.org/10.3390/act11050125 - 29 Apr 2022
Viewed by 715
Abstract
In order to enhance the environmental adaptability of peristaltic soft-bodied pipe robots, based on the nonlinear and hyperelastic characteristics of silicone rubber combined with the biological structure and motion characteristics of worms, a hexagonal prism soft-bodied bionic actuator is proposed. The actuator adopts [...] Read more.
In order to enhance the environmental adaptability of peristaltic soft-bodied pipe robots, based on the nonlinear and hyperelastic characteristics of silicone rubber combined with the biological structure and motion characteristics of worms, a hexagonal prism soft-bodied bionic actuator is proposed. The actuator adopts different inflation patterns to produce different deformations, so that the soft-bodied robot can realize different motion modes in the pipeline. Based on the Yeoh binomial parameter silicone rubber constitutive model, the deformation analysis model of the hexagonal prism soft-bodied bionic actuator is established, and the numerical simulation algorithm is used to ensure both that the drive structure and deformation mode are reasonable, and that the deformation analysis theoretical model is accurate. The motion and dynamic characteristics of the prepared hexagonal prism soft-bodied bionic actuator are tested and analyzed, the motion and dynamic characteristic curves of the actuator are obtained, and the empirical deformation formula of the actuator is fitted. The experimental results are consistent with the deformation analysis model and numerical simulation result, which shows that the deformation analysis model and numerical simulation method are accurate and can provide design methods and reference basis for the development of a pneumatic soft-bodied body bionic actuator. The above research results can also prove that the hexagonal prism soft-bodied bionic actuator is reasonable and feasible. Full article
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Article
Deployable Tubular Mechanisms Integrated with Magnetic Anchoring and Guidance System
Actuators 2022, 11(5), 124; https://doi.org/10.3390/act11050124 - 28 Apr 2022
Viewed by 716
Abstract
Deployable mechanism has received more attention in the medical field due to its simple structure, dexterity, and flexibility. Meanwhile, the advantages of the Magnetic Anchoring and Guidance System (MAGS) are further highlighted by the fact that the operators can remotely control the corresponding [...] Read more.
Deployable mechanism has received more attention in the medical field due to its simple structure, dexterity, and flexibility. Meanwhile, the advantages of the Magnetic Anchoring and Guidance System (MAGS) are further highlighted by the fact that the operators can remotely control the corresponding active and passive magnetic parts in vivo. Additionally, MAGS allows the untethered manipulation of intracorporeal devices. However, the conventional instruments in MAGS are normally rigid, compact, and less flexible. Therefore, to solve this problem, four novel deployable tubular mechanisms, Design 1 (Omega-shape mechanism), Design 2 (Fulcrum-shape mechanism), Design 3 (Archway-shape mechanism), and Design 4 (Scissor-shape mechanism) in this paper, are proposed integrated with MAGS to realize the laser steering capability. Firstly, this paper introduces the motion mechanism of the four designs and analyzes the motion characterization of each structure through simulation studies. Further, the prototypes of four designs are fabricated using tubular structures with embedded magnets. The actuation success rate, the workspace characterization, the force generation and the load capability of four mechanisms are tested and analyzed based on experiments. Then, the demonstration of direct laser steering via macro setup shows that the four mechanisms can realize the laser steering capability within the error of 0.6 cm. Finally, the feasibility of indirect laser steering via a macro-mini setup is proven. Therefore, such exploration demonstrates that the application of the deployable tubular mechanisms integrated with MAGS towards in vivo treatment is promising. Full article
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Article
Speed Control of a Multi-Motor System Based on Fuzzy Neural Model Reference Method
Actuators 2022, 11(5), 123; https://doi.org/10.3390/act11050123 - 28 Apr 2022
Viewed by 649
Abstract
The direct-current (DC) motor has been widely utilized in many industrial applications, such as a multi-motor system, due to its excellent speed control features regardless of its greater maintenance costs. A synchronous regulator is utilized to verify the response of the speed control. [...] Read more.
The direct-current (DC) motor has been widely utilized in many industrial applications, such as a multi-motor system, due to its excellent speed control features regardless of its greater maintenance costs. A synchronous regulator is utilized to verify the response of the speed control. The motor speed can be improved utilizing artificial intelligence techniques, for example fuzzy neural networks (FNNs). These networks can be learned and predicted, and they are useful when dealing with nonlinear systems or when severe turbulence occurs. This work aims to design an FNN based on a model reference controller for separately excited DC motor drive systems, which will be applied in a multi-machine system with two DC motors. The MATLAB/Simulink software package has been used to implement the FNMR and investigate the performance of the multi-DC motor. moreover, the online training based on the backpropagation algorithm has been utilized. The obtained results were good for improving the speed response, synchronizing the motors, and applying load during the work of the motors compared to the traditional PI control method. Finally, the multi-motor system that was controlled by the proposed method has been improved where its speed was not affected by the disturbance. Full article
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Article
Modeling and Control of Hysteresis Characteristics of Piezoelectric Micro-Positioning Platform Based on Duhem Model
Actuators 2022, 11(5), 122; https://doi.org/10.3390/act11050122 - 27 Apr 2022
Viewed by 657
Abstract
The hysteresis characteristic of piezoelectric micro-positioning platforms seriously affects its positioning accuracy in precision positioning. It is important to design an effective hysteresis model and control scheme. Based on the analysis of the Duhem model, this paper proposes to divide the hysteresis curve [...] Read more.
The hysteresis characteristic of piezoelectric micro-positioning platforms seriously affects its positioning accuracy in precision positioning. It is important to design an effective hysteresis model and control scheme. Based on the analysis of the Duhem model, this paper proposes to divide the hysteresis curve into two parts, the step-up section and the step-down section, to identify the model parameters, respectively, and a hybrid intelligent optimization algorithm based on the artificial fish swarm algorithm and the bat algorithm is proposed. The simulation experiment verified that the error of the improved model was reduced by 48.97%, which greatly improved the identification accuracy of the Duhem model. Finally, an inverse model of the Duhem model for the segmental identification of the improved artificial fish swarm algorithm is established, and a composite controller integrating feedforward, feedback and decoupling control is designed on the basis of the inverse model, and an experimental verification is carried out. The results show that the displacement errors of the composite controller under different voltage signals are all within 0.25%. Therefore, the established model can accurately express the hysteresis characteristics of the platform, and the use of the composite controller can effectively reduce the accuracy error caused by the hysteresis characteristics. Full article
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Article
Multidisciplinary Optimization for Weight Saving in a Variable Tapered Span-Morphing Wing Using Composite Materials—Application to the UAS-S4
Actuators 2022, 11(5), 121; https://doi.org/10.3390/act11050121 - 27 Apr 2022
Cited by 1 | Viewed by 685
Abstract
This paper is a follow-up to earlier work on applying multidisciplinary numerical optimization to develop a morphing variable span of a tapered wing (MVSTW) to reduce its weight by using composite materials. This study creates a numerical environment of multidisciplinary optimization by integrating [...] Read more.
This paper is a follow-up to earlier work on applying multidisciplinary numerical optimization to develop a morphing variable span of a tapered wing (MVSTW) to reduce its weight by using composite materials. This study creates a numerical environment of multidisciplinary optimization by integrating material selection, structural sizing, and topological optimization following aerodynamic optimization results with the aim to assess whether morphing wing optimization is feasible. This sophisticated technology is suggested for developing MVSTWs. As a first step, a problem-specific optimization approach is described for specifying the weight-saving structure of wing components using composite materials. The optimization was performed using several approaches; for example, aerodynamic optimization was performed with CFD and XFLR5 codes, the material selection was conducted using MATLAB code, and sizing and topology optimization was carried out using Altair’s OptiStruct and SolidThinking Inspire solvers. The goal of this research is to achieve the MVSTW’s structural rigidity standards by minimizing wing components’ weight while maximizing stiffness. According to the results of this optimization, the weight of the MVSTW was reduced significantly to 5.5 kg in comparison to the original UAS-S4 wing weight of 6.5kg. The optimization and Finite Element Method results also indicate that the developedmorphing variable span of a tapered wing can complete specified flight missions perfectly and without any mechanical breakdown. Full article
(This article belongs to the Special Issue Aerospace Mechanisms and Actuation)
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Article
Multi-Objective Optimization Design and Dynamic Performance Analysis of an Enhanced Radial Magnetorheological Valve with Both Annular and Radial Flow Paths
Actuators 2022, 11(5), 120; https://doi.org/10.3390/act11050120 - 26 Apr 2022
Viewed by 621
Abstract
This article proposes an analytical methodology for the optimal design of a magnetorheological (MR) valve constrained in a specific volume. The analytical optimization method is to identify geometric dimensions of the MR valve, and to determine whether the performance of the valve has [...] Read more.
This article proposes an analytical methodology for the optimal design of a magnetorheological (MR) valve constrained in a specific volume. The analytical optimization method is to identify geometric dimensions of the MR valve, and to determine whether the performance of the valve has undergone major improvement. Initially, an enhanced radial MR valve structure with effective annular and radial composite flow paths was designed. After describing the schematic configuration and operating principle of the proposed MR valve, a mathematical model of the pressure drop was derived on the basis of the Bingham model of a MR fluid. Sequentially, the multi-objective optimization problem had been formulated for the constructed approximate model exploiting the NSGA-II algorithm to find the global optimum geometrical dimensions of the enhanced radial MR valve. Meanwhile, influences of the geometrical design variables of the MR valve were analytically investigated by mapping finite element analysis numerical responses with response surface techniques. Lastly, the experimental test rig was setup to explore the pressure drop and dynamic response time of the initial and optimal MR valve, as well as the dynamic performance of the enhanced radial MR valve controlled cylinder system under different excitation conditions. The experimental results revealed that under the applied current of 1.6 A, the pressure drop and power consumption of the optimal MR valve improved significantly with values of 4.46 MPa and 16.84 W, respectively, when compared to 4.03 MPa and 27.65 W of their respective initial values. Additionally, the average response time efficiency improved by 14.29%, with its optimal value being 81 ms and initial value as 94.5 ms. Moreover, the damping force of the optimal MR valve-controlled cylinder system was 4.34 kN, which was 12.44% larger than the initial one of 3.86 kN at the applied current of 1.6 A. Full article
(This article belongs to the Section Actuators for Land Transport)
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Article
Dynamics Modeling and Adaptive Sliding Mode Control of a Hybrid Condenser Cleaning Robot
Actuators 2022, 11(5), 119; https://doi.org/10.3390/act11050119 - 24 Apr 2022
Viewed by 651
Abstract
This study examines the pose control of the 4-RPU redundant parallel mechanism of a hybrid condenser cleaning robot in response to the poor control accuracy of current cleaning robots. The kinematics of the 4-RPU mechanism is analysed, and its dynamics model is constructed [...] Read more.
This study examines the pose control of the 4-RPU redundant parallel mechanism of a hybrid condenser cleaning robot in response to the poor control accuracy of current cleaning robots. The kinematics of the 4-RPU mechanism is analysed, and its dynamics model is constructed using the virtual work principle. The theoretical calculation and virtual prototype simulation of the constructed model are conducted in MATLAB and ADAMS, which yield basically consistent results, demonstrating the precision of the model. Based on this model, an adaptive sliding mode control method is proposed that can estimate and compensate for parameter uncertainties and load perturbations simultaneously. The system stability is analysed using Lyapunov functions. The results suggest that the adaptive sliding mode control method can significantly reduce the average tracking error of each degree of freedom of the moving platform and exhibits higher control stability and convergence accuracy than the conventional sliding mode control algorithm. This study provides a reference and research basis for attitude control of the cleaning robots affected by uncertainties such as water backlash during operation. Full article
(This article belongs to the Topic Motion Planning and Control for Robotics)
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Article
An LADRC Controller to Improve the Robustness of the Visual Tracking and Inertial Stabilized System in Luminance Variation Conditions
Actuators 2022, 11(5), 118; https://doi.org/10.3390/act11050118 - 22 Apr 2022
Viewed by 706
Abstract
Disturbance from luminance variation in the identification of visual sensors causes instability in the control system of target tracking, which leads to field of vision (FOV) motion and even the target missing. To solve this problem, a linear active disturbance reject controller (LADRC) [...] Read more.
Disturbance from luminance variation in the identification of visual sensors causes instability in the control system of target tracking, which leads to field of vision (FOV) motion and even the target missing. To solve this problem, a linear active disturbance reject controller (LADRC) is adopted to the visual tracking and inertial stable platform (VTISP) for the first time to improve the system’s robustness. As a result, the random disturbance from identification can be smoothed by the tracking differentiator (TD).An improved linear extended state observer (LESO) modified by the TD is provided to obtain the high-order state variables for feedback. That makes the system avoid noise in a differential process from the MEMS gyroscope and enhances the response time and stability in tracking control. Finally, simulation and experimental studies are conducted, and the feasibility of the LADRC is verified. Moreover, compared with the other controller in the VTISP for remote sensing, the superiority of the LADRC in system response time and stability is proved by the experiments. Full article
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Article
PI Speed Control with Reverse Motion of a Series DC Motor Based on the Noise Reduction Disturbance Observer
Actuators 2022, 11(5), 117; https://doi.org/10.3390/act11050117 - 21 Apr 2022
Viewed by 650
Abstract
In this paper, the speed control of a series DC motor is presented together with the electronics necessary to ensure inverse motion. The control law is based on the classical PI controller and the noise reduction disturbance observer (NRDOB). This control strategy allows [...] Read more.
In this paper, the speed control of a series DC motor is presented together with the electronics necessary to ensure inverse motion. The control law is based on the classical PI controller and the noise reduction disturbance observer (NRDOB). This control strategy allows the use of a linear approximation of the motor dynamics due to its excellent properties regarding model uncertainties, sensor noise, and external perturbations. Consequently, a linear model based on the nonlinear modelling with magnetic saturation of the motor is also presented. The NRDOB-based control frequency-domain approach allows for the treating of structured and unstructured disturbances in the spirit of classical control theory. Although PI controllers have proved to provide excellent performance and robustness for the speed control of series DC motor, it cannot cope, without affecting or reducing the performance, with the effects of sensor noise; moreover, to further improve the performance, especially in tracking conditions, it is necessary to design and implement a power driver capable of generating inverse motion. In addition, because NRDOB is in fact an internal model control strategy, a perfect match between process and model is not required. That is, contrary to the common belief that the NRDOB is a 2-DOF, it is in fact a 3-DOF control scheme. Based on these characteristics, it was possible to design and implement a robust high-performance speed control system with reverse motion for the non-linear series DC motor with not well-defined relative degree, together with the electronics required for the reverse motion which is fully described. This results in a control system capable of overcoming the problems generated by input disturbances and sensor noise, ensuring robustness and performance in tracking and regulation conditions. Real-time experimental results are included in support of the approach presented here. Full article
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Article
A Battery-Powered Fluid Manipulation System Actuated by Mechanical Vibrations
Actuators 2022, 11(5), 116; https://doi.org/10.3390/act11050116 - 21 Apr 2022
Viewed by 789
Abstract
Miniaturized fluid manipulation systems are an important component of lab-on-a-chip platforms implemented in resourced-limited environments and point-of-care applications. This work aims to design, fabricate, and test a low-cost and battery-operated microfluidic diffuser/nozzle type pump to enable an alternative fluid manipulation solution for field [...] Read more.
Miniaturized fluid manipulation systems are an important component of lab-on-a-chip platforms implemented in resourced-limited environments and point-of-care applications. This work aims to design, fabricate, and test a low-cost and battery-operated microfluidic diffuser/nozzle type pump to enable an alternative fluid manipulation solution for field applications. For this, CNC laser cutting and 3D printing are used to fabricate the fluidic unit and casing of the driving module of the system, respectively. This system only required 3.5-V input power and can generate flow rates up to 58 µL/min for water. In addition, this portable pump can manipulate higher viscosity fluids with kinematic viscosities up to 24 mPa·s resembling biological fluids such as sputum and saliva. The demonstrated system is a low-cost, battery-powered, and highly versatile fluid pump that can be adopted in various lab-on-a-chip applications for field deployment and remote applications. Full article
(This article belongs to the Section Miniaturized and Micro Actuators)
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Article
Hysteresis Modeling and Compensation of Piezoelectric Actuators Using Gaussian Process with High-Dimensional Input
Actuators 2022, 11(5), 115; https://doi.org/10.3390/act11050115 - 20 Apr 2022
Viewed by 696
Abstract
Rate-dependent hysteresis seriously deteriorates the positioning accuracy of the piezoelectric actuators, especially when tracking high-frequency signals. As a widely-used nonparametric Bayesian method, the Gaussian process (GP) has proven its effectiveness in nonlinear hysteresis modeling. In this paper, the dimension of the input to [...] Read more.
Rate-dependent hysteresis seriously deteriorates the positioning accuracy of the piezoelectric actuators, especially when tracking high-frequency signals. As a widely-used nonparametric Bayesian method, the Gaussian process (GP) has proven its effectiveness in nonlinear hysteresis modeling. In this paper, the dimension of the input to the GP model is extended to consider more dynamic features of the tracking signal so as to improve the rate-dependent hysteresis modeling accuracy. In contrast with the traditional training set containing only the position and speed information, the acceleration and jerk information, as well as their temporal distribution information, is also included in the input of the model. An inverse hysteresis compensator (IHC) is established in the same way, and open-loop and closed-loop controllers are developed by using the IHC. Experimental results on a PEA stage show that with the increase in the input dimension, the hysteresis modeling accuracy improves greatly and, thus, the controllers based on IHC can achieve a better tracking performance. Full article
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