Search

Carbon-enriched polysiloxane-derived SiOC (C-SiOC) ceramics are promising electromagnetic wave absorption (EMA) materials. However, oxidation and impedance mismatch severely deteriorate their EMA performance at high temperatures. In this study, we used polysiloxane (PSO) to encapsulate the crosslinked precursor of C-SiOC ceramics. After pyrolysis, PSO-derived SiOC-encapsulated C-SiOC (here named PSO-C-SiOC) ceramics were obtained. The PSO-C-SiOC ceramics exhibit an improved oxidation resistance compared with C-SiOC ceramics and basically retain their original dielectric and EMA properties after exposure to air at high temperatures. Moreover, the ceramics can maintain excellent EMA properties at elevated temperatures with good impedance matching. The remarkable high-temperature EMA properties of PSO-C-SiOC ceramics in air are attributed to the protective outer-layer of PSO-derived SiOC ceramic, which enhances oxidation resistance and simultaneously controls the impedance matching. These findings underscore the potential of PSO-C-SiOC ceramics as high-temperature EMA materials. [ABSTRACT FROM AUTHOR]

The purpose of this study was to ensure the compliance and safety of a robot's movements during interactions with the external environment. This paper proposes a control strategy for learning variable impedance characteristics from multiple sets of demonstration trajectories. This strategy can adapt to the control of different joints by adjusting the parameters of the variable impedance control policy. Firstly, multiple sets of demonstration trajectories are aligned on the time axis using Dynamic Time Warping. Subsequently, the variance obtained through Gaussian Mixture Regression and a variable impedance strategy based on an improved Softplus function are employed to represent the variance as the variable impedance characteristic of the robotic arm, thereby enabling variable impedance control for the robotic arm. The experiments conducted on a self-designed robotic arm demonstrate that, compared to other variable impedance methods, the motion accuracy of the trajectories of joints 1 to 4 improved by 57.23%, 3.66%, 5.36%, and 20.16%, respectively. Additionally, a stiffness-variable segmented generalization method based on Dynamic Movement Primitive is proposed to achieve variable impedance control in various task environments. This strategy fulfills the requirements for compliance and safety during robot interactions. [ABSTRACT FROM AUTHOR]

This paper provides an adaptive impedance control strategy about docking robot, a locking mechanism scheme based on the Stewart platform developing for the problem of excessive collision contact force caused by external environmental interference during autonomous docking tasks of ground unmanned vehicles. First, the docking robot system was introduced, and an inverse kinematics model of the docking robot was constructed. Next, to solve the problem of excessive collision contact force during docking, we have designed an adaptive impedance control algorithm, which includes a steady-state error model of contact force, an adaptive compensation controller design, and system stability analysis, thus achieving active compliance control. Finally, some simulations and experiments were conducted on the docking robot. Compared with traditional impedance control, adaptive impedance control reduces docking collision contact force and achieves compliant control. In the future, the experimental results provide a new docking approach for autonomous docking of unmanned vehicles, and also serve as a reference for the development of intelligent vehicles. • A docking robot scheme based on the Stewart platform is developed for dynamic docking of UVG. • An adaptive impedance control strategy is proposed to improve adaptability to the environment. • The effectiveness of the control strategy has been verified through simulation and experimentation. [ABSTRACT FROM AUTHOR]

Construction robots have garnered attention with the rapid development of construction automation. Such tiling robots can effectively improve the construction quality and efficiency. To enhance the quality of robotic tile laying, a control method based on position servo and position impedance was proposed herein. To improve the full filling rate, the robot improved the full reduction rate of tile laying using the effective vibration from an eccentric vibrator. Experimental results showed that the proposed method could effectively improve the tile laying quality. The results of this study will promote the application of robotic tile laying to engineering and provide a reference for the improvement in the quality of robotics in construction. [ABSTRACT FROM AUTHOR]

The research on aerial manipulation systems has been increased rapidly in recent years. These systems are very attractive for a wide range of applications due to their unique features. However, dynamics, control and manipulation tasks of such systems are quite challenging because they are naturally unstable, have very fast dynamics, have strong nonlinearities, are very susceptible to parameters variations due to carrying a payload besides the external disturbances, and have complex inverse kinematics. In addition, the manipulation tasks require estimating (applying) a certain force of (at) the end-effector as well as the accurate positioning of it. Thus, in this article, a robust force estimation and impedance control scheme is proposed to address these issues. The robustness is achieved based on the Disturbance Observer (DOb) technique. Then, a tracking and performance low computational linear controller is used. For teleoperation purpose, the contact force needs to be identified. However, the current developed techniques for force estimation have limitations because they are based on ignoring some dynamics and/or requiring of an indicator of the environment contact. Unlike these techniques, we propose a technique based on linearization capabilities of DOb and a Fast Tracking Recursive Least Squares (FTRLS) algorithm. The complex inverse kinematics problem of such a system is solved by a Jacobin based algorithm. The stability analysis of the proposed scheme is presented. The algorithm is tested to achieve tracking of task space reference trajectories besides the impedance control. The efficiency of the proposed technique is enlightened via numerical simulation. [ABSTRACT FROM AUTHOR]

Despite our environment often being uncertain, we generally manage to generate stable motor behaviors. While reactive control plays a major role in this achievement, proactive control is critical to cope with the substantial noise and delays that affect neuromusculoskeletal systems. In particular, muscle co-contraction is exploited to robustify feedforward motor commands against internal sensorimotor noise as was revealed by stochastic optimal open-loop control modeling. Here, we extend this framework to neuromusculoskeletal systems subjected to random disturbances originating from the environment. The analytical derivation and numerical simulations predict a characteristic relationship between the degree of uncertainty in the task at hand and the optimal level of anticipatory co-contraction. This prediction is confirmed through a single-joint pointing task experiment where an external torque is applied to the wrist near the end of the reaching movement with varying probabilities across blocks of trials. We conclude that uncertainty calls for impedance control via proactive muscle co-contraction to stabilize behaviors when reactive control is insufficient for task success. Author summary: This work presents a computational framework for predicting how humans modulate muscle co-contraction to cope with uncertainties of different origins. In our neuromusculoskeletal system, uncertainties have both internal (sensorimotor noise) and external (environmental randomness) origins. The present study focuses on the latter type of uncertainty, which had not been dealt with systematically previously despite its importance in everyday life. Therefore, we thoroughly investigated how random disturbances occurring with some probability in a motor task shape the feedforward control of mechanical impedance through muscle co-contraction. Here we provide theoretical, numerical and experimental evidence that the optimal level of co-contraction steeply increases with the uncertainty of our environment. These findings show that muscle co-contraction embodies uncertainty and optimally mitigates its consequences on task execution when feedback control is insufficient due to sensory noise and delays. [ABSTRACT FROM AUTHOR]

Conventional robotic screw methods rely on position control and the use of a threshold value, normally a contact force value, to detect the contact between tool and screw, so the nut-runner can be placed correctly on the workpiece. In the case of a dynamic workspace, the variance of the workpiece position will likely cause the nut-runner to be positioned incorrectly and will significantly decrease the success rate of the screw task. This paper proposes a novel method based on a logistic regression model for flexible Human-Robot-Collaboration (HRC) screw assembly operations in highly dynamic workspaces. The proposed method is part of a screwing strategy based on impedance control and developed for HRC applications. The screwing strategy consists of a spiral movement executed by the robot while approaching the workpiece and it is used as a search procedure to find the screw. The proposed method is used to detect when the tool correctly interlocks with the screw head so the robot can proceed with the screwing process. The goal is to stop the spiral movement timely when the nut-runner has correctly interlocked with the screw head to ensure a successful screw task and avoid potential damage to the nut-runner or the workpiece. The proposed screw interlock recognition method utilizes a logistic regression model to observe the contact forces between tool and screw head. The learning model is trained using force data collected from experiments and then its feasibility is validated with further testing. [ABSTRACT FROM AUTHOR]

This paper proposes a novel cascade impedance control architecture designed for the upper limb exoskeleton rehabilitation robot. The proposed architecture comprises two parts: First, the impedance reference trajectory is shaped from the desired trajectory utilizing the desired impedance model and feedback contact torques. The second part of the proposed controller is an adaptive backstepping control, responsible for tracking the generated impedance reference trajectory. Notably, the proposed adaptive backstepping impedance controller is nonmodel-based control approach, eliminating the need for the robot's model. Furthermore, a genetic algorithm is employed as an offline tuning method for the inner position loop controller, namely the adaptive backstepping controller. This approach outperforms the conventional impedance controller without relying on the model of the robot, making it more robust against model uncertainties and unknown parameters. Furthermore, to mitigate undesired compliance resulting from the permanent attachment between the robot and the patient's limb, we introduce an adaptive gain. This gain dynamically adjusts the priority between compliance and tracking, ensuring that the robot complies only when necessary. [ABSTRACT FROM AUTHOR]

In the rehabilitation training process for stroke patients, the level of excitement in the patient's physiological state has a positive impact on the efficacy of the training. In order to improve patients' initiative during training and prevent dependence on assistive systems, this study proposes an assist-as-needed control strategy based on a subjective intention decline model. The strategy primarily consists of two modules: a subjective intention decline control module and a limb movement assessment module. The subjective intention decline module collects surface electromyography (sEMG) data during patient training and optimizes support vector machine (SVM) using quantum particle swarm optimization (QPSO) algorithms to establish a subjective intention decline model. The limb movement assessment module collects information such as interaction force and position error during training and proposes a method for evaluating the motion state of the affected limb. This model combines traditional impedance control with a method for assessing limb movement and subjective status, automatically adjusting the level of assistive force on the affected limb in real time to enhance its active participation in tasks. Finally, we performed two verification experiments to assess the patient's initiative in participating in the training. The experimental results show that the proposed method effectively reduced the average assist force by 65.66% for the traditional impedance control training system and effectively the average assist force by 35.2% for the control training system using only the assist force module based on force position information. At the same time, the accuracy of the subjective intention attenuation module established in the experiment to identify the fatigue level of the subjects reached 93.41%. Therefore, the proposed method effectively improves the initiative of trainers and also prevents patients from relying on the assist-as-needed control training system. [ABSTRACT FROM AUTHOR]

During polishing tasks, it is critical to guarantee that the contact force applied at the terminus of the robot manipulator is accurate and stable. However, conventional impedance control methods struggle to perfectly track the desired force signals due to the uncertainties and errors present in the environment. In this paper, a super-twisting sliding mode adaptive impedance control is proposed to overcome the issues mentioned. Firstly, the overshooting of the force signal that occurs during the initial contact phase is solved by establishing a tracking differentiator. This allows the system to apply force from zero smoothly, enabling a seamless transition from a step function to a predetermined force value, reducing the risk of damage to the workpiece or robot due to force overload. Then,for adjustment to an uncertain environment, an exponential update factor based impedance control approach is developed. In addition, super-twisting sliding mode control (STSMC) is introduced, which can effectively suppress the fluctuation of the contact force and enhance the robustness of the whole system. Eventually, simulation and strategy comparison trials show that the proposed method is effective and superior. [ABSTRACT FROM AUTHOR]

Unified force-impedance control (UFIC) aims at integrating the advantages of impedance control and force control. Compliance and exact force regulation are equally important abilities in modern robot manipulation. The developed passivity-based framework builds on the energy tank concept and is suitable for serial rigid and flexible-joint robots. Furthermore, it is able to deal either with direct force measurements or model-based contact force estimation. Thus, in this theoretical framework, the most relevant practical systems are covered and shown to be stable for arbitrary passive environments. Particular focus is also laid on a robust impedance-based contact/non-contact stabilization methodology that prevents abrupt, unwanted, and potentially dangerous movements of the manipulator in case of contact loss, a well-known problem of both impedance and force control. The validity of the approach is shown in simulation and through various experiments. Our work roots in Haddadin (2015); Schindlbeck and Haddadin (2015), where the basic UFIC regulation controller was proposed. In the present paper, we significantly advance this idea into a complete theoretical UFIC tracking framework, including rigorous stability analysis and extensive experimental evidence. [ABSTRACT FROM AUTHOR]

Force control is one of the core modules for surface finishing such as grinding, polishing and sanding. However, the current force control methods based on human skills lack in-depth analysis of data patterns or are only applicable to flat surfaces. In addition, surface finishing is mainly performed by hand, resulting in low processing efficiency and poor product consistency. Therefore, this paper proposes a force control method that incorporates human skills to achieve relatively accurate force skill transfer and complex surface finishing. Firstly, human skills consisting of the force skill and the motion skill are learned. The force skill is used to generate the desired force. Then, a series of discrete poses are obtained based on human demonstration and combined with the motion skill to generate the desired trajectory. Finally, a computed-torque impedance control method is proposed to achieve relatively accurate force skill transfer and complex surface finishing by incorporating the desired trajectory and the desired force. The experiments are conducted on a platform composed of a 7-DOF collaborative robot manipulator from Franka Emika and a complex violin surface. The results demonstrate that the proposed force control method can achieve relatively accurate force skill transfer and improve the surface quality of the workpiece. [ABSTRACT FROM AUTHOR]

The impedance control of a dual-arm space robot in orbit auxiliary docking operation is studied. First, for the closed-chain hybrid system formed by the dual-arm space robot after capture operation, the dynamic equation of position uncontrolled and attitude controlled is established. The second-order linear impedance model and second-order approximate environment model are established for the problem of simultaneous output force/pose control of the end of the manipulator. Then, aiming at the transient performance control requirements of the dual-arm space robot auxiliary docking operation in orbit, a sliding mode controller with equivalent replacement of tracking errors is designed by introducing Prescribed Performance Control (PPC) theory. Next, Radial Basis Function Neural Networks (RBFNN) are used to accurately compensate for the modeling uncertainties of the system. Finally, the stability of the system is verified by Lyapunov stability determination. The simulation results show that the attitude control accuracy is better than 0.5 ° , the position control accuracy is better than 10 − 3 m, and the output force control accuracy is better than 0.5 N when it reaches 30 N. It also indicated that the proposed control algorithm can limit the transient performance of the controlled system within the preset range and achieve high-precision force/pose control, which ensures a more stable on-orbit auxiliary docking operation of the dual-arm space robot. [ABSTRACT FROM AUTHOR]

ABSTRACT The accurate emulation of the electrical impedance of biological tissues is crucial for the development and validation of bioimpedance measurement devices and algorithms. This paper describes a digitally controllable impedance emulator capable of reproducing values representative of tissue bioimpedance in user‐specified resistance, reactance, and frequency ranges up to 1 MHz. The presented solution uses a 2R‐1C impedance model to emulate the impedance characteristics of a biological tissue. Specific selection of each element value in this model is achieved using analog multiplexers with low Ron$$ {R}_{on} $$ resistance. A MATLAB algorithm was developed for value estimation using target impedance requirements. An example design to emulate impedance from 1 kHz to 1 MHz with 10 Ω$$ \Omega $$ to 400 Ω$$ \Omega $$ resistance and −45Ω$$ -45\Omega $$ maximum reactance is provided. The nonideal behavior of this design was evaluated and compared against experimentally collected impedance measurements. Deviations of <1% were observed between experimental and theoretical resistances for values >50Ω$$ >50\Omega $$ up to 100 kHz (with approximately 5% deviations up to 1 MHz) and reactance deviations were also <1% up to 10 kHz. High frequency deviations are attributed to the parasitic capacitance in the realization of the design. The experimental results validate the design approach and realization for low frequencies. Overall, the innovation of the proposed approach is the control of both resistance and reactance for emulating electrical impedance representative of biological tissues. [ABSTRACT FROM AUTHOR]

Cable-driven robots are commonly applied in the rehabilitation field. Many tendon-based systems use parallel end-effector structures because of the advantages of fast reactions and high force outputs. We previously developed an active cable-driven robotic system that enabled accurate force control and was applied while walking on a treadmill. However, the kinematic and kinetic assistance methods need to be improved. Given the advantages of tendon-based parallel systems, this study investigated walking generated by four cables that were directly attached around the ankle. The aim of this work was to develop a tendon-based parallel robotic system to provide assisted walking on a treadmill with gait-specific position guidance and force compensation. To demonstrate the assistance effects, preliminary physiological responses of leg muscles during walking with the system were investigated. A parallel robotic system with four cable-driven units was developed. Kinematic and kinetic analyses of walking were performed, followed by the development of control algorithms for walking with impedance assistance only and walking with impedance assistance plus kinetic compensation. The muscle activity of the rectus femoris, vastus lateralis, gluteus maximus, biceps femoris, and gastrocnemius muscles was recorded and analyzed. On the basis of the kinematic and kinetic analyses, the tendon-based parallel robotic system produced treadmill walking with position and force assistance. The force control algorithms tracked the target force profile with a mean error of 6.4 N. During impedance-assisted walking, the rectus femoris, gluteus maximus and biceps femoris muscles produced a mean electromyography of 115.1% of the activity during independent walking (without assistance). However, the activity of the vastus lateralis and gastrocnemius reduced to only 82.5% of that during independent walking. Further kinetic compensation generally reduced the muscle activity, with the mean electromyography result being 88.7% of that during independent walking. From a technical point of view, the tendon-based parallel robotic system provided walking-specific position and force assistance in leg movement, accompanied by reduced muscle activity compared with independent walking. A technical feasibility study will be conducted to evaluate whether the tendon-based parallel robotic system is feasible for assisted treadmill walking in the general population and whether position guidance and force assistance are acceptable. [ABSTRACT FROM AUTHOR]

The article presents a novel control strategy for cable-driven aerial manipulators (UAMs) aimed at enhancing impedance control during contact operations in complex environments. A fractional-order nonsingular terminal sliding mode control (FONTSMC) integrated with a disturbance observer (DOB) is proposed to improve the robustness and precision of the UAM under lumped disturbances. This developed approach utilizes the flexibility of fractional calculus, the finite-time stability of nonsingular terminal sliding mode, and the real-time disturbance estimation capabilities of the DOB to ensure smooth and compliant contact interactions. The effectiveness of the proposed control strategy is validated through comprehensive simulation studies, which demonstrate significant improvements in control performance, stability, and disturbance rejection when compared to traditional methods. The results indicate that the FONTSMC-DOB framework is highly suitable for complex aerial manipulation tasks, offering both theoretical and practical insights into the design of advanced control systems for UAMs. [ABSTRACT FROM AUTHOR]

It is well understood that motor dysfunctions in patients can be restored through a certain amount of repetitive training. Robots and virtual reality offer an excellent solution to incentivize and optimize training intensity while also reducing the workload for therapists. In this paper, leveraging virtual reality technologies and haptic robots, we have developed a cost-effective robot-assisted training system and three training exercises for hand rehabilitation. The Unity game engine was utilized to create training scenarios where hand avatars interact with virtual objects. Off-the-shelf haptic robots were employed to manipulate the hand avatars, enabling completion of training tasks with a realistic tactile experience. Haptic feedback is rendered using impedance control laws. Additionally, to address the needs of both patients and therapists we propose to employ robot-assisted force and feedback force. These mechanisms are designed to provide assistance to patients during tasks if needs and to transmit the patient's force feedback to the therapist, facilitating comprehensive interaction and communication between the two parties. Several experiments were conducted involving six healthy subjects, who used electrode stimulation to simulate impaired limbs, to demonstrate the effectiveness of the proposed training frameworks. [ABSTRACT FROM AUTHOR]

This study proposes a cost‐effective, small‐size, and portable impedance analyzer using the AD5941 Analog Front End (AFE) that makes frequency sweep measurement for various applications. The design utilizes a microcontroller and an AD5941 circuit for impedance measurement. The AD541 is a high precision impedance converter system that consists of a 16‐bit, 1.6 MSPS, analog to digital converter (ADC), an integrated waveform generator, and a digital signal processing (DSP) block. The AD5941 has many advantages over the AD5933 which was used in numerous studies in the past decade. Also, the device implements the four‐wire impedance method which is an impedance measuring technique that reduces the effect of electrodes to achieve higher accuracy. A supporting Graphic User Interface (GUI) software is employed to control the Impedance Analyzer device and to visualize the measurement. This impedance analyzer achieves a frequency resolution of 0.015 Hz and can generate sinusoid up to 200 kHz. In frequency range from 10 kHz to 150 kHz, the device can measure impedance in the range of 10 Ω–100 kΩ with less than 4.3% of error in comparison with benchtop impedance analyzer, Microtest 6632. Moreover, our impedance measurement device has undergone testing involving human calf measurements and electrochemical quantification, particularly for estimating Sodium Chlorite. The experimental outcomes demonstrate that our design not only fulfills the criteria of an impedance analyzer device but also performs effectively across diverse applications. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

The increasing space debris population in critical orbits due to spacecraft failure dictates the need for action. On-Orbit Servicing (OOS) has been proposed as a method for mitigating this trend by repairing existing space assets. The development of large servicing spacecraft has been given significant attention. In this paper, we are approaching the problem with a new paradigm for a servicing spacecraft by proposing a CubeSat class servicer equipped with a one-degree-of-freedom (DoF) robotic arm. Considering the OOS context, we choose the Orbital Replacement Unit (ORU) installation on a target spacecraft as a challenging benchmark task for the proposed servicer configuration. To carry out this task, we formulate and compare performance of four controllers to achieve coordinated control of both the CubeSat and the robotic arm for the installation task. We start with a basic PD controller and progress to the more advanced impedance controller, Model Predictive Control (MPC) and Model Predictive Impedance Control (MPIC) designs. The controllers are evaluated and compared across several relevant metrics for the ORU installation and their merits for practical implementation are discussed. • Comparative analysis of model-based controllers against traditional control methods. • Monte Carlo simulations used to test robustness of the controllers. • Novel, mechanically simple CubeSat servicer for simulated ORU installation. • MPC, PD controllers show similar success rates, MPC requires higher control efforts. [ABSTRACT FROM AUTHOR]

This paper introduces a novel droop-based decentralized control scheme to address the power-sharing challenges within a PV-fed islanded AC microgrid. This novel approach integrates both conventional (P-f/Q-V) and virtual impedance concepts to optimize and manage the precise distribution of active and reactive power among parallel operating inverters posing a significant research challenge. The conventional droop control methods encounter limitations such as voltage and frequency deviations and inaccuracies in power-sharing due to line impedance disparities. To overcome these limitations, the proposed solution integrates an enhanced virtual impedance control loop alongside the conventional control loop (P-f/Q-V). The efficacy of this approach is showcased through simulations conducted using the OPAL-RT OP4510 simulator within the MATLAB/Simulink platform. The Real-time simulation outcomes confirm the efficiency of the suggested control strategy, guaranteeing precise distribution of both active and reactive power while upholding stable voltage and frequency profiles within the system. • A novel virtual impedance structure for improved power sharing capability among parallel inverters. • PCC voltage stability under load change and line impedance mismatch scenarios. • Restoration of AC MG frequency under load transient condition. • An analytical solution for choosing the equivalent output virtual impedance. [ABSTRACT FROM AUTHOR]

Enhancing the transparency of high-transmission-ratio linear actuators is crucial for improving the safety and capability of high-force robotic systems having physical contact with humans in unstructured environments. However, realizing such enhancement is challenging. A proposed solution for active body weight support systems involves employing a macro–mini linear actuator incorporating an electrorheological-fluid brake to connect a high-force unit with an agile, highly back-drivable unit. This paper introduces the use of an electromagnetic (EM) brake with reduced rotor inertia to address this challenge. The increased torque capacity of the EM brake enables integration with a low-gear-ratio linear transmission. The agile translation of the endpoint is propelled by a low-inertia motor (referred to as the "mini") via a pulley-belt mechanism to achieve high transparency. The rotor of the EM brake is linked to the pulley. Damping modulation under high driving force is achieved through the adjustment of the brake torque relative to the rotational speed of the pulley. When the brake is engaged, it prevents any relative motion between the endpoint and the moving carrier. The endpoint is fully controlled by the ball screw of the high-force unit, referred to as the "macro". A scaled prototype was constructed to experimentally characterize the damping force generated by the mini motor and the EM brake. The macro–mini linear actuator, equipped with an intrinsic failsafe feature, can be utilized for active body weight support systems that demand high antigravity force. [ABSTRACT FROM AUTHOR]

Copyright of Machine Tool & Hydraulics is the property of Guangzhou Mechanical Engineering Research Institute (GMERI) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A function approximation technique (FAT) based force sensorless adaptive impedance controller is proposed in this paper for rigid robot manipulators without using force estimators. The basic idea is to rewrite the traditional impedance controller by replacing the contact force with the target impedance so that a force sensorless impedance controller is obtained. A lumped uncertainty can then be found by collecting all the uncertainties in the new controller. The FAT is employed to facilitate the design of the adaptive loop justified by the Lyapunov stability theory. In this new design, computation of tedious regressor matrix used in most traditional robot adaptive designs are avoided. Both the renowned singularity problem and the joint acceleration feedback problem are circumvented. The number of functions to be estimated is reduced to be linear to the number of robot joints which is a great simplification in real-time computation. Simulation results show that the proposed design can give good performance regardless of various uncertainties and unavailability of the contact force signals. [ABSTRACT FROM AUTHOR]

Copyright of Ordnance Industry Automation is the property of Editorial Board for Ordnance Industry Automation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Aiming at safely capturing faulty satellites on orbit, a novel predefined‐time impedance controller is designed to address the control challenges of free‐flying flexible‐joint space robots (FFSR) considering output constraint. The FFSR system model is transformed into a singularly perturbed form consisting of both fast and slow subsystems. For the slow subsystem, an adaptive predefined‐time sliding mode observer is developed to obtain the contact torque between the end‐effector and the target. To mitigate overshooting and enhance tracking precision, a predefined‐time prescribed performance function is proposed, and the output constraint issue is reformulated as a coordinate transformation problem involving the trajectory tracking errors. Based on these, a predefined‐time impedance controller is designed to achieve the compliant capture of the target. For the fast subsystem, a new non‐singular fixed‐time controller is proposed to rapidly overcome the vibration of the flexible joints. Stability analysis proves predefined‐time stability of the FFSR system and the tracking errors can be maintained within a predefined region. Finally, numerical simulations indicate the feasibility and validity of the presented control strategy. [ABSTRACT FROM AUTHOR]

A tethered autonomous docking system, which is composed of a rope winch installed at the bottom of the unmanned aerial vehicle (UAV), a quadrotor for autonomous docking, and a connected tether, can be widely used for unmanned delivery. Frequent ups and downs can be inevitable through the deployment/retrieval of the flexible tether. Although the tether offers several advantages compared with traditional UAV transportation, new control problems can arise as well. To solve this nonlinear, underactuated, and time-varying disturbance system, a complete control scheme, including the accurate trajectory tracking of the end quadrotor under a time-varying disturbance caused by tether and the coordinated control of the rope winch, is proposed in this paper. A complete dynamics model, including the terminal quadrotor and the rope winch, is derived. A new control scheme, combining active disturbance rejection control with finite time integral backstepping, is proposed to achieve the position tracking of the quadrotor under the unknown disturbance introduced by tether and environment. In the case of obtaining the real-time position and tether tension of the quadrotor, a position-based impedance control strategy was proposed to always keep the tether slightly tensioned. Theoretical proof and simulation are given to verify the designed control algorithm, which can provide good performance of tracking and antidisturbance. [ABSTRACT FROM AUTHOR]

In recent years, with the continuous development of human exploration of the natural world, there has been a growing demand across various fields for robots capable of free movement in diverse environments. In this study, we address the issue of compliant control for a hexapod robot in diverse environments and propose a novel control method based on an adaptive impedance model for position control. Our approach enables the hexapod robot to stabilize foot force on complex terrains while preserving balance and body height. Specifically, we analyze the algorithm's parameters and stability by establishing the hexapod robot's structural and impedance control models. To tackle this challenge, we introduce an adaptive impedance control algorithm that estimates environmental parameters using Lyapunov's asymptotic stability theorem and achieves tracking of actual foot‐end forces to desired foot forces. Furthermore, to ensure body stability and height, we incorporate attitude feedback and body feedback. Experimental results from foot force control experiments conducted on a multilegged robot demonstrate that our proposed algorithm enhances the adaptability and robustness of the robot. This research holds significant implications for the stable control of hexapod robots in complex environments and has promising practical applications. [ABSTRACT FROM AUTHOR]

Due to the ability to improve the low-inertia characteristics of power systems and offer reliable voltage and frequency support, grid-forming permanent-magnet synchronous-generator wind turbines (PMSG-WTs) based on virtual synchronous-generator (VSG) technology are emerging se the direction for future developments. Previous studies on the small-signal stability of grid-forming PMSG-WTs that connect to the grid usually simplify them into grid-connected grid-side converters (GSC), potentially leading to errors in stability analyses. Therefore, this paper considers the machine-side converter (MSC) control and establishes impedance models for grid-forming PMSG-WTs. Based on the sensitivity calculation of controller parameters using symmetric difference computation based on zero-order optimization, the impact of the internal controller on outside impedance characteristics is quantitatively analyzed. Additionally, an optimization method to enhance the stability of a hybrid wind farm by adjusting the ratio of grid-forming and grid-following wind turbines is proposed. [ABSTRACT FROM AUTHOR]

A feedforward ANN was previously developed for recognition of two objects i.e. a spongy ball and a plastic bottle but was verified through simulation only. In this work, the feasibility of the ANN model is tested by applying it to the robot's impedance control which takes the exerted force at the finger as input while resulting in an output for the selection rule of the impedance stiffness parameter, named Kd. From the results, the different object textures can be distinguished by the ANN where the absolute peak values of measured rate force during contact with the ball reached 0.15 N and a slightly higher value of 0.32 N for the bottle. Kd values were found to switch between 1000 and 250 based on the ANN outputs for the ball and bottle, respectively, thus affecting the dynamics of the fingertip through modified position reference of the fingertip. However, it is also observed that the object was incorrectly classified in some moments when the exerted force was not sufficient due to the weak grasp of the object. This shows that the nonlinear factor from the hardware defects needs to be considered when refining the Kd selection rule in future studies. [ABSTRACT FROM AUTHOR]

A novel 10-Watt-Level high-power microwave rectifier with an inverse Class-F harmonic network for microwave power transmission (MPT) is presented in this paper. The high-power microwave rectifier circuit comprises four sub-rectifier circuits, a 1 × 4 power divider, and a parallel-series dc synthesis network. The simple inverse Class-F harmonic control network serves dual roles: harmonic control and impedance matching. The 1 × 4 power divider increases the RF input power fourfold, reaching 40 dBm (10 W). The parallel-series dc synthesis network enhances the resistance to load variation. The high-power rectifier circuit is simulated, fabricated, and measured. The measurement results demonstrate that the rectifier circuit can reach a maximum RF input power of 10 W at 2.45 GHz, with a maximum rectifier efficiency of 61.1% and an output dc voltage of 23.9 V, which has a large application potential in MPT. [ABSTRACT FROM AUTHOR]

Virtual synchronous generator (VSG) control has positive effects on the stability of microgrids. In practical power systems, both single-phase loads and three-phase unbalanced loads are present. The four-leg inverter is an alternative solution for the power supply of unbalanced loads and grid connections. The traditional VSG control strategy still faces challenges when using a four-leg inverter to provide a symmetrical voltage and stable frequency in the load power supply and pre-synchronization. This paper proposes a VSG-based control strategy along with a pre-synchronization method for four-leg inverters. An improved VSG control strategy is put forward for four-leg inverters. The improved virtual impedance control and power calculation methods are integrated into the control loop to suppress the voltage asymmetry and frequency ripples. Building on the improved VSG control strategy, a pre-synchronization control approach is proposed to minimize the amplitude and phase angle discrepancies between the inverter output voltage and the power grid voltage. In addition, an optimized design method for control parameters is presented to improve VSG dynamic performance. A hardware prototype of the four-leg inverter is built; the results show that the voltage unbalance ratio can be reduced by 89%, and the response time can be shortened by 50%. [ABSTRACT FROM AUTHOR]

A unidirectional link is typically incorporated into the DC input side of an inverter to ensure the reliability and stability of the microgrid power supply. Due to impedance and control variations among inverters, circulating currents may rapidly arise during the operation of parallel transient inverters. Nonetheless, the unidirectional power circulating in a DC unidirectional link results in energy accumulation on the DC side, causing DC bus voltage pumping and affecting MGs' operation safety and stability. This paper proposes a non-communication-based circulation suppression strategy to suppress power circulation in parallel transients based on the local information of inverters. First, a parallel transient is modeled, and the power circulation phenomenon and its influencing factors are analyzed. Then, the instantaneous power and absorbed active energy are calculated to adjust the phase of the inverter output voltage and suppress power circulation. Moreover, the output frequency is adjusted to balance the DC-side voltage of each inverter. Then, the stability of the parallel system after adding the circulation suppression control strategy is verified using the Lyapunov function method. Finally, simulation and experimental results verify the effectiveness of the proposed power circulation suppression strategy. [ABSTRACT FROM AUTHOR]

For specific missions of spacecraft including on-orbit assembly, docking, grasp, etc., the presence of uncertainties leads to difficulties in the analysis of impedance force control systems and evaluations of safety for space manipulators. Therefore, in this study, a novel interval uncertainty-oriented impedance force control method for space manipulators with time-dependent reliability was established. The proposed method can accurately and rapidly characterize uncertainties. Additionally, it can reflect the reliability of a control system based on an overall time history. Once the uncertainties of the dynamic models and state responses are known, their uncertainty bounds can be obtained using an established non-probabilistic propagation method with high accuracy. An interval process model and the first passage theory are employed in the non-probabilistic time-dependent model. A joint reliability index is established based on the single reliability indexes, which can more efficiently evaluate the control system reliability than the individual indexes. A numerical example related to space manipulator is used to study the developed impedance force control method and verify the effectiveness of the method. The results from the response curves reveal validity of the proposed method, while the reduction in time proves efficiency of the method. • Uncertain impedance force control method for space manipulator is proposed. • A non-probabilistic reliability-based impedance force control method is proposed. • Uncertainty analysis of kinematics and dynamics is proposed with bounded parameters. • Uncertain impedance control is established using interval uncertainty propagation. • A non-probabilistic time-dependent reliability is constituted to assess response. [ABSTRACT FROM AUTHOR]

Robotic arms have become increasingly popular and widely used in various industrial applications. However, conventional control methods are not capable of adequately controlling a robotic arm in tasks that require contact with a surface. To address this issue, this study proposes a Cartesian impedance control method to control a 3-DOF robotic arm in real-time during contact with a surface. The proposed controller consists of two control loops: an inner loop and an outer loop. The inner loop utilizes a motion control method in the joint space, with the parameters of the controller being calculated through system identification. The outer loop implements Cartesian impedance control in the Cartesian space using a mass-spring-damper model. The coefficients of the Cartesian impedance control were determined based on the over-damped response with real-time applications. By selecting the inner loop in the joint space and the outer loop in the Cartesian space, the control of the robotic arm is guaranteed. The proposed method was tested in real-time, and its performance was compared with the PID with gravity compensation control in the Cartesian space. The results indicated that the proposed method was able to successfully follow reference trajectories and reduce the contact force. [ABSTRACT FROM AUTHOR]

For the visualization of pulmonary ventilation with Electrical Impedance Tomography (EIT), most devices rely on generalized reconstruction models. Yet, fixed thorax dimensions, predetermined electrode locations, and standard lung shapes lead to multiple sources of EIT imaging distortion. The following work compares reconstructions of a library model, a practical model based on landmark fitting, and a detailed model based on manual segmentation. CT images of five pigs were segmented into torso surface, electrode positions, and lung borders. Practical models were created with reduced data, registration, and fitting. Detailed models were created by using the complete segmentation data. After EIT reconstruction and tidal image calculation, the overlap of CT lung segmentation and ventilated voxel was calculated. Compared with the results of a standardized model, the practical model reached an average ventilation/segmentation-overlap difference of an additional 12 %, and the detailed model achieved an average difference of 10 %. In conclusion, the shift of reconstructed impedance towards the segmented lung region is similar in both models when compared to the standard model, while the practical model requires a considerably less amount of information. [ABSTRACT FROM AUTHOR]

The use of robotic devices for gait neurological rehabilitation is growing, however, the available options are scarce, expensive, and with high complexity of construction and control. In this way, this paper presents the HOPE-G, a novel gait rehabilitation robot consisting of an active bodyweight support system and a dual belt treadmill servo-pneumatic module. This paper focuses on the development of the dual belt treadmill servo-pneumatic module, which has tipper movement to remove the physical barrier of the patient during the swing phase of the human gait rehabilitation. The mathematical models of the servo-pneumatic system and the treadmill module are provided. An impedance controller was designed to provide a compliant walking surface for the patient. Simulation and test rig results demonstrate the servo-pneumatic system’s capability to meet the application requirements and effectively control the surface stiffness. Therefore, it is evidenced that pneumatic systems have shock absorption capabilities, making them a cost-effective solution for application in human rehabilitation tasks. [ABSTRACT FROM AUTHOR]

In this research, a new approach to safeguard against Loss of Field (LOF) in a synchronous generator, in the presence of a series compensation capacitor, is introduced. LOF can lead to detrimental effects on both the generator and the power network. Impedance-based negative and positive offset MHO relays are employed for the rapid recognition of LOE occurrences in the network. However, issues arise when a series compensation capacitor is integrated into the system, causing maloperation of the protection relays. The introduction of the series compensation capacitor alters the total impedance value, necessitating adjustments to the relay settings for precise functionality. The variation in the overall impedance of the system leads to the underreaching and overreaching of a relay. The study provides detailed explanations and comparisons of both types of MHO relays, along with their respective settings. A simulation is applied in DIGSILENT to assess the effect of series compensation capacitors on offset MHO (negative and positive) relay LOF protection. Ultimately, the article concludes by summarizing the pros and cons of both relay schemes. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ordnance Equipment Engineering is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Plastering is dominated manually, exhibiting low levels of automation and inconsistent finished quality. A comprehensive review of literature indicates that extant plastering robots demonstrate a subpar performance when tasked with rectifying defects in the transition area. The limitations encompass a lack of capacity to independently evaluate the quality of work or perform remedial plastering procedures. To address this issue, this research describes the system design of the Puttybot and a paradigm of plastering to solve the stated problems. The Puttybot consists of a mobile chassis, a lift platform, and a macro/micromanipulator. The force‐controlled scraper parameters have been calibrated to dynamically modify their rigidity in response to the applied putty. This strategy utilizes convolutional neural networks to identify plastering defects and executes the plastering operation with force feedback. This paradigm's effectiveness was validated during an autonomous plastering trial wherein a large‐scale wall was processed without human involvement. [ABSTRACT FROM AUTHOR]

In this study, a hybrid impedance control-based portable ankle rehabilitation robot that can perform therapeutic exercises for the ankle has been developed. This 1-DOF robot can perform plantar flexion and dorsiflexion movements for the ankle. The capacity of the robotic system to perform therapeutic exercises was tested with subjects. Isotonic and resistive exercises were tested with 10 healthy subjects and stretching exercise was tested with a patient. The results showed that the hybrid impedance controlled robotic system can successfully perform passive stretching, active isotonic and active resistive exercises by providing a safe human-robot interaction. Especially when a sudden resistance increase occurs in the joint, the hybrid impedance controller acts like a physiotherapist and performs the movement without damaging the joint. [ABSTRACT FROM AUTHOR]

Upper limb exoskeleton rehabilitation devices can improve the quality of rehabilitation and relieve the pressure of rehabilitation medical treatment, which is a research hotspot in the field of medical robots. Aiming at the problems such as large volume, high cost, low comfort, and difficulty in promotion of traditional exoskeleton rehabilitation devices, and considering the lightweight, discontinuous, high flexibility, and high biomimetic characteristics of tensegrity structure, we designed an upper limb bionic exoskeleton rehabilitation device based on tensegrity structure. First, this article uses mapping methods to establish a mapping model for upper limb exoskeletons based on the tensegrity structure and designs the overall structure of upper limb exoskeletons based on the mapping model. Second, a bionic elbow joint device based on gear and rack was designed, and the stability of the bionic elbow joint was proved using the positive definite matrix method. This device can simulate the micro displacement between bones of the human elbow joint, improve the axial matching ability between the upper limbs and the rehabilitation device, and enhance the comfort of rehabilitation. Third, an impedance control scheme based on back propagation (BP) neural network was designed to address the low control accuracy of flexible structures and patient spasms. Finally, we designed the impedance control scheme of the PSO–BP neural network based on a fuzzy rehabilitation state evaluator. The experimental results show that the exoskeleton rehabilitation device has good flexion motion stability and assist ability and has significant advantages in volume and mobility. The control strategy proposed in this paper has high control precision and adaptive ability and has potential application value in the field of medical rehabilitation. [ABSTRACT FROM AUTHOR]

The bilateral teleoperation system is susceptible to model parameter uncertainty and unknown disturbances in both the master and slave manipulators, resulting in instability and inaccuracies in the force and position tracking performance. To address these issues, a novel nonlinear model reference adaptive impedance controller has been designed to achieve coordinated force and position synchronization of dual manipulators. The adaptive control laws, based on sliding mode functions, have been designed to compensate for the uncertainty of the manipulator model. Furthermore, an adaptive estimation law has been employed to appraise the unknown upper bound of external disturbances. This ensures that the closed-loop model parameters of the dual manipulator converge to the reference impedance model respectively. Simultaneously, it enables the position error between the reference model response and the end-effector task space position to asymptotically converge to zero. To verify the effectiveness of the proposed controller, simulations have been conducted on the MATLAB platform and experiments on a single degree of freedom teleoperation system have been performed. The results demonstrate that the controller exhibits strong robustness and has the capability of force-position tracking ability. [ABSTRACT FROM AUTHOR]

An adaptive interactive control system based on fuzzy rules for upper limb rehabilitation robots is proposed to address the insufficient or excessive training intensity during active rehabilitation exercises for stroke patients due to their individual differences. According to the difference of muscle strength of patients with different conditions, a fuzzy adaptive impedance controller is designed, which adjusts the damping and stiffness coefficients adaptively with fuzzy inference based on human‑machine interaction forces and system errors, altering the training intensity to achieve on‑demand assistive control for rehabilitation robots. Additionally, to ensure accurate tracking of the motion trajectory during rehabilitation training, a GA-FuzzyPID controller is designed to optimize the fuzzy rule membership functions and rule base according to an improved genetic algorithm, thereby reducing the trajectory tracking error of rehabilitation robots. Finally, trajectory tracking and adaptive impedance controlling simulation experiments are conducted for the system based on Matlab/Simulink. The results show that in the trajectory tracking experiment, the trajectory error of GA-FuzzyPID controller is reduced by 55. 9% and 34. 0% respectively compared with PID controller and FuzzyPID controller, which effectively improves the trajectory tracking accuracy. Compared with the fixed impedance method, the adaptive impedance control experiment verifies the effectiveness and feasibility of the proposed adaptive interactive control system. [ABSTRACT FROM AUTHOR]

This study proposes a dual‐band bandpass‐filtering high‐efficiency power amplifier based on dual‐function dual‐band impedance control network (DBICN) and a dual‐band bandpass‐filtering impedance transformer (DBBFIT). The dual‐function DBICN is exploited to transform the optimal fundamental complex load impedance to real one, and control the second harmonic load impedances of two bands to the high‐efficiency region in the Smith chart. Besides, two transmission zeros are constructed at dual‐band second harmonics to enhance harmonic suppression. Meanwhile, an easy‐to‐design DBBFIT is proposed by utilizing filter theory to realize real‐to‐real impedance transformation, and all design parameters can be obtained by simple closed‐form analytical equations. For validation, a prototype is designed, fabricated, and measured. The measured results indicate the drain efficiencies are 61.6% and 58.3% at 1.78 and 2.42 GHz with saturation output power of 40.8 and 39.6 dBm, respectively. Moreover, the second harmonic suppressions of the two bands are 40.1 and 47.1 dBc, respectively. [ABSTRACT FROM AUTHOR]

On-orbit capturing is a crucial step in the application of dual-arm space robots, aiming to accurately grasp a moving target and avoid damage to the arms terminal parts (i.e. the end effectors) due to contact force saturation. This paper presents a synthetic control method with target sticking for on-orbit capturing using a dual-arm space robot system from the approaching phase to pre-grasping phase. In the approaching phase, an online trajectory planning method based on visual servoing is proposed to obtain the desired trajectories for end effectors in work space. Then the joint torques are designed by the inverse kinematics and inverse dynamics to track the desired trajectories. Different from most of the current research, a new sticking phase is proposed after the approaching phase and before the pre-grasping phase. In the sticking phase, a force and motion control method is designed to maintain a close relative distance between end effectors and the target, which can avoid saturation of contact forces and avoid damage to the end effectors. In what follows, an impedance control method is proposed in the pre-grasping phase to absorb the impact energy and grasp the target accurately. The synthetic control strategy integrates the controllers of all the phases mentioned above. Automatic switching among the phases is realized by using logic judgment according to the system real states, which is more consistent with the real capturing environment. Finally, numerical simulation results demonstrate the effectiveness of the proposed synthetic control scheme. The results can be applied to the trajectory planning and control of on-orbit capturing, avoiding contact force saturation and ensuring the safety of the system. [ABSTRACT FROM AUTHOR]

Owing to the high impedance transformation ratio, the Doherty power amplifier (DPA) with a large output power back-off generally has bandwidth limitations. This study proposes an asymmetric DPA with an impedance distribution and control circuit (IDCC) at the postmatching network to improve the bandwidth. The IDCC, based on a resonance circuit and a series transmission line, distributes and controls the load impedance according to the frequency so that the bandwidth of the DPA can be extended. To verify the proposed IDCC, an asymmetric DPA was designed using GaN HEMT with a power capacity of 6 W and 10 W for the carrier and peaking amplifiers, respectively. The implemented DPA was evaluated for the broad frequency band between 3.3 GHz and 3.8 GHz using a 5G new radio (NR) signal with a bandwidth of 100 MHz and a peak-to-average power ratio of 7.8 dB. A drain efficiency between 43.2% and 50.7% and an adjacent channel leakage power ratio between –23.4 dBc and –27.3 dBc were achieved at an average power level that ranged between 33.5 dBm and 34.3 dBm. [ABSTRACT FROM AUTHOR]