Hybrid Impedance Research Articles

DESIGN, DEVELOPMENT AND HYBRID IMPEDANCE CONTROL OF AN ANKLE REHABILITATION ROBOT

DESIGN, DEVELOPMENT AND HYBRID IMPEDANCE CONTROL OF AN ANKLE REHABILITATION ROBOT

Hierarchical-porous acoustic metamaterials: A synergic approach to enhance broadband sound absorption

A novel design for hierarchical-porous acoustic metamaterials (HPAM) is proposed to enhance the functionality of Helmholtz-type resonators and porous materials, achieving continuous and efficient broadband sound absorption. This method can potentially eliminate absorption valley and improve the coupling strength through a synergistic energy dissipation mechanism and hybrid impedance matching behavior. Excellent sound-absorbing capability of the elaborately crafted HPAM was demonstrated analytically, numerically, and experimentally. Specifically, the results revealed an impressive average absorption coefficient of 0.77, with 73 % of the α points exceeding 0.8 across the entire test frequency range. Furthermore, the sound absorption of HPAM can be further optimized to attain ultra-broadband properties by modifying the hierarchical configuration and composite design of the porous materials. The physical mechanism is revealed through the integration of the hierarchical scaling effect and the energy-trapped mode. Numerical simulations revealed the emergence of three distinct absorption peaks at frequencies of 0.76, 1.4, and 3.6 kHz, respectively, and the effective absorption spectrum exceeded 3.4 kHz. Overall, the proposed design highlights the role of hierarchical structures and porous materials in synthesizing superior sound-absorbing properties that fullyelucidate the relationship between structure and performance,and provide an avenue for potential noise-control applications.

Hybrid Adaptive Impedance and Admittance Control Based on the Sensorless Estimation of Interaction Joint Torque for Exoskeletons: A Case Study of an Upper Limb Rehabilitation Robot

Physiotherapy is the treatment to recover a patient’s mobility and limb function after an injury, illness, or disability. Rehabilitation robots can be used to replace human physiotherapists. To ensure safety during robot physical therapy, the patient’s limb needs to be controlled to track a desired joint trajectory, and the torque due to interaction force/torque needs to be measured and regulated. Therefore, hybrid impedance and admittance with position control (HIPC) is required to track the trajectory and simultaneously regulate the contact torque. The literature describes two structures of HIPC: (1) a switched framework between admittance and impedance control operating in parallel (HIPCSW); and (2) a series connection between admittance and impedance control without switching. In this study, a hybrid adaptive impedance and position-based admittance control (HAIPC) in series is developed, which consists of a proportional derivative-based admittance position controller with gravitational torque compensation and an adaptive impedance controller. An extended state observer is used to estimate the interaction joint torque due to human stiff contact with the exoskeleton without the use of force/torque sensor, which is then used in the adaptive algorithm to update the stiffness and damping gains of the adaptive impedance controller. Simulation results obtained using MATLAB show that the proposed HAIPC significantly reduces the mean absolute values of the actuation torques (control inputs) required for the shoulder and elbow joints in comparison with HIPC and HIPCSW.

SISO impedance modeling and stability comparison of grid-connected inverter control system in different time domains

Due to the effects of grid impedance and the negative impedance from the phase-locked loop, the inverter may become unstable during the grid connection process. In order to analyze the small interference stability of grid-connected systems, the analysis method of impedance modeling came into being, which is particularly important for accurately analyzing and judging the oscillation instability of the system under weak grid. However, conventional impedance modeling methods often neglect the discrete characteristics of the control system, resulting in certain limitations when examining stability concerns. To solve this problem, a stability analysis approach based on single-input single-output (SISO) hybrid impedance model is proposed. Firstly, SISO continuous impedance model of system is constructed. Then, the discrete characteristics of the control system are considered, resulting in the derivation of a SISO hybrid impedance model. Furthermore, stable regions of two models are compared under different sampling frequencies. The results indicate that the hybrid impedance model proposed exhibits reduced conservatism, offering a more accurate assessment of stability and stability margins. This finding holds particular significance in guiding the design of controller parameters.

Hybrid impedance and admittance control for optimal robot–environment interaction

AbstractCompliant interaction between robots and the environment is crucial for completing contact-rich tasks. However, obtaining and implementing optimal interaction behavior in complex unknown environments remains a challenge. This article develops a hybrid impedance and admittance control (HIAC) scheme for robots subjected to the second-order unknown environment. To obtain the second-order target impedance model that represents the optimal interaction behavior without the accurate environment dynamics and acceleration feedback, an impedance adaptation method with virtual inertia is proposed. Since impedance control and admittance control have complementary structures and result in unsatisfactory performance in a wide range of environmental stiffness due to their fixed causality, a hybrid system framework suitable for the second-order environment is proposed to generate a series of intermediate controllers which interpolate between the responses of impedance and admittance controls by using a switching controller and adjusting its switching duty cycle. In addition, the optimal intermediate controller is selected using a mapping of the optimal duty cycle to provide the optimal implementation performance for the target impedance model. The proposed HIAC scheme can achieve the desired interaction and impedance implementation performance while ensuring system stability. Simulation and experimental studies are performed to verify the effectiveness of our scheme with a 2-DOF manipulator and a 7-DOF Franka EMIKA panda robot, respectively.

Active frequency selective surfaces: a systematic review for sub-6 GHz band

Abstract Radar absorption structures made of an active frequency selective surfaces (AFSS) have enormous potential in the aviation, naval, and other industries. In this research paper, a systematic review (SR) is carried out in the field of the AFSS to bring uncertainties, obstacles, challenges, classifications, applications, and design issues that arrive in the development of the sub-6 GHz architecture. To bias the AFSS component, as per the signal requirements, a unique set of circuits (PIN diode) is required, with ON and OFF state and a transmission zone. The bandwidth of which is determined by the bias voltage supplied. It can behave as a complicated hybrid impedance structure by providing ON and OFF biasing voltage to a PIN diode embodied in an FSS structure. Higher manufacturing costs of AFSS components, more significant complexities involved, a large amount of power consumption, and reactive impedance losses are some common limitations faced while implementing and designing an AFSS. Many envisioned problems are corrected with the AFSS design, current or creative implementations, and processing parameters are investigated progressively. It implies that new AFSSs will be an alternative to regular FSSs in the future. This paper is based on Kitchenham’s three-phase review procedure and supplements it with results, views, and recommendations from other leading experts in the field.

Robotic abrasive belt grinding of complex curved blades based on a novel force control architecture integrating smooth trajectories

Constant force control and smooth trajectory planning are regarded as key strategies to improve the surface quality of blades in robotic abrasive belt grinding. However, some technical challenges still remain: (1) external normal grinding force with time-consuming sensing, large fluctuations, and force overshoot, and (2) lack of global C2 continuous grinding trajectories. In this paper, a unified architecture is proposed to concurrently address the above issues. The main contribution of this paper is to provide a complete solution for robots to automatically accomplish the grinding of complex curved blades. The grinding process is arranged as follows: Firstly, cubic B-spline and C2 continuous quaternion spline curves are used to generate the global C2 continuous trajectory, thereby avoiding vibrations and unexpected slowdowns during grinding. Secondly, the actual grinding force is sensed based on a low-speed Fourier series trajectory and the least square algorithm. Finally, a novel force control scheme consisting of an adaptive hybrid impedance (AHI) control scheme and two nonlinear tracking differentiator (NTD) modules is proposed to overcome the problems of large force fluctuations and force overshoot. Experimental results demonstrate that the proposed solution delivers better performance. Furthermore, the surface roughness Ra of the machined blade is controlled within 0.8 μm, which meets the requirements of real-world industrial applications.

Neural network-based variable stiffness impedance control for internal/external forces tracking of dual-arm manipulators under uncertainties

The desired interaction between manipulators, objects, and environments has resulted in the internal/external force control for dual-arm manipulators being in increasing demand. Consequently, this study focused on the internal/external force tracking for dual-arm manipulator systems under external disturbances, geometries, and stiffness uncertainties which continuously lead to unsatisfactory internal force tracking. The proposed scheme is based on a two-level adaptive impedance control scheme, where the stiffness coefficient is adjusted to adapt to uncalibrated objects. An object-level hybrid impedance controller was used to regulate the external disturbance to produce a compliant response. A manipulator-level neural network-based variable stiffness impedance controller (NNVSIC) was proposed to regulate the internal force under various uncertainties. Additionally, an adaptive wavelet neural network was designed to compensate for the geometric estimation errors of the object. The variable stiffness coefficient could automatically adapt to an unknown object during the cooperation process. One advantage of the proposed method is that no prior knowledge was required. The same controller parameters could be adapted to various objects. The asymptotic stability of the proposed NNVSIC was proven via Lyapunov stability analysis. A series of experiments were conducted using two self-developed nine-degrees-of-freedom redundant manipulators. Furthermore, hard and soft objects of various geometries and stiffnesses were used to verify the effectiveness of the algorithm. The experimental results demonstrated the efficiency and superiority of the proposed controller through performance comparison with various algorithms.

Adaptive Impedance Control for Force Tracking in Manipulators Based on Fractional-Order PID

Force tracking control in robot arms has been widely used in many industrial applications, particularly in tasks involving end effectors and environmental contact, such as grinding, polishing, and other similar operations. However, these environments are not always precisely known. In order to address the force tracking control problem in unknown environments, this paper proposes a fractional-order PID adaptive impedance control strategy based on traditional impedance control. The unknown environmental information is estimated online using the adaptive impedance control algorithm, and the estimated parameters are used to generate reference trajectories to reduce force tracking errors. Fractional-order PID control is then introduced into the system to improve the control performance of the system model, and the theoretical proof of strategy stability is conducted. Finally, a comparison of four strategies was conducted through simulations: traditional impedance control, adaptive hybrid impedance control, adaptive variable impedance control, and the fractional-order PID impedance control proposed in this paper. The simulation results demonstrate that the strategy proposed in this paper exhibits robustness, virtually eliminates overshoot, and enhances response speed. In contrast, both adaptive hybrid impedance control and adaptive variable impedance control exhibit approximately 30% to 45% overshoot during interactions with the environment. Furthermore, in terms of force tracking error, the proposed strategy in this paper outperforms the above two strategies by approximately 29% to 60%, achieving excellent force tracking control performance.

Hybrid Impedance Control-based Autonomous Robotic System for Natural-like Drinking Assistance for Disabled Persons

Hybrid Impedance Control-based Autonomous Robotic System for Natural-like Drinking Assistance for Disabled Persons

A Hybrid Impedance Matching Network for Underwater Acoustic Transducers

The underwater acoustic transducer (UAT) is an electro-acoustic conversion device, which is a nonlinear reactive load. An impedance matching network is usually added between the power amplifier and the UAT. This paper proposes a hybrid impedance matching network (HIMN) combining passive impedance matching and active impedance matching. Compared with the conventional matching, this method can improve the matching frequency range and reduce matching delay. Firstly, the impedance model of the UAT is proposed, and the matching principle of the HIMN is analyzed. On this basis, the parameter design method is given within the required frequency range. Then, to reduce the matching delay of the system, a control method based on reference signal synchronization is proposed, including the reference compensation voltage calculation method and model prediction control (MPC) with two-step prediction. Finally, the simulation and experimental hardware in loop (HIL) results are given, which verify the effectiveness of the proposed HIMN and control algorithm proposed in this paper. The results show that the proposed HIMN can achieve a wider matching frequency range and shorter matching delay.

Hybrid impedance and admittance control of robot manipulator with unknown environment

Hybrid impedance and admittance control of robot manipulator with unknown environment

Design and hybrid impedance control of a new compliant wrist rehabilitation device

Over a decade, wrist rehabilitation robots have been proved to be efficient in the rehabilitation of patients with stroke or wrist injuries. Wrist rehabilitation devices compensate for deficiencies in manual rehabilitation training and reduce the workload of physiotherapists with their repetitive and gradual training necessary to rehabilitate patients with wrist impairments properly. Two design approaches have been reported in literature for wrist rehabilitation robotic devices. In one design approach, the strategy of placing the actuators, either linear or rotary, on the forearm to minimise the weight and inertia has been proposed. This necessitates a use of sophisticated transmission systems. In the other design approach, rotary motors have been proposed to be placed directly on the wrist joints, which results in a high weight and inertia. In this paper, a new 2-DOF compliant wrist rehabilitation device that can achieve the flexion-extension and radial-ulnar rehabilitation movements compliantly is proposed. In the proposed design, two series elastic actuators (SEAs), each consists of a servomotor and a custom-designed series elastic unit, are proposed to be placed directly on the wrist joints. In order to minimise the inertia and the required torques, the device is counterweight balanced by optimising the centre of mass of the device in the SolidWorks model. Based on the device dynamics modelled by ADAMS software, hybrid position and force tracking impedance control with the incorporation of a disturbance observer controller for the rotary SEA is developed for position and force tracking through the different therapeutic exercises. The disturbance observer controller is incorporated for high precision force control and robustness against exogenous disturbances. Simulation results demonstrate high performance of the proposed wrist rehabilitation device in terms of precise position and force trajectories tracking and robustness against exogenous disturbance as well as patient safety during all therapeutic exercises.

Load Flow and Short-Circuit Methods for Grids Dominated by Inverter-Based Distributed Generation

The use of power-electronics-based devices in distribution generation seeks to improve energy quality and reduce costs. The inverter-based distributed generator, that works in different operation modes, has emerged as a promising technology. In a high distributed generation penetration scenario it is important to know the voltage profile and fault information due to the uncertainty in the generator operation and the impact that have on the network. This study aims to use two proposed methods of analysis: for power flow, based on backward/forward sweep method, and short-circuit, based on hybrid impedance matrix, that considers the inverter operation modes and represents each generator as a voltage-controlled current source. The chosen network is the IEEE 34-Node Test Feeder with a generator on each load per phase. The voltage profiles obtained will be validated with a Simulink/Matlab phasorial model. The results show an average error of 2.39% and a gain in voltage profile processing time of 2185.24%, making its use consistent for larger systems.

Adaptive hybrid impedance control for dual-arm cooperative manipulation with object uncertainties

In this paper, a novel adaptive hybrid impedance control for a dual-arm robot is proposed to cooperatively manipulate unknown objects. The proposed adaptive hybrid control scheme could be employed to improve the control performance of motion tracking and internal force regulation when dual-arm cooperative robot grasp an unknown object. Along with the analysis of human motion in the process of transferring, the controller has a master–slave structure in three levels: the first level is an absolute-relative motion controller satisfying the closed-chain constraints; the second level introduces an adaptive impedance control with variable stiffness to regulate the internal force; the motion and force control signals are fused in the third level with a select matrix. The controller uses the forces sensed at the end-effectors to compute the internal force with only kinematics, and the dynamics of the object is not required. To verify the effectiveness of the algorithm, a dual-arm robotic system is set up with two UR5 arms and the experimental results illustrate the performance and feasibility of the proposed control strategy.

Optimal detumbling strategy for a non-cooperative target with unknown inertial parameters using a space manipulator

Capturing tumbling target is considered as one of the greatest challenges in on-orbit service missions due to tumbling motion and parameter uncertainty of the space non-cooperative target. The tumbling motion of the target should be attenuated as quickly as possible before grasping to avoid the unexpected collisions and possible damages to the space manipulator or the target, which means the shortest-time detumbling trajectory is necessary. In many studies about the optimal detumbling trajectory planning the inertial parameters of the target have been assumed to be accurately known, which is usually difficult for a non-cooperative target so that parameter identification is needed before planning a optimal detumbling trajectory. In this paper, a novel strategy for parameter identification and detumbling of a tumbling target by a space manipulator is proposed. The strategy includes two phases. First, unknown inertial parameters of the target are identified in finite-time by a new estimation method with the assumption of interval excitation (IE), which relaxes the strict persistent excitation (PE) condition required in most prior studies. Second, the shortest-time detumbling trajectory of the tumbling target is generated by formulating a time-optimal control problem (OCP) in which the target attitude bounds and the limitations of the contact force as well as the relative velocity between the space manipulator and the target are represented as extended dynamical sub-systems and saturation functions. Then, the Calculus of Variations method is used to solve the OCP to obtain a high accuracy solution. During two phases, the contact force between the space manipulator and the target is utilized to generate external moment for identifying the inertia parameters of the target and detumbling the target. Meanwhile, a unified hybrid impedance control framework is applied to the space robot to track the desired contact force and motion trajectory. The whole strategy is verified by a space manipulator capturing a tumbling target, and numerical simulations demonstrate the effectiveness of the proposed methods.

Neural network-based adaptive hybrid impedance control for electrically driven flexible-joint robotic manipulators with input saturation

In this paper, a neural network (NN)-based adaptive hybrid impedance control (AHIC) scheme is proposed for the electrically driven flexible-joint robotic manipulators (EDFJRM) with input saturation, where the hybrid impedance is designed to obtain the reference trajectory by combining the position/force control with the impedance control. The proposed scheme integrates hybrid impedance control into backstepping technique, where a smooth saturation function is employed to facilitate input saturation. Moreover, the reference input trajectory of the robot is obtained by different target dynamics in the free space and the constrained space, and NNs are employed to approximate the saturation errors term, uncertain parts and external disturbances. In this way, the control objective of the position and force tracking can be realized in both free space and constrained space. Lyapunov stability analysis shows that all the signals in closed-loop system are guaranteed to be uniformly ultimately bounded, and the steady-state tracking errors of the position in the free space and the force in the constrained space are converged to zero. Finally, simulation results of two-rigid-link EDFJRM demonstrate the effectiveness of the proposed NN-based AHIC scheme.

Acoustic and thermoacoustic properties of an additive manufactured lattice structure.

With the advent of additive manufacturing, lattice structures can be printed with precisely controlled geometries. In this way, it is possible to realize porous samples with specific acoustic and thermoacoustic characteristics. However, to this aim and prior to the manufacturing process, it is fundamental to have a design tool that can predict the behaviour of the lattices. In the literature, Luu, Perrot, and Panneton [Acta Acust. United Ac. 103, 1050 (2017)] provide a model to characterize transport parameters of fibrous material with a certain fiber orientation with respect to the direction of wave propagation. In this work, finite element numerical simulations are used to improve their model in order to compute the thermoviscous functions of lattice structures composed of cylindrical struts arranged in Tetragonal Body Centred cells. New correlations for transport parameters are suggested, which are finally coupled with the semi-phenomenological model of Johnson-Champoux-Allard-Lafarge to obtain the complex density and bulk modulus of the equivalent fluid. These results are compared with the measurements carried out on two 3-dimensional-printed samples with hybrid impedance tube techniques.

Novel fractional hybrid impedance control of series elastic muscle-tendon actuator

Purpose This paper aims to develope a novel fractional hybrid impedance control (FHIC) approach for high-sensitive contact stress force tracking control of the series elastic muscle-tendon actuator (SEM-TA) in uncertain environments. Design/methodology/approach In three different cases, the fractional parameters of the FHIC were optimized with the particle swarm optimization algorithm. Its adaptability to the pressure of the sole of the foot on real environments such as grass (soft), carpet (medium) and solid floors (hard) is far superior to traditional impedance control. The main aim of this paper is to derive the dynamic simulation models of the SEM-TA, to develop a control architecture allowing for high-sensitive contact stress force control in three cases and to verify the simulation models and the proposed controller with experimental results. The performance of the optimized controllers was evaluated according to these parameters, namely, maximum overshoot, steady-state error, settling time and root mean squared errors of the positions. Moreover, the frequency robustness analysis of the controllers was made in three cases. Findings Different simulations and experimental results were conducted to verify the control performance of the controllers. According to the comparative results of the performance, the responses of the proposed controller in simulation and experimental works are very similar. Originality/value Origin approach and origin experiment.

A Hybrid Impedance Controller for Series Elastic Actuators to Render a Wide Range of Stable Stiffness in Uncertain Environments

Accurate and wide-range stiffness control is important for safe human-robot interaction. Accurate stiffness control can be better achieved using series elastic actuators (SEAs) than conventional rigid actuators. However, the stable range of virtual stiffness rendered by SEAs is limited by the stiffness of the actual spring, which cannot be too high in order to ensure good force control accuracy. Adding a virtual damper or derivative gain can increase the stable range of virtual stiffness, but the stable range would highly depend on the environmental stiffness. To relax the stiffness limitation in uncertain environments and explore more merits of SEAs, this letter proposes a hybrid impedance controller. This new controller linearly combines the spring force feedback and inertia force feedback. The stable range of virtual stiffness can be easily increased to ten times the actual spring stiffness with minimum effect on the force control accuracy. Unlike typical impedance controllers, the environmental stiffness can be used to raise the stable range of stiffness and hence the robustness of the controller can be ensured. Experiments will be provided to verify the hybrid impedance controller. We expect that the hybrid impedance controller can be used for SEAs in unstructured environments to provide a wide range of virtual stiffness.