A Testable Robust Stability Framework for the Variable Impedance Control of 1-DOF Exoskeleton With Variable Stiffness Actuator

Liu, Lin; Misgeld, Berno J.E.; Pomprapa, Anake; Leonhardt, Steffen

doi:10.1109/tcst.2021.3051716

Cited by 19 publications

(9 citation statements)

References 34 publications

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“…Jabbari et al [29] used a neural network to compensate for the unknown nonlinear dynamics of a knee exoskeleton. Oktaviani et al [35] designed a fuzzy active disturbance rejection controller for a hip and knee exoskeleton, and Liu et al [54] proposed an impedance controller with variable gains for a knee exoskeleton. The tracking performance is provided in Table 1.…”

Section: Discussionmentioning

confidence: 99%

Online Adaptive PID Control for a Multi-Joint Lower Extremity Exoskeleton System Using Improved Particle Swarm Optimization

2021

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Robotic exoskeletons have great potential in the medical rehabilitation and augmentation of human performance in a variety of tasks. Proposing effective and adaptive control strategies is one of the most challenging issues for exoskeleton systems to work interactively with the user in dynamic environments and variable tasks. This research, therefore, aims to advance the state of the art of the exoskeleton adaptive control by integrating the excellent search capability of metaheuristic algorithms with the PID feedback mechanism. Specifically, this paper proposes an online adaptive PID controller for a multi-joint lower extremity exoskeleton system by making use of the particle swarm optimization (PSO) algorithm. Significant improvements, including a ‘leaving and re-searching mechanism’, are introduced into the PSO algorithm for better and faster update of the solution and to prevent premature convergence. In this research, a 9-DOF lower extremity exoskeleton with seven controllable joints is adopted as a test-bench, whose first-principle dynamic model is developed, which includes as many uncertain factors as possible for generality, including human–exoskeleton interactions, environmental forces, and joint unilateral constraint forces. Based upon this, to illustrate the effectiveness of the proposed controller, the human–exoskeleton coupled system is simulated in four characteristic scenarios, in which the following factors are considered: exoskeleton parameter perturbations, human effects, walking terrain switches, and walking speed variations. The results indicate that the proposed controller is superior to the standard PSO algorithm and the conventional PID controller in achieving rapid convergence, suppressing the undesired chattering of PID gains, adaptively adjusting PID coefficients when internal or external disturbances are encountered, and improving tracking accuracy in both position and velocity. We also demonstrate that the proposed controller could be used to switch the working mode of the exoskeleton for either performance or an energy-saving consideration. Overall, aiming at a multi-joint lower extremity exoskeleton system, this research proposes a PSO-based online adaptive PID controller that can be easily implemented in applications. Through rich and practical case studies, the excellent anti-interference capability and environment/task adaptivity of the controller are exemplified.

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Section: Discussionmentioning

confidence: 99%

Online Adaptive PID Control for a Multi-Joint Lower Extremity Exoskeleton System Using Improved Particle Swarm Optimization

2021

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“…Liu et al, in [ 77 ], tested the stability robustness test of a variable stiffness actuator (VSA) programmed with the Gain Scheduling-based Variable Impedance Control (GSVIC). The proposed control system follows the paradigm of the variable impedance task in accordance with human intention.…”

Section: Analytical Reviewmentioning

confidence: 99%

Sensors and Actuation Technologies in Exoskeletons: A Review

Tiboni

Borboni

Vérité

et al. 2022

Sensors

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Exoskeletons are robots that closely interact with humans and that are increasingly used for different purposes, such as rehabilitation, assistance in the activities of daily living (ADLs), performance augmentation or as haptic devices. In the last few decades, the research activity on these robots has grown exponentially, and sensors and actuation technologies are two fundamental research themes for their development. In this review, an in-depth study of the works related to exoskeletons and specifically to these two main aspects is carried out. A preliminary phase investigates the temporal distribution of scientific publications to capture the interest in studying and developing novel ideas, methods or solutions for exoskeleton design, actuation and sensors. The distribution of the works is also analyzed with respect to the device purpose, body part to which the device is dedicated, operation mode and design methods. Subsequently, actuation and sensing solutions for the exoskeletons described by the studies in literature are analyzed in detail, highlighting the main trends in their development and spread. The results are presented with a schematic approach, and cross analyses among taxonomies are also proposed to emphasize emerging peculiarities.

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“…To address the limitation of SEA, variable stiffness actuator (VSA) was proposed and developed rapidly [20][21][22][23][24][25][26][27][28][29][30][31][32][33]. However, most VSAs are equipped with two actuators (usually motors) to actively adjust the stiffness and equilibrium position independently, which leads to bulky and complex structures and causes additional power consumption.…”

Section: Introductionmentioning

confidence: 99%

Design of a torsional compliant mechanism with given discrete torque-deflection points for nonlinear stiffness elastic actuator

Kang

et al. 2023

Robotica

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Owing to inherent flexibility, compliant actuator with physical elastic elements can implement compliant interactions between robot and environment. Nonlinear stiffness elastic actuators (NSEAs) use one motor to adjust position and stiffness, which improve compactness of variable stiffness actuators, and consider high torque/force resolution and high bandwidth. The primary challenge of designing a NSEA is designing a reliable compliant mechanism with a given torque-deflection profile. In this study, a general design method of torsional compliant mechanism through given discrete torque-deflection points was proposed, where a chain algorithm based on 2R pseudo-rigid-body model was used to describe the large deformation in elastic elements. Moreover, the theoretical model of stiffness of a compliant mechanism based on series flexible beams was developed. Based on the proposed model, the dimensional parameters of proposed compliant mechanism were designed satisfying the condition of the given torque-deflection points. Finally, simulation and physical experiment of the designed compliant mechanism through three given torque-deflection points are conducted to show the effectiveness of the proposed method. The designed compliant mechanism was tested and evaluated in the self-developed NSEA.

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A Testable Robust Stability Framework for the Variable Impedance Control of 1-DOF Exoskeleton With Variable Stiffness Actuator

Cited by 19 publications

References 34 publications

Online Adaptive PID Control for a Multi-Joint Lower Extremity Exoskeleton System Using Improved Particle Swarm Optimization

Online Adaptive PID Control for a Multi-Joint Lower Extremity Exoskeleton System Using Improved Particle Swarm Optimization

Sensors and Actuation Technologies in Exoskeletons: A Review

Design of a torsional compliant mechanism with given discrete torque-deflection points for nonlinear stiffness elastic actuator

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