Model-free adaptive variable impedance control of gait rehabilitation exoskeleton

IF 1.8 4区 工程技术 Q3 ENGINEERING, MECHANICAL
Mehdi Bakhtiari, Mohammad Reza Haghjoo, Mostafa Taghizadeh
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Abstract

This paper addresses the challenges of control and human–robot interaction for lower-limb gait rehabilitation exoskeletons. To enhance the robustness of the control against unknown but bounded uncertainties, we propose a model-free adaptive sliding mode control strategy enhanced by a variable impedance approach. The adaptation law prevents the overestimation of control gain in the presence of uncertainty and ensures the sliding condition to mitigate the effects of unknown uncertainties. The variable impedance approach also allows the impedance of the entire system to adapt dynamically over the gait cycle and maintain the accuracy of the robot in tracking desired joint trajectories. We provide a detailed stability proof using Lyapunov theory and demonstrate the finite-time convergence of the defined sliding surface. The proposed strategy does not require knowledge of model parameters, resulting in reduced computational complexity. A lower extremity rehabilitation exoskeleton model was utilized as an illustrative example. To demonstrate the effectiveness of the proposed approach, we conducted several simulations using a lower-limb rehabilitation exoskeleton model. Comparative evaluations were performed against conventional control methods such as the conventional sliding mode and computed torque controllers. The results indicate the effective performance of the proposed controller in the presence of impedance, in reducing the detrimental effects of interaction forces and model uncertainty, as well as accurately tracking the desired gait trajectories.

Abstract Image

步态康复外骨骼的无模型自适应变阻抗控制
本文探讨了下肢步态康复外骨骼的控制和人机交互难题。为了增强控制对未知但有界的不确定性的鲁棒性,我们提出了一种无模型自适应滑模控制策略,并通过可变阻抗方法加以强化。自适应法则可防止在存在不确定性的情况下高估控制增益,并确保滑动条件以减轻未知不确定性的影响。可变阻抗方法还允许整个系统的阻抗在步态周期内动态适应,并保持机器人跟踪所需关节轨迹的精度。我们利用 Lyapunov 理论提供了详细的稳定性证明,并演示了所定义滑动面的有限时间收敛性。所提出的策略无需了解模型参数,从而降低了计算复杂度。以一个下肢康复外骨骼模型为例进行了说明。为了证明所提方法的有效性,我们使用下肢康复外骨骼模型进行了多次模拟。与传统控制方法(如传统滑动模式和计算扭矩控制器)进行了比较评估。结果表明,在存在阻抗的情况下,所提出的控制器能有效降低相互作用力和模型不确定性的不利影响,并能准确跟踪所需的步态轨迹。
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来源期刊
CiteScore
3.60
自引率
13.60%
发文量
536
审稿时长
4.8 months
期刊介绍: The Journal of the Brazilian Society of Mechanical Sciences and Engineering publishes manuscripts on research, development and design related to science and technology in Mechanical Engineering. It is an interdisciplinary journal with interfaces to other branches of Engineering, as well as with Physics and Applied Mathematics. The Journal accepts manuscripts in four different formats: Full Length Articles, Review Articles, Book Reviews and Letters to the Editor. Interfaces with other branches of engineering, along with physics, applied mathematics and more Presents manuscripts on research, development and design related to science and technology in mechanical engineering.
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