Low Impedance-Guaranteed Gain-Scheduled GESO for Torque-Controlled VSA With Application of Exoskeleton-Assisted Sit-to-Stand
Low Impedance-Guaranteed Gain-Scheduled GESO for Torque-Controlled VSA With Application of Exoskeleton-Assisted Sit-to-Stand
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DOI：
10.1109/tmech.2020.3032372
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发表时间：
2021-08-01
影响因子：
6.4
通讯作者：
Leonhardt, Steffen
中科院分区：
文献类型：
--
作者：
Liu, Lin;Hong, Zejun;Leonhardt, Steffen
本文研究了一种结合扰动观测器的闭环转矩控制变刚度执行器（VSA），以提高低输出阻抗。我们实现了广义扩张状态观测器（GESO），方便地测试时变VSA系统的稳定性。在我们的应用中，GESO还需要服务于低阻抗和高阻抗任务的操作。这里，最重要的方面是考虑物理刚度对输出阻抗的影响，因为VSA已经用闭环转矩控制来调节。通过互作用力矩实验，验证了采用低刚度作动器的快速动力学GESO能在人可达频率下实现低输出阻抗和稳定互作用。这些特性有助于执行低阻抗任务。当执行高阻抗任务时，需要大的扭矩命令，高刚度致动器和慢动态GESO实现高带宽和适当的跟踪性能。根据刚度值的连续可变的观测器响应是通过增益调度控制实现的。此外，本文的闭环线性参数变化系统可以被证明是二次稳定的。VSA系统然后在膝关节外骨骼上实现，用于坐到站应用。外骨骼的参考命令是根据逆动力学计算的关节扭矩。该扭矩信号也用作VSA刚度电机的参考指令。外骨骼系统的有效性进行了实验验证与一个健康的志愿者。随后，另外两名健康志愿者也成功体验了该系统。
This article investigates a closed-loop torque-controlled variable stiffness actuator (VSA) combined with a disturbance observer for enhancing low output impedance. We implement the generalized extended state observer (GESO) for conveniently testing the stability of the time-varying VSA system. In our application, the GESO is also required to serve the operation of the low- and high-impedance task. Here, the most important aspect is to consider the influence of the physical stiffness on the output impedance, because the VSA has been regulated with the closed-loop torque control. Through the interaction-torque experiments, we verify that using the fast dynamics GESO with the low-stiffness actuator can achieve low output impedance and stable interaction under the reachable frequency of a human. These properties contribute to perform the low-impedance task. When performing the high-impedance task, where a large torque command is needed, the high-stiffness actuator and the slow dynamics GESO are implemented to achieve high bandwidth and proper tracking performance. The continuously variable observer responses in accordance with the stiffness values are achieved via the gain-scheduling control. Moreover, the present closed-loop linear parameter varying system can be verified to be quadratically stable. The VSA system is then implemented on a knee exoskeleton for a sit-to-stand application. The reference command of the exoskeleton is a joint torque, calculated from the inverse dynamics. This torque signal is also used as the reference command of the stiffness motor of the VSA. The effectiveness of the exoskeleton system is experimentally verified with one healthy volunteer. Subsequently, another two healthy volunteers also successfully experienced the system.