Coupled systems analyses for high-performance robust force control of wearable robots

Abstract

A wearable robot is constantly in contact with its user. To properly and safely perform tasks together with the wearer, such as walking and load carrying, it is important that the robot is able to control its joint torques. To enhance the performance of torque/force controllers, feedforward controllers such as velocity and friction compensation are commonly used. Although such controllers are able to enhance the torque closed-loop bandwidth, they can also significantly reduce the system's robustness. For coupled systems, such as wearable robots, the soft human skin and the compliance of the human/robot attachment pose additional challenges to the performance and stability of such controllers. In this paper we investigate the robustness issues associated with the force control on coupled systems, performing thorough analyses of the torque loop sensitivity, including how the attachment stiffness and the human impedance may influence it. Based on these analyses, we propose two potential control solutions that may improve both the disturbance attenuation and torque reference tracking on wearable robots.