Gravity and Impedance Compensation of Body Weight Support System Driven by Two Series Elastic Actuators

Robotic devices that can support human's motions, such as exoskeletons, have recently drawn attention. Body weight support (BWS) systems are potential robotic devices that support and assist trunk motions with elaborate force control for rehabilitation and training exercises. This article presents a BWS system with 2-D motion assistance controlled by two series elastic actuators, which can perform not only weight compensation but also impedance compensation for trunk motion assistance. As the core technology of the proposed system, a wire-driven mechanism is developed that consists of a compact planetary-geared elastic actuator (cPEA), which is a series elastic actuator. All the dynamic aspects of the cPEA output torque, the tension-generating system using a winding drum, and the dynamics interacting with the BWS system are analyzed and used to design a motion-assistive controller. The functionality and ability of the proposed system are validated through experiments performed under various conditions. The results verify that the dynamic behavior of trunk motion can be assisted by the impedance control of the proposed BWS system. In particular, the inertial force required for the trunk motion can be reduced by the proposed BWS system.