Realization and experimental test of a body weight support unit for simultaneous position tracking and gravity offloading

Abstract

Body weight support (BWS) is important in rehabilitation robotic systems for patients with locomotion difficulties. We are building an active body weight support (ABWS) system that allows patients to move freely in the three dimensional Cartesian space and provides well-controlled supportive force against gravity. In the BWS unit, both the cable position and tension force on the cable should be controlled simultaneously, resulting in an underactuated system. A cabledriven series elastic actuator (SEA) structure has been designed to address this challenge. The elastic element couples the cable tension and displacement, and thus converts the underactuated control problem into the control of the elastic element's deformation. A cascaded control strategy was designed. Finally, experiments with the humanoid robot NAO were conducted and the results validated the feasibility of the BWS unit and the efficacy of the cable tension control strategy.