Safe Tension Control of Cable-Driven Rehabilitation Devices with Elastic Cables

Robotic rehabilitation devices based on cable-driven parallel manipulator (CDPM) have been proposed and developed by many researchers in the past decade. As rehabilitation devices are usually in direct contact with trainees, safety is paramount for rehabilitation devices. It is shown that the demand of safety can be met by applying serial elastic cables to CDPM-based rehabilitation devices. However, how to maintain cable tensions in a safe range (i.e., cables are neither slack nor overstretched) is still an unsolved problem. To improve the safety of CDPM-based rehabilitation devices with elastic cables, this paper proposes a method to maintain cable tensions in a safe range. The method guarantees all cable tensions are below a preset maximum sustainable limit and above a preset minimum limit, while not affecting the originally intended operations of the rehabilitation device. The method is mathematically derived and proved. The proposed safe tension control method is a trigger-activated method based on backstepping technique.