Low stiffness design and hysteresis compensation torque control of SEA for active exercise rehabilitation robots

Rehabilitation robots for active exercise requires compliant but consistent torque (or force) assistance (or imposition) while passive rehabilitation robots are programmed to execute certain movements for patients. This kind of torque assistance in the rehabilitation system can be provided by using SEA (Series Elastic Actuator). In this paper, low stiffness SEA and spring hysteresis compensation are proposed for the robust and accurate torque control of the rehabilitation robot. C-DSSAS (Compact Dual Spiral Spring Actuation System) is developed to implement the low stiffness SEA and a hysteresis compensation method is proposed for robust accurate torque control. Pros and cons of low stiffness SEAs are dealt with in order to explain validity of proposed application. In addition, proposed hysteresis compensation torque controller has backlash-based polynomial model and passivity-based control. Experiments of active exercise of knee were performed wearing the knee rehabilitation device using the C-DSSAS with hysteresis control. The experimental results demonstrate its improved performance of the robot in terms of the robustness and accuracy.