A Hybrid Motion Stiffness Control of Variable Stiffness Actuator for Upper Limb Elbow Joints Rehabilitation

The variable stiffness actuator (VSA) can be integrated into the robotics to improve the inherent compliance characteristics of robotics for the safe physical human robot interaction (pHRI). The output stiffness of the VSA is excepted to be independently controllable during the rehabilitation training processing. Furthermore, the motion and stiffness control of VSA can be independently controlled by VSA for rehabilitation application scenario. In this paper, a hybrid motion stiffness control strategy for achieving assist-as-needed control and suitable patient-robot interaction was proposed utilizing the compliance characteristic of VSA. The elbow joint output stiffness could be adjusted by a linear mapping method to obtain controllable assistant level, which is based on the real-time bilateral position tracking error. It is noted that the linear mapping scaler could be regulated for different patient injury-levels. The preliminary experimental results show that the proposed method can adjust the elbow joint stiffness for patients according to the real-time bilateral position errors.