Preliminary Evaluation of a Performance-based Stiffness Control for Upper Limb Elbow Joints Rehabilitation

For post-stroke patient, the interaction force between the impaired limb and the rehabilitation robotic system is an important issue for patient safety in clinical treatment. The compliance control scheme can be achieved by the rehabilitation robotics with variable stiffness actuator (VSA) for the safe physical human robot interaction. The output stiffness would be adjusted independently via variable stiffness actuator during the rehabilitation training processing. In addition, when the stiffness changing, the different impedance characteristic can be realized according to the environmental applied force. The compliance control of VSA can be utilized into the rehabilitation application scenario for improving the training safety. In this paper, a performance-based stiffness control strategy for maximum the rehabilitation effect and increasing the patient participant was proposed utilizing the compliance characteristic of VSA. The elbow joint output stiffness would be regulated according the patient's training performance which will be determined using the real-time position tracking error. It is noted that the training performance should be different to adapt the patient individual-specific. Therefore, an acceptable position tracking error range should be set in advance for the suitable training plan. The experimental results show that the proposed method can adjust the elbow joint stiffness for patients according to the real-time training performance.