Development and verification of upper extremities wearable robots to aid muscular strength with the optimization of link parameters

Abstract

In this study, we developed a wearable robot operating on the external skeleton to support the movements of a weak person’s upper limbs, mainly 3-degree of freedom (DOF) of the shoulder, 1-degree of freedom of the elbow. Moreover, we applied a redundant degree of freedom to design an upper extremities wearable robot that accurately follows the movement of the upper limbs. Namely, we applied 4 driving parts to the robot to enable 3-degree of freedom for shoulders by optimizing the conformance between the links and body movement range. The optimal design which minimizes error where the robot and the body is adjusted, improves wear sensation and signal input. We attached a multi-axes load-cell to generate motion intent signals detecting the movements of the body. According to the EMG signal measurements when moving the upper limbs with the robot on, the RMS value decreased compared to that without the robot. This is due to the decrease in muscle activity, which results from using smaller muscular strength. That is to say, when comparing the same movements, the person wearing the robot used less muscular strength with the help of the robot. Also through SEF50 analysis of the EMG signals, we were able to verify that the muscle fatigue lessened.