Kineto-Static Analysis of a Wrist Rehabilitation Robot with Compliance and Passive Joints for Joint Misalignment Compensation

Abstract

In this paper, we present a kineto-static analysis on a wrist rehabilitation robot to compensate for joint misalignment between human and robot joints. Since joint misalignment has proved to generate user–device interaction forces, which reduce the comfort and safety of the wearable devices and limit the user’s willingness to use it. The use of compliance and the addition of passive joints for joint misalignment compensation are discussed. In order to study the effect of the initial offset, we find that the initial offset in the direction perpendicular to the forearm causes a larger unwanted force. In addition, the use of the softest compliance can minimize unwanted force by 38% compared to the case without compliance. Furthermore, the effect of the addition of passive joints to the exoskeleton is investigated. From the analysis results, the soft part of the human being is regarded as a passive joint with the ability to compensate for joint misalignment. Moreover, the influence of the soft characteristics of human limbs should be considered when designing a wearable robot. This soft property, causing the movement of the braces, results in reducing the angular range of the wrist. Through the analysis results, we provide effective ideas for joint misalignment compensation to fulfill a comfortable and safer robot design.