Robot-assisted assessment method for axis misalignment of wrist joint

Abstract

Wrist rehabilitation robots have been proved to be an effective training solution to patients who lose some motor function of wrist joint. During human-robot interaction, axis misalignment between human wrist joint and robot joint may bring some discomfort and even injuries to patients. Many researches mainly focused on the analysis and validation of misalignment compensation, while the quantitative assessment of axis misalignment only attracted little attention. This paper introduced a self-aligning mechanism (SAM) on the previously developed wrist rehabilitation device and proposed a robot-assisted assessment method of axis misalignment for wrist joint by analytic geometry on the foundation of kinematic model of human-robot interaction. To validate the feasibility and accuracy of the proposed assessment method, 9 healthy subjects were invited to participate the experiments to measure rotation angle in wrist flexion/extension and radial/ulnar deviation, along with the values of self-compensation of SAM. Surface Electromyography was implemented to keep the consistency of passive motion. Experimental results showed high reliability of the axis misalignment of each subject with intraclass correlation coefficient more than 0.75, standard errors of measurement of axis misalignment less than 2.75 mm. The experiment results are consistent with previous studies well, which proves the feasibility of proposed assessment method of axis misalignment.