Robot-Assisted quantitative assessment of axis misalignment of wrist joint

Axis misalignment between the human wrist joint and the robot joint could result in undesired excessive interaction force or torque. This can bring discomfort and even injuries to patients during training. According to the state of the art, few studies have focused on axis misalignment quantitative assessment of axis misalignment of wrist joint. This paper proposed a quantitative assessment method of axis misalignment of wrist joint by introducing a self-aligning mechanism (SAM) based on the wrist rehabilitation device (WReD II). The SAM can mimic the axis variation of wrist joint naturally during human-robot interaction, and the quantitative values can be recorded to assess axis misalignment. Experiments were conducted on 10 healthy subjects to measure passive wrist extension/flexion (E/F) and radial/ulnar deviation (RD/UD). The maximums, minimums and the Linear Range of Motion (LROM) of axis misalignment were all obtained. Surface Electromyography (sEMG) was also collected to ensure the consistency of passive exercises. Preliminary data indicated high reliability of the proposed assessment method with intraclass correlation coefficient ICC (2, 1) more than 0.866, and standard error of measurement (SEM) of LROM less than 1.34 mm. Future work will focus on its validity validation, paving the way for clinical applications.