Controls for the shoulder mechanism of an upper-body exoskeleton for promoting scapulohumeral rhythm

We present a control strategy for the shoulder mechanism of an upper-body exoskeleton, called HARMONY, to assist in achieving coordinated motion at the shoulder complex. HARMONY is equipped with a novel mechanism that supports the natural mobility of the human shoulder, including the scapulohumeral rhythm, which is the coordinated motion between the upper arm (humerus) and shoulder blade (scapula). The key idea of the control strategy is to introduce a coupling torque based on impedance corresponding to a reference trajectory of the rhythmic motion after compensating for gravity force from the robot. This control scheme allows for the variability in the rhythmic motion, while gently providing a force to facilitate the scapulohumeral rhythm when the shoulder is out of the normal coordinated motion. Experimental results show that the coupling torque safely induces the rhythmic motion of the shoulder girdle in the presence of abnormal coordinated motion.