Design and control of an ergonomic robotic shoulder for wearable exoskeleton robot for rehabilitation

In this paper, we present an ergonomic robotic shoulder for upper limb exoskeleton. Most exoskeletons have been designed considering shoulder joint instantaneous center of rotation (ICR)—often termed as the center of glenohumeral joint—as fixed joint. In reality, shoulder joint ICR does move during shoulder abduction–adduction and vertical flexion–extension. The abduction–adduction causes shoulder joint ICR to move in the frontal plane, resulting from a combined motion of shoulder depression–elevation and horizontal translation, while vertical flexion–extension produces a movement of shoulder protraction–retraction. If these additional motions are not compensated in exoskeleton design, they can produce discomfort and/or pain to the robot’s wearer. While in most of the exoskeleton, shoulder joint articulation is considered as a 3-DOFs spherical joint, this research proposes a novel shoulder joint mechanism of robotic exoskeleton with two additional passive DOFs to provide ergonomic shoulder movement. The mechanisms in proposed robotic shoulder comprises of two sliders that allow above-mentioned passive movements of shoulder joint ICR. In this research, we demonstrated that the slider-1 enables shoulder joint ICR to move in the frontal plane with a quarter circular arc of 60 mm during abduction–adduction, while slider-2 allows movement of shoulder protraction–retraction as needed. Proposed mechanism has been designed to be used eventually in a 7 DOF modular robotic exoskeleton for upper limb rehabilitation. We have also applied computed torque control (CTC) to the designed shoulder. The performance of CTC shows stability and effectiveness.