Design and analysis of a novel shoulder exoskeleton with mismatch compensation capability

Abstract Most exoskeletons are designed with the shoulder joint’s instantaneous center of rotation (ICR) in mind as a fixed joint, often also known as the center of the shoulder joint. In fact, shoulder ICR changes during shoulder abduction–adduction and flexion–extension. Abduction–adduction causes the ICR to move in the frontal plane, which is caused by the joint movement of the shoulder joint, including depressed elevation and horizontal translation, while the flexion–extension movement of the sagittal plane produces the shoulder extension movement. If the change in shoulder ICoR movements is not compensated for in the exoskeleton design, they can create discomfort and pain for the robot’s wearer. Although conventional exoskeletons typically treat the shoulder joint as a three degree of freedom spherical joint, this study incorporates a more sophisticated understanding of shoulder kinematics. The developed scapulohumeral rhythm compensation mechanism successfully compensates for shoulder joint motion, with simulation results confirming kinematics that closely match ergonomic shoulder movement patterns. First, the complex kinematics of the shoulder joint are analyzed. To meet the demand for mismatch compensation, a shoulder exoskeleton based on a winding mechanism is designed. A mismatch compensation model is established, and theoretical analysis and simulation verify that the designed shoulder exoskeleton has a mismatch compensation function. While solving the mismatch problem, the human–machine coupling model is established through OpenSim software. The simulation results show that the designed exoskeleton has a good assisting effect from the perspective of muscle force generation and shoulder torque.