Modeling and analysis of a 5-degrees of freedom spatial parallel mechanism-based shoulder exoskeleton

Abstract

This work presented a biomechanically informed model and analysis of a 5-degree-of-freedom shoulder exoskeleton, constructed on a spatial parallel mechanism with a universal-prismatic-spherical joint configuration. The primary aim of the shoulder exoskeleton mechanism was to ensure the human shoulder’s natural movements. The mechanism incorporated a proposed anatomical mapping strategy to align the directions of the mechanism linkage movements with the physiological lines of action of the muscles, thereby expected to acquire effective support in aligning the shoulder exoskeleton with the physiological muscle lines of action. To facilitate spatial functionality, forward kinematics were developed based on Newton-Raphson for estimating the shoulder platform based on the actuators’ inputs. The forward kinematics were validated through a closed-form inverse kinematics that provided the actuator parameters, demonstrating geometric consistency with the anticipated configurations. Additionally, the work included the velocity and acceleration analyses, utilizing the Jacobian-based rigid body kinematics to maintain motion continuity. The model was assessed using anthropometric parameters representative of the upper extremity dimensions and was evaluated across three reference poses: neutral, flexion, and abduction. Simulation outcomes revealed a similar spatial motion of the mechanism with that of the shoulder movement range, showing close biomechanical alignment based on the actuator response. Moreover, static force analysis confirmed the efficient distribution of loads among the actuator legs while bearing both limb weight and substantial promise for applications in assistive robotics technology and rehabilitation in the context of shoulder exoskeleton development.