Analysis and Preliminary Design of a Passive Upper Limb Exoskeleton

This article reports the analysis and preliminary design of a passive, wearable, upper limb exoskeleton to support workers in industrial environments in a vast range of repetitive tasks, offering an effective strategy to reduce the risk of injuries in production lines. The system primary purpose is to compensate for gravity loads acting on the human upper limb. The proposed exoskeleton is based on 6 Degrees-of-Freedom (DoFs) kinematics with 5-DoFs for the shoulder joint (two displacements plus three rotations) and 1-DoF for the elbow. Gravity compensation is implemented with passive elastic elements to minimize weight and reduce cost. A detailed analytical tool is developed to support the designer in the preliminary design stage, investigating the exoskeleton kinetic-static behaviour and deriving optimal design parameters for the springs over the human arm workspace. By defining specific functional requirements (i.e., the user's features and simulated movements), computationally efficient optimization studies may be carried out to determine the optimal coefficients and positions of the springs, thus, maximizing the accuracy of the gravity balancing. Two different solutions for the arrangement of the elastic elements are investigated, and obtained results are validated with a commercial multi-body tool for some relevant movements of the user's arm.