Gravity Compensation and Design Modification of a Scapulohumeral Exoskeleton Joint

Abstract

This thesis investigates the design of PRISM (Parallel Rotation mechanism for the Inclusion of Scapulothoracic Motion) for the exoskeleton BLUE SABINO (BiLateral Upper-extremity Exoskeleton for Simultaneous Assessment of Biomechanical and Neuromuscular Output). PRISM (previously known as PANDORA) is the portion of BLUE SABINO that is responsible for providing shoulder protraction/retraction and elevation/depression, known as scapulohumeral rhythm. Shawn Trimble performed the original design work (Trimble, 2016). A key function of PRISM is gravity assistance. The joint responsible for shoulder elevation/depression must lift the entire exoskeleton. A gravity assistance mechanism should reduce torque requirements, maintain actuator placement, consider ergonomics, and improve safety. This process is split into two portions: designing spring attachments and selecting an appropriate spring. Thousands of springs are evaluated to discover the single spring that minimizes the change in force as PRISM actuates, minimizes the spring length, and maximizes the potential force in the spring. A structural goal of most exoskeletons is to minimize both mass and deflection. Components within PRISM that contribute to both mass and deflection (parts 2004, 2009 and 2010) were redesigned and evaluated through FEA within SolidWorks. The best design has a deflection of 0.2415 mm and a mass of 14.086 kg. This a 39% decrease in deflection and a 3% increase in mass with respect to the original design.masters, M.S., Mechanical Engineering -- University of Idaho - College of Graduate Studies, 2023-0