PRISM: Development of a 2-DOF dual-four-bar exoskeleton shoulder mechanism to support elevation, depression, protraction, and retraction

Functional impairments resulting from cerebrovascular accidents, such as stroke, and other neurological disorders affect a large and growing population of individuals annually. Recent increasing interest in (1) bilateral training and (2) early mobilization after injury have important implications on recovery of shoulder mobility of poststroke patients. Various robotic exoskeletons have been developed for assessment and rehabilitation, many of which have simplified the shoulder to a 3-degree-of-freedom (DOF) spherical joint, eliminating contributions from sternoclavicular (SC) and acromioclavicular (AC) articulations. In this work, a dual four-bar mechanism is developed that supports Parallel Remote Inclusion of Shoulder Mobility (PRISM) in exoskeleton robotics. The mechanism provides both SC and AC contributions to shoulder movement in exoskeleton designs that would otherwise have a stationary (i.e., rotating, but not translating) glenohumeral joint. An activities-of-daily-living dataset is used to provide target ranges of motion. A 2-DOF spatial parallelogram structure is used to impart clavicular translations of 10-15 cm to distally mounted hardware. The design uses a one-size-fits-all adjustment-free approach, and allows freedom of placement, making it compatible for integration with any existing 3-DOF robotic shoulder design.