H-PhIEx A: A Compact SEA-Based Hand Exoskeleton with Active Metacarpophalangeal Joints

Hand injuries have a considerable impact on daily life, requiring extensive rehabilitation efforts in both clinical and home environments. Portable wearable devices show promise in addressing this need., rendering rehabilitation repeatable., measurable., and challenging at the same time. This paper presents a novel hand exoskeleton designed to assist the thumb and index metacarpophalangeal (MCP) joints in flexion- extension movements while keeping the thumb free or locked in adduction-abduction and circumduction movements. The actuation units are based on a series-elastic architecture (SEA). Transmission chains include self-aligning mechanisms to avoid undesired parasitic forces on the user's musculoskeletal system. The device has a total weight of 190 g and can exert a maximum torque at the MCP joint up to 0.9 Nm. The lockable thumb chain enables users to lock the thumb in various configurations while assisting the flexion/extension motion. The device has been tested on the bench in position and admittance control., and with a human subject using electromyography-triggered flexion/extension movements. Results show a root mean square error in position control below 0.5 deg in all experimental conditions. The results prove that the developed hand exoskeleton can be used in rehabilitation applications.