Kinematics and Dynamics of a Biologically Inspired Index Finger Exoskeleton

Rehabilitation of upper extremity, especially hands, is critical for the restoration of independence in activities of daily living for individuals suffering from hand disabilities. In this work, we propose a biologically-inspired design of an index finger exoskeleton. The design has passive stiffness at each joint with antagonistic tendon driven actuation allowing for (1) improved kinematic and dynamic compatibility for effective therapy; and (2) conformation of exoskeleton and finger joints axes of rotation. We present a kinematics and dynamics model of the coupled index finger-exoskeleton system that incorporates human-like passive torques at the metacarpophalangeal (MCP), proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints. We carry out simulations using this coupled system model to study the role of passive stiffness on workspace and tendon forces, actuator force and displacement requirements, and reaction forces and moments acting at the finger joints for an index finger flexion-extension task. Results show that accurately modeling the coupled system can help in optimizing the design and control of the device, thus, exploiting its passive dynamics for effective functioning.