Bio-inspired 4-DOF soft hand rehabilitation device for restoring versatility and physiological movements

Abstract

Recently, many soft wearable robotic devices have been developed to help rehabilitation of the motor function of the hand for patients post-stroke. However, current soft robotic devices are mostly limited to simple opening and closing of the fingers and thumb, while the versatility of the hand, grasping and manipulating objects with various postures, is essential for accomplishing daily activities for living and has become more important recently by the increased use of electronic devices in daily life (i.e. smartphones). Also, it is difficult to adjust to between-subject variation of joint impedance of patients with a simplified actuation design, which could lead to biomechanically unnatural joint kinematics with hyperextension. In this dissertation, we propose a dexterous soft hand rehabilitation device that could provide versatile tasks and biomechanically comfortable kinematics by implementing a novel agonist-antagonist actuation mechanism, bio-inspired from the structure and orientation of the extrinsic and intrinsic muscle-tendon units of the human hand. The interconnected structure between muscle-tendon units distributes the tendon force to multiple points of the finger and thumb, preventing unnatural extension, and the combined actuation of extrinsic and intrinsic tendons enabled adjustments to varied joint impedance and provide various postures with physiological kinematics. The proposed device could achieve various grasping tasks by the enlarged workspace of the thumb by assisting 2-DOF motion (opposition/reposition and flexion/extension). The actuation was conducted with a cable-actuated agonist (active actuation) and elastomer antagonist (passive actuation) to increase the assisted degrees of freedom while maintaining the compactness of the device. The kinematic and kinetic performance of the proposed device design was experimentally evaluated with chronic stroke survivors. The proposed device was able to restore normal kinematics and kinetics for patients with various joint impedance conditions, and various grasping tasks were achievable with the assistance, which are important for effective functional rehabilitation of the hand.