An Affordable Extensible Soft Pneumatic Actuator with Bellows for a Mirror Therapy System

Restoration of motor functions with mirror therapy and the use of assistive robotic devices have had promising results. To integrate the two, soft robotics are used to promote soft interaction. Recently, Soft Pneumatic Actuators (SPAs) are components from the field of soft robotics that have made a surge in physical rehabilitation, made of deformable material designed to comply to the object in its environment. We implement bellows as a structure known to extend. Hand kinematics were first extracted from flexion-extension movement with motion capture as a reference for the SPA design. Four models of the SPA design were then made with varied bellow fold density (8, 10, 11, and 13 folds/25mm) and its characteristics investigated with finite element simulations. The SPA with 10 folds/25mm were found to have optimal results. The optimal model was fabricated and tested with an electro-pneumatic system, both for its performance and its usability as a device. With inverse kinematics, the SPA was evaluated by the joint angles of the finger it was tested on. It showed that this SPA design can accommodate the needs of motor restoration by elongation. This research exploits the unique capabilities of SPAs, in which SPAs are highly compliant even with decreased degrees of freedom.