Design, Characterization, and Testing of a Rigid Chain Actuator for an Under-Actuated, Tendon Driven Hand Exoskeleton

Abstract

Tendon driven hand exoskeletons are compact, and light weight often implemented either using a ball screw or a spool drive. Spool drives, however, have low reliability, and efficiency due to friction and wear while ball screws can become bulky depending upon the required stroke length. Rigid chain actuators, which operate in a similar manner to rack and pinion gears are compact, low maintenance, and have good mechanical efficiency. But are predominately used in the large-scale material handling equipment or push-pull applications, and have seen limited use in the wearable robotics space. Here we present the design of an under-actuated tendon-based hand exoskeleton that incorporates a rigid chain-based actuator. We performed mechanical characterization of the actuator, compared the size of the actuator to other tendon-based actuation approaches, and evaluated the grasping capabilities of the overall hand exoskeleton. Compared to a ball screw-based approach the rigid chain actuator represented a 49.1% decrease in volume although the current prototype was larger than spool drive approaches. The device also generated forces that were sufficient enough to enable grasping of a wide range of light objects. Overall, the hand exoskeleton and rigid chain actuator present a promising solution to achieve the reliability and accuracy of a ball screw-based tendon actuator in a more compact form factor. Further research is necessary to optimize the design of both the actuator and the hand exoskeleton system in terms of total volume and push-pull capabilities.