Bio-inspired tendon-driven finger design with isomorphic ligamentous joint

Abstract

This paper suggests a novel type of bio-inspired finger design in that the joints that compose the finger mimic the features of human finger joints. They have isomorphic structures but different movements, further, there is no friction between bones in the joint, and the joint has a compliance property in all the directions thanks to the elasticity of ligaments. In the proposed joints, a number of strings substitute the articular capsule and collateral ligaments based on the concept of a tensegrity structure. Ultimately, a compliant robotic finger based on the ligamentous structure of the human is proposed. In addition, adjusting the fixed positions of the strings without any structural change, the joint can have a rest position yielded from the elasticity of the strings, and thereby, the tendon is only needed to drive the finger. Especially, since the finger does not have any mechanical rotating parts such as bearings and bushes, it can freely operate even underwater. As the proposed finger design is a type of underactuated mechanism, it is able to realize active flexion, passive extension, and passive adduction and abduction.