Novel Design of a Passive Variable Stiffness Joint Mechanism: Inspiration From Biomechanics of Hand Joints

Passive variable stiffness at the human hand joints is shown to be critical for achieving stable and dexterous grasping and manipulation. Our long-term goal is to implement it in robotic hand joints. We introduce a novel design, using linear springs and non-circular cam, for a variable stiffness joint mechanism that mimics the passive stiffness characteristics of human hand joints. We present a methodology based on the principle of virtual work for synthesizing the cam shape in the joint. Key innovations of our design are a) human-like joint stiffness profile, b) large joint range of motion, and c) modular arrangement for varying torque range. We have built a prototype for validating our approach and the experimental results demonstrate that the proposed joint mechanism fulfills the design goals of our study.