Echinoderm Inspired Variable Stiffness Soft Actuator with Connected Ossicle Structure

Abstract

An echinoderm can actively modulate the structural stiffness of its body wall by as much as 10 times, using the material and structural features that make up its body, including calcite ossicles, connective tissue and interossicular muscle. This capacity for variable stiffness makes it possible to adapt to the kinematics and dynamics required to perform a given task and the surrounding environment. This characteristic can improve the ability of soft material robots, which currently have limited application because of their low load-bearing capability. This paper presents a stiffness modulation method inspired by the connected ossicle structures of echinoderms. We introduce the mechanism, structure, and stiffness variation of the proposed design with respect to different ossicle shape, interval, and elastomer. Then we built a finger-shaped stiffening structure using the proposed design, measured its stiffness according to vacuum level, and showed its load-bearing capacity under control. The proposed design was then applied to a robotic gripper, a typical device that interacts with unpredictable environments and needs variable stiffening ability.