Dynamic modeling and simulation of inchworm movement towards bio-inspired soft robot design

Inchworms have been one of the most widely used bionic templates for designing soft robotic devices. Bioresearch has shown that muscles of inchworms exhibit nonlinear hysteresis and their body structures are with hydrostatic skeleton. But effects of these properties on their dynamic movements have not been studied yet. In this work, a dynamic model based on the principle of virtual power of an inchworm is established to examine the problem. A spring-damper model with time-varying stiffness and damping coefficients is used to model controllable nonlinear properties of the inchworm muscles. The hydrostatic skeleton is applied to the model as a constant volume constraint for each segment. Based on this, simulations of three typical movements including omega-shaped arching motion, cantilevered probing motion and surprising fast looping motion are presented. The effects of the nonlinear properties including variable stiffness and damping properties of muscles on these dynamic behaviors of inchworms are illustrated. Some inspiration for designing bio-inspired crawling robots and soft slender robotic devices is obtained. And we think this work will hopefully provide better understanding and guidance for design and control of these robotic devices.