Discrete element method simulating soft actuator capable of variable-stiffness using particle-jamming technology

Abstract

Soft actuator is the foundation of soft robotic system that possesses compliance to conform to contacting objects safely. The inherent softness making a soft actuator narrow its scope of output tip force and bending torque can be compensated by particle jamming technology. Particle jamming technology applies vacuumed pressure to squeeze particles to obtain variable bending stiffness. In our work, a new stiffness-variable soft actuator using jamming technology is described. The main work is to control the joint stiffness mainly introduced by self-locking function in the upper jamming chamber in each gap section between each pair of two actuating chambers. Key to meeting the objective of variable stiffness is the larger gap between the length volume ratio of upper jamming chamber and that of lower jamming chamber. To gain an understanding of the underlying principles of particle jamming technology in soft actuators, Discrete Element Method(DEM) running in ABAQUS is applied to simulate such actuator strictly based on dry-particle contacting model and Quasi static criteria. Our work offers a physical theory (dry-particle contacting model) for particle jamming technology, and DEM is firstly introduced to soft robotics to provide researchers a tool to explore the world of soft robotics with particle jamming technology. The proposed stiffness-variable soft actuator can solve the existing problems of actuators using particle jamming that it has both actuating chambers and joint-stiffness control, and it is compact so that the actuator will not resist its bending movement and it thus can embed soft sensor easily for control. It is promising to be applied onto soft wearable devices (such as soft glove, elbow orthosis) to adjust desired stiffness and then to obtain designated force performance based on the requirements of users.