Design and Analysis of a Muti-Degree-of-Freedom Dexterous Gripper with Variable Stiffness

Variable stiffness is the focus and difficulty in the research of soft robotics technology, and the variable stiffness of the multi-degree-of-freedom (MDOF) soft structure is more challenging. Inspired by the transverse and longitudinal muscle structure of octopus arms, using parallel and spiral pneumatic artificial muscles (PAMs) to imitate the transverse and longitudinal muscle structure respectively, and then the MDOF movement and variable stiffness function of a soft finger can be realized by the mutual coupling of PAMs. Based on the rigid-flexible-soft design strategy, a rigid frame is embedded in the spiral PAM, which improves the regularity and stability of the finger module movement, and provides a good hardware foundation for simplifying theoretical model. A dexterous gripper is designed based on the MDOF variable stiffness finger module, which has four grasping modes, such as non-parallel bending inward, non-parallel bending outward, parallel bending inward, and parallel bending outward. Then the kinematics model of the soft finger is established based on the assumption of constant curvature and its workspace is solved. The MDOF variable stiffness performance of the finger module is experimentally analyzed, and a multi-target grasping experiment is carried out. It is proved that the dexterous gripper has good adaptability and flexibility, and experimental results show that the load capacity of the soft gripper can be improved by this variable stiffness method. This research provides a theoretical and technical reference for the development of MODF soft structures with variable stiffness.