Biomimetic soft robotic wrist with 3-DOF motion and stiffness tunability based on ring-reinforced pneumatic actuators and a particle jamming joint

The human wrist, a complex articulation of skeletal muscles and two-carpal rows, substantially contributes to improvements in maneuverability by agilely performing three-degree-of-freedom (3-DOF) orienting tasks and regulating stiffness according to variations in interaction forces. However, few soft robotic wrists simultaneously demonstrate dexterous 3-DOF motion and variable stiffness; in addition, they do not fully consider a soft-rigid hybrid structure of integrated muscles and two carpal rows. In this study, we developed a soft-rigid hybrid structure to design a biomimetic soft robotic wrist (BSRW) that is capable of rotating in the x and y directions, twisting around the z-axis, and possessing stiffness-tunable capacity. To actuate the BSRW, a lightweight soft-ring-reinforced bellows-type pneumatic actuator (SRBPA) with large axial, linear deformation (ηlcmax=70.6