A Circular Soft Pneumatic Actuator with Bi-Directional Bending Behavior

Most existing soft robotic actuators require multiple chambers to achieve multi-directional bending. In this paper, we present the design, fabrication, and analysis of a novel circular actuator. The actuator is made from a single soft material and is capable of bi-directional bending using only positive pressure in a single chamber. To accurately predict the required pressure for all bending angles, we developed an analytical model for the full range of motion - both uncurling and curling. We tested and analyzed actuators fabricated out of four types of silicone and found that the softest actuators have a bending range from the initial bending angle, 210°, to 0°, and to 225° in the other direction in 112 kPa. When constraining the actuators, we found they can create up to 5.1 N of blocked force in 210 kPa. Additionally, we demonstrate that a single circular actuator can grasp objects of various weights up to 800 g from both the inside and outside.