Evaluation of a Circumferential Extending Antagonist Actuator in a Soft Arm.

This paper presents a novel circumferential pneumatic actuator to be used as an antagonist in soft bending arms. The design is based on a McKibben actuator, and the circular shape is inspired by octopus musculature. The performance of the presented actuator is evaluated through characterization of individual actuators, as well as experimental analysis of the actuator’s effect on the behavior of an existing soft bending arm segment. A stack of 16 circumferential actuators is capable of producing a force of 37 N when pressurized to 32 kPa and deflected to -15% strain. When the actuators are integrated into a 75 mm diameter soft arm, the arm is able to successfully lift 600 g (285% of its own mass) to 54% of the arm’s original height, which is 2.2 times the maximum load for the arm without antagonistic actuators. When the soft arm with antagonistic actuators lifted 250 g at 40 kPa, the segment returned to 101% of its original height, compared to 59% for the arm segment without antagonistic actuators. Compared to existing antagonistic systems, this circumferential actuator produces high extension strokes and high forces at pressures below 100 kPa. The presented actuator is simple to manufacture and the design is complementary to the geometry of many soft arms, which makes the actuator a suitable choice to improve the arms’ maximum load.