Development of Light Weight, Low Cost Pleated Soft Actuators

Abstract Soft pneumatic actuators are a useful type of actuator for compliant structures, including inflatable robots, morphing wings, and assistive devices for astronauts. One type, Rubber Muscle (McKibben-like) Actuators (RMAs) provide high pulling forces by using pneumatic pressure to radially expand and axially contract a reinforced bladder. Similarly pleated rubber muscle actuators (PRMAs) are simpler to fabricate but produce very high tensile forces using an unfolding pleated bladder and straight axial reinforcements in the valleys of the pleats. This work primarily discusses the proof-of-concept development and testing of very low cost light duty pleated actuators that contract axially and geometrically equivalent bellows-type actuators. The pleated actuators use thin HDPE bladders, with strong fiberglass strapping tape as axial reinforcement. Axial bellows actuators of the same dimensions and materials were fabricated and tested for comparison. Many popular soft robots, such as Pneubotics use a type of bellows actuators. Testing showed that the axial pleated actuators produced 4 to 5 times greater force, at the same pressure and geometry, but only 1/4 to 1/3 the displacement of bellows-type actuators. However, the pleated axial actuators could lift a phenomenal 940X their own weight, while the bellows types, only an excellent 204X. Mathematical models were developed to predict the force, radial expansion, and axial contraction of an axial pleated actuator using specified geometry and pressure but not all is documented here. This beneficial work aids the development and testing of powerful actuators for low-cost human-compatible inflatable robots, morphing wings, and other types of low-cost integrated shape-adaptive structures.