Dynamic analysis and optimization of a bistable pneumatic actuator for untethered soft robots

Pneumatic actuators exhibit large strain and exceptional adaptability to various environments but often demand high energy input to achieve high performance. Integrating with bistable mechanisms can substantially enhance their performance by enabling rapid state transitions, while this typically requires bulky pneumatic supply systems, limiting their use in untethered applications. To overcome this challenge, it is essential to understand the dynamic energy transfer from the pneumatic supply to the actuator, as well as the transformation between potential and kinetic energy in the snap-through operation. This study presents a comprehensive dynamic model of a bistable pneumatic actuator, incorporating both the dynamics of the pneumatic supply and the bistable snapping subsystem. An optimal parameter design scheme is derived through quasi-static and dynamic analyses of the model and extensively validated through experiments. The optimized actuator achieved a state-switching response time of ~0.15 s and maintained stable bistable operation up to ~1.67 Hz. Using the optimized bistable actuator, an untethered crawling robot was developed, achieving a maximum average crawling speed of 0.43 BL/s and a minimum estimated cost of transport (COT, a dimensionless measure of locomotion energy efficiency) of 40.8 on a cutting mat. These results demonstrate a favorable combination of locomotion speed and transportation efficiency for an untethered pneumatic soft crawling robot.