Untethered Soft Rolling Robot Based on Pneumatic-Tendon Coupled Actuation

The Soft Rolling Robot (SRR) excels in adaptability across diverse natural terrains, demonstrating significant flexibility, environmental interaction capabilities, and impact resistance. However, the development of Untethered Soft Rolling Robots (USRR) faces challenges in locomotion speed and controllability due to the limited load-carrying capacity of untethered systems. This study introduces a novel actuation system that combines pneumatic actuation with tendon actuation to enhance USRR performance. We propose a pneumatic-tendon coupled actuated telescopic soft leg structure that uses tendons for precise position and velocity control, while concurrently adjusting stiffness through air pressure modulation. This system interconnects the gas circuits of multiple soft legs, enabling internal gas circulation during rolling motion. An octagonal planar rolling robot with a radial skeleton structure was designed and fabricated to validate this actuation method. Theoretical analysis and experimental research have shown that the interconnected gas circuit design can significantly reduce tendon tension in actuation of soft legs and enhance their output force and range of motion. Performance tests on the USRR reveal excellent speed regulation capabilities, achieving a maximum speed of 0.19 m/s, and demonstrate adaptability to various terrains including slopes, steps, grasslands, gravel roads, and shallow water.