Abstract: Pneumatic soft robots have undergone significant advancements in recent years. However, the majority of robot motion control still relies on electronic computers to regulate the valves and air pumps. Despite the potential reduction in controller dependency by utilizing soft pneumatic oscillators, challenges such as low flow rates, complex manufacturing processes, and lack of adjustment ability persist. Inspired by the geckos’ spine, we propose a Spinal Bistable Oscillator (SBO) that operates without discrete components or electronic control hardware, achieving stable oscillatory motion under constant air pressure. This oscillator employs a soft control valve and lagging pin, which can switch the direction of airflow conduction based on the oscillation angle of the spine. Different types of actuators can be controlled using a series connection. In this study, the effective working range of the soft control valve, influence of the spring pretension force on the torque during oscillation, and effect of different throttle tube lengths on the oscillation frequency were investigated. Furthermore, a self-crawling robot was developed. Experimental results demonstrate that the robot can crawl at speeds ranging from 3.6 to 5.7 mm/s (or 3.1 to 4.9 body length/min) and overcome its own gravity (with a weight of 165 g) to climb vertically. The SBO proposed in this study exhibits characteristics of lightweight, low cost, high oscillation torque, and tunable frequency. It holds promise for application in joint control of future pneumatic soft robots.

Key words: Spinal bistable oscillator, Self-crawling robot, Physical intelligence, Pneumatic soft robot