A Perceptive Pneumatic Artificial Muscle Empowered by Double Helix Fiber Reinforcement

In the last decades, soft robotics has been growing rapidly as an emerging research topic, bringing new paradigms for robotic manipulation, locomotion, and human‒machine interactions. Pneumatic artificial muscle is a powerful, lightweight, rapid response with great design flexibility, making it promising for developing biological muscle-like robotic systems. The PPAM is made of a silicone tube body with double helix coil fiber reinforcement. The double helix coil fiber restricts the radial expansion of the cylinder tube to achieve extension in actuation, and monitors the muscle length change in real time by measuring its inductance. A finite element model was built to simulate the actuation characteristics of the PPAM. A theoretical formula was derived to analyze the inductive length sensing response of the double-helix coil on the PPAM. It is verified that the PPAM can sense its length change regardless of whether it is caused by active driving or external manipulation. Rigorous testing reveals that PPAM has an ultrahigh length sensing resolution of 5.9 μm in relaxed state, with a short response time of 50 ms. The self-length sensing of PPAM is hysteresis free, and highly repeatable, showing no degradation in 1000 operation cycles. In summary, the PPAM shows promising features for developing the next-generation perceptive and responsive soft robots, intelligent hybrid robots, or safer biomedical instruments.