Development of the extension type pneumatic soft actuator with built-in displacement sensor

Abstract

This paper proposes a method for a soft pneumatic actuator to measure its displacement without external position sensors, which are usually difficult for washing and sterilization. Medical systems and food industry desire disposable, precise, and human-friendly actuators. The method utilizes a metal spring which covers the cylindrical soft actuator, as the inductance of the spring changes according to the length of the metal spring. The spring also restrains the radial expansion of the actuator during pressurization. This actuator is lightweight, weighing about 30 [g] and is washable, sterilizable and disposable. An approximation of the relationship between the frequency and position was obtained, and its validity was evaluated through experiments. The displacement sensing of the proposed actuator has good accuracy for use in medical robots and other robots working with humans.