MicroWorm: The Design, Optimization, and Control of a Modular Sub-15 Millimeter Earthworm-Inspired Robot for the Navigation of Various Terrains

This paper presents the design, optimization, and a novel feedback control loop for the first 14 mm diameter modular pneumatic soft robot that locomotes in multiple terrains by mimicking an earthworm’s motion and mechanics. This paper demonstrates two prototypes of sub-15 mm earthworm robots: The Type A robot that uses a peristaltic gait and the Type B robot that uses an anchoring gait. The validity of the proposed design will be tested through linear locomotion on three terrains: rough, smooth, and pipe. The Type A robot achieved a speed of 1.25 mm/s in a flat terrain and the Type B robot achieved a speed of 1.875 mm/s in a pipeline terrain. The robot consists of actuator modules that emulate earthworm muscles and setae through a Pneumatic Artificial Muscle (PAM)-based Elongation Module and a Radial Expansion Module (REM). Through component testing, each materially optimized Elongation Module achieved a force output of 1.68 N and 10.3% contraction. The Radial Expansion Module was able to exert up to 2.45 N of drag force, achieving a power density of 0.106 N/mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>. By adopting the peristaltic gait of an earthworm, this paper also proposes a new feedback control loop that optimizes the peristaltic gait by reducing cycle times. The robot has potential applications in exploring the complex and narrow environments in infrastructure collapse and sub-15 mm infrastructure inspection beyond just pipeline inspection. Furthermore, the compliant nature of the robot allows for safe human-robot interaction. It can also be applied to biomedical engineering, exploring narrow human intestines and minimally invasive surgery.