Phase Synthesis for Spatial Locomotion Control of Retractable Worm Robots

Retractable worm robots possess hyper-flexibility, allowing them to work in confined spaces that are difficult for humans. However, the spatial locomotion control of these robots remains challenging due to the robots' large degrees of freedom. To address this challenge, we propose a phase synthesis (PS) scheme for retractable worm robots. The scheme combines an undulating gait inspired by caterpillars with three-dimensional movement commands. We first introduce the kinematics model and real-world prototype of our retractable worm robot, called RW-Robot, and then we introduce footstep phases to express the timing of segments' spatial movement. According to the length of movement periods, we classify the movement into short-term movements and long-term movements and compress their patterns in the frequency domain. Our PS scheme aligns the patterns according to the footstep phases to generate new gaits of spatial locomotion. We evaluate the scheme in real-world experiments, including steering and climbing a slope. The experimental results indicate that our scheme allows the RW-Robot to perform flexible spatial locomotion from simple user input.