A novel serial–parallel hybrid worm-like robot with multi-mode undulatory locomotion

Abstract

Inspired by the morphology characteristics of segmented worms and the combination properties of serial–parallel structures, a novel serial–parallel hybrid worm-like robot with nine degrees of freedom (DOFs) is proposed. This robot is constructed of two symmetrically arranged 3-RPS parallel mechanisms (PMs) with single-DOF expandable platforms. According to the retrograde peristaltic wave that the locomotion mechanism of segmented worms and the kinematics of the robot, four basic gaits of three undulation modes are developed, including start-up adjustment gait and straight-going gait of rectilinear mode, turning gait of lateral undulation mode, and stair-climbing gait of vertical undulation mode. Based on which, the locomotion performance of the robot on four typical terrains including the stair, the slope, the gap, and the narrow passage is discussed. Then the corresponding locomotion controller is designed. Finally, a prototype is manufactured, the experiment results show that the robot can move in an arbitrary given direction for any given distance, and the practical locomotion performance coincides to the theoretical analysis.