Bundled Rotary Helix Drive Mechanism Capable of Smooth Peristaltic Movement

Herein, we focus on the design method of a robot, named Wave Wheel, capable of generating a smooth continuous peristaltic wave, which is driven by a bundled rotary helix drive mechanism. Wave Wheel mainly consists of a braided mesh tube, multiple helices that are arranged on the circumference, and spur gears. When a single motor rotates the helices, the wheel generates peristaltic waves. The proposed mechanism has some unique characteristics: (i) In principle, smooth peristalsis can be generated with a simple structure. (ii) It can be driven by a single motor and can propagate waves at high speed by infinite rotation of the shaft. (iii) The structure is a circle in the transversal plane and can be used as an omnidirectional drive wheel. The basic design method, such as waveform, velocity, and the collision condition are discussed from a geometrical point of view. Based on the model accounting for the mechanical constraints, we have designed and fabricate a prototype robot and experimentally tested it. The prototype (diameter of 57 mm) reached the top speed of the peristaltic locomotion of 43 mm/s when angular velocity of the helix was 60 rad/s. We obtained the trajectory of the mesh surface by motion capture, and the result showed that the velocity was not constant on the whole surface but periodically changed with time due to the sliding between the mesh and the helix.