Instability-based mechanism for body undulations in centipede locomotion

摘要

Centipedes have many body segments and legs and they generate body undulations during terrestrialnlocomotion. Centipede locomotion has the characteristic that body undulations are absent at low speeds butnappear at faster speeds; furthermore, their amplitude and wavelength increase with increasing speed. There arenconflicting reports regarding whether the muscles along the body axis resist or support these body undulationsnand the underlying mechanisms responsible for the body undulations remain largely unclear. In the presentnstudy, we investigated centipede locomotion dynamics using computer simulation with a body-mechanicalnmodel and experiment with a centipede-like robot and then conducted dynamic analysis with a simple modelnto clarify the mechanism. The results reveal that body undulations in these models occur due to an instabilityncaused by a supercritical Hopf bifurcation. We subsequently compared these results with data obtained usingnactual centipedes. The model and actual centipedes exhibit similar dynamic properties, despite centipedes beingncomplex, nonlinear dynamic systems. Based on our findings, we propose a possible passive mechanism for bodynundulations in centipedes, similar to a follower force or jackknife instability. We also discuss the roles of thenmuscles along the body axis in generating body undulations in terms of our physical model.