Abstract
Peristalsis, i.e., a motion pattern arising from the propagation of muscle contraction and expansion waves along the body, is a common locomotion strategy for limbless animals. Mimicking peristalsis in bio-inspired robots has attracted considerable attention in the literature. It has recently been observed that maximal velocity in a metameric earthworm-like robot is achieved by actuating the segments using a “phase coordination” principle. This paper shows that, in fact, peristalsis (which requires not only phase coordination, but also that all segments oscillate at same frequency and amplitude) emerges from optimization principles. More precisely, basing our analysis on the assumption of small deformations, we show that peristaltic waves provide the optimal actuation solution in the ideal case of a periodic infinite system, and that this is approximately true, modulo edge effects, for the real, finite length system. Therefore, this paper confirms the effectiveness of mimicking peristalsis in bio-inspired robots, at least in the small-deformation regime. Further research will be required to test the effectiveness of this strategy if large deformations are allowed.
Highlights
The study of self-propelled locomotors exploiting friction-induced traction as a result of body shape changes, is gaining attention because of the variety of physical systems which take advantage of such a locomotion strategy
This paper aims to provide a deeper understanding of harmonic oscillations and peristalsis as result of an optimization problem rather than an a priori hypothesis
We prove that - in the regime of small deformations - peristalsis is a symmetry property of the solution to an optimization problem
Summary
The study of self-propelled locomotors exploiting friction-induced traction as a result of body shape changes, is gaining attention because of the variety of physical systems which take advantage of such a locomotion strategy. One motivation is the desire to understand biological phenomena, such as cell migration on or within solid substrates, matrices, and tissues (Alberts et al, 2002). Another motivation is the attempt to replicate these mechanisms in robotics with the idea that biomimetic constructs may outperform traditional ones when confronted with unstructured and unpredictable environments. One of the most studied biological species is Lumbricus terrestris (commonly known as nightcrawler) which is a kind of earthworm which uses peristalsis both for surface crawling and for burrowing. Each of its metameres (body segments) is endowed with longitudinal and circular
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