<title>Design and modeling of an active crawling robotic annelid</title>

Abstract

Presented is a novel design of an active crawling robotic annelid capable of autonomously moving in a preferred direction. This preferential motion is achieved by continuous contraction and expansion of its wormlike body just like the motion of an annelid. A set of resilient cilia mounted on the outer body of the robotic annelid act as one-way motion cilia. The basic design of the robotic crawling annelid is based on a novel fibrous shape-memory alloy (SMA) actuator which utilizes a parallel array of contractile SMA wires. The fiber bundle of SMA wires is either circumscribed inside a helical compression spring with flat heads or are in parallel with a number of helical springs, end-capped by two parallel circular plates with embedded electrodes to which the ends of the SMA wires are secured. Thus, the wires can be electrically heated and subsequently contracted to compress the helical spring back and forth. This causes the body of the robotic annelid to contract and expand. If the robotic annelid is placed on a flat surface it would tend to move in a preferred direction dictated by a set of elastic one-way cilia. On the other hand, if the robotic annelid is placed inside a long passage of round cross-sections, it would still move in a preferred direction. A design model is first presented for the dynamic response of contractile fiber bundles embedded in or around elastic springs that are either linear helical compression springs, hyperelastic springs such as rubberlike materials, and nonlinear springs such as air. The fiber bundle is assumed to consist of a parallel array of contractile fibers made from contractile SMA wires. The proposed model considers the temperature-induced contraction of the fibers due to resistive heating of the SMA wires. Results of both dynamic computer simulation and dynamics of a prototype model built in our laboratory indicate a fairly good comparison.