Helical Kirigami-Enabled Centimeter-Scale Worm Robot With Shape-Memory-Alloy Linear Actuators

The wormlike robots are capable of imitating amazing locomotion of slim creatures. This paper presents a novel centimeter-scale worm robot inspired by a kirigami parallel structure with helical motion. The motion characteristics of the kirigami structure are unravelled by analyzing the equivalent kinematic model in terms of screw theory. This reveals that the kirigami parallel structure with three degrees-of-freedom (DOF) motion is capable of implementing both peristalsis and inchworm-type motion. In light of the revealed motion characteristics, a segmented worm robot which is able to imitate contracting motion, bending motion of omega shape and twisting motion in nature is proposed by integrating kirigami parallel structures successively. Following the kinematic and static characteristics of the kirigami structure, actuation models are explored by employing the linear shape-memory-alloy (SMA) coil springs and the complete procedure for determining the geometrical parameters of the SMA coil springs. Actuation phases for the actuation model with two SMA springs are enumerated and with four SMA springs are calculated based on the Burnside's lemma. In this paper, a prototype of the worm robot with three segments is presented together with a paper-made body structure and integrated SMA coil springs. This centimeter-scale prototype of the worm robot is lightweight and can be used in confined environments for detection and inspection. The study presents an interesting approach of integrating SMA actuators in kirigami-enabled parallel structures for the development of compliant and miniaturized robots.