Development of an Earthworm Robot with a Shape Memory Alloy and Braided Tube

Peristalsis motion like an earthworm has attracted attention in recent years because the movement is useful to progress in small spaces. An earthworm robot with a shape memory alloy, the BioMetal Helix, and a polyester braided tube was studied. The BioMetal is a fiber-like actuator-like muscle tissue; the BioMetal Helix (BMX series) was chosen to obtain good unit contraction force. The BMX, elongated at room temperature, becomes stiff and sharply contracts when a current is fed through it. For the unit expansion force, a polyester braided tube was used. The braided tube maintains a long and thin shape without compression, and when an external force presses the tube in the axial direction, it becomes shorter and thicker. When the external force is removed, the tube lengthens and becomes longer and thinner again. A prototype robot consisting of four units was developed. The robot was designed with three-dimensional computer-aided design, and the expansion and contraction timing of units was calculated through computer simulations. The simulated results closely resembled the experiments and the robot was improved by adaptation according to the simulated results. (C) Koninklijke Brill NV, Leiden and The Robotics Society of Japan, 2009