Mobility of a Soft Conformable Multi-Limbed Robot Actuated by Shape Memory Alloy Wires

Abstract

Soft robots promise a number of advantages over their rigid counterparts, including the ability to conform to and manipulate arbitrary geometries, conjunction acceptance through contact absorption, and an increased range of motion through deformability. Increased robustness and resilience make soft robots an interesting mobility and manipulation platform for both on-orbit and extraterrestrial applications, where topology is unknown and/or varied with highly sensitive components and materials. There they can have both geometric mapping and manipulating applications. In this paper, a possible architecture for a mobile soft robot used for sensing its environment through locomotion over a 3D surface is proposed, and an individual limb prototype is built and tested in one-g environment. A multi-limb robot architecture is proposed where each limb has more than one SMA wire actuator, allowing for additional degrees of freedom freedom when multiple SMA wires are actuated in tandem. Shape memory alloys (SMAs) are chosen as possible actuators for their better suitability for space applications, instead of traditional fluidic and pneumatic systems, to eliminate risk of losing the consumable fluid on orbit. A single limb prototype is created that consists of the SMA wire actuators, a backbone spring-shaped structure to keep the SMAs under load, a protective silicone skin, and an electrical interface. Challenges inherent to working with SMAs in creating robust mechanical and electrical interfaces, as well as providing predictability in actuation direction and force, are addressed through the limb design, and a baseline characterization of the design is presented. Experiments done to characterize the limb’s maximum displacement, load bearing ability, and longevity point to this being a promising design for further creating and testing a multi-limbed ambulating robot. A preliminary gait is discussed to show feasibility of locomotion with the achieved limb architecture and displacement.