A Mechanically Intelligent Crawling Robot Driven by Shape Memory Alloy and Compliant Bistable Mechanism

Abstract

Mechanical components in a robotic system were used to provide body structure and mechanism to achieve physical motions following the commands from electronic controller. This kind of robotic system utilizes complex hardware and firmware for sensing and planning. To reduce computational cost and increase reliability for a robotic system, employing mechanical components to fully or partially take over control tasks is a promising way, which is also referred to as “mechanical intelligence” (MI). This paper proposes a shape memory alloy driven robot capable of using a reciprocating motion to crawl over a surface without any use of electronic controller. A mechanical logic switch is designed to determine the activation timing for a pair of antagonistic shape memory alloy (SMA) actuators. Meanwhile, a compliant pre-strain bistable mechanism is introduced to cooperate with the SMA actuators achieving reliable reciprocating motion between the two stable positions. The SMA actuator is modeled base on a static two-state theory while the bistable mechanism is described by combining a pseudo-rigid-body model (PRBM) with a Bi-beam constraint model (Bi-BCM). Following this, the design parameters of the bistable mechanism and SMA actuators are determined according to theoretical simulations. Finally, a robotic prototype is fabricated using anisotropic friction on its feet to convert the reciprocating motion of the actuator to uni-directional locomotion of the robot body over a surface. Experiments are carried out to validate the presented design concept and the modeling methods.

Robot joint module based on universal joint configuration driven by SMA wires

“…The universal joint mechanism, which is mainly composed of forks and axis, can realize rotation in two directions at the same time, as shown in Figure 1. When SMA is used as actuators, the forms of wires [26][27][28] and coils [29][30][31] are studied more. The output displacement of SMA coils is large during a phase transformation, but the output force, efficiency, response, and cooling rate are much lower than those of SMA wires.…”

Elastic-instability–enabled locomotion

“…Our choices of geometry and actuation have yielded a polar, bilaterally symmetric morphology that arises naturally from a static elastic instability and enables stable and robust amphibious locomotion using relatively simple materials and power sources. The purely geometric instability to generate locomotion is timeindependent, complementing other systems that rely on dynamic bistability associated with snapping behavior (15)(16)(17), and marks the beginning of an exploration of other forms of morphological phenotypes that serve as primitives for soft robotic locomotion (18,19). In a biological context, perhaps it might not have been too difficult to harness this soft mode of deformation to effect directed movement in benthic environments, and thus enable the evolution of locomotion in primitive soft-bodied multicellular organisms, setting off a cascade whose consequences we now see around us (1).…”

Solar-driven bistable thermochromic textiles based on supercooling and space constraint anchoring electron transfer

“…6,7 Nowadays, the promising application field of bistable energy-saving materials has attracted considerable interest from camouflage, soft robots, and display. 8–11 Usually, the structure design of shape memory materials, 12–14 including a one-dimensional beam structure, 15–17 a two-dimensional surface bistable structure, 18,19 and the structures of three-dimensional domes, 20 is the main path to achieving bistability in soft actuators.…”