Reversible actuation for self-folding modular machines using liquid crystal elastomer

Robot and mechanism designs inspired by the art of Origami have the potential to generate compact, deployable, lightweight morphing structures, as seen in nature, for potential applications in search-and-rescue, aerospace systems and medical devices. To generate the folding of these origami-inspired designs, previous work has demonstrated several actuation methods (e.g. pneumatics, electrical motors, artificial muscles). However, it is challenging to obtain actuation for self-folding machines that is patternable, reversible, and made with a scalable manufacturing process. In this work, we use liquid crystal elastomer (LCE), as an artificial muscle to obtain tendon-driven actuation with a layer-by-layer process, to generate reversible self-folding modules using a Sarrus linkage mechanism. The Sarrus mechanism enables biaxial folding with a single unidirectional actuation, and allows pop-up designs of origami-inspired patterns such as a crane and a lily. In this paper, we demonstrate the design, fabrication, and reversible self-folding actuation of lightweight modules as well as distributed actuation of a crawler composed of the Sarrus mechanism modules. We predict the reversible fold angles given the contraction of the LCE actuation layer, and demonstrate that one single module is capable of lifting and holding 13 times and 38 times its weight, respectively. Additionally, we demonstrate traveling wave gaits in the modular crawler by sequentially actuating the Sarrus modules to achieve worm and caterpillar inspired locomotion, and investigate how this locomotion can be improved with directional friction pads. Finally, we show how a simplified model can be used to simulate the locomotion of this crawler, and compare the experimental and simulated locomotion.