Bundled Liquid Crystal Elastomer Actuators With Integrated Cooling for Mesoscale Soft Robots

Liquid crystal elastomer (LCE) is a promising material to develop thermally-driven soft actuators due to its high force density, large elastic strain limit, and mechanically programmable nature. However, the complex trade-off between the force generated and the response speed (i.e., cooling rate), along with the lack of systematic design guidelines necessary to design such actuators using LCE, has significantly limited its widespread adoption for soft robotic applications at the mesoscale (cm-scale). In this work, we developed thermally-driven soft actuators by bundling LCE units with integrated cooling that increased the response speed by over 400% when compared to relying only on passive cooling. We developed and experimentally validated an electro-thermo-mechanical model to predict the force and cooling rate of our actuator and established systematic design guidelines to build our actuators for different soft robotic applications. Using our proposed guidelines, we present an inchworm inspired locomotion robot with a top speed of 6 body lengths per minute. We also present a textile forearm cuff with integrated haptic feedback that can provide up to 4 mm of skin stretch feedback with a cooling rate of 1 second. Overall, the presented actuator, experimental results, and design guidelines expand the potential use cases for thermally-driven actuators in soft robotic applications at the mesoscale.