Abstract:
Bioinspired robotic actuators arise from the advances in soft materials and activation methods to achieve desired performance. Because of their intrinsic compliance, actuators built from soft materials and liquids can achieve elastic resilience and adaptability similar to their biological counterparts. Liquid metals provide great opportunities for creating an artificial muscle that generates forces at low operating voltages with scaling advantage due to dominating surface tension at small length scales. Eutectic gallium-indium (EGaIn) has been shown to have electrochemically controllable surface tension, which has been demonstrated in electric field-driven manipulation and actuation of EGaIn droplets. Thanks to their tendency to alloy with metals such as copper, surfaces of EGaIn can be locally constrained by copper pads such that the deformation of liquid metal droplets are translated into motion of copper. Such liquid-solid interaction presents an opportunity for creating arbitrary liquid metal actuators for any desired motion for robotic actuation.

In this work, we propose a generalized framework for designing liquid metal actuators by imposing wetting constraints to liquid metal droplets in various configurations in order to generate a desired motion for robotic actuation. We will show that all common actuation modalities, including linear contraction, rotation, and bending, are achievable by a specific design of liquid-solid configuration. We theorize the force-shape relationship in each design by considering the energy equilibrium of the system. From the theory we hypothesize three major advantages of the liquid metal actuators. First, the volume density of the work output of liquid metal actuators should increase as the length scale decreases, making them a favorable actuator at smaller scales and volume constraints. Second, all robotic actuation modalities, including linear contraction, rotation, bending, twisting, and multi-modal actuation schemes, are achievable through the constraint programming of liquid metal surfaces. Third, the force and motion of the liquid metal actuators are scalable by biologically inspired structures. Overall, the proposed thesis presents a liquid-based actuation paradigm by which soft robotic muscles can be created.

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Thesis Committee Members:
Carmel Majidi, Chair
Sarah Bergbreiter
Zeynep Temel
Massimo Mastrangeli, Delft University of Technology