Harnessing bistability for directional propulsion of soft, untethered robots

Abstract

In most macroscale robotic systems, propulsion and controls are enabled through a physical tether or complex onboard electronics and batteries. A tether simplifies the design process but limits the range of motion of the robot, while onboard controls and power supplies are heavy and complicate the design process. Here, we present a simple design principle for an untethered, soft swimming robot with preprogrammed, directional propulsion without a battery or onboard electronics. Locomotion is achieved by using actuators that harness the large displacements of bistable elements triggered by surrounding temperature changes. Powered by shape memory polymer (SMP) muscles, the bistable elements in turn actuate the robot's fins. Our robots are fabricated using a commercially available 3D printer in a single print. As a proof of concept, we show the ability to program a vessel, which can autonomously deliver a cargo and navigate back to the deployment point.

Bio‐inspired Design and Additive Manufacturing of Soft Materials, Machines, Robots, and Haptic Interfaces

“…[31,32] Shapememory polymers (SMPs) deform from ag lassy state to an elastic state on heating, and stay in the deformed configuration permanently.T his irreversibly programmable feature allows their shape to be modified arbitrarily to construct complex active structures. [33][34][35][36] Another important class of thermally responsive polymer is liquid-crystalline elastomers (LCEs), where self-organizing liquid-crystal mesogens are incorporated into an entropically elastic polymer network. Upon heating above ap hase-transition temperature (e.g.…”

Multistable Thermal Actuators Via Multimaterial 4D Printing

“…Multistable structures do not need additional energy to maintain their stable states. [15,16] Rotational multistable structures could be very useful for implementing certain sophisticated actuation (e.g., changing the moving direction of soft robots with a predesigned angle or changing the folding angle of a drone's wing). Especially, they remain stable over time without energy consumption because they are in stable energy positions.…”

“…Multistable actuators could be very useful, for example, for the motion control of soft robots. [15,16] Rotational multistable structures could be very useful for implementing certain sophisticated actuation (e.g., changing the moving direction of soft robots with a predesigned angle or changing the folding angle of a drone's wing). In general, rotational structures can be used together with linear, translational ones to produce more sophisticated movements.…”

“…[10][11][12][13][14][15][16] An SMP can have arbitrary temporary shapes and return to a memorized, permanent shape again upon a proper external stimulus (usually heat or light). In 4D printing, components created by 3D printing can be transformed in shape to realize active structures in reaction to environmental stimuli such as heat, moisture, light, or pH value.…”

“…For example, shape memory polymers (SMPs) can be employed as an active material in 4D printing, and this could be useful for a wide range of potential applications in actuators, switches, sensors, deployable structures, soft robotics, and medical devices. [10][11][12][13][14][15][16] An SMP can have arbitrary temporary shapes and return to a memorized, permanent shape again upon a proper external stimulus (usually heat or light). [17,18] The 4D printing of SMPs typically involves 3D printing of an original shape and then thermomechanical programming at high temperature (usually above the glass-transition temperature T g ).…”