We propose a pneumatic bending actuator integrated with a low-melting-point alloy-based variable stiffness endoskeleton that can bend at multiple points and maintain its bent shape without power supply. Local stiffness of the soft actuator can be altered by melting or hardening the endoskeleton with electric heat applied through embedded metal wires. Bending points of the actuator can be changed by selecting different points of the endoskeleton to be melted, and the bending angle can be controlled by injected air pressure. The shape of the bent actuator is maintained by hardening the alloy even when pressure is reduced to the initial state. We demonstrate that the actuator can be bent differently with only one pneumatic actuation layer by combining multipoint bending and the shape retention function, and thus the actuator can be used for lifting, holding, and unloading an object. We believe that the simple machinery of the actuator will be useful in programming complicated motions of soft robotic fingers, fins, and tentacles.
Keywords: 3D printing; pneumatic actuator; soft robotics; variable stiffness material.