A Variable Stiffness Soft Robotic Gripper with Low-Melting-Point Alloy

In this paper, we present the design, fabrication and the function of a soft actuator embedded with Low-Melting-Point Alloy (LMPA). By melting the metal via joule heating, the phase of the metal transformed from the solid state to the liquid state, by which the stiffness of the actuator changed over nearly an order of magnitude. Through a reheating-recrystallizing circle, the actuator can self-healing and recovered from the crack state. The melting speed under different electrical currents was measured. Besides, two experiments were conducted to investigate the self-healing property and stiffness enhancement of the actuator. The LMPA could be melted within 40 seconds. By using three actuators embedding with LMPA, we implemented a soft gripper with variable mechanical stiffness. Experimental results show that the actuator not only has the self-healing property but also enhance the mechanical stiffness compared to the no-LMPA actuator (control). While the LMPA was under solid (recrystallized) state, the bending stiffness of the actuator increased up to 3.5 times over that of the control; while the pull-off force of the gripper increased 6.5 times. The LMPA provide the soft robots with capacities of variable mechanical stiffness, and the self-healing provide a more robust capability for the system.