A Programmable Mechanical Freedom and Variable Stiffness Soft Actuator with Low Melting Point Alloy

Soft robotic technologies have been widely used in the fields like bio-robotics, wearable devices, and industrial manipulations. However, existing soft robots usually require multiple pneumatic/fluidic channels for pressurizing soft material segments in series or in parallel to achieve multiple mechanical degrees of freedom. In this study, we demonstrated a soft actuator embedded with Low-Melting-Point Alloy (LMPA), with which the mechanical degrees and stiffness can be selectively controlled. The LMPA was embedded in the bottom of the actuator, with the Ni-Cr wires serpentining under different positions of the LMPA layer. Through a reheating- recrystallizing circle, the actuator can self-heal and recover from the crack state. The melting process of the LMPA under different currents and different sections, the variable stiffness, the self-healing properties, and the programmable mechanical freedom of the actuator was explored through experiments. The results showed that the LMPA could be melted about 10 s under the current of 0.7 A. With the LMPA, the bending force and the elasticity modulus of the actuator could be enhanced up to 16 times and 4,000 times separately. Moreover, up to six motion patterns could be achieved under the same air pressure inflated to a typical single-chamber soft actuator. The combination of Low-Melting-Point Alloy and the soft actuators may open up a diversity of applications for future soft robotics.