A Miniaturized Variable Stiffness Soft Manipulator With a Customizable LMPA Pattern

Safe human-robot interaction and excellent motion flexibility ensure a wide range of potential applications for soft robots in industry and medicine. Although many efforts have been made to empower soft robots with variable stiffness, solutions for miniaturization, wide-range, and rapid-response stiffness have yet to be realized. To maintain the combination of motion flexibility and operation stability, in this work a soft variable stiffness manipulator with a diameter of 10.7 mm based on a low melting point alloy (LMPA) solution is proposed. Inspired by reinforced concrete structures, LMPA structures can be freely designed and optimized by a novel 2D to 3D fabrication method for the first time. The crossed pattern LMPA was selected as the variable stiffness skeleton of the manipulator through comparative experiments. Under hot and cold water circulation, the rigid-soft transition time is reduced to 10–15 seconds due to structure optimization. Tests have shown that the omnidirectional steering manipulator can easily be bent over
$180^{\circ }$
with high repeatability (standard deviation of
$1.37^{\circ }$
) in the soft state and lock the shape at any bend angle with a stiffness of about 415.45 N/m in the rigid state. The rapid and wide variation in stiffness of the soft manipulator can be used as a small platform for minimally invasive surgical tools in confined spaces.