Stiff-switch: Finite Stiffness Control Method Using a Thermo-Mechanical Structure and a Low-voltage Pinpoint Heater

Abstract

We propose Stiff-switch, thermo-mechanical stiffness control method. Phase change material (PCM) is often used to control stiffness by heat. However, high-voltage requirements and slow heating speed still limit the practical application. We present new thermo-mechanical structures that can efficiently control the stiffness by heating the minimum portion of the structure where stress is concentrated. We employed phase change materials in an H-beam structure and mechanical linkage joint to control stiffness against linear stress and torque, respectively. Additionally, we investigated carbon-based electrically heating paint as a novel joule heating method to achieve fast temperature control speed while requiring low voltage. We demonstrate the proof-of-concept by deploying a PLA filament and hot melt as phase change materials and experimentally show the wide-range stiffness control capability and robust shape-recovery function from large deformation. Finally, we discuss the possible future application scenario for airless tires, tactile tablet pens, robot hands, and finger exoskeletons.