Development of a Miniature Thermal-Based Variable Impedance Actuator Using Thermoplastic Polymers for Scalable and Compact Robotic Applications

Variable Impedance Actuators (VIAs) represent a modern class of robotic drive systems designed for safe and effective interaction with humans and uncertain environments. These actuators offer the capability to modify their impedance in response to varying external conditions. In this work, we introduce a unique and compact thermally controlled variable impedance actuator. Distinct from conventional actuators that rely on mechanical systems to vary impedance, our design achieves this functionality by modulating the temperature of a thermoplastic polymer, Polycaprolactone. The material's viscoelastic characteristics are temperature-sensitive, becoming more rigid upon cooling and more pliable when heated. To facilitate temperature modulation, we integrate flexible thermoelectric Peltier elements directly into the actuator's structure. Initial testing indicates that, although the rate of impedance change is not rapid enough for real-time applications, the actuator's minimal weight and simple design render it highly appropriate for scenarios involving offline impedance tuning-particularly where compactness and lightweight construction are prioritized. Additionally, the architecture supports scalability, and reducing the actuator's dimensions is expected to enhance the speed of impedance modulation.