Estimating stiffness and damping of a novel variable impedance actuator based on adjusting viscoelastic properties of thermoresponsive polycaprolactone in harmonic motions

This paper presents a methodology to estimate the stiffness and damping of a novel variable impedance actuator designed to adjust its effective impedance by regulating the temperature of a thermoresponsive polymer, Polycaprolactone (PCL). The actuator's PCL temperature is controlled using embedded flexible Peltier elements. However, due to the absence of internal temperature sensors, it is necessary to develop a reliable estimation method for effective stiffness and damping during harmonic motion. The proposed approach leverages experimental data, including trajectory measurements and phase delay analyses, to estimate these parameters under varying temperatures and frequencies. Experimental results demonstrate that stiffness and damping can be effectively modulated by altering the PCL temperature, with higher temperatures leading to decreased stiffness and damping due to reduced viscoelasticity. Additionally, it was observed that the system's dynamic response is frequency-dependent, which presents a challenge for precise impedance regulation solely through temperature control. Despite this limitation, the proposed estimation methodology accurately captures the system's viscoelastic behavior, offering valuable insights into the actuator's performance and potential for applications requiring adaptive impedance control.