Influence of heat treatment conditions on temperature control parameter(t1) for shape memory alloy (SMA) actuator in nucleoplasty

Abstract

Shape Memory Alloy (SMA) has recently received attention in developing implantable surgical equipments and it is expected to lead the future medical device market by adequately imitating surgeons' flexible and delicate hand movement However, SMA actuators have not been used widely because of their nonlinear behavior called hysteresis, which makes their control difficult Hence, we propose a parameter, t1, which is necessary for temperature control, by analyzing the open-loop step response between current and temperature and by comparing it with the values of linear differential equations. t1 is a pole of the transfer function in the invariant linear model in which the input and output are current and temperature, respectively; hence, t1 is found to be related to the state variable used for temperature control. When considering the parameter under heat treatment conditions, Tmax was found to assume the lowest value, and t1 was irrelevant to the heat treatment.