Improvement of the Response of an SMA Actuator Using a Temperature Sensor

The ordinary control method, pulse width modulation (PWM) control method, for the shape memory alloy (SMA) actuator has a basic defect: the response of an SMA actuator controlled by this method is very slow, because the maxi mum voltage supplied to the SMA must be kept low in order to prevent the SMA from burning because its temperature is unknown. In this paper, a new control method is proposed to improve the response speed of the SMA actuator by limiting the temperature of the SMA to below the limited value in stead of by limiting the maximum voltage supplied to the SMA. Therefore this new control method allows us to use powerful drivers for supplying voltage to an SMA so as to in crease the heating speed of the SMA. First, a temperature sensor system to detect the SMA's temperature was developed by solving several problems. Next, experiments of the position control by a new SMA actuator system with a temperature threshold for SMA were carried out. Results show that the re sponse speeds are much faster than those using the ordinary control method. In addition, some conditions to further im prove the response speed of the proposed control method for an SMA actuator were obtained.