Pulse width modulation–based temperature tracking for feedback control of a shape memory alloy actuator

Abstract

This study presents a temperature-feedback approach to control the radius of curvature of an arc-shaped shape memory alloy wire. The nonlinear properties of the shape memory alloy such as phase transformation and its dependence on temperature and stress make shape memory alloy actuators difficult to control. Tracking a desired trajectory is more challenging than controlling just the position of the shape memory alloy actuator since the desired path is continuously changing. Consequently, tracking the desired strain directly or tracking the parameters such as temperature and electrical resistance that are related to strain with a model is a challenging task. Temperature-feedback is an attractive approach when direct measurement of strain is not practical. Pulse width modulation is an effective method for shape memory alloy actuation, and it can be used along with a compensator to control the temperature of the shape memory alloy. Using the constitutive model of the shape memory alloy, the desired temperature profile can be obtained for a given strain trajectory. A pulse width modulation–based nonlinear proportional–integral–derivative controller with a feed-forward heat transfer model is proposed to use temperature-feedback for tracking a desired temperature trajectory. The proposed controller is used during the heating phase of the shape memory alloy actuator. The controller proves to be effective in tracking stepwise and continuous trajectories.