A Multi-Channel Power Controller for Actuation and Control of Multiple SMA Actuators

This paper presents a multi-channel electronic power controller device for Shape Memory Alloy (SMA) actuators. The use of shape memory alloy wires as actuators has been proposed in numerous novel applications such as Smart Inhaler System [1], BAT Micro Air Vehicle [2], etc. These systems have multiple SMA wires for actuation of their mechanisms. The SMA wires can be actuated by controlling the joule heating or the electric power in that wire. This paper describes the development of a multi-channel power device that can control multiple SMA actuators simultaneously. The device presented herewith utilizes a Field Programmable Gate Array (FPGA) board and a custom built electronic device to independently and simultaneously control electric power in three different SMA actuators. The controller adapts to the non linear and hysteretic behavior of the resistance of the SMA actuators and adjusts the pulse width modulated voltage across them to maintain the desired value of power. The controller uses the resistance measurement of the SMA actuators as feedback. With the help of modeling efforts to relate resistance to strain, it is envisioned that feedback position control of these actuators can be implemented without the necessity of a sensor. The device is tested with graphic user interface which enables a user to control various parameters during operation of this device and to monitor the results. The design and implementation of this device is detailed in this paper along with its performance charts. The results relate the input power, observed actuation strokes and measured resistances in the SMA actuators under various conditions. A relevant discussion on implementing position control in Smart Inhaler System using this device is also presented.