Bidirectional angular control of an integrated sensor/actuator shape memory alloy based system

• Direct differential resistance feedback for bi-directional control.
• Sensorless signal conditioning electronic circuit for resistance measurement.
• Design of SMA configured driving mechanism to accomplish the desired control.
• Phase transformation of SMA is influenced by the frequency of the tracking input.
• Using self-sensing achieved angular tracking of ±15° at a frequency of 1 Hz.

This article emphasises on the development of a straight forward approach for self-sensing shape memory alloy. A direct differential resistance feedback is proposed, that eliminates the computation complexity and extensive experimentation involved in conventional techniques. To establish this feedback strategy a self-designed electronic unit is presented as a sensorless signal conditioning circuit, which is system independent and compatible with any SMA driven system. The self-sensing scheme is further demonstrated by its application to a one link SMA actuated rotary manipulator employing discrete time sliding mode control. It enables direct measurement of angular position (degree) in 3D space, in terms of the electrical resistance of the SMA wires. The results demonstrate good servo control characteristics over broad range of bandwidth, due to the combined effort of prestress in antagonism and the control algorithm. The operation of the manipulator is stable, accurate and robust for payload and thermal disturbance rejection with control.