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A control system for a shape memory alloy (SMA) servo actuator, and its application to a unique medical tool, are considered. It is thought that the electric resistance value of an SMA can be utilized to monitor the transformation of the SMA directly. Therefore, an antagonistic transformation control scheme using electric resistance feedback is proposed and is verified by several experiments. This control scheme reduces the open-loop hysteresis of an SMA actuator and improves greatly its robustness against heat disturbance due to changes in the cooling condition. Research into the application of the method in an active endoscope is reported. It consists of five segments of 13 mm diameter, 40 mm length each. The bending angle of each segment can be controlled individually from outside by using antagonistic electric resistance feedback without any motion sensors. A model for smooth insertion to the colon is verified.>
Ikuta et al. (2003) studied this question.