In this paper, we present our results of modeling and characterization of antagonistic SMA spring actuators for use in a MRI-compatible intracranial robot. We develop a theoretical model to describe the behavior of the SMA spring actuators based on the constitutive model of SMA. The model shows that temperature feedback can be used to control the spring displacement and hence the joint motion of the robot. Besides, since the SMA spring can be used as a regular helical spring, we can also estimate the recovery force of the SMA spring actuator based on its displacement. Experimental results match the theoretical model well which proves that temperature feedback can be used reliably to control the joint motion of the robot as well as estimate the recovery force of the SMA spring actuators.
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