Modeling, characterization and control of antagonistic SMA springs for use in a neurosurgical robot

In this paper, we model and characterize the thermomechanical behavior of SMA springs based on Brinson´s constitutive model of SMAs. The model developed in this paper can be used to compute the recovery length of SMA springs. We used the model to develop a temperature feedback position controller to control the joint motion of the SMA spring-actuated robot. We also implemented a position controller for the robot using image feedback because the robot was designed to be operated under MRI guidance. Since the image tracking algorithm for image feedback control may fail in some situations, the temperature feedback controller can be used as a backup control scheme for the robot. The experimental results showed that the image feedback controller worked well while the temperature feedback controller did not. This is because the theoretical model did not include the nonlinear characteristics of the tendon-sheath mechanisms. Therefore, we used an empirical model to implement a temperature feedback controller and it was used to control the robot precisely.