New Actuation Mechanism for Actively Cooled SMA Springs in a Neurosurgical Robot

This paper presents the use of shape memory alloy (SMA) spring actuators with real-time cooling to control the motion of the minimally invasive neurosurgical intracranial robot (MINIR-II). A new actuation mechanism involving the passage of water as the cooling medium and air as the medium to drive out the water has been developed to facilitate real-time control of the springs. Control parameters, such as current, water flow rates, SMA predisplacement, and gauge pressure of the compressed air, are identified from the SMA thermal model and from the actuation mechanism. In-depth modeling and characterization have been performed regarding these parameters to optimize the robot motion speed. Forced water cooling has also been compared with forced air cooling and proved to be the superior method to achieve higher robot speed. An improved robot design and a magnetic-resonance-imaging-compatible experimental platform have been developed for the implementation of the actuation mechanism.