Preliminary Characterization of a Hollow Cylindrical Ultrasonic Motor by Finite Element Modeling and Digital Holographic Interferometry

Magnetic resonance imaging (MRI) provides a better visualization for diagnosis, interventional radiology, and surgery and enables the ability of intra-operative precise surgical procedures such as deep brain tumor ablation. However the limitation of using an MRI scanner with strong magnetic fields and constrained space inside the bore creates the need of using a robotic system to assist surgeons with MR-guided robot-assisted procedures. Piezoelectric ultrasonic motors are a novel class of actuators often used to drive these robots to operate in MRI environments. Hollow-type motors address the advantages of compact design with an end effector assembly, low rotary inertia, fast response time, and eliminating mechanical nonlinearities introduced by gearboxes. In this chapter, we present a custom-made ultrasonic hollow cylindrical motor with toward center amplitude and along circumference traveling waves to frictionally couple with the rotor. A finite element model of hollow stator using COMSOL Multiphysics is created in frequency- and time-dependent domains and validates the FEM simulation with time-averaged digital holography. Results show that the holographic images resulting in vibration patterns matched the FEM simulation on eigenfrequencies of excitation with the largest difference of 6.1% and yield the lowest Pearson correlation coefficient of 0.7113 with toward the center displacement curve compared to the FEM simulation results. This chapter shows the feasibility of a new type of ultrasonic motor used in the MRI environment.