Precise surgical procedures may benefit from intra-operative image guidance using magnetic resonance imaging (MRI). However, the MRI's strong magnetic fields, fast switching gradients, and constrained space pose the need for an MR-guided robotic system to assist the surgeon. Piezoelectric actuators can be used in an MRI environment by utilizing the inverse piezoelectric effect for different application purposes. Piezoelectric ultrasonic motor (USM) is one type of MRI-compatible actuator that can actuate these robots with fast response times, compactness, and simple configuration. Although the piezoelectric motors are mostly made of nonferromagnetic material, the generation of eddy currents due to the MRI's gradient fields can lead to magnetic field distortions causing image artifacts. Motor vibrations due to interactions between the MRI's magnetic fields and those generated by the eddy currents can further degrade image quality by causing image artifacts. In this work, a plastic piezoelectric ultrasonic (USM) motor with more degree of MRI compatibility was developed and induced with preliminary optimization. Multiple parameters, namely teeth number, notch size, edge bevel or straight, and surface finish level parameters were used versus the prepressure for the experiment, and the results suggested that using 48 teeth, thin teeth notch with 0.39mm, beveled edge and a surface finish using grit number of approximate 1000 sandpaper performed a better output both in rotary speed and torque. Under this combination, the highest speed reached up to 436.6665rpm when the prepressure was low, and the highest torque reached up to 0.0348Nm when the prepressure was approximately 500g.

翻译：精确的外科手术可能受益于使用磁共振成像（MRI）的术中图像引导。然而，MRI的强磁场、快速切换的梯度场以及受限空间对需要辅助外科医生的磁共振引导机器人系统提出了要求。压电致动器可利用逆压电效应在MRI环境中用于不同的应用目的。压电超声电机（USM）是一种磁共振兼容致动器，能够以快速响应时间、紧凑结构和简单配置驱动这些机器人。尽管压电电机主要由非铁磁性材料制成，但MRI梯度场感应的涡流可能导致磁场畸变，从而产生图像伪影。由MRI磁场与涡流产生的磁场相互作用引起的电机振动，可能进一步通过产生图像伪影而降低图像质量。本研究开发了一种具有更高磁共振兼容性的塑料压电超声（USM）电机，并进行了初步优化。实验中针对预压力测试了多个参数，包括齿数、槽口尺寸、边缘倒角或直边以及表面光洁度等级参数。结果表明，采用48齿、0.39mm细齿槽、倒角边缘以及约1000目砂纸对应的表面光洁度时，电机在转速和扭矩方面均表现出更优的输出性能。在此组合条件下，当预压力较低时最高转速达到436.6665rpm，当预压力约为500g时最高扭矩达到0.0348Nm。