Chapter 12 Preliminary Characterization of a Plastic Piezoelectric Motor Stator Using High-Speed Digital Holographic Interferometry Z. Zhao, P. A. Carvalho, H. Tang, K. Pooladvand, K. Y. Gandomi, C. J. Nycz, C. Furlong, and G. S. Fischer Abstract Precise surgical procedures such as deep brain tumor ablation may benefit from intra-operative image guidance using magnetic resonance imaging (MRI). However, the MRI’s strong magnetic fields and constrained space pose the need for robotic devices to assist the surgeon. Piezoelectric motors are often used to actuate these robots. The piezoelectric resonant motor (PRM) is a class of such motors that consist of a bonded piezoelectric ring stator and a frictionally coupled rotor. Steady-state excitation at certain frequencies leads to specific mode shapes on the stator with surface waves having both in-plane and out-of-plane displacement components that cause the coupled rotor to spin. High-speed digital holography (HDH) can be used to measure time variant displacements with nanometer and microsecond resolution. We present initial measurements acquired at 67 k frame per second (fps) of two custom-designed plastic stator components operating at drive frequencies of 6.788 kHz and 6.980 kHz, respectively. Circumferential motion of the traveling surface waves with outof-plane peak-to-peak displacement of approximately 100 nm peak-to-peak amplitude and a settling time of 2.99 ms was observed. Results demonstrate that plastic stators may be a promising alternative to metallic stators for use in the MRI environment. Keywords MRI compatible actuation · High-speed digital holography · Image guided surgery · Resonant piezoelectric motor 12.1 Introduction Over six hundred thousand cancer deaths were projected to have occurred in 2019 in the USA [1]. Cancer treatments have steadily advanced in the past decades and today includes immunotherapy [2], chemotherapy, radiation, and surgical intervention. In the latter, being able to leave adequate margins is paramount to reduce recurrence. Cancerous tumor recession surgeries have better long-term success rate when appropriate margins are achieved [3]. Magnetic resonance image (MRI) intra-operatively guided procedures have been shown to achieve better margins when compared to traditional methods [4]. The strong magnetic field and sensitivity to electrical noise impedes the use of most conventional actuators inside an MRI. Therefore, MRI compatible robotic devices use alternative actuators such as pneumatic [5, 6], hydraulic [7], or piezoelectric motors [8]. In the latter, non-ferromagnetic metals still remain. These metals can, in some cases, lead to distortions of the magnetic field and undesirable vibration due to gradient switching affecting image quality. Previous work has demonstrated that it is possible to substitute several of the components for plastic equivalents reducing magnetic field distortions without negatively affecting image signal-to-noise ratio [9]. In the aforementioned publication, the enclosure of the motor is modified Z. Zhao · P. A. Carvalho ( ) · K. Y. Gandomi · C. J. Nycz Robotics Engineering Program, Worcester Polytechnic Institute, Worcester, MA, USA e-mail: zzhao4@wpi.edu; pacarvalho@wpi.edu; kygandomi@wpi.edu; cjnyz@wpi.edu H. Tang · K. Pooladvand · C. Furlong Mechanical Engineering Department, Worcester Polytechnic Institute, Worcester, MA, USA e-mail: htang3@wpi.edu; kpooladvand@wpi.edu; cfurlong@wpi.edu G. S. Fischer Robotics Engineering Program, Worcester Polytechnic Institute, Worcester, MA, USA Mechanical Engineering Department, Worcester Polytechnic Institute, Worcester, MA, USA e-mail: gfischer@wpi.edu © The Society for Experimental Mechanics, Inc. 2021 M.-T. Lin et al. (eds.), Advancement of Optical Methods & Digital Image Correlation in Experimental Mechanics, Conference Proceedings of the Society for Experimental Mechanics Series, https://doi.org/10.1007/978-3-030-59773-3_12 89
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