Choi Jongsoo, Wang Thomas, Oldham Kenn
Department of Mechanical Engineering, University of Michigan, 2350 Hayward St., Ann Arbor, MI 48109, USA.
Department of Biomedical Engineering, University of Michigan, 2200 Bonisteel Blvd., Ann Arbor, MI 48109, USA.
J Micromech Microeng. 2018 Jan;28(1). doi: 10.1088/1361-6439/aa9d3c. Epub 2017 Dec 15.
The high performance and small size of MEMS based scanners has allowed various optical imaging techniques to be realized in a small form factor. Many such devices are resonant scanners, and thus their linear and nonlinear dynamic behaviors have been studied in the past. Thin-film piezoelectric materials, in contrast, provide sufficient energy density to achieve both large static displacements and high-frequency resonance, but large deformation can in turn influence dynamic scanner behavior. This paper reports on the influence of very large stroke translation of a piezoelectric vertical actuator on its resonant behavior, which may not be otherwise explained fully by common causes of resonance shift such as beam stiffening or nonlinear forcing. To examine the change of structural compliance over the course of scanner motion, a model has been developed that includes internal forces from residual stress and the resultant additional multi-axis coupling among actuator leg structures. Like some preceding vertical scanning micro-actuators, the scanner of this work has four legs, with each leg featuring four serially connected thin-film PZT unimorphs that allow the scanner to generate larger than 400μm of vertical displacement at 14V. Using an excitation near one or more resonances, the input voltage can be lowered, and complementary multi-axis rotations can be also generated, but change of the resonant frequencies with scanner height needs to be understood to maximize scanner performance. The presented model well predicts the experimental observation of the decrease of the resonant frequencies of the scanner with the increase of a dc bias voltage. Also, the effects of the magnitude and uniformity of residual stress across the scanner structure on the natural frequencies have been studied.
基于MEMS的扫描仪的高性能和小尺寸使得各种光学成像技术能够以小尺寸实现。许多这样的设备是共振扫描仪，因此过去已经研究了它们的线性和非线性动态行为。相比之下，薄膜压电材料提供了足够的能量密度，以实现大的静态位移和高频共振，但大变形反过来会影响动态扫描仪的行为。本文报道了压电垂直致动器的非常大行程平移对其共振行为的影响，这可能无法用共振偏移的常见原因（如梁刚度增加或非线性强迫）来完全解释。为了研究扫描仪运动过程中结构柔顺性的变化，开发了一个模型，该模型包括残余应力产生的内力以及致动器腿结构之间由此产生的额外多轴耦合。与一些先前的垂直扫描微致动器一样，这项工作中的扫描仪有四条腿，每条腿都有四个串联连接的薄膜PZT单压电晶片，这使得扫描仪在14V电压下能够产生大于400μm的垂直位移。使用接近一个或多个共振的激励，可以降低输入电压，还可以产生互补的多轴旋转，但需要了解共振频率随扫描仪高度的变化，以最大限度地提高扫描仪性能。所提出的模型很好地预测了扫描仪共振频率随直流偏置电压增加而降低的实验观察结果。此外，还研究了扫描仪结构上残余应力的大小和均匀性对固有频率的影响。
