Modal Engineering for MEMS Devices: Application to Galvos and Scanners

Abstract

Optical systems typically use galvanometers (aka galvos) and scanners. Galvos move optical elements such as mirrors, quasi-statically, from one static position to another, and an important figure of merit is their step-settle relaxation time. Scanners move in an oscillatory fashion, typically at the device resonant frequency. MEMS devices, which have many advantages and are often used in such optical systems, are typically high Q devices. Moving from one position to another for a galvo or one frequency/amplitude to another for scanners, can take many periods to settle following the ring down. During these transitions, the optical system is inactive and the time is not being efficiently used. In this article we show how a novel class of open loop control algorithms can be used to rapidly change position, frequency and amplitude, typically in well under the period of the device. We show how the MEMS designer can excite, with complete, high-speed control, a vibrational mode of the system. We call this modal engineering, the ability to control the modes of the system in a practical, fast way. This control of the modes is accomplished with open loop control algorithms.