Scanning Micro-Mirror with an Electrostatic Spring for Compensation of Hard-Spring Nonlinearity

Abstract

A scanning micro-mirror operated at the mechanical resonant frequency often suffer nonlinearity of the torsion-bar spring. The torsion-bar spring becomes harder than the linear spring with the increase of the rotation angle (hard-spring effect). The hard-spring effect of the torsion-bar spring generates several problems, such as hysteresis, frequency shift, and instability by oscillation jump. In this paper, a scanning micro-mirror with an electrostatic-comb spring is studied for compensation of the hard-spring effect of the torsion-bar spring. The hard-spring effect of the torsion-bar spring is compensated with the equivalent soft-spring effect of the electrostatic-comb spring. The oscillation curve becomes symmetric at the resonant frequency although the resonant frequency increases. Theoretical analysis is given for roughly explaining the compensation. A 0.5 mm square scanning micro-mirror having two kinds of combs, i.e., an actuator comb and a compensation comb, is fabricated from a silicon-on-insulator wafer for testing the compensation of the hard-spring in a vacuum and in atmospheric air. The bending of the oscillation curve is compensated by applying a DC voltage to the electrostatic-comb spring in vacuum and atmosphere. The compensation is attributed by theoretical approach to the soft-spring effect of the electrostatic-comb spring.

Scanning and Actuation Techniques for Cantilever-Based Fiber Optic Endoscopic Scanners—A Review

“…Vertical comb drives are used frequently to actuate micromirrors [ 146 , 147 , 148 ]. It is possible to place the moving comb structures at a certain angle with respect to the fixed ones to obtain an angular vertical comb drive.…”

Electrostatic metallic glass micro-mirror fabricated by the self-aligned structures

“…34,35) The electrostatic actuation micro-mirrors have the advantages such as lower power consumption and fast response. [36][37][38] The higher driving voltage of the electrostatic actuation micro-mirrors is an issue needing to be improved. The comb structure could effectively decrease the driving voltage.…”

Editorial for the Special Issue on MEMS Mirrors

“…There are 15 papers published in this special issue, covering MEMS mirrors based on all of the commonly used actuation mechanisms including electrostatic [1,2,3,4,5], electromagnetic [6,7,8], piezoelectric [9], and electrothermal [10,11,12,13,14]. Half of these papers explore various aspects of MEMS mirrors, such as working in harsh environments [1], spring hardening compensation [3], optimal packaging conditions for resonance operation [5], input saturation control [8], extremely large scan angle [9], overshoot suppression [10], electrothermal actuator modeling [13], and design optimization [14].…”

“…Half of these papers explore various aspects of MEMS mirrors, such as working in harsh environments [1], spring hardening compensation [3], optimal packaging conditions for resonance operation [5], input saturation control [8], extremely large scan angle [9], overshoot suppression [10], electrothermal actuator modeling [13], and design optimization [14]. There is also a paper reporting a passive micromirror [15].…”

“…Izawa et al applied the spring softening effect of electrostatic comb drives to compensate for the spring hardening effect of torsion-bar springs [3]. Zhao et al identified an optimal range of vacuum for operating electrostatic comb-drive micromirrors [5].…”