Design and Optimization of Mechanically Resonant Torsional Spring Mechanism for Laser Light Dispersion Applications

Abstract

A laser light scanning device consisting of an electronically driven mechanically resonant torsional spring-mirror system was developed for display applications. The original design suffers fatigue failure due to the repeated rotation of the torsional spring. The torsional spring design is investigated and analyzed to attain the lowest possible stress level while maintaining a constant resonant frequency. The finite element analysis model of the torsional spring was created and the stress was minimized by changing the geometrical parameters of the spring. Spring geometric optimization resulted in a maximum stress of 0.632 GPa, that is 12% reduction in stress from the original design, which should give an extended life span of 1 month for the intended application.

An Approach for Nonlinear Damping Characterization for Linear Optical Scanner

“…In many applications, the scanning frequency of the system must be kept above a frequency limit called critical flickering frequency (CFF). The CFF is the minimum frequency required to avoid perceptible flickering of the image generated from the scanner 25 . The CFF depends on the ambient illumination level and the brightness of the illuminated objects.…”

“…The scanner is designed specifically to operate at first torsional mode frequency of around 40 Hz, with as little energy as possible dissipated in other modes. According to the previous study 25 , merely torsional mode oscillation existed in the first mode shape. The mass of the suspended plate is about 3.4 g, while the mass of the base is about 505.1 g, thus the movement of the base is insignificant compared to the motion of suspended plate.…”

An Investigation on the Damping Characteristics of a Linear Optical Scanner

“…The CFF is the minimum frequency required to avoid perceptible flickering in the scanned image. 12 The CFF depends on the ambient illumination level and the brightness of objects. When viewing objects under bright ambient conditions, the CFF may be as high as 100 Hz.…”

“…To set the resonance frequency of the torsional spring, a geometry study of the spring was performed in previous study. 12 The coil of the scanner was actuated using a square wave voltage at the resonance frequency (40 Hz) as shown in Fig. 2.…”

“…The compliant structures namely, the flexure hinge, lateral spring, cantilever spring, and torsional spring make up the mechanism used to transfer the actuating motion to the mirror. 12 The resonance frequency also changes when the scanner is mounted onto different types of mounting bases. In addition, the scanning angle is affected by the environmental pressure as the drag forces increase with air density.…”