Optical Deflector Drive Voltage Waveform Design

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Solution Overview

Problem

Existing two-dimensional optical deflectors face challenges in avoiding higher frequency vibrations when using synchronous saw-tooth drive voltages, which either require harder mechanical systems for larger deflection angles or result in impractically small scanning periods when using sinusoidal-wave voltages.

Innovation Solution

The optical deflector employs piezoelectric actuators with drive voltages having asymmetrical rising and falling periods, ensuring these periods are longer than their counterparts, and uses complex-sinusoidal-wave or pseudo-sinusoidal-wave voltages to avoid resonating with natural frequencies, allowing for larger deflection angles and suppressing harmonic resonances.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If synchronous saw-tooth drive voltages are used for outer piezoelectric actuators, then the mirror can be rocked at low frequency (60 Hz), but harmonic frequency components resonate with natural frequencies causing higher frequency vibrations

Engineering Contradiction:

Improverocking frequencyVSAvoidhigher frequency vibration

Core Design Contradiction:

SpeedVSObject-affected harmful factors

Solution Approach 1:

The patent changes the waveform parameter from saw-tooth to complex-sinusoidal-wave, which has a fundamental frequency matching the desired low-frequency rocking (60 Hz) but lacks the harmful harmonic components that cause resonance with the natural frequencies of the mechanical system

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the harmful saw-tooth waveform (which contains resonant harmonics) into a beneficial complex-sinusoidal-wave that achieves the same low-frequency rocking function without the harmful high-frequency vibrations, effectively turning a harmful drive signal into a beneficial one

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Object-affected harmful factors

If natural frequencies are made much larger than the fundamental frequency of drive voltages to avoid resonance, then higher frequency vibrations are suppressed, but the mechanical system becomes hardened making it difficult to rock the mirror at larger deflection angles

Engineering Contradiction:

Improvehigher frequency vibrationVSAvoiddeflection angle

Core Design Contradiction:

Object-affected harmful factorsVSEase of operation

Solution Approach 1:

Instead of changing the natural frequency parameter of the mechanical system, the patent changes the drive voltage waveform parameter to eliminate resonant harmonics, thereby avoiding the need to harden the mechanical system while still suppressing vibrations

Inventive Principle:

Principle #35Parameter changes

3Object-affected harmful factors

If synchronous sinusoidal-wave drive voltages with frequency much larger than natural frequencies are used, then resonance is avoided, but the linearly-deflected period becomes too small making it impractical for image display applications

Engineering Contradiction:

ImproveresonanceVSAvoidscanning period

Core Design Contradiction:

Object-affected harmful factorsVSDuration of action of moving object

Solution Approach 1:

The patent changes the frequency parameter of the drive voltage to match the desired slow rocking frequency (60 Hz) rather than using a high frequency, and combines this with a complex-sinusoidal waveform that eliminates resonant harmonics, thereby achieving both long scanning period and resonance avoidance

Inventive Principle:

Principle #35Parameter changes

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach enables longer linear deflection periods, making the optical deflector suitable for image display applications like projectors, while effectively suppressing resonances with natural frequencies of the mechanical system.

Implementation Method 1

outer piezoelectric actuators fixed between the support body and the movable frame and serving as cantilevers for rocking the mirror through the movable frame

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS8649078B2Driver for optical deflector using complex-sinusoidal-wave drive voltages and method for setting the same

Publication Date: 2014.02.11 STANLEY ELECTRIC CO LTD

AI summary

A driver for driving an optical deflector includes a mirror, a movable frame for supporting the mirror, a support body surrounding the movable frame, and a first group of piezoelectric actuators and a second group of piezoelectric actuators alternating with the first group of piezoelectric actuators. A first drive voltage for the first group of piezoelectric actuators has first repeated waves each with a first rising period. A second drive voltage for the second group of piezoelectric actuators has second repeated waves each with a second falling period corresponding to the first rising period of the first drive voltage and a second rising period corresponding to the first falling period of the first drive voltage. Frequencies of the first and second repeated waves exclude natural frequencies of a mechanically-vibrating system of the mirror with respect to the axis thereof depending upon the piezoelectric actuators.