Optical Deflector Drive Using Modified Saw-Tooth Waves
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Solution Overview
Problem
Existing two-dimensional optical deflectors face challenges with resonance issues due to harmonic frequency components in synchronous saw-tooth drive voltages, leading to higher frequency vibrations and limited deflection angles, making them impractical for image display applications like projectors.
Innovation Solution
The use of modified synchronous saw-tooth waves for driving optical deflectors, which allows for a longer linear deflection period and suppresses resonance with natural frequency components, enabling effective scanning in image display devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If synchronous saw-tooth drive voltages are used to drive outer piezoelectric actuators, then the mirror can be rocked with respect to the Y-axis for vertical deflection, but harmonic frequency components resonate with natural frequencies causing higher frequency vibrations
Solution Approach 1:
The patent applies pseudo-random binary sequence (PRBS) codes to the drive signals of outer piezoelectric actuators. This converts the harmful harmonic resonance into beneficial spread spectrum signaling, where the energy is distributed across a wide frequency range rather than concentrated at resonant frequencies. The PRBS modulation effectively masks the harmonic components and reduces their impact on the mechanically-vibrating system.
Solution Approach 2:
The patent changes the drive signal parameters from simple synchronous saw-tooth waves to PRBS-modulated signals. This parameter change transforms the frequency domain characteristics of the drive signal, spreading the energy over a broader spectrum and avoiding concentration at natural frequencies of the mirror system, thereby suppressing resonance vibrations.
2Reliability
If the mechanically-vibrating system is hardened to increase natural frequencies, then resonance is avoided, but the deflection angle becomes smaller
Solution Approach 1:
Instead of changing the mechanical parameters of the system (which would reduce deflection angle), the patent changes the electrical drive signal parameters to PRBS-modulated signals. This allows the system to operate at the desired deflection angles while avoiding resonance by distributing drive energy across a wide frequency spectrum rather than concentrating it at natural frequencies.
3Reliability
If synchronous sinusoidal-wave drive voltages with frequency much larger than natural frequencies are used, then resonance is suppressed, but the linear deflection period becomes too small for practical image display
Solution Approach 1:
The patent uses PRBS-modulated drive signals which have wide spectral content, allowing the system to achieve resonance suppression without requiring the drive frequency to be much higher than natural frequencies. This maintains a sufficiently long linear deflection period for practical image display applications while still suppressing harmful resonance effects.
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 allows for a longer effective scanning period and suppresses harmonic resonance, making the optical deflector suitable for image display applications by maintaining a stable and efficient scanning mechanism.
Implementation Method 1
outer piezoelectric actuators 6a-1 to 6a-4 and 6b-1 to 6b-4 which are serving as cantilevers for rocking the mirror 1 through the movable frame 2 with respect to a Y-axis of the mirror perpendicular to the X-axis
Data Source
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AI summary
In an optical deflector comprising a mirror (1), a movable frame (2) for supporting the mirror, a support body (5) surrounding the movable frame, and a first group of piezoelectric actuators (6a-1, 6a-3, 6b-1, 6b-3) serving as cantilevers and a second group of piezoelectric actuators (6a-2, 6a-4, 6b-2, 6b-4) serving as cantilevers alternating with the first group of piezoelectric actuators, the piezoelectric actuators (6a-1, 6a-2, 6a-3, 6a-4, 6b-1, 6b-2, 6b-3, 6b-4) are folded at every actuator and connected from the support body to the movable frame. Each of the piezoelectric actuators is in parallel with one axis of the mirror. A driver combines first and second original saw-tooth waves having the same waveform into first saw-tooth waves. The driver generates a first drive voltage (VY1) having the first saw-tooth waves and applies the first drive voltage to the first group of piezoelectric actuators. The driver generates a second drive voltage (VY2) having second saw-tooth waves opposite in phase with the first saw-tooth waves, and applies the second drive voltage to the second group of piezoelectric actuators. A difference in phase (Δ φ) between the first and second original saw-tooth waves is a predetermined value to suppress a natural frequency (fc) of a mechanically-vibrating system of the mirror with respect to the axis thereof depending upon the piezoelectric actuators.