Optical Deflector Driver Voltage Synthesis for Mirror Vibration Control
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Solution Overview
Problem
Existing optical deflectors using MEMS technology face issues with image distortion due to higher-order harmonic frequencies causing fluctuations in mirror vibration, which affect scanning speed and image quality, despite attempts to suppress these frequencies.
Innovation Solution
A method involving a saw-tooth voltage generating unit that applies both saw-tooth and inverted voltages to piezoelectric actuators, followed by low-pass filtering and combining these voltages with delayed versions to create a combined saw-tooth voltage, which is then applied to the actuators to minimize fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If synchronous saw-tooth drive voltages are applied to outer piezoelectric actuators for vertical scanning, then the mirror can be rocked along the Y-axis, but higher-order harmonic frequencies cause fluctuations in mirror vibration that distort images and affect scanning speed
Solution Approach 1:
The patent applies input shaping technique to convert the harmful effect of harmonic frequencies into beneficial vibration suppression. By synthesizing a drive voltage that incorporates anti-phase components at specific frequencies (main natural frequency Fr and pumping natural frequency Fp), the harmful vibrations are counteracted and eliminated, resulting in smooth mirror rocking without image distortion while maintaining scanning speed
Solution Approach 2:
The patent modifies the drive voltage parameters by synthesizing a composite saw-tooth waveform that includes not only the fundamental frequency (60 Hz) but also specific harmonic components at predetermined frequencies. This parameter modification allows the drive voltage to actively cancel out resonant vibrations at Fr and Fp, thereby suppressing mirror fluctuations and improving image quality without sacrificing scanning performance
2Ease of operation
If saw-tooth drive voltage with harmonic frequency components is used, then the mirror rocking motion can be achieved, but the harmonic frequencies superpose onto natural frequencies causing mirror fluctuation and image distortion
Solution Approach 1:
The patent transforms the harmful harmonic components in the saw-tooth drive voltage into beneficial anti-resonance components. By deliberately incorporating frequency components at the main natural frequency Fr and pumping natural frequency Fp with appropriate phases and amplitudes, the drive voltage actively suppresses vibrations at these critical frequencies, thereby eliminating mirror fluctuations and ensuring stable scanning operation
Solution Approach 2:
The patent employs input shaping which is a form of open-loop feedback control. The drive voltage is synthesized based on knowledge of the system's natural frequencies (Fr and Fp), creating a control signal that anticipates and counteracts resonant vibrations before they occur. This feedback mechanism ensures that the mirror rocking motion remains stable and free from distortion-causing fluctuations
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 effectively removes substantial fluctuations from the mirror vibration, leading to improved image quality by reducing scanning distortions and maintaining a stable scanning speed.
Implementation Method 1
a piezoelectric actuator to rock a mirror around a first axis of the optical deflector
Implementation Method 2
a piezoelectric sensor to sense vibrations of the piezoelectric actuator
Data Source
AI summary
In a driver for driving an optical deflector including a mirror, a piezoelectric actuator and a piezoelectric sensor adapted to sense vibrations of the piezoelectric actuator, a saw-tooth voltage generating unit; a combined saw-tooth voltage generating unit; and a control unit, the control unit applies a saw-tooth voltage and its inverted voltage to the piezoelectric actuator; performs a low-pass filtering process using a cut-off frequency upon a sense voltage; calculates a half period of fluctuations included in a low-pass-filtered saw-tooth voltage; combines the low-pass-filtered saw-tooth voltage with a delayed low-pass-filtered saw-tooth voltage; and to applies a combined saw-tooth voltage and its inverted voltage to the piezoelectric actuator.