MEMS Micromirror Resonant Frequency Control
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Solution Overview
Problem
MEMS micromirror scanners in video projection apparatuses face challenges in accurately controlling the projected view field due to susceptibility to electromagnetic interference and environmental factors, which affect the resonant frequency and rocking angle, making it difficult to distinguish between drive voltage deviations and resonant frequency deviations.
Innovation Solution
A video projection apparatus that calculates and maintains the optimum resonant frequency, using a drive signal processing section to generate and adjust digital drive voltages for the MEMS optical deflector, and a pixel data extracting section to ensure accurate control of the projected view field by monitoring and adjusting the drive voltages based on sensed voltages from piezoelectric sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a MEMS micromirror scanner is used to scan a light beam two-dimensionally, then light utilization efficiency is improved, but the system becomes susceptible to electromagnetic interference and environmental factors causing resonant frequency deviation
Solution Approach 1:
The patent implements a feedback mechanism where a photodetector detects the actual rocking angle of the micromirror by monitoring the timing position of the output voltage with respect to the center of the projected view field. This detected angle is fed back to a control unit that calculates the deviation from the desired rocking angle and adjusts the drive voltage amplitude accordingly, creating a closed-loop control system that compensates for resonant frequency deviations caused by EMI and environmental factors.
Solution Approach 2:
The system uses the existing photodetector and timing detection mechanism to automatically detect and correct its own resonant frequency deviations. The control unit continuously monitors the rocking angle through the timing position of the output voltage and self-adjusts the drive voltage amplitude without external intervention, enabling the system to maintain optimal performance despite environmental variations.
2Measurement precision
If the resonant frequency of the micromirror changes due to environmental factors, then the rocking angle control becomes inaccurate, but increasing the drive voltage to compensate may cause the rocking angle to exceed the desired value
Solution Approach 1:
The control unit continuously monitors the actual rocking angle through the photodetector's output voltage timing position and compares it with the desired rocking angle. Based on this feedback, the control unit dynamically adjusts the drive voltage amplitude to maintain the desired rocking angle, preventing both under-correction and over-correction that would occur with fixed compensation methods.
Solution Approach 2:
The system dynamically changes the amplitude parameter of the drive voltage based on the detected rocking angle deviation. Rather than using a fixed voltage increase, the control unit adjusts the voltage amplitude in real-time according to the actual deviation caused by resonant frequency changes, ensuring precise control without exceeding the desired rocking angle.
3Reliability
If electromagnetic interference noises affect the control unit operation, then the resonant frequency cannot be maintained at optimum, but adding more noise filtering may increase device complexity
Solution Approach 1:
The patent uses the timing position of the photodetector's output voltage as an indirect but effective indicator of resonant frequency accuracy. This feedback approach allows the control unit to detect resonant frequency deviations without requiring direct frequency measurement circuits, maintaining reliability while avoiding significant increases in device complexity.
Solution Approach 2:
The photodetector and timing detection mechanism serve as an intermediary that converts complex resonant frequency variations into a simple timing position signal. This intermediary approach allows the control unit to monitor and correct resonant frequency deviations without directly processing complex frequency information, reducing the computational and hardware complexity of the control system.
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 solution allows for accurate control of the projected view field even when the drive voltage and resonant frequency deviate, stabilizing the desired rocking angle and enhancing the efficiency of light utilization by minimizing external noise interference.
Implementation Method 1
sensed voltages from piezoelectric sensors
Implementation Method 2
drive voltages for the MEMS optical deflector
Implementation Method 3
rocking angle of the micromirror varies at a resonant frequency
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A video projection apparatus includes: an optical deflector (19) having a mirror (191) projecting a first view field (F1) and projecting a second view field (F2), an actuator (193a) for rocking the mirror (191) and a sensor (197a); an optical guide unit (25) provided within the second view field (F2); a photodetector (26) ; and a control unit (14, 15, 16). The control unit (14, 15, 16) is adapted to calculate a resonant frequency (fr) of the sinusoidal-wave voltage (Vxa) ; detect a first stiming point (t0) from a sense voltage (Vxs) detect a second timing point (t1, t2, t3) from a photo detection voltage (Vpd) when the second light beam (L2) is incident to the optical guide unit (25); calculate a time, period (T) from the first timing point (t0) to the second timing point (t1); calculate a product value (P) between the time period (T) and the resonant frequency (fr) ; and control an amplitude (A) of the sinusoidal-wave voltage (Vxa).