MEMS Mirror Drive Control for Phase Alignment
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Solution Overview
Problem
Existing laser projection systems for virtual reality or augmented reality headsets face challenges in synchronizing the movement of separate projection systems for each eye, as manufacturing variations in MEMS mirrors result in phase misalignment and unequal opening angles when driven with the same frequency.
Innovation Solution
A method involving a pre-drive signal with a frequency that matches the average resonance frequency of two MEMS mirrors, generating drive control signals with different amplitudes and phases to ensure both mirrors move at the same frequency and maintain a constant opening angle, using mirror position sensors and zero cross detectors for feedback adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the same drive signal is used to drive both MEMS mirrors, then the driving complexity is reduced, but the opening angles and phases of the mirrors become unequal due to manufacturing variations
Solution Approach 1:
The patent applies local quality by providing individualized drive signals to each MEMS mirror based on its specific resonance frequency characteristics. Instead of using a uniform drive signal for both mirrors, the system tailors the drive parameters (frequency, amplitude, phase) to match the local properties of each mirror, thereby achieving consistent opening angles despite manufacturing variations.
Solution Approach 2:
The patent utilizes parameter changes by adjusting the drive signal frequency to match the resonance frequency of each individual MEMS mirror. The system measures or determines the resonance frequency of each mirror and modifies the drive parameters accordingly, allowing both mirrors to operate at their optimal resonance points and achieve equal opening angles.
2Manufacturing precision
If the drive frequency is adjusted to match individual resonance frequencies, then the opening angle consistency is improved, but the system complexity increases
Solution Approach 1:
The patent implements feedback by measuring the actual resonance frequency of each MEMS mirror and using this information to adjust the drive signal parameters. The system includes sensors or detection mechanisms that monitor the mirror behavior and provide feedback to the control circuit, which then modifies the drive frequency and amplitude to achieve the desired opening angle consistency.
Solution Approach 2:
The patent applies preliminary action by pre-characterizing each MEMS mirror's resonance frequency during manufacturing or initial setup. This information is stored and used to configure the drive signals before actual operation begins, allowing the system to operate with optimized parameters without requiring complex real-time adjustments during normal use.
3Manufacturing precision
If separate drive signals are generated for each MEMS mirror, then the opening angle equality is achieved, but the control circuit complexity increases
Solution Approach 1:
The patent applies universality by designing a control architecture where a single control circuit or processor performs multiple functions: it measures/determines resonance frequencies, generates individualized drive signals, and monitors mirror performance. This multi-functional approach reduces the need for separate dedicated circuits for each mirror while still achieving precise phase alignment and equal opening angles.
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 MEMS mirrors in dual-projection systems to operate in phase with equal and constant opening angles, reducing visual strain and ensuring high-quality image formation for each eye.
Implementation Method 1
The stator and/or rotor are driven with a drive signal which results in the rotor oscillating at resonance with respect to the stator, thereby changing the angle of reflectance of an incident light beam on the rotor
Implementation Method 2
The actuation of mirrors used in MEMS devices, referred to herein as MEMS mirrors, can be via the electromagnetic, electrostatic, piezoelectric, and thermoelectric effects, depending on application
Implementation Method 3
using mirror position sensors and zero cross detectors for feedback adjustments
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
A control circuit includes a first control circuit (14a) generating a first drive control signal (24a) from a pre-drive signal (21), which is a frequency at which an opening angle of first and second mirrors (11a,11b) is equal, for the first mirror (11a). A second control circuit (14b) generates a second drive control signal (24b) from the pre-drive signal (21) for the second mirror (11b). First and second drivers (13a,13b) generate first and second drive signals (22a,22b) for the first and second mirrors (11a,11b) from the first and second drive control signals (24a,24b). The first and second drive control signals (22a,22b) are generated so that the first and second drive signals (22a,22b) each have a same frequency as the pre-drive signal (21) but are different in amplitude from one another to cause the first and second mirrors (11a,11b) to move at a same frequency, with a same and substantially constant given opening angle as one another, and in phase with one another.