MEMS Scanner Drive Signal Locking for Resonant Mode Tracking
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Solution Overview
Problem
MEMS scanning mirrors in pico-projection systems face challenges in operating on their intended resonant mode due to multiple resonant modes, leading to suboptimal performance and inefficiency in beam deflection, as conventional peak search algorithms are susceptible to local minima and require high-resolution analog-to-digital converters and two measurements for direction determination.
Innovation Solution
A digital phase-locked loop system with a direct digital synthesis oscillator and phase comparator is used to generate drive signals that accurately match the MEMS scanner to its correct resonant mode frequency, tracking it over temperature and time while avoiding adjacent modes, utilizing a phase relationship to identify and lock onto the ideal resonant frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional peak search algorithms are used to find resonant mode, then resonant mode can be identified, but the system is susceptible to local minima and requires high-resolution ADC and two measurements per direction
Solution Approach 1:
The patent replaces conventional mechanical peak search algorithms with a digital phase-locked loop system that uses phase detection and feedback control to identify and track resonant modes, eliminating the need for high-resolution ADC and complex search procedures
Solution Approach 2:
The patent implements a feedback mechanism where the phase relationship between drive signal and sensor signal is continuously monitored and used to adjust the drive frequency, enabling automatic locking onto the resonant mode without complex search algorithms
2Adaptability or versatility
If multiple resonant modes are present in MEMS scanner, then more operational frequencies are available, but it becomes difficult to identify and operate on the intended mode
Solution Approach 1:
The phase-locked loop continuously monitors the phase relationship between drive and sensor signals, providing feedback that automatically distinguishes the intended resonant mode from other modes based on the characteristic -180 degree phase shift at resonance
Solution Approach 2:
The patent uses phase shift as a distinctive characteristic (analogous to color change) to identify the resonant mode, where the -180 degree phase shift serves as a unique identifier for the intended operational mode among multiple available modes
3Use of energy by moving object
If resonant mode operation is achieved, then beam deflection efficiency is maximized with minimal energy input, but precise frequency control is required to maintain operation
Solution Approach 1:
The phase-locked loop provides continuous feedback control that automatically adjusts the drive frequency to maintain resonant operation, ensuring maximum energy efficiency without requiring complex manual frequency control mechanisms
Solution Approach 2:
The system uses its own sensor signal as feedback to automatically regulate and maintain resonant operation, making the system self-correcting and eliminating the need for external complex control mechanisms
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 precise operation on the intended resonant mode, enhancing horizontal drive-to-angular motion efficiency, reducing retrace time, and minimizing energy input, thereby improving the overall effectiveness and accuracy of the MEMS scanner.
Implementation Method 1
The horizontal sweep is typically done at one of the resonant mode frequencies of the scanning mirror that is on the order of 18 kHz. Operating on a resonant mode allows maximum beam deflection with minimal input energy.
Implementation Method 2
A digital phase-locked loop system with a direct digital synthesis oscillator and phase comparator is used to generate drive signals that accurately match the MEMS scanner to its correct resonant mode frequency
Data Source
AI summary
A method for generating a drive signal for a micro-electro-mechanical system (MEMS) scanner is provided. The method includes generating the drive signal for the MEMS scanner using a direct digital synthesis, numerically-controlled oscillator. For a particular embodiment, the drive signal is generated by receiving a summation of (i) an initial control word and (ii) an accumulated correction signal generated based on a comparison of a horizontal drive signal for the MEMS scanner and a horizontal sensor signal received from the MEMS scanner. The summation is added to a phase accumulator output, an address is extracted from the phase accumulator output, and a digital lookup table output is addressed based on the extracted address. The digital lookup table output is converted into an analog signal with a digital-to-analog converter, the analog signal is filtered to generate the drive signal, and the horizontal drive signal is generated based on the drive signal.