MEMS Lissajous Scan Synchronization for Fast Axis Lock
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Solution Overview
Problem
Existing Lissajous scanning systems require significant time to achieve synchronization between scanning axes, leading to delays in starting up and transmitting light beams, especially in applications requiring fast start-up.
Innovation Solution
A synchronization system for microelectromechanical systems (MEMS) mirrors that includes an oscillator structure, drivers for each axis, a phase error detector, comparator circuit, reference signal generator, and synchronization controller to quickly synchronize the oscillations of two scanning axes by monitoring angular trajectories and triggering reference signals when a phase difference is within a threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the MEMS mirror's resonance curve is walked to the targeted working point and the axis is synchronized towards a reference frequency, then synchronization accuracy is improved, but the start-up time increases significantly
Solution Approach 1:
The system performs preliminary frequency adjustment and phase alignment before full synchronization is required. The control circuit pre-adjusts the driving frequency of the second axis to match the reference frequency and pre-aligns phases, so that when light beam transmission begins, the axes are already closely synchronized, reducing the time penalty of achieving Lissajous lock.
Solution Approach 2:
The system dynamically adjusts the driving frequency and phase of the MEMS mirror axes during operation. The control circuit continuously monitors the phase difference between axes and dynamically modifies the driving signals to maintain synchronization, allowing the system to adapt to frequency drift and phase errors without requiring complete re-synchronization.
2Measurement precision
If large phase errors are compensated for by adjusting the driving frequency, then synchronization is achieved, but the total start-up time is violated
Solution Approach 1:
The system applies partial phase compensation during the start-up phase rather than waiting for complete phase alignment. The control circuit compensates for phase errors progressively as the axes approach synchronization, allowing light transmission to begin before perfect phase alignment is achieved, thus meeting start-up time requirements while still achieving acceptable synchronization.
Solution Approach 2:
The system rushes through the synchronization process by allowing light beam transmission to commence before full Lissajous lock is achieved. The control circuit enables operation with approximate synchronization and continues to refine phase alignment during operation, effectively skipping the time-consuming wait for perfect synchronization.
3Adaptability or versatility
If frequency shifts are performed for control and compensation tasks, then synchronization flexibility is improved, but oscillation stability deteriorates due to collapse of the response curve
Solution Approach 1:
The system performs preliminary frequency adjustment to bring the driving frequency close to the MEMS mirror's resonance peak before making finer adjustments. By pre-positioning the operating point on the resonance curve, the system maintains oscillation stability while having the flexibility to make small frequency shifts for synchronization control without risking collapse.
Solution Approach 2:
The system carefully controls the magnitude and rate of frequency parameter changes to remain within the stable operating region of the MEMS mirror's resonance curve. The control circuit monitors oscillation amplitude and adjusts frequency parameters to maintain operation on the upper response curve, preventing collapse while achieving the necessary frequency flexibility for synchronization.
Data Source
AI summary
A method of synchronizing a first oscillation about a first axis with a second oscillation about a second axis includes: generating a first position signal that indicates a position of the first oscillation about the first axis; generating a second position signal that indicates a position of the second oscillation about the first axis; determining a phase difference between the first and the second position signals; comparing the phase difference to a threshold value to generate a comparison result; generating a reference signal having a first frequency; synchronizing the first oscillation to the first frequency; and triggering a start of the reference signal responsive to the comparison result indicating that the phase difference is less than the threshold value.