MEMS Mirror Opening Angle Measurement via Capacitance Feedback
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Solution Overview
Problem
Existing MEMS devices face challenges in precisely controlling the opening angle of oscillating mirrors due to changes in temperature and light beam characteristics, leading to inaccurate data collection and commercially undesirable performance.
Innovation Solution
A feedback measuring circuit and processing circuitry are used to determine the maximum capacitance of a movable MEMS mirror, calculating the total change in capacitance over time, and subsequently determining the opening angle, allowing for precise control of the mirror's position through a control signal generated by the processing circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional capacitance measurement methods are used to determine mirror position, then the measurement system is simple, but temperature changes and light beam variations cause measurement inaccuracies
Solution Approach 1:
The patent implements a feedback mechanism where the measured capacitance signal is continuously monitored and used to determine mirror position. The system measures capacitance at multiple points during the oscillation cycle, detects the maximum capacitance point, and uses this feedback information to accurately determine the opening angle despite environmental variations.
Solution Approach 2:
The patent performs preliminary measurement of the maximum capacitance point during each oscillation cycle before using this reference point to calculate the opening angle. By establishing this reference point in advance within each cycle, the system can accurately determine position without being affected by temperature drift or light beam variations that occur over longer time periods.
2Productivity
If the mirror oscillates to scan light beams, then scanning coverage is achieved, but precise control of the opening angle becomes difficult due to environmental factors
Solution Approach 1:
The patent replaces direct mechanical measurement of the opening angle with an electrical measurement system. Instead of using mechanical sensors or encoders to measure the mirror position, the system uses capacitance measurements of the drive signal to determine the opening angle, thereby achieving precise control without sensitive mechanical components that would be affected by environmental factors.
3Measurement precision
If capacitance measurements are taken over long time windows to improve accuracy, then measurement precision improves, but the system becomes more sensitive to environmental drift
Solution Approach 1:
The patent uses periodic action by measuring capacitance at specific points within each oscillation cycle of the mirror. Instead of taking continuous measurements over long time periods, the system captures capacitance data periodically at the maximum capacitance point and other specific phases of the oscillation cycle, allowing accurate measurement without accumulating environmental drift errors.
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 method enables accurate and precise control of the opening angle of the MEMS mirror, improving the performance of devices like wafer defect scanners and projectors by compensating for environmental factors and ensuring consistent operation.
Implementation Method 1
measuring a signal flowing through the movable MEMS mirror... determines a time at which the signal indicates that a capacitance of the movable MEMS mirror is substantially at a maximum capacitance
Data Source
AI summary
A device disclosed herein includes a feedback measuring circuit to measure a signal flowing through a movable MEMS mirror. Processing circuitry determines a time at which the signal indicates that a capacitance of the movable MEMS mirror is substantially at a maximum capacitance. The processing circuitry also determines, over a window of time extending from the time at which the signal indicates that the capacitance of the movable MEMS mirror is substantially at the maximum to a given time, a total change in capacitance of the movable MEMS mirror compared to the maximum capacitance. The processor further determines the capacitance at the given time as a function of the total change in capacitance, and determines an opening angle of the movable MEMS mirror as a function of the capacitance at the given time.