MEMS Scanning Mirror Frequency Tuning via Virtual Spring
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Solution Overview
Problem
MEMS scanning mirrors face challenges in maintaining a uniform operating frequency, which is crucial for image quality, due to manufacturing tolerances and thermal effects causing shifts in mechanical resonance frequency, making it difficult to operate at the desired scanning frequency without consuming significant power.
Innovation Solution
An active feedback loop or virtual spring is applied to the scanning mirror, adjusting its stiffness by applying a force proportional to the scanning angle, allowing the resonance frequency to be tuned to match the desired scanning frequency, thereby maintaining a constant operating frequency with minimal power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the scanning mirror operates at its mechanical resonance frequency, then power consumption is minimized, but the operating frequency becomes unstable due to manufacturing tolerances and thermal effects
Solution Approach 1:
The patent implements a feedback control system that continuously monitors the actual operating frequency of the scanning mirror and dynamically adjusts the drive signal to maintain the desired frequency. This closed-loop approach compensates for frequency drift caused by manufacturing tolerances and thermal effects, ensuring stable operation while minimizing power consumption by keeping the mirror near its resonance frequency.
Solution Approach 2:
The patent dynamically changes operational parameters (drive frequency, stiffness compensation) in response to detected frequency deviations. By adjusting these parameters in real-time, the system maintains optimal operating conditions despite environmental variations, resolving the contradiction between energy efficiency and frequency stability.
2Use of energy by moving object
If the scanning frequency is adjusted to match the mechanical resonance frequency, then power consumption decreases, but the scanning frequency may not meet external application requirements
Solution Approach 1:
The patent makes the scanning system dynamically adjustable by implementing active stiffness control through feedback. This allows the system to adapt its resonance frequency in real-time to match external application requirements while maintaining minimal power consumption. The dynamic adjustment capability enables the system to serve multiple applications with different frequency requirements.
Solution Approach 2:
The patent changes the effective stiffness parameter of the scanning mirror system through active control, which in turn adjusts the resonance frequency. This parameter modification allows the system to match both the application's frequency requirements and the mirror's resonant characteristics, achieving both energy efficiency and adaptability.
3Manufacturing precision
If manufacturing tolerances are tightened to reduce resonance frequency variations, then frequency uniformity improves, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent implements a self-service approach where the control system automatically compensates for manufacturing variations without requiring manual calibration or adjustment. The feedback control algorithm adapts to each mirror's specific characteristics, eliminating the need for tight manufacturing tolerances while maintaining frequency uniformity across production batches.
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 enables MEMS scanning mirrors to operate at a consistent frequency, enhancing image quality by reducing power requirements and compensating for manufacturing and thermal variations, allowing for synchronized operation of multiple mirrors.
Implementation Method 1
A feedback loop, sometimes referred to as a virtual spring, is applied to the scanning mirror. The feedback loop applies a force to the mirror that is proportional to an angular position of the mirror.
Implementation Method 2
A frequency of at least one component of the drive signal is other than two times the input frequency. A frequency of another component of the drive signal may equal about two times the output frequency. The system also comprises an oscillator for generating pump oscillations responsively to the drive signal and applying parametric excitation to the input oscillation at the pump oscillations.
Implementation Method 3
Simple harmonic motion is typified by oscillation of the mass m on a spring which is subject to a force F acting to extend or compress the spring by a distance, x, where the force F is (if x is small compared to the total possible deformation of the spring) linearly related to x. Therefore, F/x is a—constant, characterizing stiffness of a given spring. Herein, Ky, that constant, characterizes a physical spring's stiffness. Simple harmonic motion is sinusoidal over time and has a single frequency.
Implementation Method 4
According to Wikipedia, resonance is the increased amplitude that occurs when the frequency of a force, periodically applied to a system, equals a natural frequency of the system—relative to the (typically manifoldly) lower amplitude which occurs if the same force is applied at a frequency which differs from the system's natural frequency.
Data Source
AI summary
A method for projecting an image comprising providing a scanning mirror having a resonance frequency which is unequal to a target operating frequency (aka “scanning frequency”) at which the mirror is to operate; and/or providing logic and an actuator e.g. motor; and/or using the scanning mirror to project at least one image, including repeatedly using the logic to measure the mirror's operating frequency and to control the actuator to apply at least one force, to the mirror, which causes the mirror's instantaneous operating frequency to equal the target operating frequency.