MEMS Mirror Resonant Frequency Control via Polar Coordinate Feedback
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Solution Overview
Problem
Prior art video projection apparatuses face challenges in accurately controlling the projected view field due to susceptibility to electromagnetic interference (EMI) and environmental factors like temperature and humidity, which affect the operation of the digital phase locked loop (PLL) circuit and the monitoring of the mirror's flexing angle, leading to suboptimal resonant frequency realization.
Innovation Solution
A video projection apparatus that includes a light source, an optical deflector with a mirror, an actuator, and a sensor, where a control unit generates sinusoidal-wave voltages with a 90° phase difference, calculates convolutions between these voltages and the sense voltage, converts the orthogonal coordinates into polar coordinates, and sweeps the frequency to determine the resonant frequency based on the maximum radius component, ensuring accurate control of the projected view field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a digital phase locked loop (PLL) circuit is used to lock frequency and phase of the MEMS scanner, then the scanner can operate at high resonant frequency, but the circuit becomes susceptible to electromagnetic interference (EMI) and environmental factors causing suboptimal frequency realization
Solution Approach 1:
The patent implements a feedback mechanism where the sense voltage from the sensor is convolved with reference sinusoidal voltages, and the resulting orthogonal coordinates are converted to polar coordinates. The radius component of the polar coordinate serves as a feedback signal indicating the degree of resonance, allowing the system to adjust and maintain optimal resonant frequency operation despite environmental disturbances.
Solution Approach 2:
The patent changes the monitoring parameter from simple phase-locked frequency detection to amplitude-based resonance detection using polar coordinate transformation. By sweeping the frequency and identifying the maximum radius component in the polar coordinate system, the system can dynamically adjust the operating frequency to maintain optimal resonance conditions.
2Reliability
If the MEMS scanner is susceptible to electromagnetic interference and environmental factors, then the digital PLL circuit cannot operate at optimal frequency and phase, but increasing shielding and environmental control would increase device complexity
Solution Approach 1:
The patent enables the system to self-adjust and self-correct by using the sense voltage and convolution calculations to automatically identify and lock onto the optimal resonant frequency. The polar coordinate transformation and radius component monitoring provide inherent noise rejection capabilities without requiring complex external shielding or environmental control systems.
3Measurement precision
If only frequency and phase are locked by the digital PLL circuit, then the amplitude of the sense voltage representing the flexing angle cannot be monitored, making it difficult to accurately realize optimum resonant frequency
Solution Approach 1:
The patent transforms the one-dimensional frequency detection into a two-dimensional polar coordinate system by convolving the sense voltage with both in-phase and quadrature-phase reference signals. This dimensional transformation allows simultaneous monitoring of both amplitude (radius component) and phase (angle component), providing comprehensive resonance characterization without adding significant system complexity.
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 the determination of an optimum resonant frequency, enabling precise control of the projected view field and reducing the impact of environmental and electromagnetic noise.
Implementation Method 1
an actuator for rocking the mirror with an axis of the mirror
Implementation Method 2
a sensor provided in the vicinity of the actuator... a sense voltage from the sensor
Implementation Method 3
sweeps the frequency of the first and second sinusoidal-wave voltages so that the frequency of the first and second sinusoidal-wave voltages is defined as a resonant frequency when the radius component is maximum
Implementation Method 4
an optical deflector having a mirror for reflecting light from the light source to project a view field
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A video projection apparatus includes: a light source (22); an optical deflector (19) having a mirror (191) for reflecting light (L) to project a view field (F), an actuator (193a) for rocking the mirror (191) with an axis of the mirror (191) and a sensor (197a) provided in the vicinity of the actuator (193a); and a control unit (14, 15, 16). The control unit (14, 15, 16) generates a sine-wave voltage (Vxa) applied to the actuator (193a) and a cosine-wave voltage (Vxa'); calculates a first convolution (X) between the sine-wave voltage (Vxa) and a sense voltage (Vxsa) from the sensor (197a); calculates a second convolution (Y) between the cosine-wave voltage (Vxa') and the sense voltage (Vxsa); converts an orthogonal coordinate formed by the first convolution (X) and the second convolution (Y) into a polar coordinate formed by a radius component (R) and an angle component (θ) and sweeps the frequency (fx) of the first and second voltages (Vxa, Vxa') so that the frequency (fx) is defined as a resonant frequency (fr) when the radius component (R) is maximum.