Scanning Mirror Control for Resonant Vibration Compensation
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Solution Overview
Problem
Controlling the angular motion of mirrors in scanned light beam displays is challenging due to mechanical vibrations at various resonant frequencies, which distort the desired scan trajectories and affect the quality of display images in applications like mobile microprojectors and head-up displays.
Innovation Solution
A scanning mirror control system that modifies drive signals in real-time using feedback loops and harmonic coefficient adjustments, including iterative determination of harmonic coefficients and adaptive learning rates, to compensate for the mirror's resonant characteristics and maintain desired scan trajectories despite high mechanical gain and non-linear responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If mirrors are used to deflect light beams in scanned light beam displays, then compact and portable display packages can be created, but mechanical vibrations at resonant frequencies distort the desired scan trajectories
Solution Approach 1:
The patent implements feedback control by measuring the actual mirror position using sensors (such as capacitive or piezoresistive sensors) and comparing it with the desired position. The difference is used to generate corrective signals that are applied to the mirror drive, thereby compensating for vibrations and maintaining accurate scan trajectories despite the compact mirror-based design
Solution Approach 2:
The patent changes the electrical parameters (voltage or current) applied to the mirror drive in real-time based on the detected vibration characteristics. By dynamically adjusting drive parameters and applying counter-phase signals at resonant frequencies, the system compensates for mechanical vibrations while maintaining the compact mirror structure
2Speed
If high mechanical gain is used to amplify mirror response, then scan speed and responsiveness improve, but non-linear responses and distortion increase
Solution Approach 1:
The feedback control system continuously monitors the actual mirror response and applies corrective signals to linearize the overall system response. This allows the use of high mechanical gain for fast scanning while the feedback loop compensates for non-linearities, maintaining accurate and linear scan trajectories across the entire operating range
Solution Approach 2:
The patent employs dynamic compensation by adjusting drive signals in real-time based on the mirror's instantaneous response characteristics. The control system adapts to changing mechanical conditions and non-linear behaviors during operation, maintaining linear scan trajectories even at high scan speeds where non-linear effects are most pronounced
Data Source
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AI summary
A scanning beam projection system (100) includes a scanning mirror (116) having a fast-scan axis and a slow-scan axis. Movement on the slow-scan axis is controlled by a slow-scan scanning mirror control system (130). The control system receives position information describing angular displacement of the mirror. An outer loop of the control system operates in the frequency domain and determines harmonic drive coefficients for a scanning mirror drive signal. An inner loop of the control system operates in the time domain and compensates for a scanning mirror resonant vibration mode at a frequency within the frequency band occupied by the harmonic drive coefficients.