Galvanometer Mirror Calibration Using Laser Interferometric Feedback
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Solution Overview
Problem
High-speed galvanometer scanners in applications like laser displays and CNC machines face accuracy and calibration challenges due to torsional servo motor and mirror twist, leading to velocity and positioning errors that are difficult to measure and correct, requiring manual adjustments and relying on qualitative test patterns.
Innovation Solution
A laser-based measurement system that directly measures mirror positions, velocities, and accelerations by impinging a calibration laser beam onto the galvanometer mirrors, using techniques like laser interferometry and Doppler shifts to quantify performance and adjust settings objectively, allowing for automatic recalibration and improved control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high rotation frequencies are used to achieve high speed scanning, then scanning speed is improved, but torsional servo motor and mirror twist increases causing positioning errors
Solution Approach 1:
The patent implements a feedback mechanism using laser interferometry to continuously measure the actual mirror position and velocity, comparing these measurements with the commanded positions from the servo controller. This feedback loop enables real-time detection and correction of torsional errors, allowing the system to maintain positioning accuracy even at high rotation frequencies where mechanical twist occurs
Solution Approach 2:
The patent replaces mechanical position sensing methods with optical measurement techniques. By using laser interferometry instead of mechanical encoders, the system can accurately measure mirror position and velocity without being affected by the mechanical torsional flexibility that plagues traditional encoder-based systems at high speeds
2Manufacturing precision
If manual iterative adjustment of calibration parameters is performed to improve positioning accuracy, then calibration precision is improved, but calibration time increases
Solution Approach 1:
The patent enables the galvanometer system to perform self-calibration by automatically comparing laser-measured positions with commanded positions and adjusting calibration parameters without requiring manual intervention. The system autonomously identifies and corrects positioning errors, eliminating the need for technicians to manually iterate through calibration adjustments while maintaining high calibration accuracy
Solution Approach 2:
The patent introduces laser interferometry as an intermediary measurement system that provides objective, quantitative data about actual mirror positions. This intermediary measurement capability replaces subjective visual assessment of test patterns, enabling both automated calibration and more efficient manual calibration by providing precise numerical feedback on positioning accuracy
3Ease of operation
If qualitative test patterns are used for calibration to improve ease of operation, then calibration simplicity is improved, but measurement precision deteriorates
Solution Approach 1:
The patent replaces qualitative visual inspection of test patterns with quantitative optical measurement using laser interferometry. The laser measurement system provides precise numerical data about mirror position and velocity, replacing the subjective visual assessment method with an objective, high-precision measurement system that can detect subtle positioning errors invisible to the human eye
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 provides precise, quantitative characterization and control of galvanometer systems, reducing errors and improving calibration accuracy, enabling reproducible metrics and automated adjustments for enhanced performance and reliability.
Implementation Method 1
In some embodiments, the mirror position is determined by laser interferometry
Implementation Method 2
causing a laser measurement system to direct a laser beam onto a side region of the mirror; detecting reflected light from the laser beam
Implementation Method 3
In various embodiments, Doppler shifts in the laser frequency are used to characterize the angular velocity of the mirror
Implementation Method 4
in other embodiments the laser position is determined by time-of-flight laser positioning
Data Source
AI summary
A method and apparatus for quantitatively characterizing performance of a laser steering galvanometer mirror directs a laser beam from a calibration “sensor” onto a side region of the mirror to directly determine rotational positioning, velocity, and/or acceleration thereof using interferometry, time-of-flight measurements, and Doppler measurements. Measured positioning errors can be compared with a database to predict required calibration adjustments. Embodiments automatically adjust digital calibrations. Mirrors, splitters, and/or a plurality of sensors can apply measurement beams simultaneously or sequentially to both sides of a mirror, and/or to more than one mirror. Large rotation ranges, for example larger than +/−15 degrees, can be accommodated by applying measurement beams from a plurality of directions. The calibration apparatus can be distinct, or integral with the galvanometer, and can be used to monitor and/or to control the mirror positioning.