Laser Keyhole Depth Sensing via Chromatic Aberration Compensation
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Solution Overview
Problem
Laser processing apparatuses with galvano mirrors and fθ lenses face challenges in accurately measuring keyhole depth due to chromatic aberration, causing deviations in the irradiation positions of processing and measurement light, which affects the accuracy of keyhole depth measurement.
Innovation Solution
A laser processing apparatus that includes a movable mirror, a stage to adjust the incident angle of measurement light, and a controller to correct for chromatic aberration by generating and applying correction data, ensuring accurate alignment of processing and measurement light on the workpiece surface, thereby eliminating deviations caused by chromatic aberration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a lens is used to condense laser light for processing and measurement light, then the light can be focused on the processing point, but chromatic aberration causes deviation in arrival positions of different wavelength lights
Solution Approach 1:
The patent applies preliminary action by pre-calculating chromatic aberration deviation amounts for multiple wavelengths and storing them in a lookup table before processing. During actual laser processing, the system simply retrieves the pre-calculated correction values based on the laser wavelength, avoiding real-time complex calculations and enabling fast compensation for chromatic aberration-induced position deviations.
Solution Approach 2:
The patent changes the parameter of incident angle for measurement light to compensate for chromatic aberration. By adjusting the incident angle based on pre-calculated correction data, the system counteracts the wavelength-dependent position deviations caused by the lens, ensuring that measurement light and laser light arrive at the same processing point despite different wavelengths.
2Measurement precision
If correction data is stored for multiple wavelengths, then chromatic aberration can be compensated, but memory requirements increase
Solution Approach 1:
The patent applies local quality by creating separate correction data tables for different wavelength ranges (e.g., first wavelength range with first correction data, second wavelength range with second correction data). Each table contains correction values optimized for its specific wavelength range, allowing the system to use only the relevant correction data for the current laser wavelength, thus reducing the amount of data that needs to be actively managed while maintaining comprehensive coverage.
3Measurement precision
If the incident angle of measurement light is adjusted to compensate for chromatic aberration, then arrival position accuracy improves, but the optical path becomes more complex
Solution Approach 1:
The patent replaces complex real-time optical adjustment mechanisms with a computational approach. Instead of using additional mechanical components or complex real-time control systems to adjust the optical path, the system uses pre-calculated correction data and simple incident angle adjustments that can be implemented through software control, thereby reducing mechanical complexity while achieving accurate chromatic aberration compensation.
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 configuration allows for precise measurement of keyhole depth by correcting for chromatic aberration, ensuring accurate alignment and improving the accuracy of keyhole depth measurement in laser processing.
Implementation Method 1
generates an optical interference intensity signal based on interference caused by an optical path difference between the measurement light reflected at the processing point and reference light
Implementation Method 2
a deviation of an arrival position of at least one of the laser light for processing and the measurement light on the surface of the workpiece caused by chromatic aberration of the lens
Implementation Method 3
a lens that condenses the laser light for processing and the measurement light on the processing point
Data Source
AI summary
Laser processing apparatus includes movable mirror for changing paths of laser light for processing and measurement light, and stage for changing an incident angle of measuring light. Furthermore, laser processing apparatus includes lens for condensing laser light for processing and measurement light on processing point, controller for controlling laser oscillator, movable mirror, and stage based on corrected data for processing, and measurement processor for measuring a depth of keyhole generated at processing point. The corrected data for processing is data corrected so as to a deviation of an arrival position of at least one of laser light for processing and measurement light caused by chromatic aberration of lens on the surface of workpiece. With this configuration, an accurate depth of keyhole can be measured.