Laser Keyhole Depth Sensing via Mirror-Corrected Beam Alignment
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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, which causes deviations in the irradiation positions of processing and measurement laser light, leading to inaccurate keyhole depth measurement.
Innovation Solution
A laser processing apparatus that includes a controller to adjust the first and second mirrors based on corrected processing data, which accounts for chromatic aberration, ensuring accurate alignment and measurement of keyhole depth by generating optical interference signals and using a measurement processor to project data for precise depth measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a lens is used to collect processing laser light and measurement light at the same processing point, then both lights can be focused at the target position, but chromatic aberration occurs because the wavelengths of processing laser light and measurement light are different, causing deviation between irradiation positions
Solution Approach 1:
The system pre-calculates chromatic aberration deviation amounts for different wavelengths and processing points, and applies correction values in advance to the mirror operation amounts. This preliminary correction ensures that even though chromatic aberration occurs, the measurement light is redirected to compensate for the deviation, achieving accurate keyhole depth measurement despite the wavelength difference between processing and measurement light.
2Device complexity
If the same lens is used for both processing laser light and measurement light, then device complexity is reduced, but chromatic aberration causes deviation in arrival positions on the processing surface
Solution Approach 1:
The system changes the operational parameters of the mirrors based on wavelength-specific correction values. By adjusting the mirror operation amounts according to pre-calculated chromatic aberration characteristics for different wavelengths, the system compensates for the positional deviation caused by using a single lens for both processing and measurement light, maintaining precision without increasing device complexity.
3Device complexity
If chromatic aberration is not corrected, then the system operates simply without correction mechanisms, but the deviation between processing and measurement light arrival positions prevents accurate keyhole depth measurement
Solution Approach 1:
The system incorporates a feedback mechanism where pre-calculated chromatic aberration correction data is applied to adjust mirror operations. The correction values are determined based on the specific wavelengths and processing conditions, and this feedback loop ensures that the measurement light compensates for chromatic aberration effects, achieving accurate measurement without requiring complex hardware correction mechanisms.
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
The solution enables accurate measurement of keyhole depth by correcting for chromatic aberration, ensuring precise alignment and measurement of keyhole depth, thereby improving the accuracy of laser processing.
Implementation Method 1
generates an optical interference 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
since wavelengths of the processing laser light and the measurement light are different from each other, chromatic aberration occurs in the fθ lens
Implementation Method 3
a lens that collects the processing laser light and the measurement light at the processing point
Implementation Method 4
a first mirror that changes traveling directions of the processing laser light and the measurement light
Data Source
AI summary
A laser processing apparatus sets a processing section passing through a target position on a processing surface, sets a measurement section centered on the target position in the processing section, sets a plurality of data acquisition positions that are trajectories perpendicular to a processing direction in the measurement section. The laser processing apparatus acquires pieces of measurement data indicating shapes of keyholes at the respective data acquisition positions during processing of the processing section, and projects the pieces of measurement data in the processing direction to be superimposed on each other to create projection data. The laser processing apparatus obtains the second instruction value in a direction perpendicular to the processing direction at the target position on the basis of the projection data. Therefore, it is possible to provide a laser processing apparatus and a laser processing method capable of accurately measuring a depth of a keyhole.