Laser Beam Alignment for Keyhole Depth Measurement Accuracy
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Solution Overview
Problem
The existing laser processing apparatuses face challenges in accurately measuring the depth of a keyhole due to deviations caused by chromatic aberration characteristics of fθ lenses, which differ in wavelengths between processing and measurement laser beams.
Innovation Solution
A laser processing apparatus is designed with a galvanometer mirror and fθ lens configuration, incorporating a control unit and beam shift mechanism to adjust the incident angle and position of the measurement beam, using corrected processing data to align the processing and measurement beams accurately, thereby correcting for deviations caused by chromatic aberration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an fθ lens is used to focus both processing laser beam and measurement beam, then the laser processing apparatus can optically scan the processing laser beam using a galvanometer mirror, but a deviation occurs between the processing laser beam and measurement beam on the workpiece surface due to chromatic aberration
Solution Approach 1:
The patent divides the optical system into separate processing optical path and measurement optical path. The processing laser beam and measurement beam are transmitted through different optical paths after the dichroic mirror, allowing independent optimization of each path to avoid chromatic aberration-induced deviation while maintaining optical scanning capability.
Solution Approach 2:
A dichroic mirror is introduced as an intermediary optical element that separates the processing laser beam and measurement beam based on their different wavelengths. This mediator enables the two beams to share the galvanometer mirror for scanning while preventing chromatic aberration from causing positional deviation on the workpiece surface.
2Device complexity
If the processing laser beam and measurement beam share a coaxial configuration, then the optical system is simplified, but it becomes difficult to accurately measure the depth of the keyhole due to beam deviation
Solution Approach 1:
The patent segments the optical paths after the dichroic mirror, creating separate processing and measurement channels. This segmentation maintains relative simplicity in the overall system while enabling accurate beam positioning by eliminating chromatic aberration effects that would otherwise prevent precise keyhole depth measurement.
Solution Approach 2:
The dichroic mirror serves as an intermediary that allows the processing and measurement beams to share the initial optical path up to that point, then separates them into distinct paths. This intermediary approach preserves system simplicity while achieving the measurement accuracy needed for keyhole depth detection.
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 enables precise measurement of keyhole depth by ensuring accurate alignment and focus of both beams, improving measurement accuracy and reliability.
Implementation Method 1
generates an optical interference intensity signal based on interference generated due to an optical path difference between the measurement beam and a reference beam
Implementation Method 2
a deviation may occur between a processing laser beam and a measurement beam on a surface of a workpiece due to chromatic aberration characteristics of the fθ lens due to a difference between wavelengths
Data Source
AI summary
A laser processing apparatus is used which includes: a laser oscillator that oscillates a processing laser beam at a processing point to be processed on a surface of a workpiece; an optical interferometer that emits a measurement beam to the processing point and generates an optical interference intensity signal based on interference generated due to an optical path difference between the measurement beam reflected at the processing point and a reference beam; a first mirror that changes traveling directions of the processing laser beam and the measurement beam; a second mirror that changes an incident angle of the measurement beam onto the first mirror; a lens that focuses the processing laser beam and the measurement beam on the processing point; a memory that stores corrected processing data; a control unit that controls the laser oscillator, the first mirror, and the second mirror based on the corrected processing data; and a measurement processing unit that derives a depth of a keyhole generated at the processing point by the processing laser beam, based on the optical interference intensity signal.