Optical Amplifier for Laser Keyhole Depth Measurement
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Solution Overview
Problem
Conventional methods for measuring the depth of a vapour capillary (keyhole) in laser welding face challenges such as low light reflection due to the keyhole's small diameter and curvature, leading to inaccurate and unreliable depth measurements, especially at high feed rates and deeper welding depths.
Innovation Solution
The introduction of an optical amplifier in the laser processing system to amplify both the primary and secondary beams, enabling the use of low-power broadband light sources for Fourier domain optical coherence tomography (FD-OCT), which increases the amount of light entering the keyhole and improves signal strength, allowing for precise depth measurement of deeper vapour capillaries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical measurement methods are used to measure keyhole depth, then the measurement can be performed, but the measurement precision deteriorates due to low light reflection from the keyhole
Solution Approach 1:
An optical amplifier is introduced as an intermediary component in the optical path between the light source and the detector. The amplifier boosts the weak reflected light signal from the keyhole, enabling precise depth measurement despite the inherently low reflection intensity from the small, curved keyhole surface.
Solution Approach 2:
The system changes the parameter of light intensity by using an optical amplifier to increase the signal strength. This parameter change transforms the insufficient reflected light into a detectable signal level, resolving the contradiction between low reflection and measurement precision.
2Productivity
If high feed rates are used in laser welding, then productivity increases, but measurement reliability deteriorates due to strong keyhole curvature
Solution Approach 1:
The optical amplifier serves as a mediator that compensates for the signal degradation caused by keyhole curvature at high feed rates. By amplifying the weakened reflected light, it maintains measurement reliability even when the keyhole geometry becomes more complex due to higher welding speeds.
3Length of stationary object
If deeper vapour capillaries are measured, then the measurement range increases, but signal strength decreases leading to insufficient valid data points
Solution Approach 1:
The optical amplifier acts as a signal booster that enables detection of reflections from deeper keyhole regions. By amplifying the progressively weaker signals returning from greater depths, it maintains sufficient data validity across extended measurement ranges.
Solution Approach 2:
The system extends the measurement capability into the deeper dimension by using optical amplification to overcome the signal attenuation that naturally occurs with increased measurement depth, thereby expanding the effective measurement range.
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 solution enhances the precision and reliability of keyhole depth measurements, providing a sufficient number of valid data points for quality assurance and enabling the measurement of deeper vapour capillaries by increasing the signal-to-noise ratio and light intensity.
Implementation Method 1
at least one optical amplifier configured to amplify the primary beam and/or the secondary beam
Implementation Method 2
an evaluation unit that is configured to evaluate interference between spectral components in the frequency domain
Data Source
AI summary
The present disclosure concerns a device for distance measurement for a laser processing system. The device comprises a light source, which is configured to generate a primary beam for direction onto a workpiece, at least one detection device configured to record a secondary beam reflected from the workpiece, at least one optical amplifier configured to amplify the primary beam and/or the secondary beam, and an evaluation unit configured to evaluate interference between spectral components in the frequency domain.