Laser Focus Adjustment Using Chromatic Aberration
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for adjusting the focus of a laser beam during laser processing fail to account for thermal effects that cause changes in the effective machining point (TCP) due to thermal stress on optical components, leading to inefficiencies and inaccuracies, especially in laser cutting and welding processes.
Innovation Solution
A method and device that use adjustment light sources with different wavelengths to determine the current focus position of the laser beam, allowing for real-time adjustments during processing, incorporating chromatic aberration to decouple and detect radiation, and adaptive mirrors for precise focus control, enabling the focus to be adjusted on-line to account for thermal-induced shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If focus adjustment is performed offline before processing, then initial focus position can be set with high accuracy, but thermal effects during processing cannot be compensated leading to TCP position drift
Solution Approach 1:
The patent implements a feedback mechanism where the radiation detector continuously monitors the radiation pattern during laser processing, and the control unit adjusts the focusing optics based on this feedback to maintain optimal focus position despite thermal effects. This closed-loop control ensures both high measurement precision and process stability.
Solution Approach 2:
The patent performs preliminary focus adjustment offline before processing to establish accurate initial focus position, then maintains this focus during processing through continuous monitoring and adjustment. This combination of preliminary action and ongoing correction resolves the contradiction between initial accuracy and thermal stability.
2Ease of operation
If capacitive working distance control is used, then working distance can be regulated, but thermal-induced TCP position changes cannot be detected and compensated
Solution Approach 1:
The patent introduces a radiation detector as an intermediary measurement device that indirectly detects TCP position changes by monitoring radiation patterns. This mediator enables precise TCP position detection without direct interference with the laser processing, overcoming the limitations of capacitive control.
3Ease of operation
If capacitive distance measurement is used for laser cutting, then working distance can be controlled, but measurement accuracy deteriorates when laser beam strikes surface at acute angles due to different axial and lateral sensitivities
Solution Approach 1:
The patent replaces the capacitive measurement system with an optical measurement approach using radiation detection. This substitution eliminates the directional sensitivity issues of capacitive sensors, as the radiation detector can accurately measure TCP position changes regardless of the laser beam's angle of incidence on the workpiece surface.
4Ease of operation
If capacitive working distance measurement is used for laser welding, then working distance can be measured, but measurement precision is significantly reduced due to disturbance from metal vapor protective gas cloud
Solution Approach 1:
The patent uses radiation detection as an intermediary measurement method that is not affected by the metal vapor protective gas cloud. The radiation detector measures TCP position through optical radiation patterns that penetrate the gas cloud, providing accurate measurements in the challenging welding environment where capacitive sensors fail.
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 allows for precise and dynamic adjustment of the laser beam focus, ensuring optimal processing conditions by accounting for thermal effects, improving the accuracy and efficiency of both laser cutting and welding processes.
Implementation Method 1
The electromagnetic radiation generated around the processing point by scattering and/or reflection of the laser beam of the processing laser on the surface of the workpiece to be processed is decoupled using an optical system with chromatic aberration and guided to a first detector that records the intensity of this radiation.
Implementation Method 2
Changes in the position of the TCP occur as a result of thermal stress on the optical components of the beam guidance system and as a result of thermally induced focal length changes (so-called "thermal lensing" effects).
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
The invention relates to a method for detecting and adjusting the focus (F) of a laser beam when laser machining workpieces, having the following steps: a.) guiding and focusing a laser beam of a machining laser (1) emitted from a machining head (48) into a machining point (26) on or with respect to the surface (49) of a workpiece to be machined, wherein the focusing takes place by means of an optical focusing element (2); b.) guiding and focusing the radiation (28, 31) emitted by at least one first adjusting light source (22) and one second adjusting light source (23) onto the surface (49) of the workpiece to be machined, wherein the wavelengths of the radiation emitted by the adjusting light sources (22, 23) are different; c.) uncoupling the electromagnetic radiation arising about the machining point (26) due to scattering and/or reflecting the laser beam (1) of the machining laser at the surface (49) of the workpiece to be machined, by means of an optical system (2, 4) having chromatic aberration, and detecting the intensity thereof by means of a first detector (5); d.) uncoupling the radiation (34, 36) of the adjusting light sources (22, 23) reflected back from the surface of the workpiece to be machined by means of the optical system (2, 4) having chromatic aberration and separate detecting of the intensities of the reflected radiation (34, 36) of the adjusting light sources (22, 23) by means of at least one second detector (20); e.) determining the location of the focus (F) of the laser beam (1) of the machining laser using the intensities captured in the steps c.) and d.); and f.) adjusting the focus (F) of the laser beam (1) of the machining laser to a desired machining point (26) with respect to the surface (49) of the workpiece to be machined.