Laser Machining Head Telecentric Imaging Against Thermal Lens Drift
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Solution Overview
Problem
Laser processing heads face challenges in process monitoring accuracy due to thermal lens effects in focusing lenses, which cause focal length changes and degrade imaging properties, especially when workpieces are at varying distances or not aligned perfectly perpendicular to the laser beam.
Innovation Solution
The laser processing head incorporates an optical imaging device with a telescope design and a diaphragm positioned in the observation beam path to create a virtual aperture, allowing for telecentric imaging and compensation of thermal lens effects, ensuring accurate monitoring regardless of focal length changes or object distance variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a focusing lens is used to focus the processing laser beam, then the laser beam can be focused onto the workpiece, but thermal lens effects cause focal length changes and degrade imaging properties
Solution Approach 1:
The optical system is segmented into separate functional components: the focusing lens for laser beam focusing and a separate imaging lens for observation. This segmentation allows each component to be optimized for its specific function without interference from thermal effects in the other, resolving the contradiction between maintaining focusing power and preserving imaging accuracy.
Solution Approach 2:
A beam splitter is introduced as an intermediary element that separates the processing laser beam from the observation beam path. This allows the imaging system to observe the processing area without the observation beam being affected by thermal lens effects in the focusing lens, while still enabling the focusing lens to perform its high-power focusing function.
2Adaptability or versatility
If the object distance from the focusing lens changes, then different workpiece positions can be processed, but observation accuracy deteriorates due to non-telecentric imaging
Solution Approach 1:
The imaging system is designed with telecentric imaging characteristics, where the aperture stop is positioned at the front focal plane of the imaging lens. This dynamic design ensures that principal rays are parallel to the optical axis regardless of object distance changes, maintaining consistent magnification and observation accuracy across varying workpiece positions while preserving adaptability.
3Ease of operation
If the workpiece is not aligned exactly perpendicular to the laser beam, then flexible positioning is possible, but imaging accuracy is negatively affected
Solution Approach 1:
The imaging system creates an optical copy of the processing area through telecentric imaging, which maintains accurate geometric relationships and magnification even when the workpiece is positioned at varying angles or distances. This optical copying mechanism preserves imaging accuracy while allowing flexible workpiece positioning and orientation.
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 accuracy and flexibility of process monitoring by maintaining consistent magnification and image quality despite thermal stress and varying object distances, effectively addressing the limitations of coaxial process observation.
Implementation Method 1
a beam splitter for separation the observation beam path of the observation radiation from the processing beam path of the processing laser beam
Implementation Method 2
a focusing device for focusing a processing laser beam onto a workpiece to be processed
Implementation Method 3
absorption of the processing laser radiation in the lens substrate and in the typical Turn the existing lens coating into a thermal lens, i.e. the refractive index in the substrate is no longer homogeneous but changes with the temperature gradient that develops
Data Source
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AI summary
The invention relates to a laser-machining head (1) comprising the following: a focusing device (2) for focusing a machining laser beam (3) onto a workpiece (4) to be machined which is arranged in a machining beam path (14) of the machining laser beam (3); an optical imaging device (5) which comprises a detector (6) and which is designed to form a monitoring beam (8) from a machining region (9) of the workpiece (4) onto the detector (6) along a monitoring beam path (10) that passes through the focusing device (2); and a beam splitter (13) for separating the monitoring beam path (10) of the monitoring beam (8) from the machining beam path (14) of the machining laser beam (3). The laser-machining head (1) has an optical imaging device (5) optical imaging unit (16) arranged in the monitoring beam path (10) between the beam splitter (13) and the detector (6) and a diaphragm (15) which is arranged between the optical imaging unit (16) and the detector (6) and which is spaced from the detector (6). The optical imaging unit (16) is designed to generate an image (15a) of the diaphragm (15) in the machining beam path (14) of the machining laser beam (3) between the beam splitter (13) and the workpiece (4). The invention also relates to a laser-machining machine (20) comprising such a laser-machining head (1) and a beam source (21) for generating the machining laser beam (3).