Laser Head Distance Control Using Low-Coherence Interferometry
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Solution Overview
Problem
Current laser processing technologies face challenges in accurately determining the separation distance between the working head and the material surface, especially for non-metal materials and complex surface geometries, leading to inefficiencies in processes like cutting, drilling, and welding.
Innovation Solution
The implementation of low coherence interferometry with spatial domain detection, which uses a measurement optical path integrated in the working head and a reference optical path to generate interference fringes, allowing for precise and robust absolute distance measurements independent of material morphology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional laser processing control methods are used, then the system is simple to operate, but the separation distance measurement accuracy deteriorates for non-metal materials and complex surface geometries
Solution Approach 1:
The patent replaces traditional mechanical or capacitive sensing methods with optical interferometry. A low-coherence light source generates measurement and reference beams that interfere to produce fringes, enabling precise non-contact measurement of separation distance that works independently of material type or surface geometry complexity.
Solution Approach 2:
The patent introduces an optical intermediary system consisting of a low-coherence light source, beam splitter, and interferometric detection mechanism. This intermediary converts the separation distance measurement problem into an optical path difference measurement, which can be accurately detected through interference fringe analysis regardless of the target material properties.
2Manufacturing precision
If real-time distance measurement is implemented, then the laser processing precision is improved, but the measurement system complexity increases
Solution Approach 1:
The patent implements continuous real-time measurement by maintaining constant illumination with the low-coherence light source and continuously detecting interference fringes during laser processing. The measurement beam travels through the processing region and continuously interferes with the reference beam, providing uninterrupted separation distance data for real-time control.
Solution Approach 2:
The patent establishes a feedback loop where the detected interference fringe positions are processed to determine separation distance, which then feeds back to control the laser processing parameters or working head position. This closed-loop system continuously adjusts processing based on real-time distance measurement, improving precision while managing system complexity through automated control.
3Device complexity
If a static interferometric system is used, then computational complexity is reduced, but the measurement range may be limited
Solution Approach 1:
The patent changes the coherence parameter of the light source to low coherence, which fundamentally alters the interferometric measurement characteristics. Low-coherence light provides a longer coherence length, enabling measurement of larger separation distances while maintaining a static interferometric configuration and avoiding complex computational requirements for dynamic analysis.
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 method provides accurate and real-time distance measurements over a large range, enhancing the precision and efficiency of laser processing operations by directly visualizing interference patterns with a static system, reducing computational complexity and avoiding artifacts from reflective surfaces.
Implementation Method 1
superimposing a measurement beam M of low coherence optical radiation and a reference beam R generated by the same source and led towards a sensor arrangement in a second direction of incidence, at a predetermined angle of incidence with respect to the first direction of incidence, so as to form a pattern of interference fringes
Data Source
Figure 1
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Figure 3~4a
AI summary
A method and a system are described for determining and controlling the separation distance between a processing head of a machine tool and the surface of a material, comprising: - generating a measurement low coherence optical radiation beam, leading the measurement beam towards the material and leading the reflected or diffused measurement beam from the surface of the material towards an optical interferometric sensor arrangement in a first direction of incidence, - generating a reference low coherence optical radiation beam, and leading the reference beam towards the optical interferometric sensor arrangement in a second direction of incidence at a preset angle of incidence with respect to the first direction of incidence of the measurement beam; - superimposing the measurement beam and the reference beam on a common region of incidence of the sensor arrangement; - detecting the position of a pattern of interference fringes between the measurement beam and the reference beam on the region of incidence; and - determining a difference in optical length between the measurement optical path and the reference optical path on the basis of the position of the pattern of interference fringes along an illumination axis of the region of incidence, which is indicative of a difference between (a) the current separation distance between the working head and the surface of the material and (b) a predetermined nominal separation distance.