Low-Coherence Interferometry for Sub-Sampled Distance Sensing
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Solution Overview
Problem
Current methods for determining the separation distance between a processing tool and a material, especially in laser processing, are inaccurate and prone to errors due to the shape of the material and processing conditions, and lack robustness across a wide range of distances.
Innovation Solution
The implementation of low coherence optical interferometry techniques, which use a measurement optical path integrated in the machine tool and a reference optical path to detect interference fringes, allowing for precise and robust distance measurement independent of material morphology and processing conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional distance measurement methods are used in laser processing, then the measurement can be performed, but the measurement precision deteriorates due to material shape and processing conditions
Solution Approach 1:
The patent replaces conventional mechanical or capacitive distance measurement methods with optical interferometry. The system uses a low-coherence light source to generate interference patterns between a measurement beam (reflected from the material surface) and a reference beam, enabling non-contact, high-precision distance measurement that is immune to material shape and processing condition variations.
Solution Approach 2:
The patent changes the measurement parameter from direct intensity-based detection to interference fringe analysis. By using low-coherence light and analyzing the position and shape of interference fringes, the system achieves high measurement precision that is independent of material reflectivity, surface shape, and processing conditions such as laser power or gas flow.
2Adaptability or versatility
If the measurement range is extended to cover a large distance variation, then the adaptability improves, but the measurement precision deteriorates due to sub-sampling effects
Solution Approach 1:
The patent introduces an intermediary computational step: instead of directly measuring distance from fringe position, the system uses a lookup table or calibration curve that maps measured fringe characteristics to actual distance values. This intermediary approach allows the system to maintain high precision across a large measurement range by compensating for sub-sampling effects through pre-calibrated data.
Solution Approach 2:
The patent analyzes interference fringes in both spatial position and intensity/shape characteristics. By utilizing multiple dimensions of fringe information (position, width, intensity distribution) rather than just position alone, the system achieves accurate distance measurement even when the fringe spacing is smaller than the detector pixel size, thereby extending the measurable range without sacrificing precision.
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 approach provides accurate and robust distance measurements over a large range, unaffected by material shape or processing conditions, enabling precise control of laser processing tools like cutting, drilling, and welding.
Implementation Method 1
generating a measurement beam of optical radiation M on a measurement optical path PM and generating a reference beam R of optical radiation on a reference optical path PR; superimposing the measurement beam M and the reference beam R on a common region of incidence C of a sensor arrangement S, at a predetermined angle of incidence α, so as to form a pattern of interference fringes F
Data Source
Figure 1~2a
Figure 2b~2c
Figure 3
AI summary
A method and a system are described for determining the separation distance between an object or a material and a processing tool or an instrument for measuring the object or material, comprising: - generating a measurement low coherence optical radiation beam, leading the measurement beam towards the object and leading the reflected or diffused measurement beam from the object 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 means 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 means; - 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 processing tool or measuring instrument and the surface of the object and (b) the predetermined nominal separation distance, wherein the sensor means comprise an arrangement of photodetectors along the illumination axis, and the angle of incidence is controlled in such a way that the spatial frequency of the pattern of interference fringes is greater than the spatial frequency of the photodetectors.