Machining Head Distance Sensing via Short-Coherence Interferometry
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Solution Overview
Problem
Existing methods for measuring and controlling the distance between a machining head and a workpiece in laser machining processes, such as capacitive and camera-based triangulation sensors, face inaccuracies due to contamination, spatter interference, and inability to handle nonmetallic surfaces, especially when the workpiece surface is curved or inclined.
Innovation Solution
The method employs optical short-coherence interferometry by splitting a measurement light beam and a reference light beam, which are superimposed on the workpiece surface to determine the distance between the machining head and the workpiece, allowing for precise and dynamic adjustment of the distance and focal position, unaffected by thermal lens effects or surface conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If capacitive measurement is used for distance control, then the measurement is simple and cost-effective, but the measurement accuracy deteriorates due to contamination of the copper tip and changes in capacitance
Solution Approach 1:
The patent replaces the capacitive electrical measurement system with an optical measurement system. A laser beam is directed through the nozzle onto the workpiece surface, and the reflected light is detected by a sensor. This substitution eliminates the harmful electrical field that causes contamination and capacitance changes, providing accurate distance measurement without being affected by spatter or surface contamination.
Solution Approach 2:
The patent introduces light as an intermediary medium for distance measurement. Instead of directly measuring electrical capacitance between the nozzle and workpiece, the system uses light transmission and reflection properties to indirectly determine the distance. The laser beam serves as a mediator that interacts with the workpiece surface and provides measurement information through its reflected intensity, which is then converted into distance data.
2Adaptability or versatility
If camera-based triangulation sensors are used for distance control, then nonmetallic surfaces can be measured, but the measurement accuracy deteriorates due to spatter particles in the image field
Solution Approach 1:
The patent extracts the measurement function from the imaging path of camera-based systems. Instead of using cameras that are blocked by spatter particles, the system uses a separate laser beam path that is focused directly on the workpiece surface. The measurement is based on the intensity of reflected light from the focused beam, which is not affected by particles in the surrounding field of view, thereby maintaining accuracy while measuring nonmetallic surfaces.
Solution Approach 2:
The patent segments the measurement function from the observation function. The laser beam provides a focused measurement point on the workpiece surface, while the detection system separately measures the reflected light intensity. This segmentation allows the measurement to be performed at a specific focal point without being influenced by particles or smoke in the broader imaging area, enabling accurate measurement of nonmetallic surfaces.
3Measurement precision
If the measurement system is made more complex to achieve higher precision, then the measurement accuracy improves, but the device complexity increases
Solution Approach 1:
The patent makes the laser beam serve multiple functions simultaneously. The same laser beam that performs the machining operation also serves as the measurement probe for distance control. The focused laser beam interacts with the workpiece surface, and the reflected light intensity provides distance information. This multi-functionality eliminates the need for separate measurement devices, achieving high precision without increasing overall system complexity.
Solution Approach 2:
The patent merges the machining function and measurement function into a single integrated system. The laser beam path is used for both material processing and distance measurement. The focusing optics and detection system are combined, allowing the measurement to be performed using the same optical components that define the machining process. This merging reduces device complexity while maintaining high measurement 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 enables reliable and precise distance control and focal adjustment, even with nonmetallic materials and under conditions where capacitive methods fail, ensuring accurate machining processes by providing a robust and interference-free measurement.
Implementation Method 1
The method employs optical short-coherence interferometry by splitting a measurement light beam and a reference light beam, which are superimposed on the workpiece surface to determine the distance between the machining head and the workpiece
Implementation Method 2
a measurement light beam is coupled into a processing beam path and focused on a workpiece surface by a focusing lens of the processing beam path
Implementation Method 3
the measurement light beam reflected on the workpiece surface is superimposed with the reflected reference light beam from the reference arm
Data Source
AI summary
The invention pertains to measuring, adjusting and/or controlling a distance between a machining head, particularly a laser machining head, and a workpiece, comprising a measurement light source, a beam splitter that splits the light of the measurement light source into a measurement light beam and a reference light beam, a reference arm, through which the reference light beam is guided, an optical system for coupling the measurement light beam into a processing beam path featuring a focusing lens, an optical device for superimposing the measurement light beam, and a measurement and evaluation unit.