Annular Laser Height Detection for Transmissive Workpieces
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Solution Overview
Problem
Existing height position detection methods fail to accurately detect the upper surface of workpieces made from materials that are transmissive to visible rays, such as sapphire and quartz, due to the laser beam being transmitted through and reflected on both surfaces, making it impossible to measure the light reflected only from the upper surface.
Innovation Solution
A laser beam position detecting apparatus and method that oscillates a laser beam, forms it into an annular shape, uses a beam splitter to guide the beam into separate paths, and employs a pinhole mask to intercept light reflected from the lower surface while allowing light from the upper surface to pass through, allowing for accurate detection of the upper surface height using a diffusing means and detection surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a laser beam is used to detect the height position of a workpiece surface, then the detection speed and precision are improved, but when the workpiece is made of transmissive materials like sapphire or quartz, the laser beam is transmitted through and reflected from both surfaces, making it impossible to measure only the light reflected from the upper surface
Solution Approach 1:
The patent segments the reflected light from different surfaces by using a beam splitter to separate the optical path into first and second paths. The pinhole mask in the second path selectively blocks light from the lower surface while allowing light from the upper surface to pass through, thereby separating the mixed reflection signals into distinct detectable components.
Solution Approach 2:
The patent extracts only the useful reflected light from the upper surface by using a pinhole mask that blocks the transmitted laser beam and lower surface reflections in the second optical path. This extraction isolates the desired signal (upper surface reflection) from unwanted signals (lower surface reflection and transmitted beam), enabling accurate height position detection of transmissive workpieces.
2Adaptability or versatility
If the laser beam wavelength is changed to be transmitted through the workpiece, then the ability to process transmissive materials is improved, but the detection accuracy of the upper surface height position deteriorates due to multiple reflections
Solution Approach 1:
The patent introduces a beam splitter as an intermediary device that divides the optical path into two separate paths. This intermediary allows the system to simultaneously handle transmitted laser beams through the workpiece while separately detecting reflections from different surfaces, thereby enabling detection of transmissive materials without sacrificing measurement precision.
Solution Approach 2:
The patent creates separate optical copies of the reflected light from different surfaces by using a beam splitter to direct light into two distinct paths. The first path captures reflections from both surfaces while the second path, with the pinhole mask, selectively captures only upper surface reflections, effectively creating separate measurement channels that preserve detection accuracy for transmissive materials.
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
Enables assured and accurate detection of the upper surface height of workpieces even when they are transmissive to visible rays, by differentiating between light reflected from the upper and lower surfaces, effectively overcoming the limitations of previous detection systems.
Implementation Method 1
a beam splitter for guiding into a first path the laser beam with the annular spot shape formed to be annular by the annular spot forming means
Implementation Method 2
a pinhole mask disposed in a second path into which the laser beam reflected on the workpiece held on the holding means is dividedly guided by the beam splitter
Implementation Method 3
means for diffusing the laser beam, the diffusing means disposed on the second path at a position on a downstream side relative to the pinhole mask
Implementation Method 4
detection means having a detecting surface with a predetermined area for detecting the intensity of the laser beam diffused by the laser beam diffusing means
Data Source
AI summary
A laser beam having an annular spot shape with which a workpiece is irradiated is reflected on an upper surface and a lower surface of the workpiece. The reflected light having the annular spot shape which is reflected on the lower surface of the workpiece is intercepted by a pinhole mask, whereas the reflected light having the annular spot shape which is reflected on the upper surface of the workpiece is permitted to pass through the pinhole mask, and the intensity of light received is detected based on the latter reflected light. Therefore, the height position of the upper surface of a workpiece can be detected even where the workpiece is transmissive to visible rays. In this case, with regard to the reflected light having the annular spot shape which is reflected on the upper surface of the workpiece, the intensity of the light after diffusion by a laser beam diffusing unit is detected by a photodetector having a detecting surface with a predetermined area. This makes it possible to assuredly and accurately detect the upper surface height position of the workpiece, even in the presence of scattering of the annular spot shape.