Original article

Objective quality detection of optical element surface based on Intelligent Machine Vision

2021-03-24 15:47:59

Objective quality detection of optical element surface based on Intelligent Machine Vision

1、 Development status of optical element surface quality detection

Review of the history of optical element manufacturing

The history of optical element manufacturing can be traced back to the Renaissance. The optical system and its components made an important contribution to the enlightenment and rapid development of scientific exploration at that time, accompanied by the demand for optical components and the research and Exploration on how to manufacture them. In this process, the famous scientific inventor Leonardo da Vinci played a very important role. From 1513 to 1517, he proposed that machines could be used to grind and polish the lenses of telescopes. However, the equipment based on this concept did not finally come out until about 500 years ago, which marked the real birth of the optical manufacturing industry.


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Since then, large-scale production of optical elements has become possible, and countless optical elements have been produced

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Development status of optical element surface inspection mainstream inspection methods: manual inspection, machine aided manual inspection

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The advantages of using manual detection to realize the quality control of optical elements are as follows:
·Low initial investment cost
·It can be realized quickly and simply
The disadvantages are as follows
·The test results are subjectively influenced by the test personnel
·Inconsistency of test results
·Due to the lack of objectivity of the results, it will lead to disputes with customers, thus indirectly increasing the operating costs


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2、 Feasibility of objective detection of optical element surface quality
An important node in the history of digital camera development

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In 2002, the first mobile phone models with built-in cameras, including the Nokia 7650 and the sanvo spc-5300, were launched.
The price of a camera with a resolution of 150m (15K * 10K) or more has dropped to a reasonable price.
Since 2002, machine vision system including digital cameras has been used in more and more application scenarios.
3、 Edinburgh's related work and achievements in the research and development of optical element surface detection equipment
Light scattering types of particles / molecules
Detection medium: light
Wavelength of light wave: λ
When the size of the detected particles is between < λ (nanoscale) and ~ λ (Rayleigh Mie scattering), the light scattering is basically isotropic, that is to say, the specific shape and details of the particles are basically irrelevant.

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Light scattering from surface defects
1. The details of the defect are inevitably affected by its length, width, depth, cross-section shape, section direction and other factors, which will affect the light scattering / reflection direction.
2. Each defect is different in detail.
3. The scattered / reflected light field has no spatial symmetry.
4. To sum up, the light direction and observation direction are very important for defect detection.

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Surface quality standards of main optical components
Mil standard (US) & ISO standard (EU)
Pitting: the two are the same
Scratches:
U.S. military standard: visibility / brightness comparison results (compared with the standard board);
Subjectivity: subject to the subjective influence of testing personnel. Why not use pitting like detection rules and size for grading? Can objective measurement of scattered light be used instead?
GB: Dimension Measurement (in SI units)
How to measure scratches
O scratch brightness obtained when using dark field imaging
·If the U.S. military standard can provide the relationship between the scratch brightness and its level, then the scratch can be measured
·But this measurement result is easily affected by the ambient light

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Source: Savvy Optics Corp


O measurement of scratch size in dark or bright field
·GB provides the standard of scratch size
·The R, J and other subsequent versions of mil 13830b also provide the standard of scratch size
·However, the microstructure of the scratch will have a great impact on the measurement results, so the light setting is very important for the detection results.

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Source: Savvy Optics Corp


Optical measuring equipment of Edinburgh optinspec series
Edinburgh (Nanjing) Optoelectronic Equipment Co., Ltd. has optinspec series of different types of surface defect detectors. Its hardware structure mainly includes camera, lens, lamp source, lens tray, x, y, Z axis displacement platform, industrial computer, display, grating ruler and other devices. These devices cooperate with each other to make the surface defect detector work normally and measure all kinds of data automatically and accurately

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Desktop-amf102 -- amf104
540mm (L) x 440mm (W) x 498mm (H) less than 50kg
Model AMF102/ model AMF104 is specially designed for the surface defect detection of planar products, and automatically inspecting the plane optical elements in the gel box automatically.
Amf103 is a kind of size measuring equipment for lens and other precision parts, which is suitable for size detection of products under 12mm. It can measure length, angle, radius, area, true roundness and other relevant geometric dimensions.


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Check the software

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The sample test results show that


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Optinspec series test reports - test results can be traced back to
• MIL-PRF-13830B (Revision-H)• ANSI/OEOSC OP1.002:2017• ISO 10110-7:2017

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Conclusion:
Manual detection
1. Subjective judgment, non objective results, inconsistent, controversial; 2, need well-trained, experienced inspectors; 3, labor costs rise; 4, manual operation, low efficiency.
Optinspec
1. Will generate printable reports according to the required file format, so as to analyze errors, and then ensure and improve product quality; 2, long-term use, one-time investment; 3, simple software interface operation, easy for employees to learn and operate; 3;
4. High efficiency, manpower can be used for other work.
Disclaimer: This article is written or reproduced to convey more information and contribute to the optoelectronic industry. If the words or pictures infringe on your legitimate rights and interests or have improper parts, please contact us within 20 working days, and we will coordinate and deal with them.


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