Original article

Automatic optical inspection guide - about (AOI) machine, what do you want to know

2021-03-24 15:48:35

Instructions for automatic optical inspection (AOI) equipment
1. What is optical detection?
Before we introduce automatic optical inspection (AOI) equipment in detail, let's understand the role of optical inspection in industry.
In the manufacturing process of optical components, optical detection can be used to ensure the optical characteristics and quality of the produced components. For example, defects such as scratches and pits on the surface of optical components can be found by optical detection, and then these defects are graded according to different standards. Finally, the component is judged to be qualified by summarizing and analyzing all the grading results of defects. Therefore, generally in the final stage of optical components production process, optical detection will be used to ensure the final product quality to meet the required standards.


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Instructions for automatic optical inspection (AOI) equipment
1. What is optical detection?
Before we introduce automatic optical inspection (AOI) equipment in detail, let's understand the role of optical inspection in industry.
In the manufacturing process of optical components, optical detection can be used to ensure the optical characteristics and quality of the produced components. For example, defects such as scratches and pits on the surface of optical components can be found by optical detection, and then these defects are graded according to different standards. Finally, the component is judged to be qualified by summarizing and analyzing all the grading results of defects. Therefore, generally in the final stage of optical components production process, optical detection will be used to ensure the final product quality to meet the required standards.


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2. What is automatic optical inspection?
Automatic optical inspection (AOI) equipment is a kind of inspection equipment based on machine vision technology. It is generally used in the production process of optical components to verify the quality of optical components. The optical element to be tested may have different geometric or material characteristics, it may be planar (window piece, mirror piece, etc.) or curved surface, it may have a coating on the surface, or it may be made of special materials.

Automatic optical inspection equipment obtains images by optical imaging, and processes and analyzes them to find out the potential problems that may lead to the products not meeting the standard specifications, such as the size deviation or surface defects (pitting, scratch, edge chipping, bubbles, stains, impurities, etc.). Compared with the manual detection method, it is more efficient and accurate, so as to better guarantee the reliability of the final product quality.

With the increasing complexity and shrinking size of optical components in production and application, manual detection methods have gradually been unable to meet the demand, so automatic optical inspection (AOI) will play an increasingly important role in the quality control of optical components.

3. The working principle of AOI
The three core components of AOI equipment are lighting, imaging system and processing analysis software.
3.1 lighting
In the detection process, by using a high-intensity light source to irradiate the optical element to be detected, the surface defects of the element can be distinguished from the background, and different types of light sources will highlight different types of defects.
Automatic optical inspection (AOI) equipment is a kind of inspection equipment based on machine vision technology. It is generally used in the production process of optical components to verify the quality of optical components. The optical element to be tested may have different geometric or material characteristics, it may be planar (window piece, mirror piece, etc.) or curved surface, it may have a coating on the surface, or it may be made of special materials.

Automatic optical inspection equipment obtains images by optical imaging, and processes and analyzes them to find out the potential problems that may lead to the products not meeting the standard specifications, such as the size deviation or surface defects (pitting, scratch, edge chipping, bubbles, stains, impurities, etc.). Compared with the manual detection method, it is more efficient and accurate, so as to better guarantee the reliability of the final product quality.

With the increasing complexity and shrinking size of optical components in production and application, manual detection methods have gradually been unable to meet the demand, so automatic optical inspection (AOI) will play an increasingly important role in the quality control of optical components.

Automatic optical inspection (AOI) equipment is a kind of inspection equipment based on machine vision technology. It is generally used in the production process of optical components to verify the quality of optical components. The optical element to be tested may have different geometric or material characteristics, it may be planar (window piece, mirror piece, etc.) or curved surface, it may have a coating on the surface, or it may be made of special materials.

Automatic optical inspection equipment obtains images by optical imaging, and processes and analyzes them to find out the potential problems that may lead to the products not meeting the standard specifications, such as the size deviation or surface defects (pitting, scratch, edge chipping, bubbles, stains, impurities, etc.). Compared with the manual detection method, it is more efficient and accurate, so as to better guarantee the reliability of the final product quality.

With the increasing complexity and shrinking size of optical components in production and application, manual detection methods have gradually been unable to meet the demand, so automatic optical inspection (AOI) will play an increasingly important role in the quality control of optical components.


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The early AOI equipment tried to use many different types of lighting sources, such as fluorescent light source, incandescent light source, ultraviolet light source and infrared light source. With the progress of light source technology and continuous testing, the new version of the equipment now uses red, green, white, blue and other colors of LED light source.
Compared with other types of light sources, LED light source can provide more stable lighting, and although its output light intensity will decrease with time, it can be compensated by increasing the input current of the light source. In addition, the output light intensity of LED light source can be easily controlled by digital programming.
Therefore, LED light source, especially coaxial LED point light source and ring LED light source, is more suitable for machine vision and other applications requiring uniform lighting than fluorescent light source and incandescent light source.
In optical detection, besides the type of light source, the installation position and spatial topology of light source are also important. In order to make all defect areas have better contrast after imaging, it is necessary to ensure that all areas in the imaging field of view are effectively illuminated, which needs to be adjusted for different application scenarios.
3.2 imaging system
The main function of the imaging system is to obtain the image of the optical element to be detected and send it to the processing program in the AOI equipment for processing and analysis. Usually, AOI devices contain one or more high-definition cameras, and some types of devices can control their moving position in the device through software instructions.
According to the different requirements of application scenarios, different types of AOI devices contain different cameras, from low resolution XGA units to high-resolution video cameras, from monochrome cameras to color cameras. Generally, the new type of camera has higher frame rate, so it will produce more data, which has higher requirements for processing software and hardware.
Resolution and field of view (FOV) are two key parameters of AOI imaging system. The resolution determines the size of the smallest detail that can be captured and resolved by the device, which has a great influence on the detection accuracy and speed of AOI devices. The field of view represents the size of the physical space corresponding to the image. The larger the field of view, the larger the physical area corresponding to a single image, and the larger the size of the components that can be imaged at one time. However, it also means that capturing a single image requires more pixels and more time, that is, the lower the frame rate. On the contrary, the camera with smaller field of view can be imaged at one time The smaller the component size of the image, the higher the frame rate.
3.3 processing and analysis software

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In order to enable AOI devices to detect a specific product, some description information about the product must be provided for the processing software, which can be realized in two ways.
·Use the "gold standard". The relevant characteristics of the product can be obtained by scanning and testing the standard qualified product, and the product can be filed and stored for use in the later actual testing. In order to obtain reliable statistical data of product characteristics, it is necessary to test several "gold standard" products in practice.
·Software import. The description information of the product to be tested is obtained by direct software import, and it is filed and stored.
4. Comparison between AOI equipment and traditional manual detection method
4.1 efficiency

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Restricted by physiological conditions, manual detection staff need to rest from time to time in the process of inspection. Moreover, each employee can only check one product at a time, which will reduce the efficiency of the whole process. With the increasing market demand for production, product size is getting smaller and smaller, in many cases, manual detection is no longer a feasible option.
Compared with manual, automatic equipment can detect multiple products at one time, that is batch detection. They can work 24 hours without interruption, and can also be remotely controlled and monitored, which greatly improves the efficiency and helps manufacturers meet production needs. Of course, automation equipment will appear different types of aging phenomenon after long-term use, which needs regular maintenance, and if the equipment suddenly fails, it will lead to the stagnation of the production line.
4.2 consistency
In the process of manual detection, staff can not keep the consistency of detection results for a long time due to fatigue and other reasons. Research shows that the human can not maintain a stable performance for a long time, and the probability of error will be greatly improved after 15 minutes of continuous work, and with the increase of work complexity and daily working hours, the number of errors will be greatly improved. In addition, due to the subjective influence of the staff, there must be inconsistency between the test results of different staff.

Compared with manual, automatic testing equipment has high stability, they can keep the same objective testing standards for all products, so as to maintain the consistency of test results.

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Manual inspection usually requires more than one testing staff at the same time, so it will produce a high labor cost. The research report shows that one automatic detection equipment and one equipment operator can replace five manual detection personnel, which can save a lot of labor costs in the long run. Moreover, if more production lines are needed, more money and manpower will be saved by using automatic equipment instead of manual detection.
Compared with manual detection, automation equipment needs to invest more money in equipment procurement and operator training at the initial stage, and there will be extra expenses such as maintenance, repair and update in the process of equipment use.
4.4 test report
Manual inspection reports are mostly manually recorded, so it is easy to make mistakes, and a large number of manually recorded reports are difficult to manage, which makes it difficult to use them for production process analysis.
Different from manual operation, at each stage of the production process, automatic detection equipment will generate printable reports according to the required file format, so as to analyze errors and ensure and improve product quality. This can prevent customer complaints and returns, so as to improve customer trust and satisfaction.
5. Optinspec series - AMF vs. AOF vs. MOF

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At present, Edinburgh (Nanjing) photoelectric equipment Co., Ltd. has optinspec series of different types of surface defect detectors
Automatic micro surface defect detector (AMF)
Automatic plane surface defect detector (AOF)
Manual plane surface defect detector (MOF)
It can be seen from the name of the machine that AMF and AOF are automatic detection devices, while MOF is manual equipment that needs manual operation. These all-round surface quality testing equipment can carry out quality assurance and quality control inspection for optical elements of different materials, such as plane, curved surface and coating.
Aof and MOF machines are used to check the plane optical diameter up to 25.4 mm, while AMF system can be used to check the plane micro optical diameter up to 12 mm.
The equipment adopts American military standard (mil-prf-13830b), which can effectively detect scratches and pitting on the surface of products, and can automatically judge and classify the grades of scratches and pitting. The design conforms to the human engineering, reduces the staff operation fatigue feeling. The software interface is easy to operate, which is convenient for employees to learn and operate. Automatically generate test reports.
Optinspec-amf103 is a kind of equipment for measuring the size of lens and other precision parts, which is suitable for the size detection of products under 12mm. It can measure the length, angle, radius, area, true roundness and other related geometric dimensions.

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The product adopts the advanced design concept and hardware configuration, which can realize the measurement of the contour and size of various complex precision parts, automatically classify the tested products according to the shape, and automatically determine whether the measured size is qualified, which can greatly improve the detection efficiency of the product.image.png

In a word, in this paper, we introduce the basic information of AOI equipment, the advantages and disadvantages of artificial optics and automatic optical detection, and the differences between various AOI equipment we provide.
There is no doubt that due to the rapid development of technology, the efficiency has been improved and the operation cost has been reduced. Machines are replacing the work of human beings. However, in some links of the optical detection process, such as operation and ensuring good maintenance of equipment, manpower is still needed.
With the invention of this technology, equipment operators can acquire new skills to improve the company's productivity in other areas.


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