Machine Vision Inspection Technology Profile and Features

Machine vision print quality inspection is a kind of artificial detection method and decision logic, but at the same time it has an automatic detection method with higher detection accuracy and better consistency.

First, the characteristics of machine vision inspection

1. Introduction of Machine Vision Inspection Technology

Machine vision, in a nutshell, is the use of machines instead of humans for target identification, judgment, and measurement. It is the intersection and fusion of modern disciplines such as optics, electronics, software engineering, signal processing and system control technology.

Optical acquisition equipment: It is composed of industrial cameras, light sources and supporting image acquisition cards and other hardware. The main function is to obtain the digital image of the tag through the collection location, and provide material for subsequent analysis and processing, which is equivalent to the manually detected eye.

Judgment and identification: It consists of an industrial control computer and embedded image processing and analysis software and control software. It is the core part of visual inspection, which ultimately forms the judgment of defects and can issue instructions to subsequent executing agencies.

Automatic control: finally transforms the results of the inspection system into hardware for specific operations, such as common audible and visual alarms, reject devices or marking devices (such as inkjets, labelers, etc.).

In addition, the printing inspection equipment must also have a stable mechanical transmission control platform. For the online inspection system installed on the printing press, the transmission platform is the printing press; for the offline inspection system, the transmission platform needs to be configured separately. Such as rewinder, leaflet transmission platform.

2, printing defect detection principle

Printing defect detection mainly depends on the method of image comparison. As shown in FIG. 2 , the upper image is a real-time image captured by the camera, and the lower image is a standard image that is acquired and stored in advance. In the detection, the two images are firstly overlapped by positioning or the like, and then the colors (or brightness differences) are compared point by point (pixel by pixel). When the difference between them exceeds the preset range, it is judged as a defect.

3, machine vision detection features

A set of high-quality machine vision inspection systems must meet the following prerequisites:

1) High quality imaging system

The imaging system is called the "eye" of the visual inspection device, so the "eye" recognition ability is the most critical index for evaluating the imaging system. In general, the evaluation indicators of the imaging system are mainly reflected in three aspects:

Can you find any defects?

The most primitive and unique data that can be based on the image method is the change in color (or brightness) of the acquired image. In addition, no other data is available for reference. Therefore, a high-quality imaging system should first be an imaging system that can fully represent the color change on the surface of the test object. Therefore, in addition to the selection of high-definition cameras and lenses, the lighting design used to create the imaging environment is also very important, and sometimes there will even be special lighting systems designed for special defects. What we often call a 100% quality inspection system actually refers to a 100% inspection in an image that fully expresses various defects.

The minimum size of the defect that can be found

The smallest unit of measurement for digital images is the pixel, which does not itself represent the actual size of the subject.

The correlation between the actual size of the subject and the pixel is accomplished by a physical quantity called resolution. Resolving power refers to the actual object size represented by each unit pixel. The smaller the resolution value, the higher the fineness of the image, the smaller the defect size that the detection system can find, and the higher the detection accuracy.

Can you take images fast enough

Just as human eyes see moving objects, when the objects move fast enough, the human eye can no longer clearly observe the entire object. The "eyes" of the machine vision inspection system - the camera also has an upper shooting speed, which is the main frequency of the camera. When the subject's operating speed exceeds the upper limit of the camera's main frequency, the camera will not be able to obtain a clear, complete image, and the test will not continue normally. The higher the main frequency of the camera, the faster the acquisition speed, and the detection can remain efficient. Therefore, whether or not a camera with a sufficiently high frequency is adopted is also a key factor in evaluating whether an imaging system is high quality.

2) Mature image processing and analysis algorithms

The image processing and analysis algorithm is equivalent to the human brain's judgmental thinking in the entire detection system. Since machine vision is a highly practical discipline, evaluating an algorithm is more dependent on the verification of practical applications. Whether or not to use a more advanced or sophisticated theory. Therefore, an image processing and analysis algorithm that can fully simulate the human brain's judgment process and method and is stable and efficient is what we need, namely the so-called mature processing and analysis algorithms. Therefore, when designing a processing algorithm, it is necessary to fully analyze the human judgment process and convert it into a computer language.

3) Good operability

Good operability mainly requires the application of the testing equipment to be simple, convenient and easy to understand. For example, the system has a friendly human-computer interaction interface and a good guiding operation design.

4) Stable other supporting facilities

Other facilities refer to facilities other than inspection systems, such as transmission control platforms, defect processing devices (culling, alarms, tags, etc.). The requirements for supporting facilities must be stable, signal response timely and quickly.