With the improvement of living standards, people's requirements for printed matter are also increasing, so some packaging and printing enterprises on the quality of the requirements are also closely improved, however, in the process of large-scale product printing, printed matter surface often appear two-dimensional defects, such as dirty spots, missed printing, erase plate, white spots, deinking, flying ink, poor overprinting, etc. These defects will affect the beauty and quality of printed matter. It also affects people's identification of the content, especially in the labeling or identification of medical use, which brings great trouble to people, and once there is a quality problem, it will cause a large number of returns.

In order to reduce the risk, most printing houses have adopted the method of manual full inspection of printed matter. If the quality of printed matter is controlled by personnel, then under normal circumstances, people will be affected by subjective and objective factors such as environment and mood, resulting in inconsistent artificial detection standards, therefore, the human eye is unable to continuously and stably complete these work with high repeatability and intelligence, and other physical quantity sensors are difficult to use.

With the continuous progress of science and technology, in modern industrial automation production, more and more are involved in various application fields such as inspection, production monitoring and image recognition. Therefore, people began to consider the use of machine vision to replace artificial vision, it is the photoelectric imaging system to collect the image of the controlled target, and then through the computer or dedicated image processing module for digital processing, according to the image pixel distribution, brightness and color information, size, shape, color and other discrimination. In this way, the speed and repeatability of the computer is combined with the highly intelligent and abstract ability of human vision.

Machine vision is a comprehensive technology, including digital image processing technology, mechanical engineering technology, control technology, light source lighting technology, optical imaging technology, sensor technology, analog and machine vision technology, computer hardware and software technology, human-machine interface technology, etc.

Application of machine vision in printing and packaging industry

Machine vision inspection system is a high-tech product born according to people's production needs and the development of optoelectronic, video, printing and other technologies to a certain level. It can directly detect the printed matter in real time, and feedback the quality defects in the form of images in the fastest way, so that the operator can be intuitively guided to adjust. At the same time, it also improves the process quality and work efficiency, reduces the strength and density of manual sampling products, and reduces human uncontrollable factors. Its application can greatly improve production efficiency, reduce the waste of printing materials, can be said to be a very effective cost control system, favored by various printing enterprises.

peculiarity

1) Using high-speed linear array camera, can adapt to different lengths of detection objects;

2) Adopt foreign advanced image acquisition card and processing platform;

3) Image resolution of 0.1X0.1mm2 or more accurate;

4) Flat box structure, occupy small space;

5) Adopt high image quality lens and anti-stray light path design, so as to obtain high definition image;

In the printing and packaging industry, the light source, camera and other equipment is installed above the machine stamping roller, the symmetrical line light source will shine uniform light on the product, the image information on the surface of the product by the imaging light path, through the high image quality lens on the imaging process. The high-speed linear array completes the one-dimensional image of the product in an integral period, and the two-dimensional image is completed through the paper's own motion. The image information after imaging is entered into the computer through the data acquisition system, as shown in Figure 1. In the computer, each image is compared with the image in the program to determine whether there is a defect on the product pattern. According to the results of comparison, the quantity statistics of qualified products and waste products, identification of location, alarm signal, stop signal, etc. Each captured image will be displayed in real time on the display, where the main display can also be switched to the operating interface during the detection process for human intervention and adjustment.

The detection process of the system is in fact an image matching process, before the system carries out normal quality control, it is necessary to establish and debug the template first, that is, to develop a quality standard, and then compare each product and standard image collected by the data acquisition system to determine whether the printed product meets the quality requirements in turn. If there is a tendentious quality problem, an alarm is immediately given to remind the machine personnel to deal with it. If there is a continuous quality problem, the printing press is stopped under the control of the system and can be turned on after the machine personnel has processed it. The detection process is shown in Figure 2.

Application prospect of machine vision inspection system

For how to solve the problem of print quality control, people have developed a lot of methods, such as measurement and control strips, test versions, as well as manual spot checks, machine scanning and so on. Although these methods have played a role in print quality control to a certain extent, the use effect is still unsatisfactory, which is not conducive to competition to a certain extent. Therefore, printing enterprises are eager to get an intuitive, simple and easy to operate quality control method. In recent years, the machine vision inspection system has begun to accelerate into the printing process, replacing manual quality inspection and control, in order to improve the detection accuracy and detection efficiency. With the aging of society, this has extremely long-term strategic development significance under the background of "labor shortage". However, the printing quality inspection scheme of the whole process is not the simple stacking and combination of the quality inspection of each printing process, but the need to continue to deeply integrate and continue to develop. To address our customers' pain points, we will be implementing an online visual quality inspection system on the printer GTS 924 line, which provides product quality by detecting problems early in the process, thereby increasing productivity and reducing waste, helping customers achieve cost savings and efficiency gains.

Development trend

1) The optical imaging system and image processing software are closer to the essence of the printing process, and the final competition is not the number of CCD cameras, but the performance of the optical imaging system for various defects in the printing process.

2) The control of printing quality is gradually moving forward, and the printing quality defect detection system of the pre-press process and post-press process will be more widely used.

3) The data comprehensive analysis software of the whole-process printing quality defect detection system is adopted to realize the seamless connection between the detection system software and the customer ERP system. The whole-process detection system will provide more systematic and perfect quality analysis reports and quality decision-making suggestions to the enterprise decision makers, and finally integrate the visual inspection system into the factory quality system.