High quality of newspaper prints originates online detection technology (below)

Printing equipment R&D and manufacturing companies have been working hard on on-line inspection and control of printing presses, hoping to achieve direct inspection and control of image printing quality on high-speed presses. They see the image as being composed of symbols, just as in the normal image color detection, the printed image on the tape is considered to be composed of one dot and one dot. In the detection, the detected image CMYK data and printing paper type data are input into the spectrum, and the full-tone density of each color is defined as the control value of the image quality.

In order to ensure the calibration of the testing equipment before testing, it is very necessary to measure the full-tone area of ​​the first color printing and the second color printing at the beginning of printing, and the whiteness of the paper is calibrated and calculated as a white dot. The corresponding actual detection value is spectrophotometric. Instrument provided. The principle of spectral detection is that the bright color in the visible spectral region is absorbed, while the pure black in the infrared region is also absorbed. The result is identified by comparing the output of the gray level produced by bright color or black color.

This detection method can also be applied to print spot color measurements. Measured values ​​obtained from the printed image part of the screen are printed and the on-line color control system can be used to calculate the corresponding value of the full tone and compare it with the standard full-tone reference value. However, an important prerequisite for such measurements is that the color registration of printed images must be 100% accurate.

The idea of ​​image spectrum detection system originated from two years ago, but only one year later, the detection system has basically taken shape. This year, it has realized the installation of printing companies. This detection system can also be used to measure the density of printed images on the machine. Match. It is said that next year will design a closed-loop control system for a printing paper road, and will begin to provide customers with a complete detection system.

Closed-loop quality control in plate making

A print quality assurance system must include all areas involved in the printing process, such as the computer-to-print platemaking process. The problem with the current CTP link is that the plate speed has hindered the effective quality control of the printing plate because the printing speed required by newspaper printing is too fast.

Today, the CTP plate making speed can reach 74 sheets/hour. With the current rapid CTP system, manual inspection of each printing plate is almost impossible. With manual inspection methods, problems in production cannot be identified quickly enough. For example, some platemaking failures cannot be seen on the surface of the printing plate, but they will actually affect the service life of the printing plate. Therefore, the manual detection method does not match the closed-loop control of the printing process, and it also does not match the industrial production of newspaper printing.

The platemaking machine should be well integrated with the printing production plan, and the plate should be exposed before the printing is about to start, instead of being stored in advance after a large number of plate making. Some CTP companies have already begun to cooperate with Agfa, equipped with Agfa inspection systems for plate quality control, to ensure continuous monitoring of all process parameters during the platemaking process, and to monitor all process links through closed-loop control systems, such as platemaking machines. , plate washers, punchers and cutting machines, closed-loop control system is by no means an isolated or partial solution.

When the plate is punched, a camera is used to take a picture, and the taken image is re-evaluated during plate making. According to the evaluation result, the CTP system exposes a digital block and an analog block in the area of ​​6 mm×4 mm on the plate, and uses the digital block. A standard value of plate quality, gradation, and problematic image values ​​is generated, and the simulation block is positioned on the optical path of the laser beam to provide pre-processing for evaluating the characteristics of the plate making laser so that the plate can be completely hardened.

Future Prospects: Comprehensive Detection of Printed Images

Experts are researching and exploring and preparing to use fully automated closed-loop detection and control systems in future newspaper printing. At present, pilot printing companies have installed a CCD camera system for video density measurement. They believe that if the detection points are added to the printed image, and the corresponding wetting airflow is controlled, the printing color and the multi-paper path overprinting can be grasped, the problem of virtual image in video image detection can be avoided, and the printed image detection technology can be implemented in a closed-loop control system. Play a bigger role.

The closed-loop control system marks the real-time control and adjustment of different parameters of the printing plate making process and the printing process, which is of great benefit to the future improvement of the quality of printed matter and will be applied more widely. Printing closed-loop control is only part of the overall solution for newspaper printing, but it marks that newspaper printing is moving toward new types of industrial production.

Source: Digital Printing 2005.8