Embedded Network Detection System: New Method of Printing Quality Control

In the printing process, the control of the amount of ink is mainly done manually, which is very disadvantageous for the stability of the printing quality, the further increase of the printing speed, and the further automation of the printing process in the future. Based on the difficult status of ink volume control, combined with the idea of ​​embedded systems, we proposed the research and development of an embedded dot detection system based on color print quality control.

Research status

So far, there are mainly the following quality control tests for common color prints.

1. Artificial direct observation method. Workers use a simple hand-held magnifying glass to observe the printed product, and then adjust the water supply and the amount of ink according to experience and comparison with the proofs. This method is completely done by humans. The accuracy of ink transfer depends entirely on the workers' experience.

2. Density measurement. The principle of color printing is the subtractive color method, that is, the ink printed on the paper, selectively absorbing light of a certain wavelength from the illuminating light, reflecting other light, thereby forming a color. Therefore, in a certain range of the ink ink layer, the light absorption amount is proportional to the ink layer thickness and concentration, so the density value reflects the thickness of the ink layer. In the quality control process of printed products, measured by a densitometer, the inspector indirectly reflects the ink layer thickness by the density value.

3. Colorimetry. The instrument used for the colorimetric measurement is a colorimeter, and by directly measuring the instrument response value that is proportional to the tristimulus value of the color, the tristimulus value of the color is converted. The method of obtaining the tristimulus value by the colorimeter is accomplished by the internal optical analog integration of the instrument, that is, using the color filter to correct the spectral characteristics of the instrument light source and the detection element, so that the output electrical signal size is proportional to the tristimulus value of the color.

The above three methods currently have a lot of limitations: they are basically off-line detection, that is, workers take samples, and after manual observation or instrument detection, they can adjust the amount of ink properly. Designed control strips. The direct observation method, to a large extent, depends on the experience and quality of the workers. In the latter two methods, the cost of measuring instruments is high.

In terms of on-line inspection, many manufacturers have developed their own color monitoring and control systems for printed images. Heidelberg's CPC image control system uses spectrophotometer measurement technology to scan images. It is an attempt to control the three-dimensional spectral color from a simple planar density control. It uses dual detection of chromaticity and density, and can complete a split in 30 seconds. The inspection of the printed sheets processed the information of 160,000 measuring points, and after comparing with the standard data, the ink area information was displayed on the color touch screen. The color control system developed by Mitsubishi also uses a spectrophotometer, but it scans a special color bar on the print. The system can automatically adjust the main color settings in both horizontal and vertical directions, and displays on the smart print monitor. The color control situation. Manroland insists on monitoring and controlling the printing quality and printing process through the density of printed inks.

Although the color control systems of these famous printing companies have their own characteristics, they generally have some limitations. For example, most of them can only detect special inspection strips; Most printers are unacceptable and require higher quality workers.

Based on the above conditions, we apply the embedded system to the printing inspection and propose the development of an embedded dot detection system based on the quality control of color printing products.

Embedded Network Detection System

An embedded system is a collection of hardware and software. It can generally work independently without having to resort to other systems. It can also connect with other systems and work together. The detection system can work independently for ordinary printers and intuitively obtain test results. When the printing system is further automated in the future, it can be used as online ink detection and real-time feedback.

Considering that the printing press adjusts ink mainly by adjusting the ink volume of 32 ink segments, we now use a region image as the detection object, and 32 ink segments can be adjusted in a scanning manner one by one. We made such a device, as long as the image of the detected area is placed in the designated position of the device for detection, the calculation result, that is, the amount of ink required for each color ink can be displayed. FIG. 1 is a system block diagram of a detection apparatus.
The principle of the detection device:

1. First, the image of the detected area of ​​the printed product is illuminated, and the light passes through the optical imaging system to reach the photoelectric image sensor;

2. After the photoelectric sensor, the image information is converted into an electrical signal and output;

3. Collect the output signals of photoelectric sensors and use digital image processing methods;

4. Finally, identify the ink coverage and related parameters of each ink in the tested area, and send the results to the display module, or directly feedback to the printing control platform, and then compare the relevant parameters with the proofs, and finally guide the ink supply system to each ink. Segment to adjust the amount of ink.

In summary, the basic functions to be performed by the detection device are: (1) data acquisition and storage of images in a given area; (2) processing the collected image information; (3) outputting the operation results (ie, display or Feedback operation result).

Application prospects

In the general printing press, the basic manual or semi-automatic ink transfer, the operator's experience is more demanding, after using the detection device can be directly online to get the ink supply status of each ink segment, based on which to adjust the ink supply in order to achieve The expected printing effect, thus reducing the experience requirements for operators, reducing the scrap rate, can also reduce the printing cost.

In the automatic printing process, the detection device can be used as a feedback link for the closed-loop control of the ink path. The ink information of each ink segment is detected and fed back from the print product and provided to the printing control platform to be compared with the relevant parameters of the proof so as to be corrected. The amount of ink supplied by each ink segment can be automatically controlled in the true sense of the printing process.

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