Gravure printing machine automatic computer color control principle and application

The development of color automatic color registration device for gravure printing machines has been more than 30 years old. Its development has been greatly affected by printing machinery and electronic technology. Especially in the past 10 years, computer technology, optical fiber sensing and other modern science and technology have been used in gravure printing machines. It has been widely used to make the intelligent automatic control of the color control technology of the gravure printing machine more complete, and the printing speed and the registration accuracy are getting higher and higher. At present, some domestic high-end computer color control is more perfect, and the printing speed and register accuracy are getting higher and higher. At present, some high-grade computerized color gravure printers in China adopt a new type of automatic color register controller (such as DT-950M2 produced by Japan) controlled by a microcomputer, capable of high-speed tracking, rapid correction, high-precision printing, and printing speeds of up to 180 to 200 m/. Min, longitudinal and horizontal register accuracy are both increased to ±0.1mm, and it also has automatic pre-press version. Therefore, the productivity of the gravure printing machine is greatly improved, the quality of the printed matter is guaranteed, and the waste of raw materials is reduced. Figure 1 The arrangement of color marks printed on substrates Figure 1. Detection of color registration marks and trapping errors As we all know, when a gravure printer prints a color image, it divides the color image into a number of monochromatic images and separates them according to a certain color order. Plate making. In the printing process, the monochromatic images are then superimposed and combined into a beautifully colored image. For example, first print the first color, let it dry thoroughly through the oven, and then print the second color. In this way, the printing material will cause elongation or shrinkage due to the material passing through many rollers and drying ovens; in addition, there are synchronization errors in each printing unit mechanism and the tension changes between the plates, which will cause subtle changes in the printing materials. . If these changes are certain, then there will be no problem of trapping deviation. However, due to the above-mentioned various factors of change, the trapping deviation is unavoidable. This kind of trapping deviation is continuous in nature, and the amount of deviation is not necessarily, so it must be continuously and difficult to monitor and sample, and correct it in time, so as to better ensure the stability of high-end color printing products. The color printing pattern will not produce the "color run". When manually monitoring the color deviation, it is difficult to see the pattern directly. Instead, a cross-color registration mark (color mark) of various colors is printed on the side of the substrate. By comparing it, the color registration error can be identified. The automatic color registration controller is also designed based on this principle. The color scale it uses is to make a short horizontal line on each plate, with a line width of 0.8 to 1 mm and a line length of 10 mm. As shown in Figure 1, there are usually two kinds of color mark printing on the substrate. One is Type A. It is the horizontal alignment of each color mark in the printing material's advancing direction. If the color marks on the substrate are neatly arranged horizontally into a straight line, there is no trapping error. If the color bars are not on the same line, there is a vertical gap between them, indicating that there is a color registration error; the other is the type B. It is in the blank area on the left side of the substrate, and it is arranged longitudinally in the direction of advancement. The strict specification of the center distance of each color standard is set as 20mm. If there is no trapping error, each color standard will keep the distance of 20mm unchanged, if the spacing becomes 19. G9mm or 20.1mm, the trapping error is ±0.1mm. Photoeyes and encoders are used to monitor and detect these color patches. Second, the composition of the automatic computer chromatography system and working principle At present, the more advanced automatic color registration system uses a computer control automatic color register device, which is characterized by high-speed and accurate sampling and calculation, version of the roller every turn Corrected once in time, fully adaptable to rapid changes in the color shift. Therefore, it can ensure high-speed, accurate color registration, completely eliminating the accumulation of trapping deviation. Under normal circumstances, it is mainly composed of five parts: photoelectric eye, encoder, central controller, correcting device and display. In order to briefly describe the working principle of the system, the computer color registration control system is illustrated in FIG. 2 . Figure 2. Schematic diagram of the computer color registration control system 1. Photoelectric eye and encoder The role of the photoelectric eye is to monitor and sample the color mark on the substrate. It is installed after the second color (including the second color) in each printing unit. On the support. The encoder has the function of distinguishing between the color mark on the substrate and the pattern or other stains. It rotates synchronously with the plate roller to provide a reference for the computer. The computer program processes the sampled signal and the reference signal to obtain a color code search area. The size of the search space can also be automatically adjusted. Only within the search interval, the trap mark pulse generated by the photoelectric limit can be smoothly sent to the central controller, and the pattern or stain generated in the non-search interval will be refused to be transmitted downward. Therefore, photoelectric eyes and encoders can be used to accurately filter out the logo mark pulse and deliver it to the central controller in time. There are two kinds of photoelectric eye structures available from general equipment suppliers: single photocells and dual photocells. The principle of operation of the double optoelectronic clothing is shown in FIG. 3 . It consists of a light source, two lenses, and two photo eye tubes. Therefore, two focal spots are gathered on the reflecting surface, and the two photocells respectively receive the reflected light of the two focal spots. The shape of the focal point is shown in the right half of FIG. 3 and has two different shapes of A-type and B-type. Figure 3 The schematic diagram of the action of the double-charged eye. When the color registration marks pass through the two focal planes, the change of the reflected light is shown on the photocell. To convert this change into current, it is sent to the central controller as a change in current and called a pulse. When two pulses occur at the same time in both photocells, the color shift is zero. No matter which side occurs first in time, it exists as a trap error. The shorter this time is, the smaller the trapping deviation is. In addition, if a photocell pulse of the first color is detected as a reference, if a photocell pulse of the second color occurs earlier than this, the emission is specified as being advanced; if it occurs later than that, it is defined as a hysteresis. The principle of operation of a single photocell is basically the same. It consists of a light source, a lens, and a photocell. There is only one focal point on the reflective surface. When the color registration mark passes through the focal plane, only one color standard can be sampled. The size and direction of each color target spacing and the color shift offset are processed by a computer program, and operations and judgments are performed. 2. The central controller of the central controller is the central part of the automatic computer color registration device and plays the role of the brain. It analyzes and judges the presence or absence of the color registration error, the magnitude and the direction of the deviation based on the sampled pulse signal, and maintains the trapping deviation at the zero position, so that the accurate and timely control can be performed. It consists of mainframes, I/O ports, optical isolation boards, and dedicated power supplies. An input circuit, an arithmetic circuit, an output circuit, and the like are provided on a computer motherboard. The role of the input circuit is to automatically form the sampling pulse into a uniform regular input pulse. Because the colors of the logos are different. The pulse change produced by the photocell is different, and the shape of the pulse changes accordingly. If the shapes of the first and second colors are different, it is difficult to compare them. The shaped pulse then takes place if it is delayed by a time (T) relative to the main pulse. At this time, the main circuit generates a T-width rectangular pulse and sends it as the delay color deviation signal to the arithmetic circuit. The pulse occurs with respect to the main pulse advance (T1), and a rectangular pulse of T1 width is also generated as the advance color registration deviation signal to the operation circuit. The arithmetic circuit uses an advanced microprocessor, which is the heart of the central controller. It is sent by the input circuit according to the preset roll length, the reference pulse generated by the encoder, and the distance between each roll. The color misregistration data comes together and the calculations are performed together to obtain the correct operation result. At this point, on the one hand, the result of the operation is output to the display screen for indication; on the other hand, the value is stored and the deviation from the lower ring is monitored. According to the rate of change, the correct amount of correction can be calculated immediately. The correction amount is indicated by the output circuit to instruct the correcting device to correct the deviation. 3. Deviation correction device The correction device is an actuator that corrects the trapping deviation. It is mainly composed of trapping motor, color adjustment guide roller and a pair of ball screw. When the output circuit sends the trapping deviation correction command, start the trapping motor forward or reverse, and control the two left and right vertically installed ball screws to synchronously rotate in the same direction by the reduction gear to drive the trapping regulation guide roller to rise or fall vertically. . Adjust the length of the printing material between rolls, so that the chromatic aberration deviation approaches zero. The trapping motor only operates when there is a command signal, and stops immediately when the command disappears, so that it can accurately convey the deviation correction command sent from the output circuit to the registration adjusting guide roller. Since the above calculations and corrections are carried out at the same time as each revolution of the platen roller, even if the variation of the deviation rate is very rapid, it can also ensure that the correction work is completed smoothly, completely eliminating the accumulation of trapping deviations and enabling the computer color registration control. The device has a very high registration accuracy, and the color registration control process is also very stable and reliable. Third, the classification and selection of automatic computer chromatography system In general, low-grade gravure printing machine, if the color of the overprint is less, the printing speed is less than 50m/min, automatic computer color registration system may not be configured. For example, some medium- and low-grade foil gravure printers usually have underprint colors of less than 5 colors, and the printing speed requirement is not more than 50m/min. In addition, the aluminum foil is less prone to elongation when the temperature and tension change, and the user usually reduces the purchase cost; Configure automatic computer color registration system. When printing, more skilled workers are used to manually adjust the color deviation at any time to meet the print quality requirements. However, when the printing speed of a gravure printing machine is increased to 80m/min or more, manual adjustment cannot be used, and an automatic computer color registration system must be configured. In recent years, China-made high-grade computerized color gravure printing presses have developed rapidly, and the use of computer-controlled automatic color registration devices has become widespread. Although the computer color registration systems configured by the gravure printing machine are various in form and have their own merits, they can be summarized basically according to Figure 4. At present, some of the domestically produced high-grade gravure printing machines are more equipped with Japanese Tai Yang. Motor company's IC-470, T-520, PT-005, DT-860M2 and DT-950M2 models such as automatic color register control device. IG-470 and T-520 automatic color registration controller is a relatively simple early product, not using computer control technology, and no computing power, only suitable for the gravure printing machine with a printing speed of 80 ~ 100m/min. PT-005, DT-860M2 and DT-950M2 computer color registration controllers are the replacement products of IC-470 and T-520. They have been greatly improved on the original basis, and have adopted microcomputer control methods. All have been significantly improved, the printing speed can reach 80～2000m/min, and the accuracy of registration can be increased to ±0.1mm. It can be said that it is one of the products with advanced technology, quality and performance that are very stable and reliable. For example, the DT-860M2 type adds automatic pre-press printing (after the roll is installed, it will make the gravure printing plate version, without manual adjustment), reducing the waste of raw materials; and DT-950M2 type In addition to all the functions of the DT-860M2, it also has a horizontal register function, which allows the gravure printer to register at both the vertical and horizontal directions. This is particularly important for gravure printers where the substrate is paper. In addition, China's own computer developed color control technology has also developed rapidly. For example, the ELY-2000H prepress-to-print system and the automatic computer color registration device designed by Shunde City Debao Printing Machinery Co., Ltd. are a prominent figure. Over the past few years, it has passed the practice and test of nearly 100 sets of machines. The printing speed can reach 120-160m/min, the accuracy of registration can be increased to ±0.1-0.15mm, and it has a full-characterized operation interface and full-scale human-machine dialogue. Various tips guide function. In terms of technical performance and quality, it has reached the advanced level of domestic similar products, but its price is only 1/3 to 1/5 of similar imported products, and has won the praise of customers. Figure 4 Gravure printing machine automatic computer chromatography system classification In summary, the user should according to the requirements and use of the gravure printing machine to select the corresponding automatic computer chromatography system to ensure the quality of printed products to meet customer requirements. □