Main performance parameters of the hottest Phototy

The main performance parameters of the Phototypesetter

the main performance parameters of the laser Phototypesetter are: recording accuracy (recording resolution), repetition accuracy (registration error), format, recording speed and laser wavelength, among which the recording accuracy and repetition accuracy are the two most important indicators to measure the performance of the Phototypesetter, and also the standard to divide the grade of the Phototypesetter

1. recording accuracy and repetition accuracy

recording accuracy and repetition accuracy are two different concepts. Recording accuracy refers to the number of light spots that can be recorded by the imagesetter in unit length, that is, the recording resolution, which is usually expressed in dots per inch (DPI) or dots per centimeter (DPC) per Hubei: new material new target revenue doubled four years later. The higher the recording resolution, the smaller the size of laser spots and the higher the intensity of light spots. Because the printed image points are formed by many laser beams, the smaller the laser spot is, the more light points constitute the points under the same number of lines, and the more gray level changes of the image can be formed. In other words, make the point size smaller under the condition of ensuring the gray level, that is, get a higher number of lines. For example, figure 4 shows an example from 16 × The enlarged image of 50% points composed of 16 laser points can form 256 different gray level changes in total. Within the range of a printing point, the size of the printing point changes by one level every time the exposure of a laser point is increased or decreased, forming a gray level of different depths. Therefore, the more laser spots constitute points, the more gray levels will be generated. In this way, the current camera can produce up to 256 gray levels, that is, 16 × 16 laser points form a printing point

repetition accuracy refers to the accuracy of image position on each color plate, which is necessary for color printing. It is usually calculated based on the overlapping error of the first color plate and the last color plate. Monochrome printing does not need overprint, so the requirements for registration accuracy are not high, but for color printing, registration accuracy is a very important parameter. If the overprint accuracy is not enough, there will be dislocation between the various colors of the printed matter, white leakage between color blocks, and ghosting of small fonts. Therefore, the repetition accuracy of the Phototypesetter is very important for color printing plate making

generally, the recording accuracy of medium-grade imagesetter is 1200 ~ 2540dpi (recording points/in), and the repetition accuracy is 15 ~ 25 μ m； The recording accuracy of high-end imagesetter is above 3000dpi, and the repetition accuracy is 5 μ M or so. The recording format has octave, quarto and folio specifications

the fineness of the printed image is directly related to the recording accuracy of the imagesetter. Different from text Phototypesetting, the image needs to use the method of adding to show the color and level changes of the image. The higher the number of lines added, the more gray levels to be restored, the higher the recording accuracy of the Phototypesetter is required, or the more laser points that constitute the printing points are required, and the smaller the size of the excitation spot is required. As shown in Figure 4, the point formed by the exposure of the imagesetter is composed of many laser points. Under the same condition that 256 gray levels are required to be generated, the point when adding 175 lines is smaller than that when adding 100 lines, so the laser point should also be small, otherwise the number of lines must be reduced, and the two restrict each other. The relationship between the recording accuracy of the Imagesetter, the number of printing lines and the restored gray level is determined by the following formula:

gray level: (recording accuracy/number of lines) 20 l

at present, the maximum gray level that the Imagesetter can perform with the conventional addition method is 256, while the gray level that the human eye can distinguish is about half of this level. A higher level does not necessarily significantly improve the quality of the print, so as long as the printing plate making conditions can be reasonably controlled, There is no obvious loss of hierarchy, and this gray level series can meet the actual use needs

2. format

the imagesetter has a variety of format widths, generally including positive eight open, large eight open, positive four open, large four open, and even split and full open formats. Generally, the imagesetter can change several different format films within the maximum format range to meet different format requirements and achieve the purpose of saving films. The recording power resolution of Phototypesetter: 0.1kn recording accuracy and repetition accuracy are closely related to the format. The larger the format, the higher the accuracy requirements, and the greater the processing difficulty in manufacturing, so the price will rise exponentially

generally, the Phototypesetter with inner drum and outer drum structure can achieve high recording accuracy, because the distance between the laser and the film is always the same. However, the laser beam of the capstan type imagesetter is scanned laterally by the deflection beam of the prism (as shown in the left figure), so the distance between the laser beam and the middle and both ends of the film is different. The larger the format is, the larger the deflection angle of the laser scanning is. The greater the distance difference between the laser beam and the middle and both ends of the film is, the greater the nonlinear distortion is, and the greater the error is. Therefore, it is generally limited that the format of the winch Phototypesetter cannot exceed four openings, and we should also try to minimize the deflection angle of the exciting beam and reduce the deformation of the light spot

however, it is not because the accuracy of the winch type imagesetter is too low to be used. Usually, these problems will be considered in the design to make the error within the allowable range. In order to improve the accuracy decline caused by uneven film feeding of the winch typesetter, some winch typesetters use film buffering film feeding and receiving devices to avoid uneven film feeding caused by uneven film tension. The structure of film feeding and receiving is shown in the right figure. Because the film is loosely buffered in the process of transmission, it does not directly pull the film from the film supply box, nor directly send the film to the film receiving box, which reduces the tension of the film in the process of transmission, keeps the tension of the film consistent, and improves the uniformity of film walking

in fact, the winch type Phototypesetter has many incomparable advantages over other types of phototypesetters. For example, the length of Phototypesetter is unlimited, and it can record a long page within the width of the format. Compared with the inner drum Phototypesetter, it saves film, is convenient to operate, and is very popular with users

3. Other parameters

Phototypesetting speed is usually measured by the film moving speed when recording with 1200dpi resolution. Now the new imagesetter can move films at a very fast speed, but this is not the only factor that determines the film speed, because it is also limited by RIP speed. The time taken to output a page should be equal to the sum of the time taken to transmit data over the network, the time taken to interpret the page by rip and the time taken to record by the imagesetter. Therefore, the speed of phototypesetting only affects the recording time

another parameter of the imagesetter is the laser wavelength used by the imagesetter. The commonly used lasers of Phototypesetter include He Ne laser with wavelength of 633nm, red semiconductor laser with wavelength of 650nm or 670nm, infrared semiconductor laser with laser with wavelength of 780nm. The laser wavelength determines the type of film used, and even relates to the price of the film used. For example, at present, domestic ammonia neon laser Phototypesetting films are the cheapest. Almost all text Phototypesetting films use this kind of film, while infrared Phototypesetting films are expensive and less used

some high-end phototypesetters can be connected to the film processor so that the recorded film can be developed at any time. Generally, imagesetters use continuous film. In order to improve production efficiency, they often record a batch of layouts and then cut and develop them. Therefore, after the completion of this transaction, even the recorded pages still need to be stored in the cassette of the Phototypesetter first, and then processed together after a batch of films are recorded, making customers wait for a long time. By using the on-line washing machine, one record can be recorded and one washing can be achieved, reducing the waiting time to confirm the composition conditions and regularity of -pbo2 oxide film. But the on-line punching machine is generally more expensive, which is much more expensive than the ordinary punching machine. Some phototypesetters also have perforating devices, which make it more convenient to make up and print

at present, most of the phototypesetters used in domestic color desktop publishing systems are imported equipment. Domestic phototypesetters are mostly used for text Phototypesetting due to their low accuracy and low grade. They are rarely used to output color separations, and are mostly used to output color newspapers with low accuracy requirements. The highest recording accuracy of the winch typesetter produced by Changchun Optical Machinery Co., Ltd. can reach 2540dpi, but the disadvantage is that the registration accuracy is low, which can not meet the requirements of high-end color printing. The external roller Phototypesetter produced by the former Hangzhou communication equipment factory can meet the general requirements in terms of recording accuracy and registration accuracy, but the disadvantage is that the grade is not high, only a single film can be used, which is inconvenient to operate, and the automatic film feeding mechanism is not suitable for use in Northern areas, which is prone to failure, so it is not widely used. On the other hand, due to the continuous decline in the price of imported equipment, the price difference relative to domestic equipment has gradually narrowed, and its performance is significantly better than domestic products