The working mode of the outer drum type phototypesetting machine is similar to that of the conventional electric extension machine. The recording film attached to the outer circumference of the drum rotates with the drum, and one line is recorded every one rotation, and the laser head is traversed one line, and the next line is recorded.
The outer drum type photo-aligning machine has the advantages of high recording accuracy and registration precision, simple structure, stable work, and can make the recording format large. The disadvantages of the outer drum type photo-aligning machine are inconvenient operation and low degree of automation. Usually, manual loading and unloading are required, and manual and upper-sheet processing is required in the dark room.
The outer drum type phototypesetting machine can greatly enlarge the recording drum of the rowing machine, and needs a pumping system and a film fixing device, and the larger the recording drum, the greater the inertia when rotating, the speed is limited, and the recording speed is low, and must be Increase the recording speed by increasing the number of laser beams.
Therefore, an external phototypesetting machine of this type is currently less used. However, the outer drum type structure is very suitable for the direct plate making machine, because the direct plate making is a single plate, not a continuous piece, the plate size is fixed, and the direct plate can be operated in the bright room, partially offsetting its shortcomings, plus this The Light path of the structure is short, easy to control, and the laser loss is small, and the exposure speed can be accelerated by using multiple lasers. In addition, the external drum type phototypesetting machine has a simple method of processing the dust during the plate making process, and the upper plate mode is the same as that of the printing machine, so that the precision can be high. As the level of design increases, so does the level of automation, so it is considered to be the best direct plate-making machine structure.
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