Talking about the principle of paper positioning
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In order to check the overprinting accuracy of printed products in a specific calibration operation, 7 to 8 cross lines (or called registration lines) for overprinting are generally produced in the same part of each printing plate. Rule line), specific location. At the time of printing, the crosshairs are printed onto the substrate along with the graphic on the plate. Since the relative position of the graphic and the cross line on each printing plate in the printing plate is exactly the same when printing, the registration of the cross wire reflects the registration of the graphic after overprinting. In this way, it is only necessary to check and adjust the overlap of the crosshairs (including the offset and the off-angle) during printing to ensure the registration of the printed graphics.
The paper is conveyed forward by the paper feeding device to the front predetermined position, and the paper is placed in the forward direction of the paper by the force of the paper to be fed forward. After the paper is in the front position, the paper is moved laterally by the side gauges, and is laterally positioned against the side positioning plate. The general rule of paper positioning at the rule is that the front side (forward direction) of the paper depends on two positioning points, while the side edges only need to be placed on one positioning point, and the paper edges perpendicular to each other can rely on three positioning points in two directions. Ensure that the paper is accurately positioned. In order to position the substrate on the front and back sides of the same positioning edge, a side gauge having the same structure and opposite directions is provided on both sides of the sheet-fed lithographic printing machine. Use the side gauge of the operating surface when printing the front side and the side gauge of the driving surface when printing the reverse side.