The role of the former gauge of the positioning device of sheet-fed offset printing press (1)

The orientation of the paper in a plane must be performed in two directions: the positioning of the paper in the direction of advancement, which ensures accurate positioning of the paper up and down, and the positioning of the vertical paper in the direction of advancement to ensure that the left and right positioning of the paper is accurate.

In the actual printing process, the sheet reaches the front gauge first. After the front gauge is in a stationary state, it is pulled or pushed toward the side gauge. The front gauge positions the paper in the forward direction (circumferential), and the side gauge positions the paper laterally (axially). The general rules of the general machine are at least two or more. Most machines are equipped with four, but actually only two are used for positioning. This is because two points determine a straight line. There are less than two front rules, if more than When two are improperly adjusted, positioning actions sometimes interfere with each other. The side positioning position makes the paper have one more positioning point. From this, it can be seen that the positioning principle of the rules component actually uses the geometry principle of two points, one line and three points.

Pre-regulation

The main role of the former rules is as follows:

(1) Positioning the paper circumferentially The circumferential positioning of the paper directly determines the overlay accuracy in this direction.
(2) Change the size of the mouthwash In the printing process, sometimes the size of the mouthwash needs to be changed. There are generally three ways to solve this problem. One is to borrow the printing plate cylinder; the other is to pull the printing plate; there is another It is to adjust the position of the front and back. When the amount of change in the mouth is relatively small, it is still more convenient to move the pre-regulation. However, the pre-regulation is usually moved as little as possible.
(3) Remedy for errors in plate loading and printing plates Loading plates and printing plates sometimes makes it difficult to ensure that all images are in the standard position. Therefore, it is necessary to achieve a certain position through the slight adjustment of the front gauge.
(4) Compensating the error in the feeding process During the feeding process, the paper enters the semi-constrained state from the free state. It can be said that the paper each time it reaches the front gauge is not necessarily in the same position, but the paper arrives at the position determined by the positioning time of the front gauge. s position.
(5) The creation of conditional side regulatory positions for side regulatory positions is based on the former regulatory level.

The front gauge is generally divided into two types, swing up and down (this is according to the up and down of the swing center), the front swing adjustment and installation is very convenient, the swing down front can not completely leave the paper When the paper is fed, it can be returned to the edge of the paper feeder, increasing the positioning time of the front gauge, easily ensuring the accuracy of positioning. With the same positioning time, the speed of the machine can be increased. Therefore, the upper swing type front gauge is suitable. For low-speed large-format or high-speed small format paper, while the swing-down front gauge is suitable for high-speed large-format paper.

Most domestic offset presses use a combination of swing-type front gauges.

Figure 4-1 J2108 pre-regulator structure and working principle

As shown in Figure 4-1, the working position of the front gauge depends on the coupling position of the cam 1 and the delivery gear eccentric shaft drive gear, that is, it is in the "0" point (J2108, J2205 machine specified impression roller When the enamel tooth starts to scratch the main unit to the "0" point), the "0" mark of cam 1 comes into contact with the roller. Since the position of the cam has been accurately calibrated by the manufacturer, it is fixed by a pin, and adjustment is generally not performed when it is used. If it is found that the paper is not properly taken after the overhaul of the machine, the cam 1 can be borrowed.

The most common adjustment of the front gauge is the front-back and height adjustment of the paper stopper 17 , and the front and back adjustments are used to adjust the front gauge when printing requires slight adjustment in the circumferential direction or the printing plate is inconvenient. Loosen the lock nut 19 and turn the adjusting screw 18 to move the positioning plate 17 back and forth. After the adjustment, the nut 19 is locked.