Pneumatic design of conveying mechanism of sheet-fed offset printing machine (Part 2)

2 Pneumatic design

It can be seen from the working principle of the original paper conveying mechanism above that the motion of the paper conveying mechanism is composed of a paper pressing motion, a paper separating motion and a paper passing motion respectively. The main movement occurs when the paper is touched, and the movement trajectory in other time periods has no effect on the printing quality. Therefore, according to the motion characteristics of the original paper conveying mechanism, pneumatic components are used to pneumatically design the paper blowing nozzle mechanism, the paper separating nozzle mechanism and the paper feeding nozzle mechanism of the paper conveying mechanism.

1) The paper blowing nozzle moves.

The paper blowing nozzle mechanism is an important mechanism in the paper conveying mechanism. It is an important link to ensure the output of a single sheet of paper. The J21O8 machine uses two cams to ensure its complete function. Here, the use of two cylinders can also ensure the realization of its function (see Figure 3).

It can be seen from FIG. 3 that the air cylinder I controls the swing of the paper pressing nozzle to avoid the interference between the paper pressing nozzle and the paper when the paper separating nozzle and the paper feeding nozzle feed the paper. The small air cylinder II guarantees that the movement of the paper pressing nozzle when pressing the paper is straight up and down, so as not to rub the paper and cause paper mess.

2) Separation of nozzles.

The paper separating nozzle mechanism completes the separation of paper with the assistance of the paper blowing nozzle, and has specific requirements for its movement. The mechanism shown in Fig. 4 can well replace the cam-controlled paper separation nozzle mechanism in the original J21O8 machine to realize its function. It can be seen from FIG. 4 that the air cylinder I controls the up and down movement of the paper separation nozzle to ensure that the paper separation nozzle reliably contacts the paper and removes it from the paper stack. The air cylinder II ensures that the separation nozzle can quickly flip an angle (shaking head) immediately after sucking the paper to avoid the appearance of double sheets and multiple sheets.

3) Paper-handling and paper-absorbing movement.

The movement of the paper suction nozzle mechanism is the most complicated compared to the paper pressure blowing nozzle mechanism and the paper separation nozzle mechanism. Here, three cylinders are used to realize the necessary movement trajectory (see Figure 5). First of all, the cylinder I controls the paper delivery nozzle to descend to the paper surface. At this time, the suction valve opens and the nozzle sucks the paper; then the cylinder III controls the nozzle to realize the movement of the paper upward and the direction of the separation nozzle, so that The paper between the suction nozzles is slack to avoid paper tearing; the air cylinder II controls the paper transfer nozzle to complete the transfer of the paper to the paper feeding table. The above three pneumatic mechanisms can fully realize the movement required for the paper feeding mechanism of the sheet-fed offset printing press. For sheet-fed offset presses, the movement of the paper feed mechanism must be synchronized with the movement of the printing parts, so as to ensure the smooth progress of EO, ~ U work. The J2108 machine is synchronized through the jaw clutch. For the designed pneumatic mechanism, this method is impossible. Here, a switch cam can be installed on the impression cylinder shaft to control a stroke switch to ensure its synchronization (see Figure 6).

Due to the large number of cylinders used in this mechanism, the relay system has undoubtedly increased the unreliability of the control system, while the PI C control is compact, fast and safe to use. Therefore, the coordination between the paper pressure blowing nozzle mechanism, the paper separating nozzle mechanism and the paper feeding nozzle mechanism is controlled by PLC. Set up a ladder diagram of the PLC (see Figure 7).

Except for 0001, which is connected to a cam-driven travel switch, the other input terminals of FIG. 7 are magnetic switches of each cylinder, thereby ensuring the sequential operation of the cylinders. Stopping the suction of the paper delivery nozzle and controlling the blowing by the cam switch can ensure that the paper delivery can be synchronized with the gripper row and the front gauge at any speed.

3 Conclusion

It can be seen from the above that the pneumatic structure is simple and easy to implement, which not only can ensure the movement performance of the paper conveying mechanism, but also technically guarantees the synchronization of the work with other components. Due to the simplification of its structure, the cost of the printing mechanism will be greatly reduced, and the cam mechanism is eliminated for some reason, which can improve the dynamic characteristics of the system and reduce the hidden danger of failure.

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Product Application