Application of NezaPLCNeza on flatbed offset press
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working principle
The lithographic offset press uses indirect printing on a variety of paper sizes. Firstly, the graphic materials to be printed are made into a film base plate, and then transferred to a photosensitive PS metal plate. The printed graphic needs to be easily adhered to the ink, while other portions are stuck to the ink without ink, and the PS plate is mounted on the offset printing machine. On the roller, the adhered ink is transferred onto the blanket on the other cylinder and transferred onto the paper by the blanket. This indirect printing utilizes the high elasticity of the blanket to print a strong impression with a small roller pressure, so that even a very fine imprint can be faithfully reproduced on the paper. The offset printing machine is mainly composed of paper feeding, printing, ink supply, coding, delivery, etc. In the working process of the offset printing machine, the paper feeding is required to be stable, the paper is continuous, the paper feeding must be in place to ensure the positioning accuracy of the printing sheet. When printing color graphics, it is necessary to print multiple times, and the repeat positioning accuracy is high, otherwise "ghosting" will occur, which will make the printed sheets blurred. In the printing process, it is necessary to ensure the balance of ink and ink, and the color is uniform. The main drive is required to be stable. Otherwise, the ink bar will appear, and stepless speed regulation is required. The printed sheets will generate static electricity due to friction with the blanket, so that the paper is sucked together. The static eliminator eliminates static electricity. When the paper is delivered, the paper should be placed neatly to ensure a certain height of the printed sheet. It is automatically adjusted. When the delivery table is lowered to the limit position, the paper feed should be stopped and an alarm signal should be sent. Control system configuration: The operation panel is used as the input unit of the operation signal, and is composed of a button switch, a boat switch, a digital dial, and a potentiometer. During the work process, the position of the paper, the parameters and the state of the mechanical mechanism are detected. The information is provided by the photoelectric, inductive, capacitive sensor and the stroke switch and the micro switch to the control unit, participating in logic and mathematical operations, and the control unit is sufficient. The PLC completes, and outputs an output signal according to the operation input signal and the detection signal. The output signal controls the frequency converter to perform speed control. The electromagnet is controlled to drive the mechanical mechanism to complete various actions. In addition, the power supply unit is provided. 220V power, after the main switch, air switch protection, supply PLC, inverter, voltage regulator, its system connection diagram is as follows: 600)this.width=600" working principle is designed according to mechanical structure and operation requirements. Operation: There are two modes of operation: “manual” and “automatic”. The former is used for adjustment work before printing. After the machine adjustment is completed, it can enter the “automatic” working state and work according to the prescribed procedures.
For electrical requirements, the following functions need to be completed.
1. The main drive control must be smooth and the speed changes during the printing process need to be continuous without jumping. The speed is between 3,000 and 10,000 RPh stepless speed regulation. The speed of the forward and reverse vehicles is limited to 120RPh, and the washing roller is 6000RPh.
2. Paper feeding control During the printing process, the paper height of the paper feeding should be kept constant, the paper table can automatically adjust the rise, and whether it is a single sheet during the paper feeding process, preventing multiple sheets of paper from entering the drum and damaging the drum, such as: “Double” fault detection function and paper in-position detection function, in case of failure, alarm shutdown and troubleshoot.
3. Pressing, depressurizing, counting control When printing on paper, press and press according to the operating cycle of the machine, and count the printed paper. When printing continuously, it is necessary to lock the pressing action. Once there is no paper or “broken piece”, it will be pressed off in time to prevent “staining” behind the sheet when printing again.
4. Pendulum and pendulum control When the main motor is working, the “manual” working mode can be operated directly. When the “automatic” working mode is used, it can work simultaneously with the combined pressure.
5. Repeat Code Control The number of sheets that are repeated with the ‘number is controlled by the data entered by the dial.
6. Dusting and paper static elimination When printing, the paper rubs against the blanket and generates high static electricity, which affects the delivery and causes the paper to become dirty. Use a static eliminator to eliminate static electricity on the paper. In the case of color printing, the adhesion of the ink on the paper surface is prevented, and when the paper is fed, the powder is sprayed on the surface of the printing paper.
In order to ensure the printing quality and reliable work of the offset press, the following links should be considered:
1. Paper thickness detection In order to prevent multiple sheets of paper from entering the drum, it is called “double sheet” failure. In actual control, all papers of 50g or more are detected by the micro switch, and the paper micro switch below 50g cannot be detected. The radiation photoelectric sensor detects its thickness. After the power is turned on, the thickness of the first three sheets of paper entering the printing machine is measured, and the average value is calculated as 1.5 times as a standard value, and each sheet of paper is detected later. Any paper larger than this value is judged as "double sheet". ", stop and alarm, the analog-to-digital conversion, numerical calculation and output of the photoelectric analog signal here are completed by PLC.
2. Paper in place During the printing process, the rejected paper is used as a detecting element to detect the fault because the paper is skewed.
3. Pressing and controlling the paper fed into the pressure roller, it should be fed in a certain position of the roller to carry out the pressure. If there is no subsequent paper, it will be pressured off in time, otherwise it will cause the back surface to be "dirty" in the subsequent printing, but it is required When pressing continuously, lock the pressure to prevent the paper from being pressed every time a sheet of paper is printed. The printing cycle here is used as a standard, and the signal is taken out by the inductive sensor. The same is true for the requirements for coding and compression.
4. When the duplicate code controls the created document or the multi-invoice, it is necessary to print a number of printed sheets of the same number. The number of printed sheets is compared with the dialed disc stored in the data memory. Once the data is the same, a signal is sent to drive the dialing mechanism to dial the number.
5. Operation control of the ink roller The running speed of the ink roller affects the printing quality and maintains the ink balance. The speed should correspond to the speed of the main drive, take the speed analog quantity of the main unit from the inverter, adjust the scale factor after A/D conversion, output the corresponding pulse or pulse width, control the servo motor, and achieve the best effect of ink balance.
6. Interlocking, interlocking control In order to ensure safety, interlocking between the positive and negative vehicles is required, and interlocking between operation and jog is required. Stop feeding when the delivery table is lowered to the limit position; if it is running, if the electromechanical cover is opened, stop immediately to prevent accidents.
7. Protecting the output of the PLC Most of the output actuators of the offset press are controlled by electromagnets to drive the mechanical structure. Although the relays of the PLC can be used directly, the inductive load is unfavorable to the contacts. If a problem occurs, replace or check the PLC. The output relay is not what the average user can do. We use PLC relay to control the external relay coil, and the external relay contact controls the electromagnet to facilitate the detection and elimination of faults and prolong the service life of the PLC. Application Analysis Originally, we used integrated circuits to design control circuits, using integrated circuits such as gates, flip-flops, counters, analog switches, etc. The control system is stable and reliable, but the flexibility is poor. The advantage is low cost, and its input and output are parallel. Working, fast. However, in the market economy environment, products are continuously improved and updated, and new requirements are constantly put on the control system. The integrated circuit control system cannot keep up with the development needs, and PLC control is adopted. In the offset printing machine, the thickness detection of the paper below 50g and the adjustment of the ink balance are obtained by analog-to-digital conversion, and the control signal is taken out after the operation, and the analog-to-digital conversion time is generally about 200us, and the transmission time should be Less than 250us, the maximum speed of the offset press is calculated according to 12000RPH, one operating cycle is 0.3 seconds, and the time for the paper to stay in the front gauge position is about 0.15s. The analog-to-digital conversion can use the interrupt mode to detect the signal. If the program length is 1K, the scan period will not be greater than 2ms, and the paper thickness signal can be detected in the adjacent scan period, which can be 0. The reaction action is taken within 15 seconds, and the detection of the ink roller is not negligible and can be ignored. In 2001, the company contacted Schneider's NEZA product, which has been applied to the A45 and A46 offset presses. After debugging, it meets the technical requirements of these two models. NEZA has the following characteristics: 600)this.width=600" NEZA's instructions and The various instructions of the MCU can be one-to-one correspondence. The function block and the special function block of the Ikawa function are rich in content. It provides sending/receiving messages and control data exchange, step counters, etc., which brings very much to the design of the design control system. Great convenience, especially for those who are familiar with microcontroller applications, can make full use of PLC resources, after using NEZA, to achieve the same function, the program is reduced by 1/5, the input and output points are reduced from 60 points to 40 points. The programming is more simple and reliable, and the operation is stable. NEZA provides powerful functions and high speed. NEZA provides designers with convenient facilities, such as input common points, 24VDC and 0V, and designers can also use PNP or NPN input methods. It solves the problem of different signal input modes, solves the problem of different levels of input signal power, saves peripheral hardware circuits, and improves the transmission. The reliability of the signal improves the stability of the control circuit. The system provides the function of ten clocks and provides the output of the clock signal. It has special practical value for the supporting / home foot. The information of the problem provides a basis for improving and renovating the quality of the product. The printing function is complete and provides all the input, output and parameters and status of each function block. It provides convenience for programmers and maintenance personnel, and the status of the machine is one day. However, it is convenient to grasp the use of the situation and the elimination of faults. NEZA has a good performance-price ratio and has a great advantage in price.