working principle
Lithographic offset presses use indirect printing on paper of various specifications. First, the graphic materials to be printed are made into a film negative, and then transferred to the photosensitive PS metal plate. The graphic to be printed is easy to stick ink, while the other parts stick to water without ink. The PS plate is installed on the offset press. On the roller, the glued ink is transferred to the blanket on the other roller, and the blanket is transferred to the paper. This indirect printing utilizes the high elasticity of the blanket, and can print strong marks with a small cylinder pressure, and even very thin marks can be faithfully reproduced on the paper. The offset press is mainly composed of paper feeding, printing, ink supply, coding, paper collection and other mechanisms. During the operation of the offset press, it is required that the paper is fed smoothly, the paper is continuous, and the paper must be fed in place to ensure the positioning accuracy of the printed sheet. When printing color graphics and text, it needs to be printed multiple times, and the repeat positioning accuracy should be high, otherwise "ghosting" will appear, which will make the printed sheet blurred. In the printing process, it is necessary to ensure the balance of water and ink and uniform color. The main drive must be stable, otherwise ink sticks will appear, and stepless speed regulation will be required. The printed sheet will generate static electricity due to friction with the blanket, which will cause the paper to suck together The static eliminator eliminates static electricity. The paper should be placed neatly when receiving the paper to ensure that the printed sheet's certain height is automatically adjusted. When the receiving table is lowered to the limit position, the paper should be stopped and an alarm signal should be issued. Control system configuration: The operation panel is used as the input unit of the operation signal, which is composed of button switch, boat switch, digital dial and potentiometer. During the working process, the position, parameters and mechanical mechanism of the paper are detected. The information is provided to the control unit by photoelectric, inductive, capacitive sensors, travel switches, and micro switches. It participates in logical and mathematical operations. After the PLC is completed, the output signal is generated after the operation input signal and the detection signal are calculated. The output signal controls the inverter to control the speed; the electromagnet is controlled to drive the mechanical mechanism to complete various actions. 220V electricity, after the main switch, air switch protection, supply PLC, frequency converter, voltage regulator, the system connection diagram is as follows: 600) this.width = 600 "The working principle is designed according to the mechanical structure and operating requirements. Operation: There are two working methods: "manual" and "automatic". The former is used for adjustment before printing. After the machine adjustment is completed, you 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 control operation of the main drive must be smooth, and the speed change during the printing process needs to be continuous without jumps. The speed is stepless speed regulation between 3000 ~ 10000RPh, the speed of forward and reverse car is limited to 120RPh, and 6000RPh when washing the roller.
2. Paper feeding control During the printing process, the height of the paper surface must be kept constant, the paper table can automatically adjust the rise, during the paper feeding process, it is necessary to detect whether it is a single sheet, to prevent multiple sheets from entering the cylinder, and damage the cylinder, such as "Double sheet" fault detection function, paper in-place detection function, once a fault occurs, it will alarm and stop to eliminate the fault.
3. Closing pressure, depressurization, counting control When there is paper printing, press the depressurization according to the operating cycle of the machine, and count the printed paper. When continuous printing, it is necessary to lock the pressing action. Once there is no paper or "broken sheet", the pressure should be removed in time to prevent "dirt" behind the printed sheet when printing again.
4. Ink and water swing control When the main motor is working, the "manual" working mode can be directly operated, and in the "automatic" working mode, it works simultaneously with the closing pressure.
5. Repeat code control The number of printed sheets with the same number repeatedly is controlled by the data input from the dial.
6. Powder and paper static elimination When printing, the friction between the paper and the blanket will produce a high static electricity, which affects the paper collection and causes the paper to be dirty. Use a static eliminator to eliminate the static electricity on the paper. In color printing, to prevent the adhesion of ink on the paper surface, when collecting paper, spray powder on the printing paper surface.
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In order to ensure the printing quality and reliable operation of the offset press, the following links should be considered:
1. In order to prevent multiple sheets of paper from entering the roller, it is called a "double sheet" failure. In actual control, all paper above 50g is detected by the micro switch, and the paper micro switch below 50g cannot be detected. The photoelectric sensor detects its thickness. After turning on the machine, the thickness of the first three sheets of paper entering the printing machine are measured, and the average value is calculated as 1.5 times as the standard value. Afterwards, each sheet of paper is tested. Any paper larger than this value is judged as "double sheet" ", Stop and alarm, here the analog-to-digital conversion, numerical calculation and output of the photoelectric analog signal are completed by the PLC.
2. The paper is in place. During the printing process, due to the skew of the fed paper, it will cause waste products. It is necessary to use a reflective photoelectric sensor as a detection element to determine the fault.
3. Closing pressure control The paper fed into the pressure roller should be fed at a certain position of the roller for pressure pressing. If there is no subsequent paper, the pressure should be removed in time, otherwise it will cause the back side to be "scratched" during printing. The continuous pressure should be locked during continuous printing to prevent the pressure from being depressed every time a small piece of paper is printed. The printing cycle here is taken as the standard, and the signal is taken out by the inductive sensor. The same is true for the requirements for coding and pressing.
4. When repetitive codes control the documents or multi-invoices, it is necessary to print several sheets of the same number. The number of printed sheets is stored in the data memory for comparison with the code dial. Once the data is the same, a signal is sent to drive the code mechanism to dial.
5. The operation speed of the ink roller controls the operation speed of the ink roller, which affects the printing quality. It is necessary to maintain the water-ink balance. The speed should correspond to the speed of the main drive. Take the speed analog value of the host from the inverter. After A / D conversion, adjust the scale factor, output the corresponding pulse or pulse width, control the servo motor, and achieve the best effect of water and ink balance.
6. Interlocking, interlocking control In order to ensure safety, interlocking between positive and negative point cars is required, and interlocking between operation and jog is required. Stop the paper feeding when the paper receiving table is lowered to the board limit position; during operation, if the electromechanical shield is opened, stop immediately to prevent accidents.
7. Protect the output of the PLC. Most output actuators of the offset press are controlled by electromagnets. Although the relays of the PLC can be used directly, the inductive load is not good for the contacts. If there is a problem, the PLC must be replaced or checked. The output relay is not something that ordinary users can do. We use a PLC relay to control the external relay coil, and the external relay contacts control the electromagnet to facilitate the detection and elimination of faults and extend the service life of the PLC. Application analysis Originally, we used integrated circuits to design control circuits, using gate circuits, flip-flops, counters, analog switches and other integrated circuits. The control system is stable and reliable, but the flexibility is poor. Its advantage is low cost. Its input and output are parallel Working, fast. However, in a 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 begins to adopt PLC control. In the offset press, the thickness of the paper under 50g and the adjustment of the water and ink balance are obtained through analog-to-digital conversion, and the control signal is taken out after operation. The analog-to-digital conversion time, after consulting the relevant data, is generally around 200us, plus the transmission time Less than 250us, the maximum speed of the offset press is calculated according to 12000RPH, an operating cycle is 0.3 seconds, the time that the paper stays at the front position for detection is about 0.15s, and the analog-to-digital conversion can be interrupted to detect the signal. If the program length is 1K, the scanning period will not be longer than 2ms, and the paper thickness signal can be detected in the adjacent scanning period, which can be 0. The reaction action is made within 15s, and the detection of the ink roller has no strict time limit and can be ignored. In 2001, I contacted Schneider's NEZA products, which have been applied to A45 and A46 offset presses. After debugging, they meet the technical requirements of these two models. NEZA has the following characteristics: 600) this.width = 600 " The various instructions of the single-chip microcomputer can be one-to-one correspondence, and its functional blocks and special Sichuan functional blocks are rich in application content, and provide sending / receiving messages and control data exchange, step counters, etc., which brings a lot to the programming of the design control system. Great convenience, especially for those who are familiar with the application of single chip microcomputer, can fully utilize the resources of PLC, after using NEZA, to achieve the same function, the program is reduced by 1/5, the input and output points are reduced from the original 60 points to 40 points , Programming is more simple and reliable, and the operation is stable. NEZA provides strong functions and fast speed. NEZA provides designers with factory convenience, such as input common point, 24VDC and 0V optional, designers can also choose PNP or NPN input mode , Solves the problem of optional different signal input methods, also solves the problem of different levels of input signal power, saves peripheral hardware circuits, and improves input The reliability of the signal. The stability of the control circuit is correspondingly improved. The system provides the ten-day clock function and can provide the clock signal output, which has special practical value for the supporting / home appliances. It can accurately grasp the appearance of the machine. The information of the problem provides a basis for improving and transforming the quality of the product. The printing function is complete and provides all inputs, outputs, and parameters and status of each function block, which is convenient for programmers and maintenance personnel, and the status of the machine is one day. Of course, it is convenient to grasp its operation status and troubleshooting. NEZA has a good price-performance ratio and has a great advantage in price. Now the purchase cost of NEZAPLC is reduced by 1/3. In addition, after-sales service and technical support are timely Thoughtful, sincere attitude, and customer satisfaction.
Equipped with PLC control system and safety protecting and alarm devices;
Constant sealing with no need of changing. Easy to operate and maintain;
The length of shrink film is automatically adjusted by the electric and control timer;
The added horizontal and vertical electric eyes provide options for switch over. It`s suitable for sealing thin and small products;
With the design of side sealing, the packing length of products is unlimited.
The sealing height can be adjusted based on the product height.
Widely used in all kinds of products with different sizes and shapes
The machine is applicable to industries like food, gift, hardware, daily necessities, pharmacy, printing, etc.
Heat Sealing And Shrinking Machine
Heat Sealing Machine,Heat Shrinking Machine,Film Sealing Machine,Automatic Heat Sealing Machine
Shandong Sinolion Machinery Corp., Ltd. , https://www.sinolion.cc