At present, the new electric control technology has been widely used in domestic sheet-fed offset printing presses, such as PLC, touch screen, frequency converter, etc. These new sheet-fed offset printing presses have the advantages of high reliability, energy saving, high efficiency, and perfect functions compared to the old-style equipment several years ago. However, in many current printing companies, old-fashioned sheet-fed offset printing presses are still Has a considerable amount. If they are modified, all PLC and touch screens are used, and a large number of lines need to be changed, which is almost equivalent to remaking the electrical control system. If only the inverter is used for the main transmission part of the sheet-fed offset printing press, the circuit changes little and the workload is small. It not only retains the simple and practical characteristics of the original relay contact control, but also gives full play to the advantages of inverter reliability and energy saving, and the cost-effective transformation is high. The following is about the application of the inverter in the transformation of the domestic single and double color sheet-fed offset printing machine.
1. Technological characteristics of printing machine operation control
In order to make the inverter-driven inverter motor be well applied to the printing machine and meet the requirements of the production process, we must first understand the technological characteristics of the operation control of the printing machine, what kind of requirements does it put on the function of the inverter, and then choose which model Inverter, and how to specifically modify and connect the original line.
The operation of the sheet-fed offset printing press is driven by the motor through the belt drive, gear drive, and chain drive. The mechanical interaction between the rollers, tooth rows, and mechanisms is coordinated, so the motor that controls the main drive is Controlled the running state of the whole machine. In mechanical adjustment, inspection, installation and removal of PS version and blankets, and cleaning of the machine, it is necessary to manually control the machine to run in the reverse direction. A speed of about 4r / min is more appropriate. During the printing pause, in order to ensure that the PS plate is not damaged and the ink is not dry, the machine must be run at the same speed for a long time. When the machine started formal printing production, it had an initial speed of about 3,000 rpm. When the paper feeder starts to feed paper, it can be accelerated to make the machine produce at a higher speed, generally 6000 to 8000 rpm. In order to adapt to different production speed requirements, a high-speed potentiometer can be used to adjust the high speed, and the actual value of the speed can be indicated by the speedometer. There are two cases from the high-speed printing to the initial printing speed. One is the manual button to slow down, and the other is that paper faults are detected during the printing process, such as crooked sheets, no paper, double sheets, etc., which causes the printing machine to automatically decelerate, and various parts make coordinated actions accordingly, such as pressure release and water stop. , Remove ink, stop paper feeding, etc. At the end of production, press the stop button, and the machine stops smoothly in corresponding free stop mode. In addition, in order to ensure personal safety, a safety protection switch or an emergency stop button is installed in the dangerous part of the printing machine. As long as these switches are activated, no matter what state the machine is in, it must be stopped immediately and the whole machine is braked.
2. Requirements for the functions of the inverter
(1) There must be three-stage speed control and direction control functions to meet the requirements of positive and negative spotting, positive low speed, initial printing speed and high speed;
(2) The speed value of high-speed operation is variable, and it is best to adjust the speed steplessly by manually adjusting the potentiometer to adapt to different process requirements;
(3) There must be speed indication during the operation of the machine to make the operator know the current operation status;
(4) The acceleration and deceleration process of the machine should be stable, the speed is appropriate, and the speed change should be smooth and without impact in a timely manner. When the inverter itself is faulty, the whole machine should be stopped.
3. Inverter parameter selection According to these requirements, most inverters can be satisfied. For the occasions used, select a universal inverter. The selection of voltage capacity is based on the connected power supply and the motor used by the original machine. The inverters of 400V grade, 5.5kW for single-color machines and 11kW for two-color machines are used here. There are many types of inverters on the market. Generally, mainstream products with good quality are selected, such as Mitsubishi A540 series, Yaskawa G5, and Delta Although the price is higher, the quality is guaranteed.
For the core electrical components of a printing machine, Ning Ken will invest a large amount at one time to avoid the trouble caused by frequent failures in the future. Of course, if you are sure about the quality and performance of other inverter brands, you can also choose, so that you can save some. After you have the inverter hardware, you must set its internal parameters. As far as speed parameters are concerned, the jog frequency can be set to 2.5 Hz, the initial printing speed is 25 Hz, and the high speed is about 60 Hz. The following uses Mitsubishi inverter A540 series 400V, 11kW products as an example to describe its specific wiring and retrofit connection with the old type printing machine. The circuit of the two is shown in the figure. The relevant precautions are as follows.
(1) The main transmission device of the original printing press is the electromagnetic speed regulating (slip) motor, low speed motor, clutch, brake and other mechanisms are not used. It is replaced by a special frequency conversion speed regulating motor produced by Shanghai Tongtai Motor Company. The machine's 11kW / 380V comes with three-phase power-off brake and cooling fan. The mounting base of the original motor can be used, and the pulley of the original motor can also be removed and installed on the new motor shaft.
(2) Because the original main motor and low-speed motor have been disassembled, the wiring of the main contacts of the contactors KM1, KM2, and KM3 in the distribution box can be removed. Use the remaining available contacts according to the new circuit as the switch contacts of the inverter control signal. Because the contacts of the original relay may be used for a long time and the contact is poor, it is best to replace it. The inverter's forward input terminal STF, reverse input terminal STR, medium speed terminal RM, low speed terminal RL, reset terminal MRS, and common terminal SD wiring need to combine related contacts in series and parallel to meet the three-stage speed regulation requirements.
(3) The original electromagnetic speed regulator ZLK-11 has also been removed. It is possible to use its installation position to make a suitable speed display box, and use a 1KΩ / ZW winding potentiometer to access the analog signal input port-10E , 2.5, use a DC voltage meter with a full range of 10V in parallel at the 2.5 end. Change the indicating unit in the dial to indicate the command speed of the inverter.
(4) Connect the normally closed contacts B and C of the inverter to the series circuit of the original control line KA1 to make it have the function of emergency stop after the operation.
(5) The contactor KMa that controls the main motor is connected to the original line KA1. If there is an alarm, it will be released, and the main motor circuit will be opened. At the same time, the KA1 normally closed contact is closed, the inverter is reset, and the output is prohibited. There are two branches connecting the cooling fan and the electromagnetic brake contactor KMb coil. One is to connect the KMa normally open contact in parallel with the KMa, and the other is to connect the normally closed contact of the crank safety switch between the power supply. Normally, the branch is disconnected. When manual rocking is required, the power supply also energizes the KMB through the safety switch, and the brake can be released when the brake is released.
(6) There are two ways to install the inverter. One is to make another control box and place it in a proper position on the lower part of Feida cardboard. The other is if the control cabinet is close to the wall or column, you can fix the control box on the wall or column. The original control cabinet is connected.
4 Conclusion
After the above steps, the author successfully transformed an old J2205 single-sheet two-color lithographic printing machine. After the transformation, the captain reported stable speed, accurate speed regulation, high efficiency and energy saving, and the maintenance staff also felt that the reliability was high and almost no extra maintenance was required. We actually measured the current consumed during the production of the printing press before and after the transformation, made a comparative calculation, and reached the conclusion that at least 30% energy saving was achieved. As shown in the attached table: 20 hours of production per day, 280 days in one year, 16800kWh of electricity can be saved in one year, and 0.7 yuan per kilowatt-hour of electricity, 11760 yuan in electricity can be saved in one year. In addition, the previous low speed The electromagnetic clutch used for clutch and brake is easily damaged due to the poor working environment. With 4 replacements per year, each of 250 yuan can save another 1,000 yuan. It costs us 7,800 yuan to buy a frequency converter, 8,000 yuan for a frequency conversion motor, plus some required wires, relays, etc., totaling about 16,000 yuan. When the input is compared with the output, the entire investment can be recovered in less than a year and a half. Of course, this does not include the indirect benefits of improved productivity and improved print quality after transformation.
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