At present, new electrical control technologies have been widely used in domestic sheet-fed lithographic printing machines, such as PLCs, touch screens, and frequency converters. These new sheet-fed lithographic printing presses have the advantages of high reliability, energy-saving efficiency, and perfect functions compared with the old-fashioned devices of some years ago. In many current printing companies, the old type sheet-fed lithographic printing machines still have There is a considerable amount. If they are remodeled, all PLCs and touch screens are used, and a large number of lines need to be changed, which is almost equivalent to recreating the electrical control system. If only the main drive part of a sheet-fed lithographic printing press is used to reform the inverter, there will be less line changes and less work. It not only retains the simple and practical features of the original relay contact control, but also gives full play to the advantages of reliable and energy-saving inverter, and the cost-effectiveness of the transformation is high. In the following, we will discuss some applications of frequency converters in the transformation of domestic single-color and single-sheet lithographic printing presses.
1. Process characteristics of press control
To make the inverter-driven variable-frequency motor well applied to the printing press and to meet the requirements of the production process, it is first necessary to understand the process characteristics of the printing press operation control, what kind of requirements it imposes on the function of the inverter, and then what type of model is selected Inverter, and how to specifically modify the original line of docking.
The operation of the sheet-fed lithographic printing press is driven by the motor through a belt drive, a gear drive, and a chain drive, and the rollers, the teeth row, and the mechanism are coordinated by the mechanical connection, so the motor of the main drive is controlled. Control the running status of the whole machine. In the mechanical adjustment, inspection, installation and removal of PS plates and blankets, cleaning the machine, you need to manually control the machine forward and backward mode of operation, about 4r/min speed is more appropriate. During the pause of printing, in order to ensure that the PS plate is not damaged, the ink is not dry, and the machine is to be run at the same speed for a long time. When the machine starts formal printing production, there is an initial speed of about 3,000 rpm. When the paper feeder starts to feed paper, it can speed up, making the machine produce at a higher speed, generally 6,000 to 8,000 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 speed value can be indicated by the speed meter. From the high speed of printing to the initial printing speed, there are two cases. First, the manual button decelerates, and the other is the detection of paper failure during the printing process, such as arrogance, no paper, double sheets, etc., so that the printing press is automatically decelerated and the various parts make coordinated actions accordingly, such as pressure separation and water stoppage. , from the ink, stop the paper and so on. At the end of production, press the stop button and the machine will stop smoothly in freewheel mode. In addition, in order to ensure personal safety, a safety switch or emergency stop button is installed at the dangerous part of the printing press. As long as these switches act, the machine should be stopped immediately regardless of the state of the machine, and the whole machine should be braked.
2. Requirements for the function of the frequency converter
(1) Three speed control and direction control functions are required to meet the requirements of positive and negative point vehicles, positive low speed, initial printing speed, and high speed;
(2) The speed value of high-speed operation is variable. It is better to adjust the speed steplessly by hand-adjusting potentiometer to adapt to different process requirements;
(3) The speed of the machine must be instructed so that the operator can determine the current operating condition;
(4) The acceleration and deceleration of the machine should be steady, and the speed should be appropriate. When the speed is changed, it can be smoothly and timely without any impact. If the inverter itself has a fault, it must stop the whole machine.
3. Inverter parameter selection According to these requirements we can see that most of the inverters can meet, for the occasions used, select the universal inverter. The voltage capacity is selected according to the power supply used and the motor used in the original machine. 400V class is used here, 5.5kW single-color machine, 11kW inverter used in two-color machine, there are a wide variety of inverters on the market, generally choose the mainstream products with good quality, such as Mitsubishi A540 series, Yaskawa G5, Delta, etc. Although the price of the product is higher, the quality is guaranteed.
For an electrical core component of a printing press, rather than a one-time investment, to avoid the trouble caused by frequent failure in the future. Of course, if you have confidence in the other brand quality and performance indicators of the inverter, you can also choose to save some. After having the drive hardware, set its internal parameters. In terms of speed parameters, the jog frequency can be set to 2.5Hz, the initial printing speed is 25Hz, and the high speed is about 60Hz. The following uses the Mitsubishi A540 Series 400V and 11kW products as an example to describe its specific wiring and its connection with the old press. The two lines are shown in the attached drawings. The relevant precautions are as follows.
(1) The main drive of the original printing press is an electromagnetic speed control (slip) motor, a low-speed motor, clutches, brakes, etc. All are removed and replaced, and a special motor of frequency conversion speed control produced by Shanghai Tongtai Motor Co., Ltd. is used instead. Machine 11kW/380V comes with three-phase power 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 mounted on the new motor shaft.
(2) Since the original main motor and low-speed motor have been removed, the wiring of the main contacts of the contactors KM1, KM2, and KM3 in the distribution box can be removed. The rest of the available contacts are used in accordance with the new line as switching contacts for the drive control signals. Because the contacts of the original relay may have a longer use time and poor contact, it is better to replace it. Forward input terminal STF, reverse input terminal STR, medium speed terminal RM, low speed terminal RL, reset terminal MRS, common terminal SD wiring of the frequency inverter need to be combined in parallel with related contact strings to meet three-step speed regulation requirements.
(3) The original electromagnetic governor ZLK-11 was also removed, and it was possible to make a suitable speed gage display box using its mounting position, using a 1KΩ/ZW wire potentiometer to access the analog signal input port - 10E , 2.5, with a full-scale 10V DC voltmeter in parallel with the 2.5 side, change the indicator unit in the dial, you can indicate the command speed of the inverter.
(4) Inverter internal alarm normally closed contacts B, C connected to the serial circuit of the original control circuit KA1, so that after the action with the machine emergency stop function.
(5) Control the main motor contactor KMa and connect it to the original line KA1. If an alarm is released, the main motor circuit is disconnected and at the same time KA1 normally closed contact is closed, resetting the inverter and prohibiting output. Cooling fan, electromagnetic brake contactor KMb coil connection has two branches, one is in series KMa normally open contact with KMa in parallel, and the other is with the power supply in series into the car safety switch normally closed contact. Normally, the branch is disconnected. When a manual cranking is required, the power supply also energizes the KMb via the safety switch, and the brake is released to crank.
(6) There are two ways to install the inverter. The first is to make another control box, which is placed in the appropriate position on the bottom of the feeder plate. The other is that if the control cabinet is close to the wall or the column, the control box can be fixed on the wall or column, through the harness and the tube The original control cabinet is connected.
4 Conclusion
After the above steps, the author successfully reconstructed an old J2205 sheetfed two-color lithographic printing machine. After the transformation, the captain showed that the speed was stable, the speed was accurate, and the energy efficiency was high. The maintenance personnel also felt high reliability, and almost no extra maintenance was required. We actually measured the current consumed during the production of the printing press before and after the conversion, and made comparisons and calculations to conclude that at least 30% of energy was saved. As shown in the attached table: With 20 hours of production per day and 280 days per year, electricity consumption can be reduced to 16800kWh per year, at 0.7 yuan per kilowatt-hour electricity, and electricity savings can be saved by only 11,760 yuan per year. The electromagnetic clutch used for clutch and brake is easily damaged due to poor working environment. To replace 4 each year, each 250 yuan, and can save 1,000 yuan. We spent 7800 yuan for the inverter, 8,000 yuan for the inverter motor, plus a total of about 16,000 yuan for some wires and relays. Compared with investment and 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.