Discussion on the transformation of Web concave ma

Discussion on the transformation of Web concave machine with AC servo technology

1 preface

with the rapid development of science and technology, in order to meet people's needs for the diversification and refinement of commodity packaging, the requirements for the automation and position tracking accuracy of the packaging and printing transmission system are higher and higher. The development direction of modern printing machinery is to apply microelectronics technology, information processing technology, new sensing technology, laser technology, new processes and new materials to printing machinery to realize intellectualization, high automation and high efficiency

2 current situation of packaging and printing machinery

China's packaging and printing machinery, especially the gravure production line, started late and has a weak foundation. According to relevant statistics, China has about 300 cigarette bag gravure printing production lines, almost all of which are imported from industrialized countries such as Europe, the United States, Japan or Australia. Most of them were introduced in the 1990s, generally using the technology of the 1980s and 1990s, and some even the technology of the 1960s and 1970s. The equipment has the following characteristics

(1) the control circuit of the equipment generally adopts programmable logic controller (PLC) or computer control, in this regard. It is still relatively advanced

(2) the transmission device generally adopts DC speed regulating motor, and some equipment in the 1960s and 1970s still adopts slip speed regulating motor. The main drive drives a mechanical shaft through a DC speed regulating host (or an AC speed regulating host), and then connects various color group units and die cutting units through this mechanical shaft to rotate synchronously. This mechanical through shaft structure is still the transmission form commonly used in web gravure printing machines until now

(3) generally, the registration device adopts stepping motor with reducer mechanism (including differential, stepless transmission, etc.)

(4) generally, the tension control device also adopts the stepping motor with reducer mechanism

in recent years, electronic technology and microelectronic technology have developed at an amazing speed, which has also led to the progress of AC drive technology. The development of modern AC drive technology has experienced more than 20 years. At present, it is becoming the mainstream of electrical drive. Many leaders who have been occupied by DC drive have been occupied by AC drive through our services to enhance customers' favor for Jinan Shijin itself

3 disadvantages of mechanical through shaft structure

the six color gravure printing machine for cigarette packets on web paper can print 16 colors on web paper. Web intaglio printing is widely used because of its fast speed, rich layers and good texture. However, it requires high precision in mechanical manufacturing, especially because the paper is easy to deform and stretch due to the influence of temperature and humidity. Even though the overprint adjusting mechanism is manufactured very finely and the actions of all parts are very coordinated and accurate, if the degree of automation is not high, it is still difficult to avoid inaccurate overprint and cannot guarantee the product quality. Most of the web gravure printing equipment in China generally adopts the mechanical through shaft structure, which requires manual overprint pre positioning. The operation is complex, the positioning error is large, and the dynamic adjustment is slow. Inaccurate pre positioning leads to the fact that the equipment needs a long running time with paper, resulting in a lot of waste products

4 advantages of AC servo drive

in order to solve the above problems, some advanced printing machine manufacturing enterprises in Europe and the United States have developed electronic shaftless web gravure printing machines by using the existing AC servo drive technology. With the traditional shaft {mechanical shaft) compared with the gravure printing machine, the electronic shaftless web gravure printing machine cancels the mechanical shaft structure between the printing units. Each printing unit is independently driven by AC vector variable-frequency motor. The motor directly drives the plate cylinder, and adjusts the phase of the plate cylinder to achieve longitudinal registration. At the same time, a stepping motor drives the horizontal movement of the plate cylinder to achieve horizontal registration. This design brings the following advantages Advantages.

(1) many mechanical transmission links are omitted, which minimizes the possibility of reducing overprint accuracy due to mechanical wear, increases reliability, and reduces maintenance costs

(2) the registration time is very short and the response speed is very fast

(3) it provides a unique high-precision pre alignment function. When the plate cylinder is loaded into the printing unit, the sensor detects the zero mark on the plate cylinder, and the drive motor will automatically rotate the plate cylinder to the preset zero position. The pre registration operation can be realized by idling the equipment through the motor, and there is no need to run with paper, so there are few waste products in the pre registration process. In addition, because the shaftless transmission system has high control accuracy of the cylinder phase of the printing

plate, the information exchange is fast, and high-precision high-speed registration can be realized, so the registration accuracy can still be much higher than that of the mechanical shaft gravure press in the state of high-speed printing

5 transformation plan

our company is a cigarette bag printing plant invested and built by Hongta Group, and has an nl650 six color intaglio line die-cutting printing production line imported from France's Komori champang company. The technology used in this printing machine basically reflects the technical level at that time. The control circuit adopts Siemens PLC, and the overprint circuit adopts champang's rnp93 system. The main drive uses a DC speed regulating motor to transmit power to each printing color deck and die cutting station through a mechanical shaft, and the overprint (position follow-up and compensation) of each unit adopts the structure of stepping motor and differential, so the shortcomings of the above mechanical through shaft gravure printing machine cannot be avoided. In addition, there are the following deficiencies.

(1) the main motor adopts DC speed regulating motor, and the maintenance cost of carbon brush and commutator is high

(2) gear boxes and stepless transmissions are not only easily worn parts with perfect protective effects, with high maintenance costs, but also inevitably have mechanical clearances. When the adjustment made by the stepper motor according to the overprint instruction reaches the printing plate through these mechanisms, there will be losses and, in serious cases, oscillation

(3) the above equipment has been used for nearly 10 years, and many parts manufacturers no longer produce it, which brings great difficulties to maintenance

these problems have affected the long-term development of the company. This paper wants to explore the possibility of using AC servo system to transform this printing machine

compared with stepping motor, AC servo motor has the following obvious excellent performance

(1) the control accuracy is greatly improved

(2) low frequency characteristics are enhanced

(3) good torque frequency characteristics

(4) speed response performance, control performance (closed-loop control) and overload capacity are greatly improved

5.1 overall transformation scheme

(1) remove all main drive and step servo drive components such as DC speed regulating host and mechanical through shaft, differential gearbox, stepping motor, etc., and replace the above components with 7 groups of independent AC servo motor units to realize the transmission and position compensation functions. The seven groups of units mentioned here are six color groups plus a set of die-cutting units. If two groups of tension units are included, it should be nine groups. Therefore, the number of shafts will vary according to different model transformation schemes

(2) seven groups of AC servo motor units are directly connected to the plate shaft or die cutting shaft through high-precision maintenance free reducer (speed ratio is 5:1 or 10:1), which minimizes the mechanical transmission link between the motor and the plate shaft, and realizes 7-axis independent servo drive

5.2 specific transformation scheme

it can be seen from Figure 1 that the transmission and overprint structure before the transformation of the equipment is a 35kw DC speed regulating motor, which connects six printing units through a long shaft. The reconstruction plan is to dismantle the structure of the dotted line in Figure 1 and transform it into the structure shown in Figure 2

the printing plate motor drive unit is proposed to adopt ecodrive intelligent AC servo driver and supporting MHD High-Performance AC servo motor of Rexroth. Among them, the servo driver is equipped with current loop, speed loop and position loop (the position loop is not used in this transformation), and the motor shaft speed and position detection element is the 2500 rotary encoder (4 times the frequency) of the servo motor. The second encoder interface on the

servo driver is used to realize multi axis speed tracking and synchronization. The synchronization structure is shown in the dotted line in Figure 2

in fact, the synchronous control of the printing machine includes two aspects, one is the synchronization of the rotation speed of each printing plate shaft, the other is the synchronous control of printing overprint, that is, the actual position of the printing code marking line is detected by the photoelectric scanner, compared with the theoretical position, and the output pulse signal (forward or reverse) is sent to the actuator (stepper motor before transformation) for position adjustment, which constitutes the outer ring of synchronous control

using servo controller to control the printing plate motor in speed mode can only obtain good dynamic characteristics. However, in the printing process, due to the more or less differences in the characteristics of each motor servo driver, there must be cumulative errors in the long-term operation process, and the above outer ring control is to solve this problem that has been controversial in the market for a long time

the internal speed ring is responsible for the synchronization of the speeds of each axis, which requires good dynamic performance. The errors caused by various disturbances to the internal speed ring can be compensated by the outer ring control. The external position environmental protection proves the stability and overprint accuracy, as shown in Figure 3

the transformation scheme retains the signal detection, processing and transmission links of overprint control in the original system, and only changes the stepping motor as the actuator into an AC servo motor. Therefore, how to convert the pulse signal previously sent to the stepping motor into the signal controlling the AC servo motor is a major problem to be studied. The current assumption is to solve this problem by debugging the operating parameters (actually PID parameters) of the original overprint system and the PLD parameters on the AC servo controller

5.3 overprint principle

in multicolor printing, the rotation angle of the printing plate cylinder is generally changed to adjust the printing position. The closed-loop control principle is shown in Figure 4

according to the principle of rotary encoder, the more the number of lines, that is, the more the number of pulses generated by the printing plate per revolution, the higher the position accuracy. Assuming that the perimeter of the printing plate is 500mm and the number of lines of the encoder is 500, then 500mm corresponds to 500 pulses, 1mm corresponds to 1 pulse, 20mm corresponds to 20 pulses.

the detection of the actual printing position is to convert the detected color code signal into electrical pulses through the photoelectric scanner, and these electrical pulses are sent to the overprint system computer at the same time with the pulse train generated by the rotary encoder. The given value of the distance between the color codes of each color group is 20mm, that is, when the two colors are set, the distance between the two color codes is 20mm, which corresponds to 20 pulses of the encoder. As shown in Figure 5, 18 pulses are counted in the trigger time period of color code 1 and color code 2. If color code 1 is taken as the benchmark, it indicates that the printing plate shaft speed of color code 2 is too fast. In order to slow down its speed and correct the position deviation, the servo motor should be reversed at an angle equivalent to 2 pulses; Assuming that the number of pulses in the trigger time period of color code 2 and color code 3 is 23, taking color code 2 as the benchmark, it indicates that the printing plate shaft speed of color code 3 is too slow. In order to speed up its speed and correct the position deviation, the servo motor should be rotated forward at an angle equivalent to 3 pulses to eliminate the deviation