Configuration and application of tension control s

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The configuration and application of gravure press tension control system

gravure printing is one of the most common graphic printing methods. It not only has fast printing speed and high printing resistance of the cylinder, but also is especially suitable for mass printing. Moreover, the printing ink is thick, rich in layers and strong in three-dimensional sense, which can obtain the changes of graphic information with light and bright colors. Its product categories are very wide: books, newspapers, magazines and other publications printed on paper, as well as banknotes, certificates, stamps and so on; Paper containers and packing boxes printed with thick cardboard; Flexible packaging bags for food and medicine printed with plastic film, wall stickers, etc. Therefore, it has always occupied a very important position in the field of graphic publishing and packaging printing

at present, computer technology, optical fiber sensing and other modern science and technology have been widely used in gravure printing machines, making the intelligent automatic control of gravure printing machines more perfect, and the printing speed and accuracy are getting higher and higher. The printing speed of simple gravure printing machines is generally 20 ~ 50m/min, and the registration accuracy is ± 0.4 ~ 0.5mm. The printing speed of medium and high-end computer chromatic gravure printing machines has reached 250 ~ 300m/min, and the registration accuracy is ± 0.1mm. With the advent of the era of knowledge economy, the rapid development and industrialization of new technologies will bring revolutionary changes to China's printing industry and equipment industry. 1、 The importance and function of tension control

the tension control of gravure press can be said to be the core of the whole machine. As long as the tension control is stable and the tension change is small, the registration accuracy and scrap rate of the gravure press can be easily controlled. The fluctuation and change of tension have a great impact on the registration accuracy, especially the higher the printing speed of the equipment, the more important the tension control is. Therefore, in order to ensure the quality, efficiency and reliability of the gravure press, a tension control system with perfect functions must be equipped

the factors that make the tension of gravure press fluctuate and change in the printing process are relatively complex. If it is not effectively controlled in time and accurately, the comprehensive influence of various factors will form an irregular change mode of the tension of all parts of the whole machine. Now, the main influencing factors are briefly analyzed as follows:

1. In the process of winding and unwinding, the diameter of winding and unwinding is constantly changing, and the change of diameter will inevitably cause the change of belt tension. When the braking torque of unwinding is unchanged, the diameter decreases and the tension increases; On the contrary, if the winding torque remains unchanged, the tension will decrease as the diameter increases. And the heavier the roll is, the faster the speed changes, and the greater the change of belt tension. This is determined by the inherent characteristics of gravure press. It is also one of the main factors causing the change of belt tension

2. The manufacturing accuracy and assembly accuracy of the main components of the gravure press are out of tolerance, which is often an important factor causing tension fluctuations. Such as the flatness and straightness of the base assembly, the perpendicularity of the wallboard and the base, the levelness of each plate roll and their parallelism, etc. Each plate roller and many guide rollers are strictly required to be parallel to each other, and their circular runout deviation and mass dynamic and static balance deviation during their rotation should also be within the specified range. Otherwise, every time they rotate, the tension on the belt will change slightly, which will eventually be comprehensively reflected on the whole machine, resulting in irregular changes in tension. In addition, the main transmission system of gravure printing machine should be free of gap and precise transmission to ensure that all printing units operate synchronously. If the transmission synchronization error is caused in the printing process, the tension of each unit is bound to change. Therefore, it can be said that in the final analysis, the accuracy standard of the machine itself is the basic guarantee for the effective control of tension. The accuracy grade is high, the quality is excellent, and the tension control is easy to be stable; On the contrary, the accuracy level is too poor and the products are shoddy. Even if equipped with the most advanced tension control system, I am afraid it will backfire, and it is difficult to obtain a satisfactory tension stabilization effect

3. During the automatic cutting process without stopping the gravure machine, material receiving and breaking will cause sudden interference changes to the original stable tension of the whole machine. The higher the running speed of the machine, the greater the disturbance. The tension control system configured for the equipment shall be able to adjust automatically and randomly according to the tension disturbance of the material belt quickly, so that the tension can be restored to the original stable state in time

4. The non-uniformity of the internal material of the belt (such as the fluctuation of the elastic modulus, the change of the thickness along the length and width, the eccentricity of the coil quality, etc.) and the change of the temperature and humidity of the production environment will have a subtle impact on the tension fluctuation of the whole machine

Second, the classification principle of tension control system

in recent years, the domestic full-automatic computer chromatic gravure printing machine has developed very rapidly, and the high-precision and repeatable tension control technology has been widely used. Although the tension control systems equipped with gravure printing machines have their own advantages and various types, to sum up,

III. tension controllers and tension detection devices

at present, the tension controllers available in the domestic market are basically divided into three categories: dynamic control, semi-automatic Brazilian new plastic materials can complete degradation control and full-automatic control within 30 days. Manual tension controller is a relatively simple tension controller, which is often used in low-speed gravure printing machines. According to the change of unwinding or rewinding diameter, the operator adjusts the exciting current of the brake or clutch in stages to obtain consistent tension. Semi automatic tension controller is also called open-loop tension controller. It depends on the signal sent by the door signal generator installed on the winding or unwinding shaft to calculate the diameter of the discharge coil and the change of the corresponding coil diameter, and output the control signal, so as to adjust the tension of the material belt. The full-automatic tension controller directly measures the actual tension value of the material belt by the tension sensor (i.e. tension detector), and then converts the tension data into a tension signal and sends it back to the tension controller. This signal is compared with the preset tension value of the controller, and the control signal is calculated. From this, the exciting current of the clutch or brake is automatically adjusted to control the tension on the material belt, so that the actual tension value is equal to the preset tension value. It has the characteristics of high precision and high repeatability. It is a more advanced tension controller. Therefore, domestic computer chromatic gravure printing machines with more than 6 colors mostly choose this tension controller. For example, the le-40mta (b) full-automatic tension controller of Mitsubishi Electric Co., Ltd. of Japan, the x-3000 and s-3000 full-automatic tension controllers of Montalvo company of the United States, as well as the mcs-2000ctda full-automatic tension control of Europe and Switzerland, which deal with voltage sags and instantaneous power outages and improve the power quality of users

there are basically three kinds of tension detection devices: one is to use tension sensors (i.e. tension detectors) to detect the tension. Usually, two tension sensors are used in pairs, and they are installed at both ends of the detection roll (as shown in Figure 1a). The material belt applies load through the detection roll, causing the sensitive element of the tension sensor to displace or deform, so as to detect the actual tension value, and send the actual tension signal to the full-automatic tension controller, Finally, the tension closed-loop control is realized. At present, tension sensors include leaf spring micro displacement tension detector (Mitsubishi lx-td type in Japan), strain gauge tension detector (Montfort T Series in the United States) and piezomagnetic tension detector (abb pillow series in China), etc. Its advantages are wide detection range, fast response speed and good linearity

second, the floating roller tension detection device (as shown in Figure 1b) is used. When the tension is stable, the tension on the belt and the force of the cylinder are balanced, so that the floating roller is in the central position. When the tension changes, the balance between the tension and the force of the cylinder is destroyed, and the position of the floating roller will rise or fall. At this time, the swing rod will rotate around point m and drive the floating roller potentiometer to rotate together. In this way, the floating roller potentiometer accurately detects the change of the floating roller position. It feeds back the position signal to the tension controller. The controller calculates and outputs the control signal to control the magnetic particle brake or clutch to adjust the floating roller position so that it is always in the central position

Figure 1 Schematic diagram of tension detection mode

the characteristics of floating roller control are: it has a good inertia compensation function, which can absorb or buffer the impact of tension jump on the system, and also reduce the tension instability caused by the circular jump deviation of guide roller, speed change or other factors affecting the stable output of tension

third, the floating roll/feedback composite tension detection device is adopted, which can detect the floating roll position signal output by the floating roll potentiometer and the tension signal output by the tension detector at the same time, so as to provide the system with higher precision tension control. Its characteristic is that it not only has the function of absorbing or buffering large-scale tension jump by floating roller control, but also has the characteristics of high precision and high repeatability of tension detector closed-loop control. For example, the x/d-3000 floating roller/feedback composite tension control device of American monteford company belongs to this type

IV. configuration types of tension control system we expect more and more new products, new materials and new technologies to break through the encirclement

there are roughly three configuration types of tension control system of gravure press

the first is a two-stage closed-loop tension control system, which is composed of two parts: the tension control of the unwinding part and the tension control of the winding part (as shown in Figure 2). Its basic components mainly include full-automatic tension controller, tension detector, magnetic particle brake, magnetic particle clutch and AC motor. At the unwinding section, the tension controller and tension detector are installed on the feeding stand. Since the tension of the material belt entering the printing device is generated by the printing plate roller, a brake is set on the unwinding and loading shaft. Once the tension changes, the tension detector will send the tension signal to the controller, so as to automatically adjust the exciting current of the brake to control the tension of the material belt. In this way, the tension of the feeding belt is constant and the size is appropriate. In the winding part, the magnetic powder clutch and AC motor are installed on the winding and loading shaft, and the full-automatic tension controller and tension detector are set on the discharge stand. If the tension of the AC motor fluctuates in the coiling process, the tension detector turns the detected tension data into a tension signal and sends it back to the controller to control the exciting current of the magnetic particle clutch and change the slip torque of the clutch to keep the tension on the discharge belt stable. This type of form is often called unwinding or winding primary tension control, which can be said to be a basic type of gravure machine tension control. It can no longer meet the high-precision and repeatable tension control requirements of medium and high-end computer chromatic gravure printing machines with more than 7 colors

the second is the three-stage closed-loop tension control system, which is based on the above basic type. After the unwinding tension control, add a level of feeding tension control, or configure another level of discharging tension control before the winding tension control. However, the newly added tension control of this section must be equipped with active traction roller and magnetic powder clutch. In other words, in China, the so-called three-stage closed-loop tension control is essentially a secondary tension control for unwinding and a primary tension control for rewinding. On the contrary, unwinding is the primary tension control, and rewinding is the secondary tension control. This configuration further improves the tension control accuracy and reliability of the equipment, and can effectively weaken the adverse effects of other accidental factors on tension


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