Types and application of tension control in the pr

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Improve product quality during gravure printing; However, the type and application of cooling tension control at the hopper

in recent years, with the rapid development of intelligent and automatic chromatic control technology of gravure printing machine, some high-end computer chromatic gravure printing machines in China have adopted microcomputer control system. In addition, a new high-precision and repeatable tension control technology has also made a major breakthrough. This advanced tension control system adopts PLC programmable controller to control the whole machine, touch-screen computer human-machine interface operation, high degree of automation, simple operation, all-round parameter setting, and has the advantages of operability, high stability and durability. Therefore, due to the synchronous development of the two, modern gravure printing machines have greatly improved the quality of printed matter

I. several factors affecting the tension control of gravure press

the tension control system of gravure press is essentially a special servo system whose input changes according to an adjustable attenuation law. Tension control can be said to be the core of the whole machine control. As long as the tension control is stable and the tension change is small, the chromatic accuracy and scrap rate of the gravure press can be easily controlled

therefore, in order to ensure the quality and efficiency of gravure printing, a fully functional tension control system must be equipped. However, in the printing process, the factors that make the tension of gravure press fluctuate and change are often complex, and the main influencing factors are roughly as follows:

1 In the process of winding and unwinding of gravure machine, the diameter of winding and unwinding is constantly changing, and the change of diameter must 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 winding diameter increases. This is determined by the inherent characteristics of gravure press, and it is also one of the main factors causing the change of belt tension

2. There is a deviation between the manufacturing accuracy and assembly accuracy of the main components of the gravure press, such as the base, wallboard, guide roller, etc. For example, the flatness and straightness of the base assembly, the perpendicularity of the wallboard and the base assembly, the levelness of the assembly of each plate roll and guide roll and their parallelism, their respective runout deviation, mass dynamic and static balance deviation, etc. are all strictly required. Otherwise, when the material belt runs on the plate roller and many guide rollers, the tension on the material belt will change slightly. It will eventually be reflected on the whole machine, resulting in irregular changes in tension. In addition, the gears and reduction boxes in the main drive system of the gravure press should be accurately driven without clearance to ensure that the plate rollers of each printing unit operate synchronously. If the transmission synchronization error is caused in the printing process, the tension of each printing unit is bound to change

3. The non-uniformity of the internal material of the material belt. For example, the fluctuation of the elastic modulus of materials, the change of the thickness of materials along the width and length, the eccentricity of the mass of the coil, 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

4. In the process of automatic material receiving and changing without stopping of gravure press, material receiving and material breaking will suddenly cause interference changes to the original stable tension of the whole machine. The higher the running speed of the equipment, the greater the interference. At this time, the tension control system should be able to quickly adjust automatically and randomly according to the interference of the belt tension, so that the tension can be restored to the original stable state in time

II. Type, detection method and application of gravure machine tension control

1 The main types and characteristics of tension control

tension control refers to the ability to permanently control the tension of the material belt when it is transported on the equipment. This control must be effective for any running speed of the machine, including acceleration, deceleration and uniform speed of the machine. Even in the case of emergency shutdown, it has the ability to ensure that the belt will not be damaged at all. Gravure machine tension control is basically divided into three categories: dynamic tension control, open-loop semi-automatic tension control and closed-loop full-automatic tension control. Manual tension control means that in the process of winding or unwinding, when the coil diameter changes to a certain stage, the operator adjusts the manual power supply device to control the tension. However, the manual tension control system of modern gravure press has been basically eliminated, and only exists as an operation mode in the closed-loop full-automatic tension control system. Open loop semi-automatic tension control, also known as coil diameter detection tension control, uses the proximity switch installed at the reel to detect the rotation speed of the reel, and through the set initial value of the reel diameter and material thickness, calculates the current diameter of the winding or unwinding drum accumulatively, and outputs control signals corresponding to the change of the coil diameter, so as to control the winding torque or unwinding braking torque, so as to adjust the tension of the material belt. Because every turn of the reel, the coil diameter will change twice as much as the thickness of the strip. This kind of tension control is not affected by external stimulation, and can implement stable tension control. However, the absolute accuracy of this tension control is poor due to the influence of factors such as the torque change of the transmission device, which makes the concept of after-sales service popular, linear change and mechanical loss. The closed-loop full-automatic tension control is to directly measure the actual tension value of the material belt by the tension sensor, and then convert the tension data into a tension signal and feed it back to the tension controller. By comparing this signal with the preset tension value of the controller, the control signal is calculated, and the automatic control execution unit makes the actual tension value equal to the preset tension value, so as to achieve the purpose of tension stability. It is an advanced tension control method at present. In addition, in the tension control system of medium and high-end printing machines manufactured and sold in China, the higher printing speed and production process put forward higher requirements for tension control, so that the magnetic particle clutch is no longer competent for the executive unit of this kind of system. Therefore, in modern gravure press, high-speed slitting machine and high-speed coating compound machine, it has been replaced by AC and DC servo motor execution units to realize more advanced tension servo control

if your machine needs very accurate tension control, you must adopt closed-loop full-automatic tension control. One of the most important links is how to reasonably select the tension detection method. At present, there are basically three kinds of tension detection methods:

① tension sensor (load cell) detection method: it directly detects tension, which is closely combined with machinery, and there is no detection method of moving parts. Usually, the two sensors are used in pairs, and they are installed on the end shafts on both sides of the detection guide roller (as shown in Figure 1 (see magazine for details)). By detecting the load applied by the guide roller, the material belt causes the displacement or deformation of the sensitive element of the tension sensor, so as to detect the actual tension value, and convert this tension data into a tension signal to feed back to the tension controller. Finally, the tension closed-loop control is realized. There are many types of elastic sensors in the market, such as leaf spring micro displacement tension sensors (such as Mitsubishi lx-td type in Japan), strain gauge tension sensors (such as Montfort T Series in the United States) and piezomagnetic tension sensors (such as abb pillow series in China), etc. Its advantages are wide detection range, fast response speed and good linearity. The disadvantages are that it cannot absorb the peak value of tension, the acceleration and deceleration of machinery are difficult to deal with, and it is not easy to realize high-speed roll switching, etc. Therefore, when the tension control system in the balanced state is strongly disturbed, the system will have no time to respond instantly, and the amplitude of tension change on the belt will be large, which is unfavorable for the tension control to enter the balanced state as soon as possible

② dancer arm tension detection method: (as shown in Figure 2 (see the magazine for details)) it is an indirect tension detection method, which is essentially a position control. When the tension is stable, the tension on the belt and the force of the cylinder maintain balance, so that the float 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, and it will feed back the position signal to the tension controller. The controller calculates and outputs the control signal to control the servo drive system to correct the deviation. Then the floating roller returns to the original balance position. As the floating roller tension detection device itself is an energy storage structure, it has a good absorption and buffer effect on a wide range of tension jump by using its own residual effect, and can also weaken the influence of the eccentricity (ellipse) of the coil and the speed change on the tension. This system requires that the cylinder friction coefficient is small, the response speed is fast, and the air source is stable. The weight of floating roller and swing rod should be light and the rotation should be flexible

③ floating roller/feedback composite tension detection method: it can detect the floating roller position signal output by the floating roller potentiometer and the tension signal output by the tension sensor at the same time, so as to provide the system with higher precision tension control. Its characteristics are: it not only has the function of absorbing or buffering the large-scale tension jump by the floating roller control, but also has a good buffering and stabilizing effect on the acceleration and deceleration of the machine, and it is easy to realize high-speed roll switching. It has the characteristics of high precision and high repeatability of tension sensor closed-loop control. For example, the x/d3000 floating roller/feedback composite tension control device of American Montalvo company belongs to this type

2. Typical application of tension control

① touch screen tension numerical control system touch screen tension numerical control device is a full closed-loop automatic tension control system with four section unified control mode. The machine is controlled by the PLC programmable controller. The human-machine interface adopts the HITECH touch screen to set and display the operating parameters. The unwinding, feeding traction, discharging traction and rewinding adopt the main control cabinet to coordinate the centralized control and operation. Four section tension refers to four parts of tension, including unwinding tension, feeding traction tension, discharging traction tension and winding tension. All four sections of tension are automatically controlled by AC vector variable frequency motor. The operation panel of the receiving unit is equipped with a hitech touch screen, which can set parameters such as speed, tension and winding diameter, and can also display parameters such as speed and tension in real time. The system has high control accuracy, fast response and good stability. The operator can start, accelerate, decelerate or stop the operation at any part of the machine, which is very convenient. In addition to the tension control operation panel, the wall panel for discharging and receiving materials is also equipped with the start, stop and emergency stop switches of the whole machine. Due to the use of AC vector variable frequency motor for material receiving, the speed range of control is wide, and it has good performance at both low speed and high speed. It can realize taper tension control, and the winding effect is excellent. In addition, it also includes high-speed non-stop full-automatic material receiving and cutting, pre drive of winding and unwinding, automatic safety alarm, automatic length counting and display control functions, etc. The maximum control tension is 20kg, and the printing speed of the host is 0 ~ 200m/min

② floating roller tension servo control system floating roller tension servo numerical control device system adopts four section closed-loop full-automatic tension servo control system. Four section tension refers to four parts: unwinding tension, feeding traction tension, discharging traction tension and winding tension. The four section tension control is automatically controlled by the tension controller set in each section, which forms a closed loop through the feedback of its floating roller displacement detection device. The difference is that the unwinding and rewinding units adopt AC vector variable-frequency motor, while the feeding traction and discharging traction are single

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