The gravure tension control system analysis generally includes the following content.
1. Tension zoning and control requirements for each area
Gravure press tension control is generally divided into four areas, namely the unwinding tension zone, the feed pull tension zone, the discharge tension zone and the winding tension zone, separated by a belt-driven rubber roller. From the feed drive roller to the discharge drive roller in the printing area, the tension in the printing area is a constant tension because the registration can only be guaranteed under constant tension conditions. The unwinding tension is to serve the constant tension of the printing area. The requirement for the unwinding area is to release the material roll into the printing area to ensure that the tension of the transmission can be maintained regardless of the size of the roll diameter, otherwise the tension fluctuation will be directly Affects the constant tension in the printed area, which in turn affects the registration. The winding tension is different. In this area, multi-color printing has already been completed, and you only need to roll it smoothly. According to different winding quality requirements, the winding method has constant tension winding and variable tension winding. Common decreasing tension winding (also known as taper winding) refers to the latter. Since the variable tension winding may affect the registration accuracy of the last printing color group, the printing area and the winding area are effectively cut off, and the driving of the printing material from the printing area to the winding area advances the printing area. Constant tension, and decrement of tension in the winding area, is achieved by a rubber roller mechanism with a belt drive. Both the subsection control and the overall coordination, so that the tension in each area for the multi-color registration services, which is the key point of rotation printing in the tension control, so is the rotogravure.
2. Tension detection and feedback in each area
There are generally independent detection devices in each area, such as tension roller detection devices made up of resistance strain gauge sensors and capacitance sensors, and position detection control devices made up of floating rollers and potentiometers. These different configuration of the detection circuit in the entire system to assume the role is significantly different, the tension roller detection device response is fast, but the quality of the control of the system stability caused by the quality of the material itself is still lacking, and the position control device is not The tension is detected directly, but by controlling the relative position of the substrate under normal tension conditions in the floating roller path, it is stable, so that the purpose of controlling the tension is constant. The position control device is capable of slowing the tension fluctuation due to raw material quality problems such as non-circularity of the reel through a floating roller path, which cannot be achieved by the tension roller detection device.
3. Tension actuator
Commonly used tension actuators include electromagnetic or magnetic clutch/brake, pneumatic clutch/brake and servo motor
The conventional gear transmission system also includes a miniature actuator motor on a 360° gearbox. It is worth noting that according to the automatic control theory, the clutch brake mechanism belongs to the first-order linear link, but because the linear section only occupies the middle section in the entire curve area, the high-end and low-end sections of the curve area are mainly imitation linear, with the same linear control. The requirements are also distance, so this implementation is still flawed. Servo motor belongs to the second-order link. Under the existing control theory, both stability and followability can be taken into account. Therefore, advanced tension control systems generally use servo motor direct drive control.
4. Compensation for loss of mechanical synchronous speed during transfer of material
There are three reasons for the loss of mechanical synchronous speed: the printing pressure applied to the width of the entire web, the surface friction of the printing material in contact with the guide roller, and the resistance due to the inflexible guide roller bearing.
Among them, the main effect is the pressure applied to the printing material by the rubber roller of each color group. The pressure that must be applied during this printing process is the largest in all printing processes. According to experience, the hardness of the rubber roller used for different substrates is different, and the applied pressure is also different. For thin film printing materials, rubber rollers with a Shore hardness of 65 to 70 degrees are generally used with a unit pressure of 900 kg/m. For paper printing materials, rubber rollers with a Shore hardness of 70 to 80 degrees are used. Pressure 1800kg/m; For paperboard printing materials, rubber rollers with a Shore hardness of 80 to 90 degrees are used with a unit pressure of 4500kg/m. The use of different hardness of the rubber roller and the application of different pressure, the impact of the synchronization speed on the transfer of the printing material is obviously different, the softer the rubber roller, the greater the pressure, the greater the loss of mechanical synchronization speed.
The traditional way to compensate for the loss of mechanically synchronized speed is to increase the diameter of the active roller (ie, the platen roller) for each color group. As we all know, the line speed V = 2Ï€rn, if you want to adjust the linear speed of the printing roller, you can adjust the roller speed n (that is, the current method for increasing the motor rotation speed of each color used in the servo-type gravure printing machine), also The diameter of the printing roller can be adjusted (ie, the traditional method of increasing the diameter of the printing roller for more than 20 years). However, this compensation is based on accumulated experience rather than accurate calculations. Obviously, the characteristics of printing materials are different, the width of the applied pressure is different, and the loss of the mechanical synchronization speed is different, so the exact compensation value should also be different. However, it is now possible to use the "blurring" algorithm based on the method of increasing the roll diameter by 0.02 to 0.03 mm (even increments of 0.04 mm).
In the development of servo-type gravure printers in the domestic printing industry, it was initially thought that the rule of increasing the roll diameter could be eliminated, because when setting the rotation speed of the servo motor for each color combination, the diameter of the roll can be increased in advance. The amount of amplification is calculated in, so the servo-type gravure printer does not have to interchange printing color sequences like a traditional gravure printer. However, printing practice has proved that even servo-type gravure printers have increased the rotational speed of the roller motors of each color assembly. If the printing roller continues to maintain the diameter increase, the printing register effect is much better than the diameter of the printing roller. This shows that the current gravure servo system can only be limited to the range of experience in compensating the loss of synchronous speed, and there is still a lot of distance from the real sense of compensation control.
5. Register control
Gravure registration control must be based on stable tension control. Only after the above four problems are solved, can accurate registration of gravure be possible. The industry has misunderstood the issue of registering, especially for servo-type gravure printers. It is believed that the accuracy of the encoder can reach several million times per second, and registration is certainly not a problem. In fact, in the actual process of registering, the computer is not tracking the cursor itself but the trend of cursor movement. It is like hitting a bird with a gun. Instead of seeing the bird before pulling the trigger, it is based on the trajectory of the bird to calculate the lead-in amount. It is reliable to use this method to beat the bird. Gravure printing machine registration system is also the case, the trend of cursor movement is the premise of the registration, if you can not control the trend of cursor movement on printing materials, even if the servo motor configuration is 4 million times per second For encoders, the registration error is also likely to be exceeded, and the register loss may be unexpectedly large.
6. Compensation for deformation of printing materials
The synchronous speed compensation of printing materials in operation can be guaranteed by using servo models, but there is no reliable compensation method for the deformation of the printing materials themselves. Taking thin film printing as an example, different kinds of films have different stretching and deformation conditions under the same thickness and width conditions; for the same film with different thicknesses, such as 20 μm and 40 μm thick BOPP films. Under the same drying conditions, the stretching deformation of the two is not the same. Taking paper as an example, the paper with the same material and thickness as water content of 5% and water content of 8% has different deformation data under the same drying conditions. For these differences, mathematical models need to be established and loaded in the mathematical model of register control in order to effectively control the accuracy of the printing register. If this is not the case, the registration accuracy of gravure printing can only be relied on using thicker, less easily deformable substrates such as PET film. At the gravure production site, we often hear front-line operators complaining about poor printing plates or poor printing materials, causing misregistration or registration errors during the printing process, and resulting in cost loss, but checking the plates and Printing materials do not provide any reason why they can get the desktop. According to the author, the main reason is this.
1. Tension zoning and control requirements for each area
Gravure press tension control is generally divided into four areas, namely the unwinding tension zone, the feed pull tension zone, the discharge tension zone and the winding tension zone, separated by a belt-driven rubber roller. From the feed drive roller to the discharge drive roller in the printing area, the tension in the printing area is a constant tension because the registration can only be guaranteed under constant tension conditions. The unwinding tension is to serve the constant tension of the printing area. The requirement for the unwinding area is to release the material roll into the printing area to ensure that the tension of the transmission can be maintained regardless of the size of the roll diameter, otherwise the tension fluctuation will be directly Affects the constant tension in the printed area, which in turn affects the registration. The winding tension is different. In this area, multi-color printing has already been completed, and you only need to roll it smoothly. According to different winding quality requirements, the winding method has constant tension winding and variable tension winding. Common decreasing tension winding (also known as taper winding) refers to the latter. Since the variable tension winding may affect the registration accuracy of the last printing color group, the printing area and the winding area are effectively cut off, and the driving of the printing material from the printing area to the winding area advances the printing area. Constant tension, and decrement of tension in the winding area, is achieved by a rubber roller mechanism with a belt drive. Both the subsection control and the overall coordination, so that the tension in each area for the multi-color registration services, which is the key point of rotation printing in the tension control, so is the rotogravure.
2. Tension detection and feedback in each area
There are generally independent detection devices in each area, such as tension roller detection devices made up of resistance strain gauge sensors and capacitance sensors, and position detection control devices made up of floating rollers and potentiometers. These different configuration of the detection circuit in the entire system to assume the role is significantly different, the tension roller detection device response is fast, but the quality of the control of the system stability caused by the quality of the material itself is still lacking, and the position control device is not The tension is detected directly, but by controlling the relative position of the substrate under normal tension conditions in the floating roller path, it is stable, so that the purpose of controlling the tension is constant. The position control device is capable of slowing the tension fluctuation due to raw material quality problems such as non-circularity of the reel through a floating roller path, which cannot be achieved by the tension roller detection device.
3. Tension actuator
Commonly used tension actuators include electromagnetic or magnetic clutch/brake, pneumatic clutch/brake and servo motor
The conventional gear transmission system also includes a miniature actuator motor on a 360° gearbox. It is worth noting that according to the automatic control theory, the clutch brake mechanism belongs to the first-order linear link, but because the linear section only occupies the middle section in the entire curve area, the high-end and low-end sections of the curve area are mainly imitation linear, with the same linear control. The requirements are also distance, so this implementation is still flawed. Servo motor belongs to the second-order link. Under the existing control theory, both stability and followability can be taken into account. Therefore, advanced tension control systems generally use servo motor direct drive control.
4. Compensation for loss of mechanical synchronous speed during transfer of material
There are three reasons for the loss of mechanical synchronous speed: the printing pressure applied to the width of the entire web, the surface friction of the printing material in contact with the guide roller, and the resistance due to the inflexible guide roller bearing.
Among them, the main effect is the pressure applied to the printing material by the rubber roller of each color group. The pressure that must be applied during this printing process is the largest in all printing processes. According to experience, the hardness of the rubber roller used for different substrates is different, and the applied pressure is also different. For thin film printing materials, rubber rollers with a Shore hardness of 65 to 70 degrees are generally used with a unit pressure of 900 kg/m. For paper printing materials, rubber rollers with a Shore hardness of 70 to 80 degrees are used. Pressure 1800kg/m; For paperboard printing materials, rubber rollers with a Shore hardness of 80 to 90 degrees are used with a unit pressure of 4500kg/m. The use of different hardness of the rubber roller and the application of different pressure, the impact of the synchronization speed on the transfer of the printing material is obviously different, the softer the rubber roller, the greater the pressure, the greater the loss of mechanical synchronization speed.
The traditional way to compensate for the loss of mechanically synchronized speed is to increase the diameter of the active roller (ie, the platen roller) for each color group. As we all know, the line speed V = 2Ï€rn, if you want to adjust the linear speed of the printing roller, you can adjust the roller speed n (that is, the current method for increasing the motor rotation speed of each color used in the servo-type gravure printing machine), also The diameter of the printing roller can be adjusted (ie, the traditional method of increasing the diameter of the printing roller for more than 20 years). However, this compensation is based on accumulated experience rather than accurate calculations. Obviously, the characteristics of printing materials are different, the width of the applied pressure is different, and the loss of the mechanical synchronization speed is different, so the exact compensation value should also be different. However, it is now possible to use the "blurring" algorithm based on the method of increasing the roll diameter by 0.02 to 0.03 mm (even increments of 0.04 mm).
In the development of servo-type gravure printers in the domestic printing industry, it was initially thought that the rule of increasing the roll diameter could be eliminated, because when setting the rotation speed of the servo motor for each color combination, the diameter of the roll can be increased in advance. The amount of amplification is calculated in, so the servo-type gravure printer does not have to interchange printing color sequences like a traditional gravure printer. However, printing practice has proved that even servo-type gravure printers have increased the rotational speed of the roller motors of each color assembly. If the printing roller continues to maintain the diameter increase, the printing register effect is much better than the diameter of the printing roller. This shows that the current gravure servo system can only be limited to the range of experience in compensating the loss of synchronous speed, and there is still a lot of distance from the real sense of compensation control.
5. Register control
Gravure registration control must be based on stable tension control. Only after the above four problems are solved, can accurate registration of gravure be possible. The industry has misunderstood the issue of registering, especially for servo-type gravure printers. It is believed that the accuracy of the encoder can reach several million times per second, and registration is certainly not a problem. In fact, in the actual process of registering, the computer is not tracking the cursor itself but the trend of cursor movement. It is like hitting a bird with a gun. Instead of seeing the bird before pulling the trigger, it is based on the trajectory of the bird to calculate the lead-in amount. It is reliable to use this method to beat the bird. Gravure printing machine registration system is also the case, the trend of cursor movement is the premise of the registration, if you can not control the trend of cursor movement on printing materials, even if the servo motor configuration is 4 million times per second For encoders, the registration error is also likely to be exceeded, and the register loss may be unexpectedly large.
6. Compensation for deformation of printing materials
The synchronous speed compensation of printing materials in operation can be guaranteed by using servo models, but there is no reliable compensation method for the deformation of the printing materials themselves. Taking thin film printing as an example, different kinds of films have different stretching and deformation conditions under the same thickness and width conditions; for the same film with different thicknesses, such as 20 μm and 40 μm thick BOPP films. Under the same drying conditions, the stretching deformation of the two is not the same. Taking paper as an example, the paper with the same material and thickness as water content of 5% and water content of 8% has different deformation data under the same drying conditions. For these differences, mathematical models need to be established and loaded in the mathematical model of register control in order to effectively control the accuracy of the printing register. If this is not the case, the registration accuracy of gravure printing can only be relied on using thicker, less easily deformable substrates such as PET film. At the gravure production site, we often hear front-line operators complaining about poor printing plates or poor printing materials, causing misregistration or registration errors during the printing process, and resulting in cost loss, but checking the plates and Printing materials do not provide any reason why they can get the desktop. According to the author, the main reason is this.
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