1 Introduction
A gravure printing press is a printing machine that uses a plate with an engraved concave graphic pattern for multi-color printing. The image areas of the printing plate are recessed, while the non-image areas are on the same plane as the outer circle of the printing cylinder.
In gravure printing, the entire printing plate cylinder is inked. A doctor blade removes the ink from the blank areas, leaving only the ink for the image areas. The plate is then fed onto a printing substrate (paper, plastic film, etc.), where an impression cylinder presses against the back of the substrate, transferring the ink directly to the recessed areas. After passing through a high-temperature chamber, the ink solidifies on the substrate. Finally, the substrate is stacked or rewound into the finished product during the winding process.
Gravure printing machines generally have the capability to print multiple colors and patterns. For multi-color printing, several colors of ink and printing rollers are required, and the printing rollers achieve synchronized color registration through mechanical means.
Modern printing demands increasingly higher printing efficiency and quality, thus requiring printing machinery to have precise mechanical design and accurate electrical control.
2. Gravure Printing Machine Drive System
The main transmission system of a gravure printing machine can be divided into an unwinding section, a main motor drive section, and a rewinding section. In order to avoid the influence of eccentricity of the substrate on the tension, a traction mechanism is generally added at the unwinding stage and the rewinding stage, namely unwinding traction and rewinding traction.
Based on the number of motors used in the entire system, the gravure printing machines commonly used in the industry can be divided into: three-motor systems, five-motor systems, and seven-motor systems.
Three-motor system
The three motors are the unwinding traction motor, the main drive motor, and the winding traction motor. The unwinding uses a magnetic powder clutch to control the tension, and the winding uses a torque motor or a magnetic powder clutch, as shown in Figure 1.
Five-motor system
The five motors are the unwinding motor, the unwinding traction motor, the main drive motor, the winding traction motor, and the winding motor, as shown in Figure 2 .
Seven-motor system
Based on the five-motor system, an automatic roll changing function is added to the take-up and unwinding sections. That is, the take-up is divided into take-up A axis and take-up B axis, and the unwinding is divided into unwinding A axis and unwinding B axis, as shown in Figure 3.
3. Tension System of Gravure Printing Machine
The only difference between a five-motor system and a seven-motor system is the automatic roll-changing function. This function, under the condition that the electronic control system ensures constant tension control, can be fully guaranteed by mechanical design and the printing press's computer program logic control. Typically, when debugging a seven-motor system, it is only necessary to successfully debug the five-motor system and then set the frequency converter parameters of the take-up A-axis and B-axis, and the unwind A-axis and B-axis to be the same to achieve the operation of the seven-motor system. Therefore, for ease of understanding, this article uses a five-motor system as an example. Gravure printing presses, based on the distribution of their tension control system, can generally be called a four-segment tension system. The four tension segments are: the tension between unwinding and unwinding traction, the tension between unwinding traction and the main motor, the tension between the main motor and the take-up traction, and the tension between take-up traction and take-up. During the printing process, these four tension segments must be kept constant.
To maintain constant tension across the four sections, the main machine typically sets its operating frequency according to production speed requirements. The unwinding motor, unwinding traction motor, winding traction motor, and winding motor then need to adjust their respective operating frequencies in real time based on the main machine's operating frequency and the actual tension of the material in their respective sections, in order to achieve constant tension.
4. Technical requirements for frequency converters in gravure printing machines
1) High speed accuracy
For gravure printing presses, many materials can only withstand very low surface tension, and even slight fluctuations in tension can cause material breakage. The production of such materials requires very little tensile force, meaning a very low constant tension needs to be maintained. Therefore, for frequency converters, regardless of the frequency control method (PLC frequency control or frequency calculation using built-in tension control function), very high speed control accuracy is required to meet the constant tension control requirements.
2 ) Fast frequency command response
Similarly, in order to meet the requirements of constant tension control, when the PLC controls the frequency, the frequency converter must respond quickly to the frequency command given by the PLC, whether it is a communication command or an analog command. This requires the frequency converter to have strong signal reception and processing capabilities, high accuracy, and fast program execution speed.
3 ) Stable output torque
In some applications where there is no tension sensor, tension control relies entirely on the inverter's control of the output torque. In this case, the stability of the output torque directly determines whether the material tension is stable.
4 ) Wide speed range
Gravure printing machines require both low-speed operation for equipment debugging and high-speed operation to improve production efficiency. Currently, the gravure printing machines used in the industry have increased from below 100m/min in the early days to above 300m/min, which places higher demands on the speed regulation range of frequency converters. They not only need good low-frequency torque characteristics, but also high speed control accuracy.
5 ) It provides precise compensation for friction and fluctuations during acceleration and deceleration of mechanical equipment.
In actual production, the friction and inertia of mechanical equipment, as well as speed fluctuations during acceleration and deceleration, often affect the tension of materials. As a high-performance frequency converter with dedicated tension control function, it is necessary to take these effects into account and make precise compensations to achieve constant tension control during acceleration, deceleration, start-up, and shutdown.
5. Gravure printing solutions provided by Hypmont
In response to the current industry application characteristics of gravure printing presses, Shenzhen Haipumont Technology Co., Ltd. has developed the HD50 high-performance vector control frequency converter, which can provide a variety of solutions to meet the common and specific needs of different users and printing equipment. The following are several solutions for tension control using the HD50 high-performance vector control frequency converter.
1 ) PLC + frequency converter solution + tension sensor
In this scheme, the PLC performs tension calculations, and the winding/unwinding inverter, traction inverter, and main inverter all employ speed control. The PLC calculates the operating frequency of the inverter based on the tension and transmits the operating frequency to the inverter via analog signals or communication.
Advantages of the solution: Customers can develop and modify PLC programs according to their own product characteristics and changes.
2 ) Frequency converter + tension sensor
In this scheme, the material tension is detected by a tension sensor and fed back to the frequency converter. Tension control and roll diameter calculation are entirely handled by the frequency converter.
Advantages of this solution: Since most gravure printing machines in the industry are equipped with tension sensors, this solution can save on the cost of the PLC without requiring major modifications to the existing mechanical structure.
3 ) Inverter torque control
In this solution, the tension sensor can be eliminated, and the frequency converter can detect the motor torque to control the tension.
Advantages of the solution: It can save the cost of tension sensors and PLC components, reduce the number of failure points in the entire equipment, and facilitate maintenance.
As a high-performance vector control frequency converter, the Hipumont HD50 frequency converter has been successfully applied in various customer sites. Furthermore, in actual use, it not only fully meets customer requirements, but also, in product comparisons, meets or even surpasses well-known international brands in terms of speed response, torque response, and speed accuracy. Customers have all stated that the performance exceeded their expectations.
6. Debugging Precautions
1) Since gravure printing machines require high control precision, it is essential to correctly input the motor nameplate parameters and perform motor parameter self-tuning before using the frequency converter.
2) When using an encoder, it is essential to correctly input the relevant encoder parameters, including the number of pulses per revolution, encoder type, encoder direction, etc.
3) For applications using the HD50's built-in tension control, be sure to input the tension control method (whether or not there is a tension sensor), target tension, and roll diameter (including initial roll diameter, target roll diameter, etc.) according to the actual production conditions.
7. Application Cases Using HD50 Vector Control Frequency Inverters
A printing equipment factory uses the HD50 high-performance vector control frequency converter to achieve 7 motors and 4-segment tension control. The maximum processing speed of the equipment is 180m/min. It is designed to process X kinds of printing materials, including plastic film materials with different tensile strength coefficients.
1 ) Tension scheme
The PLC performs tension calculations, and the winding/unwinding inverter, traction inverter, and main inverter all employ speed control. The PLC calculates the operating frequency of the inverter based on the tension and transmits this operating frequency to the inverter via communication.
2 ) System Block Diagram
3 ) Parameter settings
Setting parameters | Unwinding Inverter A | Unwinding frequency converter B | Unwinding traction frequency converter | Main traction frequency converter | traction frequency converter | Rewinding Inverter A | Rewinding frequency converter B |
Local address (F17.02) | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
Motor control mode selection (F00.01) | Closed-loop vector [3] | ||||||
Maximum output frequency (F00.06) | 100.00Hz | ||||||
Maximum operating frequency (F00.08) | 100.00Hz | ||||||
Encoder interface card selection (F14.00) | OC encoder [1] | ||||||
Encoder pulses per revolution (F14.01) | 【1000】 | ||||||
Encoder direction (F14.02) | According to the actual settings | ||||||
Frequency setting channel (F00.10) | Communication settings [2] | ||||||
Command to set channel (F00.11) | Communication settings [2] | ||||||
Communication data format (F17.00) | 1-8-1, odd parity [2] | ||||||
Communication timeout detection time (F17.04) | 【2s】 | ||||||
Communication error detection time (F17.05) | 【2s】 | ||||||
8. Conclusion
The HD50 is a high-performance vector control frequency converter with a built-in tension control module. It boasts high speed accuracy, fast speed response, stable torque control, high reliability, low interference, and strong anti-interference capabilities. Furthermore, it incorporates a wealth of tension control functions specifically designed for the printing industry's specific processes. Through practical application verification in the printing industry, the HD50 series high-performance vector control frequency converter, developed by Shenzhen Haipumont Technology Co., Ltd., has effectively met the high requirements of printing equipment drive control, earning unanimous praise and recognition from customers.
