Abstract : Based on the working principle of a high-precision position tracking system in packaging and printing transmission, this paper proposes combining a PLC programmable controller with a fully digital high-performance variable frequency AC servo system. The system uses the MSD0421A series fully digital high-performance frequency converter as the actuator and the PLC as the drive device. The high-speed counter and pulse integrated output function of the PLC, combined with the pulse position control mode of the MSD0421A, constitute a position control system for packaging and printing transmission. The hardware and software development of this system were also implemented. Keywords : Packaging printing; PLC; Inverter; Position tracking system. The packaging printing drive control system has transitioned from manual adjustment and semi-automatic stages to microcomputer control and high-speed printing production process online monitoring stages, evolving into a network structure for high-speed shaftless multi-color printing presses. Microcomputer control is widely used in China, offering advantages such as small size, high reliability, and good economy, but also suffers from drawbacks like high interference and difficulty in initial calibration. Here, the MSD0421A fully digital inverter driver is used as the actuator, with pulse train control as its position control signal. It features strong anti-interference capabilities, high control accuracy, and fast response speed. Applying it to the printing drive system effectively solves technical problems such as difficult initial positioning, high interference, and difficult color registration. 1. MSD Series Fully Digital High-Performance AC Servo System The inverter driver is the Panasonic MSD fully digital vector control system. This system utilizes PWM pulse width modulation frequency conversion, boasting powerful performance suitable for high-performance position controllers. It features 38 parameter settings and 6 control modes, among which pulse train position control is unique. Because it uses a pulse signal of a certain frequency as the input signal representing the position command, it has higher accuracy and stronger anti-interference ability than the analog speed input signal in complex working environments! 2. Automatic Color Registration Principle in Packaging Printing There are many reasons for registration errors, such as inflexible parallelism of guide rollers and pressure rollers, poor motion balance, tension fluctuations, uneven ink thickness, thermal deformation of ink, and diameter errors of printing plate rollers. This registration deviation is continuously changing in nature, and the difference is not quantitative! Therefore, it is necessary to constantly monitor the registration error and correct it in a timely manner. In manual color registration, the printer usually observes the registration error with the naked eye and manually adjusts the movement of the correction roller based on experience to compensate for the registration error, which greatly limits the printing speed and color registration accuracy. However, using an automatic color registration system can improve both printing speed and color registration accuracy! Figure 1 shows a simplified diagram of the printing process of a gravure printing press production line (only the first four printing units are shown). The printing press runs from the unwinder through each printing unit sequentially, printing and drying each color, and is then rewound by the rewinder! Each color printing process involves printing a color mark on the edge of the printing material. This color mark is 10mm long and 1mm wide. For accurate registration, the marks of adjacent colors should be parallel and perpendicular (vertical) to each other, with a distance of 20mm between them. The distance between the color marks in the system is detected by a color mark sensor. In Figure 1, the photoelectric scanning head S1 detects the color marks printed by units 1 and 2. If the gap between two adjacent color marks is not equal to 20mm, it indicates a registration deviation. The deviation is calculated by the microprocessor, which outputs a control signal to drive the actuator, causing the corresponding color correction roller ML to move up and down. This dynamically corrects the registration by extending or shortening the travel distance from the previous unit's printing plate roller to the current unit's printing plate roller. The color registration of each unit's printing is based on the color mark printed by the previous unit. [align=center]Figure 1 Gravure Printing Machine Printing Flowchart[/align] 3 Introduction and Scheme Design of Color Matching Automation System This system consists of a PC, an S7-200CPU214/EDC programmable controller, and an MSD frequency conversion servo system as the control core. Its structure is shown in Figure 2. The PC plays two main roles in the system: First, it converts the control program into a data format acceptable to the PLC and transmits it to the PLC; second, it reads the switch and analog data generated during the production process from the PLC, processes it, and sends instruction data to the PLC for corrective control. [align=center]Figure 2 Control System Hardware Structure Diagram[/align] Control Principle: Initially, a rotary encoder is installed on the shaft head of the entire transmission system. As the transmission system operates, the encoder generates continuous pulse signals, i.e., n pulses per revolution. Based on the roller circumference, 20mm corresponds to how many pulses. This pulse signal serves as the input given signal and is sent to the CLOCK of the high-speed counter SHC1 through the I0.6 port of the PLC. Assume the HSC's operating mode is 1, i.e., HDEF, 1, 1. Each color roller is equipped with a color mark sensor, which can detect color marks on the edge of the printed product. The detected color mark signal is then converted into an electrical pulse signal, which is fed back to the Reset function of the high-speed counter HSC1 via the PLC's input I1.0. The PC and PLC communicate asynchronously via an RS-485 interface. The PC reads these data and status signals from the PLC, performs comparisons, analyses, calculations, and logical judgments using software, and then sends control commands and data to the PLC. This outputs control quantities to the actuators, adjusting the relative position of the color rollers and eliminating printing misalignment. In the entire printing process, the printing position is generally adjusted by changing the rotation angle of the printing plate rollers, as shown in Figure 3. In the diagram, the detection device is a color mark sensor, which converts the detected color mark signal into electrical pulses and sends them to the PLC. The actuator is an AC servo system, which is directly driven by the PLC and does not require any external circuitry. The PLC compares the detected signal with a pre-defined standard value in the memory to obtain the deviation value, and then calculates the number of pulses to be emitted based on the pulse deviation according to the calculation rules. [align=center] Figure 3 Control Principle Block Diagram[/align] The rotary encoder pulse train and the pulse detected by the color mark sensor are shown in Figure 4. According to the principle of rotary encoders, the more pulses emitted per axis angle, the higher the positional accuracy. Assuming a given value of 20mm is equivalent to 20 pulses, and the pulse triggering time between color mark 1 and color mark 2 is 18 pulses, taking ink 1 as the reference, this indicates that ink 2 is moving too fast, causing the pattern to distort. To slow down ink 2 and correct the positional deviation, the micro motor should immediately reverse by an angle equivalent to 2 pulses. Assuming the pulse triggering time between color mark 2 and color mark 3 is 23 pulses, taking ink 2 as the reference, this indicates that ink 3 is moving too slowly. To speed up ink 3 and correct the positional deviation, the micro motor should immediately rotate forward by an angle equivalent to 3 pulses to eliminate the deviation. In the control system, these compensation pulses should be output from the PLC's PTO integrated pulse output function through output terminal Q0.0 to the instruction pulse input terminal of the AC driver MSD, and the driver should be in pulse train position control mode. Parameter NO-29 should be selected as 3. This mode is pulse train + sign. The instruction sign input terminal should be sent to a high level or a low level by the PLC output terminal according to the control needs to control the forward and reverse rotation of the motor. At this time, the driver can drive the motor to rotate forward or reverse by a certain angle according to the positive or negative value of the deviation to correct the position deviation. [align=center] Figure 4 Schematic diagram of detected pulse train[/align] 4 Software Design The system software includes the main program, initialization zeroing program, counting subroutine and integrated pulse output subroutine. 4.1 Main Program When the system is put into operation, the task of the main program is to adjust the motor to rotate forward or reverse according to the deviation value obtained by comparing the randomly read count value with the standard value by the PLC. The program flowchart is shown in Figure 5. [align=center]Figure 5 Main Program Flowchart[/align] 4.2 Counting Subroutine First, the control byte SMB47 of the high-speed counter HSC1 is set to 16#FC, which means: forward counting, can update the preset value (PV), can update the current value (CV), and activates HSC1. Then, the instruction HDEF is used to set the high-speed counter HSC1 to working mode 1, that is, only reset without start input and no direction selection. The current value SMD48 is reset to 0, and the preset value SMD52 is set to FFFF (hexadecimal). When the color mark pulse signal of the color mark sensor is input to the PLC I1.0, an interrupt is triggered, the current value of the counter is read, and the high-speed counter is started with the instruction HSC1. 4.3 Integrated Pulse Output Subroutine The CPU214/DC has 2 pulse outputs, which can be used to control the pulses of the AC driver. The program flowchart is shown in Figure 6. 1) Three conditions for starting the motor: Pressing the "START" button generates a rising pulse edge (from 0 to 1) at input terminal I1.0; no interlock, i.e., interlock flag M0.2=0; the motor is in a stopped state, i.e., operation flag M0.1=0. If all three conditions are met, M0.1=0 is set, and the PLS O instruction is executed during control, outputting a pulse at output terminal Q0.0. Other prerequisite conditions are set in the first scan (SM0.1=1), mainly the basic data of the pulse output function, such as time base, period, and pulse count. [align=center] Figure 6 Flowchart[/align] 2) Two conditions for stopping the motor: Pressing the "STOP" button generates a rising pulse edge (from 0 to 1) at input terminal I1.1; the motor is in a running state, i.e., operation flag M0.1=1. If both conditions are met, flag M0.1=1 is reset, and the pulse output at output terminal Q0.0 is interrupted. 3) Interlock. To protect the safety of personnel and equipment, after pressing the “STOP” button (I1.1), the drive interlock must be specified, the interlock flag M0.2 must be set, and the drive must be shut off immediately. The motor can only be restarted after M0.2 is reset! When the “STOP” button is released, to prevent the motor from starting unexpectedly, M0.2 can only be reset after both the “START” button and the “STOP” button (I1.1) are released. If the motor is to be started again, a start signal must be generated again! 5 Conclusion Using the pulse train position control method and using the all-digital frequency converter to drive the AC servo motor as a correction device can significantly improve the position tracking quality of the system! The application results show that the system has high control accuracy and fast dynamic response! References : [1] Ma Xiaoliang. High-power AC-AC frequency converter speed regulation and vector control technology (2nd edition) [M]! Beijing: Machinery Press, 1996. [2] Marlen Vamm4sky A LMWvelopnwnt and comparatwe analysis 0f [3] Hu Binghua. Computer-automatic color matching position tracking system for six-color printing machine [J]. Electrical Transmission, 1998, 28(2): 25-27.