Abstract: This paper details the successful application of a control system comprised of Delta HMI, text display, EH series programmable logic controller (PLC), and V and B type AC frequency converters on the XJ4142 large-format four-color offset printing press manufactured by Henan Xinji Co., Ltd. The entire electrical control system primarily utilizes the MODBUS protocol to construct an integrated bus control system. After more than a year of use by the user, the results have been ideal. Keywords: Delta, EASY, PLC, LINK, frequency converter, HMI, large-format multi-color printing press 1 Introduction The XJ4142 large-format four-color offset printing press is an integrated optical, mechanical, electrical, and pneumatic product independently developed by Henan Xinji Co., Ltd., and is a leader in the domestic large-format offset printing press field. The machine is functionally divided into four components: paper feeding unit; main drive system; four color printing units; and paper receiving unit. The machine's process flow is as follows: the cut paper is conveyed by the paper feeding unit to the first color printing unit, first undergoes regular positioning, then passes through the four printing units sequentially for printing, and finally is transferred to the paper receiving unit to collect the printed paper neatly. The machine is twelve meters long and has twelve control panels. The complete machine system includes: two paper table lifting motors; two paper suction pumps; one oil pump; one powder spraying pump; one air compressor; four water outlet roller motors and one main motor; and twenty-two solenoid valves and electromagnets. The machine also has numerous photoelectric switches for monitoring and limit switches for safety protection. These electrical components are mainly distributed on the machine's drive and control sides. Due to the dispersed nature of the electrical components, if only one PLC is installed in one electrical cabinet to form the control system, the connection cables from the parts of the machine furthest from the cabinet will be numerous and long. 2. A New Control System Based on the Communication Function of Delta EH Series PLC 2.1 Scheme Design Based on the above analysis of the new XJ4142 offset printing machine and the functions of the Delta EH series PLC, we collaborated with Delta Electronics to propose a new electrical control system using two EH series PLCs as the master and slave stations respectively. The Delta text display, human-machine interface, and four B-type frequency converters are connected to the PLCs via communication ports. Delta EH series PLC adopts a dual-processor chip design architecture, which has a very fast computing speed. In addition to two built-in serial communication ports (COM1: RS-232, COM2: RS-485), it can also expand with a communication port COM3. In terms of instruction processing speed, it is close to high-end PLCs abroad, while it has more built-in communication ports than foreign brands. Delta DVP-PLC has developed a variety of convenient MODBUS serial communication instructions specifically for RS-485 communication ports. Among them, Delta EH series PLC has EASY LINK function, which can be used for network control between Delta PLC and frequency converter. 2.2 System characteristics (1) The main motor provides transmission power for all parts of the machine. It is required to start at full load at low speed. When the machine is printing, the speed is required to be adjustable and the speed stability is good. Therefore, Delta V series high-performance magnetic flux vector control frequency converter is selected. (2) When printing on paper, the offset printing press needs to apply water and ink to the printing plate first. The amount of water on the plate needs to be adjusted frequently during printing. Therefore, four Delta B-series frequency converters are selected to control the speed of the water roller motors of the four printing press units. (3) The machine is equipped with a main control console electrical box and a main electrical cabinet. The main control console electrical box is located on the operating side of the paper feeder, and the main electrical cabinet is located on the transmission side. The master PLC is located in the main control console electrical box, and the slave PLC is located in the main electrical cabinet. The master PLC is mainly used for signal acquisition and processing of the paper feeder and the first and second color printing press units. The slave PLC is mainly used for the control of the main motor frequency converter, signal acquisition and processing of the third and fourth color printing press units and the paper receiving machine. The master PLC and the slave PLC are connected by an RS-485 communication line. The main control console electrical box also contains the water roller frequency converter of the first and second color printing press units, and the main electrical cabinet contains the main motor frequency converter and the water roller frequency converter of the third and fourth color printing press units. The first and second color water roller frequency converters and the main station PLC are connected and controlled by RS-485 communication lines. The third and fourth color water roller frequency converters and the main station PLC are connected and controlled by RS-485 communication lines. In this way, the water roller frequency converters and slave station PLCs of the four printing units are all used as slave and master station PLCs to form an RS-485 communication network. The EASY LINK function of Delta PLC can be used to implement 1:N control. For safety and reliability, the main motor frequency converter still adopts I/O control, see Figure 1. [align=center] Figure 1 Electrical control cabinet[/align] (4) The display adopts Delta TP04 text display and DOP-AE10THTD human-machine interface. The text display is on the main control console, mainly displaying and adjusting the machine speed, displaying the printing count, monitoring the machine operation status and fault indication. The human-machine interface is on the viewing table at the back of the machine. In addition to the text display, the machine can also be operated. The water volume of the four printing presses can be centrally displayed and adjusted here, and the registration display and adjustment of the printing plates of the four presses can also be performed. The text display and the COM1 port of the main station PLC communicate via RS-232, and the HMI and the COM3 expansion communication port of the main station PLC communicate via RS-485. See Figure 2 for the main screen design. [align=center] Figure 2 HMI[/align] 3 Control System Structure 3.1 Hardware System Architecture 3.2 Communication Control Software Architecture The 1:N master-slave communication control software architecture is implemented using PLC EASY LINK programming: 4 Technical Parameter Design 4.1 Inverter Parameter Design Water roller inverter parameters; set the frequency and operation control source as RS485 communication input, set the communication station number, communication transmission speed, and communication data format. The communication transmission speed and communication format set in the inverter must be the same as the communication transmission speed and communication format set in the program of the main station PLC. 4.2 Process Parameter Design Process parameter human-machine interface setting; the human-machine interface mainly realizes the means of human participation in the control system. It mainly includes: display section, setting section, operation section, and historical fault section; among which, the setting mainly includes the main unit speed setting, four-color unit water volume setting, and four-color unit printing plate registration and positioning. 5. Debugging Summary The communication transmission speed and communication format set in the frequency converter must be the same as the communication transmission speed and communication format set in the master station PLC program. After Delta PLC LINK is set to automatic mode and started, the master station begins to detect the total number of connected slave stations. To improve the reliability of the communication connection, a delay program is added to the master station PLC program, waiting for the entire system to power up and stabilize before starting PLC LINK. When individual slave stations are not working properly, to check whether these slave stations have successfully communicated with the master station PLC, a computer can be connected to the master station PLC, and the "Device Monitoring" command in the Delta PLC programming software can be used to monitor the LINK connection flag register of each slave station. 6 Conclusion More than twenty of these machines have been produced so far. After use by numerous users, the electrical control system has proven to be stable and reliable. The network electrical control system, composed of RS485 communication, realizes distributed control of electrical components in large machines, greatly reducing the number of connecting lines between different parts. This system uses two small PLCs in combination to replace the large machine, significantly reducing system costs. This system features simple structure, convenient operation, beautiful interface, stability and reliability, low cost, and convenient maintenance. References [1] Use and Adjustment of Offset Printing Machine. Feng Changlun. Printing Industry Press, 2002 [2] VFD-B Type Inverter User Manual. Delta Electronics Co., Ltd., 2003 [3] VFD-V Type Inverter User Manual. Delta Electronics Co., Ltd., 2003 [4] DOPA Series Human-Machine Interface Application Technology Manual. Delta Electronics Co., Ltd., 2003 [5] DVP-PLC Application Manual Program Section. Delta Electronics Co., Ltd., 2003