Abstract: This paper studies INTERBUS fieldbus technology and designs a brand-new PLC control system based on SIEMENS S7-400 PLC and INTERBUS fieldbus, according to the process characteristics of GD packaging machines. Over three years of operation have shown that the system design proposed in this paper is very successful, and the engineering modification of GD PLC according to this scheme is also very successful. Keywords: GD packaging machine, S7400 PLC, INTERBUS fieldbus I. Introduction Currently, many packaging machines in Chinese cigarette factories are X1/X2 model packaging machines produced by GD Company. Since this model was introduced in the early 1990s, its electrical control system is an FZ control system, mainly using logic circuit boards as its main control equipment. With long-term operation, the shortcomings of the logic circuit control method have gradually become apparent. The main problems are as follows: 1) High failure rate; 2) Difficult maintenance; 3) Difficulty in fault location for machine operators; 4) Difficulty in realizing network data acquisition function; 5) The original machine uses software and hardware produced by GD Company, which has poor versatility. Furthermore, GD Company has announced that it will no longer provide spare parts for the old FZ electronic control system, thus causing significant difficulties for future maintenance. Due to these problems, it is necessary to technically upgrade the control system. In addition to ensuring the normal production function of the original machine, the upgraded control system must also be advanced, conform to the development trend of modern tobacco machine control systems, provide an intuitive human-machine interface, have a computer network interface, and be able to perform single-machine data acquisition. II. Upgrade Plan To address the above problems and requirements, we designed a completely new PLC control system based on the German SIEMENS S7-400 PLC and using the INTERBUS fieldbus to replace all the circuit boards used in the original GDX1 packaging machine. The upgraded system mainly consists of a PLC control system, an INTERBUS bus, and a host industrial computer, as shown in Figure 1. [align=center]Figure 1 System Composition Block Diagram[/align] With the continuous development of computer and communication technologies, serial data transmission technology has gradually entered industrial automation control systems. This transmission technology can connect field signals in series with each other through several wires for communication. Because this serial data transmission is widely used in field devices such as transmitters/actuators, this method is also known as a fieldbus system. This way, only one cable is needed to replace hundreds or thousands of input/output lines, greatly reducing the complexity of field wiring, reducing network hardware equipment, and lowering costs. INTERBUS is a fieldbus product launched by Phoenix Contact, an economical, simple, and open sensor-actuator bus. It is mainly used for interconnection between production field devices and PLC control systems, building industrial field control networks with high real-time requirements, and has the ability to quickly transmit simple input and output data. It has the following advantages: 1) The INTERBUS bus adopts lumped frame data loop communication, which ensures strict synchronization and periodicity of data transmission; 2) Full-duplex communication and a consistent 500K data rate ensure real-time data communication; differential signal transmission and dedicated bus loop checks ensure strong anti-interference capabilities and real-time equipment monitoring; 3) The INTERBUS network transmission medium can be mixed, including fiber optic cables, optical fibers, and infrared, all as required; 4) The INTERBUS bus system is easy to debug, plug-and-play, easy to install, requires no terminating resistors, has short debugging time, and avoids address overlap; 5) When a fault occurs, INTERBUS can accurately tell the operator the location, type, and solution of the error, and has extremely strong diagnostic functions. In addition, INTERBUS is particularly suitable for applications with small data blocks but frequent transmissions, making it ideal for retrofitting GD packaging machines. The bus adapter controller is the core of communication between the INTERBUS bus system and the PLC control system, and also the bridge between the INTERBUS bus system and the PLC. Its performance has a significant impact on the entire control system. The PLC control system of this system uses a Siemens S7-400 PLC, so the Phoenix Contact IBS S7 400 DSC/IT (Dir mode), a fourth-generation bus adapter controller specifically manufactured for the Siemens S7-400 control system, was selected. This controller communicates with the PLC system using direct I/O mode. Direct mode means that the input and output data of the INTERBUS system are directly copied to the input and output address areas of the PLC. In practice, the IBS S7 400 DSC/IT is considered an S5 module of the S7-400 control system. As a fourth-generation standard diagnostic controller (DSC), the IBS S7 400 DSC/IT is fully compatible with the Siemens S7-400 PLC. The modified system mainly consists of a PLC control system, an INTERBUS bus, and a host industrial computer. The PLC primarily handles the logic and temperature control of various devices within the packaging unit. The host industrial computer performs functions such as fault display, speed display, setting and displaying actual temperature values, parameter modification, production and material consumption statistics, and historical data storage. The PLC exchanges data with the host industrial computer via the MPI communication protocol, and the host industrial computer then transmits various machine data to the plant-level MIS system via CAN bus or Ethernet. The controller connects to the field devices via the INTERBUS bus. As shown in Figure 1, some of the detection and control signals from various sensors and operation buttons are input to the PLC via the INTERBUS I/O module group, while others are sent to the PLC to directly drive the actuators, reducing intermediate links and improving system reliability. Low-voltage electrical appliances such as relays and circuit breakers are installed in the active electrical cabinet. The original 13 temperature controllers have all been eliminated, and the PLC module directly performs PID fuzzy control, allowing temperature setting and display at each temperature point on the industrial computer screen. The bus configuration software for the control system is Phoenix Contact's fourth-generation INTERBUS system configuration software, IBS CMD G4 4.51. IBS CMD G4 is a configuration software independent of the PLC control system. This software allows users to interactively configure, operate, and diagnose all connected devices in the INTERBUS network in a visual manner, and to set the memory areas for communication between INTERBUS bus devices and the PLC control system. By configuring the bus adapter controller, standard registers and address areas are set, and these registers are ultimately mapped to the PLC's input and output areas. The standard registers include two diagnostic registers and three standard function registers. The diagnostic registers include diagnostic status registers (input words) and diagnostic parameter registers (input words). PLC control software programming uses STEP 7. Its programming philosophy and process are as follows: 1) Digest the original machine drawings and understand its control logic; 2) Understand the process operation on-site and become familiar with the process flow; 3) The software control logic is basically consistent with the original control board logic, such as signal linkage, interlocking, and shift register operations; 4) Simplify and modify some logic based on the on-site process to make the control method more concise and reasonable; 5) Seamlessly integrate other detection signals into the current control software. III. Results of the Upgrade Currently, the system is in normal operation in more than 10 cigarette factories nationwide, with the longest operating time exceeding 3 years. It has consistently performed well, significantly reducing the failure rate and maintenance costs compared to the original system, while also offering intuitive and convenient operation. Furthermore, the system's comprehensive detection functions ensure excellent control over cigarette pack quality. It boasts the following advantages: 1) It retains all the functions and operating methods of the original system, and can add corresponding control functions as needed. 2) It maintains the original overall layout and interface methods, facilitating on-site installation. An additional industrial control computer is added for displaying faults, temperatures, statistical data, and setting parameters. Fault display is intuitive and accurate. The touchscreen features a user-friendly Chinese human-machine interface, greatly facilitating operation and maintenance. 3) Due to the powerful bus configuration, monitoring, and fault diagnosis functions of INTERBUS, the status of each bus device can be easily monitored and fault diagnosed through the bus control board, greatly improving the maintainability and reliability of the control system. 4) The PLC cabinet has a reasonable design structure. The upper-level industrial control computer sets the temperature, and the PLC hardware module completes the PID control of the heater temperature, making it easy to operate and highly stable. 5) This system has data statistics functions. It statistically analyzes data such as output, effective operating rate, and material consumption, and automatically generates reports. Historical data can be saved and retrieved for any time period as needed. Fault query is intuitive and convenient, and it has intelligent alarm functions. The network interface of the upper-level computer can directly send various required production data and equipment operating status to the plant-level MIS system, thus possessing excellent network data acquisition capabilities. 6) In addition to ensuring all the original machine's detection functions, the new control system adds seal misalignment detection and package missing detection functions, seamlessly integrating them into the original system instead of using the previous patchwork control method. Furthermore, the control system's electrical control cabinet and field substation distribution boxes use Rittal electrical cabinets, and the main electrical control cabinet uses Rittal refrigeration equipment. Low-voltage electrical appliances use SIEMENS products, while the integrated industrial control computer, switching power supply, relays, optocouplers, and terminal blocks use Phoenix Contact products. The system boasts high reliability and versatility, and its performance is comparable to current foreign control systems. IV. Conclusion Several years of operational experience have demonstrated the success of the proposed INTERBUS-based GD packaging machine control system design. Furthermore, the engineering modifications to the GD PLC based on this design have also been highly successful, achieving technical and performance levels comparable to next-generation foreign control systems. This further strengthens our confidence in domestically developed upgrades, reinforcing our belief that we are capable of successfully modifying equipment ourselves, without necessarily relying on foreign systems!