1. Introduction Currently, with the continuous development of automation in the tobacco industry, the application of network-based distributed automatic control systems is becoming increasingly widespread. This system divides the industrial production system into two main parts: the production site and the control center. These are connected through a dedicated network, allowing for bidirectional information transmission and coordinated operation. A control center can remotely monitor multiple nearby production sites in real time, forming a distributed automatic control system. This system allows workers to stay away from noisy or harmful production sites, improving working conditions, achieving unattended operation and reduced maintenance, lowering labor costs, reducing production errors, and improving product quality. Therefore, network-based distributed automatic control systems have been a trend in industrial production development both domestically and internationally. This control model has been widely promoted in the tobacco system and other industries both domestically and internationally, and it is of great significance for optimizing China's industrial structure and enhancing the overall technological level and competitiveness of the industry. 2. Technological Principle of Tobacco Re-drying Machine The tobacco re-drying machine is the main equipment in the tobacco re-drying line. Its function is to adjust the moisture content of tobacco leaves, remove impurities, kill insect eggs and pathogens, and ensure that the moisture content and temperature of the tobacco leaves meet the process requirements of the pre-compression and baling machine for long-term storage, aging, and artificial fermentation, thus standardizing the quality of the tobacco leaves. The entire re-drying machine consists of a tobacco sheet re-drying machine, a leaf crushing machine, and storage tanks. The tobacco sheet re-drying machine mainly consists of a feeding section, a drying section, a cooling section, a re-moistening section, a discharge section, a conveyor belt, and a pipeline system. The feeding and discharge sections, together with the conveyor belt, form the tobacco sheet conveying system; the drying section consists of an upward-blowing drying zone, a downward-blowing drying zone, and a dehumidification system. The temperature of each zone in the drying section is automatically controlled, and the temperature of each zone is set according to the drying temperature curve; the cooling section reduces the temperature of the dried tobacco sheets to a certain level and stabilizes it, preparing the tobacco sheets for re-moistening; the re-moistening section ensures that the re-moistened tobacco sheets meet the requirements for pre-compression and baling. The function of the leaf crushing section is to dry the collected leaf fragments from the sand screening machine and leaf blowing section to the required moisture content for packaging and to separate them according to the specifications of the fragments. Larger fragments are sent to the packaging section, while smaller fragments are installed separately or processed separately. The storage cabinet is used to store tobacco leaves and acts as a buffer. 3. Automation system of tobacco re-drying section 3.1 Automation system of tobacco re-drying line The automation system of tobacco re-drying line mainly includes: (1) Digital part: 58 motors in the whole line, each motor circuit consists of air switch, contactor and relay, of which 13 motors require frequency conversion speed regulation. Several field sensors (photoelectric switch, proximity switch). (2) Analog part: The temperature of each drying zone is automatically controlled by PID adjustment. 3.2 Electrical control process The electrical control is designed with two control modes: manual and automatic. Automatic control is issued by the operator to the PLC through the operation button on the touch screen, and the PLC responds and executes. During operation, the touch screen (HMI) monitors the running status of the PLC in real time; manual control is only used as an auxiliary means for maintenance and debugging. Adhering to the principle of smooth material flow, the entire line starts in reverse order from the tail end to the head end during startup. When shutting down the entire line, it stops in the forward order from the head end to the tail end. 3.3 Design Philosophy The design philosophy of this control system is to keep pace with the latest technologies in the international automatic control field, ensuring its advanced nature, high reliability, practicality, and maintainability. It aims to achieve intelligent and integrated management of the leaf re-drying line's production process. This line adopts fieldbus and distributed I/O control technology, fully leveraging the advantages of network information technology. It achieves automated control and management of the production line through a three-layer network (management network, control network, and equipment network). The entire system utilizes the latest control technology from Mitsubishi Corporation of Japan. The PLC is a QNA series product, the control network uses a MelsecNT/10 network, the equipment bus uses a CC-Link field open network, and the monitoring system uses Mitsubishi's newly launched high-tech product, the A985GOT. Major components such as frequency converters also use Mitsubishi's products, thus achieving harmony and unity throughout the line. Other low-voltage electrical components use products from German companies such as Merle and Siemens, improving the project's scientific and technological content, increasing system stability, and facilitating operation and maintenance. The entire system is controlled by a single PLC as the master control layer. The equipment layer consists of remote I/O modules, remote programming modules, frequency converters, and analog remote input/output modules. To simplify on-site wiring and reduce cable laying, local control is handled by remote I/O modules. The frequency converters are connected as substations to the equipment network via CC-Link. To achieve the required accuracy for analog control and avoid signal attenuation due to excessive cable length, analog input/output modules are also connected to the equipment network. This saves cable and effectively overcomes signal attenuation and instability. Furthermore, for ease of operation, a touchscreen is placed on-site and also connected as a substation to the equipment network. This makes the system's control logic very clear: the upper layer is controlled by the PLC; remote I/O modules, frequency converters, and touchscreens all act as substations communicating with the PLC via CC-Link and exchanging data with the upper management network through a 10-bit network panel. System startup, shutdown, and frequency converter data adjustments can all be achieved through operation of the on-site touchscreen. This design approach simplifies the operator's work. Since each part is connected by only one network cable (shielded twisted pair), it greatly facilitates system installation and maintenance, while also reducing costs. 4. Network Configuration and Hardware Components To implement the above design concept, the network distribution diagram shown in the attached figure is provided:
(1) In the main station section, A61P is the power supply module; 10net is the network module for communication with the host computer; CC-Link is the network module for connection with the device network; Input is the input module; Output is the output module. (2) In the substation section, RY represents the remote input module, model: AJ65SBTB1-32D; RX represents the remote output module, model: AJ65SBTB1-32T; A/D represents the analog input module, model: AJ65BT-64RD4; D/A represents the analog output module, model: AJ65BT-64DAI; G4 represents the remote programming module, model: AJ65BT-G4; BP represents the frequency converter; GOT represents the touch screen. 5. Monitoring System This monitoring system adopts the currently popular touch screen display (HMI) in the industry. In order to achieve uniformity of the entire control system, this system adopts the GOT985 touch screen from Mitsubishi Corporation of Japan. Through this screen, the operating status and alarm status of the motors of the entire production line can be monitored, the parameters of the frequency converter can be set, the temperature of each drying zone can be displayed and controlled, and alarm information and solutions can be released in a timely manner. This is very convenient for monitoring the equipment operation and adjusting and modifying the program, with a good user interface and optimal communication and network interface. The monitoring system consists of 13 operation screens, namely the cover, operation station screen, storage cabinet monitoring screen, feeding section screen, re-drying section monitoring screen, leaf crushing section monitoring screen, 5 temperature control screens, alarm analysis screen, and frequency converter operation monitoring screen. Among them: (1) Cover screen: Information screen displayed after power-on. (2) Operation station screen: Includes some buttons for starting and stopping, automatic and manual operation of this section, as well as some fault indicator lights. When the equipment malfunctions, the corresponding indicator light flashes. (3) Monitoring screens for storage tank section, re-drying section, feeding section, and leaf crushing section: Specific monitoring of all motors on the entire line. The main information includes: normal shutdown is indicated by a stationary red light; normal operation is indicated by a stationary green light; local switch not closed is indicated by a flashing yellow light; overcurrent alarm is indicated by a flashing red light; solenoid valve closed is indicated by a red light, and open is indicated by a green light. (4) Temperature monitoring screen: Specific monitoring of the temperature of the five drying zones in the re-drying section. The temperature of each zone and the PID parameter are set, and the actual temperature is displayed, along with corresponding bar charts and trend graphs. (5) Inverter monitoring screen: The actual parameter values of all inverters on the entire line can be monitored, and some parameters can be modified and set online. (6) Alarm analysis screen: The alarm occurrence time is recorded, the cause of the alarm is analyzed, and solutions are provided. At the same time, floating alarms can be viewed at the bottom of any screen. 6. Conclusion This control system has been installed and debugged at Sichuan Sanyou Leaf Re-drying Co., Ltd. and is now operating normally. Practice shows that this control concept of the system is practical and reliable. The operation is very stable, the failure rate is extremely low, the network communication is very smooth, the temperature control is good, and all indicators are qualified. It has brought rich benefits to the factory and has thus been recognized and praised by users and the same industry. References [1] Yang Xianhui. Fieldbus Technology and Application [m]. Beijing: Tsinghua University Press, 1999. [2] Fei Minrui, Lang Wenpeng. Open Industrial Control Technology and System [m]. Shanghai: Shanghai University Press, 2001. About the author Liu Ming (1975-) Engineer Graduated from the Department of Automation of Hebei Polytechnic in 1997. He is now engaged in electrical design work in the Electrical Control Room of Qinhuangdao Tobacco Machinery Co., Ltd.
