Abstract: This paper introduces the overall structure, communication network, software design and system functions of a distributed control system for corrugated board production lines. The system is based on VIPA's PLC and combines Ethernet and field bus Profitbus for data communication. ConTROL LAB is used to design the software system, which makes the whole system have better reliability and expandability, and realizes the work of corrugated board production line. Status display, production control, order management and shipping management.
Keywords: corrugated board; distributed control system; communication network; PLC; fieldbus
1 Introduction
DCS distributed control system (also called distributed control, distributed control system) is developed on the basis of a single-loop microcomputer control system. It integrates computer technology, communication technology, CRT display technology and process control technology, and adopts hierarchical classification. The structural principles and design principles of decentralized control, centralized operation, hierarchical management, and autonomous separation have solved the drawbacks of computer control hazard concentration in the past, single simulated analog instruments, excessive dispersion, and inconvenience of human-machine contact. DCS's safety, reliability, versatility, excellent control and comprehensive management capabilities make it widely used in industrial control.
Corrugated cardboard is widely used as packaging materials for electrical appliances and everyday products. In China, where modern large-scale industrial automation is lagging behind and high-speed industrial and economic development is taking place, cross cutters and stackers form a continuous production process. At present, the production of corrugated board in China is relatively backward.
The monitoring system uses a distributed control system based on a programmable controller PLC, uses the PLC as a site acquisition control station, uses Ethernet and Profitbus for data communication, and completes the display of operating conditions and production operations for the Jialong corrugated board production line in Zhaoqing, Guangdong. Order management and shipment management finally achieved the enterprise management-control integration.
2, the overall structure of the system and communications network
2.1 The overall structure of the system
Jialong corrugated board production line monitoring system uses a distributed computer monitoring system as shown in Figure 1. It is divided into three levels of structure: field level, control level and management level.
The first level is the field level. The three PLC substations installed in the field assist with other measurement and control equipment (such as encoders, infrared measuring instruments, frequency converters, etc.) to perform on-site control of various data collection and production lines. The on-site acquisition controller completes the input and output of on-site signals, performs data processing and control output according to a given working procedure, and sends the processing results to the operation station. The PLC station adopts the products of German VIPA company, including a CPU station and two I/O stations, which are equipped with the following:
V200CPU station: mainly includes CPU 288L, FM250, SM221 and SM222 modules. Mainly used for bonding machine and cross cutting machine various status signal acquisition and control signal output.
V200 station 1: Mainly includes SM221, SM222, SM232 and FM250 module; It is mainly used for gluing machine and No. 1 corrugating machine state signal acquisition and control signal output.
V200 station 2: mainly includes modules such as SM222, SM232 and FM250; it is mainly used for the signal acquisition of the 2nd and 3rd corrugator and the output of control signals.
The second level is the control level, equipped with 5 industrial PCs. Including one main operation station, one gluing machine operation station and three corrugator operation stations. The main operating station is set in the workshop control room, and other operating stations are set in the corresponding parts of the production line to complete the management of field level inspection, control, and protection functions. Each HUB is composed of a HUB as a local area network. Each operation station is independent and can be used as backup. It processes, analyzes, and stores all data collected on the first level, completes the collection and distribution of all control instructions, and expresses the operating status of the entire production line in various ways (such as flowcharts, trend charts, etc.). The configuration of system functions, the production of flow charts, the setting of protection values, and the modification of control models are also performed at this level of operation stations.
The third level is the management level, equipped with multiple ordinary PCs, printers, and a database server. Among them, the PC is set as a management terminal in the corresponding management department. The printer is responsible for regularly printing the production status report file. The database server is responsible for receiving and storing various real-time data and historical data sent from the supervisory control level. The managers of each department can observe the operating status of the production line and order execution at any time through the management terminal. The management level can also accept the management department's management data input, complete the order management, shipping management and other functions.
2.2 Communication Network
Since the structure of a multiprocessor is widely used in a distributed control system, data communication between processors becomes extremely important.
As one of the hot spots in the field of automation technology, fieldbus technology is known as the computer LAN in the field of automation. It adapts to the decentralized, networked and intelligent development direction of industrial control systems. Profitbus is the only fully-integrated H1 (process) and H2 (factory automation) fieldbus solution. It is a development-free fieldbus standard that does not depend on manufacturers. It can be widely used in manufacturing processes, processes and building automation. In this monitoring system, Profitbus is used for data communication between the three site-level PLC stations to achieve the collection of the status data of the cardboard production line and the transfer of control signals.
Ethernet Ethernet was originally developed by Xeroex in the 1970s as a method of networking transmission and later improved by Xeroex, Digital Equipment Corporation (DEC) and Intel. This flexible technology can run on various network media and provide good capacity with reasonable overhead. So far, Ethernet is the most popular logical topology for LANs. In this monitoring system, Ethernet is used for data communication between control level operation stations and between management level terminals. Realization of mutual redundancy between various operating stations and access to management data.
Communication between DCS levels has always been one of the technical hotspots of engineers and technicians. The system uses the Ethernet port of VIPA's PC-CPU 288L to solve the communication problem between the field level and the control level. Real-time real-time data transmission and control-level signal downward transfer are realized. Because the control level and management level use Ethernet at the same time, they are directly connected by hubs (HUBs) to communicate with each other.
In the monitoring system, Ethernet (Ethernet) and fieldbus are combined to realize data communication between PLC stations, between operation stations, between management terminals, and between field level, control level, and management level.
3, software design
The system software uses the ConTROL LAB software package, and its hierarchy is shown in Figure 2. 
The field-level V200 CPU station uses a fast, predictable real-time kernel with a periodic time-to-work (Jitter-Time) of up to 2 microseconds (300 MHz CPU). Data exchange between PLC and hardware modules and fieldbus are performed in real-time tasks, ensuring that the delay of such data exchange in the operating system does not exceed a few microseconds. The control task is executed as a real-time task, and its shortest working period can reach 0.01 milliseconds.
The PLC monitoring program is programmed with the graphical configuration tool ControlChart, which is a development-oriented control software based on the IEC1131-3 flowchart language and complies with industry standards. Engineers can use the off-the-shelf modules to freely combine, observe and debug online at the control level operation station, which greatly shortens the debugging time of the control system. The control task of the corrugated board assembly line is mainly to coordinate the running speed of various units on the line. In the speed adjustment, the bonder is used as a host, and the gluing machine, trimming machine, cross cutting machine, and stacking machine operate synchronously with the host. The monitoring system speed control flow chart shown in Figure 3.
ZJL, DJL, DDCL and SJCL correspond to the amount of pulp (corrugating machine), accumulation amount, order production and actual production, respectively, and the speed of the bonding machine and the corrugating machine are adjusted accordingly based on the measured values ​​of the above quantities.
In the control level and management level software based on WINDOWS NT platform, using easy-to-learn and easy to use Visual Basic6.0 programming, which uses ActiveX, OPC, TCP / IP and other international general-purpose technology and standards, users can be extremely convenient with other software systems Free communication and function expansion. The control level operation station inspection screens mainly include the total operation diagram, the corrugator monitoring chart, the bonder inspection chart, the gluing machine monitoring chart, the trimming machine monitoring chart and the cross cutting machine monitoring chart. The management level terminal includes an order management screen and a shipping management screen.
4, system function
The functions of the corrugated board production line monitoring system implemented on the basis of hardware and software are shown in Figure 3. Monitoring system functions are divided into monitoring and management functions. The monitoring is mainly the display of working conditions and production operations. The management is mainly order management and shipment management.
4.1 Working status display The status data of the production line collected on the site is displayed in the control level operation station and the terminal of the management level, mainly including: the type of cardboard in production, the size and specification; the current production speed and motor current of each unit; Machine base paper accumulation amount; bonder paper output amount, each section temperature; current actual number of sheets, the total number of orders, still loosing the actual number of sheets; finished product, the number of bad products (manual defective input) the remaining length of the base paper Wait. Display methods include numbers, histograms, and trend charts. Based on this, over-limit alarms such as speed, current, temperature, and accumulation amount are performed.
4.2 Production operation
According to the signals collected at the scene, the monitoring software can automatically control the production line, mainly including:
(1) Under normal circumstances, the bonding machine is used as a host to perform single line speed control, and other units can adapt to synchronous acceleration or synchronous deceleration according to their process requirements.
(2) Automatically detect the stacking capacity of the corrugator machine and automatically adjust the production speed of the corresponding unit. When the accumulation amount exceeds the upper limit, the speed of the bonder and other related units is automatically increased. In emergency situations, emergency deceleration can be performed on the production line.
(3) According to the product specifications entered by the management personnel, the trimming machine and crosscutting knife lines are automatically adjusted at the beginning of the order execution and can be automatically adjusted during the production process.
(4) From the total number of sheets and the size of the order, the total number of meters required for production is automatically calculated. Each main machine station can produce the corresponding length of sheet paper due to its own actual unit distance.
At the same time, the monitoring software has two automatic and manual control modes. The staff can control the production line according to the situation in the manual mode.
4.3 Order Management Order management is implemented on the basis of production operation functions. Its main functions are:
(1) The management personnel can enter the order of the day on the office terminal, including the date of receipt, order number, customer type, paper quality, paper width, delivery date and other data. According to the paper quality, the paper width prints the order statistics for each month.
(2) According to the paper quality, delivery date and production line status required by the order, the monitoring program can automatically execute new orders. At the same time, the staff can manually make the system execute new orders according to the situation.
(3) Record the completion of the order in real time, and print the order production report on a regular basis according to the completion of the order.
At the same time, user rights are set in the database server, so the order data can be secured.
4.4 Shipment Management
Shipment management mainly orders that have been scheduled for production
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