1. Project Overview
The Changan Automobile Factory originally could produce 6 types of cars, with an annual output of about 80,000 vehicles. His final assembly line was manufactured in the late 1980s with the introduction of American technology in the 1950s. Due to many defects in design and manufacturing, the system has many problems such as high failure rate and low production efficiency. In order to adapt to the impact of China’s entry into the WTO on the automobile industry and maintain the leading position of China’s mini-car production enterprises, Changan Company has continuously launched new models, and the manufacturing capacity of the production line has become a bottleneck for the development of the enterprise. Through our transformation of the final assembly line, the production efficiency has been greatly improved, the output has been increased to 200,000 vehicles per year, and we have the ability to mix various models, which can meet the production needs of continuously launching new models.
2. Determination of the renovation plan
The original production line control system of the assembly workshop adopts the Mitsubishi PLC system, the traditional control mode. All the signals distributed in the workshop are connected to the PLC cabinet by IO cables. The fault alarm information of the equipment is all displayed by BCD codes. The intervention of workers on the production line is limited to start, stop and emergency stop operations. According to the actual situation of on-site production, the control system has been unable to meet the production requirements:
1. It cannot provide accurate detection and judgment of faults. Time is of the essence for the assembly workshop, especially after the output reaches a certain scale. When a fault occurs, maintenance personnel need to find and solve the problem as quickly as possible. In the old system, workers must find the fault location according to the alarm code, and then analyze the cause based on experience. Especially when the PLC itself fails, more time is often wasted.
2. Maintenance is difficult. There are many signals in the assembly workshop, and the distribution area is very wide. The cable laying in the bridge is very crowded. In addition, the time is relatively long, and the line numbers are blurred. Maintenance workers need to replace cables, electrical components, etc. It takes a lot of work.
3. The factory resource management information system (MRPII) cannot provide fast and accurate production information. The logistics of parts and components in the workshop cannot be reasonably scheduled according to the actual production progress.
Siemens’ PROFIBUS fieldbus network technology provides a complete solution for this system. In the past decade or so, with the rapid growth of decentralized structures in production floor automation and process automation, the use of fieldbus systems has become increasingly common. One of the reasons for this is that the fieldbus system enables data transfer between digital and analog input/output modules, intelligent signaling devices and process regulators, and programmable logic controllers (PLCs) and PCs, dispersing I/O channels to The actual need of the field equipment is near, so that the cost of installation and wiring is reduced to a minimum, resulting in significant cost savings. The second reason is that the standardized fieldbus has an “open” communication interface, allowing users to select distributed I/O devices and field devices from different manufacturers.
The structure of the PROFIBUS field bus system is transparent and open. Only then will engineers be able to choose the best products from the large number of field devices and components available on the market to form their own systems. The field bus PROFIBUS fulfills the important requirement for data accessibility at the field level in the production process. On the one hand it covers the communication needs of the sensor/actuator field, and on the other hand it has all the network communication functions in the cell level field. Especially in the field of “distributed I/O”, because there are a large number of, complete, connectable field devices to choose from. At the same time, the bus system also provides a wealth of equipment diagnostic information, the operator can directly understand the robustness of the entire workshop system equipment through the monitoring computer, provides a straightforward auxiliary means for fault judgment, and greatly reduces the troubleshooting time.
Profibus makes use of existing national and international standards. Its protocol is based on the international ISO (International Standards Organization) standard OSI (Open Systems Interconnection) reference model. The ISO/OSI communication standard model is organized in 7 layers and is divided into two categories. One is user-facing layers 5 to 7, and the other is network-facing layers 1 to 4. Layers 1 through 4 describe the transfer of data from one place to another, while layers 5 through 7 provide users with appropriate ways to access network systems.
3. System structure
Based on the operation and management of similar systems at home and abroad and the actual experience in the industry, in accordance with the development trend of the international automatic control field, and in line with the principles of safety, reliability, simplicity and practicality, and advanced (not backward in ten years), we give full play to Siemens automation. The technical advantages of the product are based on the S7 control platform and the open field bus network ProfibusTM system, and the latest controller, drive, network architecture and industrial control software products are used to provide users with a computer, PLC, and field distributed I/O. It is composed of a multi-level, open, modular, real-time multi-task distributed and scalable data acquisition and control system.
The system adopts a hybrid three-layer architecture composed of integrated industrial fieldbus, control bus and 100/1000M high-speed Ethernet, and supports both browser-based B/S structure system and C/S structure system.
The input/output information of the entire assembly workshop is in various forms (including multimedia forms such as images, graphics, text, voice, numbers, etc.), with a large amount of information and high requirements for system functions. The task of control and monitoring is not limited to the detection and control of a single machine, but also realizes the monitoring, fault diagnosis, logistics optimization, production forecasting and scheduling of the entire workshop. The information processing mechanism with PLC and computer as the core completes the management of comprehensive information, the planning, scheduling, monitoring and automatic control of the production process. The system has the following three main functions:
1. On-site production data collection, analysis, processing, dynamic tracking, process control and other front-end production site detection and control;
2. Background information management such as vehicle model data, equipment failure information, and installation station management;
3. Workshop operation monitoring and planning dispatch command, internal telephone monitoring, LED and other multimedia systems.
In order to realize the integration of the above functions, key technologies such as multimedia technology, field bus technology, high-speed Ethernet technology, industrial control technology, communication technology and video image monitoring technology are widely used in the assembly workshop, which can be defined as high-speed Ethernet integrated with field industrial bus. Multimedia computer information management and control system. The architecture of the whole system is divided into three levels.[page]
(1) Information layer
The standard TCP/IP Ethernet structure is used for data exchange within the assembly workshop and other departments in the same plant area, and the Siemens fieldbus structure is used for the industrial control part. This design can distinguish the production information management network from the industrial control network, realize information diversion, and facilitate network settings according to the different requirements of information management and industrial control on network speed and transmission reliability. The reliability of data interaction can also ensure the real-time and accuracy of industrial control signal transmission. The users of monitoring workstation, management workstation, on-site information LED server, database and application software realize the transmission and sharing of information through TCP/IP communication protocol. The data in the database can only communicate with users and field devices through the server (except the monitoring computer). Users can obtain and interact with the production site information through the built-in IE browser in Windows, or directly exchange information with the data server, and then control the field equipment through the monitoring computer. Users do not directly participate in the control of field devices and databases, which not only ensures the security of data, the robustness of the underlying devices, and the transparency and friendliness of the human-computer interaction interface.
(2) Control layer
The on-site control station adopts the Siemens S7 platform as the control core and is distributed in each process section. The PLC master station and the central monitoring computer are connected through the Profibus-FMS network protocol to realize high-speed transmission of control signals. PLC automatically monitors the operating status of important equipment, and automatically controls the equipment, and can manually intervene to adjust process parameter changes. Profibus-FMS uses layers 1, 2 and 7. The application layer (layer 7) includes FMS (Fieldbus Message Specification) and LLI (Lower Layer Interface). FMS contains application protocols and provided communication services. The LLI establishes various types of communication relationships and provides the FMS with device-independent access to Layer 2. The FMS handles data communication at the unit level (PLC and PC). Powerful FMS services can be used in a wide range of applications and offer great flexibility for solving complex communication tasks.
(3) Device layer
We use Profibus_DP network to connect sensors and actuators distributed in the workshop, and directly use bus cables to connect frequency converters, field distributed I/O, process equipment with bus interfaces, etc., to realize digital and analog input/output signals, intelligent signals The digital transmission of data between the device and the process regulator and the programmable logic controller (PLC) disperses the I/O signal channels near the actual required field devices, minimizing the cost of installation and wiring, thereby reducing the cost of The cost is greatly saved, and the low-cost and high-efficiency information integration mode of the underlying equipment is realized. PROFIBUS-DP uses layer 1, layer 2 and user interface layer. Layers 3 to 7 are unused, this streamlined structure ensures high-speed data transfer. Direct Data Link Mapper (DDLM) provides access to Layer 2. The application functions of PROFIBUS-DP devices are specified in the user interface, as well as the behavior characteristics of various types of systems and devices. This PROFIBUS protocol optimized for high-speed transmission of user data is especially suitable for communication between programmable controllers and distributed I/O devices at the field level.
4. System Features
The system was successfully put into operation at one time, and has been running stably so far. It has passed the user’s acceptance and has been well received. The system closely combines the control of field equipment with production management through Profibus fieldbus technology, realizes the mechatronic integration of control, management and monitoring, improves the comprehensive automation level of the production line, and can be widely used in automobile and motorcycle industries. Production links such as final assembly and engine assembly.
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