1 Introduction There are a total of more than 20 stations on the assembly line, including 7 ordinary turntables, 2 maintenance turntables, 4 rollerless lifting platforms, 7 unidirectional roller lifting platforms and 2 turning machines. The entire controlled object includes 22 stations, each station contains the necessary transfer motors or lifting motors, in addition to 32 production line transmission motors. Each station consists of an ET200S and an ET200eco slave station, which is used for the I/O point data acquisition and transmission and distributed control of the station. 2 System structure and function The system includes several parts such as operator station, engineer station, automation system, network and field I/O station. The functions of each part of the system: Operator station: Provides a full-Chinese man-machine interface to realize the monitoring and operation functions of the control system (operation, display, report, alarm, trend), and you can directly view the corresponding step7 source program on the man-machine interface. Engineer station: used for system configuration and maintenance. Automation system: Use SIMATIC controller to complete loop adjustment and logic operation. Field I/O station: Use fieldbus technology to directly collect field instrument signals at the equipment site and control the actuators on site. Fieldbus ProfiBus: used to connect the control unit and the operator station and management network. This system uses PLC300CPU to connect with CP342-5 and CP343-1 interface modules to form the main station of the system. CP342-5 is a master/slave interface module used to connect S7-300 and profibus-DP, and CP 343-1 is an interface module used to connect S7-300 and industrial Ethernet. In this control system, in addition to the above-mentioned master station, the slave station is composed of 22 ET200S and 22 ET200eco, which are respectively distributed on two profibus networks. The profibus-DP interface that comes with the CPU forms the profibus I line, and the CP 342-5 interface module forms the profibus II line. There are two types of IM151-1 interface modules used on ET200S slave stations in the system: basic type and standard type. The number of power management modules and I/O modules that can be connected to the basic type interface module ranges from 2 to 12, The standard interface module ranges from 2 to 63. Therefore, when there are many slave I/O modules, standard interface modules should be used. The interface module is equipped with a profibus address setting dial switch. In the system, the ET200eco slave station selects 8DI and 16DI modules. The module has a compact structure. The power supply of the module uses a 7/8' power cord, and the communication of the module uses M12 communication connectors. The wiring is flexible and fast, easy to plug and unplug. The interface module has two rotary coding switches for profibus address assignment. Network equipment considers the selection of different protection levels according to the degree of adapting to the industrial site environment and the layout of the production line. The module in the control box adopts the ET200S I/O module with protection level 20. Corresponding to each control box, there is also an ET200eco module with protection level 67, which is placed under the rollers of the production line, because the module needs to be exposed to the harsher on-site The production environment therefore needs to have functions such as waterproof, oil and dustproof. 3 Target control system 3.1 System design The automobile engine assembly line is an assembly line process of sequential assembly of engines. Due to the cumbersomeness of the process, the computer control system of the project considers the use of distributed control and centralized management of distributed control mode, and adopts a computer control system composed of PLC as the core. Each independent station control system realizes data information and resources through the network. shared. The assembly line is critical in the entire production process. Since each station is an assembly line, the control of each link must have high reliability and a certain sensitivity to ensure the continuity and stability of production. Each ET200S station in the slave station and its corresponding ET200eco station together constitute a station. ET200eco is mainly used for collecting field data. The module of the ET200S station is placed in a small control box, and there are two methods for the basic operation of the station, the manual mode of the local control box and the local automatic mode. Because the operation progress of each control station is inconsistent, the operator can switch automatically according to the assembly requirements. Under special circumstances, the workpiece position can also be corrected by manual operation. The distributed I/O modules ET200S and ET200eco installed in each station collect the main monitoring parameters of the system (mainly switching values) through field detection elements and sensors. ET200S and ET200eco convert field analog signals into high-precision data Through the Profibus-DP field bus network with the highest speed up to 12M, the collected data is uploaded to the central controller. The controller processes the data according to the specific process requirements, and then transmits the control output to the ET200S through the Profibus-DP network to realize each process. Bit control flow. PROFIBUS is the most widely used process fieldbus system in the world. There are three types of PROFIBUS: FMS, DP and PA. PROFIBUS-FMS can be used for general automation; PROFIBUS-DP is used for manufacturing automation; PROFIBUS-PA is used for process automation. Using PROFIBUS process fieldbus technology can save more than 40% of hardware, engineering design, installation, debugging and maintenance costs. The technical performance of PROFIBUS-DP makes it applicable to all fields of industrial automation, including metallurgy, chemical industry, environmental protection, light industry, pharmaceutical and other fields. In addition to simple installation, it has a very high transmission rate of up to 12Mbits/s, and a communication distance of up to 1000 meters. If a repeater is added, the communication distance can be extended to tens of kilometers. It has a variety of network topologies (bus type , Star type, ring type) to choose from. A maximum of 32 Profibus-DP slave stations, namely ET200S or ET200eco, can be connected on a network segment.
