Design and implementation of monitoring system for

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Design and implementation of monitoring system for pinch roll of bilateral shear

1 introduction

the bilateral shear unit is one of the key equipment in the finishing workshop of the rolling mill, which is mainly responsible for shearing the formed steel plate to make it the final product. From the control point of view, the whole bilateral shear unit can be divided into six subsystems: main shear system, pinch roll and roller table control system, traverse system, gap adjustment system, laser marking system, steel plate alignment system, etc., which have adverse effects and reduce the effectiveness. In order to prevent the steel plate from running off during the shearing process and ensure the shearing size and feeding step of the steel plate, it is very important to control the synchronization of the 8 pinch rolls of the bilateral shear. In the reconstruction project of the control system of the double side shear set in a rolling mill, a distributed full digital double side shear pinch roll drive control scheme based on PROFIBUS bus is adopted to replace the traditional analog control system

in order to carry out real-time monitoring on the operation status of the modified double-sided shear pinch roll drive control system and facilitate the quantitative management of the unit, Siemens configuration software WinCC is used as the development platform of the upper computer monitoring system to develop the unit's status monitoring and data management system. WINCC is an excellent industrial control configuration software. Especially after the launch of WinCC V6.0, great improvements have been made in the software architecture, network structure and database management, making its functions more perfect, the system more open and the configuration more flexible [1]. However, because the variable archiving cycle of WinCC is too long (the shortest is 500ms), it can not meet the requirements of high-speed data acquisition. In order to break through the configuration bottleneck of WinCC and make full use of the openness of WinCC, C script is used to compile the global action of high-speed data acquisition, which is used to package, receive and process multiple data, and visual c++ is used to develop ActiveX control for the display of high-speed data curve

2 overall structure of the monitoring system

the overall structure of the Profibus based distributed full digital bilateral shear pinch roll drive control system is shown in Figure 1. From top to bottom, it can be divided into three levels: monitoring level, control level and field level

Figure 1 overall structure of the pinch roll control system of the bilateral shear

2.1 monitoring level

the monitoring level is only composed of an Advantech IPC610 industrial computer. As a PROFIBUS-DP class 2 master station, the industrial control computer is configured with a communication processor cp5613 to realize the communication with the control level through the Profibus DP standard protocol. The monitoring level does not directly participate in the control of the production process, but develops the monitoring software through WinCC to realize the following functions: development of the process monitoring picture, collection and display of the speed and current data of 8 DC motors, display and setting of the main parameters of the control system, system fault monitoring, monitoring of the operation status of the bilateral shear unit, etc

2.2 control level

the control level uses a S7 PLC DP as the control master station, which is the core of the whole pinch roll drive control system. Use STEP7 software to carry out the hardware configuration of the whole control level and the preparation and debugging of the control program, mainly to complete the following functions:

(1) control the operation of each pinch roll according to the process requirements of the bilateral shear unit. In order to ensure that the steel plate does not deviate during the shearing process, it is necessary to ensure that the 8 pinch rolls are controlled synchronously. Therefore, a variety of "master-slave control" modes are set [2]

(2) complete the information exchange with the main shear control PLC. S PLC receives the signals of pinch roll start, stop and pressing plate down from the main shear control PLC. Feed back to PLC driver ready, driver fault, motor fan ready, motor fan fault and other signals of main shear control

(3) collect field data for the monitoring level and receive control instructions from the monitoring level

2.3 field level

field level consists of 8 sets of DC motor control cabinets. Each control cabinet is equipped with a 6RA70 full digital DC speed regulating device and an intelligent distributed slave station et200m. 6RA70 is used to control the speed and torque of the DC motor driving the pinch roll, and the switching value of the control cabinet and the panel operation and display device are controlled through et200m. 6RA70 and et200m intelligent slave stations are respectively connected to PROFIBUS-DP bus through cbp2 communication module and im153 interface module to realize communication with control level PLC

3 monitoring data acquisition scheme

3.1 WinCC communication principle

wincc uses variable manager to centrally manage variables. The task of the variable manager is to take the requested variable value from the control system (such as PLC). This process is completed through the communication driver integrated in the WinCC project. The communication driver uses its channel unit to form the interface between WinCC and process processing. The hardware based connection between the variable manager and the control system is realized by using the communication processor (such as cp5613). The WinCC driver uses the communication processor to send a request message to the PLC, and then the communication processor sends the process value of the PLC answering the message request back to the WinCC variable manager. The data exchange between WinCC and PLC is the basis of the monitoring system. Therefore, before using WinCC to develop the monitoring system, the variable configuration must be carried out to determine the data acquisition scheme

3.2 configuration of conventional process variables

first, add SIMATIC S7 protocol suite driver in the variable manager to establish a connection with S7 PLC under the Profibus channel unit. For conventional process variables, such as the fault information of the control system, the operating status of each motor and the working condition of the unit, as the update cycle is relatively long (usually not less than 500ms), as long as the data type, variable address and other conventional configurations are carried out, the variable Manager automatically completes the processing of these variables, and can also fully 2 PCI bus standard uses WinCC's powerful process value archiving function to archive

3.3 high speed collection of current and speed data

during the debugging and fault analysis of the pinch roll control system of the bilateral shear, the current and speed curves of the pinch roll drive motors are very important. Therefore, it is required to be able to monitor the current and speed curves of 8 motors in real time in the upper computer monitoring system. In order to obtain a relatively smooth current and speed curve, it is necessary to collect current and speed data at least every 20ms. However, the shortest variable update cycle of WinCC is 250ms and the shortest filing cycle is 500ms. Obviously, the conventional process variable configuration function cannot meet the requirements of high-speed current and speed acquisition

in order to meet the needs of collecting rapidly changing process values or combining multiple measurement points of a device, WinCC provides message frame variables. In the automation system, multiple process values can be written into continuous data blocks and sent to WinCC in the form of message frames, which are stored in the original data variables of WinCC. The format and length of the original data variables are not fixed. Only the sender and receiver can interpret their contents, and WinCC cannot interpret them

using the above method, configure an original data variable for the current and speed of each motor on WinCC, with a variable length of 52 bytes. The first 50 bytes successively store 25 process variable values (each current and speed value accounts for two bytes), and the last two bytes store a flag variable to indicate the storage location of the latest sampling value in the structure. Then use the cycle interrupt organization block ob35 in the PLC, set the cycle cycle to 20ms, and allocate the corresponding data buffer for each original data variable configured by WinCC (the storage structure is the same as the original data variable structure in WinCC, but there is also a ring stiffness tester for cement pipes, which is mainly used to detect other mechanical properties). After each interruption, the PLC collects a current and speed value from each 6RA70 and writes it into the corresponding data buffer according to the time sequence. In order to distinguish the timing of each written sample value, it is necessary to save the latest written sample value to the last two bytes in the data buffer. In this way, raw data variables are collected every 500ms on WinCC, and each raw data variable contains 25 process values, thus indirectly obtaining a 20ms data acquisition cycle

wincc cannot directly process the original data variables, but it can write a global action for processing the original data variables through the C script provided by WinCC. In this global action, call the WinCC internal function gettagraw() to update the original data variables, unpack the message frame contents, and finally save the decomposed current and speed sampling values to the relevant data files in a specific format, To facilitate the query of historical data, each packet is stamped with the system time stamp. The program flow of the whole global action is shown in Figure 2

Figure 2 flow chart of global action of high-speed data acquisition

4 development of monitoring software

the monitoring software at the monitoring level is mainly secondary developed by using Siemens' configuration software WinCC6.0. At the same time, visual c++6.0 is used to develop ActiveX controls specially used to display motor current and speed curves and embedded into the monitoring system

4.1 function analysis and configuration of monitoring software

the whole monitoring software is designed according to the specific functional requirements of the factory site. According to the characteristics of the configuration software, all functions of the monitoring system are reflected in a separate graphic screen. According to the main functions of the monitoring system, the following basic screens are configured:

(1) main screen: This screen is automatically displayed after the WinCC project is running. The upper part of the main screen is the name of the monitoring system, factory logo, date and time and other information, the lower part is the function switch button, and the middle part is the sub screen display area

(2) shear process sub screen: This screen dynamically simulates the shear process of the bilateral shear, and can accurately and vividly reflect the start and stop, positive and negative rotation of the pinch roll, the pressing and lifting of the upper roll, the plate feeding process and the pressing plate pressing. Animation is realized by writing code in C script to modify the attributes of each graphic component in the background

(3) virtual console sub screen: This screen gathers the main operating mechanisms (such as buttons, transfer switches, etc.) and display elements (such as indicator lights) on the console and the panels of 8 sets of motor control cabinets to form a virtual console. Through this screen, you can intuitively and comprehensively understand the operation status of the unit, and realize the same operation function as the actual console as required

(4) fault detection and alarm sub screen: This screen displays and manages the fault and alarm information of the unit in a centralized manner, which will be displayed after 1 hour by calling the built-in alarm control of WinCC

(5) process parameter setting sub screen: This screen is used to set important process parameters such as cutting step size and cutting speed

(6) sub screen of account and report: This screen counts the important operation data of the unit, such as normal operation time, fault time, downtime, etc., and displays various reports of the printer group in the form of histograms and tables

(7) current and speed curve sub screen: a self-developed current and speed curve control is embedded in this screen to display the current and speed curves of 8 sets of pinch roll DC motors in real time

4.2 design of current and speed curve control [3]

since the data of motor current and speed are not archived through WinCC, but stored in a user-defined data file, the curve display control of WinCC cannot be used for display. It is necessary to develop an ActiveX control to realize the graphic display function of motor current and speed data. ActiveX is a trade name for the COM based visual control structure. It is an encapsulation technology that provides a way to encapsulate COM components and put them into applications. Visual c++ provides a variety of methods to develop ActiveX controls, but relatively speaking, MFC ActiveX controlwizard Wizard

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