Design of automatic batching control system based on plc and multihead weigher

Author: Smartweigh–Multihead Weighter

1 Foreword In the field of Zhongshan Smart weigh manufacturing, seasoning is generally the mixing of raw materials in a certain proportion to produce a new raw material. Therefore, seasoning is a key component of manufacturing in this field. In the process of processing, various raw materials must be uniformly mixed in strict accordance with the proportion, and must be carried out by seasoning machinery. At this stage, processing plants generally use two methods. The first method uses manual weighing, and then will become The proportion of various raw materials is separately put into the batching machine and mixed. Another way is automatic weighing, fully automatic mixing.

Because many initial raw materials are powders or granules, when manpower seasoning, the body is very easy to inhale dust and other dirt, causing occupational hazards, increasing production risks and human capital costs. Therefore, manpower seasoning cannot be managed on the construction site, and it is very prone to mismatch, not only the quality cannot be guaranteed, but also the management cost is increased. In order to better ensure product quality and improve productivity, it is stipulated that accurate and reliable automatic batching system software should be selected. 2 According to the automatic batching system of PLC, industrial control computer and multihead weigher In the current automatic batching system of Zhongshan Smart weigh, the workers first transport the raw materials to the weighing workshop. After the weighing is finished, the raw materials are manually sent to the batching machine. To carry out seasoning, the weighing production workshop uses the multihead weigher of Hangzhou Sifang to carry out weighing. According to the RS232 port, it is connected to the industrial automation server. The industrial automation server located in the main control room is responsible for recording the weighing results and displaying the weighing data information. , In addition, the operator can manually control the start and stop of the whole process of seasoning in the main control room according to the control circuit.

This kind of method is not efficient. In addition, the DOS program process developed and designed in C language is running on the server [1], which has poor scalability and difficult human-computer interaction technology, and cannot carry out all the provisions for automatic batching. In order to better improve production efficiency and control costs, an automatic automatic batching system must be selected. The new system adopts the master-slave relational structure.

The industrial computer is used as the upper server, and the Siemens PLC PLC[2], soft starter and multihead weigher are used as the upper and lower slaves. The server is in the leading role, completes the communication management and operation of each slave, and connects the RS-232 asynchronous communication port of the industrial control computer with the PLC after the pulse signal conversion, creating a physical safety channel for the communication between the upper and lower computers; Connect another RS-232 port of the server to the communication port of the multihead weigher to form a second physical security channel. The upper computer software selects the polling method to communicate with the slave stations one by one.

The upper computer software transmits the results of the overall planning of the daily tasks to the PLC. During the whole process of PLC operation, the upper computer software uses the connection instructions of the upper computer software to monitor the operation of the lower computer and the content of the data information area, and loads the PLC data immediately. The real-time data of the internal situation and its multihead weigher are displayed on the host computer software. On the whole, the system software has the following functions: ① Fully automatic batching. After the secret recipe is set, the system software automatically weighs the ingredients according to the secret recipe without the intervention of the actual operating staff; ② It has the function of form, which can generate daily reports and real-time forms. and monthly reports, annual reports, etc.; ③Dynamic enhancement and modification of the table, the system software grants professional and technical personnel or actual operating staff to modify according to the set management authority, enhances the control of the secret recipe, and records the time and actual operation of the modification. Staff serial number; 4. Power-off repair function, the system software can repair the accurate measurement records before the power is turned off when the power is suddenly turned off; 5. Local area network sharing function, the server can share resource data information in the local area network, and the production workshop is responsible People keep track of construction progress and other conditions. 2.1 Composition of the system All automatic batching mixers are composed of industrial computer, PLC, industrial production multihead weigher, soft starter, vibration motor, mixer, sensor, conveyor belt, etc.

The upper industrial control computer displays the human-computer interaction technology page, and performs functions such as manipulation of information content input, database management, data information display information, storage, statistical analysis and forms. The upper computer software uses IPC810 industrial control computer. Its key tasks are as follows: The industrial automation server first loads the secret recipe of a certain serial number according to the order of the actual operating staff, and then, according to the proportion and order of the seasoning in the secret recipe, transmits the command to start the seasoning to the PLC, so that the PLC can start the special software. Launcher. In the whole process of seasoning, the industrial automation server uses the polling method to load the status word of the PLC in real time to master the operation of the PLC and its subordinate machines; The weighing data information, according to the seasoning strategy, when the weighing is close to the preset value in the secret recipe, the server sends a command to the PLC to terminate the seasoning. When all the raw materials on a secret recipe have been prepared, the whole process of all seasonings is suspended, waiting for the order of the actual operating staff.

During the whole process of the system software operation, the PLC communicates with the host computer software in real time to ensure the consistency between the data information displayed on the page and the specific data information on the spot. All can be sent to the PLC immediately. The key tasks of the PLC include: ①Accept the instructions pushed by the software of the upper computer, and control the start, stop and speed of the vibration motor according to the soft starter; ②Load the operation status of the soft starter into operation in real time The memory data information area is loaded by the industrial control computer; ③ Prepare various conditions of itself in the form of status words, and the industrial control computer can be loaded immediately. 2.2 The control method and the whole process of seasoning According to the analysis of the characteristics of the whole process of seasoning, it is obtained that the whole process of seasoning has the following characteristics: (1) The measured target is a unilateral irreversible system software. There is no way for the raw material to return to the conveyor belt again from the batching machine.

(2) It has a significant time lag. When the seasoning reaches the preset value, the PLC controls the motor to stop the transmission of raw materials. At this time, there are some raw materials on the conveyor belt that cannot be purchased, so the system software has a significant time lag. (3) The controllable feature is that the power supply is switchable.

The start and stop operations of the system software are all switching quantities. (4) The automatic batching system is linear in all normal working areas. Therefore, we take into account the use of control methods such as rapid, slow speed, and early transmission of the termination feeding command, and the use of PLC's self-locking and interlocking technology to ensure the smooth development of the seasoning.

After the system software is started, the industrial control computer transmits the data signal of the beginning of feeding to the PLC, and the PLC controls the soft starter to drive the motor to start feeding rapidly. In addition, the industrial automation server continuously loads the weighing data information of the multihead weigher according to the serial communication. When the net weight value is close to the preset value, the industrial automation server transmits the control code for terminating the feeding to the PLC. At this time, the PLC controls the soft starter to carry out slow feeding, and the preset value and specific feeding may be determined according to the residual raw materials on the transmission organization in advance. When the error and the residual raw material on the transmission structure are abnormal, the PLC actually sends out a termination command, which is executed by the soft starter, and then controls the motor to shut down. The steps are shown in Figure 1. Automatic batching system software 3 Industrial automation server software development The key daily tasks of the industrial control computer are as follows: (1) Show the animation display information of the whole process of seasoning.

(2) Send out the control code to the PLC and load the operation of the PLC. (3) Load the weighing data signal on the multihead weigher, display the weighing value on the display screen, and push the command to the PLC according to the weighing data information. (4) Database query and form, store seasoning data information, copy form.

(5) The improvement and modification of the secret recipe. (6) Other functions such as auxiliary alarm for common faults in seasoning. 3.1 The page design of the seasoning mobile phone software The industrial control computer application Longchuanqiao configuration design scheme industrial touch screen, the industrial control system configuration is actually a development software service platform that can be developed by customers according to their own needs.

We can develop and design a friendly industrial touch screen for all video surveillance systems on the service platform according to the processing technology regulations, and the operator can interact with the on-site machinery and equipment in real time according to this page. Longchuanqiao mobile phone software is an HMI/SCADA industrial control automation configuration, which provides a development tool with integrated aspect ratio and data visualization. This software has the following characteristics: (1) Various communication functions.

The Longchuan Bridge configuration [3] is suitable for the following communication functions: 1) It is suitable for serial communication methods such as RS232, RS422, and RS485, as well as methods such as repeater, telephone dialing, telephone polling and dialing. 2) Ethernet interface communication is also applicable to cable TV Ethernet interface and wireless network Ethernet interface. 3) The driver software of all machines and equipment are applicable to GPRS, CDMA, GSM and other mobile Internet specifications.

(2) Convenient development and design system software. A variety of components and controls form a powerful HMI development and design system software; the improved connection color and asymptotic color effects solve the problem from the source that many similar mobile phone software use too many connection colors and asymptotic colors, which is a serious threat to interface update The problem of high speed and high efficiency of system software operation; more forms of vector material sub-graphs make it more convenient to make engineering project interface; show object-oriented thinking method, embedded indirect independent variables, intermediate variables, database query independent variables, Applicable to custom functions and custom orders. (3) Open.

The openness of Longchuan Bridge configuration is mainly manifested in the following aspects: 1) Use Excel to browse the database query with VBA. 2) The mobile phone software is an open system architecture, which is fully applicable to DDE, OPC, ODBC/SQL, AcTIveX, and DNA specifications. It provides external browsing sockets in various forms such as OLE, COM/DCOM, dynamic link library, etc., which is convenient for customers to use various common development environments (such as VC++, VB, etc.) to carry out in-depth secondary development.

3) The system architecture of Longchuan Bridge configuration I/O driver software is an open structure, and part of the source code of its sockets is completely published, and customers can develop driver software independently. (4) Database query function. The Longchuan Bridge configuration is embedded with a time series database, and a variety of functional blocks are embedded in the time series database for data processing methods and storage, which can complete summarization, statistical analysis, manipulation, and linearization. etc. various functions. (5) Applicable to a variety of machines and equipment and system buses.

It is suitable for PLC, controller, multi-function instrument, mobile intelligent terminal and intelligent control module produced by most famous manufacturers all over the world; in addition, it is also suitable for standard computer interfaces such as Profibus, Can, LonWorks and Modbus. 3.2 The I/O level of the system Longchuan Bridge configuration uses time series database points to indicate I/O points. After analysis, the system software must have three I/O points, and two data reference points are used to control the start and stop of the motor according to the PLC. Therefore, the data information connection of these two points is selected as two data volume I/Os of the PLC. Exit.

A simulation point is used to represent real-time data loaded from the multihead weigher, so the data information at that point is connected to the exact measurement of the multihead weigher. 4 Communication programming design The communication programming design includes three parts, the first part is the communication between the server and the PLC; the second part is the communication between the server and the multihead weigher; the third part is the communication between the PLC and the soft starter. 4.1 The communication configuration between the server and the PLC is generally embedded with the popular PLC driver software. First, a new PLC virtual machine is created in the Longchuan Bridge configuration. The model and specification of the virtual machine must be consistent with the actual application. The PLC models and specifications are the same. If the required PLC model specifications cannot be found in the configuration, the mobile phone software manufacturer can be authorized to develop and design a new PLC driver of this type and specifications completely free of charge.

The virtual machine is used to project the real machine. Here, the PLC used by everyone is SimensS7-300, and the server is set to communicate with the PLC according to serial communication 1. 4.2 Communication between the server and the multihead weigher For the multihead weigher, we use the multihead weigher from Hangzhou Sifang. In order to make the communication between the instrument panel and the configuration very good, we especially authorized Longchuanqiao Enterprise to develop the instrument panel. The driver software is designed. First of all, we select a necessary type of machine equipment from the configured drive directory, and for this type, create a virtual machine equipment for projecting the real multihead weigher, and then set the communication port number between the dashboard and the computer and communication protocols.

4.3 Communication between PLC and soft starter Because there are a variety of raw materials in the seasoning production workshop, we have set up several conveyor belts for better seasoning convenience. Therefore, one PLC of the automatic batching system must be connected to several soft starters. Therefore, we use the Profibus system bus between the PLC and the soft starter to carry out communication, insert the special Profibus communication control module into the soft starter, and set the detailed address of the slave station of the soft starter, and then connect according to the Profibus radio frequency. The controller is connected to the PLC, and the PLC completes the push and reception of the message format to the soft starter according to the programming, sends the operation word to the soft starter, and loads the status word from the soft starter home. CPU315-3DP is used as a Profibus domain name, and each soft starter that communicates with the domain name can be regarded as a Profibus slave station.

During communication, the domain name selects the slave station to transmit data according to the detailed address identifier in the communication message format. The slave station itself cannot actively transmit data, and each slave station cannot immediately carry out the transmission of information content. The soft starter models and specifications used in the system software are all Siemens MicroMaster430 series products [4].

The key communication key between PLC and soft starter involves two definitions. The first is the data message format, and the second is the manipulation word and the status word. (1) Communication message format.

The format of each message starts with the identifier STX, then the length indicates LGE and the number of bytes of the detailed address ADR, followed by the selected data information identifier. The message format ends with the detector BCC of the data information block. The key Field names are expressed as follows: The STX field is a one-byte ASCII identifier (02hex) that indicates the beginning of a message content. The LGE area is a byte, indicating the number of bytes followed by the content of this piece of information. The ADR area is one byte, which is the detailed address of the station node (ie, the soft starter).

The BCC area is a checksum with a length of one byte, which is used to check whether the content of the information is reasonable. It is the total number of bytes before the BCC in the message content“XOR”the result of the calculation. If the information content received by the soft starter is invalid according to the calculation result of the checksum, it will discard the information content, and will not send a reply data signal to the domain name.

(2) Manipulation word and status word. The PLC can read and write the variable value of the soft starter according to the PKW area of ​​the soft starter, and then change or master the running state of the soft starter. In this system software, the PLC reads the data information in this area and puts it in a special data information area for the industrial control computer to view, and the viewing result displays the information on the industrial control computer.

5 Results The system software completed the required automatic batching daily tasks according to the mutual cooperation of the industrial control computer, PLC and soft starter. The system software has been delivered and used since May 2008. The daily batching weight is 100 tons, and 10 secret recipes are carried out. Up and down, it can not only display the working status of information in real time, but also show the functions of secret recipe changes and upgrades; the specific operation instructions, the system software operates smoothly and reliably, the industrial touch screen is beautiful and elegant, and the actual operation is convenient. In addition, the system software adopts the configuration development design, It can provide convenience for subsequent upgrades.

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