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PLC based material packaging and conveying monitoring system


the working environment of the material packaging and conveying system is usually relatively bad. The environment in which the equipment is located is generally dusty, the relative humidity of the air is high, and the operation is scattered. Therefore, the requirements for the safety, reliability, and simplicity of maintenance of the conveying and packing control system are high. In the past, most electrical control systems used discrete relays, contactors and other electrical components as control components. Its control system was complex, difficult to operate, and the workload of installation and wiring was large, it was difficult to modify the control strategy, and the amount of maintenance was large, which seriously affected the normal production. Therefore, the material conveying control system has become a bottleneck restricting production. The control system composed of PLC and WinCC monitoring software with high reliability is used as the main equipment for data acquisition, control loop, automatic sequential operation and calculation. The belt process control of the packaging system and the real-time monitoring, automatic control and system operation diagnosis of the conveying process flow are realized, which meets the requirements of system reliability, stability and real-time

1 system introduction

the packaging and conveying control system is divided into two groups: bulk warehouse and packaging warehouse. Bulk warehouse is mainly used to store bulk materials that do not need packaging, and packaging warehouse is used for finished product packaging. It mainly includes: 1 # ~ 8 #, a line (9 #, 15 #, 16 #), B line (10 #, 19 #, 20 #), C line (11 #, 17 #), D line (12 #, 18 #), e line (13 #, 21 #), f line (14 #, 22 #). The process flow of each line is shown in Figure 1. In this process, in addition to the sequential start and stop of each belt and the problems of belt slip and deviation, the relevant supporting equipment must also be considered. The system mainly includes 67 digital inputs, 16 analog inputs and 52 digital outputs; The processes that need to be controlled include the startup, shutdown and safe operation of each belt, the selection of each chute and the handling of equipment failure

Figure 1 process flow

2 hardware design of PLC control system

2.1 hardware configuration

according to the equipment and process requirements, the packaging and conveying system is composed of an upper computer and a lower computer. The upper computer uses two PCs: one is used as an operation station to realize the monitoring and data detection of the whole system; The other is used as an engineer station to complete the design and development of configuration software, the development of PLC program and the transmission of software to the CPU unit of PLC through PROFIBUS bus. The lower computer adopts the programmable controller Siemens s series PLC with powerful function, high reliability, convenient maintenance and strong anti-interference ability to complete the control function of the equipment, and the lower computer is divided into two racks, which are placed in the packaging warehouse and bulk warehouse respectively. The s of the bulk warehouse rack and the packaging room rack constitute the PROFIBUS-DP network structure. The system hardware structure configuration is shown in Figure 2, and its specific composition is as follows:

Figure 2 system hardware structure configuration figure

(1) central control unit

central control unit selects cpudp as the core component of PLC to carry out logical and digital operations and coordinate the work of all parts of the whole control system

(2) power supply unit

the power supply unit uses 1:1 isolation transformer to supply power to the 220V AC switch input card of PLC, and uses Sitop power supply to supply power to the 24V switch output card of PLC. The built-in ps-307/5a DC power supply supplies power to the CPU and some cards that will produce some metal chips

(3) input and output unit

the system uses two 8-point analog input units ai8 × 12bit, two 32-point output units do32 × Dc24v/0.5a, a 16 point output unit DO16 × Dc24v/0.5a, five 16 point digital input unit di16 × AC120/230V。

(4) communication module

in order to ensure the normal communication between the packaging warehouse operation station and the bulk warehouse operation station (the distance is about 300 meters), CP communication module is selected in this system, which is configured and programmed through PROFIBUS

2.2 variable allocation

the PLC variable allocation of the control object is shown in Table 1

3 design idea of packaging and conveying control program

3.1 system control mode

the control mode of packaging and conveying control system is divided into automatic control, single machine control and on-site manual control. The single machine starting mode refers to that the start and stop buttons are set in the interlocking diagram of the upper computer, and the belt can start/stop independently when it does not enter the interlocking state

3.2 control program design

the belt conveying system has a total of 22 belts, which can be divided into two parts according to the belt conveying process: 1 # ~ 8 # line and a~f line

according to the operation of the packaging room, bulk warehouse control room and on-site belt, it is concluded that the PCU of the transportation 181 construction engineering large formwork system is more resistant to hydrolysis in vitro than other medical commercial PCU polymers:

(1) select the control mode: remote automatic control, on-site manual control or remote manual control

(2) control the operation of the packaging assembly line and bulk storage assembly line according to the packaging or not, and stop in the required order

(3) control the start and stop of line a~f according to the material level of the chute

the STEP7 user program in this system is divided into organization block (OB), function block (FC) and data block (DB). Function blocks are used to establish user programs according to control tasks. According to the process, the whole control process is divided into analog signal processing, a~f line start/stop, 3~8# line belt start/stop,

total material level calculation, analog quantity transformation, material level calculation of material trough, alarm processing, 1~6# belt speed processing, 1~2# belt start/stop, distributor selection and other program blocks. According to the specific situation of the technological process, it is programmed in the form of statement table (LAD). Figure 3 shows the flow chart of 3#~6# belt control. The data block is used to store the data of belt speed and chute level

3.3 control design idea

(1) the circuit starting sequence is from downstream to upstream (the incoming direction is upstream), and it is started one by one according to a certain delay. If there is no fault in the process of circuit starting, it is normal start; If there is a fault, it is an abnormal start. When the program starts and encounters a fault, it will not continue to start

(2) the loop stop sequence is from upstream to downstream, which includes normal stop and accident stop. Normal stop is sequential stop, that is, during normal operation, the program stops the equipment one by one from upstream to downstream according to a certain time delay. Accident stop means that when a device in the circuit fails during startup or normal operation, the upstream device stops immediately and the downstream device can operate

(3) in the logic ladder diagram, all interlocking circuits with branches have memory function. Because the previous equipment can start the equipment of each branch circuit below as needed, the memory function of circuit ladder logic can ensure that the equipment with fault circuit can stop correctly

(4) the upper function shows the running state of the whole belt. It can also display the equipment running in a single circuit

4 WinCC configuration software structure design

industrial control configuration software is a software that can collect data in real time from programmable controllers, various data acquisition cards and other devices, issue control commands and monitor whether the system operates normally. The configuration software can make full use of the powerful graphic function of windows, display the running state of the monitoring equipment in the form of animation, conveniently form the monitoring screen and realize the control function, and can generate reports, historical trends, etc., which provides a convenient software development platform for the development of industrial monitoring software and improves the quality of industrial control software as a whole. WINCC developed by Siemens is a configuration software running on Windows2000. Its function is to establish a dynamic display window. Through the provided toolbox, it is convenient to establish real-time curve, historical curve and alarm record display. In the picture window, the corresponding animation connection is established through the configuration settings of various graphic objects, and the industrial control process is reflected with a clear and vivid picture. According to the requirements of the packaging control system, figure 4 shows the structure of the monitoring software

wincc and S7-PLC are Siemens products, which are seamlessly integrated and have their own communication protocol connection. The control system and the upper computer configuration software realize the requirements of the material transportation measurement and control system. The process flow of the whole system is simulated concisely and vividly, and the operator can observe all the conveying conditions, including various alarms, on the computer screen in the control room. The operator who has obtained the permission can operate any belt individually or in a chain in the control room, and switch between manual and automatic operation

5 the main functions of the monitoring system

(1) display functions: process flow, measured value, equipment operation status, operation mode, alarm and other display, picture call and other functions

(2) alarm processing and report generation function: record the alarm occurrence time, fault content and other information, and manage the alarm information. The system reports include times, and monthly reports

(3) historical trend function: display the belt speed and the material level of the chute in a curve graph. The screen displayed by each trend curve mainly includes screen name, time, trend, etc

(4) the picture system modifies the material level parameters of the system to realize the automatic/manual switching of the system

(5) management authority: realize different levels of system management authority, and the system operator can select the operation mode, view the trend curve and report, etc; The system engineer can modify the monitoring software and the lower computer software

(6) operation control function: each belt can be operated according to the buttons on the interface, such as start and stop; Set and select the material level according to the process requirements

6 conclusion

the automatic control system of material transportation described in this paper has been in normal operation in the industrial site for one year. Since the whole material transfer process is controlled by a complete control system, the coordination and interlocking design between each sub process is strict. In addition, in the PLC control program and the upper man-machine interface, alarm information prompts are set for each parameter control variable, so that the operator can quickly find the fault point and deal with the fault in time. And each key operation command is provided with corresponding confirmation prompt to eliminate the possibility of misoperation. This control method improves the automation level of the existing system and reduces the labor intensity of workers. (end)

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