1. Introduction
Programmable logic controller (PLC) plays an important role in factory automation (FA). The continuous development of technology has greatly promoted the improvement of control function and control level of the control system based on PLC.
At the same time, the requirements of its control mode and operation level are higher and higher, so the requirements of interactive operation interface, alarm recording and printing have become important contents of the whole control system.
For those industrial control systems with complex process and more control parameters, it is particularly important. The emergence of a new generation of industrial HMI (human machine interface) provides a simple and feasible way to realize the above functions in the construction of PLC based industrial control system.
Figure 1: PLC based industrial control system
2. Features and Functions of Industrial HMI
Human machine interface (HMI), also known as touch screen monitor, is an intelligent operation control display device. The industrial man-machine interface consists of a specially designed 32-bit RISC CPU chip, and a transparent resistive network touch screen on the STN, TFT LCD or EL display. When you touch the screen, the resistance and voltage on the resistance network change, and the touch position is calculated by the software.
The functions of HMI include: data input and display; real-time information display of system or equipment operation status; setting touch control on HMI to control HMI as operation panel; alarm processing and printing. In addition, new generation of industrial HMI also has the functions of simple programming, data processing, data login and formula intelligent control.
Figure 2: ABB HMI CP430B
3. Application of HMI in PLC Based Industrial Control System
We will taking the main control system of cold end cutting area of a large domestic float glass production line as an example, this paper introduces the application of HMI in PLC based industrial control system.
3.1 System
The cutting area is an important section in the float glass production line, which includes many production control equipment, such as measuring and signaling, longitudinal cutting, transverse cutting, breaking acceleration, breaking edge, longitudinal breaking and vertical dividing, conveying roller table, etc.
The hardware of the system is basically composed of controller PLC, field equipment control device (including servo controller, frequency converter, analog signal and pulse signal processor, etc. ) and HMI. As the core of the whole control system, the main control system of the cutting area coordinates the work of each single machine control subsystem according to the production process requirements during normal production, formulates the cutting plan, and realizes the full automation of the whole production process.
The core control part of the whole system is completed by GE Fanuc 90-30 PLC, and the monitoring and interactive operation interface of the system will be undertaken by HMI. The main contents are as follows: parameter setting; dynamic screen display; fault alarm and diagnosis and report printing. Among them, the HMI is GP-577 of Japanese digital company.
Figure 3: PLC control cabinet
3.2 Communication Between HMI and PLC
When HMI is used in PLC control system, the communication between HMI and PLC is realized by direct link through serial port. In this mode, HMI can directly read the data of PLC or write the data into the corresponding address of PLC according to the requirements.
Because PLC is equipped with communication protocol, there is no need to compile communication program. As long as the type of PLC is specified, that is, communication protocol, communication can be realized during operation. Therefore, this greatly reduces the burden of PLC user program.
In the system design, the HMI can automatically exchange data with PLC when the control unit and its corresponding PLC's I / O, register and control are specified directly. Directly read or rewrite the content of PLC corresponding address, and change the display content on the screen accordingly. At the same time, through the touch operation of HMI, data can be input to the corresponding address of PLC.
3.3 HMI Monitoring of the Main Screen
The whole HMI monitoring system adopts tree structure, which is composed of main monitoring screen and corresponding function sub screen. A control function key is set at the lower end of the main monitoring screen. Pressing the function key can enter the corresponding sub screen in turn to perform the required functions.
In each sub screen, the screen can be switched in the same functional group through the "previous page" and "next page" function keys. In any sub screen, the screen can be returned to the main monitoring screen through the "main screen" function key.
The system automatically collects relevant data, and displays some important production process parameters such as cutting plan, measuring pulse and roller speed on the main screen, which is convenient for operators to observe. There is also a dynamic display of the production process on the main monitoring screen.
On the dynamic screen, the operation of the main control equipment is simulated in various forms, such as the action of the photoelectric switch, the closing of the solenoid valve, the stop of the motor, which intuitively and vividly reflects the process on site, and facilitates the operators to understand the production situation and the working conditions of the equipment.
Digital HMI programming software ProPB3Win provides a wealth of control components, including button components, screen switching components, indicator components, data text display components, in order to achieve the above functions, as long as the corresponding control components are selected according to the needs and their properties are defined.
ProPB3Win adopts the general mode of monitoring software, and the attributes of all control components are completed by configuration to realize the corresponding control functions. It is easy to construct the simulation picture of the production site by using the library and drawing tools of ProPB3Win. The rich drawing tool library makes the picture vivid and colorful.
In addition, you should make full use of the advantages of HMI to replace the switches and indicator lights originally arranged on the control cabinet with the control components in HMI as far as possible, so as to reduce the hardware equipment, simplify the wiring between field equipment, and more importantly, bring a lot of convenience to the design and debugging.
Figure 4: Pro-face Remote HMI Client for Windows allows users to view monitoring status on desktop computers.
3.4 HMI Parameter Setting Function
There are nearly 100 parameters to be set in the main control system. According to the control function, it is divided into interlocking, cross cutting, cross breaking, speed, edge breaking, vertical breaking and equipment parameter groups to make the structure of the whole system more reasonable.
At the same time, the HMI touch operation makes the parameter setting very intuitive and simple. When setting parameters, the numeric keyboard is designed as pop-up type by using its internal numeric keyboard. When the operator wants to set parameters, press the "set" key to pop up the numeric keyboard for operation.
Each parameter is defined and assigned the corresponding PLC address in the part attribute.
After confirmation, the input data will be stored in the address specified by PLC. After the operation, press the "—" key to cancel the numeric keyboard. This design mode can maximize the effective area of the screen.
Meanwhile, each parameter is set with upper and lower limits. When the input value exceeds the limit, the system will refuse to accept it and send an alarm to the operator. In addition, for the important parameter group of system equipment, for the sake of security, we write a simple program setting screen through the "D-script" statement in the tool library to enter the operation password, give the operator different operation permissions, and increase the security of the system.
3.5 HMI Alarm and Printing Function
In the system alarm design, the fault information is edited in the alarm editor, and the alarm record display unit is set in the alarm record sub screen for fault information display.
When the system fails, HMI will display the corresponding fault information in the alarm editor in the alarm record sub screen according to the fault signal transmitted by PLC.
At the same time, on the main monitoring screen, the fault signal lamp will flash and the sound alarm will be given. At this time, the operator can enter the alarm record sub screen, find the cause according to the fault information, and deal with it in time.
The printer interface of HMI supports standard printer and can realize data printing. Set the printer control word in HM data area to 1 to activate the printer. The system has the printing function in the sub screen of cutting plan, which can print the cutting plan report in time for the use of production management personnel.
Figure 5: Siemens HMI 6AV2 123-2GA03-0AX0
4. Summary
After the PLC based industrial control system is put into use, it is welcomed by users. The system is safe, intuitive and simple. The realization of monitoring, fault diagnosis and printing in PLC based industrial control system greatly improves the reliability of production operation. Practice has proved that HMI has a wide application prospect in PLC control system, and will play a more and more important role in factory automation.
