Design of Control System for Gyratory Compactor

This article introduces the application of Panasonic FPO and Hitech touch screen technology in the control system of the rotary compactor, and gives the hardware structure and software design ideas of the system. Practice has proved that the system runs reliably and achieves good results.
Keywords : PLC touch screen rotary compactor

1 Introduction
Modern industrial control is constantly developing towards intelligence and automation. Various automated production lines and flexible manufacturing systems are constantly emerging, which greatly promotes the application of intelligent controllers such as PLC in system maintenance. At the same time, people's requirements for on-site operability and maintainability are also increasing. The touch screen has the advantages of simple operation, friendly interface, simple programming, good communication with PLC, and strong anti-interference ability. It can better meet these requirements of people, which makes touch screen technology more and more widely used in the industrial field.
The rotary compactor is a mechanical and electrical system used for processing asphalt standard samples for performance testing. Because the performance detection of asphalt standard samples is of great significance to highway construction, once asphalt with unqualified performance is used in highway construction, it will inevitably affect the construction quality of the highway and may even endanger driving safety. Therefore, the processing process of the standard sample for testing is very important. The rotary compactor integrates machinery, electricity, and instrumentation, and has high quality requirements for its processing standard samples, which also requires its electrical control system to have high automation and intelligence. This paper describes a PLC system controlled by communication with a touch screen.

2 System working principle and control requirements
Figure 1 is a simple schematic diagram of the mechanical structure of the rotary compactor. This system needs to realize two forms of motion, linear and rotation. A total of two motors are used (as shown in Figure 1). One is an AC motor driven by a DC servo to control the feed of the rod, realizing variable-speed linear motion: the other is a permanent magnet low-speed motor controlled by a turntable controlled by a frequency converter. The frequency converter has two speed outputs. The low-speed section realizes the eccentric angle correction of the turntable, and the high-speed section realizes the forward and reverse motion of the turntable. The entire system is controlled by electrical and mechanical systems, including elevation and speed measurement, pressure detection, speed measurement and other requirements. In addition, there must be travel limits and proximity switches to detect the mechanical state to ensure the safety of the system. The entire system completes parameter setting and display through the touch screen. 2.1 Working principle This system uses the principle of rotary shaking. The rod feed control motor drives the rod to move the pressure head downward at the rated speed, and decelerates before entering the drum to enter the drum. During the entire downward process, the pressure borne by the pressure head is continuously detected. When the pressure head reaches the asphalt standard sample and the pressure head reaches a certain pressure, the rod feed control motor decelerates according to the proportional relationship between pressure and speed. At the same time, the turntable rotation control motor drives the turntable to shake the asphalt standard sample, and compresses it into the required standard sample under the action of the pressure head. 2.2 Control requirements ① Elevation requirements: The downward distance of the rod is obtained by counting the speed measurement pulses of the rod feed control motor and then converting it according to the rod feed rate. Several operating stages of this system are related to the height. Inaccurate speed measurement and inaccurate height measurement will affect the safe operation of the system. Therefore, the speed measurement accuracy requirement is very high. ② Low speed and speed regulation requirements: When the pressure head compresses the asphalt standard sample, since the pressure head bears a certain pressure, the rod is generally in a low-speed operation stage. If the rod feed control motor runs too fast, the rod feed control motor torque is too large, and the pressure borne by the pressure head is too high, it will affect the safe operation of the system. Therefore, the low speed requirement is high. In addition, the feed control motor of the rod is required to automatically adjust the running speed when the pressure changes. During the automatic operation of the system, how to accurately count the speed pulses and how to accurately adjust the speed are the key to the control of this system. 3 Control system design 3.1 Control system functions (1) Realize the basic functions of the rotary compactor; (2) Realize the human-computer dialogue screen; (3) Realize the self-diagnosis function of the fault during the operation of the system and display it through the human-computer screen; (4) When a fault occurs, the system automatically stops and sounds an alarm at the same time; (5) Can print necessary information at any time. 3.2 Control system composition As shown in Figure 2, this system uses Panasonic FP0 series 14-point PLC, including 8 input points and 6 output points, and has an RS232C communication port and an RS422 programming port. The human-machine interface uses a PWSl711STN touch screen with an RS232/RS485 communication port. The human-machine interface communicates with the PLC through the RS232 port. The AC220 and DC24V power supplies required by the system are both supplied externally.

3.3 Control system software design
The system software design mainly consists of two parts, one is the screen design of the touch screen, and the other is the PLC software design.
(a) Human-machine interface software design The
human-machine interface is the key to the user setting process parameters and an important device for information display. The touch screen used in this system can support communication with multiple PLC languages. Its programming software ADP3 provides powerful macro instructions, which can greatly save the program capacity of the PLC during programming and optimize the control accuracy and efficiency of the PLC.
The human-machine interface mainly consists of two parts, one is the setting of system working parameters, including manual working mode and automatic working mode. The manual working mode is mainly used in the test phase of the rotary compactor, and the automatic working mode is used for the automatic operation of the rotary compactor. The automatic operation has two modes of speed and elevation control; the other part is the alarm function setting.
The entire human-machine interface includes the following screens: main screen (Figure 3), automatic mode screen (Figure 4), manual mode selection screen (Figure 5), and alarm screen (Figure 6).
The main screen (as shown in Figure 3) includes the maximum operating pressure setting, the minimum pressure setting for the pressure head, the maximum pressure setting before entering the barrel, the automatic mode selection, and the manual test mode selection.

The automatic mode screen is used in the automatic operation stage of the rotary compactor (as shown in Figure 4), including the operation status display, elevation setting, the forward and reverse rotation number setting of the turntable control motor, the current elevation display, the remaining number of revolutions display, and the current pressure display. In addition, there are two control mode options (speed control and elevation control) and a print button, where the print function is realized by editing the macro command in the human-machine interface.
The manual test screen (as shown in Figure 5) is used in the test stage of the rotary compactor, including six operation modes for two motors, in order to detect whether each motor can work normally.
The alarm screen (as shown in Figure 6) displays the possible fault information during the operation. There are four possible fault information: the pressure head is not aligned with the barrel, the pressure exceeds the maximum pressure, the elevation exceeds H1, and the elevation is lower than H4 (as shown in Figure 1).

(b) PLC software design
The PLC program is executed in a cyclic manner, starting from the main program, and then returning to the main program after execution. The program scan cycle is several milliseconds. The entire PLC program is completed using Boolean ladder diagrams on Panasonic's FPWIN platform. The PLC flow of the entire system's speed control mode is shown in Figure 8, and the elevation control mode process is similar.

During the on-site debugging of the PLC program, some problems were encountered. For example, the pressure value converted from the pressure sensor fluctuated greatly, which had a great impact on the stable operation of the system. Therefore, digital filtering was used in the program to eliminate the fluctuation of the pressure value and make the system run stably and safely. 4 Conclusion The combination of programmable controller and touch screen can be used in many industrial control fields. The application in the rotary compactor is just a typical example. The system has been used on-site, with reliable performance, precise control, friendly human-computer dialogue, and can fully meet the user's requirements. It can completely replace similar foreign products. 

References:

［１］Mi Hongtao. Principles and Applications of Programmable Logic Controller (PLC) [M]. Beijing: China Water Power Press, 1999
［２］Panasonic Electric Works Co., Ltd. FP0 programming manual [S]. Osaka, 2000
［３］Hitech Corp. Industrial Human-Machine Interface User Manual [S]. Taiwan, 2000