Design of the Rotary Compaction Tester Control System

　　This paper introduces the application of Panasonic FPO and Hitech touch-screen technology in the control system of a rotary compactor, and presents the system’s hardware architecture and software design concepts. Practical experience has demonstrated that this system operates reliably and achieves excellent results.

　　Keywords: PLC, touch screen, rotary compactor

　　1 Introduction

　　Modern industrial control is continuously evolving toward intelligence and automation, with various automated production lines and flexible manufacturing systems emerging one after another, greatly boosting the application of intelligent controllers such as PLCs in system maintenance. At the same time, people’s demands for on-site operability and maintainability are steadily increasing. Touch screens offer advantages such as simple operation, user-friendly interfaces, straightforward programming, excellent communication with PLCs, and strong anti-interference capabilities, effectively meeting these growing requirements. As a result, touch-screen technology is finding increasingly widespread applications in the industrial sector.

　　The rotary compactor is a mechanical and electrical system used for preparing asphalt reference samples for performance testing. Since the performance evaluation of asphalt reference samples is of great significance to highway construction, asphalt that fails to meet the required performance standards, once used in expressway construction, will inevitably compromise the quality of the road and could even pose a threat to driving safety. Therefore, the processing procedure for preparing these reference samples is critically important. This rotary compactor integrates mechanical, electrical, and instrumentation components into a single unit; given its high-quality requirements for the prepared reference samples, its electrical control system must exhibit advanced levels of automation and intelligence. This article describes a PLC system controlled via communication with a touch screen.

　　2 Operating Principle and Control Requirements of the System

　　Figure 1 is a simplified schematic diagram of the rotary compactor’s mechanical structure. This system is designed to achieve two types of motion—linear and rotational—and employs two motors in total (as shown in Figure 1). One is an AC motor driven by a DC servo controller, used for controlling the feed rod and enabling variable-speed linear motion. The other is a permanent-magnet, low-speed motor driven by a frequency converter that regulates its speed. The frequency converter provides two speed levels: the low-speed setting is used to correct the eccentric angle of the turntable, while the high-speed setting enables both forward and reverse rotation of the turntable. The entire system is controlled through coordinated operation of electrical and mechanical components, including requirements for measuring rotational speed, detecting pressure, and monitoring velocity. Additionally, limit switches and proximity sensors are incorporated to monitor the mechanical status and ensure system safety. All parameter settings and system displays are managed via a touch screen.

　　2.1 Working Principle

　　This system operates on the principle of rotational mixing: the rod-feed control motor drives the rod to move in a rotating motion, causing the punch head to descend at a rated speed. Before entering the drum, the punch head slows down and enters the drum gradually. Throughout the entire downward movement, the system continuously monitors the pressure exerted on the punch head. Once the punch head comes into contact with the asphalt standard sample and reaches a predetermined pressure level, the rod-feed control motor adjusts its speed according to the proportional relationship between pressure and velocity. Simultaneously, the turntable rotation control motor rotates the turntable, thoroughly mixing the asphalt standard sample. Under the action of the punch head, the sample is compressed into the required standard form.

　　2.2 Control Requirements

　　① Elevation requirements: The downward travel distance of the worm rod is determined by counting the speed pulses generated by the worm-rod feed control motor and then converting these pulses based on the worm-rod feed rate. Several operational phases of this system are closely related to height measurements. If the speed measurement is inaccurate or the measured height lacks sufficient precision, it could compromise the safe operation of the system; therefore, high accuracy in speed measurement is crucial.

　　② Low-speed and speed-regulation requirements: When the punch compresses the asphalt standard sample, since the punch is subjected to a certain pressure, the ram generally operates at a low speed. If the feed control motor for the ram runs too fast or generates excessive torque, the pressure borne by the punch will become excessively high, thereby compromising the safe operation of the system. Therefore, high precision in low-speed operation is essential. Additionally, the feed control motor for the ram is required to automatically adjust its running speed in response to changes in pressure.

　　During the system’s automatic operation, accurately counting speed pulses and precisely adjusting the speed are both critical aspects of this system’s control.

　　3 Control System Design

　　3.1 Control System Power

　　(1) Implement the basic functions of a rotary compactor;

　　(2) Implement the human-machine dialogue interface;

　　(3) Implement a self-diagnosis function for faults occurring during system operation, and display the results via the human-machine interface.

　　(4) When a fault occurs, the system automatically shuts down and simultaneously emits an audible alarm.

　　(5) Can print necessary information at any time.

　　3.2 Composition of the Control System

　　As shown in Figure 2, this system employs a Panasonic FP0 series PLC with 14 points, including 8 input points and 6 output points. It is equipped with an RS232C communication port and an RS422 programming port. The human-machine interface uses a PWSl711STN touch screen with both RS232 and RS485 communication ports; the HMI communicates with the PLC via the RS232 port. The AC 220V and DC 24V power supplies required by the system are both provided externally.

　　3.3 Control System Software Design

　　The system software design consists of two main parts: one is the touchscreen interface design, and the other is the PLC software design.

　　(a) Human-machine interface software design

　　The human-machine interface is a crucial component for users to set process parameters and serves as an important device for information display. The touch screen used in this system supports communication with multiple PLC languages. Its programming software, ADP3, provides powerful macro instructions that significantly reduce the program capacity required for the PLC, thereby optimizing the PLC’s control accuracy and efficiency.

　　The human-machine interface consists of two main parts: one part is for setting system operating parameters, which includes both manual and automatic operation modes. The manual mode is primarily used during the testing phase of the rotary compactor, while the automatic mode is used for the rotary compactor’s automated operation. Within the automatic mode, there are two control modes: one for rotational speed and another for elevation. The other part is the alarm function settings.

　　The entire human-machine interface includes the following screens: the main screen (Figure 3), the automatic mode screen (Figure 4), the manual mode selection screen (Figure 5), and the alarm screen (Figure 6).

　　The main screen (as shown in Figure 3) includes settings for the maximum operating pressure, the minimum working pressure for the head, the maximum pressure before entering the bucket, automatic mode selection, and manual test mode selection.

　　The automatic-mode screen is used during the automatic operation phase of the rotary compactor (as shown in Figure 4) and includes functions such as display of the operating status, elevation setting, setting of the forward and reverse rotation speeds for the turntable control motor, display of the current elevation, display of the remaining number of rotations, and display of the current compaction pressure. In addition, it provides two control mode options—rotation-based control and elevation-based control—as well as a print button. The printing function is implemented by editing macro commands within the human-machine interface.

　　The manual test screen (as shown in Figure 5) is used during the rotary compaction tester’s testing phase and includes two motors operating in six different modes. Its purpose is to verify whether each motor is functioning properly.

　　The alarm screen (as shown in Figure 6) displays fault information that may occur during operation. There are four possible types of fault messages: the pressing head is not aligned with the cylinder, the pressure exceeds the maximum allowable pressure, the elevation exceeds H1, or the elevation falls below H4 (as shown in Figure 1).

　　(b) PLC software design

　　The PLC program is executed in a cyclic manner, starting from the main program. Once the main program has been fully executed, the program returns to the main program again. The program scan cycle lasts several milliseconds. The entire PLC program was developed using Boolean ladder diagrams on Panasonic’s FPWIN platform. The PLC flowchart for the system’s rotational-speed control mode is shown in Figure 8; the process for the elevation-control mode is similar.

　　During the on-site debugging of the PLC program, we encountered several issues—for example, the pressure values converted from the pressure sensor fluctuated significantly, severely impacting the stable operation of the system. Therefore, we adopted a digital filtering approach in the program to eliminate these pressure fluctuations, ensuring that the system operates smoothly and safely.

　　4 Conclusion

　　The combination of programmable controllers and touch screens can be applied in many industrial control fields; the application in rotary compaction machines is just one particularly typical example. This system has already been deployed in the field and demonstrates reliable performance, precise control, and a user-friendly human-machine interface. It fully meets users’ operational requirements and can completely replace similar foreign products.