Abstract: This paper introduces the composition, configuration, function, and key technologies of the control system for automatically controlling the grinding time of cemented carbide raw materials. The system has been running stably in the ball milling process of the user unit for six months, achieving the design objectives and meeting the process requirements. Keywords: Ball milling/unloading time automatic control and monitoring system 1. Introduction: The production process of cemented carbide raw materials consists of multiple processes, among which the material grinding time in the ball milling process is a crucial process parameter. Arbitrarily advancing or delaying the execution time of each process segment of the ball mill, failing to perform ball milling according to the set time in the event of power outages, mechanical failures, or failure to promptly detect and continue the remaining grinding time will all result in unqualified physical and chemical properties of the ball-milled material, affecting subsequent production and compromising product quality. Currently, cemented carbide manufacturers use various ball mills to grind WC raw materials, producing the required powder material for cemented carbide through different grinding times. Our company has a wide variety of ball mills, most of which have been in use for decades. Originally, they were controlled manually by timers, which was not only technologically outdated, but also resulted in highly arbitrary control of the ball milling process time. Product quality depended entirely on the operator's skill and responsibility; furthermore, effective monitoring and management of the equipment's operation and the production process were impossible. Therefore, we designed a control system based on a Siemens S7 300 PLC to technically upgrade this type of equipment. This involved adding corresponding automatic detection and control methods, changing the control and management mode, eliminating the adverse effects of human factors on product quality fluctuations, ensuring the ball milling process is executed flawlessly, improving the precision of ball milling time control, and ultimately improving product quality. 2. Ball Milling Process Flow and Functional Requirements The main function of a ball mill is to grind lumpy materials into powder through the rotation of the ball mill and the interaction between the material and the grinding balls. The process is as follows: Load raw materials—cover with seamless cover—start the ball mill—time expires—stop ball milling—automatically or jog to turn the feed inlet upwards—change to discharge grate cover—start the ball mill—time expires—discharge completed, production completed. 1) During the first start of the ball mill in the ball milling stage, if the feed inlet is not in the correct position, it can be manually jogged back to the correct position. At this time, the raw materials can be put into the ball mill. After loading the raw materials, switch the indexing switch to ball mill to prepare for the ball milling stage. Set the ball milling time. If no time is set, the original time setting will be used. Press the start button to start the ball mill. At this time, the display will show that the ball mill is in the ball milling state and the remaining ball milling time. After the set time expires, the ball mill will automatically stop and the display will show that the ball milling has ended and is in the discharge stage. 2) During the unloading stage, replace the feed inlet cover with a grid-covered unloading cover. The feed inlet then becomes the unloading outlet. Set the selector switch to the unloading position and start the ball mill. The system will then display that the ball mill is in the unloading stage and the remaining unloading time. After the set time, the ball mill will automatically stop, and the unloading outlet will be positioned directly above the feed inlet. The main functions to be implemented are: 1) The ball mill will stop strictly according to the time set for the process segment; 2) Time retention function in case of failure (i.e., after the failure is resolved, the operation can continue according to the remaining ungrinded time); 3) Display, set, and record operating process parameters, as well as alarm display and recording functions; 4) Automatic return to the correct position: To improve production efficiency, the ball mill will automatically return to the correct position after each stop, eliminating the need for operators to manually adjust the feed inlet position. 5) System safety: Operators must obtain the appropriate username and password to perform normal operations and record relevant information. To prevent operator error on-site, monitoring authorization is set; remote operation is not permitted on the monitoring computer during normal operation or maintenance of the equipment. 6) The system can perform manual/automatic selection, remote/local equipment start authorization, and each subsystem is independent of the others, so the operation of the entire system will not be affected by the failure of one piece of equipment. 3. Control System Composition and Configuration Based on the above production process flow and requirements, this project implements automatic control and monitoring management for the six ball mills on the production site. The two main stages to be controlled are ball milling and unloading. All controlled objects are digital switch quantities and follow a sequential control method. The six ball mills have a total of 48 input points and 6 output points, specifically: system start/stop, motor start/stop, motor fault, speed sensor, ball milling/unloading, maintenance, and other switch signals. Since the six ball mills on site are located in two separate rooms, the I/O points are relatively dispersed. Therefore, the designed monitoring system consists of a monitoring computer (host computer), a communication network, a lower-level PLC + I/O, a field operation box, and the ball mills. The system structure is shown in Figure 1: Figure 1: System Structure Diagram 3.1 Monitoring Computer The monitoring computer system, consisting of an Advantech IPC-610H industrial PC, a 17" monitor, and an Ethernet switch, is installed in the management office. It mainly displays, processes, and stores production process parameters, and can dynamically display the operating status of production equipment. It is a powerful tool for production management personnel to control production. The monitoring computer configuration is as follows: Industrial PC: Advantech IPC610-H (P4 3.0GHz/1GB DDR2 667/160GB HD/16X DVD) System Software: WINDOWS XP SP2 Professional Edition HMI: KingSCADA 6.53 Monitor: 17" LCD Ethernet Switch: D-LINK 8 x 10/100Mbps ports 3.2 Field PLC Control System and Touch Screen The PLC is the core of this system, configured with one Siemens S7 313C-2DP and two TP270 A 10.4" touchscreen, 6 I/O modules, and a field control box form the field control system. The field PLC mainly performs various functions of the automatic group control system, such as data acquisition and timing calculation. It receives operation commands from the industrial control computer to control the start and stop of the motor; it receives grinding and unloading time parameters from the industrial control computer to accurately control the ball milling time, and automatically memorizes the status and time when power is off; it transmits the equipment operating status to the monitoring computer in real time via Ethernet communication. 3.3 I/O System and Network System The function of the I/O system is to collect the status of field contactors, sensors, buttons, and other devices and convert them into digital signals, which are then transmitted to the main control PLC via the PROFIBUS-DP bus. The I/O modules of this system are Turck PDP (BL20) input modules: 2 modules with 16 points each, and output modules: 4 modules with 2 points each. The I/O modules have point diagnostics and point protection functions, and high waterproof and dustproof performance. They are easy to expand and suitable for relatively dispersed ball mill sites. A network system comprised of Ethernet and PROFIBUS-DP buses with a transmission rate of up to 100Mbps is used for communication between the PLC controller and I/O modules, as well as between the PLC controller and the monitoring computer. The PROFIBUS-DP bus has a high data transmission rate, allowing for high-speed, periodic, small-batch data communication, making it ideal for applications with stringent ball milling time control requirements. The field control box, although at the lowest level of the control system, is a crucial component. Operators control the ball mill's operation using buttons, switches, and indicator lights on the control box. When the equipment is under maintenance, the switch can be used to temporarily disconnect the equipment from control, ensuring its safety and reliability. The field control box is shown in Figure 2: Figure 2: Field Control Box 4. Key Technologies for Achieving Automatic Control of the Ball Mill This system upgrades old equipment that has been in use for decades. To organically integrate it with modern control technology, achieving automatic operation of the ball mill except for loading and unloading, and realizing timed control of the ball milling time while ensuring automatic replenishment of remaining grinding time in case of abnormal power outages or mechanical failures, the following key issues must be addressed to achieve the expected upgrade goals. 4.1 Precise Control of Ball Mill Loading and Unloading Positions: The ball mill utilizes proximity switches and sensing elements to achieve precise control of the loading and unloading positions in both manual and automatic modes. In automatic mode, no manual intervention is required; the ball mill automatically returns to the correct position after each shutdown. If the ball mill's inlet and outlet are not in the correct position, the control can be switched to manual mode on the on-site control box, and the inlet and outlet can be jogged back to the correct position. Specifically, a proximity switch is installed on the housing of the coupling section, and a sensing element (iron block) is installed on the coupling. The main controller PLC can only stop the ball mill when it simultaneously receives a signal from the proximity switch and a stop command. Figure 3 shows the installation positions of the proximity switch and sensing element. Figure 3: Schematic diagram of the installation position of the sensing element. 4.2 Precise Control of Ball Milling Time and Unloading Time, and Alarm and Recording of Abnormal Power Failures: Because the ball milling process is critically time-sensitive, arbitrarily advancing or delaying the milling time without supervision, or experiencing abnormal power outages, will result in the ball milling material failing to meet physical and chemical standards. Therefore, precise control of the milling time and unloading time, as well as alarm and recording of abnormal power outages, are essential. The design utilizes the aforementioned proximity switches and sensing elements to accurately detect the ball mill motor's operation, start/stop, and power outage status. A PLC programmable controller performs counting, calculation, data processing, time accumulation, and alarm functions to achieve precise control of the ball mill's running time. 5. Software System Design: 5.1 The upper-level monitoring system uses an Advantech IPC-610H industrial computer, running on Chinese Windows. XP is the operating platform, making full use of the graphical functions of the WINDOWS system; the configuration software adopts Beijing Yacon Configuration King V6.53, and a simple, intuitive and convenient human-machine interface is designed. The main body of the monitoring screen is an overall view, 6 sub-screens and several auxiliary screens (such as record display screen, alarm overview screen, report system, etc.). The functions include: displaying the running status of all ball mills, set time, process stage (ball milling, unloading, homing, etc.), real-time alarm information, operation buttons, authorized login operation, and all information of a single ball mill. As shown in Figures 4, 5 and 6 below: The functions of the industrial control computer are: (1) Process personnel can input the grinding time and unloading time specified by the process on the monitoring computer, compile and send, and read the process data on site. (2) The upper control computer is equipped with start and stop buttons for 6 ball mills. When the button is activated, the status of the corresponding button can be displayed accordingly. Display the total ball milling time, current time used, remaining time, number of ball millings, etc. (3) The upper control computer displays the process flow diagram animation of the ball mill and the current running status. (4) It can store commonly used ball milling processes. The number of processes is limited only by the hard disk capacity. Various reports can be compiled and output. (5) The ball mill start and stop buttons automatically generate data reports and update them in real time. It can realize the traceability and query of process execution. (6) Various generated reports and alarm information can be saved, displayed and queried. 5.2 The lower computer PLC control software adopts Siemens Step7 V5.3 and Wincc Flexible2005 touch screen programming software for program design. The PLC control flowchart compiled according to the ball mill process flow is as follows: It has the following functions: (1) Timed control: When the ball mill is in manual control or computer automatic control, it can realize accurate ball milling and unloading time timing function and control according to the specified process time. (2) Automatic return: When running automatically and unloading, it can accurately stop at the loading and unloading position. When in manual jogging state, it can stop at any position. (3) It can accurately control the start, stop and unloading of the ball mill according to the set process time and can automatically perform various fault judgments. (4) The touchscreen on the field control cabinet allows for manual editing or retrieval of the ball mill process from the monitoring computer, displaying various parameters of the ball mill's current operating status. (5) The mill automatically memorizes the grinding time during power outages. The PLC can handle abnormal power outages or manual power cuts, memorizing the current time and the grinding time already completed. The mill resumes the unfinished process when power is restored. The mill stops normally when the cumulative grinding time reaches the predetermined time. 6. Conclusion This system was installed on six ball mills in the powder division of Zigong Hard Alloy Company, realizing automatic control of ball milling and unloading times, and effectively monitoring and managing the equipment's operating status and process execution. After six months of practical application, the system has proven to fully achieve the following: ball mills strictly stop according to the set time of the process segment; time retention function in case of failure; display, setting, and recording functions for operating process parameters, as well as alarm display and memory; equipment safety assurance and independent operation. Simultaneously, it also achieves the goal of standardizing operators to strictly adhere to process discipline and improving the control accuracy of ball milling and unloading times (control accuracy approximately 1 second). This system also features decentralized control and centralized management, compact structure, high execution speed, easy expansion, convenient operation, and stable and reliable performance, making it worthy of widespread application. References: 1. Zheng Sheng, Gong Jianping, Zhang Xue, Modern Programmable Logic Controller Principles and Applications, Science Press, 2002. 2. "Automation Information", Chinese Association of Automation, Sichuan Provincial Association of Automation and Instrumentation, 2008-7. 3. Zhou Shengan, Hard Alloy Manufacturing Technology, 2005.