Abstract: This paper describes the working principle, hardware structure, and software programming of a compound feed control system based on IPC (Industrial Personal Computer). The system utilizes dynamic link library (DLL) technology and multi-tasking technology to control and manage the compound feed process. My work on DLL technology has been published in your journal; this paper mainly discusses the implementation method of multi-tasking and provides a software flowchart for this method. This concept is also applicable to the control of other multi-tasking systems and has high reference value. Keywords: I/O interface; multi-tasking; software design 1 Introduction Visual Basic (VB) is an integrated development environment launched by Microsoft, with advantages such as ease of learning, powerful functions, and low software cost. It provides the fastest and simplest way to develop Windows applications. Whether for experienced Windows application developers or beginners, VB provides a complete set of tools to facilitate application development. The high degree of encapsulation and modularity in VB reduces the burden on programmers, but it also deprives developers of many opportunities to access low-level API functions and interact directly with Windows, making them less capable of controlling interface hardware and performing low-level operations. However, in VB, Win32 API functions can be called, or programmers can develop dynamic link libraries (DLLs) using C/C++, etc., to accomplish tasks that are impossible in VB, greatly enhancing VB's programming capabilities. In this way, VB and DLLs can easily create user-friendly interfaces and control external devices. I used this technology to develop a feed mill compound feed control system. 2. System Overview The IPC compound feed control system is used for the automatic batching process in a feed mill. This system can automatically control the batching and mixing process. During the batching process, functions such as system process monitoring interface, production parameter configuration interface, hopper feeding, pause feeding, jog feeding, automatic feed column tracking, and printing of batching data for each hopper are designed, realizing the automation of the batching process. The system hardware configuration uses a high-reliability industrial control microcomputer. The switch input and output interface circuit boards connected to the field use opto-isolation technology, improving the system's anti-interference and stability, and extending its service life. The human-machine interface is user-friendly, fully compliant with Windows interface specifications, using drop-down menus to list all functions. The interface combines graphical representations with Chinese prompts, requiring no professional training; users can operate smoothly by following the prompts. 3. Control Principle During batching, the feeding motor releases material into the weighing hopper. The change in weight in the hopper causes a change in the electrical signal output by the sensor. This signal is amplified by the amplifier board and sent to the A/D board, where it is converted into a digital value and input to the computer. The computer analyzes and compares the digital value according to the program requirements. When the digital value is much lower than the set value, the feeding motor continues to release material; if it is close to the set value, the feeding is jogged, with each jog lasting 2 seconds. If the set value is reached, the feeding motor is shut off, and the motor for the next hopper is started. After all the ingredients have been prepared, if there is no material in the mixer, the weighing hopper door is opened to release material. After the material is emptied, the door is closed, and the next batching process begins. The system input signals include: (1) millivolt-level voltage signal of the load sensor; (2) weighing hopper gate closing response, used to detect whether the weighing hopper gate is closed in place. Only when it is closed in place can the feeding motor start feeding. If the computer still does not detect the weighing hopper gate closing response signal after the set closing time has expired, the system alarm prompts the user to handle; (3) mixer door opening response, when the mixer mixing time is up, the computer controls the mixer door to open. The computer starts to detect the mixer door opening response signal. After it is opened in place, the timer starts. When the timer expires, the mixer is closed. If the mixer door opening response signal is not detected after the opening time has expired, the computer alarm prompts the user to handle; (4) mixer door closing response, used to detect whether the mixer door is closed in place before the weighing hopper gate can be opened to discharge material. If the timer expires, the alarm prompts the user to handle; (5) solid additive response, used to detect whether solid additives have been added. The system output signals include: (1) control of the feeding motor; (2) control of the weighing hopper gate; (3) control of the mixer door opening; (4) control of the mixer door closing; (5) solid additive prompt; (6) control of liquid additive. 4. System Hardware Configuration The system hardware configuration is shown in Figure 1. [align=center]Figure 1 System Hardware Configuration[/align] The A/D board used is model AB1057, which has 8 channels of analog voltage input, with an input range of 0-5V. The DI/DO board used is AB720, with 32 channels of TTL level digital input, input range of 0V or 5V, and 32 channels of TTL level digital output, output range of 0V or 5V. The opto-isolated digital input board used is AB782, with 8 channels of opto-isolated digital input, input range of 12V, and output range of 0V or 5V. The solid-state relay output board used is AB786, a 16-channel solid-state relay output board, with an input range of 0V or 5V and an output range of 220VAC. The signal conditioning amplifier board used is AB001, with an input range of 0-50 millivolts and an output range of 0-5V. 5. System Software Design The system software mainly consists of a system management module, a production parameter configuration module, a system debugging module, and a production monitoring module. The most crucial part is the production monitoring module, which is also the control core of this system. During production monitoring, the system simultaneously executes multiple tasks: automatic batching, mixer mixing control, solids addition control, oil addition control, printing production data for each batch, and executing various user requests (including: changing feed hoppers during production, pausing production, resuming production, requesting real-time data printing, exiting production, etc.). These tasks are executed according to production process requirements under certain conditions. To achieve this functionality, I designed separate task modules for each task during the monitoring process, such as a batching process module for executing the batching process, a mixer mixing module for executing the mixing task, and a production data printing module for executing the printing task. During the execution of each module, the system dynamically displays its progress on the monitoring screen and provides necessary prompts. The key to this batching system is how to ensure the orderly execution of these multiple tasks according to process requirements. I have successfully solved this problem and applied this method to other multi-task production control processes, with excellent results in practice. Here, I will mainly introduce the implementation process of this part of the software and provide a software flowchart. The main program loops to determine whether each task meets the execution conditions. If the execution conditions are met, the task is started. Each task has a separate task module. If the execution conditions are not met, the main program continues to determine the next task. This idea is also suitable for multi-task control written in other languages. The main program loop flow is shown in Figure 2. [align=center] Figure 2 Main program loop flow chart[/align] 6 Conclusion This system has been widely used in the automatic batching production process of feed mills. Practice shows that the system has the characteristics of simple operation, reliable operation, powerful functions, and high batching accuracy. It has won the Hebei Provincial Science and Technology Achievement Award and achieved great economic and social benefits. It has strong practical value and promotion value. The innovation of the author of this paper: the design method of multi-task control system. This design method is suitable for multi-task control of production process implemented in multiple languages. References: [1] Xu Huipan, Wang Dianhong, Kong Lingbin, Zhang Lu. Design and implementation of local control unit of water turbine based on PCC. Microcomputer Information, 2006, 1-1: P6-8. [2] Li Huaiming, Luo Yuan, Wang Yuxin, Visual Basic 6.0 Chinese Version Reference Explanation, Tsinghua University Press, 2000. [3] Tan Haoqiang, Visual Basic Programming, Tsinghua University Press, 2004.