I. PLC Control Related Experiments
Research topic: Using a large-scale PLC sequential controller to control the operation of a machine tool machining center.
Experiment Requirements: A PLC (Programmable Logic Controller) is an industrial controller developed by integrating advanced technologies such as computers and automatic control, with a central processing unit as its core. It possesses many unique advantages, including high reliability, comprehensive functions, flexible combination, simple programming, and low power consumption. It has been widely used in various sectors of the national economy.
This machining center is equipped with over two hundred different types of cutting tools, enabling it to perform drilling, milling, boring, reaming, tapping, and other machining operations. It features automatic tool changing and automatic linear cutting and continuous toolpath control. Its complexity far exceeds the capabilities of relay contact control systems. Therefore, using a large PLC sequential controller for the operation control of this machining center is the most suitable choice.
Experimental Process: First, we understood the mechanical motion process of the machining center, including the conversion from drawings to programs, tool changing methods and control requirements, linear cutting and continuous tool path control requirements, control coordination of various parts, and overall control requirements. Then, we developed a PLC overall control scheme, determined specific control methods for each part, compiled the PLC control program, installed and debugged it, and completed the development process.
II. PLC Control Technology
Control achieved through the continuous repetition of a program is called scanning mode. This is a method of real-time computer control. In addition, computers also use interrupt-driven control. In interrupt-driven mode, the control requiring processing first requests an interrupt. Once the interrupt is handled, the currently running program stops and switches to handling the interrupt (running the relevant interrupt service routine). After handling the interrupt, the program returns to its original state. Only the control requiring processing requests an interrupt; those that do not are ignored. Clearly, interrupt-driven control differs from scanning mode.
In interrupt mode, the computer can be fully utilized, and urgent tasks can be handled promptly. However, what if several tasks that need to be processed arrive simultaneously? High-priority tasks are manageable, but what about low-priority ones? Some tasks might be overlooked. Therefore, interrupt mode is not well-suited for daily use in the workplace.
However, while PLCs primarily use the scanning method, they do not exclude the interrupt method. That is, while most control operations are performed using the scanning method, urgent tasks can be handled by interrupting the scanning process and redirecting the execution of the specific task. This ensures that all controls are adequately addressed, while also allowing for the processing of individual emergencies.
The actual working process of a PLC is more complex than described here, and there are still some theoretical issues to analyze its basic principles. If relevant personnel can study the above-described input/output transformation, physical implementation—information processing, I/O circuits—spatial and temporal relationships—scanning methods supplemented by interrupt methods as a way of thinking, and understand it, they will be able to better understand how the PLC achieves control and grasp the key points of the basic principles of the PLC.
PLC automatic control systems are a key medium for promoting PLC automatic control technology. In industrial production and company development, PLC automatic control systems have irreplaceable functions. The main characteristics of this system are as follows:
(1) High efficiency in compilation. When compiling PLC automatic control systems, the program programming is clearer and more efficient. The "ladder logic flow table" can be used to complete PLC automatic control technology. At the same time, the control board in the system is easier to modify. It can be integrated with the actual needs of industry and company to design the function of PLC automatic control system program and improve the overall efficiency of various production activities and construction projects.
(2) High stability. After the PLC automatic control system is combined with the frequency converter, it can be directly used in the company's production process, and the system operates smoothly and reliably. According to the relevant personnel's testing of the PLC automatic control system, the system has strong anti-interference ability and low failure frequency during system operation, which can sufficiently maintain the stability of the company's production and automatic control platform, and ensure the company's production efficiency.
(3) Easy assembly. The PLC automatic control system is very easy to install, and the system itself can be integrated into different production activities. It has strong corrosion resistance and toxicity resistance. When used in conjunction with frequency converters, the PLC automatic control system has significantly stronger executability and can create more economic benefits for companies and industrial activities.
