Characteristics of CNC system task management based on different operating systems In the past, most domestic CNC systems were built on the DOS operating system platform and other dedicated real-time operating systems. It is convenient to develop the CNC system on a dedicated real-time operating system, but it is expensive. It is not suitable for the development of CNC technology in China, and it is not conducive to the openness of CNC system.

It is economical to develop CNC system on DOS platform. The CNC machine tool designed and manufactured by China mainly relies on DOS system. Due to the limitation of 640K system memory in DOS system, it has greatly restricted its real-time development capability. However, its operating system is single-tasking. It does not make full use of the hardware resources of the i386 system. Its memory is only 640K, the network function is lacking, and there is no protection machine. It is more troublesome to add real-time multi-tasking modules on DOS. Windows is a multitasking operating system, but it is not a real-time operating system and therefore cannot be used directly in the development of CNC systems. In recent years, Linux has developed rapidly, but Linux is not a real-time system. It needs to be modified in the numerical control system. Generally, it needs to join the real-time kernel RTLinux to realize the preemption mechanism of high-priority tasks to meet the hard-time performance of the CNC system. The requirements make it a good application in CNC systems.

The application of embedded Linux in the numerical control system This example applies the embedded Linux technology to the rolling machine tool, and develops the rolling machine numerical control system based on the Linux platform. The development and research of the system are introduced below.

System Modeling The NC rolling machine is a machine tool that uses numerical control technology. It uses a computer as the control system, and its composition is as shown. CNC machine tool block diagram Modern CNC system is basically composed of upper layer software, data acquisition, program interpretation, PLC management, tool compensation processing, interpolation calculation, position control and so on. Its general data flow is as shown. First, the program interpretation task interprets the program processing G code, normalizes the processing and puts it into the tool compensation buffer, and then performs the tool compensation processing, and the data after the tool compensation processing is inserted. The buffer is used for interpolation task processing. The interpolation task is mainly to complete the position increment calculation of each axis in the interpolation task cycle. Finally, the position control task is mainly to issue motion commands to control the motion of each axis; PLC main processing Machine tool I/O, control of logic control and machine tool auxiliary functions, handling of unexpected events, etc. Among them, real-time related tasks include data acquisition, program interpretation, PLC management, tool compensation processing, interpolation calculation, position control, etc., which need to be called periodically, and synchronization problems should be considered between tasks.

The numerical control system data flow is based on the analysis of the machine tool function. We use the embedded technology and the characteristics of the rolling mill to design the embedded CNC system software architecture as shown. The processes in Linux run in two modes: system mode (core mode) and user mode (user mode). In real-time Linux, in order to ensure that the real-time tasks of the CNC system can respond in time, all real-time related tasks must be placed in the core state, each task is executed by a separate kernel process, including: position control, interpolation Computing, PLC management and data processing. Non-real-time tasks are placed in user mode, they do not interrupt the operation of real-time tasks at any time, including: status display, human machine interface, file management and parameter settings.

The communication between the core state and the user state process is mainly based on the real-time FIFO and shared memory provided by the real-time extension component RTAI.

The system real-time solution from the Linux process scheduling three strategies: "non-real-time, real-time first-in, first-out, real-time based on priority rotation method" can be seen that Linux has special treatment for real-time tasks ("soft real-time"), Although it does not meet the "hard real-time" requirements, this soft real-time can meet the requirements of general embedded systems. RT_Linux is a Linux operating system that provides real-time functionality and was developed by the New Mexico Institute of Technology.

RT_Linux provides the ability to run special real-time tasks and interrupt handlers, and is a hard real-time system. On X86 machines, RT_Linux performs interrupt handlers with a latency of no more than 15 microseconds. When scheduling a recurring task, the task is executed in 35 microseconds, allowing it to handle real-time tasks. Specifically, the RT_Linux kernel treats the normal operating system as a low-priority task. It can preempt ordinary Linux tasks when needed. This is achieved by controlling the interrupts, thus meeting the real-time requirements of the CNC system. . In the CNC system, various tasks are queued according to priority requirements according to real-time requirements. RT_Linux and Linux work together to handle tasks in the CNC system according to real-time requirements. The RT_Linux kernel is responsible for real-time tasks. Some non-real-time tasks can be handled by the Linux kernel. There are multiple ways to communicate between the two cores, such as FIFO, shared memory, etc., and the two cores coordinate with each other to complete the processing tasks.

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