YIZHUN INTELLIGENT MANUFACTURING CO.,LTD

CNC (numerical control machine tool) is the abbreviation of computer numerical control. It is an automatic machine tool controlled by program.

Basic concepts

The control system can logically process the program with control code or other symbol instructions, and decode it by computer, so that the machine tool can perform the prescribed action, and the blank can be processed into semi-finished products by cutting tool.

Main structure

CNC system is a special real-time multi task computer system. Many advanced technologies in computer software technology are integrated into its control software, among which the most prominent are multitask parallel processing and multiple real-time interrupts. The following are introduced respectively. 1. Multitask parallel processing (1) multitasking of CNC system. CNC system is usually used in industrial automation production as an independent process control unit, so its system software must complete the two major tasks of management and control. The management part of the system includes input, I / O processing, display and diagnosis. The control part of the system includes decoding, tool compensation, speed processing, interpolation and position control. In many cases, some work of management and control must be carried out at the same time. For example, when the CNC system is working in the processing control state, in order to make the operator know the working state of the CNC system in time, the display module in the management software must run simultaneously with the control software. When CNC system works in NC machining mode, the part program input module of management software must run simultaneously with control software. When the control software is running, some of its processing modules must also run at the same time. For example, in order to ensure the continuity of the machining process, that is, the cutter does not stop cutting between the program segments, the decoding, tool compensation and speed processing modules must run simultaneously with the interpolation module, and the interpolation must be carried out simultaneously with the position control. The following shows the task decomposition diagram of CNC system (Fig. 3-10 (a)) and task parallel processing diagram (Fig. 3-10 (b)). In Figure 3-10 (b), the two-way arrow indicates that there is a parallel processing relationship between the two modules. (2) The concept of parallel processing. Parallel processing means that the computer completes two or more kinds of the same or different tasks at the same time or at the same time interval. The most significant advantage of parallel processing is to improve the speed of operation. Compared with N-bit serial operation and n-bit parallel operation, the operation speed of the latter is almost n times higher than that of the former under the same processing speed. This is a parallel processing method of repeated resources, which greatly improves the operation speed according to the principle of "winning by quantity". But parallel processing is more than a simple repetition of devices, it has more meaning. Such as time overlap and resource sharing. The so-called time overlap is based on the pipeline processing technology, so that multiple processing processes are staggered in time, and several parts of the same set of equipment are used in turn. Resource sharing is based on the principle of "time sharing", which enables multiple users to use the same set of equipment in chronological order. In the hardware design of CNC system, the parallel processing method of resource duplication has been widely used, such as using multi CPU system architecture to improve the system speed. The resource sharing technology is mainly used in resource sharing of CNC system. (3) Time sharing of resources. In the single CPU CNC system, the principle of CPU time sharing is mainly used to solve the problem of multitask running at the same time. Generally speaking, in the computer system using time sharing parallel processing, the first problem to be solved is the allocation principle of CPU time occupied by each task, which has two meanings: one is when each task occupies the CPU; the other is to allow each task to occupy CPU for a long time. In CNC system, the use of CPU for each task is solved by the combination of cycle rotation and interrupt priority. Figure 3-10 (c) is a time allocation diagram of a typical CNC system in which each task shares a CPU.After initialization, the system automatically enters the time allocation loop, and processes each task in turn. For some real-time tasks in the system, they are queued according to the priority and placed on different interrupt priorities. The tasks outside the ring can interrupt the execution of the tasks in the ring at any time. The time allowed for each task to occupy the CPU is limited, which is usually handled in this way. For some tasks that occupy more CPU time, such as interpolation preparation, breakpoints can be set in some places. When the program runs to the breakpoint, the CPU is automatically released, and it will automatically jump to the breakpoint to continue execution at the next running time. (4) Resource overlapping flow processing. When CNC system is in NC mode, the data conversion process is composed of four sub processes: part program input, interpolation preparation (including decoding, tool compensation and speed processing), interpolation and position control. If the processing time of each subprocess is respectively, then the data conversion time of a part program segment will be if each part program segment is processed in sequence, that is, the second program segment will be processed after the first part program segment is processed, and so on. The temporal and spatial relationship of this sequential processing is shown in Figure 3-11 (a). As can be seen from the figure, if you wait until the first segment is processed before processing the second segment, there will be an interval of t between the outputs of the two segments. There is also a time gap between the output of the second and third segments, and so on. This time interval is reflected in the motor is the motor time to stop, reflected in the tool is the tool time travel time stop. No matter how small the time interval is, it is not allowed to stop in the processing technology. The method to eliminate this interval is to use pipelining technology. The temporal and spatial relationship after pipelining is shown in Fig. 3-11 (b). The key of pipelining is time overlap, that is, two or more subprocesses are processed instead of one subprocess in a period of time interval. It can be seen from Fig. 3-11 (b) that there is no interval between the outputs of each program segment from the start of time after pipelining, thus ensuring the continuity of motor rotation and tool movement. As can be seen from figure 3-11 (b), pipelining requires that each processing subroutine has the same operation time. In CNC system, the processing time of each subprogram is not equal. The solution is to take the longest subprogram processing time as the processing time interval. In this way, when the processing time is short, the waiting state will be entered after the processing is completed. (a) Sequential processing (b) pipelining Fig. 3-11 resource overlapping pipelining in a single CPU CNC device, the time overlap of pipelining is only of macroscopic significance, that is, in a period of time, the CPU processes multiple subprograms, but from a microscopic point of view, each subprogram takes up CPU time.2. Real time interrupt processing another important feature of CNC system control software is real-time interrupt processing. The multitasking and real-time performance of CNC system determines that system interruption becomes an essential part of the whole system. The interrupt management of CNC system mainly depends on hardware, and the interrupt structure of CNC system determines the structure of system software. The types of interrupt include external interrupt, internal timing interrupt, hardware fault interrupt and program interrupt. (1) External interrupt. There are mainly read hole interruption of paper tape photoelectric reader, external monitoring interruption (such as emergency stop, meter in place, etc.) and keyboard operation panel input interruption. The first two kinds of interrupts have high real-time requirements. They are usually placed at a higher priority, while keyboard and operation panel input interrupts are placed at a lower priority. In some systems, it is even processed by query. (2) Internal timing interrupt. There are mainly interpolation cycle timing interrupt and position sampling timing interrupt. In some systems, these two kinds of timing interrupts are combined into one. But in processing, the position control is always processed first, and then the interpolation operation is processed. (3) Hardware failure interrupt. It is the interrupt sent by various hardware fault detection devices, such as memory error, timer error, interpolation operation timeout, etc. (4) Procedural interruption. It is a kind of computer numerical control system (CNC) which is called CNC system for short. It is a special computer system which uses the computer to realize the NC function by executing the program in its memory, and is equipped with interface circuit and servo drive device. Under the control of CNC system, CNC machine tool can automatically process the workpiece according to the given processing program. Therefore, computer numerical control system is a kind of digital control system including computer. ---Since the first CNC milling machine appeared in 1952, the CNC equipment has been used to control the CNC machine tool. After about 20 years, computer control was introduced in 1971. In the beginning, small computers were used to replace the traditional hardware numerical control (NC) in CNC system. However, with the development of computer technology, most modern CNC machine tools use microcomputers with low cost, strong function and high reliability to replace small computers for numerical control of machine tools, which is simply called MNC, but people still call them CNC. The working principle of computer control and microcomputer control is basically the same. CNC system is a position control system. The control process is based on the input information (processing program), data processing, interpolation operation, to obtain the ideal trajectory information, and then output to the executive part, processing the required workpiece. The core of CNC system is CNC device. Due to the use of computer, the performance and reliability of CNC device are improved, and the rapid development of CNC system is promoted. The hardware composition of CNC device generally includes CPU and bus, memory, input device interface, I / O circuit interface, position controller, display device interface, and communication network interface. The following is a brief introduction to the main components. CPU and bus 1. CPU overview CPU is the core of CNC device, which has the ability to perform calculation and control. CPU is mainly composed of control unit, arithmetic logic unit and some temporary registers. When the signal is sent out to the control unit of the CNC unit in the next step, the signal is sent out to the control unit of the CNC unit in order to execute the next operation instruction.2. Bus bus is the channel of transmitting various signals between independent modules in computer system. In the computer system, various functional modules are connected organically through the bus, and the information transmission and communication between them are realized through the bus. Bus can be divided into chip bus, internal bus and external bus. Chip bus is a component level bus, which is the connection bus between chips of a small system or CPU plug-in. Chip bus includes address bus, data bus and control bus, which is called three bus structure. Internal bus, also known as system bus, is board level bus, which is used for connection and communication between plug-in boards in CNC device. Such as S-100 bus, PC bus, multi bus, STD, ibm-at, standard bus, etc. External bus, also known as communication bus, is used for communication between systems. This kind of bus includes RS-232C, RS-422, IEEE-488, etc. The practical application and theoretical analysis prove that STD bus is a better industrial bus, which has been widely used in the world, and is also the preferred industrial standard bus for development in China. The CPU template of STD bus can contain almost all 8-bit and 16 bit microprocessors, such as Z80, 8080, 68-00, 8086, 8088, 80286, and 8031, 8098, etc., and can match with various general memory and I / O interface modules. The industrial interface board of STD bus can be directly connected with various mechanical and electrical equipment in the control field, and can drive AC motors, DC motors, stepping motors, relays and contactors of various powers. It not only reduces the cost, but also improves the reliability of the system, and simplifies the system design. The remarkable characteristics of STD bus are modularization and high reliability, which can be summarized as follows: (1) board structure, single function, STD products adopt small board structure, standard size 165mmxll4mm ', a template usually has only one function, users can flexibly form their own practical system according to their needs. (2) Standard layout, safe and reliable. All kinds of templates are designed according to the standard layout. The layout on the template is basically driven by the bus and connected to the I / O interface through functional modules. This structure design has the shortest path, reduces the mutual interference of various signals, and improves the reliability of the module. There are nearly 1000 kinds of STD bus products in the world, and many companies supply them. They can provide a variety of functional modules of STD bus.