In the past 10 years, with the rapid development of computer technology, the architecture of numerical control devices is moving toward standardization and openness. As far as the architecture is concerned, the numerical control systems in the world today can be roughly divided into three types: 1 Traditional architecture: This is a special closed-structure numerical control device. For its function expansion, change and maintenance, it must turn to system suppliers. The market for such CNC systems is being challenged and has gradually decreased. 2PC embedded Nc architecture: This structure is embedded in the PC based on the traditional structure. Its purpose is to inherit both the numerical control software technology accumulated over the years and the abundant software resources of the PC. This kind of system structure is more complicated. 3 Based on PC architecture: The structure is based on standard PC = machine hardware, based on a common operating system (such as Windows, LINIX, etc.) developed under the support of real-time multi-tasking system to achieve a variety of CNC functions. This is a widely adopted architecture of modern numerical control devices. The numerical control device based on this structure has a high performance-cost ratio and a long life. A typical appearance of a CNC device based on a PC architecture is shown in FIG. 1, and a hardware block diagram thereof is shown in FIG. 2.
Figure 1 appearance of the CNC device
The function of each hardware module in Figure 8-4 is discussed below in terms of functionality.
1. Computer motherboard and system bus board (motherboard) The computer motherboard is the core of the CNC device. Because it is a PC-based architecture, each hardware module is also compatible with the PC bus standard. Its purpose is to use the rich software and hardware resources of the PC to improve the system's adaptability and openness. Lower prices and shorten the development cycle of new products. The computer system of the CNC device is slightly different in structure from the ordinary commercial PC. Starting from the reliability of the system, the motherboard and the motherboard are separated, that is, the system bus is a separate passive motherboard, the motherboard is made into a card format, and the integration is higher, the so-called ALL-IN-ONE Motherboard. This motherboard mainly includes the following functional structures: 1 CPU chip and its peripheral chips. 2 memory unit, cache and its peripheral chips. 3 communication interface (serial port, parallel port, keyboard interface). 4 soft and hard drive interface. The principle of composition of each functional structure is exactly the same as that of ordinary microcomputers, and will not be repeated here. The main role of the computer motherboard is. Various arithmetic data and information (part machining programs, various I/O information, etc.) input to the CNC device are subjected to corresponding arithmetic and logic operations, and based on the processing results thereof, control commands are issued to other functional modules to transmit data. Make the user's instructions executable.
Figure 2 The hardware structure of the CNC device
The system bus (motherboard) consists of a set of physical wires that carry digital information. It is a channel for data or information exchange inside the CNC device. The principle of composition is exactly the same as that of ordinary microcomputers. The bus mother board, which is generally used as an industrial Pc machine, is an independent passive four-layer printed circuit board. That is, the two sides of the board are signal line routing surfaces, and the power supply and ground lines are in the middle, and its reliability is higher than two layers. board. Its specifications are 6 slots, 8 slots, 12 slots and 14 slots, etc. Users can choose according to the number of CNC device function boards.
2. Display Module The display module, or display card, is a very versatile module. In the CNC device, the CRT display is a very important function. It is an important medium for human-computer communication and provides the user with an intuitive operating environment so that the user can quickly become familiar with the operation process. The main function of the display card is to receive the control commands and data for display from the CPU, modulate the scan signals of the CRT, and then generate the video signals required by the CRT display. The electron guns in the CRT scan the screen to generate the result. Needed screen. The hardware of the display card is not only available on the market at any time, but it also has very rich supporting software, so it does not require the user to develop it.
3. Input/output module input/output module is also a standard PC module
—— Multi-function cards are generally not required to be developed by users themselves. The input/output module is an interface board for exchanging data and information between the CNC device and the outside world. That is, the CPU in the CNC device can obtain data from an external input device through this interface, and can also send the data in the CNC device to the external output device. If the computer motherboard is an ALL-IN-ONE motherboard, this board can be omitted because the motherboard has integrated this function.
The above three parts, coupled with keyboard, power supply and chassis, are actually a general-purpose microcomputer system. This system is the core of the CNC device. In a sense, the grade and performance of the CNC device determine the grade and performance of the CNC device. Therefore, the rational selection of the computer subsystem of the CNC device is crucial.
4. Electronic Disk (Storage Module) The electronic disk is a unique storage module of the CNC device. In the CNC device it is used to store the following data and parameters: 1 system software and system-specific data; 2 system configuration parameters (number of axes that the system can control, axis definition, system gain, etc.); 3 user parts Processing program.
In CNC devices, electronic memory devices are often used as external memories rather than magnetic memory devices. The main consideration is that the working environment of CNC devices may be subject to electromagnetic interference, the reliability of magnetic devices is low, and the electronic storage devices are electromagnetically resistant. Interference ability is relatively stronger. Because these storage units made up of electronic devices are managed by the disk, they are called electronic disks.
5. PLC control module The CNC system controls the equipment into two categories: one is the "trajectory control" of the speed and position of each coordinate axis; the other is the "sequential control" of the operation of the equipment. For CNC machine tools, “sequential control†refers to the condition of digital signals within the CNC and the machine's each trip switch, sensors, buttons, relays, etc., in the course of the operation of the CNC machine tool, and in a predetermined logical order such as Spindle start and stop, reversal, tool replacement, workpiece clamping, release, hydraulic, cooling, lubrication system operation and other controls. The module that implements sequence control in the CNC device is a PLC control module. This module mainly receives from the operation panel, the various trip switches on the machine, sensors, buttons, relays in the power cabinet, as well as the relevant signals for spindle control and magazine control. After processing, it controls the operation of the corresponding devices.
6. Position control module The position control module is an important part of the feed servo system. It is an interface module that connects the CNC device and the servo drive system when trajectory control is implemented. In numerically controlled machine tools, the feed axes, usually controlled by several feed servo systems, constitute the forming motion system. Each coordinate axis (feed axis) has a set of independent position controllers. The role of the position controller is: receiving position control commands (such as â–³X, â–³Y, â–³Z, etc.) output after CNC interpolation operation, and corresponding adjustment operations (position control usually adopts proportional adjustment operation) and corresponding transformation ( Such as D / A conversion, pulse conversion, etc.). Output speed control command to the speed control unit to control the servo motor operation. For closed-loop or semi-closed-loop control, the actual position signal and actual speed signal are also recovered for position and velocity closed-loop control calculations.
7. Function Interface Module The function interface module is an interface board that implements user-specific function requirements. For example, the profiler controller for laser profiling, the automatic focus tracking function of the laser cutting machine (Z-axis floating controller), and the tool monitoring system Signal collectors, etc. All added functions must be added to the CNC device to achieve this. As far as the current situation is concerned, user-specific functional requirements must be customized to the manufacturer of the CNC system. Generally speaking, users themselves cannot do it. The reason is because the current CNC system is closed, not open. One of the trends in the development of numerical control technology is to study open-structured CNC systems. Once successfully developed and used, users can increase or decrease the functionality of the CNC system according to their own requirements. This is what people are pursuing.
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