Hardware architecture of the hottest CNC device

CNC device hardware architecture

I. overview

cnc device from its hardware composition structure, if divided according to the number of CPUs contained therein, it can be divided into the following categories:

single machine system: the whole CNC device has only one CPU, which centrally controls and manages the whole system resources, and realizes various NC functions through time-sharing processing

master-slave structure. In the system, only one CPU (called master CPU) has the control and use right of system resources. Other functional components with CPU can only accept the control commands or data of the master CPU, or send request information to the master CPU to obtain the required data. That is, it is in a subordinate position, so it is called the dominant subordinate structure

multi machine system: there are two or more CPUs in the CNC device, that is, some functional modules in the system also have CPUs. According to the relationship between components, they can be divided into:

multi master structure: there are two or more module components with CPUs in the system, which have control or use rights to system resources. The modules are tightly coupled, with a centralized operating system. The bus contention problem is solved through the arbiter, and the information is exchanged through the common memory

distributed structure: the system has two or more functional modules with CPU. Each module has its own independent operating environment. Loose coupling is used between modules, and communication is used to exchange information

II. Function introduction of single machine or master-slave structure module

cnc device is constructed according to the modular design method

modular design method: the control system is divided into several unit modules with independent functions according to functions, and equipped with corresponding drive software. When the system is designed, different functional modules are selected according to the functional requirements and inserted into the control unit motherboard to form a complete control system. The unit motherboard is generally a passive motherboard with bus structure, which provides the signal path for the interconnection between modules

the condition to realize the modular design of CNC system is the standardization of bus. When adopting modular structure, the design of CNC system can be reduced to the reasonable selection of functional modules

1. Computer motherboard and system bus (motherboard)

computer motherboard is the core of CNC device

functional structure:

cpu and its peripheral chips; Memory unit and its peripheral chip; Communication interface (serial port, parallel port, keyboard interface). Soft and hard drive interfaces

main functions of computer motherboard:

perform corresponding arithmetic and logic operations on various data and information (part processing program, various i/o information, etc.) input into CNC device. According to the processing results, control commands are sent to each functional module to transmit data, so that the user's instructions can be executed

system bus (motherboard): it is composed of a group of physical wires that transmit digital information. It is the channel for data or information exchange within the computer system:

data bus: 8 data lines, bus width 8 bits; Address bus: 16 address lines (direct addressing 64K)

control bus:

the bus motherboard of industrial PC is an independent passive four layer board (wiring surface, component surface, power supply layer and ground wire layer), and its reliability is higher than that of two-layer board. Its specifications include 6 slots, 8 slots, 12 slots, 14 slots, etc

2. Display module (display card)

main functions of display card:

receive control commands and display data from CPU, generate video signals required by CRT display after modulation with CRT scanning signal, and generate required pictures on CRT

in CNC devices, CRT display is a very important function. It is an important medium for human-computer communication. It provides users with an intuitive operating environment, so that users can quickly familiarize themselves with and adapt to their operating process

display card is a module with strong versatility. It is not only available in the market at any time, but also has a very rich support software, so users do not need to develop it themselves

3. Input/output module (multi-function card)

it is the interface board for the CNC device to exchange data and information with the outside world, that is, the CNC device can obtain data from the input device through this interface, and can also send the data in the CNC device to the output device

this module is also a standard PC module, which generally does not need to be developed by users themselves. If the computer motherboard is a standard motherboard, this board can be omitted

the above three parts (computer motherboard, display card, input/output), together with keyboard, power supply and chassis, are actually a general microcomputer system, which is the core of CNC device. In a sense, the grade and performance of CNC device are determined by it. Therefore, the reasonable selection of computer system in CNC device is very important. 4. Electronic disk (storage module)

electronic disk is a unique storage module of CNC device. In CNC device, it is used to store the following data and parameters:

system software, system inherent data; Configuration parameters of the system (number of feeding axes that the system can control, definition of axes, system gain, etc.); User's part processing program

there are three types of storage devices used in the computer field:

magnetic storage devices, such as soft/hard disks (read/write). Optical storage devices, such as optical discs (read only). Electronic (semiconductor) storage devices, such as RAM, ROM, flash, etc

the first two types are generally used as external memory, which is characterized by large capacity and low price

electronic memory devices are generally used as memory devices, and their prices are higher than the first two categories. According to its read-write performance, it can be divided into three categories:

read only memory elements (ROM, prom, EPROM, E2PROM); Volatile random access memory element (RAM). Nonvolatile read/write storage element

such devices include:

e2prom; FLASH； RAM with backup battery

in CNC devices, electronic memory devices are often used as external memory, mainly considering that the working environment of CNC devices may be subject to electromagnetic interference, the reliability of magnetic devices is low, and the anti electromagnetic interference ability of electronic memory devices is relatively stronger

because the storage unit composed of electronic devices is managed according to the way of disk, it is called electronic disk. The specifications of the electronic disk are: 1.44MB, 2.88mb, 6MB, 12MB, etc

5. PLC (programmable logic controller) module

plc module: the module of CNC device to realize sequential control

function of PLC module: receive relevant signals from the operation panel, travel switches, sensors, buttons on the machine tool, relays in the strong current cabinet, spindle control and tool magazine control, and output them after processing to control the operation of corresponding devices

switching signal, analog signal and pulse signal

due to its type, level, power and anti-interference, the above signals generally cannot be directly connected with CNC devices, and an interface is needed to transform and process these signals

this also brings a larger market for consumer enterprises of instruments. Therefore, the purpose of PLC module transformation is:

to meet the input and output requirements of CNC system. Signal conversion mainly includes several aspects:

level conversion; A/d, d/a conversion; Digital quantity and pulse quantity are mutually converted; Power matching; Block external interference signals from entering the computer, and electrically isolate the CNC device from external signals, so as to improve the reliability of CNC device operation

plcs for CNC machine tools are generally divided into two categories:

built-in type PLCs (or integrated and embedded). Stand alone type PLC (or general type)

6. Position control module

position control module is an important part of the feed servo system and an interface module between CNC device and servo drive system when realizing trajectory control

commonly used position control modules are:

open loop position control module: the interface between CNC device and stepping motor drive power supply; Closed loop (including semi closed loop) position control module: the interface between CNC device and DC and AC servo drives

7. The functional interface module

realizes the interface board required by the user's specific functions. Examples:

profiling controller interface; Laser processing focus automatic tracker interface; Interface board of signal collector in tool monitoring system

III. introduction to CNC system (hardware)

CNC system in China is one of the high-performance CNC systems with independent copyright. Based on the general industrial PC, it adopts an open architecture, and the reliability and quality of the system are guaranteed. It is suitable for multi coordinate (axis) CNC boring and milling machines and machining centers. After adding corresponding software modules, it can also be applied to other types of CNC machine tools (CNC grinding machines, lathes, gear processing machines, etc.) and special processing machines (laser processing machines, wire cutting machines, etc.)

IV. introduction to CNC system hardware with multi master structure

in the multi master CPU structure, there are two or more CPU components, which are tightly coupled, and there is a centralized operating system. The bus contention problem is solved through the bus arbiter (composed of hardware and software), and the information exchange is carried out through the common memory

1. Characteristics of multi master structure:

it can realize real parallel processing, with fast processing speed, and can realize more complex system functions. Strong fault tolerance. After a module fails, it can still continue to work through system reorganization.

2. Structural form of multi master structure:

shared bus structure; Shared memory structure

structural features:

functional modules are divided into master modules and slave modules (ram/rom, i/o modules) with CPU. Taking the system bus as the center, all master and slave modules are inserted on the strictly defined standard system bus. The bus arbitration mechanism (circuit) is used to adjudicate the competition of multiple modules requesting to use the system bus at the same time

advantages of shared bus structure:

simple structure, flexible system configuration, relatively low cost and high reliability

disadvantages of shared bus structure:

bus is the bottleneck of the system. Once the system bus fails, the whole system will be affected; Since the use of the bus needs to be arbitrated, the information transmission rate is reduced

structural features:

it is designed for common memory, that is, multi port is used to realize the interconnection and communication between main modules, and multi port control logic is used to solve the conflict between multiple modules accessing multi port memory at the same time

because the design of multi port memory is complex, and for more than two main modules, the contention memory may cause the blocking of memory transmission information, so this structure generally adopts dual port memory (dual port RAM)