Comparison of DNC structure of two NC machine tool

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Comparison of two kinds of CNC machine tool network DNC structure

at present, the two kinds of CNC machine tool network DNC with single PC corresponding to single machine tool and single PC corresponding to multiple machine tools are often used in the production of manufacturing enterprises. By comparing their advantages and disadvantages in detail, this paper shows that single PC corresponding to multiple machine tools should be the best structure of CNC machine tool network DNC

I. overview

with the continuous deepening of the use of numerical control technology and the continuous development of computer technology and network technology, people increasingly use these high and new technologies to improve their production efficiency. It is inevitable to use network technology to manage numerical control machine tools. After more than 20 years of development in China, DNC technology of NC machine tool network has also experienced a difficult process from paper tape to single machine, then to simple network, and finally developed into advanced network. The paper tape method has been basically completely abandoned; When the number of machine tools is small, some users still use single machine communication mode; When the number of machine tools develops to a certain number, machine tool users generally adopt the way of network DNC. However, through a large number of investigations, we find that there are two main structures of network DNC of CNC machine tools in China. One is to adopt the way that a single computer corresponds to a single machine tool, and these computers are connected through local area. Its structure is shown in Figure 1; The other is to adopt the method that a single computer corresponds to multiple machine tools, and its structure is shown in Figure 2. (this paper mainly discusses the network communication of RS232 mode, regardless of the communication of machine tool Ethernet and bus mode). Although there is a great difference between the two modes in terms of technology, as far as we know, there are still quite a few users who adopt the one-to-one mode, "existence is reasonable". Therefore, we will make a detailed comparative analysis and explanation on the DNC of the two structures below for the reference of a wide range of machine tool users

Figure 1 single machine to single machine mode

Figure 2 single machine to multi machine mode

2. Description of the advantages and disadvantages of single machine to single machine network

single machine to single machine mode is a common way of early NC machine tool network DNC (mainly in the early 1990s), which is basically equivalent to single machine communication mode, but the computer is connected on the basis of single machine communication. At that time, computer technology and network technology, especially serial communication technology, were not very developed, and a single PC could not meet the requirements of DNC processing of multiple machine tools at the same time in terms of software and hardware. It was a natural assumption to use a single PC to control a single machine tool. Its advantages and disadvantages are as follows:


1 Overview of double head grinding machine 1 Separate control without mutual interference: the failure of a single computer will not affect the operation of other machines. Moreover, due to the redundancy of PC resources, the failed PC can be temporarily replaced with the PC of other machine tools. Obviously, this mode is conducive to the stable operation of the system

2. Simple network structure: it is only a simple local network, which is conducive to the maintenance of the system

3. Simple software requirements: for users with relatively simple functional requirements, they only need a simple stand-alone communication program without complex network communication program. Many users using this mode use V24, pc-in, Pcomm, or other stand-alone software

4. Low system construction cost: since each machine tool only needs to be equipped with one computer, the software can be basically free, and manufacturers with relatively high level can also carry out wiring construction and system installation by themselves, so the cost is low


1 The computer layout is scattered and difficult to manage. Especially in today's era of rampant computer viruses, a moment's neglect of management may cause the paralysis of the whole network. In some poorly managed workshops, operators use computers to play games. In order to solve this problem, some manufacturers often remove the computer floppy drive and optical drive. Although it can inhibit the occurrence of virus, it is a practice of cutting feet to suit shoes after all

2. Ordinary computers in the processing environment for a long time will reduce their service life. Especially in the processing environment, there is more dust, large voltage fluctuation and strong electronic interference. The use of computer peripherals, such as floppy drive, optical drive, mouse and other equipment, is very frequent, which accelerates the damage of these peripherals. If the industrial computer is replaced, although these effects can be reduced, the system cost will be greatly increased

3. It is difficult to upgrade and maintain the system: Generally speaking, the service life of the PC is about years. Once it reaches the renewal age of the PC, all PCs in the workshop must be replaced, which is equivalent to the reconstruction of the DNC network system, and the cost is very expensive

4. The number of computers placed on the production site is too large, occupying a large amount of valuable workshop area, which brings trouble to the arrangement of the workshop production site

5. In order to save money, some users share one computer with two or more machine tools, which is equivalent to completely returning to the single machine communication state. The serial port needs to be plugged in and out frequently, which increases the possibility of serial port damage and is not conducive to the simultaneous service demand of multiple machine tools

6. Poor compatibility of stand-alone software: due to the use of free stand-alone software, various CNC systems are not fully compatible. Various CNC systems use different comprehensive consideration communication software, which brings a lot of trouble to workshop operators

7. The function of stand-alone software is too simple, which is not conducive to system expansion: the stand-alone software used by most users is free software such as V24. The function is very simple, which can only meet the needs of program communication. It also needs the echo of PC end and CNC end. Although PC and CNC are generally very close under this structure mode, it is not very convenient in the end, There are many functions that can not be completed by the stand-alone software in the following chapters

8. The program management is open, which is unable to carry out standardized management and is not conducive to technical confidentiality

9. The integration degree of the system is too low: each single computer is responsible for the program management of a single CNC. At most, PCs can only share files through the local network. There are a large number of software and hardware resources that can not be shared, which is actually a waste of resources

III. description of advantages and disadvantages of multi machine network

with the continuous development of serial communication technology, stable and reliable multi-channel serial communication equipment began to be sold in the market in the mid-1990s. In addition, the CPU speed of the computer has been greatly improved, and the perfect support of Windows95 in multi threading can perfectly solve the requirements of single PC to meet the simultaneous DNC processing of multiple machine tools in terms of software and hardware, Therefore, the network technology of NC machine tools has developed the communication mode that a single computer controls multiple machine tools. Based on this, DNC developers have developed many other more perfect DNC functions. Its advantages and disadvantages are as follows:


1 Highly integrated management of the system: a single PC completely replaces the previous work of dozens of PCs, which not only eliminates the pain of managing many computers in the workshop, but also saves the trouble caused by placing many computers in the workshop, but also makes the software and hardware resources used shared to the greatest extent

2. Good PC operating environment: due to the adoption of client/server network mode, the only main PC as the server can be placed in the office with relatively good environment, which avoids the severe test of PC in the workshop processing environment, protects the core information resources of the enterprise, prolongs the service life of the machine and enhances the stability and reliability of the system

3. High software compatibility: due to the adoption of a set of network DNC system, it can meet the communication needs of various systems. Workshop operators can operate the communication process of machine tools as long as they can, without being familiar with the special conventions of various systems, and the operation is simple and concise

4. Processing files, such as NC program, machine tool parameters and tool compensation parameters, can be managed in a standardized process to improve the management level of enterprises

5. The networking software has powerful functions: since it is a networking software, it has not only the basic functions of the stand-alone communication program, but also can meet the various communication needs of multiple machine tools in the workshop under various modes, but also adapt to the continuous development and changes of workshop production. The functions of networked DNC software are listed as follows:

1) two way transmission of NC program: all NC equipment implements joint and centralized management, and multiple machine tools can be used for two-way transmission of NC program and DNC processing at the same time, so as to realize mass storage and integrated management of NC program

2) client/Server Structure: define each NC machine tool as a client device. Using the RS-232 interface and communication function of the NC system (without any change to the NC system), the operator can carry out two-way data transmission at the NC machine tool end and all operations of accessing and managing the data at the server end. The server end automatically processes the operation requests of the control end without human intervention

3) quantity and distance: each computer can manage 256 CNC machine tools at most, and the communication distance can reach 2km at most

4) communication protocol: the system supports multiple communication modes (RS232/422/485, TCP/IP) to meet the communication requirements of various machine tools

5) program format processing: it has the ability to process processing programs for different machine tool control systems, that is, during transmission, program headers and special control characters can be replaced, added and deleted

6) interactive event response mechanism: every operation at the NC end will have a feedback message, that is, whether the operation is correct or not, the operator can get prompt information at the NC equipment end

7) data sharing: the operator can access other CNC equipment in the local CNC equipment to facilitate the transfer and processing of parts. When a NC machine tool needs NC programs on other NC machines of the same type, it can be realized by modifying the number of the NC machine tool in the uploaded file. Similarly, when the process personnel compile the processing program, they only need to put the program file into the specified machine tool directory or virtual machine tool directory, and the workers can download it from the specified directory during processing

8) query and download: if the annotation character is written in the NC program according to the regulations, the computer will automatically process the file according to the content of the annotation character when the NC program is uploaded from the NC machine end to the server

9) DNC processing: DNC processing in full client mode enables the startup, entry, exit, interruption, breakpoint continuation and other functions of DNC processing to be realized at the NC machine tool end, while external subroutine call, line number reset, breakpoint intelligent connection and other functions are integrated into the system without manual intervention

10) information collection: realize the real-time collection of machine tool processing information through the I/O variable output function of NC system (for NC system without I/O variable output function, report output mode)

11) networking platform: realize the networking management of tool parameter information, equipment fault information, process information and production task information processing through DNC networking platform

the functions listed above are not available in the stand-alone DNC software


1) too high degree of integration: integrated management is also a double-sided blade. On the one hand, integrated management can indeed bring benefits to us, which is our goal, but excessive integration may bring hidden dangers to the stability and reliability of the system. Once the PC server main machine is paralyzed, the whole machine tool network DNC will be paralyzed, resulting in immeasurable losses to workshop production. This is also like "putting eggs in one basket is safe or putting them in multiple baskets is safe"男性不育少精弱精治疗要多久

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