The network analysis analyzes the composition of the network numerical control system, which includes two aspects: internal network and external network.
First, the internal network
The internal network is connected to the fieldbus network by the CNC unit in the index control system and the units such as servo drive and I/O logic control.
Second, the external network
The external network is an index control system that is connected to the network through other Internet control systems or external host computers. Remote control and unmanned operation of remote processing program transmission, remote diagnosis and remote maintenance services, technical services, and resource sharing through remote control of the equipment.
1 Work platform supporting multiple operating systems
Network CNC is a resource that supports global manufacturing. The most basic requirement is to support cross-platform operations. Using the functionality provided by Java to achieve hardware and operating system independence, you can build an open control platform. The Java language is more reliable than the c and c++ languages, especially suitable for network automation. It makes remote diagnosis, remote monitoring of remote services and remote processing easier through the network. Therefore, the United States, Japan, Europe and other countries are actively studying Java-based. Language network control system. However, Java does not fully meet the needs. It has two defects:
(l) Dynamic management of memory. Java automatically clears the memory space that is not used in memory for the user, making the uncertainty of the GC algorithm contradict the real-time calculation;
(2) Cannot access the underlying memory hardware. Once users directly access the underlying device, it is bound to undermine the cross-platform features of Java.
At present, it is common to integrate the operating platform architecture into the Browser/Server architecture (B/S architecture), which is also an important difference from the traditional CNC system. In order to achieve portability in a heterogeneous environment, that is, when the monitoring computer and the gateway use different operating systems, the network numerical control system should not need to modify the software system, and the access interface provided by the gateway to the monitoring computer is implemented by the web: from the scene The obtained data is provided to the monitoring computer through the web server through the web server in the form of an HTML page; the monitoring computer implements the interaction process by using the browser as a client tool for access, and the processing instruction or program is transmitted to the site through the web server through the web server in the form of an HTTP message. Node, to achieve control of the CNC machine.
2 Network communication function of network numerical control system
The key issue of network numerical control technology is to study the network communication function of the numerical control system. In order to share the resources of the computer network, it is necessary to realize communication between entities in different numerical control systems. The entities here include computer terminals and various network CNC systems and other related equipment. In order to achieve compatibility with different manufacturers' communication network equipment, and provide a framework for the development of computer network standards. The International Organization for Standardization (ISO) has developed an open CNC network interconnection standard communication model (OSI). It is a standard framework for connecting heterogeneous computers. Its purpose is to provide a common basis for the development of system interconnection standards, and to guide the development of computer network and data communication system products, and at the same time play a guiding role in the development of network technology.
3 Real-time operation and reliability of CNC system
At present, the Internet and Intranet mostly adopt TCP/IP network protocols, and high-speed Ethernet and ATM networks support such network protocols. However, within an open intranet, TCP/IP network protocols are not readily available for real-time communication. The main reason is that most computer networks do not allow continuous transmission of data of any length, but split long data into small pieces of data—packets are sent separately. In the event of data loss, the lost data needs to be resent. At the same time, the method of transmitting data while processing has its own limitations. On the one hand, the transmission process is prone to unpredictable errors such as on-site interference. On the other hand, a transmission computer is added to the processing to reduce the reliability of the numerical control system. More importantly, the speed bottleneck of the communication of the dedicated controller of the network numerical control system is formed. Today's complex profile cutting processes generally have high-precision and high-speed requirements. When the length of the complex facet interpolation straight section is less than 0.05mm, the transmission speed of the dedicated controller is only a few hundred millimeters per minute. This is far from meeting the requirements of high-speed machining such as profile engraving and high-precision surface milling.
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