1 The basic structure of CNC system
Figure 1 The basic structure of CNC
The CNC machine tool is the basic of network CNC. At this stage, the communication network between the master computer and the CNC machine tool mostly uses the field bus. Most CNC machine tools and fieldbuses are connected in two ways: The first connection method is used for new CNC machine tools. It has a network interface that conforms to the MAP standard and can be directly connected to the bus: The second connection method is an industrial computer. Connected with a single CNC machine to complete the NC program and data transfer. Thus, the monitoring of the machining process is completed. The basic structure is shown in Figure 1. 2 The technical background of video technology applied to network NC machining monitoring The increasing degree of automation of CNC machine tools and the rapid increase in complexity have caused increased maintenance costs and huge downtime losses. Therefore, the role of the monitoring system in network NC becomes very important. Through the real-time monitoring of the machining process of the machine tool, faults or abnormal conditions can be found in time and field workers can be notified. At the same time, remote fault diagnosis can be implemented in the remote monitoring center using remote video technology and the fault can be quickly eliminated at the remote site. The development of global computer networks, the maturity of multimedia technologies, and the large-scale application of sensor technologies have provided a solid technical foundation for the remote monitoring of networked CNC systems. In the machining process of CNC machine tools, there are some field characterizations that cannot be described by electronic signals. Such as pure mechanical failure, production environment, etc. These can all be solved by having cameras and single-frequency acquisition devices in the field. Video technology is used at the production site, real-time video transmission, scene dialogue, video conferencing, etc., enabling remote monitoring centers or operators to monitor the situation on the site more effectively. On-line monitoring also includes the monitoring of the main parts of the underlying equipment, sensor signals of components, directly-detectable equipment operating signals, fault warning lights and status change indicator signals of the underlying equipment and controllers, software alarm codes that can be displayed on numerical control equipment CRTs, etc. . All information can not only be processed in a timely manner in the local, but also all monitoring information can be processed into a form that can be transmitted on the Internet and sent to the remote monitoring and diagnosis center.
Figure 2 Online monitoring system information flow diagram
The online monitoring system information flow is shown in Figure 2. 3 Implementation Plan of Remote Video Surveillance With the further acceleration of the construction of domestic information highways, the bandwidth problems that have plagued people for many years will no longer exist. In the face of this tremendous change, the construction of a local area network for enterprises and the network numerical control system at the workshop level must be fully considered in terms of physical composition and the functions to be realized: the future information highway will realize the optical fiber of broadband transmission, and exchange technology. ATM (that is, packet-oriented asynchronous transmission mode based on fixed-length unit) Multimedia of integrated services (video/audio/image/graphic/text, especially video, single-frequency real-time interactive transmission) and information sharing database distribution The intelligentization of network management. Therefore, the transmission of the remote video uses the ATM network as the access network of the system. At the same time, the gateway is used to interconnect with different types of networks (ISDN, DDN, frame relay, etc.) in the earlier period. The system adopts a new type of MCU (including built-in gateway) to realize point-to-multipoint video and audio transmission. The built-in gateway's protocol conversion function can realize different types of enterprise LANs and different video communication systems (H.323 video terminals or H.320). Video terminal) smooth connection and communication. Remote video technology uses video conferencing. The video conference system will be integrated with the existing network CNC system. Through video conference perfect real-time multimedia interactive functions, a good collaborative work environment will be created. The video conference system's text chat, electronic whiteboard and application sharing capabilities can be used as an extension of the network's digital remote monitoring and diagnostic capabilities. In order to consider the compatibility of the system, different video conference system products should meet the International Telecommunication Union (ITU) T.120, H.320, H.323 and other international standards. The video conference system is embedded using the B/S network solution, which means that manufacturers, manufacturing companies and remote monitoring centers are connected through the ATM network. With the new MCU, the user only needs to log in to the server where the MCU's Web management software is installed through the browser, and then can join the conference according to the authorization. Through the conference management function of the management software, the user can initiate the multi-point conference function, which facilitates the timely elimination of the failure of the CNC machine tool. The implementation of the system is shown in Figure 3.
Figure 3 Network NC remote monitoring structure
4 System configuration videoconferencing endpoint: POLYCOM ViewStationMP. 1 Support H.323, video conferencing can be conducted on the Internet/intranet network, transmission speed up to 768kbps: 2 full-duplex digital audio, automatic background noise reduction and echo suppression: 3 automatic voice-activated tracking camera: 4 built-in web-based synthesis The demo system sends demo data for the remote site: In the multipoint conference, the language incentive switching method is used to enable participants to place themselves in the actual conference environment and automatically switch the screen to the speaker. Interactive Whiteboard: SmartBoard. VTEL's products can easily establish data networks, realize file transfer and sharing, graphic display and file image storage in multi-point conferences. It enables conference participants to exchange ideas, make records, and improve discussions. (Depending on the specific needs of the company, it can be determined whether or not it is equipped.) Multipoint Control Unit (MCU): AccordMGC-100. 1 Carrier-class modular structure: 2 Built-in gateway function enables H.320 (ISDN, DDN), H.323 (LAN, Internet, Intranet) and H.310 (ATM) different networks to operate on one system: 3 multiple encoding The conversion, different protocols have different algorithms, frame rates, bandwidth requirements, must be converted: 4 dynamic split-screen technology, which can simultaneously monitor multiple scenarios: 5 firewall solution technology, the standard firewall set by enterprises does not support real-time video, Audio streaming through the MGC-100 can effectively solve this type of problem. 5 Key technologies implemented by the system The multimedia communication protocol system adopts the H.323 protocol. The H.323 protocol system is a packet network-based multimedia communication system. It defines the functional components of terminals and devices for multimedia services provided on the packet network and the communication process. Providing voice, image and data communication protocols over packet networks. It adapts to packet-switched networks that provide reliable transmission (TCP) and unreliable transmission (UDP) mechanisms. Supports the video conference on INTERNET network, has provided the standard for intercommunication of multimedia communication products on INTERNET, INTRANET network. H.323 provides a variety of media encoding methods, such as G.711, G722, G728, and G.729 for audio, H.261 encoded CIF and QCIF, and H.263. Optional, data transmission using T.123, T.126, T.125 protocols in the Y.120 series, etc. These different combinations provide multiple options for different quality transmission applications. The ATM access technology ATM (Asynchronous Transfer Mode) will become the main transmission mode of the next-generation broadband network. ATM network adopts fixed cell and asynchronous way to guarantee the transmission efficiency, can do fixed bandwidth allocation, have high bandwidth, high efficiency and provide QoS guarantee, especially suitable for high-speed, real-time multimedia communication application. ATM can achieve up to 155 ~ 622Mb / s exchange rate. The use of an ATM network to connect to a real-time distribution system has the advantage of reducing the hosting capacity of the host, thus providing real-time services to the users and also supporting the TCP/IP network protocol.
Figure 4 Logical Subnet (LIS)
IPOVER ATM technology, as shown in the figure: Logical Subnet (LIS) is a combination of routers and routers connected directly to the ATM network based on the connection requirements of users and network managers. Each LIS has an ARP server responsible for the resolution of IP addresses and ATM addresses. IP packets can be transmitted over the permanent virtual channel (PVC) and the ATM switching virtual channel (SVC) of the point-to-point ATM. MCU (multipoint control unit) The multipoint control unit (MCU) is the main control and forwarding device of the video communication system. Through the MCU, multiple manufacturing companies can be added to the conference system, so that the system has good scalability. The function of the MCU is to realize the control and exchange of information between terminals. Specifically, the multi-point audio signal is mixed: a desired one-way signal is selected from each received video signal: the above-mentioned video and audio signals sent to each relevant user are mixed to form a composite output signal. The MCU allocates information in two ways: one is the multicast mode, which means that a user's multimedia information is allocated to several users at the same time. The second method is the Bridge mode, in which multiple users' multimedia information is synthesized and then distributed to multiple users. Online users. Newer MCUs, such as Accord’s MGC-100, incorporate advanced technologies such as built-in gateway technology: multiple-encoded conversions: dynamic split-screen technology: firewall solutions. Can realize the interconnection of H.320 network and H.323 network. 6 Conclusion Remote video technology as a good collaboration tool in the application of network NC, not only allows operators to more fully understand the operation of CNC machine tools, but also provides an intuitive environment for remote monitoring and operation. At the same time, real-time video and audio transmission facilitates timely feedback of remote fault diagnosis and solutions. At this stage, it is an effective means to improve enterprise agility. The system has passed the test on the campus of the university and achieved clear and stable images at the transmission speeds of 128kbps, 384kbps, and 512kbps.
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