Abstract With the rapid development of Internet technology, World-Wk-Web technology has also been widely used in the field of system control. With the WWW, operators and experts can directly obtain data or conduct real-time monitoring from the control system. This article applies WWW technology to the design of a DNC system. Through the WWW, functions such as querying management information and engineering manufacturing data, system monitoring, uploading and downloading NC code, and feedback on operating status can be realized in the DNC system. Keywords: WWW, DNC, three-tier mode, client/server mode 1. Basic Structure Design of DNC System Based on Client/Server Mode The DNC system adopts the hierarchical control architecture that has been widely accepted, decomposing complex control functions into various levels, reducing the complexity of engineering development technology, and lowering investment risks. This hierarchical control and management system is based on work sections [or work units (WK CeU)] to realize distributed control and management. Under the control and management of work sections, the system has a two-level control mode: workstation control level and equipment control level. The equipment in the workstation control level is the workstation controller; the equipment in the equipment control level is the equipment controller. The workstation controller mainly includes: machining workstation and measurement workstation; the equipment controller mainly includes: control devices for various CNC machine tools, cleaning machines and measuring machines. The machining workstation, under the production management and control of the section level, is supported by the integrated environment of network and database, and mainly completes the corresponding workshop machining operations; the measurement workstation, under the control of the product quality manager, mainly completes the corresponding workshop measurement operations. The client/server model of the DNC system is shown in Figure 1. (1) The section level server has the function of formulating daily production operation plans and daily resource demand plans, and performs real-time scheduling of production and statistics of unit production information. (2) The workstation queries the work orders (process flow cards) and part process information issued by the unit controller, transmits the NC machining program and NC measurement program of the part over the network, manages the storage of local NC programs, and manages the local tool magazine. (3) The unit level client, with the support of the section level server, constitutes the client/server model, is responsible for section control, has the function of formulating daily production operation plans and daily resource demand plans, performs real-time scheduling of production and statistics of unit production information. (4) DNC workstation clients can access the section-level server to query the work orders (process flow cards) and part process information issued by the unit controller, transmit the part NC machining program and NC measurement program over the network, manage the storage of the local NC program, and manage the tool magazine of the local machining center. 2 Design of DNC system based on WWW 2.1 Internet structure mode The development of computer information technology has generally gone through three stages. The earliest information system was the so-called centralized model, namely the IBM mainframe era; later it developed into the master-slave client/server model; the current trend is the three-tier structure model. WWW is the most typical and common three-tier structure. No matter what browser users use to access WWW sites on the Internet, they can see the same operation interface. This feature also meets the requirement of DNC users to have a single operation interface, and also retains the overall flexibility, and the back-end server can still be expanded as needed. 2.2 Structure and design implementation of DNC system based on WWW The structure of the DNC system based on the three-tier architecture of the Web server is shown in Figure 2. The regional server within the dashed box is not included in the DNC system; this indicates a scheme where the DNC system is integrated with the higher-level system via WWW. In Figure 2, the DNC workstation (client) directly controls the NC machine tool through the web server, which serves as the human-machine interface for the DNC controller. The use of a universal browser interface facilitates system operation and upgrades. The DNC controller is the device that actually performs DNC functions within the DNC workstation control level. The section-level server contains various manufacturing information, such as manufacturing process information (machine tool operating status, machining status, etc.), manufacturing management information (daily job calculations, etc.), process data (NC codes including machining and measurement), and manufacturing resource data (tools, clamps, gauges, blanks, raw materials, etc.). The section manager uses the web server to allocate machining jobs and manage workshop tooling, equipment, process documents, quality information, etc. The processing results reside on the section-level server. The DNC workstation client can obtain this data through a web gateway and then control the DNC controller to perform corresponding tasks. Simultaneously, the DNC workstation client can also obtain on-site operating status information from the DNC controller and feed it back to the section server via the web gateway for processing by the section manager. Software on the web server (called a gateway) can execute external programs via CGI. For example, a DNC workstation client sends an application through the gateway. The gateway is connected to the URL. Once there is a request for the URL, the gateway will be executed, and the request parameters and the URL application will be sent together. The result of the gateway execution is formatted in HTML standard and sent back to the applicant. CGI (Common Gateway Interface) technology works as follows: (1) The DNC workstation sends a request to the web server, that is, outputs a standard Uniform Resource Address (URL). This request includes the type of service requested, the service program path, the CGI program, and user data. (2) The web server parses the request. If it is a CGI service, it starts the CGI program. The CGI program parses the information entered by the user. This data is passed to the CGI program, usually through environment variables, command line parameters, or standard input stream. (3) The CGI program in the WWW acts as a client of the DNC controller, outputs control commands (such as NC code download) to the DNC controller, and returns information such as the processing status of the DNC system from the DNC controller. (4) The CGI program generates a dynamic HTML document based on the data. (5) The Web server returns the HTML document to the DNC workstation. The DNC workstation can then complete the control and query operations. 3 Conclusion The WWW-based DNC system has cross-platform characteristics and a single user interface, providing a good solution for integrated manufacturing. Therefore, by adopting Internet technology in the DNC system, not only can the performance of the DNC system itself be improved, but it is also conducive to the information integration of the DNC system with other subsystems, thereby improving the operating efficiency of the DNC system. Therefore, the web-based DNC system has high practical value. References 1 Wu Zhui Research on DNC structure and DNC remote signaling structure. Modular Machine Tool & Automated Machining Technology. 1994(8) 2 Jin Zunhe. Research and development of distributed DNC system. Computer Integrated Manufacturing System, 1995. 3 Wang Shige, Liu Fei. Development of DNC integration technology. China Mechanical Engineering. 1998(2) 4 Li Yongjin et al. 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