Third, the integration of SanPDM and CAD/CAM
PDM, with its comprehensive management of information in the product life cycle, not only becomes an important part of the CAD/CAM integrated system, but also provides the possibility of CAD/CAM integration with PDM system as a platform. From a development point of view, this system has a good application prospect.
(1) Integration of CAM and PDM
Since only the document information such as the location file, NC code, and product model is exchanged between the CAM and the PDM system, the application package is used between the CAM and the PDM to meet the information integration requirements between the two.
(2) Integration of CAPP and PDM
In addition to document exchange between CAPP and PDM, the operation of CAPP system needs to obtain equipment resource information and raw material information from PDM system. The process information generated by CAPP, in order to support the information integration with MRP-II or the workshop control unit, also needs to be decomposed into basic information units (such as processes, work steps, etc.) and stored in the process information database for PDM and MRP-II integration. Use. Therefore, the integration between CAPP and PDM requires interface exchange. On the basis of implementing application encapsulation, the information exchange interface is further developed, so that the CAPP system can directly obtain the support of device resources and raw material information from the PDM through the interface, and generate it. The process information is stored directly in the PDM process information library via the interface. Since the PDM system does not directly provide the equipment resource library, the raw material library, and the process information library, the user needs to develop the management module of the above library by using the PDM development tool.
(3) Integration of CAD and PDM
The integration of CAD and PDM is the most demanding and difficult part of PDM implementation. The key is to ensure that the data changes in the CAD are consistent with the changes in the data in the PDM. From the perspective of user needs, the integration of CAD and PDM should achieve a true sense of tight integration. The application package of CAD and PDM only solves the problem of document management in CAD production. The component description attribute and the product list need to be imported into the PDM through the interface. At the same time, through the interface exchange, the two-way asynchronous exchange of data between the PDM and the CAD system is realized. However, this exchange still does not fully guarantee the consistency of product structure data in CAD and PDM. Therefore, in order to solve this problem, we must realize the tight integration between CAD and PDM, that is, establish a shared product data model between CAD and PDM, realize interoperability, and ensure the interaction between the modification in CAD and the modification in PDM. Consistency, truly two-way synchronization consistency. At present, this tight integration still has some difficulty. A PDM system can only achieve close integration with one or two CAD products.
Fourth, Ethernet-based DNC system
1 Ethernet-based DNC communication technology
Ethernet has become the mainstream technology of office automation because of its low cost, stability and high reliability. However, because its MAC layer protocol adopts CSMA/CD, it has the defect of queuing delay uncertainty, which makes it impossible to be effective in industrial control. use. With the development of IT technology, the 802.3 standard has increased the Ethernet speed from the original 10Mbps to 1 000Mbps. The application of sufficient bandwidth and switching hub solves the uncertainty of Ethernet, enabling Ethernet to meet the real-time system. Claim. For example, switching Ethernet is used to make the nodes accessing the network monopolize one line to avoid conflicts. If high-speed backplane switching or microprocessor switching is used, the response time is determined. According to ARC analysis, 126 nodes are 100M exchanged. Ethernet has a response time of 2-3 ms and can meet the requirements of various control systems. It is precisely because of the advantages that Ethernet already has, the extension of Ethernet as the mainstream technology of office automation to field devices has become the current development direction. The communication interface of CNC machine tool determines the communication technology used in DNC system. Although the new CNC machine tool provides Ethernet interface with the development of network technology, serial communication is mainly realized in point-to-point or star structure in DNC system. Or use the field bus as the communication network and connect the CNC machine tool with the serial port converter to realize the field bus communication. These communication methods have the disadvantages of not being able to release information networks, slow transmission speeds, and low performance-price ratios. This paper proposes an Ethernet-based DNC communication technology, and its network topology is shown in the figure below. The DNC controller is a programmable logic controller with network interface, serial port and digital and analog input and output interfaces. It has embedded Web service function and can realize HTTP access.
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