Application of the hottest CAN Fieldbus in DNC Int

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The application of CAN Fieldbus in DNC Integrated Manufacturing Technology

1 introduction

in the past ten years, people have devoted a lot of energy to FMS (flexible manufacturing system) in the research of automatic machining workshop. Since FMS not only pays attention to the integration of information flow, but also emphasizes the integration and automation of material flow, the practice in the past 10 years has proved that although FMS has the advantages of high operation efficiency and high degree of automation, it has high investment risk, slow effectiveness and poor reliability. Compared with FMS, DNC (direct numerical control or distributed numerical contro1) is an integrated manufacturing system with small investment, fast efficiency and good flexibility. With the development of computer technology, numerical control technology and network communication technology, the connotation and function of DNC are also expanding. The current DNC system has the functions of manufacturing data transmission (NC program upload, NC program correction file download, tool instruction download, etc.), status data acquisition and processing (machine tool status, tool information, etc.), tool management, production scheduling and monitoring, unit control, CAD/CAPP/CAM interface, etc. In the past research, DNC Integrated Manufacturing System mostly adopts serial or local communication mode to realize. The serial communication mode is simple but has poor reliability and low efficiency, while the local communication mode has complex communication protocol, which is difficult to meet the real-time requirements of DNC system, so it is more suitable for D (5) to read values, record experimental data, and prepare the communication between the next impact NC system and the upper control computer

2 DNC Integrated Manufacturing System Based on CAN bus

the integration method of CNC system and upper control computer is the most critical technology in DNC, and its communication mode depends on the communication interface and communication protocol of CNC system. Because the foreign production environment is relatively good, and most CNC systems use high-end CNC systems with DNC communication interface, some DNC Integrated Manufacturing software has appeared abroad, such as visual DNC, etc. However, these software can not adapt to the situation of Chinese enterprises. Therefore, the study of DNC system suitable for the characteristics of Chinese manufacturing enterprises has become an inevitable requirement for the development of modern manufacturing system

in view of the characteristics of the existing machine tools in domestic enterprises, such as complex interface, decentralized layout and complex lower level communication, and in view of the problems existing in point-to-point and local areas, this system proposes to realize the integration of heterogeneous NC systems based on CAN bus communication standard and taking software plug-in technology as the core. As a communication standard in industrial environment, can is more suitable for the interconnection of field level equipment. It is the best choice for the communication connection between DNC bottom and CNC machine tools at present. At present, the emergence of many can modular products in China has laid the foundation for the application of CAN bus. Therefore, can bus mode is an ideal DNC communication mode of heterogeneous CNC system

3 functional model design of DNC Integrated Manufacturing System

the system is mainly composed of network server, DNC host, can intelligent module and other parts. The system hardware is shown in Figure 1. Its structure is the architecture of client and server. The network server manages the database, stores production tasks, numerical control programs, 198 PVC door and window pulley drawings, process documents and other information, and can be connected with enterprises or Internet upwards to realize resource sharing within or among enterprises. It can be connected with CAD/CAM/CAPP system and DNC host through local area, so as to exchange various manufacturing information conveniently through the network; DNC host is equipped with network interface card and can interface card, which is the core of the whole system. Its main task is to communicate with can intelligent module through can interface card to realize communication control and communication management of NC machine tool. When the machine tool applies for NC program, queue management and distribution of tasks are carried out according to the collected machine tool status information, so as to realize real-time monitoring of communication process. When there is no application, communication et log management or NC program and equipment management can be carried out. The visual human-computer interaction interface of DNC host is simple to operate, which can facilitate the insertion, query, modification, and other operations of records in the database

Figure 1 DNC Integrated system hardware principle machine network topology structure diagram

the key to realize DNC integration is to solve the problem of two-way communication between NC machine tools and computers. This system not only considers the NC machine tools with RS232 interface, which are widely used in China, but also takes into account the new machine tools with map interface, and connects with NC machine tools with various topologies. Its structure is shown in Figure 1. This system has three types of typical connection modes:

the first type of connection mode is mainly used for new machine tools with map connection i=i. Because this machine tool interface meets the map standard, it can be directly connected to the local area

the second type of connection mode is mainly for a few economic CNC machine tools that do not have serial connection i=i. for this kind of machine tools, an adapter should be added between the can intelligent module and the machine tool to connect to the can network

the third type of connection mode is mainly used for CNC machine tools with serial interface, which cannot be directly connected. Therefore, CAN fieldbus technology is used to connect the machine tools such as DNC network. The network function of CAN bus is realized by DNC host equipped with can interface card and can intelligent control unit. Here, the can communication card adopts pci5110 single-way intelligent can connection i=i card and can232b intelligent can converter of Zhou Ligong single chip microcomputer company, The communication card provides drivers under windows and dos and can general interface library, which can fully realize the can communication function between DNC host and CNC in this system; The core of the can converter is the processor of the CAN controller and the can transceiver, and an electrical isolation circuit is added between the microprocessor and the can transceiver to improve the anti-interference of the system. With one RS232 channel and one can channel, the machine tool can easily access the can network without changing the original hardware structure. The can232b intelligent can converter provides basic control commands and configuration software, The serial communication parameters are set by simple control commands, which can be configured according to the requirements of machine tools from different NC manufacturers, which solves the problem of poor portability between platforms and improves the openness of the system

4 system software implementation

in this system, the client/server architecture is adopted between the database server and the DNC main control computer, and the background database server is a DBMS with SQL as the language; We use c++builder enterprise6.0 as the foreground user development tool. C++builder is the latest visual programming tool released by Borland company. It perfectly combines the object-oriented programming method with advanced technologies such as database technology, network technology and visualization, and uses its rich controls to intuitively and quickly develop high-quality windows applications; In the process of software design, the modular design idea is used to divide the operation platform into different functional modules, so that each module can process the corresponding information and complete a specific function, which has a certain degree of independence; Each module forms a complete system (as shown in Figure 2)

Figure 2 functional structure diagram of software module

the host, can intelligent control unit and CNC system work in a request/response manner. For the remote control of the NC system, the host sends the command first, and the NC program can be loaded and downloaded by the NC system first. The can intelligent control unit mainly completes the two-way transmission of information between the host and the conditioning ruler NC system. At present, the communication protocol of CNC system generally has three layers, namely, physical layer, data link layer and application layer. Due to the addition of CAN bus, it is necessary to establish a new protocol correspondence between the host, front-end and CNC system. But the communication protocol of CNC system is different, and the front-end program is different. Therefore, the host program should establish the corresponding communication protocol conversion software module for different NC system communication protocols and NC functions, and package it into the "software plug-in library", so that the module can be directly downloaded to the can communication front-end unit connected to the machine tool

therefore, the following technologies are mainly used in the whole system design process:

(1) client/server based architecture in recent years, the most effective open architecture of distributed database is client/server architecture. This structure is a network computer structure composed of client and server, which solves the problem of distributed processing of client applications and server databases. The tasks of the application are shared by the client (DNC host) and the server respectively. On the one hand, the processing capacity of the client is given full play, and on the other hand, the burden of the server is reduced. In this system, in order to manage and maintain the processing equipment, processing program, machine tool status and other information in time, we establish the connection between the client/server through the controls in the ADO component group provided by c++builderenterprise6.0, and set its connectionstring attribute to realize the access to the local machine or remote SQL database. In addition to task allocation and relevant drawings, process information The transmission of NC program code and other information, so the system must have networking function. We implement it through socket control

(2) the introduction of the idea of software plug-ins

due to the different types of NC processing equipment purchased by enterprises, the different NC systems configured, and their data transmission interfaces and communication protocols, how to realize the integrated control of heterogeneous systems is a technical problem worth studying. At present, CNC system manufacturers all over the world have been actively looking for a way to solve the problem of communication protocol standardization. Before the standardization of communication protocol, many CNC machine tool integrated control only developed intelligent hardware equipment and interface standards, relying on intelligent hardware devices to realize the communication of heterogeneous systems. These hardware devices have long development cycle, high cost and poor adaptability, and their promotion and application are limited. Taking software as the main technical means to realize the integrated management of heterogeneous systems has not been paid enough attention. As we all know, by inserting a hardware card (called a hard plug-in) into the computer bus slot, the computer can realize the corresponding functions. Accordingly, the function of DNC hardware device can also be realized by software. We use the idea of modularization to develop different communication protocol software for different NC system protocols to form a communication protocol conversion library. When different NC systems are connected, we only need to call different communication programs to set the corresponding communication parameters. This is "software plug-in technology", and this communication protocol conversion library is "software plug-in library", This technology provides a new architecture for DNC system communication

5 conclusion

this system makes full use of the special advantages of CAN bus group, solves the inherent limitations of the common local area network NC system, and has the advantages of reliable operation, simple structure, low cost, good real-time and scalability; Software plug-in technology is used as the design core of communication protocol conversion software of heterogeneous CNC system; In the design process of the system, the communication competition is considered and solved, which greatly improves the number of controlled devices, communication speed and communication distance. In a word, the development of this system can easily realize the information sharing with other CAD/CAM systems, and successfully laid the necessary technical foundation for the further development of FMS and CIMS products


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