Network control system of CNC machine tools based on industrial Ethernet

The networking of CNC equipment and computers in the manufacturing workshop to form a DNC (Distributed Numerical Control) system has become one of the core technologies that urgently need to be solved to achieve CAD/CAM integration and computer-aided production management integration. The realization of the communication network is the most critical technology for building an integrated DNC system. It generally includes two levels. The upper level is the communication between the DNC host and the CAD/CAM/CAPP, MRPII system server, and the lower level is the communication between the DNC host and various CNC equipment in the workshop. There are many methods for networking CNC machine tools, such as serial communication methods, MAP communication technology, fieldbus, Ethernet, etc. Although these communication methods have achieved the networking of CNC machine tools to a certain extent, they have more or less some shortcomings in application. In order to improve the integrability of the CNC machine tool networking control system and meet the real-time scheduling function, the author proposed a CNC machine tool networking control system based on industrial Ethernet.

1 System Structure

The structure of the system is mainly selected according to actual needs. The factors that need to be considered mainly include the environment of the workshop, the degree of automation of the factory, and the information integration of the management level. The system uses industrial Ethernet as the network platform. The anti-interference design of industrial Ethernet ensures smooth and real-time communication in the harsh environment of the workshop, and is easy to integrate with the management level. The system adopts a bus + star topology. The backbone network adopts a bus structure, which is easy to form a redundant ring network. The local star structure is used to avoid the failure of a certain device affecting other devices. The topology of the system is shown in Figure 1.

The protocol converter that realizes the connection between CNC machine tools and industrial Ethernet is essentially a converter between industrial Ethernet data packets and RS232 data packets. It is connected to industrial Ethernet upwards, using an industrial-grade RJ45 interface, and is connected downwards to CNC machine tools with RS232 serial ports. The protocol converter can be installed on the CNC machine tool as a component of the machine tool.

2 System Functions

2.1 Communication function

(1) Bidirectional transmission of NC programs All CNC equipment implements networked centralized management, and uses the network to perform bidirectional transmission of NC programs (including machine tool parameters, tool compensation files, macro programs, etc.), thereby realizing massive storage and integrated management of NC programs. Each CNC machine tool is defined as a client device. Using the CNC system's own communication port (usually RS-232) and communication function, the operator can perform bidirectional data transmission on the CNC machine tool side and access all operations of the server-side data. The server side automatically processes the operation request of the CNC side without human intervention. Ensure that all networked CNC devices can perform concurrent communication transmission at the same time.

(2) Online processing requires the CNC system itself to support online processing functions, which can realize breakpoint resumption, subroutine call and other functions.

(3) Data sharing allows operators to access other CNC equipment or virtual machine tool information on local CNC equipment, facilitating part transfer processing.

2.2 Control function

In this module, the DNC server communicates with the CNC, and can collect the processing status, networking status, tool information, operation history, and tool life of the CNC machine tool in real time. And through certain authority confirmation, various equipment parameters and operating parameters can be modified online, so as to achieve complete monitoring of the underlying equipment. By processing the collected working condition data, the data required for production management such as processing performance and machine tool utilization can be obtained in time. Due to the ever-changing production conditions, many random situations will occur in the production process. Therefore, professionals from different locations and departments need to have a free communication platform to work on the same equipment, realize information interaction and experience exchange through the network, and finally realize remote monitoring of the equipment. The remote monitoring module uses computer technology and network technology to provide a platform for sharing resources in a wide area, and provides support for real-time monitoring and fault diagnosis. Users can query the equipment operation status and the working conditions of the equipment site at any time through the network, and conduct real-time remote monitoring of the production process.

2.3NC program management

As a very important resource in the machining process, efficient data management of NC programs has become an indispensable part of the DNC system. According to the different management targets, the management of NC programs can be divided into the management of the program life cycle and the management of NC program internal information.

The management of the internal attributes of NC programs mainly includes the management of program number, program annotation, part drawing number, part number to be processed, processing process number, processing range, machine tool, user information, etc. In this system, the program can be searched for multiple conditions according to the drawing number, part name, process, machine tool, etc., and the editing history of the processing program, the list of tools used, process cards, etc. can be managed at the same time. Sometimes it is impossible for the processing program written by the NC programmer to meet the processing requirements at one time. According to the processing process, the program is divided into 4 states: ① Editing - the program is divided into folders specified by each programming software. When the programmer loads it into the program library, the associated information includes: program number, program name, program text, part number, part name, process file name, process number, step number, writer, writing date, tool table, part picture. ② Trial cutting - the program is in the trial cutting verification stage. ③ Locking - the program is transferred back from the machine tool to the computer after the trial cutting is correct. ④ Finalization - the program that is reviewed and archived.

The program management process is as follows: after the programmer (with the authority to edit and modify) completes the modification, simulation verification and other work, the program is loaded into the trial cutting verification area of ​​the corresponding database, and the NC program related information is input by filling in the form. At this time, the program is in the editing state. After the approval of the programming supervisor (with the authority to unlock), the program is changed to the debugging state. After that, it can be sent to the machine tool for trial cutting, or the program can be called remotely from the machine tool's control panel; the program with no errors in trial cutting verification and debugging is sent back to the lock area of ​​the database with the approval of the program supervisor, and the program status is locked at this time; after the technical supervisor (with the authority to approve) reviews and confirms that it is correct, it is officially entered into the database for finalization and archiving, and the program becomes read-only and cannot be modified in the future (only a few people with authority can modify it). The entire management process is shown in Figure 2.

3 Key System Components - Converter Design

The working principle of the industrial Ethernet protocol and RS232 serial port protocol converter is to transparently transmit any information from the serial port device to any computer on the industrial Ethernet, and to transparently transmit any control information from the upper layer to the CNC device. By configuring the IP address for the protocol converter, the CNC machine tool becomes a node in the network, thereby achieving the functions of centralized management of CNC machine tools, such as file transfer, status monitoring, etc. The structure of the protocol converter is shown in Figure 3.

The protocol converter is an embedded system. Using the ARM (Advanced RICS Machines) chip produced by PHILIPS as the processor, in the integrated development environment ADS1.2 (ARM Developer Suite) of ARM, by transplanting the real-time operating system C/OS-Ⅱ and TCP/IP protocol on the chip, the serial port monitoring software based on C/OS-Ⅱ is developed to realize the conversion of serial 17 data to industrial Ethernet data packets. Its working process is as follows: once the serial port monitoring software finds that data has arrived on the serial 17, an interrupt is triggered, and the system calls the protocol conversion interrupt service program to convert the data into industrial Ethernet data packets, and then sends them to the management computer through the intelligent switch. The whole working process is shown in Figure 4.

4 Conclusion

Industrial Ethernet communication can meet the communication requirements of network control of CNC machine tools in workshops. The DNC system based on industrial Ethernet unifies the information network of workshops and even the entire enterprise with the DNC communication network. It achieves the integrity, transparency and consistency of the information of the entire workshop, and can directly connect CNC machine tools to the Internet to realize remote information transmission, which meets the needs of network manufacturing. TT, IIeVAX has become the development trend of industrial field control. The network control system of CNC machine tools realized by this technology has reliable performance, is easy to promote and apply in enterprises, and has broad application prospects.