PC-based open CNC system
Completely open numerical control system, expounds the software and hardware structure of this kind of numerical control system and the realization method.
In the past 50 years, CNC systems have gone through two stages and six generations of development. After developing into the microprocessor era, with the rapid development of computing technology, information technology, and network technology, closed and dedicated systems have increasingly exposed their Inherent problems. Different operating systems, programming languages, man-machine interfaces, communication interfaces, etc., have given designers and integrators of CNC systems an attempt to adopt a fast The integration of the system into different environments has caused great difficulties. For this reason, people have put forward standardization, that is, open design issues to facilitate parallel cooperation and rapid integration; among them, the most influential research projects include OSEC in Japan, OSACA in Europe, and OMAC in the United States. In recent years, foreign parts The design of the CNC system has begun to realize its openness within a certain range, such as the MTC200 system of Indramat of Germany and the Acramatic 2100 system of Vickers Electronic System of the United States. At present, domestic research mainly focuses on open CNC systems based on software chips, open CNC system monuments based on Windows 95/NT, and open CNC systems based on SERCOS fieldbus technology. The main purpose of the CNC system is to establish a modular, reconfigurable, and expandable system platform, improve the interconnectivity of the control system, and enhance the flexibility and integration of the CNC system. The openness of the CNC system can be roughly divided into 3 ways, as shown.
1.1 Open man-machine interface This way enables intercommunication within the system, between the system and external equipment, between the system and the communication network, and between this system and other systems, and can give full play to the exclusive use of each manufacturer on the basis of maintaining the original numerical control. The special function of the chip, but the opening of the man-machine interface only provides users with a way to flexibly customize the operation interface according to their own needs.
1.2 Open control kernel layer interface This method can determine the composition of system components according to specific application conditions, and can integrate its own control software modules according to the interface protocol.
It can give full play to the role of the PC, and use it to complete some tasks that are not real-time or non-periodic, while the control tasks with strong real-time performance can be completed by NC or PLC.
1.3 Controlling the full openness of the kernel layer is a completely open solution. It is actually a DNC structure, that is, a digital servo is connected with a PC-based NC device with an optical cable to form a highly reliable. Real-time, complete CNC system; it allows users to develop software modules and hardware modules in special application areas according to open structure standards and specifications, or configure system functions on demand without relying on any system manufacturer and developer .
2 A PC-based open CNC system hardware structure As a truly completely open, high-end CNC system, its hardware structure should be simplified as much as possible, and system functions should be implemented through software as much as possible. The hardware structure of the open CNC system developed by the author is shown as the bus interface and data exchange protocol, which is currently the ** international standard for digital servo and drive data communication. m. SERCOS is connected by optical cable to form a closed loop. The different addresses of the servo system and the PLC use the SOFTSERCANS card inserted in the computer to realize the real-time data communication between the computer and the digital servo system. Real-time data communication mainly completes the data exchange of command value and actual value between PC and servo. In this system, the data exchange is completed within 2ms.
2.2 Software structure Due to the simplification of system hardware, the entire development process is mainly software design, software development and operating environment WindowsNT 2.2.1 Real-time control High-precision, high-speed CNC systems require high real-time performance, generally within 1ms the following. But under the Windows95/NT platform, to achieve such high timing accuracy, it is difficult to meet the real-time performance of high-end CNC systems through multithreaded programming. Therefore, the NT subsystem is selected in this system and it has its own operating environment and applications. Programming interface; its thread management has the highest priority, and it can independently realize the real-time control of the system without responding to messages. In this system, RTX4.2 is used to develop application programs to realize the real-time transmission of cyclic data and part of acyclic data.
2.2.2 Data exchange between PC and servo The data exchange between PC and servo is realized with the help of SOFTSERCANS card. The software is divided into 4 steps. After each step is completed, there is a status return to determine whether the next step is to proceed: check whether the optical cable ring is closed; confirm the servo driver in the optical cable ring, and write the corresponding address into the system parameters; read /Write the system parameters in the servo drive and confirm the status of the drive; data exchange, send the command value from the command value channel to the servo system, and send the actual value from the actual value channel to the PC at the same time.
2.2.3 Development of soft PLC Soft PLC is a key technology based on PC open CNC system using software to realize control. Since the logic of the machine tool is related to the motion of the machine tool, and the control signals are mostly switches, they are processed by commands in the software design; if there is an M08 instruction in the NC program or the operator turns on the cooling switch, the software calls the corresponding subroutine to process , So as to realize the function of hard PLC.
3 Conclusion This system has completed the preliminary overall design. Since SERCOS has more than 30,000 parameters, most of the current systems in SERCOS parameter settings use default values. This still has a big gap for the development of high-speed and high-precision open CNC systems. Deep analysis of each SERCOS parameter The function will be the focus of the next research.