High-end CNC machine tools have always been regarded as critical strategic materials and subjected to embargoes by Western countries, hindering the sustained and efficient development of China's economy. How to address this predicament? During the 11th Five-Year Plan period, the Chinese government proposed developing high-end CNC machine tools with independent intellectual property rights. However, the software system is the core of CNC machine tools, and currently, all CNC machine tools on the market adopt embedded systems.

Embedded systems are characterized by strong specificity and real-time performance. They emerged as an alternative solution primarily due to the slow data exchange speed and poor real-time performance of traditional general-purpose computing systems in interacting with external devices. Their biggest drawback lies in the relative difficulty of system upgrades—user-initiated upgrades often require full machine replacement, necessitating substantial new investments. This poses a significant burden given China's relatively weak economic foundation at that time.

Therefore, it is inappropriate to follow the outdated path of foreign countries; instead, we should blaze a distinctive development trail tailored to our own needs. With the rapid advancement of general-purpose computer processor speeds, another development route for CNC machine tools emerged in the late 1990s and early 2000s—the so-called 6th-generation open CNC system. Based on PC architecture, this system aligns with China's national conditions.

This paper proposes a USB-based communication interface and, from the perspectives of software and relevant applications, discusses an integrated CAD/CAM/CNC trinity system with a general-purpose computer as the control core. The conditions required for serial communication speed to meet real-time information exchange needs—with a general-purpose computer as the real-time control core—are now fully satisfied, and the advantages of this architecture are remarkably evident.

The information exchange speed between a computer and external devices is the key to achieving effective real-time control, and it was the only limitation that prevented traditional general-purpose computers from directly performing high-speed real-time control. Despite their unparalleled CPU operating speed and declining prices, they could not directly operate in the CNC mode.

The traditional RS232 serial communication speed is generally 9600 bit/s, which is completely inadequate for direct connection to machine tools for real-time machining control—its only application being text transmission, limiting CNC machine tools to DNC (Direct Numerical Control) machining mode.

In recent years, the emergence of new serial communication interface technologies such as USB 2.0 and IEEE 1394 has enabled a breakthrough in the serial communication speed of general-purpose computers. The communication speed has increased by tens of thousands to hundreds of thousands of times compared to RS232: USB 2.0 can reach 480 Mbit/s, and IEEE 1394 up to 2 Gbit/s. This speed not only meets but also exceeds the requirements of high-speed real-time control.

Taking USB 2.0 as an example, for 4-axis simultaneous machining, the communication speed per axis is 120 Mbit/s. Assuming a machining feed rate of 40 mm/s and a system dimension word length of 5 bytes (format: FFFF.FFFF, i.e., 40 bits), the bidirectional communication time is 6.6×10⁻⁷ seconds. Since computer processing and serial communication are synchronized, the theoretical error caused is approximately 40 × 6.6×10⁻⁷ = 0.0264 μm—far smaller than the actual allowable error, fully complying with real-time control requirements. If the allowable error is 0.2 μm, theoretically, 20-40 axis simultaneous machining can be achieved. Notably, IEEE 1394’s speed is more than four times that of USB 2.0.

Why choose serial communication? The fundamental reason is that computers have very limited resources for other communication interfaces, whereas USB can support up to 127 peripheral devices simultaneously. Therefore, the communication speed required for computers to directly operate in the CNC mode is now fully realized.