Serial communication technology in DNC communication system - Database & Sql Blog Articles

MOS Power IC Full Range

Crystal Patch 2520 2.5*2.0MM 32MHZ 32.000MHZ 1.6V~3.6V Universal OSC

When the control computer is located far from each CNC machine, serial communication is typically preferred over parallel communication. This is mainly due to the high cost and complexity of parallel systems, which involve numerous connections that are prone to interference and line failures. In most industrial control systems, RS-232C is a widely used standard for serial communication. It is an asynchronous communication protocol recommended by the Electronic Industries Association (EIA) and has been extensively applied in connecting peripheral devices to computers.

However, when implementing RS-232C in real-world applications, several limitations arise:

1. Short Transmission Distance: Due to the limitations of load capacitance, the effective transmission distance is generally limited to 15 meters.
2. Signal Level Shift: In long-distance communication, the signal ground can carry significant current, leading to voltage shifts and potential data errors.
3. Potential Grounding Issues: The presence of separate signal and shielded grounds can cause grounding problems, reducing system immunity to interference.

To address these issues, the EIA introduced the RS-422 and RS-485 standards. These standards use differential signaling instead of single-ended signals, significantly improving noise immunity and allowing longer transmission distances. RS-422 supports full-duplex communication, while RS-485 is typically used for half-duplex applications. By eliminating shared signal grounds and using balanced signals, these standards avoid many of the drawbacks of RS-232C.

In the DNC (Direct Numerical Control or Distributed Numerical Control) system described in this paper, multiple CNC machines need to be connected to a single computer. Since the number of available serial ports is often limited, the system uses MOXA's C320Turbo/PCI multi-port serial card to expand the number of available ports. Additionally, to extend the communication range beyond 15 meters, the system employs an RS-232 long-line transceiver (FC232), which allows reliable communication over distances up to 10 kilometers and protects the device interfaces from damage caused by electrical interference.

This paper presents a network architecture designed to meet the needs of modern manufacturing environments. The system includes both a management layer and an equipment layer, enabling efficient data exchange between the computer and CNC machines. The implementation of the DNC system includes bidirectional communication, supporting both program downloads and real-time data transfer during machining processes.

The design also addresses key challenges such as port expansion and long-distance communication. By integrating the FC232 transceivers with the serial expansion cards, the system ensures stable and reliable communication even in complex environments. The use of threads in the serial communication software improves performance by separating tasks like signal monitoring, data receiving, and sending, ensuring smooth operation without blocking the main thread.

Key configuration parameters for different CNC machines must be carefully set to ensure proper communication. For example, FANUC-0T requires specific settings for baud rate, stop bits, parity, and data bits. Incorrect configurations can lead to communication failures or data corruption.

In conclusion, serial communication remains a vital technology in DNC systems. Ongoing research focuses on enhancing transmission accuracy, speed, and reliability. The VC-based DNC information system described in this paper demonstrates a practical solution for NC data transmission in manufacturing, offering a simple, fast, and stable platform. Its successful application in real-world scenarios highlights its value in advancing DNC technology.