The development of mechanical manufacturing has evolved from single-machine automation to distributed DNC (Direct Numerical Control) systems, marking a significant advancement in the integration and communication of CNC machines. This evolution addressed the critical challenge of information exchange between CNC machines and PCs, making it a central focus of DNC control systems. To support this, the author designed a PC-based RS422 communication board and established a set of reliable and efficient communication protocols.
The network architecture of the DNC system is structured into two levels: a master-slave bus topology. The communication network itself follows a three-layer structure—physical, data link, and application layers. At the physical layer, the balanced RS422 interface is used to enhance data transmission reliability. In this standard, both the transmitter and receiver operate differentially, using two wires for each signal. This differential signaling eliminates the need for a common ground wire, with signal levels defined by the voltage difference between the two conductors, ranging from -6V to +6V. A positive difference of +4 to +6V represents a binary '0', while a negative difference of -4 to -6V indicates a binary '1'. The RS422 interface can transmit at up to 10 Mb/s over short distances (within 10 meters), and still maintains a rate of 100 kb/s over 1,000 meters. This design effectively isolates the signal from ground interference and common-mode EMI, allowing for more stable communication.
At the data link layer, the system employs asynchronous serial communication. Data transmission includes a positive and negative code check. When sending command or status words, two BREAK signals are first transmitted, followed by the actual word, and then its inverse. For file transfers, data is divided into 32-word blocks, each containing a positive and negative code. The application layer is user-focused, handling real-time commands from the lower machine and file transfer commands from the host. It also provides feedback through correct or error flags displayed on the screen.
The communication protocol of the DNC system is unbalanced, as the host computer manages the entire network. The system uses one byte to carry either command or status information along with an address. The lower four bits represent the address (coded from 1 to 3), while the upper four bits hold the command or status code. For example, if the host wants to stop a machine with address 1, it sends the command code 041. Other machines ignore it. Similarly, if the host receives a status word of 02, it identifies that the machine with address 2 is in edit mode.
To ensure reliable data transmission, the system uses special start characters (BREAK, defined as 0x80) and forward/reverse code checks. These techniques prevent misinterpretation of random data during file transfers. Both the host and the lower machine must send two consecutive BREAKs before transmitting a command or status word, followed by its inverse. This frame-based approach ensures accurate communication, with error recovery mechanisms in place if no response is received within a set time.
The author implemented the communication modules using Borland C++ 3.1 for DOS and Z80 assembly language, ensuring robust and efficient performance. The DNC system has been successfully deployed in the three-side punching machine system at the Zhejiang Huaneng CNC Research Institute and has been adopted by the Ningbo Metallurgical Machinery Spare Parts Factory. The system operates stably and reliably, fulfilling its intended control objectives, thereby demonstrating the effectiveness and reliability of RS422 communication in industrial applications.
Radiator Hose
A radiator hose is a vital component of a vehicle's cooling system, responsible for transferring coolant from the engine to the radiator. It is a flexible tube made of rubber or silicone that connects the engine's coolant passages to the radiator, ensuring proper circulation and cooling of the engine.
The primary function of a radiator hose is to carry coolant from the engine to the radiator, where it is cooled before returning to the engine. This process helps maintain optimal operating temperature, preventing overheating and potential engine damage.
Radiator hoses are typically made of durable rubber or silicone materials that can withstand high temperatures and pressure. The rubber used in radiator hoses is often reinforced with fabric or wire to enhance its strength and resistance to wear and tear. The hose's flexibility is crucial, allowing it to bend and adapt to the engine's movements without causing leaks or blockages.
Radiator hoses come in various sizes and shapes to fit different vehicle models and engine configurations. They can be straight, curved, or have multiple bends, depending on the specific requirements of the cooling system. The length of the hose also varies, depending on the distance between the engine and the radiator.
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