Introduction to the drive and control system of CNC machine tools (2)

3. Servo drive and position detecting device

Function: Accept the feed speed and displacement command signal from the CNC device, and after the servo drive circuit (such as the speed control unit) performs certain conversion and amplification, drive the machine table through the servo drive device (such as DC servo motor). Movement, at the same time, the actual position of the actuator is detected by the displacement sensor, and fed back to the CNC device to realize the closed-loop drive, so that the position and speed of the machine feed member can be accurately controlled.

4. Auxiliary function drive circuit

This part realizes the information transmission and transformation of the CNC device and the machine tool. Its function is to accept the CNC signal, and control the operation of the spindle, lubrication, cooling, tool change and other motors through the machine's strong electric power and other auxiliary functions. In addition, some state information of the machine tool is transformed and sent to the CNC device, such as: tool in place, table overtravel, and the like. In the high-end CNC system, the control of this part is done by the "built-in" programmable controller (PC) belonging to the CNC device, or by the "universal" programmable controller independent of the CNC device ( PC) to complete.

5. CNC system software

The working process of the numerical control system is carried out under the support of hardware and executes the whole process of the software. Part or all of the CNC functions are implemented by software.

Figure 4-2 is a schematic diagram of the Fujitsu CNC system, which is a microcomputer CNC system, through which the composition principle of the CNC system can be further understood.

Microprocessor: M6800, 8-bit microprocessor. The ROM stores the control program, the RAM stores the intermediate data and the user processing program, and has an input/output interface connected with the machine operation panel, the tape reader, the manual pulse generator, and the machine tool controller, the DC servo motor drive, and the pulse code disk detection. The displacement implements position feedback. Large-scale integration (LSI) circuits implement interpolation operations with high computational speed.


Second, the main features of the CNC system

The main features of the CNC system are as follows.

1. The system is flexible, easy to change and expand, and has strong versatility

This is the most prominent feature of the CNC system. It is not like hardware numerical control. Once a certain mode and function is formed, it cannot be changed at will, because the connection between hardware is realized by wiring. For the CNC system, as long as the structure of the software is changed, new functions can be added and developed at any time to suit different requirements.

2. Easy to implement multi-function

Since the computer has a rich instruction system and can perform complex calculations, it is much more convenient to implement multi-function, high-complexity control than to use a hardware system. For example, high-order curve interpolation, tool radius compensation, multi-coordinate linkage control, etc., some CNC systems can also perform NC programming while controlling machining, which is impossible in hardware systems.

3. High system reliability

In the hardware CNC system, the machining program is input by the reader one by one, but the CNC system can input the machining program into the memory once, which can reduce the input failure. Since the CNC system hardware is much less than the NC system, the system component error rate is also relatively reduced, making the system work stable and reliable. Since the functions of the CNC system are implemented by software, as long as the software is perfect, it is impossible to generate software running errors in the continuous operation of the system in the future, so the CNC system has a continuous trouble-free time of tens of thousands of hours.

4. Easy maintenance

Due to the strong function of the CNC system, the system functions are modularized, and software fault diagnosis is adopted to make the CNC maintenance convenient.

5.CNC system communication function

With the development of manufacturing technology, CNC system is required to be centrally controlled, then this function is indispensable. For example, in DNC, FMS, and CIMS systems, communication links are required between systems.

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