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The basic composition of CNC machine tools

2021-09-18 15:56:15

The basic composition of the machine tool in CNC lathe processing includes processing program carrier, NUMERICAL control device, servo drive device, machine tool body and other auxiliary devices. The following is a brief description of the basic working principles of each component.

Processing program carrier

Numerical control machine tool work, do not need workers to operate the machine tool directly, to control the NUMERICAL control machine tool, must prepare the processing program. Parts processing program, including the tool and the workpiece on the relative motion track, process parameters (feed spindle speed, etc.) and auxiliary motion. The parts processing program with a certain format and code, stored in a program carrier, such as perforated tape, cassette tape, floppy disk, etc., through the CNC machine input device, the program information is input to the CNC unit.

Numerical control device

Numerical control device is the core of CNC machine tools. Modern Numerical Control devices are CNC (Computer Numerical Control) form, this CNC device generally uses a number of microprocessors, in the form of programmatic Software to achieve Numerical Control function, so also known as Software NC (Software NC). CNC system is a position control system, it is according to the input data interpolation of the ideal movement track, and then output to the executive parts to process the required parts. Therefore, the NUMERICAL control device is mainly composed of three basic parts: input, processing and output. And all these work are organized reasonably by the computer system program, so that the whole system works harmoniously.

1) Input device: the NUMERICAL control instruction is input to the numerical control device. According to the different carrier of the program, there are different input devices. There are mainly keyboard input, disk input, CAD/CAM system direct communication mode input and DNC (direct NUMERICAL control) input connected to the superior computer, there are still many systems still retain the photoelectric reader paper tape input form.

(1) Paper tape input mode. The paper tape photoelectric reader can read the parts program and directly control the movement of the machine tool. The paper tape content can also be read into the memory and the parts program stored in the memory can control the movement of the machine tool.

(2) MDI manual data input mode. The operator can use the keyboard on the operation panel to input the instructions of the processing program, which is suitable for relatively short programs.

Under the control device EDIT state, the processing program is input by software and stored in the control device memory. This input method can reuse the program. This method is generally used for manual programming.

In the numerical control device with session programming function, according to the problem prompted on the display, choose different menu, the method of human machine dialogue, input the relevant size number, can automatically generate processing program.

(3) Using DNC direct NUMERICAL control input mode. The parts program is stored in the superior computer, and the CNC system receives the subsequent program from the computer while processing. DNC is mainly used to design complex workpiece with CAD/CAM software and directly generate the program of the part.

2) Information processing: the input device transmits the processing information to the CNC unit and compiles it into the information that can be recognized by the computer. After the information processing part stores and processes the information according to the provisions of the control program, the position and speed instructions are sent to the servo system and the main motion control part through the output unit. The input data of CNC system includes: contour information of parts (starting point, end point, straight line, arc, etc.), processing speed and other auxiliary processing information (such as tool change, speed change, coolant switch, etc.). The purpose of data processing is to complete the preparation work before interpolation operation. The data processing program also includes tool radius compensation, speed calculation and processing of auxiliary functions.

3) Output device: the output device is connected with the servo mechanism. The output device receives the output pulse of the arithmetic unit according to the command of the controller, and sends it to the servo control system of each coordinate. After power amplification, the servo system is driven to control the movement of the machine tool according to the specified requirements.

Servo and measurement feedback system

Servo system is an important part of CNC machine tool, which is used to realize feed servo control and spindle servo control of CNC machine tool. The role of the servo system is to receive the command information from the NUMERICAL control device, after power amplification, shaping treatment, into the linear displacement or angular displacement movement of the machine tool implementation components. Because is the last link of CNC machine tool servo system, its performance will directly affect the precision and speed of the nc machine tools and other technical indicators, as a result, the numerical control machine tool servo drive device, requires performance of rapid response, accurate and sensitive tracking digital command signal from the numerical control device, and can be faithfully execute instructions from the numerical control devices, Improve the dynamic tracking characteristic and static tracking precision of the system.

Servo system includes driving device and actuator two parts. The drive device is composed of spindle drive unit, feed drive unit, spindle servo motor and feed servo motor. Stepper motor, DC servo motor and AC servo motor are commonly used driving devices.

The measuring element detects the actual displacement value of each coordinate axis of THE CNC machine tool and feeds it into the CNC device of the machine tool through the feedback system. The CNC device compares the actual displacement value of the feedback with the command value, and outputs the displacement instruction required to reach the set value to the servo system.

Machine main body

The machine tool host is the main body of CNC machine tool. It includes bed, base, column, beam, slide seat, worktable, spindle box, feed mechanism, tool holder and automatic tool changing device and other mechanical components. It is a mechanical part that automatically completes various cutting processes on CNC machine tools. Compared with traditional machine tools, CNC machine tools have the following structural characteristics:

1) Adopt the new structure of machine tool with high stiffness, high shock resistance and small thermal deformation. Usually improve the static stiffness of the structure system, increase damping, adjust the quality of structural parts and natural frequency and other methods to improve the stiffness and earthquake resistance of the machine tool host, so that the main body of the machine tool can adapt to the CNC machine tool continuous automatic cutting needs. The influence of thermal deformation on the main machine can be reduced by improving the structure layout of the machine tool, reducing the heat, controlling the temperature rise and using the thermal displacement compensation.

2) The wide use of high-performance spindle servo drive and feed servo drive device, so that the TRANSMISSION chain of CNC machine tools shortened, simplified the structure of the machine mechanical transmission system.

3) Use high transmission efficiency, high precision, no clearance of the transmission device and moving parts, such as ball screw nut pair, plastic sliding guide rail, linear rolling guide rail, static guide rail and so on.

CNC machine tool auxiliary device

Auxiliary device is to ensure the full play of CNC machine tool functions necessary supporting devices, commonly used auxiliary devices include: pneumatic, hydraulic device, chip removal device, cooling, lubrication device, rotary table and CNC indexing head, protection, lighting and other auxiliary devices.

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