Today, the flourish engineer will take you to understand the basic composition of CNC machine tools. The basic composition of CNC machine tools includes processing program carriers, numerical control devices, servo drives, machine tool bodies and other auxiliary devices. The basic working principles of each component are briefly described below.
When the CNC machine tool is working, workers do not need to directly operate the machine tool. To control the CNC machine tool, the customized CNC machining processing program must be compiled. In the part processing program, it includes the relative motion trajectory of the tool and workpiece on the machine tool, process parameters (feed amount, spindle speed, etc.) and auxiliary motion, etc. The part processing program is stored in a program carrier in a certain format and code, such as perforated paper tape, cassette tape, floppy disk, etc., and the program information is input to the CNC unit through the input device of the CNC machine tool.
The numerical control device is the core of the numerical control machine tool. Modern numerical control devices all adopt the form of CNC (Computer Numerical Control). This kind of CNC device generally uses multiple microprocessors to realize numerical control functions in the form of programmed software, so it is also called software numerical control (Software NC). The CNC system is a position control system. It interpolates the ideal motion trajectory according to the input data, and then outputs it to the execution part to process the required parts. Therefore, the numerical control device is mainly composed of three basic parts: input, processing and output. And all these tasks are rationally organized by the computer system program, so that the whole system can work in harmony.
1) Input device: input the numerical control command to the numerical control device, and there are different input devices according to the different program carriers. There are mainly keyboard input, disk input, CAD/CAM system direct communication input and DNC (direct numerical control) input connected to the upper computer. There are still many systems that still retain the paper tape input form of the photoelectric reader.
(1) Tape input mode. The part program can be read by a paper tape photoelectric reader to directly control the movement of the machine tool, or the content of the paper tape can be read into the memory, and the part program stored in the memory can be used to 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.
In the edit state (EDIT) of the control device, use the software to input the processing program and store it in the memory of the control device. This input method can reuse the program. This method is generally used in manual programming.
On the CNC device with conversational programming function, you can choose different menus according to the questions prompted on the display, and use the method of man-machine dialogue to input the relevant size numbers, and then the processing program can be automatically generated.
(3) Adopt DNC direct numerical control input mode. Save the part program in the upper-level computer, and the CNC system receives subsequent program segments from the computer while processing. The DNC method is mostly used in the case of using CAD/CAM software to design complex workpieces and directly generate part programs.
2) Information processing: The input device transmits the processing information to the CNC unit, compiles it into information that can be recognized by the computer, and the information processing part stores and processes it step by step according to the regulations of the control program, and then sends position and speed commands to the servo through the output unit System and main motion control section. The input data of the CNC system includes: the contour information of the part (start 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 insertion Preparatory work before complement operation. The data processing program also includes tool radius compensation, speed calculation and auxiliary function processing.
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, and drives the servo system through power amplification, so as to control the movement of the machine tool according to the specified requirements.
The servo system is an important part of the custom CNC machining tool, which is used to realize the feed servo control and spindle servo control of the CNC machine tool. The function of the servo system is to convert the instruction information received from the numerical control device into the linear displacement or angular displacement movement of the machine tool execution parts after power amplification and shaping. Since the servo system is the last link of the CNC machine tool, its performance will directly affect the technical indicators such as the precision and speed of the CNC machine tool. Therefore, the servo drive device of the CNC machine tool is required to have good fast response performance and accurately and sensitively track the CNC device. The digital command signal sent out can faithfully execute the command from the numerical control device, improving the system's dynamic following characteristics and static tracking accuracy.
The servo system includes two parts: the drive device and the actuator. The drive device is composed of a spindle drive unit, a feed drive unit, a spindle servo motor, and a feed servo motor. Stepper motors, DC servo motors and AC servo motors are commonly used drives.
The measuring element detects the actual displacement value of each coordinate axis of the CNC machine tool and inputs it to the CNC device of the machine tool through the feedback system. The CNC device compares the actual displacement value fed back with the command value, and outputs to the servo system to reach the set value The desired displacement command.
The machine tool host is the main body of the CNC machine tool. It includes mechanical components such as bed, base, column, beam, slide, worktable, spindle box, feed mechanism, tool holder and automatic tool changer. It is a mechanical part that automatically completes various cutting processes on a CNC machine tool. Compared with traditional machine tools, the main body of CNC machine tools has the following structural characteristics:
2) The high-performance spindle servo drive and feed servo drive are widely used to shorten the transmission chain of the CNC machine tool and simplify the structure of the mechanical transmission system of the machine tool.
3) Adopt high-efficiency, high-precision, no-gap transmission devices and moving parts, such as ball screw nut pairs, plastic sliding guides, linear rolling guides, static pressure guides, etc.
Auxiliary devices are necessary supporting devices to ensure full play of the functions of CNC machine tools. Commonly used auxiliary devices include: pneumatic, hydraulic devices, chip removal devices, cooling and lubrication devices, rotary table and CNC dividing head, protection, lighting, etc. assisting equipments.