a CNC machine tool（3）

MRCM share / 2022-02-18 / Hits(2123)

This composition OF THE CNC MACHINE


The processing of CNC machine tools can accurately estimate the processing time in advance, standardize and modernize the tools and fixtures used, and easily realize the standardization of processing information. It has been organically combined with computer-aided design and manufacturing (CAD/CAM), It is the basis of modern integrated manufacturing technology.
This composition includes the processing program carrier, the numerical control device, the servo drive device, the main body of the machine tool and other auxiliary devices. The basic working principle of each component is briefly described below.
1. Processing program carrier
When a CNC machine tool is working, it is not necessary for workers to directly operate the machine tool. To control the CNC machine tool, a processing program must be compiled. The part processing program includes the relative motion trajectory of the tool and the workpiece on the machine tool, process parameters (feed rate, spindle speed, etc.) and auxiliary motion. The part processing program is stored in a certain format and code on a program carrier, 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.
2. Numerical control device
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), which 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, which interpolates the ideal motion trajectory according to the input data, and then outputs it to the execution components 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's system program, so that the whole system can work in coordination.
1) Input device: input the numerical control command to the numerical control device, according to the different program carriers, there are different input devices correspondingly. There are mainly keyboard input, disk input, CAD/CAM system direct communication input and DNC (Direct Numerical Control) input connected to the upper-level computer. There are still many systems that still retain the paper tape input form of photoelectric readers.
(1) Paper tape input method. The paper tape photoelectric reader can be used to read the part program to directly control the machine tool movement, or the paper tape content can be read into the memory, and the machine tool movement can be controlled by the part program stored in the memory.
(2) MDI manual data input method. 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 editing state of the control device (EDIT), the processing program is input by software and stored in the memory of the control device. This input method can reuse the program. This method is generally used in manual programming.
On the numerical control device with the function of conversational programming, you can choose different menus according to the questions prompted on the display, use the method of man-machine dialogue, and input the relevant size numbers, and the processing program can be automatically generated.
(3) DNC direct numerical control input method is adopted. 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 for complex workpieces designed by CAD/CAM software and the part program is directly generated.
2) Information processing: The input device transmits the processing information to the CNC unit, and compiles it into information that can be recognized by the computer. The information processing part stores and processes it step by step according to the regulations of the control program, and 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: contour information of the part (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 insertion Preparation before the complement 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 accepts 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 machine tool to move according to the specified requirements.