2.1.2 Functions of CNC system
The function of CNC system refers to the methods and means to meet the requirements of user operation and machine tool control. The functions of NC system include basic functions and selection functions. No matter what occasion the CNC system is used for, the basic functions are all necessary CNC functions; The selection function is for users to select according to the characteristics and purpose of the machine tool. Table 2-2 describes the main functions of the NC system in detail.
Table 2-2 Main Functions of CNC System
| Serial No | Main functions | Detailed description |
| 1 | Control function | The number of feed axes that can be controlled and linked by the CNC system is an important performance index of the CNC system The control axes of the NC system are: moving axes (X, Y, Z) and rotating axes (A, B, C); Basic axis and additional axis (U, V, W) CNC lathe generally only requires X-axis and Z-axis linkage control. CNC milling machines, drilling machines and machining centers require three-axis control and three-axis linkage control. The more the number of linkage control axes, the more complex the CNC system is and the more difficult it is to program |
| 2 | Preparation function (G function) | The function of instructing the action mode of the machine tool. It includes basic movement, program pause, plane selection, coordinate setting, tool compensation, mirror image, fixed cycle processing, metric English conversion, subroutine and other instructions |
| 3 | Interpolation function and fixed cycle function | Interpolation function is the function of NC device to realize part contour, (plane or space) processing path calculation. The methods to realize the interpolation function include point by point comparison method, digital integration method, direct function method and double DDA method Fixed cycle function is the function of NC device to realize typical processing cycles (such as drilling, tapping, boring, deep hole drilling and thread cutting) |
| 4 | Feed function | Feed function refers to the control function of feed speed, which includes the following contents: ① Feed speed: control the movement speed of the tool relative to the workpiece ② Synchronize the feed speed to synchronize the cutting speed and feed speed, in mm/r. Only the machine tool with the position encoder on the spindle can command the synchronous feed speed ③ Feed rate: manually adjust the preset feed rate in real time. The machine tool uses the multiplying switch on the operation panel during processing to change the feed speed without modifying the part processing program |
| 5 | Spindle function | Spindle function refers to the control function of the spindle of the CNC system, which includes the following contents: ① Spindle speed: control function of spindle speed ② Constant linear speed control: the control function that makes the cutting speed of the tool cutting point constant. This function is mainly used in turning and grinding to improve the quality of workpiece end face ③ Spindle magnification: manually adjust the preset spindle speed in real time. The machine tool uses the multiplying switch on the operation panel during processing to change the spindle speed without modifying the part processing program ④ Spindle accurate stop: This function enables the spindle to stop accurately at a certain position in the radial direction. The machining center must have the spindle stop function. After the spindle stop, it can perform the action of tool unloading and tool loading |
| 6 | Auxiliary function (M function) | Auxiliary function refers to the function used to instruct the auxiliary operation of the machine tool. It is mainly used to specify the forward rotation, reverse rotation and stop of the spindle, the opening and closing of the cooling pump, tool change and other actions |
| 7 | Tool management function | Tool management function realizes the management of tool geometry, life and tool number ① Tool geometry (radius and length) for tool compensation ② The tool life refers to the time life. When the tool life expires, the CNC system will prompt the user to replace the tool ③ The tool number (T) management function is used to identify the tools in the tool library and automatically select the processing tools |
| 8 | Compensation function | ① Tool radius and length compensation function: realize the function of controlling the tool center path by the program compiled according to the part contour ② Transmission chain error: including pitch error compensation function and reverse clearance error compensation function ③ Non linear error compensation function: For such things as thermal deformation, static elastic deformation, spatial error and machining error caused by tool wear, the CNC system uses the compensation function to input these compensation amounts into its internal memory, and then add them according to a certain calculation method when controlling the machine tool feed |
| 9 | Man machine dialogue function | The environment for realizing man-machine conversation function includes: menu structure operation interface, editing environment of part processing program, display, query or modification page of system and machine tool parameters, status, fault information, etc |
| 10 | Self diagnosis function | The NC device automatically realizes fault prediction and fault location. Various diagnostic programs are installed in the NC device. These programs can be embedded in other functional programs to check and diagnose during the operation of the NC device |
| 11 | Communication function | The communication function refers to the function of exchanging information and data between the CNC system and the outside world. The communication function mainly completes the data and command transmission between the superior computer and the CNC system |
