Detailed explanation of common terms of CNC system, necessary information for machining personnel
Increment pulse coder
The rotary position measuring element is installed on the motor shaft or ball screw, and sends out pulses at equal intervals to indicate the displacement when it rotates. Since there is no memory element, it cannot accurately represent the position of the machine tool. Only after the machine tool returns to zero and establishes the zero point of the machine tool coordinate system, can the position of the worktable or the tool be displayed. When using it, it should be noted that there are two ways for the signal output of the incremental encoder: serial and parallel. Correspondingly, individual numerical control systems have serial interfaces and parallel interfaces.
Absolute pulse coder
The rotary position measuring element has the same purpose as the incremental encoder, and has a memory element, which can reflect the actual position of the machine tool in real time. The position after shutting down will not be lost, and the machine tool can be put into processing operation immediately without returning to the zero point after turning on the machine. Like the incremental encoder, you should pay attention to the serial and parallel output of the pulse signal when using it.
Spindle orientation (Orientation)
In order to perform spindle positioning or tool change, the machine tool spindle must be positioned on a certain corner in the circumferential direction of rotation as the reference point for the action. Generally, there are the following four methods: orientation by position encoder, orientation by magnetic sensor, orientation by external one-turn signal (such as proximity switch), and orientation by external mechanical method.
Dual drive control (Tandem control)
For a large workbench, when the torque of one motor is not enough to drive, two motors can be used to drive jointly. One of the two shafts is the master shaft and the other is the slave shaft. The driving shaft receives the control command from CNC, and the driven shaft increases the driving torque.
Rigid tapping
The tapping operation does not use a floating chuck but is realized by the rotation of the spindle and the synchronous operation of the tapping feed axis. When the spindle rotates one turn, the feed rate of the tapping axis is equal to the pitch of the tap, which can improve accuracy and efficiency. Metal processing WeChat, the content is good, it is worth paying attention to. To realize rigid tapping, the spindle must be equipped with a position encoder (usually 1024 pulses per revolution), and it is required to compile the corresponding ladder diagram and set the relevant system parameters.
Tool compensation memory A, B, C (Tool compensation memory A, B, C)
The tool compensation memory can generally be set as any one of type A, type B or type C by parameter. Its external performance is: Type A does not distinguish the geometric shape compensation amount and wear compensation amount of the tool. Type B separates geometry compensation from wear compensation. Type C not only separates geometry compensation from wear compensation, but also separates tool length compensation codes from radius compensation codes. The length compensation code is H, and the radius compensation code is D.
DNC operation (DNC Operation)
It is a way of working automatically. Connect the CNC system or computer with RS-232C or RS-422 port, the processing program is stored on the hard disk or floppy disk of the computer, and input to CNC segment by segment, each segment of program is processed, which can solve the limitation of CNC memory capacity.
Advanced preview control (M)
This function is to read multiple program segments in advance, interpolate the running track and preprocess the speed and acceleration. In this way, the following error caused by acceleration and deceleration and servo lag can be reduced, and the tool can more accurately follow the part contour instructed by the program at high speed, which improves the machining accuracy. Pre-reading control includes the following functions: linear acceleration and deceleration before interpolation; corner automatic deceleration and other functions.
Polar coordinate interpolation (T)
Polar coordinate programming is to change the Cartesian coordinate system of the two linear axes into a coordinate system in which the horizontal axis is a linear axis and the vertical axis is a rotary axis, and use this coordinate system to compile a machining program for non-circular contours. Typically used for turning straight grooves, or grinding cams on a grinding machine.
NURBS Interpolation (M)
Most of the molds used in industries such as automobiles and airplanes are designed by CAD. In order to ensure the accuracy, non-uniform rationalized B-spline functions (NURBS) are used in the design to describe sculpture (Sculpture) surfaces and curves. Metal processing WeChat, the content is good, it is worth paying attention to. Therefore, the CNC system has designed a corresponding interpolation function, so that the expression of the NURBS curve can directly instruct the CNC, avoiding the use of tiny straight line segments to approach the surface or curve of complex contours.
Automatic tool length measurement
Install a contact sensor on the machine tool, and compile a tool length measurement program (using G36, G37) as in the machining program, and specify the offset number used by the tool in the program. Execute the program in automatic mode, make the tool contact with the sensor, measure the length difference between it and the reference tool, and automatically fill the value into the offset number specified by the program.
Cs axis contour control (Cs Contour control)
Cs contour control is to change the spindle control of the lathe into position control to realize the positioning of the spindle according to the rotation angle, and can interpolate with other feed axes to process workpieces with complex shapes.
Manual absolute ON/OFF
It is used to determine whether to add the coordinate value manually moved after the feed pause to the current position value of automatic operation during automatic operation.
Manual handle interruption
Shaking the handwheel during automatic operation can increase the moving distance of the movement axis. Used for stroke or dimension correction.
PMC control axis (Axis control by PMC)
Feed servo axis controlled by PMC (Programmable Machine Tool Controller). The control instructions are compiled in the program (ladder diagram) of the PMC. Because it is inconvenient to modify, this method is usually only used for the control of the feed axis with a fixed moving amount.
Cf Axis Control (Cf Axis Control) (T series)
In the lathe system, the rotary position (rotation angle) control of the main shaft is realized by the feed servo motor like other feed axes. This axis interlocks with other feed axes to process any curve. (common in older lathe systems)
Location Tracking (Follow-up)
If the mechanical position of the table moves when the servo is turned off, emergency stop or servo alarm, there will be a position error in the position error register of CNC. The position tracking function is to modify the position of the machine tool monitored by the CNC controller, so that the error in the position error register becomes zero. Of course, whether to perform position tracking should be determined according to the needs of actual control.
Simple synchronous control
One of the two feed axes is the master axis, and the other is the slave axis. The master axis receives the movement commands from the CNC, and the slave axis follows the movement of the master axis, so as to realize the synchronous movement of the two axes. CNC monitors the moving position of the two axes at any time, but does not compensate for the error of the two axes. If the moving position of the two axes exceeds the set value of the parameter, the CNC will issue an alarm and stop the movement of each axis at the same time. This function is often used for double-axis drive of large worktables.
Three-dimension tool compensation (M)
In multi-coordinate linkage machining, tool offset compensation can be performed in three coordinate directions during tool movement. Compensation can be realized by tool side machining, and compensation by tool end face machining can also be realized.
Tool nose radius compensation (Tool nose radius compensation) (T)
The tool tip of the turning tool has an arc. For precise turning, the radius of the tool tip arc is compensated according to the direction of the tool during machining and the relative orientation between the tool and the workpiece.
Tool life management
When using multiple tools, group the tools according to their lifespan, and pre-set the use order of the tools on the CNC tool management table. When the tool used in processing reaches the life value, the next tool of the same group can be replaced automatically or manually, and the tool of the next group will be used after the tool of the same group is used up. Whether the tool replacement is automatic or manual, a ladder diagram must be prepared.
