Detailed Explanation Of Common Terms In CNC System!
Increment pulse coder
The rotary position measuring element is mounted on the motor shaft or ball screw, and emits pulses at equal intervals when rotating to indicate the displacement. 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 the zero point of the machine tool coordinate system is established, can the position of the worktable or the tool be displayed. It should be noted that there are two ways to output the signal of the incremental encoder: serial and parallel. Individual numerical control systems correspond to this with serial interface and parallel interface.
Absolute pulse coder
The rotary position measuring element has the same purpose as the incremental encoder, with a memory element, which can reflect the actual position of the machine tool in real time. The position after shutdown will not be lost, and the machine tool can be put into machining operation immediately without returning to the zero point after it is turned on. As with the incremental encoder, attention should be paid to the serial and parallel output of the pulse signal when using it.
Orientation
In order to perform spindle positioning or tool change, the machine spindle must be positioned at a certain corner in the circumferential direction of rotation as the reference point of the action. Generally, there are the following 4 methods: Orientation by position encoder, Orientation by magnetic sensor, Orientation by external one-turn signal such as proximity switch, Orientation by external mechanical method.
Tandem control
For large workbenches, when the torque of one motor is not enough to drive, two motors can be used to drive together. One of the two axes is the driving axis and the other is the driven axis. The master axis receives the control commands from the CNC, and the slave axis increases the driving torque.
Rigid tapping
The tapping operation does not use a floating chuck but is realized by the rotation of the main shaft and the synchronous operation of the tapping feed axis. The spindle rotates once, and the feed of the tapping axis is equal to the pitch of the tap, which can improve accuracy and efficiency. Metal machining WeChat, the content is good and worthy of attention. To achieve rigid tapping, a position encoder usually 1024 pulses/revolution must be installed on the spindle, and the corresponding ladder diagram must be compiled and related system parameters set.
Tool compensation memory A,B,C
Generally, the tool compensation memory can be set to any one of A type, B type or C type with parameters. Its external performance is: Type A does not distinguish between the geometric shape compensation amount and the wear compensation amount of the tool. Type B separates geometry compensation from wear compensation. Type C not only separates geometry compensation and wear compensation, but also separates tool length compensation code and radius compensation code. The length compensation code is H and the radius compensation code is D.
DNC Operation
It is a working mode of automatic operation. Connect the CNC system or computer with RS-232C or RS-422 port. The machining program is stored on the computer’s hard disk or floppy disk, and input to the CNC section by section. Each section of the program is processed, which can solve the limitation of CNC memory capacity.
Advanced preview control M
This function is to read in multiple blocks in advance, interpolate the running track and preprocess the speed and acceleration. In this way, the following error caused by acceleration, deceleration and servo lag can be reduced, and the tool can more accurately follow the part contour of the program command at high speed, so that the machining accuracy is improved. Pre-reading control includes the following functions: linear acceleration and deceleration before interpolation; automatic deceleration at corners and other functions.
Polar coordinate interpolation T
Polar coordinate programming is to change the Cartesian coordinate system of two linear axes into a coordinate system where the horizontal axis is a linear axis and the vertical axis is a rotary axis, and the non-circular contour machining program is compiled with this coordinate system. It is usually used for turning straight grooves or grinding cams on a grinder.
NURBS Interpolation M
Most industrial molds used in automobiles and airplanes are designed with CAD. In order to ensure accuracy, non-uniform rational B-spline function NURBS is used to describe the surface and curve of sculpture Sculpture in the design. Metal machining WeChat, the content is good and worthy of attention. Therefore, the CNC system has designed the corresponding interpolation function, so that the expression of the NURBS curve can be directly commanded to the CNC, avoiding the use of tiny straight line approximation methods to process complex contour surfaces or curves.
Automatic tool length measurement
Install the contact sensor on the machine tool, and program the tool length measurement program like the machining program using G36, G37, and specify the offset number used by the tool in the program. Execute the program in automatic mode to make the tool contact with the sensor to measure the length difference between the tool and the reference tool, and automatically fill this value into the offset number specified by the program.
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 it can be interpolated with other feed axes to process workpieces with complex shapes.
Manual absolute ON/OFF
It is used to determine whether the coordinate value of manual movement after feed pause is added 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 motion axis. Used for stroke or size correction.
Axis control by PMC
Feed servo axis controlled by PMC Programmable Machine Controller. The control instructions are compiled in the PMC program ladder diagram. Due to the inconvenience of modification, this method is usually only used for the control of the feed axis with a fixed amount of movement.
Cf Axis Control T series
In the lathe system, the rotation position rotation angle of the main shaft is controlled by the feed servo motor like other feed axes. This axis is linked with other feed axes for interpolation, machining arbitrary curves. Common in older lathe systems
Follow-up
When the servo is turned off, emergency stop or servo alarm, if the worktable moves mechanically, there will be a position error in the position error register of the 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 actual control needs.
Simple synchronous control
One of the two feed axes is the master axis and the other is the slave axis. The master axis receives CNC motion instructions, and the slave axis follows the movement of the master axis, thus realizing the synchronous movement of the two axes. The CNC monitors the moving positions of the two axes at any time, but does not compensate for the errors between the two. If the moving positions of the two axes exceed the parameter setting value, the CNC will send an alarm and stop the movement of each axis at the same time. This function is often used for dual-axis drive of large worktables.
Three-dimension tool compensation M
In multi-coordinate machining, tool offset compensation can be performed in three coordinate directions during tool movement. It can realize the compensation of the side machining of the tool and the compensation of the end machining of the tool.
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 cutting direction and the relative orientation between the tool and the workpiece during machining.
Tool life management
When using multiple tools, group the tools according to their life, and pre-set the order of use of the tools on the CNC tool management table. When the tool used in machining reaches the life value, the next tool in the same group can be replaced automatically or manually. After the tools in the same group are used up, the tools in the next group can be used. Ladder diagrams must be compiled for tool replacement whether it is automatic or manual.
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Commonly Used CNC Machine Parameters
1. The hand pulse generator is damaged.
A FANUC0TD CNC lathe has a fault with the hand-operated pulse generator, so that the tool cannot be fine-tuned, and the faulty parts need to be replaced or repaired. At that time, there is no suitable spare part. You can set parameter 900#3 to “0” first, temporarily leave the manual pulse generator unused, and use the jog button single pulse generator to perform fine-tuning of the tool. Set this parameter to “1” after the hand pulse generator is repaired.
2. When the machine tool is turned on and returns to the reference point, an over-travel alarm occurs.
The above machine tool has 510 or 511 overtravel alarm during the process of returning to the reference point. There are two treatment methods: 1 If the X axis is returning to the reference point, 510 or 511 overtravel alarm occurs, you can set the value of parameter 0700LT1X1 After changing to +99999999 or changing the value of 0704LT1X2 to -99999999, return to the reference point again. If there is no problem, change the value of parameter 0700 or 0704 to the original value. 2 Press the P and CAN keys at the same time and turn on the machine to eliminate the overtravel alarm.
3. A FANUC 0i CNC lathe has an ALM701 alarm shortly after it is turned on.
The maintenance manual explains that the fan in the upper part of the control unit is overheated. Open the electrical cabinet of the machine tool, check that the fan motor is not working, and check that the fan power supply is normal. It can be determined that the fan is damaged. Change to “1” to release the ALM701 alarm first, and then cool by the forced cooling air. After the fan is purchased, change PRM8901 to “0;
4. Common maintenance parameters
- 4.1, 701 alarm: system fan detection is abnormal, set 8109#0=1 to shield this alarm.
- 4.2. Set the absolute position encoder: 1815#4 and 1815#5. When the machine tool is to be set as an absolute position encoder, set 1815#5=1, then move the axis to the 0 o’clock position, and then set 1815#4 =1. If the setting is unsuccessful, please move the axis a certain distance, then return to the origin and reset.
- 4.3, Fully closed loop to semi-closed loop: 1815#1, set this parameter to 0, the machine tool is semi-closed loop. Then modify the parameters 2084 and 2085, and reset them according to the screw pitch.
- 4.4. Lock the SYSTEM key of the machine tool: In the SETTING setting screen, set parameter 3208#1=1.
- 4.5, soft overtravel alarm: the alarm number is 500 or 501, set the parameter 1320 or 1321 to 9999999 and -99999999, after removing the alarm, return the machine tool to the origin, and then input the original parameter value. This type of failure usually occurs when the lead screw, the motor is replaced or the parameters are re-entered.
- 4.6. Machine tool interlock signal: Refer to the description of parameter 3003 to determine the reason why the machine tool is locked and unable to move.
- 4.7, Chinese display: 3102#3=1
- 4.8, Servo adjustment screen display: 3111#0=1; spindle monitoring screen: 3111#1=1; operator monitoring: 3111#5
- 4.9, Spindle positioning: 4077. Used to adjust the spindle tool change position.
- 4.10, Operation without returning to zero: If the machine tool does not return to zero, it can run in automatic mode, set 1005#0=1.
- 4.11, Macro program protection: release macro program protection 3202#0=0 8000-8999; 3202#4=0 9000-9999.
- 4.12. Shield the serial spindle: Sometimes the serial spindle needs to be isolated for maintenance, 3701#1=1.
Link to this article：Common Terms Of CNC System｜Commonly Used CNC Machine Parameters
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