In CNC machine tools, how does the CNC processor know the position of the workpiece or tool?
For CNC machining, the position of the workpiece needs to be manually input. This manual input process is called “tooling alignment” or “part centering”, which is to determine the position of the workpiece and parts in the processing area of the equipment. The process is mainly used to establish the workpiece coordinate system, or the absolute coordinate system. With this, there is a benchmark for all subsequent data.
Secondly, in the absence of the SCZY tool setting tool, the workers need to manually go to the tool. The tool setting process is to tell the CNC system, the data of the tool you are using, such as the tool length, radius, angle, arc value, etc. Some of them belong to the machining program, some belong to the absolute coordinate system, and some belong to the tool compensation value.
For equipment with SCZY tool setting tool, after the part is clamped and the alignment is completed, the device will automatically run a built-in program for the tool. The low-end contact tool set tool will let the tool touch the sensor to determine the tool. The relevant data, the high-end SCZY laser tool setter is directly scanned by laser, and the measured data is more accurate, but because of the high price of the tool, it is not used too much.
As for how the device knows the data of the axis, it depends on the measurement system.
There are roughly three categories here:
1.Directly using the motor to calculate, the motor is generally a stepper motor, (the stepper motor that can often be seen in life should be a quartz clock, imagine the way of operation, a circle is divided into many grids, the angle of each grid is the same By calculating the motor "going a few steps" to calculate the rotation angle, and thus how much the coordinate axis of the motor connection is moved, this scheme is generally called "open loop control", that is, telling the motor how much to go, the actual walking is not Precise, but also to see the creation, this program is the cheapest, but the accuracy is also the worst.
2. The encoder installed behind the servo motor (usually a permanent magnet AC synchronous motor) calculates the movement value of the coordinate by measuring the rotation angle of the motor. The linear axis is generally a screw, and the rotary shaft is generally a worm gear with a transmission ratio. It can be calculated, but the existence of mechanical error is the main factor affecting the accuracy. At the same time, the encoder can also assist in correcting the following error of the motor. Therefore, this is generally called “semi-closed loop control”. That is, the motor + encoder mutually assists More accurate calculations, such as relatively low-priced devices, or devices with less precise requirements.
3. On the basis of the scheme 2, the third measurement system is added, that is, the actual measurement system, for example, the linear axis increases the grating scale, the rotation axis increases the magnetic grid, the circular grating, etc., and these things are things that can determine how much the coordinate axis has gone. Assuming that the data of the motor and the encoder need to be mentally calculated, the data such as the grating is the result of direct observation. This scheme is the auxiliary measurement of the three data of the motor, the encoder and the actual measurement reading, which is usually called “all. Closed loop control" is the most accurate one of the common solutions. The disadvantage is that it is expensive, and the accuracy is at a certain level. All the accessories are expensive, not only in the third measuring system. tool