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Pitch Compensation

Oct 08, 2019

Due to the rapid development of mechanical and electronic technology, CNC machine tools have attracted more and more attention as an automatic processing equipment with high precision, high efficiency and stability. The positioning accuracy of the numerical control system is an important factor affecting its high-precision performance. The use of the pitch compensation and sag compensation function of the Siemens 840D numerical control system can greatly reduce the positioning error of the machine tool and improve the positioning accuracy of the machine tool.


The following ALLES CNC will share with you how pitch compensation reduces the impact of geometric accuracy on positioning accuracy.


The pitch compensation function of the 840D CNC system is an absolute compensation method, and the pitch compensation is performed on the axis. We set the compensation starting point position a, the compensation end point position b, and the compensation interval distance c, then the number n of intermediate points that need to be interpolated, where n=1+(b-a)/c.

The specific steps are as follows:

1) Set the axis data MD38000 MM_ENC_COMP_MAX_POINTS[t] = n. Modifying this parameter will cause the NCK memory to be reallocated. So after the modification, you should make a backup of the NC under the service menu. (t=axis number of the compensated axis)

2) After the NCK reset is performed on the system, the “M4400” alarm will appear, indicating that the axis parameters are lost. At this time, the NC backup load under the 1) step is loaded into the NC system.

3) Copy "CEC_DATA" under the Nc-Active-Data menu to a newly created backup document directory *.MDN.

4) Find and open the compensation file form in the new directory, and change the corresponding compensation point directly in the table according to the data measured by the surveyor. Save and close the editor.

5) Set the axis parameter MD32700 ENC_COMP_ENABLE=0 and load the modified compensation table into the NC system.

6) Set the axis parameter MD32700 ENC_COMP_ENABLE=1 to do an NCK reset.

7) The axis returns to the reference point and the new compensation data is valid.

You can see the data changes under "Diagnostics" ------ "Service display" ------ "Service Axis" interface.

Pitch compensation acquisition compensation data generally passes through the laser detection instrument, usually going through two steps, one single step, two more steps. The former is to establish a compensation curve based on the machine axis error, and the latter is to detect the backlash of the axis, positioning accuracy, repeatability, and positional deviation.

Taking the actual operation of PAMAφ140 after an electrical transformation as an example, the X-axis travel is -50mm~5870mm, the compensation starting point position is a=0, the compensation end point position is b=5800, and the compensation interval distance is c=200, then interpolation is required. The number of intermediate points is based on n = 1 + (ba) / c, that is, n = 30, and the number of cycles p = n - 2, that is, p = 28.


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