06.93 12 Functional Descriptions
12.1 Leadscrew error compensation 6FC5 150-0AH01-0AA0
12 Functional Descriptions

12.1 Leadscrew error compensation

6FC5 150-0AH01-0AA0

12.1.1 Corresponding data

• NC-MD 316* (Reference point pointer for + compensation)
• NC-MD 320* (Reference point pointer for - compensation)
• NC-MD 324* (Distance between 2 leadscrew error compensation points)
• NC-MD 328* (Compensation value)
• NC-MD 344* (Modulo value for rotary axis)
• NC-MD 6000 to 6249 (Leadscrew error compensation points)
• Option 6FC5 150-0AH01-0AA0
Note carefully:
Changes to NC MD data for leadscrew error compensation do not go into effect until after
completion of POWER ON and reference point approach.

12.1.2 Functional description

The principle of "indirect measurement" in NC controlled machines assumes that the pitch of
the leadscrew is constant at any point within the traversing range, thus allowing the actual axis
position to be derived from the position of the drive spindle.
However, varying deviations result from manufacturing tolerances in the various spindle
qualities. In addition, measuring system errors (although comparatively insignificant) and any
other possible machine-dependent errors must also be taken into account.
The checksum error can be determined by plotting an error curve over the entire traversing
range of the axis. The reference measuring system used must be a high-precision instrument,
e.g. a laser interferometer. The dimensional deviation at the workpiece can be significantly
reduced by means of compensating values which are input to the control at the time of
installation.
The errors in each axis can be compensated separately. To this end, a total of 1000 compen-
sation points (positions) are available for all axes. The compensation position spacing for each
axis is selectable over a range of 1 to 32,000 units. It is possible to set a compensating value
of 0 to 100 units which is identical for all positions on each axis.
Leadscrew error compensation can also be used with C axes. Yet another difference
compared with earlier software versions concerns the "Direction-dependent leadscrew error
compensation": No positioning error now occurs when switching from follow-up mode to
position control mode, even if any changes of position during follow-up mode or a non position
control mode occur.
Caution:
Changes to NC MD data for leadscrew error compensation do not take effect until POWER ON
and reference point approach have been executed.
© Siemens AG 1992 All Rights Reserved 6FC5197- AA50 12–1
SINUMERIK 840C (IA)