Leadscrew error compensation

Compensation process

Leadscrew error compensation (referred to below as LSEC) is an axial compensation.
The position setpoint of the compensated axis is changed by a compensation value in the position controller cycle in order to compensate for leadscrew errors, for instance.

This compensation is cancelled by computation for the measured actual position values so that the compensation performed does not appear in the display data of the controller.

Compensation table

The compensation values are taken from a table in which the profile of the compensation curve is stored as a function of the axis position. The axis positions entered in the table are called interpolation points and the corresponding values of the compensation curve are called compensation values.

The compensation value is linearly interpolated for axis positions that lie between interpolation points.

The table containing compensation values is referred to in the following as the compensation table.

Bilateral/unilateral LSEC

You can specify a separate compensation table for each direction of axis motion; this type of compensation is called bilateral compensation.

With bilateral leadscrew error compensation, any backlash that may be present can also be compensated for; additional backlash compensation (see Section “Backlash compensation“) is therefore not necessary.

With bilateral leadscrew error compensation, the parameter P-AXIS-00243 specifies the number of cycles for distribution of the compensation offset in case of a reversal in direction.

If a table is used for both directions of axis motion, it is referred to as unilateral compensation.

The compensation tables are stored to a file for each axis (compensation value list).
Axis dynamics are not taken into account in the output of compensation values.

The graphic below shows an example of a compensation value curve. The meaning of the parameters used in the graphic will be explained later.

Compensation table with equidistant interpolation point grid and unilateral compensation

Properties

Leadscrew error compensation (LSEC) has the following characteristics:

When bilateral compensation is used, the same interpolation point positions must be used for both value tables.
You can define a compensation table only for a partial motion range of an axis. For axis positions outside the compensation table, the value at either end of the table continues to be used.
Any compensation value other than 0 can be present at the reference point.
The distance between interpolation points in the value tables can be selected either equidistant or non-equidistant.
As of CNC Build V3.1.3079.06 you can adjust the size of the compensation table. The parameter P-COMP-00059 defines the maximum number of table entries. The actual number of entries used by P-COMP-00020

Effectiveness

The LSEC is effective under the following conditions:

The LSEC was activated for the slave axis.
A compensation table for the axis must be transferred to the controller.
he axis was referenced or uses an absolute measuring system.