July 2013 6.4 Axis-error compensation 673
Links to axis-error compensation tables
Variable deviations can be described as a function of axis positions (referred to
below as compensation function). The compensation function is described in
the form of a table, in which compensation points are entered. The path
between the individual compensation points is interpolated linearly
(corresponds to the behavior of tables for nonlinear axis error compensation).
The compensation points can be entered as discrete values (in [mm] or [°], the
decimal character is a point), or they can also be defined as indiscrete data
through PLC words. If PLC words are used, the compensation points will be
updated by the contents of the respective PLC words every second. The
contents of the PLC words are interpreted as 1/10000 mm or 1/
10000 degrees.
The compensation functions are defined in the tables available for nonlinear
axis error compensation (*.COM). To make this possible, the tables were
extended by the six columns C1 to C6. The compensation function is assigned
to a Trans line of the kinematics table by an identifier in the column COMPTAB.
The first part of the identifier refers to the axis, the second part refers to the
column of the error table *.COM belonging to that axis.
Example: A4C1 means that the compensation function of the 4th axis in
column C1 is selected. The compensation value table is assigned to an axis as
previously via the active line of the selected *.CMA file.
Each compensation value table can contain a maximum of six compensation
functions (= columns C1 to C6), which can be assigned to the Trans lines of
the kinematics table. Only one compensation value table per machine axis is
permissible (as previously).
If an axis position is changed, a new collective compensation value is
calculated in the X, Y and Z axes. This compensation value is the result of a
re-calculation of the entire kinematics chain, including the current
compensation values. The position of the TCP Tool Center Point is corrected
by adding the collective compensation value to the axis positions.
Machine parameter MP4070 is used to limit the change rate of the
compensation (maximum compensation value per PLC cycle).
Compensation is not shown in the position display of the control. The
compensation values can be read with PLC module 9040 or 9041 (transfer
value 8). The module supplies the values to be added to the ACTUAL position
of the axis. This means that the algebraic sign must be neglected in order to
attain the compensation values that are traversed by the machine axes.
The DCM collision monitoring function of the iTNC 530 does not consider the
compensation. All collision bodies are enlarged by MP1292 by the value
entered there in order to ensure a reliable collision protection.
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