Siemens sinumerik 840D sl Function Manual page 152

Detailed description
2.2 Referencing and synchronization of gantry axes
Referencing from part program with G74
The referencing and synchronization process for gantry axes can also be initiated from the
part program by means of command G74. In this case, only the axis name of the leading
axis may be programmed. The operational sequence is analogous to that described for axis-
specific referencing.
Position measuring system with distancecoded reference marks
In order that return traverses do not have to be made over large distances, it is possible to
use a position measuring system with distance-coded reference marks as a sole or second
measuring system for gantry axes. In this way the measuring system is referenced after
traversal of a short path (e.g. 20 mm). The procedure for referencing the gantry axes is the
same as that described for the normal incremental measuring system.
References:
/FB1/ Function Manual, Basic Functions, Reference Point Approach (R1)
Absolute encoder
During the course of the synchronization compensatory motion, all axes in the gantry axis
grouping traverse to the reference point value of the leading axis defined in the machine
data:
MD34100 $MA_REFP_SET_POS (reference point value/destination point for distancecoded
system)
The absolute encoders and distanced-coded encoders of the leading axis will be set to the
current actual position of the leading axis or to the reference point by the following machine
data:
MD34330 $MA_REFP_STOP_AT_ABS_MARKER (Distancecoded linear measuring system
without destination point)
Activation of axis compensations
Compensation functions can be activated for both the leading axis and the synchronized
axes. Compensation values are applied separately for each individual gantry axis. These
values must therefore be defined and entered for the leading axis and the synchronized axes
during start-up.
The compensations do not become operative internally in the control until the axis is
referenced or the gantry grouping synchronized. The following applies:
Compensation type
Backlash compensation
LEC
Sag compensation
Temperature compensation
If a movement by the synchronized axis (axes) is caused by an active compensation, a travel
command is displayed for the synchronized axis (axes) independently of the leading axis.
20
Takes effect when
Axis is referenced
Axis is referenced
Gantry grouping is
synchronized
Gantry grouping is
synchronized
Function Manual, 11/2006, 6FC5397-2BP10-2BA0
PLC interface signal
"Referenced/Synchronized"
"Referenced/Synchronized"
"Gantry grouping is synchronized"
"Gantry grouping is synchronized"
Special functions: Gantry Axes (G1)