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6.7 Reference Marks
6.7.1 Definition
Reference marks
6.7.2 Traversing the Reference Marks
6 – 98
The position value (coordinates) of an axis position is defined with respect to
a freely selectable datum. When the axes are moved, the ACTUAL position is
calculated incrementally. If there is an interruption in power, the reference
between the axis position and the position value is lost.
HEIDENHAIN linear encoders are designed with one or more reference marks.
The reference marks identify an axis position at a known distance from the
machine datum. The position of the freely selectable datum is defined with
respect to the machine datum.
The datum and the actual position can be reproduced as soon as the reference
marks are traversed.
HEIDENHAIN recommends position encoders with distance-coded reference
marks. With distance-coded reference marks, the position value can be
reestablished after traverse of a short distance over any two reference marks.
Workpiece
datum
0
Machine table
Position encoder
The reference marks must be traversed after any interruption in power:
7 7 7 7
Press the machine START button: The reference marks are automatically
traversed. The sequence of axes is predetermined.
or:
7 7 7 7
Press the machine axis-direction button. The user determines the sequence
of the axes.
After the reference marks have been traversed:
n
The software limit switches are activated.
n
The most recently saved datum and machine datum are reproduced.
n
PLC positioning and positioning with M91 and M92 become possible.
n
The counter is set to zero for axes in an open loop.
+Z
REF value
REF value
–44.985
0
10 20 30 40
Workpiece
Reference mark
Machine datum
HEIDENHAIN Technical Manual TNC 426, TNC 430
+X
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