HEIDENHAIN TNC 122 Technical Manual - Manual (Page 19)

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TNC 122 9 Machine Integration 4/97
MP 910
Positive traverse direction
Entry range: –9999.999 to +9999.999 [mm]
MP910.0 Software limit switch axis X+
MP910.1 Software limit switch axis Y+
MP910.2 Software limit switch axis Z+
MP 920
Negative traverse direction
Entry range: –9999.999 to +9999.999 [mm]
MP920.0 Software limit switch axis X–
MP920.1 Software limit switch axis Y–
MP920.2 Software limit switch axis Z–
Set Reset
M2624
Limit switch axis X+ NC NC
M2625
Limit switch axis X– NC NC
M2626 Limit switch axis Y+ NC NC
M2627
Limit switch axis Y– NC NC
M2628
Limit switch axis Z+ NC NC
M2629
Limit switch axis Z– NC NC
9.3 Reference Marks
For workpiece machining, the datum setting procedure assigns a unique position value (coordinate)
to each axis position. Since the actual position values are generated incrementally by the encoder,
this relationship between axis positions and position values must be restored each time the power is
interrupted.
HEIDENHAIN linear encoders are provided with one or more reference marks. When a reference
mark is traversed, a signal is generated that identifies that position as a reference point. After a
power interruption, crossing over the reference marks will restore the relationship between axis
slide positions and position values that was last established through the datum setting procedure.
Crossing over the reference marks also restores all machine-based references.
Since it is inconvenient to move the axes over large traverses to restore the reference point,
HEIDENHAIN recommends position encoders with distance-coded reference marks. On these
encoders the absolute position value is available after crossing two reference marks.