HEIDENHAIN TNC 306 Technical Manual - Manual (Page 128)

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TNC 406/TNC 306 2 Reference marks 3/97
2.1 Passing over the reference marks
The reference marks for axes must be passed over after the control is switched on. This can be
achieved by
– pressing the external START key. The axis sequence is determined by machine parameter
MP1340.X (automatic passing of the reference marks),
– pressing the external axis direction keys. The sequence is determined by the operator.
Only after passing over the reference mark
– can the software limit switch be activated,
– can the most recently set datum point be reproduced,
– is PLC positioning and positioning with the miscellaneous functions M91 and M92 possible,
– is the counter value for non-controlled axes set to zero.
For encoders with distance-coded reference marks, the software limit switches, PLC positioning and
positioning by M91 and M92 are referenced to the Zero reference mark. In linear encoders the Zero
reference mark is the first reference mark after the start of the measuring length; in angular
encoders the Zero reference mark is marked.
The direction of traverse and the velocity on passing the reference marks is defined by machine
parameters (MP1320, MP1330.X).
The functional sequence for passing the reference marks can be fixed specifically for the axes by
machine parameters (MP1350.X).
The operating condition "PASS OVER REFERENCE MARKS" is sent to the PLC by the NC (M2057 or
W272).
In order to avoid exceeding the traverse range when passing over the reference marks a trip dog
(reference end-position) is necessary. This trip dog must be fixed at the end of the traverse range by
the machine manufacturer. The trigger signal from the trip dog is connected to an available PLC
input. In the PLC program this PLC input is combined with the markers for "Reference end position"
(M2556 to M2560).