HEIDENHAIN TNC 335 Technical Manual - Manual (Page 135)

4-38
TNC 360 2 Reference Marks 8/95
2.1 Passing over the reference marks
The reference marks for axes must be traversed after switching on the control. 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 is...
– the software limit switch activated,
– the most recently set datum point reproduced,
– PLC positioning and positioning with the miscellaneous functions M91 and M92 possible,
– the counter value set to zero for non-controlled axes.
For distance-coded measuring systems the machine datum is the Zero Reference mark. In linear
measurement systems the Zero Reference mark is the first reference mark after the start of the
measuring length; in angular measurement systems 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 each axis by
machine parameters (MP1350.x).
The operating condition "PASS OVER REFERENCE MARKS" is sent to the PLC by the NC (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 manufacturer of the machine. 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 M2559).