HEIDENHAIN TNC 122 User Manual - Manual (Page 14)

1 Fundamentals of Positioning
14 TNC 122
Machine axis movements and position feedback
Programming tool movements
During workpiece machining, an axis position is changed either by
moving the tool or by moving the machine table on which the
workpiece is fixed.
Reference marks
The scales of the position encoders have one or more reference
marks. When a reference mark is passed over, it generates a sig-
nal which identifies that position as the reference point (scale ref-
erence point = machine reference point). With the aid of this refer-
ence mark the TNC can re-establish the assignment of displayed
values to machine axis positions.
If the position encoders feature distance-coded reference marks,
each axis need only move a maximum of 20 mm (0.8 in.) for linear
encoders, and 20° for angle encoders.
Y
X
Z
+X
+Z +Y
Position feedback
The position feedback encoders convert the movement of the ma-
chine axes into electrical signals. The control evaluates these sig-
nals and constantly calculates the actual position of the machine
axes.
If there is an interruption in power, the calculated position will no
longer correspond to the actual position. When power is restored,
the TNC can re-establish this relationship with the aid of the encod-
ers' reference marks.
When entering tool movements in a part program you
always program as if the tool is moving and the work-
piece is stationary.
Fig. 1.8: Linear position encoder, here for the
X axis
Fig. 1.9: Linear scales: above with distance-
coded reference marks, below with
one reference mark
Fig. 1.7: On this machine the tool moves in
the Y and Z axes; the workpiece
moves in the X axis.