I Introduction
1.2 Fundamentals of NC
Programming tool movements
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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.
.-
Yau always program 8s if
the mat
is moving and the workpiece is
stationary.
Position encoders
r
The position encoders - linear encoders for linear axes, angle encoders
for rotary axes - convert the movement of the machine axes into
electrical signals. The control evaluates these signals 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 returned, the TNC can
re-establish this relationship.
Fig. 1.21: On this machlne the tool moves in
the
Y and 2 axes; the workpiece
moves in the X axis.
Y
Fig. 1.22:
Linear posltlon encoder, here for
the X axis
‘-
Reference marks
The scales of the position encoders contain one or more reference
marks. When a reference mark is passed over, it generates a signal
which identifies that position as the machine axis reference point.
With the aid of this reference mark the TNC can re-establish the assign-
ment of displayed positions 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.
Fig. 1.23: Linear scales: above with
distance-coded-reference marks,
below with one reference mark
TNC 370
l-25
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