HEIDENHAIN TNC 360 ISO Programming - Manual (Page 30)

TNC 360 1-13
1 Introduction
Fig. 1.20: On this machine the tool moves in
the Y and Z axes; the machine
table moves in the positive X' axis
direction.
Fig. 1.21: Linear position encoder, here for
the X axis
Fig. 1.22: Linear scales: above with
distance-coded-reference marks,
below with one reference mark
+X
+Z +Y
Y
X
Z
1.2 Fundamentals of NC
Programming tool movements
An axis position is changed either by moving the tool or by moving the
machine table on which the workpiece is fixed, depending on the individu-
al machine tool.
You always program as if the tool is moving and the workpiece is
stationary.
If the machine table moves in one or several axes, the corresponding axes
are designated on the machine operating panel with a prime mark (e.g. X’,
Y’). When an axis is designated with a prime mark, the programmed
direction of axis movement is the opposite direction of tool movement
relative to the workpiece.
Position encoders
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.
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 these reference marks the TNC can re-establish the
assignment 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.