Zero Angle Reference Axis; Position Encoders - HEIDENHAIN ND 780 Handbuch

Zero Angle Reference Axis

The Zero Angle Reference Axis is the 0 degree position. It is defined
as one of the two axes in the plane of rotation. The following table
defines the Zero Angle where the position of the angle is zero for the
three possible planes of rotation.
For angular positions, the following reference axes are defined:
Plane Zero Angle Reference Axis
XY +X
YZ +Y
ZX +Z
Positive direction of rotation is counterclockwise if the working plane
is viewed in the negative tool axis direction.
Example: Angle in the working plane X / Y
Angle Corresponds to the...
+ 45° ... bisecting line between +X and +Y
+/- 180° ... negative X axis
- 270° ... positive Y axis

Position Encoders

The position feedback encoders convert the movement of the
machine axes into electrical signals. The ND 780 constantly evaluates
these signals and calculates the actual positions of the machine axes,
which it displays as a numerical value on the screen.
If there is an interruption in power, the calculated position will no
longer correspond to the actual position. When power is restored, this
relationship can be re-established with the aid of the reference marks
on the position encoders, and the ND 780's reference mark evaluation
feature (REF).
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I Operating Instructions