HEIDENHAIN PT 855 for Milling - Manual (Page 11)

I - 1 Fundamentals of Positioning
Fundamentals of Positioning
POSITIP 855 Operating Instructions 9
1
Fig. 6: Position definition through absolute
coordinates
Y
X
Z
I
S
R
Nominal position, actual position and distance-to-go
The position that the tool is to move to is called the nominal posi-
tion, while the position of the tool at any given moment is called
the actual position. The distance from the nominal position to the
actual position is called the distance-to-go.
Sign for distance-to-go
The distance-to-go has a positive sign if the axis direction from the
actual towards the nominal position is negative.
The distance-to-go has a negative sign if the axis direction from the
actual towards the nominal position is positive.
Fig. 5: Nominal position , actual position
and distance-to-go
Y
X
Z
1
20
10
Z=15mm
X=20mm
Y=10mm
15
I
Z=–15mm
Y
X
Z
2
10
5 5
15
20
10
10
I X=10mm
I
Y=10mm
3
0
0
S
3
2
2
3
I
R
Fig. 7: Position definition through incremental
coordinates
Absolute workpiece positions
Each position on the workpiece is uniquely identified by its absolute
coordinates.
Example: Absolute coordinates of position :
X = 20 mm
Y = 10 mm
Z = 15 mm
If you are drilling or milling a workpiece according to a workpiece
drawing with absolute coordinates, you are moving the tool to the
value of the coordinates.
Incremental workpiece positions
A position can also be referenced to the preceding nominal posi-
tion. In this case the relative datum is always the last programmed
position. Such coordinates are referred to as incremental coordi-
nates (increment = increase). They are also called incremental or
chain dimensions (since the positions are defined as a chain of di-
mensions). Incremental coordinates are designated with the
prefix I .
Example: Incremental coordinates of position referenced to
position
Absolute coordinates of position :
X = 10 mm
Y = 5 mm
Z = 20 mm
Incremental coordinates of position :
I X= 10 mm
I Y= 10 mm
I Z = –15 mm
If you are drilling or milling a workpiece according to a drawing
with incremental coordinates, you are moving the tool by the value
of the coordinates.
An incremental position definition is therefore a specifically relative
definition. Likewise, a position defined by the distance-to-go to
the nominal position is also a relative position (in this case the rela-
tive datum is in the nominal position).