1 Introduction
.-
An incremental position definition is therefore intended as an immediate-
ly relative definition. This is also the case when a position is defined by
the distance-to-go to the target position (here the relative datum is
located at the taruet oosition). The distance-to-go has a negative
algebraic sign if the target position lies in the negative
the actual position.
axis direction from
The polar coordinate system can also express
both types of dimensions:
l
Absolute polar coordinates always refer to
the pole (CC) and the reference axis.
l
Incremental polar coordinates always refer to
the last programmed nominal position of the
tool.
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10
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_-_- -----
1.2 Fundamentals of NC
Absolute workpiece positions
Each position on the workpiece is clearly defined by its absolute coordi-
nates.
Example: Absolute coordinates of the position 0:
X=20mm
Y=lOmm
Z=15mm
If you are drilling or milling a workpiece according to a workpiece
drawing with absolute coordinates, you are moving the tool to the
coordinates.
Incremental workpiece positions
A position can be referenced to the previous nominal position: i.e. the
relative datum is always the last programmed position. Such coordinates
are referred to as incremental coordinates (increment = growth), or
also incremental or chain dimensions (since the positions are defined as
a chain of dimensions). Incremental coordinates are designated with the
prefix I.
Example: Incremental coordinates of the position
0 referenced to position 0
Absolute coordinates of the position 0 :
X= IOmm
Y= 5mm
Z=20mm
Incremental coordinates of the position 0 :
IX= IOmm
IY= IOmm
IZ = -15 mm
If you are drilling or milling a workpiece according to a workpiece
drawing with incremental coordinates, you are moving the tool by the
coordinates.
Fig. 1.17: Posltion definition through
absolute coordinates
Fig. 1 ,I 8: Position definition through
incremental coordinates
0”
-
X
Fig, 1.19: Incremental dimensions in polar coordinates (designated
with an “I”)
L
TNC 370
1-23
L
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