HEIDENHAIN PT 855 for Turning - Manual (Page 8)

I - 1 Fundamentals of Positioning
POSITIP 855 Operating Instructions 9
2
Z
X
15
5
35 65
1
0
Z
X
1
10
5
35 30
2 3
I S
Z
X
R
Nominal position, actual position and distance-to-go
The positions to which the tool is to move are called the nominal
positions, while the position at which the tool is actually located at
any given moment is called the actual position (see Figure 6). 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 carries a positive sign when the path from the
actual to the nominal position is in the negative axis direction.
The distance-to-go carries a negative sign when the path from the
actual to the nominal position is in the positive axis direction.
Absolute workpiece positions
Each position on the workpiece is uniquely defined by its absolute
coordinates (see Figure 7).
Example: Absolute coordinates of position :
X = 5 mm
Z = –35 mm
Absolute coordinates of position :
X = 15 mm
Z = –65 mm
If you are working according to a workpiece drawing with absolute
dimensions, you are moving the tool to the coordinates.
Incremental workpiece positions
A position can also be defined relative to the previous nominal po-
sition (see Figure 8). The datum for the dimension is then located
at the previous nominal position. Such coordinates are termed in-
cremental coordinates (increment = increase) or chain dimen-
sions (since the position is defined by a chain of dimensions).
Incremental coordinates are identified by a preceding I .
Example: Incremental coordinates of position referenced to
position
:
I X = 10 mm
I Z = 0 mm
Incremental coordinates of position referenced to
position
:
I Z = –30 mm
Incremental coordinates of position referenced to
position
:
I X = 10 mm
I Z = –30 mm
If you are working according to a workpiece drawing with incre-
mental dimensions, you are moving the tool by the dimension.
Sign for incremental dimensioning
An incremental dimension has a positive sign when the axis is
moved in the positive direction.
An incremental dimension has a negative sign when the axis is
moved in the negative direction.
Fig. 6: Nominal position , actual position
and distance-to-go
Fig. 7: Positions and are absolute
workpiece positions
Fig. 8: Positions and are ncremental
workpiece positions
1
3
1
2
S I
R
1 2
1 3
1
3
2
2