
B–63523EN–1/03
4. REFERENCE POSITION ESTABLISHMENT
597
(2)When an incremental command is specified
Movement is made along each axis by a specified distance. (The
movement is indicated with the bold line in the figure below. Note that
the intermediate tool path is not always of the linear interpolation
type.) The coordinates at the end point are those in a newly established
coordinate system. When there is a difference (a, b) between the
newly established coordinate system and the old coordinate system,
the coordinates at the end point are shifted by (a, b). For example,
when G91 G00 X100.Y30.; (M series) or G00 W100.U30.; (T series)
is specified from the position of which absolute coordinates are (0,0),
the distance of movement along each axis is (100,30), and the
coordinates of the end point are (100–a, 30–b).
(100,30) in the new coordinate system
Workpiece origin offset
Workpiece origin offset
Start point
Difference between the machine coordinate system at power–on and the
machine coordinate system after the reference position is established (a, b)
Position at which the
reference position is
established
New workpiece coordinate system
(accurate coordinate system)
New machine coordinate system
(accurate coordinate system)
Specified end point (100,30) = Actual end point (100–a, 30–b)
Workpiece coordinate system before the reference position is
established (inaccurate coordinate system)
Machine coordinate system before the reference position is
established (inaccurate coordinate system)
Fig. 4.9 (f) Operation when an incremental command is specified
When a short distance is specified, the end point can be reached before
three or four reference marks are passed. Even in such a case, the CNC
makes a movement at the FL feedrate while detecting reference marks, but
the CNC does not establish the reference position even when the end point
is reached.
If the reference position is not established, the next G00 command causes
the reference position establishment operation again. The CNC does not
use data on the reference marks detected through the previous movement
and detects three or four reference marks again to establish the reference
position.
When a feed hold has been applied during reference position
establishment operation, the reference position establishment operation
is not performed after execution is restarted. After the restart, non–linear
type positioning is performed. In this block, the reference position is not
established, so reference position establishment operation is performed
again when the next G00 command is specified.
When a reset or emergency stop is applied during reference position
establishment operation, the reference position establishment operation
is interrupted. Since the reference position is not established, reference
position establishment operation is performed again when the next G00
command is specified.
D When a short distance is
specified
D Interruption by feed hold
D Interruption by reset or
emergency stop