
B-65280EN/05 FANUC AC SPINDLE MOTOR αi series 5.FUNCTION DESCRIPTIONS
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(2) Cautions about position error
When the spindle fine Acc./Dec. (FAD) function is in use, the
following two types of position error can occur because the spindle
software applies smoothing to a motion command from the CNC.
• Actual position error related to the command from the CNC:
(Regular) position error
• Position error used within the spindle software: FAD position
error
These position error are used for the following purposes.
• (Regular) position error: Excessive-error check and in-position
check
• FAD position error: Error display on the spindle adjustment
screen
NOTE
The (regular) position error becomes larger by the
amount of an influence of fine Acc./Dec. (FAD)
smoothing. So, include this amount when specifying
excessive-error and in-position check levels.
An increase in the position error caused by fine
Acc./Dec. (FAD) is obtained by:
[When the linear type is used.]
Increase in
pos. error
(pulses)
feedrate (min
-
)
60
×1000
detection
unit
= ×
FAD time
constant (ms)
2
+1
+1
[When the bell-shaped type is used.]
Increase in
pos. error
(pulses)
feedrate (min
-
)
60
×1000
detection
unit
= ×
FAD time
constant (ms)
2
+1
Letting the FAD time constant and feedrate be,
respectively, 64 ms (bell-shaped type) and 3000
min
-1
for rigid tapping (with a detection unit of 4096
pulses/rev):
Increase in
pos. error
(pulses)
3000
60
×1000
4096
=
64
2
+1
= 6758