
B–61404E/08
5. FEED FUNCTIONSPROGRAMMING
75
NOTE
1 This function is also usable with linear acceleration/deceleration before interpolation. In this
case, no arc radius error is caused by acceleration/deceleration before interpolation. When the
time constant for acceleration/deceleration after interpolation is set to 0, an approximate arc
radius error can be obtained using Expression 4:
2 This function is also usable with linear acceleration/deceleration after interpolation for cutting
feed. In this case, an approximate circular cutting error can be obtained from Expression 5:
where
∆ r : Maximum radius error (mm)
v : Feedrate (mm/sec)
r : Arc radius (mm)
T
1
: Time constant for linear acceleration/deceleration in cutting feed (sec)
T
2
: Time constant for the servo motor (sec)
3 Expressions 1, 4, and 5 can be used only to find approximate values based on the NC theory.
They do not determine actual machining errors. Let ∆r
all
be the actual machining error. Then,
the following can be written:
This function controls or suppresses only those errors caused by the first term on the right–hand
side of Expression 6, that is, errors caused by the time constant for acceleration/deceleration
(T
1
) and that for the servo motor (T
2
). This function has no effect on errors caused by the
machine. Note also that Expressions 1, 4, and 5 can determine only approximate values. As
the arc radius decreases, the approximation precision degrades; in this case, even if the
feedrate is clamped to the maximum allowable feedrate (v) obtained using Expression 3, the
error may not be suppressed to within the allowable range.
D r = T
2
2
× (Expression 4). . . . . . . . . . . . . . . . . . . . . . . . . . .
1
2
V
2
r
D r = ( T
1
2+
T
2
2
) (Expression 5). . . . . . . . . . . . . . . . . . . . . . . . . . .
1
24
1
2
V
2
r
D r
all
= D r
NC
+ D r
machine
(Expression 6). . . . . . . . . . . . . . . . . . . . . . . . . . .
Error caused by the machine
Error caused by the acceleration/deceleration time
constant (T
1
) and servo motor time constant (T
2
).