B--63003EN--1/02
7. FEEDRATE CONTROL/ACCELERATION
AND DECELERATION CONTROL
552
When an arc is cut at a high speed in circular interpolation, a radial error
exists between the actual tool path and the programmed arc. An
approximation of this error can be obtained from the following
expression:
0
Y
X
r
∆r:Error
∆r: Ma x imum radial error (mm)
v: Feedrate (mm/s)
r: Arc radius (mm)
T
1
: Time c onstant for exponential acceleration/deceleration of
cutting feed (s)
T
2
: Time constant of the servo motor (s)
∆r= (T
1
2
+T
2
2
) (Expression 1)....
2
1
r
v
2
Programmed path
Actual path
When actual machining is performed, radius r of the arc to be machined
and permissible error ∆r are given. Then, maximum allowable feedrate
v (mm/min) is determined from the above expression.
The function for clamping the feedrate by the arc radius automatically
clamps the feedrate of arc cutting to the value set in a parameter. This
function is effective when the specified feedrate may cause the radial error
for an arc with a programmed radius to exceed the permissible degree of
error.
When the permissible error ∆r is determined, the maximum permissible
speed V for the arc radius R is obtained from expression 2.
∆r= (T
1
2
+T
2
2
)
2
1
R
V
2
(Expression 2).....
For the arc radius r, the maximum permissible speed v to set the
permissible error to ∆r is obtained from expression 1. From expressions
1 and 2, the following expression is obtained:
(T
1
2
+T
2
2
)
2
1
r
v
2
=
(T
1
2
+T
2
2
)
2
1
R
V
2
∴ v =
r
R
V (Expression 3)...
7.1.11
F eedrate Clamping by
Arc Radius (M series)
General