
B-63943EN-1/02 7.FEEDRATE CONTROL/ACCELERATION AND DECELERATION CONTROL
- 751 -
- Speed control with acceleration in circular interpolation
When high-speed cutting is performed in circular interpolation, helical
interpolation, or spiral interpolation, the actual tool path has an error
with respect to the programmed path. In circular interpolation, this
error can be approximated from the equation given below.
Specified path
ctual path
r : Maximum radius error (mm)
v : Feedrate (mm/sec)
r : Arc radius (mm)
a : Acceleration (mm/sec
2
)
T
1
: Time constant of
acceleration/deceleration after
interpolation at cutting (sec)
T
2
: Time constant of servo motor (sec)
r : Error
0
Y
X
r
a)
2
2
T
2
1
T(
2
1
2
v
)
2
2
T
2
1
T(
2
1
r ⋅+=+=∆
................................ (Equation 1)
In actual machining, permissible error ∆r is given, so the maximum
permissible acceleration a (mm/sec
2
) in equation 1 is determined.
When a specified feedrate causes the radial error from an arc having a
programmed radius to exceed the permissible error, speed control with
acceleration in circular interpolation automatically clamps the
arc-cutting feedrate by using parameter settings.
Let the permissible acceleration calculated from the permissible
acceleration set for each axis be A. Then, maximum permissible
feedrate v with programmed radius r is expressed as follows:
rAv ⋅= ........................................................................... (Equation 2)
If a specified feedrate exceeds feedrate v obtained from equation 2,
the feedrate is clamped at feedrate v automatically.
The permissible acceleration is specified in parameter No. 1735. If
there is a difference in permissible acceleration between two axes for
circular interpolation, the lower acceleration is regarded as the
permissible acceleration.
If the radius of an arc is small, too small value can be calculated as
deceleration v. In such a case, the lower feedrate limit can be set in
parameter No. 1732 to prevent the feedrate from being decreased too
much.