
B-63944EN-2/02 PROGRAMMING 3.INTERPOLATION FUNCTION
- 25 -
Inward offset
OVR = Rcp/(Rcp + Rofs) × 100
Outward offset
OVR = Rcp/(Rcp - Rofs) × 100
where,
Rcp : Radius of curvature at the center of the tool of the
involute curve passing through the center of the tool
Rofs : Radius of the cutter
- Clamping the override
The lower limit of override is specified in parameter No. 5620 so that
the override for inward offset by cutter compensation or the override
in the vicinity of the basic circle will not bring the speed of the tool
center to zero in the vicinity of the basic circle.
The lower limit of override (OVR1o) is specified in parameter No.
5620 so that the inward offset will not reduce the speed of the tool
center to a very low level in the vicinity of the basic circle.
Accordingly, the feedrate is clamped but does not fall below the level
determined by the programmed feedrate and the lower limit of
override (OVR1o).
The outward offset may increase the override to a very high level, but
the feedrate will not exceed the maximum cutting feedrate.
- Clamping the acceleration in the vicinity of basic circle
If the acceleration calculated from the radius of curvature of the
involute curve exceeds a value specified in the corresponding
parameter, the tangential velocity is controlled so that the actual
acceleration will not exceed the value specified in the parameter.
Because the acceleration is always limited to a constant level, efficient
velocity control can be performed for each machine. Because
smooth velocity control can be performed continuously, impacts in
machining in the vicinity of the basic circle can be reduced.
To calculate the acceleration, the radius of curvature of the involute
curve and the tangential velocity are substituted into the following
formula of circular acceleration:
Acceleration = F × F/R
F: Tangential velocity
R: Radius of curvature
The maximum permissible acceleration is specified in parameter No.
1735.
If the calculated acceleration exceeds the maximum permissible
acceleration, the feedrate is clamped to the level calculated by the
following expression:
onaccelerati epermissibl Maximum curvature of Radius level Clamp ×=
If the calculated clamp level falls below the lower limit of feedrate,
the lower limit of feedrate becomes the clamp level. The lower limit
of feedrate is specified in parameter No. 1732.