Fanuc Series 15i/150i-MA (Programming) Operators Manual

- 684 -
In fine HPCC mode, an optimum feedrate that
causes the accelerations on individual axes to fall
within the range of permissible acceleration is
calculated even if the permissible accelerations
specified for the axes are different.
In a mode other than fine HPCC mode (in normal
mode), the smaller of the permissible accelerations
on the two axes of circular interpolation is used. If
either of the values of the two interpolation axes is 0,
the non-zero value is used as the permissible
acceleration. If both values are 0, deceleration is
not performed.
If the radius of the arc is small, the calculated deceleration speed v may
become very small. To prevent the feedrate from becoming too low,
the minimum feedrate can be specified in a parameter. The following
parameters are used to specify the minimum feedrate:
In fine HPCC mode: Parameter 1483
In a mode other than fine HPCC mode (in normal mode): Parameter
- Linear acceleration/deceleration after interpolation in cutting feed
If the function for linear acceleration/deceleration in cutting feed is
applied, an error in circular cutting can be approximated using formula
+=+= ............(Formula 3)
Because the relationship of formula 2 holds, as indicated by formula 3,
deceleration by linear acceleration/deceleration after interpolation can
be based on the acceleration during circular interpolation.
- Actual error
Formulas 1 and 3 provide only the theoretical approximate errors
obtained by the CNC. Those values are not errors in actual machining.
The error in actual machining r all is given by the following formula:
r all =r NC +r machine...................................(Formula 4)
r machine : Error caused by the machine
r NC : Error resulting from acceleration/deceleration time constant
(T1) and servo motor time constant (T2)
This function keeps only the first term on the right side, which is the
error resulting from the acceleration/deceleration time constant (T1)
and servo motor time constant (T2), constant and is unrelated to the
error caused by the machine.
Formulas 1 and 3 are expressions of approximations. The precision of
the approximation decreases with a decrease in the radius of the arc.
Even if the speed is clamped to the maximum permissible speed v
obtained by formula 2, the error may not be permissible.

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