
B–63523EN–1/03
7. FEEDRATE CONTROL/ACCELERATION
AND DECELERATION CONTROL
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As shown below, when a curve is formed by very short successive line
segments, there is no significant feedrate difference along each axis at
each corner. Consequently, the tool need not be decelerated to compen-
sate for feedrate differences. When taken as a whole, however, successive
feedrate differences generate a large acceleration along each axis.
In this case, the tool must be decelerated to minimize the stress and strain
imposed on the machine, as well as the machining error that may result
from such excessive acceleration. The tool is decelerated to the feedrate
at which the acceleration along each axis, found from the formula below,
is equal to or less than a specified allowable acceleration.
The allowable acceleration is determined from a maximum cutting
feedrate (set in parameter No. 1432, No. 1430, or No. 1422) and the time
needed to reach the maximum cutting feedrate (set in parameter No.
8470).
Acceleration along each axis =
Feedrate difference along each axis at a corner
Travel in the previous block
F
max (
Travel in the next block
F
)
,
The reduced feedrate required for each corner is calculated. The tool is
decelerated to the decreased feedrate found at either the start point or the
end point of each block, whichever is smaller.
Example: In the example shown below, the tool is accelerated too
quickly from N2 to N4 and from N6 to N8 (as indicated by the
dashed–line inclinations in the feedrate graphs) when automatic
feedrate control is not used. So, the tool is decelerated.
Example of feedrate
determination based on
acceleration along each
axis