
B–63833EN–1/02
7. FEEDRATE CONTROL/ACCELERATION
AND DECELERATION CONTROL
356
When a curve is made up of a series of short straight lines as shown in the
figure below, the difference in feedrate on each axis at each corner is not
large. Therefore, deceleration by feedrate difference is not effective.
Small feedrate differences occur successively, however, so a large
acceleration will be generated on each axis as a whole.
In such cases, deceleration is performed to reduce the machining error and
the stress imposed on the machine, both of which are caused by excessive
acceleration. The target feedrate to be reached by deceleration is set so
that the acceleration on each axis, as obtained from the expression below,
does not exceed the allowable acceleration set for all axes.
The allowable acceleration is set using the maximum cutting feedrate
(parameter 1432) and the time required to reach the maximum cutting
feedrate (parameter 1785).
Acceleration on an axis =
Amount of travel in
the previous block
,
Amount of travel
in the next block
max
Difference in feedrate on the axis at a corner
FF
A target feedrate to be reached by deceleration is obtained for each corner.
The actual feedrate is the feedrate to be reached by deceleration, as
obtained at the start point of a block, or the feedrate to be reached by
deceleration as obtained at the end point of the block, whichever is the
lower.
Example:
In the following example, too great an acceleration/deceleration (the
inclination of the dotted lines in the feedrate graphs) is observed
between N2 and N4 and between N6 and N8, so deceleration is
performed in these areas.
N8
N9
N7
N6
N5
N1
N4
N3
N2
Feedrate clamping by
acceleration