
B-65150E/04 3. α SERIES PARAMETER ADJUSTMENT
− 79 −
Radius R
Feedrate F
Acceleration
in the normal
direction
(6) Adjustment of the parameters for arc radius based feedrate clamping
[Purpose of adjustment]
As mentioned above, velocity feed-forward coefficient
adjustment can improve a velocity loop response delay, thus
reducing figure errors in areas where specified acceleration
changes to a large extent. However, velocity feed-forward
coefficient adjustment alone cannot fully eliminate figure errors.
Moreover, if the rigidity of a machine itself is low, the machine
may vibrate due to a change in acceleration.
To reduce changes in specified acceleration in areas where
acceleration changes to a large extent, the specified feedrate in the
tangent direction is reduced. In part machining (advanced
preview control), the arc radius based feedrate clamp function
performs this feedrate reduction. By adjusting the parameter of
this function, an acceleration value in the normal direction
allowable with a machine can be found. As detailed below, such
an acceleration value can be used as a guideline for setting the
parameter for feedrate reduction by acceleration in high-precision
contour control (small successive blocks).
In the figure at left, let R be the
radius of the arc, and F be the
feedrate. Then, the acceleration in
the normal direction is F
2
/R. The
arc radius based feedrate clamp
function specifies R and F as its
parameters to ensure that the
acceleration in the normal direction
at a specified arc does not exceed
the specified value.
For example, suppose that when R = 5 mm and F = 4000 mm/min are
specified as the parameters of the arc radius based feedrate clamp
function, the acceleration in the normal direction at the arc is:
F
2
/R = (4000/60)
2
/5 = 889 mm/sec
2
When using the high-precision contour control function, set about the
same value as this acceleration as the parameter for feedrate reduction
function based on acceleration in small blocks. In the example above,
if a cutting feedrate of F4000 (mm/min) is set, the time required to
reach this feedrate is calculated as follows:
4000/60/889*1000 = 75 msec