rates with
higher feedrates and smaller radius
cuts. It
is important to know the maximum feedrate that the machine
can achieve without losing
the required contouring
accuracy Chart
2 shows the deviations in radius, circularity, and feedrate
at a nominal radius. Chart 3 shows the deviations in
radius and circularity at, various
feedrates. Determining the
velocity profile at high feedrate and small radius can indicate whether the
servo controller is
properly tuned. Chart
4 is
the displacement, velocity,
and acceleration of Using Optodyne's MCV-500 system, data on all these volumetric
errors (3 linear, 6
straightness, and 3 squareness) can be collected in about 2 hours ( I meter volume).
Laser/ballbar
helps pinpoint contouring
accuracy. Chart 2 shows the deviations in
radius, circularity, and feedrate at a
nominal
radius; Chart 3 shows the deviations
in radius and circularity at various feedrates.
The shape
of displacement is sinusoidal, as
well as the
velocity and
the acceleration. All is smooth and well
con-trolled; the machine is
well dimensioned and well tuned. an axis while making a 25mm
(0.984”) circular
pattern at a
feedrate of
4800mm/min (189 ipm) Chart 4 shows the displace-ment velocity and acceleration of an axis of a
different machine making a 1"(25.4mm)
circular pattern at
a feedrate of 150 ipm (3800mm/min). This
dynamic information
was obtained by
using Optodyne's
laser/ballbar. The
laser measurement is
accurate to lµm/m
(lppm) and traceable to NIST In Chart
4 we can see that the shape of
displacement, as well as the velocity and
the acceleration, is sinusoidal.
All is smooth and well controlled: the machine is
well dimensioned and
well tuned. In
Chart 5, the displacement
looks sinusoidal, but with further
analysis we can see velocity with
a triangular wave
and the acceleration with a
square wave. The servo system
is acting with two basic
conditions only, The
displacement
looks
sinusoidal in
Chart.5, but with further analysis
we can see
velocity with a
triangular wave and
the acceleration with a
square wave. The
servo system is
acting
with
two
basic
conditions
only, full power
forward
and
full
power
backward,
trying to follow the imposed position.
Thesystem
needs to
be tuned, increasing the loop gain, for instance.
full power forward
and full power backward,
trying to follow the imposed
position. The system needs
to be tuned, for
instance, by= increasing the loop
gain. The laser/ballbar is one system that can perform
all of the
following functions: verify linear
position accuracy; measure servo
mismatch; measure
nonround-ness;
measure reversal errors;
generate data for
comp files; generate data to
tune servo controller; measure
tangential velocity; and
enable continuously variable
radius from 0.1” to 3.0”. For more information from Optodyne Inc, Compton, CA,
http://
www.optodyne.com Reprinted from the July 1999 issue of Tooling & Production
magazine.
