Angular measurements are
performed using a dual beam laser setup and the roll measurements are performed using a dual beam laser setup with a
long flat-mirror as target. After the
completion of the angular error measurements these results
will be fed to the
computer and future readings compensated for
these errors. Linear,
perpendicularity, and straightness errors will
be measured using the Vector or Sequential Diagonal technique[1, 2].
III. How
it works 1. Pitch and
yaw angular error measurement Using two laser heads with parallel laser beams and a fixed
separation, the pitch or yaw angular errors
can be measured either statically or on-the-fly. This method
is more accurate than using the
quad-detector method. This is because the air turbulence deflecting the laser beam (similar to the twinkling
stars in the evening) and introducing
angular errors (See Ap- 1102). 2. Roll angular error measurement
Usually, roll
angular error cannot be
measured by a conventional
laser interferometer.
Instead, a precision level is used. However, a
level can not be used to
measure along a vertical or z-axis.
Here, using two laser heads with
parallel laser beams and a fixed
separation, and a long flat-mirror as target, the roll angular errors of all three axes can be measured.
This is because the MCV-5000 laser
head is single-aperture, and a flat-mirror can be used as a target(See
AP-1104 and AP-1108).
It is noted that with a flat
mirror as the target, any displacement parallel to the flat-mirror will not displace the
return laser beam and will not
effect the measurement. Hence only the
displacement along the laser beam direction is measured. For long travel, it is more
convenient to divide the total travel to
several measurements and each measurement with the travel of the
maximum length of the long flat-mirror.
Another method to measure the roll is to perform two straightness error measurement separated by a fixed
distance. 3. Displacement errors, straightness errors, and
squareness errors measurement The
displacement errors, straightness
errors and squareness errors
can be measured
by the vector or
sequential diagonal measurement
developed by Optodyne [1,2].
This method has been
applied to the calibration
and compensation of
many CNC machine centers [3,4].
Briefly, for conventional laser body diagonal displacement measurement [5], the movement
is a straight line along
the body diagonal. It requires moving
all three axes simultaneously along a body diagonal and collecting data at each preset
increment. The new vector or sequential diagonal measurement method,
suggest moving the X, Y and Z-axis in
sequence and collect data after each axis is moved. Hence the
position errors due to the movement of each
axis can be separated. The collected data
can be processed as deviations measured in the body diagonal direction due
to X-axis movement, Y-axis movement and
Z-axis movement respectively. Hence three
times more data is collected for each
diagonal measurement. For the four
diagonal measurements, there
are 12 sets of data to determine
the three linear position
errors, the six straightness errors and three squareness errors.
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