Proceedings of the Measurement Science Conference, Los Angeles, LA
January 24-25, 2002 2
measurement of the body diagonal
displacement errors is recommended by many international standards such as ISO 230-6 and
ASME B5.54 [1] for a fast check
of the volumetric performance. This is because the body diagonal
displacement measurement is sensitive to all of the error components. However, if the errors exceed the
specification, there is not enough information for the identification of the error sources and for
their compensation. The
laser vector measurement techniques or in
other words the method of laser sequential diagonalmeasurement techniques [2,3] can
measure all those volumetric errors by
using a Laser
Doppler Displacement Meter (LDDM) which is a new generation of laser
interferometer with a single beam and
single aperture, and able to use a flat mirror as target. II. Body Diagonal Displacement Measurement
The body diagonal
displacement measurement method is recommended for a fast examination
of the positioning
and geometrical performances of
the machine in all its
components. Practically
it is the measurement
of the volumetric positioning
accuracy by a laser
interferometer. A retroreflector is
mounted on the spindle and illuminated by the laser beam, which is aligned along the machine diagonal, for example from
the lower left corner (X=0 Y=0 Z=0) to the
upper right corner (Xmax, Ymax, Zmax). Starting from the zero position and
at each increment of
the three axes, which are moved
together to reach the new position
along the diagonal,
the displacement error is measured.
The accuracy of each position along
the diagonal depends on
the positioning accuracy of the three
axes, and usually also by the
machine geometry. Hence the
body diagonal displacement measurement is a good method for the machine verification, but there is not enough information
for the identification of the error sources. III.
Vector or Sequential
Diagonal Measurement The new vector measurement
method or Sequential Diagonal Measurement Methoddiffers from the
traditional method because each axis is
moved separately and the positioning error
is collected after each single
movement of the X axis, of the Y axis and than of the Z axis. For this
reason, 3 times more data is collected and
also the positioning error due to each single axis movement can be separated.
The collected data can be processed
as the projection of the
displacement of each single axis
along the diagonal. It is possible to determine the positioning
errors for each one of the three axes.
In the conventional body diagonal
displacement measurement, the target trajectory is a straight
line and it is
possible to use the corner cube as
target that can tolerate a small
lateral displacement. In the
vector method, the movement is alternatively along the X axis, than along
the Y axis and than along the Z axis, and
repeated until the opposite corner of the diagonal is reached. As shown in Fig. 1, the trajectory of the target
is not a straight line and the lateral movement is quite large.
Hence it is not possible to
use a conventional interferometer that
cannot tolerate such
large lateral movement. A laser
interferometer with single aperture is
used with either a
standard corner cube or a flat mirror as target. It is noted that with a
flat mirror as target, the movement
parallel to the mirror do not displace the laser beam and do not
change the distance from
the source so the measurement is not
influenced. Hence, it measures the movement along the beam direction and tolerates a
large lateral movement of the target.
IV. Measurement on a JOBS 5-axis machine
The measurement
was performed on a JOBS-LINKS COMPACT 5AX linear motor machine in
thethe Piacenza facility. The machine
working volume is 2 m by 3 m by 1 m (80” x 120” x 40”), andPlease click
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