2 dominate errors are the straightness and squareness errors
rather than the linear displacement errors.
Hence, the above definition is no longer valid. IV.New definition
of volumetric accuracy The positioning error in each axis direction, Dx(x,y,z),
Dy(x,y,z), and Dx(x,y,z), is the sum of displacement error and
straightness errors as the following. Dx(x,y,z) = Dx(x) + Dx(y) + Dx(z),
Dy(x,y,z) = Dy(x) + Dy(y) + Dy(z),
Dz(x,y,z) = Dz(x) + Dz(y) + Dz(z).
Then the volumetric error is the root-mean-square sum of
these total errors. That is, Volumetric error = sqrt {[Max Dx(x,y,z)-Min
Dx(x,y,z)]² + [Max Dy(x,y,z)-Min Dy(x,y,z)]² + [Max Dz(x,y,z)- Min
Dz(x,y,z)]²}. However, using a conventional laser interferometer, the
measurement of these straightness and
squareness errors are time consuming. Hence, the body diagonal displacement error measurement in the ASME B5.54 [2]
or ISO 230-6 [3] standard is a good quick
check of the volumetric error. V.The body diagonal displacement measurement The volumetric positioning errors, including 3 displacement
errors, 6 straightness errors, squareness
errors and some angular errors, will show up as the 4 body diagonal displacement errors [4]. Hence it is
a good and efficient measurement of the
volumetric error. The volumetric error can be defined as
[Max Dr(x,y,z) – Min Dr(x,y,z)],
where Dr(x,y,z) is the diagonal displacement error. The introduction of B5.54
and ISO230-6 machine tool
performance measurement
standards are increasing the popularity of
laser body diagonal displacement measurement for a quick
check of the volumetric error. The
B5.54 body diagonal displacement tests have
been used by Boeing Aircraft Company and
many others for many years with very good results and success. VI.The sequential step diagonal or vector
measurement For a machine with small
body diagonal displacement errors, the volumetric error is small. However for a machine with large body
diagonal displacement errors, there is not
enough data to determine which errors are causing the large volumetric error. Using
Optodyne’s Laser Doppler
displacement meter (LDDM), the sequential step diagonal or vector measurement, 12
sets of data can be collected by the 4
sequential step diagonal measurement[4,5]. Hence the 3 displacement errors, 6 straightness errors and 3
squareness errors can all be
determined. These measured errors can
be used to compensate the Click
here to download "article16.pdf" file
