|
Contact Us
Site Map
Application: Product:
|
REVIEW OF
SCIENTIFIC INSTRUMENTS VOLUME 71, NUMBER 10 OCTOBER 2000 Laser
vector measurement technique for the determination and compensation of volumetric position errors.
Part II: Experimental
verification John
Janeczko Giddings
and Lewis Machine Tools, 142 Doty Street, Fond du Lac, Wisconsin 54936
Bob
Griffin and Charles Wang Optodyne, Incorporated, 1180 Mahalo Place, Compton, California 90220
(Received 2 May 2000;
accepted for publication 8 July 2000) A Giddings and
Lewis, model RAM 630 horizontal machine
center was used to verify the laser
vector measurement technique. The
repeatability of the machine and the repeatability of the vector measurements
were verified over a six
month period. A compensation file was
generated based on the laser vector measurement
technique and the body diagonal
measurements were used to check the volumetric accuracy of the machine. The
results indicated that a gain of a factor
of 3-4 in accuracy was achieved with the volumetric compensation than
without compensation. The
time required to compensate for the machine using
the laser vector measurement technique is
significantly less than that using conventional measurement procedures. © 2000
American Institute of Physics. [S0034-6748(00)04110-1] I. INTRODUCTION The basic concept and theory of the laser vector
measurement technique for the determination
of the volumetric positioning errors of
a computer numerically
controlled (CNC) machine tool,
a coordinate measuring machine
(CMM), or a precision instrument are described in Part I of this
article.' To experimentally verify the
theory, extensive measurements
and testing over a period of six
months have been
performed at Giddings and
Lewis (G & L)
Machine Tools on a RAM 630 machining
center.'` A laser Doppler displacement
meter (LDDMTM) model MCV-500 linear calibration systems with a diagonal steering mirror and a 3 in. X4 in.
flat-mirror target as used.
The repeatability of the
machine and the repeatability of the
laser vector measurement
technique have been
checked. Comparisons with conventional measurement results 4 and the effect of
volumetric compensation have
been studied. The results
are described in the following.
II. MEASUREMENT SETUP A. Machine description The Giddings and Lewis RAM
630 machining center is a horizontal milling machine. The machine is considered machine
type XFYZ, where the axis slides are
stacked as pallet (x) to floor (F) to headstock (Y) to ram (Z). The
machine configuration is shown below. Error
measurements and compensation are done for
the three linear
axes; the rotary table
axis is not included.
The error measurement and compensation envelope consists of X = 500 mm,
Y = 500
mm, and Z= 500 mm.
The headstock hydraulic pad
compensation feature used to correct ram
pitch error is normally the only
compensation active during imple- mentation
of volumetric measurements. No other compensations are used. The machine accuracy was measured by laser
interferometers and the angular errors are
less than a few arcsec. B.
Setup description For the testing
here, the respective coordinates are X: from -240 to 260 mm, Y: from 253 to 753 mm, Z: from 160 to 660 mm. The
laser head was mounted on the machine bed
using a steering mirror to point the laser
beam in the diagonal direction. The flat mirror was mounted in the spindle and the mirror surface was perpendicular
to the laser beam, shown
in Fig. 1. The machine was programmed
to move the spindle
starting from one corner to the
opposite corner. The laser beam
is aligned to parallel to the spindle diagonal motion. Typical alignment tolerance was less than 0.5 mrad or 0.5 mm
over a distance of 1 m. FIG. 1. Photo of the
Giddings and Lewis RAM 630 machining
center with the laser head mounted on the pallet and the
flat-mirror target in the spindle. 0034-6748/2000/71(10)/3938/4/$17.00
3938
0 2000 American
Institute of Physics Click here to
download this article Next
