is short, the equipment is compact, the setup and alignment is
simple and the cost is low.
III. For manual machines
For a manual machine, higher accuracy
can be achieved by numerical display the
volumetrically corrected position. Install a rotary encoder
and a home position switch for each axis.
Use a desk top PC with 3 counter
cards, and volumetric positioning error
lookup tables to display
the machine coordinate or parts coordinate. The software will
display the 3-axis positions corrected with
the volumetric positioning error
lookup table. The software can also
record the actual 3-axis position during the laser vector measurement. For large
temperature changes in
the shop floor, material
temperature sensors can be
installed to
compensate the machine thermal
growth. A block
diagram is shown in Fig. 1.
IV. For CNC machines without volumetric
compensation capability For
CNC machines without the volumetric
compensation capability, such
as Fanuc 0, Siemens 802, etc, the machine can only compensate
the pitch errors of each axis. First
use the laser vector technique to measure
the volumetric positioning
errors and generate an
error compensation lookup
table. A software, such as Shadow
Map, will use the error
compensation lookup table to correct the x-, y-, and z-axis coordinates in the parts
program (G-code). Enter the corrected
parts program to the controller to cut a
more accurate part. A block diagram of off-line error compensation is shown in Fig. 2 and a
block diagram of on-line error compensation
is shown in Fig. 3. V. For advanced CNC
machines with volumetric
compensation capability For
advanced CNC machines
with volumetric
compensation capability,
such as Fanuc
15, 16 and
18 with straightness
compensation, Siemens 840 and 810 with sag
compensation capability, first
use the laser vector
technique to measure the
volumetric positioning errors
and generate a volumetric error compensation file. Then download the
volumetric error compensation
file to the controller. The CNC machine after the volumetric error
compensation will cut more accurate parts.
A block diagram is shown in Fig. 4. MachineAccuF100902.doc 2
