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NOTE
If
the
distance
between
the
laser
head
and
the
reflector
is
0.5
metres
(20
inches)
or
more,
the
formula
given
in the
paragraph
on
Visual
Alignment
determines
the
cosine
error
based
on
the
offset
of
the
return
beam
at
the
laser
head.
For
example,
a
distance
between
the
laser
head
and
reflector
of
0.5
metres
(20
inches)
and
an
offset
of
the
return
beam
at
the
small
aper-
ture
of
the
laser
of
500
micrometres
(0.0202
inches)
the
cosine
error
is
approximately
0.5
parts
per
million.
Adjust the laser head angularly until the return beam reflected from the reflector re-
turns and is centered on the small aperture of the laser head. Slight lateral adjust-
ments of the interferometer may be required to ensure that the reference beam from
the interferometer is centered on the receiver alignment target.
NOTE
For high accuracy alignment and installations where there is
less than 0.5 metre (20 inches) between the laser head and
reflector, perform steps 6 through 8.
Remove the receiver alignment target and interferometer alignment target and rotate
the turret of the laser head to select the large aperture.
With a fast responding voltmeter (preferably a meter type) attached to the receiver
test point, angularly fine adjust the laser beam (laser head or interferometer, depend-
ing on axis) until a signal is received on the receiver. (The voltmeter will suddenly jump
to some value greater than 0.25 volts.) This is a critical adjustment and may initially
require great care to achieve the desired result.
Peak the voltmeter reading (which will be fluctuating) by fine adjusting the laser
beam in both angular axes. This will align the laser beam to within f15 arcseconds to
the reflector surface. If the reflector surface is aligned to the direction of travel within
f15 arcseconds, the laser beam will be aligned to the direction of travel within k30 arc-
seconds or approximately 0.04 parts per million. That is 0.04 micrometre per metre
of travel (0.04 microinches per inch) of cosine error.
Lock down the laser head and interferometer securely. Make sure the alignment is
not disturbed. Remove the reflector and the opaque material.
10.
Adjust the retroreflector until the return measurement beam is centered on the re-
ceiver alignment target and overlaps the reference beam from the interferometer.
11. Remove the receiver alignment target and interferometer alignment target and rotate
the turret on the laser head to the large aperture. Verify that the LED indicator on the
receiver is illuminated and the voltage at the receiver test point is between 0.6 and
1.5 Vdc.
NOTE
Steps 12 through 21 constitute the Y-axis autoreflection alignment.
12.
Adjust the 50% beam splitter angularly until the reflected laser beam is centered on
the beam bender aperture. Slight lateral adjustments of the 50% beam splitter may
be necessary to ensure there is no beam clipping. Lock down the 50% beam splitter
securely.
13.
Adjust the beam bender until the reflected beam is centered on the aperture of the
single beam interferometer. The single beam interferometer alignment target can be
used as an aid and then removed. Lock down the beam bender securely.
14.
Place the receiver alignment target on the receiver and rotate the turret of the laser
head to select the small aperture.
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Table of Contents
Troubleshooting
