HP 5501A Operating And Service Manual page 84

NOTE
In Step 10, make sure the alignment is not disturbed.
10. Lock the laser head and X-axis optics down securely. Remove the receiver alignment
target. 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 1 1 through 20 constitute the Y-axis visual alignment procedure.
Place the alignment target on the Y-axis single beam interferometer and on the Y-axis
receiver. Place a piece of opaque material between the single beam interferometer
and the retroreflector.
Adjust the 50% beam splitter angularly until the reflected laser beam is centered in
the beam bender entrance 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.
Adjust the beam bender until the reflected beam is centered on the alignment target
installed on the single beam interferometer. Lock the beam bender securely in place.
With the single beam interferometer and retroref lector at the closest point, adjust
the single beam interferometer until the reference beam is centered on the receiver align-
ment target. Remove the opaque material.
Adjust the Y-axis retroreflector until the measurement beam is centered on the re-
ceiver alignment target.
16. Traverse the retroreflector to its furthest point of travel.
Angularly adjust the single beam interferometer to center the return beam from the
retroreflector on the receiver alignment target. When adjusting the single beam inter-
ferometer angularly, it may also be necessary to make slight lateral adjustments to
ensure that the reference beam from the single beam interferometer is also centered
on the receiver alignment target.
Return the retroreflector to the closest point to the single beam interferometer.
Repeat steps 15 through 18 until the return beam from the retroreflector is centered
on the receiver alignment target. Lock down the single beam interferometer securely
making sure the alignment is not disturbed.
Remove the single beam alignment target and the receiver alignment target. 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.
2.45 Autoreflection Alignment Procedure
The autoreflection alignment technique is used in short travel applications of less than 0.5
metre (20 inches). It is based on the principle of aligning a mirrored surface normal to the
direction of travel and aligning the laser beam perpendicular to this mirrored surface (i.e.,
parallel to the direction of travel) to minimize cosine error. This technique is also used when it
is necessary to make cosine error a s small as possible regardless of travel distance.
Figure 2-54 shows a measurement setup similar to Figure 2-53 except that the autoreflection
technique is used for alignment.