Chapter 4 Angular Measurements
Angular Position Measurements
4-42 Measurements Reference Guide
Choosing the moveable optic
Use the Agilent 10771A Angular reflector as the moveable optic whenever
possible. This setup can easily accommodate the 2 mm lift required for
clearance between the top and base of the precision index table.
A setup with the Angular reflector as the moveable optic can handle lifts
greater than 2 mm. However, since moving (translating) the reflector
translates the return beam at the Laser Head by twice the amount of the
lift, you may not be able to maintain adequate return beam strength
throughout your measurement.
If the lift required by your measurement causes so much return beam loss
that you lose the measurement signal, you can try using the
Agilent 10770A Angular interferometer as the moveable optic, with the
Laser Head set for STRAIGHTness, and the beam pointed directly into
the reflector’s “corner” so the return beam is along the same path. (See
Figure 4-30A/B.) Be aware, however, that the interferometer’s
specification for this use is not as good as that of the reflector, and you will
have to perform an additional calibration procedure.
When the Angular interferometer is the moveable optic, the return beam
is not translated when the optic is moved. The primary limit to lift
distance in this situation is the difference in diameter between the laser
beam (6 mm) and the diameter of the interferometer’s clear aperture
(about 20.83 mm). Environmental conditions and alignment can also
affect maximum lift with this configuration.
Mounting the moveable optic
Figure 4-23 shows two different arrangements that can be used for
mounting the moveable optic in the angular position measurements
fixture. Screws for both mounting arrangements are included in the
Agilent 55290A or 55290B kit.
The top-screw mounting arrangement is recommended for use with newer
versions of the retroreflector, whose housings have the required hole
configuration.
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