LRS Micro-g LaCoste FG5, Manual, Page: 30 / 149

Design: Components and Function
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2.5.6.2.ROTATION MONITOR
The rotation monitor (Figure 2-12) is used to monitor and record the rotation of
the test mass during each drop. The rotation monitor consists of a rigid anodized
aluminum housing mounted on the top flange of the dropping chamber, above
the viewing port. The rotation monitor employs a very sensitive optical lever
system to measure and record the rotation of the test mass which can be used as
a means to reject bad drops or determine when the mechanical system is not
functioning properly. A diode laser produces a visible beam which is directed
onto and reflects from a mirror attached to the top of the dropped object. The
reflected beam is sent through a lens and is focused onto a two axis position
sensitive photodetector. This system rejects translation and is only sensitive to
rotation. The diode laser beam reflects off mirror #1 and the beamsplitter (mirror
mount #2). The beam then passes down through the dropping chamber viewing
port, where it reflects off a flat mirror which is mounted to the top of the test
mass. The return beam from the test mass mirror passes through the
beamsplitter and reflects off mirror #3. The beam then passes through the 200
mm focusing lens, which is adjusted to eliminate cross coupling of translations
which would otherwise appear as rotations. The beam is then reflected off
mirror #4 and enters the detector box. The output from the quad detector is used
to provide rotation information to the computer/system controller. Each
rotation monitor is calibrated by Micro-g Solutions to determine the rotation and
translation sensitivity. These data are used to calculate rotation errors. The
rotation data can also be displayed on the computer screen, and is recorded in
the DDT output data file.
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