18th annual conference on manual control.pdf - Acgsc.org

three microswitches. To latch safely requires that all three microswitches
are on. This in turn requires a simultaneous contact at points A, B and C.
After simultaneous contact the payload is latched by a motor which pulls it
aft along the horizontal notch in the guides and locks it in place. It is
noted that the location (A, B and C) of the three microswitches is invisible
to the operator once the payload guide pins are inside the V-shaped guides.
The initial placement of the payload during the test runs contained some
small translational and/or rotational misalignments relative to the V-shaped
guides and relative to the contact plane of the latch assembly as shown in
picture (a) of Figure 7. Consequently: during a "down" motion of the MDFarm,
someof the payload guide pins contacted the inside edgeof the V-shaped guides
generating undesired contact forces and torques between the payload and the
latch assembly. This can lead to (a) an uneven contact between the payload and
the bottom plane of the latch assembly preventing the simultaneous closing of
all three (A, B and C) microswitches in the contact plane, (b) overloading the
latch assembly: or (c) jamming the payload guide pins into the V-shaped guides.
Ideally, only a small "down" force should be acting between the payload and
the latch assembly at the terminal contact, and all lateral forces and all
torques should be zero or near zero. Pictures (a), (b) and (c) of Fig. 7
show a full berthing sequence.
INFORMATIONANDCONTROLCONDITIONS
The operator had three basic sources of information for guiding and controlling
the RMSduring the tests: (a) direct visual access to the scene through
the cockpit windows, (b) two closed circuit TV monitors showing the scene selectable
from several TV cameras located on the wrist and elbow of the RMSand
around the cargo bay area of the Shuttle mock-up, and (c) a graphics display
of the force-torque sensor information.
The basic RMScontrol was manual using two three-dimensional hand controllers
for RMScontrol in resolved rate control mode: one hand controller (operated
by the left hand, see Fig. 8) controls the three translational components
of RMSend effector motion, the second hand controller (operated by the right
hand, see Fig. 8) controls the three rotational components of RMSend effector
motion. The on-off switch, which controls the opening and closing of the RMS
end effector: was replaced with a linear potentiometer arrangement providing
proportional rate control capability for opening and closing the claws.
The direct visual and TV information sources and the basic RMScontrol are
Shuttle baseline arrangements. The graphics display and the proportional claw
control were specifically developed for the force-torque control experiments.
Graphic
Display
The forces and torques measured by the sensor at the base of the claws
were displayed to the operator on a 9-inch B/W monitor in graphics format.
This monitor was mounted to the right of the TV monitors as shown in Fig. 8.
The graphics display generator used in the present experimental system has a
resolution of 512 by 512 pixels and is capable of displaying up to eight colors.
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