3
tables were selected primarily because of their straightness charac
teristics and because they minimize "sticktion" or stick-slip motion
which is necessary to permit zero positioning of the tables without
excessive hunting or loss of correlation. Each carriage is floated
on a thin film of low pressure air (about 5 lb.). The base upon
which the carriages are floated consists of a base and rails which
are assembled to form a channel. The y-carriage, which is floated
on the base, also has a channel in which the x-carriage is floated.
Both carriages have precisely machined pads on the bottom and side of
each carriage against which the air acts to provide the cushion for
floating and guiding the tables. The x and y tables are driven by
a steel tape and friction pully.
A Ferranti moire fringe metering system is used to provide the
measuring capability. Ten-inch, 250 lines/mm gratings are used to
give the one micron read-out. The table servo drive system in the
fine mode consists of an anti-backlash worm gear reduction clutch,
and a magnetically detented stepper motor. In the coarse of rapid
slewing mode the tables are translated at a rate of approximately
0.3 in/sec using D-C servo motors. In the fine mode, the motors
are geared so that each step causes a table translation of approxi
mately 0.6 microns and maximum speed of 120 microns/second. Manual
control is provided by a joy stick. The signal provided from this
joy stick controls the drive velocity so that the displacement of
the joy stick in any direction from its center position will control
the table drive speed in that direction. A button on top of the
joy stick can be depressed intermittently to give single step motion.
The marking system consists of a die (two for each table) which
produces the desired mark on the emulsion, a heating element to
maintain the die temperature at approximately 300° F., guidance
bushing to provide linear vertical travel of the die, logic to trans
late the table to its proper position under the die and a vertical
drive to raise and lower the die (See Figure 5). The marking dies
are fabricated to produce concentric circular marks on the emulsion.
Several sizes of dies have been produced for test purposes. Each
produced die has two concentric circles, an outside circle or "flag
ging" mark 2mm in diameter and an inner circle or dot of varying
dimensions (See Figure 6). For instance, the inside circle may be
a dot of 25 or 50 microns or a circle having an inside diameter of
50, 75, 100, 200, 500 microns. When the requirements for the com
plete map compilation system have been finalized one die size will
be selected. Since the marking system bushing is held stationary