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Any
of the several modes
of
controlling tape
movement and reading
may be adopted.
For
example, tape movement and reading can
be
controlled by separate
pulses,
or
different bit
levels can be
read
by separate
pulses
.
Normally, the
same
pulse that advances the tape also
interrogates
the r
ead
contacts.
If
individual pulse sources are
used for tape movement and read..:
ing,
all pulses
must
be simultaneous within
±
0.5
millisecond. At maximum reading rate
of
60
·
characters
per second, the drive pulses are 16.7
milliseconds apart (leading
edge
to leading edge).
1.4 Outputs
The functional
output of the system consists of
three
leads
to each
of
the eight form C
switches.
A read
pulse at the
movable wire
contact of
the
switch
will be delivered to the lower
fixed contact
when
a
tape
hole is sensed,
and to
the
upper fixed
contact
when no holes are present.
Sensing
of
a
particular
character code,
such as a stop
code, can
be used by
external
equipment to
;
interrupt the
drive
pulses
and stop
the
reader. Whenever drive pulses are
stopped,
the reader
1
will
come
to rest in
position
to read the next
character.
1.5 Tape Handling
The Model
424
Tape Reader is available with two types
of tape
handling
equipment:
fanfold,
and
reeling.
The 424 CF
and
424 PF Models (Figure
3)
are
fitted
with fanfold tape trays
mounted on either side of the
read head. The tape is fed by
the capstan
from
one tray into
the
other,
neatly folding
itself
in either direction without additional handling equipment.
The 424 PR Model
(Figures 4
and
5) is supplied
with bi-directional
tape
reeling equip-
ment mounted on either side of
the read
head.
The
tape
reels
are
rotated by a differential gear
and brake mechanism actuated by tape tension arms. Both mechanisms are driven by belts from
the capstan
drive
assembly. Since
the units
are
bi-directional, either reel
can be the
take-up
or
supply side
depending
upon
direction
of tape movement.
No
tape threading change
is required
when
reversing
the direction of
tape movement. All
slack on
the
supply
reel is taken up through
the action
of
the
tension arms.
The 424 PR Model
can
be
supplied
with either 6"
or
10" reels. The reels (Figures 2
and
4)
have
a
demountable front flange and
only
a light pressure need be applied
to
the flange to
release
the
ball
detent lock;
thus tape
may
be
easily removed
or
placed
on
the reel.
1.6 Environmental
Conditions
The
unit is designed for
continuous operation in
a temperature
range
between
40 and 120
degrees
Fahrenheit.
2.0
MECHANICAL OPERATION
2.1 Motor
and Capstan
Drive
(See
Figure 6)
Drive power
is transmitted
from the motor
by
a lug belt and pulleys (
1)
to
the
input
shaft
with bevel
gear (6) through
the two idler bevel
gears (4
and 15)
and
to the
two clutch
assem-
blies
(7).
When
the tape is not
being
moved, an
armature
(19)
on
each
of
two
escapement
assem-
blies
(5
and
18)
engages a tooth of
the escapement wh.eel
on the
corresponding
clutch
assembly,
causing
the clutches to slip.
When the tape is to be advanced (capstan rotation
counter-clockwise),
an
electric
pulse
energizes
the
electromagnet on
the forward
escapement
assembly
(18)
disen-
gaging
the
armature from
the escapement wheel and permitting the
forward clutch
assembly to
rotate. Rotation
of
the clutch
assembly transfers
torque
from the
clutch
through the differential
(8
and
9)
to the capstan shaft
(13).
When the
escapement coil
is de-energized, allowing the
armature to
drop
and
enga.
g e
the next tooth
of
the
escapement
wheel, the capstan
(17)
is stopped
in position to
read
the next character.
SEATTLE
Page
3
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