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Release
of
the reverse clutch
assembly
will cause the capstan to be rotated
clockwise
and move
the
tape in
the
reverse direction.
2 .2 Tape Read Head
As the
capstan
moves the tape
through
the read head,
the tape
is fed and taken up so as
to
provide approximately 120 degrees
wrap
on the capstan
(see
Figure 7). This retards elonga-
tion of sprocket
holes in tapes that must be read hundreds
of
times. The strippers on either side
of
the
capstan
prevent the
tape
from wrapping around the
capstan.
Perforations (holes)
in
the
tape
are
sensed
by the
five
point
star
wheels. Spring pressµre
applied to the
star wheel lever
by
each pair of
movable
contacts,
Figure 7a, holds the
s~ar
wheel
lightly
against
the
tape.
MOVABLE
WIRE
CONTACT
2
(COMM
ON)
------:;;:.
/
N /C
CO
r
I
u~~"~--·
~=--~)_
,
~
\
1'-- ' . . .
--
'·
-
·~~
((
r
- - -
-
ST
AR
WHEEL
/
.
I
; - - - - i
II
u
'
LEVER
ARM
f.,
I
TAPE
~-<r----
-r-
-
--
t-rr
!
CAPSTAN
/
/~-
/
(A) NO
-HOL
E
(
8
)
HOLE
Figure 7
.
Starwheels
Reading Perforated Tape
As
shown in
Figure
7a,
when
a
no-hole
condition is sensed, -the star
wheel rides
the
tape
on two of
its
points
, and the movable contact is i;witched
to
the
upper,
normally closed
(N/
C)
position. When
a hole
is
sensed
(with
the
tape
moving
in
either
direction),
one of
the star wheel
points drops through the hole as shown in Figure 7b, and the movable
contact
is switched down-
ward to the normally
open
(N/
O) position
. T
herefore, an
electric
pulse delivered to the
movable
contact wire (common)
will
be
conducted
to
the
N/
C terminal
if
a
no-hole
is
sensed
or
to
the
N/
O terminal
if
a hole is sensed
.
By definition, the normally
closed
contact
(N/
C) is
that contact
which ts closed when
the
star
wheel reads
a
no-hole condition
on the tape. Similarly, the normally open
(N/
O)
contact
is
closed
when
the star
wheel reads a hole
in
the tape.
3.0
ELECTRICAL OPERATION
3
.1
Escapement
Operation
To advance
the
tape (capstan
rotation counter-clockwise), a
drive pulse is applied to the
forward
escapement assembly.
The
energized electromagnet
disengages
the armature
from the
escapement whee
l
allowing the clutch assembly to rotate
.
Similarly,
the
tape
may
be
moved
in
a
S
CATTL[
Page
5
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