IBM Selectric I/O Manual Of Instruction page 14

Latch Sai I
The cycle shaft has five double lobed cams mounted on it
(Fig. 18). Two positive cams, one 5-unit ,:am and two latch
pusher cams. The two positive and one 5-unit cam provide
the motion to position the· typehead. The positive cams are
paired to operate the latch bai I located beneath the cycle
shaft. The 5-unit and latch pusher cams wi
1/
be discussed
later.
t.....::----- Positive Cams
Latch Bail
FIGURE 18. Cycle Shaft and LCltch Bail
The cycle shaft powers the positioning of the typehead by
operating the selector latch bai I. The latch bai I is a box-
shaped frame located just beneath the cyc Ie shaft (Fig. 18).
Two short arms of the frame extend forward where they pivot
on a shaft mounted to the powerframe. Each si de of the latch
bai I contains a roller that is constant Iy in contact with its re-
spective cyc Ie shaft cam. An extension spring at the rear of
the latch bai I applies a constant upward pressure to hold the
rollers against the cams. Each time the cye Ie shaft operates
180
0
,
the bai I is forced down pivoting about the bai I shaft
and is a 1I0wed to return to its upward positi on.
The rear of the latch bai I is recessed at six points. All six of
the recesses contain selector latches. Across the rear of the
latch bai I is a plate attached by two screws. Each selector
latch has a lip formed to the rear just under the bai I plate
(Fig. 19). An extension spring holds each latch to the rear.
Five of the selector latches are components of the differential
POl
Positive Cam
~
o
@
0
Selector latch
01
~l
;;==-*
Latch Bail
\
,
: 0
\1
\
/
;
"--------<-
-~--
Latch Bail Plate
FIGURE 19. Latch Bail
-SidE~View
7
lever assembly that determines how much tilt and rotate the
head wi II receive. The first and third latches to the left are
concerned with ti Iting the head, whi Ie the three on the right
deal with rotating the head. The second latch from the left
is referred to later.
If the latches remain to the rear under the plate, they wi II be
pulled down when the bail is operated. If any latch is held
forward, it is not hooked under the bai I plate and wi II not be
pulled down during an operation of the latch bail. The meth-
od of operating the various latches forward is discussed in
later secti ons •
Tilt Differential
The two tilt latches are attached at each end of a short lever
by ball shouldered rivets (Fig. 20). The ball shape of the
shoulders allows the latches to pivot in all directions. The lever
isattachedbyadouble vertical link to the tilt bellcrank. The
bellcrankpivotsonastudat the top of the differential bracket.
The connection of the double I ink is not in the middle of the
lever; therefore the leverage developed by one tilt latch is
greater than that of the other.
Tilt Tape
Left Side Frame
Tilt Bel/crank
Tilt Pulley
Tilt-2 Latch
Latch
FIGURE 20. Tilt Differential At Rest
A horizontal I ink connects the top of the tilt bellcrank to the
tilt arm. Operation of the bel/crank forces the tilt arm to the
left to exert a pull on the tilt tape. The tilt arm is sometimes
referred to as the' tilt multiplying arm, because the movement
ofthehorizontallinkisincreasedatthepulley due to the lever-
age deve loped.
The left hand tilt pulley is mounted to the ti It arm on a ball
shouldered pivot screw. This allows the pulley to remain hori-
zonta

regardless of the position of the tilt arm. It must remain
horizontal to prevent the tilt tape from coming off the pulley.
The tilt bel/crank is rotated by a pull on the tilt latches. When
the left latch is held to the front whi Ie the right one remains to
the rear, only the right latch is forced down by the latch bail
(Fig. 21). As the latch pulls down on its attached lever, the
left end of the lever pivots against a stop lug formed out from
the differential bracket. The vertiCal I ink from the lever is