IBM Selectric I/O Manual Of Instruction page 74

C. R. Clutch Spring
C. R. Actuating Arm
FIGURE 141. Carrier Return Clutch Actuating Mechanism
rear of the clutch latch actuating arm contains an elongated
hole. An eccentric adjusting screw connects the arm to the
carrier return clutch latch which pivots at the rear of the
powerframe. As the actuating arm moves down the clutch
latch is also lowered. Spring loaded against the forward edge
of the clutch latch is a hook-like part called the carrier re-
turn latch keeper. When the clutch latch has been pulled
down into its active position, the keeper hooks over the latch
to hold it down (Fig. 140).
The carrier return mechanism remains latched in the active
position unti I the carrier reaches the left margin. At that
time the clutch is unlatched and the escapement pawl is re-
stored to the escapement rack ready for a typing operation.
The margin rack is mounted between the side frames just in
front of the carri er. The margin rack has (] sma II amount of
lateral movement. When the carrier is away from the left
margin, a spring located at the left end of the rack loads the
margin rack to the right. As the carrier moves to the left
during a return operation, the carri er strikes the left margin
stop forcing the margin rack to the left. The extreme right
end of the margin rack contains a roll pin. Movement of the
rack to the left causes the pin to operate the carrier return
unlatching bellcrank that pivots on a stud outside the right
side frame (Fig. 142). A link connects the bellcrank to the
carrier return latch keeper at the rear.
As
the bellcrank
operates, the unlatching link pulls the keeper forward re-
leasing the clutch latch. The latch is restored to the rest
position by its spring and the action of the escapement torque
bar spring. A small spring connected near the carrier return
shoe holds the shoe away from the clutch spring in the rest
position (Fig. 141).
The clutch latch does not hold the cam follower in the active
position during a return operation; therefore the cam and fol-
lower immediately restore to the rest position ready for the
next operation. Depression of the keylever with the carrier
in motion releases the interposer to cause another carrier re-
turn operation. Because the carrier is already in motion, this
reduces to nothing more than another tine spa'ce operation.
If the carrier is already resting at the left margin when a car-
rier return operation begins, the clutch is prevented from
latching. The cam is not prevented from operating, however,
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Carrier Return
Latch Keeper
FIGURE 142. Carrier Return Clutch Unlatching Mechanism
so a carrier return operation must occur. The platen is in-
dexed and the carrier return spring clutch attempts to wind
the carrier return cord onto the drum. The carrier cannot be
pulled farther to the left, because it is already against the
left margin. The pull continues to be exerted on the cord un-
til the cam follower passes the high point of the cam at which
time it restores and allows the shoe to move away from the
clutch spring.
During the time the cord is being pulled without being able
to move the carrier, the carrier return clutch mechanism must
be allowed to slip in order to reduce
+e
strain and prevent
breakage to the parts. The carrier return clutch arbor is in-
directly driven by the operational shaft. The large shoulder
on the arbor fits into a heavy clutch spring at the left called
the torque limiter spring (Figs. 143& 144). The left end of
the spring is clamped to the torque limiter hub and the torque
limiter hub is set screwed to the operational shaft. The car-
rier return clutch arbor is then driven by means of the torque
limiter spring.
Cycle Clutch Pulley
C. R. Clutch
Arbor
Torque limiter Spring
FIGURE 143. Torque Limiter - Cut Away View