IBM Selectric I/O Manual Of Instruction page 73

If the clutch spring is to tighten, friction must exist between
the spring and the hub it is to drive. By pressing the loose
end of the carrier return clutch spring against the pinion hub,
friction is applied causing the spring to tighten around the
hub and drive the pini on. The spring is pressed against the
pinion hub by a nylon shoe just to the rear of the carrier re-
turn pinion (Fig. 139). The clutch spring decreases in dia-
meter as it tightens around the pinion hub. The tension of the
spring resists any change in size; therefore, when the pressure
from the shoe is relaxed, the spring snaps back to normal size
and ceases to drive the pinion.
Actuating Arm
- - - Pivot Pin
C. R. Pinion
C. R. Clutch Spring
C. R. Clutch Arbor
Operational Shaft
FIGURE 139. Carrier Return Mechanism
In order to obtain a full carrier return, the carrier return shoe
must press the spring against the pinion hub and hold it there
until the carrier has reached the left margin. It must then re-
lease the clutch spring to end the carrier return operation.
The power to operate the shoe against the clutch spring is
taken from the single lobed operational cam. Depression of
the carrier return keylever sets the mechanism into operation.
The keylever operates at the right side of the keyboard be-
side the backspace keylever. The keylever pivots around the
fulcrum rod at the rear and operates in the keylever guide
comb at the front. The limits of the keylever travel are the
same as for the backspace lever.
When the keylever is depressed, the keylever pawl attached
at the rear of the keylever releases the carrier return inter-
poser to the rear. The interposer causes the cam to be en-
gaged and pushes the carri er return operati ona I latch under
the cam follower into position to be pulled down. When the
56
cam operates, the cam follower pulls down on the latch. It
also pulls down on the index pawl carrier link, attached at
the rear of the follower, causing a line space operation.
The carrier return operational latch is mounted on the carrier
return latch arm that pivots around a shaft on the operational
latch bracket at the rear of the powerframe (Fig. 140). The
shaft is called the pivot pin and also acts as a pivot point for
the escapement trigger lever and the spacebar latch lever.
Attached solidly to the right end of the pivot pin is a bell-
crank ca lied the clutch latch actuating arm (Fig. 140). As
the cam follower moves the operational latch down, an ad-
justing screw at the right side of the carrier return latch arm
rotates the clutch latch actuating arm and pivot pin. This
acti on causes three thi ngs to occur.
Torque Bar
Clutch latch Actuating Arm
C. R. la tch Arm
------.~
C. R. Operational latch
FIGURE 140. Carrier Return latch Operation (11 Inch)
1 • The top of the clutch latch actuating arm forces a lug
of the escapement torque bar to the rear rotating it to remove
the escapement and backspace pawls from their racks (Fig.
140). This prevents the pawls from dragging along their racks
as the carri er is returned.
2. The carrier return clutch spring tightens around the
pinion hub and drives the carrier return operation. An arm
ca lied the carri er return clutch arm, at the left end of the
pivot pin pulls up on a heavy extension spring (Fig. 141).
The lower end of the spring is connected to a bellcrank-like
part called the carrier return actuating arm. The upward pull
on the spring rotates the nylon shoe (at the top of the arm)
against the clutch spring forcing the spring to tighten and
drive the pinion gear. After the shoe is pressing against the
clutch spring, the heavy carrier return actuating spring is ex-
tended slightly to maintain a constant pressure against the
clutch spring.
3. The clutch latch actuating arm is latched in the opera-
ted positi on to maintain pawl release and to continue the
pressure of the shoe against the clutch spring (Fig. 140). The