IBM Selectric I/O Manual Of Instruction page 87

Carrier
Movement
Continues
+
Escapement Paw
Re I eased From
Tab Lever Lug
Carrier Movement
Conti nues Unti I Stopped
By The Escapement Pawl
A.
Tab-Lever
Latch
Remains
Latched
B.
Pawl Enters
Rack Teeth
-----~ -.~.~-~~---
-_mE:
.-~--------:l---
,
I""", __ ..... _ . . . ,'
C.
Tab Lever Unlatched And
Restores Toward The Front
FIGURE 172. Tab-Unlatching Operation
It should be noted that the escapement pawl is allowed to en-
ter the rack before the backspace pawl. The escapement pawl
must be allowed to enter early to insure that it wi II enter the
correct tooth of the escapement rack. If the backspace pawl
were allowed to enter at the same time, the adjustment of the
backspace rack could allow the backspace pawl to enter its
rack stopping the carrier slightly to the left of the desired
point. Delaying the entry of the backspace pawl prevents
this possibility.
68
The trigger moves to the right with the carrier during the un-
latching travel of the carrier. At about the same time the tab
lever is released by the tab latch, the tab lever trigger moves
in front of a notch in the tab lever (Fig. 173). The tab levE'!r
is then allowed to move forward into the rest position. The
tab lever is restored by the acti on of the spri ngs on the tab
lever and the backspace pawl.
Tab Torque Bar Holds
Trigger To The Rear
Trigger Enters No
Of Tab Lever Allowing
Tab Lever To Restore
Forward
FIGURE 173. Tab Lever Trigger Operation
When the tab lever trigger restores, the tab lever is allowed
to reset for the next operation. As the trigger moves out of
the notch in the tab lever, the tab lever is snapped to the
right by its spring into position to be operated by the trigger.
At the same time, the tab lever lug resets to the right in front
of the escapement pawl ready for pawl release on the next
operation. A forward extension of the tab lever rests against
the escapement bracket. A lug at the rear of the tab lever
trigger rests against the tab lever to prevent the trigger from
resting against the tab torque bar. Imprope\r rest position of
the tab lever can cause backspace problems if the backspace
pawl is not allowed to mesh deeply enough into its rack. The
tab lever will also fail to reset to the right in front of the es-
capement pawl, if the tab lever rests too for t·o the rear. The
tab mechanism wou Id then be inoperative, belcause no pawl
release could be obtained.
Tab Interlock
The tab lever is prevented from latching to the \rear during a
carriage return operation. If the tab lever were' allowed to
latch, the tab lever pawl attached to the end of the tab lever
would strike the right side of a set tab stop locking the car-
rier. The tab lever is prevented from latching by restricting
the tab latch from rotating into its latching position. A lug
at the rear of the tab latch extends down behind the escape-
ment torque bar (Fig. 174). Whenever the escapement torque
bar is operated, as during a carrier return, the tab latch is
rotated counterc lockwise away from the tab lever. Thus, the
tab lever cannot latch.