IBM Selectric I/O Manual Of Instruction page 69

Stem
Stabil izing Link
Restoring Spring
Y"'~:---
(Repeat Bail) (Optional)
FIGURE 133. Spacebar Lever Mechanism - Late Level
Spacebar Lockout - Early Style
As previously mentioned, both the spacebar escapement and
the print escapement operate by actuating the escapement
trigger lever to cause an escapement operation. Because of
the inter-relationship of these two mechanisms, operating both
of them together causes only one space of escapement. Like-
wise if they are alternately operated too rapidly in succession,
only one space of escapement wi II result ... This happens oc-
casionally when the operator hits the spacebar too soon after
striking a letter keylever. As a result no space appears be-
tween the words. The spacebar fai Is to operate the escape-
ment trip because the escapement trigger does not have suf-
ficient time ,to reset above the lug on the torque bar before
being actuated down again. Operator timing seldom causes
the print escapement to fai I after a spacebar operati on.
In order to insure that the spacebar wi II alwClYs actuate the
escapement following a print operation, it is necessary to
place the spacebar mechanism into storage unti I the print
escapement is completed. The spacebar can then operate to
space the carrier. The spaceba( storage feature greatly re-
duces the possibi lity of spacebar fai lure during a letter-space-
letter operation. Failure results only if the spacebar opera-
tion is not stored. The spacebar will fail to store only if
the spacebar and letter keylever are depressed simultaneously.
Spacebar storage is accomplished by blocking the rearward
movement of the spacebar interposer. The interposer travel
is blocked by the spacebar lockout cam on the filter shaft
(Fig. 134). The lockout cam is spring-loaded toward the
right against the escapement cam. In the rest position, the
lockout cam is held to the left by the lateral camming sur-
faces on the two cams. In this position, the spacebar inter-
poser is free to operate without interference (Fig. 1 34A) •
During a charader operation, rotation of the filter shaft
allows the lockout cam to move toward the right because the
high points of the lateral camming surfaces me no longer in
contact (Fig. 134B). The lockout cam is prevented from ro-
tating with the fi Iter shaft by a guide bracket that fits in a
slot in the front of the cam. As the lockout cam slides to
the right an extensi on at the bottom of the cam moves into
the path of a lug on the spacebar interposer (Fig. 134B).
53
Escapement Cam
Spacebar Lockout Cam
A. FILTER SHAFT AT REST
FIGURE 134A. Spacebar Lockout Mechanism
Interposer
~Lockout
Cam
/ Blocks Path
Of Interposer
With Filter
Shaft Actuated
B. FILTER SHAFT ACTIVE
FIGURE 134B. Spacebar Lockout Mechanism