IBM Selectric I/O Manual Of Instruction page 100

FABRIC RIBBON MECHANISM (LATE STYLE)
The design and operation of the new style fabric ribbon mech-
anism is basically the same as the earlier level mechanism ex-
cept for the areas of feed and reverse. Therefore, only these
areas wi II be covered in this section.
Ribbon Feed
The motion for a feed operation is provided by a cam on the
print sleeve called the ribbon feed and detent cam. As the
cam rotates during a print cycle, it causes a cam follower
called the ribbon feed lever to pivot in the counterclockwise
direction about its mounting stud (Fig. 202). The ribbon feed Feed Plate
lever is C-clipped to its mounting stud which is located on a
heavy vertica I support riveted to the underside of the ribbon
feed plate. An extension spring fastened to the feed lever
and anchored to the support loads the lever in a clockwise
direction, causing the lower lug to ride against the cam
throughout a feed operation (Fig. 202). The reason for the
upper lug wi
II
be explained in the reverse operation.
Lower Lug
FIGURE 202 Ribbon Feed Lever (Beginning
of Feed Operation)
As the ribbon feed lever is rotated in the counterclockwise
direction by the cam, its upper extension, which projects
through a window in the feed and reversing plate, sl ides the
plate toward the rear (Fig. 202). The feed and reverse plate
is mounted on the top side of the ribbon feed plate in a man-
ner that permits it to slide back and forth with each revolu-
tion of the cam. A shouldered rivet anchored to the feed
plate passes through an elongated slot in the feed and reverse
plate (Fig. 203). Th is rivet acts as a guide for the rear of
the plate as it operates back and forth. The front of the plate
is secured and guided by a recessed pin that is riveted to a
part of the reversing mechanism called the IIratchet detent
leverll (Fig. 203).
80
FIGURE 203 Ribbon Feed
&
Reverse Plate Mounting
The back and forth movement of the feed and reverse plate is
transmitted to the ratchet teeth of a ribbon feed ratchet by a
feed pawl. This pawl is attached to the feed and reverse
plate by a shouldered rivet. An extension spring anchored
to the vertical lug of the ribbon feed lever loads the feed
pawl into engagement with the ratchet teeth (Fig. 204). Each
time the feed cam makes one revolution, the feed pawl wi II
drive the ribbon feed ratchet approximately 2-1/2 teeth. The
timing of the cam causes the ribbon feed action to occur early
in the print cycle. At the time the typehead prints, the rib-
bon has completed its feeding operation except for the restor-
ing of the feed pawl. As the feed pawl restores to the front,
it slides along the teeth into its rest position. The drag of
the pawl over the ratchet teeth tends to rotate the ribbon feed
ratchet backwards, thus, unwinding the ribbon. To prevent
this from occurring a lug on the ratchet detent lever is spring-
loaded into the ratchet teeth (Fig. 204). This lug acts as a
check pawl.
Feed Pawl
Lug Engages
Ratchet Teeth
FIGURE 204
Ribbon Feed Plate Mounting
Screws
Lug Acts As
A Check Pawl
Feed Pawl
&
Ratchet Checking