IBM Selectric I/O Manual Of Instruction page 101

Since feed is not a smooth operation but occurs in a series of
jerks, the ribbon spool that is acting as a supply spool would
tend to over-spin or IIspool offll between feed operations un-
.. less a drag or braking action were placed upon it. This neces-
'sary drag is provided by placing a leaf-type spring against the
ratchet teeth of the ribbon feed ratchet (Figl. 204). This leaf
is an extension 'of the retainer/brake spring which also func-
tions as a clamping device for the ribbon cartridge. Both
retainer/brake springs are held in place on top of the ribbon
feed plate by the same screws that mount the feed plate to
•
the carrier (Fig. 204).
Ribbon Reverse
The ribbon is fed from the supply spool onto the take-up spool
until the supply spool becomes empty (Fig. 205). At this
time, the process must be reversed; that is, the lIemptyll sup-
ply spool becomes the take-up spool and the IIfull ll take-up
spool becomes the supply spool. To achieve this reversing
process, it is merely necessary to shift the ribbon feed pawl
to the ribbon feed ratchet that contains I-he empty spool.
Since the feed pawl is riveted to the feed clnd reverse plate,
the reversing operation is a.ccompl ished by shifting the front
of the feed and reverse plate to either the left or right de-
pending on which spool is'empty (Fig. 206).
Supply Spool
RL
:>n
Feed
Pawl
Take-Up Spool
FIGURE 205 Right Hand Ratchet Driver
Ribbon Feed
&
Supply Spool
Ribbon Feed
Pawl
• FIGURE 206 Ribbon Feed Pawl Transferred To
L.
H. Ratchet
A small bellcrank mounted in the core of each ribbon feed
ratchet acts as a sensing device to determine when the revers-
ing operation is to take place. As long as there is ribbon
wrapped around the core of the supply spool, the ribbon will
hold this bellcrank called the reverse trigger in its inactive
position. Once the last loop of ribbon is pulled off the sup-
ply spool core, a spring finger causes the reverse trigger to
pivot out of the core. This action causes the lower portion
of the trigger to protrude below the bottom surface of the rib-
bon feed ratchet (Fig. 207). The reverse trigger actua Ily
drops down and rides on the top surface of the ribbon feed
plate.
Feed Plate
• FIGURE 207 Reverse Trigger (Activated)
•
81
As the ribbon continues to feed, the almost empty spool ro-
tates slightly further. This causes the lower extension of the
reverse trigger to swing into the path of a notch in the feed
and reverse plate as the plate is operating back and forth
during the feed operation. On the forward or restoring
stroke of the plate, the reverse trigger restricts one side of
the plate from sliding forward (Fig. 208). The other side
continues to slide forward, thereby causing a pivoting action
to the entire plate about the point of restriction. This makes
the front of the plate swing towards the opposite side, posi-
tioning the feed pawl in line with the ratchet tr;eth of the
ribbon feed ratchet containing the empty ribbon spool.
Point of
Feed & Reverse Plate at
Beginning of Restoring Stroke
FIGURE 208 Reverse Action