Alignment - IBM Selectric I/O Manual Of Instruction

The cycle clutch sleeve has two steps on its exterior surface
180
0
apart. As the cyc Ie clutch is drivi ng the cyc Ie shaft,
one of the steps on the clutch sleeve contacts a vertical
latch that is placed in the path of the sleeve (Fig. 78). This
latch, ca lied the cyc Ie clutch latch, stops the rotati on of
the clutch sleeve thereby stopping the right end of the cycle
clutch spring. The left end of the cycle clutch spring rotates
farther after the right end is stopped because of the momentum
built up in the cycle shaft, filter shaft, and print shaft. This
additional rotation given to the left end of the cycle clutch
spring is in the unwinding direction and causes the spring to
expand about the hub on the cycle clutch pulley. This un-
winding breaks the driving connection between the hub and
the spring.
Cycle Clutch Sleeve
Cycle CI utch Latch
FIGURE 78. Cycle Clutch Latch - Side View
Since the shaft tends to travel beyond its rest position due to
momentum, an overthrow stop is required. Two lugs on the
side of the nylon cycle clutch restoring cam project into
notches in the left side of the cycle clutch sleeve and operate
as an overthrow stop (Fig.
79).
When the sleeve is stopped
by its latch, the cycle shaft continues to rotate under momen-
tum (expanding the cycle clutch spring) until the nylon stop
contacts the lugs on the sleeve stopping the overthrow of the
shaft.
Cy. CI. Collar
Cy. CI. Sleeve
FIGURE 79. Cycle Clutch Stop
29
The shock of stopping the overthrow of the cycle shaft tends
to bounce the cycle shaft backwards. To prevent this from
occurring, a check pawl drops into a notch in a check
ratchet located on the left end of the cycle shaft (Fig. 80).
The pawl drops in when the clutch is disengaged.
Cycle Clutch
Check Pawl
FIGURE
80.
Cycle Clutch Check Pawl
Both the overthrow stop and the check pawl assure that the
cycle shaft wi II return exactly to its rest position at the com-
pletion of each cycle operation. (The cycle shaft is in its
rest position when the positive selector cams are on their low
dwells and the working face of a notch on the check ratchet
is against the working face of the check pawl.)
The shock of stopping the overthrow of the cycle shaft, fi Iter
shaft, and print shaft is transmitted from the cycle shaft
through the collar, the overthrow stop, the sleeve, and to
the cycle clutch latch. This is why the cycle clutch latch is
designed to absorb shock (vulcanized rubber mounting).
The same effect is true in the shift mechanism. The shock of
stopping the momentum of the shaft cam is transmitted from
the shift cam through the overthrow stop, the lug on the
ratchet, and to the shift release arm. The release arm is
shaped like a horseshoe so that it can absorb this shock.
The cycle clutch is allowed to engage by pivoting the cycle
clutch latch forward out of the lath of the step on the clutch
sleeve. The clutch spring then quickly decreases in diameter
because of its own spring tension. The rotating clutch pulley
hub tightens the spring and drives the cycle shaft. The en-
tire clutch assembly rotates through 180
0
•
The second step
of the clutch sleeve then contacts the cycle clutch latch
which has been moved back to the rear into its path. This
causes the cycle clutch to be disengaged again as previously
described.
ALIGNMENT
Alignment is the process of positioning the typehead, both
horizontally and vertically, to an exact printing point. This
process cannot be accomplished by simply rotating and ti Iting
the type head because each rotate and ti It positi on is affected
differently by adjustment of tolerances, inertia, momentum,
elasticity of the system, changing spring loads, and many
other factors. All these factors cause the alignment of the
typehead to vary in a haphazard way. Any variati on in
alignment of the typehead directly affects the print quality
of the machine. Alignment variation is undesirable and must
be el iminated.