IBM Selectric I/O Manual Of Instruction page 43

Positive...---:-
o
1 ... Negative
- -2
-3
"'4-
-...s
Rotate Tape
FIGURE 91 A. Zero Rotate Position
Side Frame
Nylon Roll
Rotate Arm
Compensgting Arm
FIGURE 918. Negative 5 Position
Figure 91-C shows the wear compensator in the zero rotate
position with wear introduced into the rotate differential
system.
Note that the wear compensator has dri fted away from the
zero rotate position in a negative direction. The wear that
34
--.; i . . . . . . . . . . ---
Drift
0
1
-1
1
Tape
-~I""'-Drift
(Wear)
FIGURE 91C. Zero Rotate Position With Drift
was introduced into the rotate system was felt as play in the
system. The rotate tape tensi on and the compensating arm
spring removed the play in a negative direction which al-
lowed the wear compensator to "drift" in a negative direction.
This places the rotate arm less than five units away from the
side frame when the rotate differential system is in the zero
position. The rotate differential system is not aware of this
and wants to supply five units of motion to the compensating
arm when a negative 5 character is selected. The rotate arm
cannot travel a full five units because this wou Id carry it be-
yond the sideframe. The sideframe limits the motion of the
rotate arm at exactly the rotate negative five position. Since
there is nothing to stop the motion of the compensating arm,
it continues to travel the full five units of motion supplied to
it by the rotate differential system. The V-shaped wedging
slot opens up and the nylon roller drops lower in the slot
{Fig. 91-D}. When the wear compensator returns to the zero
rotate position, the drift has been elimindted and wear has
been compensated for.
Basically, this is how the wear compensator works. In order
for the wear compensator to operate efficiently, we must
overcome the effects of a changing spring load on the rotate
differential system as the eccentric stud on the rotate arm
contacts the sideframe.
In the zero rotate position, there are many parts in the rotate
differential system that are resisting the combined spring
tension of the rotate pulley spring and the compensating arm