IBM Selectric I/O Manual Of Instruction page 46

Rotate Eccentric
Arm Spring
FIGURE 95. Negative 5 Position
The wear compensator compensates for drift due to the wear
in the system from the rotate arm down through the linkage
to the negative 5 cam. Although wear occurs throughout this
whole area, the major portion of wear comes from the differ-
entia I system and related linkages. Compensating for wear
in these areas is the major requirement of the wear compen-
sator. Wear in the tape system constitutes only a small por-
tion of the total wear in the system.
Because there is some drift due to the wear in the tape system
I
the typehead is initially set ("homed") to favor the positive
direction, relative to the rotate detent. As wear comes into
the tape system, the typehead will drift slightly in the nega-
tive direction.
After the initial break-in period, the rate of wear levels off
in both the differential system and the tape system. Although
wear sti II occurs, it progresses at a very s low rate.
The wear compensator cannot compensate for wear in the pos-
itive latches, the latch bai I, and the positive cams because
these components are not in use during a compensating oper-
ation (negative 5). Wear at these points constitute a portion
of the band width and must be considered when achieving an
allowable band width.
Figure 96 points out two other springs which have a direct
bearing on the wear compensator operation.
An extension spring called the compensator assist spring is
connected between the rotate arm and the carriage side frame.
The purpose of this spring is to keep the rotate arm in contact
with, and applying pressure against, the nylon roller
through~
out a posi tive operati on. Wi thout the assist spri ng
1
the ro-
tate arm tends t'o overthrow beyond the positive positi on se-
lected because of a momentum built up in the rotate arm,
tape system, rotate pu Iley, type head , etc. Thi s
overthr~w
allows the V-shaped wedging slot to open up resulting in
unwanted roller droppage.
37
Compensator Assist
Spring
FIGURE 96. Wear Compensator
The compensator damper spring (Figure 96) is a leaf spring
designed to absorb the shock of stopping the rotate arm at
the negative 5 position. This prevents unnecessary stress on
the components and eliminates vibrations in the tape system
that wou Id otherwise resu It. It a Iso prevents the rotate arm
from rebounding off the side frame. Rebounding would cause
the V-shaped wedging slot to open, resulting in slight roller
droppage.
Detent Timing
The timing of the print shaft with respect to the cycle shaft
controls the timing of the detents. Detent timing must be set
accurately in order to prevent damage from occurring in the
tape system or the typehead. If the rotate detent is allowed
to engage the typehead too soon, it may enter the wrong de-
tent notch. If this occurred during a negative rotation of the
typehead, the rotate tape would tend to slacken and jump off
its pu lIeys. This cou Id lead to tape breakage' or roller drop-
page in the wear compensator. If the detent is a \lowed to
engage the typehead too soon during a positive rotation, tape
or typehead breakage may result due to the continued pull on
the tape. Also, retarding the detent timing may lead to
breakage or roller droppage because the detent would remain
in the typehead notch when the head is trying to restore.
Detent timing can also affect print alignment. It is possible
for the detents to begin to withdraw before the type head
prints. For this reasonthe detent timing shou Id be adjusted
as late as possible without restri cting the type head from re-
storing.