IBM Selectric - Page 55

10. Rotate Arm Motion - The- adjustable plate on the bottom
of the rotate arm{Fig. 122) should be adjusted up or down
so that a half-cycled upper case +5 rotate character de-
tents the same as a hal f-cycled upper case -3 rotate char-
acter. When observing the detenting remove the head
play I ightly in the negative direction.
FI GURE 122. Rotate Arm Movement
The
rotate arm motion is measured only as far as the nega-
tive three position in the negative direction. The nega-
tive four and five positions are not used because these
two positions are affected by the ratio change operation
of the wear compensator.
By comparing the detenting of the -3 and +5 characters,
it can be determined whether or not the rotate arm is
multiplying the motion, received from the rotate link,
enough to rotate the typehead to the selected position.
Once the -3 and +5 characters are detenting the same,
then all of the selections between positive five and nega-
tive three will detent well within the acceptable band
width provided that all of the previous adjustments have
been made correctly. If a slight difference in detent-
ing must exist between the -3 and +5 characters it is per-
missible and sometimes desirable provided that the -3
character detents more negative than the +5 character.
In other words, it is better to have too much rotate arm
motion
than too little. The reason for this is to place a
small amount
of wear potential into the system for the
areas of the differential mechanism where wear cannot
be compensated for (positive latches and latch bai I) •
Thus, as wear occurs in these areas causing the rotate
arm motion to decrease, the detenting variation be-
tween the +5 and -3 characters wi II also reduce.
Figure 123 illustrates the effects on detenting caused by
insufficient rotate arm motion. Notice that the largest
detenting variation occurs between the +5 and -3. This
Is be'cause the +5 and -3 characters operate in opposite
directions and the error that appears when these two
positions
are compared is the combined error of both posi-
tive and negative motion.
Ifthe rotate arm motion was excessive the detenting pat-
tern would remain the same except that each detent would
be on
the opposite side of its detent notch.
NOTE: The adjustment may be left loose during each
check until the correct position is obtained.
11. Eccentric Stud Adjustment (Typehead Homing) - Use the
following procedure to adjust the eccentric stud:
a. Damper spring stop - asa preliminary adjustment,
slide the damper spring stop down as low as it will
go behind the damper spring (Fig. 124).
b. Raise the compensator roller all the way to the top
of the V-shaped wedging slot.
FIGURE 124. Damper, Spring Stop - Preliminary Adjustment
15 +-4 +3 +2 +1 0 -1 -2 -3 -4 -5
1\
1\ I\. " " I). /\ /\ 1\ 1\ /\
I I \ I \ I ). I, \ .( \ I \ / \ / \
'/ I).,. I, \ I L -, I \ < \ / \
I , / \ I I I L_, / r- ..... \ I , \ / \ / \
I >. 1\ / L_~ I \ I \ 'r-'" \ I' / \
I I, I L."",\ I , I \ I \ / , I " ,
L_:""'; V V v \I 'v v \
~
Affected By
Ratio Change
FIGURE 123. Insufficient Rotate Arm Motion
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