IBM Selectric I/O Manual Of Instruction page 54

• FIGURE 105.13 Low Velocity Magnet
When the armature is attracted, it contacts an extension on
the low velocity latch and rotates the latch out of the way
of the adjustable stop on the low velocity cam follower (Fig.
105.14).
I
I
l
"
"
Low Velocity Cam Follower
....
- -,
(}
/ -
Magnet -
Mounting
Bracket
Terminal
• FIGURE 105.14 Low Velocity Magnet Assembly Operation
The rest of the low velocity operation is exactly the same as
previousl y described.
Impression Control Mechanism - (" Stick Shift")
The impression made by the typing element is determined by
the velocity of the typing element upon impact with the paper,
the impression control lever is none other than a type head
velocity control. By increasing or decrecJsing the velocity of
the typing element with the impression control lever, the im-
pression for all characters can be changed equally regardless
of the automatic velocity selection mechanism.
The impression control lever may be positioned by the operator
to one of five different impression settings. The lever is held
in its selected position by detent notches cut into a detent plate
as shown in Fig. 105.15. When chang ing the lever to a new setting
it must be pushed to the right (disengaging it from the detent
notches) before moving itforward or back. Do not ratchet the
impression control lever across the teeth o,n the detent plate as
th is could cause the plate to become loose.
•
41. 4
I
Impression
/' - - " Control
I
/
Lever
-"""I(t---..,..j~~:f:.- ,~,
\
I
.;>"':-" ,,'-,
1\""
I
.~; ,. '<.. --ll 1,\,
I
15' ... \
~',
.J)\
I
I~';," .. \
<1' /
I f A ' . . ; . , • """
I.
~.,'
"
~
, ,\
L,
"r
~
, ..
,)~
I
"'fl , " , - "
1"
Ii"}
I .
_ J
(~~{~~J ~I
"
i ___
J
Rocker Restoring
Spring
\,
\
Print Cam Follower
FIGURE 105.15 Impression Control Mechanism
Changing the position of the impression control lever causes
the pin on the lower portion of the lever to move forward or
back to a new position in the forked slot of the print cam fol-
lower (Fig. 105.15). Just as in the early style print mechanism,
the front to rear position of the pin determines the amount of
powered travel that the typehead receives from the print cam
follower. Th is plus the amount of free fl ight that is in the
system determines the velocity of the typehead upon impact
with the paper.
When the impression control lever is pulled forward to a new
position, the pin on the lower extension moves toward the rear
in the forked slot of the follower thereby increasing the amount
of powered travel that the typing element will receive. The
forked slot in the follower is designed so that most of the change
in powered travel will be felt as a change in the rest position
of the type head and not as a change in the amount of free
fl ight (determined by the I imit of powered travel). Throughout
the entire range of the impression control lever the free
f\
ight
of the type head should change sl ightly (approximately .015).
Th is is necessary in order to maintain the correct timing rela-
tion between type head detenting and type head printing as the
velocity of the type head is increased or decreased by the im-
pression control lever. In other words, by increasing or de-
creasing the amount of free fl ight to compensate for a change
in type head velocity, the print time of the type head requires
constant in the machine cycle regardless of the impact veloc ity
of the typing element.