Keyboard Section And Character Selection - IBM Selectric I/O Manual Of Instruction

rear of the five-unit bai I. When the latch is operated for-
ward the bai I is a II owed to rise (Fig. 32). The force whi ch
raises the bail comes from the rotate pu Iley spring and the
spring attached to the rotate arm. These springs are applying
a constant force on the rotate bellcrank in the clockwise di-
recti on.
Latch Allows Bail To Rise
FIGURE 32. Five-Unit Bail During Negative Rotate Cycle
The five-unit bail is restored down by the extreme right hand
cam on the cycle shaft. The high point of the cam is 90° from
the high point of the other two cams. This insures that when
the latch bail is driven DOWN in the active position, the five-
unit bai I can be UP in the active position. Conversely, when
the latch bai I is UP in the rest position, the five-unit bai I wi II
be DOWN in the rest position.
It should be noted that the five-unit bail is held down in the
rest position by the cam rather than by the five-unit latch.
In the rest position there is a clearance between the latch and
the adjusting screw in the five-unit bail. The clearance must
be present to insure resetting of the latch at the completion of
a cycle. During a positive rotate or no rotate cycle, the
five-unit bail rises slightly before being restricted by the five-
unit latch (Fig. 31). This upward movement of the five-unit
bail allows a slight clockwise, or negative rotation of the type
head. The type head rotates from the rest position to a position
known as the "latched-home" position. Consider all positive
and negotive rotations to occur from the latched-home position.
Movement of the five-unit bai I from the latched-home point to
the low point of the cam allows sufficient clockwise movement
ofthe rotate bellcrank to permit a five character negative rota-
tion ofthe typehead (Fig. 33). If less than five units of nega-
FIGURE 33. Negative-Five Rotate Operation
12
tive rotation is desired, it is necessary to pull down on the left
end of the balance leveras the right end goes up. This reduces
the amount of clockwise movement of the rotate bell crank •
Operating one or more positive rotate latches down in con junc-
tion with allowing the five-unit bail to rise allows different
amounts of negative rotation. The positive rotate-one and
negative-five combine to allow a negative-four rotation. A
positive-two and negative-five combination gives a negative-
three rotation (Fig. 34). A positive-three and a negative-five
operation permits a negntive-two rotation. A positive-four
plus a negative-five combination gives a negative-one rotation.
FIGURE 34. Negative-Three Rotate Operation
KEYBOARD SECTION AND CHARACTER SELECTION
The keyboard section is a compact unit that contains all the
keylevers and allied parts, and a selection mechanism for the
differential latches. Depression of any printing keylever pre-
pares the selection mechanism for operation and trips the cy-
cle clutch latch to allow a cycle operation.
Keylevers
The keylevers pivot on a fulcrum rod at the rear (Fig. 35).
A rubber covered rod limits the upward travel of the keylevers
and the bottom of the guide comb slots I imit the downward
travel of the keylevers in the front guide comb. A lower ex-
tension on each keylever operates in the keylever bearing sup-
port to stabi I ize the keylever.
The keybuttons are designed in the shape of a pyramid to make
the use of a keyplate unnecessary. The tops of the keybuttons
form a concave slope to the keyboard for ease of operation.
Keylevertension issupplied bya set of flat spring fingers under
the front of the keylevers. The forward end of each spring
finger is cupped so that the spring wi II maintain its position
under the keylever. Different spring tension is supplied to the
four rows of letter keylevers by auxi I iary leaf springs under the
keylever springs. The auxi I iary spring fingers vary in length
to offset the leverage difference among the four rows of key-
levers. This variation in spring tension results in a uniform
operating force requirement for all keylevers.
A shoulder rivet attaches a keylever pawl to each keylever at
the rear. A small spring attached from the pawl to the keyle~er
holds the pawl in the rest position. The pawl extends below
and is formed under the keyleverin position to strike the top
of an interposer (Fig. 35).