Tabulator - IBM Selectric I/O Manual Of Instruction

The left side of the platen ratchet contains two heavy lugs
that form a channel (Fig.
158).
The platen variable driver
operates left to right in the slot and a Iways turns with the
ratchet~.
A compression spring between the ratchet and the
driver loads the driver to the left so that serrations on the
outer surface of the driver mesh with matching serrations in-
side the platen end plug (Fig.
158).
The meshing of the ser-
rat ions causes the platen, the drive r, and the ratchet to be
locked together and turn as a unit.
When the. driver is disengaged from the platen end plug, the
platen can be turned' to the desired position. The driver can
then engage different serrations and lock the platen in the
new position. The left hand platen knob is mounted to a
shaft that slides left or right inside the platen. A light com-
pression spring holds the shaft toward the right to prevent free
play. The shaft has two pins attached to the right end that
operate throug h ho les in the platen end plug (Fig. 158). The
pins on the push rod extend through the end plug to the
right and rest against the platen variable driver. Movement
of the platen knob toward the right is transferred to the driver
to disengage it from the platen end plug.
PUShRod~
Ratchet
~~
--"
FIGURE 158. Platen Variable Mechanism
Platen Variable - Pin Feed
The variable is used for typing above or be low the writing
line, for locating the writing line after reinserting the paper,
and for typing on lines of other than six-lines-per-inch spac-
ing.
The platen ratchet must remain stationary when selecting a
new writing line so that the detent roller wi II be seated be-
63
tween two teeth of the ratchet at the new position. A clutch
mechanism connects the ratchet to the platen so that it can
be engaged for line spacing and disengaged for the variable
operation. The clutch can be disengaged by pushing the
right-hand platen knob toward the left. As long as the knob
is he Id to the left, the platen can be rotated free Iy while
the ratchet remains stationary. When the knob is released,
the clutch is automatically re-engaged by spring tension.
A compression spring keeps the right-hand platen knob to-
wardthe right (Fig.
159).
The platen-variable drive is at-
tached to the same shaft as the platen knob. When the var-
iable drive is to the right, the serrations on the outer surface
of the driver mesh with matching serrations inside the platen
ratchet. The variable driver is a Iso engaged in two slots in
the platen guide. The platen guide is attached to the platen.
Moving the variable driver then causes the platen to move.
When the variable driver is engaged with the ratchet, the
ratchet drivesit and causes normal spacing. When the right-
hand platen knob is pushed toward the left, the variable
driver is disengaged from the ratchet and the platen can be
turned by turning the platen knob.
~
~
.',
Pinwheel
.E
fr, '
Guide
~
I
Platen Variable Driver ...
;~.
_ .. "
Ratchet
~~
VI
FIGURE
159.
Pin-Feed Piaten Assembly
TABULATOR
Tabu lator Operation
The tabu lator mechanism faci litates positi oning the carrier
quickly to a predetermined point on the writing line.
For a tabulator operation to take place, several basic things
must occur. The stopping point must be predetermined. The
escapement and backspace pawls must b.e released for carr!er
movement. The pawls must be latched In the released
POSI"-
tion to continue the movement. The speed of the carrier must
be controlled, and the pawls must restore to their racks at the
proper time.
The power for a tab operation is furnished by the same cam
thot operates the back~pace and the spacebar mechanisms.