Carrier Return (Early Style) - IBM Selectric I/O Manual Of Instruction

Escapement Pawl Moves
To Next Rack Tooth
A . . BACKSPACE ACTUATING STROKE
Pin Holds Backspace
Pawl To The Left
Backspace Pawl Moves
To Next Rack Tooth
Escapement Pawl
Holds Carrier Position
Backspace Rack
Restores To
The Right
B . . BACKSPACE RESTORING STROKE
FIGURE 137. Backspace Operation
The backspace rack is actuated by a bellcrank pivoted on the
front of the back plate (Fig. 136). The bellcrank operates
the rack through an adjustable intermediate lever pivoted at
the top of the operational latch bracket. The backspace op-
erational latch is mounted to the horizontal arm of the
back~
space bellcrank by a ball shouldered rivet to permit free rota-
tion of the latch. The latch extends down into position to
hook under the bai I of the operati ona I cam follower. When
the backspace interposer is released, the latch is pushed to
the rear under the cam follower. Operati on of the cam causes
the cam follower to pull the latch down rotating the backspace
bellcrank. A large headed adjusting screw on the vertical alim
of the bellcrank operates the intermediate backspace lever to
force the backspace rack to the left.
The intermediate backspace lever is adjustable forward or
back to obtain the proper throw of the backspace rack. The
intermediate lever is' adjusted farther forward on the 12 pitch
machines than on the 10 pitch. The 12 pitch intermediate
lever is shorter than the 10 pitch to prevent interference with
the power frame. It is too short to be used on 10 pitch ma-
chines. The 12 pitch intermediate lever is identified by a
notch in the right side. The 10 pitch lever is unmarked.
The backspace interposer is released by depression of the
backspace keybutton located at the upper right hand corner
of the keyboard (Fig. 138). The backspace keylever is
mounted in the keyboard assembly in the same manner as the
letter keylevers. An extensi on spring between the keylever
and the keylever guard restores the keylever to the rest posi-
tion. A keylever pawl attached to the rear of the keylever
55
Backspace Interposer
FIGURE 138. Backspace Keylever Mechanism
extends down through a slotted guide stud in position just
above the backspace interposer. Depression of the keylever
causes the interposer to be released to the rear to begin the
operation.
The upward travel of the keylever is limited by a fu Icrum rod
located at the top of the gui de comb. The final travel of the
keylever is reached when the keylever bottoms in the guide
comb.
CARRIER RETURN
11 Inch Printer
The carrier return mechanism provides the operator with a
powered return of the carrier to the left margin and an auto-
matic line spacing of the paper.
The carrier return operates by winding the carrier return cord
onto a drum at the rear of the machine (Fig. 139). The car-
rier return cord is hooked to the bottom of the carrier, passes
around two pu Ileys at the left, extends back to the right over
a gu ide roll er, and attaches to the carri er return cord drum.
The drum has spiral grooves for winding up the cord as on the
escapement cord drum. The carrier return cord drum is at-
tached by set screws to the escapement shaft just in front of
the mainspring. Rotation of the escapement shaft causes the
drum to wind up the cord and move the carrier to the left.
Movement to the left opposes the mainspring tension causing
the mainspring to tighten. The power to rotate the escape-
ment shaft in opposition to the mainspring is taken directly
from the operati ona I cam shaft. The escapement cord drum
(at the front of the escapement shaft) has a beveled gear
molded on its front (Fig. 139). This beveled gear meshes with
a small pinion gear on the operational shaft. The piniongear
pivots freely on the shaft between two C-clips. By means of
a spring clutch the pinion is made to rotate with the opet a -
tional shaft. The pinion gear drives the escapement cord drum
in a clockwise direction causing the carrier return cord to be
wound onto its drum. The carrier return pinion has a hub that
forms a part of the spring clutch. A second hub just to the left
of the pinion is in continuous rotation with the operational
shaft. A clutch spring fits around the two hubs to complete
the spring clutch. A steel band clamps the left end of the
spring around its hub so that no slippage can occur at that
point. The clamp causes the spring to rotate with the opera-
tional shaft. The shaft turns in the tightening direction of
the spring; but no tightening occurs, because the pinion hub
is smaller than the inside diameter of the clutch spring.