re-enter the escapement rack and stop the
movement of the carrier. The tab lever is
mounted in an elongated hole at its pivot
point. An extension spring holds the tab
lever to the right. As the carrier moves
toward the right, the tip of the tab lever
contacts the set tab stop and is prevented
from moving further (Figure 4-93A). The
carrier continues to the right carrying the
pawls and the tab latch with it. Movement is
HCS-220003
Section
IV allowed by the elongated hole at the tablever pivot. As the escapement pawl moves to the right in relation to the tab lever, a notch in the pawl allows it to drop off the lug of the tab lever and restore to the escape-ment rack (Figure 4-938). Further moveescape-ment of the carrier moves the tab latch to the right out of the notch of the tab lever (Figure 4-93C) The tab lever then restores and allows the backspace pawl to re-enter its rack.
It should be noted that the escapement pawl is allowed to enter the rack before the back-space pawl. The escapement pawl must be allowed to enter early to insure that it will enter the correct tooth of the escapement rack. If the backspace pawl were allowed to enter at the same time, the adjustment of the backspace rack could allow the backspace pawl to enter its rack stopping the carrier slightly to the left of the desired point.
Delaying the entry of the backspace pawl prevents this possibility.
The trigger moves to the right with the carrier during the unlatching travel of the carrier.
At about the same time the tab lever is released by the tab latch, the tab lever trigger moves in front of a notch in the tab lever
When the tab lever trigger restores, the tab lever is allowed to reset for the next operation. As the trigger moves out of the notch in the tab lever, the tab lever is snapped to the right by its spring into position to be operated by the trigger. At the same time, the tab lever lug resets to the right in front of the escapement pawl ready for pawl re-lease on the next operation. A forward extension of the tab lever rests against the escapement bracket. A lug at the rear of the tab lever trigger rests against the tab lever to prevent the trigger from resting against the tab torque bar. Improper rest position of the tab lever can cause backspace problems if the backspace pawl is not allowed to mesh deeply enough into its rack. The tab lever will also fail to reset to the right in front of the
es-Tab-Lever Latch
Tab-Lever Lug Escapement Rack
Carrier
Section IV HCS-220003 to the rear. The tab mechanism would then be inoperative, because no pawl release could be obtained.
h. Tab Interlock
The tab interlock prevents the tab lever from being latched to the rear during a carrier re-turn operation. If the tab lever were allowed to latch, the tab lever pawl could strike the right side of a set tab stop during
a
carrier return operation and lock the carrier. To prevent this from happening, the tab lever latch has a lower lug extending behind the escapement torque bar. When the escapement torque bar is pivoted, the tab lever latch will be rotated out of its latching position, thuspreventing the tab lever from being latched out. The escapement torque bar pivots during a carrier return operation, spacebar operation, or print escapement operation. (Figure 4-95)
Tab Lever Trigger
Tab Lever Cannot Latch
Although Operated To The Rear---'
~14. ·
CARRIER RETURN AND INDEX
The carrier return mechanism returns the carrier to the left hand margin and automatically line spaces the paper whenever the carrier return keylever is depressed. Further depression of the carrier return keylever causes additional index operations.The carrier is moved to the left hand margin by winding the carrier return cord onto a drum mounted on the rear of the escapement shaft in front of the mainspring. As the escapement shaft rotates, the carrier return cord drum will wind up the cord and move the carrier to the left.
The carrier return cord passes to the left over a roller guide and around two pulleys on the left hand side of the machine. It is then hooked to the bottom of the carrier. (Figure 4-96)
The power to turn the escapement shaft is taken directly from the operational shaft. The escapement cord drum has a beveled gear molded on its front which meshes with a carrier return pinion gear that turns freely on the operational shaft. A spring clutch is employed to cause the carrier return pinion gear to rotate with the opera-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.
(Figure 4-97)
The left hand end of the carrier return pinion forms the arbor for the carrier return spring clutch.
A
second hub, the carrier return clutch arbor, is just to the left of the carrier return pinion. This hub is in constant rotation with the operational shaft and the carrier return clutch spring is anchored to this hub by a spring clip. The opera-tional shaft turns in the tightening direction of the spring, however, no drive occurs because the pinion hub is smaller than the inside diameter of the spring clutch. When the loose end of the carrier return clutch spring is pressed against the pinion hub, the spring clutch will tighten around the hub and drive the pinion. The tension of the spring clutch resists any change in size and will snap back to its normal size when the external pressure is re-leased.The external pressure required to cause the carrier return spring clutch to drive is applied by a nylon shoe. The power to operate the nylon shoe against the clutch spring is taken from a single
Arm
C.R.
Cord
Nylon Shoe
C.R. Actuating Arm
Operational Shaft
Left Front View
Torque Limiter Hub Sleeve
Torque Limiter Hub
Nylon Insert
Torque Limiter Spring Spring Clip
C.R.
HCS-220003
Escapement Shaft
Escapement Cord Drum
C.R. Pinion
R. Clutch Arbor
Carrier Return Clutch Arm
Figure 4-96.
C. R. Larch .Actuating Arm
Right Front View
Carrier Return/Index Cam
Escapement Cord Drum Carrier Return Pinion
Figure 4-97. Figure 4-98.
Section IV
0
4-39