The trigger components.
The purpose of the "Controlled Key" mechanism is to ensure the accuracy of Comptometer calculations by preventing two of the most common operator errors - failing to fully depress a key, and commencing a repeated keystroke before the key has fully risen.
The "incomplete upstroke" problem is solved with a "pinion ratchet reverse lock", which is engaged during the upstroke to prevent reversal of the segment lever.
The "incomplete downstroke" problem is solved with an elaborate "trigger" mechanism. The trigger is "armed" at the commencement of every keystroke, and disarmed at the very bottom of the downstroke. If the key reverses while the trigger is armed, the mechanism trips a "touch-off bar" which drops a set of locks onto the segment levers in every column. The entire keyboard immediately locks, except for the column causing the error. The operator is immediately aware of the problem, completes the offending keystroke, releases the lock, and the calculation continues without error.
The trigger components.
This view shows the components of the trigger mechanism in each column.
The trigger itself is the black multi-armed lever, just over 3" long, at the top right-hand side. A pivot near its centre connects to a vertical mounting link and a long horizontal connecting link.
The four parts below the trigger assembly are (left to right): the trigger retainer horizontal, the trigger retainer vertical, the pinion ratchet reverse lock, and the accumulator locking hook.
The trigger connecting link.
The tail of the trigger connecting link attaches to the segment lever bell crank via a pin-and-slot and a short horizontal spring. The short downward arm on the brake lever acts as a retainer to prevent the link falling off the bell crank pin.
This view also shows the two nested key stop levers pivoted above the segment and lock levers at the rear of the machine, and passing between the two vertical arms of the bell crank.
The trigger retainers.
The two trigger retainers (perhaps better called "latches") are mounted on the same 1/16" shaft near the top centre of the frame.
The lower (right-hand) arm of the trigger retainer horizontal passes behind the frame plate and rests on a vertical projection on the top of the segment lever. It is pulled downwards by a light spring (not shown). The two small downward projections on the frame plate prevent the arm from rubbing on the plate, and limit its vertical movement.
The trigger retainer vertical is also spring-loaded so that its forward arm rests on the central stop rod. The spring (shown disconnected) is normally attached to a pin on the inside of the next frame plate.
The trigger installed.
The trigger is suspended from a wide U-shaped link which occupies the full width of the column. The trigger is spring-loaded anti-clockwise and rearwards by the two coil springs attached to its forward arm.
The rearward arm of the trigger has a horizontal cross-arm (just forward of the stop rod), which extends across to the right-hand side of the column and rests on the top of the segment lever.
With the segment lever and cross-arm correctly adjusted, the upwards vertical arm of the trigger, just behind the supporting link, should sit just under (but not touching) the tip of the upper arm of the trigger retainer horizontal.
The downward vertical arm at the rear of the trigger also has a short cross-ways section, which sits just below (but not touching) the point near the bottom of the trigger retainer vertical.
The accumulator interlocks.
The pinion ratchet reverse lock is nested inside the accumulator locking hook on the same 1/16" shaft, immediately below the eccentric frame spacers at the front of the machine. A second larger shaft (actually the pivot for the subtraction cutoff levers) passes through a cut-out in the vertical arm of the reverse lock and serves to limit its rearward travel. The two levers are positioned laterally by a tag on the top of the locking hook which fits into a slot in the under side of the frame spacer.
The yoke on the rear of the accumulator locking hook fits around the pin on the front of the trigger.
The two interlock levers are interconnected by a spring-and-stop arrangement near their hubs, such that one or the other is always engaged with the accumulator.
With the trigger in its rest position, the front of the accumulator locking hook is raised clear of the lantern wheel, and the pinion ratchet reverse lock is spring-loaded lightly against the outside shell of the pinion ratchet. When the trigger pin is raised, the accumulator lock will drop onto the lantern wheel, and the reverse lock will be released. (The sequence of operations will be described shortly).
The touch-off bar.
The touch-off bar is a 1/16" square bar suspended on fixed arms under a 1/8" x 1/4" mounting bar. The mounting bar extends the full width of the machine, and pivots between the two outside frame plates. The touch-off bar is held forward against a stop by gravity and a light spring.
With the machine at rest, the rear-facing projection on the tail of the trigger is positioned just above the touch-off bar.
As the trigger is armed, its tail moves forward and then down, bringing it directly in front of the vertical face of the touch-off bar.
If the keystroke is completed normally, the tail of the trigger will reverse its travel and move up and back to its original position. However, if the trigger is tripped by a short keystroke, it will move directly rearwards, pushing the touch-off bar rearwards and activating the locking mechanism.
The column lock mechanism.
Just rearward of the touch-off bar is a second 1/8" x 1/4" bar pivoted between the outside frame plates. The cross-arms on this "column lock retainer bar" support two round shafts, which are retained by the bronze leaf spring at the left-hand end.
The "column lock" or "segment lever locking hook" is a small black U-shaped bracket which is suspended from a 0.088" shaft. The bracket passes behind the frame plate, and is positioned laterally by a tab on its right-hand side which curls over the top of the plate.
The locking hook is pulled forward via a light spring (not shown) connected to the arm on its top left-hand side, but is held back by the short rearward arm at its top right which rests on the front column lock retainer shaft. Allowing this shaft to drop will let the lock swing forward to catch the corresponding hook on the top of the segment lever.
Touch-off operation.
This view from the left-hand rear shows how the column lock retainer shaft is held in the raised position by an extended cross-arm which rests on the top surface of the 1/16" square touch-off bar. (The outermost touch-off bar support has been removed for illustration).
If the trigger pushes the touch-off bar rearwards, the extended arm and the front retainer shaft will drop, allowing the springs to pull the locking hooks forward. (The spring actually connects to the trigger retainer horizontal, so that the one spring serves two purposes). The hooks will immediately lock any columns that are at rest, and will catch the others as soon as their segment lever rises.
The lock release button on the keyplate presses down on the rear shaft on the column lock retainer bar, raising the front shaft and the extended arm. This releases the locking hooks, and allows the touch-off bar to spring back into position for the next operation.
Trigger operation - stage 1 - at rest.
The remainder of ths section describes and illustrates the sequence of operations that the "Controlled Key" mechanism makes on every machine cycle. The movements involved are generally less than 1/8 inch, so the differences in the photographs are rather subtle.
The first view shows the trigger mechanism at rest prior to a keystroke.
The trigger is spring-loaded anti-clockwise, with its rear horizontal cross arm resting on the top of the segment lever. The tail of the trigger is sitting just above the touch-off bar (not shown), while the pin and yoke at the front are holding the accumulator locking hook raised clear of the lantern wheel.
Trigger operation - stage 2 - moves forward.
As the keystroke begins, the right-hand shoulder on the keystem presses down on the lock lever. The lock lever rotates the segment lever bell crank clockwise, pushing the trigger connecting link forward. The trigger slides forward horizontally, rotating its support link anti-clockwise. The trigger movement is less than 1/8", and ceases when the forward arm on its supporting link strikes the underside of the spring/stop rod. Any excess movement of the bell crank is absorbed by the slot and spring at the rear of the trigger connecting link. The tail of the trigger is now positioned above and just forward of the touch-off bar.
As the trigger slides forward, the downward vertical arm at its rear end strikes the ramped face of the hook on the trigger retainer vertical and pushes it forward. (It's hard to see in the picture, but note how it has raised the trigger retainer's horizontal arm off the stop rod). The trigger must not pass above the retainer hook as it slides forward.
Trigger operation - stage 3a - rotates to armed position.
As the key continues downward, its right-hand shoulder starts to move the segment lever. The trigger rotates anti-clockwise as its rear arm follows the segment lever downwards, until it reaches the large stop rod under the centre of its rearward arm. The movement at this point is less than 1/16". The extreme ends of the trigger move almost 1/8", bringing the rear tail downwards to the "armed" position directly in front of the touch-off bar (not shown).
As the trigger rotates backwards, the trigger retainer horizontal (which also rests on the segment lever) rotates forward, until the tip of its upper arm comes to rest on the tip of the vertical trigger arm.
Trigger operation - stage 3b - sets accumulator locks.
As the trigger rotates rearwards, the pin on its forward arm raises the yoke on the accumulator locking hook. This lowers the front of the hook into engagement with the lantern wheel pins. The locking hook is linked to the pinion ratchet reverse lock, which is pushed rearward and clear of the ratchet.
The mechanism is now ready to complete the downstroke - the trigger is armed, the accumulator is locked, and the pinion ratchet reverse (ie, downwards) lock is disengaged.
Trigger operation - stage 4 - full keystroke.
Towards the bottom of the keystroke, the left-hand shoulder on the keystem reaches one or other of the key stop levers and begins to activate the key stops.
At the very end of the stroke, a small tag on the horizontal arm of the keystop presses down on the forward arm of the trigger, just forward of the springs. The trigger is rotated to a position slightly more clockwise than its rest position, allowing the trigger retainer horizontal to drop behind the vertical arm, and the trigger retainer vertical to swing under the bottom tag on the rear of the trigger. The trigger is now disarmed, with its rear tail raised clear of the touch-off bar. The two trigger retainers hold the trigger in this position as the key rises and the key stops are released.
As the trigger is pushed downwards by the key stop, the accumulator locking hook is raised clear of the lantern wheel, and the pinion ratchet reverse lock moves forward into engagement with the ratchet. As the segment lever rises, it drives the accumulator clockwise, with the reverse lock clicking over on each step on the ratchet. If the operator attempts to start a new downstroke before the key has fully risen, it will be immediately caught by the pinion ratchet reverse lock and the key will block. The reverse lock is not released until the trigger has been reset and re-armed at the beginning of the next keystroke.
Towards the top of the keystroke, the segment lever raises the trigger retainer horizontal so that the trigger is free to move rearward. Finally, the lock lever releases the segment lever bell crank, and the bell crank spring pulls the trigger rearward and clear of the trigger retainer vertical. The trigger drops slightly until its cross-arm rests on the segment lever. The mechanism is now back to its starting position. This sequence of operations occurs on every keystroke in every column.
Trigger operation - stage 5a - short keystroke.
In this view, the operator has released the key before completing the downstroke and disarming the trigger. The segment lever attempts to drive the accumulator forward (clockwise), but the lantern wheel is held fast by the accumulator locking hook and the lever is unable to rise.
The mechanism is now under considerable pressure, with the full tension of the segment lever springs being taken by the segment, pinion, ratchet, lantern wheel, and the locking hook.
Trigger operation - stage 5b - touch-off tripped.
Although the segment lever is held by the accumulator locking hook and is unable to rise, the key continues upwards under pressure of the keypiece spring, and the lock lever follows under pressure from the segment lever bell crank spring. The relative motion between the lock lever and the segment lever allows the spring to rotate the bell crank anti-clockwise. The connecting link pulls the trigger rearward to the position shown, operating the touch-off bar and dropping the segment lever locking hooks.
Note that the segment lever in the offending column is still held depressed and will not be caught by the column locking hook. When the operator returns to complete the keystroke, the lock lever and bell crank will again push the trigger forward, restoring the trigger to the armed position (but without resetting the touch-off bar). The cycle will proceed to completion as already described, except that the column locking hook will catch the segment lever when it returns to the top of its stroke. The operator then presses the red release button and proceeds as if nothing had happened.