These notes describe the key features of the internal operation of the Adwel machine during its various operating cycles. The notes should be read in conjunction with the physical descriptions on the previous pages.
"Forward" and "return" strokes refer to the movement of the operating
handle .
Angular measurements are given to the nearest 5°, and refer to
the position of the mainshaft (the rotor shaft). The position of the
operating handle is similar, but does not follow exactly because of the
intermediate linkage.
Assume that the addition cycle starts from the "clear" state following a Total cycle. The operator enters a number on the keyboard and pulls the handle forward. A non-return pawl on the LHS of the mainshaft ensures that the machine can not be short-cycled before completing its full stroke. The non-return pawl operates on both forward and return strokes.
The register control mechanism on the LHS pushes the register forward, disengaging it from the rotor at 10°. A spring-loaded locking rod prevents the register gears moving while disengaged.
The keylink bail starts rearward at 15°, allowing the spring-loaded key links to follow. The keylink travel is stopped when the tags on the keyboard transfer links strike the depressed keystems in the corresponding columns.
As the keylink bail moves rearward, it allows the saw-tooth bar across the bottom front of machine to rotate rearward into the path of the key column locking levers (via a spring-loaded sliding link on the inside of the outer LH side plate). This saw-tooth bar stops the key column locking levers from moving sideways, thus preventing any further keyboard operation once the mainshaft has passed 30°.
There are no Zero keys, so the links in Zero columns are stopped by the extensions on the key column locking levers at 30°.
As the handle is pulled further forward, the keylinks continue rearward, raising the corresponding rotor disks into their positions for printing. At the same time, the leading-zero supression mechanism moves forward, lowering the leftmost rotor disks into a non-printing position below Zero. The transfer from keyboard to rotor is completed when the links in Nines columns reach their stops at 75°.
From 80° to 90°, a locking bail rises against the lower rear set of rotor teeth, so as to hold the numerals firmly in alignment during printing. The locking bail is operated from a slotted cam on the mainshaft, on the inside of the inner LH side plate.
The platen roller contacts the paper at 90°, and the forward stroke completes at 95° when the non-return pawl disengages.
At the start of the return stroke, the register control mechanism pushes the register rearward, engaging it with the top front set of rotor teeth at 85°.
The keylink bail picks up keylinks at 75° and pushes them forward, pulling the rotor disks back down towards zero. As the rotor disks return, the register gears advance (CCW from RHS) by the same number of positions.
At 45°, the outermost snail cam on the RHS of the mainshaft starts to push rearward on a long horizontal sliding link on the outside of the RH side plate. The forward end of this link operates the clearing bar at the top rear of the keyboard (through several intermediate levers), releasing the keyboard locking bars and the keystems at 15°. The sliding link resets at 5°, and the cycle ends when the non-return pawl disengages at 0°.
The register remains engaged at the completion of the cycle.
Note that the leftmost disk on the rotor has no corresponding keyboard column, but functions only to accumulate carries into the 100,000 place. A stop prevents this keylink moving during the addition cycles. The rightmost disk on the rotor is a symbol disk which prints a single character to indicate the operation performed.
The carry mechanism relies on the two-part construction of the rotor disks, which was ignored in the previous section in order to simplify the description of the basic operation.
The rotor disks consist of two interconnected sectors. The rear sector carries the numerals for printing, and is connected to the keylinks and the keyboard. The front sector engages with the register and the carry mechanism. The two sectors are held together by a fairly stiff spring, but can rotate relative to each other (against the spring) by a distance of about 1.5 teeth.
Consider the situation as the keylinks are pushed towards Zero on the return stroke (with no carries pending). The rotor disk rotates rearward as a unit until the slot in the front sector is stopped by the pin on the carry link at 30°. The keylink bail continues pushing until 10°, forcing the rear sectors further back by a distance of one tooth, against the tension of the sector connecting springs. If there are no carries, this excess motion will be recovered at the start of the next addition cycle, and will have no overall effect.
If a carry occurs as the register is incremented on the return stroke, the wide tooth at the Zero position on the register will push upwards on the ramp on the underside of the corresponding carry sense finger. The finger will move rearward, allowing the carry link for the next digit to rise by a distance of exactly one tooth.
Nothing further happens until the mainshaft returns past 30°, when the raised carry link allows the rotor disk to rotate one tooth further than before, thus advancing the register by one additional position.
If successive register positions to the left also stand at 9, the next carry sense finger will trip when the register has advanced by about half of the additional tooth. At this stage, the mainshaft is at 25° and has started tensioning the rotor sector springs. As soon as the carry link is released, the sector spring will pull the front sector rearward, advancing the register and triggering an immediate ripple carry across the machine.
The cycle ends with the carry links still raised and the sector springs released on those columns where a carry has occurred.
The carry links and the sense levers are reset on the forward stroke of the next addition cycle by a clearing bail, which is operated via an over-centre lever assembly from the keylink bail. The clearing bail begins to push the carry links downwards from 35°, allowing the carry sense fingers to reset at 50°. The bail reaches maximum stroke at 70° and releases fully at 85°, ready for the carry mechanism to operate on the return stroke.
Pressing the "Minus" key reverses the direction of rotation of the register by engaging the lower set of gears. Otherwise, the subtraction cycle is the same as addition.
The Minus key is held down by a latch on the outer right-hand side. Interlocks ensure that it can only be pressed when the machine is idle, and can not be released until the cycle is completed.
Pressing the key tensions a spring in a lever assembly located between the two RH side plates. The spring attempts to raise the register assembly, but is unable to do so because the upper register is still engaged with the front rotor sectors.
When the register is fully disengaged at 25° on the forward stroke, the spring raises the register assembly into the upper position. This means that on the return stroke, the lower register gears will engage with the front rotor sectors, and the upper (addition) gears will rotate in the opposite direction. The carry teeth on the lower register are displaced by an appropriate amount from the upper, but otherwise operate as previously described.
The sliding clearing link on the outer RHS releases the minus key latch at 15°. A small spring which appears to relate only to the symbol disk stop is important in returning the lever assembly to its home position clear of the interlocks.
The minus cycle ends with the register assembly still in the raised position. It will drop by gravity when fully released at 25° on the next addition cycle.
To initiate a sub-total cycle, the "S/T" key is drawn forward until it latches. This holds the keyboard clearing bar in the operated position, ensuring that the keystems and zero tags are clear of the keylinks. It raises a stop from the leftmost keylink, allowing the eighth rotor disk to operate. It also acts on the register control mechanism to inhibit the initial forward motion that disengages the register. An interlock lever on the inside of the outer RH side plate prevents the key operating if Minus is selected. A second interlock holds the key firmly in position from about 10° while the cycle is in progress.
On the forward stroke, the upper register remains engaged with the front rotor sectors.The spring-loaded keylinks follow the keylink bail rearward, allowing the numerals to rise while driving the register gears in the reverse direction (clockwise from the right-hand side). The motion stops when the wide carry teeth at the zero position strike the flat tops of the carry sense fingers. At this stage, the register contents have been transferred to the rotor and the register stands at zero.
The rotor contents are then printed, and the operation is reversed on the return stroke. The S/T key latch and interlocks are released at the end of the stroke.
To initiate a Total & Clear cycle, the S/T key is pressed rearward as the handle is pulled. The key does not latch immediately, but is held securely by the internal interlock once the mainshaft passes 5°.
The forward stroke begins as for sub-total, with the register contents being transferred to the rotor. But at the 90° point, a lowered tag on the register control mechanism is struck by an extension on the left of the keylink bail. The register is pushed forward and disengaged from the rotor, and its contents, which stand at zero, are secured by the spring-loaded locking rod. The rotor disks are prevented from moving by the rear sector locking bail, which has risen in preparation for printing.
On the return stroke, the sector locking bar retracts after printing is completed. There is now nothing holding the rotor or the key links, so the links spring fully rearward, raising the numeral sectors. The keylink bail then returns the links to the home position. At about 10° the register control mechanism re-engages the registers in preparation for the next cycle.
This machine always takes its totals and sub-totals from the upper register. If the total is negative, the printout will be in complement form.
To convert a complement to its normal representation, the Adwel operator would clear the machine, enter the complement on the keyboard, subtract once, and print the result. A spurious 9 remains at the left-hand side, because the keyboard has one less column than the register.
For comparison, more elaborate machines of this general design often sense a sign change via a carry out of the leftmost register position, and then change the ribbon colour and select the complement register for printout.
The description of the total cycles has been simplified by ignoring the fact that the carry mechanism is not reset until late in the forward stroke of the following addition cycle.
If a carry has occurred, the carry links and sector springs will still be in the released state at the beginning of the next cycle. There will be a difference of one tooth position between the numeral sectors and the register sectors, compared to a column which did not have a carry. This is normally taken up as the next addition cycle commences with the register disengaged.
However, if a sub-total cycle is attempted at this stage, the register will not be disengaged, but will immediately begin transferring its contents to the rotor disks. The columns where a carry had occurred will be offset by one tooth relative to the others, and will print one digit less than required.
The Adwel works around this problem by requiring the operator to reset the carries manually (by means of an additional "add-a-zero" cycle) before it will allow a total or sub-total cycle to be performed.
An interlock lever on the inside of the outer RH side plate normally sits over a pin on the inside of the S/T lever and prevents it moving. The interlock is released at the beginning of each cycle by a cam on the mainshaft, but is immediately tripped again if any rotor digit advances beyond zero. The trip is implemented by the extended teeth on the rear sectors pushing rearward on a hinged trip bail located below and behind the rotor. The only time the S/T key can be operated is immediately following an "add zero" cycle.
A separate mechanism operated from the S/T key disables the carry reset function in both Total and Sub-Total cycles. The purpose of this interlock is unclear, given that the "add zero" cycle ensures that the carries are already reset.
For comparison, other machines of this general design reset the carry mechanism early in the forward stroke, and do not engage the register on the Total cycles until after the carries have been cleared. The Total cycles function as expected, with no requirement for additional dummy operations. It would be interesting to see how Adwel explained this "feature" in their operator's instructions.