CA1110913A - Check-digit printing means - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The invention contemplates a document printer for the automatically indexed sequential account numbering of successive documents, with the added feature of printing alongside each sequential number an automatic indication of the validity or invalidity of the number printed, said indication being a "check digit" which, in conjunction with the printed account number, renders the printed account number self-checking.
The invention is described in application to weighted-modulus self-checking systems of the Modulus 10 and Modulus 11 varieties, inter alia.

Description

CffECK-DIGIT PRINTING ME~JS

The invention relates to an improved document printer for the sequential numbering of documents wherein a weighted-modulus check digi-t is printed alongside the serial number to render the printed number self-checking.
: . With the advent of machines which can read various type faces at very high speeds, and of computers that can perform any calculations for verification, there is a need for a system to insure that-serialized numbers printed on forms, cards and the like are accurate, that there are no duplicate numbers or missing numbers. Por

-2-, .... . .

, . . .

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users, such as hospitals, :insurance companies, financial institutions, frcight forwarders, and dcl-artment stores, to name only a few industries, the assurancc that the consecutive numbering on a form is correct and that it can be verified when entering the system can save thousands of dollars a day by the elimination of numbering errors.
The weighted-modulus numbering system provides such substantially improved accuracy, by increasing reliability of consecutive numbering to over 95 pcrcent. To accomplish this, each consecutive number printed is multiplied by a formula which generates a self-check digit that is printed alongside the consecutive number, e.g., to the right of the units position of the printed consecu-tive number. Based upon the formula used, there can be only one acceptable self-check digit for each consecutive number and the verification of this number in the system, whether by computer or keypunch-ing, insures that an absolute minimum of numbering errors is ever allowed into the system.
There are two basic weighted-modulus self-checking systems from which many derivations have been developed for specific applications. The Modulus 10 system w;ll detect the three most common types of errors; namely, errors of (1) transcription, ~2) transposition, and (3) random errors. The Modulus 11 system will detect double-transposition errors in addition to the noted Modulus 10 features and does so with 10~ percent accuracy, all except for random errors, which the Modulus 11 system will catch 97 percent of the time.
So far as we know, there has been no previous application of weighted-modulus check-digit printing in conjunction with consecutive num-bering of documents such as business forms, without involving a computer op-eration; neither has there been any means of developing a check digit for each of a particular succession of consecutive numbers without performing all the computative steps required by the formula of the particular weighted-modulus system involved.

It is accord;ngly an object of the invention to provide an im-provcd consecutive-llumbering document printcr which additionally prints a self-check digit for each consecutive number, according to a predetermined weighted-modulus system.
Another object is to meet the above object with means having ap-plicaticn to a high-speed consecutive-number printing mechanism.
A further object is to meet the above objects with relatively simple mechanism which lends itself to relatively inexpensive retrofit of existing consecutive-numbering document printers.
It is also an object to meet the above objects with mechanism hav-ing the capacity to selectively serve both Modulus 10 and Modulus 11 self-checking systems, with simple and ready set-up for or change-over from one to the other of these systems.
Still another object is to meet the above objects with printing means of the character indicated, which lends itself with equal facility to forward or to backward consecutive numbering and which is inherently oper-able whatever the starting or the finishing number in the consecutive series to be printed, within the digit-position printing capacity of the particular printing means to which the invention is applled.
A specific object is to meet the above objects with simplified ; check-digit-determining means which does not involve or require a separate formula computation for each check digit to be printed.
Another specific object, in conjunction with a Modulus 11 employ-ment of the invention is to provide means automatically operative to print an invalidating indicium adjacent the printed consecutive number, whenever the Modulus 11 formula calls for a two-digit solution.
Still another specific object is to provide a consecutive-number ~- printing system with automatic check-digit printing involving multiple-digit . check-digit numbers.
:~ 30 A further specific object is to provide a self-check system of the above character, employing r~odulus 97.
Other objects and various fllrther features of no~elty and inven-tion will be poi.nted out or will occur to those skilled in the art from a reading of the following specification~ in conjunction with the accompanying drawings. In said drawings which show, for illustrative purposes only, pre-ferred embodiments of the invention:
Figure 1 is a perspective view of a document printer to which check-digit printing means and an associated control unit of the invention have been applied;
Figure 2 is a sectional view ta.ken substantially at the plane 2-2 of Figure l;
Figure 3 is a simplified electrical block diagram illustrating the functional relation between consecutive-number counting and check-digit shift, for each style of consecutive-number printing in the machi.ne of Fig-ure l;
Figure 4 is a front view of the set-up panel within the control mit of Figure l;
Figure 5 is a fragmentary showing of circuit components and con-nections within the block diagram of Figure 4;
Figure 6 is a perspective view of a consecutive-number print head, with check-digit printing means employable in the machine of Figure l;
Figure 7 is an enlarged and exploded view in perspective, showing a replaceable check-digit printing component in the printing head of Figure 6;
Figure 8 is a view similar to Figure 7 to show a modificati.on;
Figures 9 and 10 are diagrams of the general nature of Figures 3 and 5, respectively, to lllustrate a two-digit check-digi.t embodiment of the invention;
Figures 9A and 9B are simplified diagrams of a coded-wheel compon-ent, used in the circu~t diagram of Figure 9; and ..

; .

gil3 Figurc 11 is a fragmentary block diagram to show modification of a part of l;gure 9.
Briefly stated, the invention proceeds from the basic observation that in any series of consecutive numbers, and regardless of the number of digits in a particular number within the series, the formation of the next-consecutive number in the series involves but a one-digit shift in the "units" position of the number involved, unless the particular number in-volved happens to have a "9" in the "units" position, in which case the one-digit increment makes said next-consecutive number a "10", namely, a two-digit number involving a "O" in the "units" position and a one-digit in-crement in the "tens" position. Thus, only every tenth single-digit incre-ment gives rise to a one-digit change in the "tens" position. Similarly, only every 100th single-digit increment gives rise to a one-digit change in the "lOO's" position; only every 1000th single-digit increment gives rise to a one-digit change in the "lOOO's" position; only every lO,OOOth single-digit increment gives rise to a one-digit change in the "lO,OOO's" position;
and so on, as to the geometrically descending frequency with which a single-digit increment produces a one-digit change in a particular h:igher-order position in the multiple-digit numbers involved. Stated in other words, and if all zeros are ignored in the sequence of consecutive numbers, a one-digit increment from one to the next-consecutive number in the series always in-volves one and only one numerical-digit change, in one and only one of the digit positions, and only to the extent of a one-digit change in said one digit position. It is observed that to ignore all zeros in any check-digit evaluation is to strictly observe a point in common for all weighted-modulus systems, namely, that in performing the basic operative steps of the calcu-lation, one must individually multiply a pre-assigned digit-position weight-ing number by the particular numerical digit in the given digit position;
and if that particular digit happens to be a zero, the multiplying step must develop a product equal to zero, meaning that such product is of zero value in the ensuing summation forming part o.f the succession of formula steps.
Tlle .invent:ioll also proceecls from the basic observation that, what-ever the moclulus system or whatever the digit-position weighting pattern adopted in connection therewith, the unit check-digi.t change, for a one-digit incremerlt wholly :in the "units" position, will always be in the same magnitude and di.rection of change; the same can be said as to each one-digit increment whicll involves a one-digit change in the "tens", "lOO's", "l,OOO's", or any other higller-order digit position; except that such one-digit change in each higher-order digit position will always involve a check-digit change of magnitude and direction unique to the particular digit position involved. Thus, for example, in one illustrative weighted Modulus 11 system, a one-digit change in consecutive numbering having eight digit positions will involve:
A. a check-digit decrement of two, if the number change :is in the "uni.ts" position;
B. a check-digit decrement of seven, if the number is in the "tens" position;
C. a check-digit decrement of three, if the number change is i.n the "lOO's" position;
D. a check-digit decrement of one, if the number change is in the "lOOO's" position;
E. a check-digit decrement of one, if the number change is in the "lO,OOO's" position;
~:. a check-digit decrement of three, if the number change is in the "lOO,OOO's" position;
G. a check-digit decrement of one, if the number change is in the ~1, ono, ooo ~ S~ pOS ition; and H. a check-digit decrement of six, if the number change is in the "lO,OOO,OOO's" position.
It is convenient to tabulate the foregoing check-digit decrements, by digit positioll, as follows:
Digit 10 10 10 10 10 10 10 units Check-l)igit Decrements: -6 -1 -3 -1 -1 -3 -7 -2 And to additional]y describe this particular illustrative Modulus 11 sys-tem, we tabulate tne weighting pattern, by digit position, as follows:

Position: 107 1o6 105 104 103 1o2 lol units Positional Weighting: 3 2 7 6 5 4 3 2 The invention utilizes the foregoing observations by providing a check-digit print wlleel, mounted upon and preferably adjacent to the "units"
end of a conventional sequential-numbering print head having one print wheel for each of the digit positions of the numbers to be printed. In an Arabic-numbering sequence, each of the print wheels of the print head has ten in-dexible positions, engraved in accordance with the ten-digit sequence of a decade, and conventional actuating means are utilized to establish a single-digit advance (or decrease, if so selected) in the multiple-digit number se-quence, the advance being to present at a printing-plane orientation the correct engraved digit of each print wheel to assure printing of the number currently set; synchronizing means assure correlation of each single-digit advance with the retracted or inactive portion of the print-stroke cycle of the document printer to which the invention is applied. Also synchronized with the print-stroke cycle is control mechanism for determining and effect-ing the applicable increment or decrement involved in repositioning thecheck-digit print wheel, appropriate to the particular one-digit increment involved in the series of consecutive numbers. To this end, the control mechanism senses the particular digit position at which a numerical change (other than to a zero) is involved; having sensed the particular digit posi-tion involved in the change, the control mechanism employs the check-digit decrement unique to that digit position, in the controlled drive of a posi-~$~

tioning motor for the check-cligit print wheel.
In the case of a Modulus ll system, the check-digit print wheel is engraved for indexed positioning to print in one of eleven positions, representing the eleven possible different solutions of the weighted-modulus formula involved. Ten of these engraved positions are assigned different single digits of the succession of ten in a single decade. The eleventh position, being numerically indentifiable only with two digits, and a two-digit solution being incompatible with existing Arabic-decade print readers, the eleventh-position check-digit solution is deemed to be invalid, and the "invalid" position is suitably engraved to indicate the invalidity, as by the word "VOID". Thus, for example, in the illustrative-weighting pattern given above, an eight-number sequence involving an "invalid" number and decrements attributable to number changes in different digit positions can be tabulated, with accounting for check-digit numbers and the digit posi-tions responsible for particular decrements, as follows:

Digit Position Serial Check Digit Involving Single-NumberCheck Digit* Decrement Digit Change -2 Units

-3 10 -2 Units -2 Units 00100002 "VOIU"
-2 Units -2 Units * An ll-position check-digit wheel, printing "VOID" at the position between "0" and "1".

Referring initia]ly to Figi~res I and 2, the invention is shown in application to a high-speed document printer of the type disclosed in great-er detail in Shoup, et al., United States Letters Patent No. 3,254,596, and in the present application it is of significant importance that a print head 10 shall be operative not only to print consecutive numbers upon each suc-cessive business form or other product passing continuously through the ma-chine but also to print a correct check digit adjacent each such consec-utively printed number. In the machine to be described, the consecutive numbers are accommodated within an eight-digit capacity, and the check digit is limited to a single digit placed adjacent the "units" position of the consecutive numbering; this is true for all numbers unless, as in the spec-ific weighted "Modulus 11" system to be first described, the particular con-secutive number happens to be "invalid" within such system, in which case the print-head prints the word "VOID" as a clear warning of the "invalidity"
of the particular document. A separate count of the currently applicable and printed consecutive number is kept in a check-digit control module 11 having a flexible control connection 12 to a drive motor 13 forming part of the print head lO. The module 11 presents at 14 an upper-surface display of the current serial number within the consecutive series being printed, and set-up control means to be described (in connection with Figures 3 to 5) is ac-cessible only upon unlocking and opening an access door at the front of mod-ule 11.
The document printer of Figures 1 and 2 provides support of a con-tinuous web 15 in the horizontal plane of a table 16, across which there is selective availability of web-feeding on either of two orthogonally oriented paths of continuous movement; these paths are labeled "End-IN" to "End-OUT'', and "Front-IN" to "Rear-OUT", the web 15 being shown set up for the latter of these paths. Printing is accomplished by reacting impact of a hammer 17 against the currently-characterized face of print head lO, via web 15 and a - 30 pigmented ribbon 1~ (Figure 2) from a supply reel 19.

~ 4~ 3 Aithougll the invention will be described in connection with con-tinUOllS web hclving provision fo~ sprocket feeding, it will be appreciated that such feeding is illustrative, in that it happens to be the means of synchronizing web placement for precise location of printing impressions.
For "unit documents" (e.g., cut sheets, individual forms, cards, or the like), suitable feeding devices (not shown) may be employed to continuously deliver each unit document to the printing region for precisely synchron-ized imprinting. Thus, it will be understood that reference to "web mate-rial" herein contemplates continuous or intermittent feed of continuous web as well as of suitably fed cut or other unit documents.
The printing machine of Figure 1 is based on a frame 20, shown as the top deck of supporting structure which may be at essentially counter height, and which together with module 11 may be supported on casters for mobility in application and use. The machine frame includes a pair of up-standing end plates 21 secured to base plate 20 and providing journal support for various shafts. Side plates 22 also support the table 16, over which web 15 is drawn. Printing occurs at a central location within table 16, and, at the particular printing location, there is a table opening 23 (Figure 2). Each of the end plates 21 extends substantially above the web-supporting surface of table 16 and, at the level of table surface, is pro-vided with a slotted opening 24 through which web (suggested at 15') may be fed freely, should the "End-IN" to "End-OUT" direction of web movement be selected. Above the slot location or plane of table 16, the plates 21 pro-vide support for an elongate spacer and guide bar 25, for adjustably sup-porting the printing head 10 and a carriage 26 for the ribbon-support and feed mechanism.
For the presently illustrated embodiment, the machine accommodates continuous web material having marginal apertures of standard configuration, ;~; and the feed mechanism embodies sprockets at both the "IN" and "OUT" ends of web travel through the machine, whichever particular direction is selected.

Thlls, in Figure l, for web 15 enterilig thc "Front-lN" side of the machine, the wel- passes over a first pair oE sprockets 27, adjustably positioned and spaced on a sprocket-drive shaE~ 28, journaled in the end plates 21. It will be un~erstood that at the "Rear-OUT" end of the trajectory for web 15, and after having passed the printing location, further web-feeding sprocket means including a further drive shaft 29 (Figure 2) may draw off the im-printed-web product for feeding to suitable folding, stacking, cutting, col-lating or other device (not shown). For the "End-IN" to "End-OUT" direction of movement of web 15', similar "IN" and "OUT" sprocket drives are provided;
of these~ the "IN" shaft 30 for spaced sprockets 31 is visible in Figure 1, the same having a bevel-gear pick-off at 32 from drive shaft 28 to assure their operation in unison; a similar "OUT" sprocket drive ~not shown) for web 15' will be understood also to have a bevel-gear pick-off connection to shaft 28 on the far side of the machine, the same being masked by the far plate 21 in Figure 1. Electric-motor means (not shown) will be understood to provide drive to the shafts 28-29-30 and to other shafts including a print-cycle shaft 33 (Figure 3) for driving a trip member or cam 34 (Figure 2) for operating the print hammer 17. Phase-adjustment means to enable ad-justment for predetermined tension or slack in web 15 (15') between the "IN"
and "OUT" sprockets, and to enable the exact timing of print-hammer action to achieve desired printing location within each unit-product area of the web, are described in detail in said patent and therefore need not be re-peated here.
The print head 10 is shown in Figure 6 to comprise a rugged base 35 with dovetail formations 36 to enable adjusted retention by and at a se-lected position along a dovetail groove 37 on the underside of spacer bar 25. The print-head base includes a pair of spaced projecting end plates 38-39 for journaled support of a plurality of print wheels (a, b, c, ...h) for printing the current consecutive number; each such print wheel is character-ized by a single-digit numerical type face at each of a succession of ten equal anglllar spacings, and the number of such ~rint wheels is shown to be eight, consistent with thc 8-digit serial-number capacity of the machine.
A serial-number index-actuating crank 40 external to plate 38 carries a fol-lower pin or roll 41 to engage the slot 42 (Figure 2) and an oscillating crank 43; crank 43 is mounted to a shaft 44 which will be understood to de-rive angular oscillation in synchronism with the print cycle, such means being shown in said patent. Thus, crank 40 will be understood to impart to the print wheels a, b, c, ...h a one-way engaging unit-advancing actuation, once per print cycle.
The print head 10 incorporates further mechanism for imprinting a check digit, unique to each serial number in the consecutive series. The means for deriving the check digit to be printed will be later described, but it suffices here to identify a check-digit print wheel 45 (see also Fig-ure 7) having suitable engraved single-digit numerical printing indicia at each of ten out of eleven equally divided print locations at the printing end 46 of wheel 45. The central body 47 of wheel 45 is grooved to accept the mount of an insert 48 to print "VOID" in the eleventh (and remai.ning) print location, a locking set screw 49 being shown to retain the assembled insert. The other end of body 47 carries a drive gear 50 by which the out-put spur gear (not shown) of the check-digit positioning motor 13 drives gear SO via adjustably positionable idler means 51. The consecutive-number print wheels, a, b, c, ...h will be understood to be advanced in one-digit increments, and only in accordance with oscillation of shaft 44, in syn-chronism with the print cycle; the check-digit wheel 45, with its single-digit printing end 46 adjacent the "units" end of the consecutive number print wheels, will be understood to have no mechanical connection with the consecutive-number print wheels, other than journal support on the same axis between plates 38-39, the only actuation of digit wheel 45 being via the in-dicated gear-train connection from motor 13.
It will be understood that each indexing of a print wheel or whecls brings thc a~ licable type face into alignment with all other type faccs to ~e l~rirlte~, s~lcll al:ignment being in a single fixed horizontal print-impressioll pkllle at the ~mderside of print head 10 and parallel to the dovetail mount 36 thereof. This print-impression plane contains the currently set impression face of printing head 10, closely adjacent and in facing relation to the plane of the web 15 (or 15'), i.e., close to the plane of the table surface 16. To make a printing impression, hammer means 17 is pivotally suspended below the table surface 16 and its striking end rises for momentary striking impact against the print face, the web and the pigmented ribbon 1~ being momentarily squeezed by the impact. For present purposes it suffices to state that the hammer mechanism receives its re-cycling synchronized actuation from cam 34 on shaft 33 which is continuously rotating, once per unit-document advance of web 15 along the table surface 16. The hammer-operating cycle comprises a gradual downwardly cammed dis-placement of the strike end of hammer 17, against increasing force reaction from preloading spring means 52, and cam 34 is contoured to release hammer means 17 for printing impact at a predetermined instant in the cycle of shaft 33. Synchronizing connections as between drive to shaft 33 and oscil-lating drive to number-advancing shaft 44 will be understood to assure suit-able interlace of the printing function with respect to the number-indexing function.
THE CHECK-DIGIT OPERATING MEANS
Referring to Figure 3, the check-digit determination, and actua-tiOll of positioning motor 13 in accordance with such determination, are ef-fected in response to control stimuli which are also synchronized to occur in phase-interlace with the hammer-release function of cam 34. To this end, two further cams 55-56 on the print-cycle shaft 33 are se~uentially oper-ative to close timing-pulse switches 57-58, at a predetermined delay therebetween. Switch 57 supplies one pulse per cycle to an 8-digit counter 59 (with display at 14), which may contain eight individual digit-position count indicators and a step switch associated with each count indicator.
Output connections exist betweell eacll digit-position step switch and a cor-responding digit-position multiplier in a modulus-functioll unit 60.
The modulus-function unit comprises a series of single-digit dis-plays at each of the eight digit positions corresponding to those of the digit-position capacity of serial-number display and step-switching at 59.
As shown, each of the eight single-digit displays at unit 60 is associated with a thumb switch whereby individual single-digit numbers can be manually selected, so as to determine a binary-coded decimal (BCD) output appropri-ate to the selected single-digi-t number. As will later more clearly appear, in any given cycle only one operative connection is ever made between a step switch (within the display and switching unit 59) and a corresponding thumb switch (within the modulus-function unit 60); to make this point unambig-uously, we have used dashed-line interconnections between corresponding step switches at 59 and thumb switches at 60, except for a single solid-line connection 61 which is illustratively shown for the most frequently oper-ative digit position, namely, the "units" position.
Since in any given print cycle only a one-digit change is involved in only one digit position*, the four conductor BCD outputs of all thumb switches at 60 may be connected in parallel. The thus-connected BCD lines are identified in Figure 3 by their respective BCD values (1-2-4-8), and are fed directly to an index-control signal generator 62. Generator 62 may be a commercially available pulse generator producing on command a precisely num-bered quick succession of position-controlling pulses, for direct drive of a compatible and commercially available stepping motor, here used as the check-digit position motor 13. In an illustrative employment of generator 62, a succession of ten pulses, on command, is operative upon motor 13 to actuate a one-digit positional decrement of the check-digit print wheel 45, at the plane of printing impression. The illustrative current cycle (Figure 3) establishes connection 61 at the "units" position, where the thumb switch * It being recalled that all zeros are ignored in any weighted-modulus system. - 15 -setting happens to be "2". This bcing the case, the BCD output of module69 is "2", i.e., a "1" in the second-digit line, and "0" in each of the first, third and fourth of the BCD output lines. Generator 62 is thus set, on command, to apply a two-digit decremental displacement signal (2 x 10, or 20 pulses, in the illustrative case) to motor 13; the command is issued by the ~ _-delayed pulse produced by switch 58, operatively connected to gen-erator 62.
In the case of a cycle in which the consecutive-number advance (zeros ignored) occurs at a different digit position, for example in the lO's position, the applicable thumb-switch setting is "7", and generator 62 will be caused, upon command from switch 58, to genera~e a motor-drive train of 70 pulses, causing motor 13 to impart a 7-digit decrement shift in the positioning of check-digit wheel 45. For consistency of presentation in ap-plication to the above-described weighted Modulus 11 system, the thumb-switch settings shown in Figure 3 at the respective digit positions of unit 60 are in exact accord with the tabulation set forth above. Also, the ser-ial number selected for display at 59 accords with one involving a "units"-position advance in the succession of seven consecutive numbers discussed above.
Before proceeding with a more detailed description of electrical interconnection of step switches at S9 with thumb switches at 60, it is helpful to consider the control panel of Figure 4, accessible upon opening the door of module 11, and used only to set up the described machine for a particular printing job run. It will be recalled that the upper-surface display at 14 reflects the current consecutive-number setting of the print head 10, but since there is no direct connection between display 14 and the serial number setting of print head 10, provision is made for the set-up man to correlate display 14 with the initial serial-number setting at 10.
Let us say that the job to be run requires 10,000 consecutively numbered documents, from serial number 10,567,001 to serial number 10,577,000, completc with check digits in the above-described Modulus 11 systcm, I)ositionally weiglltcd according to thc succession 3-2-7-6-5-4-3-2 as also descril)c(~ ovc. But let it further be assumed that the previous use of the machine WcLS in application to a Modulus 10 syste,n, requiring a different check-digit print wheel, as will later be described. To set up for the new Modulus 11 rlm, therefore, the Modulus 10 print head 10 must be disassembled from its dovetail mount 37 to the machine, and a Modulus 1]
print head 10 installed. Before applying the Modulus print head, the oper-ator will set the consecutive-number wheels a, b, c, ....h to the desired start number (10,567,000), less a conservative allowance of say 50, to allow for check out of all necessary phase and synchronizing adjustments for the particu]ar job, as to assure correct placement of printed numbers within the specified unit-document format. Having installed print head 10 with the particular number 10,566,950 (10,567,000, minus 50), he must set the dis-play at 14 accordingly; this is done by operating a series of push buttons at 63 on the panel of Figure 4, there being one push button for each digit position, and a one-digit advance being produced at 14 for each push-button operation at 63. Having made this initial correlating adjustment, the dis-play at 14 will thereafter always correctly indicate the current serial-number print setting of the print head 10, because both the oscillation cycle of mechanical serial-number advance (at 10) and the cam (55) operated cycle of electrical serial-number advance ~at 14) are synchroni ed with the print-cycle shaft 33, such mechanical syr.chronizing of oscillation shaft 44 being symboli~ed by an eccentric pick-off connection 44' to shaft 33 in Fig-ure 3.
Ilaving correlated his serial-number settings, the operator next sets his thumb switches at 60 on the panel of Figure 4, thus displaying at 69 that he has set each digit position for its correct check-digit decre-ment, shown in the left-to-right or descending order of digit positions as 6-1-3-1-1-3-7-2.

Y'~

l~ext, having now only the need to assure ~a) that the module-indic-ted serial nllmber at 14 is fully coordinated with each successively printed number and (b~ that all phasing adjustments are made, and making sure that a selec.or switch 64 is set to its run-mo~e position (with con-firming lamp indication at 65), the machine may be briefly operated to pro-duce a trial succession, e.g., five or ten consecutive document printings.
This will confirm to the operator not only that the printed serial numbers are consecutively advancing but that their advance is matched by the display at 14. If there should prove to be, say, a one-digit lagging disparity be-tween printed and displayed serial numbers, it is a simple matter to add aone-digit advance to the display 14, by a single pressing of the "units" but-ton at 63. lf there should prove to be a similar but leading disparity be-tween printed and displayed serial numbers, switch 64 should be shifted to its set-up mode position (with confirming lamp indication at 65'), thereby internally disabling the pulse-generating functions of cam switches 57-58, and the machine can be jogged through one or more print cycles to enable the instantaneously set consecutive number at print head 10 to catch up to the number displayed at 14.
~hile in the set-up mode, further adjustments may be required to assure correct initial setting of the check-digit print wheel 45, to corre-spond with the formula-computed check digit for the currently displayed ser-ial number. The above-described trial run will have produced a "check-digit"
impression alongside each printed serial number, but the check digit may not be corract. By comparing a printed check-digit (for a given printed serial number) against the formula-computed check-digit solution, the operator can determine whether and to what extent the check-digit print wheel 45 should be displaced. A selector switch enables him to select whether he will make the correcti~e step in the "forward" or "backward" direction, upon each press of a manual index button 67. To simplify his correctional displacements, an-other selector switch 68 provides the option at a "1.0" position, of calling for a full-step (i.e., one-digit) change in the positioning of the check-digit print wheel 45 (i.e., for cach press of index button 6-l, a 10-pulse control-signal train from generator 62 to motor 13); switch 68 provides the further option, at a "0.1" position, of calling for a much smaller indexing stcp, involving but a single pulse control signal from generator 62 to motor 13, for each press of index button 67. It will be appreciated that in the "0.1" selected position of switch 68, and with switch 66 positioned as may be directionally appropriate, the operator is enabled to bring the printed correct check digit into exactly aligned adjacent relation to all concurrent-ly printed consecutive-number digits.
Having performed adjustments as noted above, the operator has placed the machine in readiness for automatic operation, upon return of switch 64 to its run-mode position. The door of Module 11 may be closed and locked, leaving visible only the current consecutive-number display at 14.
To the extent that this number is still short of the specified job-start num-ber, the machine should be run until several document printings have been made beyond the specified job-start number, to permit removal and destruc-tion of every printed-number prior to the job-start number, and the printing run may then proceed to completion. Alternatively, the straight run of the machine can produce a continuous succession of documents from a point pre-ceding the job-start number, the documents having the unspecified serial num-bers preceding and following the specified 10,000-document range being sev-ered and destroyed prior to packing and shipment to the customer.
As a double-check on or verification of the fidelity of check-digit printing on the above-described 10,000-document job, it is suggested that a small commercially available programmable printing calculator, such as the Hewlett-Packard H-P 9~15A be programmed to independently perform the rigor-ous formula operations involved in the specified 10,000-number sequence, i.e., from serial number 10,567,001 to 10,577,000, and that the print-out be made complete with the adjacent individually computed check digit for each serial number, the "invalid" numbers being programmed for print-out of the word "VOID" in place of a check digit. A complete 10,000-number sequence would of course show and thereEore permit checking of all calculated check digits against those printed by the machine. Alternatively, we find it sat-isfactory to program the calculator only to print out the "VOID"-identified numbers, which can also be more readily spotted in a visual check against a particular one or more of the "VOID"-printed documents of the production run. After a few such experiences, confidence in printed check-digit accur-acy will build, and the need for checking will reduce to a minimum, as for example, to verifying the first and the last "VOID"-printed documents in the job run.
Reference is now made to the electrical schematic diagram of Fig-ure S, which specifically shows decade-counting stepping switches 70h, 70g....70a, contained within the counting unit 59 and respectively serving the "units" (10), "tens" (101) and 107 digit positions within the 8-digit position capacity of the illustrative embodiment, it being understood that similar stepping switches, similarly connected, also serve the intervening digit positions of the consecutive-number counting unit 59. The mode-selec-tion switch 64 is seen, in the "run" position to have plural completed con-tacts 64-1, 64-2, 64-4, 64-8 serving to connect the BCD output lines from the thumb-switch unit 60 to the index-control signal generator 62; addition-ally, in the "run" selected position, contacts 64' provide circuit completion from the index-command cam switch 58 to the index-control signal generator 62, and further contacts 64" complete a circuit for the run-mode indicator lamp 65, which may be mounted for ~xternal visibility, as alongside the con-secutive-number display 14. In the "set-up" mode position of switch 64, the BCD-output circuit connections are opened, the index cam switch 58 is effec-tively disabled, and the set-up mode lamp 65' is lighted to the exclusion of ; lamp 65; additionally, a further contact 64 "' enables the "1.0" vs. 1~0.ll!
selector switch 68, determinative of the displacement increment of motor 13, .

for each prcss of the ma~ al index push-button switch 67.
The contact arm of the "units" step-switch is subjected to one single-step counterclockwise advance for cach actuation of an associated "units" counter coil 71h, the same being actuable upon each print-cycle tim-ing pulse via cam switch 57 or via the associated set-up push button 63h within unit 63. At the same time and in response to the same stimuli, it will be understood that there is a corresponding one-digit advance in the consecutive-number display at 14. Also associated with the "units" counter is a contact 72h which is closed only for the ninth step position of the "units" decade; when thus closed, contact 72h is the means of relaying a print-cycle timing pulse from cam switch 58 to the next or "tens" counter coil 71g, via a protective coupling diode 73h, so that, upon the next index-ing-initiating pulse from cam switch 57, (i) the step switch 70g of the "tens" decade may be given a one-digit advance via the "tens" counter coil 71g, while (ii) the step switch 70h of the "units" decade is advanced to its "0"-contact position.
The contact arm of the "units" step switch 70h is continuously con-nected via line 74h to the 10-pulse (i.e., basic one-digit advancing) input control connection of the check-digit indexing-control signal generator 62, and when the "units" step switch 70h is indexed into its "0"-contact posi-tion, this direct connection to generator 62 is transferred via a line 74g to the contact arm of the "tens" step switch 70g. Of course it will be understood, from the analogous connections provided for all decade step switches, that if the "tens" step switch 70g happens to be in its "0"-contact position at the same time as the "units" step switch 70h is in its "0"-con-tact position, then the same direct connection to generator 62 is transferred via a line 74f (in series with lines 74g and 74h) to the contact arm of the "hundreds" step switch 70f; and so on, depending upon the number of digit positions for which the step switch contact arm is in its "O"--contact posi-tion.

In Figure 5, the thumb switches at unit 60 are shown in groups of threc like switches 75-76-77, and each of these is marked with a letter sub-scipt appropriate to the digi.t position thereby served (corresponding to the letters adopted for successive digit-position print wheels in the consecu-tive-number printing portion o:f print head 10). Thus, the three thumb switches 75h-76h-77]1 serve the "units" digit position, and each one of these is individually settable, as described for the single switches of unit 60 in Figure 3. Also as described in Figure 3, the three thumb switches for all digit positions provide BCD outputs which are connected in parallel, as con-trol inputs to the signal generator 62. The reason for providing thumbswitches in clusters of three for each digit position will later appear in connection with a Modulus-10 employment of the invention, but as has already been explained in connection with Figures 3 and 4, a single thumb switch for each digit positi.on within unit 60 will adequately serve a wei.ghted Modulus-11 system.
The first BCD-output thumb switch 75h serving the "units" step switch 70h is shown connected to the first four contacts (1-2-3-4) of switch 70h; this thumb switch 74 should be set to its "2"-indicated position, to en-able a two-digit advance of the check-digit print wheel 45, whenever (i) the "units" step switch 70h is in one of its first four contact positions and (ii) an index-actuating pulse is provided by cam switch 58. The second BCD-output thumb switch 76h serving the "units" step swi.tch 70h is shown connect-ed to only contact "5" of switch 70h, while the third BCD-output thumb switch 77h serving the "units" step switch 70h is shown connected to all of the re-maining non-zero contacts (6-7-8-9) of switch 70h; for the described weighted Modulus-ll system, each of these thumb switches 76h-77h should be set to its "2~ indicated posi.tion, to enable a two-digit advance of the check-digit print wheel 45, for each print cycle in which the "units" step switch 70h is not in its "0"-contact position. Of course, when the "units" step switch 70h : 30 is in its "0"-contact position, the above-described decade-transferring ~Lf~3 function of lines 74g-74, etc. will be operati~re as appropriate (via its cluster of BCD switches, as at 75g-76g-77g) to call for that check-digit print-whee1 index multiple which l1as already been discussed as being unique-ly applicable to the particular digit position involved.
It thus appears that for the indicated weighted Modulus-ll system, all three thumb switches 75a-76a-77a serving the "10 " digit-position step switch 70a should be set to provide the indentical BCD output of "6", mean-ing a call for a six-digit indexing decrement in the position of check-digit print whecl 45, for each print cycle in which a one-digit consecutive-number change occurs in the "1O7" digit position. By the same token, thumb switches 75b-76b-77b serving the "106" digit-position switch 70b (not shown) should be set to provide the identical output of "l"; the "105" thumb switches should be set for the identical output of "3", the "104" thumb switches should be set for the indentical output of "1", the "103" thumb switches should be set for the identical output of "1", and the "102" thumb switches should be set for the identical output of "3", it having already been noted that thumb-switch settings are identically "7" and "2", respectively for the "tens" and "units" digit-position step switches 70g-70h.
Example ~or Differently Weighted Modulus-ll Application For simplified discussion, the foregoing has been limited to a single illustrative Modulus-ll system, wherein the positional weighting follows the succession 3-2-7-6-5-4-3-2, in the descending order of digit positions within the 8-digit consecutive-number capacity of the apparatus.
Other Modulus-ll systems may be adapted to precisely the same apparatus, merely by first determining and then entering at 60 the check-digit printing wheel index-displacement multiple which is uniquely applicable to each digit position. For example, in an illustrative "geometrically" weighted Modulus-11 system, tabulations, analogous to those explained above for 3-2-7-6-5-4-3-2 weighting, may be expressed for a particular geometrically weighted sys-tem, as follows:

.3 A. Wcighting pattcrn:
Digit 10 10 10 10 10 10 10 units Weighting 28 27 ~6 25 24 23 22 2 (256) (128) (64) (32) (16) ~8) (4) (2) B. Check-digit print wheel, index decrements:
Digit 10 10 10 10 10 10 10 units Check-Digit Decrements: -5 -6 -1 -4 0 -9 -8 -2 By merely setting all thumb-switch settings (at each digit position) to the indicated decrements 5-6-1-4-0-9-8-2 at unit 69, the apparatus is immediate-ly converted to serve the indicated geometrically weighted Modulus 11 sys-tem. The "0" decrement noted above for the "103" digit position is meaning-ful because it applies to a particular one of the ten possible settings of the applicable thumb wheels; thus, no check-digit print wheel shift will be made upon any numerical change (i.e., not to zero) in the "10 " digit posi-tion. This situation is illustratively presented in the following tabula-tion for consecutive numbers preceding and following a "103" digit-position change:

Setting of Digit Position Serial Check-DigitCheck-DigitInvolving Single Number Print Wheel 45DecrementDigit Change _ --2 units -2 units - -2 units .

Setting of Digit Position Serial Cileck-Digit Check-Digit Involving Single Number Pr Wheel 45 Decrement Digit Change nooo7002 2 -2 units 00007003 "VOID
-2 units Example for Modulus-10 Application In application of the invention to weighted Modulus-10 systems, of course the particular formula will always develop one of ten possible sing]e-digit check-digit solutions, so that the check-digit print wheel should have ten index positions, rather than the eleven discussed in connec-tion with wheel 45. And since only one of ten check-digit answers ever ex-ists, there is no "invalid"-solution situation, so that the word "VOID" is unnecessary. ~igure 8 shows such a 10-position check-digit print wheel 45', closely resembling the print wheel 45 and therefore having its corresponding parts identified by the same reference numerals, with primed notation. The print wheel 45' will be understood to include a gear-toothed end 50' of such size as to mesh with idler 51 upon substitution for print wheel 45 and, in ; conjunction with the same drive motor 13 to produce a one-digit index (1/10 revolution) of wheel 45' for each 10-pulse index-controlling input to motor 13.
Having substituted the check-digit print wheel 45' appropriate to a Modulus-10 system, there remains only the need to enter correct thumb switch settings (at switches 75a-76a-77a...75h-76h-77h), appropriate to the positional weighting pattern selected. ~or example, in an illustrative 8-digit Modulus-10 system wherein the positional weighting is 1-2-1-2-1-2-1-2, the indexing decrements for the check-digit print wheel 45' may be tabulated analogous to the foregoing tabulations of Modulus-ll systems. However, since application of this weighting pattern produces weighting multiples (in every other digit position) wherein the product is ten (e.g., 5 times 2*), it is necessary to make special provision for the contact "5" step-switch position at the affected digit positions. It is for this reason that a special BCD thumb switch is shown in Figure 5, unique to contact "5" posi-tions. Thus, in the following Modulus 10 tabulations, the three numbers indicated for thumb-switch settings at particular digit positions will be understood to apply for the respective 75-76-77 switches involved at each particular digit position:
Digit 107 1o6 105 104 103 1o2 lol units Thumb-Switch Settings: 8-8-8 8-9-8 6-6-6 6-7-6 4-4-4 4-5-4 2-2-2 2-3-2 The functional result of such settings is illustrated for a se-quence of consecutive numbers involving "units" and "10 " position changes, the sequence being extensive enough to illustrate contact-"5" corrections due to the above-noted 2 x 5 situation:

* When the weighting product of a weight digit (e.g., "2") times a numerical digit (e.g., 5, 6...9) is a two-digit number (e.g., 10, 12....18), each digit is added separately (e.g., 10, or "1" plus "0" equals 1; 12, or "1" plus "2" equals 3; and 18, or "1" plus "8" equals 9).

Setting of ~igit Position Serial Check-nigit Check-Digit Involving Single-Number Print Wheel 45' Decrement Digit Change -3 units -2 units -2 units -2 units -2 units -5 1o2 -2 units -2 units -2 units 000005~3 3 -2 units -3 units -2 units ~: -2 units EXAMPLE I~OR WEICI-ITED MODULUS-97 APPI.ICATION
In the examples thus far given, it has been assumed that only one digit position i.s avai.lable for check-digit printing, and that the printed check digit is to be readable within a single decade of numbers, specifical-ly, one of the numbers 0, 1, 2, ...9. However, self-checking systems are known or possible in which two or more digit positions are assigned for check-di.git printing, thus, two-digit printing of a much larger variety of check digits, from within as many as ten decades (or hundreds) of different check-digit numbers, are machine-rendable for printing of check-digit num-bers having two or more digits. In ensuing discussion, two different two-digit modulus systems will be illustratively considered: a weighted Modulus -97 system, and one of the weighted Modulus-ll systems which has already been discussed for single-digit print-out.
The Modulus-97 system selected for illustrative discussion happens to be that which is described and set forth in United States Patent No.
3,913,067, particularly in respect to Figure 4 of said patent, wherein the weighting pattern may be expressed as follows:

: Position: 107 1o6 105 104 103 1o2 lol units Positional : Weighting: 03 30 09 90 27 76 81 34 In accordance with the invention, check-digit increments for two~digit print-out of this weighting are expressed as:
B. Printed check-digit index increments:

Position: 107 1o6 105 104 103 1o2 lolunits Check-Di.git +81 +87 +50 +68 +54 +11 +66+34 Increments For application of the invention to a thus-weighted Modulus-97 system, the already described components and circuitry are directly utili.z-able, except for the fact that the print head must be capable of printing both "tens" and "units" positional components of check digits, as by employ-ing two print wheels of the nature shown in Figure 8 (i.e., inscribed to print one of the dig:its 0, 1, 2 ...9 in the associated one of ten equally divided angular increments, per print-wheel revolution). Circuitry and com-ponents to achieve this purpose and result are shown in Figurcs 9 and 10.
Referring more particularly to Figure 9, a two-digit (illustrat-ively Modulus-97) check-digit employment of the invention utilizes a print head 10' which may resemble the head 10 of Figure 6 in all respects except for inclusion of a first or "tens" print wheel 45A and a second or "units"
print wheel 45B mounted in side-by-side adjacency and for independent rota-tionally indexed positioning about the axis of the serial-number print wheels a, b, c ...h. A first stepmotor 80 is provided for the "tens" posi-tioning of print wheel 45A, via gear means 81, and a second stepmotor 82 is similarly provided for the "units" positioning of print wheel 45B, via gear means 83. The basic position-control information required for operation of motors 80 and 81 is provided by a "97-position" coded wheel 84 (in view of illustrative consideration of a Modulus-97 system) having BCD coding of "tens" angular-position data on its left face 84A and having BCD coding of "units" angular-position data on its right face 84B (see Figures 9A and 9B).
As will become clear, angular repositioning of the coded wheel 84 is syn-chronized to occur in phase-interlace with print-hammer action, i.e., in camshaft-timed control of the switch pulses developed in lines 57-58, from cams 55-56, respectively. And the drive of each stepmotor 80 (82) involves independent employment of a driver circuit 85 (86) which unidirectionally advances the stepmotor 80 (82) ~mtil a comparator circuit 87 (88) senses, by read-out at 91 (92), that a motor-position coded wheel 89 (90) has achieved the BCD position called for by an instantaneously applicable read-out at 93 (94) of the relevant coded face 84A (84B) of the coded wheel 84. A synchron-izing-control connection 62" from generator 62' to each of the comparators 87-88 will be understood to determine comparator output only after comple-tion of each index-control operation of whee] 84.

It will be understood that for simplicity in Figures 9A and 9B, the full four-elemellt binary code ~BCD) has not been drawn for each of the "tens" and ~'~mits~ faces 84A and 84B involved. It should suffice to indi-cate that on the "tens" code face, the four channels of tens-dividing sec-tors are BCD-identifiable through suitably coded marking of the four concen-tric circular regions shown, the basic decades of tens subdivision being labeled as sectors, ending with a small sector labeled "90", meaning that it serves the last seven of the possible 97 angular positions involved for wheel 84. In similar fashion, the corresponding sectors of the "units" face 84B are labeled for the individual units-divided BCD-encoding with which they are inscribed.
A glance at the remainder of Figure 9 reveals the close similarity between functional units 59-60-62 serving the single-digit positioning step-motor 13 in Figure 3 and the corresponding functional units 59'-60'-62' serving the single stepmotor 13' by means of which the "97-position" coded wheel 84 is advanced, from one serial-number print cycle to the next such cycle, in check-digit increments called for by thumb-switch settings at 60'.
In this connection, successively applicable serial-number identities will be displayed at 59', and the two-digit check-digit increment, for each serial-number digit position, will appear at correspondingly arrayed display loca-tions in thumb-switch decimal/binary circuitry 60'. Thus, for the particu-lar Modulus-97 system outlined above, the two thumb wheels at the units lo-cation are shown to have been set to display the number "34", meaning that for each succeeding single-digit count advance in this serial-numbering se-quence (other than an advance from units position "9" to units position "0"), the binary-coded output of circuitry 60' will, via generator 62', cause mo-tor 13' to develop a controlled output-shaft advance equal to 4/97 of a single rotation, i.e., a 34-position advance of the "97-position" coded wheel 84. As shown, separate groups of four BCD OUtpllt lines serve the re-spective "units" and "tens" components of the 34-position advance required for each such unitary seria]-number advance, the "un;ts" lines being indi-cated "l", "2", "4", "8", and the "tens" lines bcing ;ndicatcd "10", "20", "40", "80".
Step-switch circuitry to achieve the foregoing at 60' is shown in Figure 10 and wi11 be recognized for its similarity to the circuitry of Fig-ure 5, although certain elements s~ch as switch-stepping coils 71 and their related connections 72-73 and controls (e.g., 63) have been omitted in the simplified showing of Figure 10. In Figure 10, decade step switches 170a, 170b ...170g, 170h are associated with the respective digit positions of the instantaneously applicable serial number in the advancing sequence thereof, and for each of these step switches, nine of the output contacts are inter-connected for actuation of the associated binary-encoding thumb-switch units 175a-176a, 175b-176b ...175g-176g, 175h-176h, as the case may be. The re-maining contact of each decade step switch is connected directly to the sweep arm of the next-succeeding higher-order step switch, as by line 174h connecting this single contact of the "units" step switch 170h to the sweep arm of the "tens" step switch 170g; similar connections 174g and 174b are shown for higher-order code-wheel-advance controls applicable to the "tens"
switch 170g and to the 107 switch 170a, respectively.
The following table is in two parts, respectively indicating oper-ational sequences in the indicated Modulus-97 system, first involving 34-position advances of coded-wheel 84 just prior to and following the 54-posi-tion advance which accompanies the serial-number advance from 00000999 to 00001000, and then involving the 34-position advances which precede and follow the 87-positioll advance which accompanies the serial-number advance from 00999999 to 01000000, it being noted that the respective 34, 54 and 87-position advances in these illustrations correspond to the serial-number digit positions for which precisely these check-digit incremental advances were required by thumb-wheel settings indicated at 60'. In every case, it will be understood that the check-digit print wheels 45A and 45B will have beell set in such interlace with each print-hammer cycle as to correctly impress the applicable two-digit check-digit along-side the currently ap-plicablc serial number which is concurrently impressed on a document.

Setting of Check-Digit Digit Position Serial Print Wheels Check-Digit Involving Single-Number 45A-45B Increment _ Digit Change 34 units 34 units 34 units 34 units 0l000000 30 34 units 34 units EXAMPLE FOR TWO-DIGIT WEIGHTED MODULUS-ll APPLICAIIONS
It will be seen that Modulus-ll systems may be employed in appar-atus as described in connection with Figures 9 and 10, merely (a) by substi-tuting an appropriately coded "ll-position" wheel for the "97-position"
wheel 84 and ~b) by setting the two-digit thumb wheel settings at 60' as appropriate for the particular positional weighting employed.

Y~L~

Thus, for the first above-described Modulus-ll weighting wherein check-digit decrements have the following relatlon to positional weighting:
Digit 107 1o6 105 104 103 1o2 lol units Positional Weighting: 3 2 7 6 5 4 3 2 Check-Digit Decrements: -6 -1 -3 -1 -1 -3 -7 -2 the necessary thumb-wheel settings at 60' need only be made in the "units"
settings, the "tens" settings thereof being set to zero. The resultant printing of check digits by wheels 45A and 45B will involve almost exclus-ive use of the "units" wheel 45B, the "tens" wheel 45A being set at zero at all times except when it becomes set to "1", meaning "10" in order to be able to print this eleventh number (in place of "VOID" in the earlier de-scribed embodiment), it being understood that the printed number "10" is eleventh in the succession 00, 01, 02 ...10.
It will also be understood that with the same "ll-position" coded-wheel replacement for the "97-position" wheel 84, and by setting "units"
thumb wheels at 60' in accordance with the geometrically weighted Modulus-ll system described above, the corresponding two-digit check-digit printing re-sult will be obtained, i.e., with a "10" print-out in place of the previous-ly described "VOID" print-out. To produce this result, the relation of po-sitional weighting to check-digit decrement settings at 60' will be:
Digit 107 1o6 105 104 103 1o2 lol units Positional 8 7 6 5 4 3 2 Weighting: 2 2 2 2 2 2 2 2 Check-Digit Decrement Setting:-05 -06 -01 -04 -00 -09 -08 -02 The preceding discussion makes apparent that the instant invention n~ot only provides a novel means for printing an automatic indication of the validity or invalidity of a serial number printed with a single check-digit print ~heel in a conseclltive series, but the inve!ntion also lends itself to use of multiple-digit moduli, with multiple-digit check-digit printing; and by simple modification, the invention may utilize a number of different weighted moduli. Furtllermore, the invention requires no computer processing to achieve the printed check-digit. Instead, the invention achieves the computation and printing of the check-digit by electromechanical means. The invention thus provides a novel approach to solving the problem of printing serially coded documents having a high assurance of accuracy.
While the invention has been described in detail for preferred em-bodiments, it will be understood that modifications may be made without de-parting from the scope of the invention. For example, it will be appreciat-ed the modulus-related coded wheel 84 (i.e., "97-position", in the case of Modulus 97) is but one form of cyclical-storage means for which the current-ly indexed condition is usefully available as a digital output, herein de-scribed as a first or "tens" BCD output and a second or "units" BCD output.
Thus, coded wheel 84 and its drive means 13' are effectively, if not the functional equivalent of, a ring counter having a modulus-related number of counting elements per ring cycle. In the fragmentary diagram of Figure 11, we schematically show substitution of a completely electronic ring-counter 184 for the more mechanical ring counter represented by coded wheel 84.
More particularly, the ring counter 184 in Figure 11 illustrative-ly serves a Modulus-97 system and may therefore comprise a continuously and sequentially operative "ring" of ninety-seven flip-flop elements, connected for sequential change of state for each index-count pulse or pulse group issued by the index-control signal generator 62'. The ring counter 184 will also be understood to include a digital output indicative of the currently indexed flip-flop element from among the ninety-seven. Such digital output is schematically shown as a "Tens" BCD output 193 supplied to the "Tens"
comparator 87 and as a "Units" BCD output 194 supplied to the "Units" com-parator 88. The drivers 85-86 then function in response to the respective 3.~3 comparator-derived signals to reposition one or both of the check-digit print wheels 45A-45B in interlace with print-hammer action, in the manner described for operation of Figure 9. Of course, in application to other moduli, the number of flip-flops per ring at 184 will be understood to cor-respond to the particular modulus number, with a plurality of orders of BCD
output appropriate to the size of the modulus selected; in Figure 11, a man-ual knob 184', which may be inscribed with a pointer which is readable against a fixed scale, wil] be understood to suggest switch means whereby the size of the ring (e.g., number of flip-flops currently used in the cycle of the ring) may be selectively varied, to reflect selection of different moduli.

Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a document printer with means for feeding successive docu-ments to be successively serial-number printed in successive printing cy-cles, said printer including a sequentially indexible numerical print head and means synchronized with the printing cycle for numerically indexing said head in predetermined equal successive increments from one to the next printing cycle, the improvement which comprises indexible decimal check-digit print means carried by said printer and including means synchronized with said printing cycle for check-digit imprinting of each successive doc-ument in accordance with the indexed position of said check-digit print means, and further means synchronized with said printing cycle for changing the indexed position of said check-digit print means in accordance with each successive index increment required by a particular weighted-modulus system of computing check-digits, said further means including decimal-indexing drive means for said check-digit printing means, an indexible cyclic storage device having a number of discrete storage units per cycle corresponding to the particular modulus number involved, said storage device producing an out-put reflecting the currently indexed storage condition thereof, a plurality of control devices having control connection to said storage device and set-table uniquely for each digit position within the serial-number capacity of said print head, said control devices being preset to determine different unit-indexing control of said storage device in accordance with the require-ments of the particular weighted-modulus system, means responsive to the instantaneous serial-number setting of said print head and determining which digit position of the serial number undergoes a single-digit change other than to zero for each successive printing cycle, said last-defined means producing for each printing cycle an output connection to that particular control device which is uniquely set for the particular digit position under-going the single-digit change other than to zero, and a control connection from said storage device to said decimal-indexing drive means, whereby said check-digit printing means may be reset in synchronism with said printing cycle for check-digit printing in accordance with the currently indexed con-dition of said storage device.

2. The improvement of claim 1, in which said check-digit print means comprises a plurality of different-order independently indexible ten-position print wheels each of which is characterized by different indicia within a decade of printing indicia, said decimal-indexing drive means pro-viding independent decimal-indexing drive of the respective print wheels, as appropriate for the digit position at which each of said wheels is to print for a given required check digit.

3. The improvement of claim 2, in which said plurality is two.

4. The improvement of claim 3, in which said control connection in-cludes a "units" BCD output connection from said storage device to one of said decimal-indexing drives for "units"-indexed positioning of one of said print wheels, and a "tens" BCD output connection from said storage device to the other of said decimal-indexing drives for "tens"-indexed positioning of the other of said print wheels.

5. The improvement of claim 1, in which said storage device com-prises indexible wheel means having a number of discrete indexible positions which corresponds to the particular modulus number involved, wheel-index drive means for positioning said wheel means, said control devices having control connection to said wheel-index drive means.

6. The improvement of claim 5, in which said wheel means is in-scribed with circumferentially distributed index-position digital indicia, said control connection including stationary digital read-out means posi-tioned to sense the digital indicium for a currently indexed position of said wheel means.

7. The improvement of claim 6, in which said circumferentially dis-tributed index-position indicia include a first circumferentially distribut-ed set of decimal "units" divided BCD indicia, and a second circumferential-ly distributed set of decimal "tens"-divided BCD indicia.

8. The improvement of claim 1, in which said storage device is a ring counter having a number of discrete counting elements per ring cycle corresponding to the particular modulus involved.

9. The improvement of claim 1, in which said ring counter includes selectively operable means for changing the number of said counting elements per ring cycle, whereby a modulus-number change may be selected.

10. The improvement of claim 2, in which said print wheels are so oriented with respect to said indexible numerical print head as to enable two-digit check-digit printing adjacent to and in alignment with serial-num-ber printing.

11. As an article of manufacture, a print-head unit including a frame with means for removably mounting the same to a document-printing ma-chine having continuously operating means for repeating a printing operation thereof once per print cycle, multiple-digit consecutive-numbering means com-prising a nested plurality of print wheels journaled on a common axis in said frame, there being one print wheel for each digit position of numbers to be consecutively printed, actuating means adapted for synchronizing con-nection to a print-cycle operative part of the document-printing machine for imparting a one-digit indexing advance to the next-higher-order one of said print wheels upon making the last indexing advance per revolution of said each print wheel, check-digit print-wheel means journaled on said common axis and comprising a nested plurality of check-digit print wheels journaled for independent rotation on said common axis, each of said check-digit print wheels having ten equally spaced index positions about said common axis and including consecutively numbered single-digit printing means at the respective index positions thereof, and independent drive means associ-ated with each of said check-digit print wheels for imparting periodic in-dexing drives thereto in increments which are integer multiples of one tenth of a revolution of each of the respective check-digit print wheels.

12. The article of claim 11, in which said plurality of check-digit print wheels is two.

13. The article of claim 11, in which each of said drive means in-cludes an indicator of the currently indexed position of its associated check-digit print wheel.

14. The article of claim 13, in which said indicator is BCD-coded for the respective applicable index positions.