GB2287223A - Fraud-resistant print-wheel setting mechanisms for postage meters. - Google Patents

Abstract

In a print-wheel setting mechanism of the kind in which a reciprocable toothed driving member [e.g. a rack (14)] drives a print-wheel driving pinion (10), an endmost tooth (16') of one component is of reduced height and meshes with a complementary root (12') of reduced depth on the other component. If a fraud (of the kind in which the mesh of the drive component and pinion is displaced by one or more teeth) is attempted, the mismesh of a full sized tooth with the undersized root will prevent the driving component from being set back to the zero position during intitialisation (i.e. prior to a value setting operation) thereby rendering proper operation impossible. The apparatus may be rendered wholly inoperable by the resulting jam. <IMAGE>

Description

A Drive Gear for an Adiustable Printwheel; and a Printwheel Selection Mechanism and a Franking Machine Incorporating such a Drive Gear This invention relates to a drive gear for an adjustable printwheel in e.g. value printing apparatus such as a postage meter.

Postage meters incorporate printwheel or value selection mechanisms whereby the printwheels of the machine may be incremented to present a desired part of the printwheel to a mail piece for frankic a postage value thereon.

U.S. Patent No. 4,050, 374, entitled Meter Setting Mechanism, discloses a mechanism for selecting postage values which are to be printed by a rotary postage meter. The drive shaft of the drum includes a plurality of selectable racks, each of which is slidably movable in engagement with a different pinion gear, connected to an associated printwheel within the drum, for selectively rotating the printwheel to dispose a printing element or font thereof at the outer periphery of the drum for printing purposes. The value selection mechanism includes a first stepper motor which is operable for actuating the selected rack for selectively rotating the desired printing element of its associated printwheel to the printing position thereof. An electronic control system, which is coupled to a keyboard, serves for processing postage value entries made by an operator, and selectively drives the respective stepper motors in response to keyboard entries.

Value selection mechanisms of the aforesaid types have from time to time become physically damaged such that one or more rack gears have become dissociated from a printwheel drive gear engaged therewith. When this happens the printwheels may be rotated independently of the drive gear, whereupon a postage value can be printed which is different from that which has been selected by roans of the associated rack gear.

Although the occurrence of such physical damage is usually apparent to a postage meter user, some users continue to use their meters despite such a malfunction condition in order fraudulently to print postage values without payment therefor. Since postage meters are required to be physically inspected on a semi-annual basis, and more frequently when the Postal Service inspectors, through internal postage indicia inspection controls and accounting practices, suspect that a postage meter is dispensing more postage than has currently been paid for, such physical damage is inevitably discovered promptly. Nevertheless, any postage payment losses are rightfully of great concern to Postal Services and to postage meter manufacturers. As a result, a series of experimental activities with postage meters has been conducted to determine the basic cause, if any, of dissociation of postage selecting racks and printwheels.

It has been experimentally determined that most instances in which such dissociations occur arise from force being exerted against the print wheel to separate the same from the drive train therefor.

According to the invention in a first aspect, there is provided a drive gear for an adjustable printwheel in e.g. value printing apparatus, said drive gear being engageable by a printwheel adjusting member and comprising a plurality of gear teeth spaced from one another by a corresponding plurality of root zones, the number of gear teeth corresponding to the number of operative positions of the printwheel, whereby the root zones respectively correspond to positions of the printwheel intermediate its operative positions, wherein one of the root zones is at least partially filled in thereby to prevent or hinder engagement of said root zone by a printwheel adjusting member.

The advantage of this arrangement is that a fraudulent user of a damaged selection mechanism is prevented from printing postage values by the jamming of the selection mechanism of his meter on rotation of the printwheel.

In preferred embodiments of the invention, the filled in root zone corresponds to a position of the printwheel eg. intermediate the positions thereof for the printing of numerals 9 and 0.

Conveniently, the infill optionally includes a V-notched surface, with the angles between the faces of the notch preferably being greater than the angle between the walls of an unfilled notch, and most preferably about 120 . Alternatively, other surface designs may be employed. A particularly preferred option is a flat or plain surface of the infill.

According to a second aspect of the invention, there is provided a printwheel selection mechanism comprising a driveable shaft including drive transmission means; selection rack means operatively connected to the drive transmission means, whereby drive from the driveable shaft is transmitted as linear movement of the selection rack means; a rotatable printwheel; and a drive gear generally as specified herein operatively interconnecting the selection rack means and the printwheel, whereby linear movement of the selection rack means is transmissible as rotary movement of the printwheel, the selection rack means including a portion in driving engagement with the drive gear whereby, on engagement of said portion of the selection rack means with the filled root zone of the drive gear, the mechanism jams, slows or otherwise indicates an abnormal condition.

A printwheel selection mechanism of this kind can readily be retrofitted to a postage meter initially manufactured without any means of preventing the fraudulent printing of postage values on damaging of the selection mechanism.

According to a third aspect of the invention, there is provided a postage meter incorporating a drive gear as defined above and/or a selection mechanism as defined above.

There now follows a description of preferred embodiments of the invention, by way of example, with reference being made to the accompanying drawings in which: Figure la is a schematic representation of a drive gear according to the invention, together with associated components; Figure lb shows an alternative form of drive gear according to the invention; and Figure 2 is a schematic representation of a selection mechanism according to the invention.

Referring firstly to Figure la, there is shown a drive gear 10 according to the invention. Drive gear 10 includes a number of peripherally mounted teeth 11 separated from one another by root zones 12 in a conventional manner.

Drive gear 10 is in driving connection with e.g. a settable printwheel 13 of a postage meter. Rotation of drive gear 10 causes rotation of the printwheel to increment or decrement the postage value to be printed, by presenting selected printing elements 15 to eg. a mail piece.

In practical embodiments of the drive gear 10, there is a gear tooth and root zone pair corresponding to each value to be printed by the printwheel to which the drive pair is connected.

Most postage meter printwheels print the numerals from 0 to 9 inclusive. The associated drive gear would therefore have 10 tooth and root zone pairs. The numerals printable by the printing elements visible in Figure la are marked at the ends of the radial chain lines thereof.

The drive gear is driven by means of a printwheel rack 14 that is reciprocable longitudinally in driving engagement with the drive gear 10.

Printwheel rack 14 has at its free end a series of gear teeth 16b as shown that meshingly engage the drive gear 10.

Reciprocating longitudinal movement of the printwheel rack 14 causes reciprocating rotational movement of the drive gear 10, and hence the printwheel 13. Since in embodiments of the invention the number of tooth and root zones pairs on the drive gear corresponds to the number of different values printable by the printwheel according to a 1:1 ratio, there will be one root zone 12' of the drive gear that in normal use would never be engaged by the teeth 16 of the printwheel rack 14. In the case of a printwheel intended to print numerical postage value numerals from O to 9 inclusive, the root zone 12' that is never ordinarily engaged by the teeth 16 is the one that corresponds to positioning of the printwheel to present the zone intermediate the numerals "9" and "0". (This position is never normally adopted by the printwheel, since it is never required to drive the printwheel beyond the position for printing the numeral 9 in one direction, and beyond the position for printing the numeral 0 in the other direction. It is established practice in the postage meter art to decrement the printwheel from, e.g. a high number such as 9 towards a low number such as O by virtue of the reciprocatory motion of the printwheel and not to allow the printwheel to increment beyond 9 to reach the low numbered numerals. One reason for this is that the rack gear constituted by teeth 16 can as a result be kept to a reasonable length. The printwheel 13 of Figure la is positioned to print the numeral "O". To print the numeral "9", the printwheel 13 must be rotated clockwise to present the printing element "9" in the top dead centre position. This is achieved by moving printwheel rack 14 in the direction indicated by arrow A.) AM shown in Figure la, the root zone 12' has formed therein a solid infill 17 that occupies the bulk of the space of the root zone 12'.

Infill 17 of Figure la has a flat surface. Infill 17 as shown in the alternative drive gear of Figure lb has a surface consisting of two faces inclined towards one another to meet at a central gulley 17', in other words infill 17 has a V-notched surface in Figure lb. The angle a between the inclined faces of the infill 17 is in the embodiment of Figure lb approximately 1200, although other angles can be used.

The infill 17 may alternatively have a surface which is a shallow curve. The use of a flat, planar surface as shown in Figure la is preferred in low-cost embodiments of the invention, since it is simple to manufacture within acceptable dimensional tolerances. In the embodiment of Figure la, the endmost tooth 16' of rack 14 is flattened to allow for its possible engagement with root zone 12'.

If force is applied to the printwheel in an attempt to dissociate the printwheel from the set position of the printwheel rack 14 (in the manner indicated as aforesaid) the drive gear 10 will be rotationally shifted relative to the teeth 16 of the printwheel rack 14. Once such shifting has occurred, it is inevitable that during subsequent movement of the rack 14, at least one of the conventional teeth 16 will at some point in the travel of the rack 14 engage the root zone 12'. When this occurs, the operation of the selection mechanism is severely hampered, to the extent that the mechanism almost certainly will jam completely, most probably with the printwheel in a position where no imprinting members are presented for franking of mail. Even if the mechanism does not jam, such other malfunction will occur as to render the mechanism subsequently inoperative. For instance, the teeth 16 may break or deform, or the rack 14 may deform. Combinations of such failures may occur. Thus, a drive gear according to the invention automatically prevents fraudulent operation of the selection mechanism in the manner previously described.

It is common in printwheel selection mechanisms to incorporate a spring loaded detent such as detent 18 in Figure 1. Detent 18 is a lever arm pivotably attached to the chassis of the postage meter, and biassed into engagement with the drive gear 10 by means of a suitable spring. The detent 18 operates as a pawl to limit rotation of the drive gear 10 to provide incremental movement thereof and hence of the printwheel 13.

Hitherto, the head 20 of the detent 18 has been manufactured with a profile approximately complementary to the root zones 12, so that detent 18 can firmly engage with the root zones. However, it will be appreciated that during normal operation of the drive gear 10 the root zone 12' will from time to time be engaged by the head 20 of detent 18. Therefore, the inclinedly abutting faces 20a, 20b of the head 20 are inclined to one another at an angle B e.g. approximately 1200. It has been found that a head 20 of this profile will satisfactorily engage all of the root zones 12, 12' of the drive gear 10 whilst still providing an adequate pawl function.

When the infill 17 includes the gulley 17' as shown in Figure lb, the angle a between the inclined surfaces of the infill 17 and the angle B are chosen to be approximately equal, to avoid jamming of the head 20 in the infill 17.

Other head profiles may be employed if desired, or a different pawl mechanism entirely may be used without necessarily affecting the usefulness of the invention.

Referring to Figure 2, there is shown in a simplified form a selection mechanism incorporating a printwheel drive gear 10 according to the invention.

Printwheel rack 14 is driven by a selection rack 22 drivingly engaged therewith. The end of selection rack 22 remote from printwheel rack 14 includes rack teeth 23 in driven engagement with a drive pinion 24 rigidly secured on a postage meter drive shaft 25.

Drive shaft 25 also carries a rotatable encoder disk 26 and a sensor such as an optical sensor 28, whereby the setting of the printwheel can be determined and output to a display forming part of the postage meter.

The travel of printwheel rack 14 is limited by a pair of abutments shown schematically by reference numerals 29 and 30. (Abutments 29 and 30 limit the travel of the selection rack 22, which in turn limits movement of the printwheel rack 14.) The abutment 29 prevents excessive travel of the rack 22 such that drive gear 10 becomes disengaged from the free end of rack 14. (If this occurs, the printwheel would be freely rotatable relative to the rack.) The abutment 30 prevents excessive travel of the rack 22 towards a position thereof in which the printwheel drive gear 10 attempts to engage a portion of rack 14 having no teeth. (Such engagement would cause jamming of the selection mechanism.) Additionally, the abutments 29 and 30 define "home" positions of the rack 22 in embodiments employing relative (as opposed to absolute) rack positior sensing. (Such sensing is achieved via the encoder 26 and sensor 28.) Probably the most common method employed by those wishing to frank mail fraudulently is to apply force directly to the printwheel 13, eg. by striking an implement that is in contact with the periphery of the printwheel. If the rack 22 is intermediate the abutments 29 and 30, quite possibly the application of such force will not result in dissociation of the printwheel drive gear 10 from the engaged rack tooth/root, since the selection mechanism will simply be moved against the resistance of the drive train.

However, if the rack 22 abuts one of the abutments, or if the drive train has become stiff, the application of force to the printwheel 13 as aforesaid would result in fraudulent dissociation.

Some would-be fraudsters attempt carefully to apply force and dissociate the printwheel from the rack setting by one numeral only, thereby permitting the fraudulent printing of the majority of the numerals between eg. 0 and 9 (ie. those numerals that remain "associated").

The provision of the abutment 29 tends to limit the number of positions of the printwheel 13 in which force may successfully be applied without breaking the entire drive train. By judicious positioning of the abutment 29 and/or the infill 17, it is possible to allow "successful" dissociation of the printwheel from the rack only to permit a lower postage value than that set to be franked. Since a postage meter user pays for postage according to the set value to be franked, such a situation clearly is of no benefit to the would-be fraudster.

The drive gear of the invention may additionally be employed in numerous applications unrelated to the postage meter art. For instance, the drive gear could be employed in ticket printing machinery and machinery adapted for the validation of documents, certificates, cheques and similar items.

Claims (14)

1. A drive gear for an adjustable printwheel in e.g. value printing apparatus, said drive gear being engageable by a printwheel adjusting member and comprising a plurality of gear teeth spaced from one another by a corresponding plurality of root zones, the number of gear teeth corresponding to the number of operative positions of the printwheel, whereby the root zones respectively correspond to positions of the printwheel intermediate its operative positions, wherein one of the root zones is at least partially filled in thereby to prevent or hinder engagement of said root zone by a printwheel adjusting member.

2. A drive gear according to Claim 1 suitable for driving a printwheel adapted to print the numerals from 0 to 9 inclusive, wherein said filled in root zone corresponds to a position of the printwheel intermediate the positions thereof for printing of the numerals 9 and 0.

3. A drive gear according to Claim 1 or Claim 2 wherein said root zone is filled in by means of an infill having a flat surface.

4. A drive gear according to Claim 1 or Claim 2 wherein said root zone is filled in by means of an infill having a V-notched surface.

5. A drive gear according to Claim 4, wherein the angle between the faces of the V-notch is greater than the angle between the walls of the unfilled root zones.

6. A drive gear according to Claim 5 wherein the angle between the faces of the V-notch is approximately 120O.

7. A printwheel selection mechanism comprising: a driveable shaft including drive transmission means; selection rack means operatively connected to the drive transmission means, whereby drive from the driveable shaft is transmissible as linear movement of the selection rack means; a rotatable printwheel; and a drive gear according to any preceding claim operatively interconnecting the selection rack means and the printwheel, whereby linear movement of the selection rack means is transmissible as rotary movement of the printwheel, the selection rack means including a portion in driving engagement with the drive gear whereby, on engagement of said portion of the selection rack means with the filled root zone of the drive gear, the mechanism jams, slows or otherwise indicates an abnormal condition.

8. A selection mechanism according to Claim 7, including position detecting means operable to detect the position of the driveable shaft.

9. A selection mechanism according to Claim 7 or Claim 8 including a resiliently biassed detent means adapted for engagement in the respective root zones, the arrangement being such that the detent means is engageable to a generally equal extent with the filled root zone as with the unfilled root zones.

10. A selection mechanism according to Claim 9, wherein the detent means includes a root engaging surface having two faces inclined to one another at an angle of approximately 1200.

11. A selection mechanism according to any of Claims 7 to 10, including an abutment for limiting the travel in the mechanism.

12. A drive gear generally as herein described, with reference to or as illustrated in the accompanying drawings.

13. A printwheel selection mechanism generally as herein described, with reference to or as illustrated in the accompanying drawings.

14. A postage meter incorporating a drive gear according to any of Claims 1 to 6 and/or a selection mechanism according to any of Claims 7 to 11.