Multiple bit matrix configuration for key-latched printheads

Abstract

A mechanical key scheme is integrated into a composite pattern on both a print cartridge and its corresponding printer carriage chute. In a preferred embodiment the pattern incorporates a plurality of adjacent contiguous columns on both sides of a latch, with each column capable of defining multiple position bits in order to precisely differentiate between different types and/or different families of print cartridges.

Description

BACKGROUND OF THE INVENTION

[0002] This invention relates generally to print cartridges mountable on printer carriages, and more specifically to mechanical techniques for preventing inkjet print cartridges from being used with non-compatible printers.

[0003] The ability to ship and store print cartridges prior to installation on a printer has many benefits to the manufacturer, distributor and user. Similarly the life of a printer can be extended by providing removable print cartridges as well as replaceable print cartridges. However, the proliferation of such removable and replaceable print cartridges has created many problems arising from inadvertent use of similar appearing print cartridges in non-compatible printer carriages.

[0004] Moreover the use of different types of inks, print media, and product implementations (facsimile machines, monochrome printers, color printers, copiers, multiple-function printers/fax/copiers, single chute carriages for holding different types of print cartridges, multiple chute carriages, cartridges capable of carriage refill, cartridges capable of periodic on-carriage ink replenishment, continuous on-carriage ink replenishment systems) has created the need to differentiate between similar appearing print cartridges which have different intended uses.

[0005] The problems of maintenance and warranty have also become aggravated when similar appearing print cartridges have been customized under joint development agreements for different end use implementations, some of which require mounting on standard carriages which move across a print zone while others are mounted alone or in groups on stationary carriages. Value added resellers want assurances that general use print cartridges outside of their control cannot be inadvertently used in their customized printing systems. In order to be able to provide some guarantee of quality, availability, warranty, maintenance and support, there is a growing need to uniquely identify print cartridges as well as to uniquely identify printer carriages and individual carriage chutes in a simple mechanical way. Electronic identification systems tend to be more expensive and are sometimes less reliable than mechanical encoding systems.

[0006] Conventional label identification systems are extensively used but are often ignored by users and distributors, and even high visibility color coding of print cartridges has not provided satisfactory results.

[0007] A prior mechanical technique is described in U.S. Pat. No. 5,519,422 entitled METHOD AND DEVICE FOR PREVENTING UNINTENDED USE OF PRINT CARTRIDGES wherein a first level tab system controls initial insertion of a print cartridge, and a second level barrier system controls a final mounting step into a printer carriage. The implementation required different customized mechanical parts on two separate portions of the print cartridge as well as two corresponding separate portions of a carriage chute. Also there was a risk of tampering with the first level tabs by breaking them off in order to alter the ID system.

[0008] Another prior mechanical technique has been employed by Lexmark which uses a rudimentary dual system where a large upstanding cap extending about one and one/half centimeters above the print cartridge has a central convex protrusion for one group of cartridges used in Xerox and Compaq printers and a central concave recess for another group of cartridges used in Lexmark printers. A second level of identification is provided with a pair of equally spaced apart narrow slots on the Xerox and Compaq print cartridges which are respectively located at different lateral positions relative to the central convex protrusion. Very few combinations are possible with this system, and it requires excessive space on both the print cartridge and the carriage.

BRIEF SUMMARY OF THE INVENTION

[0009] The present invention provides many combinations of ID for print cartridges and corresponding printer carriages and individual carriage chutes. A low profile pattern of columns which form a multiple bit matrix configuration is provided on a print cartridge and on its corresponding carriage. The columns are positioned to be contiguous for efficient use of space, and are capable of different lengths as measured from a default position.

[0010] One embodiment incorporates separate blocks to define each bit position on a column, while another preferred embodiment provides a continuous contoured edge which moves back and forth depending on the matrix code which identifies a particular family of print cartridges (or carriages) as well as individual print cartridges (or carriages) within each family.

[0011] Universal compatibility, family subset compatibility as well as unique one to one compatibility are possible with this multi-bit matrix scheme. The number of combinations can be expanded by either increasing the number of columns and/or by increasing the number of bit positions on a column. In a preferred form of the invention, the corresponding columns achieve complete matchup when the forward boundary of a print cartridge key matrix fits together with the forward boundary of a carriage key matrix.

[0012] Compatibility is achieved by limiting the total combined length of one or more particular columns in the carriage and print cartridge key matrices, while lockout is achieved by increasing the total combined length of one or more particular columns in the carriage and print cartridge key matrices. Thus the rationale for achieving various different combinations which allow successful mounting of a print cartridge depends on controlling the pattern of the forward boundary of a key matrix as well as controlling the combined lengths of aligned columns in the carriage and print cartridge matrices.

[0013] Unique differentiation between print cartridges is accomplished by having at least one column in a key matrix of a first print cartridge longer than a corresponding column in a key matrix of a second print cartridge.

[0014] While the possible number of columns and column lengths (multiple position bits) in theory is endless, implementations in various embodiments of the invention include a five column three bit key matrix, an eight column three bit key matrix separated in the middle by a latch to provide a par of four column three bit key matrices, and a six column four bit key matrix.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a perspective view of a single chute carriage in a printer incorporating the invention, with a print cartridge mounted therein;

[0016] FIG. 2 shows a double chute carriage in the printer of FIG. 1, with two print cartridges mounted therein;

[0017] FIG. 3A is a perspective view of a print cartridge having a five column implementation of the invention using a key matrix formed with two rows of separate spaced-apart blocks;

[0018] FIG. 3B is a top view schematic showing the five column implementation of FIG. 3A using two rows of separate contiguous blocks;

[0019] FIG. 4 is a side view schematic showing the print cartridge of FIG. 3A with a biasing carriage spring engaging a print cartridge latch;

[0020] FIG. 5 is a perspective view of the print cartridge of FIG. 3A mounted on a single chute carriage having a matching carriage key matrix formed with an exposed integral five column plate, without showing the biasing carriage spring;

[0021] FIG. 6 is a fragmentary/perspective view of an empty single chute carriage having a covered carriage key matrix, and showing the biasing carriage spring;

[0022] FIG. 7 is a bottom view of the empty single chute of FIG. 6;

[0023] FIG. 8 is a perspective view of a print cartridge having an eight column implementation of the invention using a low profile key matrix formed on both sides of a print cartridge latch;

[0024] FIG. 9 is a top plan view of the print cartridge of FIG. 8;

[0025] FIGS. 10A and 10B are schematic views looking up at two integral four column plates which together form a covered carriage key matrix having predetermined edge contours which match the low profile key matrix on the print cartridge of FIGS. 8 and 9;

[0026] FIGS. 11A-11F are schematic representations of exemplary print cartridge key patterns which respectively identify different print cartridge families;

[0027] FIGS. 12A-12F are schematic representations of exemplary print cartridge key patterns of the single print cartridge family of FIG. 11A, with each key pattern being sufficiently different to be uniquely compatible with a particular printer carriage configuration;

[0028] FIG. 13 is a schematic representation of an exemplary universal carriage key matrix capable of matchup with all print cartridge key patterns of the print cartridge family of FIGS. 12A-12F;

[0029] FIG. 14 schematically shows a four column matchup of key matrix patterns;

[0030] FIGS. 15-19 schematically show various lockout combinations of a four column key matrix pattern which occur when a print cartridge is inserted into a non-compatible printer carriage;

[0031] FIGS. 20A-20C schematically show a hybrid print cartridge key matrix capable of matchup with a subset of different carriage key patterns;

[0032] FIGS. 21A and 21B schematically show a exemplary universal key matrix for a print cartridge capable of matchup with all carriage key patterns;

[0033] FIGS. 22 schematically shows a six column matchup of key matrix patterns; and

[0034] FIGS. 23 schematically shows a possible lockout combination of the six column key matrix patterns of FIG. 22 when a print cartridge is inserted into a non-compatible printer carriage.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0035] An exemplary printing mechanism as shown in FIG. 1 includes a frame 30, support bar 32, angled guide bar 34, encoder strip 36, and carriage drive motor 38. A carriage member 40 has a cylindrical bushing 42 which rides on the support bar 32 back and forth in a carriage scan direction 44 while media is periodically advanced along a platen 46 in a media advance direction 47 through a print zone. The carriage drive motor is mounted on a back of the frame 30 and carries a drive gear 48 coupled through transfer gear 50 to belt gear 52 which engages an inside toothed surface of a carriage drive belt 54. The left end of the encoder strip is cut away to show the details of the carriage drive mechanisms.

[0036] In order to facilitate proper positioning of the carriage over the print zone, a guide bracket 56 is attached at the top rear of the carriage member 40 to slide along the angled guide bar 34. A print cartridge 60 is shown mounted on a abbreviated chute 61, and includes a housing 62, and cap member 63 having right and left protruding ribs 64 and laterally extending grooves 66 for manual gripping during installation and removal of the print cartridge from the chute. A nozzle array 67 is located on a bottom surface of the print cartridge for applying ink drops to media on the platen.

[0037] The low profile of the cap member is an important feature of the invention (see FIGS. 1 and 4), and the cap includes an upstanding central latch 68 with adjacent key-coded projections 70, 72 that extend only three mm and two mm, respectively, above a top surface of the cap member 63. Space 75 is available on the cap for display of a company trademark or logo. A metal biasing spring 76 extending from the chute presses its V-shaped end 78 downwardly against the central latch 68 and at an angle toward an electrical interconnect 80 on the chute to provide conductive contact with a print cartridge interconnect 82, without causing any interference with the key-coded projections 70, 72.

[0038] The invention is applicable to single chute carriages (FIG. 1) as well as carriages having additional chutes for holding other identical print cartridges and well as other different types of print cartridges. Traditional carriages holding four print cartridges and high performance carriages holding eight, twelve and more print cartridges can also incorporate the benefits of the invention. A presently preferred embodiment for multiple print cartridges is shown in FIG. 2 with a first tri-compartment print cartridge 60 holding cyan, magenta and yellow ink mounted in chute 61, alongside a black ink print cartridge 60a with similar external size specifications mounted in chute 61a. The key-coded projections on print cartridge 60 are different from the key-coded projections on print cartridge 60a to prevent using the print cartridges in the wrong chutes.

[0039] The print cartridge 60 includes left and right flex ribbon circuits 86, 88, and encoder flex 90, while print cartridge 60a includes similar flex components 86a, 88a, and 90a for providing communication through end terminals 92, 94, 92a, 94a which are attachable to a printed circuit board (not shown) on the printer.

[0040] One implementation of the key-coded projections on a print cartridge is shown in FIGS. 3A, 4 and 5 which show a five column two row matrix 100 extending across the entire front portion of the cap in front of the latch. While FIG. 3A shows blocks 102 spaced apart from blocks in adjacent rows and columns, a variation is shown in FIG. 3B with adjacent blocks 104 being contiguous. However the spaced apart block implementation makes it easier to create an encoded key pattern on a manufacturing line by selectively removing certain blocks without causing any damage to those blocks which remain to form the matrix pattern. When mounted in a compatible carriage chute 106 (see FIG. 5), a matching continuous edge matrix key 107 with some remaining blocks such as 108 and some blocks removed creates no lockout interference between any of the five aligned columns 110, 111, 112, 113, 114. It will be understood from FIG. 5 by those skilled in the art that all disclosures, descriptions and variations recited for key-coded patterns on a print cartridge are equally applicable to matrix patterns on a carriage chute. Conversely all disclosures, descriptions and variations recited for key-coded patterns on a carriage are equally applicable to print cartridge matrices.

[0041] FIGS. 6 and 7 show more details of a preferred embodiment of a carriage chute key-coded pattern with the print cartridge removed. The pair of continuous edge patterns 116, 118 are located under protective plates 120, 122. The datum notches 124, 126 at a lower end of the chute are provided to capture pivot legs 128, 130 on a print cartridge, and a side-biasing spring 132 helps to secure the print cartridge. It is important to note that while lockout combinations of print cartridge and carriage key matrices allow both initial engagement of the side-biasing spring 132 with a print cartridge and the capturing of pivot legs by the datum notches, it is not until the V-shaped end of the metal biasing spring reaches its closed position against the latch on the print cartridge cap that a print cartridge achieves stable completed mounting and full conductive contact of the interconnects. The encoded key patterns are located so that such closed position of the metal biasing spring is prevented by abutting contact of aligned columns of non-compatible print cartridges and carriage chutes.

[0042] FIG. 8 and 9 show a presently preferred embodiment of a cap portion of a print cartridge with finger shaped grooves 66a, and with a narrow centrally located latch having a beveled face 136 which raises the V-shaped end of the biasing spring upon initial engagement, an apex 138, and a recess 140 for receiving the V-shaped end in the absence of any lockout preventing completion of the mounting procedure. A separate key-coded projection 142 on one side of the latch has continuous edge 143 defined by four columns 144, 145, 146, 147 while another separate key-coded projection 148 on the opposite side of the latch has continuous edge 149 defined by four additional columns 150, 151, 152, 153. The different lengths of the various columns are shown in the following table:

TABLE 1
Column #	144	145	146	147	150	151	152	153
Bit Position	3rd	1st	2nd	3rd	3rd	2nd	2nd	1st

[0043] FIGS. 11A-11F show a presently preferred implementation of columns 144, 145 and 145 as shown by bracketed portion 155 for encoding different patterns of column lengths to identify each family of print cartridges. Of course the inverse bit positions for each column will provide the matching patterns, respectively, for all of the compatible printer carriages/chutes (see columns 144a, 145a and 146a in FIG. 10A). The pattern for FIG. 11B identifies the family of print cartridges shown in FIGS. 8 and 9.

[0044] FIGS. 12A-12F show a presently preferred implementation of columns 147, 150, 151, 152 and 153 as shown by bracketed portion 157 for encoding different patterns of column lengths to identify a particular print cartridge within a single family. Such different matrix patterns on print cartridges provide a unique mechanical identification for different carriage configurations. Of course the inverse bit positions for each column will again provide the matching patterns, respectively, for all of the compatible printer carriages/chutes (see columns 147a, 150a, 151a, 152a and 153a in FIGS. 10A and 10B). The pattern for 12A identifies the particular print cartridge shown in FIGS. 8 and 9.

[0045] Comparative analysis of the matrix patterns of column locations 4 to 8 in FIGS. 12A-12F illustrate the technique of having at least one column in a key matrix of a first print cartridge longer than a corresponding column in a key matrix of a second print cartridge. Thus when considering the pattern in FIG. 12A shaped to match a key pattern of Carriage I, it is noted that lockout occurs because column #8 in FIGS. 12B, 12C, 12E and 12F is longer than column #8 in FIG. 12A, and because column #6 in FIGS. 12D, 12E, and 12F is longer than column #6 in FIG. 12A.

[0046] FIG. 13 shows a pattern of completely truncated columns at 160, 161 in order to provide a universal carriage key for receiving all print cartridges of the family exemplified in FIGS. 12A-12F. A similar complete truncation of columns on a print cartridge creates a universal printhead key (see FIGS. 21A and 21B) for installation on all carriages without causing any lockout.

[0047] FIGS. 15-19 show examples of lockout when the overall length of aligned columns is three bit lengths 162 or four bit lengths 164 which both exceed the maximum of two bit lengths for matching compatibility.

[0048] FIGS. 14, 20A-20C, and 21A-21B all show examples of compatibility when the overall length of aligned columns is not more than two bit lengths 166. By completely truncating all of the columns (FIGS. 21A-21B), none of the corresponding columns on any carriage are individually long enough to cause a lockout. When columns are partially truncated (FIGS. 20A-20C), some universality is achieved where all corresponding columns on various carriages have a length of one bit or less. This provides a way to prevent lockout of certain types of print cartridges having widespread use in many different printer carriages/chutes.

[0049] Finally, it will be understood upon reference to FIGS. 22-23 that the invention is applicable to virtually all combinations of column/row sizes depending on the available space on a print cartridge. In that regard, FIGS. 22-23 show a six column/four bit matrix using separate blocks to define the columns. Where the overall length of aligned columns is not more than three bit lengths 168, then compatible matchup occurs. When the overall length of aligned columns is four bit lengths 170, then lockout occurs since the maximum of three bit lengths has been exceeded.

[0050] There are other ways to define column lengths in order to implement the present invention. For example a first bit position could be a slot, a second bit position a flat, and a third bit position a nub. If there is a need for more easily configured keys, a tab break-off design or machinable tab could be used such that a first bit position is “no tabs”, a second bit position is “one tab” (or ½ height tab), and a third bit position is “two tabs” (or full height tab).

[0051] The following table shows how the combination that yields the maximum number of unique keys is selected for a five position three bit embodiment.

	TABLE II
	Number of Knubs (x)
	0	1	2	3	4	5
Total	Number	Number of		Number of Key
Number of	of	Slot Con-	Remaining	Configurations with
Positions	Slots	figurations	Positions	Slots & Knubs
(n)	(r)	(nCr)	(p)	(nCr × pCx)
5	0	1	5	1	5	10	10	5	1
	1	5	4	5	20	30	20	5	—
	2	10	3	10	30	30	10	—	—
	3	10	2	10	20	10	—	—	—
	4	5	1	5	5	—	—	—	—
	5	1	0	1	—	—	—	—	—

[0052] As shown in Table II a scheme of “two nubs/two slots/one flat” or “two nub/one slot/two flats” or “one nub/two slots/two flats” each yield 30 unique combination. Even though it appears that adding these combination will increase the total number of configurations, some of them do not create the desired uniqueness required for lockout.

[0053] Therefore although adding together the combinations of slot configurations will give us the theoretical maximum, the keys without the nubs will fit in the carriage designed to accept the keys with the nubs, hence making them unusable as unique keys.

[0054] It is to be understood that the specific embodiments disclosed are by way of example only, and those skilled in the art will appreciate that various changes, improvements and modifications can be made to the examples given without departing from the spirit and scope of the invention as set forth in the following claims.

Claims

1. An inkjet print cartridge which is mountable on a printer carriage, comprising: a housing; a printhead on said housing; an ink reservoir in said housing and in communication with said printhead; an electrical interconnect on said housing and coupled to said printhead for activating said printhead to eject ink; a latching component on said housing for holding the print cartridge in a fully mounted position such that said electrical interconnect is in conductive engagement with a carriage interconnect; and a mechanical key on said housing formed into a predetermined pattern having a plurality of columns with each column capable of defining one or more multiple bit positions such that at least one of said columns acts as a barrier preventing the print cartridge from staying in the fully mounted position in certain non-compatible printer carriages.

2. The print cartridge of claim 1 wherein said mechanical key includes a predetermined pattern having at least one column capable of defining at least three different bit positions.

3. The print cartridge of claim 1 wherein said mechanical key includes a predetermined pattern having a plurality of columns with each column capable of determining at least three different bit positions.

4. The print cartridge of claim 3 wherein said plurality of columns includes three or more columns.

5. The print cartridge of claim 3 wherein said plurality of columns includes four or more columns.

6. The print cartridge of claim 1 wherein said latching component and said mechanical key are located on a same outer wall of said housing.

7. The print cartridge of claim 6 wherein said outer wall is a cap member forming a top wall of said housing.

8. The print cartridge of claim 1 wherein said mechanical key is formed into a predetermined pattern defined by upstanding blocks which form said plurality of columns, with each block representing one bit of said multiple bit position.

9. The print cartridge of claim 8 wherein said blocks are spaced apart from blocks in adjacent columns.

10. The print cartridge of claim 8 wherein said blocks are spaced apart from blocks in the same column representing an adjacent bit of said multiple bit position.

11. The print cartridge of claim 1 wherein said plurality of columns respectively include fixed ends at a default position and variable ends, and wherein said mechanical key is formed in a predetermined pattern defined by a boundary line along said variable ends.

12. The print cartridge of claim 11 wherein said boundary line is formed by a continuous raised edge.

13. An inkjet print cartridge which is mountable on a printer carriage having one or more chutes for holding the cartridge, comprising: a housing with an ink reservoir therein, and having an outer surface; a nozzle member on said outer surface and in communication with said ink reservoir and having an array of nozzles to eject ink; an electrical interconnect on said housing for selectively activating said array of nozzles; a location datum on said housing for engaging a chute on a printer carriage when the print cartridge is mounted in a printing position on the printer carriage; a latching component on said outer surface of said housing for receiving a biasing member on the printer carriage when the print cartridge is mounted in the printing position on the printer carriage; and a mechanical key on said outer surface of said housing and formed by a predetermined pattern of multiple columns having forward ends which define a boundary, said boundary having a variable position depending a length of each of said multiple columns as measured from a default end of said columns.

14. The print cartridge of claim 13 wherein said mechanical key includes a predetermined pattern which is formed by a matrix of three or more columns each having at least three different bit positions which define a length of the column.

15. The print cartridge of claim 13 wherein said mechanical key includes a predetermined pattern which is formed by a matrix of multiple columns each having at least three different bit positions which define a length of the column, and wherein said pattern has a low profile extending less than five mm above said outer surface of said housing.

16. The print cartridge of claim 15 wherein said pattern has a low profile extending less than three mm above said outer surface of said housing.

17. The print cartridge of claim 13 wherein said mechanical key and said latching component are both located on a same side of said outer surface of said housing.

18. The print cartridge of claim 13 wherein at least one of said columns acts as a barrier preventing the print cartridge from being mounted in said printing position in a non-compatible chute of a printer carriage.

19. The print cartridge of claim 13 wherein at least two of said columns act as a barrier preventing the print cartridge from being mounted in said printing position in a non-compatible chute of a printer carriage.

20. The print cartridge of claim 13 which includes a supply of liquid ink in said ink reservoir.

21. A method of encoding a mechanical key latch on different types of inkjet print cartridges intended for installation in a secure operating mode on various printing devices, comprising: creating a print cartridge key matrix on a plurality of print cartridges by forming a first plurality of columns on each print cartridge, with the columns each having a first range of different lengths; creating on a printer carriage a related carriage key matrix associated with one or more of the print cartridge key matrices, with the related carriage key matrix forming another plurality of columns each also having the same first range of different lengths; and differentiating between different print cartridges by having at least one of the plurality of columns in one print cartridge longer than a corresponding column in another print cartridge.

22. The method of claim 21 wherein the first range of different lengths includes at least three different lengths.

23. The method of claim 22 wherein the plurality of columns includes at least three columns which each define multiple bit positions.

24. The method of claim 21 wherein the highest length in the first range defines a benchmark, and wherein any total length of two corresponding aligned columns on the print cartridge and the carriage, respectively, which exceeds the benchmark prevents the print cartridge from being mounted in operating mode on the printer carriage.

25. The method of claim 21 wherein the highest length in the first range defines a benchmark, and wherein a print cartridge is provided with truncated columns which are all shorter than the benchmark to enable such print cartridge to be mounted in operating mode on several different printer carriages.

26. The method of claim 21 wherein at least four different columns are provided for both the print cartridges and the carriages, which columns each have at least four multiple bit positions.

27. The method of claim 21 wherein a first portion of the columns define a pattern which identifies one family of a plurality of different print cartridge families.

28. The method of claim 27 wherein a second different portion of the columns define a pattern which identifies a type of printer which is compatible with a particular print cartridge in the one family.

29. The method of claim 21 wherein the highest length in the first range defines a benchmark, and wherein a carriage is provided with truncated columns which are all shorter than the benchmark to enable such carriage to receive several different types of print cartridges mounted in operating mode on such carriage.

30. The method of claim 21 which includes providing two or more chutes on the printer carriage, each chute having its own carriage key matrix for allowing secure installation of certain print cartridges while preventing secure installation of other non-compatible print cartridges.

31. A carriage assembly for holding one or more inkjet print cartridges mounted thereon, comprising: a frame; a support member on said frame; a chute carried on said support member for holding the one or more print cartridges; an electrical interconnect on said chute for coupling to said one or more print cartridges in order to selectively activate said print cartridges to eject ink; a biasing member on said chute for holding said one or more print cartridges in a secure mounted printing position; and a mechanical key on said chute formed into a predetermined pattern having a plurality of columns with each column capable of defining one or more multiple bit positions such that at least one of said columns acts as a barrier preventing a non-compatible print cartridge from staying in the secure mounted printing position.

31. The carriage assembly of claim 30 which includes at least two chutes for respectively holding two print cartridges.

32. The carriage assembly of claim 31 wherein said mechanical key includes a predetermined pattern having at least one column capable of defining at least three different bit positions.

33. The carriage assembly of claim 31 wherein said mechanical key includes a predetermined pattern having a plurality of columns with each column capable of defining at least three different bit positions.

34. The carriage assembly of claim 31 wherein said plurality of columns includes three or more columns.

35. The carriage assembly of claim 31 wherein said plurality of columns includes four or more columns.

36. The carriage assembly of claim 31 wherein said plurality of columns respectively include fixed ends at a default position and variable ends, and wherein said mechanical key is formed in a predetermined pattern defined by a boundary line along said variable ends.

37. The carriage assembly of claim 36 wherein said boundary line is formed by a continuous raised edge.

38. The carriage assembly of claim 31 wherein at least one of said columns acts as a barrier preventing the print cartridge from being mounted in said printing position in a non-compatible chute of a printer carriage.

39. The print assembly of claim 31 wherein at least two of said columns act as a barrier preventing the print cartridge from being mounted in said printing position in a non-compatible chute of a printer carriage.

40. The carriage assembly of claim 31 which includes at least two chutes for respectively holding at least two print cartridges.

41. The carriage assembly of claim 31 wherein said mechanical key on said chute is covered by a protective plate to facilitate proper alignment between columns of the print cartridge and the carriage.

42. The carriage assembly of claim 31 which further includes a platen for holding media passing through a print zone, and a mechanism for moving said carriage back and forth over said platen.

43. The method of claim 21 wherein a supply of liquid ink is provided to the print cartridge.