EP1145860A1 - Inkjet printhead mounting cartridge - Google Patents

Abstract

A cartridge mounting assembly is provided for an inkjet printheadof the type including an ink cartridge having a plurality of inkjet nozzles and aplurality of exposed electrical contacts for conducting control signals to thenozzles. The mounting assembly has a retainer for releasably securing the inkcartridge, a printer control circuit having a plurality of electrical contactsregistrable with the ink cartridge contacts, and a plurality of individuallycantilevered spring members for pressing the circuit contacts into conductiveengagement with the cartridge contacts. The mechanical independence of each ofthe cantilevered spring members allows them to effectively apply a conductivelyengaging force between the contacts of the control circuit and the ink cartridgeregardless of differences in thickness, planarity, or center alignment between thetwo pairs of contacts caused by manufacturing tolerances, dried ink deposits, orsmall misalignments in contact registry.

Description

• Ink jet printers have multiple electrical connection points andprovide a means whereby the user can change the replaceable ink holdingcomponent in an out of a cartridge. The cartridge in tun provides a means to alignwith the electrical connections of the ink holding component and to providecontact pressures for electrical connectivity between the contact locations of theink holding component and the "cartridge that supports and locates this inkholding component."
• This invention generally relates to cartridge-type inkjet printheadsof the type formed by the combination of an ink cartridge and a mountingassembly, and is particularly concerned with a mounting assembly whichconsistently and reliably applies a conductively engaging force between electricalcontacts on the ink cartridge and control circuitry carried within the mountingassembly.
• Cartridge-type inkjet printheads are known in the prior art. Suchprintheads are formed by the combination of an ink cartridge and mountingassembly. The ink cartridge includes a row of inkjet nozzles on its bottomsurface, and an array of electrical contact pads on this surface for conductingprinter control signals to each of the various inkjet nozzles. The mountingassemblies for such printheads are provided with a control circuit having aplurality of contact buttons registrable with the contact pads of the cartridgewhich transmit printer control signals. Such mounting assemblies further includea mechanism for detachably securing the ink cartridge within the assembly in aposition such that the electrical pads of the cartridge are in registry with thecontact buttons of the printer control circuit.
• Such cartridge-type inkjet printheads are particularly adapted foruse with document scanners which optically scan the printed information ondocuments, and convert the written information into digital form. In such anapplication, the printheads are used to print an identifying number on each of thedocuments being scanned. The printhead number allows the user of the scanner to identify the image scanned in case a rescan is necessary due to poor or missingimage information. It is important that the printhead be easily mountable on andremovable from the scanner or other device as the ink cartridge must beperiodically replaced due to exhaustion of its ink reservoir. For the same reason,the ink cartridge should be easily installable in and removable from the mountingassembly. Additionally, when the printhead is installed in the scanner, the inkjetspresent on the bottom surface of the cartridge must align properly with thedocuments fed through a paper transport device in the scanner in order to insurethat the index number printed on the documents is in a desired location. Finally,whenever a new cartridge is installed in the mounting assembly, some sort ofalignment mechanism must be present to insure registry between the contact padsand buttons. Additionally, some sort of resilient means must be provided toinsure that an electrically-conductive engagement is reliably created between thecontact pads of the ink cartridge and the contact buttons of the control circuitrypresent within the mounting assembly.
• In prior art mounting assemblies, the necessary alignment betweenthe contact pads of the ink cartridge and the contact buttons of the controlcircuitry is achieved through a plurality of assembled parts. Additionally, thepressure to form the necessary electrical engagement between these contacts isgenerated by a single compliant, elastomeric pad that has a series of projections orsprings that press the contact pads and buttons together.
• While such prior art mounting assemblies are capable ofperforming their intended functions, the inventors have observed a number ofshortcomings associated with the design of such assemblies. The multi-partaspect of such designs adds unwanted cumulative tolerances to the assembledprinthead which can provide non-optimal alignment between the cartridge contactpads and circuit buttons. Such multi-part designs are also relatively expensive tomanufacture due to the cost of fabricating the individual pieces, as well as theassembly time and labor necessary to put them together. The use of a single,elastomeric pad to generate the necessary engagement force between the contact pads and buttons creates unwanted non-uniformities in the pressures generatedbetween adjacent pairs of pads and buttons due to the fact that when any one ofthe pressure-focusing projections or nubs on the pad is above or below the planeof the others, it will experience more or less pressure, which is in turn transferredto the neighboring projections through the beam strength of the pad. The endresult is that the projections or nubs on such pads can create unequal contactpressure which in turn can interfere with the reliability of the electrical connectionmade between the contact pads and buttons of the ink cartridge and controlcircuitry, respectively. In addition to the potential for unequal pressures, thedimensional molding accuracy of such elastomeric pads is not as precise as that ofa straight injection molded plastic. When this factor is added to the placementaccuracy of aligning the pad to the support structure, the ability to apply evenpressures exactly where they are needed for good electrical contact is furtherdiminished. The end result of the cumulative tolerances necessitated by multi-partconstruction and the uneven contact pressures generated by the use ofelastomeric pads is that the engagement force necessary to conduct electricitybetween the contact pads and buttons of the ink cartridge and control circuitrymay not be reliably generated. These problems are further compounded over thelife time of the printhead, where dried ink deposits can further cause non-uniformitiesin the thicknesses and planarity of the circuit board substratessupported the contact pads of the ink cartridge, and the flexible circuit boardmaterial that carries the contact buttons of the control circuitry.
• Clearly, what is needed is a printhead cartridge having a mountingassembly formed from a small number of easily assembled parts to reduce theproblems associated with the cumulative tolerances and the expenses associatedwith multi-part construction. Ideally, such a mounting assembly should have aplurality of mechanically independent spring members for generating thenecessary contact pressure between the pads of the ink cartridge and the buttonsof the control circuitry to insure that the necessary contact pressure is consistently and reliably generated, despite any misalignments and non-uniformities andplanarities caused by cumulative tolerances and dried ink deposits.
• Generally speaking, the invention is an inkjet printhead thateliminates or ameliorates all of the aforementioned problems associated with theprior art. To this end, the inkjet printhead comprises an ink cartridge having aplurality of inkjet nozzles, and a plurality of electrical contacts for conductingcontrol signals to the nozzles, and a mounting assembly having a retainer forreleasably securing the ink cartridge, and a plurality of mechanically independentspring members for pressing electrical contacts of a printer control circuit intoconductive engagement with the contacts of the ink cartridge. Each of theindependent spring members is preferably independently cantilevered from a wallof the mounting assembly. Each spring member may have a proximal end that isintegrally connected to the wall of the mounting assembly, and a distal end thatincludes a projecting nub for engaging one of the printer control circuit contacts.The wall of the mounting assembly is preferably formed from an injectionmoldable plastic material, and the integral connection and formation of thecantilevered spring members with the wall advantageously provides a design thatis easily accurately manufactured, and which provides uniform engagementpressures between the contacts.
• The retainer of the mounting assembly includes at least one lockingmember for engaging the contacts of the ink cartridge against the contacts of thecircuit when the retainer secures the ink cartridge in the mounting assembly. Theretainer may include a pair of leg members pivotally mounted in side walls of themounting assembly, and locking lugs at each end of each leg for applying anengagement force against lock flanges provided on the ink cartridge. To insureproper registration between the contacts of the ink cartridge and the control circuitof the mounting assembly, the mounting assembly and the cartridge includeinterfitting members such as pegs and holes for creating the desired alignment.An alignment means for the control circuit captured within the mountingassembly is also provided which may take the form of registry holes in the control circuit through which alignment pegs of a circuit retainer are inserted during theconstruction of the mounting assembly.
• The mounting assembly may further include a mechanism fordetachably connecting the printhead to a printer. The mounting assembly maytake the form of resilient fingers which snap-fit into opposing slots provided in aprinter well of the printer, in combination with alignment ribs which are insertableinto a selected one of a plurality of slots in the printer well. Such a structureallows the position of the printhead on the printer to be adjusted so that theposition of the printed index number or other image may be adjusted on the paperfed through the printer.
• The invention and its objects and advantages will become moreapparent in the detailed description of the preferred embodiment presented below.
• Figure 1 is a side view of the scanner printer that the printhead ofthe invention may be used in combination with;
• Figures 2A and 2B are perspective views of the printer of theinvention, illustrating how it can be removed from the printer for cartridgereplacement or other servicing;
• Figure 3 is a perspective bottom view of the printhead of theinvention as seen along line 3-3 in Figure 2B;
• Figure 4 is a perspective, exploded view of the printhead,illustrating in particular the components of the mounting assembly of theinvention;
• Figure 5 is a perspective, plan view of the mounting assemblyalong the line 5-5 in Figure 4, and
• Figure 6 is a bottom, perspective view of the ink cartridge.
• With reference now to Figures 1, 2A, and 2B, theprintheadassembly 1 of the invention is particularly adapted for use in ascanner 2 thatscans documents and converts the printed information thereon into digitized form.In such an application, theprinter assembly 1 prints an identifying number ondocuments fed through thescanner 2, which number is also incorporated into the digitized, electronic document created by the CCD module of thescanner 2. As isbest seen in Figures 2A and 2B, theprinthead assembly 1 is detachably mountedto a printer well 3 that is likewise detachably mounted on the exterior surface of asemi-cylindrical paper guide 4. As is best seen in Figure 1, thescanner 2 includesa plurality ofrollers 6 for conveying documents around the semi-circular pathdefined by thepaper guide 4. A paper sensor 8 is provided on the exterior of theguide 4 for actuating theprinter assembly 1. Together, theprinthead assembly 1,we113,paper guide 4,rollers 6, and paper sensor 8 form a printer 9 for thescanner2. Acamera assembly 10 is disposed within thesemi-cylindrical paper guide 4for optically reading the printed information on the documents fed through thepaper guide 4. Thecamera assembly 10 includes ahousing 12 and the previouslymentionedCCD module 14. A plurality ofmirrors 16 allows the CCD module todetect light reflected from documents circulating around thepaper guide 4through aslide 18 provided in aninner guide member 20. With the exception oftheprinthead assembly 1 and well 3, the various components of thescanner 2 areconventional, and form no part of the instant invention.
• With reference to Figures 3, 4, and 5, theprinthead assembly 1 isformed from the combination of amounting assembly 25, and anink cartridge 27.As will be seen hereinafter more clearly, the principal purposes of themountingassembly 25 are (1) to establish secure electrical connections between the printercircuit board in theink cartridge 27 and the control circuitry of the printer; (2) toprovide a means whereby theprinthead assembly 1 may be easily installed andremoved from the printer well 3 via a snap-fit arrangement, and (3) to provide ameans for the ink cartridge to be easily secured into and removed from themounting assembly for replacement or maintenance.
• To the first of these ends, themounting assembly 25 includes abottom wall 30 over which theink cartridge 27 is mountable.Bottom wall 30includes a plurality of cantileveredspring members 31. As is best seen in Figure5, each of thesecantilevered spring members 31 terminates in a projectingnub 33.As will be described in more detail hereinafter, the integral, cantilevered structure of thespring members 31 in combination with the projectingnubs 33, formindependent, spring-loaded members which are responsible for securing electricalconnection between contact pads ofink cartridge 25 and the contact buttons of aprinter control circuit.Bottom wall 30 also includesinner alignment holes 34a,bandouter alignment holes 35a,b which cooperate with similar alignment holes inthecircuit assembly 60 of the printer to align button contacts present in this circuitwith the aforementioned, spring-loadednubs 33.
• The mountingassembly 25 further includes a pair of opposingsidewalls 36a,b. Each of these side walls includes aresilient retaining fingers 37a,b.These fingers, 37a,b, are insertable intocomplementary slots 37c,d present in theprinter well 3 in order to detachably connect theprinter assembly 1 via a snap-fitmechanism (as is indicated in Figure 2B). Each of theside walls 36a,b furtherincludes analignment rib 38a,b which is insertable into a selected one of severalvertically-orientedslots 38c,d in theprinter well 3. The various pairs ofvertically-orientedslots 38c,d allow the position of theprinthead 1 to be adjustedrelative to the documents fed through thepaper guide 4. A pair ofaxle holes39a,b is also present in each of theside walls 36a,b for a purpose which willbecome clear presently. Mountingassembly 25 also has aback wall 40 integrallyconnected to thebottom wall 30 andside walls 36a,b. Backwall 40 includes,near its upper end, acircuit admission slot 42 for receiving the flexible circuitassembly of theprinter 1. A pair of retainingclips 44a,b project from the backside of thewall 40 for securing the connector terminal of the circuit assembly.
• As is best seen in Figure 4, the mountingassembly 25 has acartridge retainer 46 formed from ahandle 48 and two opposinglegs 50a,b. Stubaxles 52a,b project from each of thelegs 50a,b and are snap-fittable into theaxleholes 39a,b due to the resiliency of the plastic or other material forming theretainer. Each of thelegs 50a,b has a longitudinally-shaped locking recess 53a,bat its lower end. These recesses cooperate with the inner side of each of thepreviously discussed retainingfingers 37a,b present inside walls 36a,b to helpsecure the cartridge retainer 36 in a cartridge-retaining position when theretainer 46 is pivoted into the position illustrated in Figures 2B and 3. A pair of lockingcams 54a,b are defined by the flat bottom surfaces of each of thelegs 50a,b of theretainer 46. Finally, flat portions projecting from the front of thelegs 50a,b formstop portions 56a,b which abut theback wall 40 of the mountingassembly 25when theretainer 46 is pivoted into a cartridge-retaining position.
• With reference again to Figure 4, theprinter assembly 1 further hasaflexible circuit assembly 60. Thecircuit assembly 60 includes afoot portion 62having an array ofcontact buttons 64. Each of thesecontact buttons 64 isregistrable with a contact pad located on the bottom wall of theink cartridge 27.Disposed outside of thecontact buttons 64 are two pairs ofalignment holes 66a,b.Thecircuit assembly 60 further includes, on its opposite end, aconnector terminal68 which snap-fits into position behind the upper portion ofback wall 40 of themountingassembly 25 via retainingclips 44a,b. As is also best seen in Figure 4,acircuit retainer 70 is provided for securing the central portion of theflexiblecircuit assembly 60 to theback wall 40 of the mountingassembly 25. Thecircuitretainer 70 has a pair of retainingfeet 72a,b, as shown. Thesefeet 72a,b includealignment pegs 74a,b which are registrable with thealignment holes 66a,b presentin thefoot portion 62 of thecircuit assembly 60. Thecircuit retainer 70 also has aretainingwall 76 integrally connected to the retaining feet 72 for capturing andpressing the central portion of thecircuit assembly 60 against theback wall 40 ofthe mountingassembly 25. Finally, at its upper end, theretainer 70 is providedwith a pair of opposing,resilient fingers 78a,b which snap-fit into opposing sidesof thecircuit admission slot 42 ofback wall 40 in order to secure theretainer 70onto the mountingassembly 25.
• With reference to Figure 6, theink cartridge 27 of theprinterassembly 1 includes anink reservoir 80 for storing a supply of ink. Ahandle 82extends from the side of theink reservoir 80 to facilitate the insertion and removalof thecartridge 27 from the mountingassembly 25. Thebase 84 of theinkcartridge 27 is provided with a pair ofalignment pegs 86a,b which are registrablein and insertable intoouter alignment holes 35a,b located on thebottom wall 30 of the mountingassembly 25. Centrally disposed on the bottom of thebase 84 isacircuit board 88 having a plurality ofcontact pads 90. Each of thecontact pads90 controls one of the plurality ofprinting orifices 92 present on theprinter face94. Finally, thebase 84 of theink cartridge 27 includes a pair of opposingretaining flanges for a purpose which will become evident shortly.
• In operation, the mountingassembly 25 of theprinthead 1 is firstmounted by extending thefoot portion 62 of theflexible circuit assembly 60through the back of theadmission slot 42 of theback wall 40. The alignmentholes 66 of the foot portion 52 are next placed into registry with theinneralignment holes 34a,b present on thebottom wall 30, as is partly shown in Figure5. The alignment pegs 74a,b of thecircuit retainer 70 are next inserted throughthe registeredalignment holes 66a,b and 34a,b and theresilient fingers 78a,b aresnapped into the ends of theslot 42 ofback wall 40.Terminal connector 68 isthen attached to the upper rear portion of theback wall 40 via retainingclips44a,b. When the mountingassembly 25 is so assembled, the projectingnubs 33of each of the cantileveredspring members 31 will be applying pressure beneatheach one of thecontact buttons 64 oncircuit foot portion 62.
• To install anink cartridge 27, thehandle 48 of thecartridgeretainer 46 is pivoted against theback wall 40 in the direction indicated by thearrow in Figure 3. Theink cartridge 27 is then slid over thebottom wall 30 of themountingassembly 25 until the alignment pegs 86a,b are aligned and inserted intotheouter alignment holes 35a,b of thebottom wall 30. Thehandle 48 of thecartridge retainer 46 is then pivoted away from theback wall 40 in the directionopposite from that indicated by the arrow in Figure 3. When this occurs, thelocking cams 54a,b located on the bottom of thecartridge retainer 46 forcefullyengage the retainingflanges 96a,b on thebase 84 of theink cartridge 27downwardly to press thecontact pads 90 of thecartridge 27 againstcontactbuttons 64. Moreover, thelegs 50a,b of thecartridge retainer 46 are snap-fittedinto this cartridge locking position by the action of theresilient retaining fingers37a,b snapping into the locking recesses 53a,b on the bottom portion of the legs ofcartridge retainer 46. The registration and insertion of the alignment pegs86a,b of theink cartridge 27 with theouter alignment holes 35a,b ofbottom wall30 insures the registration of thecontact buttons 64 of theflexible circuitassembly 60 with thecontact pads 90 of theink cartridge 27. The upward springpressure that thenubs 33 on the ends of the cantileveredspring members 31 applyto thecontact buttons 64, in combination with the downward pressure that thelocking cams 54a,b of thecartridge retainer 46 apply to the base of theinkcartridge 27 insures that a reliable electrical connection is made between thecontact buttons 64 and thecontact pads 90. Moreover, the independent resiliencyof each of thespring members 31 achieved by virtue of the independentlycantilevered structure of these members insures that a sufficient electrical contactpressure will be applied to each of thecontact buttons 64 regardless ofmisalignments, variations in the thicknesses of thebuttons 64, orpads 90, orirregularities in the planarity or thicknesses of thecircuit foot portion 62 orcartridge circuit board 88 caused by deposits of dried ink.

Claims (10)

1. An inkjet printhead, comprising:

   an ink cartridge having a plurality of inkjet nozzles, and a pluralityof electrical contacts for conducting control signals to said nozzles, and

   a mounting assembly having a retainer for releasably securing saidink cartridge, and a plurality of mechanically independent spring members forpressing electrical contacts of a printer control circuit into conductive engagementwith said contacts of said ink cartridge.
2. The inkjet printhead defined in claim 1, wherein each ofsaid independent spring members is a cantilevered spring member.
3. The inkjet printhead defined in claim 2, wherein eachspring member is cantilevered from a wall of said mounting assembly.
4. The inkjet printhead defined in claim 3, wherein eachspring member has a proximal end that is integrally connected to said wall of saidmounting assembly.
5. The inkjet printhead defined in claim 1, wherein eachspring member includes a projecting nub for engaging one of said contact buttons.
6. The inkjet printhead defined in claim 4, wherein eachspring member has a distal end that includes a projecting nub for engaging one ofsaid circuit contacts.
7. The inkjet printhead defined in claim 1, wherein saidretainer includes at least one locking member for engaging said contacts of saidink cartridge against said contacts of said circuit when said retainer secures saidink cartridge.
8. The inkjet printhead defined in claim 7, wherein saidretainer includes a pair of leg members pivotally mounted in side walls of saidmounting assembly, and locking lugs at an end of each leg for applying forceagainst said ink cartridge.
9. The inkjet printhead defined in claim 1, wherein saidmounting assembly and said cartridge include interfitting members for aligningsaid contacts of said cartridge and said assembly.
10. The inkjet printhead defined in claim 1, wherein saidmounting assembly includes means for aligning said circuit contacts with saidplurality of spring members.

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