Patent Publication Number: US-7914133-B2

Title: Carrier for an ink distribution assembly of an ink jet printhead

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 10/485,652 filed on Feb. 4, 2004, now issued U.S. Pat. No. 7,284,843, which is a national phase application (371) of PCT/AU02/01056, filed on Aug. 6, 2002, which is a Continuation of U.S. patent Ser. No. 09/922,105, filed on Aug. 6, 2001, now Issued U.S. Pat. No. 6,918,654, which is a Continuation-In-Part of U.S. patent Ser. No. 09/113,053, filed on Jul. 10, 1998, now Issued U.S. Pat. No. 6,362,868, all of which are herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to ink jet printheads. More particularly, this invention relates to an ink jet printhead that incorporates through-chip ink ejection nozzle arrangements. 
     BACKGROUND TO THE INVENTION 
     The Applicant has invented an ink jet printhead that is capable of generating text and images at a resolution of up to 1600 dpi. 
     In order to achieve this, the Applicant has made extensive use of micro electro-mechanical systems technology. In particular, the Applicant has developed integrated circuit fabrication techniques suitable for the manufacture of such printheads. The Applicant has filed a large number of patent applications in this field, many of which have now been allowed. 
     The printheads developed by the Applicant can include up to 84000 nozzle arrangements. Each nozzle arrangement has at least one moving component that serves to eject ink from a nozzle chamber. The components usually either act directly on the ink or act on a closure which serves to permit or inhibit the ejection of ink from the nozzle chamber. 
     The moving components within the printheads are microscopically dimensioned. This is necessary, given the large number of nozzle arrangements per printhead. The Applicant has spent a substantial amount of time and effort developing configurations for such printheads. 
     One of the reasons for this is that, as is known in the field of integrated circuit fabrication, cost of on-chip real estate is extremely high. Furthermore, it is important that levels of complexity are kept to a minimum since these significantly increase the cost of fabrication. 
     As a result of the need to keep on-chip real estate to a minimum, the Applicant has developed printhead chips that are extremely thin, having a high length to width ratio. These chips are positioned end-to-end to span a medium on which ink is to be deposited. 
     A substantial difficulty to be overcome with such printheads is the supply of ink to the nozzle arrangements. A possibility investigated by the Applicant was the provision of ink passages extending the length of the printhead chips, each passage carrying a different color. However, it will be appreciated by those of ordinary skill in the field of fluid mechanics that ink driven through such passages would be subject to an extremely high pressure drop. This pressure drop inhibits the ink from being carried at a suitably high flow rate. In  FIG. 1  of the drawings, there is shown a printhead chip  1  incorporating three passages  2 , one for each color, extending the length of the printhead chip. The problem associated with pressure drop in the passages is immediately apparent to a person of ordinary skill in the field of fluid mechanics, given the small cross sectional area of these passages. 
     An important requirement for the nozzle arrangements of this form of printhead is that they be refilled quickly once ink has been ejected from the nozzle chambers. This ensures that the nozzle arrangements can re-fire in a very short time, leading to rapid printing, which is an advantage sought by the Applicant. The high pressure drop mentioned in the previous paragraph inhibits the development of a suitable flow rate to the nozzle chambers and consequent rapid re-firing. 
     In order to address this issue, one example of a printhead chip has rows of ink inlet openings defined therein into which ink is fed. Each row of ink inlet openings corresponds to a differently colored ink. Thus, the necessity of having ink flowing lengthwise in each chip is obviated. 
     For color printing, at least three different inks must be provided to the printhead chip. These are Cyan, Magenta and Yellow inks. It is critical that these inks are kept separate from each other up to the point of impact on the print medium since the printhead chip prints a dithered image. It follows that it is necessary to provide each inlet opening with an ink of a different color. This is shown schematically in  FIG. 2 . As can be seen in  FIG. 2 , this can be achieved by providing a primary channel or reservoir  3  for each color. The ink from each reservoir  3  is fed into smaller channels  4 , which in turn feed into the rows of ink inlet openings in a printhead chip  5 . 
     It is to be appreciated that an ink distribution assembly comprising the reservoirs  3  and the smaller channels  4  must be manufactured with a high degree of accuracy due to the small size of the channels in the printhead chip  5  and the necessity for consistent ink flow to the openings in the printhead chip  5 . 
     One way of achieving this accuracy would be to machine the assembly out of silicon. However, Applicant has found that this would result in a product that is far too costly to be commercially competitive. 
     It follows that the assembly should preferably be molded of a plastics material. The principle forms of molding plastics material are extrusion molding and injection molding. Applicant has found that extrusion molding is not capable of producing a product that has the required accuracy and structural stability for the assembly in question. 
     Substantial advances have been made in injection molding over the past years. Applicant has found that this form of molding can provide an assembly with the required accuracy and stability of construction. However, Applicant has identified a difficulty in injection molding an assembly having more than two reservoirs for ink. This is associated with the fact that it would appear that such a structure would require the construction of side mover cores when fabricating the molds to be used in the injection molding process. These cores are generally complex and expensive to manufacture. In  FIG. 3 , there is shown what would be an intuitive assembly including three ink reservoirs  6  molded in a plastics material, one for each ink of a particular color. It is clear that injection molding such an assembly would require the use of side mover cores. 
     The Applicant has thus developed a distribution assembly that obviates the need for such side mover cores in its fabrication. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention, there is provided an ink distribution assembly for a page width ink jet printhead in the form of at least one printhead chip having sets of ink inlet openings, each set having at least one inlet opening for receiving an ink of a particular color to be supplied to the printhead chip, the assembly comprising 
     a carrier having an elongate structure with a printhead side that is engageable with the printhead and an opposed ink supply side, and defining feed openings through the carrier to be in fluid communication with respective ink inlet openings of the printhead, the ink supply side of the carrier defining a number of discrete feed formations, each feed formation being configured to receive ink of a particular color and to be in fluid communication with the, or each, inlet opening of a respective set, via the feed openings, and the printhead side of the carrier defining at least one ink supply formation, the carrier defining at least one passage in fluid communication between the, or each, ink supply formation and at least one of the feed formations; and 
     a cover that is engageable with the carrier at the ink supply side, the cover and the ink supply side of the carrier being shaped so that, when the cover is in position, the cover serves to define a roof for the feed formations and so that the cover and the ink supply side of the carrier define ink pathways that are in fluid communication with respective feed formations, one of the carrier and the cover defining ink supply openings in fluid communication with respective ink pathways. 
     According to a second aspect of the invention, there is provided a molded component for an ink distribution assembly for a page width ink jet printhead in the form of at least one printhead chip having sets of ink inlet openings, each set having at least one inlet opening for receiving an ink of a particular color to be supplied to the printhead chip, the molded component comprising: 
     a carrier having an elongate structure with a printhead side that is engageable with the printhead and an opposed ink supply side, and defining feed openings through the carrier to be in fluid communication with respective ink inlet openings of the printhead, the ink supply side of the carrier defining a number of discrete feed formations, each feed formation being configured to receive ink of a particular color and to be in fluid communication with the, or each, inlet opening of a respective set, via the feed openings, and the printhead side of the carrier defining at least one ink supply formation, the carrier defining at least one passage in fluid communication between the, or each, ink supply formation and at least one of the feed formations. 
     According to a third aspect of the invention, there is provided a page width printing device which comprises: 
     a page width ink jet printhead in the form of at least one printhead chip having sets of ink inlet openings, each set having at least one inlet opening for receiving an ink of a particular color to be supplied to the printhead chip; 
     a carrier having an elongate structure with a printhead side that is engageable with the printhead and an opposed ink supply side, and defining feed openings through the carrier to be in fluid communication with respective ink inlet openings of the printhead, the ink supply side of the carrier defining a number of discrete feed formations, each feed formation being configured to receive ink of a particular color and to be in fluid communication with the, or each, inlet opening of a respective set, via the feed openings, and the printhead side of the carrier defining at least one ink supply formation, the carrier defining at least one passage in fluid communication between the, or each, ink supply formation and at least one of the feed formations; and 
     a cover that is engageable with the carrier at the ink supply side, the cover and the ink supply side of the carrier being shaped so that, when the cover is in position, the cover serves to define a roof for the feed formations and so that the cover and the ink supply side of the carrier define ink pathways that are in fluid communication with respective feed formations, one of the carrier and the cover defining ink supply openings in fluid communication with respective ink pathways. 
     The invention is now described, by way of example only, with reference to the accompanying drawings. The specific nature of the following description is not to be construed as limiting the scope of this summary in any way 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, 
         FIG. 1  shows a three dimensional view of a printhead chip incorporating ink supply passages extending a length of the chip; 
         FIG. 2  shows a layout of an ink distribution assembly that addresses the problem of pressure drop within an ink jet printhead; 
         FIG. 3  shows a schematic end view of an ink distribution assembly indicating problems associated with moulding such an assembly; 
         FIG. 4  shows a schematic view of an ink distribution assembly, in accordance with the invention; 
         FIG. 5  shows a three dimensional, exploded view of a printing device incorporating an ink distribution assembly of the invention; 
         FIG. 6  shows a three dimensional view of a carrier for the ink distribution assembly, from a printhead side of the carrier; 
         FIG. 7  shows a detailed view of the printhead side of the carrier; 
         FIG. 8  shows a three dimensional view of the carrier, from an ink supply side of the carrier; 
         FIG. 9  shows a detailed plan view of part of the ink supply side of the carrier; and 
         FIG. 10  shows a schematic, cross-sectioned view of the ink distribution assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     In the drawings,  FIGS. 1 ,  2  and  3  have already been discussed in the background to the invention above. These drawings indicate the provision of three separate ink reservoirs in an ink distribution assembly and, in particular, indicate the problems associated with molding such an assembly. 
     In  FIGS. 4 and 5 , reference numeral  10  generally indicates an ink distribution assembly, in accordance with the invention, for an ink jet printhead, indicated at  12 . The printhead  12  can include one or more printhead chips  14  so that the printhead  12  defines a page width printhead. 
     The printhead chip  14  is the product of an integrated circuit fabrication technique. Furthermore, the printhead chip  14  incorporates a large number of nozzle arrangements, each connected to drive circuitry within the printhead chip  14 . The nozzle arrangements are each in the form of a micro electro-mechanical device that is operable upon receipt of a signal from the drive circuitry to eject ink from the nozzle arrangement. Details of the printhead chip  14  are clearly set out in the above referenced applications. It follows that these details are not be described in this specification. 
     The printhead chip  14  includes three sets or rows  16  of ink inlet openings  18  which are etched into a rear side  20  of the printhead chip  14 . 
     Each row  16  corresponds to ink of a particular color to be fed to the printhead  12 . In this particular example, the printhead  12  is configured to accept cyan, magenta and yellow inks that are conventionally used for colour printing. It will readily be appreciated that this invention is applicable to those printhead chips that are configured to accept six or even more differently colored inks. 
     The concept behind the present invention is indicated in  FIG. 4 . Broadly, the Applicant has provided a supply  11  for cyan ink and a supply  13  for yellow ink above a back side of the printhead  12  and a supply  15 A and  15 B of magenta ink on each side of the printhead  12 . This arrangement permit the distribution assembly  10  to be manufactured in a single shot injection molding process, as will become clear below. 
     The assembly  10  includes a carrier  22 . The carrier  22  has a generally planar central portion  24  and a pair of opposed sidewall portions  26 . The carrier  22  is elongate with the portions  24 ,  26  extending the length of the carrier  22 . 
     The central portion  24  has an ink supply side  28  and a printhead side  30 . The printhead side  30  defines a retaining formation in the form of a recess  32 . The recess  32  is dimensioned so that the printhead  12  is a snug fit within the recess  32 . 
     The rows  16  of ink inlet openings  18  in the printhead chip  14  are referred to in this specification as a central magenta row  34 , an outer cyan row  36  and an outer yellow row  38  of inlet openings  18 . The reference to the particular colors is simply for purposes of convenience and ease of description. It will readily be appreciated that they can be interchanged depending on the configuration of the printhead chip  14 . 
     A floor  40  of the recess  32  defined by the carrier  22  has three rows  42 ,  44 ,  46  of ink feed openings  48  defined therein. For the purposes of this description, the row  42  will be referred to as the magenta row, the row  44  will be referred to as the cyan row and the row  46  will be referred to as the yellow row. Again, it will be appreciated that this is simply for the purposes of illustration and ease of description. 
     The ink feed openings  48  are positioned so that, when the printhead  12  is received in the recess  32 , each ink feed opening  48  in the magenta row  42  is in register with a corresponding opening  18  in the magenta row  34  of the printhead  12 . The same applies to the cyan row  44  and the yellow row  46  of ink feed openings  48  with respect to the cyan row  36  and yellow row  38  of ink inlet openings  18 . 
     The ink supply side  28  of the central portion  24  of the carrier  22  defines a magenta feed channel  50  with the magenta row  42  of ink feed openings  48  defined in the magenta feed channel  50 . In particular, a pair of opposed longitudinal walls  54  that extend from the floor  52  defines the magenta feed channel  50 . Detail of the magenta feed channel  50  and the walls  54  is shown in  FIG. 9 . 
     The printhead side  30  of the central portion  24  defines a pair of ink supply channels  56 . The recess  32  is positioned between the ink supply channels  56 . 
     A plurality of laterally extending dividing walls  58  is connected to and extends from each wall  54 . The dividing walls  58  are spaced to define a plurality of laterally extending, spaced ink feed channels  60  positioned on each side of the magenta feed channel  50 . Each dividing wall  58  has a narrowed portion  62  proximate its respective longitudinal wall  54 . Thus, each ink supply channel  60  widens at the longitudinal walls  54 . 
     As can be seen in the drawings, there are two rows  66 ,  68  of the feed channels  60 . Again, for the purposes of illustration and ease of description, the row  66  is referred to as the cyan row while the row  68  is referred to as the yellow row. Thus, in keeping with this terminology, there is provided a discrete cyan feed formation  70  on one side of the magenta feed channel  50  and a discrete yellow feed formation  72  on the other side of the magenta feed channel  50 . Each ink feed opening  48  of the cyan row  44  and the yellow row  46  is defined in respective feed channels  60 . 
     The ink distribution assembly  10  includes a cover  78 . The cover  78  has a generally T-shaped cross section with a rectangular leg portion  80  and a top portion  82 . The leg portion  80  is dimensioned to be received between the opposed side wall portions  26  of the carrier  22 . The leg portion  80  has a flat bottom surface  84  which bears against the dividing walls  58  to define a roof for the ink feed channels  60  and the magenta feed channel  50 . 
     As can be seen in  FIG. 10 , when the leg portion  80  is received between the sidewall portions  26 , an elongate, longitudinally extending ink pathway  86  is defined between each sidewall portion  26  and the leg portion  80  of the cover  78 . 
     Still further, each dividing wall  58  has a free end that is spaced from its respective sidewall portion  26 . It follows that each pathway  86  is in fluid communication with a row  66 ,  68  of ink feed channels  60 . Again, for the purposes of illustration and ease of description, the pathways  86  are referred to as a cyan pathway  88  and a yellow pathway  90 . One end  92  of the carrier  22  has three inlet openings defined therein. These are, again for the purposes of convenience, referred to as a central magenta inlet opening  94 , a cyan inlet opening  96  and a yellow inlet opening  98 . 
     When the cover  78  is in position, the cyan inlet opening  96  is in fluid communication with the cyan pathway  88 . Likewise, in this condition, the yellow inlet opening  98  is in fluid communication with the yellow pathway  90 . It will therefore be appreciated that an ink flow path is defined from the openings  96 ,  98 , to the rows  36 ,  38  of ink inlet openings  18  in the printhead  14  via the pathways  88 ,  90 , the feed channels  60  of the rows  66 ,  68  and the openings  48  of the rows  44 ,  46 . 
     Each of the dividing walls  58  has a magenta ink flow passage  100  defined therein, which is in fluid communication with one of the ink supply channels  56 . Further, each dividing wall  58  has a magenta conduit  102  defined therein, one end of which is in fluid communication with a respective magenta ink flow passage  100  and the other end of which is in fluid communication with the magenta feed channel  50 . It follows that the dividing walls  58  and the longitudinal walls  54  define a magenta feed formation  116 . 
     A pair of magenta ink supply openings  104  is defined in the central portion  24  proximate said one end  92  of the carrier  22 . The leg portion  80  is configured so that when the cover  78  is in position, the magenta inlet opening  94  is in fluid communication with both of the magenta ink supply openings  104 . 
     It will therefore be appreciated that an ink flow path is defined between the magenta inlet opening  94  and each of the ink inlet openings  18  in the magenta row  34  of the printhead  14  via the magenta ink supply openings  104 , the ink supply channels  56 , the magenta ink flow passages  100 , the magenta conduits  102 , the magenta feed channel  50  and the openings  48  in the magenta row  42 . 
     It will further be appreciated that each of the feed formations  70 ,  72 ,  116  defines a pathway that is repeatedly divided into narrower portions as the ink approaches the printhead  12 . 
     The assembly  10  includes a pair of cover plates  106  which are fastenable to the printhead side  30  of the central portion  24  to form roofs for the ink supply channels  56 . In  FIG. 5 , there is shown a printing device that incorporates the assembly  10 . The printing device, for example, includes a tape automated bonding (TAB) strip that connects the drive circuitry within the printhead  12  to a control system (not shown) to control operation of the printhead  12 . Further, an outer side  108  of each sidewall portion  26  defines guide formations  110  for rollers  112 . The rollers  112  are used to drive a print medium  114  past the printhead  12  during printing. Details of the TAB strip and the rollers are set out in the above referenced applications. It follows that these details are not described in this specification. 
     The carrier  22  is the product of an injection molding process. The carrier  22  can thus be of a thermoplastics material or of a thermosetting material. 
     In its broadest terms, injection moulding requires the injection of a hot liquid resin or a thermosetting resin into a closed mould, under pressure, until the moulded part is cooled or cured and can be ejected from the mould. 
     As is known to those of skill in the field of moulding, it is desirable if a component to be moulded can be moulded by a machine requiring only movement to and fro in a single direction. In general, such machines comprise a rear platen, a moving platen and a stationery platen. Dies are positioned between the moving platen and the stationery platen and define, between them, a volume into which pre-molded material is injected. 
     In the event that a component is required to have an enclosed volume and be injection molded, it is often necessary to provide what are known as side mover cores that operate together with the moulding machinery to generate the component having the included volume. Such side mover cores are known to be extremely expensive and complex both to manufacture and to operate. 
     In the present invention, it would be intuitive to provide three distinct enclosed volumes, as shown in  FIG. 3 , for the provision of ink reservoirs from which ink is supplied to each of the rows  34 ,  36 ,  38 . However, it is clear that an injection-molding machine to generate this form of molding would require side mover cores. This could result in the component being excessively expensive and complicated to manufacture, especially on a mass basis. 
     The present invention is based on an idea conceived by the Applicant of defining such an enclosed volume or reservoir on the printhead side  30  of the carrier  22 . The difficulty with this is to provide an ink flow from the printhead side  30  of the carrier  22  to the ink supply side  28 . Applicant has achieved this with the present invention. 
     It is apparent both from the above description and the drawings that it would be clear to a person of ordinary skill in the field of injection molding that the carrier  22  can be manufactured using a standard injection-molding machine without the requirement for side mover cores. 
     As is also clear from the drawings, the cover  78  is of a relatively simply shape and can also be manufactured with a standard injection-molding machine. 
     Applicant believes that the invention provides a means whereby an ink distribution assembly for a page width ink jet printhead can be achieved which lends itself to a simple, one-shot injection molding process. This has far reaching cost implications as printing devices incorporating such ink distribution assemblies are intended for mass manufacture.