Patent Publication Number: US-8113625-B2

Title: Flexible printhead assembly with resiliently flexible adhesive

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of Ser. No. 11/442,413 filed on May 30, 2006, which is a continuation of Ser. No. 10/487,838 filed on Feb. 27, 2004, now granted U.S. Pat. No. 7,070,265, which is a 371 of PCT/AU02/01057 filed on Aug. 6, 2002, which is a continuation of U.S. Ser. No. 09/942,549, filed on Aug. 31, 2001, now granted U.S. Pat. No. 6,616,271, which is a continuation-in-part of U.S. Ser. No. 09/425,421, filed on Oct. 19, 1999, now granted U.S. Pat. No. 6,312,114 all of which is herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a print head assembly. More particularly, this invention relates to a print head assembly and to a method of assembling a print head. 
     BACKGROUND OF THE INVENTION 
     The Applicant has developed a page width ink jet print head that is the subject of a large number of United States patents and patent applications. The print head is capable of printing text and images having resolutions as high as 1600 dpi. 
     An integral part of the print head is one or more print head chips. The print head chips are the product of an integrated circuit fabrication technique. In particular, each print head chip comprises a plurality of nozzle arrangements that are positioned along a length of silicon wafer substrate. Each nozzle arrangement is in the form of a micro electro-mechanical system. The applicant has developed technology that allows for the fabrication of such print heads having up to 84,000 nozzle arrangements. 
     In general, during assembly of a print head, the print head chips are positioned in some form of carrier. The carrier forms part of an ink distribution arrangement such as an ink distribution manifold. Instead, the carrier can itself be attached in some way to an ink distribution arrangement to define some form of interface between the print head chips and the ink distribution arrangement. 
     The positioning of the print head chips in their respective carriers usually takes place by way of simply urging the print head chip into a recess defined in the carrier. The recess is thus dimensioned so that the fit is a snug fit or an interference fit to ensure that the print head chip is retained in position in the carrier. 
     Due to the elongate nature of the print head chip, the print head chip is susceptible to flexure. As a result, any stresses that are exerted on the carrier during normal handling and operation can result in flexure of the carrier and thus the print head chip. It will be appreciated by those of ordinary skill in the art that the fact that the nozzle arrangements are each in the form of a micro electro-mechanical system makes such flexure highly undesirable. 
     A particular problem with such a fit stems from the possible ingress of particulate matter into the recess. This is especially so if the matter is in the form of one or more relatively hard particles. When the chip is urged into the recess, such a particle can become sandwiched between the print head chip and a wall of the recess. This results in a region of stress concentration at that point on the print head chip that is impinged upon by the particle. Thus, when the chip is subjected to a small amount of flexure that would usually not cause a problem, the stress concentration can cause a fracturing of the print head chip. 
     The Applicant has conceived the present invention to address this problem and to alleviate the necessity for the print head manufacturer to achieve a particulate free environment for the assembly stage of the print head. As is well known, chip manufacturers incur substantial expense to ensure that chip fabrication environments are kept sterile. Applicant believes that it is desirable that the need for such sterile environments does not extend to the print head assembly stage. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention, there is provided an ink jet print head assembly that comprises 
     
         
         
           
             at least one elongate ink jet print head chip that is the product of an integrated circuit fabrication technique; 
             at least one corresponding ink jet print head chip carrier that defines an elongate recess having a pair of opposed side walls, the, or each, print head chip being received in one respective recess, the, or each, ink jet print head chip and said respective recess being dimensioned so that a gap is defined between the, or each, ink jet print head chip and each side wall; and 
             resiliently deformable material that is positioned in each gap to retain the, or each, print head chip in position in said respective recess. 
           
         
       
    
     According to a second aspect of the invention, there is provided a method of assembling an ink jet print head having at least one elongate ink jet print head chip that is the product of an integrated circuit fabrication technique and at least one corresponding inkjet print head chip carrier that defines an elongate recess having a pair of opposed side walls, the, or each, ink jet print head chip and said respective recess being dimensioned so that a width of said the, or each, print head chip is less than a width of said respective recess to a predetermined extent, the method comprising the steps of:
         positioning the, or each, ink jet print head chip in said respective carrier so that a gap is defined on each side of the ink jet print head chip by said pair of opposed side walls and the ink jet print head chip; and   at least partially filling each gap with an adhesive that is selected from a group of adhesives that cure into elastically deformable material to fix the, or each, ink jet print head chip in said respective recess.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, 
         FIG. 1  shows a schematic, three dimensional view of a first embodiment of an inkjet print head assembly, in accordance with the invention; 
         FIG. 2  shows a three dimensional view of a second embodiment of an ink jet print head assembly, in accordance with the invention; 
         FIG. 3  shows an exploded view of one module of the inkjet print head assembly of  FIG. 2 ; 
         FIG. 4  shows a three dimensional view of the module of  FIG. 3 ; 
         FIG. 5  shows a plan view of the module of  FIG. 3 ; 
         FIG. 6  shows a view from one side of the module of  FIG. 3 ; 
         FIG. 7  shows a view from an opposite side of the module of  FIG. 3 ; 
         FIG. 8  shows a front sectioned view of the module of  FIG. 3 , taken through A-A in  FIG. 5 ; and 
         FIG. 9  shows a detailed view of part of the module of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     In  FIG. 1 , reference numeral  10  generally indicates a first embodiment of an ink jet print head assembly, in accordance with the invention. 
     The ink jet print head assembly  10  is in the form of a page width ink jet print head. 
     The ink jet print head assembly  10  includes an ink jet print head chip carrier  14 . An ink distribution manifold  12  is positioned on the carrier  14 . 
     The ink jet print head chip carrier  14  includes a support member  16 . An elongate recess or channel  18  is defined in the support member  16 . 
     The ink jet print head  10  includes a number of ink jet print head chips, one of which is indicated at  20 . The ink jet print head chip  20  is the product of an integrated circuit fabrication technique. Further, the ink jet print head chip  20  comprises a plurality of nozzle arrangements (not shown). Each nozzle arrangement is in the form of a micro electro-mechanical system. Thus, each nozzle arrangement has at least one moving component that acts on ink within a nozzle chamber to eject that ink from the nozzle chamber. 
     The ink jet print head chip  20  and the channel  18  both have a rectangular cross section, with the channel  18  being larger than the ink jet print head chip  20 , to a predetermined extent. In particular, a width of the channel  18  is larger, to a predetermined extent, than the print head chip  20 . A width of the channel  18  can be between approximately 310 microns and 5100 microns. A width of the ink jet print head chip  20  can be between approximately 300 microns and 5000 microns. 
     During assembly, the chip  20  is inserted into the channel  18  as shown by the arrow  21 . The ink jet print head chip  20  is fixed in the channel  18  with an adhesive that, when cured, defines a resiliently flexible material, indicated at  22 . As a result of the differing dimensions set out above, when the print head chip  20  is positioned in the channel  18 , a gap  26  is set up between each side  24  of the print head chip  20  and a corresponding side wall  28  defining the channel  18 . The gap  26  therefore has a width of between approximately 5 and 50 microns. The gaps  26  are filled with the resiliently flexible material  22 . 
     As set out in the above referenced patent applications, the print head chip  20  has an extremely high length to width ratio. The reason for this is that the fabrication process allows the Applicant to conserve chip real estate by keeping the width of the chip  20  as small as possible, while retaining a substantial length to permit page width printing. Furthermore, the carrier  14  and the ink distribution manifold  12  also have relatively high length to width ratios. It follows that the print head  10  is susceptible to flexure during normal handling and operation. It will be appreciated that, without the gap  26 , this flexure would be transmitted directly to the print head chip  20 , which would be undesirable. In the event that particulate matter contaminated the side  24  of the chip  20  or one of the side walls  28 , a point of stress concentration would be set up where the particulate matter impinged on the side wall  28 , when the chip  10  was fitted into the channel  18 , as has been the practice prior to this invention. Any subsequent flexure of the carrier  14  could then result in a fracturing of the chip  20  at the point of stress concentration. 
     It follows that the gaps  26  allow for a certain amount of flexure of the carrier  14  without this flexure being transmitted to the chip  20 . Further, the adhesive, once cured into the resiliently flexible material  22 , serves to accommodate flexure of the carrier  14 , while retaining the chip  20  in position in the channel  18 . 
     The adhesive is of the type that cures into an elastomeric material. In particular, the adhesive is a silicon rubber adhesive. 
     In  FIGS. 2 to 9 , reference numeral  30  generally indicates a second embodiment of an ink jet print head assembly, in accordance with the invention. With reference to  FIG. 1 , like reference numerals refer to like parts, unless otherwise specified. 
     The print head assembly  30  is similar to the print head assembly that is the subject of the above referenced U.S. patent application Ser. Nos. 09/693,644, 09/693,737 and 09/696,340. It follows that this description will be limited to the manner in which the print head chip  20  is mounted and will not set out further detail that is already set out in the above US patent applications, except in a broad fashion. 
     The print head assembly  30  is a modular print head assembly having a number of modules  32 . Each module  32  has a carrier  34  that defines a channel  36  in which the print head chip  20  is received. The relative dimensions of the channel  36  and the print head chip  20  are the same as those of the print head assembly  10 . It follows that a gap  38  is also defined between each side  24  of the print head chip  20  and a corresponding side wall  40  of the channel  36 . As with the print head assembly  10 , the print head chip  10  is fixed in its respective channel  36  with an adhesive that cures into a resiliently flexible material, indicated at  42 . The benefits of the gaps  38  and the resiliently flexible material  42  are set out above. 
     As can be seen in  FIG. 2 , the print head  30  includes a retaining structure  44  in which the modules  32  are positioned. Each carrier  34  is in the form of a tile that is mounted in the retaining structure  44 . In this example, there are three tiles  34  mounted in the retaining structure  44 . Depending on the requirements, there can be more than one retaining structure  44  in the print head  30 . The retaining structure  44  has a pair of opposed side portions  46  and a floor portion  48 , which define a region  50  in which the tiles  34  are mounted. 
     The tiles  34  each define nesting formations  56  so that the tiles  34  can nest together in an end-to-end manner along the region  50 . Details of the manner in which the tiles  34  are positioned in the region  50  are set out in the above referenced patent applications. 
     Each tile  34  has a first molding  52  that is positioned on a second molding  54 , with both moldings  52 ,  54  mounted in the region  50  of the retaining structure  44 . Structural details of the moldings  52 ,  54  are provided in the above referenced patent applications. The channel  36  is defined in the first molding  52 . 
     A plurality of raised ribs  58  is defined by the first molding  52  on one side of the channel  36 . The raised ribs  58  serve to maintain print media passing over the print head chip  20  at a desired spacing from the print head chip  20 . A plurality of conductive strips  60  is defined on an opposed side of the channel  36 . The strips  60  are wired to electrical contacts of the chip  20  to connect control circuitry (not shown) to the print head chip  20 . 
     The first molding  52  defines a recess  62  approximately midway along its length. The recess  62  is positioned and dimensioned to engage a catch  64  defined by one of the side portions  46  of the retaining structure  44 , when the tile  34  is mounted in the region  50  of the retaining structure  44 . Again, details of the manner in which the tiles  34  are mounted in the retaining structure  44  are provided in the above referenced applications. 
     As can be seen in  FIG. 3 , the first molding  52  has a plurality of inlet openings  66  defined therein. The openings  66  are used to supply ink to the print head chip  20 . 
     The openings  66  are in fluid communication with corresponding openings  68  defined at longitudinally spaced intervals in the second molding  54 . In addition, openings  70  are defined in the molding  54  for the supply of air. Further details are provided in the above referenced applications. 
     The tiles  34  and the retaining structure  44  are configured so that a certain amount of relative movement between the tiles  34  and the retaining structure  44  can be accommodated. Details of how this is achieved are set out in the above referenced applications. For example, collared structures  72  are positioned on the floor portion  48  of the retaining structure  44 . The collared structures  72  are of a resiliently flexible hydrophobic material and engage complementary recesses defined in the second molding  54 . Thus, a tight seal is maintained, in spite of such relative movement. The collars  72  circumscribe openings of passages  74  ( FIG. 8 ) defined in the floor portion  48 . Again, further details are provided in the above referenced applications. 
     Details of the manner in which ink and air is supplied to the chip  20  are set out in the above referenced applications and will therefore not be set out here. Briefly, however, the passages  74  are in fluid communication with the openings  68  in the second mounting, which, in turn, are in fluid communication with the openings  66 . The passages  74  are divided into six sets that can receive, for example, cyan, yellow, magenta, black and infrared inks and fixative respectively. Other combinations of up to six types of ink can be used. It follows that the chip  20  is a “six color” chip. 
     As can be seen in  FIG. 8 , the print head  30  includes a nozzle guard  76  that covers a nozzle layer  78 . The nozzle layer  78  is mounted on a silicon inlet backing  80  as described in greater detail in the above referenced U.S. patent application Ser. No. 09/608,779. 
     The gaps  38  and the resiliently flexible material  42  can clearly be seen in  FIG. 9 . 
     It will be appreciated by persons skilled in the art that the provision of the gaps  38  together with the resiliently flexible material  42  provides a means whereby a point of stress concentration that may result from the ingress of particulate matter between the chip  20  and the sidewalls  40  of the channels  36  can be avoided. The gaps  38  and the resiliently flexible material  42  obviate the need for press fitting or even snugly fitting the chips  20  in their respective channels  36 . Thus, the detrimental effects of the ingress of such particulate matter are alleviated to a substantial extent. 
     It will further be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The two embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.