Patent Publication Number: US-2015062245-A1

Title: Print bar structure

Description:
BACKGROUND 
     In some inkjet printers, a media wide arrangement of stationary printheads is used to print on paper or other print media moved past the printheads. In one type of print bar for less expensive media wide inkjet printers for personal and small business users, long narrow molded plastic parts support and carry ink to the printheads. 
    
    
     
       DRAWINGS 
         FIG. 1  is a block diagram illustrating an inkjet printer implementing one example of a new print bar structure. 
         FIG. 2  is a diagrammatic partial section view illustrating a print bar structure such as the one shown in the block diagram of  FIG. 1 . 
         FIG. 3  is an end view of a print bar implementing the print bar structure shown in  FIG. 2 . 
         FIG. 4  is an end view illustrating the print bar of  FIG. 3  installed in a printer showing the primary, Z direction spacing between the printheads and the print media. 
         FIG. 5  is a perspective view of a print bar implementing one example of the new print bar structure viewed looking toward the exposed printheads, which is typically the bottom of the print bar when the print bar is installed in a printer. 
         FIGS. 6 and 7  are exploded views of the print bar of  FIG. 5 . 
         FIGS. 8 and 9  are top and bottom plan views, respectively, of the chassis from the print bar structure in the print bar of  FIGS. 5-7 . 
         FIGS. 10 and 11  are section views of the print bar structure in the print bar of  FIGS. 5-7  taken along the lines  10 - 10  and  11 - 11 , respectively, in  FIG. 8 . 
     
    
    
     The same part numbers are used to designate the same or similar parts throughout the figures. 
     DESCRIPTION 
     One of the challenges making print bars for less expensive media wide inkjet printers that use molded plastic parts is precisely controlling the position of the printheads on the print bar to maintain the desired spacing and alignment between the printheads and the print media during printing. The length of the print bar corresponds to the width of the print media. Controlling the dimensions of and between plastic parts is more difficult in longer parts. Dimensional control includes not only the initial accuracy of a part for size, position and flatness but also the changes that occur in or between parts during use and over time. 
     A new print bar structure has been developed to help improve dimensional control in a page wide print bar by introducing a rigid chassis to support and constrain the molded plastic parts that make up other parts of the structure. The chassis is made from die-cast aluminum or another suitably rigid material and serves as a “backbone” for the lower cost plastic parts. Select areas of the chassis may be machined as necessary or desirable to improve dimensional attributes such as size, position, flatness, parallelism, and perpendicularity. The mechanical properties of the aluminum along with the geometry of the chassis enable a part that can span the width of the printed page while maintaining the dimensional stability needed for the print bar. Other parts in the print bar may be mounted to the chassis directly or indirectly to take advantage of its solid structural foundation, enabling the use of lower cost materials and assembly techniques. 
     This and other examples shown in the figures and described herein are non-limiting examples. Other examples are possible and nothing in this Description should be construed to limit the scope of the invention which is defined in the Claims that follow the Description. 
     As used in this document, “elongated” means a part is longer than it is wide; and a “printhead” means that part of an inkjet printer or other type of inkjet dispenser that expels fluid from one or more openings. “Printhead” and “print bar” are not limited to printing with ink but also include inkjet type dispensing of other fluids and/or for uses other than printing. 
       FIG. 1  is a block diagram illustrating an inkjet printer  10  with a print bar  12  implementing one example of a new print bar structure  14  in which a flat rigid flange on the chassis helps control the position and alignment of the ink manifold and the printhead mounting substrate.  FIG. 2  is a diagrammatic partial section view illustrating a print bar structure  14  such as the one shown in the block diagram of  FIG. 1 .  FIG. 3  is an end view of a print bar  12  implementing the print bar structure  14  shown in  FIG. 2 .  FIG. 4  illustrates print bar  12  installed in a printer showing the primary, Z direction spacing between the printheads and the print media. 
     Referring first to  FIG. 1 , printer  10  includes print bar  12  spanning the width of a print media  16 , flow regulators  18  associated with print bar  12 , a media transport mechanism  20 , ink supplies  22 , and a printer controller  24 . Print bar  12  in  FIG. 1  includes an arrangement of multiple printheads  26  for ejecting ink or other printing fluid on to a sheet or continuous web of paper or other print media  16 . Each printhead  26  is electrically connected to printer controller  24  and fluidically connected to one or more ink supplies  22  through flow regulators  18  and a typically complex ink flow path in print bar  12  that includes an ink manifold  28  and a printhead mounting substrate  30 . Controller  24  in  FIG. 1  represents generally the programming, processor(s) and associated memories, and the electronic circuitry and components needed to control the operative elements of a printer  10 . In operation, printer controller  24  selectively energizes ink ejector elements in a printhead  26 , or group of printheads  26 , in the appropriate sequence to eject ink on to media  16  in a pattern corresponding to the desired printed image. 
     Referring now also to  FIGS. 2-4 , print bar structure  14  includes a chassis  32  supporting ink manifold  28  and printhead mounting substrate  30 . Ink flows to printheads  26  from ink supplies  22  and flow regulators  18  through manifold  28  and substrate  30 , as indicated generally by a simplified flow path  34  and openings  36  in  FIG. 2 . A shroud  38  extends along the bottom of print bar  12 , covering exposed portions of substrate  30  and printheads  26  while leaving the face of each printhead  26  exposed for jetting ink. As described in detail below with reference to  FIGS. 5-11 , manifold  28  and mounting substrate  30  are assembled against a flat rigid flange  40  on print bar chassis  32 . The front and rear faces  42 ,  44  of flange  40  lie in planes parallel to a plane defined by reference surfaces  46 A,  46 B,  46 C on chassis  32 . Reference surfaces  46 A,  46 B,  46 C establish three points of contact for mounting print bar  12  in printer  10  that form a primary, Z datum  48  to help maintain the desired spacing between printheads  26  and print media  16  during printing. 
     Referring specifically to  FIG. 4 , print media  16  is moved through a print zone  50  between printheads  26  and a platen  52  at the urging of media transport rollers  54 ,  56 . Z datum contact surfaces  46 A- 46 C abut mating surfaces on the printer chassis (not shown) to establish the correct Z direction spacing between printheads  26  and platen  52  when print bar  12  is installed in printer  10 , and thus help establish the correct spacing between printheads  26  and print media  16  during printing. Six points of contact may be used to correctly position and fully constrain print bar  12  in all six degrees of freedom of motion. For example, as described below with reference to  FIGS. 5-11 , three points of contact  46 A,  46 B and  46 C form a primary, Z datum  48  ( FIGS. 5 and 6 ), two points contact  58 A,  58 B form a secondary, Y datum  60  ( FIG. 5 ), and one point of contact  62  forms a tertiary, X datum  64  ( FIG. 5 ). The three primary, Z datum contact points  46 A- 46 C stop translation in the Z direction and rotation about the X and Y axes. The two secondary, Y datum points  58 A and  58 B stop translation in the Y direction and rotation about the Z axis. The single tertiary, X datum contact point  62  stops translation in the X direction. 
     Referring now to the example of print bar  12  shown in  FIGS. 5-11 , printhead mounting substrate  30  includes ink slots  66  that carry ink to each printhead  26  from a corresponding set of ink ports  68  in manifold  28 , as best seen in the section view of  FIG. 11 . (Section lines  10 - 10  and  11 - 11  in  FIG. 8  indicate the location of the sections of print bar substrate  12  shown in  FIGS. 10 and 11 , respectively.) Each set of ink slots  66  is surrounded by a mounting surface  70  on the front face  72  of substrate  30  for mounting printheads  26 . Manifold  28  and substrate  30  are joined to one another along surface(s)  74  on the front face  76  of manifold  28  and corresponding surface(s)  78  on the rear face  80  of substrate  30 . To help develop high quality personal and small business printers at an affordable price, it is often desirable or even necessary to use molded plastic parts, particularly for ink flow components with complex shapes like manifold  28 , substrate  30  and parts of printheads  26 . Accordingly, printheads  26  and manifold  28  are usually glued or welded to the respective substrate face  72 ,  80 . The close spacing between ink slots  66 , however, means substrate  30  and manifold  28  must be kept very flat during assembly to minimize the amount of adhesive or energy needed to join the parts. More adhesive to accommodate gluing non-flat parts increases the risk adhesive will flow into and obstruct an ink slot. Similarly, more energy to accommodate welding non-flat parts increases the risk softened plastic will flow into and obstruct an ink slot. However, it is difficult to consistently mold flat long, narrow plastic parts, like manifold  28  and substrate  30 , that hold their shape after being released from the mold. 
     To overcome this difficulty, flat reference surfaces  82 ,  84  are formed on a metal or other suitably rigid chassis  32 . For example, machining datum contact pads  62 ,  58 A- 58 B, and  46 A- 46 C and reference surfaces  82 ,  84  on to a cast aluminum chassis  32  enables consistently manufacturing suitably flat print bar structures  14 . X, Y, and Z datum contact pads  62 ,  58 A- 58 B, and  46 A- 46 C are machined flat on chassis  32  after casting to define X datum  64 , Y datum  60 , and Z datum  48 . Reference surfaces  82  and  84  are machined on to flange  40  in X-Y planes parallel to the X-Y plane defined by primary Z datum  48 . Chassis flange  40  surrounds an opening  86 . In the example shown, flange  40  completely surrounds opening  86 . Other configurations are possible. For example, it may be desirable in some implementations to utilize a discontinuous flange  40  that only partially surrounds opening  86 . In either case, one or both of manifold front face  76  and substrate rear face  80  extend into or through chassis opening  85 . In the example shown, as best seen in  FIG. 11 , the front face  76  of manifold  28  extends into chassis opening  86 . 
     During assembly, an alignment surface  88  on the rear face  80  of mounting substrate  30  is forced against chassis reference surface  82  and an alignment surface  90  on the front face  76  of manifold  28  is forced against chassis reference surface  84 . Forcing substrate  30  and manifold  28  against the flat chassis reference surfaces  82 ,  84  eliminates warp and establishes a uniform gap  92  between the attachment surfaces  94 ,  96  on the two parts  28 ,  30 . For a glue joint  98 , adhesive is used to fill gap  92  to join the two plastic parts  28 ,  30 . For a weld joint  98 , plastic flows into gap  92  to join the two parts  28 ,  30 . The biasing force on the plastic parts  28 ,  30  is maintained until the adhesive cures or until the weld is completed. Once joint  98  is secure, printhead mounting substrate  30  maintains contact with chassis reference surface  82  so that the printhead mounting surfaces  70  on substrate  30  are flatter and more parallel to primary, Z datum  48  than is possible without the “backbone” provided by chassis  32 . (The relationship between chassis flange  40 , opening  86 , alignment surfaces  88 ,  90 , attachment surfaces  94 ,  96 , and joint  98  is also shown in the simplified, diagrammatic view of  FIG. 2 .) 
     A second difficulty constructing a media wide print bar  12  is enabling print bar structure  14  to withstand the dimensional changes that occur as manifold  28 , substrate  30 , and chassis  32  expand and contract during temperature fluctuations. The stresses associated with dimensional changes in the parts can result in joint failure or permanent dimensional changes that compromise print quality. Examples of the new print bar structure  14  include features that help the structure withstand the stresses of dimensional change without damaging the print bar. To minimize tolerances and improve part-to-part alignment, as described in detail below, the alignment features for both manifold  28  and mounting substrate  30  are located directly adjacent to one another on chassis  32 . Also, manifold  28  and substrate  30  are molded from the same plastic to have substantially the same coefficient of thermal expansion (CTE). While the CTE of a plastic manifold  28  and substrate  30  is different from the CTE of chassis  32 , and chassis  32  will expand or contract differently than manifold  28  and substrate  30 , manifold  28  and substrate  30  are joined to one another but not to chassis  32 . Thus, the parts with different CTEs can move relative to one another in the XY plane along chassis flange  40 . Allowing the parts to move in the XY plane helps relieve dimensional change stresses without changing the position of substrate  30  (and thus printheads  26 ) with respect to the primary, Z datum  48 . 
     Referring to  FIGS. 6-11 , printhead mounting substrate  30  extends lengthwise in the X direction. Two alignment slots  110  are located on opposite ends of chassis  32  in the X direction. Corresponding pins  112  at each end of mounting substrate  30  fit tightly in chassis alignment slots  110  in the Y direction (across the width of slots  110 ) and loosely in the X direction (along the length of slots  110 ). Pins  112  are located at the mid-point of substrate  30  in the Y direction—the neutral point from which expansion and contraction in the Y direction will occur in substrate  30 . The tight fit of pins  112  across the width of slots  110  constrains mounting substrate  30  in the Y direction while the loose fit along the length of slots  110  allows substrate  30  to move in the X direction during expansion or contraction. A third alignment slot/pin pair  114 ,  116  is located at the mid-point of mounting substrate  30  in the X direction—the neutral point from which expansion and contraction in the X direction will occur in substrate  30 . The tight fit of pin  116  across the width of slot  114  constrains mounting substrate  30  in the X direction while the loose fit along the length of slot  114  allows substrate  30  to move in the Y direction during expansion or contraction. 
     The slot/pin pair interfaces form a slip joint  118  between printhead mounting substrate  30  and chassis  32  that helps control part-to-part alignment during heating and cooling. Although the part-to-part alignment will change during heating and cooling, slip joint  118  created by the pin/slot interface helps determine how the alignment changes—the slot acts like a track for the pin to follow in the event of a dimensional change during a thermal event. As long as there is contact between the pin and the slot, the path the parts take during expansion (heating) should be the same as the path they take during contraction (cooling). Thus, the parts should return to the same place they were before the thermal event occurred. 
     A slip joint  120  between ink manifold  28  and chassis  32  is achieved in the same way, but the alignment features are reversed. Alignment slots  122 ,  124  in manifold  28  fit on corresponding pins  126 ,  128  on chassis  32 . In the example shown, each chassis pin  126 ,  128  is configured as a continuation of the sidewalls  130  that define chassis slots  110  and  114 . This configuration, in which the substrate/chassis and manifold/chassis slip joints are positioned back-to-back, allows forming the plastic joint features by the same side of the mold, reducing positional tolerances and improving alignment between substrate ink slots  66  and manifold ink ports  68 . Better alignment, in turn, helps minimize the risk of ink slot/port obstruction during gluing or welding. 
     As noted above, the CTEs of plastic parts  28 ,  30  and a metal chassis  32  are not the same. Upon heating or cooling the plastic manifold  28  and substrate  30 , which are affixed to one another, will expand or contract about the same but differently than chassis  32 . Allowing the parts to slip in the X and Y direction at joints  118  and  120  helps keep the parts from loosening in the Z direction by reducing joint stress during thermal events. Slip joints  118  and  120  allow the parts to expand or contract in the XY plane, minimizing bowing and other distortion in the Z direction. Maintaining a tight fit in the Z direction is desirable because the alignment of printheads  26  to the primary, Z datum helps define the spacing between printheads  26  and print media  16  in print zone  50  during printing (FIG.  4 )—properly controlling the printhead-to-media spacing is important to good quality printing. 
     Reversing the male/female relationship between the parts in slip joints  118  and  120  in print bar structure  114  also helps control part-to-part alignment during both heating and cooling. The pins track in the slots during expansion and contraction. To avoid sloppy tracking, the pins should stay tight in the slots during heating and cooling. This is achieved by reversing the male/female relationship based on the CTEs of the two materials—for example an aluminum chassis  32  with a larger CTE and a plastic manifold  28  and printhead mounting substrate  30  with a smaller CTE. During heating, when the parts expand, the male features on substrate  30  (pins  112 ,  116 ) get a little bigger while the female features on chassis  32  (slots  110 ,  110 ) get a lot bigger, creating unwanted slop and loosening at slip joint  118 . However, the male features on chassis  32  (pins  126 ,  128 ) get a lot bigger while the female features on manifold  28  (slots  122 ,  124 ) only get a little bigger, tightening slip joint  120 . Manifold  28  and substrate  30  are affixed to one other and, consequently, the still tight slip joint  120  maintains control during heating. During cooling, when the parts contract, slip joint  120  may loosen but slip joint  118  will tighten. Thus, by reversing the male/female relationship of the slip joints, one of the two slip joints should remain tight to maintain control during both heating and cooling. 
     “A” and “an” as used in the claims means one or more. 
     The examples shown in the Figures and described above illustrate but do not limit the invention. Other forms, details and examples may be made without departing from the spirit and scope of the invention which is defined in the following claims.