Abstract:
In one embodiment, an assembly includes: a print bar; first and second guide rods oriented parallel to one another; a first bracket slidable along the first guide rod and connected loosely to one end of the print bar; and a second bracket slidable along the second guide rod and connected loosely to the other end of the print bar. In another embodiment, a method includes: directly constraining a print bar in Z and theta Y at a first connection; indirectly constraining the print bar in theta Y at a second connection; and neutralizing the theta Y constraint at the second connection through a third connection between the first connection and the second connection.

Description:
BACKGROUND 
       [0001]    In some inkjet printers, a media wide arrangement of stationary printheads is used to print on paper or other print media moving past the printheads. Unlike scanning printheads, there is no scan axis along which these stationary page wide array (PWA) printheads may be moved to a service station. Thus, another technique is needed to bring the PWA printheads and the service station together. 
     
    
     
       DRAWINGS 
         [0002]      FIG. 1  is a block diagram illustrating one example of an inkjet printer in which embodiments of the new print bar lift may be implemented. 
           [0003]      FIGS. 2 and 3  are perspective views illustrating one example embodiment of a print bar lift installed in a chassis.  FIG. 2  shows a print bar supported in the lift. The print bar is omitted from  FIG. 3 . 
           [0004]      FIGS. 4 and 5  are perspective and side elevation views, respectively, and 
           [0005]      FIGS. 6 and 7  are elevation end views, illustrating the print bar lift of  FIGS. 2 and 3  in more detail. 
           [0006]      FIGS. 5A and 5B  are detail views taken from  FIG. 5 , 
           [0007]      FIG. 6A  is a detail view taken from  FIG. 6 , and 
           [0008]      FIG. 7A  is a detail view taken from  FIG. 7  illustrating one example embodiment of the connection between the print bar and the print bar lift shown in  FIGS. 2-5 . 
           [0009]      FIGS. 8 and 9  are schematic end views illustrating one example embodiment for the position of a print bar and print bar lift such as that shown in  FIGS. 2-5  installed in a printer. 
           [0010]      FIG. 10  is a detail perspective view showing one example embodiment for mounting the lift guide rods to the chassis. 
           [0011]      FIG. 11  is an elevation view, and 
           [0012]      FIGS. 12-13  are plan views showing one example embodiment for mounting the lift brackets to the guide rods in the print bar lift of  FIGS. 2-5 . 
           [0013]      FIGS. 14-18  illustrate one example sequence of operation of the print bar lift shown in  FIGS. 2-5 .  FIGS. 14 and 16  show the lift in a raised, servicing position and in a lowered, printing position, respectively.  FIGS. 15 and 17  show the lift in a raised, servicing position and in a lowered, printing position, respectively, with an optional spacer for a larger printhead to platen spacing.  FIG. 18  is a more detailed view showing the areas of contact between a stop and the print bar. 
       
    
    
       [0014]    The same part numbers are used to designate the same or similar parts throughout the figures. 
       DESCRIPTION 
       [0015]    Embodiments of the new print bar lift were developed to facilitate servicing stationary PWA printheads. (Stationary in this context means that the printheads and the print bar holding the printheads remain stationary during printing.) In one example embodiment, the print bar is constrained in the correct printing position but “floats” on loose connections when raised to a servicing position, to reduce the risk of binding on the lift guide rods even when using a lower cost, light duty drive train. In one example embodiment, the lift is configured to simultaneously move both ends of the print bar along the guide rods. Embodiments of the new lift are not limited PWA printheads. The embodiments shown in the figures and described below are non-limiting, example embodiments. Other embodiments are possible and nothing in the following description should be construed to limit the scope of the disclosure, which is defined in the Claims that follow this Description. 
         [0016]    Although embodiments of the new print bar lift are not necessarily limited to printers dispensing ink or other liquids, and may be used for devices dispensing other fluids, inkjet printheads generally are not practical for dispensing fluids composed primarily of gas(es). Thus, “liquid” as used in this document means a fluid not composed primarily of a gas or gases. 
         [0017]    A “printhead” as used in this document refers to that part of an inkjet printer or other type of inkjet drop dispenser that expels drops of liquid from one or more openings, including what is commonly referred to as a printhead die, a printhead die assembly and/or a printhead die carrier assembly. A “print bar” as used in this document means a structure or device holding an arrangement of printheads that remains stationary during printing. “Printhead” and “print bar” are not limited to printing with ink but also include inkjet type dispensing of other liquids and/or for uses other than printing. 
         [0018]    In this document, “parallel” and “perpendicular” mean substantially parallel and substantially perpendicular. Therefore, small misalignment due to loose connections is included within the definition of each of these terms. 
         [0019]    The translational and rotational degrees of freedom of a print bar and parts of a print bar lift are described with reference to X, Y and Z axes, where the X axis extends in a direction laterally across a print zone perpendicular to the direction the print media moves through the print zone, the Y axis extends in a direction parallel to the direction the print media moves through the print zone, and the Z axis is perpendicular to the X and Y axes. Theta X refers to rotation about the X axis, theta Y refers to rotation about the Y axis, and theta Z refers to rotation about the Z axis. 
         [0020]      FIG. 1  is a block diagram illustrating one example of an inkjet printer in which embodiments of the new print bar lift may be implemented. Referring to  FIG. 1 , an inkjet printer  10  includes a print bar  12  spanning the width of a print media  14 . Printer  10  also includes flow regulators  16  associated with print bar  12 , a media transport mechanism  18 , ink supplies  20 , and an electronic printer controller  22 . Print bar  12  in  FIG. 1  includes an arrangement of multiple printheads for ejecting drops of ink on to a sheet or continuous web of paper or other print media  14 . Each printhead is electrically connected to printer controller  22 , typically through a flexible circuit tape holding multiple electrical conductors. Each printhead is fluidically connected to one or more ink supplies  20  through a typically complex ink flow path in print bar  12  and through flow regulators  16 . In operation, printer controller  22  selectively energizes ink ejector elements in a printhead, or group of printheads, in the appropriate sequence to eject ink on to media  14  in a pattern corresponding to the desired printed image. Controller  22  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 . 
         [0021]      FIGS. 2 and 3  are perspective views illustrating one example embodiment of a print bar lift  24  mounted in a chassis  26 .  FIG. 2  shows a print bar  12  supported in lift  24 . Print bar  12  is omitted from  FIG. 3  to better illustrate other parts.  FIGS. 4 and 5  are perspective and side elevation views, respectively, and  FIGS. 6 and 7  are elevation end views, illustrating print bar lift  24  in more detail. 
         [0022]    Referring first to  FIGS. 2 and 3 , chassis  26  represents generally a stationary structure (relative to print bar  12 ) for supporting lift  24  in a printer  10  ( FIG. 1 ). In the embodiment shown, chassis  26  is constructed as a sheet metal frame that includes side panels  28 ,  30  and struts  32 ,  34 ,  36  extending between side panels  28 ,  30 . Chassis  26 , for example, may be part of a single integrated printer chassis or one component of a multi-component printer chassis. Chassis  26  also supports a pair of stationary stops  38  and  40  mounted opposite one another on side panels  28  and  30 , respectively. As described in more detail below, print bar  12  lands on stops  38  and  40  to help properly position print bar  12  for printing. 
         [0023]    Referring now also to  FIG. 4-7 , lift  24  includes a pair of guide rods  42 ,  44  and a corresponding pair of lift brackets  46 ,  48  that slide along guide rods  42 ,  44 . Each guide rod  42 ,  44  is mounted to a corresponding side panel  28 ,  30  of chassis  26  as shown in  FIGS. 2 and 3 . Mounting details for guide rods  42 ,  44  in chassis  26  are described below with reference to  FIG. 10 . Print bar  12  is supported by lift brackets  46 ,  48  at each end  50 ,  52 . Lift  24  also includes a motor  54  connected to each lift bracket  46 ,  48  through a transmission  56 . In the example embodiment shown in  FIGS. 2-7 , transmission  56  includes a rack  58 ,  60  on each lift bracket  46 ,  48 , a pinion shaft  62  carrying pinions  64 ,  66  that simultaneously engage racks  58 ,  60 , respectively, and a drive train  68  coupled between motor  54  and pinion shaft  62 . Drive train  68  represents generally any suitable mechanism for transmitting the desired motive force from motor  54  to shaft  62 . 
         [0024]    To reduce the risk of brackets  46 ,  48  binding on guide rods  42 ,  44  when raising and lowering print bar  12 , while still allowing print bar  12  to be properly positioned for printing, print bar  12  is loosely connected to lift brackets  46 ,  48  in some degrees of freedom but tightly connected in other degrees of freedom. This mounting scheme allows for the vertical translation of a page wide printbar  12  along guide rods  42 ,  44  without precisely aligning rods  42 ,  44  in a parallel orientation. Binding and over constraint conditions may be minimized by managing each degree of freedom, X, Y, Z and theta X, theta Y, and theta Z even when using lower cost, light duty lift and transmission components. Print bar  12 , however, must be constrained when print bar  12  is in the printing position for proper printhead to media spacing and alignment. Stops  38  and  40  ( FIGS. 2-4 ) affixed to chassis  26  ( FIGS. 2 and 3 ) define the lower limit of travel, and constrain print bar  12  in the correct printing position parallel to and properly spaced from the print platen as shown in  FIGS. 8 and 9 . 
         [0025]    One example embodiment for the print bar, lift bracket and guide rod connections will now be described with reference to  FIGS. 5-13 . In this embodiment, as detailed below, the connections between lift brackets  46 ,  48  and guide rods  42 ,  44  constrain each bracket  46 ,  48  in X, Y, theta X and theta Y. Stops  38 ,  40  constrain print bar  12  in Z and theta Y (when print bar  12  is lowered onto stops  38 ,  40 ). Thus, two systems are competing to constrain print bar  12  in theta Y—rods  42 ,  44  acting through brackets  46 ,  48  and stops  38 ,  40 . Because theta Y is an important print zone control, effecting ink drop flight distance (along with Z and theta X), the more accurate vertical motion stops  38 ,  40  are used exclusively to constrain theta Y. Consequently, the theta Y constraint attempted by lift rods  42 ,  44  is neutralized by allowing each end of print bar  12  to pivot in theta Y at the connection with lift brackets  46 ,  48 . Similarly, the connections between rod  42 ,  44  and the corresponding lift bracket  46 ,  48  are competing to constrain theta X. The theta X constraint attempted by one of the rod/bracket connections  44 / 48  is neutralized by allowing the lift bracket to pivot in theta X at the connection with print bar  12 . 
         [0026]    Referring first to  FIGS. 6 ,  6 A and  8 , print bar first end  50  is constrained with respect to lift bracket  46  at a first lift bracket connection  70  in Y, Z and theta X with two pins  72 ,  74  protruding from print bar end  50  into mating holes  76 ,  78  in first lift bracket  46 . The use of two pin/holes  72 / 76  and  74 / 78  spaced apart in the Y direction constrains print bar  12  in theta X. Each pin/hole connection  72 / 76 ,  74 / 78  constrains print bar  12  in Y and Z. In the example embodiment shown in  FIG. 6 , round pins  72 ,  74  with flats fit into square holes  76 ,  78 . Other suitable pin/hole configurations may be used. Referring now to  FIG. 5A , print bar first end  50  is constrained in X by a rib  79  protruding from bracket  46  and abutting print bar end  50 . Rib  79  is narrow in Z to allow print bar first end  50  freedom in theta Y. Ribs  79  spaced apart along Y at each pin/hole connection also constrain print bar first end  50  in theta Z. 
         [0027]    Referring to  FIGS. 7 ,  7 A and  9 , print bar second end  52  is connected to second lift bracket  48  at a single pin connection  80 . A pin  82  protruding from print bar second end  52  fits into a mating hole  84  in second lift bracket  48 . The single pin/hole connection  80  constrains print bar second end  52  in Y and Z with respect to bracket  48  but allows freedom in theta X. Referring to  FIG. 5B , for second end connection  80 , a shortened rib  85  leaves a gap  87  between print bar second end  52  and second lift bracket  48 , allowing print bar second end  52  freedom in X. The connections between rod  42 ,  44  and the corresponding lift bracket  46 ,  48  are competing to constrain X. The X constraint attempted by rod/bracket connection  44 / 48  is neutralized by allowing print bar second end  52  this freedom in X. 
         [0028]    Print bar ends  50 ,  52  may be secured to lift brackets  46 ,  48  by screws or other suitable fasteners at each pin/hole connection  72 / 76 ,  74 / 78  and  82 / 84 . Screw holes are shown in the ends of pins  72  and  82  in  FIGS. 6A and 7A  but screws are not shown in the figures to avoid obscuring the alignment features at each connection. 
         [0029]    The mounting details for guide rods  42 ,  44  in chassis  26  and for lift brackets  46 ,  48  on guide rods  42 ,  44  will now be described with reference to  FIGS. 10-13 .  FIG. 10  shows one example embodiment for mounting lift guide rods  42 ,  44  to chassis  26 .  FIGS. 11-13  show one example embodiment for mounting lift brackets  46 ,  48  to guide rods  42 ,  44 . 
         [0030]    Referring to  FIG. 10 , each guide rod  42 ,  44  is mounted to chassis  26  with a lower, rigid mounting tab  86 , a spring tab  88 , and an upper, rigid mounting tab  89 . The mounting for guide rod  42  is shown in  FIG. 10 . The mounting for guide rod  44  on the opposite side of lift  24  is the same as that shown for guide rod  42 . In the example embodiment shown, mounting tabs  86  and  89  are pressed out of a sheet metal chassis side panel  28 . A tapered lower end  90  of guide rod  42  fits into a hole  91  in rigid tab  86 . The upper end  92  of guide rod  42  snaps in under spring tab  88  to press lower rod end  90  down into hole  91  in tab  86 , constraining guide rod  42  in X, Y and Z. Although other suitable mounting configurations are possible, the configuration shown allows for an easy and secure assembly of guide rod  42  into chassis  26 . 
         [0031]      FIG. 11  is an elevation and partial section view showing the connection between first lift bracket  46  and first guide rod  42 .  FIG. 12  is a plan view looking down on the top of lift bracket  46  on guide rod  42 .  FIG. 13  is a plan view looking up at the bottom of lift bracket  46  on guide rod  42 . The mounting of second lift bracket  48  on second guide rod  44  is the same as that shown in  FIGS. 11-13 . As shown in  FIG. 12 , a top retainer part  94  of bracket  46  is beveled on one side in the Y direction in a truncated V shape. As shown in  FIG. 13 , a bottom retainer part  96  of bracket  46  is beveled on the other side in the Y direction in a truncated V shape. The weight of print bar  12  and its cantilever positioning extending out in the Y direction creates a torque on lift bracket  46  in theta X that holds lift bracket  48  in contact with guide rod  44  at the V shaped top  94  and at the V shaped bottom part  96 , as shown in  FIGS. 12 and 13  at contact arrows  98 . That is to say, the weight and position of print bar  12  automatically “preloads” guide rod  42  into the V shaped retainer parts of bracket  46  to prevent lift bracket  46  from rocking back and forth on guide rod  42  when print bar  12  is raised and lowered. Clearances C X  and C Y  between the inside dimension of lift bracket  46  and outside dimension of guide rod  42  help reduce the risk of bracket  46  binding on rod  42 . The small bearing surface contact between lift bracket  48  and guide rod  42  at these V shaped parts  94  and  96  allows lift bracket  46  to move freely along guide rod  42 . The bearing surfaces may be lubricated to help ensure free movement. 
         [0032]    One example sequence of operation of lift  24  will now be described with reference to  FIGS. 14-18 .  FIGS. 14 and 16  show lift bracket  46  in a raised, servicing position and in a lowered, printing position, respectively, with an optional spacer  100  retracted for smaller printhead to platen spacing.  FIGS. 15 and 17  show lift bracket  46  in a raised, servicing position and in a lowered, printing position, respectively, with spacer  100  extended for a larger printhead to platen spacing. Each spacer  100  is mounted to a corresponding lift bracket  46 ,  48  such that it can be extended into an operative position over stops  38 ,  40 , as shown in  FIGS. 15 and 17 , or retracted out of the way as shown in  FIGS. 14 and 16 . Alternatively, each spacer  100  could be mounted to print bar  12 .  FIG. 18  is a more detailed view from the front of print bar  12  showing the areas of contact between stop  38  and print bar first end  50  and spacer  100 . Although only once side of lift  24  is shown, both sides are raised and lowered simultaneously through pinion shaft  62 . 
         [0033]    Referring to  FIGS. 14 and 15 , pinions  64  and  66  are driven clockwise on shaft  62  to simultaneously raise print bar  12  connected at each end  50 ,  52  to lift brackets  46 ,  48 . Referring to  FIGS. 16 and 17 , pinions  64  and  66  are driven counter-clockwise on shaft  62  to simultaneously lower print bar  12 . Referring now also to  FIG. 18 , at the lower limit of travel shown in  FIG. 16 , with spacer  100  retracted, one or more datum reference surfaces  102  on each end of the print bar  12  engage mating datum reference surface(s)  104  on stops  38  and  40  to properly position the print bar for printing at a smaller printhead to platen spacing (PPS). The contact between datums  102  and  104  corresponding to  FIG. 16  is indicated by line  106  in  FIG. 18 . At the lower limit of travel shown in  FIG. 17 , with spacer  100  extended, datum reference surface(s)  102  on each end of the print bar  12  engage mating datum reference surface(s)  108  on spacer  100  to properly position the print bar for printing, but at a larger printhead to platen spacing (PPS). The contact between datums  102  and  104  corresponding to  FIG. 17  is indicated by line  110  in  FIG. 18 . Spacer  100  may be a single thickness, as shown, for only one PPS adjustment or spacer  100  may be stepped or wedge shaped to allow for multiple PPS adjustments. 
         [0034]    Referring again to the schematic end views of  FIGS. 8 and 9 , print bar  12  in printer  10  includes printheads  112  spaced apart from a platen  114  carrying paper  14  or other print media at a desired PPS. The desired PPS in  FIGS. 8 and 9 , for example, may be a smaller PPS (i.e., without a spacer  100 ) or a larger PPS (i.e., with a spacer  100 ). 
         [0035]    Referring again to  FIGS. 4 and 5 , in the example embodiment shown, an encoder  116  is used to help control lift  24 . Encoder  116 , for example, includes an encoder disk  118  that rotates with shaft  62  and a sensor  120  that senses markings or other indicia on disk  118 . The data/signals from sensor  120  indicate characteristics of disk  118  such as position, speed and acceleration and, accordingly, the corresponding characteristics of print bar  12 . This information may be used by printer controller  22  ( FIG. 1 ) to control motor  54  to move print bar  12  to a desired position at a desired speed and acceleration. For example, it may be desirable when raising and lowering print bar  12  to accelerate and decelerate lift  24  slowly to avoid rocking lift brackets  46 ,  48  on rods  42 ,  44  (by overcoming the guide rod preload described above). For another example, information from encoder  116  allows controller  22  ( FIG. 1 ) to accurately position print bar  12  at any location along its full range of travel on lift  24 . 
         [0036]    As noted above, the example embodiments shown in the Figures and described above do not limit the disclosure. Other embodiments are possible. For example, although guide rods  42 ,  44  are shown as having a round cross-section, they may be rectangular or any other suitable shape. Also, guide rods  42 ,  44  need not be vertical. While it is expected that guides rods  42 ,  44  will usually be oriented vertical and perpendicular to the long axis of print bar  12 , rods  42 ,  44  may be disposed at other orientations. Accordingly, these and other forms, details and embodiments may be made without departing from the spirit and scope of the disclosure, which is defined in the following claims.