Abstract:
A device and method for the alignment, in up to six degrees of freedom, of printheads in a printer is disclosed. The device has a support, wherein the printhead is secured to a substantially center location of the support. The device further has a fixed plate biased against the support by plurality of first screws extending substantially in a Z direction, a plurality of a second screws extending substantially in a Y direction, and a third screw extending substantially in an X direction. The fixed plate, and thus the printhead, may be translated in each of the X, Y and Z directions and may be rotated about each of the X, Y, and Z axes by manipulation of the screws to achieve possible alignment in all six degrees of freedom.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention is directed to direct marking systems that utilize multiple staggered printheads in order to achieve full width printing per pass. More specifically, this invention is directed to a device and method for the alignment, in six degrees of freedom or less, of multiple printheads in a printer by providing adjustments in up to all six degrees of freedom for each printhead. 
     2. Description of Related Art 
     Misalignment of printheads may be due to, for example, poor manufacturing tolerances, thermal expansion of the printhead and associated parts of the printer, vibration of the printhead, or the like. Thus, aligning the printheads with sufficient accuracy to allow high image quality is desired. 
     Devices for alignment of printheads in a printer are known. For example, U.S. Pat. No. 6,068,415 to Smolenski discloses a printhead that is spring loaded, permitting it to float in both the vertical and horizontal directions. Smolenski also discloses placing the printhead on a comparatively short and rigid pivoting arm. 
     U.S. Pat. No. 6,298,783 to O&#39;Mera at al. discloses an alignment device for mounting an alignable part, such as a thermal printhead, on a support frame. The printhead is adjustable on the support frame relative to a reference plane about a pivot axis on the support frame and also laterally of the reference plane. 
     Known mechanisms for alignment of printheads are limited in the number of degrees of translation and rotation of the printhead that can be independently adjusted. This is not suitable since misalignment may occur in any of the six degrees of freedom (translation and rotation). Some existing technologies use an additional alignment mechanism for each increment in degree of freedom. However, this leads to a larger footprint area of the alignment mechanisms, more parts, and thus more thermal expansion and vibration, further leading to misalignment of the printhead. 
     SUMMARY OF THE INVENTION 
     There is a need for an alignment mechanism for printheads in all six degrees of freedom or less, with sufficient accuracy to allow high image quality. 
     There is a need for an alignment mechanism for printheads that may align a plurality of printheads with respect to each other and with respect to the print medium. 
     There is a need for an alignment mechanism that can align multiple staggered printheads. 
     There is a need for a more compact alignment mechanism. 
     The above and other advantages are achieved by various embodiments of the invention. 
     The alignment device of the present invention consists of plates that are spring loaded together. Adjustment screws are used to move the plates relative to each other, thereby allowing the printhead to be adjusted independently in any of the six degrees of freedom. 
     In exemplary embodiments, a printhead may be aligned in up to six degrees of freedom. 
     In exemplary embodiments, the thermal expansion of the printhead may be reduced by minimizing the number of required alignment mechanisms for a multiple staggered printhead assembly for a printer. 
     In exemplary embodiments, the vibration of the printhead may be reduced by a more compact alignment mechanism that may be more centrally located with respect to the printhead. 
     In exemplary embodiments, increased life of the printer can be achieved by the reduction in vibration and thermal expansion of the different parts of the printer. 
     In exemplary embodiments, improved print quality may be achieved by an improved alignment mechanism for printheads. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a front view of an alignment mechanism for printheads; 
         FIG. 2  illustrates a rear view of an alignment mechanism for printheads; 
         FIG. 3  illustrates multiple alignment mechanisms with a printhead for a single printer; and 
         FIG. 4  illustrates a front view of an embodiment of multiple alignment mechanisms with a printhead for a single printer. 
         FIG. 5  illustrates a rear view of an embodiment of multiple alignment mechanisms with a printhead for a single printer. 
         FIG. 6  illustrates a front view of an embodiment of multiple alignment mechanisms with a printhead for a single printer. 
         FIG. 7  illustrates a rear view of an embodiment of multiple alignment mechanisms with a printhead for a single printer. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Six degrees of freedom, as used herein, refers to each of the degrees of translation and rotation with respect to the X, Y, and Z axes. That is, the six degrees of freedom comprise (1) translation in the X direction, (2) translation in the Y direction, (3) translation in the Z direction, (4) rotation about the X axis, (5) rotation about the Y axis and (6) rotation about the Z axis. 
     Referring to  FIGS. 1 and 2 , an alignment mechanism  10  of the present invention is illustrated. The alignment mechanism contains a plate  12  having a front surface  14  and a back surface  16 . A plurality of protrusions  18  are located on the front surface  14  of the plate  12 . Two of the plurality of protrusions  18  are each located on opposite sides of the plate  12  and extend from the front surface  14  of the plate  12 . Openings  20  in the plate  12  are located at least under each of the two protrusions  18 . The openings  20  allow for a reduced total mass of the alignment mechanism and may be designed to accommodate different parts of the alignment mechanism and/or the printing device in which the alignment mechanism is located. 
     The plate  12  has a protruding lip  22  on which a printhead (not shown) can be secured. The lip  22  may preferably have a channel or groove  24  on which the printhead may be secured to the plate  12  in a substantially central location of the alignment mechanism  10 . Thus, by aligning the plate  12 , the printhead secured thereon may be aligned in six different degrees of freedom. 
     The back surface  16  of the plate  12  is biased against a face  26  of a fixed plate  28  in the Z direction. Projections  30  on the face  26  of the fixed plate  28  extend through or into each of the openings  20  under the two protrusions  18  of the plate  12  when the plate  12  is biased against the fixed plate  28 . 
     The plate  12  is biased against the face  26  of the fixed plate  28  via springs  32  connected between the plate  12  and the fixed plate  28 . Three independent adjustment screws  34 ,  36  and  38  are secured to the fixed plate  28  via threaded holes (not shown). The adjustment screws  34 ,  36  and  38  extend between the fixed plate  28  and the plate  12 . The springs  32  provide a load that applies a force to the plate  12  in a direction counter to the adjustment screws  34 ,  36  and  38 . 
     Rotation of the adjustment screws  34 ,  36  and  38  results in translation of the plate in the Z direction at adjustment points  40 ,  42  and  44 , respectively. To adjust the a printhead uniformly in the Z direction, all three adjustment screws  34 ,  36  and  38  must be rotated an equal amount in the same direction (i.e., either the clockwise or counter-clockwise direction) thereby adjusting the plate  12  on which the printhead is attached. 
     The adjustment screws  34 ,  36  and  38  preferably maybe located at right angles with respect to each other and within the same vertical plane. Each of the adjustment screws  34 ,  36  and  38  are also spaced apart to the extent sufficient to permit rotation upon adjustment (i.e., rotation of the screw), thereby allowing independent rotation of the plate  12  (and thus the printhead) about an X and/or Y axis. More specifically, the adjustment screws  36  and  38  are preferably each located adjacent and inside two separate protrusions  18  and within the same horizontal plane, while the adjustment screw  34  is located at a right angle from the adjustment screw  36  and in the same vertical plane as the adjustment screw  36 . Thus, for example, to rotate the printhead about the X axis, adjustment screws  36  and  38  would be uniformly rotated while the adjustment screw  34  remains fixed. To rotate the printhead about the Y axis, the adjustment screw  38  would be rotated while the adjustment screws  34  and  36  remain fixed. 
     Alignment of the printhead in the Y direction is accomplished via two independent adjustment screws  46  and  48 . The adjustment screws  46  and  48  preferably may each be located at right angles with respect to each of adjustment screws  34 ,  36 , and  38 . The adjustment screws  46  and  48  are secured to a top surface  50  of the plate  12  or to a bottom surface  51  of the plate  12  via threaded holes (not shown) on opposite ends  52  and  54  of the plate  12 . Each of the adjustment screws  46  and  48  extend through the plate  12  into each of the openings  20  under the two protrusions  18  of the plate  12 , and into the projections  30  on the face  26  of the fixed plate  28 , when the plate  12  is biased against the fixed plate  28 . Two compression springs  56  bias a bottom  58  of each of the openings  20  under the two protrusions  18  against a tip (not shown) of each of the adjustment screws  46  and  48 . 
     Rotation of the adjustment screws  46  and  48  results in translation of the plate  12  in the Y direction. To adjust the plate  12  uniformly in the Y direction, both of the adjustment screws  46  and  48  must be rotated an equal amount and in the same direction while keeping the adjustment screws  34 ,  36  and  38  fixed. 
     Rotation of the adjustment screws  46  and  48  also results in rotation of the plate  12  about the Z axis. To rotate the plate  12  about the Z axis, either of the adjustment screws  46  or  48  may be rotated while keeping the adjustment screws  34 ,  36  and  38  fixed. 
     Alignment of the printhead in the X direction is accomplished via an adjustment screw  60 . The adjustment screw  60  preferably may be located at a right angle with respect to each of the adjustment screws  34 ,  36 ,  38 ,  46  and  48 . The adjustment screw  60  is secured to a side  62  of the fixed plate  28  via a threaded hole (not shown) in the fixed plate  28 . The adjustment screw  60  extends through the fixed plate  28  into a window  64  located in the fixed plate  28  and into or through another protrusion  19  extending from the back surface  16  of the plate  12 . The plate  12  is biased against the adjustment screw  60  by another compression spring  66  extending from a wall  68  of the window  64  to a tip (not shown) of the adjustment screw  60 . 
     Adjustment in the X direction is accomplished by rotation of the adjustment screw  60 . 
     Although the adjustment screws  34 ,  36 ,  38 ,  46 ,  48  and  60  as described herein allow for translation and/or rotation of the printhead, each of the adjustments screws  34 ,  36 ,  38 ,  46 ,  48  and  60  may also be designed to remain fixed. Accordingly, any of the adjustment screws  34 ,  36 ,  38 ,  46 ,  48  and  60  may be, for example, a rod or other fixed object that remains fixed. 
     Further, it is envisioned that the alignment mechanism may be constructed with fewer than the six adjustment screws  34 ,  36 ,  38 ,  46 ,  48  and  60  thereby providing translation and rotation in less than all six degrees of freedom. Alternatively, the six adjustment screws  34 ,  36 ,  38 ,  46 ,  48  and  60  or less than the six adjustment screws may be located at varying angles and directions with respect to each other without exceeding the intended scope of this invention. 
     The alignment mechanism  10  as described with reference to  FIGS. 1 and 2  can be used in a printer within a direct marking print engine where the adjustment of the printhead is required. Further, more than one alignment mechanism  10  may be incorporated into the printer to accommodate more than one printhead. 
       FIGS. 3–5  illustrate more than one alignment mechanism  10  mounted to different parts of the printer.  FIG. 3  illustrates a first alignment mechanism  100  and a second alignment mechanism  102  mounted on a frame  104 . A printhead assembly  106  is shown with a printhead  108  attached to the second alignment mechanism  102  as described above. Here, the first alignment mechanism  100  and the second alignment mechanism  102  allow for relative alignment of multiple printheads in the same printer. 
     In another embodiment, different parts of a printer may be used as the fixing plate for a plurality of alignment mechanisms. Referring to  FIGS. 4–7 , a plate  110  (as described above with respect to plate  12  of the alignment mechanism  10 ), may be biased against a frame  112  (as described above with respect to the fixing plate  28  of the alignment mechanism  10 ). The frame  112  may be sheet metal, a casting, or any fixed object in an image forming device. Adjustment screws  114 ,  116  and  118  may allow for adjustment of a printhead in six degrees of freedom as described above with respect to the adjustment screws  60 ;  46  and  48 ; and  34 ,  36  and  38 , respectively. 
     It is envisioned that the alignment mechanism of the present invention may be used to manually adjust printheads or may be used in conjunction with a motor for automatic adjustment of the printheads without human intervention. 
     Further, the alignment mechanism of the present invention allows for mounting of the printhead nearer to the center of mass of the alignment mechanism, thereby reducing vibration of the printhead and alignment mechanism. 
     Still further, the alignment mechanism allows for a reduced number of parts required to align the printhead in the six different degrees of freedom, thereby reducing thermal expansion. By reducing thermal expansion and vibration of the different parts, the life of the parts of the printers may be increased and required realignment of the printhead decreased. 
     Further, the alignment mechanism of the present invention allows for improved print quality. 
     The plate  12  and fixed plate  28  as well as the other parts of the alignment mechanism discussed herein may be of any shape or size and the shape illustrated herein is not intended to limit the embodiments of the invention discussed herein. 
     It is envisioned that the alignment mechanism for printheads of the present invention may be used in a variety of different environments, such as, for example, with printers, copiers, fax machines, and the like. 
     While certain exemplary embodiments have been described in detail and shown in the accompanying drawings, those of ordinary skill in the art will recognize that the invention is not limited to the embodiments described and that various modification may be made to the illustrated and other embodiments of the invention described above, without departing from the broad inventive scope thereof. It will be understood, therefore, that the invention is not limited to the particular embodiments or arrangements disclosed, but is rather intended to cover any changes, adaptations or modifications which are within the scope and spirit of the invention as defined by the appended claims.