Alignment mechanism for direct marking printheads and a method for aligning printheads in a printer

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.

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'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.

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 toFIGS. 1 and 2, an alignment mechanism10of the present invention is illustrated. The alignment mechanism contains a plate12having a front surface14and a back surface16. A plurality of protrusions18are located on the front surface14of the plate12. Two of the plurality of protrusions18are each located on opposite sides of the plate12and extend from the front surface14of the plate12. Openings20in the plate12are located at least under each of the two protrusions18. The openings20allow 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 plate12has a protruding lip22on which a printhead (not shown) can be secured. The lip22may preferably have a channel or groove24on which the printhead may be secured to the plate12in a substantially central location of the alignment mechanism10. Thus, by aligning the plate12, the printhead secured thereon may be aligned in six different degrees of freedom.

The back surface16of the plate12is biased against a face26of a fixed plate28in the Z direction. Projections30on the face26of the fixed plate28extend through or into each of the openings20under the two protrusions18of the plate12when the plate12is biased against the fixed plate28.

The plate12is biased against the face26of the fixed plate28via springs32connected between the plate12and the fixed plate28. Three independent adjustment screws34,36and38are secured to the fixed plate28via threaded holes (not shown). The adjustment screws34,36and38extend between the fixed plate28and the plate12. The springs32provide a load that applies a force to the plate12in a direction counter to the adjustment screws34,36and38.

Rotation of the adjustment screws34,36and38results in translation of the plate in the Z direction at adjustment points40,42and44, respectively. To adjust the a printhead uniformly in the Z direction, all three adjustment screws34,36and38must be rotated an equal amount in the same direction (i.e., either the clockwise or counter-clockwise direction) thereby adjusting the plate12on which the printhead is attached.

The adjustment screws34,36and38preferably maybe located at right angles with respect to each other and within the same vertical plane. Each of the adjustment screws34,36and38are also spaced apart to the extent sufficient to permit rotation upon adjustment (i.e., rotation of the screw), thereby allowing independent rotation of the plate12(and thus the printhead) about an X and/or Y axis. More specifically, the adjustment screws36and38are preferably each located adjacent and inside two separate protrusions18and within the same horizontal plane, while the adjustment screw34is located at a right angle from the adjustment screw36and in the same vertical plane as the adjustment screw36. Thus, for example, to rotate the printhead about the X axis, adjustment screws36and38would be uniformly rotated while the adjustment screw34remains fixed. To rotate the printhead about the Y axis, the adjustment screw38would be rotated while the adjustment screws34and36remain fixed.

Alignment of the printhead in the Y direction is accomplished via two independent adjustment screws46and48. The adjustment screws46and48preferably may each be located at right angles with respect to each of adjustment screws34,36, and38. The adjustment screws46and48are secured to a top surface50of the plate12or to a bottom surface51of the plate12via threaded holes (not shown) on opposite ends52and54of the plate12. Each of the adjustment screws46and48extend through the plate12into each of the openings20under the two protrusions18of the plate12, and into the projections30on the face26of the fixed plate28, when the plate12is biased against the fixed plate28. Two compression springs56bias a bottom58of each of the openings20under the two protrusions18against a tip (not shown) of each of the adjustment screws46and48.

Rotation of the adjustment screws46and48results in translation of the plate12in the Y direction. To adjust the plate12uniformly in the Y direction, both of the adjustment screws46and48must be rotated an equal amount and in the same direction while keeping the adjustment screws34,36and38fixed.

Rotation of the adjustment screws46and48also results in rotation of the plate12about the Z axis. To rotate the plate12about the Z axis, either of the adjustment screws46or48may be rotated while keeping the adjustment screws34,36and38fixed.

Alignment of the printhead in the X direction is accomplished via an adjustment screw60. The adjustment screw60preferably may be located at a right angle with respect to each of the adjustment screws34,36,38,46and48. The adjustment screw60is secured to a side62of the fixed plate28via a threaded hole (not shown) in the fixed plate28. The adjustment screw60extends through the fixed plate28into a window64located in the fixed plate28and into or through another protrusion19extending from the back surface16of the plate12. The plate12is biased against the adjustment screw60by another compression spring66extending from a wall68of the window64to a tip (not shown) of the adjustment screw60.

Adjustment in the X direction is accomplished by rotation of the adjustment screw60.

Although the adjustment screws34,36,38,46,48and60as described herein allow for translation and/or rotation of the printhead, each of the adjustments screws34,36,38,46,48and60may also be designed to remain fixed. Accordingly, any of the adjustment screws34,36,38,46,48and60may 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 screws34,36,38,46,48and60thereby providing translation and rotation in less than all six degrees of freedom. Alternatively, the six adjustment screws34,36,38,46,48and60or 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 mechanism10as described with reference toFIGS. 1 and 2can be used in a printer within a direct marking print engine where the adjustment of the printhead is required. Further, more than one alignment mechanism10may be incorporated into the printer to accommodate more than one printhead.

FIGS. 3–5illustrate more than one alignment mechanism10mounted to different parts of the printer.FIG. 3illustrates a first alignment mechanism100and a second alignment mechanism102mounted on a frame104. A printhead assembly106is shown with a printhead108attached to the second alignment mechanism102as described above. Here, the first alignment mechanism100and the second alignment mechanism102allow 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 toFIGS. 4–7, a plate110(as described above with respect to plate12of the alignment mechanism10), may be biased against a frame112(as described above with respect to the fixing plate28of the alignment mechanism10). The frame112may be sheet metal, a casting, or any fixed object in an image forming device. Adjustment screws114,116and118may allow for adjustment of a printhead in six degrees of freedom as described above with respect to the adjustment screws60;46and48; and34,36and38, 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 plate12and fixed plate28as 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.