# Patent

## Title
Mounting for a modular printhead

## Abstract

A modular printhead mounting for a digital printer wherein the modules (2) may be mechanically aligned using specifically designed frame (3) supporting the modules (2). The frame (3) has a plurality of mounting sites (19) for mounting respective printhead modules (2) to the frame (3). At least one of the mounting sites (19) includes a mechanical adjustment mechanism (15, 16, 17 and 18) for reducing input movements to effect minute adjustments of the position of the printhead module (2) with respect to the frame (3).

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This is a Continuation of U.S. Ser. No. 10/636,286 filed on Aug. 8, 2003, now issued Pat. No. 6,739,701, which is a Continuation of U.S. Ser. No. 10/129,433 filed May 6, 2002, now issued Pat. No. 6,672,707, which is a national phase (371) of PCT/AUO1/00217 filed Mar. 2, 2001.


FIELD OF THE INVENTION
The present invention relates to inkjet printers and in particular to pagewidth inkjet printers.
CO-PENDING APPLICATIONS
Various methods, systems and apparatus relating to the present invention are disclosed in the following co-pending applications filed by the applicant or assignee of the present invention on 24 May 2000:















PCT/AU00/00578
PCT/AU00/00579
PCT/AU00/00581
PCT/AU00/





00580


PCT/AU00/00582
PCT/AU00/00587
PCT/AU00/00588
PCT/AU00/





00589


PCT/AU00/00583
PCT/AU00/00593
PCT/AU00/00590
PCT/AU00/





00591


PCT/AU00/00592
PCT/AU00/00584
PCT/AU00/00585
PCT/AU00/





00586


PCT/AU00/00594
PCT/AU00/00595
PCT/AU00/00596
PCT/AU00/





00597


PCT/AU00/00598
PCT/AU00/00516
PCT/AU00/00517
PCT/AU00/





00511









The disclosures of these co-pending applications are incorporated herein by cross-reference. Also incorporated by cross-reference, is the disclosure of a co-filed PCT application, PCT/AU01/00216 (deriving priority from Australian Provisional Patent Application No. PQ5959).
BACKGROUND OF THE INVENTION
The printheads used by inkjet printers traditionally traverse back and forth within the printer as a page is fed past the printhead. To increase printing speed, pagewidth printheads have been developed so that the printhead does not need to traverse across the page.
For a number of reasons, it is relatively expensive to produce pagewidth printheads in a unitary form. Therefore, to minimize costs it is preferable to produce a modular pagewidth printhead made up of a series of printhead modules.
It is necessary to align each module so that the printing from one module precisely abuts the printing from the adjacent modules. For most types of printing, it is sufficient to electronically align the modules. This is done by configuring the modules such that they slightly overlap with each other, and then digitally adjusting the printing from each module for a smooth transition of the print data.
Unfortunately, this requires complex manipulation of the print data allocated to the respective modules. The digital controller for the printer needs to be relatively powerful to accommodate this and the associated costs can be prohibitive for the SOHO (small office/home office) market.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a modular printhead for a digital printer, the modular printhead including:
a support frame and a plurality of printhead modules, the frame having a plurality of mounting sites for mounting respective printhead modules to the frame; wherein,
at least one of the mounting sites has an adjustment mechanism for reducing input movements to effect minute adjustments of the position of the printhead module with respect to the frame.
A modular printhead mounting for a digital printer including:

    
    
        a support frame;
        a plurality of mounting sites, each mounting a print head module;
        at least one of the mounting sites including:
        
            a module engagement plate upon which the printhead module is mounted, the module engagement plate being connected to the support frame by flexible arms, said flexible arms constraining said plate to substantially linear movement relative to the frame; and
            an adjustment mechanism, the adjustment mechanism including:
            
                a lever arm pivotally attached to the frame and also attached to said plate remote from an effective fulcrum wherein pivotal movement of the lever arm causes movement of said plate; and
                a movable member in engagement with the lever arm causing said pivotal movement of the lever arm.
            
            
        
        
    
    


Preferably, the adjustment mechanism uses a system of levers and pivots for geared reduction of the input movements to minute adjustments of the printhead module relative to the frame. In a further preferred form, the ratio of input movement to the resultant adjustment is at least 500 to 1.
In a particularly preferred form, the movement of the printhead module relative to the frame is less than 100 μm.
In some embodiments, the adjustment mechanism includes an input lever fulcrumed against the support frame for acting on a module engagement plate, the module engagement plate being connected to the support frame by hinged link arms such that the resultant movement of the plate is substantially linear. Preferably, the movement of the input lever is substantially normal to the resultant movement of the engagement plate. In a further preferred form, the input lever for each of the adjustment mechanisms is actuated by a respective grub screw threadedly engaged with the support frame. Conveniently, the ratio of axial movement of the grub screw to the movement of the plate is about 1000 to 1.
Conveniently, the adjustment mechanism is integrally formed with the frame wherein the fulcrum and hinged connections are formed by localized necks in the frame material.



BRIEF DESCRIPTION OF THE DRAWINGS
A preferred embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which:
FIG. 1 shows a perspective view of the underside of a modular printhead according to the present invention;
FIG. 2 shows an exploded perspective view of the modular printhead shown in FIG. 1;
FIG. 3 is a perspective view of the support frame for the modular printhead shown in FIG. 1;
FIG. 4 is a plan view of the adjustment mechanism for one of the printhead modules shown in FIG. 1;
FIG. 5 is a cross-sectional view of the modular printhead shown in FIG. 1;
FIG. 6 is a perspective view of the adjuster block shown in FIG. 2;
FIG. 7 is a perspective view showing the top and side of a printhead module;
FIG. 8 is a perspective view showing the underside of a printhead module; and
FIG. 9 shows a perspective view of the micro moulding that houses the printing chip in each printhead module.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the figures, the modular printhead (1) includes a plurality of printhead modules (2) mounted to a metal chassis (3) which acts as a support frame. The modules (2) are sealed units with four independent ink chambers that feed the inkjet nozzles in a printhead chip (8). As best seen in FIG. 2, each printhead module (2) is plugged into a reservoir moulding (11) that supplies the ink through a self sealing elastomeric strip (12).
The entire modular printhead (1) may itself be a module of a larger printhead having two levels of modularity. Accordingly, the length of the overall printhead is arbitrary.
Referring to FIGS. 7 to 9, the printhead modules (2) each comprise a printhead chip (8) bonded to a TAB (tape automated bond) film (6) accommodated and supported by a micro moulding (5), which is in turn adapted to mate with the cover moulding (4). The printhead chip (8) is typically a micro electro mechanical system(s) (MEMS) device.
The present invention will now be described with particular reference to the Applicant's MEMJETTM technology, various aspects of which are described in detail in the cross referenced documents. It will be appreciated that MEMJETTM is only one embodiment of the invention and used here for the purposes of illustration only. It is not to be construed as restrictive or limiting in any way on the extent of the broad inventive concept.
A MEMJETTM printhead is composed of a number of identical printhead modules (2) described in greater detail below. A MEMJETTM printhead is a drop-on-demand 1600 dpi inkjet printer that produces bi-level dots in up to 6 colors to produce a printed page of a particular width. Since the printhead prints dots at 1600 dpi (dots per inch), each dot is approximately 22.5 μm in diameter, and the dots are spaced 15.875 μm apart. Because the printing is bi-level, the input image is typically dithered or error-diffused for best results.
The modules (2) are designed such that the printhead chips (8) of adjacent modules can exactly abut one another so that there are no gaps or overlap in the printing produced. To achieve this, the modules (2) must be precisely aligned with each other after being mounted on the metal chassis (1).
Aligning the modules (2) using digital control of the chips (8) is possible but relatively difficult and costly given the complex manipulation of the print data necessary to seamlessly join the printing from adjacent modules. The required degree of alignment can be cost effectively provided by the mechanical adjustment mechanism of the present invention.
Referring to FIGS. 3 and 4, the apertures (20) in the module engagement plate (19) receive the ink funnels for each module (2). The engagement plate (19) is integrally formed with the metal chassis (3) via hinged arms (15, 16, 17 & 18). Input lever (13) is fulcrumed against the metal chassis (3) to act on the engagement plate (19) via the hinged link arm (16). Movement of the input lever (13) is reduced by the lever arms to produce a minute movement of the engagement plate (19).
By careful configuration of the input lever (13) and the hinged link arms (15, 16, 17 & 18), the resultant movement in the engagement plate (19) is substantially linear and parallel to the longitudinal axis of the metal chassis (3). The skilled artisan will readily appreciate that it is convenient to configure the input lever (13) and the hinged link arms (15, 16, 17 & 18) such that input movement is substantially normal to the resultant movement for ease of access to the input lever (13). The apertures (21, 22) in each of the input levers (13) are used to fit any convenient intermediate integer (not shown) selected for applying the input force to their respective input lever (13).
Referring to FIG. 2, the intermediate integers chosen for the present embodiment are a series of adjuster blocks (10) individually fixed to each of the input levers. Grub screws (9) threadedly engaged with the metal chassis (3) to bear against each of the adjuster block (10).
This arrangement allows precise alignment of the modules (2) by reducing the axial input motion of the grub screw (9) by ratio of about 1000 to 1 to produce minute movement of the engagement plate (19) with respect to the metal chassis (3).
The invention has been described herein by way of example only. Skilled workers in this field will readily recognize many variations and modifications that do not depart from the spirit and scope of the broad inventive concept.

## Claims

1. A modular printhead for a digital printer, the modular printhead including:
a support frame and a plurality of printhead modules, the frame having a plurality of mounting sites for mounting respective printhead modules to the frame; wherein,
at least one of the mounting sites includes:
a module engagement plate upon which the printhead module is mounted, the module engagement plate being connected to the support frame by flexible arms, said flexible arms constraining said plate to substantially linear movement relative to the frame; and
an adjustment mechanism, the adjustment mechanism including:
a lever arm pivotally attached to the frame and also attached to said plate remote from an effective fulcrum wherein pivotal movement of the lever arm causes movement of said plate; and

a movable member in engagement with the lever arm causing said pivotal movement of the lever arm.

2. A modular printhead according to claim 1 wherein the ratio of movement of the movable member to the movement of the module engagement plate is at least 500 to 1.

3. A modular printhead according to claim 1 wherein the movement of the printhead module relative to the frame is less than 100 μm.

4. A modular printhead according to claim 1 wherein the movement of the lever arm is substantially normal to the movement of the engagement plate.

5. A modular printhead according to claim 1 wherein the movable member is a grub screw that actuates the lever arm for each respective adjustment mechanism, said screw being threadedly engaged with the support frame.

6. A modular printhead according to claim 5 wherein the ratio of axial movement of the respective grub screw to the movement of its respective module engagement plate is about 1000 to 1.

7. A modular printhead according to claim 1 wherein the adjustment mechanism is integrally formed in the frame with the respective flexible arms having localized necks formed at each end allowing constrained movement of the respective module engagement plate.

8. A modular printhead according to claim 1 wherein the lever arm is integrally formed in the frame, said lever arm having at least one localized neck formed with said plate remote from the effective fulcrum.