Manually aligned printhead modules

Manually Aligned Printhead Modules

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/AUOO/OO582

PCT/AUOO/OO583

PCT/AU00/00592

PCT/AU00/00594

PCT/AUOO/OO598

PCT/AU00/00579

PCT/AU00/00587

PCT/AU00/00593

PCT/AUOO/00584

PCT/AU00/00595

PCT/AU00/00516

PCT/AU00/00581

PCT/AUOO/OO588

PCT/AU00/00590

PCT/AUOO/OO585

PCT/AU00/00596

PCT/AU00/00517

PCT/AUOO/OO58O

PCT/AU00/00589

PCT/AU00/00591

PCT/AU00/00586

PCT/AUOO/00597

PCT/AU00/00511

The disclosures of these co-pending applications are incorporated herein by crossreference. 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).

RECTIFIED SHEET (Rule 91)

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

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-2to 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.

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 100pm.

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.

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-3Conveniently, 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:

Figure 1 shows a perspective view of the underside of a modular printhead according to the present invention;

Figure 2 shows an exploded perspective view of the modular printhead shown in Figure 1;

Figure 3 is a perspective view of the support frame for the modular printhead shown in Figure 1;

Figure 4 is a plan view of the adjustment mechanism for one of the printhead modules shown in Figure 1;

Figure 5 is a cross-sectional view of the modular printhead shown in Figure 1;

Figure 6 is a perspective view of the adjuster block shown in Figure 2;

Figure 7 is a perspective view showing the top and side of a printhead module;

Figure 8 is a perspective view showing the underside of a printhead module; and

Figure 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 Figure 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 Figures 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

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-4by 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 MEMJET™ technology, various aspects of which are described in detail in the cross referenced documents. It will be appreciated that MEMJET™ 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 MEMJET™ printhead is composed of a number of identical printhead modules (2) described in greater detail below. A MEMJET™ 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 22.5pm in diameter, and the dots are spaced 15.875pm 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 Figures 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

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-5parallel 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 Figure 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 recognise many variations and modifications that do not depart : from the spirit and scope of the broad inventive concept.

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