This invention relates to a printhead maintenance assembly for an inkjet printhead. It has been developed primarily for facilitating maintenance operations, such as cleaning particulates from an ink ejection face of the printhead.

Inkjet printers are commonplace in homes and offices. However, all commercially available inkjet printers suffer from slow print speeds, because the printhead must scan across a stationary sheet of paper. After each sweep of the printhead, the paper advances incrementally until a complete printed page is produced.

It is a goal of inkjet printing to provide a stationary pagewidth printhead, whereby a sheet of paper is fed continuously past the printhead, thereby increasing print speeds greatly. The present Applicant has developed many different types of pagewidth inkjet printheads using MEMS technology, some of which are described in the patents and patent applications listed in the above cross reference list.

Notwithstanding the technical challenges of producing a pagewidth inkjet printhead, a crucial aspect of any inkjet printing is maintaining the printhead in an operational printing condition throughout its lifetime. A number of factors may cause an inkjet printhead to become non-operational and it is important for any inkjet printer to include a strategy for preventing printhead failure and/or restoring the printhead to an operational printing condition in the event of failure. Printhead failure may be caused by, for example, printhead face flooding, dried-up nozzles (due to evaporation of water from the nozzles - a phenomenon known in the art as decap), or particulates fouling nozzles.

Particulates, in the form of paper dust, are a particular problem in high-speed pagewidth printing. This is because the paper is typically fed at high speed over a paper guide and past the printhead. Frictional contact of the paper with the paper guide generates large quantities of paper dust compared to traditional scanning inkjet printheads, where paper is fed much more slowly. Hence, pagewidth printheads tend to accumulate paper dust on their ink ejection face during printing. This accumulation of paper dust is highly undesirable.

In the worst case scenario, paper dust blocks nozzles on the printhead, preventing those nozzles from ejecting ink. More usually, paper dust overlies nozzles and partially covers nozzle apertures. Nozzle apertures that are partially covered or blocked produce misdirected ink droplets during printing - the ink droplets are deflected from their intended trajectory by particulates on the ink ejection face. Misdirects are highly undesirable and may result in acceptably low print quality.

One measure that has been used for maintaining printheads in an operational condition is sealing the printhead, which prevents the ingress of particulates and also prevents evaporation of ink from nozzles. Commercial inkjet printers are typically supplied with a sealing tape across the printhead, which the user removes when the printer is installed for use. The sealing tape protects the primed printhead from particulates and prevents the nozzles from drying up during transit. Sealing tape also controls flooding of ink over the printhead face.

Aside from one-time use sealing tape on new printers, sealing has also been used as a strategy for maintaining printheads in an operational condition during printing. In some commercial printers, a gasket-type sealing ring and cap engages around a perimeter of the printhead when the printer is idle. A vacuum may be connected to the sealing cap and used to suck ink from the nozzles, unblocking any nozzles that have dried up. However, whilst sealing/vacuum caps may prevent the ingress of particulates from the atmosphere, such measures do not remove particulates already built up on the printhead.

In order to remove flooded ink from a printhead after vacuum flushing, prior art maintenance stations typically employ a rubber squeegee, which is wiped across the printhead. Particulates are removed from the printhead by flotation into the flooded ink and the squeegee removes the flooded ink having particulates dispersed therein.

However, rubber squeegees have several shortcomings when used with MEMS pagewidth printheads. A typical MEMS printhead has a nozzle plate comprised of a hard, durable material such as silicon nitride, silicon oxide, aluminium nitride etc. Moreover, the nozzle plate is typically relatively abrasive due to etched features on its surface. On the one hand, it is important to protect the nozzle plate, comprising sensitive nozzle structures, from damaging exposure to the shear forces exerted by a rubber squeegee. On the other hand, it is equally important that a rubber squeegee should not be damaged by contact with the printhead and reduce its cleaning efficacy.

Therefore, it would be desirable to provide an inkjet printhead maintenance station, which does not rely on a rubber squeegee wiping across the nozzle plate to remove flood ink and particulates. It would further be desirable to provide an inkjet printhead maintenance station, which removes flooded ink and particulates from the nozzle plate without the nozzle plate coming into contact with any cleaning surface.

It would further be desirable to provide an ink jet printhead maintenance station that is simple in design, does not consume large amounts power and can be readily incorporated into a desktop printer.

US5912680 discloses a printhead maintenance assembly for maintaining a printhead in an operable condition, said maintenance assembly comprising a printhead assembly consisting of a printhead having an ink ejection face, said face having a first edge portion and a second edge portion opposite said first edge portion; and a film guide on the film being positioned to guide a film through a transfer zone, said transfer zone being defined by a plane spaced apart from said face; and an ink transport assembly consisting of a film for transporting ink away from said printhead; and a transport mechanism for feeding said film through said transfer zone and away from said printhead, said transport mechanism feeding said film in a directional sense which is from said first edge portion to said second edge portion.

EP1557270 discloses a printhead maintenance assembly for maintaining a printhead in an operable condition, said maintenance assembly comprising a printhead assembly consisting of a printhead having an ink ejection face, said face having a first edge portion and a second edge portion opposite said first edge portion; and a film guide being positioned to guide a film over the ejection face pressed thereto by a pressing member; and an ink transport assembly consisting of a film for transporting ink away from said printhead; and a transport mechanism for feeding said film over and away from said printhead, said transport mechanism feeding said film in a directional sense which is from said first edge portion to said second edge portion.

According to claim 1, there is provided a printhead maintenance assembly for maintaining a printhead in an operable condition, said maintenance assembly comprising:

1. (i) a printhead assembly comprising:
   • a printhead having an ink ejection face, said face having a first edge portion and a second edge portion opposite said first edge portion; and
   • a film guide sealingly bonded to said first edge portion, said film guide being positioned to guide a film through a transfer zone, said transfer zone being defined by a plane spaced apart from said face; and
2. (ii) an ink transport assembly comprising:
   • a film for transporting ink away from said printhead; and
   • a transport mechanism for feeding said film through said transfer zone and away from said printhead, said transport mechanism feeding said film in a directional sense which is from said first edge portion to said second edge portion;
     wherein, in use, said film contacts with said film guide thereby forming a cavity defined at least partially by said film, said film guide and said face.

The maintenance assembly and method of the present application advantageously allow particulates to be removed from a printhead, whilst avoiding contact of the printhead with an external cleaning device. Hence, unlike prior art squeegee-cleaning methods, the unique cleaning action of the present invention does not impart any shear forces across the printhead and does not damage sensitive nozzle structures. Moreover, the film in the present invention, which does not come into contact with the printhead, is not damaged by the printhead and can therefore be used repeatedly whilst maintaining optimal cleaning action.

A further advantage of the maintenance assembly is that it has a simple design, which can be manufactured at low cost and consumes very little power. The suction devices of the prior art require external pumps, which add significantly to the cost and power consumption of prior art printers. By obviating the need for a vacuum pump, the power requirements of the printer are significantly reduced.

A further advantage of the maintenance assembly and method is that it consumes very little ink compared to prior art suction devices.

The principle of the cleaning action used by the present invention will be described in more detail below.

Optionally, said printhead is a pagewidth inkjet printhead.

Optionally, said first and second edge portions are longitudinal edge portions.

Optionally, said film guide is comprised of a solid polymeric material.

Optionally, said film guide encapsulates wire bonds extending from said first edge portion of said printhead.

Optionally, said transfer zone is substantially parallel with said ink ejection face.

Optionally, said transfer zone is less than 1 mm from said face.

Optionally, said film is wetting.

Optionally, said film is an endless loop.

Optionally, said ink transport assembly further comprises a film cleaner, said transport mechanism being configured to feed said film past said film cleaner.

Specific forms of the present invention will be now be described in detail, with reference to the following drawings, in which:-

• Figure 1 is a perspective view of part of a printhead having wire bonding pads along one longitudinal edge portion;
• Figure 2 is a schematic side view of a printhead maintenance assembly according to the invention in a cleaning configuration;
• Figure 3 is a schematic side view of a printhead maintenance assembly according to the invention in a printing configuration;
• Figure 4 shows in detail the motion of ink in the cavity adjacent the ink ejection face; and
• Figure 5 is a process flow diagram for a printhead cleaning operation.

Referring to Figure 1, there is shown part of a printhead 1 comprised of aligned printhead integrated circuits 2 abutting along their transverse edges 3. A complete pagewidth printhead (not shown) is formed by an array of printhead integrated circuits 2 abutting across the width of a page. Each printhead integrated circuit 2 comprises rows of nozzles 4, which eject ink onto a print media (not shown) fed past the printhead. Fudicials 5 assist in aligning the array of printhead integrated circuits 2.

A longitudinal edge portion 6 of the printhead 1 comprises a plurality of bonding pads 7 to which will be attached wire bonds (not shown) in the fully assembled printhead. An opposite longitudinal edge portion 8 of the printhead 1 does not have any bonding pads.

Referring now to Figure 2, there is shown a schematic side view of a printhead maintenance assembly 10 comprising a printhead assembly 11 and an ink transport assembly 12. The printhead assembly 11 comprises the printhead 1 mounted to an ink supply manifold 13, which is itself mounted on a carrier frame 14. The ink supply manifold 13 supplies ink to ink supply channels etched into a backside of the printhead 1. The ink supply manifold 13 receives ink, via an ink supply system 16, from an ink reservoir 15. The ink reservoir 15 comprises a plurality of ink bags 15a-d, each ink bag containing a different colored ink (e.g. CMYK).

A polymeric encapsulant 17 extends from the longitudinal edge portion 6 of an ink ejection face 18 of the printhead 1. The encapsulant 17 encapsulates wire bonds (not shown) extending from the bonding pads. The wire bonds connect drive circuitry in the printhead 1 to a microprocessor (not shown), which controls operation of the printhead.

The ink transport assembly 12 comprises a film 20, which is wound in a loop around rollers 21. At least one of the rollers 21 is connected to a drive motor (not shown) for feeding the film 20 in the direction shown by the arrows. As shown in Figure 2, the film 20 is in sealing contact with a surface of the encapsulant 17, which acts as film guide. The film 20 is fed in the direction shown through a transfer zone 22, which is a plane spaced apart from and parallel with the ink ejection face 18. A cavity 23 is defined at least partially by the film 20 in the transfer zone, the encapsulant 17 and the ink ejection face 18.

Ink 24 in the cavity 23 is transferred onto the film 20 in the transfer zone 22, and the film transports the ink away from the printhead 1. The ink transport assembly 12 also comprises an absorbent foam pad 25, which cleans the film 20 before it re-enters the transfer zone 22.

As shown in Figure 2, the film 20 is engaged with the encapsulant 17 and a paper guide (not shown) is retracted in the carrier frame 14. However, the entire ink transport assembly 12 is moveable out of engagement with the encapsulant 17 when the printhead 1 is required to print.

Figure 3 shows the ink transport assembly 12 disengaged from the encapsulant 17 and a paper guide 26 in position for guiding paper 27 past the printhead 1. The paper 27 is fed in an opposite direction to the film 20.

Figure 4 shows in detail the cavity 23 and the movement of ink 24 which is flooded into the cavity as the film 20 is fed through the transfer zone 22. The cavity 23 is defined by the ink ejection face 18, the encapsulant 17 and the film 20 in the transfer zone 22. The encapsulant 17 is bonded to first longitudinal edge portion 6 and encapsulates wire bonds (not shown) extending from the printhead 1. At the opposite edge portion 8, the cavity 23 is open to the atmosphere and a meniscus 30 of ink 24 pins between this edge portion 8 and the film 20. As the film 20 is fed through the transfer zone 22, ink 24 is transferred onto the film by the motion of the film and the wetting surface characteristics of the film. A laminar flow of ink 24 is created in the cavity 23 (as shown by the arrows in Figure 4), which continuously transfers ink onto the film 20 as it passes through the transfer zone 22. The ink 24 has particulates (not shown) from the ink ejection face 18 dispersed therein and these particulates are also transferred onto the film 20 and transported away from the printhead 1. Hence the ink ejection face 18 of the printhead 1 is cleared of particulates without being contacted.

Figure 5 is a process flow for a cleaning operation using the printhead maintenance assembly described above. In a first step, the paper guide 26 is retracted away from the path of the film 20. At the same time, or shortly thereafter, a positive pressure pulse is applied to the ink reservoir 13, which purges ink channels and floods the ink ejection face 18 with ink. During this step, particulates on the ink ejection face 18 are dispersed into the flooded ink by flotation. In a second step, the ink transport assembly 12 is moved into an engaged position in which the film 20 is positioned in the transfer zone 22 and sealingly contacts the encapsulant 17. In a third step, the film 20 is fed through the transfer zone 22, and ink 24 from the cavity 23 is transferred onto the firm. Ink is cleaned from the film 20 by feeding the film past an absorbent pad 25 after it has passed through the transfer zone 22. Finally, in a fourth step, the ink transport assembly 12 is disengaged and the paper guide 26 repositioned for printing. The ink purging and film transport steps may be repeated in order to ensure complete remediation and cleaning of the printhead.

It will, of course, be appreciated that the present invention has been described purely by way of example and that modifications of detail may be made within the scope of the invention, which is defined by the accompanying claims.