Patent Application
20100079536
This invention relates to inkjet printhead maintenance. It has been developed primarily for facilitating maintenance operations, such as cleaning particulates from an ink ejection face of the printhead.
The following applications have been filed by the Applicant.
The disclosures of these co-pending applications are incorporated herein by reference.
Various methods, systems and apparatus relating to the present invention are disclosed in the following US patents/patent applications filed by the applicant or assignee of the present invention:
The disclosures of these applications and patents are incorporated herein by reference.
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 included in the cross reference list above.
The contents of these patents and patent applications are incorporated herein by cross-reference in their entirety.
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 obscured 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 newly purchased printers, sealing has also been used as a strategy for maintaining printheads in an operational condition in between print jobs. 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.
In our earlier U.S. patent application Ser. Nos. 11/246,707 (Docket No. FNE001US), 11/246,706 (Docket No. FNE002US), 11/246,705 (Docket No. FNE003US), 11/246,708 (Docket No. FNE004US) all filed Oct. 11, 2005 and 11/482,958 (Docket No. FNE010US), 11/482,955 (Docket No. FNE011US) and 11/482,962 (Docket No. FNE012US), all filed Jul. 10, 2006, the contents of which are herein incorporated by reference, we described a method for removing particulates from a printhead. This involves flooding the printhead face with ink and transferring the flooded ink onto a transfer surface moving past the face, but not in contact with the face.
It would be desirable to provide an ink jet printhead maintenance station and method that consume minimal quantities of ink during maintenance cycles and provides effective removal of particulates from the printhead face without any damaging contact therewith.
In a first aspect the present invention provides a method of removing particulates from an ink ejection face of a printhead, said method comprising the steps of:
(i) providing a liquid foam on said face, thereby dispersing said particulates in said foam; and
(ii) transferring said foam, including said particulates, onto a transfer surface moving past said face.
Optionally, said transfer surface does not contact said face.
Optionally, said foam collapses to a liquid droplet as it is transferred onto said transfer surface.
Optionally, said liquid foam is an ink foam.
Optionally, ink in said ink foam is provided by ink contained in said printhead.
Optionally, said ink foam is provided by passing a gas through ink supply channels in said printhead, thereby expelling the ink foam from nozzles in said ink ejection face.
Optionally, air is forced under pressure though said ink channels.
Optionally, said transfer surface contacts said foam when moving past said face.
Optionally, said transfer surface is less than 1 mm from said face when moving past said face.
Optionally, said transfer surface is moved past said face immediately as said foam is provided on said face.
Optionally, said transfer surface is a surface of a film.
Optionally, said transfer surface is an outer surface of a first transfer roller.
Optionally, said transfer surface is moved past said face by rotating said roller.
Optionally, said roller is substantially coextensive with said printhead.
In a further aspect the present invention provides a method further comprising the step of:
(iii) removing foam or ink from said transfer surface using an ink removal system.
Optionally, said transfer surface is an outer surface of a first transfer roller and said ink removal system comprises a cleaning pad in contact with said first transfer roller.
Optionally, said transfer surface is an outer surface of a first transfer roller and said ink removal system comprises a second transfer roller engaged with said first transfer roller.
Optionally, said second transfer roller has a wetting surface for receiving ink from said transfer surface.
Optionally, said second transfer roller is a metal roller.
Optionally, a cleaning pad is in contact with said second transfer roller.
In a second aspect the present invention provides a printhead maintenance system for maintaining a printhead in an operable condition, said maintenance system comprising:
(a) a printhead having an ink ejection face;
(b) a foaming system for providing a liquid foam on said face; and
(c) a foam transport assembly comprising:
Optionally, said liquid foam is an ink foam.
In a further aspect there is provided a maintenance system further comprising a valve configurable in first and second positions, wherein in a first position said printhead is in fluid communication with an ink supply system and in a second position said printhead is in fluid communication with said foaming system.
Optionally, said foaming system supplies a gas to ink supply channels in said printhead, thereby expelling an ink foam from nozzles in said ink ejection face.
Optionally, said foaming system comprises a pump for supplying air to said ink supply channels.
Optionally, said foaming system comprises an accumulator vessel pressurizable by said pump.
Optionally, said foaming system is configured such that said pump and said accumulator vessel cooperate to supply pressurized air to said ink supply channels.
Optionally, said foaming system comprises a foam dispenser having a nozzle for dispensing a liquid foam onto said face.
Optionally, said transfer surface is a surface of a film.
Optionally, said transfer surface is an outer surface of a first transfer roller.
Optionally, said transfer surface is fed through said transfer zone by rotating said roller.
Optionally, said roller is substantially coextensive with said printhead. Optionally, said transfer zone is spaced less than 1 mm from said face.
Optionally, said ink transport assembly is moveable between a first position in which said transfer surface is positioned in said transfer zone and a second position in which said transfer surface is positioned remotely from said printhead.
In a further aspect there is provided a maintenance system further comprising:
(d) an ink removal system for removing ink from said transfer surface.
Optionally, said transfer surface is an outer surface of a first transfer roller and said ink removal system comprises a cleaning pad in contact with said first transfer roller.
Optionally, said transfer surface is an outer surface of a first transfer roller and said ink removal system comprises a second transfer roller engaged with said first transfer roller.
Optionally, said second transfer roller has a wetting surface for receiving ink from said transfer surface.
Optionally, a cleaning pad is in contact with said second transfer roller.
In a further aspect there is provided a maintenance system further comprising a control system for coordinating the transport mechanism with said foaming system.
Optionally, said control system is configured to activate said transport mechanism at the same time as said foaming system is activated to provide a liquid foam on said face.
In a third aspect the present invention provides a printhead assembly comprising:
(a) a printhead having an ink ejection face;
(b) an ink supply system for supplying ink to said printhead; and
(c) a foaming system for providing a liquid foam on said face.
Optionally, said assembly is configurable such that ink supply channels in said printhead are in fluid communication either with said ink supply system or said foaming system.
Optionally, in a printing configuration, said printhead is in fluid communication with said ink supply system, and in a maintenance configuration, said printhead is in fluid communication with said foaming system.
In a further aspect there is provided a printhead assembly further comprising a valve configurable in first and second positions, wherein in a first position said printhead is in fluid communication with said ink supply system and in a second position said printhead is in fluid communication with said foaming system.
Optionally, said foaming system supplies a gas to ink supply channels in said printhead, thereby expelling an ink foam from nozzles in said ink ejection face.
Optionally, said foaming system comprises a pump for supplying air to said ink supply channels.
Optionally, said foaming system comprises an accumulator vessel pressurizable by said pump.
Optionally, said foaming system is configured such that said pump and said accumulator vessel cooperate to supply pressurized air to said ink supply channels.
Optionally, said ink supply system comprises a priming/de-priming system for de-priming said nozzles prior to foaming and/or re-priming said nozzles with ink after foaming.
Optionally, said foaming system comprises a foam dispenser having a nozzle for dispensing a liquid foam onto said face.
Optionally, said ink supply system comprises one or more ink reservoirs.
In a further aspect there is provided a printhead assembly further comprising:
(d) a foam removal system for removing the liquid foam from said face.
Optionally, the foam removal system comprises a transfer surface onto which said foam collapses.
Optionally, said transfer surface does not contact said face.
As used herein, the term “ink” refers to any liquid fed from an ink reservoir to the printhead and ejectable from nozzles in the printhead. The ink may be a traditional cyan, magenta, yellow or black ink. Alternatively, the ink may be an infrared ink, Alternatively, the ‘ink’ may be a cleaning liquid (e.g. water, dyeless ink base, surfactant solution, glycol solution etc.) which is not used for printing, but instead used specifically for cleaning the ink ejection face of the printhead (see Applicant's earlier application Ser. Nos. 11/482,976 (Docket No. FNE025US) and 11/482,973 (Docket No. FNE026US) both filed Jul. 10, 2006, the contents of which are incorporated herein by reference).
The present application, in its preferred form, advantageously allows 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 cleaning action of the present invention does not impart any shear forces across the printhead and minimizes damage sensitive nozzle structures. Moreover, the transfer surface 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 present invention is that it consumes relatively little ink compared to prior art suction devices and systems requiring printhead face flooding. In particular, the present invention requires a fraction of the ink used by maintenance systems requiring flooding the printhead face with ink (see, for example, 11/246,707 (Docket No. FNE001US), 11/246,706 (Docket No. FNE002US), 11/246,705 (Docket No. FNE003US), 11/246,708 (Docket No. FNE004US) all filed Oct. 11, 2005 and 11/482,958 (Docket No. FNE010US), 11/482,955 (Docket No. FNE011US) and 11/482,962 (Docket No. FNE012US) all filed Jul. 10, 2006).
A further advantage of the present invention is that a foam has been found to be more efficacious than flooded ink in removing particulates from a printhead face. An explanation of this improved efficacy is provided in more detail below.
Specific forms of the present invention will be now be described in detail, with reference to the following drawings, in which:—
Referring to
The printhead maintenance system 1 comprises a plurality of ink reservoirs 4a, 4b, 4c and 4d, each supplying ink to the printhead 2 via respective ink conduits 5a, 5b, 5c and 5d. The printhead 2 is attached to an ink manifold 6, which directs ink supplied by the ink conduits 5a, 5b, 5c and 5d into a backside of the printhead. A plurality of solenoid valves 7a, 7b, 7c and 7d are positioned in respective ink conduits 5a, 5b, 5c, 5d and are controlled by a printhead maintenance control system.
Each valve 7 may be configured for either normal printing or printhead maintenance. In a first printing configuration, as shown in
The foaming system 10 comprises a pump 11 having an air inlet 13 and an outlet connected to an accumulator vessel 12. With a stop-valve 14 closed, the pump 11 charges the accumulator vessel 12 to a predetermined pressure. When an ink foam on the printhead face 3 is required, the valves 7a, 7b, 7c and 7d are connected to the foaming system 10. The stop-valve 14 is then opened to force pressurized air from the accumulator vessel 12 into the printhead 2 via an air conduit 15. The pressurized air foams any ink in the printhead 2 and the resultant ink foam 30 is expelled through nozzles in the printhead onto the ink ejection face 3.
As shown in
Foaming may be performed on a fully primed or a de-primed printhead 2. If the printhead 2 is de-primed, there is generally still sufficient residual ink (ca. 0.1 mL) in ink channels in the ink manifold 6 and/or printhead 2 to generate an ink foam 30 across the ink ejection face 3. Obviously, if the printhead 2 is fully primed, then more ink will be consumed by foaming. Accordingly, foaming a de-primed printhead 2 has the advantage of consuming less ink. In our earlier U.S. patent application Ser. Nos. 11/482,982 (Docket No. SBF001US), 11/482,983 (Docket No. SBF002US), 11/482,984 (Docket No. SBF003US and simultaneously co-filed US Application SBF004US (temporarily identified by its docket number), which are all incorporated herein by reference, describe methods of priming and de-priming a printhead for storage or maintenance operations. SBF004US describes a printer fluidics system, which incorporates an ink supply system suitable for priming/de-priming a printhead and foaming system for providing a foam across the printhead face. It will be understood that the maintenance system of the present invention may include the system described in SBF004US.
Not only does the ink foam 30 consume less ink than merely flooding the ink ejection face 3, it also provides for more efficacious removal of particulates 32. Whereas flooded ink relies primarily on flotation of particulates 32 into the ink, the ink foam 30 provides a multidirectional attractive force onto each particulate, which encourages the particulates to become entrained in the foam, as opposed to remaining on the printhead face 3.
The particulates 32a and 32b become entrained or dispersed into the foam 30 and occupy positions defined by Plateau border vertices.
In addition, and depending on the pressure in the accumulator vessel 12, the blast of air through the printhead nozzles (e.g. 33) during foaming will also have the effect of dislodging particulates 32 which may be trapped in or on the nozzles themselves.
Having entrained the particulates 32 into the foam 30, as shown in
Referring now to
An outer surface of the transfer film 22 defines the transfer surface 24, which receives the ink foam 30 during printhead maintenance operations. The intermediate layer 23 provides resilient support for the transfer film 22, thereby allowing resilient engagement between the transfer surface 24 and an ink removal system (not shown in
The first transfer roller 20 is moveable between a printing configuration (as shown in
The first transfer roller 20 is rotatable about its longitudinal axis so as to allow the transfer surface 24 to be fed through the transfer zone and away from the printhead 2. Rotation of the first transfer roller 20 is provided by means of a transport mechanism (not shown in
A method of maintaining of removing particulates the ink ejection face 3 of the printhead 2 will now be described with reference to
When printhead maintenance is required, the first transfer roller 20 is moved into its printhead maintenance position, in which the transfer surface 24 is positioned in a transfer zone adjacent the ink ejection face 3, as shown in
Next, the valves 7a, 7b, 7c and 7d are configured so that ink channels in the printhead 2 communicate with the foaming system 10 (as shown in
As shown more clearly in
As shown in
Referring now to
The ink 40 collected on the transfer surface 24 is removed by an ink removal system, which is not shown in
Referring initially to
It is, of course, possible for the second transfer roller 51 to be absent in the ink removal system, and for the cleaning pad 52 to be in direct contact with the first transfer roller 20. Such an arrangement is clearly contemplated within the scope of the present invention. However, the use of a metal second transfer roller 51 has several advantages. Firstly, metals have highly wetting surfaces (with contact angles approaching)0°, ensuring complete transfer of ink from the first transfer roller 20 onto the second transfer roller 51. Secondly, the metal second transfer roller 51, unlike a directly contacted cleaning pad, does not generate high frictional forces on the transfer surface 24. The metal second transfer roller 51 can slip relatively easily past the cleaning pad 52, which reduces the torque requirements of a motor (not shown) driving the rollers and preserves the lifetime of the transfer surface 24. Thirdly, the rigidity of the second transfer roller 51 provides support for the first transfer roller 20 and minimizes any bowing. This is especially important for pagewidth printheads and their corresponding pagewidth maintenance stations.
As shown more clearly in
The chassis 53 further comprises engagement formations in the form of lugs 55 and 56, positioned at respective ends of the chassis. These lugs 55 and 56 are provided to slidably move the chassis 53 upwards and downwards relative to the printhead 2 by means of an engagement mechanism (not shown). Typically the engagement mechanism will comprise a pair of arms engaged with the lugs 55 and 56, and arranged so that rotational movement of the arms imparts a sliding movement of the chassis 53 via a camming engagement with the lugs.
Referring now to
As an alternative to the ink foaming system 10, which generates the ink foam 30 by passing air through residual ink in the printhead 2, a liquid foam may be generated by a separate foam dispenser, which does not use ink supplied to the printhead to generate the foam.
The liquid foam 72 provided on the ink ejection face of the printhead 2 may be removed by a transfer surface, such as the transfer surface 24 described above, moving past the face.
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.
The present application is a Continuation of U.S. application Ser. No. 11/495,816 filed Jul. 31, 2006, the entire contents of which are now incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11495816 | Jul 2006 | US |
| Child | 12630614 | US |
