# Patent

## Title
Method of removing particulates from a printhead using a liquid foam

## Abstract

A method of removing particulates from an ink ejection face of a printhead is provided. The method comprises the steps of: (a) providing a liquid foam on the face, thereby dispersing the particulates in the foam; and (b) transferring the foam, including the particulates, onto a transfer surface moving past the face. Ink consumption is minimized by use of a foam and damage to the face is avoided since the transfer surface typically does not contact the face.

## Background
FIELD OF THE INVENTION
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.
CO-PENDING APPLICATIONS
The following applications have been filed by the Applicant simultaneously with the present application:
















11/495,814
11/495,823
11/495,822
11/495,821
11/495,820


11/495,818
11/495,819
11/495,816
11/495,817









The disclosures of these co-pending applications are incorporated herein by reference.
CROSS REFERENCES TO RELATED APPLICATIONS
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:


















09/517,539
6,566,858
6,331,946
6,246,970
6,442,525
09/517,384
09/505,951


6,374,354
09/517,608
09/505,147
6,757,832
6,334,190
6,745,331
09/517,541


10/203,559
10/203,560
10/203,564
10/636,263
10/636,283
10/866,608
10/902,889


10/902,833
10/940,653
10/942,858
10/727,181
10/727,162
10/727,163
10/727,245


10/727,204
10/727,233
10/727,280
10/727,157
10/727,178
10/727,210
10/727,257


10/727,238
10/727,251
10/727,159
10/727,180
10/727,179
10/727,192
10/727,274


10/727,164
10/727,161
10/727,198
10/727,158
10/754,536
10/754,938
10/727,227


10/727,160
10/934,720
11/212,702
11/272,491
11/474,278
10/296,522
6,795,215


10/296,535
09/575,109
10/296,525
09/575,110
09/607,985
6,398,332
6,394,573


6,622,923
6,747,760
10/189,459
10/884,881
10/943,941
10/949,294
11/039,866


11/123,011
11/123,010
11/144,769
11/148,237
11/248,435
11/248,426
11/478,599


10/922,846
10/922,845
10/854,521
10/854,522
10/854,488
10/854,487
10/854,503


10/854,504
10/854,509
10/854,510
10/854,496
10/854,497
10/854,495
10/854,498


10/854,511
10/854,512
10/854,525
10/854,526
10/854,516
10/854,508
10/854,507


10/854,515
10/854,506
10/854,505
10/854,493
10/854,494
10/854,489
10/854,490


10/854,492
10/854,491
10/854,528
10/854,523
10/854,527
10/854,524
10/854,520


10/854,514
10/854,519
10/854,513
10/854,499
10/854,501
10/854,500
10/854,502


10/854,518
10/854,517
10/934,628
11/212,823
10/728,804
10/728,952
10/728,806


10/728,834
10/728,790
10/728,884
10/728,970
10/728,784
10/728,783
10/728,925


10/728,842
10/728,803
10/728,780
10/728,779
10/773,189
10/773,204
10/773,198


10/773,199
10/773,190
10/773,201
10/773,191
10/773,183
10/773,195
10/773,196


10/773,186
10/773,200
10/773,185
10/773,192
10/773,197
10/773,203
10/773,187


10/773,202
10/773,188
10/773,194
10/773,193
10/773,184
11/008,118
11/060,751


11/060,805
11/188,017
11/298,773
11/298,774
11/329,157
6,623,101
6,406,129


6,505,916
6,457,809
6,550,895
6,457,812
10/296,434
6,428,133
6,746,105


10/407,212
10/407,207
10/683,064
10/683,041
6,750,901
6,476,863
6,788,336


11/097,308
11/097,309
11/097,335
11/097,299
11/097,310
11/097,213
11/210,687


11/097,212
11/212,637
MTD001US
MTD002US
11/246,687
11/246,718
11/246,685


11/246,686
11/246,703
11/246,691
11/246,711
11/246,690
11/246,712
11/246,717


11/246,709
11/246,700
11/246,701
11/246,702
11/246,668
11/246,697
11/246,698


11/246,699
11/246,675
11/246,674
11/246,667
11/246,684
11/246,672
11/246,673


11/246,683
11/246,682
10/760,272
10/760,273
10/760,187
10/760,182
10/760,188


10/760,218
10/760,217
10/760,216
10/760,233
10/760,246
10/760,212
10/760,243


10/760,201
10/760,185
10/760,253
10/760,255
10/760,209
10/760,208
10/760,194


10/760,238
7,077,505
10/760,235
7,077,504
10/760,189
10/760,262
10/760,232


10/760,231
10/760,200
10/760,190
10/760,191
10/760,227
10/760,207
10/760,181


11/446,227
11/454,904
11/472,345
11/474,273
MPA38US
11/474,279
MPA40US


MPA41US
11/003,786
11/003,616
11/003,418
11/003,334
11/003,600
11/003,404


11/003,419
11/003,700
11/003,601
11/003,618
11/003,615
11/003,337
11/003,698


11/003,420
6,984,017
11/003,699
11/071,473
11/003,463
11/003,701
11/003,683


11/003,614
11/003,702
11/003,684
11/003,619
11/003,617
11/293,800
11/293,802


11/293,801
11/293,808
11/293,809
CAG006US
CAG007US
CAG008US
CAG009US


CAG010US
CAG011US
11/246,676
11/246,677
11/246,678
11/246,679
11/246,680


11/246,681
11/246,714
11/246,713
11/246,689
11/246,671
11/246,670
11/246,669


11/246,704
11/246,710
11/246,688
11/246,716
11/246,715
11/246,707
11/246,706


11/246,705
11/246,708
11/246,693
11/246,692
11/246,696
11/246,695
11/246,694


FNE010US
FNE011US
FNE012US
FNE013US
FNE015US
FNE016US
FNE017US


FNE018US
FNE019US
FNE020US
FNE021US
FNE022US
FNE023US
FNE024US


FNE025US
FNE026US
KIP001US
KPE001US
KPE002US
KPE003US
KPE004US


11/293,832
11/293,838
11/293,825
11/293,841
11/293,799
11/293,796
11/293,797


11/293,798
11/293,804
11/293,840
11/293,803
11/293,833
11/293,834
11/293,835


11/293,836
11/293,837
11/293,792
11/293,794
11/293,839
11/293,826
11/293,829


11/293,830
11/293,827
11/293,828
11/293,795
11/293,823
11/293,824
11/293,831


11/293,815
11/293,819
11/293,818
11/293,817
11/293,816

10/760,254


10/760,210
10/760,202
10/760,197
10/760,198
10/760,249
10/760,263
10/760,196


10/760,247
10/760,223
10/760,264
10/760,244
10/760,245
10/760,222
10/760,248


10/760,236
10/760,192
10/760,203
10/760,204
10/760,205
10/760,206
10/760,267


10/760,270
10/760,259
10/760,271
10/760,275
10/760,274
10/760,268
10/760,184


10/760,195
10/760,186
10/760,261
10/760,258
11/442,178
11/474,272
11/474,315


11/014,764
11/014,763
11/014,748
11/014,747
11/014,761
11/014,760
11/014,757


11/014,714
11/014,713
11/014,762
11/014,724
11/014,723
11/014,756
11/014,736


11/014,759
11/014,758
11/014,725
11/014,739
11/014,738
11/014,737
11/014,726


11/014,745
11/014,712
11/014,715
11/014,751
11/014,735
11/014,734
11/014,719


11/014,750
11/014,749
11/014,746
11/014,769
11/014,729
11/014,743
11/014,733


11/014,754
11/014,755
11/014,765
11/014,766
11/014,740
11/014,720
11/014,753


11/014,752
11/014,744
11/014,741
11/014,768
11/014,767
11/014,718
11/014,717


11/014,716
11/014,732
11/014,742
11/097,268
11/097,185
11/097,184
11/293,820


11/293,813
11/293,822
11/293,812
11/293,821
11/293,814
11/293,793
11/293,842


11/293,811
11/293,807
11/293,806
11/293,805
11/293,810
11/124,158
11/124,196


11/124,199
11/124,162
11/124,202
11/124,197
11/124,154
11/124,198
11/124,153


11/124,151
11/124,160
11/124,192
11/124,175
11/124,163
11/124,149
11/124,152


11/124,173
11/124,155
11/124,157
11/124,174
11/124,194
11/124,164
11/124,200


11/124,195
11/124,166
11/124,150
11/124,172
11/124,165
11/124,186
11/124,185


11/124,184
11/124,182
11/124,201
11/124,171
11/124,181
11/124,161
11/124,156


11/124,191
11/124,159
11/124,175
11/124,188
11/124,170
11/124,187
11/124,189


11/124,190
11/124,180
11/124,193
11/124,183
11/124,178
11/124,177
11/124,148


11/124,168
11/124,167
11/124,179
11/124,169
11/187,976
11/188,011
11/188,014


MCD062US
11/228,540
11/228,500
11/228,501
11/228,530
11/228,490
11/228,531


11/228,504
11/228,533
11/228,502
11/228,507
11/228,482
11/228,505
11/228,497


11/228,487
11/228,529
11/228,484
11/228,489
11/228,518
11/228,536
11/228,496


11/228,488
11/228,506
11/228,516
11/228,526
11/228,539
11/228,538
11/228,524


11/228,523
11/228,519
11/228,528
11/228,527
11/228,525
11/228,520
11/228,498


11/228,511
11/228,522
111/228,515
11/228,537
11/228,534
11/228,491
11/228,499


11/228,509
11/228,492
11/228,493
11/228,510
11/228,508
11/228,512
11/228,514


11/228,494
11/228,495
11/228,486
11/228,481
11/228,477
11/228,485
11/228,483


11/228,521
11/228,517
11/228,532
11/228,513
11/228,503
11/228,480
11/228,535


11/228,478
11/228,479
6,238,115
6,386,535
6,398,344
6,612,240
6,752,549


6,805,049
6,971,313
6,899,480
6,860,664
6,925,935
6,966,636
7,024,995


10/636,245
6,926,455
7,056,038
6,869,172
7,021,843
6,988,845
6,964,533


6,981,809
11/060,804
11/065,146
11/155,544
11/203,241
11/206,805
11/281,421


11/281,422
PFA001US
RMC001US
SBF001US
SBF002US
SBF003US
09/575,197


7,079,712
09/575,123
6,825,945
09/575,165
6,813,039
6,987,506
7,038,797


6,980,318
6,816,274
09/575,139
09/575,186
6,681,045
6,728,000
09/575,145


09/575,192
09/575,181
7,068,382
7,062,651
6,789,194
6,789,191
6,644,642


6,502,614
6,622,999
6,669,385
6,549,935
6,987,573
6,727,996
6,591,884


6,439,706
6,760,119
09/575,198
6,290,349
6,428,155
6,785,016
6,870,966


6,822,639
6,737,591
7,055,739
09/575,129
6,830,196
6,832,717
6,957,768


09/575,162
09/575,172
09/575,170
09/575,171
09/575,161









The disclosures of these applications and patents are incorporated herein by reference. Some of the above applications have been identified by their filing docket number, which will be substituted with the corresponding application number, once assigned.
BACKGROUND OF THE INVENTION
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, 11/246,706, 11/246,705, 11/246,708 all filed Oct. 11, 2005 and Ser. Nos. 11/482,958, 11/482,955 and 11/482,962, 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.
SUMMARY OF THE INVENTION
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:
    
        a transfer surface for receiving the foam from said face; and
        a transport mechanism for feeding said transfer surface through a transfer zone and away from said printhead,
    
    
    wherein said transfer zone is adjacent to and spaced apart from said face.


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 applications Ser. Nos. 11/482,976 and 11/482,973 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, Ser. Nos. 11/246,707, 11/246,706, 11/246,705, 11/246,708 all filed Oct. 11, 2005 and Ser. Nos. 11/482,958, 11/482,955 and 11/482,962 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.



BRIEF DESCRIPTION OF THE DRAWINGS
Specific forms of the present invention will be now be described in detail, with reference to the following drawings, in which:
FIG. 1 is a schematic view of a printhead maintenance system according to the present invention;
FIG. 2 is a schematic view of the printhead maintenance system shown in FIG. 1 with an ink foam provided across the printhead;
FIG. 3 is a schematic view of the printhead maintenance system shown in FIG. 2 with the transfer surface positioned in the transfer zone;
FIG. 4A is a magnified view of particulates trapped on a printhead face and covered with flooded ink;
FIG. 4B shows one of the particulates in FIG. 4A floating in the flooded ink;
FIG. 5A is a magnified view of particulates trapped on a printhead face and covered with an ink foam;
FIG. 5B is a magnified view of particulates entrained in the ink foam shown in FIG. 5A;
FIG. 6 is an enlarged view of the transfer zone in FIG. 3;
FIG. 7 is a schematic view of the printhead maintenance station shown in FIG. 1 with ink being transported on a transfer surface;
FIG. 8 is a section through line A-A of the printhead maintenance station shown in FIG. 10;
FIG. 9 a section through line B-B of the printhead maintenance station shown in FIG. 10;
FIG. 10 is a front view of a printhead maintenance station;
FIG. 11 is an exploded perspective view of the printhead maintenance station shown in FIG. 10; and
FIG. 12 is a schematic view of an alternative foaming system.



DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
Printhead Maintenance System with Ink Foaming System
Referring to FIG. 1, there is shown a printhead maintenance system 1 for maintaining a printhead 2 in an operable condition. During printing, paper dust and other particulates may build up on the ink ejection face 3 of the printhead 2, leading to misdirected ink droplets from partially obscured nozzles or even blocked nozzles. Paper dust is a particular problem in high-speed printing where paper is fed over a paper guide at high speed, generating relatively high abrasive forces compared to low-speed printing. The printhead maintenance system 1 is configured to maintain the printhead in an optimal operating condition by removing particulates from the ink ejection face 3 and/or unblocking nozzles which may be blocked with particulates.
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 FIG. 1, each valve 7a, 7b, 7c and 7d provides fluid communication between the printhead 2 and the ink reservoirs 4a, 4b, 4c and 4d. In a second maintenance configuration, as shown in FIG. 2, each valve 7a, 7b, 7c and 7d provides fluid communication between the printhead 2 and a foaming system 10.
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. FIG. 2 shows the printhead 2 having an ink foam 30 across its ink ejection face 3.
As shown in FIG. 2, the ink foam 30 is generated without a transfer roller 20 in a maintenance position. However, the ink foam 30 preferably generated with the transfer roller 20 in its maintenance position, whilst initiating rotation of the roller at about the same time as the foam is generated, as shown in FIG. 3. This prevents the ink foam 30 from spreading excessively over other printer components, such as a wire-bond encapsulant 8 which covers wire-bonds connecting the printhead 2 to power and logic provided by a print controller (not shown).
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, 11/482,983, 11/482,984 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.
FIGS. 4 and 5 compare flooded ink 31 and ink foam 30 as a means for removing particulates 32 from an ink ejection face 3 having a nozzle 33. In FIG. 4A, there is shown one particulate 32a resting on the ink ejection face 3 and another particulate 32b trapped partially inside a nozzle 33. As shown in FIG. 4B, the flooded ink 31 provides sufficient flotation force on particulate 32a to lift it away from the face 3 and the particulate 32a becomes dispersed in the flooded ink 31. However, the relatively weak flotation force is insufficient to lift the other particulate 32b out of the nozzle 33 and it remains trapped, meaning that the nozzle 33 is blocked and inoperative.
FIG. 5A, on the other hand, shows the same two particulates 32a and 32b surrounded by the ink foam 30. The foam 30 comprises randomly-packed Voronoi polyhedra. Ink is contained in Plateau borders 35 between adjacent polyhedra, with voids 36 in the foam 30 being filled with air. Each Plateau border 35, where it meets a particulate 32, exerts an attractive force on that particulate. Given the random nature of the foam 30, each particulate receives a multidirectional lifting force as indicated by the arrows in FIG. 4A. The result is that each particulate 32 receives a stronger force lifting it away from the ink ejection face 3. As shown in FIG. 4B, this stronger multidirectional force is sufficient to not only lift the particulate 32a away from the face 3, but also dislodge the particulate 32b, which is more firmly trapped in the nozzle 100.
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 FIGS. 5B and 6, the foam is then transferred onto a transfer surface 24 and transported away from the printhead 2. Generally, the ink foam 30 collapses to an ink droplet upon contact with the transfer surface 24. The surface characteristics and movement of the transfer surface 24 ensure that the ink foam 30 collapses onto the transfer surface and not back onto the printhead face 3. As mentioned earlier, foam generation and foam transfer preferably occur simultaneously so as to avoid excessive spreading of the foam 30.
Referring now to FIG. 6, there is shown a first transfer roller 20 comprising a stainless steel core roller 21 having an outer transfer film 22. A resiliently deformable intermediate layer 23 is sandwiched between the transfer film 22 and the core roller 21. The first transfer roller 20 is coextensive with the printhead 2, which is a pagewidth inkjet printhead. Hence, the metal roller 21 provides rigidity in the first transfer roller 20 along its entire length.
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 FIG. 6).
The first transfer roller 20 is moveable between a printing configuration (as shown in FIG. 1) in which the roller is distal from the printhead 2, and a printhead maintenance configuration (as shown in FIG. 6) in which the transfer surface 24 is positioned in a transfer zone. When positioned in the transfer zone, the transfer surface 24 is adjacent to but not in contact with the ink ejection face 3 of the printhead 2. The transfer surface 24 may or may not be in contact with the wire-bond encapsulant 8 bonded along an edge portion of the printhead 2 when it is positioned in the transfer zone.
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 FIG. 1), operatively connected to the core roller 21. The transport mechanism typically comprises a simple motor operatively connected to the core roller 21 via a gear mechanism.
A method of maintaining of removing particulates the ink ejection face 3 of the printhead 2 will now be described with reference to FIGS. 1, 3, 6 and 7. Initially, as shown in FIG. 1, the first transfer roller 20 is in an idle or printing position, with the transfer surface 24 distal from the printhead 2. During idle periods or during printing, the valve 14 is closed and the accumulator vessel 12 is charged with air by the pump 11. Hence, the accumulator vessel 12 is charged with pressurized air in readiness for maintenance operations.
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 FIGS. 3 and 6. Typically, a minimum distance between the transfer zone and the ink ejection face 3 is less than about 2 mm, or less than about 1 mm, or less than about 0.5 mm.
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 FIG. 3) rather than the ink reservoirs 4a, 4b, 4c and 4d. An ink foam 30 is then generated by opening the stop-valve 14 and at the same time the transfer roller 20 is rotated.
As shown more clearly in FIG. 6, the ink foam 30 has particulates 32 of paper dust entrained therein, which have lifted from the ink ejection face 3. The ink foam 30, including its entrained particulates 32, is transferred onto the transfer surface 24 by rotation of the first transfer roller 20, thereby feeding the transfer surface through the transfer zone and away from the printhead 2. The transfer film 22 may be a plastics film comprised of polyethers, polyolefins (e.g. polyethylene, polypropylene), polycarbonates, polyesters or polyacrylates. Typically, the transfer film is comprised of a wetting or hydrophilic material to maximize transfer of ink onto the transfer surface 24. Accordingly, the transfer film 22 may be comprised of a hydrophilic polymer or, alternatively, the transfer surface 24 may be coated with a hydrophilic coating (e.g. silica particle coating) to impart wetting properties. A polyoxymethylene transfer film 22 is particularly preferred due to its relatively wetting surface characteristics.
As shown in FIGS. 3 and 6, the first transfer roller 20 is rotated anticlockwise so that the transfer surface 24 transports ink away from the side of the printhead 2 not having the encapsulant 8 bonded thereto. This arrangement maximizes the efficacy of ink transfer.
Referring now to FIG. 7, there is shown the printhead maintenance system 1 after completion of a printhead maintenance operation. The ink foam 30 has collapsed onto the transfer surface 24 as a droplet of ink 40 containing entrained particulates. The ink ejection face 3 is left clean and free of any particulates.
The ink 40 collected on the transfer surface 24 is removed by an ink removal system, which is not shown in FIGS. 1 to 7, but which will now be described in detail with reference to FIGS. 8 to 11.
Referring initially to FIG. 8, a maintenance station 50 comprises a first transfer roller 20, as described above, engaged with a stainless steel second transfer roller 51. An absorbent cleaning pad 52 is in contact with the second transfer roller. The second transfer roller 51 and cleaning pad 52 together form the ink removal system. Ink is received from the first transfer roller 20 and deposited onto the cleaning pad 52 via the highly wetting surface of the second transfer roller 51.
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 FIG. 11, the first transfer roller 20, second transfer roller 51 and cleaning pad 52 are all mounted on a moveable chassis 53. The chassis 53 is moveable perpendicularly with respect to the ink ejection face 3, such that the transfer surface 24 can be moved into and out of the transfer zone. The chassis 53, together with all its associated components, is contained in a housing 54. The chassis 53 is slidably moveable relative to the housing 54.
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 FIG. 9, it can be seen that rotation of the first and second transfer rollers 20 and 51 is via a suitable gear arrangement. A main drive gear 57, operatively mounted at one end of the second transfer roller 51, drives a subsidiary drive gear 58, operatively mounted at one end of the first transfer roller 20, via intermeshing idler gears 59 and 60. A flipper gear wheel (not shown), driven by a drive motor (not shown) can intermesh with the main drive gear 58 through a slot 61 in the housing 54 (see FIGS. 10 and 11). Hence, the gear arrangement comprising the main drive gear 57, subsidiary drive gear 58 and idler gears 59 and 60 forms part of a transport mechanism, which rotates the first and second transfer rollers 20 and 51 synchronously, thereby feeding the transfer surface 24 through the transfer zone.
Alternative Foaming System
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.
FIG. 12 shows a liquid foam dispenser 70 positioned adjacent the printhead 2. The foam dispenser 70 has a nozzle 71, which generates a liquid foam 72 by injection of pressurized gas into the nozzle. A liquid reservoir 73 feeds a liquid for foaming into the foam dispenser 70. The reservoir 73 may contain a cleaning liquid, such as water, surfactant solution, dyeless ink base, glycol solution etc. A source of pressurized gas 74 supplies the pressurized gas to the nozzle 71 for foam generation.
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.

## Claims

1. 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;
(ii) transferring said foam, including said particulates, onto a transfer surface moving past said face; and,
(iii) removing foam or ink from said transfer surface using an ink removal system; wherein,
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.

2. The method of claim 1, wherein said transfer surface does not contact said face.

3. The method of claim 1, wherein said foam collapses to a liquid droplet as it is transferred onto said transfer surface.

4. The method of claim 1, wherein said liquid foam is an ink foam.

5. The method of claim 4, wherein 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.

6. The method of claim 5, wherein air is forced under pressure though said ink channels.

7. The method of claim 1, wherein ink in said ink foam is provided by ink contained in said printhead.

8. The method of claim 1, wherein said transfer surface contacts said foam when moving past said face.

9. The method of claim 1, wherein said transfer surface is less than 1 mm from said face when moving past said face.

10. The method of claim 1, wherein said transfer surface is moved past said face immediately as said foam is provided on said face.

11. The method of claim 1, wherein said transfer surface is moved past said face by rotating said roller.

12. The method of claim 11, wherein said roller is substantially coextensive with said printhead.

13. The method of claim 1, wherein 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.

14. The method of claim 13, wherein said second transfer roller has a wetting surface for receiving ink from said transfer surface.

15. The method of claim 14, wherein said second transfer roller is a metal roller.

16. The method of claim 13, wherein a cleaning pad is in contact with said second transfer roller.