Abstract:
An inkjet printer that has a printhead for printing onto a media substrate, and a reservoir for containing a quantity of ink, the reservoir having a lower portion for holding ink and an upper portion defining a headspace of air above the ink. A fluid connection extends between the printhead and the reservoir. A pump draws air from the headspace to lower its air pressure and thereby controls the hydrostatic pressure of the ink at the printhead.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to printers and in particular the fluidic architecture of inkjet printers. 
       CO-PENDING APPLICATIONS 
       [0002]    The following application has been filed by the Applicant simultaneously with the present application: 
       SBF009US 
       [0003]    The disclosure of this co-pending application is incorporated herein by reference. The above application has been identified by its filing docket number, which will be substituted with the corresponding application number, once assigned. 
       CROSS REFERENCES TO RELATED APPLICATIONS 
       [0004]    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: 
         [0000]                                                        6276850   6520631   6158907   6539180   6270177   6405055   6628430       6835135   6626529   6981769   7125338   7125337   7136186   10/920372       7145689   7130075   7081974   7177055   7209257   6443555   7161715       7154632   7158258   7148993   7075684   10/943905   10/943906   10/943904       10/943903   10/943902   6966659   6988841   7077748   7255646   7070270       7014307   7158809   7217048   11/225172   11/255942   11/329039   11/329040       7271829   11/442189   11/474280   11/483061   11/503078   11/520735   11/505858       11/525850   11/583870   11/592983   11/592208   11/601828   11/635482   11/635526       10/466440   7215441   11/650545   11/653241   11/653240   7056040   6942334       11/706300   11/740265   11/737720   11/739056   11/740204   11/740223   11/753557       11/750285   11758648   11/778559   11834634   11/838878   11845669   6799853       7237896   6749301   10/451722   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11/740925   11/763444   11/763443   7249942   7206654   7162324       7162325   7231275   7146236   10/753475   10/753499   6997698   7220112       7231276   10/753440   7220115   7195475   7144242   11/499746   11/501774       11/525858   11/545501   11/599335   11/706380   11736545   11/736554   11/739047       11749159   11/739073   11/775160   11/853755   TEST   6786420   6827282       6948661   7073713   10/983060   7093762   7083108   7222799   7201319       11/442103   11/739071   11/518238   11/518280   11/518244   11/518243   11/518242       7032899   6854724   11/084237   11/084240   11/084238   11/357296   11/357298       11/357297   6350023   6318849   6592207   6439699   6312114   11/246676       11/246677   11/246678   11/246679   11/246680   11/246681   11/246714   11/246713       11/246689   11/246671   11/246670   11/246669   11/246704   11/246710   11/246688       11/246716   11/246715   11/246707   11/246706   11/246705   11/246708   11/246693       11/246692   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10/913372   7138391   7153956   10/913380   10/913379       10/913376   7122076   7148345   11/172816   11/172815   11/172814   11/482990       11/482986   11/482985   11/454899   11/583942   11/592990   11849360   11/831961       11/831962   11/831963   60951700   11/832629   11/832637   60971535   10/407212       7252366   10/683064   10/683041   7275811   10/884889   10/922890   10/922875       10/922885   10/922889   10/922884   10/922879   10/922887   10/922888   10/922874       7234795   10/922871   10/922880   10/922881   10/922882   10/922883   10/922878       10/922872   10/922876   10/922886   10/922877   7147792   7175774   11/159193       11/491378   11766713   11/841647   11/482980   11/563684   11/482967   11/482966       11/482988   11/482989   11/293832   11/293838   11/293825   11/293841   11/293799       11/293796   11/293797   11/293798   11/124158   11/124196   11/124199   11/124162       11/124202   11/124197   11/124154   11/124198   11/124153   11/124151   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6997537   7004567   6916091   7077588   6918707       6923583   6953295   6921221   7001008   7168167   7210759   11/008115       11/011120   11/012329   6988790   7192120   7168789   7004577   7052120       11/123007   6994426   7258418   7014298   11/124348   11/177394   7152955       7097292   7207657   7152944   7147303   11/209712   7134608   7264333       7093921   7077590   7147297   11/239029   11/248832   11/248428   11/248434       7077507   7172672   7175776   7086717   7101020   11/329155   7201466       11/330057   7152967   7182431   7210666   7252367   11/450586   11/485255       11/525860   6945630   7018294   6910014   6659447   6648321   7082980       6672584   7073551   6830395   10/309025   7001011   6880922   6886915       6644787   6641255   7066580   6652082   10/309036   6666544   6666543       6669332   6984023   6733104   6644793   6723575   6953235   6663225       7076872   7059706   7185971   7090335   6854827   6793974   10/636258       7222929   6739701   7073881   7155823   7219427   7008503   6783216       6883890   6857726   10/636274   6641256   6808253   6827428   6802587       6997534   6959982   6959981   6886917   6969473   6827425   7007859       6802594   6792754   6860107   6786043   6863378   7052114   7001007       10/729151   10/729157   6948794   6805435   6733116   10/683006   7008046       6880918   7066574   6983595   6923527   7275800   7163276   7156495       6976751   6994430   7014296   7059704   7160743   7175775   11/058238       7097283   7140722   11/123009   11/123008   7080893   7093920   7270492       7128093   7052113   7055934   11/155627   11/149324   11/159197   7083263       7145592   7025436   11/281444   7258421   11/478591   11/478735   7226147       11/482940   7195339   11/503061   11/505938   11/520577   11/525863   11/544577       11/540576   11/585964   11/592991   11/599342   11/600803   11/604321   11/604302       11/635535   11/635486   11/643842   11/655987   11/650541   11/706301   11/707039       11/730388   11/730786   11/730785   11/739080   11/764746   11/768875   11/779847       11/829940   11847240   11/834625   11/863210   11/865680   7067067   6776476       6880914   7086709   6783217   7147791   6929352   7144095   6820974       6918647   6984016   7192125   6824251   6834939   6840600   6786573       7144519   6799835   6959975   6959974   7021740   6935718   6938983       6938991   7226145   7140719   6988788   7022250   6929350   7011393       7004566   7175097   6948799   7143944   10/965737   7029100   6957811       7073724   7055933   7077490   7055940   10/991402   7234645   7032999       7066576   7229150   7086728   7246879   11/144809   7140718   11/144802       7144098   7044577   11/144808   11/172896   7189334   7055935   7152860       11/203188   11/203173   11/202343   7213989   11/225156   11/225173   11/228433       7114868   7168796   7159967   11/272425   7152805   11/298530   11/330061       7133799   11/330054   11/329284   7152956   7128399   7147305   11/446241       11/442160   7246884   7152960   11/442125   11/454901   11/442134   11/450441       11/474274   11/499741   7270399   6857728   6857729   6857730   6989292       7126216   6977189   6982189   7173332   7026176   6979599   6812062       6886751   10/804057   10/804036   7001793   6866369   6946743   10/804048       6886918   7059720   10/846561   10/846562   10/846647   10/846649   10/846627       6951390   6981765   6789881   6802592   7029097   6799836   7048352       7182267   7025279   6857571   6817539   6830198   6992791   7038809       6980323   7148992   7139091   6947173   7101034   6969144   6942319       6827427   6984021   6984022   6869167   6918542   7007852   6899420       6918665   6997625   6988840   6984080   6845978   6848687   6840512       6863365   7204582   6921150   7128396   6913347   7008819   6935736       6991317   11/033122   7055947   7093928   7100834   7270396   7187086       11/072518   7032825   7086721   11/171428   7159968   7010456   7147307       7111925   11/144812   7229154   11/505849   11/520570   11/520575   11/546437       11/540575   11/583937   11/584619   11/592211   11/592207   11/635489   11/604319       11/635490   11/635525   11/650540   11/706366   11/706310   11/706308   11/785108       11/744214   11744218   11748485   11748490   11/764778   11/766025   11/834635       11/839541   11/860420   11/865693   11/863118   11/866307   11/866340   11/869684       11/869722   11/869694   11/872714                    
The disclosures of these applications and patents are incorporated herein by reference.
 
       BACKGROUND OF THE INVENTION 
       [0005]    Inkjet printing is a popular and versatile form of print imaging. The Assignee has developed printers that eject ink through MEMS printhead IC&#39;s. These printhead IC&#39;s (integrated circuits) are formed using lithographic etching and deposition techniques used for semiconductor fabrication. 
         [0006]    The micro-scale nozzle structures in MEMS printhead IC&#39;s allow a high nozzle density (nozzles per unit of IC surface area), high print resolutions, low power consumption, self cooling operation and therefore high print speeds. Such printheads are described in detail in U.S. Ser. No. 10/160,273 (Our Docket No. MJ40US) filed Jun. 4, 2002 and U.S. Ser. No. 10/728,804 (Our Docket No MTB01US) filed on Dec. 8, 2003 to the present Assignee. The disclosures of these documents are incorporated herein by reference. 
         [0007]    The small nozzle structures and high nozzle densities can create difficulties with color mixing between nozzles of different color. During periods of prolonged inactivity (or ‘standby mode’) the separate fluidic lines for each ink color can undergo slight pressure changes relative to each other. Different rates of heating and outgassing in different ink lines will generate a slight pressure differential. If paper dust or ink residue on the nozzle face extends between nozzles of the different ink lines, the dust or residual ink can forge a fluid connection between the two ink lines. The ink lines try to equalize the pressure difference between them and this drives an ink from the higher pressure line to the lower pressure line. If left unchecked, the ink contamination in the lower pressure ink line can extend to the ink tank. In this case, the contaminated ink supply is irretrievable and needs replacement before the ink lines are flushed through to the nozzles. 
         [0008]    The ink tanks can be isolated from the printhead by a shut off valve upstream of the printhead. This protects the tanks from contamination during standby, but there is a risk that the tank and the printhead will generate a pressure difference during the standby period. If this happens, the sudden pressure equalization causes a pulse through the ink line which floods the nozzle plate. 
       SUMMARY OF THE INVENTION 
       [0009]    Accordingly, the present invention provides an inkjet printer comprising: 
         [0010]    a printhead for printing onto a media substrate; 
         [0011]    a reservoir for containing a quantity of ink, the reservoir having a lower portion for holding ink and an upper portion defining a headspace of air above the ink; 
         [0012]    a fluid connection extending between the printhead and the reservoir; and, 
         [0013]    a pump for drawing air from the headspace into atmosphere. 
         [0014]    The invention uses a fluidic system that controls the air pressure in the headspace of an ink reservoir to control the hydrostatic pressure of the ink at the key points along the ink line. Controlling the ink pressure in one of the ink reservoirs (either the ink tank supplying the printhead or the ink sump collecting waste ink) can maintain a more consistent negative pressure (i.e. a hydroststatic pressure less than atmospheric) at the printhead nozzles. The negative pressure at the printhead nozzles prevents, or at least reduces color mixing by ensuring that the ink meniscus at each nozzle is drawn inwards. An inwardly drawn meniscus significantly reduces the chance that paper dust or residual ink can establish a fluid connection between nozzles of different color. Drawing air from the headspace in the sump helps to equalize the pressure in the different ink lines as the sump headspace is common to all the color channels. By the same token, it is a simple matter to use a single pump to connect the respective headspaces for each ink tank. In this way, the air pressure in each ink tank is equal and so the hydrostatic pressure of the ink at the nozzles will only vary by the variations in the ink levels of the ink tanks. In a normal usage profile, the ink levels remain roughly the same for each ink tank. To further minimize variations, the tanks can have a wide and squat shape to reduce the change in hydrostatic pressure from full to empty. With equal pressures (or at least very nearly equal pressures) in each ink line, there is no pressure differential to drive a color mixing process other than diffusion. As the fluid connection across the nozzle is so small, mixing by diffusion is negligible. 
         [0015]    Preferably, the reservoir is a sump that collects waste ink drained from the printhead. 
         [0016]    Preferably, the reservoir is an ink tank for supplying ink to the printhead. In a further preferred form, the printer is a color printer for printing a plurality of differently colored inks, each of the differently colored inks being stored in a respective ink tank for supplying the printhead, the headspace of each of the tanks is connected to the pump such that they are in fluid communication with each other. 
         [0017]    Preferably, the reservoir has a vent for venting the headspace to atmosphere, and for allowing a throttled flow of air into the headspace as the pump is drawing air out of the headspace. In a further preferred form, the vent has a filter for removing particulate contaminants from the throttled air flow into the headspace. 
         [0018]    Preferably, the printing further comprises an upstream valve positioned upstream of the printhead. In a further preferred form, the printer further comprises a downstream valve positioned downstream of the printhead. 
         [0019]    Preferably, the pump is reversible such that it can increase the air pressure in the headspace and force ink towards the printhead. In a further preferred form, the pump is used to prime the printhead. In another preferred form, the pump is used to purge ink from the nozzles and flood the printhead. 
         [0020]    Preferably, the printhead has a distribution manifold and a plurality of printhead integrated circuits mounted to the distribution manifold such that priming the distribution manifold with ink also primes the printhead integrated circuits. In some embodiments, the printer further comprises a maintenance station having a capper and blotter for the printhead integrated circuits. In specific embodiments, the pump is in fluid communication with the maintenance station and the sump such that ink collected by the maintenance station can be transferred to the sump by running the pump in one direction and air drawn from the headspace by running the pump in the other direction. In a particularly preferred form, the printhead is provided as a user removable and replaceable cartridge which is fluidly detachable from the printer via the upstream and the downstream valves. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Preferred embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings in which: 
           [0022]      FIG. 1  shows a schematic diagram of a printer fluidic system according to the present invention; and, 
           [0023]      FIG. 2  shows a schematic diagram of another printer fluidic system according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    Referring to  FIG. 1 , the printer fluidics system is shown schematically for the purposes of illustration. A single ink line for one color is shown in full. The ink tanks  10  and  12  for other color are shown in dotted line. A color printer would have complete ink lines for each ink color. Most of the individual components within the system are shown and described in much greater detail in the Applicant&#39;s co-pending application U.S. Ser. No. 11/688,863 (Our Docket RRE001US), filed on Mar. 21, 2007, the contents of which are incorporated herein by cross reference. Components of the present system that are not shown in the cross referenced document, are commercially available. 
         [0025]    The fluidic system shown in  FIG. 1  has a printhead  2  supplied with ink  14  from an ink tank  8  via an upstream ink line  20 . Waste ink from the printhead  2  drains to a sump  28  through downstream ink line  24 . The upstream ink line  20  has a shut off valve  18  and the downstream ink line has shut off valve  26 . These valves can be used for priming and purging ink (discussed below) and as detachable fluid connections is the printhead is provided in the form of user removable and replaceable cartridge such as that shown in the above referenced U.S. Ser. No. 11/688,863 (Our Docket RRE001US), filed on Mar. 21, 2007. 
         [0026]    The printhead has a maintenance station  22  for capping and blotting the nozzles. A drain line  16  connects the maintenance station  22  to the sump  28 . 
         [0027]    The printhead  2  is an assembly of an ink distribution manifold  4  on which a series of printhead integrated circuits (ICs)  6  are mounted. The printhead ICs  6  define the nozzle arrays which eject the ink to the media substrate. The nozzles are MEMS devices which can be thermally actuated such as those described in U.S. Ser. No. 11/482,953 (Our Docket No. MTD001US) filed on Jul. 10, 2006 or mechanically actuated such as those disclosed in U.S. Ser. No. 10/160,273 (Our Docket No. MJ40US) filed Jun. 4, 2002. 
         [0028]    The ink distribution manifold  4  is an LCP molding with a system of large channels feeding a network of smaller channels to supply the ink to many points along the length of each printhead IC  6 . An embodiment of the distribution manifold  4  and the printhead ICs  6  is disclosed in detail in the U.S. Ser. No. 11/688,863 (Our docket No. RRE001US) filed Mar. 21, 2007 reference listed above. This document also details the manner in which the printhead is primed with ink or, if necessary, purged of ink to correct any cross channel color contamination and/or bubble removal. 
         [0029]    In standby mode, the air pump  30  draws air from the headspace  32  in the tank  8 . The air pressure in the headspace drops and air is drawn back into the headspace  32  through the filtered vent  40 . The air constriction from the vent  40  is carefully controlled to create a predetermined negative air pressure. The tubing  38  fluidly connects the headspaces  34  and  36  in tanks  10  and  12  such that all the headspaces are at the same air pressure. Tanks  10  and  12  can have their own vents to atmosphere (not shown) but the system will operate with a single vent. 
         [0030]    With the headspaces  32 ,  34 , and  36  at the same pressure, the hydrostatic pressure in the ink is very early equal. The hydrostatic pressure of the ink at the nozzles will only vary by the variations in the ink levels of the ink tanks. Normal usage is designed to keep the ink levels roughly the same in each ink tank. To further minimize variations, the tanks can have a wide and squat shape to reduce the change in hydrostatic pressure from full to empty. With equal pressures (or at least very nearly equal pressures) in each ink line, there is no pressure differential to drive a color mixing process other than diffusion. As the fluid connection across the nozzle is so small, mixing by diffusion is negligible. 
         [0031]    The pump  30  is reversible so it can be used to pressurize the headspaces  32 ,  34  and  36  in order to prime the printhead  2  or purge ink through the printhead ICs  6 . Priming requires the upstream and downstream shut off valves  18  and  26  to be open. Ink from the tanks  8 ,  10  and  12  is forced down the upstream ink line  20 , through the distribution manifold  4  and into the sump  28  via the downstream ink line  24 . The printhead ICs  6  prime by capillary action from the ink in the distribution manifold. 
         [0032]    To purge the printhead ICs  6  (to recover dried nozzles, outgassing bubble blockages etc) the down stream valve  26  is closed as the pump  30  pressurizes the headspace  32 . Ink is forced from the nozzles and the resulting flood on the nozzle plate is cleared with the maintenance station  22 . 
         [0033]    It will be appreciated that the pump  30  operates during a power up standby mode. That is, during periods of inactivity between print jobs, but the printer is still plugged in and connected to a power supply. During a power off standby, the shut off valve  18  and  26  are closed to isolate the printhead and prevent mixing. When the printer powers up again, the pump  30  can be used to ready the printhead by priming or purging (if necessary) as discussed above. 
         [0034]      FIG. 2  shows the pump  30  operating on the headspace  32  of the sump  28  instead of the ink tank  8 . Again, a single ink line is shown but the color printer will have several color lines all draining to the same sump  28 . As long as all the down stream ink lines  24  for each color connect to the sump headspace, a single pump can be used to change the hydrostatic pressures in the ink at the nozzles. 
         [0035]    With the pump  30  connected to the sump  28 , the upstream shut off valve  18  is closed during power down standby. The negative air pressure in the headspace  32  draws on the column of ink hanging from the printhead  2 . This ensures that a sufficiently negative pressure is maintained at the nozzles. More importantly, the negative pressure in the nozzles of each color is the same. As discussed above, this removes the mechanism that drives the color mixing process. 
         [0036]    The pump  30  is marginally more complex in that it needs to be able to handle an ink/air mixture. It is in the drain line  16  from the maintenance assembly  22  to the sump  28  to assist the transfer of blotted ink to the sump  28  but needs to be able to draw air from the headspace  32  or from atmosphere through the filter  42 . 
         [0037]    In this embodiment, priming requires the upstream valve  18  to be open and the pump  30  to create a low pressure in the sump  28  to draw the ink from the tank  8  down the upstream ink line  20 , through the distribution manifold  4  and into the downstream ink line  24 . Again the printhead ICs  6  prime by capillarity. 
         [0038]    To purge, the upstream valve  18  is closed and the pump  30  creates a positive pressure in the headspace  32  to force the ink in the down stream ink line  24  and the distribution manifold  4  to flood the printhead ICs  6 . 
         [0039]    The invention has been described by way of example only. Ordinary workers in this field will readily recognize any variations and modifications which do not depart from the spirit and scope of the broad inventive concept.