INKJET PRINTER WITH SELECTIVELY ISOLATABLE PUMP

Description

FIELD OF THE INVENTION

[0001] The present invention relates to printers and in particular the fluidic architecture of inkjet printers.

BACKGROUND OF THE INVENTION

[0002] Inkjet printing is a popular and versatile form of print imaging. The Assignee has developed printers that eject ink through MEMS printhead IC's. These printhead IC's (integrated circuits) are formed using lithographic etching and deposition techniques used for semiconductor fabrication.

[0003] The micro-scale nozzle structures in MEMS printhead IC'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 US 6746 105 (Our Docket No.MJ40US) filed June 4, 2002 and US7246886 (Our Docket No MTB01US) filed on December 8, 2003 to the present Assignee.

[0004] The small nozzle structures and high nozzle densities can create difficulties with nozzle clogging, de-priming, nozzle drying (decap), color mixing, nozzle flooding, bubble contamination in the ink stream and so on. Each of these issues can produce artifacts that are detrimental to the print quality. The component parts of the printer are designed to minimize the risk that these problems will occur. The optimum situation would be printer components whose inherent function is able to preclude these problem issues from arising. In reality, the many different types of operating conditions, and mishaps or unduly rough handling during transport or day to day operation, make it impossible to address the above problems via the 'passive' control of component design, material selection and so on.

[0005] To address this, the Applicant has developed printers with active control of the fluidic systems. These active fluidic systems are described in co-pending application and US7645034, US7637602, US 7645033, US 7661803, US7841708, US7771029, US 2007-026050, US 7658482. While these systems provide the user with the ability to actively manage the static and dynamic fluid conditions throughout the printer, it has been found that the active components within a printer are responsible for a large proportion of the ink borne contaminants. Pumps in particular are prone to shedding particles into the ink flow which can be detrimental to the operation of the nozzles. The wear and friction of surfaces acting against each other eventually generate particle which are directly entrained in the ink flow. Many of the above referenced fluidic designs use peristaltic pumps which introduce additional problems. The flexible tubing within the pump can eventually crack and leak, the tubing loses elasticity and no longer returns to a fully open condition, and the pump has a high torque requirement because of the need to compress the tubing enough to form a seal. To meet the torque requirements, the pump needs to be relatively large which is counter a compact form factor for the printer as a whole.

[0006] Ink borne contaminants can be removed with a filter upstream of the printhead. However, the particle size requires the filter pore size to be very small. To maintain the ink flow rate required by a high speed, pagewidth printhead, the filter surface area needs to be impractically large and precludes the compactness required by market expectations.

SUMMARY OF THE INVENTION

[0007] Accordingly, the present invention provides an inkjet printer according to claim 1.

[0008] The invention is predicated on the realization that the purging and priming functions of the pump can be performed while in fluid communication with the printhead and then be fluidically isolated from the printhead when printing. By removing the pump from the direct fluid line between the reservoir and the printhead, the valve arrangement allows it to connect to the reservoir or the printhead only when necessary. The purging and priming operations have become a two-stage processes where the pump initially draws a charge of ink from the reservoir and then delivers it to the printhead. The ink from the pump can be passed through a fine filter to remove any particulate contaminants without then constricting the ink flow from the reservoir during normal printing operations.

[0009] Further aspects of the invention are shown in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Preferred embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a schematic diagram of a printer fluidic system according to the present invention whilst in a standby mode;

Figure 2 shows the fluidic system of Figure 1 in a ink tank pressurization mode;

Figure 3 shows the fluidic system of Figure I in a printhead priming/purging mode;

Figure 4 shows the fluidic system of figure I in the printing mode; and,

Figure 5 schematically shows an alternative ink pump arrangement for the fluidic system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Referring to Figures 1 to 3, the printer fluidics system is shown schematically for the purposes of illustration. The fluidic architecture shown in the figures is for a single ink line for one color only. A color printer would have separate lines and ink tanks for each ink color. Most of the individual components within the system are shown and described in much greater detail in the Applicant's co-pending application USSN 11/688863 (Publication number US 2007-0206056) (Our Docket RRE001US), filed on March 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.

[0012] The fluidic system shown in Figures I to 3 has a printhead 2 supplied with ink 46 from an ink tank 8 via an upstream ink line 20. The upstream ink line 20 has a three-way valve 18 which connects to the pump 30 via a filter 32. A downstream line 24 connects the printhead 2 to a sump 28 via a shut off valve 26. The printhead has a maintenance station 22 for capping, blotting and wiping the nozzles. A drain line 34 connects the maintenance station 22 to the sump 28.

[0013] 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 US 7654645 (Our Docket No. MTDOOIUS) filed on July 10, 2006 or mechanically actuated such as those disclosed in US 6746105 (Our Docket No.MJ40US) filed June 4, 2002.

[0014] 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 USSN 11/688863 (Publication number US 2007-0206056) (Our docket No. RRE001US) filed March 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.

[0015] The ink tank 8 and the bubble point pressure regulator 10 are described in copending US 7841685 (Our Docket RMCO10US) filed October 16, 2007, incorporated herein by reference. However, for the purposes of this description, the regulator 10 is shown as a bubble outlet 76 in the tank headspace 12 and vented to atmosphere via microchannel 74 extending to an air inlet 78. Ink is retained in the microchannel 74 by capillary action. As the printhead IC's 6 consume ink, the pressure in the tank 8 drops until the pressure difference at the bubble outlet 76 sucks air into the tank. The air is drawn through an air filter 16 to remove contaminants that might clog or obstruct the microchannel 74. The filtered air forms a bubble in the ink within the micrchannel 74 which travels to the outlet 76. This pressure difference is the bubble point pressure and will depend on the diameter (or smallest dimension) of the microchannel 74 and the Laplace pressure of the ink meniscus. This maintains a constant negative pressure in the headspace 12. The hydrostatic pressure in the ink at the outlet to the tank 8 will vary as the ink level drops. To minimize this variation, the ink tanks 8 are dimensioned to be short and squat.

[0016] Figure 1 shows the printer is a standby mode. The printhead 2 is fluidically isolated from the ink tank 8 by the three-way valve 18. This prevents any ink mixing across the nozzles of the printhead ICs 6 from diffusing up into the tank 8. The valve 18 connects the tank 8 to the pump 30 via the branch line 36. The pump 30 is a piston 38 that reciprocates in a chamber 40. It is possible to use a peristaltic pump but these suffer the problems discussed above in the background to the invention. Namely, the potential for failure of the tubes, inaccuracy as the tubes no longer return to their original uncompressed shape and high torque requirements. A more suitable pump is shown in Figure 5. The branch line 36 feeds a bulb 30 of elastomeric material. Actuator 38 compresses or releases the bulb 30 to pump ink toward the printhead or draw ink from the tank.

[0017] During long periods of standby, the pressure in the headspace 12 can rise above the bubble point pressure. Outgassing of dissolved gases, and diurnal temperature variation can cause pressure increases. In the worst case, the headspace 12 pressure is no longer negative relative to atmosphere.

[0018] Figure 2 shows the printer coming out of standby and preparing for a print job. The piston 38 retracts in the chamber 40 to draw ink 46 out of the tank 8. The ink displacement lowers the air pressure in the headspace 12 until the bubble point regulator 10 allows air into the tank 8. With the headspace at the bubble point pressure, the negative hydrostatic pressure of the ink is within the expected operating range required by the printhead 2.

[0019] Figure 3 shows the priming or purging of the printhead 2 in preparation for printing. The valve 18 is reconfigured to close fluid communication between the pump 30 and the tank 8, and open fluid communication between the pump 30 and the printhead 2. The ink in the pump is forced out of the chamber 40 by depressing the piston 38. The ink is forced through the filter 32 to remove any particulate contaminants shed by the pump. To prime the printhead 2, ink is forced into the main channels of the ink distribution manifold 4 and from there, capillary action primes the small conduits and the nozzles in each of the printhead ICs 6. This is done with the shut off valve 26 in the downstream line 24 open so that any excess ink feeds straight to the sump 28.

[0020] If the printhead 2 contains ink when it is brought out of standby, it may be necessary to remove air bubbles or mixed ink. The problem of ink mixing is discussed in detail in the cross referenced application USSN 11/688863 (Publication number US 2007-0206056) (Our docket No. RRE001US) filed March 21, 2007, listed above. Put briefly, the ink from nozzles of one color can wick across the surface of the printhead ICs 6, and diffuse into ink in the nozzles and supply lines for another color. This is corrected with a printhead purge. The downstream shutoff valve 26 is closed and filtered ink from the pump 30 is forced through the distribution manifold 4 to flood the printhead ICs 6. The maintenance station 22 cleans away the flooded ink.

[0021] Figure 4 shows the printer in printing mode. The three-way valve 18 is configured to fluidly connect the tank 8 to the printhead 2. The blind end 44 seals off the branch line 36 to the pump 30. The ejection of ink from the nozzles on the printhead ICs 6 draws ink from the ink tank 8. The upstream ink line 20 is not constricted by the filter 32 or any of the structural elements of the pump 30. In the embodiment shown US 7654640 (Our Docket RRE010US), filed on March 21, 2007, the printhead 2 is a pagewidth printhead that prints full color at photographic quality resolution at a rate greater than one page per second. This requires a high ink supply flow rate which is not throttled by unnecessary elements in the upstream ink line 20.

[0022] At the completion of the print job, the printer can return to standby mode as shown in Figure 1. The valve 18 moves the blind end 44 over the upstream ink line 20 to seal the printhead 2 from the tank 8. This prevents any ink mixing at the printhead from reaching the ink tank. Ink contamination in the tank would be irretrievable and has to be replaced. As a further safeguard against color mixing, the shut off valve 26 is held open during standby. The sump 28 is at a lower elevation relative to the printhead ICs 6. This allows the column of ink in the downstream ink line 24 to 'hang' from the distribution manifold 4 to create a negative hydrostatic pressure at the printhead ICs 6. A negative pressure at the nozzles draws the ink meniscus inwards and inhibits color mixing.

[0023] The maintenance station 22 that seals the nozzles during standby periods to avoid dehydration of the printhead ICs 6 and shield the nozzle plate from paper dust and other particulates. The maintenance station 22 is also configured to wipe the nozzle plate to remove dried ink and other contaminants. Dehydration of the printhead ICs 6 occurs when the ink solvent, typically water, evaporates and increases the viscosity of the ink. If the ink viscosity is too high, the ink ejection actuators fail to eject ink drops. Dehydrated nozzles are typically a problem when reactivating the printer after a power down or standby period.

[0024] The problems outlined above are not uncommon during the operative life of a printer and can be effectively corrected with the relatively simple fluidic architecture shown in the figures. It also allows the user to initially prime the printer, deprime the printer prior to moving it, or restore the printer to a known print ready state using simple trouble-shooting protocols. Several examples of these situations are described in detail in the above referenced US 7771029 (Our Docket SBF006US) filed on February 21, 2007.

Claims

1. An inkjet printer comprising:

a printhead (2) for printing onto a media substrate;

a reservoir (8) for supplying ink to the printhead;

a piston-actuated pump (30); and,

a three-way valve (18) positioned between the pump (30)and the reservoir (8), the three-way valve having:

a first configuration in which the pump is in fluid communication with the reservoir only;

a second configuration in which the reservoir is in fluid communication the printhead only; and

a third configuration in which the pump is in fluid communication with the printhead only.

2. An inkjet printer according to claim 1 further comprising a filter (32) positioned between the pump (30) and the three-way valve (18).

3. An inkjet printer according to claim 1 wherein the pump (30) has a chamber (40) with a reciprocating piston (38).

4. An inkjet printer according to claim 1 wherein the pump (30) comprises a bulb of elastomeric material (40) for holding a volume of ink and a piston actuator (38) for selectively compressing the bulb.

5. An inkjet printer according to claim 1 wherein the reservoir has a pressure regulator.

6. An inkjet printer according to claim 1 wherein the printhead comprises a distribution manifold and a plurality of printhead integrated circuits mounted to the distribution manifold.

Ansprüche

1. Ein Tintenstrahldrucker, umfassend:

einen Druckkopf (2) zum Drucken auf ein Mediensubstrat;

ein Reservoir (8) zum Zuführen von Tinte zu dem Druckkopf;

eine Kolben-betätigten Pumpe (30), und

ein Drei-Wege-Ventil (18) zwischen der Pumpe (30) und dem Reservoir (8), der Drei-Wege-Ventil mit positioniert ist:

eine erste Konfiguration, bei der die Pumpe in Fluidverbindung mit dem Reservoir nur;

eine zweite Konfiguration, in der das Reservoir in Fluidverbindung der Druckkopf nur, und

eine dritte Konfiguration, in der sich die Pumpe in Fluidverbindung mit dem Druckkopf nur.

2. Tintenstrahldrucker gemäß Anspruch 1, ferner umfassend einen Filter (32) zwischen der Pumpe (30) und dem Drei-Wege-Ventil (18) angeordnet ist.

3. Tintenstrahldrucker gemäß Anspruch 1, wobei die Pumpe (30) eine Kammer (40) mit Hubkolben (38).

4. Tintenstrahldrucker gemäß Anspruch 1, wobei die Pumpe (30) einen Kolben aus elastomerem Material (40) zum Halten einer Menge der Tinte und einer Kolben-Aktuator (38) zum selektiven Zusammendrücken der Lampe.

5. Tintenstrahldrucker gemäß Anspruch 1, wobei das Reservoir gekennzeichnet hat einen Druckregler.

6. Ein Tintenstrahldrucker nach Anspruch 1, wobei der Druckkopf einen Verteiler und eine Vielzahl von Druckkopf integrierten Schaltungen, die an dem Verteiler.

Revendications

1. Une imprimante jet d'encre comprenant:

une tête d'impression (2) pour l'impression sur un substrat support;

un réservoir (8) pour alimenter en encre la tête d'impression;

une pompe à piston actionné par (30), et,

une vanne à trois voies (18) positionné entre la pompe (30) et le réservoir (8), la soupape à trois voies ayant:

une première configuration dans laquelle la pompe est en communication de fluide avec le réservoir seulement;

une seconde configuration dans laquelle le réservoir est en communication de fluide que la tête d'impression, et

une troisième configuration dans laquelle la pompe est en communication fluidique avec la tête d'impression uniquement.

2. Imprimante à jet d'encre selon la revendication 1 comprenant en outre un filtre (32) positionné entre la pompe (30) et la soupape à trois voies (18).

3. Imprimante à jet d'encre selon la revendication 1, dans lequel la pompe (30) comporte une chambre (40) avec un piston à mouvement alternatif (38).

4. Imprimante à jet d'encre selon la revendication 1, dans lequel la pompe (30) comprend une ampoule de matériau élastomère (40) pour maintenir un volume d'encre et un actionneur de piston (38) pour comprimer sélectivement l'ampoule.

5. Imprimante à jet d'encre selon la revendication 1, dans lequel le réservoir a un régulateur de pression.

6. Imprimante à jet d'encre selon la revendication 1, dans lequel la tête d'impression comprend un collecteur de distribution et une pluralité de circuits intégrés de tête d'impression montée sur le collecteur de distribution.

Drawing