EP1945459B1

EP1945459B1 - Method of maintaining a printhead using air blast cleaning

Info

Publication number: EP1945459B1
Application number: EP05791415A
Authority: EP
Inventors: Vesa Karppinen; Kia Silverbrook; David William Jensen
Original assignee: Silverbrook Research Pty Ltd
Current assignee: Silverbrook Research Pty Ltd
Priority date: 2005-10-10
Filing date: 2005-10-10
Publication date: 2010-08-18
Anticipated expiration: 2025-10-10
Also published as: AU2005337421B2; CA2619862C; ATE477933T1; EP1945459A4; DE602005023073D1; CA2619862A1; AU2005337421A1; EP1945459A1; WO2007041749A1

Abstract

A method of maintaining a printhead (10) in an operable condition is provided. The method comprises the steps of: (a) flooding an ink ejection face (12) of the printhead (10) with ink; and (b) removing the ink by blasting air across the face (12).

Description

Field of the Invention

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

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 listed in the above cross reference list.
Notwithstanding the technical challenges of producing a pagewidth inkjet printhead, a crucial aspect of any inkjet printing is maintaining the printhead in an operational printing condition throughout its lifetime. A number of factors may cause an inkjet printhead to become non-operational and it is important for any inkjet printer to include a strategy for preventing printhead failure and/or restoring the printhead to an operational printing condition in the event of failure. Printhead failure may be caused by, for example, printhead face flooding, dried-up nozzles (due to evaporation of water from the nozzles - a phenomenon known in the art as decap), or particulates fouling nozzles.
Particulates, in the form of paper dust, are a particular problem in high-speed pagewidth printing. This is because the paper is typically fed at high speed over a paper guide and past the printhead. Frictional contact of the paper with the paper guide generates large quantities of paper dust compared to traditional scanning inkjet printheads, where paper is fed much more slowly. Hence, pagewidth printheads tend to accumulate paper dust on their ink ejection face during printing. This accumulation of paper dust is highly undesirable.
In the worst case scenario, paper dust blocks nozzles on the printhead, preventing those nozzles from ejecting ink. More usually, paper dust overlies nozzles and partially covers nozzle apertures. Nozzle apertures that are partially covered or blocked produce misdirected ink droplets during printing - the ink droplets are deflected from their intended trajectory by particulates on the ink ejection face. Misdirects are highly undesirable and may result in acceptably low print quality.
One measure that has been used for maintaining printheads in an operational condition is sealing the printhead, which prevents the ingress of particulates and also prevents evaporation of ink from nozzles: Commercial inkjet printers are typically supplied with a sealing tape across the printhead, which the user removes when the printer is installed for use. The sealing tape protects the primed printhead from particulates and prevents the nozzles from drying up during transit. Sealing tape also controls flooding of ink over the printhead face.
Aside from one-time use sealing tape on new printers, sealing has also been used as a strategy for maintaining printheads in an operational condition during printing. In some commercial printers, a gasket-type sealing ring and cap engages around a perimeter of the printhead when the printer is idle. A vacuum may be connected to the sealing cap and used to suck ink from the nozzles, unblocking any nozzles that have dried up. However, whilst sealing/vacuum caps may prevent the ingress of particulates from the atmosphere, such measures do not remove particulates already built up on the printhead.
In order to remove flooded ink from a printhead after vacuum flushing, prior art maintenance stations typically employ a rubber squeegee, which is wiped across the printhead. Particulates are removed from the printhead by flotation into the flooded ink and the squeegee removes the flooded ink having particulates dispersed therein.
However, rubber squeegees have several shortcomings when used with MEMS pagewidth printheads. A typical MEMS printhead has a nozzle plate comprised of a hard, durable material such as silicon nitride, silicon oxide, aluminium nitride etc. Moreover, the nozzle plate is typically relatively abrasive due to etched features on its surface. On the one hand, it is important to protect the nozzle plate, comprising sensitive nozzle structures, from damaging exposure to the shear forces exerted by a rubber squeegee. On the other hand, it is equally important that a rubber squeegee should not be damaged by contact with the printhead and reduce its cleaning efficacy.
Therefore, it would be desirable to provide an inkjet printhead maintenance station, which does not rely on a rubber squeegee wiping across the nozzle plate to remove flood ink and particulates. It would further be desirable to provide an inkjet printhead maintenance station, which removes flooded ink and particulates from the nozzle plate without the nozzle plate coming into contact with any cleansing surface.
It would further be desirable to provided an inkjet printhead maintenance station that is simple in design, does not consume large amounts power and can be readily incorporated into a desktop printer.
US 5,559,536 discloses a cleaning device for an ink jet recording head, having at least one discharge port for ejecting recording liquid. The device includes a cap member for facing a region of the recording head having the discharge port therein, a supply path for supplying a fluid medium to the cap member for flow along the discharge port region and a discharge path for discharging the medium from the cap member. The flow of the medium inside the cap member from the supply path to said discharge path is constricted by a protruding portion in the cap member, which protruding portion is disposed in the cap member such that the discharge port is spaced opposite the protruding portion when the discharge port region faces the cap member, and the medium flows along the discharge port region such that a negative pressure is generated for drawing recording liquid from the discharge port into the flow of the medium.
DE 203 18 248 U1 discloses a negative pressure device. The device provides abrupt negative pressure impact to suction space which causes high flow speed for short time in all parallel suctioned jets, which causes quick release of small air bubbles and debris and smaller amount of ink is sucked out.
US 2004/04185 discloses an ink jet recording apparatus which is structured to perform discharges in the capping status.
EP 1,077,133 discloses an ink jet serial printer having a function of flushing a printing head and being capable of setting a print available region to a region wider than the width of a recording medium.

SUMMARY OF THE INVENTION

Accordingly, a first embodiment of the invention provides a method as detailed in claim 1. Advantageous embodiments are provided in the dependent claims.

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:-

Figure 1 is a front perspective view of a capper and engagement mechanism for a printhead maintenance station according to the present invention;
Figure 2 is a rear perspective view of the capper and engagement mechanism shown in Figure 1;
Figure 3 is a tranverse section of the capper engaged with a printhead assembly;
Figure 4 is an enlarged view of the capper and printhead assembly shown in Figure 3;
Figure 5 is a schematic diagram of a fluidics system for the printhead maintenance station;
Figure 6 is a schematic side view of a dabbing device; and
Figure 7 is a transverse section of an alternative capper engaged with a printhead assembly.

Detailed Description of Specific Embodiments

Referring to Figures 1 and 2, there is shown part of a printhead maintenance station 1 comprising a capper 2 and an engagement mechanism 3. The capper 2 takes the form of an elongate capping chamber 4 having a perimeter gasket 5 fixed around one end. The capping chamber 4 with gasket 5 is configured to fit and form a seal around a pagewidth printhead 10 (see Figures 3 and 4).
In the embodiment shown, the engagement mechanism 3 takes the form of a pantograph 6, which raises and lowers the capper 2 into sealing engagement and out of engagement from around the printhead 10. The pantograph 6 is actuated using a motor 7, which raises and lowers the pantograph via a cam arrangement (not shown). Other types of engagement mechanism suitable for raising and lowering the capper 2 will, of course, be readily apparent to the person skilled in the art.
Referring to Figures 3 and 4, the capper 2, engaged around the printhead 10, is shown in more detail. The printhead 10 is mounted on an ink manifold 11, which supplies ink to a backside of the printhead. A wirebond encapsulant 13 is bonded to the ink manifold 11 and extends from one side of the printhead 10. The encapsulant 13 protects wirebonds, which connect CMOS circuitry in the printhead 10 to an external microprocessor (not shown). On an opposite side of the printhead 10, a paper guide 14 is attached to the ink manifold 11. During printing, paper is guided over the paper guide 14 and ink is ejected from an ink ejection face 12 of the printhead 10 onto the paper via a plurality of inkjet nozzles (not shown). The capper 2 is disengaged when the printhead 10 is being used for printing.
As shown in Figure 4, with the capper 2 in its engaged position, the perimeter gasket 5 forms a seal around the printhead 10. Longitudinal sides 5A and 5B of the perimeter gasket 5 sealingly engage with the paper guide 14 and wirebond encapsulant 13 respectively.
A constriction member 15 extends from a base 16 of the capping chamber 4 towards the printhead 10. The constriction member 15 divides the capper chamber 4 into an air inlet channel 17 and a vacuum channel 18. With the capper 2 engaged around the printhead 10, the air inlet channel 17 and the vacuum channel 18 are in fluid communication via a constricted blast channel 19. The constriction member 15 and the ink ejection face 12 together define the width of the blast channel 19 therebetween. Typically, the blast channel 19 has a width of about 0.2 mm.
An air inlet 20 and a vacuum aperture 21 are defined in the base 16 of the capping chamber 4 and are connected to an air inlet port 22 and vacuum port 23 respectively. The air inlet 20 and vacuum aperture 21 open into the air inlet channel 17 and vacuum channel 18 respectively.
The air inlet port 22 is connected via hose to an air inlet valve 30, while the vacuum port 23 is connected via a hose to a vacuum system 31. The air inlet valve 30 and vacuum system 31 cooperate with the capper 2 to purge and clean the printhead 10. The purging and cleaning operations are described in further detail with reference to Figure 5.
Referring to Figure 5, the vacuum system 31 comprises a vacuum pump 32 connected to a vacuum reservoir 33. A check valve 34 between the vacuum pump 32 and the reservoir 33 ensures that the reservoir remains charged after the pump is switched off. The vacuum reservoir 33 is connected to the vacuum channel 18 in the capping chamber 4 via a vacuum line 37 and the vacuum port 23 (not shown in Figure 5). A first solenoid valve 35 and an ink dump 36 are positioned in the vacuum line 37 between the vacuum reservoir 33 and the capping chamber 4.
The air inlet valve 30 takes the form of a second solenoid valve 38, which is connected to the air inlet channel 17 in the capping chamber 4 via the air inlet port 20 (not shown in Figure 5). The air inlet valve 30 has an air intake 39, which may receive unfiltered or filtered air from the atmosphere.
At the beginning of a typical printhead maintenance operation, the vacuum reservoir 33, having a volume of about 1 to 1.5 litres, is initially charged with a vacuum. The vacuum reservoir 33 may be charged independently of the capper 2 by switching the first solenoid valve 35 to a charging position (not shown). The vacuum reservoir 33 may, for example, be charged during idle periods or during active printing when the capper 2 is disengaged. The time period for charging the vacuum reservoir 33 may vary, depending on the size of the reservoir and the power of the pump 32. Typically, charging will last for a maximum of about 45 seconds, ensuring that the printhead can be regularly maintained or remediated.
With the vacuum reservoir 33 charged, the capper 2 is engaged around the printhead 10 and the first solenoid valve 35 is opened to the vacuum reservoir, as shown in Figure 5. Since the capper 2 is sealed around the printhead 10, a negative pressure is generated above the ink ejection face 12 and, as a result, ink floods from printhead nozzles onto the ink ejection face.
Immediately after subjecting the printhead 10 to vacuum (e.g. after about 50 to 500 ms), the second solenoid valve 38 is opened. As a result, air is drawn into the air intake 39 and rushes from the air inlet channel 17 through to the vacuum channel 18 and on into the vacuum system 31. Air is blasted through the blast channel 19 at high velocity due to the small gap (about 0.2 mm) between the constriction member 15 and the ink ejection face 12. Typically, the air flow rate through the blast channel 19 is about 5 to 7 litres per second, which ensures complete removal of flooded ink from the ink ejection face 12 of the printhead 10. Ink removed from the ink ejection face 12 by the air blast is deposited into the ink dump 36.
With the ink purging and cleaning operation complete, the vacuum reservoir 33 is recharged by the vacuum pump 32 in preparation for the next printhead maintenance cycle.
After air blasting, any ink remaining on areas surrounding the ink ejection face 12 may be removed by a simple dabbing device. Figure 6 shows a dabbing device 40 comprising a microfibre film 41, which is fed between a pair of spools 42. The film 41 is used to dab the paper guide 14 and wirebond encapsulant 13 after disengagement of the capper 2. After dabbing, the film 41 is advanced so that a clean portion of film is ready for subsequent dabbing.
The printhead maintenance station 1 as described above may be used for maintaining any type of printhead in an operable condition. It is especially suitable for use with pagewidth MEMS inkjet printheads, where it is desirable to avoid physical contact of the printhead with a cleaning device.
An important aspect of the station is alignment of the clapper 2 with the printhead 10, so that constriction member 15 is accurately positioned to define the blast channel 19. Figure 7 shows an alternative printhead maintenance assembly 50, wherein the capper 2 and the printhead support have complementary alignment features for aligning the capper into position. Specifically, a locating pin 51 extends from a roof of the capping chamber 4, and engages with a complementary slot 52 in the paper guide 14. It will be appreciated that a plurality of such complementary alignment features may be provided to assist in aligning the capper 2 into its optimum maintenance position.
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

A method of maintaining a printhead (10) in an operable condition, said method comprising the steps of:
(a) flooding an ink ejection face (12) of said printhead with ink by generating a vacuum above said face; and

(b) removing said ink by blasting air across said face,
characterized in that:
the air is blasted through a blast channel (19) adjacent said face by releasing said vacuum to atmosphere.
The method of claim 1, wherein a capper (2) is sealingly engaged around said printhead (10) during printhead maintenance.
The method of claim 2, wherein said capper (2) is in fluid communication with a vacuum system (31), said vacuum system flooding said face (12) by generating said vacuum above said face.
The method of claim 3, wherein said capper (2) comprises a constriction member (15), said constriction member defining the blast channel (19) adjacent said printhead when said capper is engaged around said printhead.
The method of claim 4, wherein said capper (2) is in fluid communication with an air inlet valve (30), wherein said vacuum system (31), said constriction member (15) and said air inlet valve cooperate to blast air through said blast channel (19).
The method of claim 5, wherein said vacuum system (31) further comprises a vacuum reservoir (33), said reservoir being charged before flooding of said face.
The method of claim 6, wherein said reservoir (33) is discharged during air blasting.