Patent Application
20090085962
This invention relates to a maintenance station for an inkjet printhead. It has been developed primarily for facilitating maintenance operations, such as sealing, cleaning or unblocking nozzles in an inkjet printhead.
The following applications have been filed by the Applicant simultaneously with U.S. patent application Ser. No. 11/246,677:
The disclosures of these co-pending applications are incorporated herein by reference.
Various methods, systems and apparatus relating to the present invention are disclosed in the following US patents/patent applications filed by the applicant or assignee of U.S. patent application Ser. No. 11/246,677:
The disclosures of these applications and patents are incorporated herein by reference.
Inkjet printers are commonplace in homes and offices. More recently, inkjet printers have been proposed for use in portable devices, such as digital cameras, mobile phones etc. Furthermore, with the advent of MEMS technology, whereby inexpensive photolithographic techniques from the semiconductor industry are used to manufacture microelectomechanical systems, the possibility of disposable inkjet printers is becoming a commercial reality. The present Applicant has developed many different types of MEMS inkjet printheads, some of which are described in the patents and patent applications listed in the above cross reference list.
The contents of these patents and patent applications are incorporated herein by cross-reference in their entirety.
Although the cost and power requirements of inkjet printheads is being reduced through the use of MEMS technology and improved inkjet nozzle designs, it is also necessary to reduce the cost and power requirements of other printer components, in order to incorporate inkjet printers into portable devices or to provide disposable inkjet printers.
A crucial aspect of 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.
In some cases, printhead failure may be remedied by simply firing nozzles periodically using a ‘keep wet cycle’. This strategy does not require any external mechanical maintenance of the printhead and may be appropriate when a nozzle has not been fired for a relatively short period of time (e.g. less than 60 seconds). A ‘keep wet cycle’ can be used to address decap, and the consequent formation of viscous plugs in nozzles, during active printing.
However, a ‘keep wet cycle’ cannot be used when the printer is left idle over long periods of time, for example, when it is in between print jobs, switched off or in transit. Furthermore, a ‘keep wet cycle’ is not appropriate for clearing severely blocked nozzles and does not address the problem of printhead face flooding. Accordingly, inkjet printers typically include a printhead maintenance station, which is designed to prevent printhead failure and/or remediate printheads to an operational condition.
One measure that has been used for preventing printhead failure is sealing the printhead, thereby preventing evaporation of water and the drying up of 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. With the printhead capped in this way, evaporation of water from the nozzles is minimized, and a relatively humid atmosphere can be maintained above the nozzles, thereby minimizing the extent to which nozzles dry up.
Furthermore, gasket-type sealing rings have been combined with suction cleaning in prior art maintenance stations. A vacuum may be connected to the sealing cap and used to suck ink from the nozzles. The sealing cap minimizes nozzle drying and entrance of particulates from the atmosphere, while the suction ensures any blocked nozzles are cleared prior to printing. Hence, this type of maintenance station employs both preventative and remedial measures.
Another remedial strategy used in prior art printhead maintenance stations is a rubber squeegee. The squeegee does not act as seal; rather, it is wiped across the printhead and removes any flooded ink. Squeegee cleaning may be used immediately prior to printing, after the vacuum flush described above.
The printhead maintenance strategies described above have several shortcomings, especially in the present age of inkjet printing. Modern inkjet printers are required to have smaller drop volumes, and hence smaller nozzle openings, for high resolution photographic printing. It is also desirable to use stationary pagewidth printheads for high-speed printing, as opposed to scanning printheads. It is also desirable to reduce the overall cost of inkjet printers and incorporate them into low-powered portable devices, such as digital cameras and mobile phones.
Current printhead maintenance strategies are unable to provide inkjet printers, which meet these demands. With smaller nozzle openings (of the order of 5-20 microns), nozzle blocking due to decap becomes a serious problem. At present, the only reliable way of dealing with blocked nozzles is to use a suction pad. However, suction devices are bulky, expensive and consume large amounts of power, making them unsuitable for many inkjet applications. Furthermore, suction pads are wasteful of ink and can consume up to 0.25 ml of ink with each remediation.
Additionally, none of the prior art maintenance stations are able to provide a printhead ready for printing after a single maintenance operation. Typically, it is necessary to employ separate preventative (e.g. sealing) and remedial (e.g. suction and squeegee-cleaning) measures in order to provide a fully operational printhead. However, operations such as squeegee-cleaning are not suitable for all types of printhead, because it exerts shear stress across the printhead and can damage sensitive nozzle structures.
Therefore, it would be desirable to provide an inkjet printhead maintenance station, which combines both preventative and remedial measures. It would further be desirable to provide an inkjet printhead maintenance station, which can be fabricated at low cost and is therefore suitable for fabrication of a disposable printer. It would be further desirable to provide an inkjet printhead maintenance station, which does not significantly impact on the overall size of the printer and is therefore suitable for incorporation into handheld electronic devices. It would be further desirable to provide an inkjet printhead maintenance station, which does not impact on the overall power consumption of the printer and is therefore suitable for incorporation into battery-powered electronic devices. It would be further desirable to provide an inkjet printhead maintenance station, which does not waste large quantities of ink with each remedial operation. It would further be desirable to provide an inkjet printhead maintenance station, which cleans ink from a flooded printhead without exerting high shear stresses across the printhead.
According to an aspect of the present invention, a printhead maintenance station comprises an elastically deformable pad having a contact surface adapted for sealing engagement with an ink ejection face of a printhead; and an engagement mechanism for moving the pad between a first position in which the contact surface is sealingly engaged with the face and a second position in which the contact surface is disengaged from the face. The engagement mechanism moves the pad between the first position and the second position in a substantially perpendicular direction with respect to the face, and the contact surface is a curved surface, whereby the contact surface is progressively contacted with the face during sealing engagement and peeled away from the face during disengagement.
Specific forms of the present invention will be now be described in detail, with reference to the following drawings, in which:—
In general terms, and as mentioned above, the present invention relies on an understanding of contact angles—specifically, a hysteresis between advancing and receding contact angles.
The shape of a droplet of liquid on a solid surface is determined by its contact angle(s). Depending on factors such as the surface tension in the liquid and the interactive forces between the solid and the liquid, the shape of the droplet will change.
The contact angles shown in
For a typical droplet of ink moving across a silicone surface, the advancing contact angle is about 90°, whereas the receding contact angle is about 15°. Without wishing to be bound by theory, it is understood by the present inventors that this contact angle hysteresis is responsible for the cleaning action provided by the present invention.
In
In
As will be readily appreciated from the foregoing discussion, the present invention may be implemented in many different forms, provided that the contact surface 7 is contacted with the ink ejection face 8 so as to produce a contact angle hysteresis. Various forms of the invention are described in detail below.
Referring to
A housing 30 comprises a body 31 and a cap 32, which is snap-fitted to the body with a plurality of snap-locks 33. The two-part construction of the housing 30 enables it to be assembled by receiving the pad sub-assembly in the body 31 and then snap-fitting the cap 32 onto the body. The lugs 26 protruding from each end of the support arm 25 are received in complementary slots 34 in the housing 30. Accordingly, the support arm 25 is slidably movable within the slots 34, allowing the pad 6 to move slidably relative to the housing 30.
The extent of movement of the pad 6 is defined by the slots 34. In a first position shown in
As shown in
The pad 6 is movable between the first and second positions by means of an engagement mechanism 40, which is shown in
In the first position, the contact surface 7 is sealingly engaged with the ink ejection face 8, as shown in detail in
In the embodiment shown in
However, the contact surface may adopt other profiles and still achieve a similar effect when moved perpendicularly with respect to the ink ejection face 8.
As shown in
Any of these alternative pads may readily be incorporated into the printhead maintenance station 20 described above by simple replacement of the pad 6 in
In all the embodiments described thus far, the contact surface 7 has been sloped. With a sloped contact surface 7, linear motion of the pad 6 produces the peeling action required by the invention. However, as an alternative, the pad 6 may be moved rotationally in order to achieve the progressive engagement and peeling disengagement from the ink ejection face 8.
In
As shown in
As shown in
The roller 70 is rolled across the ink ejection face using a rolling mechanism 73. The rolling mechanism 73 comprises a pivot arm 74 to which the roller 70 is rotatably mounted at one end. The pivot arm 74 is pivoted about a pivot 75, and an opposite end of the arm is moved by means of a solenoid 76. Actuation of the solenoid 76 causes the pivot arm 74 to pivot and the roller 70 is consequently rolled transversely across the ink ejection face 8.
In all the embodiments described above, the cleaning action of the pad 6 generally deposits ink towards a predetermined region of the contact surface 7, which is typically an edge portion. Some ink may also be deposited on an edge portion of the ink ejection face 8—either a transverse edge portion or a longitudinal edge portion depending on the configuration or movement of the pad 6.
The pad 6 and wicking element 80 are configured to move ink away from an opposite longitudinal edge portion 84 of the printhead 5, which comprises wirebond encapsulant 85. The encapsulant 85 protects wirebonds (not shown) connecting the printhead 5 to other printer components (not shown).
The crowded environment around the printhead 5 means that the wirebonded edge portion 84 is relatively inaccessible. It is an advantage of the present invention that the pad 6 can access and move ink away from this severely crowded edge portion 84.
The wicking element 80 is formed from an absorbent material, such as paper or foam, and is positioned in a cavity defined between a print media guide 86 and a support 87 on which the printhead 5 and print media guide are mounted. The print media guide 86 has a guide surface 88 for guiding print media past the printhead 5 when the pad 6 is fully disengaged from the ink ejection face 8.
An ink collector 89 receives ink that has wicked through the wicking element 80, ensuring that ink is always removed away from the printhead 5.
With repeated maintenance operations, the wicking element 80 may become damaged after repeated engagement of the pad 6. In particular, if the wicking element 80 is comprised of paper and saturated with absorbed ink, it may disintegrate when contacted with the contact surface 7. Whilst more robust wicking materials may be used, a problem remains in that wicking rates through the material are relatively slow.
In an alternative embodiment, and referring to
The film 120 is typically a biaxially oriented polyester film (e.g. Mylar® film). Due to the stiffness and resilience of the film 120, attachment to the support 87 along the distal longitudinal edge 122 provides a tapered wicking channel 124. A channel inlet 125 is provided adjacent the longitudinal edge 83 of the printhead 5, while a channel outlet 126 is provided distal from the printhead 5.
Due to the tapering of the wicking channel 124, ink received in the channel inlet 125 wicks rapidly along the channel towards the channel outlet 126 by capillary action, thereby removing ink away from the printhead 5. Furthermore, since the anchor points 123 are spaced apart along the distal longitudinal edge 122 of the film 120, ink can flow in between the anchor points and exit the channel outlet 126.
A secondary wicking element 127 is positioned between the media guide 86 and the support 87 at the channel outlet 126. The secondary wicking element 87 is positioned to receive ink from the channel outlet 126 and wicks ink into the ink collector 89. The secondary wicking element 127 is comprised of an absorbent material, such as paper or foam. Since the secondary wicking element 127 is not physically contacted by the pad 6 during printhead maintenance operations, it has a comparatively long lifetime compared to the wicking element 80 described above.
Referring to
Referring to
In
Once the ink 81 has entered the channel inlet 125, it is rapidly wicked towards the channel outlet 126 due to the tapering of the channel 124 and the capillary action provided thereby. The ink 81 is subsequently received by the secondary wicking element 127 and deposited into the ink collector 89. Hence, efficient and rapid removal of ink 81 away from the contact surface 7 and/or printhead 5 is achieved.
Engagement Mechanism with Rotating Pad-Cleaning Action
As described above, a wicking element 80 or film 120 may be positioned adjacent an edge portion 83 of the printhead 5, so that ink 81 is removed from the contact surface 7, ready for the next cleaning sequence.
In an alternative embodiment, the maintenance station may be configured so that ink is removed from contact surface 7 after the pad 6 is disengaged from the printhead face 8. In this embodiment, the engagement mechanism is configured to move the contact surface 7 into engagement with a remote cleaning means after it has disengaged from the printhead face 8. For example, rotation of the pad 6 after disengagement may be used to bring the contact surface 7 into cleaning engagement with a squeegee or blotter. Rotation may, for example, rock the pad through an arc and past a squeegee. Alternatively, rotation may be fully through 180° using a similar mechanism to those used in rotating ‘self-inking’ stamps. Self-inking stamps have been known for decades in the stamping art (see, for example, U.S. Pat. Nos. 239,779; 405,704; 669,137; 827,347; 1,121,940; 2,079,080; 2,312,727; 2,919,645; 3,364,856; 3,402,663; 3,631,799; 3,952,653; 3,988,987; 4,432,281 and 4,852,489, the contents of which are incorporated herein by cross-reference), and the skilled person will readily appreciate how such stamping mechanisms may be used to rotate the pad 6 through 180° onto a blotter after it has disengaged from the printhead face 8.
Referring to
Referring now to
In
In
Finally, the cradle 101 is moved back into the position shown in
It will, of course, be appreciated that the present invention has been described purely by way of example and that modifications of detail may be made within the scope of the invention, which is defined by the accompanying claims.
The present application is a continuation of U.S. application Ser. No. 11/246,677 filed on Oct. 11, 2005, all of which are herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11246677 | Oct 2005 | US |
| Child | 12276381 | US |
