Information
-
Patent Grant
-
6817707
-
Patent Number
6,817,707
-
Date Filed
Wednesday, June 18, 200321 years ago
-
Date Issued
Tuesday, November 16, 200419 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Meier; Stephen D.
- Dudding; Alfred
Agents
- Luedeka, Neely & Graham, P.C.
-
CPC
-
US Classifications
Field of Search
US
- 347 85
- 347 86
- 347 87
- 347 49
-
International Classifications
-
Abstract
An ink jet printhead assembly for a pressure controlled ink jet printhead. The assembly includes an ink reservoir made of a first material having a first melting point and having an open top cavity defined by sidewalls, a bottom wall and a peripheral edge. A pressure control structure made of a polymeric material having a second melting point lower than the first melting point is included. The pressure control structure has a first surface, a second surface opposite the first surface, a side surface, and an aperture therein. A sealing structure for forming a liquid tight seal is provided between the sidewalls of the ink reservoir and the side surface of the pressure control structure. A pressure regulating film is attached over the aperture to the first surface of the pressure control structure. A cover is attached to the ink reservoir.
Description
FIELD OF THE INVENTION
The invention relates to pressure controlled ink jet printheads and in particular to improved printhead assemblies and to improved methods for assembling ink jet printheads.
BACKGROUND
Ink jet technology continues to be improved in order to increase printing speed and print quality or resolution. One means for improving print speed and quality is to increase the number of nozzle holes in an ink jet printhead and to decrease the diameter of the nozzle holes. However, improvements in print speed and quality often result in operational problems not experienced with lower quality slower speed printers.
In an ink jet printer, ink is provided to the printhead from an ink cartridge or supply tank. The ink flows from the tank through a connecting conduit from the ink cartridge through an ink via in a semiconductor chip or around the edges of a semiconductor chip and into ink flow channels and an ink chamber. The ink chamber is situated in axial alignment with a corresponding nozzle hole and a heater resistor defined on the surface of the semiconductor chip. As electrical impulse energy is applied to an ink ejector adjacent an ink chamber to cause ink adjacent the ejector in the chamber to be forced through a nozzle hole onto a print medium. By selective activation of a plurality of ink ejectors on a printhead, a pattern of ink dots are applied to the print medium to form an image.
A critical aspect of the printing process is the controlled supply of ink to the ink ejectors from the ink supply. If the pressure of the ink supply is too high, ink may run out freely from the nozzle holes onto the print medium before the ink ejector is activated. If the pressure of the ink supply is too low, ink channels and chambers in the printhead will not refill fast enough. If the ink chambers and channels are not refilled fast enough there will be missing ink dots or the print speed must be lowered to allow time for ink to refill the ink chambers. Furthermore, as ink is used from the ink supply, the pressure of the ink supply may decrease to a point which inhibits flow of the remaining ink to the ink ejectors. Accordingly, as the number of nozzles holes on a printhead increases and the diameter of the holes decreases, maintaining a predetermined ink supply pressure in the ink supply system becomes more critical.
There are two primary methods for maintaining ink supply flow to printheads. The first method includes the use of a porous capillary member such as foam which is saturated with ink and provides a controlled flow of ink to the printheads. The second method includes the use of a diaphragm or bellows to provide pressure or back pressure on the ink in the cartridge. Use of a diaphragm or bellows enables an ink supply reservoir to be filled with liquid ink as opposed to the use of foam saturated with ink. Accordingly, the ink jet printhead assembly may be made smaller for the same volume of ink ejected onto the print media during the life of the printhead. One disadvantage of smaller ink jet printhead assemblies which use a diaphragm or bellows for pressure control is that manufacturing techniques become more complicated because of a greater number of different materials required for use in the printhead assembly.
There is a need therefore for an improved pressure controlled ink supply assembly and improved methods for assembling pressure controlled ink jet printheads.
SUMMARY OF THE INVENTION
With regard to the foregoing and other objects and advantages, the invention provides an ink jet printhead assembly for a pressure controlled ink jet printhead. The assembly includes an ink reservoir having an open top cavity defined by sidewalls, a bottom wall and a peripheral edge. The ink reservoir is made of a first material having a first melting point. A pressure control structure having a first surface, a second surface opposite the first surface, a side surface, and an aperture extending therethrough from the first surface to the second surface is also provided. The pressure control structure is made of a polymeric material having a second melting point lower than the first melting point. A sealing structure is provided for forming a liquid tight seal between the sidewalls of the ink reservoir and the side surface of the pressure control structure. A pressure regulating film is attached to the first surface of the pressure control structure closing the aperture therein. A cover is attached to the ink reservoir to protect the pressure regulating film from damage.
In another embodiment, the invention provides method for assembling a pressure controlled ink jet printhead assembly. The method includes providing an ink reservoir having an open top cavity defined by sidewalls, a bottom wall and a peripheral edge. The ink reservoir is made of a first material having a first melting point. A pressure control structure having a first surface, a second surface opposite the first surface, a side surface, and an aperture extending therethrough from the first surface to the second surface is also included. The pressure control structure is made of a polymeric material having a second melting point lower than the first melting point. A sealing structure is applied to the side walls of the pressure control structure for forming a liquid tight seal between the sidewalls of the ink reservoir and the side surface of the pressure control structure. The pressure control structure is inserted in the open top cavity of the ink reservoir. A pressure regulating film is attached to the first surface of the pressure control structure thereby closing the aperture therein. A cover is attached to the ink reservoir to protect the pressure regulating film from damage.
The invention provides a number of advantages over conventional ink jet printhead assemblies. For one, components of the assembly may be sub assembled and combined using only mechanical means. Also, there is no need for use of a two step injection molding process to provide inner and outer frames made of different materials. Another advantage of the invention is that the components may be assembled with a high degree of assurance of substantially no ink leakage from the assembled components. Also, a pressure control film may be made of a single material rather than from a laminate construction of two or more different materials thereby improving the pressure control response of the assembly.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other aspects and advantages of the invention will become further apparent by reference to the following detailed description of preferred embodiments when considered in conjunction with the accompanying drawings in which:
FIG. 1
is an exploded, perspective view, not to scale, of a printhead assembly according to the invention;
FIG. 2
is a cross-sectional view, not to scale, of a portion of a printhead assembly according to the invention; and
FIG. 3
is a bottom plan view, not to scale, of a printhead assembly according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to FIG. I there is provided an exploded view in perspective of an ink jet printhead assembly
10
according to a preferred embodiment of the invention. The assembly
10
includes a substantially rectangular-shaped ink reservoir
12
having an open top cavity
14
defined by side walls
16
surrounding the cavity
14
. A bottom wall
18
is connected to a first end
20
of the side walls
16
. A second end
22
of the side walls
16
contains a peripheral edge
24
.
The ink reservoir
12
component of the assembly is preferably made of a first material having a first melting point. The first material may include metals, plastics, glass, ceramics, and composites of two or more of the foregoing. More preferably the ink reservoir
12
is molded from a material selected from the group consisting of thermoplastic materials including but not limited to polyphenylene oxide/polystyrene alloys, polypropylene, acrylonitrile/butadiene/styrene terpolymers, polystyrene/butadiene alloys or copolymers, polyetherimide, polysulfone, polyesters and the like, having a melting point or softening point above about 150° C. A particularly preferred material for ink reservoir
12
is a polyphenylene ether/polystyrene resin from GE Plastics of Pittsfield, Mass. under the trade name NORYL SE1701.
An important component of the printhead assembly is a pressure control structure
26
. The pressure control structure
26
has a first surface
28
and a second surface
30
opposite the first surface and a side surface
32
around the periphery thereof. An aperture
34
extends through the pressure control structure
26
from the first surface
28
to the second surface
30
.
Unlike the ink reservoir
12
, the pressure control structure
26
is preferably made of a polymeric material, preferably a thermoplastic material having a second melting point lower than the first melting point. Suitable materials for the pressure control structure
26
include materials selected from polypropylene and polyethylene materials. The most preferred material is polyethylene material having a melting point of about 120° C.
As will be described in more detail below, a flexible film is preferably melt attached to the pressure control structure
26
. Accordingly, making the pressure control structure
26
from a material that enables melt attachment of a film thereto improves the manufacturing process for the assembly
10
. It is also important that the ink reservoir
12
be made of a higher melting material than the pressure control structure
26
. Such a higher melting material is less susceptible to warping and deformation due to high printhead temperatures during printing operations.
A sealing structure
36
is provided on side surface
32
for forming a liquid tight and air tight seal between the inner surface
38
of side walls
16
and the side surface
32
of the pressure control structure
26
. The sealing structure
36
preferably provides a liquid tight and air tight seal by purely mechanical means. Accordingly the sealing structure
36
may be selected from elastomeric materials and adhesives. A particularly preferred sealing structure
36
is an elastomeric o-ring made from ethylene propylene diene monomer (EPDM). Regardless of whether the sealing structure
36
is an adhesive or elastomeric o-ring material, it is preferred that the sealing structure
36
be substantially chemically resistant to the components of ink used in the printhead assembly
10
.
As shown in more detail in
FIG. 2
, the pressure control structure
26
preferably includes a peripheral groove
40
in the side surface
32
thereof. The groove
40
is preferably dimensioned to accept an o-ring or bead of adhesive as the sealing structure
36
. Because the sealing structure
36
provides a liquid tight and air tight seal between the side surface
32
and the inner surface
38
of side walls
16
, each of the major components
12
and
26
may be separated formed or molded from different materials. Also, tolerances between the inner surface
38
of side walls
16
and the side surface
32
of the pressure control structure
26
are less critical because the sealing structure
36
is capable of spanning any gap
42
between the two. In order to improve assembly between the pressure control structure
26
and the ink reservoir
12
, stops
44
or a ledge may be provided to limit the distance the pressure control structure can be moved into the cavity
14
.
A pressure regulating film
46
is preferably attached to the first surface
28
of the pressure control structure
26
to close or otherwise cover the aperture
34
in the pressure control structure
26
. The pressure regulating film
46
may be made from a wide variety of materials including, but not limited to, films that are compatible with the inks used in the ink printhead assembly
10
and films adaptable to welding or adhesive attachment thereof to the first surface
28
of the pressure control structure
26
. Such films include polyethyelene films and polypropylene films having a thickness ranging from about 1.5 to about 3 mils.
A particularly preferred film
46
is for controlling pressure in the assembly
10
is a copolymer polypropylene material available from Triangle Plastics of Raleigh, N.C. under the trade name CPP40. The copolymer polypropylene material may be laminated with an adhesive available from Minnesota Mining and Manufacturing Company of Minneapolis, Minn. under the trade name 3M-845. It is preferred however, to use a non-laminated film
46
that is capable of being heat welded to the first surface
28
of the pressure control structure
26
. Heat welding of the film
46
to the surface
28
may be accomplished by providing a pressure control structure
26
made from a polymeric material having a similar melting point to that of the film
46
or having a lower melting point than the melting point of the film
46
. In a particularly preferred embodiment, the film
46
is preferably selected from a material having substantially the same melting point as that of the material of the pressure control structure
26
.
A cover
48
is preferably attached to the ink reservoir
12
to protect the film
46
from damage and to provide additional sealing between the ink reservoir
12
and the pressure control structure
26
. The cover
48
may be heat welded, adhesively attached or snap fit to the ink reservoir
12
. In a preferred embodiment, the cover
48
is adhesively attached to the peripheral edge of the ink reservoir
12
.
A bottom wall
18
of the ink reservoir
12
preferably includes a pocket or recessed area
50
for attaching a nozzle plate
52
and semiconductor chip
54
thereto (FIGS.
2
and
3
). The nozzle plate
54
preferably includes a plurality of nozzle holes
56
for ejection of ink therethrough toward a print media. The nozzle holes
56
may be provide in one or more arrays
58
along the length of the nozzle plate
52
. An ink feed via
60
in the chip
54
provides a flow of ink to ink ejectors on the chip
54
. The ink ejectors may be selected from thermal or electromechanical type ejectors including heater resistors and piezoelectric devices.
Because the pressure regulating structure
26
and ink reservoir
12
components of the assembly
10
may be made separately from different materials, assembly of the components to provide the printhead assembly
10
can be achieved in a variety of ways. For example, the film
46
may be attached to the first surface
28
of the pressure control structure
26
prior to inserting the pressure control structure
26
into the cavity
14
of the ink reservoir
12
. In the alternative, the pressure regulating structure
26
may be inserted into the cavity
14
of the ink reservoir
12
before attaching the film
46
to the first surface
28
of the pressure control structure
26
. Either method will provide an improved pressure controlled ink jet printhead assembly
10
according to the invention.
Ink is preferably inserted into cavity
14
before attaching the film
46
to the pressure control structure
26
when the pressure control structure
26
is first inserted into cavity
14
. If the film is first attached to the pressure control structure
26
before the pressure control structure is inserted into cavity
14
, then the ink is inserted into the cavity
14
before inserting the pressure control structure
26
into cavity
14
.
After the cavity
14
is filled with ink, and the cover
48
is attached to the ink reservoir
12
, a reduced pressure or back pressure is applied to the cavity
14
, preferably through an opening in the ink reservoir
12
, to provide a predetermined pressure differential between cavity
14
and the nozzle plate/chip assembly
52
/
54
. As ink is ejected through the nozzle holes
56
, the volume of ink in cavity
14
decreases. The pressure regulator structure
26
and film
46
are effective to maintain a predetermined pressure in cavity
14
as the volume of ink in the cavity decreases. The pressure regulator structure
26
and film
46
also helps to compensate for pressure changes in ink cavity
14
due to ambient temperature and pressure changes. In most instances, the predetermined minimum pressure or back pressure maintained in the cavity
14
ranges from about −8 to about −24 centimeters (cm) of water.
In a particularly preferred embodiment, a biasing device such as a coil spring, leaf spring, resilient foam or the like is included in the pressure cavity
14
to bias the film
46
away from the bottom wall
18
of the ink reservoir
12
in order to maintain a predetermined pressure on ink in the reservoir
12
. In an alternative embodiment, the biasing device may be disposed between the cover
48
and the film
46
to bias the film
46
toward the bottom wall
18
of the ink reservoir
12
in order to maintain a predetermined pressure in the reservoir
12
.
The foregoing description of certain exemplary embodiments of the present invention has been provided for purposes of illustration only, and it is understood that numerous modifications, alterations, substitutions, or changes may be made in and to the illustrated embodiments without departing from the spirit and scope of the invention.
Claims
- 1. An ink jet printhead assembly for a pressure controlled ink jet printhead comprising:an ink reservoir having an open top cavity defined by sidewalls, a bottom wall and a peripheral edge, the ink reservoir being made of a first material having a first melting point; a pressure control structure having a first surface, a second surface opposite the first surface, a side surface, and an aperture extending therethrough from the first surface to the second surface, the pressure control structure being made of a polymeric material having a second melting point lower than the first melting point; a sealing structure for forming a liquid tight seal between the sidewalls of the ink reservoir and the side surface of the pressure control structure; a pressure regulating film attached to the first surface of the pressure control structure closing the aperture therein; and a cover attached to the ink reservoir to protect the pressure regulating film from damage.
- 2. The ink jet printhead assembly of claim 1 wherein the side surface of the pressure control structure further comprises a peripheral groove.
- 3. The ink jet printhead assembly of claim 2 wherein the sealing structure comprising an elastomeric o-ring disposed in the peripheral groove.
- 4. The ink jet printhead assembly of claim 2 wherein the sealing structure comprises a bead of adhesive disposed in the peripheral groove.
- 5. The ink jet printhead assembly of claim 1 wherein the sealing structure comprising an elastomeric o-ring.
- 6. The ink jet printhead assembly of claim 1 further comprising a semiconductor substrate and nozzle plate attached to the bottom wall of the ink reservoir.
- 7. The ink jet printhead assembly of claim 1 wherein the pressure regulating film is melt attached to the first surface of the pressure control structure.
- 8. A method for assembling a pressure controlled ink jet printhead assembly comprising:providing an ink reservoir having an open top cavity defined by sidewalls, a bottom wall and a peripheral edge, the ink reservoir being made of a first material having a first melting point; and a pressure control structure having a first surface, a second surface opposite the first surface, a side surface, and an aperture extending therethrough from the first surface to the second surface, the pressure control structure being made of a polymeric material having a second melting point lower than the first melting point; applying a sealing structure to the side walls of the pressure control structure for forming a liquid tight seal between the sidewalls of the ink reservoir and the side surface of the pressure control structure; inserting the pressure control structure in the open top cavity of the ink reservoir; attaching a pressure regulating film to the first surface of the pressure control structure thereby closing the aperture therein; and attaching a cover to the ink reservoir to protect the pressure regulating film from damage.
- 9. The method of claim 8 wherein the side surface of the pressure control structure further comprises a peripheral groove.
- 10. The method of claim 9 wherein the sealing structure comprising an elastomeric o-ring, and wherein the step of applying the sealing structure comprises disposing the o-ring in the peripheral groove.
- 11. The method of claim 9 wherein the sealing structure comprises a bead of adhesive and wherein the step of applying the sealing structure comprises disposing the adhesive in the peripheral groove.
- 12. The method of claim 8 wherein the sealing structure comprising an elastomeric o-ring.
- 13. The method of claim 8 further comprising attaching a semiconductor substrate and nozzle plate to the bottom wall of the ink reservoir.
- 14. The method of claim 8 wherein the step of attaching the pressure regulating film comprises melt attaching the film to the first surface of the pressure control structure.
- 15. A method for assembling a pressure controlled ink jet printhead assembly comprising:providing an ink reservoir having an open top cavity defined by sidewalls, a bottom wall and a peripheral edge, the ink reservoir being made of a first material having a first melting point; and a pressure control structure having a first surface, a second surface opposite the first surface, a side surface, and an aperture extending therethrough from the first surface to the second surface, the pressure control structure being made of a polymeric material having a second melting point lower than the first melting point; applying a sealing structure to the side walls of the pressure control structure for forming a liquid tight seal between the sidewalls of the ink reservoir and the side surface of the pressure control structure; attaching a pressure regulating film to the first surface of the pressure control structure thereby closing the aperture therein; inserting the pressure control structure in the open top cavity of the ink reservoir; and attaching a cover to the ink reservoir to protect the pressure regulating film from damage.
- 16. The method of claim 15 wherein the side surface of the pressure control structure further comprises a peripheral groove.
- 17. The method of claim 16 wherein the sealing structure comprising an elastomeric o-ring, and wherein the step of applying the sealing structure comprises disposing the o-ring in the peripheral groove.
- 18. The method of claim 16 wherein the sealing structure comprises a bead of adhesive and wherein the step of applying the sealing structure comprises disposing the adhesive in the peripheral groove.
- 19. The method of claim 15 wherein the sealing structure comprising an elastomeric o-ring.
- 20. The method of claim 15 further comprising attaching a semiconductor substrate and nozzle plate to the bottom of the ink reservoir.
- 21. the method of claim 15 wherein the step of attaching the pressure regulating film comprises melt attaching the film to the first surface of the pressure control structure.
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Lee et al. |
Dec 2002 |
B1 |
6508545 |
Dowell et al. |
Jan 2003 |
B2 |
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Sharma et al. |
Mar 2003 |
B2 |
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Pan |
Mar 2003 |
B1 |
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Pawlowski, Jr. et al. |
Jul 2001 |
A1 |
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Underwood et al. |
Aug 2001 |
A1 |
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Kobayashi et al. |
Aug 2001 |
A1 |
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Hauck |
Sep 2001 |
A1 |
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Kobayashi et al. |
Oct 2001 |
A1 |
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Shimizu |
Nov 2001 |
A1 |
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Otis et al. |
Jan 2002 |
A1 |
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Hoen et al. |
Feb 2002 |
A1 |
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Hall et al. |
Mar 2002 |
A1 |
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Nanjo et al. |
Apr 2002 |
A1 |
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Seccombe |
May 2002 |
A1 |
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Dowell et al. |
Jun 2002 |
A1 |
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Yamada et al. |
Aug 2002 |
A1 |
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Pan et al. |
Oct 2002 |
A1 |
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Anma et al. |
Dec 2002 |
A1 |
20020191061 |
Dowell et al. |
Dec 2002 |
A1 |
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Hayashi et al. |
Jan 2003 |
A1 |
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Scheffelin et al. |
Mar 2003 |
A1 |