U.S. patent application number 09/989278 was filed with the patent office on 2002-05-02 for simplified ink jet head.
Invention is credited to Adams-Brady, David, Barss, Steven H., Biggs, Melvin L., Gailus, David W., Hine, Nathan P., Hoisington, Paul A., Mackay, Diane, Moynihan, Edward R., Palifka, Robert G., Paulson, Bruce A..
Application Number | 20020051039 09/989278 |
Document ID | / |
Family ID | 23607943 |
Filed Date | 2002-05-02 |
United States Patent
Application |
20020051039 |
Kind Code |
A1 |
Moynihan, Edward R. ; et
al. |
May 2, 2002 |
Simplified ink jet head
Abstract
In the embodiments of the simplified ink jet head described in
the specification, a carbon body is formed with ink passages, such
as internal passages extending through a carbon plate, pressure
chambers on one side of a carbon plate, flowthrough passages on the
other side of the same plate and ink supply passages, and a
piezoelectric plate is affixed to the pressure chamber side of the
carbon plate by a thin layer of epoxy adhesive. The piezoelectric
plate may have a conductive coating on one side which is
photoetched to produce an electrode pattern corresponding to the
pattern of the pressure chambers in the carbon plate. An orifice
plate may have specially profiled orifice openings to assure axial
projection of drops and may be affixed by a thin layer of epoxy
adhesive to a carbon plate having orifice passages supplying ink
from the pressure chambers to the orifices. Since the carbon plate
is conductive, it can be used, if desired, as an electrode on the
opposite side of the piezoelectric plate and, to assure grounding
of the piezoelectric plate, a conductive epoxy adhesive may be used
to bond the piezoelectric plate to the carbon plate. Moreover,
since the carbon plate is porous, it can provide a communication
path between a vacuum source and an air-permeable, ink-impermeable
layer on the ink passages to remove dissolved air from the ink in
the passages. In one alternative embodiment, an ink jet head
assembly contains two separate carbon pressure chamber plates, a
carbon manifold plate and a carbon collar to retain the carbon
plates in an assembly.
Inventors: |
Moynihan, Edward R.;
(Lebanon, NH) ; Gailus, David W.; (Merrimack,
NH) ; Palifka, Robert G.; (Orford, NH) ;
Hoisington, Paul A.; (Norwich, VT) ; Hine, Nathan
P.; (South Strafford, VT) ; Adams-Brady, David;
(Meriden, NH) ; Biggs, Melvin L.; (Norwich,
VT) ; Barss, Steven H.; (Wilmot Flat, NH) ;
Mackay, Diane; (Corinth, VT) ; Paulson, Bruce A.;
(Newport, NH) |
Correspondence
Address: |
BAKER & BOTTS
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
|
Family ID: |
23607943 |
Appl. No.: |
09/989278 |
Filed: |
November 20, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09989278 |
Nov 20, 2001 |
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08406427 |
Mar 20, 1995 |
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5474032 |
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08406427 |
Mar 20, 1995 |
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08215301 |
Mar 21, 1994 |
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5659346 |
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Current U.S.
Class: |
347/68 |
Current CPC
Class: |
A01K 15/025
20130101 |
Class at
Publication: |
347/68 |
International
Class: |
B41J 002/045 |
Claims
We claim:
1. An ink jet head comprising at least one member made of carbon
and formed to provide at least one ink passage in the member.
2. An ink jet head according to claim 1 wherein the carbon member
is formed with an array of closely spaced ink passages.
3. An ink jet head according to claim 2 wherein the array of
closely spaced ink passages extend along a surface of the carbon
member.
4. An ink jet head according to claim 2 wherein the array of
closely spaced ink passages extend within at least a portion of the
carbon member.
5. An ink jet head according to claim 5 wherein the carbon member
includes two sections each formed on a surface with an array of
closely spaced grooves, the two sections being bonded together with
the grooves in alignment to form the array of closely spaced
passages within the member.
6. An ink jet head according to claim 2 wherein the carbon member
comprises a pressure chamber plate formed with an array of closely
spaced pressure chamber passages along one side surface and a
corresponding array of orifice passages extending through an
adjacent end surface of the member and communicating with the
corresponding pressure chamber passages.
7. An ink jet head according to claim 2 wherein the carbon member
includes an array of closely spaced ink passages formed in a
surface of the carbon member and a corresponding array of internal
ink passages communicating with the surface passages.
8. An ink jet head according to claim 7 wherein the carbon member
is a pressure chamber member and wherein the ink passages formed in
a surface of the pressure chamber member comprise pressure
chambers, and including a piezoelectric plate affixed to the
surface of the pressure chamber member.
9. An ink jet head according to claim 8 wherein the piezoelectric
plate is affixed to the surface of the pressure chamber member with
a conductive adhesive material.
10. An ink jet head according to claim 8 wherein the piezoelectric
plate is affixed to the surface of the pressure chamber member with
an adhesive material and wherein the surfaces of the pressure
chamber member and the piezoelectric plate are in point-to-point
physical contact.
11. An ink jet head according to claim 8 wherein the array of
pressure chambers is formed in a first surface of the pressure
chamber member and includes a second array of closely spaced
pressure chambers formed in a second surface of the pressure
chamber member which is parallel to the first surface and a second
array of internal ink passages corresponding to and communicating
with the second array of pressure chambers and a second
piezoelectric plate affixed to the second surface of the pressure
chamber member.
12. An ink jet head according to claim 11 including a second carbon
pressure chamber member having first and second arrays of closely
spaced pressure chambers formed in first and second parallel
surfaces, respectively, and having first and second arrays of
closely spaced internal ink passages and also having first and
second piezoelectric plates affixed to the first and second
surfaces, respectively, a carbon collar member for holding the
pressure chamber member and the second pressure chamber member in
fixed parallel relation with outlet openings from the arrays of
internal passages therein terminating in a common plane, and a
carbon manifold member having a first surface extending in the
common plane of the outlet openings of the pressure chamber members
and having corresponding passages aligned therewith and extending
through the manifold member and having a second surface formed with
ink passages extending from the corresponding passages toward and
terminating in a common line extending along the second
surface.
13. An ink jet head according to claim 12 including an orifice
plate affixed to the second surface of the manifold member and
having a linear array of orifices aligned with the common line to
receive ink from the ink passages formed in the second surface.
14. An ink jet head according to claim 13 wherein each orifice in
the orifice plate has a cylindrical nozzle opening at the outlet
end, a larger diameter cylindrical inlet opening at the inlet end,
and a tapered conical section extending between the inlet opening
and the nozzle opening.
15. An ink jet head according to claim 14 wherein the cylindrical
inlet opening has a diameter which is no more than about twice the
diameter of the cylindrical nozzle opening and has a length at
least as long as that of the nozzle opening.
16. An ink jet head according to claim 15 including an ink
reservoir affixed to the carbon collar and an ink passage formed in
the collar member, the manifold member and the pressure chamber
members to supply ink to the pressure chambers in the pressure
chamber members.
17. An ink jet head according to claim 16 including a heater
disposed at least in part in the collar member.
18. An ink jet head according to claim 11 wherein the arrays of
internal passages terminate in a common plane at a further surface
of the pressure chamber member and including a carbon manifold
member formed with arrays of internal ink passages corresponding to
the arrays of internal ink passages in the pressure chamber member
and having a first surface engaging the further surface of the
pressure chamber member, and retaining means for releasably
retaining the first surface of the manifold member and the further
surface of the pressure chamber member in engagement with the
corresponding arrays of internal passages therein maintained in
alignment.
19. An ink jet head according to claim 18 wherein the manifold
member has a second surface formed with passages extending from the
arrays of internal passages therein toward and terminating in a
common line extending along the second surface, and an orifice
plate affixed to the second surface of the manifold member having a
linear array of orifices with axes intersecting the common line on
the second surface of the manifold member.
20. An ink jet head according to claim 19 wherein each of the
orifices in the array has a cylindrical nozzle opening at the
outlet end and a larger diameter inlet opening at the inlet end and
a tapered conical section extending between the inlet opening and
the nozzle opening.
21. An ink jet head according to claim 20 wherein the cylindrical
inlet opening has a diameter which is no more than about twice the
diameter of the cylindrical nozzle opening and has a length at
least as long as that of the nozzle opening.
22. An ink jet head according to claim 1 including a tubular member
made of air-permeable, ink-impermeable material disposed within the
ink passage and connected to a source of subatmospheric
pressure.
23. An ink jet head according to claim 22 including porous support
means disposed within the tubular member.
24. An ink jet head according to claim 1 including a heater
disposed in heat-transmitting relation to the carbon member.
25. An ink jet head comprising an orifice plate having orifices
through which ink is selectively ejected, a carbon plate formed
with orifice passages to supply ink to the orifices in the orifice
plate and formed on one side with pressure chambers communicating
with the orifice passages and formed with ink supply passages
leading to the pressure chambers, and a piezoelectric plate having
one side affixed to the side of the carbon plate in which the
pressure chambers are formed and provided on its opposite side with
an electrode pattern corresponding to the pattern of pressure
chambers in the carbon plate.
26. An ink jet head according to claim 25 wherein the orifice plate
is affixed to the side of the carbon plate opposite from the
piezoelectric plate and including flowthrough passages formed on
the side of the carbon plate adjacent to the orifice plate leading
from the orifice passages to the ink supply passages.
27. An ink jet head according to claim 25 wherein the carbon plate
has an edge in which the orifice passages are formed and wherein
the orifice plate is affixed to the edge of the carbon plate
containing the orifice passages.
28. An ink jet head according to claim 28 wherein the carbon plate
is about 1020% porous.
29. An ink jet head according to claim 25 including a thin layer of
epoxy adhesive between the piezoelectric plate and the carbon
plate.
30. An ink jet head according to claim 25 including a heating
element formed on the surface of the piezoelectric plate.
31. An ink jet head according to claim 25 including a thin layer of
epoxy adhesive between the orifice plate and the carbon plate.
32. An ink jet head according to claim 25 including a plurality of
sets of orifice passages in the carbon plate and a plurality of
separate ink supply passages for supplying different colored ink to
each set of orifice passages.
33. An ink jet head according to claim 25 including deaeration
means for deaerating ink in the ink jet head.
34. An ink jet head according to claim 33 wherein the deaeration
means includes an air-permeable, ink-impermeable layer adjacent to
an ink flowpath in the ink jet head and a vacuum source
communicating with the air-permeable, ink-impermeable layer.
35. An ink jet head according to claim 34 wherein the carbon plate
is porous and wherein the vacuum source communicates with the
air-permeable, ink-impermeable layer through the porous carbon
plate.
36. An ink jet head according to claim 35 wherein the
air-permeable, ink-impermeable layer is a coating on the surfaces
of passages formed in the carbon plate.
37. An ink jet head according to claim 35 wherein the
air-permeable, ink-impermeable layer is a membrane disposed between
a portion of the carbon plate and an adjacent ink passage in the
ink jet head.
38. An ink jet head according to claim 37 wherein the adjacent ink
passage is formed in a further plate affixed to the carbon
plate.
39. An ink jet head according to claim 34 wherein the orifice plate
is affixed to one side of the carbon plate and including
flowthrough passages formed on the side of the carbon plate
adjacent to the orifice plate leading from the orifice passages to
the ink supply passages to permit circulation of ink through the
passages and through the deaeration means.
40. An ink jet head according to claim 39 including heater means
formed on the piezoelectric plate to heat ink in the passages in
the carbon plate and produce thermal convective circulation thereof
through the passages and the deaeration means.
41. An inkjet head according to claim 25 including a plurality of
piezoelectric plates affixed in adjacent relation to the pressure
chamber side of the carbon plate.
42. An ink jet head according to claim 41 wherein the orifice
passages are formed in an edge of the carbon plate and including
further passages extending between the orifice passages and the
corresponding pressure chambers.
43. An ink jet head according to claim 25 wherein the orifice
passages are formed in an edge of the carbon plate and including
passages extending perpendicular to the orifice passages and the
pressure chambers to connect the pressure chambers to the orifice
passages.
44. An ink jet head according to claim 25 wherein the carbon plate
has a projecting portion containing the orifice passages and
extending away from the side of the plate opposite from the
pressure chambers.
45. An ink jet head according to claim 25 including a coating of a
material having a high modulus of rigidity on the surfaces of the
pressure chambers formed in the carbon plate.
46. A method for making an ink jet head comprising forming a carbon
plate with a plurality of orifice passages, with a plurality of
pressure chambers communicating with the orifice passages,
respectively, and with an ink supply passage leading to the
pressure chambers, affixing a piezoelectric plate to one side of
the carbon plate so that a pattern of actuating electrodes is
provided adjacent to the corresponding pressure chambers, and
affixing an orifice plate having ink jet orifices to the carbon
plate so that the orifices are aligned with the orifice passages in
the carbon plate.
47. A method according to claim 46 including affixing the
piezoelectric plate to the carbon plate with epoxy adhesive.
48. A method according to claim 46 including affixing the orifice
plate to the carbon plate with epoxy adhesive.
49. A method according to claim 46 including forming the plurality
of orifices in the orifice plate by electrical discharge
machining.
50. A method according to claim 46 including affixing a
piezoelectric plate having a conductive coating on the exposed
surface to one side of the carbon plate and forming the actuating
electrodes on the exposed surface of the piezoelectric plate by
photoetching the conductive coating.
51. A method for making an ink jet head comprising affixing a
piezoelectric plate having an exposed conductive surface to a
surface of an adjacent plate having a pattern of pressure chambers
formed therein and photoetching the conductive coating on the
piezoelectric plate to produce an electrode pattern conforming to
the pattern of pressure chambers in the adjacent plate to which the
piezoelectric plate is affixed.
52. A method according to claim 51 wherein the piezoelectric plate
is affixed to the surface of the adjacent plate by spraying one of
the surfaces of the plates with a thin layer of epoxy adhesive.
53. A method according to claim 51 wherein the photoetching step is
carried out by applying a layer of photoresist to the conductive
coating, subjecting the photoresist to a radiation pattern,
developing the photoresist, and etching the conductive layer in the
region exposed by the developed photoresist.
54. A method of forming a plurality of ink jet head components
comprising forming a plurality of patterns of orifice passages,
pressure chambers and ink supply passages at a plurality of
locations in a carbon plate, applying a plurality of piezoelectric
plates having conductive coatings on the exposed surfaces thereof
to one surface of the carbon plate, and photoetching the conductive
coatings on the piezoelectric plates to produce patterns of
electrodes corresponding to the patterns of pressure chambers
formed in the carbon plate.
55. A method according to claim 54 including separating the carbon
plate into a plurality of plate portions, each including one of the
piezoelectric plates.
56. A method for making an ink jet head comprising forming a
pattern of orifice passages, pressure chambers and ink supply
passages in a porous carbon plate and coating the passages in the
plate with an air-permeable, ink-impermeable layer.
57. A method according to claim 56 including affixing a
piezoelectric plate to one side of the carbon plate adjacent to the
pressure chambers formed therein, affixing an orifice plate having
orifices aligned with the orifice passages to a surface of the
carbon plate containing the orifice passages, and providing an
exposed surface of the porous carbon plate for communication with a
vacuum source.
58. A method for poling a piezoelectric plate comprising
compressing a piezoelectric plate between electrode plates with a
slightly conductive rubber sheet interposed between each electrode
plate and the piezoelectric plate.
59. A method for poling a piezoelectric plate comprising applying
one surface of a piezoelectric plate to a ground plate and applying
electric charge from a corona discharge device to the opposite
surface of the piezoelectric plate.
60. An orifice plate for an ink jet head comprising a metal plate
having an array of orifices wherein each of the orifices has a
cylindrical nozzle ink outlet portion at one side of the plate, a
cylindrical ink inlet portion at the opposite side of the plate
having a larger diameter than the nozzle portion, and a tapered
conical portion joining the inlet portion and the nozzle
portion.
61. An orifice plate according to claim 50 wherein the diameter of
the inlet portion is no more than about twice the diameter of the
nozzle portion.
62. An orifice plate according to claim 60 wherein the length of
the inlet portion is greater than the length of the nozzle
portion.
63. A deaeration member for an ink jet head comprising a tubular
member made of air-permeable, ink-impermeable material and adapted
to be inserted into an ink passage in an ink jet head, one end of
the tubular member being sealed and the other end of the tubular
member being connectable to a source of subatmospheric
pressure.
64. A dearation member according to claim 63 wherein the tubular
member is made of polytetrafluoroethylene.
65. A dearation member according to claim 63 including a porous
support member disposed within the tubular member.
66. A dearation member according to claim 63 wherein the tubular
member has a 0.1 mm wall thickness and a 1.5 mm diameter.
67. An ink jet head comprising an orifice plate having an array of
ink jet orifices, a manifold plate affixed to the orifice plate and
having spaced arrays of ink passages extending through the manifold
plate and arrays of passages in the surface of the manifold plate
adjacent to the orifice plate which communicate with the orifices
in the orifice plate.
68. An ink jet head according to claim 67 including a pressure
chamber plate having an array of pressure chambers formed in a
first surface and a corresponding array of internal ink passages
leading from the pressure chambers to a second surface, and
retaining means for retaining the orifice plate, the manifold plate
and the pressure chamber plate in assembled relation with the
passages therein arranged to provide communication between each of
the pressure chambers and a corresponding orifice.
69. An ink jet head according to claim 68 including a collar member
assembled to the pressure chamber plate and the manifold plate and
an ink passage formed in the pressure chamber plate, the manifold
plate and the collar member to supply ink to the pressure chamber
plate from a reservoir connected to the collar member.
70. An ink jet head according to claim 68 including a filter member
disposed between the second surface of the pressure chamber plate
and the manifold plate.
71. An ink jet head according to claim 68 wherein the retaining
means comprises screws.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to ink jet head arrangements and,
more particularly, to a new and improved ink jet head arrangement
having a simple and inexpensive structure.
[0002] Conventional ink jet heads, in which ink received from an
ink reservoir is ejected selectively through a series of orifices,
have been made using thin plates of metal or ceramic material
having appropriate passages which are bonded together in adjacent
relation in an assembly, as described, for example, in the Roy et
al. U.S. Pat. No. 5,087,930 and the Hoisington et al. U.S. Pat. No.
4,835,554. In such arrangements, each chamber or passage in the
flowpath leading from the ink inlet to the orifice, through which
the ink is ultimately ejected, is provided in one or more of the
several plates in the assembly. This requires an array of plates
having different thicknesses, each of which must be separately
machined to precise dimensions to produce the appropriate chambers
and passages, and also requires precise positioning of all of the
chambers and passages in the plates. Moreover, the plates must be
assembled and bonded together and to a piezoelectric plate in
highly precise alignment, and each plate must be flat and free from
burrs that would cause voids between adjacent plates. Furthermore,
because of differences in the coefficients of thermal expansion
between the materials used in the plates, bond stresses are
generated by temperature variations which occur in connection with
the manufacture and use of the ink jet head which must be
overcome.
[0003] In hot melt ink jet printheads, which operate at elevated
temperatures, the printhead materials must be good conductors of
heat so that the printhead will warm up quickly and the temperature
gradients during operation will be small. The stresses created when
parts of different materials expand differently with changes in
temperature is another concern. The prime mover in a printhead is
usually a piezoelectric ceramic (PZT) which has a relatively low
thermal expansion coefficient. For optimum printhead design, the
challenge is to find other materials which are close to this
expansion. If the printhead materials cannot be matched, it is
desirable to have low-modulus materials to reduce the stresses.
[0004] The ink passages in an ink jet printhead are fine features
with tight tolerances. To maintain such tight tolerances, the
manufacture of the printhead requires low machining forces, small
tool deflection and small machining errors, no plastic deformation
and no burrs. Moreover, it may be desirable, particularly in
development, that the manufacture should be carried out using
standard machining methods, such as grinding, milling, drilling and
shaping.
[0005] In addition, the printhead should be made of materials which
are chemically inert and do not change shape over time when loaded
or oxidize or interact with organic chemicals found in hotmelt and
other inks or with pigments or dyes in the inks.
[0006] Heretofore, some plates used in ink jet heads have been
photoetched to provide the appropriate chambers and passages, which
has the advantage that the plates are generally burr-free and can
be made from Kovar, stainless steel and other materials that have
appropriate mechanical and thermal expansion characteristics. The
materials useful for photoetching, however, have drawbacks when
used in connection with ink jet heads from which hot melt ink is
ejected since they generally have low thermal conductivity. In
addition, the photoetching process has the disadvantage of being a
batch process with lotto-lot variations and, moreover, when used in
this manner, produces a relatively large quantity of chemical
waste.
[0007] Furthermore, conventional piezoelectric plates used in ink
jet heads are thin, fragile and susceptible to damage during
processing. Because of the greater likelihood of damage to larger
plates, the maximum size of piezoelectric plates is normally quite
small, for example, less than about 100 mm, which correspondingly
limits the length of an array of orifices through which ink is
ejected as a result of the actuation of the piezoelectric
plate.
SUMMARY OF THE INVENTION
[0008] Accordingly, it is an object of the present invention to
provide an ink jet head which overcomes the disadvantages of the
prior art.
[0009] Another object of the invention is to provide an ink jet
head having a simple structure which is inexpensive to develop, is
convenient to manufacture and is capable of providing high
resolution ink jet printing.
[0010] These and other objects and advantages of the invention are
attained by providing an ink jet head having at least one or more
components formed from a carbon member. A preferred carbon
component is one in which ink pressure chambers and connecting
passages from ink supply lines and to ink jet orifices are formed.
In one embodiment, a carbon component is a plate having pressure
chambers formed on one side and flowthrough passages to permit
continuous ink circulation through the pressure chambers formed on
the other side of the plate with connecting passages leading to an
orifice plate and to an ink supply extending through the carbon
plate. In addition, an orifice plate is affixed to one side of the
carbon plate with the orifices aligned with orifice passages in the
carbon plate and a piezoelectric plate is affixed to the other side
of the carbon plate with actuating electrodes aligned with the
pressure chambers to cause the piezoelectric material to be
deflected so as to apply pressure to the corresponding pressure
chamber and eject a drop of ink through a corresponding orifice in
the orifice plate.
[0011] In another embodiment, a carbon pressure chamber plate is
formed on opposite sides with linear arrays of pressure chambers
having ink inlet and outlet passages at opposite ends. Both sides
of the carbon plate are covered by corresponding piezoelectric
actuation plates and a plurality of such carbon pressure chamber
plates are retained in laterally adjacent relation in a carbon
collar member with the ink outlet passages therein positioned in
alignment with corresponding ink passages extending through a
carbon manifold plate. A manifold plate has one side retained
against the ends of the plurality of pressure chamber plates and
has lateral ink passages formed in the opposite side leading to a
line of orifices in an orifice plate mounted on the opposite
side.
[0012] In accordance with one aspect of the invention, the carbon
pressure chamber plate has an ink deaeration passage through which
ink is supplied to the inlet passages leading to the pressure
chambers and an internally supported, thin-walled tubular member
made of air-permeable, ink-impermeable material connected at one
end to a source of reduced pressure is inserted into the ink
deaeration passage to provide a unitary ink deareating and pressure
chamber carbon plate. This arrangement accomplishes the necessary
deaeration of ink immediately before it is supplied to the pressure
chambers with minimal space requirements and without necessitating
recirculation of ink to an ink reservoir.
[0013] In connection with the assembly of carbon plate components
of the above type in an ink jet head, it has been learned
surprisingly that it is not necessary to cement or otherwise
physically bond together carbon plate components having
communicating a passages or to provide a gasket between them.
Because the engaging surfaces of such carbon plate components can
be made very smooth and flat and carbon plates are sufficiently
rigid to avoid flexing, such plates can be mechanically fastened
together by screws or the like without causing ink to flow between
the components and, if desired, a filter layer may be interposed
between the surfaces of such fastened components.
[0014] Because the carbon body can be machined precisely without
causing burrs using conventional machining techniques and, since
carbon has a low thermal coefficient of expansion, dimensional
variations resulting from thermal expansion during machining are
minimized on the plate. In addition, the carbon expansion
coefficient is especially compatible with the piezoelectric plate
which is affixed to it, thereby reducing or eliminating stresses
between the plates which might otherwise be produced by temperature
variations such as occur when the ink jet head is used with hot
melt ink. Moreover, carbon is chemically inert with respect to
materials in which it comes in contact in an ink jet head. It does
not oxidize nor does it interact with organic chemicals found in
hot-melt and other inks or with pigments or dyes used in inks.
[0015] According to another aspect of the invention, the
piezoelectric plate has actuating electrodes on only one side of
the plate and is prepared by a photoetching technique in which a
piezoelectric plate coated on one side with electrode material is
affixed to the pressure chamber side of the carbon plate with the
electrode material-coated side exposed. The exposed side of the
plate is coated with a photoresist material and is then exposed to
a desired electrode pattern in precise alignment with the pressure
chamber pattern in the carbon plate, after which the photoresist is
developed, the exposed electrode material is etched away, and the
remaining photoresist is removed to produce an electrode pattern
conforming exactly in shape and position to the pattern of pressure
chambers in the carbon plate. In addition, the electrode pattern
thus formed on the piezoelectric plate can include other electrical
elements such as a heater to heat ink in the passages in the carbon
plate.
[0016] In accordance with a further aspect of the invention, the
carbon plate is porous, preferably being about 8090% dense, and the
porosity and a vacuum source communicating with the surface of the
plate can extract dissolved air from ink in the ink passages
separated from the porous carbon material by an air-permeable,
ink-impermeable layer.
[0017] If desired, a page-size carbon plate can be prepared with a
row of separate piezoelectric plates affixed to one side of the
plate. Moreover, the carbon plate may have orifice passages formed
in an edge of the plate rather than in one of the sides of the
plate.
[0018] Since engineering grade carbon is friable, i.e., microscopic
grains are readily broken away from a carbon body, it is easily
shaped without producing burrs. As described in "Graphite Machinery
Made Easy", EDM Today, September/October 1993 pp. 24ff, the
relative softness and lack of ductibility of such carbon allows it
to be cut at high feed rates with little distortion and low tool
wear. These characteristics permit carbon blocks to be readily
formed into components of ink jet heads by conventional or unique
machining techniques.
[0019] In one example, the formation of an array of closely
adjacent pressure chambers for an ink jet head which have a long
aspect ratio and require highly precise and uniform channel
dimensions, would require prohibitively long machine cycle times
using a conventional end mill. In accordance with another aspect of
the invention, however, the process for manufacturing a carbon
plate component of an ink jet head is greatly simplified by shaping
the carbon plate using a series of linear motions against the
surface of the carbon plate with a shaping tool having the desired
profile. For the pressure chambers of a carbon pressure plate, for
example, a tool having a series of closely spaced short teeth is
scraped across the surface in several strokes to produce a series
of precise channels of the required dimensions. To make a row of
small diameter holes of substantial depth in one end of a body, two
carbon plates may be shaped in a similar way with matching arrays
of grooves having a depth equal to half the diameter of the desired
holes and then cemented together with the grooves in alignment.
Using certain tool shapes the holes may have a hexagonal shape
rather than a circular shape.
[0020] Other machining techniques especially useful in shaping
carbon bodies are electric discharge machining, which facilitates
convenient formation of complex shapes, and laser machining, which
can be used effectively for through holes and slots.
[0021] According to still another aspect of the invention, improved
directionality of ink drop ejection from orifices supplied from
non-axial orifice passages is achieved by providing orifice plate
orifices having cylindrical outlet nozzle passages, larger diameter
cylindrical inlet passages, and a conical intermediate section
joining the outlet and inlet passages.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Further objects and advantages of the invention will be
apparent from a reading of the following description in conjunction
with the accompanying drawings, in which:
[0023] FIG. 1 is a schematic perspective sectional view
illustrating a representative embodiment of a simplified ink jet
head arranged in accordance with the invention;
[0024] FIG. 2 is a plan view showing the pressure chamber side of a
typical carbon plate for a multicolor ink jet head showing the
arrangement of the pressure chambers and the related ink passages
formed in the carbon plate;
[0025] FIG. 3 is a view of the carbon plate of FIG. 2 from the same
side shown in FIG. 2, but illustrating the passages formed in the
opposite side of the carbon plate;
[0026] FIG. 4 is a schematic view illustrating a typical
arrangement of electrodes on the exposed surface of a piezoelectric
plate used with the carbon plate shown in FIGS. 2 and 3;
[0027] FIG. 5 is a schematic plan view of a typical large-size
carbon plate having a series of piezoelectric plates mounted on one
surface in accordance with another embodiment of the invention;
[0028] FIG. 6 is a schematic perspective view illustrating another
representative embodiment of the invention;
[0029] FIG. 7 is a schematic perspective sectional view similar to
FIG. 6, illustrating another typical embodiment of the
invention;
[0030] FIG. 8 is a schematic perspective view illustrating a
further representative embodiment of the invention;
[0031] FIG. 9 is a fragmentary perspective view illustrating a
modified form of the invention;
[0032] FIG. 10 is a perspective view showing a typical shaping tool
for shaping arrays of ink passages in a carbon body for use in an
ink jet head;
[0033] FIG. 11 is a fragmentary view in longitudinal section
showing the shape of an orifice in an orifice plate in accordance
with the invention;
[0034] FIG. 12 is a schematic view illustrating one representative
method for poling a piezoelectric plate;
[0035] FIG. 13 is a schematic view illustrating another
representative method for poling a piezoelectric plate;
[0036] FIG. 14 is an exploded perspective view illustrating another
representative embodiment of a simplified ink jet head arrangement
in accordance with the invention;
[0037] FIG. 15 is a side view illustrating a representative carbon
pressure chamber plate of the type used in the arrangement shown in
FIG. 14;
[0038] FIG. 16 is an end view of the representative carbon pressure
chamber plate shown in FIG. 15;
[0039] FIG. 17 is a top view of the carbon collar block used in the
arrangement shown in FIG. 14;
[0040] FIG. 18 is a side view of the collar block shown in FIG.
17;
[0041] FIG. 19 is a plan view showing one side of a representative
carbon manifold plate of the type used in the arrangement shown in
FIG. 14; and
[0042] FIG. 20 is a plan view showing the opposite side of the
manifold plate of FIG. 19;
DESCRIPTION OF PREFERRED EMBODIMENTS
[0043] In the typical embodiment of the invention schematically
shown in FIG. 1, an ink jet head 10 includes a reservoir 11 on one
side containing ink which is to be selectively ejected in the form
of drops through an array of orifices 12 formed in an orifice plate
13 mounted on the opposite side of the head. Ink from the reservoir
11 is supplied through a passage 14 to a deaerator 15 in which an
ink path 16 extends between air-permeable, ink-impermeable
membranes 17, each of which is backed by a vacuum plenum 18
connected through ports a to a remote vacuum source (not shown) to
extract dissolved air from the ink. Deaerated ink from the passage
16 is conveyed through a passage 19 to a pressure chamber 20 from
which it is ejected on demand through an orifice passageway 21 and
a corresponding orifice 12 in the orifice plate 13 in response to
selective actuation of the adjacent portion 22 of a piezoelectric
plate 23.
[0044] The general arrangement of the ink jet head 10 and the
deaerator 15 is of the type described, for example, in the Hine et
al. U.S. Pat. No. 4,937,598, the disclosure of which is
incorporated herein by reference. The ink in the reservoir 11 may,
if desired, be hot melt ink which is solid at room temperature and
liquid at elevated temperatures, in which case heaters (not shown)
are mounted at appropriate locations in the ink jet head 10.
[0045] In order to permit the ink supplied to the orifices to be
deaerated continuously even though ink is not being ejected through
the orifices 12, the head includes a flowthrough passage 24
extending from each orifice passage 21 to a return passage 25
leading back to the deaeration path 16 in the deaerator 15, and a
continuous slow circulation of ink through the duct 19, the chamber
20, the orifice passage 21, the flowthrough passage 24 and the duct
25 back to the deaerator passage 16 is maintained by thermal
convection, as described, for example, in the Hine et al. U.S. Pat.
No. 4,940,995 issued Jul. 10, 1990, the disclosure of which is
incorporated herein by reference. For this purpose, a heater (not
shown in FIG. 1) is arranged to heat the ink near the lower end of
the flowpaths consisting of the passages 19, 20, 21, 24 and 25
above its normal temperature to cause a convective flow of the ink
through those passages, thereby conveying the ink back to the
deaerator 16.
[0046] In accordance with the invention, the passages 19, 20, 21,
24 and 25 are formed in a plate 26 made of engineering carbon
graphite, which is preferably about 8090% dense, providing a
slightly porous plate structure. The carbon plate 26 is machined by
micromachining techniques from opposite sides to produce the
chambers and passages required for the ink jet head. The carbon
plate can be machined by milling, drilling, broaching, grinding and
the like, using conventional tools providing high material removal
rates with minimum tool wear, to produce openings with much closer
tolerances than the conventional metal plates of the type
described, for example, in the Hoisington et al. U.S. Pat. No.
4,835,554. Because the carbon material is friable, no burrs are
produced during machining. Moreover, the coefficient of thermal
expansion of the carbon graphite body is substantially the same as
that of the ceramic piezoelectric material of which the
piezoelectric plate 23 is made so as to reduce or substantially
eliminate thermal stresses which occur between those components of
the head as a result of variations in temperature.
[0047] The preferred carbon material for use in forming components
on ink jet heads is polycrystalline graphite, which is a mixture of
small crystals of graphite sintered with amorphous carbon (lamp
black). This produces an amorphous matrix of small (0.0255 .mu.)
grains and smaller (0.0050.2 .mu.) pores. This material, which is
different from powdered graphite and carbon fiber materials, offers
many benefits, including good thermal conductivity, coefficient of
thermal expansion close to ceramic piezoelectric materials, good
machinability, dimensional stability and chemical inertness.
[0048] The thermal properties of polycrystalline graphite (Grade
DFPL available from POCO Graphite, Inc., Decatur, Tex.) and other
materials which might be considered for printheads are compared
with those of lead zinc titanate (PZT) ceramic piezoelectric
material in Table 1 below:
1TABLE 1 Thermal Conductivity Expansion Modulus Material (W/CmK)
(.mu./m/deg C.) (.times.10.sup.5 kg/cm_) PZT .015 2 to 4 7
Thermoplastic 0.0022 56 0.15 (Ultem) Aluminum (6000) 1.7 23.4 7
Carbon (DFP-1) .75 8.4 1.1
[0049] The Ultem (as well as other thermoplastics) has both poor
conductivity and a very high thermal expansion coefficient. The
conductivity of aluminum is attractive, but its high thermal
expansion and modulus are problems. Polycrystalline carbon offers a
good combination of all three properties.
[0050] A potentially prohibitive aspect of the use of carbon
members for ink jet components is the forming of closely spaced
arrays of pressure chambers and other multitudinous, long aspect
ratio, channels with precise dimensions. Using an end mill for
these features could be expected to result in excessively long
machine cycle times. To overcome this problem, a desired array of
adjacent channel profiles is shaped in the surface of a carbon body
by a specially formed tool 95, shown in FIG. 10, in a series of
repeated linear motions or "scrapes." In the tool 95 for example,
an array of 64 short uniformly spaced teeth 96 may be provided at
one end of the tool to cut 64 parallel pressure chambers in the
surface of a carbon plate. If the tool cuts at 0.025 mm per scrape,
a depth of 0.15 mm can be achieved in 6 scrapes, which requires
only a few seconds of machine time. The tool 95 makes an array of
channels equal to the width of the tool, and can make a wider array
by taking repeat adjacent passes. Tool irregularities are averaged
out by taking finish cuts in the reverse direction or at a
one-tooth offset. Reversing the tool also allows the formation of
steeper channel ends when this is required. This technique can be
used to make pumping chambers, manifold passages, flowthrough
passages, and the like. Finally, channels of variable or tapered
depth can be made as well, by raising or lowering the tool as a cut
is being made.
[0051] For an array of closely spaced deep, small diameter holes in
a carbon body, where the depth is more than 3 times the drill
diameter, drilling can become difficult and expensive. To provide
an array of closely spaced holes having a diameter of, for example,
0.28 mm through a carbon plate 1.75 mm thick would require a great
deal of time and a number of expensive drills. To form such an
array in a simple manner, matching arrays of channels (which may be
semi-hexagonal in shape) 0.14 mm deep are formed in two matching
blocks of carbon which are then bonded together with adhesive to
form a single block containing an array of parallel, long 0.28 mm
diameter holes. This block is then sliced perpendicularly to the
axes of the holes and ground flat to form the array bodies. The
adhesive joint down the middle of the array body has been found to
be very strong.
[0052] Polycrystalline carbon is easily bonded by a variety of
adhesives. Three systems are particularly compatible with carbon in
hot melt ink jet head applications. The first is a simple dispensed
epoxy which works well for coarse scale joints. The second is a
thermoplastic sheet adhesive. Using this technique, a thin teflon
(TFE) sheet compressed at elevated temperature and pressure
provides a tenacious bond between flat surfaces of polycrystalline
carbon. Similarly, acrylic sheet adhesives should perform well at
lower temperature. In the third technique, a dilute sprayed B-stage
epoxy system is applied to the surfaces to be bonded. This has been
shown to be adaptable to the complex geometries of ink jet
printheads, yet high in strength at elevated temperatures.
[0053] There is some challenge in bonding a porous material like
carbon with a spray application technique. Since excess adhesive
will clog small passages, and thin layers may be drawn by capillary
forces into the carbon body pores, careful control of process
variables is required. In particular, the carbon pore structure
must be uniform, the spray-deposited layer thickness must be small
compared to the particle/pore size, and the heat cure process must
be tuned to the adhesive rheology.
[0054] FIG. 2 illustrates a representative arrangement of pressure
chambers 20 and orifice passages 21 as viewed from the
piezoelectric plate side of the typical carbon monolithic plate 26
of FIG. 1, while FIG. 3 illustrates the other ends of the orifice
passages 21 and the flowthrough passages 24 which are formed in the
opposite side of the monolithic array 26. FIG. 3, while showing the
passages on the side of the monolithic array 26 which face the
orifice plate 13, is illustrated with the passages seen as they
would be viewed in the same direction as FIG. 2.
[0055] FIGS. 2 and 3 show supply passages for supplying four
different color inks, e.g., black, yellow, magenta and cyan, to
four different groups 27, 28, 29 and 30 of the orifice passages 21.
Since black ink is normally used to a much greater extent than the
colored inks, half of the orifice passages 21 are arranged to
supply black ink, and one-third of each of the remaining passages
are arranged to supply each of the colored inks.
[0056] As illustrated in FIG. 2, the pressure chambers 20 of the
array are alternately disposed on opposite sides of the line of
orifice passages 21 and are supplied from grooves formed in the
pressure chamber side of the graphite plate 26, for example, from
grooves 32 and 33 supplying black ink, grooves 34 and 35 supplying
magenta ink, grooves 36 and 37 supplying yellow ink, and grooves 38
and 39 supplying cyan ink. The appropriate color ink is supplied to
these grooves through corresponding apertures 40 and 41, 42 and 43,
44 and 45 and 46 and 47, which extend through the carbon plate 26
to corresponding sets of grooves 50 and 51, 52 and 53, 54 and 55
and 56 and 57, formed in the opposite side of the plate. Those
grooves, shown in solid lines in FIG. 3 and in dotted lines in FIG.
2, communicate with further apertures 60 corresponding to the
passages 19 and 25 of FIG. 1, which extend through the plate to
convey ink from the deaerator ink path 16 of FIG. 1 to the pressure
chamber supply grooves 3239. As shown in FIG. 3, the flowthrough
passages 24 convey ink between the orifice passages 21 and the
groove patterns 5057 on the opposite side of the carbon plate to
complete the continuous path for circulation of ink through the
deaerator 15.
[0057] In addition, the carbon plate 26 is especially advantageous
for ink jet heads used with hot melt ink. Because of its high
thermal conductivity, the carbon plate provides excellent heat
conduction from heaters mounted at relatively remote locations in
the head to all of the ink passages in the head. This assures that
the hot melt ink at each of the orifices 12 is at the same
temperature and therefore has the same viscosity, thereby providing
good uniformity of operation throughout the length of the array of
orifices.
[0058] A typical carbon plate 26 may be about 2 mm thick and have
orifice passages 21 about 0.2 mm in diameter, pressure chambers
about 9 mm long, 0.5 mm wide and 0.2 mm deep, supply grooves about
1.0 to 1.5 mm wide and 0.5 mm deep, flowthrough passages about 4 mm
long, 0.1 mm wide and 0.05 mm deep, and apertures 60 about 1.5 mm
in diameter. With this arrangement, a 96 aperture linear array of
the type shown in the drawings can be provided in a carbon plate 26
having dimensions of about 4 cm by 7 cm with the orifice passages
21 spaced by about 0.5 mm. When oriented at an appropriate angle
with respect to the scanning direction, an ink jet head using an
array of this type can produce a resolution of about 300 dots per
inch (120 dots per cm) in the subscanning direction and, when
actuated at a rate of about 14 Khz at a scanning rate of 1 m/sec to
produce 100 picoliter drops, can produce the same resolution in the
scanning direction.
[0059] In certain high-frequency ink jet applications, the rigidity
of the walls of the pressure chambers 20 formed in the carbon plate
may be less than desired, requiring a higher operating voltage for
the piezoelectric actuating plate. To alleviate this, the surfaces
of the pressure chambers 20 formed in the carbon plate may be
coated with a thin layer, such as 0.01 to 0.1 mm thick, of a very
hard (i.e., high modulus of rigidity) material such as a carbide or
nitride, e.g., silicon carbide or nitride, boron carbide or
nitride, tungsten carbide or nitride, tantalum carbide or nitride,
or the like. Preferably, the coating is applied by chemical vapor
deposition.
[0060] In order to actuate the piezoelectric plate 23 so as to
selectively eject ink from the pressure chambers 20 through the
orifice passages 21 and through corresponding orifices 12 in the
orifice plate 13, the piezoelectric plate 23, which is mounted on
the pressure chamber side of the carbon plate, has no electrodes on
the carbon plate side and is patterned with an electrode array of
the type shown in FIG. 4 on the exposed side. In the array shown in
FIG. 4, a common electrode 65 extends along the portion covering
the orifice passage array in the carbon plate and also extends
laterally into regions 66 over the carbon plate surface portions
between the pressure chambers.
[0061] Interlaced between the lateral extensions 66 is a spaced
array of individual electrodes 67 which are positioned directly
over the pressure chambers in the carbon plate so that, when
selectively actuated by application of appropriate potential to a
corresponding terminal 68, the piezoelectric plate 23 is
mechanically distorted in the shear mode in the direction toward
the adjacent pressure chamber 20 so as to cause ejection of an ink
drop from the orifice with which that pressure chamber
communicates. Shear-mode operation of a piezoelectric plate is
described, for example, in the Fischbeck et al. U.S. Pat. No.
4,584,590, the disclosure of which is incorporated herein by
reference. Such shear-mode operation does not require any electrode
on the opposite side of the piezoelectric plate but, if desired,
the carbon plate 26, being conductive, can be used to provide an
electrode on the opposite side of the plate.
[0062] The electrode pattern shown in FIG. 4 also includes a heater
conductor 70 having a thermistor temperature control switch 71
extending between two terminals 72 and 73 and arranged to heat the
ink in the passages in the lower portion of the carbon plate 26 so
as to cause circulation of the ink in the manner described above by
thermal convection. Because the carbon material in the plate 26 has
a high thermal conductivity, the plate acts as a thermal conductor
between the heater and the adjacent ink passages in the plate.
[0063] In order to form an electrode pattern of the type shown in
FIG. 4 on the piezoelectric plate 23, the plate, which is initially
provided with a continuous conductive coating on the exposed side,
is permanently affixed by an epoxy adhesive to the pressure chamber
side of the carbon plate 26. Since the carbon plate is slightly
porous, an epoxy adhesive can be used to mount not only the
piezoelectric plate 23, but also the orifice plate 13, to the
opposite surfaces of the carbon body. For this purpose, one of the
surfaces of the plates to be joined is preferably spray-coated with
a layer of B-stage epoxy adhesive about 2 microns thick before the
piezoelectric plate 23 or the orifice plate is applied to it. Such
a thin layer of epoxy adhesive provides excellent seals between the
plates, including the very narrow portions between the orifice
passages, but does not flow into the passages or apertures in such
a way as to interfere with the operation of the head.
[0064] In order to ground the surface of a the piezoelectric plate
which is bonded to the carbon body, the epoxy adhesive may be doped
with conductive particles. Alternatively, the clamping force
applied during bonding of the piezoelectric plate to the carbon
body is increased until the epoxy adhesive is driven into the
carbon body to provide a large number of point contacts between the
plate and the carbon body.
[0065] The use of single sided piezoelectric plates requires
special techniques for poling the plates. According to one
technique, schematically shown in FIG. 11, a piezoelectric plate
140 is compressed between two electrodes 141 and 142 separated from
the plate 140 by two slightly conductive rubber sheets 143 and 144
to provide intimate electrical contact throughout the surfaces of
the plate while limiting the current available for arcing if a
breakdown occurs. When this procedure is carried out in two steps
to minimize piezo stresses, high yield poling of unmetalized
piezoelectric plates is achieved.
[0066] The other poling technique, shown in FIG. 12, uses a corona
discharge to set up a poling field across the piezoelectric plate.
A piezoelectric plate 150 is laid on a flat ground plate 151, and a
corona discharge device 152 rains charges 153 down onto the
surface. When the applied charge is sufficient to create an
occasional breakdown through the plate, which is nondestructive
because of the high surface resistance of the piezoelectric
material, the plate is poled. This process is preferably carried
out at an elevated temperature, such as 100-150.degree. C., to
ameliorate poling stresses.
[0067] The orifices 12 in the orifice plate 13 of FIG. 1, which may
be a stainless steel plate about 0.05 mm thick, are preferably
about 0.05 mm in diameter and are formed by electrical discharge
machining. By selecting the appropriate size wire and controlling
the current/voltage profile, the size and shape of the orifice can
be controlled accurately. Bonding of the orifice plate to the
surface of the carbon body is accomplished in the same way as the
bonding of the piezoelectric plate.
[0068] With conventional bell-mouthed shaped orifices in an orifice
plate of the type shown, for example, in the Hoisington et al. U.S.
Pat. No. 5,265,315 in which the orifice diameter decreases at a
continuously decreasing rate from a large diameter on the side of
the orifice plate facing the ink jet head to a smaller diameter
about one-third that of the large diameter on the side of the
orifice plate through which the ink drop was ejected, the direction
of ink drop ejection is very sensitive to asymmetries in the ink
path near the periphery of the entrance to the bell-mouthed
orifice. Moreover, it is not possible to space such bell-mouthed
orifices as closely as desired for high resolution printing.
[0069] To overcome this problem, electrical discharge machining is
used to form orifices 97 having the shape shown in FIG. 13 with a
cylindrical inlet section 98, a smaller diameter cylindrical nozzle
section 99 providing the outlet from the orifice plate and a
tapered section 100 having a conical surface joining the inlet
section and the nozzle section. It has been found that with an
orifice design of this type, the non-axial velocity component of an
ejected drop, i.e. the extent of deviation from the axial arrow 101
resulting from asymmetry of the passage leading to the orifice is
reduced by more than 50%.
[0070] In a typical orifice plate 13 having a thickness of 0.05 mm,
a nozzle 99 having a diameter of 0.054 mm and a length of 0.01 mm,
a tapered section 100 having a cone angle of 30.degree. and a
length of 0.01 mm and an inlet section 98 having a diameter of 0.11
mm and a length of 0.03 mm, a substantial improvement in axial
projection of drops supplied from an asymmetric ink path leading to
the orifice was obtained. For an orifice plate 13 having a
thickness of 0.075 mm and having the same nozzle and tapered
section dimensions described above, and having an inlet section
0.055 mm long, a similar improvement in the direction of projection
of drops was obtained at a slightly increased pressure drop.
Preferably, the diameter of the inlet portion 98 of the orifice is
no more than twice the diameter of the nozzle portion 99 and the
length of the inlet portion 98 is greater than that of the nozzle
portion. Such orifice shapes having successive conical and tapered
cylindrical sections can be obtained by appropriate conventional
electrical discharge machining techniques.
[0071] In accordance with one aspect of the invention, after the
piezoelectric plate 23 has been affixed to the carbon plate, a
layer of photoresist material is coated on the exposed surface and,
using the precisely known positions of the pressure chambers from a
reference edge in the carbon body, the photoresist is exposed to
produce a pattern which corresponds exactly with the locations of
the pressure chambers, and the unexposed resist is removed in the
usual manner. Thereafter, the conductive layer is etched away from
the exposed surface of the piezoelectric plate and the remaining
resist is then removed to provide the final electrode pattern.
[0072] In this way, the piezoelectric plate 23, which is preferably
only about 0.1 to 0.25 mm thick and is quite fragile, is protected
from damage during the formation of the electrode pattern and other
head-manufacturing steps. Consequently, substantially large
piezoelectric plates, for example, 50 mm by 100 mm or more, can be
used without substantial risk of damage during processing.
Moreover, large-scale production is facilitated since a large-size
carbon plate can be machined with multiple identical or similar
patterns, and a corresponding number of piezoelectric plates can be
bonded to the pattern locations on the large sheet and
simultaneously exposed and etched to form electrode patterns
corresponding precisely to the structures of the adjacent portions
of the carbon plate, after which the large-size plate is separated
into individual plates.
[0073] Furthermore, instead of separating a large-size carbon plate
into smaller plates, a single carbon plate 20 cm wide, or even 150
cm wide, if appropriate, may be made to provide a page-width ink
jet head by mounting a row of piezoelectric plates to one surface
and simultaneously processing the piezoelectric plates in the
manner described above. A typical page-width inkjet head is shown
in FIG. 5, in which a carbon plate 26 has a row of adjacent
piezoelectric plates 23 affixed to one side. The ink jet head of
FIG. 5 has internal passages arranged to supply ink to an orifice
plate 74 mounted on one edge, as described hereinafter with respect
to FIG. 8. Alternatively, if desired, the large-size plate 26 of
FIG. 5 may have internal passages of the type described above with
respect to FIG. 1 leading to an orifice plate (not shown in FIG. 5)
mounted on the opposite side of the carbon plate.
[0074] As an alternative to the deaerator arrangement 15 shown in
FIG. 1, the use of a carbon plate 26 which is slightly porous
permits the plate to act as a conduit between the vacuum plenum and
the ink in the passages within the carbon plate in the manner shown
in the alternative embodiment of FIG. 6 so that dissolved air can
be extracted. For this purpose, the surfaces of the plate passages
are coated with a layer 75 of an air-permeable, ink-impermeable
epoxy resin and one or more openings 76 are provided in the
piezoelectric plate 23 to expose the adjacent surface of the carbon
plate 26 to a vacuum source 77 which replaces the deaerator 15, the
other exposed surfaces of the carbon plate 26 being sealed to
prevent entry of air into the porous plate. The vacuum source 77
may be connected to a remote vacuum supply through the port 18a, or
it may be a replaceable vacuum reservoir of the type described in
the copending Hine application Ser. No. 08/143,165, filed Oct. 26,
1993, the disclosure of which is incorporated herein by
reference.
[0075] In another modified deaerator arrangement shown in FIG. 7,
ink passages 80 extending between the passages 24 and 25 are formed
in a plate 81 which is mounted on the front surface of the carbon
plate 26 and an air-permeable, ink-impermeable membrane 82, similar
to the membranes 17 of FIG. 1, is positioned between the carbon
plate 26 and the plate 81. In this case, the coating 75 applied to
the various passages within the carbon plate 26 is impermeable to
air and only the portion of the plate 26 adjacent to the membrane
82 is used to extract air from the ink in the passages 80. If
desired, a filter may also be incorporated in the plate 81 in the
path of the ink between the passages 24 and 25. Otherwise, the
arrangement of FIG. 7 is the same as that shown in FIG. 6.
[0076] Because the high thermal conductivity of the carbon plate 26
assures heat conduction from relatively remote heaters through the
carbon plate to hot melt ink adjacent to an orifice plate, a hot
melt ink jet head according to the invention may be arranged so
that the ink is ejected from an orifice plate mounted on an edge of
a carbon plate rather than from an orifice plate mounted on one
side of the carbon plate. Moreover, even if the ink used in the ink
jet head is not hot melt ink, the easy machinability of the carbon
plate provides a distinct advantage in an arrangement of this type
in contrast to a conventional laminated plate arrangement, in which
edges of the plates adjacent to the orifice plate cannot be
perfectly aligned, leading to irregularities in the mounting of the
orifice plate.
[0077] This arrangement is shown in FIG. 8, in which a carbon plate
85 has pressure chambers 86 formed in one side and a piezoelectric
plate 87 affixed to that side of the plate, and a bottom cover
plate 88 affixed to the opposite side of the plate. A row of
orifice passages 89, which are drilled into one edge 90 of the
carbon plate 85, communicate with the pressure chambers 86 through
perpendicular passages 91 extending through the plate 85. With a
carbon plate 85 of this type, the end surface 90 can be ground
perfectly flat and the plate can then be drilled to form the
passages 89 and 91 to connect with the pressure chambers 88, after
which an orifice plate 92 is affixed to the edge 90 by epoxy
adhesive in the manner described above.
[0078] An ink jet head made in this way is especially advantageous,
not only because it requires only a very narrow strip for the
orifice plate 92, but also because it permits the bulk of the
printhead to be spaced from the paper path and also permits
stacking of multiple printheads.
[0079] If desired, the ink jet head of FIG. 1 can be modified to
provide similar advantages by forming the carbon plate 26 with a
projecting portion 94 through which orifice passages 93 extend to
an orifice plate 92, as illustrated in FIG. 9.
[0080] In a further embodiment of the invention shown in FIGS.
1420, an ink jet head is assembled from a plurality of carbon
components. In this embodiment, as illustrated in the exploded view
of FIG. 14, two carbon pressure plate assemblies 102, described in
greater detail hereinafter, are assembled in a carbon collar 103 so
that their end surfaces, which contain ink outlet passages, are
aligned with corresponding openings in a manifold plate 104 to
which the pressure chamber plate assemblies 102 are affixed by
screws 105 extending through the manifold plate and into an
adjacent pressure chamber plate 106. An orifice plate 107 has a
linear array of closely spaced orifices 108 which are aligned with
the ends of arrays of passages 109 (FIG. 20) in the manifold plate
104 so as to eject ink in response to selective actuation of the
pressure plate assemblies.
[0081] Interposed between the ends of the pressure plate assemblies
102 and the manifold plate 104 is a filter layer 110 having pores
or openings slightly smaller than the orifices 108 in the orifice
plate 107 so as to prevent potentially orifice-clogging solid
material from reaching the orifices 108 but large enough to permit
particles of solid material smaller than the size of the orifices
to pass through the filter layer. This type of filter is described,
for example, in the copending Moynihan et al. application for
"Filter Arrangement For Ink Jet Head" Ser. No. 08/231,102, filed
Apr. 22, 1994.
[0082] An ink reservoir 111, mounted against one side of the collar
103 has an ink supply opening 112 which supplies ink to the collar
103. As best seen in FIG. 16, a corresponding opening 113 in the
collar is aligned with the opening 112 to receive ink from the
reservoir 111. In addition, if hot melt ink is to be used in the
ink jet head, a cartridge heater 114 is mounted in a groove 115
formed in the side of the reservoir and in a corresponding groove
116 (FIG. 18) in the side of the collar 103 and is controlled so as
to maintain the ink within the assembled ink jet head at a desired
temperature during operation of the system.
[0083] Each pressure chamber assembly 102 includes a pressure plate
106 having arrays 117 of closely spaced pressure chambers formed on
opposite sides of the plate 106 and each of those arrays is covered
by a piezoelectric plate 118 of the type described previously with
respect to FIG. 4, having an array of electrodes 119 arranged with
respect to the array of pressure chambers 117 to change the volume
of the corresponding pressure chamber in response to appropriate
electrical signals.
[0084] The pressure chamber plate 106, which is illustrated in
greater detail in FIGS. 15 and 16, has a longitudinally extending
opening 120 which, in the illustrated embodiment receives ink
through an internal passage 123 terminating at an end surface 124
which faces the manifold plate 104 as seen in FIG. 14. As shown in
FIG. 19, the surface of the manifold plate 104 facing the pressure
chamber plate, has an opening 125 which receives ink from the
collar passage 113 and supplies it to a groove 126 (FIG. 20) on the
opposite side of the manifold plate, from which ink passes through
two further openings 127 in the manifold plate to the passages 123
in the pressure plates 106 so that the ink is distributed through
the longitudinal opening 120 to all of the pressure chambers in
both of the arrays 117 in each plate.
[0085] In order to extract dissolved air from the ink as it is
being supplied to the arrays 117 of pressure chambers, a deareator
128 consisting of a tubular member 129 made of air-permeable,
ink-impermeable material, such as extruded polytetrafluoraethylene
having a 0.1 mm wall thickness and a 1.5 mm internal diameter,
extends through an opening 130 in the edge of each pressure chamber
plate 106 and into the longitudinal opening 120. A plug 131 closes
the inner end of the tube and the end projecting out of the opening
130 in the plate 106 is connected to a vacuum source 132 supplying
sufficient negative pressure, such as 0.7 atmosphere, to reduce the
dissolved air content of the ink being supplied to the pressure
chambers below the level at which air bubbles can form in the
pressure chamber during operation of the ink jet system. In order
to prevent the tube 129 from collapsing in response to application
of negative pressure, a porous support, such as a rod of porous
carbon or a helical wire having a diameter substantially equal to
the internal diameter of the tube, is inserted into the tube.
[0086] As shown in FIG. 16, the end surface 124 of the carbon plate
106 has two arrays of ink passages 133 which extend perpendicularly
to the end surface 123 and each of those passages communicates
internally with the adjacent end of a corresponding pressure
chamber in the arrays 117. Consequently, upon actuation of one of
the pressure chamber, ink is forced out of the plate 106 through a
corresponding one of the passages 133.
[0087] After passing through the filter layer 110, ink from each of
the passages 133 is supplied through a corresponding passage 134 in
an adjacent surface of the manifold plate 104 shown in FIG. 17 and,
as shown in FIG. 20, the arrays of passages 109 in the opposite
surface of the manifold plate extend horizontally along the surface
of that plate to convey the ink supplied through the passages 134
in a lateral direction toward the center of the manifold plate.
Those passages terminate in a central line 135 extending
longitudinally along the manifold plate so as to be in line with
the line of ink jet orifices 108 in the orifice plate 107.
[0088] Although carbon is the preferred material for the manifold
plate 104, especially for ink jet heads used with hot melt ink,
other materials which can be formed with a sufficiently flat
surface and which have a thermal expansion coefficient compatible
with adjacent components may also be used. For example, steel and
ceramics such as alumina and glass, in which appropriate passages
can be formed by photoetching, may also be used to form the
manifold plate.
[0089] In a typical embodiment of the type shown in FIGS. 1420,
each pressure chamber plate 106 is approximately 75 mm long, 22 mm
wide and 2.5 mm thick and each pressure chamber array 117 contains
64 pressure chamber approximately 9 mm long, 1 mm wide and 0.15 mm
deep and the manifold plate 104 is approximately 1.4 mm thick.
[0090] Heretofore it was believed that the total length of the
descender, which is the ink path leading from the end of the
pressure chamber to the orifice in the orifice plate, should be as
short as possible, i.e. no more than about 1 mm. Although it is
clear that each descender should have a constant cross-section
similar to that of the pumping chamber so that its acoustic
properties do not result in undesirable reflections, and that it
should be short enough that viscus flow losses are not excessive
and that it should also be fluidically stiff so that pressure
energy losses from the surrounding structure are not excessive, it
has now been determined that, in ink jet heads made of carbon
components, the descender need not be so limited in length and can
consist of a plurality of passages such as those in the manifold
plate and within the pressure chamber plate which total as much as
7 mm in length without loss of performance. This permits greater
flexibility in the design of ink jet heads in several respects. For
example, the piezoelectric plate, which is quite fragile, can be
spaced a significantly greater distance away from the substrate
being printed by the head and the body of the ink jet array may be
made thick enough to be mechanically robust and to provide good
thermal uniformity. Moreover, laterally spaced pressure chambers
such as those in the arrays 117 may be connected through laterally
spaced passages 133 to supply ink to a single line of orifices 108
by using an arrangement of laterally directed passages 109 such as
that incorporated into the manifold plate 104.
[0091] With the simplified ink jet head according to the invention,
the problems caused by burrs and dimensional variations resulting
from heat produced in machining, by differences in temperature
coefficient of expansion of the materials used in the ink jet head,
and by the necessity for assembling a number of previously formed
plates in precise relation, and the problems of bond stresses
during temperature cycling are effectively eliminated in a
convenient and inexpensive manner. Moreover, the number of steps
required for the formation of the electrode pattern on the
piezoelectric plate and application of the plate to the ink jet
head is substantially reduced and variations in electrode
positioning with respect to the pressure chamber positions are
eliminated.
[0092] Although the invention has been described herein with
reference to specific embodiments, many modifications and
variations therein will readily occur to those skilled in the art.
Accordingly, all such variations and modifications are included
within the intended scope of the invention.
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