Information
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Patent Grant
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6394589
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Patent Number
6,394,589
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Date Filed
Wednesday, December 1, 199924 years ago
-
Date Issued
Tuesday, May 28, 200222 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
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International Classifications
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Abstract
An ink jet printhead composed of: a reservoir storing a quantity of printing ink, an ink manifold defining an ink supply volume in communication with the reservoir for holding a supply of ink received from the reservoir and a plurality of individually controlled ink jet delivery channels, each of the channels having an ink drop ejection transducer and an orifice to eject successive ink drops on demand in response to pressure pulses produced by the transducer, and each of the channels being in communication with the ink supply volume for receiving ink from the ink supply volume. The manifold is constructed to give the ink supply volume a large acoustic compliance to minimize propagation of pressure disturbances in the ink supply volume and acoustic signal crosstalk between the channels.
Description
BACKGROUND OF THE INVENTION
The present invention relates to inkjet printheads in which ink in the liquid state is delivered to a plurality of nozzles and ink drops are ejected on demand from each nozzle in response to actuation of an associated ejection transducer.
Ink jet printers are widely used for printing documents in both the office and the home, as well as for industrial printing applications on a variety of surfaces. Such printers include an ink jet printhead having a plurality of ink ejection chambers, or channels, each containing one or more ink jet ejection orifices, or nozzles. The ejection of ink from each nozzle is controlled by a pattern of pressure pulses.
Each nozzle constitutes the outlet end of an ink delivery channel. The inlet ends of all of the channels communicate with an ink supply volume formed within an ink manifold. As ink is withdrawn from the manifold, it is replaced by fresh ink from a reservoir that is in communication with the manifold. The printhead is designed so that the ink supply volume is always filled with ink.
The pressure pulses for ejecting ink from each nozzle are produced by an associated ink jet ejection transducer. The transducer, in turn, is responsive to electrical drive pulses produced by a print engine.
When a pressure pulse is generated within a channel, one part of the resulting pressure disturbance acts to eject an ink drop from the associated nozzle while another part of the resulting pressure disturbance is propagated in a backward direction through the channel and into the ink supply volume within the manifold. Pressure disturbances which enter the ink supply volume are transmitted acoustically throughout the ink supply volume.
As a result, a time varying manifold pressure, known as crosstalk, will influence the pressure in all of the other channels. This will affect the flow dynamics within all of the channels. In particular, crosstalk can cause variations to occur in the velocity, shape and/or size of the ink drops ejected from the nozzles of the other channels and such variations will have an adverse effect on the quality of the resulting printed material.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to minimize the transmission of pressure disturbances, or crosstalk, between the channels of a printhead of the type described above.
The invention is embodied in an ink jet printhead comprising: a reservoir storing a quantity of printing ink; at least one ink manifold defining an ink supply volume in communication with the reservoir for holding a supply of ink received from the reservoir; and a plurality of individually controlled ink jet delivery channels, each of the channels having an ink drop ejection transducer and an orifice to eject successive ink drops on demand in response to pressure pulses produced by the transducer, and each of the channels being in communication with the ink supply volume for receiving ink from the ink supply volume, wherein the manifold is constructed to give the ink supply volume a large acoustic compliance to minimize propagation of pressure disturbances in the ink supply volume and acoustic signal crosstalk between the channels.
The invention is applicable to any existing type of printhead, including those of the bubble jet type.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
FIG. 1
is a cross-sectional view of a printhead according to a preferred embodiment of the present invention.
FIG. 2
is a perspective view of the embodiment shown in FIG.
1
.
FIG. 3
is a detail plan view of a component of a second embodiment of the invention.
FIG. 4
is a cross-sectional view along line IV—IV of FIG.
3
.
FIG. 5
is a simplified pictorial view of a third embodiment of the invention.
FIG. 6
is a perspective view showing the basic components of a printhead to which the invention may be applied.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1
is a cross-sectional view of an inkjet printhead which utilizes hot-melt inks with properties (surface tension, viscosity, density etc.) in a certain range. However, the invention can be applied to printheads using any ink having properties in the design range and being chemically compatible. The basic components of the printhead include, as will be described in greater detail below, a reservoir
12
holding a supply of ink, a manifold which receives ink from the reservoir and which remains filled with ink until the reservoir supply has been exhausted and a plurality of individually controlled ink jet delivery channels, each ending in a nozzle from which successive ink drops can be ejected.
Referring more specifically to
FIG. 1
, reservoir
12
is coupled to the interior of a manifold via an ink supply conduit
14
.
The manifold provides an ink supply space, or volume,
16
delimited, or enclosed, by a chamber plate
18
, wall members
20
,
22
,
24
and
26
and a thin plate
30
. Plate
30
is supported by further wall member
34
.
A filter
38
extends across space
16
, and conduit
14
is in communication with the portion of space
16
that is located between filter
38
and plate
30
.
The printhead further includes a plurality of delivery channels each of which has an inlet end communicating with space
16
. The plurality of channels are arranged in a stack perpendicular to the plane of
FIG. 1
, the elements of one of these channels being visible in FIG.
1
. Each channel includes an inlet path
40
and an outlet chamber
42
. Outlet chamber
42
is bounded by an orifice plate
44
in which is formed a plurality of nozzles, or ink ejection orifice,
46
. Each chamber
42
communicates with a single nozzle
46
.
Each delivery channel further includes a diaphragm
50
located at the side of chamber
42
that is remote from nozzle
46
. Diaphragm
50
is coupled to a respective transducer
54
that may be a piezoelectric transducer composed of a stack of piezoelectric plates. Transducer
54
is enclosed by silicone members
56
. Each transducer
54
is sandwiched between an associated diaphragm
50
and a ceramic plate
58
that is common to all channels. Electrodes (not shown) are connected in a conventional manner to each transducer
54
via passages (not shown) provided in plate
58
.
The printhead is completed by a member
62
that serves to support a portion of members
34
and
56
and diaphragm
50
, along with two side plates
66
and
68
that form parts of the housing for the printhead.
It will be noted that in the illustrated embodiment, the ink manifold has an inlet in communication with reservoir
12
and outlets in communication with inlet paths
40
of the delivery channels, and the ink manifold outlets are spaced from the ink manifold inlet in the direction of ink flow through the manifold. Wall
30
extends generally perpendicular to the direction of ink flow through space
16
. However, wall
30
can have other orientations relative to the direction of ink flow through the manifold, provided that it forms one boundary wall of space
16
. In addition, wall
30
, which constitutes one of the surfaces bounding space
16
, preferably has an area at least as large as the area of any other one of the surfaces bounding space
16
.
When a drop of ink is to be ejected from any one orifice
46
, an electrical actuation pulse is applied to transducer
54
, causing the transducer to expand momentarily and deflect diaphragm
50
. The deflection of diaphragm
50
creates a pressure pulse in chamber
42
and this pulse acts to eject a drop of ink from orifice
46
.
A portion of the energy of the pressure pulse produced by deflection of diaphragm
50
is propagated as a pressure disturbance via inlet path
40
into space
16
, where it will influence the pressure in the other ink jet delivery channels.
According to the present invention, the propagation of pressure disturbances between ink jet deliver channels is prevented, or at least substantially minimized, by giving the manifold, or more specifically space
16
, a high fluidic compliance. In the illustrated embodiment, this is achieved by forming plate
30
to be sufficiently flexible to minimize the pressure disturbances that are propagated into space
16
.
According to one preferred embodiment of the invention, this is achieved by forming plate
30
as a stainless steel sheet having a thickness on the order of 12 μm, although smaller thicknesses can be envisioned. The degree of compliance increase afforded by the present invention is influenced by the mechanical characteristics of both plate
30
and filter
38
.
As a general rule, the compliance increase afforded by the present invention will be inversely proportional to the thickness of plate
30
. A thickness less than 12 μm may prove advantageous if such a thickness proves to be feasible in practice.
Filter
38
may be made of stainless steel, nickel, etc., an electroformed nickel material presently being preferred. Because of the necessary position of filter
38
in space
16
, the compliance of filter
38
will influence the compliance the manifold. The compliance of filter
38
will depend on the size and number of the ink passages therein, which are determined by the required ink flow and filtering parameters, and the thickness and material of filter
38
. The compliance of filter
38
will be essentially inversely proportional to its thickness. The thickness can have any value compatible with the required ink flow and filtering parameters and mechanical strength. It is presently believed that the thickness can be between 10 and 25 μm, although other thickness values can be used.
For a filter
38
having given dimensions and given ink passage size and spacing, an electroformed nickel filter will have a higher compliance than a stainless steel filter.
Depending on the combination of materials and dimensions chosen for plate
30
and filter
38
, it is believed that the compliance of the manifold can be increased by a factor of the order of 140 or more.
It may be noted that, apart from plate
30
, the printhead shown in
FIG. 1
can be constructed according to techniques and principles already known in the art.
FIG. 2
is a partly cut-away perspective view of the embodiment shown in FIG.
1
. Elements already shown in
FIG. 1
are identified with the same reference numerals.
FIG. 2
illustrates several additional elements which were omitted from
FIG. 1
to facilitate an understanding of the basic structure of an ink manifold and ink jet delivery channels according to the invention.
Additional elements that are illustrated in
FIG. 2
include a heater
70
which maintains ink at a desired temperature for printing, a bonding plate
72
, a further support plate
74
and a restricter plate
76
. In addition,
FIG. 2
shows a silicone rubber sheet
80
positioned between a transducer
54
and diaphragm
50
. Also shown in
FIG. 2
are electrodes
82
associated with several transducers
54
. All of these elements are, however, conventional in the art.
According to a second embodiment of the invention, plate
30
can be replaced by a plate
90
, as shown in
FIGS. 3 and 4
. This plate is provided with an array of capillary orifices
92
. In the illustrated embodiment, orifices
92
taper from a relatively large diameter at the side
94
of plate
90
which faces ink volume
16
to a small diameter at the side
96
of plate
90
that faces wall
34
. However, orifices
92
need not be tapered. As illustrated in
FIGS. 1 and 2
, an air space exists between wall
34
and plate
30
, or plate
90
of
FIGS. 3 and 4
, and this air space may be vented to the environment.
Each passage
92
is delimited by a surface formed by rotating a generatrix constituted by a quarter circle around the longitudinal axis of the passage. Each passage
92
, and particularly the small diameter end thereof, has a sufficiently small diameter that ink present in space
16
will not flow out of passages
92
. Ink contained within each passage
92
will form a meniscus
98
.
When a pressure disturbance occurs in space
16
, it will be attenuated by a variation in the quantity of ink in each passage
92
, associated with a change in the position and/or curvature of each meniscus
98
. Under normal operating conditions, this variation will not result in the flow of ink into the air space between plate
90
and wall member
34
.
The spacing between passages
92
is determined by the compliance that it is desired to provide for space
16
. The closer the spacing between passages, the greater will be the resulting compliance. The maximum number of passages
92
is limited essentially only by the surface area of plate
90
.
The maximum size of passages
92
is determined by the requirement for the surface tension of meniscus
98
and to prevent meniscus
98
from being pulled back into space
16
in the presence of the normal operating pressure, which may be of the order of 2-3 cm below atmospheric The maximum hole size also depends on the surface tension of the ink. Assuming a surface tension of 30 dyne/cm, these considerations would lead to a maximum radius of about 150 microns at the outlet end of each passage
92
.
Since a large number of passages having this size would provide a more than adequate increase in compliance, a practical form of construction of this embodiment could satisfactorily employ smaller diameter passages. The exit diameter of each passage
92
could typically be in the range of 75 to 100 microns.
These passages may be formed in a thin plate by a variety of processes, including etching, drilling, laser drilling, electroforming, piercing, or electro-discharge machining. Passages having the form illustrated in
FIGS. 3 and 4
result naturally from using a thin film electroform process.
In normal practice, during priming or purging of a printhead, it is necessary to apply a relatively high positive pressure to the ink in the manifold. In view of this, it may be desirable to provide an additional device which would cover passages
92
while pressure is being applied, in order to prevent ink from leaking out through passages
92
.
In further accordance with the invention, plate
90
can be made relatively thin to have a flexibility comparable to that of plate
30
of
FIGS. 1 and 2
. In this case, a high level of compliance can be provided by a combination of the flexing of plate
90
and the effect produced in capillary passages
92
.
Yet another embodiment of the invention is shown in
FIG. 5
which is a simplified, diagrammatic plan view of the interior of a manifold. According to this embodiment, a thin walled air sac
102
may be installed in space
16
. Sac
102
is filled with air and may be made of a material which can be made very thin and is chemically compatible with the ink employed in ink jet printers. For some inks, latex rubber may be compatible. Pressure disturbances within space
16
will be attenuated, or dissipated, by compression or expansion of the air within sac
102
. The nominal pressure of the air in sac
102
may be equal to or slightly greater than the nominal pressure of ink in space
16
. Sac
102
can be made of other materials and can, for example, be a thin-walled metal box made of stainless steel. In the latter form of construction, the nominal pressure within the box can be slightly lower than the nominal pressure of ink in space
16
.
It should be appreciated that the embodiment shown in
FIG. 5
can be combined with the embodiments of
FIGS. 1 and 2
or
FIGS. 3 and 4
to provide space
16
with a very high level of compliance with respect to pressure disturbances.
FIG. 6
is a respective view showing, in simplified form, the basic physical form of one exemplary printhead which may be equipped with manifolds according to the present invention. This is a color printhead in which reservoir
12
is provided with a plurality of receptacles
110
each for storing a supply of ink of a respectively different color. The printhead includes a plurality of vertical rows of nozzles (not shown), each row being associated with a row of transducers
114
. Each transducer corresponds to transducer
54
shown in
FIGS. 1 and 2
. Adjacent each row of transducers
114
is a respective manifold that contains an ink space
16
. Each manifold may be constructed to have the form shown in
FIGS. 1 and 2
and/or
FIGS. 3 and 4
and may optionally be provided with a sac
102
as shown in FIG.
5
. As is conventional in this art, reservoir
12
would lower than the manifolds to maintain a negative pressure at all orifices. Although
FIG. 6
shows three receptacles
110
and six rows of nozzles, there can also be provided, in accordance with standard practice in the art, four receptacles and, correspondingly, eight rows of nozzles. As will be apparent to those skilled in the art, the number of rows of nozzles can vary from those mentioned above.
For some printing applications the printhead may be used with reservoirs other than the built-in ones shown e.g. if another orientation of the printhead is required.
While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention.
The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
Claims
- 1. An ink jet printhead comprising:a reservoir storing a quantity of printing ink; at least one ink manifold defining an ink supply volume in communication with said reservoir for holding a supply of ink received from said reservoir; and a plurality of individually controlled ink jet delivery channels, each of said channels having an ink drop ejection transducer and an orifice to eject successive ink drops on demand in response to pressure pulses produced by said transducer, and each of said channels being in communication with said ink supply volume for receiving ink from said ink supply volume, wherein said manifold includes a thin, flexible wall bounding said ink supply volume to provide said ink supply volume a large acoustic compliance to minimize propagation of pressure disturbances in said ink supply volume and acoustic signal crosstalk between said channels, and said wall has a thickness of the order of not more than 12 μm.
- 2. The printhead of claim 1 wherein said wall is made of stainless steel.
- 3. The printhead of claim 2 wherein said ink manifold has an inlet in communication with said reservoir and outlets in communication with said delivery channels, said outlets being spaced from said inlet in an ink flow direction and said wall extending substantially perpendicular to the ink flow direction.
- 4. The printhead of claim 3 wherein said ink flow volume is delimited by a plurality of surfaces and said wall constitutes one of the surfaces and has an area at least as large as the area of any other one of the surfaces.
- 5. An ink jet printhead comprising:a reservoir storing a quantity of printing ink; at least one ink manifold defining an ink supply volume in communication with said reservoir for holding a supply of ink received from said reservoir; and a plurality of individually controlled ink jet delivery channels, each of said channels having an ink drop ejection transducer and an orifice to eject successive ink drops on demand in response to pressure pulses produced by said transducer, and each of said channels being in communication with said ink supply volume for receiving ink from said ink supply volume, wherein said manifold includes a thin, flexible wall bounding said ink supply volume to provide said ink supply volume a large acoustic compliance to minimize propagation of pressure disturbances in said ink supply volume and acoustic signal crosstalk between said channels, and said ink manifold has an inlet in communication with said reservoir and outlets in communication with said delivery channels, said outlets being spaced from said inlet in an ink flow direction and said wall extending substantially perpendicular to the ink flow direction.
- 6. The printhead of claim 5 wherein said ink flow volume is delimited by a plurality of surfaces, and said wall constitutes one of the surfaces and has an area at least as large as the area of any other one of the surfaces.
- 7. An ink jet printhead comprising:a reservoir storing a quantity of printing ink; at least one ink manifold defining an ink supply volume in communication with said reservoir for holding a supply of ink received from said reservoir; and a plurality of individually controlled ink jet delivery channels, each of said channels having an ink drop ejection transducer and an orifice to eject successive ink drops on demand in response to pressure pulses produced by said transducer, and each of said channels being in communication with said ink supply volume for receiving ink from said ink supply volume, wherein said manifold includes a thin, flexible wall bounding said ink supply volume to provide said ink supply volume a large acoustic compliance to minimize propagation of pressure disturbances in said ink supply volume and acoustic signal crosstalk between said channels, and said ink supply volume is delimited by a plurality of surfaces, and said wall constitutes one of the surfaces and has an area at least as large as the area of any other one of the surfaces.
- 8. An ink jet printhead comprising:a reservoir storing a quantity of printing ink; at least one ink manifold defining an ink supply volume in communication with said reservoir for holding a supply of ink received from said reservoir; and a plurality of individually controlled ink jet delivery channels, each of said channels having an ink drop ejection transducer and an orifice to eject successive ink drops on demand in response to pressure pulses produced by said transducer, and each of said channels being in communication with said ink supply volume for receiving ink from said ink supply volume, wherein said manifold includes a thin, flexible wall bounding said ink supply volume to provide said ink supply volume a large acoustic compliance to minimize propagation of pressure disturbances in said ink supply volume and acoustic signal crosstalk between said channels, and said thin, flexible wall bounding said ink supply volume includes a plurality of capillary passages which communicate between said ink supply volume and an air space.
- 9. The printhead of claim 8 wherein said capillary passages are dementioned to be partially filled with ink under normal pressure conditions within said ink supply volume.
- 10. The printhead of claim 9 wherein each of said capillary passages tapers from a large diameter and communicating with the ink supply volume to a small diameter and communicating with the air space.
- 11. The printhead of claim 10 wherein the small diameter end of each of said passages has a diameter not greater than 100 microns.
- 12. An ink jet printhead comprising:a reservoir storing a quantity of printing ink; at least one ink manifold defining an ink supply volume in communication with said reservoir for holding a supply of ink received from said reservoir; a plurality of individually controlled ink jet delivery channels, each of said channels having an ink drop ejection transducer and an orifice to eject successive ink drops on demand in response to pressure pulses produced by said transducer, and each of said channels being in communication with said ink supply volume for receiving ink from said ink supply volume, wherein said manifold includes a thin, flexible wall bounding said ink supply volume to provide said ink supply volume a large acoustic compliance to minimize propagation of pressure disturbances in said ink supply volume and acoustic signal crosstalk between said channels; and a sac filled with air and installed within said ink supply volume.
- 13. The printhead of claim 12 wherein said sac is made of a material that is compatible with the printing ink.
- 14. The printhead of claim 13 wherein said sac is made of latex rubber or metal.
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