Information
-
Patent Grant
-
6585352
-
Patent Number
6,585,352
-
Date Filed
Wednesday, August 16, 200023 years ago
-
Date Issued
Tuesday, July 1, 200321 years ago
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Inventors
-
Original Assignees
-
Examiners
-
CPC
-
US Classifications
Field of Search
US
- 347 40
- 347 12
- 347 43
- 347 15
- 347 62
- 347 65
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International Classifications
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Abstract
A compact monochrome ink jet printhead having a staggered high-density arrangement of ink drop generators for high-performance printing. The present invention provides a high-performance design that enable high-resolution and high-speed printing while reducing cost due to an efficient use of printhead space. In particular, the compact, high-performance printhead of the present invention includes several thermally-efficient aspects that allow a large number of ink drop generators to be placed on a compact printhead while minimizing problems such as thermal excursions. In a preferred embodiment, the ink drop generator density on the compact printhead exceeds 10 ink drop generators per square millimeter and the compact printhead contains at least 350 nozzles. The ink drop generators are arranged in at least four parallel rows. Each row is staggered (or offset) relative to an adjacent row to provide a greater effective pitch that a non-staggered arrangement. The ink drop generators of the present invention include high resistance resistors and a thin passivation to increase thermally efficiency. Further thermal control is achieved by ejecting low-weight ink drops from the thermally-efficient ink drop generators at a high ejection frequency that exceeds 12 kHz.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to thermal ink jet (TIJ) printheads and more specifically to a system and method for high-performance printing that uses a compact monochrome printhead having staggered, high-density arrangement of ink drop generators.
2. Related Art
Thermal ink jet (TIJ) printers are popular and widely used in the computer field. These printers are described by W. J. Lloyd and H. T. Taub in “Ink Jet Devices,” Chapter 13 of
Output Hardcopy Devices
(Ed. R. C. Durbeck and S. Sherr, San Diego: Academic Press, 1988) and U.S. Pat. Nos. 4,490,728 and 4,313,684. Ink jet printers produce high-quality print, are compact and portable, and print quickly and quietly because only ink strikes a print medium (such as paper).
An ink jet printer produces a printed image by printing a pattern of individual dots (or pixels) at specific defined locations of an array. These dot locations, which are conveniently visualized as being small dots in a rectilinear array, are defined by the pattern being printed. The printing operation, therefore, can be pictured as the filling of a pattern of dot locations with dots of ink.
Ink jet printers print dots by ejecting a small volume of ink onto the print medium. An ink supply device, such as an ink reservoir, supplies ink to the ink drop generators. The ink drop generators are controlled by a microprocessor or other controller and eject ink drops at appropriate times upon command by the microprocessor. The timing of ink drop ejections generally corresponds to the pixel pattern of the image being printed.
In general, the ink drop generators eject ink drops through an orifice (such as a nozzle) by rapidly heating a small volume of ink located within a vaporization or firing chamber. The vaporization of the ink drops typically is accomplished using an electric heater, such as a small thin-film (or firing) resistor. Ejection of an ink drop is achieved by passing an electric current through a selected firing resistor to superheat a thin layer of ink located within a selected firing chamber. This superheating causes an explosive vaporization of the thin layer of ink and an ink drop ejection through an associated nozzle of the printhead.
Ink drop ejections are positioned on the print medium by a moving carriage assembly that supports a printhead assembly containing the ink drop generators. The carriage assembly traverses over the print medium surface and positions the printhead assembly depending on the pattern being printed. The carriage assembly imparts relative motion between the printhead assembly and the print medium along a “scan axis”. In general, the scan axis is in a direction parallel to the width of the print medium and a single “scan” of the carriage assembly means that the carriage assembly displaces the printhead assembly once across approximately the width of the print medium. Between scans, the print medium is typically advanced relative to the printhead along a “media (or paper) advance axis” that is perpendicular to the scan axis (and generally along the length of the print medium).
As the printhead assembly is moved along the scan axis a swath of intermittent lines is generated. The superposition of these intermittent lines creates the appearance as text or image of a printed image. Print resolution along the media advance axis is often referred to as a density of these intermittent lines along the media advance axis. Thus, the higher the density of the intermittent lines in the media advance axis the greater the print resolution along that axis.
The density of the intermittent lines along the media advance axis (and thus the print resolution) can be increased by increasing the number of ink drop generators on the printhead. This results in better print resolution and increased print speed. Moreover, due to several factors, it is desirable to increase the number of ink drop generators without increasing the size of the printhead. However, merely increasing the number of drop generators on an existing printhead greatly increases the amount of heat dissipated in the printhead during print operations. This increased heat dissipation can cause unwanted printhead thermal excursions. These large thermal excursions on the printhead adversely affect printhead operation and can cause print quality defects, printhead thermal shutdown and even failure of the entire printhead.
One technique that may be used to avoid large thermal excursions is to slow down the speed of the printhead. This technique, however, negates the positive effect of providing more ink drop generators on the printhead. Another technique that may be used to avoid a large thermal excursion is to increase the size of the printhead. A primary disadvantage of this technique, however, is that increasing printhead size increases the cost of the printing system. This is unacceptable because printing systems are rapidly decreasing in price and a printing system having the added cost of a larger printhead will not be competitive in the marketplace. What is needed, therefore, is a way of providing a compact, high nozzle count, and high performance printhead that does not suffer from deleterious thermal excursions.
SUMMARY OF THE INVENTION
To overcome the limitations in the prior art as described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention is embodied in a compact monochrome ink jet printhead having a high-density of ink drop generators. The present invention provides a high-performance design that enable high-resolution and high-speed printing while reducing cost due to an efficient use of printhead space. In particular, the compact, high-performance printhead of the present invention includes several performance improving aspects that allow a large number of ink drop generators to be placed on a compact printhead while minimizing problems such as thermal excursions.
The compact, monochrome ink jet printhead of the present invention enables high-performance printing that includes high-resolution and high-speed printing. In particular, one technique used to increase print resolution and speed is to increase the number of ink drop generators, stagger them with respect to groups of other ink drop generators and operate the ink drop generators at a high frequency. This staggered, high-density arrangement helps increase an effective resolution of the printhead. The present invention includes a high-density staggered arrangement of ink drop generators disposed on a compact printhead substrate. Each ink drop generator is a thin-film structure formed in printhead substrate that is fluidically coupled to an ink supply device and includes a nozzle. Ink is supplied to the ink drop generators and at the appropriate time heated and ejected from the associated nozzle.
In a preferred embodiment, the ink drop generator density on the compact printhead exceeds 10 ink drop generators per square millimeter and the compact printhead contains at least 350 nozzles. The ink drop generators (and corresponding nozzles) are arranged in at least three parallel rows. Each row is staggered (or offset) relative to an adjacent row to provide a greater effective pitch that a non-staggered arrangement.
The present invention also reduces costs associated with a printhead having a high-density of ink drop generators by placing the generators on a compact printhead. In order to facilitate a high density of ink drop generators on a compact substrate the present invention includes several techniques to improve thermal efficiency. One technique for improving thermal efficiency is providing thermally-efficient ink drop generators having a thin-film structure that includes high-resistance resistors and a thin passivation layer.
The high-density arrangement of ink drop generators on a compact printhead provides high-performance printing in a portable and low-cost package. Specifically, by using thermally-efficient ink drop generators and providing exceptional thermal control of the compact printhead, the present invention can provide high-speed, high-resolution and high-quality printing. The present invention also includes a method of high-performance printing using the compact ink jet printhead of the present invention.
Other aspects and advantages of the present invention as well as a more complete understanding thereof will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. Moreover, it is intended that the scope of the invention be limited by the claims and not by the preceding summary or the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention can be further understood by reference to the following description and attached drawings that illustrate the preferred embodiment. Other features and advantages will be apparent from the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the present invention.
Referring now to the drawings in which like reference numbers represent corresponding parts throughout:
FIG. 1
is a block diagram of an overall printing system incorporating the present invention.
FIG. 2
is an exemplary printing system that incorporates the compact high-performance, high-density ink jet printhead of the present invention and is shown for illustrative purposes only.
FIG. 3
illustrates an exemplary carriage assembly of the printing system of
FIG. 2
that supports the compact high-performance, high-density ink jet printhead of the present invention.
FIG. 4
is a perspective view of the printhead assembly of the present invention and is shown for illustrative purposes only.
FIG. 5A
is a plan view representation of an exemplary printhead of the present invention illustrating the arrangement of nozzles.
FIG. 5B
depicts a plan view of a portion of the printhead of
FIG. 5A
with the orifice layer removed and illustrating the staggered arrangement of ink drop generators.
FIG. 5C
is a cut-away isometric view of the printhead of
FIG. 5A
illustrating the various layers of the printhead.
FIG. 6
is a plan view representation of the exemplary printhead of
FIG. 5
with the nozzle layer of the printhead removed and revealing the pattern of resistors that underlie the nozzles.
FIG. 7
is an exemplary embodiment of primitive power routing for the printhead
500
shown in FIG.
5
A.
FIG. 8A
is one exemplary embodiment illustrating a single ground connection lead for the printhead shown in FIG.
5
A.
FIG. 8B
is another exemplary embodiment illustrating two ground connection leads for the printhead shown in FIG.
5
A.
FIG. 9
is a cut-away perspective view of an exemplary ink drop generator of the present invention.
FIG. 10A
is a plan view of firing resistor shown in FIG.
9
.
FIG. 10B
is a side view of the firing resistor of
FIG. 10A
illustrating the thin-film structure of the firing resistor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the following description of the invention, reference is made to the accompanying drawings, which form a part thereof, and in which is shown by way of illustration a specific example whereby the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.
I. General Overview
The present invention is embodied in a compact monochrome printhead having a high-density arrangement of staggered ink drop generators. This arrangement provides the present invention with high-resolution and high-speed printing. In order to achieve optimum printing system performance, a number of aspects of the present invention are important.
One aspect of the present invention concerns the use of a high-resolution printhead having a high nozzle count that operates at high frequency. Resolution of a printhead (as opposed to a printed document) is measured according to a number of nozzles per linear inch. This is measured in a direction that is aligned with the media advance axis, and, in the case of scanning printheads, transverse to the scan axis. In an exemplary embodiment, the printhead of the present invention has a nozzle array size of one-third of an inch and a combined resolution of 1200 dots per inch (dpi) measured along the media advance axis. In addition, the operating frequency of the printhead in this exemplary embodiment is at least 12 kilohertz (kHz).
The printhead of the present invention uses a staggered arrangement of ink drop generators to increase print quality, speed and resolution. In particular, a plurality of ink drop generators are disposed along multiple axes and are positioned to scan across the same portion of print media in the media advance axis direction. Each plurality of ink drop generators along an axis (or axis groups) have centerlines and the centerlines of all axis groups are parallel to the media advance axis and are spaced apart from each other in a direction transverse to the media advance axis. The nozzles of each axis group are staggered relative to other axis groups such that at least three axis groups have a combined resolution (measured along the media advance axis) of greater than double the resolution of a single axis group. Staggering provides higher resolution printing in fewer passes and provides high print speed at high resolution by increasing the effective nozzle density in the media advance axis. Further details of the printhead of the present invention are discussed in co-pending patent application Ser. No. 09/640,286 entitled “High-Performance, High-Density Ink Jet Printhead Having Multi-Mode Operation” by Joe Torgerson et al. and filed on the same date of the present application.
In an exemplary embodiment, the printhead contains four axis groups having centerlines that are mutually parallel and are spaced apart from each other in a direction transverse to the centerlines. Each axis group has an axis pitch (or resolution) of approximately 300 dpi. The staggered arrangement provided by the present invention provides an effective pitch of all four combined axis groups of 1200 dpi (measured along the media axis). Preferably, the ends of the four axis groups are aligned to within {fraction (1/300)}
th
of an inch so that the effective pitch of the combination of all four axis groups will be 1200 dpi from end to end for the swath covered during a print scan.
Another aspect of the present invention includes using a space efficient layout of the large number of nozzles to minimize the size of the printhead, and enable the use of the printhead in a relative low cost printing system. This space efficient layout includes a high aspect ratio substrate having two central ink feed slots that have a very compact arrangement and primitives of ink drop generators having common ground leads. Still another aspect of the present invention includes an energy efficient design for the ink drop generators. By using relatively high resistance resistors that have relatively low thermal impedance protection layers, the amount of thermal energy transferred to the substrate per drop generated is minimized.
II. Structural Overview
FIG. 1
is a block diagram of an overall printing system incorporating the present invention. The printing system
100
can be used for printing on a media, such as ink on a print media
102
(which can be paper). The printing system
100
is coupled to a host system
105
(such as a computer or microprocessor) for producing print data. The printing system
100
includes a controller
110
, a power supply
120
, a print media transport device
125
, a carriage assembly
130
and a plurality of switching devices
135
. An ink supply device
115
is fluidically coupled to a printhead assembly
150
for selectively providing ink to the printhead assembly
150
. The print media transport device
125
provides a means to move a print media
102
(such as paper) relative to the printing system
100
. Similarly, the carriage assembly
130
supports the printhead assembly
150
and provides a means to move the printhead assembly
150
to a specific location over the print media
102
as instructed by the controller
110
.
The printhead assembly
150
includes a compact printhead structure
160
. As described in detail below, the printhead structure
160
of the present invention contains a plurality of various layers including a substrate (not shown). The printhead substrate may be a single monolithic substrate that is made of any suitable material (preferably having a low coefficient of thermal expansion), such as, for example, silicon. The printhead structure
160
also includes a high-density, staggered arrangement of ink drop generators
165
formed in the printhead substrate. The arrangement of ink drop generators
165
includes a thermally-efficient design that permits a large number of ink drop generators to be disposed on a relatively compact printhead substrate without large thermal excursions. In addition, each one of the arrangement of ink drop generators
165
includes a plurality of elements for causing an ink drop to be ejected from the printhead assembly
150
. The compact printhead structure
160
also includes an electrical interface
170
that provides energy to the switching devices
135
that in turn provide power to the high-density, staggered arrangement of ink drop generators
165
.
During operation of the printing system
100
the power supply
120
provides a controlled voltage to the controller
110
, the print media transport device
125
, the carriage assembly
130
and the printhead assembly
150
. In addition, the controller
110
receives the print data from the host system
105
and processes the data into printer control information and image data. The processed data, image data and other static and dynamically generated data are provided to the print media transport device
125
, the carriage assembly
130
and the printhead assembly
150
for efficiently controlling the printing system
100
.
Exemplary Printing System
FIG. 2
is an exemplary printing system that incorporates the high-performance, high-density ink jet printhead of the present invention and is shown for illustrative purposes only. As shown in
FIG. 2
, the printing system
200
includes a tray
222
for holding print media. When a printing operation is initiated, the print media is transported into the printing system
200
from the tray
222
preferably using a sheet feeder
226
in a direction of a media advance axis
227
. The print media is then transported in a U-direction within the printing system
200
and exits in the opposite direction of entry toward an output tray
228
. Other print media paths, such as a straight paper path, may also be used.
Upon entrance into the printing system
200
the print media is paused within a print zone
230
and the carriage assembly
130
, which supports at least one printhead assembly
150
of the present invention, is then moved (or scanned) across the print media in a scan axis
234
direction for printing a swath of ink drops thereon. The printhead assembly
150
can be removeably mounted or permanently mounted to the carriage assembly
130
. In addition, the printhead assembly
150
is coupled to the ink supply device
115
. The ink supply device
115
may be a self-contained ink supply device (such as a self-contained ink reservoir). Alternatively, the printhead assembly
150
may be fluidically coupled, via a flexible conduit, to the ink supply device
115
. As a further alternative, the ink supply device
115
may be one or more ink containers separate or separable from the printhead assembly
150
and removeably mounted to the carriage assembly
130
.
FIG. 3
illustrates an exemplary carriage assembly of the printing system of
FIG. 2
that supports the high-performance, high-density ink jet printhead of the present invention. The carriage assembly
130
includes a scanning carriage
320
that supports the printhead assembly
150
, which may be removable or permanently mounted to the scanning carriage
320
. The controller
110
, is coupled to the scanning carriage
320
and provides control information to the printhead assembly
150
.
The scanning carriage
320
is moveable along a straight path direction in the scan axis
234
. A carriage motor
350
, such as stepper motor, transports the scanning carriage
320
along the scan axis
234
according to commands from a position controller
354
(which is in communication with the controller
110
). The position controller
354
is provided with memory
358
to enable the position controller
354
to know its position along the scan axis
234
. The position controller
354
is coupled to a platen motor
362
(such as a stepper motor) that transports the print media
102
incrementally. The print media
102
is moved by a pressure applied between the print media
102
and a platen
370
. Electrical power to run the electrical components of the printing system
200
(such as the carriage motor
350
and the platen motor
362
) as well as energy to cause the printhead assembly
150
to eject ink drops is provided by the power supply
120
.
In general, a print operation occurs by feeding the print media
102
from the tray
222
and transporting the print media
102
into the print zone
230
by rotating the platen motor
362
and thus the platen
370
in the media advance axis
227
. When the print media
102
is positioned correctly in the print zone
230
, the carriage motor
350
positions (or scans) the scanning carriage
320
and printhead assembly
150
over the print media
102
in the scan axis
234
for printing. After a single scan or multiple scans, the print media
102
is then incrementally shifted by the platen motor
362
in the media advance axis
227
thereby positioning another area of the print media
102
in the print zone
230
. The scanning carriage
320
again scans across the print media
102
to print another swath of ink drops. The process is repeated until the desired print data has been printed on the print media
102
at which point the print media
102
is ejected into the output tray
228
.
III. Printhead Architecture
The compact printhead of the present invention includes a high-density staggered arrangement of ink drop generators that provides high-resolution printing at high speed. The high-density arrangement of ink drop generators has a thermally efficient design to permit a high-density of ink drop generators to be disposed on a compact printhead substrate. In a preferred embodiment, the compact printhead substrate has an ink drop generator density exceeding approximately ten ink drop generators per square millimeter. Moreover, in a preferred embodiment the ink drop generators are arranged in groups along at least four axes (each known as an axis group) with each axis group having a plurality of nozzles. The plurality of nozzles for each axis group is approximately one-third of an inch in length resulting in approximately twelve nozzles per square millimeter. The thermally-efficient ink drop generator of the present invention is a thin-film structure that includes a thermally-efficient resistor structure having a high resistance and a thin passivation.
Another aspect of the present invention is having a reduced number of input leads to the printhead relative to the number of ink drop generators located on the compact printhead substrate. In particular, ink drop generators are arranged in groups called primitives, and in the present invention the number of ground connections from the printer is less than the number of primitives. In a preferred embodiment, there are four ground connections for sixteen primitives. Moreover, another aspect is having ink drops being ejected with a low drop weight at a high ejection frequency. For example, in a preferred embodiment the ink drops have an ink drop weight of about 15 nanograms and are ejected at an ejection frequency of greater than 12 kilohertz (kHz).
FIG. 4
is a perspective view of the printhead assembly of the present invention and is shown for illustrative purposes only. A detailed description of the present invention follows with reference to a typical printhead assembly used with a typical printing system, such as printer
200
of FIG.
2
. However, the present invention can be incorporated in any printhead and printer configuration. Referring to
FIGS. 1 and 2
along with
FIG. 4
, the printhead assembly
150
is comprised of a thermal inkjet head assembly
402
and a printhead body
404
. The thermal inkjet head assembly
402
can be a flexible material commonly referred to as a Tape Automated Bonding (TAB) assembly and can contain interconnect pads
412
. The interconnect pads
412
are suitably secured to the printhead assembly
150
(also called a print cartridge), for example, by an adhesive material. The contact pads
408
align with and electrically contact electrodes (not shown) on the carriage assembly
130
.
High Performance Nozzle Arrangement
FIG. 5A
is a plan view representation of an exemplary printhead of the present invention illustrating the arrangement of nozzles. It should be noted that
FIG. 5A
is a simplified illustration. For example, the number of nozzles illustrated has been greatly reduced from the exemplary or intended commercial embodiment. An exemplary printhead
500
includes a compact substrate
510
having a plurality of ink drop generators therein, input pads
515
and an orifice layer
520
. The orifice layer
520
contains a plurality of nozzles
530
corresponding to the plurality of ink drop generators.
In an exemplary embodiment of
FIG. 5A
, the printhead has a combined nozzle resolution of approximately 1200 dots per inch (dpi). Stated another way, the combined (or effective) pitch of the printhead is {fraction (1/1200)}
th
of an inch measured along a reference axis L. The nozzles of the printhead each operate with an operating frequency that can exceed 12 kHz.
To achieve a high print resolution, the exemplary printhead of the present invention as shown in
FIG. 5A
has the nozzles arranged into four axis groups (shown as Groups
1
-
4
in FIG.
5
A). Each axis group has a centerline (shown as dashed lines in
FIG. 5A
) that is generally parallel to the centerlines of the other axis groups and to the reference axis L. In operation, the reference axis L is aligned with the media advance axis
227
. Each axis group has a axis pitch P measured relative to the reference axis L. The nozzles from each axis group are staggered with respect to the nozzles of the other axis groups and relative to the reference axis L. As shown in
FIG. 5A
, each axis group has an axis pitch of P, and the effective pitch for the combination of all four axis groups is P/4 relative to reference axis L (or one-fourth of the pitch of any single axis group). Moreover, Group
1
and Group
3
may be combined to provide an effective pitch of P/2. Similarly, Group
2
and Group
4
may be combined to provide an effective pitch of P/2. In this exemplary embodiment, the axis pitch P of each axis group is {fraction (1/300)}
th
of an inch, but this technique of staggering three or more axis groups to provide an increased resolution can be applied to any axis pitch. While the nozzles of each axis group are illustrated to be substantially collinear, it should be noted that some of the nozzles of an axis group may be slightly off the centerline of the axis group. This may occur, for example, when there is a need to compensate for firing delays.
FIG. 5B
depicts a plan view of a portion of the printhead of
FIG. 5A
with the orifice layer removed and illustrating the staggered arrangement of ink drop generators. Specifically, the printhead
500
includes ink drop generators
540
disposed on the compact substrate
510
. The nozzles
530
overlying the ink drop generators
540
are arranged into axis groups, including Group 1, Group 2, Group 3 and Group 4. The axis groups of ink drop generators are spaced apart from each other transversely relative to the reference axis L. In a preferred embodiment, the reference axis L is aligned with the media advance axis
227
. A single axis group of ink drop generators has a certain axis resolution defined as 1 divided by an axis pitch (1/P) for a single pass of the printhead
500
over the print media. In an exemplary embodiment, the axis resolution (1/P) is approximately 300 dpi. By using this staggered arrangement of axis groups, the effective resolution of the combined axis groups is increased to approximately 4/P when operating with all four axis groups, and approximately 2/P when operating with a properly selected pair of the four axis groups.
The axis pitch (P) of a particular of a particular axis group equals the center-to-center spacing between two nearest ink drop generators projected onto or measured according to the reference axis L. In a preferred embodiment, P is approximately equal to {fraction (1/300)}
th
of an inch. Groups 1, 2, 3, and 4 are staggered relative to each other along reference axis L by P/4 (or {fraction (1/1200)}
th
of an inch if P is approximately equal to {fraction (1/300)}
th
of an inch) for any two axis groups that are nearest neighbors. As illustrated in
FIG. 5B
, this provides a combined center-to-center spacing (again measured along the reference axis L) equal to P/4 ({fraction (1/1200)}
th
of an inch in an exemplary embodiment). With this arrangement, the combined center-to-center spacing of Groups 1 and 3 (denoted as P13) equals P/2, or {fraction (1/600)}
th
of an inch. The combined center to center spacing of Groups 2 and 4 (denoted as P24) also equals P/2. This high-density staggered arrangement permits the printhead of the present invention to provide high-performance printing in a compact printhead design.
FIG. 5C
is a cut-away isometric view of the printhead
500
of
FIG. 5A
illustrating the various layers of the printhead
500
. The printhead
500
includes the compact printhead substrate
510
(such as silicon) and having various devices and thin film layers formed thereon. The printhead
500
also includes the orifice layer
520
disposed on a barrier layer
550
that in turn overlays the substrate
510
. The substrate
510
includes ink drop generators that are arranged in a high-density, staggered arrangement including a first plurality of ink drop generators
560
within Group 1 and a second plurality of ink drop generators
565
within Group 2 arranged around a first ink feed slot
570
. In this exemplary embodiment, a second ink feed slot
572
is provided whereby Group 3 and Group 4 are arranged around the second ink feed slot
572
. Nozzles
530
are formed into the orifice layer
520
and arranged such that each nozzle
530
has an underlying ink drop generator. Ink is supplied through the first ink feed slot
570
to the ink drop generators where it is heated and ejected through the nozzles
530
.
A lamination process is typically used to attach the orifice layer
520
to the barrier layer
550
. Although
FIG. 5C
depicts the barrier layer
550
and orifice layer
520
as being separate discrete layers, they can also be formed in an alternative embodiment as one integral barrier and orifice layer. A firing chamber
575
is defined by both the orifice layer
520
and the barrier layer
550
together. The firing chamber
575
is where ink is heated by a resistor
580
until the drop is expelled through the nozzle
530
.
Compact, Elongate Printhead Substrate
The present invention includes a high-density arrangement of ink drop generators disposed on a compact printhead substrate. The printhead has an elongate (or narrow width) shape and, in a preferred embodiment, the compact printhead substrate is a rectangle having a width of approximately 3 millimeters and a length of approximately 12 millimeters. Contained on this compact printhead substrate is at least 350 nozzles with a preferred number of 416 nozzles. In a preferred embodiment, the result is a compact printhead having approximately 12 nozzles per square millimeter.
Ink drop generators contained on the printhead substrate eject ink from nozzles that are arranged in at least four staggered rows having 104 nozzles each, with each row of nozzles about ⅓ of an inch in length. The four rows of nozzles are arranged in pairs around two elongate ink feed slots, with each ink feed slot having a width of approximately 200 microns. Preferably, each ink feed slot is located approximately 680 microns from the center of the printhead.
FIG. 6
is a plan view representation of the exemplary printhead of
FIG. 5
with the nozzle layer of the printhead removed and revealing the pattern of resistors
580
that underlie the nozzles. Each nozzle of the present invention has a corresponding and underlying operable resistor
580
. The number of resistors illustrated in
FIG. 6
has been reduced for purposes of simplifying the illustration.
The resistors
580
are arranged on a highly compact printhead substrate
510
such that a density of resistors is at least 10 resistors per square millimeter of the printhead substrate
510
. This high-density arrangement allows the cost of the printhead to be lower than many other printheads having fewer nozzles. In an exemplary embodiment, there are approximately 12 resistors per square millimeter of the printhead substrate
510
. It should be noted that the area of any ink feed slots is included in a calculation of the resistor density.
The printhead substrate
510
as shown in
FIG. 6
has an elongate form factor, with a length of the substrate
510
generally aligned with the reference axis L. In a preferred embodiment, at least 350 ink drop generators are arranged upon the substrate
510
having a width of less than approximately 3 millimeters and a length of less than approximately 12 millimeters. In a preferred embodiment, the substrate
510
contains
416
resistors and has a width of approximately 2.9 millimeters and a length of approximately 11.5 millimeters.
The printhead substrate
510
has two elongate ink feed slots including the first ink feed slot
570
and the second ink feed slot
572
. Each of the ink feed slots
570
,
572
provides ink from an ink supply device to resistors
580
in two axis groups. For example, as shown in
FIG. 6
, the first ink feed slot
570
provides ink to resistors in Groups 1 and 2 and the second ink feed slot
572
provides ink to resistors in Groups 3 and 4. Each of the ink feed slots
570
,
572
has a centerline (shown as dashed lines in
FIG. 6
) that is generally parallel to the reference axis L and approximately divides each of the ink feed slots
570
,
572
equally along their respective lengths. The centerlines of the ink feed slots
570
,
572
are spaced apart and transverse from each other in a direction approximately parallel to the reference axis L. Each of the ink feed slots
570
,
572
has two longitudinal edges that generally are the length of the slot. In particular, the first ink feed slot
570
includes a first longitudinal edge
610
adjacent which are arranged Group 1 resistors and a second longitudinal edge
620
adjacent which are arranged Group 2 resistors. Similarly, the second ink feed slot
572
includes a third longitudinal edge
630
and a fourth longitudinal edge
640
having Groups 3 and 4 adjacent the respective edge.
At opposite ends of the length of the printhead substrate
510
are end portions having input pads
515
that provide energy for the resistors of each axis group. Switching circuitry (such as a plurality of transistors) couples signals being delivered from the input pads
515
to the resistors in the axis groups. This technique helps to reduce the width of the printhead substrate
510
.
Each of the resistors
580
is coupled to a switching circuit (such as a field effect transistor (FET)) that provides current pulses to the resistor
580
. These switching circuits are discussed in detail below. The resistors
580
, along with their respective switching circuits, are arranged into groupings called primitives (as shown in
FIG. 6
as by the numerals
1
-
16
). In an exemplary embodiment shown in
FIG. 6
, each of the axis groups is divided into 4 primitives. Preferably, each of the primitives each has 26 nozzles, for a total of 104 nozzles per axis group. Although for the purpose of simplicity
FIG. 6
illustrates only four resistors (and corresponding ink drop generators) per primitive, it is understood that most printhead designs will tend to have greater than 10 resistors (and ink drop generators) per primitive.
Low Ink Drop Weight
Preferably, the high-density arrangement of ink drop generators uses low-weight ink drops. A low-weight ink drop is smaller and provides a finer resolution print than is achieved with higher weight ink drops. Using low-weight ink drop with a high-density array of ink drop generators provides the present invention with high print resolution at high print speeds. In a preferred embodiment, the present invention uses black ink drops that weigh approximately 15 nanograms (ng), with preferred range of from 14 to 16 ng.
High Ejection Frequency
In general, a preferred embodiment of the present invention operates the ink drop generators at a high ejection frequency in order to facilitate the use of low-weight ink drops and still maintain a high print speed. Preferably, this ejection frequency is in the kilohertz (kHz) range. This high ejection frequency combined with the high-density array of ink drop generators provides high-speed printing with high resolution.
In a preferred embodiment, the ink drop generators of the present invention use an ejection frequency in excess of 12 kHz. A preferred frequency range is approximately from 15 to 18 kHz, with 18 kHz as the preferred value.
Printhead Circuitry
The present invention includes a high-performance yet economical printhead that uses a compact design to decrease cost and is thermally efficient to allow the high-performance design to be used on a compact printhead substrate. In particular, the thermally-efficient design of the printhead enables a high density of ink drop generators to be placed on a compact printhead substrate while minimizing thermal excursions. One way the present invention enables a high-performance yet compact design involves printhead circuitry. Specifically, the printhead circuitry is designed such that low power is required to operate each ink drop generator and a minimum of thermal energy is produced.
One technique includes providing a particular primitive with a primitive power lead (that provides power to the particular primitive) that is separately energizable from each of the primitive power leads for each of the remaining primitives. Thus, a particular primitive power lead is coupled to all of the primitive power leads associated with each of the switching circuits within a particular primitive. In a preferred embodiment where the switching circuits are FETs, the particular primitive select lead is coupled to each of the source or drain connections for each FET within the particular primitive.
Another technique of the invention concerns separately energizable gate leads with each gate lead coupled to a single switching device of each of a plurality of primitives. The number of gate leads is 1 to N (where N is the number of resistors in the largest primitive). In a preferred embodiment, the primitives each have 26 resistors (N=26) and thus there are 26 gate leads. When the switching devices are FETs, each FET in a primitive has one of the gate leads connected to its gate. When a particular switching device is activated a current pulse flows from a primitive power lead, through the switching circuit, through the heater resistor, and back through a return or ground lead. In order for a particular switching device to be activated, the gate lead and the primitive power lead associated with that switching device must be simultaneously activated or energized.
During printhead operation, the gate leads are activated one at a time and in sequence. As a result, only one switching device in a particular primitive can be activated at a time. However, some or all of the primitives can be operated simultaneously since each gate lead is connected to one switching device of a plurality of primitives. In a preferred embodiment, each primitive has at most one gate connection for each of the 26 gate leads. Since the printing system cycles through gate leads during operation, only one ink drop generator can be operated at a time within a primitive. However, since most gate leads are shared by the primitives, multiple primitives can be fired simultaneously. In a preferred embodiment, there are at least three and preferably four primitives that overlap in the scan axis (that is transverse to the paper axis and transverse to axis L) that can be operated simultaneously. This allows for much more complete and higher resolution coverage in a single scan.
FIG. 7
is an exemplary embodiment of primitive power routing for the printhead
500
shown in FIG.
5
A. For a particular primitive, there is a primitive power lead that is coupled at a first end to a corresponding primitive contact pad that is one of the input pads
515
(shown as P
1
-P
16
in
FIG. 7
) and coupled along an edge to the switching devices corresponding to that particular primitive power lead. For example, as shown in
FIG. 7
, primitive
12
has a primitive power lead
700
coupled at a first end as a primitive
12
contact pad
710
(on the far right side of the top row of input pads
515
) and along an edge
720
coupled to the switching devices of primitive
11
(not shown). In an exemplary embodiment, each primitive power lead is connected to either the source or drain connection for each FET within that primitive. These contact pads (P
1
-P
16
) are used to input the energy required to energize each of the primitives on the printhead
500
.
FIGS. 8A and 8B
illustrate two embodiments of ground connection leads for of the printhead
500
of the present invention. As discussed previously, each of the ink feed slots
570
,
572
has two longitudinal edges. Adjacent to each longitudinal edge is one of the four axis groups of resistors. To reduce the number of input pads
515
, more than one primitive shares the same ground connection lead. In both the embodiment of
FIGS. 8A and 8B
, the two ends of each axis group are commonly connected to reduce the ground lead parasitic resistance difference between resistors near the center of the compact printhead substrate
510
relative to the ends of the substrate
510
.
FIG. 8A
is one exemplary embodiment illustrating a single ground connection lead for the printhead
500
shown in FIG.
5
A. In this embodiment, a single ground connection lead
810
is used to connect to all 16 primitives to ground. Thus, all 16 primitives are connected by a single ground connection lead to ground. Alternatively,
FIG. 8B
is another exemplary embodiment illustrating two ground connection leads for the printhead
500
shown in FIG.
5
A. In this particular embodiment there is a first ground connection lead
820
and a second ground connection lead
830
. Each of the two ground connection lead
820
,
830
connect all the primitives of around particular ink feed slot to ground. For example, as shown in
FIG. 8B
, the first ground connection lead
820
connects the primitives around the first ink feed slot
570
to ground and the second ground connection lead
830
connects the primitives surrounding the second ink feed slot
572
to ground.
Thermally-Efficient Thin Film Resistor Structure
Each of the ink drop generators of the present invention is thermally efficient to enable the ink drop generators to be packed onto the compact printhead substrate at a high density. In order to achieve this thermal efficiency, each ink drop generator includes a thin-film resistor structure that decreases the power required for each resistor. In particular, the present invention uses high-resistance resistors to reduce the power required to energize the resistor and a thin passivation layer to reduce the input power dissipated due to parasitic energy dissipation. Both resistor structures facilitate using high-frequency printing bursts in the printing system by reducing the power requirements of the printhead and eliminating a major increase in thermal energy due to an increased power requirement. In other words, reducing the power requirement enables less power to be used by the printhead even though there are more resistors, thereby allowing the printhead to operate at a lower temperature and reducing thermal excursions.
In particular,
FIG. 9
is a cut-away perspective view of an exemplary ink drop generator of the present invention. The ink drop generator
540
is disposed on a compact printhead substrate
510
and includes a thin-film resistor structure
580
(shown in greater detail in FIGS.
10
A and
10
B). Overlying the resistor structure
580
is the barrier layer
550
and an orifice layer
520
, both discussed further below. The top of the thin-film resistor structure
580
and the barrier and orifice layers
550
,
520
form a firing chamber where ink is vaporized by the resistor structure
580
and ejected through an orifice (such as a nozzle
530
). Preferably, the orifice diameter is within a range of between about 10 to 20 microns, with an exemplary value of approximately 16 microns. Each component and layer of the ink drop generator
540
may be formed separately or integrally and various methods for forming these components and layers are known in the art. For example, the barrier and orifice layers
550
,
520
can be applied separately or formed integrally and then applied to the underlying compact printhead substrate
510
.
One technique used by the present invention to reduce thermal excursions is to decrease the power required to fire a resistor
580
by increasing the resistance of the firing resistors
580
so that the ratio of connecting trace resistance (or parasitic resistance) to total resistance is decreased. This resistance ratio is directly related to power dissipated in the connecting traces, and is known as the “parasitic power loss. Each resistor
580
has connecting traces that connect the resistor
580
to various electrical connections. In conventional designs, the resistance of the connecting traces may be up to one-third or greater of the firing resistor
580
resistance. This parasitic power loss can cause up to one-third of the input energy to be dissipated within the connecting traces. Parasitic power loss becomes even more significant in the present invention because there is a high resistor density (the number of resistors per unit area of the compact printhead) and there is less room for the connecting traces and a greater total power requirement.
The present invention decreases the parasitic power loss by increasing the resistance of each firing resistor
580
thereby decreasing the power dissipated within the connecting traces. Preferably, the resistance of each firing resistor
580
is at least 70 ohms with a preferred value of over 100 ohms. Higher resistance may be achieved by reducing the thickness of the resistor
580
or by using a resistor material of higher resistivity. In a preferred embodiment, however, the thickness of the resistor and resistivity of the resistor material are unchanged and the resistor path length is increased to obtain a higher resistance. This is achieved by splitting the resistor body into a plurality of segments that are connected in series by a coupling device or conducting link. This split resistor increases the resistance of the firing resistor
580
because the resistance of each segment is added to the previous segment in the series. An increase in the resistor resistance also increases the total resistance (while keeping the connecting trace resistance nearly constant) and thereby decreases the parasitic power loss (the ratio of trace resistance to the total resistance).
FIG. 10A
is a plan view of firing resistor shown in FIG.
9
. In this exemplary embodiment, the firing resistor
580
comprises a first segment
1004
and a second segment
1008
that are connected in series by a coupling device or conductor
1012
. An input pad
1016
for receiving electrical signals is located adjacent the first segment
1004
and an output pad
1020
for transmitting electrical signals is located adjacent the second segment
1008
. In this preferred embodiment, a current control device
1021
is used to reduce current crowding that would otherwise occur in the coupling device
1012
. This current control device
1021
interrupts an otherwise straight current path through the coupling device
1012
. In the exemplary embodiment shown in
FIG. 10A
, the current control device
1021
is a notch
1021
formed in the coupling device
1012
between the first segment
1004
and the second segment
1008
.
In this exemplary embodiment, each segment
1004
,
1008
is approximately 24 microns long and 13 microns wide. This provides a total of approximately four squares, with each square having a resistance of about 29 ohms, resulting in a total resistance of 130 ohms (including the connecting traces). Preferably, the parasitic resistance is approximately in the range between about 7 to 8 percent and is tuned for an ink drop weight of about 5 nanograms (ng). Alternatively, a resistance of at least 80 ohms would result in a parasitic resistance of approximately 12 percent. The width of a gap
1022
between the opposing segment is approximately 3 microns.
Another technique used by the present invention to improve thermal efficiency is to reduce the thermal resistance of a passivation layer on the thin-film resistor structure
580
. A thinner passivation layer means that less energy is required to energize the resistor. This means that less thermal energy needs to be dissipated from the ink drop generator and results in better thermal efficiency. The present invention accomplishes this by reducing the thickness of the passivation layer to allow a minimum amount of energy to energize the resistor
580
and cause an ink drop to be ejected.
Preferably, with the thinner passivation layer, energies of less than 1.4 microjoules are required to energize the resistor
580
, with a preferred energy range being between about 0.8 to 1.0 microjoules. The power required to energize the resistor
580
is also affected by ratio of trace resistance to total resistance (parasitic power loss), with a lower parasitic power loss generally meaning that less power is required. The present invention preferably reduces thermal excursions on the printhead by using both a low ratio of trace resistance to total resistance (a low parasitic power loss) and a thinner passivation layer.
FIG. 10B
is a side view of the firing resistor of
FIG. 10A
showing the thin-film structure of the firing resistor
580
.
FIG. 10B
is a cross-section along AA′ from the resistor
580
shown in FIG.
10
A. In this exemplary embodiment, the resistor layer
1023
is made of Ta Al and overlies a layer of PSG
1024
and FOX
1026
disposed on the compact printhead substrate
510
(preferably made of silicon). In a preferred embodiment the resistor layer
1023
is approximately 900 angstroms thick. Overlying a portion of the resistor layer
1023
is a conductor layer
1032
comprised of AlSiCu.
The resistor layer
1023
is protected from damage by a first passivation layer
1034
comprised of Si
3
N
4
and a second passivation layer
1036
comprised of SiC. In a preferred embodiment, the thickness of the first passivation layer
1034
is 2570 angstroms and the thickness of the second passivation layer
1036
is 1280 angstroms. The combination of the first passivation layer
1034
and the second passivation layer
1036
comprise a total passivation layer. Preferably, the total passivation layer is kept to a thickness of less than about 5000 angstroms with a preferred range between about 3500 to 4500 angstroms. At this passivation layer thickness the energy required to energize the resistor layer
1023
is less than 1.4 microjoules.
Overlying the second passivation layer
1036
is a cavitation layer
1040
that protects the resistor layer
1023
and passivation layers
1034
,
1036
from damage due to ink drop cavitation and collapse. Preferably, the cavitation layer
1040
is comprised of tantalum (Ta) having a thickness of 3000 angstroms. The barrier layer
550
(preferably approximately 14 microns thick) and the orifice layer
520
(preferably approximately 25 microns thick) overlie the cavitation layer
1040
. The cavitation layer
1040
, barrier layer
550
and orifice layer
520
create the firing chamber
575
where ink is vaporized by the resistor layer
1023
and ejected from the nozzle
530
created in the orifice layer
520
.
The foregoing description of the preferred embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description of the invention, but rather by the claims appended hereto.
Claims
- 1. An ink jet printhead including an ink supply device for providing ink of a certain color, comprising:a printhead substrate; and a plurality of ink drop generators fluidically coupled to the ink supply device and formed in the printhead substrate in a density of greater than approximately ten ink drop generators per square millimeter of the printhead substrate, the plurality of ink drop generators arranged in at least four staggered axis groups along axes that are approximately parallel and spaced transverse to each other.
- 2. The ink jet printhead of claim 1, wherein the density of ink drop generators is between approximately eleven and thirteen ink drop generators per square millimeter of the printhead substrate.
- 3. The ink jet printhead of claim 2, wherein each one of the plurality of ink drop generators includes a firing resistor having a resistance of at least seventy ohms.
- 4. The ink jet printhead of claim 1, wherein each of the axis groups of ink drop generators is grouped into a plurality of primitives with each of the primitives commonly coupled to a single ground lead on the printhead substrate.
- 5. The ink jet printhead of claim 1, wherein each of the plurality of ink drop generators includes a thin-film resistor structure having a resistance of at least seventy ohms.
- 6. The ink jet printhead of claim 1, wherein the plurality of ink drop generators arranged along the axes are staggered with respect to each of the axes to decrease an effective printhead pitch to approximately one-fourth that of a plurality of ink drop generators arranged along a single axis.
- 7. The ink jet printhead of claim 1, wherein each of the at least four axis groups of ink drop generators includes at least one-hundred ink drop generators.
- 8. The ink jet printhead of claim 1, further comprising two ink feed slots each having two longitudinal edges and wherein each of the axis groups of ink drop generators is adjacent to each of the longitudinal edges.
- 9. The ink jet printhead of claim 1, wherein the plurality of ink drop generators operates at an ejection frequency of greater than approximately twelve kilohertz.
- 10. A fluid ejection device, comprising:a printhead substrate; at least three-hundred fifty ink drop generators disposed on the printhead substrate and disposed within a compact area of less than approximately thirty six square millimeters.
- 11. A fluid ejection device of claim 10, wherein the compact area has a length of less than approximately twelve millimeters and a width of less than approximately three millimeters.
- 12. A fluid ejection device of claim 10, wherein the ink drop generators are configured as:a first plurality of ink drop generators arranged along a first axis to form a first axis group; a second plurality of ink drop generators arranged along a second axis to form a second axis group and staggered with respect to the first axis group; a third plurality of ink drop generators arranged along a third axis to form a third axis group and staggered with respect to the first and second axis groups; wherein the first, second and third axes are mutually parallel and spaced apart transverse to one another.
- 13. A compact monochrome ink jet printhead, comprising:a printhead substrate; ink drop generators disposed on the printhead substrate and disposed within a compact area of less than approximately thirty six square millimeters, the ink drop generators further comprising:, a first plurality of ink drop generators arranged along a first axis to form a first axis group; a second plurality of ink drop generators arranged along a second axis to form a second axis group and staggered with respect to the first axis group; a third plurality of ink drop generators arranged along a third axis to form a third axis group and staggered with respect to the first and second axis groups; and wherein the first, second and third axes are mutually parallel and spaced apart transverse to one another.
- 14. The ink jet printhead of claim 13, wherein the compact area has a length of less than approximately twelve millimeters and a width of less than approximately three millimeters.
- 15. The ink jet printhead of claim 13, comprising at least three-hundred fifty ink drop generators disposed within the compact area.
- 16. The ink jet printhead of claim 15, further comprising at least four hundred ink drop generators.
- 17. The ink jet printhead of claim 13, wherein each of the ink drop generators includes a thin-film resistor having a high resistance.
- 18. The ink jet printhead of claim 17, wherein the thin-film resistor is at least approximately seventy ohms.
- 19. The ink jet printhead of claim 13, wherein each of the ink drop generators includes a thin-film structure passivation layer.
- 20. The ink jet printhead of claim 19, wherein the thin-film structure passivation layer has a thickness of less than approximately five-thousand angstroms.
- 21. The ink jet printhead of claim 13, further comprising an ink supply device coupled to each of the ink drop generators.
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