Information
-
Patent Grant
-
6688718
-
Patent Number
6,688,718
-
Date Filed
Friday, July 2, 199925 years ago
-
Date Issued
Tuesday, February 10, 200420 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Meier; Stephen D.
- Huffman; Julian D.
-
CPC
-
US Classifications
Field of Search
US
- 029 8901
- 029 611
- 347 18
- 347 87
- 347 44
-
International Classifications
-
Abstract
This present invention is embodied in a printing system with thermally efficient heat transfer capabilities for reducing dimpling of a nozzle member during fabrication of the printhead portion of an inkjet printer. The printing system of the present invention includes a printhead assembly and an ink supply for printing ink on print media. The printhead assembly includes a printhead body having a heat transfer device, ink channels and a nozzle member having plural nozzles coupled to respective ink channels. The nozzle member is secured to the printhead body with a suitable adhesive layer. The heat transfer device can be defined by a portion of or the entire printhead body for reducing thermal expansion of the printhead body during exposure to heat. Namely, the heat transfer device of the printing system of the present invention is capable of efficiently reducing thermal expansion of the printhead body during the process of adhering (which includes heating and curing the adhesive) the nozzle member to the printhead body. As a result, trajectory errors of ejected ink droplets from the nozzles are reduced.
Description
FIELD OF THE INVENTION
The present invention generally relates to inkjet and other types of printers and more particularly, to a printing system with thermally efficient heat transfer capabilities for a printhead portion of an inkjet printer.
BACKGROUND OF THE INVENTION
Inkjet printers are commonplace 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. Inkjet printers produce high quality print, are compact and portable, and print quickly and quietly because only ink strikes a printing medium, such as paper.
An inkjet printer produces a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations are conveniently visualized as being small dots in a rectilinear array. The locations are sometimes “dot locations”, “dot positions”, or pixels”. Thus, the printing operation can be viewed as the filling of a pattern of dot locations with dots of ink.
Inkjet printers print dots by ejecting very small drops of ink onto the print medium and typically include a movable carriage that supports one or more print cartridges each having a printhead with a nozzle member having ink ejecting nozzles. The carriage traverses over the surface of the print medium. An ink supply, such as an ink reservoir, supplies ink to the nozzles. The nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller. The timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed.
In general, the small drops of ink are ejected from the nozzles through orifices by rapidly heating a small volume of ink located in vaporization chambers with small electric heaters, such as small thin film resistors. The small thin film resistors are usually located adjacent the vaporization chambers. Heating the ink causes the ink to vaporize and be ejected from the orifices. Specifically, for one dot of ink, an electrical current from an external power supply is passed through a selected thin film resistor of a selected vaporization chamber. The resistor is then heated for superheating a thin layer of ink located within the selected vaporization chamber, causing explosive vaporization, and, consequently, a droplet of ink is ejected from the nozzle and onto a print media. One very important factor in assuring high print quality is the accuracy of the trajectory of the ejected droplet since this affects where it lands upon the print media. The accuracy of this trajectory is mostly dependent upon the particular geometry of the nozzle.
One challenge in controlling the nozzle geometry and hence trajectory of the droplets is to regulate bending and/or buckling of the nozzle member, otherwise known as “dimpling” of the nozzle member. Dimpling of the nozzle member causes the nozzles to be skewed, which leads to imprecise nozzle geometry. Dimpling tends to be induced during print cartridge manufacturing, which includes cartridge assembly processes such as adhesively bonding the printhead to the cartridge. More specifically, dimpling can be caused by inadvertent bending and/or buckling of the nozzle member due to structural thermal expansions and contractions occurring when the nozzle member is adhesively sealed to the print cartridge. For example, during the heat, cure and cool process when the nozzle member is adhered to the cartridge, the cartridge experiences thermal expansions and contractions. These thermal expansions and contractions cause the nozzle member to buckle, bend and deform, thereby skewing the nozzles. Typical heat and cure processes include curing the adhesive by applying hot air to the nozzle member, which heats an upper portion of the print cartridge.
Since dimpling of the nozzle member skews the nozzles, it tends to adversely affect nozzle geometry, thereby causing nozzle trajectory errors. A measure of this bending of the nozzle member is referred to as the “nozzle camber angle” (NCA), which is proportional to the bending of the nozzle member from an ideal flat state. Poor nozzle camber angles (NCAs) causes ink drop trajectory errors and uncontrolled ink drop directionality. In other words, when the printhead assembly is scanned across a recording medium, the NCA-induced ink drop trajectory errors will affect the location of printed dots and, thus, affect the quality of printing. Also, the bending of the nozzle member can restrict ink flow into nozzles, thus limiting the refill speed and hence the maximum droplet ejection frequency. This is turn limits printer speed. Therefore, what is needed is a nozzle member that has incurred limited bending or deformation during manufacturing of the print cartridge and to be as flat as possible. What is also needed is a printing system incorporating a device that reduces dimpling of a nozzle member during manufacture of a printhead portion of an inkjet printer.
SUMMARY OF THE INVENTION
To overcome the limitations in the prior art 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 printing system with thermally efficient heat transfer capabilities for reducing dimpling of a nozzle member during fabrication of the printhead portion of an inkjet printer.
The printing system of the present invention includes a printhead assembly and an ink supply for printing ink on print media. The printhead assembly includes a printhead body having a heat transfer device, ink channels and a nozzle member having plural nozzles coupled to respective ink channels. The nozzle member is secured to the printhead body with a suitable adhesive layer. The heat transfer device can be defined by a portion of or the entire printhead body for reducing thermal expansion of the printhead body during exposure to heat. Namely, the heat transfer device of the printing system of the present invention is capable of efficiently reducing thermal expansion (which in turn reduces the thermal contraction) of the printhead body during the process of adhering (which includes heating and curing the adhesive) the nozzle member to the printhead body. As a result, trajectory errors of ejected ink droplets from the nozzles are reduced.
In another embodiment, a controlled process is used to heat and cure the adhesive for reducing the amount of heat applied to the printhead body, thereby reducing the thermal expansion of the printhead body. In particular, hot gimbaled rails can be placed in direct contact with the nozzle member to conductively heat and cure the adhesive directly below the contact area between the nozzle member and printhead body. Since the rails only contact the nozzle member, heat can be applied to localized areas with controlled amounts. For instance, a minimum required amount of heat to cure the adhesive can be applied to a controlled area directly above the adhesive. As a result, only a portion of the printhead body is heated, thereby efficiently reducing thermal expansion of the printhead body. Consequently, trajectory errors of ejected ink droplets from the nozzles are reduced.
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 invention.
FIG. 1
shows a block diagram of an overall printing system incorporating the present invention.
FIG. 2
is an exemplary printer that incorporates the invention and is shown for illustrative purposes only.
FIG. 3
shows for illustrative purposes only a perspective view of an exemplary print cartridge incorporating the present invention.
FIG. 4
is a schematic cross-sectional view taken through section line
4
—
4
of
FIG. 3
showing the heat transfer device of the print cartridge of
FIGS. 1 and 3
.
FIG. 5
is a schematic cross-sectional view taken through section line
4
—
4
of
FIG. 3
showing another heat transfer device of the print cartridge of
FIGS. 1 and 3
and a controlled heating process.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the following description of the invention, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration a specific example in which 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.
General Overview
FIG. 1
shows a block diagram of an overall printing system incorporating the present invention. The printing system
100
of the present invention includes a printhead assembly
110
, an ink supply
112
and print media
114
. The printhead assembly
110
includes a printhead body
116
, a nozzle member
118
with orifices or nozzles
120
fluidically coupled to associated ink channels
121
. The printhead body
116
includes a heat transfer device
122
for reducing the thermal expansion of the printhead body
116
during exposure to heat, which in turn reduces the thermal contraction during cooling. The nozzle member
118
is preferably fixedly coupled to the printhead body
116
, such as with an adhesive.
During a printing operation, ink is provided from the ink supply
112
to an interior portion (such as an ink reservoir) of the printhead body
116
. The interior portion of the printhead body
116
provides ink to the ink channels
121
for allowing ejection of ink through adjacent nozzles
120
. Namely, the printhead assembly
110
receives commands from a processor (not shown) to print ink and form a desired pattern for generating text and images on the print media
114
. Print quality of the desired pattern is dependent on accurate placement of the ink droplets on the print media
114
.
One way to increase print quality is to improve the accuracy and precision of ink droplet placement. This can be achieved by limiting the skew of the nozzles by minimizing nozzle camber angles (NCA). In one embodiment, the present invention is embodied in a printhead body
116
with an aperture for efficiently limiting the thermal expansion of the printhead body
116
when exposed to heat during adhesion of the nozzle member
118
to the printhead body
116
. In another embodiment, a controlled process is used to heat and cure the adhesive for reducing the amount of heat applied to the printhead body
116
, thereby reducing the thermal expansion of the printhead body
116
. In both cases, nozzle
120
skewing is reduced and NCA is improved. Consequently, trajectory errors for the ejected ink droplets from the nozzles
120
are reduced. It should be noted that the above embodiments could be performed in combination to further reduce thermal expansion of the printhead body.
Exemplary Printing System
FIG. 2
is an exemplary high-speed printer that incorporates the invention and is shown for illustrative purposes only. Generally, printer
200
includes a tray
222
for holding print media
114
(shown in FIG.
1
). When a printing operation is initiated, print media
114
, such as a sheet of paper, is fed into printer
200
from tray
222
preferably using a sheet feeder
226
. The sheet then brought around in a U direction and travels in an opposite direction toward output tray
228
. Other paper paths, such as a straight paper path, can also be used. The sheet is stopped in a print zone
230
, and a scanning carriage
234
, supporting one or more print cartridges
236
, is then scanned across the sheet for printing a swath of ink thereon. After a single scan or multiple scans, the sheet is then incrementally shifted using, for example, a stepper motor and feed rollers to a next position within the print zone
230
. Carriage
234
again scans across the sheet for printing a next swath of ink. The process repeats until the entire sheet has been printed, at which point it is ejected into output tray
228
.
The present invention is equally applicable to alternative printing systems (not shown) such as those incorporating grit wheel or drum technology to support and move the print media
114
relative to the printhead assembly
110
. With a grit wheel design, a grit wheel and pinch roller move the media back and forth along one axis while a carriage carrying one or more printheads scans past the media along an orthogonal axis. With a drum printer design, the media is mounted to a rotating drum that is rotated along one axis while a carriage carrying one or more printheads scans past the media along an orthogonal axis. In either the drum or grit wheel designs, the scanning is typically not done in a back and forth manner as is the case for the system depicted in FIG.
2
.
The print cartridges
236
may be removeably mounted or permanently mounted to the scanning carriage
234
. Also, the print cartridges
236
can have self-contained ink reservoirs in the body of the printhead (shown in
FIG. 3
) as the ink supply
112
(shown in FIG.
1
). The self-contained ink reservoirs can be refilled with ink for reusing the print cartridges
236
. Alternatively, the print cartridges
236
can be each fluidically coupled, via a flexible conduit
240
, to one of a plurality of fixed or removable ink containers
242
acting as the ink supply
112
(shown in FIG.
1
). As a further alternative, ink supplies
112
can be one or more ink containers separate or separable from print cartridges
236
and removeably mountable to carriage
234
.
FIG. 3
shows for illustrative purposes only a perspective view of an exemplary printhead assembly
300
(an example of the printhead assembly
110
of
FIG. 1
) incorporating the present invention. A detailed description of the present invention follows with reference to a typical printhead assembly used with a typical printer, 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. 3
, the printhead assembly
300
is comprised of a thermal head assembly
302
and a printhead body
304
. The thermal head assembly
302
can be a flexible material commonly referred to as a Tape Automated Bonding (TAB) assembly. The thermal head assembly
302
contains a nozzle member
306
and interconnect contact pads
308
and is secured to the printhead assembly
300
. The thermal head assembly
302
can be secured to the print cartridge
300
with suitable adhesives. An integrated circuit chip (not shown) provides feedback to the printer
200
regarding certain parameters of printhead assembly
300
. The contact pads
308
align with and electrically contact electrodes (not shown) on carriage
234
. The nozzle member
306
preferably contains plural parallel rows of offset nozzles
310
through the thermal head assembly
306
created by, for example, laser ablation. It should be noted that other nozzle arrangements can be used, such as non-offset parallel rows of nozzles.
Component Details
FIG. 4
is a cross-sectional schematic taken through section line
4
—
4
of
FIG. 3
of the inkjet print cartridge
300
utilizing the present invention. A detailed description of the present invention follows with reference to a typical printhead used with print cartridge
300
. However, the present invention can be incorporated in any printhead configuration. Also, the elements of
FIG. 4
are not to scale and are exaggerated for simplification.
Referring to
FIGS. 1-3
along with
FIG. 4
, as discussed above, conductors (not shown) are formed on the back of thermal head assembly
302
and terminate in contact pads
308
for contacting electrodes on carriage
234
. The other ends of the conductors are bonded to the printhead
302
via terminals or electrodes (not shown) of a substrate
410
. The substrate
410
has ink ejection elements
416
formed thereon and electrically coupled to the conductors. The integrated circuit chip provides the ink ejection elements
416
with operational electrical signals.
An ink ejection or vaporization chamber
418
is adjacent each ink ejection element
416
, as shown in
FIG. 4
, so that each ink ejection element
416
is located generally behind a single orifice or nozzle
420
of the nozzle member
306
. The nozzles
420
are shown in
FIG. 4
to be located near an edge of the substrate
410
for illustrative purposes only. The nozzles
420
can be located in other areas of the nozzle member
306
, such as centered between an edge of the substrate
410
and an interior side of the body
304
. Each ink ejection element
416
acts as ohmic heater when selectively energized by one or more pulses applied sequentially or simultaneously to one or more of the contact pads
308
via the integrated circuit. The ink ejection elements
416
may be heater resistors or piezoelectric elements. The orifices
420
may be of any size, number, and pattern, and the various figures are designed to simply and clearly show the features of the invention. The relative dimensions of the various features have been greatly adjusted for the sake of clarity.
The printhead body
304
is defined by a headland portion
426
located proximate to the back surface of the nozzle member
306
and includes an inner raised support
430
. An adhesive layer
432
is located between the back surface of the nozzle member
306
and a top surface
434
of the inner raised support
430
to securely affix the nozzle member
306
to the headland
426
. The inner raised support
430
preferably includes an overflow slot
436
for receiving excess adhesive (i.e., adhesive overflow during fabrication of the printhead). The adhesive layer
432
forms an adhesive seal between the nozzle member
306
of the thermal head assembly
302
and the headland
426
. Some adhesives that can be used include hot-melt, silicone, UV curable adhesive, and mixtures thereof. Further, a patterned adhesive film may be positioned on the headland
426
, as well as a dispensed bead of adhesive.
Referring to
FIGS. 1-4
, during a printing operation, ink stored in an ink reservoir
424
defined by the printhead body
304
generally flows around the edges of the substrate
410
and into the vaporization chambers
418
. Energization signals are sent to the ink ejection elements
416
and are produced from the electrical connection between the print cartridges
236
and the printer
200
. Upon energization of the ink ejection elements
416
, a thin layer of adjacent ink is superheated to provide explosive vaporization and, consequently, cause a droplet of ink to be ejected through the orifice or nozzle
420
. The vaporization chamber
418
is then refilled by capillary action. This process enables selective deposition of ink on print media
114
to thereby generate text and images.
During typical fabrication of the printhead assembly
300
and adhesion of the nozzle member
306
to the headland
426
, dimpling is usually formed in the nozzle member
306
and thermal head assembly
302
. Dimpling is caused by inadvertent bending or deformation of the nozzle member
306
and thermal head assembly
302
. Bending and deformation can be caused by disproportionate thermal expansion and contraction of the headland
426
as compared to the thermal expansion and contraction of the nozzle member
306
. In other words, since the nozzle member
306
and the headland
426
are typically made of different materials, their respective coefficients of thermal expansion and contraction are different so they deform disproportionately.
Thermal expansion occurs when a dispersed (non-localized) heat source, such as hot air, is applied to the nozzle member
306
to initiate curing of the adhesive. Thermal contraction occurs when cooling is applied to the nozzle member
306
to finalize curing of the adhesive and seal the nozzle member
306
to the headland
426
. This dimpling of the nozzle member
306
creates skewed nozzles
420
, thereby causing trajectory errors for the ejected ink droplets from the nozzles
420
. Consequently, when the printhead assembly
300
is scanned across the print media during printing, the ink trajectory errors will affect the location of the ejected ink and reduce the quality of printing.
In one embodiment, the headland
426
of the present invention includes an integrated heat transfer device
440
for reducing thermal expansion of the printhead body
304
. The integrated heat transfer device
440
can be any suitable device for reducing the thermal expansion of the headland
426
by reducing the temperature of the bulk volume of the headland
426
during exposure to heat, such as when the adhesive is heated to initiate curing. For example, as shown in
FIG. 4
, the heat transfer device
440
can be an aperture or cutaway portion of the headland
426
. The aperture or cutaway
440
reduces the cross sectional area of the headland
426
, thereby minimizing heat transfer from the curing adhesive
432
to the printhead body
304
and headland
426
. As a result, dimpling is reduced because thermal expansion of the headland
426
is reduced during exposure to heat when the nozzle member
306
is adhesively sealed to the headland
426
.
Specifically, this can be accomplished, for example, by having the integrated heat transfer device
440
, such an aperture or cutaway, located in close proximity to the bottom portion
450
of the inner raised support
430
. This reduces a cross sectional portion of the headland
426
, thereby reducing heat transfer to a top portion of the headland
426
and thus, limiting thermal expansion of the headland
426
. For instance, the aperture or cutaway
440
can be located near the overflow slot
436
and between the bottom portion
450
, as shown in FIG.
4
.
FIG. 5
is a schematic cross-sectional view taken through section line
4
-
4
of
FIG. 3
showing another heat transfer device of the print cartridge of
FIGS. 1 and 3
and a controlled heating process. In another embodiment, the integrated heat transfer device
440
is a cutaway of the bottom portion
450
of the inner raised support
430
to form a slotted portion
510
for reducing heat transfer to a top portion
452
of the headland
426
, as shown in FIG.
5
.
In yet another embodiment, a controlled process is used to heat and cure the adhesive
432
for reducing the amount of heat applied to the printhead body
304
by localizing the application of the heat. Reducing the amount of heat applied to the printhead body
304
reduces the thermal expansion of the headland
426
. In particular, hot gimbaled rails
520
can be placed in direct contact with the nozzle member
306
at a contact area
522
to conductively heat and cure the adhesive
432
. The contact area
522
is preferably located directly above the adhesive
432
between the nozzle member
306
and the headland
426
. Since the rails
520
only contact the nozzle member
306
, heat can be applied to a regulated area, such as the contact area
522
, with controlled amounts of temperature. For instance, a minimum required amount of heat to cure the adhesive
432
can be applied to a controlled area
460
directly above the adhesive
432
.
In addition, an insulator device
530
can be used to insulate other areas from the heat. Namely, an insulated gimbal locating device
530
can be placed in direct contact with the nozzle member
306
at a contact area
532
to insulate certain areas. The contact area
532
is preferably located in direct contact with the headland
426
of the printhead body
304
to reduce the bulk temperature of the body
304
when the body is exposed to the heat. Since the insulated gimbal locating device
530
directly contacts a portion of the headland
426
, the temperature of the headland
426
near the contact area
532
can be reduced. As a result of this localized heating method, only a small portion of the headland
426
is heated, thereby efficiently reducing thermal expansion of the headland
426
, which reduces bending, deformation and dimpling of the thermal head assembly
302
. Consequently, trajectory errors of ejected ink droplets from the nozzles
420
are reduced. It should be noted that the above embodiments could also be performed in combination to further reduce thermal expansion of the printhead body.
The foregoing has described the principles, preferred embodiments and modes of operation of the present invention. However, the invention should not be construed as being limited to the particular embodiments discussed. As an example, the above-described inventions can be used in conjunction with inkjet printers that are not of the thermal type, as well as inkjet printers that are of the thermal type. Thus, the above-described embodiments should be regarded as illustrative rather than restrictive, and it should be appreciated that variations may be made in those embodiments by workers skilled in the art without departing from the scope of the present invention as defined by the following claims.
Claims
- 1. A printhead having a body, the printhead comprising:a nozzle member that receives ink from a refillable ink supply for ejecting the ink on a print media; a headland securing the body to the nozzle member and having an adhesive overflow slot formed within the headland; and a heat transfer device formed within the headland and separate from the adhesive overflow slot to reduce thermal expansion of the headland and body when the printhead is exposed to heat.
- 2. The printhead of claim 1, wherein the extended overflow slot is located proximate to an adhesive used to secure the headland to the nozzle member between the nozzle member and the body for reducing heat transfer to a top portion of the headland.
- 3. The printhead of claim 2, wherein the adhesive is cured by an externally controlled heater.
- 4. The printhead of claim 1, wherein the printhead is coupled to an ink supply for providing ink to the printhead.
- 5. The printhead of claim 4, wherein the ink supply is a removeably mounted ink container.
- 6. The printhead of claim 1, wherein the printhead is capable of being supported by a carriage over a print media.
- 7. The printhead of claim 1, further comprising a substrate having a front surface and an opposing back surface and ink ejection elements formed on the front surface.
- 8. A printing method for an inkjet printhead, comprising:selectively reducing thermal expansion of the printhead when the printhead is exposed to heat with a heat transfer device that is formed within a headland of the printhead and separate from an adhesive overflow slot that is formed within the headland for adhesively supporting a nozzle member to the inkjet printhead; providing ink from an ink supply to the inkjet printhead to enable the inkjet printhead to print the ink; and refilling the ink supply.
- 9. The method of claim 8, wherein the adhesive overflow slot is located proximate to an adhesive used to secure the headland to the nozzle member between the nozzle member and the body for reducing heat transfer to a top portion of the headland.
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Name |
Date |
Kind |
5367328 |
Erickson |
Nov 1994 |
A |
5852460 |
Schaeffer et al. |
Dec 1998 |
A |
5936649 |
Ikeda et al. |
Aug 1999 |
A |
6076912 |
Murthy |
Jun 2000 |
A |