PROCESS OF MANUFACTURING A
DROP-ON-DEMAND INK JET PRINTHEAD
HAVING THERMOELECTRIC
TEMPERATURE CONTROL MEANS
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CROSS-REFERENCE TO RELATED
APPLICATION
This application is a Continuation-In-Part of U.S. patent application Ser. No. 08/066,396, U.S. Pat. No. 5,435,060 10 filed May 20,1993 and a Continuation-In-Part of U.S. patent application Ser. No. 08/220,835 filed Mar. 31, 1994, both of which are assigned to the Assignee of the present invention and hereby incorporated by reference as if reproduced in their entirety. 15
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to ink jet printhead 20 apparatus and, more particularly, to an ink jet printhead . having thermoelectric temperature control means incorporated therein for the selective heating or cooling of the printhead.
2. Description of Related Art
A piezoelectrically actuated drop-on-demand ink jet printhead is a relatively small device used to selectively eject tiny ink droplets onto a paper sheet operatively fed through a printer, in which the printhead is incorporated, to thereby 3Q form from the ejected ink droplets selected text and/or graphics on the sheet. In one representative configuration thereof, an ink jet printhead has a horizontally spaced parallel array of internal ink-receiving channels. These internal channels are covered at their front ends by a plate 35 member through which a spaced series of small ink discharge orifices are formed. Each channel opens outwardly through a different one of the spaced orifices.
A spaced series of internal piezoelectric sidewall portions of the printhead body separate and laterally bound the 40 channels along their lengths. To eject an ink droplet through a selected one of the discharge orifices, the two printhead sidewall portions that laterally bound the channel associated with the selected orifice are piezoelectrically deflected into the channel and then returned to their normal undeflected 45 positions. The driven inward deflection of the opposite channel wall portions increases the pressure of the ink within the channel sufficiently to initiate the ejection of a small quantity of ink, in droplet form, outwardly through the discharge orifice. 50
A drop-on-demand ink jet printhead such as that described herein could be further enhanced if provided with the ability to control its temperature, particularly if the printhead could both selectively raise and lower its operating temperature. More specifically, both the active piezoelectric material used 55 to form sidewall actuators for the ink-carrying channels of the printhead, as well as the ink which fills those channels, are sensitive to temperature changes. Specifically, performance of the piezoelectric material, i.e. the extent to which the piezoelectric material deforms in response to the appli- 60 cation of a voltage thereto, will begin to vary if the temperature of the piezoelectric material strays outside of a preferred range. This causes the magnitude of the pressure pulse imparted to the ink contained in an actuated channel to vary from that expected. As the size of the droplet ejected 65 from an actuated channel will vary depending on the magnitude of the pressure pulse, spot size, i.e. the size of an ink
spot produced when the ejected droplet strikes a physical medium such as a sheet of paper, will become unpredictable. As a result, the quality of the representation produced using the above described printing process will be degraded.
Similarly, variations in printhead temperature may cause problems with the ink which fills the channels of the printhead. For example, it is contemplated that, in one application of the disclosed printhead, phase change ink will be used. Typically, phase change ink is solid at room temperature. As such, it is necessary that it be heated above room temperature before it will flow effectively from the supply source to and through the small channels within the printhead. Furthermore, once supplied to the channels, it must be maintained at the elevated temperature to prevent a partial or total return to the solid state and thereby ensure that the printhead will be able to properly eject a droplet of ink upon demand. For example, should the temperature of the ink drop such that a solid particle of ink is formed, that particle could adversely affect operation of the printhead in many of the same ways that foreign particulate matter affects the printhead, for example, by clogging an ink ejection orifice associated with a channel of the printhead. Even minor variations in temperature could potentially result in a change in the viscosity of the ink sufficient to cause a modification of the operating characteristics of the printhead.
While a device or system, either separate to or incorporated therewith, for lowering the temperature of a drop-ondemand ink jet printhead is not known by us, several heating systems which elevate temperature and are suitable for use with ink jet printhead apparatus are known. In many of these configurations, the ink supply and the printhead itself are separate units. In these configurations, the ink is heated by an external heating apparatus positioned on both the ink supply source and the printhead itself. The ink, most commonly, the aforementioned phase change ink, is heated sufficiently to achieve a liquefied ink that will easily flow through the entire printhead ink distribution system. After the ink has been sufficiently heated at the supply source, the ink is transferred from the supply source to the printhead that is heated by an external heating apparatus. The heated printhead maintains the ink's liquidity so that it will flow freely though the small printhead channels and orifices. The ink is then ejected from the printhead onto the paper. In those configurations where the ink supply source and the printhead are one unit, the entire unit is heated by a single external heating apparatus.
In view of the foregoing it can readily be seen that it would be desirable to provide a drop-on-demand ink jet printhead having temperature control means configured to both selectively heat and cool the printhead and a method of manufacturing a printhead having the aforementioned temperature control means incorporated therewith.
It is accordingly an object of the present invention to provide such a printhead and associated method of manufacture.
SUMMARY OF THE INVENTION
In one embodiment, the present invention is of a method of manufacturing a drop-on-demand ink jet printhead in which a channel array constructed of a thermally conductive material and having a top side surface, a front side surface, a spaced series of internal ink-carrying channels which extend rearwardly from the front side surface and piezoelectric actuation means acoustically coupled to each of the
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ink-carrying channels for selectively imparting pressure pulses thereto is first provided. To complete assembly, thermoelectric temperature control means, which includes means for heating and cooling the channel array, are mounted to the top side surface of the channel array. In one 5 aspect thereof, the thermoelectric temperature control means are mounted to the top side surface of the channel array by providing a plurality of n-type and p-type thermoelectric carriers and thermoconductively mounting bottom side surfaces of each one of the plurality of n-type and p-type w thermoelectric carriers to the top side surface of the channel array. A bottom side surface of a thermally conductive cover plate is then thermoconductively mounted to the top side surface of each one of the plurality of n-type and p-type thermoelectric carriers. The plurality of n-type and p-type 15 thermoelectric carriers are then serially connected to a power source such that application of a first current causes the plurality of n-type and p-type thermoelectric carriers to cool the channel array by transferring heat from the channel array to the cover plate while application of a second, 2Q reverse, current causes the plurality of n-type and p-type thermoelectric carriers to heat the channel array by transferring heat from the cover plate to the channel array.
In further aspects thereof, a first plurality of electrodes are formed on the top side surface of the channel array for 25 electrical connection with n-type and p-type thermoelectric carriers, a second plurality of electrodes are formed on the bottom side surface of the cover plate, again for electrical connection with n-type and p-type thermoelectric carriers, a third plurality of electrodes are formed on the top side 30 surface of the channel array for electrical connection with respective single ones of a second plurality of thermoelectric carriers thermoconductively mounted on the top side surface and a fourth plurality of electrodes are formed on the bottom side surface of the cover plate, again for electrical connec- 35 tion with respective single ones of the second plurality of thermoelectric carriers. Preferably, the third plurality of electrodes extend to a rear edge of the top side surface of the channel array where they are electrically connected to the power source while the fourth plurality of electrodes extend 40 to a front edge of the bottom side surface of the cover plate, again where they are electrically connected to the power source. In a still further aspect thereof, a thermocouple is mounted to the channel array and electrically connected to the power source. In this aspect, the power source selec- 45 tively applies the first or second current to selectively cool or heat the channel array based upon the channel array's temperature as determined by the thermocouple.
In an alternate aspect of this embodiment of the invention, a first plurality of electrodes are formed on the top side 50 surface of the channel array as a first series of generally parallel rows which extend thereacross such that a first electrode in each of the rows has a leading edge spaced a first distance from a front edge of the top side surface and a last electrode in each of the rows extends to a rear edge of the 55 top side surface. A plurality of n-type and p-type thermoelectric carrier pairs are electrically connected with corresponding ones of the first plurality of electrodes other than the last electrode in each of the rows such that, for each of the rows, the n-type and p-type thermoelectric carrier pairs 60 are arranged in an alternating pattern and a single thermoelectric carrier is electrically connected with the last electrode in each of the rows. A second plurality of electrodes are formed on the bottom side surface of the cover plate as a second series of generally parallel rows which extend across 65 the bottom side surface. A first electrode in each of the rows of the second series of rows extends to a front edge of the
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bottom side surface and a last electrode in each of the rows of the second series of rows has a trailing edge spaced a second distance from a rear edge of the bottom side surface.
In this embodiment, each one of the second plurality of electrodes other than the first electrode in each of the second series of rows are electrically connected with an n-type thermoelectric carrier of a first n-type and p-type thermoelectric carrier pair and a p-type thermoelectric carrier of a second n-type and p-type thermoelectric carrier pair while the first electrode in each of the rows of the second series of rows is electrically connected with a single thermoelectric carrier of one of the n-type and p-type thermoelectric carrier pairs. Preferably, the electrodes formed on the top side surface of the channel array which extend to the rear edge thereof are electrically connected to a first side of the power source while the electrodes formed on the bottom side surface of the cover plate which extend to the front edge thereof are electrically connected to a second side of the power source. As before, a thermocouple may be mounted to the channel array and electrically connected to the power source such that the power source selectively applies the first or second current to selectively cool or heat the channel array based upon the channel array's temperature as determined by the thermocouple.
In an alternate embodiment thereof, the channel array for the ink jet printhead may be manufactured by providing an insulative lower body portion having a plurality of generally parallel, longitudinally extending strips of conductive material formed along a top side surface, a corresponding plurality of conductive pins projecting from a bottom side surface and means for electrically connecting each of the pins with a corresponding one of the strips is provided. A bottom side surface of a first active intermediate body portion poled in a first direction generally parallel to the lower body portion is conductively mounted to the top side surface of the lower body portion and a bottom side surface of a second active intermediate body portion poled in a second, opposite, direction is conductively mounted to a top side surface of the first active intermediate body portion.
In this embodiment, a plurality of generally parallel, longitudinally extending grooves which extend through the first and second intermediate body portions to expose generally parallel, longitudinally extending portions of the top side surface of the lower body portion located between the strips of conductive material are then formed at spaced locations along a top side surface of the second intermediate body portion. A bottom side surface of an insulative upper body portion is then conductively mounted to the top side surface of the second intermediate body portion. In a particular aspect of this embodiment of the invention, a controller which controls the application of voltage to the first and second intermediate body portions may then be mounted to the plurality of conductive pins projecting from the bottom side surface of the lower body portion.
In yet another embodiment, the present invention is of a drop-on-demand ink jet printhead comprised of a channel array having a plurality of ink-carrying channels which extend rearwardly from a front side surface thereof, piezoelectric actuation means acoustically coupled to each of the plurality of ink-carrying channels and thermoelectric temperature control means thermoconductively mounted to a top side surface of the channel array. In one aspect thereof, the thermoelectric temperature control means is comprised of a plurality of n-type and p-type thermoelectric carriers, each having a lower side surface thermoconductively mounted to the top side surface of the channel array, and a cover plate constructed of a thermally conductive material
and having a bottom side surface thermoconductively mounted to a top side surface of each of the plurality of n-type and p-type thermoelectric carriers.
In an alternate aspect thereof, the thermoelectric temperature control means is comprised of a first plurality of 5 electrically conductive strips formed on the top side surface of the channel array and a plurality of thermoelectric carrier pairs, each comprised of an n-type thermoelectric carrier and a p-type thermoelectric carrier, thermoconductively mounted to the top side surface of the channel array such 10 that each of the thermoelectric carrier pairs is in electrical contact with a corresponding one of the plurality of conductive strips. A lower side surface of a thermally conductive cover plate is thermoconductively mounted to each one of the n-type and p-type thermoelectric carriers and a second 15 plurality of electrically conductive strips are formed on the lower side surface of the cover plate such that each one of the second plurality of electrically conductive strips electrically contacts the n-type thermoelectric carrier of a first thermoelectric carrier pair and the p-type thermoelectric 2Q carrier of a second thermoelectric carrier pair. Means for serially connecting the plurality of thermoelectric carrier pairs to a power source are also provided.
In an alternate embodiment thereof, the channel array for the ink jet printhead may be comprised of a lower body 25 portion having a plurality of conductive sections mounted to a top side of the lower body portion and a corresponding plurality of conductive pins projecting from a bottom side of the lower body portion. Each of the conductive sections is electrically connected to the corresponding one of the con- 30 ductive pins. A bottom side surface of each one of a plurality of generally parallel, longitudinally extending first intermediate body portions, each formed of an active piezoelectric material poled in a first direction parallel to the top side surface of the lower body portion, is conductively mounted 35 to a portion of the top side surface of the lower body portion. A bottom side surface of each one of a plurality of generally parallel, longitudinally extending second intermediate body portions, each formed of an active piezoelectric material poled in a second direction opposite to the first direction, is 40 conductively mounted to a top side surface of a corresponding one of the first intermediate body portions. A bottom side surface of an insulative upper body portion is then conductively mounted to a top side surface of each of the plurality of second intermediate body portions. In a particular aspect 45 of this embodiment of the invention, a controller which controls the application of voltage to the first and second intermediate body portions may then be mounted to the plurality of conductive pins projecting from the bottom side surface of the lower body portion. 50
In yet another embodiment, the present invention is of a method of manufacturing a drop-on-demand ink jet printhead in which thermally conductive lower and upper body portions of a channel array are provided. Thermoelectric temperature control means are mounted to a top side surface 55 of the upper body portion and the lower and upper body portions mated to form a channel array having a spaced series of internal ink-carrying channels which extend rearwardly from front side surfaces of the lower and upper body portions. In one aspect thereof, thermoelectric temperature 60 control means are mounted to the top side surface of the upper body portion by providing a plurality of n-type and p-type thermoelectric carriers, thermoconductively mounting a bottom side surface of each one of the plurality of n-type and p-type thermoelectric carriers to the top side 65 surface of the upper body portion and thermoconductively mounting a bottom side surface of a thermally conductive
cover plate to the top side surface of each one of the plurality of n-type and p-type thermoelectric carriers.
In a further aspect thereof, the bottom side surface of each one of the plurality of n-type and p-type thermoelectric carriers are mounted to the top side surface of the upper body portion by forming a first plurality of electrodes on the top side surface of the upper body portion and electrically connecting an n-type thermoelectric carrier and a p-type thermoelectric carrier with each one of the first plurality of electrodes. The bottom side surface of the cover plate is then thermoconductively mounted to the top side surface of each one of the plurality of n-type and p-type thermoelectric carriers by forming a second plurality of electrodes on the bottom side surface of the cover plate and electrically connecting each one of the second plurality of electrodes with an n-type thermoelectric carrier and a p-type thermoelectric carrier.
In still further aspects thereof, third and fourth plurality of electrodes may be respectively formed on the top side surface of the channel array and the bottom side surface of the cover plate. The third plurality of electrodes extend to a rear edge of the top side surface and the fourth plurality of electrodes extend to a front edge of the bottom side surface. A second plurality of thermoelectric carriers are then mounted on the top side surface such that a single one of the second plurality of thermoelectric carriers is electrically connected with one of the third plurality of electrodes.
In another embodiment, the present invention is a method of manufacturing a drop-on-demand ink jet printhead in which thermally conductive lower and upper body portions of a channel array are provided. A first plurality of electrodes are formed on a top side surface of the upper body portion array and a bottom side surface of the upper body portion is mated with a top side surface of the lower body portion to form a channel array having a spaced series of internal ink-carrying channels which extend rearwardly from front side surfaces of the lower and upper body portions. Thermoelectric temperature control means, which includes means for heating and cooling the channel array, are then mounted to the top side surface of the upper body portion by electrically connecting it with the first plurality of electrodes formed on the top side surface of the channel array. In one aspect thereof, the thermoelectric temperature control means is electrically connected with the first plurality of electrodes by providing a plurality of n-type and p-type thermoelectric carriers and thermoconductively mounting bottom side surfaces of each one of the plurality of n-type and p-type thermoelectric carriers to the top side surface of the upper body portion such that an n-type thermoelectric carrier and a p-type thermoelectric carrier are electrically connected with each one of the first plurality of electrodes. A bottom side surface of a thermally conductive cover plate is then thermoconductively mounted to the top side surface of each one of the plurality of n-type and p-type thermoelectric carriers. The plurality of n-type and p-type thermoelectric carriers are then serially connected to a power source such that application of a first current causes the plurality of n-type and p-type thermoelectric carriers to cool the channel array by transferring heat from the channel array to the cover plate while application of a second, reverse, current causes the plurality of n-type and p-type thermoelectric carriers to heat the channel array by transferring heat from the cover plate to the channel array.
In further aspects thereof, a second plurality of electrodes are formed on the bottom side surface of the cover plate, again for electrical connection with n-type and p-type thermoelectric carriers, a third plurality of electrodes are formed
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on the top side surface of the upper body portion for electrical connection with respective single ones of a second plurality of thermoelectric carriers thermoconductively mounted on the top side surface and a fourth plurality of electrodes are formed on the bottom side surface of the cover 5 plate, again for electrical connection with respective single ones of the second plurality of thermoelectric carriers. The third plurality of electrodes are formed on the top side surface of the upper body portion prior to the mating of the upper and lower body portions and preferably extend to a 10 rear edge of the top side surface of the upper body portion where they are electrically connected to the power source while the fourth plurality of electrodes extend to a front edge of the bottom side surface of the cover plate, again where they are electrically connected to the power source. 15
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a perspective view of a lower body portion of a drop-on-demand ink jet printhead;
FIG. IB is a cross-sectional view taken along lines IB—IB of FIG. 1A which illustrates the structure for interconnecting the ink jet printhead with an associated drive system;
FIG. 2 is a perspective view of the lower body portion of 25 FIG. 1A after first and second intermediate body portions have been conductively mounted thereto;
FIG. 3 is a perspective view of the lower and first and second intermediate body portions of FIG. 2 after a series of generally parallel, longitudinally extending grooves have 30 been formed therein;
FIG. 4 is a perspective view of the grooved lower and first and second intermediate body portions of FIG. 3 after an upper body portion has been conductively mounted thereto to form a channel array for an ink jet printhead;
FIG. 5 is a perspective view of the channel array of FIG.
4 after a series of conductive strips have been mounted to a top side surface thereof;
FIG. 6 is a perspective view of the channel array of FIG. 40
5 after a series of thermoelectric carriers are mounted to the top side surface thereof;
FIG. 7 is a perspective view of a lower side surface of a cover plate for the thermoelectric carriers of FIG. 6;
FIG. 8 is a perspective view of a fully assembled ink jet 45 printhead constructed in accordance with the teachings of the present invention and having thermoelectric temperature control means incorporated therein;
FIG. 9 is an enlarged partial cross-sectional view taken along lines 9—9 of FIG. 8 and illustrating the ink-carrying 50 channels and associated piezoelectric sidewall actuators for the ink jet printhead of FIG. 8; and
FIG. 10 is an enlarged cross-sectional view taken along lines 10—10 of FIG. 8 and illustrating the thermoelectric carriers of FIG. 8.
DETAILED DESCRIPTION
Referring first to FIG. 1A, a lower body portion 10 of an ink jet printhead 12 interconnectable with an associated 60 drive system from a lower side thereof and having thermoelectric temperature control means 11 mounted to a top side surface thereof may now be seen. The lower body portion 10 includes a base portion 14 formed from a block of patternable insulative material, for example, a block of fotoceram 65 material. Formed on a top side surface 14a of the base portion 14 are a series of generally parallel, longitudinally
extending strips 16, each formed of a conductive material such as metal. As will be more fully described below, each strip 16 provides an electrical connection between an external drive system and a sidewall actuator for the ink jet printhead 12. Formed along each strip 16 is a metal plated aperture or via 18 which extends from the top side surface 14a, where it is electrically connected with the corresponding strip 16, to a bottom side surface Mb of the lower body portion 10 where it is electrically connected with a corresponding conductive pin 20. Preferably, the vias 18 are formed in a staggered pattern which produces a contact pitch easy to interconnect therewith. Furthermore, it is contemplated that all of the vias 18 may be formed in the front end of the printhead 12 so that the rear end may be used to form a manifold and internal conduit for supplying ink to the printhead 12.
As will be more fully described below, the pins 20 are used to interconnect one side of the ink jet printhead 12 with a drive system (not visible in FIG. 1A) for applying voltages to selected piezoelectric sidewall actuators of the ink jet printhead 12 to cause the deflection of the selected sidewall actuators into an ink-carrying channel partially defined by the selected sidewall actuators, thereby imparting a compressive pressure pulse capable of initiating the ejection of a droplet of ink therefrom.
Referring next to FIG. IB, a cross-section taken across line IB—IB of FIG. 1A illustrates the electrical interconnection of a conductive strip 16 with a corresponding conductive pin 20. As may now be seen, each conductive pin 20 is insertably mounted in a corresponding aperture 18, for example, using a soldering process, such that each pin 20 engages conductive plate 15 formed along an inner side surface of the corresponding aperture 18 and electrically connected to the corresponding conductive strip 16. In this manner, each pin 20 is electrically connected to a corresponding strip 16 of conductive material.
Referring next to FIGS. 1A and 2-4, a method of manufacturing a channel array 45 for the ink jet printhead 12 will now be described in greater detail. Starting with the lower body portion 10, a first intermediate body portion 22 constructed of an active piezoelectric material, for example, lead zirconate titante (or "PZT"), poled in a first direction 23 generally parallel to the lower body portion 10, and having first and second layers 26, 28 of a conductive material, for example, metal, mounted to top and bottom side surfaces 22a and 22b, respectively, is aligned, mated and conductively bonded, for example, using a conductive adhesive (not shown), for example, conductive epoxy, such that the conductive layer 28 is conductively mounted to the conductive strips 16. Next, a second intermediate body portion 30 constructed of an active piezoelectric material, for example, PZT, poled in a second direction 32, opposite to the first direction 23 but also parallel to the lower body portion 10, and having first and second layers 34, 36 of a conductive material, for example, metal, mounted to top and bottom side surfaces 30a and 30b, respectively, is aligned, mated and conductively bonded, again using a conductive adhesive (not shown) such as conductive epoxy, to the top side surface 22a of the first intermediate body portion 22.
Referring next to FIG. 3, a series of longitudinally extending, generally parallel grooves 38 are formed in the channel array 45, most commonly, using a conventional diamond sawing process. Preferably, each groove 38 should be formed such that it extends through the conductive layer 34, the second intermediate body portion 30, the conductive layer 36, the conductive layer 26, the first intermediate body portion 22, the conductive layer 28 and partially through the
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