WO1999011461A1

WO1999011461A1 - Integrated head assembly for an ink jet printer

Info

Publication number: WO1999011461A1
Application number: PCT/US1998/016106
Authority: WO
Inventors: Andreas Bibl; Mats G. Ottosson; Deane A. Gardner; John A. Higginson; Charles R. Griggs
Original assignee: Topaz Technologies, Inc.
Priority date: 1997-08-29
Filing date: 1998-07-31
Publication date: 1999-03-11
Also published as: AU8765398A; WO1999011461A8

Abstract

A print head for a drop on demand ink jet printer comprising a support (105) having an integrated heater (107) disposed thereon. Affixed to the support is a plate (110, 115) which covers the ink channels (120, 125) of a piezoelectric actuator (29). The actuator and plate each have an electrode (24, 112, 117) that are in electrical communication with each other. The actuator has a plurality of addressable electrodes (22, 60) that can have an electrical drive signal applied thereto. The electrical drive signal deforms the individual ink channels of the actuator, which expels ink droplets.

Description

DESCRIPTION

Integrated Head Assembly For An Ink Jet Printer

Background Of The Invention

1. Field of the Invention This invention relates generally to the field of ink jet printers and more specifically relates to integrated head assemblies for use in piezoelectric ink jet printers.

2. Description of the Prior Art

Ink jet printers, and more particularly, drop-on-demand ink jet print heads having a piezoelectric transducer actuated by electrical signals, are known in the art. Typical print heads consist of a transducer mechanically coupled to an ink chamber, wherein the application of an electrical signal to the transducer material causes the transducer to deform in shape or dimension within or into the ink chamber, thereby resulting in the expulsion of ink from an ink chamber orifice. One disadvantage of prior art print head structures is that they are relatively large in overall dimension, and thus cannot be placed together into a densely packed array. This reduces available output dot density, which will decrease the overall output definition of a printer. Another disadvantage with prior art devices is that the large number of components in these devices tends to increase the costs and difficulty of manufacture. Further, the prior art structures, when placed next to each other within an array to create a multi-channel print head, tend to produce undesirable "crosstalk" between adjacent ink chambers, which interferes with the accurate ejection of ink from the print head.

Print heads can be constructed of many different materials. One such material is piezoelectric material ("PZT") . An example of a print head constructed of PZT is disclosed in co-pending U.S. Application Serial No. 08/703,924, entitled Ink Jet Print Head Apparatus, and assigned to the same assignee as the present invention. The disclosure of U.S. Application Serial No. 08/703,924 is incorporated herein by reference in its entirety.

One factor affecting the performance of an ink jet printer is temperature. The viscosity of the inks used in ink jet printers vary as a function of their temperature. Furthermore, print heads that are constructed of poled PZT increase in temperature as electrical stimuli are applied thereto. This increase in temperature affects the performance of the PZT and also affects the viscosity of the ink. In addition, print heads like those disclosed in Application Serial No. 08/703,924 have the ability to eject ink from specific (i.e., individually addressable) ink channels. The portion of the PZT in the vicinity of the channels that are firing increase in temperature while the portion of the PZT in the vicinity of the channels that are not firing do not have as great an increase in temperature. This results in uneven temperature along the PZT, which results in varying ink viscosities, which can degrade print quality. Thus, it would be desirable to control the temperature of the print head so that it remains constant and predictable throughout the entire individual print head and among all of the print heads used in a single printer.

One factor in the quality of a printed image is the number of ink dots that can be applied to a given area of the medium. In general, the greater the number of ink dots per unit area that can be applied to the medium, the higher the quality of the image that will be created. Thus, it would be desirable to pack as many ink channels from a print head into as small an area as possible.

In general, images are created on a medium by applying four different colored "dots" thereon. The "dots" are created with inks of four different colors. In general, these inks are the colors black, cyan, magenta, and yellow. Images are created on the medium by moving a carriage that contains heads with nozzles across the medium, thereby creating an image swath across the medium. When the image swath has been applied to the medium, the medium is advanced and the carriage applies another image swath. The successive image swaths must be applied such that the entire image printed on the medium is unified together. Thus, the individual image swaths must be stitched together in a fashion that provides a unified high- resolution image.

Therefore, there is a need in the art for an integrated print head assembly that can be advantageously and economically manufactured, pack a large number of ink channels for a given area, provide excellent stitching of image swaths, and that has integrated temperature controls.

Summary Of The Invention

A new type of head assembly for a drop-on-demand ink jet printer is disclosed. The print head of the present invention includes a support comprising an elongated member. First and second resistive elements that extend substantially the entire length of the support are disposed on opposing faces of the support . A first ink channel cover is laminated to the support such that it covers a portion of the first resistive element.

A second ink channel cover is laminated to the support such that it covers a portion of the second resistive element.

A first actuator affixed to the first ink channel cover and a second actuator is affixed to the second ink channel cover. Each of the first and second actuators comprise an ink supply edge, an ink ejection edge, an ink channel side and an air channel side. Each of the first and second actuators comprise a plurality of ink channels. Each of the plurality of ink channels is defined by walls formed in the first and second actuators and by either the first or second ink channel cover. The plurality of first ink channels are linearly adjacent and substantially parallel to each other and extend from the ink supply edge to the ink ejection edge.

The first and second actuators also comprise a plurality of addressable electrodes which are formed on the air channel side. The plurality of addressable electrodes receive electrical drive signals which cause the poled PZT material to deform the ink channels in the desired direction. The first and second actuators further comprise a metallization layer which is substantially contiguous with the air channel side thereof. In addition, first and second wings are laminated to the air channel sides of the first and second actuators.

The support, first and second ink channel covers, first and second actuators, and first and second wings are laminated together such that a first planar surface is created which exposes the ink ejection edge of the first and second actuators. In preferred embodiments, the first planar surface has a nozzle plate affixed thereto. Each nozzle or orifice of the nozzle plate is aligned to be coaxial with one of the plurality of ink channels. In addition, the support, first and second ink channel covers, and first and second actuators are laminated together such that a second planar surface is created which exposes the ink supply edge of the first and second actuators. In preferred embodiments, an ink fill gasket having a plurality of apertures is affixed to the second planar surface. The ink fill gasket is aligned such that each aperture formed therein is coaxial with one of the plurality of ink channels.

In an aspect of the present invention, a electrically conductive first heating clip is placed on a first end of the support and a conductive second heating clip is placed on a second end of the support. First and second heating clips complete an electrical circuit between the first and second resistive elements. When electrical current is applied to this circuit, the first and second resistive elements create heat, which acts to maintain the first and second actuators at a constant temperature.

In another aspect of the present invention, the first and second ink channel covers have a common electrode disposed thereon. The common electrodes are disposed such that they are in electrical communication with the metallization layers disposed on the air channel side of the first and second actuators .

In another aspect of the present invention, the metallization layer on the first and second actuator extends over the ink channel side thereof, around the ends thereof, and onto a portion of the air channel side thereof. The portion of metallization layer that lies on the air channel side forms a grounding electrode that allows the metallization layer to be placed in electrical communication with a constant electrical potential such as ground.

In another aspect of the present invention, an integrated head assembly is disclosed. The integrated head assembly of the present invention comprises an integrated actuator assembly which is affixed to a reservoir. The reservoir is completely sealed and comprises a plenum having a cover installed thereon.

Within the plenum is a reservoir filter which prevents particulate matter from entering into the ink channels of the actuator assembly. Between the reservoir and the actuator assembly can be a fill block that acts as an interface between the ink reservoir and the head assembly.

In another aspect of the present invention, a snap-on head assembly for mounting on a printer carriage is disclosed. The snap-on print head comprises a plurality of print heads which are disposed substantially parallel to each other. The print heads mounted on the snap-on print head are also disposed such that consecutive ones of the plurality of print heads descend with respect to a perpendicular plane common to all of said plurality of print heads. The above and other preferred features of the invention, including various novel details of implementation and combination of elements will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular methods and circuits embodying the invention are shown by way of illustration only and not as limitations of the invention. As will be understood by those skilled in the art, the principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.

Brief Description Of The Drawings

Reference is made to the accompanying drawings in which are shown illustrative embodiments of aspects of the invention, from which novel features and advantages will be apparent.

Fig. 1 is a perspective view of the components that comprise an integrated actuator assembly of a presently preferred embodiment of the present invention.

Fig. 2 is a cross-sectional view of the components that comprise an integrated actuator assembly of a presently preferred embodiment of the present invention with the components shown partially assembled.

Fig. 3 is a cross-sectional view of an assembled integrated actuator assembly of a presently preferred embodiment of the present invention.

Fig. 4a is a perspective view of an assembled integrated actuator assembly of a presently preferred embodiment.

Fig. 4b is an enlarged perspective view of a portion of the assembled integrated actuator assembly shown in Fig. 4a. Fig. 4c is a top view of an assembled integrated actuator assembly of a presently preferred embodiment.

Fig. 5 is a front view of a portion of a presently preferred integrated actuator assembly without a nozzle plate installed thereon that shows the arrangement of ink channels. Fig. 6 is a front view of a portion of the structure of a sheet of transducer material for an array of ink channels according to the embodiment of the present invention.

Fig. 7 is a perspective view of the sheet of transducer material shown in Fig. 6.

Fig. 8 is a top view of a wafer of PZT material that has ink channels cut therein prior to being diced into an actuator.

Fig. 9 is a top view of a wafer of material that will be diced into ink channel covers. Fig. 10 is a bottom view of a wafer a PZT material that has air channels cut therein and a wafer of material affixed thereto.

Fig. 11 is a top view of a presently preferred fill block constructed in accordance with the present invention. Fig. 11a is a cross-sectional view of the fill block shown in Fig. 11.

Fig. 12 is a side view of a presently preferred ink reservoir constructed in accordance with the present invention.

Fig. 13 is a perspective view of the components that comprise the presently preferred ink reservoir of the present invention.

Fig. 14 is a cross-sectional view of a plenum of a preferred embodiment of the present invention.

Fig. 15 is a top view of a plenum of a preferred embodiment of the present invention.

Fig. 16 is a first perspective view of an integrated ink jet print head constructed in accordance with the present invention.

Fig. 17 is a second perspective view of an integrated ink jet print head constructed in accordance with the present invention.

Fig. 18 is a side view of an integrated ink jet print head constructed in accordance with the present invention. Fig. 19 is a perspective view of an integrated ink jet print head sled assembly having multiple print heads that is constructed in accordance with the present invention.

Fig. 20 is a perspective view of the components that comprise a snap-on integrated ink jet print head assembly having multiple print heads that is constructed in accordance with the present invention.

Fig. 21 is a top view of a snap-on head integrated ink jet print head assembly used to offset the print heads which is constructed in accordance with the present invention.

Fig. 22 is a simplified view of a single exemplary swath of or print output in accordance with an aspect of the present invention.

Fig. 23 is a perspective view showing one method of electrically affixing a flex circuit or cable to an integrated actuator assembly of the present invention.

Fig. 24 is a side view of an assembled integrated actuator assembly showing how various electrodes on an actuator are electrically connected to a flex circuit or cable.

Detailed Description Of The Drawings

Turning to the figures, the presently preferred apparatus and methods of the present invention will now be described.

With reference to Figs. 1-7, the arrangement of the components that form a single ink jet integrated actuator assembly 100 of the present invention are shown. Integrated actuator assembly 100 comprises a support 105 comprising an elongated member. Support 105 is preferably constructed of a material that is stiff, has similar coefficients of thermal expansion to the coefficients of PZT, has a high modulus of elasticity, and is highly thermally conductive. In the presently preferred embodiment, support 105 is a six-sided

(i.e., a top surface, a bottom surface, first and second side surfaces, and two end surfaces) elongated member constructed of aluminum nitride. However, other materials with the above- described characteristics could provide satisfactory results. A resistive element 107 is placed on the first and second side surfaces of support 105. In the presently preferred embodiment, resistive element 107 comprises a layer of nickel- chrome alloy that is sputtered on the first and second side surfaces of support 107 and that has a thickness of approximately one thousand Angstroms. Resistive element 107 preferably has a resistance of between ten to two-hundred Ohms. Due to the thinness of the resistive element 107, it is only shown in Figs. 2, 4a, and 4b. As will be discussed below, the resistive element 107 that is sputtered onto support 105 is used to maintain the temperature of the actuators 120, 125 of the integrated actuator assembly 100 at a substantially constant temperature. Bonded to support 105 is a first ink channel cover 110 and a second ink channel cover 115. The method of bonding the support 105 to first ink channel cover 110 and second ink channel cover 110 is disclosed in co-pending U.S. Application Serial No. 08/920,496 entitled Method And Apparatus For Providing Thin Films, filed on August 29, 1997, (Lyon & Lyon Docket Number 227/210). The disclosure of U.S. Application Serial No. 08/920,496 (Lyon & Lyon Docket Number 227/210) are incorporated herein by reference in its entirety. First ink channel cover 110 and second ink channel cover 115 close off the lengthwise lateral opening in the ink channels 29 disposed in the first actuator 120 and second actuator 125. Details of the first actuator 120 and second actuator 125 are discussed below. First ink channel cover 110 and second ink channel cover 115 are also preferably constructed of aluminum nitride. However, in the presently preferred embodiments, first ink channel cover 110 and second ink channel cover 115 are thinner than the support 105. For reasons that will be discussed below, one side of each of the first ink channel cover 110 and of the second ink channel cover 115 is metallized with gold, thereby forming a first common electrode 112 and a second common electrode 117, respectively (see Fig. 2) . First common electrode 112 and second common electrode 117 are applied to the first ink channel cover 110 and to the second ink channel cover 115 by sputtering a layer of gold thereon that is approximately one micron thick. Due to the thinness of the first common electrode 112 and the second common electrode 117, they are only shown in Fig. 2.

A first actuator 120 is bonded to first ink channel cover 110, and a second actuator 125 is bonded to second ink channel cover 115. A detailed description of the first actuator 115 and of the second actuator 120 is provided with reference to Figs. 6 and 7. First actuator 120 and second actuator 125 have multiple ink channels 29 in the array that are linearly adjacent and substantially parallel to its neighboring ink channel 29 (See Figs. 4 and 5) . As will be discussed below, a single block, sheet, or wafer of piezoelectric material 21 is preferably used to manufacture the actuator portion of the array of ink channels. Figs. 6 and 7 show a portion of piezoelectric sheet 21 into which a series of substantially identical and generally parallel ink channels 29 have been cut in a first face 51 of sheet 21.

Directly opposite from the first face 51 of sheet 21, a series of substantially identical and generally parallel air channels 50 are cut into a second face 53, with each air channel 50 inter-spaced between a pair of adjacent ink channels 29. During the manufacturing process, the air channels 50 are initially cut to a depth approximately halfway along the cut depth of each ink channel 29, to approximately the relative distance marked by dashed lines 54 in Fig. 6. A metallization layer 24 is then deposited onto the inner surfaces and interior end of each ink channel 29, and over the first face 51 of sheet 21. Metallization layer 24 can be deposited by sputtering, or by electroplating. In the presently preferred embodiment, the metallization layer 24 comprises gold. Metallization layer 24 forms a continuous electrical conductor from ink channel to ink channel, and will preferably be maintained at ground potential. Another metallization layer 22 (which will define the addressable electrodes 60) is deposited with the same method onto the inner surfaces and interior end of each air channel 50 (up to and including the surface marked by dashed lines 54) and over the second face 53 (Fig. 7) of sheet 21, with the metallization layer 22 initially connected from air channel to air channel at the bottom 54 of each air channel 50. An electrode-separation channel 52 (extending beyond dashed lines 54) is then cut into each air channels 50 using precision micromachining tools, which also breaks the connection between the individual metallization layers 22 within each air channel 50. Thus, the metallization layer 22 for each addressable electrode 60 is a discrete element, and the addressable electrodes 60 can then be separately and selectively connected to an electrical drive signal source. The type and shape of the waveforms of the desired electrical drive signals that are applied to the addressable electrodes 60 are disclosed in co- pending U.S. Application Serial No. 08/808,608, the disclosure of which is incorporated herein in its entirety by reference. As discussed in co-pending U.S. Application Serial No. 08/808,608, the electrical drive signals that are applied to the addressable electrodes 60 act to deform the material comprising the first actuator 120 and second actuator 125, thereby causing the selected channels 29 to draw ink from a reservoir (described below) and eject ink droplets therefrom. Exemplary types of deformations include moving the inner walls 34 of the channels 29 closer together (i.e., compressing the longitudinal axis of the channel 29) or farther apart (i.e., expanding the longitudinal axis of the channel 29) .

As will be discussed below, each of the addressable electrodes 60 are connected to a drive signal source by discrete circuit traces on a flexible circuit assembly or cable (known in the electronics art as a "flex circuit"). These connections can be seen most clearly in Fig. 24. The electrode-separation channel 52 significantly extends the cut gap created by the combined cut depths of the air channel 50 and the electrode-separation channel 52 toward the first face 51 of piezoelectric sheet 21.

Because each integrated head assembly of the present invention utilizes two separate actuators 120, 125 for firing ink droplets onto a print medium, the number of ink droplets fired for a given printed image swath is increased. As discussed, this is highly desirable because it increases the quality of the printed image. This is because the first actuator 120 and second actuator 125 are preferably mounted such that their channels 29 are disposed at a one-half pitch difference between them, which is indicated by arrows 80 in Fig. 5. This means that center of an ink channel 29 located in the first actuator 120 is offset by a length of one-half of the channel-to-channel pitch with respect to an ink channel located in the second actuator 125. It is noted that the distance 80 shown in Fig. 5 shows the offset between the center of an air channel 50 located in first actuator 120 and center of an air channel 50 located in second actuator 125. The offset 80 between air channels 50 and ink channels 29, is substantially the same.

The first ink channel cover 110 and second ink channel cover 115 are bonded to the first actuator 120 and the second actuator 125, respectively, such that the first common electrode 112 disposed on the first ink channel cover 110 and the second common electrode 117 disposed on the second ink channel cover 115 are in electrical communication with the metallization layer 24 disposed on the first actuator 120 and second actuator 125, respectively. As discussed, the metallization layer 24 that is disposed on first actuator 120 and second actuator 125 is preferably maintained at ground potential. However, even with current manufacturing techniques, it is very difficult to apply metallization layers on a surface that has deep channels and vertical walls like those present in first actuator 120 and second actuator 125. Because of this, the metallization layer 24 can have varying thickness, and could even have gaps where no metal is present. This makes maintaining metallization layer 24 at a constant potential very difficult because, depending upon how thin the metallization is, there could be electrical resistance or even open circuits that exist from one end of the metallization layer 24 to the other .

The present invention solves this problem by placing the metallization layer 24 that is on each of the first actuator

120 and the second actuator 125 in electrical contact with the first common electrode 112 and the second common electrode 117, respectively. In the presently preferred embodiment, the first common electrode 112 and second common electrode 117 are in electrical communication with ground, which then places the metallization layer 24 at ground. This minimizes the voltage drop across the entire length of the first and second actuators

120, 125. The presently preferred structures of the actuator assembly 100 that facilitate electrical connection of metallization layer 24 on each of the first actuator 120 and second actuator 125 and the first common electrode 112 and the second common electrode 117 to ground is discussed below with reference to Fig. 24.

A first wing 130 (Figs. 1 and 3) is bonded to the second face 53 of first actuator 120 and a second wing 135 is bonded to second actuator 125. The preferred method of bonding is described in copending U.S. Application Serial No. 08/920,496

(Lyon & Lyon Docket No. 227/210) . First wing 130 and second wing 135 do not cover the entire surface of the second face 53.

This allows access to the addressable electrodes 60. First wing 130 and second wing 135 should be constructed of an inert material that is stiff, is an electrical insulator, is substantially translucent and has a coefficient of thermal expansion similar to poled PZT. In the presently preferred embodiment, the first wing 130 and second wing 135 are constructed of a boro-silicate glass. The translucent characteristic of first wing 130 and the second wing 135 allows the head assembly 100 to be checked for lamination defects after construction.

Due to the arrangement of ink channels 29, air channels 50 and the electrode-separation channels 52, the first actuator 120 and second actuator 125 are flexible in a direction perpendicular to the longitudinal axis of the ink channels 29 grooves. Thus, the first actuator 120 and second actuator 125 can exhibit an "accordion" like flexibility. The first wing 130, in conjunction with the first ink channel cover 110, constrains the flexibility of the first actuator 120. Furthermore, when an individual channel 29 (or any combination thereof) is deformed in a plane transverse to the longitudinal axis of the ink channels 29, the first wing 130 and first ink channel cover 110, by imposing structural stiffness on the overall assembly, assist each other in ensuring that energy created by deforming the channel is directed to ejecting ink droplets and is not wasted in unnecessary movements of the first actuator 120. Likewise, the second wing 135, in conjunction with the second ink channel cover 115, constrains the flexibility of the second actuator 125. The second wing 135 and second ink channel cover 115 also assist each other in ensuring that energy created by deforming the channel is directed to ejecting ink droplets and is not wasted in unnecessary movements of the second actuator 125. Referring to Fig. 2, it is seen that first wing 130 has front portion 131 and a rear portion 136. Second wing 135 has a front portion 136 and a rear portion 134. First actuator 120 has an ink ejection edge 121 and an ink supply edge 119. Second actuator 125 has an ink ejection edge 126 and an ink supply edge 124. First ink channel cover 110 has a front portion 111 and a rear portion 109. Second ink channel cover 115 has a front portion 116 and a rear portion 114. Finally, support 105 has a front portion 106 and a rear portion 104. Integrated actuator assembly 100 is assembled such that it has a first planar surface 140.

With reference to Fig. 2, it is seen that first planar surface 140 comprises front portion 131 of first wing 130, ink ejection edge 121 of first actuator 120, front portion 111 of first ink channel cover 110, front portion 106 of support 105, front portion 116 of second ink channel cover 115, ink ejection edge 126 of seco d actuator 125, and front portion 136 of second wing 135. In addition, integrated actuator assembly 100 is assembled such that it has a second planar surface 145.

With reference to Fig. 2, it is seen that second planar surface 145 comprises ink supply edge 119 of first actuator 120, rear portion 109 of first ink channel cover 110, rear portion 104 of support 105, rear portion 114 of second ink channel cover 115, ink supply edge 124 of second actuator 125, and rear portion 134 of second wing 135. It is noted that due to the extreme thinness of the first common electrode 112, resistive element 107, and second common electrode 117, they are not considered to form a portion of first planar surface 140 or 145, although they do add a de minimus amount of thickness to the integrated actuator assembly 100. After these components have been assembled (the method of assembling these components is discussed in detail below) , the first planar surface 140 and second planar surface 145 are polished with a wafer back-grinding process to form extremely smooth surfaces. Thereafter, the first planar surface has a nozzle plate 150 (see Figs. 1-3) fastened thereto. The presently preferred structure and method of manufacturing the nozzle plate 150 is disclosed in co-pending U.S. Application Serial No. 08/844,244, the disclosure of which is hereby incorporated by reference in its entirety. Nozzle plate 150 comprises a series of orifices or nozzles that are precisely aligned with individual ink channels 29. The nozzles aid in the ejection of ink droplets from the heads, as is described in co-pending U.S. Application Serial No. 08/844,244. When installing the nozzle plate 150 on the first planar surface 140, the nozzles in nozzle plate 150 must be aligned such that they each communicate with individual ink channels 29. Nozzle plate 150 is preferably fastened to first planar surface 140 with epoxy using the method described in co-pending application serial no. 08/920,496 (Lyon & Lyon Docket No. 227/210). It is noted that the surface of nozzle plate 150 which will be laminated to first planar surface 140 has an adhesion-promoting layer applied thereto. Furthermore, the surface of nozzle plate 150 that faces the print media has a thin gold layer either sputtered of electroplated thereon.

As discussed, second planar surface 145 comprises ink channels 29 that are open at the ink supply edge 119 of first actuator 120 and ink supply edge 126 of the second actuator 125. Ink is supplied to the channels 29 from this area. As will be discussed below, ink to be supplied to the ink channels 29 resides in a reservoir (see discussion below) that is fastened to the integrated transducer assembly 100. An ink fill gasket 155 is fastened to the second planar surface 145. Ink fill gasket 155 (Figs. 2, 4a) is used to direct ink from an ink plenum (see discussion below) into each individual channel 29. The ink fill gasket 155 must be porous in that it must allow ink to pass there through. However, ink fill gasket 155 must also have some resistance to permeability so that the ink fill gasket 155 acts to attenuate reflected pressure waves generated by the first actuator 120 and the second actuator 125 that travel therefrom and into the plenum 305 and the adjacent ink channels 29. Thus, ink fill gasket 155 has apertures 160

(See Fig. 1) formed therein that perform these functions. Ink fill gasket 155 must also be highly resistant to heat, as the integrated actuator assembly is assembled at high temperatures. Ink fill gasket 155 must also be constructed of a material which can have apertures 160 etched therein with a laser. In the presently preferred embodiment, ink fill gasket 155 is preferably constructed of polyimide material, which for example 5 is available as Kapton® brand polyimide.

As is seen in Figs. 4a, 4b and 4c, each completed actuator assembly 100 is constructed such that support 105 has a length greater than the first and second wings 130, 135, first and second actuators 120, 125, and first and second ink 0 channel covers 110, 115 of the actuator assembly 100. Thus, support 105 has extensions 106 that extend beyond these components. Extensions 106 serve several purposes. First, extensions 106 make it easier to mount the integrated actuator assembly onto an ink reservoir (which will be discussed below) . 5 Secondly, extensions 106 allow improved access to the resistive elements 107. This allows an electric heating current to be applied to the resistive elements 107. As is best illustrated in Fig. 4c, the first and second wings 130, 135, first and second actuators 120, 125, and first and second 0 ink channel covers 110, 115 have a length "A". As is also best illustrated in Fig. 4c, support 105 has length "B" . Resistive elements 107 extend only slightly less than the length "B". Thus, resistive elements 107 extend beyond the first and second wings 130, 135, first and second actuators 120, 125, and first

25 and second ink channel covers 110, 115, thereby allowing for easy accessibility.

In the presently preferred embodiment, support 105 has a length of approximately 48.6 millimeters, while first and second ink channel covers 110, 115, first and second actuators

30 120, 125 and first and second wings 130, 135 all have a length of approximately 42.6 millimeters. In the presently preferred embodiment, each actuator has one hundred twenty-eight ink channels 29, for a total of two-hundred fifty-six ink channels 29 per actuator assembly 100. Each pair of adjacent ink

35 channels 29 has a center-to-center spacing of approximately 0.282 millimeters (with a tolerance of approximately 0.005 millimeters) .

As discussed above, the support 105 has a resistive elements 107 disposed thereon. Resistive elements 107 are used as a heating element for the integrated actuator assembly 100. Since the viscosity of inks used in ink jet printers varies as a function of their temperatures, when the ink viscosity varies, there can be undesirable variations in the printed image because the same deformation of an ink channel 29 in an actuator will not result in the output of the same volume of ink. Thus, without any temperature control, the ambient temperature of the environment in which the actuator assembly 100 is operating will affect the viscosity of the ink being ejected onto the print medium. Furthermore, as discussed, the first actuator 120 and second actuator 125 generate heat when they are firing ink droplets. This additional heat varies the viscosity of the ink in the channels being fired because the ink is passing directly through the ink channels 29.

In addition, each channel 29 of the first actuator assembly 120 and second actuator assembly 125 is individually addressable via the addressable electrodes 60 located thereon. During printing, some channels 29 may be firing ink droplets while other channels 29 on the same actuator (or on another actuator), will be at idle. The result of this is that different actuators in the same printer (as will be discussed, presently preferred printers have four discrete integrated head assemblies, meaning that there will be eight discrete actuators) can be operating at different temperatures. Furthermore, because different channels 29 of the same actuator can be firing ink droplets at different times, the temperature of an individual actuator can vary along its length (i.e., the temperature of an ink channel 29 at a first end of an actuator may be different from that of an ink channel 29 at the second end of the actuator, or at various points intermediate the two ends. In the presently preferred embodiment, resistive elements 107 comprise a nickel-chrome alloy having a thickness of one thousand Angstroms. They sputtered onto the lengthwise dimensions of the support 105 which face the first ink channel cover 110 and second ink channel cover 115. When the integrated actuator assembly 100 is in use, resistive elements 107 are placed in electrical communication with a current source (not shown) . As will be discussed below, in the presently preferred embodiment, this heating current is delivered to the resistive elements 107 via the flex circuits that are part of the integrated head assembly. When the heating current flows through resistive elements 107, the resistive elements 107 generate heat. As discussed, support 105, first ink channel cover 110, and second ink channel cover 115 are constructed of materials that are very efficient conductors of heat. Thus, when resistive elements 107 generate heat, it is conducted through first ink channel cover 110 to first actuator 120 and through second ink channel cover 115 to second actuator 125. The magnitude of the heating current that is supplied to the resistive elements 107 is chosen such that the heat created by resistive elements 107 raises the temperature of first actuator 120 and second actuator 125 above the ambient temperature. The heating current can be varied so that the temperature can be elevated to a point whereby the viscosity of the ink can be optimized for the particular ink being used.

As is seen in Fig. 4c, support 105 also has grooves 102,

103 cut therein that extend the length of support 105. Grooves

102, 103 abut the edges of support 105 such that when the actuator assembly 100 is constructed, the portions of the first ink channel cover 110 and the second ink channel cover 115 and the walls of grooves 102, 103 form depressed recesses. Grooves 102, 103 act as epoxy moats. Providing epoxy moats allows epoxy that is used to laminate the various components of the actuator assembly 100 to migrate into the grooves 102 as the lamination is taking place. Otherwise, epoxy could migrate to undesirable locations, such as ink channels 29.

With reference to Figs. 8-11, the presently preferred method of assembling the integrated actuator assembly 100 will now be discussed. The first step in manufacturing the integrated actuator assembly 100 of the present invention is to construct a single block, sheet, or wafer of piezoelectric material 150 in the fashion described above. In the presently preferred method of manufacturing the first actuator 120 and second actuator 125, a wafer of PZT material is used. Initially, the ink channels 29 (for ease of understanding, only a representative number of ink channels 29 are shown in Fig. 8) and metallization layer 24 (not shown in Fig. 8) that forms a continuous electrode are fabricated on the PZT wafer. Ink channels 29 are cut into the PZT wafer 150 with micromachining tools. The ink channels 29 are preferably cut such that they extend more than three-quarters of the thickness of the PZT wafer 140. The metallization layer 24 is sputtered onto the PZT wafer 140. After the ink channels 29 and metallization layer 24 are formed, a plate 200 is laminated onto the PZT wafer 150. This lamination is done by applying extremely thin lines of adhesive using the methods disclosed in U.S. Application Serial No. 08/920,496 (Lyon & Lyon Docket No. 227/210) to those portions of the first surface 51 of PZT wafer 150 that are not cut (between the ink channels 29) . Thus, the portion of the first face 51 of the PZT wafer 150 that does not have ink channels cut therein will have adhesive applied thereto. In the preferred embodiment, the adhesive that is used for this application is a highly chemically resistant epoxy. However, other adhesives that can be applied very thinly, have a coefficient of thermal expansion similar to PZT and aluminum nitride and form extremely strong bonds are also acceptable. After applying the adhesive, plate 200 is placed on top of the PZT wafer 150 such that the adhesive, once it is dried and cured, fixes plate 200 to PZT wafer 150. Plate 200 comprises a wafer of material with a series of gold strips 205, 210, 215, 220, 225 applied thereto. Strips 205, 210, 215, 220, 225 are preferably plated or sputtered onto the plate 200. As discussed, in the presently preferred embodiment, the plate 200 will be constructed of aluminum nitride. Gold strips 205, 210, 215, 220, 225 will form the first and second common electrodes 112, 117 when the actuator assembly 100 is complete.

After the plate 200 is laminated onto the PZT wafer 150, the parallel air channels 50 are cut into the opposite face of the PZT wafer 150, as is shown in Fig. 10. As seen in Fig. 6, the parallel air channels 50 are cut such that they extend approximately halfway into the PZT wafer 150. In addition, each air channel 50 is cut such that there is an ink channel 29 disposed immediately adjacent thereto. It is noted, however, that in the presently preferred embodiment, the ink channels 29 extend deeper into the PZT wafer 150 than do the air channels 50. The method of cutting air channels 50 into the PZT wafer 150 is the same as that used for cutting the ink channels 29. However, it is noted that after ink channels 29 are fabricated on the first face 51 of the PZT wafer 150, the PZT wafer 150 is more susceptible to cracking, especially if one were to cut the air channels 50 onto the second face 53 immediately thereafter. One of the benefits to laminating plate 200 to PZT wafer 150 prior to cutting the air channels 50 into the second face 53 of PZT wafer 150 is that it provides mechanical strength that significantly reduces the possibility that the PZT wafer 150 will crack while air channels 50 are being cut therein. After the air channels 50 are cut into the PZT wafer 150, the metallization layer 22 is plated onto the second face 53 (i.e., the side of the PZT wafer 150 having the air channels formed thereon) . As discussed, the preferable method for applying the metallization layer 22 is to sputter an extremely thin layer of gold onto the second face 53. After the metallization layer 22 is applied to the second face 53, the addressable electrodes 60 are formed by cutting electrode-separation channels 52 into each of the air channels 50. Cutting the electrode-separation channels 52 breaks the 5 connection between the individual metallization layers 22 within each air channel 50, thereby forming a plurality of addressable electrodes 60.

After the addressable electrodes 60 are formed on the second face 53 of the PZT wafer 150, the PZT wafer 150/plate

10 200 lamination is diced or "sliced" to provide for individual actuator-ink channel cover assemblies. In the presently preferred embodiment, a single PZT wafer 150 that is bonded to a single plate 200 will result in five (5) actuator-ink channel cover assemblies.

15 A pair of PZT wafer 150/plate 200 laminations are then laminated to the support 105 using the same fastening method as that described in U.S. Patent Application Serial No. 08/920,496 (Lyon & Lyon Docket No. 227/210). Prior to laminating the PZT "wafer 150/plate" 200 laminations to the

20 support 105, the resistive elements 107 are formed thereon. Thus, it is important that the adhesive used to fasten the PZT wafer 150/plate 200 laminations to the support 105 be capable of holding the material that comprises first and second ink channel covers 110, 115 to resistive elements 107.

25 Furthermore, this adhesive must be highly resistive to heat, as the purpose of resistive elements 107 is to produce elevated temperatures. This adhesive must also have the ability to deform in shape without cracking or otherwise failing.

The next step in manufacturing an actuator assembly 100

30 of the present invention is to bond the first wing 130 to the second face 53 of first actuator 120 and the second wing 135 to the second face 53 of second actuator 125. Preferably, the method disclosed in U.S. Application Serial No. 08/920,496

(Lyon & Lyon Docket No. 227/210) is used to fasten first wing 130 and second wing 135 to first actuator 120 and second actuator, respectively.

Once the first and second wings 130, 135, first and second actuators 120, 125, first and second ink channel covers 110, 115 and support 105 are bonded together, the first planar surface 140 and second planar surface 145 are polished using a wafer back grinding process. Care must be taken when polishing the second planar surface 145 to ensure that the grooves 102, 103 still exist after polishing. Then, the nozzle plate 150 is installed on the first planar surface 140 and the ink fill gasket 155 is installed on the second planar surface.

Once the integrated actuator assemblies 100 are complete, a fill block 250 is affixed over the ink fill gasket 155. Fill block 250 is discussed with particular reference to Figs. 11 and 11a. Fill block 250 comprises a series of openings 255 that in the preferred embodiment have a semi-rectangular shape. This is shown in Fig. 11. In the presently preferred embodiment, the fill block 255 is substantially the same length as the support 105. Openings 255 correspond to the apertures 160 formed in ink fill gasket 155 and are used by the manufacturer to precisely align the reservoir 300 (discussed below) with the apertures on the ink fill gasket 155. As is seen in Fig. 11a, which is a cross-sectional view of the fill block 250, each opening 255 is separated from the adjacent opening 255 by a web 260. Webs 260 are thin bridges that act to maintain the position of the first opposing edge 270 of the fill block 250 with respect to a central support 272 when the first and second actuators 120, 125 are being deformed (i.e., firing ink droplets) . In addition, webs 260 act to maintain the position of the second opposing edge 275 of the fill block 250 to the central support 272 when the first and second actuators 220, 225 are being deformed (i.e., firing ink droplets). Webs 260 are preferably thin, i.e., they do not extend the entire height of the fill block 250, to minimize the acoustic coupling between the ink channels 29. In the presently preferred embodiment, fill block 250 is constructed of a liquid crystal polymer such as Vectra A530 available from Hoechst Celanese Corporation. However, other materials that have a thermal coefficient of expansion that is similar to PZT and has a low glass transition temperature can provide satisfactory results.

With reference to Figs. 12-13, the ink reservoir apparatus 300 of the present invention will now be discussed. The reservoir comprises a plenum 305 that holds ink prior to being drawn through the fill block 250 and into the ink channels 29 by the first and second actuators 120, 125 or being pumped by a pump. Reservoir 300 also comprises a cover 310 that is affixed to the plenum 305. Cover 310 comprises an ink supply neck 315 that comprises an extended portion 320 and a locking mechanism 325 such as a luer lock. Ink is supplied to ink supply neck 315 via an ink supply tubes or pipe (not shown) that is fastened to the locking mechanism 325, which thereby creates a sealed ink supply system is created. Thus, the entire length of the ink supply path, from the ink bottles, through the ink supply tube or pipes, and into ink supply neck 315 is sealed. This prevents ink leakage and allows pressure differences to be created along the ink supply path, thereby causing ink to move from one location to another. In addition, as will be seen below, the integrated head assemblies 400 (discussed below) are installed in a snap-on head assembly 500 (also discussed below) . The snap-on head assembly or "sled" 500 will be attached to the print head carriage and thereby will move linearly across the print medium during printing operations. The ink that is in the plenum while the head 400 is moving will be moving, i.e., head sled 500 movements cause ."sloshing" of the ink within the reservoir assembly 300, which can cause undesirable pressure variations within the reservoir. Reservoir assembly 300 can act as a buffer stage that minimizes the pressure variations as a function of head sled 500 travel. There are additional pressures which are caused by ink being drawn into the ink channels. Finally, acoustic pressure waves are reflected toward ink fill gasket 155 from ink channels 29. The relative outward deformation of actuators 120, 125 (resulting in an increase in the volume of an ink channel 29) 5 acts to draw ink into the ink channels 29 and the relative inward deformation of the actuators 120, 125 causes the ink to be ejected onto the printing medium. Because the ink supply path is sealed, driving the first and second actuators 120, 125 to fire ink droplets, and therefore drawing ink from the plenum

10 305, creates a pressure differential between the interior of the plenum and the operating environment. Thus, the plenum 305 must be constructed to handle this pressure differential. In the presently preferred embodiment, plenum 305 is constructed of injection molded plastic. Such a plastic can be a liquid

15 crystal polymer such as Vectra A530 available from Hoechst Celanese Corporation.

Reference is now made to Fig. 13, in which additional details of the ink reservoir apparatus 300 are shown. A plurality of apertures 330 are disposed in a cover 310. In the

20 presently preferred embodiment, two apertures 330 are provided. Inserted in apertures 330 are a first ink level detection electrode 335 and a second ink level detection electrode 340. The first ink level detection electrode 335 comprises a lead 337 and a terminal 339. The second ink level detection

25 electrode 340 comprises a lead 342 and a terminal 344. In the presently preferred embodiments, leads 337, 342 and terminals 339, 344 are formed from integral electrically conductive material. First ink level detection electrode 335 and the second ink level detection electrode 340 are inserted in

30 apertures 330 such that terminals 339 and 340 are exposed so that they can be placed in electrical communication with an external device (not shown) that can use the electrical signals created by the first ink level detection electrode 335 and second ink level detection electrode 340 to determine whether

35 ink is present in the plenum 305. Ink level detection is accomplished by placing low level current through either the first ink level detection electrode 340 or the second ink level detection electrode 345. Because the inks used are typically electrically conductive, they complete an electrical circuit between the first ink level detection electrode 340 and the second ink level detection electrode 345. When the ink in the plenum 305 drops to a level in which it no longer is in contact with either the first ink level detection electrode 340 or the second ink level detection electrode 345, an open circuit is created. This open circuit is detected by an external system (not shown) that sends a signal to a pumping mechanism (not shown) , which then acts to pump more ink into the reservoir 300.

In addition, the first ink level detection electrode 335 and the second ink level detection electrode 340 must be installed such that the ink reservoir 300 remains sealed. Thus, prior to placing the first ink level detection electrode 335 and second ink level detection electrode 340 in apertures 330, a sealing adhesive such as epoxy is placed in the apertures 330. Then, the first ink level detection electrode 335 and second ink level detection electrode 340 are inserted through the apertures 330. Once the sealant dries, it forms an airtight seal between the apertures 330 and the first ink level detection electrode 335 and second ink level detection electrode 340.

A reservoir filter 345 rests at the bottom of the interior of plenum 305. The purpose of reservoir filter 345 is prevent any particulate matter that may be present in the ink solution from passing from the plenum 305 to the integrated actuator assembly 100. If any particulate matter were to get into the actuator assembly 100, the first or second actuators 120, 125 could attempt to draw such particles into the ink channels 29. Depending upon the size of the particles, this could result in poor print quality (if even a few channels 29 experience clogging) or even catastrophic failure integrated actuator assembly 100. In a presently preferred embodiment, reservoir filter 345 is comprised of a number 304 stainless steel mesh with ten micron (seventeen micron absolute) perforation size. Plenum 305 is constructed with other features which allow for integration of the various components of the integrated actuator assembly 100 and the ink reservoir 300. One end of the plenum 300 comprises tabs 350, 355 that extend therefrom to define a first gap 360. At the opposite end of plenum 300 is a similar arrangement of tabs that define a second gap. In Fig. 13, tab 365 is shown, but the corresponding tab and the second gap is not shown.

Referring to Fig. 14, a cross-sectional view of plenum 305 is shown. As is seen, the lower portion of the plenum 305 comprises a rail 365 that is disposed between guides 370. Rail 365 has a length that is slightly longer than length "A", that is the length of the actuators 120, 125. Rail 365, however, is not as long as length "B", that is the length of support 105. Thus, the support 105 has extensions 106 at its first end 101 and second end 102 that extend beyond the length of the rail 365 of plenum 305, thus exposing the resistive elements 107. As will be seen below, it is important that length "B", that is the length of support 105, be longer than rail 365.

Rail 365 has the fill block 250 fitted and affixed therein. As seen in Fig. 15, disposed through rail 365 are a plurality of openings 375 that allow ink to pass from the plenum 305, through the fill block 250 and into the ink channels 29. The openings 375 are formed by webs 380 and central member 385 and mate with openings 255 in fill block 250 to create ink passages.

With reference to Figs. 16-18, an integrated ink jet print head 400 of a presently preferred embodiment is shown. Integrated ink jet print head 400 comprises the integrated actuator assembly 100, fill block 250, and ink reservoir 300. Integrated ink jet print head 400 also comprises a first flex circuit 405 and a second flex circuit 410 (second flex circuit 410 can be only seen in Fig. 16) . First flex circuit 405 and second flex circuit 410 comprise a flexible circuit substrate (which is generally constructed of an electrical insulator such 5 as Mylar) , circuit traces 85 and leads 90 that are used to interconnect circuit elements. To simplify the drawings, circuit traces 85 are not shown in Figs. 16-18, but can be seen in Fig. 23. To further simplify the drawings, leads 90 are not shown in Figs. 16-18, but can be seen in Fig. 24. 0 First flex circuit 405 has one circuit trace for each addressable electrode 60 on first actuator 120. Each of these circuit traces is electrically connected to a single addressable electrode 60. Each of these circuit traces is also in electrical communication with a source of electrical drive 5 signals that are used to cause the deformations in the first actuator 120. Likewise, the second flex circuit 410 has one circuit trace for each addressable electrode 60 on second actuator 125. Each of these circuit traces is electrically connected to a single addressable electrode 60. Each of these 0 circuit traces is also in electrical communication with a source of electrical drive signals that are used to cause the deformations in the second actuator 125.

The manner in which first flex circuit 405 is affixed to integrated actuator assembly 100 is shown in Fig. 23. An

25 actuator assembly 100 constructed in accordance with the present invention has thin coating of eutectic plating applied to each of the addressable electrodes 60. The first flex circuit 405 is then placed on the actuator assembly such that the proper circuit lead 90 (see Fig. 24) on the flex circuit

30 405 is placed over the corresponding addressable electrode 60. A hot bar 600 is then applied to the portion of the first flex circuit 405 to be affixed to the actuator assembly 100. The hot bar 600 applies heat and pressure to the first flex circuit 405. This acts to bond the first flex circuit 405 to the

35 actuator assembly 100. It is noted that the first flex circuit 405 is aligned so that other circuit traces on thereon are placed on other components of the actuator assembly 100 in the manner discussed herein. It is further noted that second flex circuit 410 is affixed to the actuator assembly with the same method.

In addition, first flex circuit 405 and second flex circuit 410 can supply the heating current that passes through resistive elements 107 located on support 105. Specifically, a circuit trace (which for simplicity is not shown) carries the current necessary to cause resistive elements 107 to create the desired elevated temperature. The presently preferred manner in which this current is delivered to the resistive elements will now be discussed. The circuit trace carrying the heating current is directed to a tab 415 that extends from the first flex circuit 405. Tab 415 can be seen most clearly in Figs. 17 and 18. Tab 415 fits into a first heater clip 420 that clamps onto the extension 106 at the first end 101 of support 105.

Tab 415 has an electrically conductive terminal (not shown) that is electrically connected to a heater clip 420. Heater clip 420 is substantially "U" shaped such that it wraps around the first end 101 of support 105. In addition, a second heater clip 425 is disposed such that it wraps around the second end 102 of support 105. Second heater clip 425 is also substantially "U" shaped. First heater clip 420 and second heater clip 425 are constructed of an electrically conductive material. In the presently preferred embodiment, the first heater clip 420 and second heater clip 425 are constructed of a phosphor bronze substrate with gold plating and a nickel finish.

First heater clip 420 and second heater clip 425 place both resistive elements 107 located on support 105 in electrical communication with each other. Thus, first heater clip 420, second heater clip 425, and resistive elements 107 form an electrical circuit, and therefore, any electrical current that is supplied by the flex circuit to the tab 415, and then to the first heater clip 420 causes current to flow through the resistive elements 107. The resistance of the resistive elements 107 and the heating current are selected 5 using Ohm's law such that the temperature of the integrated actuator assembly is raised to a predetermined temperature. The predetermined temperature will create the desired viscosity in the ink.

The presently preferred structures of actuator assembly

10 100 that facilitate electrical connection of metallization layer 24 onto each of the first actuator 120 and second actuator 125 and the first common electrode 112 and the second common electrode 117 to ground will now be discussed with reference to Fig. 24. Fig. 24 shows a portion of a presently

15 preferred actuator assembly 100. First flex cable 405 is affixed to first actuator 120 such that leads 90 are electrically communicating with a single addressable electrode 60. In addition, metallization layer 24 is disposed on first actuator 120 such that it extends over the first face 51

20 (including the inner surfaces and interior end of each ink channel 29) , around the end 55, and onto a portion of the second face 53. By disposing a portion of metallization layer 24 on a portion of the second face 53, that portion forms a grounding electrode 61 which lies in substantially the same

25 plane as addressable electrodes 60 and is therefore accessible to first flex circuit 405. Grounding electrode 95 is placed in electrical communication with a lead 95 on the first flex circuit 405. Lead 95 is in electrical communication with a circuit trace 85 that is maintained at ground potential. While

30 the discussion related to Fig. 24 has referred to only a portion of the integrated actuator assembly 100, it will be understood that such an arrangement of features can be implemented at both ends of first actuator 120 (i.e., not just at end 55) , and also can be implemented in the same fashion on

35 second actuator assembly 125 and second flex circuit 410. Referring now to Figs. 19-21, an integrated snap-on head assembly 500 having integrated print heads 400 will be described. Snap-on head assembly 500 will be mounted on a printer carriage (not shown) that moves across the print

5 medium.

Snap-on head assembly 500 comprises four heads 400. Each head 400 is fixedly mounted in a base 510 which is preferably constructed using number 304 stainless steel. The details of this will be described below with reference to Fig. 21. A case 10 520 is mounted to base 510. In the presently preferred embodiment, the case 520 is attached to the base 510 with bolts (not shown) which extend through through-hole 524 on the case 520 to a threaded opening 512 on base 510. In alternative embodiments, the threaded opening 512 can comprise a non- 15 threaded hole which receives a self-threading bolt. By using such a fastening mechanism, the case 520 can be removed to allow either maintenance or replacement of the print heads 400. Case 520 comprises four separate sleeves 522 into each of which one integrated head assembly 400 will be slidably mounted. 20 Each sleeve 522 fits over a corresponding head 400 such that each head 400 is maintained in a substantially fixed position. This prevents any movements of the heads 400 which would degrade print quality. In the presently preferred embodiment, the case 520 is constructed of injection molded plastic. Such 25 a plastic can be a liquid crystal polymer such as Vectra A530 available from Hoechst Celanese Corporation.

A printed circuit board 530, which has circuit traces

(for simplicity not shown) printed therein and thereon, is mounted on the top of case 520. The circuit traces are

30 connected to leads 536 which are electrically connected to corresponding leads on the first and second flex circuits 405,

410.

A cover 540, having openings 542 therethrough, is fastened to case 520 and when installed on the case 520, the

35 cover 540 allows a portion of the extended portion 320 and the locking mechanism 325 of ink supply neck 315 to extend through openings 542. This in turn permits the ink supply tubes or pipes (not shown) to provide ink to the integrated head assemblies 400. Cover 540 is fastened to the case 520 with bolts (not shown) which pass through through-holes 544 in the cover 540, through-holes 534 in circuit board 530, and into through-holes 526 in the case 520. As discussed, by using bolts, the cover 540, circuit board 530, and case 520 can be easily and simply removed to allow either maintenance or replacement of the print heads 400.

Mounted onto cover 540 is a head latch bar 550 which acts to compress the case 520, the circuit board 530 and the cover 540 onto the base 510.

As discussed above, ink is fired by each print head 400 as the snap-on head assembly 500 is moved linearly across a print medium. Therefore, an image is created by placing a plurality of swaths of printed images onto the print medium.

To create an image on the print medium that appears uniform

(i.e., with no evidence of discrete swaths), it is important that each swath be integrally "stitched" together with both the previously printed swath and the swath that will be printed in the next linear movement of the carriage. As discussed, most ink jet printers have four individual heads, one for each color. In prior art printers, each head produces four swaths of ink which are printed directly on top of each other during each linear carriage movement. By doing this, it is difficult to achieve quality stitching of each swaths to the swath printed immediately before and immediately after that swath. The reason for this is that each head must be precisely aligned with extremely tight tolerances with respect to the other heads. Moreover, because the print heads prints swaths by moving with respect to the print medium, in the prior art, the heads typically must be held in their position by an extremely rugged mechanism. Such a rugged mechanism adds considerable cost and complexity to the system and makes field repairs (for example, head replacement) difficult.

The present invention solves this problem by mounting each integrated print head 400 in base 510 such that each print 5 head 400 is offset from the other by a predetermined amount. This is illustrated with particular reference to Figs. 21-22. Fig. 22 shows a top view of the base 510 of snap-on head assembly 500. Base 510 has four apertures 514, 515, 516, 517 extending therethrough. Each of the apertures 514, 515, 516, 10 517 are substantially parallel to each other and are shaped such that the integrated actuator assemblies fit therein, thereby exposing the nozzles of the nozzle plate 150 such that they are directly opposite the print medium. As seen in Fig.

21, each of the apertures 514, 515, 516, 517 is arranged such 15 that each consecutive one descends with respect their common perpendicular plane.

An exemplary swath 600 that is printed onto a print medium from the print snap-on head assembly 500 having the heads 400 arranged such that each consecutive one descends with

20 respect to their common perpendicular plane is shown in Fig.

22. The print head that is disposed through first aperture 514 produces first swath component 605. The print head that is disposed through second aperture 515 produces second swath component 610. The print head that is disposed through third

25 aperture 516 produces third swath component 615. Finally, the print head that is disposed through fourth aperture 517 produces fourth swath component 620. Swath 600 is thus comprised of a first swath component 605, a second swath component 610, a third swath component 615, and a fourth swath

30 component 620.

Swath 600 comprises seven regions, each of which contains either all of the swath components or only a subset of the swath components. First region 625 contains only one color (i.e., first swath component 605). Second region 630 contains

35 two colors (i.e., first swath component 605 and second swath component 610). Third region 635 contains three colors (i.e., first swath component 605, second swath component 610 and third swath component 615) . Fourth region 640 contains all four colors (i.e., first swath component 605, second swath component 610, third swath component 615 and fourth swath component 620) . Fifth region 645 contains three colors (i.e., second swath component 610, third swath component 615 and fourth swath component 620). Sixth region 650 contains two colors (i.e., third swath component 615 and fourth swath component 620) . Seventh region 655 contains only one color (i.e., fourth swath component 620) .

By offsetting each of the heads as in the present invention, stitching need only by done on a per color basis. In other words, the first component swath 605 of a swath 600 need only be stitched with the corresponding first component swath of the swath printed immediately following. This is true for the remaining swath components. Thus, any misalignment of one head only applies to the corresponding swath component printed by that one head. Furthermore, if one swath component does not stitch as desired, it will be less visible because it is likely that the other swath components will stitch properly and because the improperly stitched swath component will be covered by as many as three swath components that are not stitched at that location. Because the swath components that are not stitching as well as desired are covered by the three other swath components that are stitching at that location, the poor stitching is likely to be less visible.

Applicant notes that positional orientation terms such "lateral", "top", and "rear" are used to describe certain relative structural aspects of the preferred embodiment. However, these relative positional terms are used only to facilitate the explanation of the invention, and are not intended to limit in any way the scope of the invention.

Thus, a preferred print head apparatus and method of manufacturing same has been described. While embodiments, applications and advantages of the invention have been shown and described with sufficient clarity to enable one skilled in the art to make and use the invention, it would be equally apparent to those skilled in the art that many more embodiments, applications and advantages are possible without deviating from the inventive concepts disclosed, described, and claimed herein. The invention, therefore, should only be restricted in accordance with the spirit of the claims appended hereto or their equivalents, and is not to be restricted by specification, drawings, or the description of the preferred embodiments.

Claims

1. A print head for a drop on demand ink jet printer comprising: a support, said support having a first end and a second end; a first resistive element disposed on a first face of said support, said first resistive element extending substantially from said first end of said support to said second end of said support; a second resistive element disposed on a second face of said support, said second resistive element extending substantially from said first end of said support to said second end of said support; a first ink channel cover affixed to said support and covering a portion of said first resistive element; a second ink channel cover affixed to said support and covering a portion of said second resistive element; a first actuator affixed to said first ink channel cover, said first actuator having an ink supply edge, an ink ejection edge, an ink channel side and an air channel side, said first actuator comprising a plurality of first ink channels, each of said plurality of first ink channels defined by walls of said first actuator and said first ink channel cover, said plurality of first ink channels being linearly adjacent and substantially parallel to each other and extending from said ink supply edge to said ink ejection edge, said first actuator further comprising a plurality of addressable electrodes, each of said plurality of addressable electrodes capable of deforming one of said plurality of first ink channels, said first actuator further comprising a first metallization layer disposed on said ink channel side; a second actuator affixed to said second ink channel cover, said second actuator having an ink supply edge, an ink ejection edge, an ink channel side and an air channel side, said second actuator comprising a plurality of second ink channels, each of said plurality of second ink channels defined by walls of said second actuator and said second ink channel cover, said plurality of second ink channels being linearly adjacent and substantially parallel to each other and extending from said ink supply edge to said ink ejection edge, said second actuator further comprising a plurality of addressable electrodes, each of said plurality of addressable electrodes capable of deforming one of said plurality of second ink channels, said second actuator further comprising a second metallization layer disposed on said ink channel side; a first wing affixed to said air channel side of said first actuator; and a second wing affixed to said air channel side of said second actuator.

2. The print head of claim 1 wherein both said first actuator and said second actuator are constructed of a piezoelectric material.

3. The print head of claim 1 wherein said support is constructed of aluminum nitride.

4. The print head of claim 1 wherein both said first ink channel cover and said second ink channel cover are constructed of aluminum nitride.

5. The print head of claim 1 wherein said support, said first ink channel cover, said second ink channel cover, said first actuator, said second actuator, said first wing and said second wing are laminated together such that a first planar surface comprising said ink ejection edge of said first actuator and said second actuator is created.

6. The print head of claim 5 wherein said first planar surface has a nozzle plate having a plurality of orifices extending therethrough affixed thereto, each of said plurality of orifices corresponding to one of said plurality of first ink channels or one of said plurality of second ink channels.

7. The print head of claim 5 wherein said support, said first ink channel cover, said second ink channel cover, said first actuator and said second actuator form a second planar surface which defines an ink supply edge of both said first actuator and said second actuator.

8. The print head of claim 7 wherein said second planar surface has affixed thereto an ink fill gasket having apertures corresponding to one of said plurality of first ink channels or one of said plurality of second ink channels.

9. The print head of claim 1 wherein said first resistive element and said second resistive element each is constructed of a nickel chrome alloy.

10. The print head of claim 1 further comprising a reservoir which is in fluid communication with said second planar surface and includes an ink plenum, said ink plenum sealed by a cover, said cover comprising an ink supply neck.

11. The print head of claim 10 further comprising a fill block disposed between said reservoir and said second planar surface.

12. The print head of claim 1 wherein said first ink channel cover comprises a first common electrode in electrical communication with said first metallization layer disposed thereon, and wherein said second ink channel cover comprises a second common electrode in electrical communication with said second metallization layer disposed thereon.

13. A snap-on head assembly for a drop on demand ink jet printer, said print snap-on head assembly capable of moving linearly across a printing medium, said print snap-on head assembly comprising: a plurality of print heads, each of said plurality of print heads comprising: an actuator assembly, said actuator assembly comprising at least one actuator having a plurality of ink channels formed therein, said plurality of ink channels disposed linearly adjacent and substantially parallel to neighboring ones of said plurality of ink channels, said plurality of ink channels having an axial dimension that is oriented to be perpendicular to the printing medium; a reservoir affixed to said actuator assembly; a base for mounting said plurality of print heads, said plurality of print heads arranged such that they are substantially parallel to other ones of said plurality of print heads, said plurality of print heads further arranged such that consecutive ones of said plurality of print heads descends with respect to a perpendicular plane common to all of said plurality of print heads.

14. A actuator assembly for a drop on demand ink jet printer comprising: a support, said support having a first end and a second end, said first end and said second end defining a first linear dimension; a resistive element disposed on a first face of said support, said first resistive element extending substantially from said first end of said support to said second end of said support; an ink channel cover affixed to said support, said ink channel cover comprising a second linear dimension, said second linear dimension being smaller than said first linear dimension; an actuator affixed to said ink channel cover, said actuator having an ink supply edge, an ink ejection edge, an ink channel side and an air channel side, said actuator comprising said second linear dimension, said actuator comprising a plurality of ink channels, each of said plurality of ink channels defined by walls formed in said actuator and said ink channel cover, said plurality of ink channels being linearly adjacent and substantially parallel to each other and extending from said ink supply edge to said ink ejection edge, said actuator further comprising a plurality of addressable electrodes, each of said plurality of addressable electrodes capable of deforming one of said plurality of ink channels, said actuator further comprising a metallization layer disposed on said ink channel side; and a first wing affixed to said air channel side of said actuator, said first wing comprising said second linear dimension.

15. A printer system comprising the print head of claim

16. A printer system comprising the actuator assembly of claim 14.

17. A print head for a drop on demand ink jet printer comprising: an elongated support member; an ink channel cover affixed to said elongated support member, said ink channel cover comprising a common electrode disposed on one side thereof; an actuator affixed to said ink channel cover, said actuator comprising a plurality of ink channels disposed in a first side of said actuator, said actuator further comprising a plurality air channels disposed in a second side of said actuator and separating each of said plurality of ink channels; a metallization layer extending lengthwise across said first side of said actuator and forming a contiguous electrical conductor, said metallization layer in electrical communication with said common electrode; and a wing affixed to said actuator.

18. The print head of claim 17 wherein said elongated support member comprises aluminum nitride.

19. The print head of claim 17 wherein said ink channel cover comprises aluminum nitride.

20. The print head of claim 17 wherein said actuator further comprises a plurality of addressable electrodes, each of said plurality of addressable electrodes being separated by one of said plurality of air channels.

21. A printer system comprising the print head of claim 17.

22. A drop on demand ink jet printer comprising: a print head, said print head comprising: an elongated support, said elongated support affixed to an ink channel cover, said ink channel cover affixed to an actuator, said actuator comprising ink channels and air channels, said ink channels and air channels disposed on opposing sides of said actuator; and a heating element disposed on said elongated support and facing said ink channel cover, said heating element running substantially along a lengthwise face of said elongated support.

23. The drop on demand ink jet printer of claim 22 wherein said support comprises aluminum nitride.

24. The drop on demand ink jet printer of claim 22 wherein said heating element comprises a resistive element.

25. The drop on demand ink jet printer of claim 22 wherein said resistive element comprises nickel-chrome alloy.