Integrated Multi-Color Ink Jet Printhead

1. Field of the Invention

The present invention generally relates to ink jet printhead apparatus and, more particularly, to an integrated multi-color drop-on-demand type ink jet printhead having longitudinally extending sidewall actuators.

2. Description of Related Art

Ink jet printing systems use the ejection of tiny droplets of ink to produce an image. The devices produce highly reproducible and controllable droplets, so that a droplet may be printed at a location specified by digitally stored image data. Most ink jet printing systems commercially available may be generally classified as either a "continuous jet" type ink jet printing system where droplets are continuously ejected from the printhead and either directed to or away from the paper depending on the desired image to be produced or as a "drop-on-demand" type ink jet printing system where droplets are ejected from the printhead in response to a specific command related to the image to be produced.

In drop-on-demand type ink jet printing systems, a volumetric change in the fluid is induced by the application of a voltage pulse to a piezoelectric material which is directly or indirectly coupled to the fluid. This volumetric change causes pressure/velocity transients to occur in the fluid and these are directed so as to produce a droplet that issues from an orifice. Recently, considerable interest has been directed to piezoelectric drop-on-demand type ink jet printheads which utilize sidewall actuators to impart droplet ejecting pressure pulses into the ink carrying channels. See, for example, U.S. Pat. Nos. 4,536,097 to Nilsson, 4,879,568 to Bartky et al., 4,887,100 to Michaelis et al. and 5,016,028 to Temple.

In Ser. No. 07/748,220, a U type drop-on-demand ink jet printhead was disclosed. The U type ink jet printhead included a lower body portion formed from an active piezoelectric material, a plurality of intermediate sections formed from an active piezoelectric material and an upper body portion formed from an inactive material. The lower body portion further included an upper side surface and a plurality of generally parallel spaced projections vertically projecting therefrom. Lower side surfaces of a plurality of intermediate sections were conductively mounted to top side surfaces of the lower body projections and the upper body portion was conductively mounted to upper side surfaces of the plurality of intermediate sections. In this manner, an ink jet printhead in which the lower body portion, the plurality of intermediate sections and the upper body portion defined a plurality of generally parallel, longitudinally extending ink ejecting channels was formed. For this ink jet printhead, the intermediate sections further defined first and second actuators and the projections and upper surface of the lower body portion defined a third actuator for each of the channels.

Like most other previously disclosed ink jet printing systems, the aforementioned configuration for an ink jet printhead provides for only one fluid system and is, therefore, capable of printing in only one color, most commonly, black. Color printing, however, requires multiple ink colors. For example, the use of four ink colors--the primary colors (yellow, magenta and cyan) and black-has proven quite satisfactory for producing color images. When manufacturing multiple color ink jet printheads, the most common approach has been to produce a printing system having a separate printhead for each ink color. However, there are numerous difficulties which arise when using multiple printheads in a single ink jet printing system.

Of primary concern is the requirement that the separate printheads must be properly aligned (or "registered") with each other in order for the printing system to properly produce color images. Furthermore, as ink jet printheads must be readily replaceable, permanently fastening the ink jet printheads after registration is not a feasible solution to this problem. Thus, in order to achieve registration of the separate printheads, some type of alignment capability which allows the printing system to determine the pitch and position of each printhead and make appropriate adjustments must be incorporated into the printing system. For example, it is contemplated that control software may be used to maintain proper registration of each printhead in such a printing system. However, not only is it difficult to ensure that such systems always accurately align the printheads, they add considerable cost and complexity to multi-color ink jet printing systems.

Furthermore, the use of multiple printheads in multi-color printing systems represents a significant obstacle to the production of smaller, less expensive multi-color ink jet printers. Each printhead is an independent system which requires its own transport, ink supply and actuation mechanisms. Thus, there are numerous redundant systems in a multiple printhead multi-color ink jet printer which, due to the independent nature of each printhead, resists integration. As a result, each printhead demands a significant amount of space, thereby impeding the successful construction of a compact, multi-color ink jet printhead.

It is, therefore, an object of this invention to provide an ink jet printhead which integrates multiple fluid systems in a single assembly, thereby permitting the manufacture of a multi-color ink jet printhead.

In one embodiment, the present invention is of an integrated multi-color drop-on-demand type ink jet printhead having a main body portion and a plurality of generally parallel, longitudinally extending ink-carrying channels arranged into at least two channel arrays. A manifold corresponding to each of the at least two channel arrays and in communication with each of the ink-carrying channels of the corresponding array is formed in the main body portion. Transport means are used to provide colored ink to each of the at least two channel arrays from a corresponding ink source, each of which is filled with a different color of ink.

In one aspect thereof, the main body portion is comprised of a lower body portion having a top side surface and a plurality of longitudinally extending, generally parallel grooves extending downwardly therefrom and an upper body portion having a bottom side surface. By mounting the bottom side surface of the upper body portion to the top side surface of the lower body portion, the plurality of ink-carrying channels are formed. In a further aspect, each of the at least two manifolds are formed in the upper body portion such that, when the lower and upper body portions are mounted together, the manifolds are placed into communication with the ink-carrying channels of the corresponding channel array. In another aspect, an internal conduit having a first opening in communication with one of the manifolds and a second opening interconnected with one of the ink supplies via a corresponding external conduit is formed in the upper body portion. Preferably, four ink sources for respectively providing black, yellow, magenta and cyan colored ink to first, second, third and fourth channel arrays should be provided.

In another embodiment, the present invention is of an integrated multi-color drop-on-demand type ink jet printhead having a lower body portion formed from an active piezoelectric material and having a plurality of generally parallel spaced projections projecting vertically from an upper side thereof. A bottom side surface of a corresponding intermediate section formed from an active piezoelectric material is conductively mounted to a top side surface of each of the plurality of projections and a bottom side surface of an upper body portion is conductively mounted to a top side surface of each of the intermediate sections. At least two manifolds are formed in the upper body portion such that, when the upper body portion is mounted to the intermediate sections, a plurality of generally parallel, longitudinally extending ink-carrying channels, each having first, second and third actuators and arranged into at least two channel arrays, are formed. In turn, each of the channel arrays is in communication with a corresponding one of the manifolds. At least two sources of colored ink, each of which is filled with a different color of ink, are connect with the ink jet printhead to supply ink to a corresponding one of the at least two channel arrays.

The invention will be more clearly understood and its numerous objects and advantages will become apparent to those skilled in the art by reference to the accompanying drawing in which:

FIG. 1 is a perspective view of an integrated multi-color ink jet printhead constructed in accordance with the teachings of the present invention;

FIG. 2 is a front view of the integrated multi-color ink jet printhead of FIG. 1 with the cover plate removed;

FIG. 3 is a side view of the integrated color ink jet printhead of FIG. 1;

FIG. 4 is an enlarged partial cross-sectional view taken along lines 4--4 of FIG. 3; and

FIG. 5 is a perspective view of the integrated color ink jet printhead of FIG. 1 with the cover plate and upper body portions removed.

Referring first to FIG. 1, a drop-on-demand type multi-color ink jet printer 10 constructed in accordance with the teachings of the present invention may now be seen. The multi-color ink jet printer 10 includes an integrated multi-color ink jet printhead 12 provided with a main body portion 14 having a plurality of ink carrying channels (not visible in FIG. 1) longitudinally extending therethrough. Typically, each of the ink carrying channels extend from a first end located within the main body portion 14 and terminate at an opening along a front side surface 16 of the main body portion 14. Preferably, the ink carrying channels should be generally parallel to each other along their entire length. As will be described in greater detail below, the ink carrying channels longitudinally extending through the main body portion 14 should be arranged in plural channel arrays, one for each color of ink to be ejected by the multi-color ink jet printhead 14, each separated from adjacent channel arrays by a separation distance sufficient to prevent cross-contamination of the various inks. For example, it is contemplated that four channel arrays, one for each of the ink colors (black, yellow, magenta and cyan) to be ejected by the multi-color ink jet printhead, each separated from adjacent channel arrays by about 2.2 mm., will be suitable for use.

The ink carrying channels of each channel array is supplied by a corresponding ink supply 18a, 18b, 18c, 18d via an external conduit 20a, 20b, 20c, 20d. A different color ink is stored in each of the ink supplies 18a, 18b, 18c, 18d. For example, the ink supply 18a contains black ink, the ink supply 18b contains yellow ink, the ink supply 18c contains magenta ink and the ink supply 18d contains cyan ink. It should be noted, however, that while four structurally independent ink supplies 18a-d have been schematically illustrated in FIG. 1, it is specifically contemplated that the ink supplies 18a-d could be integrated into a single ink supply having separate chambers for storing each color of ink. In such a configuration, it is further contemplated that, as they extend away from the multi-color ink jet printhead 12, the external conduits 20a-d would be physically tied together before again separating for interconnection with a respective access opening of one of the chambers of the integrated ink supply. Further details as to how the each ink supply 18a, 18b, 18c, 18d supplies a respective color of ink to each of the channel arrays shall be described in detail later.

Continuing to refer to FIG. 1, the integrated color ink jet printhead 12 further includes a cover plate 22 having a back side surface 24 fixedly secured to the front side surface 16 of the main body portion 14, a front side surface 26 and a plurality of tapered orifices 28 extending therethrough. The tapered orifices 28 are arranged in four orifice arrays 29a, 29b, 29c and 29d and the cover plate secured to the main body portion 14 such that each orifice in the orifice arrays 29a, 29b, 29c, 29d is in communication with one of the ink carrying channels of the corresponding channel array. While it is contemplated that each orifice array 29a-d would contain eighteen orifices 28, for ease of illustration, only nine such orifices 28 are shown in FIG. 1 for each orifice array 29a-d. Preferably, the cover plate 22 should be formed of polyamide or another suitable material and fixedly secured to the front side surface 16 such that each orifice 28 is located in the general center of the corresponding one of the ink carrying channels.

Continuing to refer to FIG. 1, the main body portion 14 will now be described in greater detail. The main body portion 14 is comprised of a lower body portion 30 formed of an active piezoelectric material, for example, lead zirconate titante (or "PZT"), poled in direction P1 (see FIG. 4) and having a layer 38 of a conductive material, for example, metal, formed on a top side surface 40 thereof, an intermediate body portion 32, also formed of an active piezoelectric material, poled in direction P1 (again, see FIG. 4) and having layers 42, 44 of a conductive material formed on bottom and top side surfaces 46, 48, respectively, and an upper body portion 34 formed of an inactive material, for example an unpoled piezoelectric or ceramic material, and having a layer 50 of a conductive material formed on a lower side surface 52 thereof.

Referring next to FIG. 2, the channel arrays 35a, 35b, 35c and 35d may now be seen. Each channel array is comprised of a plurality of generally parallel, longitudinally extending ink carrying channels 36. While the number of channels 36 in a channel array 35a-d may be varied depending on the particular dimensions of the integrated multi-color ink jet printhead 12, it is contemplated that four channel arrays 35a-d, each comprised of eighteen ink carrying channels 36 separated from adjacent channels by about 0.2 mm. would be suitable for the purposes contemplated herein. For each channel array 35a, 35b, 35c, 35d, a corresponding manifold 21a, 21b, 21c, 21d is formed in the upper body portion 34, for example, using a conventional grooving process. Each manifold 21a, 21b, 21c, 21d is formed across a portion of the lower side surface 52 of the upper body portion 34 in a direction generally normal to the corresponding channel array 35a-d selected such that, when the upper body portion 34 is later mounted to the intermediate body portion 32 in the manner described below, the manifolds 21a, 21b, 21c, 21d is in communication with each channel 36 of the corresponding channel array 35a, 35b, 35c, 35d. Also formed in the upper body portion 34 are internal conduit 23a, 23b, 23c, 23d, each of which vertically extends between the top and bottom side surfaces 51, 52 of the upper body portion 34, is in communication with the corresponding manifold 21a, 21b, 21c, 21d on one end thereof and has an opening 25a, 25b, 25c, 25d along the top side surface 51 of the upper body portion 34 on the other end. The internal conduits 23a-d may be formed using a conventional drilling process. The external conduits 20a, 20b, 20c, 20d are mated with the corresponding internal conduits 23a, 23b , 23c, 23d, for example, by inserting one end of each of the external conduits into the corresponding internal conduit and securing it therein. In this manner, when droplets of various colors of ink are ejected from the channels 36 of the various channel arrays 35a-d, additional ink from the corresponding ink supplies 18a-d is drawn into those channels 36 via the manifolds 21a-d, the vertical conduits 23a-d and the external conduits 20a-d, respectively.

While the number and dimensions of the manifolds 21a-d and the internal conduits 23a-d will vary depending on the separation between the channels 36, the number of channels 36 in each channel array 35a-d and the number of channel arrays 35a-d (or colors) in the multi-color ink jet printhead 12, manifolds 21a-d having a length of about 4.2 mm., a width of about 1.3 mm. and separated from adjacent manifolds by about 2.2 mm. would be suitable for the purposes contemplated herein. It should be further noted that while the manifolds 21a-d are shown in a generally oblong shape, it is specifically contemplated that the particular shape of the manifolds 21a-d may be formed in various other shapes not illustrated herein without departing from the scope of the present invention. Furthermore, while the position of each internal conduits 23a-d may be varied relative to the corresponding manifold 21a-d, it is preferred that the internal conduits 23a-d be located in the general center of the corresponding manifold 21a-d. As before, while various shapes and dimensions for the internal conduits 23a-d would be suitable, a generally tubular conduit having a diameter of about 1.3 mm is suitable for the uses contemplated herein. Finally, while the manifolds 21a-d and internal conduits 23a-d may be located anywhere along the upper body portion 34, for ease of interconnection with the corresponding ink supplies 18a-d, it is preferred that the manifolds 21a-d and internal conduits 23a-d be located in the rear part of the upper body portion 24.

Referring next to FIGS. 1, 2, 4 and 5, the manufacture of the integrated multi-color ink jet printhead 12 will now be described in greater detail. To manufacture the integrated multi-color ink jet printhead 12, a layer of conductive adhesive (not shown) is applied to the conductive layer 38 formed on the upper side surface 40 of the lower body portion 30. Front side surfaces 39, 41 of the lower and intermediate body portions 30, 32, respectively, are then aligned and the lower and intermediate body portions 30, 32 mated and bonded with each other. As may be best seen in FIG. 5, the lower body portion 30 continues to extend rearwardly past the intermediate body portion 32, thereby providing a so-called "back porch" 43 for the integrated multi,color ink jet printhead 12 where electrical interconnections between the actuation system for the channel 36 of the channels arrays 35a-d for the integrated multi-color ink jet printhead 12 to be more fully described below and a controller (not shown) is provided. To better facilitate this electrical interconnection, it is preferred that the conductive layer 38 formed on the top side surface 40 of the lower body portion 30 extend only partway along the back porch 43. This may be accomplished by covering a portion of the back porch 43 with a thin layer of an insulative material, for example, teflon, before forming the conductive layer 38 on the top side surface 40, most commonly, using a conventional deposition process.

After the lower body portion 30 and the intermediate body portion 32 are conductively mounted together, a machining process is then utilized to form the channels 36, grouped together as channel arrays 35a-d for the integrated multi-color ink jet printhead 12. As may be seen in FIG. 5, a series of longitudinally extending, substantially parallel channels 36 are formed by machining grooves which extend through the intermediate body portion 32 and the lower body portion 30. Preferably, the machining process is performed such that each channel 36 formed thereby extends downwardly such that portions of the conductive layer 44, the intermediate body portion 32, the conductive layer 42, the conductive adhesive layer between conductive layers 42 and 38 (not shown), the conductive layer 38 and the lower body portion 30 are removed. It is further preferred that the machining process be performed such that the grooves formed thereby longitudinally extend from the front side surfaces 39, 41 to rear side surfaces 49, 51 of the lower and intermediate body portions 30, 32, respectively.

The manifolds 21a-d and vertical conduits 23a-d are then formed in the upper body portion 34 in the manner previously described. A layer 54 of conductive adhesive is then applied to the remaining conductive layer 50 not removed during the formation of the manifolds 21a-d, for example, using a patterning process. A front side surface 45 of the upper body portion 34 is then aligned with the front side surface 41 of the intermediate body portion 32 and the two conductively mounted together. An insulative composite material 69 is then used to form back walls for the channels 36 of the channel arrays 35a-d by closing the open ends of the channels 36 along the rear side surfaces 49, 51 of the lower and intermediate body portions 30, 32.

By forming grooves in the lower and intermediate body portions 30, 32 and mounting the upper body portion 34 to the grooved intermediate body portion 32 in this manner, a series of channels 36 which comprise the channel arrays 35a-d for the integrated color ink jet printhead 12 are formed. Each channel 36 formed in this manner is separated from an adjacent channel by a first sidewall portion 60 integrally formed with the lower body portion 32 and having a conductive strip 66 formed along a top side surface 68 of the sidewall portion 60 and a second sidewall portion 62 having conductive strips 70, 72 formed along bottom and top side surfaces 74, 76 of the second sidewall portion. The conductive strips 66 and 74 are bonded together by a strip 78 of conductive adhesive. Finally, each conductive strip 66 is electrically connected, for example, by a soldering process, along the back porch 43 to an electrical conductor 80 associated with a controller (not shown) and the conductive layer 50, which is electrically connected to the second sidewall portions 62 of every channel 36 of the channel arrays 35a-d, is connected to ground, thereby providing a common ground for the channel arrays 35a-d.

As more fully described in Ser. No. 07/748,220, each channel 36 has three actuators for imparting a pressure pulse into the channel. Two of these actuators are respectively comprised of the second sidewall portions 62 which partially define first and second sidewalls of the channel 36. The third (or "U-field") actuator 64 is comprised of the pair of first sidewall portions 60 which partially define the first and second sidewalls of the channel 36, respectively, and that portion of the lower body portion 30 which interconnects the pair of first sidewall actuator portions 60. Further details regarding how the actuators 62 and 64 impart pressure pulses to the channels 36 to cause the ejection of droplets of ink therefrom is set forth in greater detail in Ser. No. 07/748,220 and need not be discussed in greater detail here. Briefly, in order to impart droplet ejecting pressure pulse to a channel 36, a positive voltage is applied to the conductive strip 66 connecting the first and second sidewall portions 60, 62 on one side of the channel 36 while an equal magnitude negative voltage is applied to the conductive strip 66 connecting the first and second sidewall portions 60, 62 on the other side of the channel 36. After maintaining the preselected voltages for a predetermined time period, the voltages applied to the conductive strips 66 are reversed and held at the reverse voltage for the predetermined time period. This ink ejecting voltage waveform is further described in Ser. No. 08/060,294, filed May 10, 1993, entitled "Droplet Volume Modulation Techniques for an Ink Jet Printhead" and hereby incorporated by reference as if reproduced in its entirety.

It should be noted that while FIG. 5 suggests that each channel array 35a-d corresponding to a color is electrically connected to a separate controller for that color, it is specifically contemplated that, in accordance with one aspect of the invention, a single controller may be used to control the ejection of droplets of ink from any one of the channel arrays 35a-d. Accordingly, when forming a full color image, the controller will actuate selected ones of the channels 36 from the various channel arrays 35a-d at desired times as the multi-color ink jet printhead 12 moves, relative to substrate 71, for example, a sheet of paper, in direction "A", by selectively applying voltage to the conductive strips 66 on either side of the selected channels must eject a droplet of ink. In response thereto, the selected channels will eject a droplet of the selected color of ink which strikes the substrate 71 at the desired location.

Thus, there has been described and illustrated herein, an ink jet printhead which incorporates multiple channel arrays, each configured for the selective ejection of a different color of ink therefrom. By providing the capability of printing multiple colors using a single ink jet printhead, a simple, relatively compact multi-color ink jet printhead which overcomes the problems associated with prior multi-color ink jet printing systems which utilized multiple single color printheads disadvantageously requiring repeated registration therebetween to ensure the proper formation of images thereby. By overcoming this disadvantage associated with prior ink jet system, the integrated multi-color ink jet printhead disclosed herein will be more reliable and produce color images with greater accuracy than prior multiple printhead color ink jet printing systems.

Those skilled in the art will recognize that many modifications and variations besides those specifically mentioned may be made in the techniques described herein without departing substantially from the concept of the present invention. Accordingly, it should be clearly understood that the form of the invention as described herein is exemplary only and is not intended as a limitation on the scope of the invention.