Abstract:
An ink jet printhead assembly for ink jet printing apparatus and a method for the manufacture thereof. The piezoelectrically operable ink jet printhead assembly has two arrays of driving channels aligned with a single orifice array in which each orifice connects through a fluid channel to a single driving channel.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to an ink jet printhead assembly for ink jet printing apparatus and a method for the manufacture thereof. More particularly, the present invention relates to a piezoelectrically operable ink jet printhead assembly having two arrays of driving channels aligned with a single orifice array in which each orifice connects through a fluid channel to a single driving channel. 
     2. Description of the Prior 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. Most commercially available ink jet printing systems may be classified as “continuous jet” or “drop-on-demand” systems. In continuous jet systems, droplets are continuously ejected from the printhead and either directed to or away from the paper or other substrate depending on the desired image to be produced. In drop-on-demand systems, droplets are ejected from the printhead in response to a specific command related to the image to be produced. 
     Drop-on-demand printing systems are based upon the production of droplets by thermal or electromechanically induced pressure waves. In one type of electromechanical printing system, a volumetric change in the fluid to be printed 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 which are directed to produce a droplet that issues from an orifice in the printhead. According to such drop-on-demand printing systems voltage is applied only when a droplet is desired. 
     The use of piezoelectric materials in ink jet printers is well known. Most commonly, piezoelectric material is used in a piezoelectric transducer by which electric energy is converted into mechanical energy by applying an electric field across the material, thereby causing the piezoelectric material to deform. This ability to deform piezoelectric material has often been utilized in order to force the ejection of ink from the ink-carrying passages or channels of ink jet printers. Illustrative patents showing the use of piezoelectric materials in ink jet printers include U.S. Pat. Nos. 3,857,049, 4,584,590, 4,825,227, 4,536,097, 4,879,568, 4,887,100, 5,227,813, 5,235,352, 5,334,415, 5,345,256, 5,365,645, 5,373,314, 5,400,064, 5,402,162, 5,406,319, 5,414,916, 5,426,455, 5,430,470, 5,433,809, 5,435,060, 5,436,648 and 5,444,467. 
     In a representative configuration of a piezoelectrically actuated ink jet printhead, the ink jet printhead has, within its body portion, a single internal array of horizontally spaced, parallel ink receiving channels. The internal channels are covered at their front ends by a plate member through which a spaced series of small ink discharge orifices are formed. Each channel opens outwardly through a different one of the spaced orifices. 
     A spaced series of internal piezoelectric wall portions of the printhead body (typically formed from a piezoceramic material such as lead zirconate titanate “PZT”) separate and laterally bound the channels along their lengths. To eject an ink droplet through a selected one of the discharge orifices, the two printhead sidewall portions that laterally bound the channel associated with the selected orifice are piezoelectrically deflected out of and then into the channel and then returned to their normal undeflected positions. The inward driven deflection of the opposite channel wall portions increases the pressure of the ink within the channel sufficiently to force a small quantity of ink, in droplet form, outwardly through the discharge orifice. 
     It can readily be seen that it would be highly desirable to provide an ink jet printhead, of the general type described above, in which the discharge orifice density (i.e., the number of ink discharge orifices per inch) is doubled without correspondingly doubling the size the printhead or the total number of components needed to fabricate the printhead. It is accordingly an object of the present invention to provide such an ink jet printhead. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a high discharge orifice density ink jet printhead having a plate member with a single orifice array. Preferably, the orifices are oriented in a single line and centered on the plate member. Each orifice in the plate member connects through a fluid channel to a single driving channel in the ink jet printhead. 
     In a preferred embodiment of the present invention, the ink jet printhead comprises a printhead body subassembly comprising a first piezoelectrically deflectable block structure having first and second opposite sides and a front end, first and second layers of a metallic material respectively disposed on the first and second block structure sides, and first and second sheets of a piezoelectrically deflectable material respectively secured to front end portions of the outer sides of the first and second metallic layers. The first block structure is preferably a unitary block structure. 
     The first block structure includes a first and second spaced series of elongated, parallel exterior surface grooves disposed on the first and second sides of the first block structure, respectively. The grooves laterally extend into the first and second sides of the first block structure, through the piezoelectric sheets and the associated metallic layers, and have open outer sides and front ends. 
     Second and third piezoelectric blocks are respectively secured to the outer sides of the first and second piezoelectric sheets, cover the outer sides of the grooves, and form with the grooves first and second series of driving channels disposed within the body of the printhead and are laterally bounded along their lengths, on opposite sides thereof, by first and second series of piezoelectrically deflectable side wall segments of the subassembly. 
     A cover or plate member is secured to the front end of the printhead body, over the front ends of the first and second series of driving channels, and has an array of ink discharge orifices formed therein and operatively communicated with the front ends of the first and second series of driving channels. The plate member preferably comprises a nonwetting coating on the outside surface thereof. 
     The rear ends of the driving channels are sealed and an ink supply is in fluid communication with the first and second series of driving channels. The segments of the metallic layers remaining after the grooves are formed therethrough are used as electrical leads through which driving signals may be transmitted to the channel side wall sections to piezoelectrically deflect selected opposing parts thereof in a manner to discharge ink from the channel which they laterally bound through the discharge orifice associated with such channel. 
     According to a preferred embodiment of the present invention, the first and second series of grooves, and thus the first and second series of driving channels are laterally displaced so that the number of orifices per inch in the plate member is twice the number of driving channels per inch in the printhead body. 
     According to another preferred embodiment of the present invention, a method is provided for forming a cover or plate member for an ink jet printhead having an array of ink discharge orifices formed therein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages and features of the invention will become more apparent with reference to the following detailed description of presently preferred embodiments thereof in connection with the accompanying drawings, wherein like reference numerals have been applied to like elements, in which: 
     FIG. 1 is a perspective view of a schematically illustrated ink jet printhead according to the present invention; 
     FIG. 2A is an enlarged partial cross-sectional view of a first embodiment of the ink jet printhead of FIG. 1 taken along line  2 — 2 ; 
     FIG. 2B is an enlarged partial cross-sectional view of a second embodiment of the ink jet printhead of FIG. 1 taken along line  2 — 2 ; 
     FIG. 2C is an enlarged partial cross-sectional view of a third embodiment of the ink jet printhead of FIG. 1 taken along line  2 — 2 ; 
     FIG. 3 is a side elevational view of a component of the ink jet printhead of FIG. 1; 
     FIG. 4A is a side-elevational view of a component of the ink jet printhead of FIG. 1; 
     FIG. 4B is a cross-sectional view of the component of the ink jet printhead taken along line  4 B— 4 B of FIG. 4A; 
     FIG. 4C is a cross-sectional view of the component of the ink jet printhead taken along line  4 C— 4 C of FIG. 4A; 
     FIG. 5 which consists of FIGS. 5A-5F shows the ablation sequence for forming a component of the ink jet printhead of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings wherein thicknesses and other dimensions have been exaggerated in the various figures as deemed necessary for explanatory purposes and wherein like reference numbers designate the same or similar elements throughout the several views, an ink jet printhead  10  according to the present invention is shown in FIG.  1 . The ink jet printhead  10  may be used in connection with the devices disclosed and claimed in U.S. Pat. Nos. 5,227,813, 5,235,352, 5,334,415, 5,345,256, 5,365,645, 5,373,314, 5,400,064, 5,402,162, 5,406,319, 5,414,916, 5,426,455, 5,430,470, 5,433,809, 5,435,060, 5,436,648 and 5,444,467, the entire disclosures of which are hereby incorporated herein by reference. As shown in FIG. 1, the ink jet printhead  10  includes a body portion  12  having a top side  14 , a bottom side  16 , and a front end  18 . The body portion  12  may be formed from materials well known to those of ordinary skill in the art such as piezoceramic material including an active poled piezoelectric material, such as lead zirconate titanate (PZT), polarized in the direction indicated by the arrows  20  in FIGS. 2A,  2 B and  2 C. 
     As shown in FIG. 2A, thin layers  22  and  24  of a metallic material are disposed on the top side  14  and bottom side  16 , respectively, of the body portion  12 , and relatively thin sheets  26  and  28  of PZT are respectively disposed on the outer side surfaces of front portions of the metallic layers  22  and  24 . The PZT sheets  26  and  28  are poled in the direction indicated by arrows  30  and  32  in FIG.  2 A. 
     Also, as shown in FIG. 2A, top and bottom blocks  34  and  36  of PZT are disposed on the outer sides of the PZT sheets  26  and  28 , respectively. Blocks  34  and  36  are laterally aligned with body portion  12  sandwiched therebetween, have front ends  38  and  40 , respectively, which are aligned with the front end of the body portion  12 , are poled in the direction indicated by arrows  39  and  41  in FIG. 2A, and have rear ends  42  and  44 , respectively, that are aligned with one another and stop short of the rear end of the body portion  12 . Accordingly, as best illustrated in FIG. 1, a portion  12   a  of the body portion  12  extends rearwardly beyond the top and bottom blocks  34  and  36 . 
     As shown in FIG. 2B, thin layers  22  and  24  of a metallic material are disposed on the top side  14  and bottom side  16 , respectively, of the body portion  12 . A relatively thin sheet  26  of PZT having thin layers  70 ,  72  of a metallic material is mounted on the outer side surface of the metallic layer  22 . A first layer of a conductive adhesive  74 , for example, an epoxy material, is provided to conductively attach the metallic layer  70  attached to the sheet of PZT  26  and the metallic layer  22  attached to the top side  14  of the body portion  12 . A relatively thin sheet  28  of PZT having thin layers  76 ,  78  of a metallic material is mounted on the outer side surface of the metallic layer  24 . A second layer of a conductive adhesive  80 , for example, an epoxy material, is provided to conductively attach the metallic layer  76  attached to the sheet of PZT  28  and the metallic layer  24  attached to the bottom side  16  of the body portion  12 . In each of the embodiments shown in FIGS. 2A and 2B the PZT sheets  26  and  28  are poled in the direction indicated by arrows  30  and  32 . 
     Also, as shown in FIG. 2A, top and bottom blocks  34  and  36  of PZT are disposed on the outer sides of the PZT sheets  26  and  28 , respectively. 
     As shown in FIG. 2B, top block  34  of PZT having a thin layer  82  of a metallic material is mounted on the outer side surface of the metallic layer  72 . A third layer of a conductive adhesive  84 , is provided to conductively attach the metallic layer  82  attached to the top block  34  of PZT and the metallic layer  72  attached to the sheet  26  of PZT. Also, as shown in FIG. 2B, bottom block  36  of PZT having a thin layer  86  of a metallic material is mounted on the outer side surface of the metallic layer  78 . A fourth layer of a conductive adhesive  88 , is provided to conductively attach the metallic layer  86  attached to the bottom block  36  of PZT and the metallic layer  78  attached to the sheet  28  of PZT. 
     As shown in FIG. 2C, the body portion  12  is formed of a first body section  90  and a second body section  92 . A fifth layer of an adhesive  94 , for example, an epoxy material, is provided on the first body section  90  or the second body section  92 . The fifth layer of an adhesive  94  enables the first body section  90  to be secured to the second body section  92 . 
     In each of the embodiments shown in FIGS. 2A,  2 B and  2 C, blocks  34  and  36  are laterally aligned with body portion  12  sandwiched therebetween, have front ends  38  and  40 , respectively, which are aligned with the front end of the body portion  12 , are poled in the direction indicated by arrows  39  and  41 , and have rear ends  42  and  44 , respectively, that are aligned with one another and stop short of the rear end of the body portion  12 . Accordingly, as best illustrated in FIG. 1, a portion  12   a  of the body portion  12  extends rearwardly beyond the top and bottom blocks  34  and  36 . 
     Prior to the attachment of the top and bottom blocks  34  and  36  to the PZT sheets  26  and  28  or the metallic layers  72  and  78 , spaced series of grooves  50  and  52  are respectively formed in the top and bottom sides of the body portion  12 , through the metallic layers  22  and  24  and the PZT sheets  26  and  28  thereon, or through the metallic layers  22  and  24 , the adhesive layers  74  and  80 , through the metallic layers  70  and  76  and the PZT sheets  26  and  28  thereon, by means well known to those of ordinary skill in the art including precision dicing sawing such as disclosed in U.S. Pat. No. 5,414,916, the entire disclosure of which is hereby incorporated herein by reference. Grooves  50  and  52  are laterally displaced so that the walls of the body portion  12  and the PZT sheet  26  separating the grooves  50  are vertically aligned with the grooves  52 , and the walls of the body portion  12  and the PZT sheet  28  separating the grooves  52  are vertically aligned with the grooves  50 . Both sets of grooves  50  and  52  longitudinally extend from the front end of the body portion  12  to its rear end. After the formation of the grooves  50  and  52 , elongated segments  22   a  of the top metal layer  22  are interdigitated with the grooves  50 , and elongated segments  24   a  of the bottom metal layer  24  are interdigitated with the grooves  52 . The metal layer segments  22   a  and  24   a  are used as electrical leads through which control signals are transmitted by means of controller  29  in FIG. 1 to cause the operative piezoelectric deflection of internal portions of the printhead body. Similar electrical connection is made to metal layer segments  22   a  and  24   a . 
     After the top and bottom PZT blocks  34  and  36  are secured to the PZT sheets  26  and  28  they respectively cover the open sides of front portions of the grooves  50  and  52  to thereby form, within the printhead  10  a top series of interior driving channels  50  and a bottom series of interior driving channels  52 . The driving channels  50  and  52  are sealed at the rear portions of the top and bottom PZT blocks  34  and  36 , respectively. 
     Along their lengths the driving channels  50  are laterally bounded by opposing pairs of interior side walls  54  (see FIGS. 2A,  2 B and  2 C) each having in a vertically intermediate portion thereof a segment of the metallic layer  22  or segments of the metallic layer  22 , the adhesive layer  74  and the metallic layer  70 . In a similar manner, along their lengths the driving channels  52  are laterally bounded by opposing pairs of interior side walls  56  each having in a vertically intermediate portion thereof a segment of the metallic layer  24  or segments of the metallic layer  24 , the adhesive layer  80  and the metallic layer  76 . 
     A horizontally elongated orifice plate member  58  (see FIG. 1) is secured to the front ends  18 ,  38  and  40  of the body portion  12  and the top and bottom blocks  34  and  36 , and has a single horizontally extending array A 1  of small diameter orifices  60  formed therethrough. Each of the orifices is in fluid communication with a different one of the driving channels  50  and  52 . Ink manifolds (not shown) are interiorly formed within rear end portions of the top and bottom PZT blocks  34  and  36  and are supplied with ink from a suitable source thereof (not shown) via exterior ink supply conduits  62  and  64 . The orifices  60 , preferably, are tapered and may be formed according to methods well known to those of ordinary skill in the art, such as those disclosed in U.S. Pat. No. 5,208,980, the entire disclosure of which is hereby incorporated herein by reference. As shown in FIG. 3, the orifices  60  disposed in the horizontally elongated orifice plate member  58  (see FIG. 1) are generally cylindrical. Also, each orifice  60  is in fluid communication with a fluid channel  66  (shown in dotted lines) disposed on the obverse of the plate member  58 . Each fluid channel  66  in turn is in fluid communication with one of the driving channels  50  and  52 , thereby providing fluid ejection nozzles for the ink jet printhead  10 . 
     The plate member  58  may be formed of any suitable material and may include one or more of the following commercially available materials: a polyimide material, polyethylene terephthalate, polybutylene terephthalate, polyesters, polyamides, cellulosic polymers, vinyl polymers, acrylic polymers, fluorinated polyethylenes, polyolefins, polyether ketones, polyoxazoles, polythiazoles, metallic films, metallized films, plates and glasses as are well known to those of ordinary skill in the art. 
     As shown in FIGS. 4A and 4B, the plate member  58  may be formed by applying a layer of adhesive  68 , for example, an epoxy material, to a block of material suitable for forming the plate member  58 . 
     A layer of backing material (not shown) is superposed on the adhesive layer  68  to protect the adhesive layer  68  during formation of the orifices  60  and fluid channels  66 . 
     The orifices  60  and fluid reservoirs  66  may be formed in the plate member  58 , adhesive  68  and backing material composite structure by removing portions of each of the backing material, adhesive  68  and plate member  58  according to any suitable technique well known to those of ordinary skill in the art such as by excimer laser ablation as disclosed in U.S. Pat. No. 5,208,980, the entire disclosure of which is incorporated herein by reference. According to the excimer laser ablation process, the laser energy is focused on the composite structure through a sequence of masks. FIG. 4A shows the plate member  58  and adhesive  68  structure after formation of the fluid channels  66  and orifices  60 . FIG. 4B shows a cross-section of the fluid channels  66  and orifices  60  extending within the plate member  58 . 
     FIG. 5 shows the ablation sequence for forming the orifices  60  and fluid reservoirs  66  in the plate member  58 , adhesive  68  and backing material  98  composite structure  100  shown in FIG.  5 A. First, a mask  102  having openings  104  as shown in FIG. 5B, is superposed on the backing material  98  of the composite structure  100 . Excimer laser energy is focused on the composite structure  100  through the openings  104  in the mask  102  to remove portions of the backing layer  98 , adhesive  68  and plate member  58  to result in the structure shown in FIG.  5 C. Next, a mask  106  having orifices  108  as shown in FIG. 5D, is superposed on the backing material  98  of the composite structure  100 . Excimer laser energy is focused on the composite structure  100  through the orifices  108  to remove portions of the plate member  58  to form the orifices  60  in the plate member  58  and result in the structure shown in FIG.  5 E. 
     To mount the plate member  58  to the respective leading edges of the body portion  12 , the thin metallic layers  22  and  24 , the PZT sheets  26  and  28  and the top and bottom blocks  34  and  36 , as well as the metallic layers  70 ,  72 ,  76 ,  78 ,  82  and  86  and the adhesive layers  74 ,  80 ,  84  and  88  (as appropriate) the remaining portions of the backing material layer  98  may be removed to expose the layer of adhesive  68  as shown in FIG.  5 F. The exposed portions of the layer of adhesive  68  are then aligned with and superposed on the front end  18  of the body portion  12 , the front ends of the thin metallic layers  22  and  24 , the front end of the PZT sheets  26  and  28  and the front ends  38  and  40  of the top and bottom blocks  34  and  36 , as well as the metallic layers  70 ,  72 ,  76 ,  78 ,  82  and  86  and the adhesive layers  74 ,  80 ,  84  and  88  (as appropriate). 
     FIG. 4C shows an alternate embodiment of the plate member  58  which also includes a nonwetting coating  59  on the surface of the plate member  58  opposite the front ends  18 ,  38  and  40  of the body portion  12  and the top and bottom blocks  34  and  36 . The nonwetting coating  59  may be formed of any suitable material and preferably may include commercially available modified polytetrafluoroethylene (Teflon®). Those of ordinary skill in the art will recognize that the nonwetting coating  59  may be selected from many other suitable nonwetting coating materials that are well known to those of ordinary skill in the art. 
     The ablation sequence discussed above with respect to FIG. 5 may also be used to form the cover plate  58  including the nonwetting coating  59  except that the composite structure  100  also includes the nonwetting coating  59  and the ablation step shown in FIG. 5D involves focusing excimer laser energy on the composite structure  100  through the orifices  108  in the mask  106  to remove portions of the plate member  58  and the nonwetting coating  59  to form the orifices  60  in the plate member  58 . 
     During operation of the printhead  10  ink disposed within the driving channels  50  and  52  may be discharged through selected ones of the associated orifices  60  by transmitting electrical driving signals through the segments of the metallic layers  22  and  24 , as well as the segments of the metallic layers  22  and  24 , the adhesive layers  74  and  80  and the metallic layers  70  and  76  (as appropriate) to piezoelectrically deflect the interior side walls of the channels communicating with the selected orifices to cause the forward discharge of ink outwardly through the selected orifices. 
     For example, if it is desired to discharge ink in droplet form from an orifice  60  associated with the top channel  50   a  shown in FIG. 2A, appropriate electrical driving signals are transmitted through the pair of metallic lead segments  22   a  within the opposing interior side walls  54  that laterally bound the channel  50   a . These driving signals are first used to piezoelectrically deflect the bounding pair of side walls  54  outwardly away from the selected channel  50   a , and then reversed to piezoelectrically deflect the bounding pair of side walls  54  into the selected channel  50   a  to increase the ink pressure therein and responsively force a droplet of ink outwardly through the associated orifice  60 . In a similar manner, electrical driving signals may be transmitted through associated pairs of the bottom metallic lead segments  24   a  to force ink, in droplet form, outwardly from a selected bottom channel  52  through its associated orifice  60 . 
     Those of ordinary skill in the art will recognize that while the body portion  12  is shown in FIGS. 1,  2 A and  2 B as being formed from a unitary block of PZT material with grooves cut in the top and bottom of the block, the body portion  12  can also be formed by bonding together two blocks of PZT material each having grooves cut in one side thereof in which the grooves are misaligned such as is shown in FIG.  2 C. 
     Those of ordinary skill in the art will recognize that compared to a conventionally configured ink jet printhead assembly having only a single driving channel array in its main piezoelectric block portion, the ink jet printhead  10  of the present invention advantageously provides a substantially higher discharge orifice density due to the fact that two laterally misaligned channel arrays are formed on opposite sides of the main printhead body portion defined by the main piezoelectric block  13 , the metallic layers  22  and  24 , and the opposite side sheets of piezoelectric material  26  and  28 . The provision of these dual channel series in this manner substantially reduces the overall size of the printhead to create this substantially increased orifice density. The lateral displacement of the driving channels makes the printhead easier to make and use since alignment tolerances between the first and second series of driving channels  50  and  52  are reduced which consequently reduces print errors. 
     While the present invention has been described with reference to a presently preferred embodiment, it will be appreciated by those of ordinary skill in the art that various modifications, changes, alternatives and variations may be made therein without departing from the spirit and scope thereof as defined in the appended claims.