Patent Publication Number: US-6986566-B2

Title: Liquid emission device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 10/273,916, filed Oct. 18, 2002, now U.S. Pat. No. 6,761,437 B2, and assigned to the Eastman Kodak Company which is a continuation-in-part of U.S. patent application Ser. No. 09/470,638, filed Dec. 22, 1999, now U.S. Pat. No. 6,497,510, and assigned to the Eastman Kodak Company. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to micro electro-mechanical (MEM) liquid emission devices such as, for example, inkjet printing systems, and more particularly such devices which employ a thermal actuator in some aspect of drop formation. 
     BACKGROUND OF THE PRIOR ART 
     Ink jet printing systems are one example of digitally controlled liquid emission devices. Ink jet printing systems are typically categorized as either drop-on-demand printing systems or continuous printing systems. 
     Until recently, conventional continuous ink jet techniques all utilized, in one form or another, electrostatic charging tunnels that were placed close to the point where the drops are formed in a stream. In the tunnels, individual drops may be charged selectively. The selected drops are charged and deflected downstream by the presence of deflector plates that have a large potential difference between them. A gutter (sometimes referred to as a “catcher”) is normally used to intercept the charged drops and establish a non-print mode, while the uncharged drops are free to strike the recording medium in a print mode as the ink stream is thereby deflected, between the “non-print” mode and the “print” mode. 
     U.S. Pat. No. 6,079,821, issued to Chwalek et al., Jun. 27, 2000, discloses an apparatus for controlling ink in a continuous ink jet printer. The apparatus includes a source of pressurized ink communicating with an ink delivery channel. A nozzle bore opens into the ink delivery channel to establish a continuous flow of ink in a stream with the nozzle bore defining a nozzle bore perimeter. A heater causes the stream to break up into a plurality of droplets at a position spaced from the nozzle bore. The heater has a selectively-actuated section associated with only a portion of the nozzle bore perimeter such that actuation of the heater section produces an asymmetric application of heat to the stream to control the direction of the stream between a print direction and a non-print direction. 
     U.S. Pat. Nos. 6,554,410 and 6,588,888, both of which issued to Jeanmaire et al., on Apr. 29, 2003 and Jul. 8, 2003, respectively, disclose continuous ink jet printing systems which use a gas flow to control the direction of the ink stream between a print direction and a non-print direction. Controlling the ink stream with a gas flow reduces the amount of energy consumed by the printing system. 
     Drop-on-demand printing systems incorporating a heater in some aspect of the drop forming mechanism are known. Often referred to as “bubble jet drop ejectors”, these mechanisms include a resistive heating element(s) that, when actuated (for example, by applying an electric current to the resistive heating element(s)), vaporize a portion of a liquid contained in a liquid chamber creating a vapor bubble. As the vapor bubble expands, liquid in the liquid chamber is expelled through a nozzle orifice. When the mechanism is de-actuated (for example, by removing the electric current to the resistive heating element(s)), the vapor bubble collapses allowing the liquid chamber to refill with liquid. 
     U.S. Pat. No. 6,460,961 B2, issued to Lee et al., on Oct. 8, 2002, discloses resistive heating elements that, when actuated, form a vapor bubble (or “virtual” ink chamber) around a nozzle orifice to eject ink through the nozzle orifice. However, these types of liquid emitting devices have nozzle orifices that share a common ink chamber. As such, adjacent nozzle orifices are susceptible to nozzle cross talk when corresponding resistive heating elements are actuated. 
     Attempts have been made to reduce nozzle cross talk. For example, U.S. Pat. No. 6,439,691 B1, issued to Lee et al., on Aug. 27, 2002, positions barriers at various locations in the common ink chamber. This, however, increases the complexity associated with manufacturing the liquid emitting device because the common ink chamber is maintained. U.S. Pat. Nos. 6,102,530 and 6,273,553, issued to Kim et al., on Aug. 15, 2000, and Aug. 14, 2001, respectively, also attempt to reduce nozzle cross talk by offsetting each nozzle orifice relative to the common ink chamber. Doing this, however, provides only one refill port necessary to refill the portion of the ink chamber located under the nozzle orifice. Having only one refill port can reduce overall speeds associated with ejecting the liquid because the time associated with chamber refill is increased. 
     SUMMARY OF THE INVENTION 
     According to a feature of the present invention, a print head includes a body. Portions of the body define an ink delivery channel and other portions of the body defining a nozzle bore. The nozzle bore is in fluid communication with the ink delivery channel. An obstruction having an imperforate surface is positioned in the ink delivery channel. 
     According to another feature of the present invention, a print head includes a fluid delivery channel. A nozzle bore is in fluid communication with the fluid delivery channel. A heater is positioned proximate to the nozzle bore. An insulating material is located between the heater and at least one of the fluid delivery channel and the nozzle bore. An obstruction having an imperforate surface is positioned in the fluid delivery channel. 
     According to another feature of the present invention, a liquid emission device includes a body. Portions of the body define a fluid delivery channel. Other portions of the body define a nozzle bore. The nozzle bore is in fluid communication with the fluid delivery channel. An obstruction having an imperforate surface is positioned in the fluid delivery channel. A drop forming mechanism is operatively associated with the nozzle bore. An insulating material is positioned between drop forming mechanism and the body. 
     According to another feature of the present invention, a liquid emission device includes an ink delivery channel. A nozzle bore is in fluid communication with the ink delivery channel. An ink drop forming mechanism is operatively associated with the nozzle bore. An obstruction having an imperforate surface is positioned in the ink delivery channel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a liquid emission device according to the present invention; 
         FIG. 2  is a schematic illustration of the liquid emission device configured as a continuous ink jet print head and printing system; 
         FIG. 3  is a cross-sectional view of one nozzle from a prior art nozzle array showing d 1  (distance to print medium) and θ 1  (angle of deflection); 
         FIG. 4  is a top view of a nozzle having an asymmetric heater positioned around the nozzle; 
         FIG. 5  is a cross-sectional view of one nozzle incorporating one embodiment of the present invention showing d 2  and θ 2 ; 
         FIG. 6  is a cross-sectional view of one nozzle incorporating another embodiment of the present invention; 
         FIG. 7  is a cross-sectional view of one nozzle incorporating a preferred embodiment of the present invention showing d 3  and θ 3 ; 
         FIG. 8  is a graph illustrating the relationships between d 1 –d 3 , θ 1 –θ 3 , and A; 
         FIG. 9  is a perspective top view of the liquid emission device according to the present invention; 
         FIG. 10  is a top view of the liquid emission device according to the present invention; 
         FIG. 11  is a bottom view of the liquid emission device according to the present invention; 
         FIG. 12  is a cross-sectional side view of one ejection mechanism of the liquid emission device shown in  FIG. 11  as shown along line  12 — 12 ; 
         FIG. 13  is a cross-sectional side view of one ejection mechanism of the liquid emission device shown in  FIG. 12  as shown along line  13 — 13 ; 
         FIG. 14  is a cross-sectional side view of one ejection mechanism of the liquid emission device shown in  FIG. 11  as shown along line  14 — 14 ; 
         FIG. 15  is a cross-sectional bottom view of one ejection mechanism of the liquid emission device shown in  FIG. 11  as shown along line  15 — 15 ; 
         FIG. 16  is an alternative embodiment of a drop forming mechanism; and 
         FIGS. 17–20  illustrate operation of the liquid emission device configured as a drop on demand print head. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present description will be directed, in particular, to elements forming part of, or cooperating directly with, apparatus or processes of the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. 
     As described herein, the present invention provides a liquid emission device and a method of operating the same. The most familiar of such devices are used as print heads in inkjet printing systems. The liquid emission device described herein can be operated in a continuous mode and/or in a drop-on-demand mode. 
     Many other applications are emerging which make use of devices similar to inkjet print heads, but which emit liquids (other than inks) that need to be finely metered and deposited with high spatial precision. As such, as described herein, the term liquid refers to any material that can be ejected by the liquid emission device described below. 
     Referring to  FIG. 1 , a schematic representation of a liquid emission device  10 , such as an inkjet printer, is shown. The system includes a source  12  of data (say, image data) which provides signals that are interpreted by a controller  14  as being commands to emit drops. Controller  14  outputs signals to a source  16  of electrical energy pulses which are inputted to the liquid emission device, for example, an inkjet print head  18 . During operation, liquid, for example, ink, is deposited on a recording medium  20 . Typically, liquid emission device  10  includes a plurality of ejection mechanisms  22 . 
     Referring to  FIG. 2 , print head  18  of liquid emission device  10  is shown configured as a continuous ink jet printer system. Print head  18  includes a plurality of ejection mechanisms  22  forming an array of nozzles with each nozzle of the array being associated with a drop forming mechanism (for example, nozzle heater(s)  24 ). Print head  18  also houses heater control circuits  26  (shown schematically in  FIG. 4 ) which process signals from controller  14 . Heater control circuits  26  take data from the image memory  12 , and send time-sequenced electrical pulses to the array of nozzle heaters  24 . These pulses are applied at an appropriate time, and to the appropriate nozzle, so that drops formed from a continuous ink jet stream will form spots on recording medium  20 , in the appropriate position designated by the data sent from the image memory. Pressurized ink travels from an ink reservoir  28  to an ink delivery channel  30  and through nozzle array  22  onto either the recording medium  20  or a gutter  32 . 
     Referring to  FIG. 3 , an enlarged cross-sectional view of a single nozzle of ejection mechanism  22  from the nozzle array shown in  FIG. 2  is shown as it is in the prior art. Note that ink delivery channel  30  shows arrows  34  that depict a substantially vertical flow pattern of ink headed into nozzle bore  36 . There is a relatively thick wall  38  which serves, inter alia, to insulate the ink in the channel  30  from heat generated by the nozzle heater sections  24   a / 24   a ′ (described below). Wall  38  may also be referred to as an “orifice membrane.” An ink stream  40  forms from a meniscus of ink initially leaving the nozzle bore  36 . At a distance below the nozzle bore  36  ink stream  40  breaks into a plurality of drops  42 ,  44 . 
     Referring to  FIG. 4 , and back to  FIG. 3 , an expanded bottom view of heater  24  is shown. Line  3 — 3 , along which line the  FIG. 3  cross-sectional illustration is also shown. Heater  24  has two sections (heater sections  24   a  and  24   a ′). Each section  24   a  and  24   a ′ covers approximately one half of the nozzle bore opening  36 . Alternatively, heater sections can vary in number and sectional design. One section provides a common connection G, and isolated connection P. The other has G′ and P′ respectively. Asymmetrical application of heat merely means applying electrical current to one or the other section of the heater independently. By so doing, the heat will deflect the ink stream  40 , and deflect the drops  42 , for example, away from the particular source of the heat. For a given amount of heat, the ink drops  42  are deflected at an angle θ 1  (in  FIG. 3 ) and will travel a vertical distance d 1  to gutter  32  (or onto recording media  20 ) from print head  18 . There also is a distance “A”, which distance defines the space between where the deflection angle θ 1  would place the deflected drops  42  in gutter  32  or on recording medium  20  and where the drops  44  would have landed without deflection. The stream deflects in a direction anyway from the application of heat. The ink gutter  32  is configured to catch deflected ink droplets  42  while allowing undeflected drop  44  to reach a recording medium. An alternative embodiment of the present invention could reorient ink gutter (or catcher)  32  to be placed so as to catch undeflected drops  44  while allowing deflected drops  42  to reach the recording medium  20 . 
     The ink in the delivery channel emanates from pressurized reservoir  28  (shown in  FIG. 2 ) leaving the ink in the channel under pressure. In the past the ink pressure suitable for optimal operation would depend upon a number of factors, particularly geometry and thermal properties of the nozzles and thermal properties of the ink. A constant pressure can be achieved by employing an ink pressure regulator (not shown). 
     Referring to  FIGS. 5 and 6 , during operation, the lateral course of ink flow patterns  46  in the ink delivery channel  30 , are enhanced by, a geometric obstruction  48 , placed in the delivery channel  30 , just below the nozzle bore  50 . This lateral flow enhancing obstruction  48  can be varied in size, shape and position, and serves to improve the deflection, based upon the lateralness of the flow and can therefore reduce the dependence upon ink properties (i.e. surface tension, density, viscosity, thermal conductivity, specific heat, etc.), nozzle geometry, and nozzle thermal properties while providing greater degree of control and improved image quality. Preferably the obstruction  48  has a lateral wall parallel to the reservoir side of wall  52 , and cross sectional shapes such as squares, rectangles, triangles (shown in  FIG. 6  with like features being represented using like reference symbols), etc. Wall  52  can serve to insulate portions of ejection mechanism  22  in a manner similar to, or identical to, wall  38  (discussed above). Ejection mechanism  22  can include additional material layer(s)  53  stacked on wall  52 . Layer(s)  53  can also serve to insulate other portions of mechanism from the heat generated by heater  24 . 
     The deflection enhancement may be seen by comparing for example the margins of difference between θ 1  of  FIG. 3  and θ 2  of  FIG. 5 . This increased stream deflection enables improvements in drop placement (and thus image quality) by allowing the recording medium  20  to be placed closer to the print head  18  (d 2  is less than d 1 ) while preserving the other system level tolerances (i.e. spacing, alignment etc.) for example see distance A. The orifice membrane or wall  52  can also be thinner. We have found that a thinner wall provides additional enhancement in deflection which, in turn, serves to lessen the amount of heat needed per degree of the angle of deflection θ 2 . 
     Referring to  FIG. 7 , drop placement and thus image quality can be even further enhanced by an obstruction  48  which provides almost total lateral flow  54  at the entrance to nozzle bore  56 . Again, wall  52  can serve to insulate portions of ejection mechanism  22  like wall  38  (discussed above). Ejection mechanism  22  can include additional material layer(s)  53  stacked on wall  52 . Layer(s)  53  can also serve to insulate other portions of mechanism from the heat generated by heater  24 . The distance d 3  to print medium  20  is again lessened per degree of heat because deflection angle θ 3  can be increased per unit temperature. 
       FIG. 8  shows the relationship of a constant drop placement A as distances to the print media d 1 , d 2 , and d 3  become less and less and as deflection angles θ 1 , θ 2 , and θ 3  become increasingly larger. As a consequence of enhanced lateral flow, the ability to miniaturize the printer&#39;s structural dimensions while enhancing image size and enhancing image detail is achieved. 
     Referring to  FIGS. 9–11 , print head  18  of liquid emission device  10  includes a plurality of ejection mechanisms  22  positioned in a linear array along a length dimension  58  of print head  18 . Ejection mechanisms  22  can be positioned in other types of arrays, for example, two dimensional arrays in which nozzle bores  56  are aligned in rows or staggered in rows. Other positions known in the art are also permitted. Ejection mechanism  22  includes a drop forming mechanism operatively associated with a nozzle bore  56 . In  FIGS. 9–11 , the drop forming mechanism includes a heater  24  positioned about a nozzle bore  36 . Heater  24  has been described above with reference to  FIGS. 3 and 4 . Heater  24  can be positioned about nozzle bore  36  on a top surface  60  of a material layer, for example, one of layers  52  or  53 . Alternatively, heater  24  can be positioned within a material layer, for example, one of layers  52  or  53 . Print head  18  also includes a width dimension  62 . 
     Referring to  FIG. 12 , a cross-sectional view of one of the plurality of thermally actuated drop ejection mechanisms  22  is shown. Nozzle bore  56  is formed in wall  52  and any additional material layer(s) present, for example, material layer  53 , for each ejection mechanism  22 . When additional material layer(s)  53  are present, the additional layers are stacked on top of one another, as is known in the art and commonly referred to as a dielectric stack. 
     Obstruction  48  is positioned in delivery channel  30 . Obstruction  48  can be centered over nozzle bore  56  with a lateral wall  64  that extends perpendicular to nozzle bore  56  as viewed along a plane that is perpendicular to nozzle bore  56 , as shown in  FIG. 12 . Lateral wall  64  is also typically positioned parallel to wall  52  and spaced apart from wall  52  such that delivery channel  30  intersects nozzle bore  56 . 
     A surface  66  of wall  64  is imperforate which causes fluid in delivery channel  30  to flow around obstruction  48  to arrive at and pass through nozzle bore  56 . Imperforate surface  66  at least partially creates lateral flow  54  when ejection mechanism  22  is operated in a continuous manner, as described above. Imperforate surface  66  also at least partially creates ejection chamber  68  when ejection mechanism  22  is operated in a drop on demand manner, described below. 
     A vertical wall or walls  70  of obstruction  48  is positioned in delivery channel  30  at a location relative to nozzle bore  56  that causes surface  66  to overlap nozzle bore  56 . This helps to further define ejection chamber  68  and/or create lateral flow  54 . Alternatively, vertical wall(s)  70  can be located such that surface  66  extends through the diameter of nozzle bore  56 , as shown in  FIGS. 5 and 6 . 
     Heater  24  is operatively associated with nozzle bore  56  and in  FIG. 12  is shown positioned on an outer surface of material layer  53 . However, as described above, heater  24  can be located in other areas as long as heater  24  is operatively associated with nozzle bore  56 . These other areas can include, for example, on a surface of wall  52 , within wall  52 , partially within wall  52 , partially within material layer  53 , within material layer  53 , etc. Additional heater(s)  24  can be included within ejection chamber  68 . For example, heater(s)  24  can be positioned on obstruction  48 . 
     Referring to  FIG. 13 , another cross-sectional view of thermally actuated drop ejection mechanism  22  is shown. In  FIG. 13 , print head  18  is shown including a plurality of ejection mechanisms  22 . Delivery channel  30  supplies liquid (for example, ink) from source  28  through nozzle bores  56 . An obstruction  48  is positioned in delivery channel  30  relative to each nozzle bore  56 , as described above. As such, it can be said that each ejection mechanism  22  includes an individual obstruction  48 . Obstruction  48  is supported by wall(s)  72 . Typically, this is accomplished by integrally forming each obstruction  48  with wall(s)  72  during the ejection mechanism  22  fabrication process. However, obstruction  48  can be supported relative to nozzle bore  56  is any known manner provided delivery channel  30  has access to nozzle bore  56 . 
     Referring to  FIGS. 13 and 14 , wall(s)  72  are positioned on opposing sides of nozzle bore  56  perpendicular to the length dimension  58  of print head  18 . Wall(s)  72  are also typically positioned parallel to the width dimension  62  of print head  18 . However, wall(s)  72  can be positioned at other angles relative to the length dimension  58  and width dimension  62  depending on the location pattern of each nozzle bore  56 . 
     Referring to  FIG. 14 , another cross-sectional view of ejection mechanism  22  is shown. As shown in  FIG. 14 , wall  72  does not extend to wall  52  on the side of wall  52  opposite nozzle bore  56 , but does extend to wall  52  on the side of wall  52  that includes nozzle bore  56 . As such, delivery channel  30  has access to multiple nozzle bores  56  while the location of wall(s)  72  helps to define ejection mechanism  22 . The positioning of wall(s)  72  reduces problems that typically occur when multiple nozzle bores share a common delivery channel (nozzle to nozzle cross talk, etc.) while still providing source  28  with access to a plurality of nozzle bores  56  through delivery channel  30 . 
     Referring to  FIG. 15 , another cross-sectional view of ejection mechanism  22  is shown with like features being represented using like reference signs. The cross-sectional view of ejection mechanism  22  is the same cross-sectional view of ejection mechanism  22  shown in  FIGS. 1 and 7  above and  FIGS. 17–20  below. 
     Referring to  FIG. 16 , an alternative embodiment of heater  24  is shown. In this embodiment, heater  74  has an annular portion  76  and is positioned around nozzle bore  56 . Heater  74  also has a common connection G and a connection P connected to annular portion  76 . In this embodiment, heater  74  is actuated as a whole. 
     Referring to  FIGS. 17–20  and back to  FIG. 1 , operation of ejection mechanism  22  in a drop on demand mode will be described. Controller  14  outputs a signal to source  16  that causes source  16  to deliver an actuation pulse to heater  24  (or  74 ). The actuation of heater  24  (or  74 ) causes a portion of the fluid (for example, ink) typically maintained under a slight negative pressure in ejection chamber  68  to vaporize forming vapor bubble(s)  78 . Vapor bubble(s)  78  expands forcing fluid in ejection chamber  68  to be ejected through nozzle bore  56  in the form of a drop  80 . The direction of vapor bubble(s)  78  expansion is opposite to the direction of drop  80  ejection. Vapor bubble(s)  78  collapse after heater  24  (or  74 ) is de-energized. This allows delivery channels  30  to refill ejection chamber  68 . The process is repeated when an additional fluid drop(s) is desired. 
     In another example embodiment, vapor bubble(s)  78  expand at least partially sealing ejection chamber  68  from delivery channels  30 . The expansion of vapor bubble(s)  78  also forces fluid in ejection chamber  68  to be ejected through nozzle bore  56  in the form of a drop  80 . The direction of vapor bubble(s)  78  expansion is opposite to the direction of drop  80  ejection. Vapor bubble(s)  78  collapse after heater  24  (or  74 ) is de-energized. This allows delivery channels  30  to refill ejection chamber  68 . The process is repeated when an additional fluid drop(s) is desired. 
     In another example embodiment, vapor bubble(s)  78  expand and contact obstruction  48  (or a portion of wall  52 ) sealing ejection chamber  68  from delivery channels  30 . The expansion of vapor bubble(s)  78  also forces fluid in ejection chamber  68  to be ejected through nozzle bore  56  in the form of a drop  80 . The direction of vapor bubble(s)  78  expansion is opposite to the direction of drop  80  ejection. Vapor bubble(s)  78  collapse after heater  24  (or  74 ) is de-energized. This allows delivery channels  30  to refill ejection chamber  68 . The process is repeated when an additional fluid drop(s) is desired. 
     Heater  24  (or  74 ) activation pulse can take the shape of any wave form (including period, amplitude, etc.) known in the industry. For example, heater  24  (or  74 ) activation pulse can be shaped like one of the waves forms, or a combination of the wave forms, disclosed in U.S. Pat. No. 4,490,728, issued to Vaught et al. on Dec. 25, 1984. However, other wave form shapes are also possible. 
     Although ejection mechanism  22  can be fabricated such that one or more delivery channels  30  feed ejection chamber  68 , it has been discovered that two delivery channels  30  adequately allow ejection chamber  68  to be refilled without sacrificing fluid ejection speeds while reducing nozzle to nozzle cross talk. However, alternative embodiments of ejection mechanism  22  can include more or less delivery channels  30  feeding ejection chamber  68  depending on the application specifically contemplated for ejection mechanism  22 . 
     Additionally, positioning delivery channels  30  on opposing sides of ejection chamber  68  facilitates implementation of heater  24  having individually actuateable sections  24   a  and  24   a ′ as the drop forming mechanism. Heater section  24   a  is positioned to seal off one delivery channel  30  when section  24   a  is activated while heater section  24   a ′ is positioned to seal off the other delivery channel  30  when section  24   a ′ is activated. 
     Experimental Results 
     An ejection mechanism  22  was fabricated using known CMOS and/or MEMS fabrication techniques. Ejection mechanism  22  included a nozzle bore  56  (having a diameter of approximately 10 microns) and a heater  24  (or  74 ) (having a width of approximately 2 microns) positioned approximately 0.6 microns from nozzle bore  56 . Heater  24  (or  74 ) was positioned on wall (or “orifice membrane”)  52  (having a thickness of approximately 1.5 microns). Obstruction  48  in conjunction with walls  52  formed ejection chamber  68 . (Ejection chamber  68  had a height of approximately 4 microns, the distance between wall  52  and obstruction  48 , and a width of approximately 30 microns, the distance between delivery channels or the width of obstruction  48 ). Ejection chamber  68  was in fluid communication with two delivery channels  30  (each delivery channel having dimensions of approximately 30 microns×120 microns). 
     Experimental ejection mechanism  22  was operated in the manner described above. Heater  24  (or  74 , a 234 ohm heater) was supplied through a cable with a 6 volt electrical pulse having a duration of approximately 2.8 microseconds causing a drop of approximately 1 pico-liter to be ejected through nozzle bore  56 . The energy required to accomplish this was approximately 0.4 micro-joules. Subsequent math modeling, a common form of experimentation in the CMOS and/or MEMS industry, has shown that this energy requirement can be substantially reduced to approximately 0.2 micro-joules or less. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention.