Abstract:
A continuous ink jet printhead and method are provided. The printhead includes an ink delivery channel. A plurality of nozzle bores are in fluid communication with the ink delivery channel. An individual obstruction is associated with each nozzle bore. Each individual obstruction is positioned in the ink delivery channel such that each obstruction creates a lateral flow pattern in ink continuously flowing through each of the plurality of nozzle bores as measured from a plane perpendicular to the plurality of nozzle bores.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application 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 the field of digitally controlled ink jet printing systems. It particularly relates to improving those systems that asymmetrically heat a continuous ink stream, in order to deflect the stream&#39;s flow between a non-print mode and a print mode. 
     BACKGROUND OF THE PRIOR ART 
     Ink jet printing is only one of many digitally controlled printing systems. Other digital printing systems include laser electrophotographic printers, LED electrophotographic printers, dot matrix impact printers, thermal paper printers, film recorders, thermal wax printers, and dye diffusion thermal transfer printers. Ink jet printers have become distinguished from the other digital printing systems because of the ink jet&#39;s non-impact nature, its low noise, its use of plain paper, and its avoidance of toner transfers and filing. 
     The ink jet printers can be categorized as either drop-on-demand or continuous systems. However, it is the continuous ink jet system which has gained increasingly more recognition over the years. Major developments in continuous ink jet printing are as follows: 
     Continuous ink jet printing itself dates back to at least 1929. See U.S. Pat. No. 1,941,001 which issued to Hansell that year. 
     U.S. Pat. No. 3,373,437, which issued to Sweet et al. in March 1968, discloses an array of continuous ink jet nozzles wherein ink drops to be printed are selectively charged and deflected towards the recording medium. This technique is known as binary deflection continuous ink jet printing, and is used by several manufacturers, including Elmjet and Scitex. 
     U.S. Pat. No. 3,416,153, issued to Hertz et al. in December 1968. It discloses a method of achieving variable optical density of printed spots, in continuous ink jet printing. Therein the electrostatic dispersion of a charged drop stream serves to modulate the number of droplets which pass through a small aperture. This technique is used in ink jet printers manufactured by Iris. 
     U.S. Pat. No. 4,346,387, also issued to Hertz, but it issued in 1982. It discloses a method and apparatus for controlling the electrostatic charge on droplets. The droplets are formed by the breaking up of a pressurized liquid stream, at a drop formation point located within an electrostatic charging tunnel, having an electrical field. Drop formation is effected at a point in the electric field, corresponding to whatever predetermined charge is desired. In addition to charging tunnels, deflection plates are used to actually deflect the drops. 
     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. 
     Recently, a novel continuous ink jet printer system has been developed which renders the above-described electrostatic charging tunnels unnecessary. Additionally, it serves to better couple the functions of (1) droplet formation and (2) droplet deflection. That system is disclosed in our copending U.S. Pat. No. 6,079,821 entitled “CONTINUOUS INK JET PRINTER WITH ASYMMETRIC HEATING DROP DEFLECTION”. Therein disclosed is an apparatus for controlling ink in a continuous ink jet printer. The apparatus comprises an ink delivery channel, a source of pressurized ink in communication with the ink delivery channel, and a nozzle having a bore which opens into the ink delivery channel, from which a continuous stream of ink flows. A droplet generator inside the nozzle causes the ink stream to break up into a plurality of droplets at a position spaced from the nozzle. The droplets are deflected by heat from a heater (in the nozzle bore) which heater has a selectively actuated section, i.e. a section associated with only a portion of the nozzle bore. Selective actuation of a particular heater section, at a particular portion of the nozzle bore produces what has been termed an asymmetrical application of heat to the stream. Alternating the sections can, in turn, alternate the direction in which this asymmetrical heat is applied and serves to thereby deflect the ink droplets, inter alia, between a “print” direction (onto a recording medium) and a “non-print” direction (back into a “catcher”). 
     Asymmetrically applied heat results in steam deflection, the magnitude of which depends upon several factors, e.g. the geometric and thermal properties of the nozzles, the quantity of applied heat, the pressure applied to, and the physical, chemical and thermal properties of the ink. Although solvent-based (particularly alcohol-based) inks have quite good deflection patterns, and achieve high image quality in asymmetrically heated continuous ink jet printers, water-based inks until now, have not. Water-based inks require a greater degree of deflection for comparable image quality than the asymmetric treatment, jet velocity, spacing, and alignment tolerances have in the past allowed. Accordingly, a means for enhancing the degree of deflection for such continuous ink jet systems, within system tolerances would represent a surprising but significant advancement in the art and satisfy an important need in the industry for water-based, and thus more environmentally friendly inks. 
     SUMMARY OF THE INVENTION 
     According to a feature of the present invention, a continuous ink jet printhead includes an ink delivery channel. A plurality of nozzle bores are in fluid communication with the ink delivery channel. An individual obstruction is associated with each nozzle bore. Each individual obstruction is positioned in the ink delivery channel such that each obstruction creates a lateral flow pattern in ink continuously flowing through each of the plurality of nozzle bores as measured from a plane perpendicular to the plurality of nozzle bores. 
     According to another feature of the present invention, a continuous ink jet printhead includes a body, portions of the body defining an ink delivery channel, other portions of the body defining a nozzle bore, the nozzle bore being in fluid communication with the ink delivery channel. An obstruction is positioned in the ink delivery channel such that the obstruction creates a lateral flow pattern in ink continuously flowing through the nozzle bore as measured from a plane perpendicular to the nozzle bore. 
     According to another feature of the present invention, a method of enhancing ink deflection in a continuous ink jet printhead includes providing a continuous flow of ink through a nozzle bore; creating a lateral flow pattern in the ink; and causing the ink to deflect as the ink flows through the nozzle bore. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a schematic diagram of an exemplary continuous ink jet print head and nozzle array as a print medium (e.g. paper) rolls under the ink jet print head; 
     FIG. 2 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. 3 shows a top view directly into a nozzle with an asymmetric heater surrounding the nozzle; 
     FIG. 4 is a perspective top view of a continuous ink jet print head incorporating the present invention; 
     FIG. 5 is a cross sectional bottom view of the printhead shown in FIG. 4 incorporating the present invention; 
     FIG. 6A is a cross-sectional view of one nozzle incorporating one embodiment of the present invention showing d 2  and θ 2 ; 
     FIG. 6B 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 ; and 
     FIG. 8 is a graph illustrating the relationships between d 1 -d 3 , θ 1 -θ 3 , and A. 
    
    
     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. 
     Referring to FIG. 1, a continuous ink jet printer system is generally shown at  10 . The print head  1 , from which extends an array of nozzle heaters  2 , houses heater control circuits (not shown) which process signals to an ink pressure regulator (not shown). 
     Heater control circuits read data from the image memory, and send time-sequenced electrical pulses to the array of nozzle heaters  2 . 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 a recording medium  3 , in the appropriate position designated by the data sent from the image memory. Pressurized ink travels from an ink reservoir  26  to an ink delivery channel  4  and through nozzle array  2  onto either the recording medium  3  or the gutter  9 . 
     Referring now to FIG. 2, an enlarged cross-sectional view of a single nozzle heater  2   a / 2   a ′ from among the nozzle array  2  shown in FIG. 1, is illustrated, as it is in the prior art. Note that ink delivery channel  4  shows arrows  5  that depict a substantially vertical flow pattern of ink headed into nozzle bore  6 . There is a relatively thick wall  7  which serves, inter alia, to insulate the ink in the channel  4  from heat generated in the nozzle heater  2   a / 2   a ′. Thick wall  7  may also be referred to as the “orifice membrane.” An ink stream  8  forms as a meniscus of ink initially leaving the nozzle bore  6 . At a distance below the nozzle bore  6  ink stream  8  breaks into a plurality of drops  11 . 
     Referring to FIG. 3, and back to FIG. 2, an expanded bottom view of heater  2   a / 2   a ′ showing the line  2 — 2 , along which line the FIG. 2 cross-sectional illustration is viewed. Heater  2   a / 2   a ′ can be seen to have two sections (sections  2   a  and  2   a ′). Each section covers approximately one half of the nozzle bore opening  6 . 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  8 , and deflect the drops  11 , away from the particular source of the heat. For a given amount of heat, the ink drops  11  are deflected at an angle θ 1  (in FIG. 2) and will travel a vertical distance d 1  onto recording media  3  from the print head. There also is a distance “A”, which distance defines the space between where the deflection angle θ 1  would place the deflected drops  11  on the recording media (or a catcher) and where the drops  12  would have landed without deflection. The stream deflects in a direction anyway from the application of heat. The ink gutter  9  is configured to catch deflected ink droplets  11  while allowing undeflected drop  12  to reach a recording medium. An alternative embodiment of the present invention could reorient ink gutter (“catcher”)  9  to be placed so as to catch undeflected drops  12  while allowing deflected drops  11  to reach the recording medium. 
     The ink in the delivery channel emanates from a pressurized reservoir  26 , 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 FIG. 4, printhead  1  has a plurality of nozzle bores  16  positioned along a length dimension  30  of printhead  1 . A nozzle heater  2   a / 2   a ′ is positioned about each nozzle bore  6  on a top surface  32  of printhead  1 . Alternatively, nozzle heater  2   a / 2   a ′ can be imbedded within the top surface  32  of printhead  1 . Printhead  1  also includes a width dimension  34 . 
     Referring to FIG. 5, printhead  1  includes an ink delivery channel  4  which supplies ink from ink source  26  through nozzle bores  6 . An individual geometric obstruction  20  is positioned in ink delivery channel  4  below each nozzle bore  6 . Each geometric obstruction  20  is supported by walls  36 . Typically, this is accomplished by integrally forming each obstruction  20  with walls  36  during the printhead fabrication process. 
     Referring to FIGS. 6A and 6B, in the operation of the present invention, the lateral course of ink flow patterns  14  in the ink delivery channel  4 , are enhanced by, a geometric obstruction  20 , placed in the delivery channel  4 , just below the nozzle bore  16 . This lateral flow enhancing obstruction  20  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  20  has a lateral wall parallel to the reservoir side of wall  18 , such as squares, rectangles, triangles (shown in FIG. 6B with like features being represented using like reference symbols), etc. The deflection enhancement may be seen by comparing for example the margins of difference between θ 1  of FIG.  2  and θ 2  of FIGS. 6 a  and  6   b . This increased stream deflection enables improvements in drop placement (and thus image quality) by allowing the recording medium  3  to be placed closer to the print head  1  (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  18  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 now to FIG. 7 drop placement and thus image quality can be even further enhanced by an obstruction  20  which provides almost total lateral flow  22  at the entrance to nozzle bore  24 . The distance d 3  to print medium  3  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.