Abstract:
Apparatus for controlling ink in a continuous inkjet printer in which a continuous stream of ink is emitted from a nozzle bore, including a reservoir containing pressurized ink; a rigid nozzle element defining an ink staging chamber and defining a nozzle bore in communication with the ink staging chamber arranged so as to establish a continuous flow of ink in a ink stream; ink delivery structure intermediate the reservoir and the ink staging chamber for communicating ink between the reservoir and defining first and second spaced ink delivery channels; and heat responsive bimorph flexible elements disposed in the first and second spaced ink delivery channels to control the flow of ink to the nozzle and thereby change the direction of ink from the nozzle.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly-assigned U.S. patent application Ser. No. 09/468,987 filed Dec. 21, 1999 entitled “Continuous Ink Jet Printer With Micro-Valve Deflection and Method of Making Same” by Lebens et al, and U.S. patent application Ser. No. 09/981,281 filed Oct. 17, 2001, entitled “Continuous Inkjet Printer with Actuable Valves for Controlling the Direction of Delivered Ink” by Furlani et al, the disclosures of which are incorporated herein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to continuous inkjet printheads which integrate multiple nozzles on a single substrate and in which print nonprint operation is effected by controlled deflection of the ink as it leaves the printhead nozzle. 
     BACKGROUND OF THE INVENTION 
     Many different types of digitally controlled printing systems have been invented, and many types are currently in production. These printing systems use a variety of actuation mechanisms, a variety of marking materials, and a variety of recording media. Examples of digital printing systems in current use include: laser electrophotographic printers; LED electrophotographic printers; dot matrix impact printers; thermal paper printers; film recorders; thermal wax printers; dye diffusion thermal transfer printers; and inkjet printers. However, at present, such electronic printing systems have not significantly replaced mechanical printing presses, even though this conventional method requires very expensive setup and is seldom commercially viable unless a few thousand copies of a particular page are to be printed. Thus, there is a need for improved digitally controlled printing systems, for example, being able to produce high quality color images at a high-speed and low cost, using standard paper. 
     Inkjet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because, e.g., of its non-impact, low-noise characteristics, its use of plain paper and its avoidance of toner transfers and fixing. Inkjet printing mechanisms can be categorized as either continuous inkjet or drop on demand inkjet. Continuous inkjet printing dates back to at least 1929. See U.S. Pat. No. 1,941,001 to Hansell. 
     U.S. Pat. No. 3,373,437, which issued to Sweet et al. in 1967, discloses an array of continuous inkjet nozzles wherein ink drops to be printed are selectively charged and deflected towards the recording medium. This technique is known as binary deflection continuous inkjet, and is used by several manufacturers, including Elmjet and Scitex. 
     U.S. Pat. No. 3,416,153, which issued to Hertz et al. in 1966, discloses a method of achieving variable optical density of printed spots in continuous inkjet printing using the electrostatic dispersion of a charged drop stream to modulate the number of droplets which pass through a small aperture. This technique is used in inkjet printers manufactured by Iris. 
     U.S. Pat. No. 3,878,519, which issued to Eaton in 1974, discloses a method and apparatus for synchronizing droplet formation in a liquid stream using electrostatic deflection by a charging tunnel and deflection plates. 
     U.S. Pat. No. 4,346,387, which issued to Hertz in 1982 discloses a method and apparatus for controlling the electric charge on droplets formed by the breaking up of a pressurized liquid stream at a drop formation point located within the electric field having an electric potential gradient. Drop formation is effected at a point in the field corresponding to the desired predetermined charge to be placed on the droplets at the point of their formation. In addition to charging rings, deflection plates are used to deflect the drops. 
     Conventional continuous inkjet utilizes electrostatic charging rings that are placed close to the point where the drops are formed in a stream. In this manner individual drops may be charged. The charged drops may be deflected downstream by the presence of deflector plates that have a large potential difference between them. A gutter (sometimes referred to as a “catcher”) may be used to intercept the charged drops, while the uncharged drops are free to strike the recording medium. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a high-speed continuous inkjet apparatus whereby drop deflection may occur at high repetition. 
     It is another object of the present invention to provide a high-speed continuous inkjet apparatus whereby drop formation and deflection may occur at high repetition. 
     These objects are achieved in an apparatus for controlling ink in a continuous inkjet printer in which a continuous stream of ink is emitted from a nozzle bore; the apparatus comprising: 
     a reservoir containing pressurized ink; 
     a rigid nozzle element defining an ink staging chamber and defining a nozzle bore in communication with the ink staging chamber arranged so as to establish a continuous flow of ink in a ink stream; 
     ink delivery means intermediate the reservoir and the ink staging chamber for communicating ink between the reservoir and defining first and second spaced ink delivery channels; 
     a first actuable flow delivery valve spaced from the nozzle bore and positioned in operative relationship with the first ink delivery channel and a second actuable flow delivery valve spaced from the nozzle bore positioned in operative relationship with the second ink delivery channel; 
     the first and second actuable flow delivery valves each including a flexible heat responsive element which when heated moves to a position that restricts flow in its corresponding ink delivery channel; and 
     means for selectively heating the first and second actuable flow delivery valves so that when both first and second actuable flow delivery valves are unheated ink is delivered through the nozzle along a first path and when the first actuable flow delivery valve is heated and the second actuable flow delivery valve is unheated, ink is delivered through the nozzle along a second path and when the second actuable flow delivery valve is heated and the first actuable flow delivery valve is unheated, ink is delivered through the nozzle along a third path wherein the first, second and third paths are spaced from each other. 
    
    
     These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a simplified block schematic diagram of one exemplary printing apparatus according to the present invention; 
     FIG. 2 shows in schematic form a cross-section of a segment of a continuous inkjet printhead illustrating the inkjet flow through a nozzle element with the nozzle element in an unactuated state and the inkjet flow along a first path; 
     FIGS. 3 a  and  3   b  illustrate a top and side view of a flexible heat responsive element, respectively; 
     FIGS. 4 a  and  4   b  illustrate cross sectional views of an actuable flow delivery valve in an unactivated and activated state, respectively; 
     FIG. 5 shows in schematic form a cross-section of a segment of continuous inkjet printhead illustrating the inkjet flow through a nozzle element with the nozzle element in a first actuated state and the inkjet flow along a second path; 
     FIG. 6 shows in schematic form a cross-section of a segment of continuous inkjet printhead illustrating the inkjet flow through a nozzle element with the nozzle element in a second actuated state and the inkjet flow along a third path; and 
     FIG. 7 shows in schematic form a cross-section of a segment of continuous inkjet printhead illustrating the inkjet flow along a second path wherein the inkjet is subjected to a thermal modulation which induces drop formation. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with 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 inkjet printer system includes an image source  10  such as a scanner or computer which provides raster image data, outline image data in the form of a page description language, or other forms of digital image data. This image data is converted to half-toned bitmap image data by an image processing unit  12  which also stores the image data in memory. The image processing unit  12  applies control signals  13  to a plurality of valve control circuits  14  which, in turn, apply time-varying electrical pulses to a set of electrically controlled valves and heater circuitry that are part of a printhead  16 . These pulses are applied at an appropriate time, and to the appropriate nozzle in the printhead  16 , so that drops formed from a continuous inkjet stream will form spots on a recording medium  18  in the appropriate position designated by the image data in the image memory. 
     Recording medium  18  is moved relative to printhead  16  by a recording medium transport system  20 , and which is electronically controlled by a recording medium transport control system  22 , which in turn is controlled by a micro-controller  24 . The recording medium transport system  20  shown in FIG. 1 is a schematic only, and many different mechanical configurations are possible. For example, a transfer roller could be used as recording medium transport system  20  to facilitate transfer of the ink drops to recording medium  18 . Such transfer roller technology is well known in the art. In the case of page width printheads, it is most convenient to move recording medium  18  past a stationary printhead. However, in the case of scanning print systems, it is usually most convenient to move the printhead along one axis (the sub-scanning direction) and the recording medium along the orthogonal axis (the main scanning direction) in a relative raster motion. 
     Micro-controller  24  may also control an ink pressure regulator  26  and valve control circuits  14 . Ink is contained in an ink reservoir  28  under pressure. The pressure can be applied in any convenient manner such as by using a standard air compressor. In the non-printing state, continuous inkjet drop streams are unable to reach recording medium  18  due to an ink gutter  17  that blocks the stream and which may allow a portion of the ink to be recycled by an ink recycling unit  19 . The ink recycling unit  19  reconditions the ink and feeds it back to ink reservoir  28 . Such ink recycling units  19  are well known in the art. The ink pressure suitable for optimal operation will depend on a number of factors, including geometry and thermal properties of the nozzles and thermal properties of the ink. A constant ink pressure can be achieved by applying pressure to ink reservoir  28  under the control of ink pressure regulator  26 . 
     The ink is distributed to the back surface of printhead  16  by an ink channel device  30 . The ink preferably flows through slots and/or holes etched through a silicon substrate of printhead  16  to its front surface, where a plurality of nozzles and heaters are situated. With printhead  16  fabricated from a silicon substrate, it is possible to integrate valve control circuits  14  with the printhead  16 . 
     Turning to FIG. 2, a segment of printhead  16  is shown schematically in cross-section illustrating the inkjet flow through a nozzle element  32  with the nozzle element  32  in an unactuated state. Each nozzle element  32  includes an ink staging chamber  40  having a nozzle bore  42  from which ink under pressure is emitted in the form of an inkjet  44  in a first direction which is indicated by flow arrow  46 . The pressurized ink from reservoir  28  is communicated to the ink staging chamber  40  by ink channel device  30 . The nozzle element  32  further includes an ink delivery means which includes a dividing wall  48  which defines a first ink delivery channel  50  and a second ink delivery channel  60 . The direction of ink flow through the first ink delivery channel  50  is indicated by flow arrow  52  and the flow is controlled by a first actuable flow delivery valve  54 . The direction of ink flow through the second ink delivery channel  60  is indicated by flow arrow  62  and the flow is controlled by a second actuable flow delivery valve  64 . The first actuable flow delivery valve  54  is controlled by a first valve control circuit  56 , and the second actuable flow delivery valve  64  is controlled by a second valve control circuit  66  as described below. The first and second valve control circuits  56  and  66  receive control signals from the valve control circuits  14  (FIG. 1) as shown. Each nozzle element  32  further includes a heater element  68  which surrounds the nozzle bore  42 . The heater element  68  is activated by a heater circuit  88 . 
     FIGS. 3 a  and  3   b  are respective top and side views of a flexible heat responsive element  70  in an unactuated state. The flexible heat responsive element  70  is used for the first and second actuable flow delivery valves  54  and  64 . The flexible heat responsive element  70  is a cantilevered structure that is fixedly attached at one end to support structure  72 . Preferably, the flexible heat responsive element  70  consists of two layers, a heater layer  74  and a support layer  76 . However, it is understood that the flexible heat responsive element  70  could be constructed of multiple layers and still provide the same function. The heater layer  74  consists of an electrically conductive strip that extends from the supported end of the cantilever up it length and back down as shown. The heater layer  74  should have a nonzero coefficient of thermal expansion and can be made from aluminum or other standard conductive metals and materials. The support layer  76  of the flexible heat responsive element  70  is made from a thermal and electrical insulator material such as silicon oxide or silicon nitride and has a lower coefficient of thermal expansion than the heater layer  74 . The ends of the heater layer  74  are connected to electrical terminals  78  and  80 . The terminals  78  and  80  are connected to the valve control circuit  56  for the first actuable flow delivery valve  54 , and to the valve control circuit  66  for the second actuable flow delivery valve  64 . When a voltage is applied to electrical terminals  78  and  80  with the polarity shown (i.e., terminal  70  at a higher potential than terminal  80 ) a current will flow along the heater layer  74  as indicated by current flow arrows  82 . The flexible heat responsive element  70  can be coated with a passivation layer (not shown) to protect it from chemical degradation and to provide electrical insulation as is well known. Such a layer may not be needed for some applications in which case it may be deleted. 
     FIGS. 4 a  and  4   b  illustrate cross sectional views of the flexible heat responsive element  70  in an unactivated and activated state, respectively. The unactuated state shown in FIG. 4 a  occurs when the flexible heat responsive element  70  is unheated at the ambient temperature. It is understood that the flexible heat responsive element  70  will have some curvature even at the ambient temperature even when it is unheated due to the difference in thermal expansion coefficients of the heater layer  74  and support layer  76 . To activate the flexible heat responsive element  70  a voltage is applied across the electrical terminals  78  and  80  which, in turn, causes a current to flow in the heater layer  74 . When current flows in the heater layer  74  its temperature increases due to joule heating and it tends to elongate in accordance with its coefficient of thermal expansion. The support layer  76  does not elongate as much as the heater layer  74  because it has a lower coefficient of thermal expansion and it is at a lower or equal temperature. The difference in elongation between the heater layer  74  and support layer  76  results in a bending of the flexible heat responsive element  70  as is well known. A typical activated profile of flexible heat responsive element  70  is shown in FIG. 4 b . Once actuated the flexible heat responsive element  70  will bend, and after the voltage is discontinued it will gradually relax to its unactuated state as its temperature decreases due principally to thermal conduction and convection of heat to the surrounding fluid and structure as is well known. 
     FIG. 5 shows in schematic form a cross-section of a segment of continuous inkjet printhead  16  illustrating the ink flow through a nozzle element  32  with the nozzle element  32  in a first actuated state. In the first actuated state the first valve control circuit  56  applies a voltage across the electrical terminals  78  and  80  of the first actuable flow delivery valve  54 . The first valve control circuit  56  receives control signals from the valve control circuits  14  (FIG.  1 ). The voltage applied by the first valve control circuit  56  creates a current in the heater layer  74  of the first actuable flow delivery valve  54  that causes it to bend down as shown thereby restricting the flow of ink in the first ink delivery channel  50 . Therefore, when the first actuable flow delivery valve  54  is actuated and the second actuable flow delivery valve  64  is unactuated the ink flow through the first ink delivery channel  50  is less than the ink flow through the second ink delivery channel  60 . This is illustrated by the bold flow arrow  62  as compared to the nonbold flow arrow  52 . Because the ink flow through the first ink delivery channel  50  is less than the ink flow through the second ink delivery channel  60  the jet  44  that forms from the nozzle element  32  is tilted toward the ink delivery channel  50  and away from the second ink delivery channel  60  along a second path as indicated by flow arrow  46 . Therefore, by actuating the first actuable flow delivery valve  54  with the second actuable flow delivery valve  64  unactuated the jet  44  can be directed away from the recording medium  18  toward the ink gutter  17  or vice versa. 
     FIG. 6 shows in schematic form a cross-section of a segment of continuous inkjet printhead  16  illustrating the ink flow through a nozzle element  32  with the nozzle element  32  in a second actuated state. In the second actuated state the second valve control circuit  66  applies a voltage across the electrical terminals  78  and  80  of the second actuable flow delivery valve  64 . The second valve control circuit  66  receives control signals from the valve control circuits  14  (FIG.  1 ). The voltage applied by the second valve control circuit  66  creates a current in the heater layer  74  of the second actuable flow delivery valve  64  causing it to bend down as shown thereby restricting the flow of ink in the second ink delivery channel  60 . Therefore, when the second actuable flow delivery valve  64  is actuated and the first actuable flow delivery valve  54  unactuated the ink flow through the second ink delivery channel  60  is less than the ink flow through the first ink delivery channel  50 . This is illustrated by the bold flow arrow  52  as compared to the nonbold flow arrow  62 . Because the ink flow through the second ink delivery channel  60  is less than the ink flow through the first ink delivery channel  50  the inkjet  44  that forms from the nozzle element  32  is lilted toward the second ink delivery channel  60  and away from the first ink delivery channel  50  along a third path as indicated by flow arrow  46 . Therefore, by actuating the second actuable flow delivery valve  64  with the first actuable flow delivery valve  54  unactuated the inkjet  44  can be directed away from the recording medium  18  toward the ink gutter  17  or vice versa. 
     FIG. 7 shows in schematic form a cross-section of a segment of continuous inkjet printhead  16  illustrating the inkjet flow along a second path with the inkjet  44  subjected to a thermal modulation which causes drop formation. Specifically, the inkjet  44  is heated as it leaves the nozzle bore  42  via heater element  68 . Heater element  68  includes a continuous strip of electrically conductive material fixedly attached to the rigid nozzle plate  90  and substantially surrounding the nozzle bore  42  with two spaced apart ends that serve as electrical terminals. To activate the heater element  68 , a voltage is applied to its terminals and current flows through it causing a joule heating as is well known. The voltage through the heater element  68  is supplied by the heater circuit  88  which receives control signals from the valve control circuit  14  (FIG.  1 ). The voltage supplied by the heater circuit  88  is typically in the form of a sequence of voltage pulses  94 . The magnitude and duration of the voltage pulses  94  are chosen to cause the inkjet  44  to break into drops  100  in a predicable fashion. Specifically, the heater element  68  heats the surface of the inkjet  44  as it leaves the nozzle bore  42  and causes variation of the surface tension of inkjet  44  which, in turn, stimulates drop formation as described by Furlani et al “Surface Tension Induced Instability of Viscous Liquid Jets,” Proceedings of the Fourth International Conference on Modeling and Simulation of Microsystems, Applied Computational Research Society, Cambridge Mass., 186, 2001. Thus, when the inkjet  44  is directed toward the recording medium  18  the thermal modulation due to heater element  68  will cause ink spots to form on the recording medium  18  in the appropriate position designated by the data in the image memory. 
     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 spirit and scope of the invention. 
     Parts List 
       10  image source 
       12  image processing unit 
       13  control signals 
       14  valve control circuits 
       16  printhead 
       17  ink gutter 
       18  recording medium 
       19  ink recycling unit 
       20  recording medium transport system 
       22  transport control system 
       24  micro-controller 
       26  ink pressure regulator 
       28  ink reservoir 
       30  ink channel device 
       32  nozzle element 
       40  ink staging chamber 
       42  nozzle bore 
       44  ink jet 
       46  flow arrow 
       48  dividing wall 
       50  first ink delivery channel 
       52  flow arrow 
       54  first actuable flow delivery valve 
       56  first valve control circuit 
       60  second ink delivery channel 
       62  flow arrow 
       64  second actuable flow delivery valve 
       66  second valve control circuit 
     Parts List cont&#39;d 
       68  heater element 
       70  flexible heat responsive element 
       72  support structure 
       74  heater layer 
       76  support layer 
       78  electrical terminal 
       80  electrical terminal 
       82  current flow arrows 
       88  heater circuit 
       90  rigid nozzle plate 
       94  voltage pulses 
       100  ink drops