Abstract:
According to one aspect of the invention, an ink droplet forming mechanism for use in an ink jet printer system includes an ink discharge nozzle for discharging a printing ink; at least two heating elements activatable individually to heat a printing ink at the nozzle to form an ink droplet; and a controller connected individually to each heating element for activating at least two heating elements so that should one heating element fail at least one other will heat a printing ink at said nozzle to form an ink droplet.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Reference is made to commonly assigned application Ser. No. 09/751,232, entitled CONTINUOUS INK-JET PRINTING METHOD AND APPARATUS and filed Dec. 28, 2000 in the names of David L. Jeanmaire, et al. which is incorporated herein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to the field of ink jet printer systems, and in particular to an ink droplet forming mechanism for use in an ink jet printer system. 
     BACKGROUND OF THE INVENTION 
     It is not uncommon for an ink droplet forming mechanism in a continuous ink jet printer system to include a printhead, a plurality of ink supplies in pressurized fluid communication with respective ink discharge nozzles on the printhead, and a controller for ink heaters associated with each ink discharge nozzle. When the controller activates or energizes a heater, a resistive heating element in the heater is heated to in turn heat an ink stream flowing from the associated nozzle. The heated ink then releases an ink droplet, which is used for printing an image pixel on a receiver medium such as a paper sheet. 
     Since there is usually only one resistive heater element per ink discharge nozzle, failure of the heater element disables the ink droplet forming mechanism. In this connection, however, prior art U.S. Pat. No. 6,019,457 issued Feb. 1, 2000, generally teaches the use of a main resistive heating element and a redundant resistive heater element per ink discharge nozzle in a drop-on-demand bubble ink jet printer. The redundant heating element appears to be activated only when the main heating element fails. This requires, as stated in the patent, a sensing circuit to sense a failure of the main heating element and then activate the redundant heating element. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, an ink droplet forming mechanism for use in an ink jet printer system comprises: 
     an ink discharge nozzle for discharging a printing ink; 
     at least two heating elements activatable individually to heat a printing ink at the nozzle to form an ink droplet; and 
     a controller connected individually to each heating element for activating at least two heating elements so that should one heating element fail at least one other will heat a printing ink at said nozzle to form an ink droplet. 
     According to another aspect of the invention, an ink droplet forming method in an ink jet printer system comprises: 
     discharging a printing ink from an ink discharge nozzle; 
     including at least two heating elements separately activatable simultaneously to heat a printing ink at the nozzle to form an ink droplet; and 
     separately activating at least two heating elements to heat a printing ink at the nozzle to form an ink droplet, but should one heating element fail activating at least one other, so that at least one heating element will heat a printing ink at said nozzle to form an ink droplet. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts in a schematic block form an ink droplet forming mechanism for use in a continuous ink jet printer system as disclosed in the cross-referenced application; 
     FIGS. 2A through 2F are timing diagrams illustrating activation or energization of a heater, in a printhead included in the ink droplet forming mechanism, to heat a single resistive heating element in the heater in order to create ink droplets as disclosed in the cross-referenced application; 
     FIG. 3 is a cross-section view of the printhead and the ink droplets as disclosed in the cross-referenced application, illustrating separation of the ink droplets into small volume printing droplets and large volume non-printing droplets along respective paths; and 
     FIG. 4 is plan view of an improvement to the heater, by which at least two resistive heating elements in the heater are activatable individually so that should one fail the other is still used, according to a preferred embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Commonly assigned prior art U.S. Pat. No. 6,079,821, issued Jun. 27, 2000, discloses a continuous ink jet printer system including an image source such as a scanner or computer which provides raster image data, outline image data in the form of 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 which also stores the image data in a memory. A plurality of heater control circuits read data from the memory and apply time-varying electrical pulses to a set of nozzle heaters that are part of a printhead. These pulses are applied at an appropriate time, and to the appropriate nozzle heater, so that ink droplets will be formed from a continuous ink jet stream to create spots on a recording medium moving relative to the printhead. 
     The Cross-referenced Application (FIGS.  1 ,  2 A- 2 F,  3 ) 
     FIG. 1 shows an ink droplet forming mechanism  10  which can be used in a continuous ink jet printer system such as the one disclosed in incorporated U.S. Pat. No. 6,079,821. 
     The ink droplet forming mechanism  10  shown in FIG. 1 has a printhead  12 , at least one ink supply  14  and a controller  16 . It is depicted in a schematic block form, which is not to scale simply for the sake of clarity. The controller  16  may, for example, be a known type logic control device or suitably programmed microprocessor as in the incorporated patent. 
     The printhead  12  can be formed from a semiconductor material, e.g. silicon, using known semiconductor fabrication techniques, e.g. CMOS circuit fabrication techniques or micro-electro mechanical structure (MEMS) fabrication techniques. 
     At least one ink discharge nozzle or outlet  18  is included on the printhead  12 . The ink discharge nozzle  18  is in pressurized fluid-receiving communication with the ink supply  14  via an ink passage  20 . Of course, as shown in FIG. 1, the printhead  12  may include a plurality of ink supplies and associated ink passages, and also the same number of ink discharge nozzles  18 , in order to provide multi-color printing using three or more ink colors such as yellow, cyan and magenta. On the other hand, black and white or single-color printing may be accomplished using a single ink supply  14  and associated ink passage  20 , and also a single nozzle  18 . 
     Respective ink heaters  22  are at least partially formed or positioned on the printhead  12  around the ink discharge nozzles  18  as shown in FIG.  1 . Although each heater  22  may be disposed radially away from an edge of a nozzle  18 , preferably it is disposed close to the nozzle and concentric about the nozzle. As shown in FIG. 1, each heater  22  is formed in a substantially circular or ring shape and has an annular resistive heating element  24  electrically connected to a conductive contact pad  26  via a conductor  28 . Each conductor  28  and contact pad  26  in FIG. 1 are at least partially formed or positioned on the printhead  12 , and they provide an electrical connection between the controller  16  and one of the heaters  22 . 
     FIG. 2A depicts an example of an electrical heater-activation pulse-waveform which is provided by the controller  16  separately to each heater  22  in order to activate or energize the heater successive times (via successive activation pulses) by heating its resistive heating element  24 . FIG. 2B depicts successive ink droplets  30 ,  31  and  32  resulting from successive activations of a single heater  22  and a substantially constant “jetting”, i.e. a substantially constant flow rate, of a printing ink from the nozzle  18  on that heater. Generally speaking, as indicated in FIGS. 2A and 2B, a high frequency of activation of a heater  22  results in a small volume printing droplet, e.g.  31  or  32 , and a low frequency of activation of the heater results in a large volume non-printing droplet, e.g.  30 . 
     Assuming there are to be formed multiple ink droplets per image pixel as shown in FIGS. 2A and 2B, a cycle or total time  39  associated with the printing of a single pixel consists of at least one short time sub-interval or delay time, e.g.  36  or  37 , for creating a small volume printing droplet  31  or  32 , and a long time sub-interval or delay time  38  for creating a large volume non-printing droplet  30 . In FIGS. 2A and 2B, there are shown two successive delay times  36  and  37  for creating respective small volume printing droplets  31  and  32  during a cycle or total time  39  for printing a single pixel. However, this is shown only for simplicity of illustration. It should be understood that a greater or lesser number of delay times is possible for creating a corresponding number of small volume printing droplets. 
     In FIGS. 2A and 2B, each successive cycle or total time  39  associated with the printing of successive pixels is the same. Moreover, the delay times  36  and  37  during a single cycle or total printing time  39  for the printing of a single pixel are identical, and the delay time  38  during the same cycle printing is longer than the sum of the delay times  36  and  37 . 
     When printing a single pixel during a cycle or total time  39  in FIGS. 2A and 2B, a pulse order in the waveform can be as follows. First, a small volume printing droplet  31  is created as a consequence of an activation pulse  34  in the waveform which activates or energizes a heater  22  by heating its resistive heating element  24 . Then, a small volume printing droplet  32  is created as a consequence of an activation pulse  35  in the waveform which activates or energizes the same heater by heating its resistive heating element. And finally, a large volume non-printing droplet  30  is created as a consequence of an activation pulse  33  in the waveform which activates or energizes the same heater by heating its resistive heating element. Since the delay time  36  from an activation pulse  33  to an activation pulse  34  is the same as the delay time  37  from an activation pulse  34  to an activation pulse  35  during a single cycle or total time  39  in FIG. 2 a , the small volume printing droplets  36  and  37  created in that cycle have the same volume. Since the delay time  38  from an activation pulse  35  to an activation pulse  33  is longer than the similar delay times  36  and  37  during the same cycle, the large volume non-printing droplet  30  created in that cycle has to have a larger volume than the small volume printing droplets  36  and  37  created in that cycle. In other words, it is ultimately the particular delay time  36 ,  37  or  38  for the activation pulse  34 ,  35  or  33  that determines the particular volume of an ink droplet  31 ,  32  or  30 . 
     The duration of the activation pulse  33  for a large volume non-printing droplet  30  is typically from 0.1 to 10 microseconds, and more preferentially is from 0.5 to 1.5 microseconds. The duration of the activation pulses  34  and  35  for small volume printing droplets  31  and  32  is typically 1 to 100 microseconds, and more preferentially is from 3 to 6 microseconds. All of the activation pulses  33 ,  34  and  35  in FIG. 2A have the same amplitude (although that is not required). 
     FIGS. 2A and 2B when compared with FIGS. 2C-2F indicate that a large volume non-printing droplet  30  will vary in volume depending on the number of preceding small volume printing droplets created during a cycle or total time  39  for printing a single pixel. For example, in FIG. 2D, only one small volume printing droplet  31  is created before creating a large volume non-printing droplet  30  in a single cycle or total time  39  in FIG.  2 C. As such, the volume of a large volume non-printing droplet  30  in FIG. 2D is greater than the volume of a large volume non-printing droplet  30  in FIG.  2 B. The reason for this, in essence, is that the delay time  38  in FIG. 2C is greater than the delay time  38  in FIG.  2 A. In FIGS. 2E and 2F, three small volume printing droplets  31 ,  32  and  136  are created in accordance with the delay times  36 ,  37  and  134  (delay time  134  in FIG. 2E is for an activation pulse  132 ). As such, the volume of a large volume non-printing droplet  30  in FIG. 2F is less than the volume of a large volume non-printing droplet  30  in FIG.  2 D. The reason for this, in essence, is that the delay time  38  in FIG. 2E is less than the delay time  38  in FIG.  2 C. The volume of a large volume non-printing droplet  30  in FIG. 2F is greater than the volume of small volume printing droplets  31 ,  32 ,  136  in FIG. 2F, preferably by at least a factor of four (4). 
     Preferably, small volume printing droplets  31 ,  32  and  136  impinge on a print or receiver medium (not shown) such as a paper sheet on a rotating print drum, and large volume non-printing droplets  30  are collected in an ink gutter (not shown) in order to be recycled back to the ink supply  14 . However, the opposite is possible, i.e. large volume droplets  30  can serve as printing droplets that impinge on the receiver medium, and small volume droplets  31 ,  32  and  136  can serve as non-printing droplets which are collected in the ink gutter to be recycled. All that is required to effect the change, essentially, is to re-position the ink gutter so that it collects small volume droplets  31 ,  32  and  136  instead of collecting large volume droplets  30 . Using large volume droplets  30  as printing droplets allows for varying-volume printing droplets as can be seen by comparing FIGS. 2B,  2 D and  2 F. 
     FIG. 3 shows a pressurized ink  140 , originating at the ink supply  14 , and flowing from a nozzle  18  at a heater  22  on the printhead  12 , to form a filament or stream of printing ink  145  at the nozzle. As previously explained, small volume printing droplets  31  and  32  and a large volume non-printing droplet  30  can be created when the heater  22  is activated or energized successive times during a cycle or total time  39  for printing a single pixel as in FIGS. 2A and 2B, etc. 
     In FIG. 3, large volume non-printing droplets  30  and small volume printing droplets  31  and  32  when separated from the filament or stream of printing ink  145  at a nozzle  22  initially move along a droplet path X leading to the ink gutter. A droplet deflector  40  uses a pressurized gas to apply a gas force  46 , in a direction transverse to the droplet path X, to ink droplets  30 ,  31  and  32  as they travel along the droplet path. The gas force  46  interacts with ink droplets  30 ,  31  and  32  along the droplet path X, causing ink droplets  31  and  32  to alter course. Since ink droplets  30  have different volumes than ink droplets  31  and  32 , the gas force  46  causes small volume printing droplets  31  and  32  to separate from large volume non-printing droplets  30 . Small volume printing droplets  31  and  32  diverge from droplet path X and into a droplet or print path Y leading to the receiver medium. Although large volume droplets  30  can be slightly affected by the gas force  46 , they either remain in the droplet path X or deviate slightly from that path into a close path Z (close to the droplet path X) which, like the droplet path X, leads to the ink gutter. Thus, the large volume non-printing droplets are not moved out of a collecting range of the ink gutter. 
     Preferred Embodiment (FIG.  4 ) 
     According to the invention, each heater  22  positioned around an ink discharge nozzle  18 , instead of having only one annular resistive heating element  24  as in FIG. 1, has at least two resistive heating elements disposed about the nozzle. 
     In FIG. 4, there is shown a circular arrangement of separate resistive heating elements  44 A,  44 B,  44 C,  44 D and  44 E disposed in evenly spaced relation about the nozzle  18  to substantially define a segmented circle around the nozzle. The heating elements  44 A,  44 B,  44 C,  44 D and  44 E are electrically connected via respective conductors  45  as shown in FIG. 4 to the controller  16 . 
     In operation, all of the resistive heating elements  44 A,  44 B,  44 C,  44 D and  44 E in a heater  22  are activated individually via the controller  16  to each (collectively or separately) serve to create small volume printing droplets, e.g.  31  and  32 , and a large volume non-printing droplet  30  during a cycle or total time  39  for a single pixel as in FIGS. 2A and 2B. Thus, should one heating element fail, the others can continue to serve as stated. 
     The controller  16  activates all of the resistive heating elements  44 A,  44 B,  44 C,  44 D and  44 E to the same operating temperature, e.g. 20—less than 100 degrees centigrade, and preferably 40-60 degrees centigrade  50 . This is below the boiling point of a filament or stream of working ink  145  at a nozzle  22 . See FIG.  3 . 
     If at least one, but not all, of the resistive heating elements  44 A,  44 B,  44 C,  44 D and  44 E fail when the controller  16  is attempting to activate them individually, then those resistive heating element that are actually activated may be asymmetrical about a nozzle  22 . In spite of this, the ink droplets  30 ,  31  and  32  will substantially adhere initially to the droplet path X as shown in FIG. 3 so that there is no negative impact. 
     While the description of the invention includes many details and specificities, it is to be understood that these have been included for purposes of explanation only, and are not to be interpreted as limitations of the invention. Many modifications to the description can be made without departing from the spirit and scope of the invention, as is intended to be encompassed by the following claims and their legal equivalents. 
     PARTS LIST 
       10 . ink droplet forming mechanism 
       12 . printhead 
       14 . inksupply 
       16 . controller 
       18 . ink discharge nozzle 
       20 . ink passage 
       22 . heater 
       24 . annular resistive heating element 
       26 . conductive contact pad 
       28 . conductor 
       30 . large volume non-printing ink droplet 
       31 . small volume printing droplet 
       32 . small volume printing droplet 
       33 . activation pulse after  38   
       34 . activation pulse after  36   
       35 . activation pulse after  37   
       36 . delay time 
       37 . delay time 
       38 . delay time 
       39 . cycle or total time associated with the printing of a single pixel 
       40 . droplet deflector 
       44 A. resistive heating element 
       44 B. resistive heating element 
       44 C. resistive heating element 
       44 D. resistive heating element 
       44 E. resistive heating element 
       45 . conductors 
       46 . gas force 
       132 . activation pulse after  134   
       134 . delay time 
       136 . small volume printing droplet 
       140 . pressurized ink 
       145 . filament or volume of printing ink 
     X. droplet path 
     Y. droplet or print path 
     Z. close path