Patent Publication Number: US-6984014-B2

Title: Inkjet printing system employing multiple inkjet printheads and method of performing a printing operation

Description:
TECHNICAL FIELD 
     This invention relates generally to inkjet printing devices. In particular, the present invention is an inkjet printing system having multiple printheads for depositing ink droplets onto print media to form images and text on different areas of the print media at the same time. The use of multiple printheads printing at the same time on different portions of the print media results in greatly increased print media throughput for the inkjet printing system. 
     BACKGROUND OF THE INVENTION 
     Throughout the business world, inkjet printing systems are extensively used for image reproduction. Inkjet printing systems frequently make use of one or more inkjet printheads mounted within a carriage that is moved back and forth across print media, such as paper. For example, the carriage may include a single printhead that is capable of printing a single color (i.e., black), a single printhead capable of printing multiple colors (i.e., black, cyan, magenta and yellow), a first printhead capable of printing one color (i.e., black) and a second printhead capable of printing multiple colors (i.e., cyan, magenta and yellow), or four printheads each capable of printing a single color. As the carriage is moved across the print media, a control system activates the printhead(s) to deposit or eject ink droplets onto the print media to form images and text. Such systems may be used in a wide variety of applications, including computer printers, plotters, copiers and facsimile machines. 
     Ink is provided to the printhead(s) mounted to the carriage by one or more supplies of ink that are either carried by the carriage or mounted to the printing system such that the supplies of ink do not move with the carriage. For the case where the ink supplies are not carried with the carriage, the ink supplies can be in fluid communication with the printhead(s) to replenish the printhead(s) or the printhead(s) can be intermittently connected with the ink supplies by positioning the printhead(s) proximate to a filling station to which the ink supplies are connected whereupon the printhead(s) are replenished with ink from the refilling station. 
     For the case where the ink supplies are carried with the carriage, one ink supply may be integral with each printhead whereupon the entire printhead and ink supply is replaced when ink is exhausted. Alternatively, the ink supplies can be carried with the carriage and can be separately replaceable from the printhead(s). 
     For convenience, the concepts of the invention are discussed in the context of thermal inkjet printheads. A thermal inkjet printhead die includes an array of firing chambers having orifices (also called nozzles) which face the print media. The ink is applied to individually addressable ink energizing elements (such as firing resistors) within the firing chambers. Energy provided by the firing resistors heats the ink within the firing chambers causing the ink to bubble. This in turn causes the ink to be expelled out of the orifice of the firing chamber toward the print media. As the ink is expelled, the bubble collapses and more ink is drawn into the firing chambers, allowing for repetition of the ink expulsion process. 
     Typically to increase print media throughput (i.e. to increase the speed of printing per page of print media), it is to necessary to increase the firing rate of the firing chambers, maximize the density of the firing chambers (i.e. firing resistors) and/or increase the number of firing chambers. With regards to increasing the firing rate of the firing chambers, the ability to do this somewhat limited by ink composition and the heat generated by the process of repeatedly firing the firing chambers. Hence, the ability to increase the print media throughput of a printing system by increasing the firing rate of the firing chambers of the printhead(s) is somewhat limited given the already high firing frequency of printhead firing chambers. 
     Maximizing the density of the firing chambers and/or increasing the number of firing chambers to increase print media throughput, typically necessitates an increase in the size of the printhead die and/or a miniaturization of printhead die components. With regards to miniaturization of the printhead die components, once a certain degree of miniaturization has been reached, conventional manufacturing by assembling separately produced components becomes more difficult and costly. In addition, the substrate that supports firing resistors, the barrier that isolates individual resistors, and the orifice plate that provides a nozzle above each resistor are all subject to small dimensional variations that can accumulate to limit miniaturization. Further, the assembly of such components for conventional printheads requires precision that limits manufacturing efficiency. Hence, increasing the print media throughput of a printing system by miniaturization of printhead die components of the printhead(s) is somewhat limited by manufacturing practicalities and costs. 
     With regards to increasing the size of the printhead die to increase print media throughput, printheads employing Page Wide Arrays (PWA&#39;s) have already been developed. In a PWA printhead, the firing chambers extend across the full width of the print media thereby eliminating the need of the carriage supporting the PWA printhead to be moved back and forth across the print media. In other words, to perform a full page printing operation using a PWA printhead, the print media need only be stepped past the PWA printhead while the PWA printhead remains stationary. This elimination of the movement of the PWA printhead results in an increase in print media throughput. Although the use of a PWA printhead increases print media throughput, there are some disadvantages to the use of PWA printheads. Namely the cost associated with manufacturing PWA printhead die components and the subsequent cost to consumers of replacing a PWA printhead at the end of printhead life. 
     As such, there is a need for printing systems with increased print media throughput. In particular, there is a need for an increased print media throughput printing system that makes use of conventional, non PWA printheads that can be moved back and forth across the print media. 
     SUMMARY OF THE INVENTION 
     The present invention is a printing system for depositing marking fluid on print media. The printing system includes first and second marking engines. The first marking engine deposits a first marking fluid only on a first portion of the print media. The second marking engine deposits a second marking fluid only on a second portion of the print media that is different than the first portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this specification. The drawings illustrate the embodiments of the present invention and together with the description serve to explain the principals of the invention. Other embodiments of the present invention and many of the intended advantages of the present invention will be readily appreciated as the same become better understood by reference to the following detailed description when considered in connection with the accompanying drawings, in which like reference numerals designate like parts throughout the figures thereof, and wherein: 
         FIG. 1  is a schematic drawing of a printing system having first and second printhead assemblies for increasing print media throughput in accordance with the present invention. 
         FIG. 2  is a schematic drawing of an alternative printing system having first, second and third printhead assemblies for increasing print media throughput in accordance with the present invention. 
         FIG. 3  is a schematic drawing of a further alternative printing system having first and second printhead assemblies that scan across a length dimension of print media. 
         FIG. 4  is a schematic drawing similar to  FIG. 1  illustrating another alternative printing system in which each of the first and second printhead assemblies includes two printheads. 
         FIG. 5  is a schematic drawing similar to  FIG. 1  illustrating still another alternative printing system in which each of the first and second printhead assemblies includes four printheads. 
         FIGS. 6A–6F  illustrate the operation of the printing system of  FIG. 1  to perform a print job in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  depicts a schematic representation of a printing system, such as a thermal inkjet printing system  10  which includes a printing mechanism  12  for enhancing (i.e., increasing) print media throughput of the printing system  10  in accordance with the present invention. The printing mechanism  12  is defined by a first marking engine or printhead assembly  14  and a second marking engine or printhead assembly  16  which is spaced from the first printhead assembly  14 . The first printhead assembly  14  deposits a marking fluid, such as ink, only on a first or upper portion  13  of print media  22 , such as paper, while the second printhead assembly  16  deposits a making fluid, such as ink, only on a second or lower portion  15  of the print media  22 . The lower portion  15  is different than the upper portion  13 . As seen in  FIG. 1 , a dashed line  17  represents the dividing line between the upper and lower portions  13 ,  15  of the print media  22 . 
     In one preferred embodiment, the first and second printhead assemblies  14 ,  16  are identical, so only the first printhead assembly  14  will be described with particularity. Moreover, like parts are labeled with like numerals with the first printhead assembly  14  being designated by the subscript “a” and the second printhead assembly  16  being designated with the subscript “b”. 
     As seen best in  FIG. 1 , the first printhead assembly  14  includes a first drive mechanism  18   a . The first drive mechanism  18   a  is defined by a carriage  20   a  linearly movable back and forth across the print media  22 . The carriage  20   a  linearly moves along and is therefore guided by a linear guide rod  24   a  mounted to the printing system  10 . The first drive mechanism  18   a  is further defined by a drive motor, such as stepper motor  26   a  which is spaced from a pulley  28   a . A drive element, such as a drive belt  30   a  extends about the stepper motor  26   a  and the pulley  28   a . Free ends  32   a  of the drive belt  30   a  are coupled to the carriage  20   a . Operation of the stepper motor  26   a  causes movement of the drive belt  30   a , and thereby linear movement (as represented by double headed arrow  34   a ) of the carriage  20   a  along the linear guide rod  24   a  back and forth across the print media  22 . The stepper motors  26   a ,  26   b  of the first and second drive mechanisms  18   a ,  18   b  of the first and second printhead assemblies  14 ,  16 , respectively, are linked by signal transmission lines  36   a ,  36   b  to printing system control electronics  38 . The control electronics  38  control movement of the carriages  20   a ,  20   b  via the stepper motors  26   a ,  26   b  in accordance with the print job to be performed on the print media  22  by the first and second printhead assemblies  14 ,  16 . 
     As seen best in  FIG. 1 , the printing system  10  further includes a print media feed mechanism  40  for linearly moving the print media  22 , in a known manner, in only a first direction, as represented by feed arrow  42 , relative to the first and second printhead assemblies  14 ,  16 . The print media  22  moves in a direction substantially perpendicular to the directions of movement of the first and second printhead assemblies  14 ,  16 . The print media feed mechanism  40  is coupled to the control electronics  38  via a signal transmission line  44 . The control electronics  38  control movement of the print media  22  via the print media feed mechanism  40  in accordance with the print job to be performed on the print media  22  by the first and second printhead assemblies  14 ,  16 . 
     Although, in one preferred embodiment, the printing system  10  is illustrated as including only first and second printhead assemblies  14 ,  16 . It is to be understood that the printing system  10  could include more than two printhead assemblies. For example, alternatively as illustrated in  FIG. 2 , the printing system  10  could include the first and second printhead assemblies  14 ,  16  and a third printhead assembly  45 . The third printhead assembly  45  is identical to the first and second printhead assemblies  14 ,  16  as such like elements in  FIG. 2  are labeled with like numerals with the inclusion of the subscript “c” designating the components of the third printhead assembly  45 . 
     The print media  22  has a width dimension “W” and a length dimension “L” which is greater than the width dimension “W” (see  FIG. 1 ). In one preferred embodiment illustrated in  FIG. 1 , the first and second drive mechanisms  18   a ,  18   b  move the carriages  20   a ,  20   b  of the first and second printhead assemblies  14 ,  16  back and forth across the width dimension “W” of the print media  22 . In an alternative embodiment illustrated in  FIG. 3 , the first and second drive mechanisms  18   a ,  18   b  move the carriages  20   a ,  20   b  of the first and second printhead assemblies  14 ,  16  back and forth across the length dimension “L” of the print media  22 . 
     As previously stated, in one preferred embodiment, the first and second printhead assemblies  14 ,  16  are identical. In this one preferred embodiment, each of the carriages  20   a ,  20   b  carries a single replaceable printhead  46   a ,  46   b  for printing multiple colors of marking fluid, such as ink. The multiple colors of ink in the single printhead  46   a  of the first printhead assembly  14  are identical to the multiple colors of ink in the single printhead  46   b  of the second printhead assembly  16 . These multiple colors of ink are black, cyan, magenta and yellow. Alternatively, the single printhead  46   a  of the first printhead assembly  14  could include ink of different colors or composition than the colors of ink and ink composition of the single printhead  46   b  of the second printhead assembly  16 . As a further alternative, the single printhead  46   a  of the first printhead assembly  14  and the single printhead  46   b  of the second printhead assembly  16  could each include only a single color of ink. That single color of ink could be black. As still a further alternative as illustrated in  FIG. 4 , each of the carriages  20   a ,  20   b  can carry a first replaceable printhead  48   a ,  48   b , and a second replaceable printhead  50   a ,  50   b . The first printhead  48   a ,  48   b  would print a single color of ink, such as black, while the second printhead  50   a ,  50   b  would print multiple colors of ink, such as cyan, magenta and yellow. As another alternative as illustrated in  FIG. 5 , each of the carriages  20   a ,  20   b  can carry a first replaceable printhead  52   a ,  52   b , a second replaceable printhead  54   a ,  54   b , a third replaceable printhead  56   a ,  56   b , and a fourth replaceable printhead  58   a ,  58   b . The first printhead  52   a ,  52   b  would print a single color of ink, such as black, the second printhead  54   a ,  54   b  would print a single color of ink, such as cyan, the third printhead  56   a ,  56   b  would print a single color of ink, such as magenta, and the fourth printhead  58   a ,  58   b  would print a single color of ink, such as yellow. 
     Operation, in accordance with the present invention, of the first and second printhead assemblies  14 ,  16  of the printing system  10  shown in  FIG. 1 , is illustrated in  FIGS. 6A–6F .  FIG. 6A  illustrates the print media  22  in the printing system  10  in position to be printed upon (i.e., ready for the creation of text, characters and/or illustrations) by the first and second printhead assemblies  14 ,  16  in accordance with a print job.  FIG. 6B  illustrates the beginning of linear movement (see arrow  60 ) of the carriages  20   a ,  20   b  of the first and second printhead assemblies  14 ,  16  along the linear guide rods  24   a ,  24   b  of the first and second drive mechanisms  18   a ,  18   b  and the creation of text as a result of the ejection of ink droplets from printheads  46   a ,  46   b  as directed by the control electronics  38  in accordance with the print job. As can be seen in  FIG. 6B  (as well as subsequent  FIGS. 6C–6F ), in one preferred embodiment, the control electronics  38  control movement of the first and second printhead assemblies  14 ,  16  so that the printhead assemblies  14 ,  16  move in unison (i.e., together) back and forth across the width dimension “W” of the print media  22 . In other words, the first and second printhead assemblies  14 ,  16  start movement across the print media  22  at the same time, the first and second printhead assemblies  14 ,  16  move across the print media in the same direction, the first and second printhead assemblies  14 ,  16  move back and forth across the print media  22  at the same speed, and the first and second printhead assemblies  14 ,  16  stop movement at the same time. Alternatively, as represented by the dashed outline of the second printhead assembly  16  in  FIG. 6B , the second printhead assembly  16  can operate independently of the first printhead assembly  14 . In other words, the second printhead assembly  16  can start and stop movement at a different time, can move at a different speed, and/or can move in a different direction than the first printhead assembly  14 . 
       FIG. 6C  illustrates the completion of first lines of text produced by printheads  46   a ,  46   b  of the first and second printhead assemblies  14 ,  16 , the completion of linear movement (see arrow  62 ) of the carriages  20   a ,  20   b  of the printhead assemblies  14 ,  16  back along the linear guide rods  24   a ,  24   b  of the first and second drive mechanisms  18   a ,  18   b , and the advance of the print media  22  along the direction  42  as a result of operation of the print media feed mechanism  40  so that second lines of text can be printed upon the print media  22 .  FIG. 6D  illustrates the formation of these second lines of text as a result of movement of the printhead assemblies  14 ,  16  and operation of the printheads  46   a ,  46   b .  FIG. 6E  illustrates the formation of further lines of text due to movement of the first and second printhead assemblies back and forth across the print media  22  and operation of the printheads  46   a ,  46   b .  FIG. 6F  illustrates the completion of the print job. As can be readily seen when viewing  FIGS. 6B–6E , the first printhead assembly  14  deposits ink only on the upper portion  13  of print media  22 , while the second printhead assembly  16  deposits ink only on the lower portion  15  of the print media  22 . The control electronics  38  controls the print media feed mechanism  40  and the first and second drive mechanisms  18   a ,  18   b  to insure that the printhead  46   a  deposits ink only on the upper portion  13  and the printhead  46   b  deposits ink only on the lower portion  15 . As can be readily understood, the use of two scanning printhead assemblies  14 ,  16  doubles the print media throughput of a conventional printing system that employs only a single scanning printhead assembly. In other words, the print media throughput of the printing system  10  is increased over a conventional printing system having a single scanning printhead assembly by a factor of “n”, where “n” is the number of printhead assemblies. 
     The dashed line  17  represents the dividing line between the upper and lower portions  13 ,  15  of the print media  22 , with these upper and lower portions  13 ,  15  being equal in one preferred embodiment. Alternatively, the lower portion  15  could be larger than the upper portion  13  (see the dotted line  66  in  FIG. 6E ). In this alternative version the printhead  46   b  would assume a greater print burden of the print job with the printhead  46   a  being shut off during one or more of its passes. For example, if the print job consisted of only three lines of text equally spaced along the print media  22 , the printhead  46   a  would print the first line of text at the same time the printhead  46   b  prints the second line of text. The third line of text would be printed by the printhead  46   b  while the printhead  46   a  would make a non printing pass across the print media  22 . This process may be useful for printing of certain types of illustrations. 
     With regards to  FIG. 2  and the inclusion of the third printhead assembly  45 , it is to be understood that the first printhead assembly  14  would deposit ink only a first portion  70  of print media  22 , the second printhead assembly  16  would deposit ink only on a second portion  72  of the print media  22 , while the third printhead assembly  45  would deposit ink only on a third portion  74  of the print media  22 . Dashed lines  76  and  78  represent the dividing lines between these first, second and third portions  70 ,  72 ,  74  of the print media  22 , with these first, second and third portions  70 ,  72 ,  74  being equal in size. As can be readily understood, the use of three scanning printhead assemblies  14 ,  16 ,  45  triples the print media throughput of a conventional printing system that employs only a single scanning printhead assembly. 
     The printing system  10  makes use of multiple conventional, non PWA printhead assemblies  14 ,  16  ( 45 ) to increase the print media throughput of the printing system  10 . In particular, the printing system uses at least first and second printhead assemblies  14 ,  16 , with each printhead assembly being movable back and forth across the print media  22  to deposit ink on different portions  13 ,  15  of the print media  22  at the same time. This greatly increases the print media throughput of the printing system  10  especially compared to conventional printing systems employing a single printhead assembly movable relative to print media. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.