Abstract:
Apparatus and method controls and varies a spacing between multiple print elements, such as ink jet print orifices, in a printing system. A signal representing at least one of an advance speed of a print medium in a feed direction in the printing system and an approximate drying time of an ink after being applied to the print medium is supplied to a controller. A device, responsive to the controller, varies the spacing between at least two print elements on the basis of at least one of the advance speed of the print medium and the approximate drying time of the ink.

Description:
This is a continuation-in-part of U.S. patent application Ser. No. 08/806,172 filed Feb. 26, 1997 now U.S. Pat. No. 5,923,348. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to printers, and, more particularly, to apparatus and method for varying a spacing between at least two printing elements, such as ink jet nozzles, in a printing system. 
     2. Description of the Related Art 
     An ink jet printer typically includes a printhead having an array of ink emitting orifices, or nozzles, formed therein. The printhead is mounted on a carriage assembly which scans a width of the print medium. During a scan of the carriage assembly, ink is jetted from selected ones of the ink emitting orifices to produce a desired print image on the print medium. 
     It is also known to provide an ink jet printer with a printhead which extends substantially across the width of the print medium. For an ink jet printer with a 300 dot per inch (dpi) resolution, a single row of ink emitting orifices in such a printhead would include at least 2400 ink emitting orifices (i.e., 300 orifices/inch * 8 inches/page width=2400 orifices/page width). 
     With a page wide printhead as described above, a print quality problem may arise with respect to the associated physical geometry of the printhead due to the spatial locality of the ink emitting orifices. Because the orifices are located in a substantially linear array extending across the width of the print medium, ink dots from adjacent orifices which are to be placed within a given raster are placed on the print medium at approximately the same time. If the printhead includes multiple rows of orifices extending across the width of the page, adjacent ink dots in a given row and adjacent ink dots between rows are placed on the print medium in close proximity to each other with respect to time. For various print media, particularly transparencies, poor print quality results when ink dots are placed at adjacent positions on the print medium at approximately the same time. 
     SUMMARY OF THE INVENTION 
     The present invention is related to apparatus and method for varying a spacing between multiple print elements in a printing system. In preferred embodiments, a controller receives a signal representing at least one of an advance speed of a print medium in a feed direction in the printing system and an approximate drying time of an ink after being applied to the print medium. A device, responsive to the controller, then varies the spacing between the multiple print elements on the basis of the at least one of the advance speed of the print medium and the approximate drying time of the ink. Such print elements can be, for example, ink jet print nozzles. 
     In one embodiment, a first nozzle is associated with a first printhead and a second nozzle is associated with a second printhead. The device for varying the spacing includes a drive mechanism coupled to one of the first printhead and the second printhead, and an electromechanical device coupled to the drive mechanism, which when actuated by the controller, effects a change in spacing between the first printhead and the second printhead. 
     In another embodiment, a piezoelectric material is positioned between at least two components comprising a drive train, such that when the piezoelectric material is electrically energized, a mechanical variation in the spacing between the two components is effected. 
     An advantage of the present invention is that the spacing between at least two ink emitting orifices, or nozzles, or between at least two rows of ink emitting orifices, may be dynamically varied in the feed direction a distance which allows the ink jetted from one of the rows of orifices to substantially dry before ink is jetted from an adjacent row of orifices. 
     Other features and advantages of the invention may be realized from the drawings and detailed description of the invention that follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a schematic view of an embodiment of a page-width printhead of the present invention for use in an ink jet printer, with which the method of the present invention may be carried out; 
     FIG. 2 is an enlarged, fragmentary view of a portion of the printhead shown in FIG. 1; 
     FIG. 3 is a schematic view of another embodiment of a page width printhead of the present invention for use in an ink jet printer, with which the method of the present invention may be carried out; and 
     FIG. 4 is a schematic view of a system for varying a spacing between adjacent columns, or rows, of ink emitting orifices. 
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one preferred embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings and more particularly to FIGS. 1 and 2, there is shown an embodiment of a page width printhead  10  of the present invention for use in an ink jet printer for jetting an ink (not shown) onto a print medium such as paper  12 . Printhead  10  may be used to carry out the method of printing of the present invention, as will be described hereinafter. 
     Printhead  10  includes at least two rows of ink emitting orifices  14  and  16  which extend substantially across a width “W” of paper  12 . Row  14  includes a plurality of individual ink emitting orifices  13  and row  16  includes a plurality of individual ink emitting orifices  15 . Each orifice  13  and  15  within rows  14  and  16 , respectively, is spaced at a common distance “D” from an adjacent orifice within the same row of orifices  14  or  16 . In the embodiment of printhead  10  shown in FIGS. I and  2 , orifices  13  within row  14  are staggered a distance of approximately ½ the common distance “D” relative to orifices  15  within row  16  in a direction transverse to a feed direction  18  of paper  12 . 
     The print medium such as paper  12  is moved in a feed direction  18  relative to the page wide printhead  10  extending thereacross. During printing, paper  12  is moved in feed direction  18  at a particular advance speed or velocity “v”. The advance speed “v” typically remains constant during a particular print job; however, it is possible that the advance speed may also vary during a particular print job. As paper  12  is moved in feed direction  18  past printhead  10 , ink is selectively jetted from orifices  13  of row  14  and orifices  15  of row  16 . The ink which is jetted from orifices  13  and  15  has a known approximate drying time after being jetted onto paper  12  from printhead  10 . Of course, many types of inks are available for possible use with printhead  10 . However, in the embodiment shown, only one particular ink having known physical characteristics and a known approximate drying time is used with printhead  10 . The specifically chosen ink may vary dependent upon the particular application for which printhead  10  is to be used. 
     Referring now more specifically to FIG. 2, each row of orifices  14  and  16  are spaced apart from each other in the feed direction  18  a distance “S” which is dependent upon an advance speed of print medium  12  and an approximate drying time of the ink jetted from printhead  10 . Spacing “S” is established between rows  14  and  16  such that ink is jetted from orifices  15  of rows  16  after the ink which is jetted from orifices  13  of row  14  onto paper  12  has substantially dried. This provides an improved print quality and inhibits the formation of print artifacts on paper  12 . 
     More particularly, the ink which is jetted from selected ones of the orifices  13  from row  14  is allowed to substantially dry before the ink is jetted from selected ones of the is orifices  15  from row  16 . The particular ink which is jetted from printhead  10  is selected such that the drying time of the ink satisfies the mathematical relationship: 
     
       
         S/ v≧t   
       
     
     where 
     S=spacing in the feed direction between the two rows of orifices  14  and  16  (in.); 
     v=advance speed of the paper in the feed direction (in./sec.); and 
     t=drying time of the jetted ink (sec.); 
     which may be mathematically manipulated such that the spacing “S” is determined from the formula: 
     
       
         S≧ t*v.   
       
     
     It is thus possible, using the known advance speed of paper  12  and the drying time of the ink, to manufacture printhead  10  with a spacing “S” between the rows of orifices  14  and  16  which provides an improved print quality and inhibits the formation of print artifacts in the print image on paper  12 . 
     During printing on paper  12  using printhead  10 , paper  12  is advanced in feed direction  18  at a known advance speed. Ink is jetted from selected orifices  13  within row  14  onto paper  12  as paper  12  is advanced in feed direction  18 . Thereafter, ink is jetted from selected orifices  15  within row  16  onto paper  12  after the ink jetted from orifices  13  has substantially dried. 
     For comparison purposes, an orifice  15 A within row  16  is shown in relation to two orifices  13  within row  14  in FIG.  2 . Orifice  15 A would conventionally be placed at location  20  between the two orifices  13 . If the orifice  15 A was placed at location  20  in a conventional manner, it would thus be necessary to jet ink from orifice  15 A at location  20  for a desired pixel associated with paper  12  as paper  12  travels past row  14 . As described above, however, this may result in a poor print quality and formation of a print artifact on paper  12 . By moving orifice  15 A in printhead  10  a distance corresponding to spacing “S” in the feed direction, as shown, a time delay is created between adjacent ink dots which results in an improved print quality. 
     FIG. 3 is a schematic view of another embodiment of a page width printhead  30  of the present invention for use in an ink jet printer, with which the method of printing described above may be carried out. Printhead  30  includes two rows of orifices  32  and  34 , with individual orifices being respectively referenced  36  and  38  in FIG.  3 . Row  32  includes twice as many orifices as the row of orifices  14  of printhead  10  shown in FIGS. 1 and 2. Likewise, row  34  includes twice as many orifices  38  as the row of orifices  16  of printhead  10 . 
     In contrast with the embodiment of printhead  10  shown in FIGS. 1 and 2, the row of orifices  34  of printhead  30  are substantially aligned relative to the row of orifices  32  in a direction transverse to feed direction  18  (that is, a line drawn parallel to feed direction  18  through the center of an orifice  36  in row  32  also extends through an approximate center of an orifice  38  in row  34 ). Within the row of orifices  32 , only alternating orifices  36  are actually used during printing. For example, in the embodiment shown, the alternating orifices  36  used during printing have been filled-in or blackened. Likewise, within row of orifices  34 , only alternating orifices  38  are used during printing, again represented by filledin or blackened orifices  38 . It is apparent from FIG. 3 that ink which is jetted from the filled in orifices  38  in row of orifices  34  are offset or staggered relative to the filled in orifices  36  which are used in the row of orifices  32 . Thus, it will be noted that the orifices  36  and  38  which are actually used within printhead  30  are disposed in a staggered relationship relative to each other similar to the embodiment of printhead  10  shown in FIGS. 1 and 2. 
     The non-used orifices  36  within the row of orifices  32  and the non-used orifices  38  within the row of orifices  34  function as redundant orifices in the embodiment shown allowing continued use of printhead  30  in the event a particular orifice  36  or  38  fails. Such a failure might be the result of a blockage of an orifice  36  or  38 , or a failure of a heater element associated with a particular orifice  36  or  38 . In the event of a failure of an orifice  36  or  38 , an adjacent orifice in an adjacent row of orifices may be used to allow continued use of printhead  30 . 
     FIG. 4 is a schematic illustration of a printing system  100  having a printing mechanism  102  and a printer chassis  104 . Printing mechanism  102  includes a first printhead  106  and a second printhead  108 . Printheads  106  and  108  each include at least one ink emitting orifice, and preferably, include a row of ink emitting orifices  110  and  112 , respectively. As shown, printhead  106  is fixedly mounted to chassis  104 , and printhead  108  is movably mounted to chassis  104 . Printheads  106 ,  108  are juxtapositioned at a location above print medium, or sheet, M such that orifices  110 ,  112  are adjacent sheet M. Sheet M is transported in the sheet feed direction  114  under printheads  106 ,  108 , for example, by a pair of transport rollers  116  and a pair of exit rollers  118 . 
     Chassis  104  includes a pair of printhead guide rods  120 ,  122 , which slidably engage openings  124 ,  126 , respectively, of printhead  108 , such that printhead  108  can be moved in a direction parallel to the sheet M in sheet feed direction  114  so as to vary a spacing “S” between orifice row  112  and orifice row  110 . Movement of printhead  108  is effected by actuating an electromechanical device, such as a motor  128 , which can be for example, a stepper motor or other DC motor. Motor  128  includes a rotatable shaft  130  having a pinion gear  132  mounted thereto. The teeth of gear  132  engage the teeth of a rack gear  134 . Together, gears  132  and  134  form a mechanical actuator. One end of rack  134  is attached to printhead  108  by a fastening device  136 , such as a pin, screw, bolt, etc. Thus, by controlling the rotation of motor shaft  130 , the spacing “S” between orifice rows  110  and  112  can be varied and controlled. The actuation and control of motor  128  is achieved by a motor controller  138  which supplies electrical signals to motor  128  via a motor control line  138   a.    
     Preferably, the spacing “S” between printhead orifice rows  110  and  112  is defined by the mathematical relationship S≧V×T D , 
     wherein: S is the distance between orifice rows  110  and  112 ; 
     V is the velocity of the print medium; and 
     T D is the ink drying time. 
     Thus, controller  138  positions printhead  108  to satisfy the equation above, so as to compensate for one or more of 1) changes in the print media velocity “V”, and 2) changes in the drying time T D  of the ink, such changes occurring, for example, due to the drying characteristics of various types of inks, or the enviromnental changes which affect ink drying time of a particular ink. To accomplish this spacing control, an input signal representing velocity “V” of the print medium and/or ink drying time T D is received by controller  138  from input device  139  via input line  138   b . Input device  139  can be, for example, a memory unit containing stored information relating to print medium velocity, ink drying time, or other data relating to a desired spacing between the orifices of orifice rows  110  and  112 , which is accessed by a microprocessor of controller  138 . Such information can be, for example, in the form of a look-up table. Alternatively, input unit  139  may supply signals representing real-time measured and/or calculated values for velocity “V” of the print medium and/or ink drying time T D . 
     As a secondary means for controlling the spacing “S”, and so as to provide for fine dynamic control of the position of printhead  108 , preferably, a piezoelectric material  140  is positioned at some location in the drive train between the teeth of gear  130  and printhead  108 . The location of the piezoelectric material can be, for example, at, or form all or part of, fastener  136 . Those skilled in the art will recognize that the piezoelectric material  140  can be positioned between any two adjacent components of the drive train comprised by elements  128 ,  130 ,  132 ,  134 ,  136  and the associated printhead to achieve the desired results. 
     The piezoelectric material  140  is energized by a variable frequency oscillator  141  via line  142 , wherein the actuation of oscillator  141  is controlled by controller  138  via an oscillator control line  138   c . Upon energization of piezoelectric material  140 , the mechanical structure of piezoelectric material  140  is modified so as to compensate for dynamic perturbations in the print medium velocity “V” which occurs at frequencies beyond the reaction capabilities of motor  128  and gear train  132 ,  134 . 
     It is to be understood that in practicing the invention, the spacing of at least two printing elements can be achieved by operating the system in a static mode, wherein the spacing change is effected prior to beginning printing, and/or a dynamic mode, wherein the spacing change(s) is/arc effected after printing has commenced. 
     Although the embodiment of FIG. 4 is directed to moving one of a plurality of printheads, those skilled in the art will realize that the invention can be easily adapted to variably control the position of any or all of the plurality of printheads. Furthermore, in view of the invention, one skilled in the art will recognize that the motor/gear train system may be replaced with other types of electrical, mechanical or electro-mechanical systems for effecting a change in spacing between the printheads, such as for example, by replacing the motor with another type of electromechanical device, e.g., an electrical solenoid, and by replacing the gear train with another form of mechanical actuator, e.g., a linkage. 
     In the embodiments of the present invention shown in the drawings, the print medium is in the form of paper  12 . However, it is also to be understood that other types of print media, such as transparencies, card stock, etc., may be utilized with the method of the present invention. 
     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.