Means for higher speed inkjet printing

Abstract

A method and apparatus for subdividing and printing regions of a substrate with multiple print heads or multiple print head assemblies which substantially decreases printing time is described. The method includes a feathering method which reduces overlap artifacts which is useful in any printing situation where adjacent regions are printed that could be misaligned, offset, or have slightly different colors.

What is claimed is: 
     
         1 . An apparatus for printing on a print medium as said print medium advances along a selected path, said apparatus comprising:
 a print material delivery assembly including at least one print device with each print device having at least one nozzle, said print material delivery assembly disposed to deposit droplets of a print material on at least a portion of said print medium a plurality of times;   wherein said at least one print device comprises a print array having a main body with a plurality of printing segments mounted thereon with a portion of adjacent ends of each pair of said printing segments overlapping a corresponding same portion of said selected path with said print array mounted across said selected path with said printing segments facing said selected path with each of said printing segments having a preset number of print nozzles disposed to deposit droplets of said print material on said print medium with the print nozzles that overlap said corresponding same portion of said selected path disposed to deposit droplets of said print material to a same region of said print medium; and   a print firing controller to generate a print firing signal for each, and coupled to, said at least one nozzle to selectively deposit said droplets onto said print medium utilizing correction factors to modify the number of droplets to be fired from a corresponding printhead at least one nozzle to achieve the desired density of said droplets using substantially uncorrelated halftone masks to independently adjust each print firing signal as each droplet is deposited on a same nominal position of said print medium, the halftone masks being substantially uncorrelated so that the halftone masks are different from each other;   wherein said print firing controller generates said print firing signal for, and is coupled to, each of said nozzles in each printing segment of said print array where, in the overlapped regions utilizing said correction factors and feathering functions to achieve the desired density of said droplets using said substantially uncorrelated halftone masks to independently adjust each print firing signal.   
     
     
         2 . An apparatus for printing a print medium as in  claim 1  wherein:
 the relationship between the print firing signals for said printhead nozzles of each of adjacent printing segments in the corresponding overlap region at the x axis position within the overlap region with one printhead segment to the left of the other printhead segment and one printhead segment being to the right of the other printhead segment is
     F=F ·Alpha  l+F ·Alpha  r ·(1 −F ·Alpha  l )
 
 
 
       where:
 F=the print density of dark pixels desired to be delivered in the overlap region; 
 Alpha l=the fraction of said print density to be delivered from the left printhead segment; and 
 Alpha r=the fraction of said print density to be delivered from the right printhead segment; 
 with Alpha l gradually varying from 1 to 0 and Alpha r gradually varying from 0 to 1 with increasing x in the overlap region, wherein the Alpha values represent the fraction of the value of print firing signal that would be applied to the corresponding printhead segment nozzles if only the left or right printhead were printing in the overlap region. 
 
     
     
         3 . The apparatus for printing on a print medium as in  claim 2  wherein said correction factors are developed using a feathering algorithm, the feathering algorithm being calculated by Alpha l and Alpha r. 
     
     
         4 . The apparatus for printing on a print medium as in  claim 1  wherein the relationship between the print firing signals for said printhead segment nozzles of each of adjacent printheads segments in the corresponding overlap region at any x axis position within the transition region with one printhead segment to the left of the other printhead segment, and one printhead segment being to the right of the other printhead segment is
     D ( F )= D (Alpha  l·F )+{1 −D (Alpha  l·F )}· D (Alpha  r·F )
 
 where: 
 D(F)=the image density; 
 F=the dot density in the overlap region or, equivalently, the number of pixels dark per unit area; 
 Alpha l=the fraction of pixels used from the left printhead segment or, equivalently, the correction factor of the left printhead segment to set the fraction of F to be delivered by the left print head segment; and 
 Alpha r=the fraction of pixels used from the right printhead segment or, equivalently, the correction factor of the right printhead to set the fraction of F to be delivered by the right print head segment; 
 with Alpha l gradually varying from 1 to 0 and Alpha r gradually varying from 0 to 1 with increasing x in the transition region, wherein the Alpha value represents the fraction of the value of print firing signal that would be applied to the corresponding printhead segment nozzles if only the left or right printhead segment were printing in the overlap region. 
 
     
     
         5 . The apparatus for printing on a print medium as in  claim 4  wherein said correction factors are developed using a feathering algorithm, the feathering algorithm being calculated by Alpha l and Alpha r. 
     
     
         6 . The apparatus for printing on a print medium as in  claim 4  wherein said correction factors are generated with interpolation functions of Alpha r (F) vs. Alpha l (F) to generate the print firing signals for use in adjacent printable portions and the overlap region. 
     
     
         7 . The apparatus for printing on a print medium as in  claim 1  wherein a sum of said print droplets deposited in said overlap region to form an image of a selected density by adjacent printheads segments is greater than the sum of said print droplets printed by one printhead segment in a portion of an adjacent printable region of a width equal to a width of said overlap region when printing said image of said selected density so the apparent print droplet densities printed by said adjacent printhead segments are equalized with each other when printing. 
     
     
         8 . The apparatus for printing on a print medium as in  claim 1 , wherein said correction factors adjust the print droplet densities to be deposited by the respective printhead segments. 
     
     
         9 . The apparatus for printing on a print medium as in  claim 1  wherein said correction factors are generated with a correction table to generate the print firing signals for use in adjacent printable portions and the overlap region. 
     
     
         10 . The apparatus for printing on a print medium as in  claim 1  wherein:
 said print medium has a top side and a bottom side; 
 said print material delivery assembly includes:
 a first printhead mechanism disposed to deposit droplets of said print material to said top side of said print medium; and 
 a second printhead mechanism disposed to deposit droplets of said print material to said bottom side of said print medium. 
 
 
     
     
         11 . An apparatus of  claim 1  where multiple drops per pixel are applied in non-overlapping regions. 
     
     
         12 . The apparatus for printing on a print medium as in  claim 1  further comprising:
 a print medium advancing mechanism to advance said print medium in discrete steps beneath said print array; and a system processor coupled to said print medium advancing mechanism and said print firing controller to coordinate the positioning of said print medium, and the firing of said nozzles in each said printing segment to selectively deposit droplets of said material in successive swaths across said print medium; and 
 an apparatus to measure printing errors and color values and feedback corrections to the printer controller or internal processor. 
 
     
     
         13 . An apparatus of  claim 12  that uses at least one of manual measurements, automatic measurements and default values for corrections. 
     
     
         14 . An apparatus of the  claim 12  where the feedback is performed by a densitometer or spectrometer incorporated in the printing device. 
     
     
         15 . An apparatus of the  claim 12  where the feedback is performed during the printer manufacture or by the end user of the printer. 
     
     
         16 . An apparatus of the  claim 12  where the controller uses an on board optical sensor to detect and correct dot placement. 
     
     
         17 . An apparatus of the  claim 12  where process grey is optionally used where grey would have been used. 
     
     
         18 . An apparatus of  claim 1  where at least one of the nozzles is a showerhead nozzle. 
     
     
         19 . An apparatus for printing on a print medium as said print medium advances along a selected path, said apparatus comprising:
 a print material delivery assembly including at least one print device with each print device having at least one nozzle, said print material delivery assembly disposed to deposit droplets of a print material on at least a portion of said print medium a plurality of times;   a print firing controller to generate a print firing signal for each, and coupled to, said at least one nozzle to selectively deposit said droplets onto said print medium utilizing correction factors to modify the number of droplets to be fired from a corresponding printhead at least one nozzle to achieve the desired density of said droplets using substantially uncorrelated halftone masks to independently adjust each print firing signal as each droplet is deposited on a same nominal position of said print medium, the halftone masks being substantially uncorrelated so that the halftone masks are different from each other; and   an apparatus to measure printing errors and color values and feedback corrections to the printer controller or internal processor.   
     
     
         20 . An apparatus of  claim 19  that uses at least one of manual measurements, automatic measurements and default values for corrections. 
     
     
         21 . An apparatus of the  claim 19  wherein the feedback is performed by a densitometer or spectrometer incorporated in the printing device. 
     
     
         22 . an apparatus of the  claim 19  wherein the feedback is performed during the printer manufacture or by the end user of the printer. 
     
     
         23 . An apparatus of the  claim 19  wherein the controller uses an on board optical sensor to detect and correct dot placement. 
     
     
         24 . An apparatus of the  claim 19  wherein process grey is optionally used where grey would have been used. 
     
     
         25 . An apparatus of  claim 19  wherein at least one of the nozzles is a showerhead nozzle. 
     
     
         26 . An apparatus for printing on a print medium as said print medium advances along a selected path, said apparatus comprising:
 a print material delivery assembly including at least one print device with each print device having at least one nozzle, said print material delivery assembly disposed to deposit droplets of a print material on at least a portion of said print medium a plurality of times; and   a print firing controller to generate a print firing signal for each, and coupled to, said at least one nozzle to selectively deposit said droplets onto said print medium utilizing correction factors to modify the number of droplets to be fired from a corresponding printhead at least one nozzle to achieve the desired density of said droplets using substantially uncorrelated halftone masks to independently adjust each print firing signal as each droplet is deposited on a same nominal position of said print medium, the halftone masks being substantially uncorrelated so that the halftone masks are different from each other;   wherein said print controller utilizes feedback to correct one or more of drop volume, alignment errors and image density.   
     
     
         27 . The apparatus of  claim 26  wherein the print controller uses said feedback to shift dot rows to partially compensate for alignment errors. 
     
     
         28 . The apparatus of  claim 26  wherein the print controller uses said feedback to correct alignment errors by one or more of:
 dot size modulation; 
 use of additional colors; and 
 number and placement of dots. 
 
     
     
         29 . The apparatus of  claim 26  wherein at least one nozzle is a showerhead nozzle. 
     
     
         30 . The apparatus of  claim 26  wherein the apparatus uses uncorrelated masks and a feathering function. 
     
     
         31 . The apparatus of  claim 26  wherein at least one print device deposits at least two droplets on a pixel. 
     
     
         32 . An apparatus for printing on a print medium as said print medium advances along a selected substantially linear path, said apparatus comprising:
 a print material delivery assembly including at least two print devices with each print device having at least one nozzle, said print material delivery assembly disposed to deposit at least one droplet of said print material from each of the at least two print devices in dot rows on at least a portion of said print medium a plurality of times; and   a print controller that utilizes feedback to correct one or more of drop volume or alignment errors or image density.   
     
     
         33 . The apparatus of  claim 32  where the print controller uses said feedback to shift said dot rows to partially compensate for alignment errors. 
     
     
         34 . The apparatus of  claim 33  where the print controller uses said feedback to correct alignment errors by at least one of dot size modulation, use additional colors and number and placement of dots. 
     
     
         35 . The apparatus of  claim 32  where at least one nozzle is a showerhead nozzle. 
     
     
         36 . The apparatus of  claim 32  where the apparatus uses uncorrelated m asks and a feathering function. 
     
     
         37 . The apparatus of  claim 32  where at least one print device of the at least two print devices deposits at least two droplets on a pixel. 
     
     
         38 . An apparatus as in  claim 37  further comprising a segmented array. 
     
     
         39 . The apparatus of  claim 38  where the print controller uses said feedback to shift dot rows to partially compensate for alignment errors. 
     
     
         40 . The apparatus of  claim 39  where the print controller uses said feedback to correct alignment errors by at least one of dot size modulation, use of additional colors and number and placement of dots. 
     
     
         41 . The apparatus of  claim 38  where at least one nozzle is a showerhead nozzle. 
     
     
         42 . The apparatus of  claim 38  where the apparatus uses uncorrelated m asks and a feathering function. 
     
     
         43 . The apparatus of  claim 38  where at least one print device of the at least two print devices may deposit at least two droplets on a pixel.