EP0730969B1 - Dot alignment in mixed resolution printer - Google Patents

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• EP-A-0 654 352 (Art. 54.3 EPC), published on 24.05.1995,entitled MIXED RESOLUTION PRINTING FOR COLOR ANDMONOCHROME PRINTERS, by Donald G. Harris, et al, representsthe closest prior art.
• This application also relates to the copendingapplications EP-A-0 622 206,entitled DATUMFORMATION FOR IMPROVED ALIGNMENT OF MULTIPLE NOZZLEMEMBERS IN A PRINTER, by Jeffrey A. Thoman, et al., andEP-A-0 592 221, entitledPRINTHEAD WITH REDUCED INTERCONNECTIONS TO A PRINTER,by Michael B. Saunders, et al., both owned by theassignee of this application and incorporated herein byreference.
BACKGROUND OF THE INVENTION
• This invention relates generally to printers, andmore specifically to printing devices and techniquesfor monochrome and color printers capable of achievinghigh quality resolution.
• High quality printers are typically characterizedby numbers indicating their resolution in dots per inch(dpi). This resolution is usually described in the context of a two dimension coordinate system where onenumber indicates the resolution in the x-axis (as usedherein, x-axis means the carriage scan axis for a swathprinter), and another number indicates the resolutionin the y-axis (as used herein, y-axis means the mediaadvance axis for a swath printer). Thus, a resolutionof 300/300 dpi generally indicates a carriage-scan axisresolution of 300 dots per inch and a media-advanceaxis resolution of 300 dots per inch. If only a singledpi number is given, it is assumed the dpi in both axesare equal.
• The resolution of a printhead is primarilydetermined by the actual printout dot size as itappears in a printout.
• Hewlett-Packard has developed a 600 dpi inkjet penfor producing a very high resolution printout. Oneembodiment of this pen is described inHewlett-Packard's EP-A-0 564 069 byBrian J. Keefe, et al., entitled INK DELIVERY SYSTEMFOR AN INKJET PRINTHEAD, incorporated herein byreference. The nozzle array of this 600 dpi pencontains 300 nozzles and prints a swath approximatelyone-half inch wide along the x-axis. Some ofHewlett-Packard's color printers will include ascanning carriage housing the 600 dpi pen, containingblack ink, as well as one or more color inkjet pens.Currently these color inkjet pens have a resolution of300 dpi and a width on the order of one-third inch.
• The particular alignment of the 600 dpi and300 dpi resolution printheads in the carriage as wellas the particular alignment of the printed highresolution dots and lower resolution dots can beselected to achieve certain characteristics andadvantages.
• Prior art document IBM Technical Disclosure Bulletin, Volume 23, No.7a,December 1980 discloses a mixed resolution printer with a frame for holding a mediumfor being printed upon in a print zone, a scanning carriage supported in said frame to bepositioned proximate to said print zone and first and second printheads supported by thecarriage. The first printhead is a high resolution black printhead and the secondprinthead is a low resolution black printhead in order to provide a printer which printsblack in a variety of modes.
• Prior art document JP-A-5261941 discloses a mixed resolution printhead unitincluding four printheads including a black printhead which prints dots that are largerthan dots printed by the colour printheads.
BRIEF SUMMARY OF THE INVENTION
• According to a first aspect of the present invention there isprovided a mixed resolution printer as defined in the claims.According to a second aspect of the present invention thereis provided a method for printing as defined in the claims.
• In the preferred form, a scanning carriage in acolor inkjet printer houses a high resolution printheadfor black (or monochrome) printing and one or morelower resolution printheads for color printing.
• The nozzle arrangements, paper feed increments,and ink drop firing frequency for the black printheadand color printhead(s) are selected to provide variousalignments between the larger color ink dots and thesmaller black ink dots to achieve maximum ink coveragewith a minimum of ink or to achieve additional colorshades. In one embodiment, the centroid of a group offour smaller dots is aligned with the centroid of alarger dot along the scanning direction (i.e., xdirection). In another embodiment, the midpointbetween two vertically aligned smaller dots is alignedwith the centroid of a larger dot along the scanningdirection. Each smaller dot in a cluster of foursmaller dots may be positioned around the centroid ofthe cluster at 90° angles with respect to the x and yaxes or at 45° angles with respect to the x and y axes.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 shows a typical inkjet printer which canincorporate the apparatus and method of the presentinvention;
• FIG. 2 shows a carriage having removablemulti-color print cartridges, which can incorporate theapparatus and method of the present invention;
• FIG. 3 shows an exemplary lower resolution colorinkjet print cartridge used in one embodiment of theinvention;
• FIG. 4 is a perspective view of a carriageincorporating one embodiment of the invention in aninkjet printer;
• FIG. 5 is a top view of the carriage of FIG. 4;
• FIG. 6 is a fragmentary view of the flex-circuitinterconnect on the carriage of FIGS. 4 and 5, with theinterior carriage walls cut away;
• FIG. 7 is a schematic block diagram of the printcartridges in one embodiment of the invention;
• FIG. 8 is a schematic bottom view as seen lookingup from the media showing one alignment relationship ofthe nozzle arrays of FIG. 7;
• FIG. 9 is a schematic view showing the use of afoam member for operatively connecting a flex-circuitto a higher resolution black inkjet cartridge;
• FIG. 10 is an exploded view showing a flex-circuitframe portion of a carriage, with the foam springmember of FIG. 9 for assuring pressure connection of aflex-circuit to a higher resolution black inkjetcartridge, and a metal spring member for assuringpressure connection of a flex-circuit to lowerresolution color inkjet cartridges;
• FIG. 11 is a front view of the flex-circuit frameof FIG. 10;
• FIG. 12 is a schematic diagram showing therelative resolution between a 600 dpi printout of theblack printhead and a 300 dpi printout of the colorprintheads in one embodiment of the invention;
• FIGS. 13A-13D are schematic views as seen lookingup from the media showing four different alignmentsbetween a high resolution nozzle array and one or morelower resolution nozzle array(s);
• FIGS. 14, 15 and 16 are schematic views ofsingle-plate nozzle arrays for three different tricolorinkjet pens;
• FIG. 17 is a schematic view of the nozzle arraysof three separate color pens as positioned within thecarriage of FIG. 2;
• FIGS. 18-24 illustrate various possible alignmentsbetween printed high resolution dots and lowerresolution dots.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
• In a multiple pen printer, it is important toimprove the output quality of a printed page andincrease the speed at which that output can be obtainedas economically and simply as possible. In a printermechanism, the output quality of a printed page is afunction of printhead resolution. The higher theresolution the better the print quality. Also, in aswath printer employing a scanning carriage, the speedat which the output can be obtained is a function ofthe width of the swath which is covered by theprinthead.
• In current multi-pen printers, each pen has thesame resolution and usually the same swath width. Thismeans that all the supporting structure, mechanics andelectronics needs to be scaled up to support theresolution of the entire set of pens. All thishardware is more expensive than the hardware to supporta multi-resolution, multi-swath width pen set where onepen is at the desired higher resolution and largerwidth, and the other pens in the set are at a lowerresolution and smaller size.
• One embodiment of the invention incorporates ahigh resolution inkjet pen and one or more lowerresolution inkjet pen(s) in the same scanning carriagein a printer. The higher performance pen can be usedto improve output quality by enhancing certain keyfeatures that appear frequently in a printed page suchas text. Such a pen also improves throughput by beingable to print these frequent features faster. Theother lower performance pens can be used for less frequent or less demanding features such as graphicsand color printing.
• In the presently preferred embodiment of theinvention disclosed herein, we have combined a 600dpi1/2 inch swath black pen with three 300 dpi color penseach generating a swath of approximately 1/3 inch. Thehigh performance black pen is typically used forprinting text and other "black only" features, and thusthe output quality and throughput of these features isgreater. It also improves the output quality of colorgraphics and color features by teaming with the threelower performance color pens when printing colorgraphics or color features. The black component of thegraphics, which is often a large portion of colorgraphics content, is at a higher resolution and thus ata higher output quality level. The larger swath canthen be combined with printing algorithms to improvethe throughput of color graphics.
• Even though the invention can be used in anyprinting environment where text and/or graphics areapplied to media using monochrome and/or colorcomponents, the presently preferred embodiment of theinvention is used in an inkjet printer of the typeshown in FIG. 1. In particular,inkjet printer 10includes aninput tray 12 containing sheets ofmedia 14which pass through a print zone, and are fed past anexit 18 into anoutput tray 16. Referring toFIGS. 1-2, amovable carriage 20 holdsprint cartridges22, 24, 26, and 28 which respectively hold yellow (Y),magenta (M), cyan (C) and black (K) inks. The front ofthe carriage has asupport bumper 30 which rides alongaguide 32 while the back of the carriage has multiplebushings such as 34 which ride alongslide rod 36. Theposition of the carriage as it traverses back and forthacross the media is determined from an encoder strip 38in order to be sure that the various ink nozzles on each print cartridge are selectively fired at theappropriate time during a carriage scan.
• In another embodiment printer, thecolor printcartridges 22, 24, and 26 are replaced by a singletricolor cartridge having a nozzle plate such as shownin FIG. 14, 15, or 16.
• Referring to FIGS. 3-6, a 300 dpicolor inkjetcartridge 40 having a tab-circuit with a four columnthirty-two padelectrical interconnect 42 is removablyinstalled in threechutes 44, 46, 48 of a unitarycarriage 50 (FIG. 4). A flex-circuit member 52(FIG. 6) having three matching sets ofconductive pads54, 56, 58 is mounted on flex-frame pins 60 foroperative engagement with the cartridge pads when thecartridge is inserted into its appropriate chute. Anenlarged set ofconductive pads 62 covering a largerarea, having a different layout, and constituting anarray of six columns totaling fifty-two conductive padson the flex-circuit member is designed for operativeengagement with cartridge pads on a 600 dpi blackinkjet cartridge 64 (see FIG. 9).
• The preferred structure and techniques forpreventing mistaken installation of a 600 dpi blackprinthead in a color printhead chute, or alternativelythe mistaken installation of a 300 dpi color printheadin a black printhead chute is described in thecopending applications identified above andincorporated by reference herein.
• Because of the differently configured electricalinterconnect on the 600 dpi cartridge, and in order toavoid substantially changing the existing X/Y/Z datumconfiguration of the carriage, a unique interconnectscheme is employed. In that regard, theX-axiscartridge datums 65 engage theX-axis carriage datums66, and the Y-axis cartridge datums 67 engage theY-axis carriage datums 68, and the Z-axis cartridge datums 69 engage the Z-axis carriage datums 70 in amanner more fully described in the copendingapplications identified above and incorporated byreference herein.
• As best shown in FIGS. 9-11, a spring assemblyincluding a backing sheet 74, a plate 76 and agimbalspring 78 are sized for fitting intoapertures 80 offlex-circuit frame 82 to assure proper electricalinterconnection for the three color cartridges.
• A unique spring assembly for the 600 dpi cartridgeinterconnect includes a unitaryresilient foam member84 which fits in aseat 86 which is larger than theaperture 80. A mountingpeg 88 fits into matchinghole90 which along with bottom andlower ledges 91, 93 andupper side andtop ledges 92, 94 hold the foam memberin proper position to assure operative engagementacross the electrical interconnect.
• FIGS. 7-8 show one possible mounting relationshipbetween a 300dpi nozzle array 96 of the colorprintheads and a 600dpi nozzle array 98 of the blackprinthead. Control circuitry 99 (including amultiplexer) on the substrate enables the three hundredfiring resistors of the black printhead to becontrolled through fifty-two electrical interconnectpads, and similarly enables all one hundred four firingresistors of each color printhead to be controlledthrough thirty-two electrical interconnect pads.
• FIG. 12 schematically shows the difference betweenthe 300 dpi printout produced by the color pens (i.e.,pen cartridges) and the 600 dpi printout of the blackpen of the preferred embodiment described herein. Thetype of paper used, along with other well knownfactors, affect ink bleed. Therefore, the diameters ofthe actual printed dots in FIG. 12 will vary.
• Of course, it would be possible to incorporatedifferent combinations of resolution in different printheads wherein the resolution difference may bearbitrary, depending on the printheads available andalready developed, or wherein the resolution differencemay be decimally related (e.g., 20% greater resolution,30% greater resolution, etc.) or fractionally related(300 dpi with 400 dpi; 300 dpi with 450 dpi, etc.). Inthat regard, the invention can be implemented with anyof the existing inkjet cartridges which are currentlyavailable, with the best results occurring withprintheads in the range of 180 dpi or greater.
• Although FIGS. 8 and 12 show a preferredembodiment of the alignment between a high resolutionnozzle array and a lower resolution nozzle array and apreferred embodiment of the alignment between the highresolution printed dots and the lower resolutionprinted dots, other alignments are possible and haveparticular advantages.
• FIGS. 13A, 13B, and 13C illustrate three differentalignments between a one-half inch, 600 dpiblackinkjet pen 110 and one or more color inkjet pens 112when thesepens 110, 112 are housed in a singlecarriage. Only the nozzle array faces are illustratedfor simplicity.
• If a tricolor (CMY) pen is used, then only oneinkjet pen 112 need be used with theblack inkjet pen110. In the embodiments of FIGS. 13A-13D, twoadditional color pens 112, employed when tricolor pensare not used, are shown in dashed outline.
• FIGS. 14, 15, and 16 show three differentembodiments of a printheadnozzle array face 113, 114,and 115, respectively, for such a tricolor inkjet penhaving three separate ink compartments for the cyan,magenta, and yellow ink. Identified in FIGS. 14-16 arethe three sets of nozzles in the nozzle array face forthe cyan (C), magenta (M), and yellow (Y) ink. Thenozzles for each of the colors may be vertically aligned as in FIG. 14, staggered as in FIG. 15, orhorizontally aligned as in FIG. 16. Two rows of offsetnozzles 116 are provided for each color to provide ahigh vertical density of dots. A printer incorporatinga tricolor cartridge may resemble that of FIG. 1 exceptthatcartridges 22, 24, and 26 would be a singletricolor cartridge alongside theblack inkjetcartridge 28.
• FIG. 17 illustrates the nozzle arrays of threeseparate color pens 118, 119 and 120 when installed inthecarriage 50 of FIG. 4.Pen 118 may be a cyan pen,pen 119 may be a magenta pen, and pen 120 may be ayellow pen, as also illustrated in FIG. 2, but theorder of pens is not very significant to thisinvention.
• In FIG. 13A, the tops of the printheads of thecolor pens 112 are positioned near or aligned with thetop of the printhead of theblack pen 112 so as to befarther from the paper outlet or output rollers. Thedirection of paper transport is shown byarrow 124.This alignment allows the color ink to be placed on thepaper farther from the output rollers so that the colorink is given more time to dry before the paper isejected by the output rollers. One contrasting exampleof the positioning of printheads relative to the outputroller of a color printer is shown in U.S. PatentNo. 5,376,958, entitled STAGGERED PENS IN COLOR THERMALINK-JET PRINTER, by Brent W. Richtsmeier, et al.,assigned to the present assignee and incorporatedherein by reference. The concepts described herein maybe used in conjunction with that printer or any otherprinter. The relative alignments shown in FIG. 13Aprovide the above-mentioned benefit irrespective of theactual distance from the nozzle arrays to the outputrollers.
• FIG. 13B shows an embodiment where the bottoms ofthe printheads of the color ink jet pens 112 arepositioned near or aligned with the bottom of theprinthead of theblack inkjet pen 110 so as to benearer the paper output rollers. This allows the inkfrom theblack pen 110 to spend less time in theprinting area before the paper is ejected. This isdesirable since the printer area can be at a hightemperature or experience other harsh conditions.
• In FIG. 13C, the centers of the printheads of thecolor inkjet pens 112 are aligned near or at the centerof the printhead of theblack inkjet pen 110. Thiswould generally cause the characteristics of the paperto be symmetrical with respect to the centers of thepens 110 and 112. This may result in print qualityadvantages by balancing the benefits obtained by theprevious two alignments. The alignment ofpens 110 and112 may also be off from center to variable degrees toachieve the best printing results. For example, thedimension of A in FIG. 13C may be 2 or 3 times thedimension of B or vice versa.
• In FIG. 13D, a high resolutionblack pen 110 hasthe same printhead size as the printheads of the lowerresolution color pens 112. The edges of the printheadsofpens 110 and 112 are aligned. One drawback of theembodiment of FIG. 13D is that color printheads havingthe same width as the printhead of theblack pen 10 maynot be available.
• In a preferred embodiment, the high resolutionnozzle array has a one-half inch swath and 300 nozzles(150x2 offset columns), and the ink drop volume foreach nozzle is approximately 35 picoliters. The inkreservoir for this high resolution pen containsapproximately 42 milliliters of black ink. Color inkmay also be used.
• In one embodiment of a tricolor pen, having anozzle plate such as that shown in either FIGS. 14, 15,or 16, the ink drop volume for each nozzle isapproximately 30 picoliters per drop. An ink reservoirfor each of the three colors in the tricolor pen maycontain approximately 19.1 milliliters of ink. Eachcolor is in fluid communication with 64 nozzles in asingle printhead.
• In a preferred embodiment of eachindividual colorpen 118, 119, or 120 illustrated in FIG. 17, the inkdrop volume for each nozzle is approximately 104picoliters, and the ink reservoir holds approximately42 milliliters of ink. Each printhead containsapproximately 104 nozzles at a dpi of 300.
• In addition to the consideration being paid to thealignments between the color inkjet printheads and theblack inkjet printhead, the alignment between theindividual dots printed by theblack pen 110 and thecolor pen or pens 112 may also be selected to providethe desired print characteristics.
• FIGS. 18-22 illustrate various alignments betweenthe high resolution dots, having diameters of about1/600 inch, and the lower resolution dots, havingdiameters of about 1/300 inch. Ink bleed may cause theink from adjacent dots to merge. The dots inFIGS. 18-22 are shown separated for clarity. The papertransport direction is assumed to be downward withrespect to the page, and the pen scan direction isperpendicular to the paper transport direction.
• In FIG. 18, thecentroid 130 of a cluster of fourhigh resolution dots 132 is aligned with thecentroid134 of a singlelower resolution dot 136. One goal isto maximize the ink coverage on the page while at thesame time minimizing the amount of ink put down on thepage. The alignment of dots in FIG. 18 comes close to,if not achieves, this goal. In one particular application, thecentroid 134 of thelower resolutiondot 136 may overlap thecentroid 130 of a cluster offourhigh resolution dots 132. Such an overlap isshown. This may be desirable for achieving particularcolors or print characteristics. Also, one or morecolumns of thehigh resolution dots 132 may be printedbetween columns of thelower resolution dots 136.Additionally, alower resolution dot 136 may becompletely surrounded byhigher resolution dots 132 aswould be the case if a singlelower resolution dot 136were placed in the middle of the array ofhighresolution dots 132 shown in FIG. 18.
• FIG. 19 illustrates another dot alignment wherethelower resolution dots 136 are shifted up or downone-half of ahigh resolution dot 132 diameter. Theoverlap of alower resolution dot 136 and fourhighresolution dots 132 is shown.
• FIG. 20 illustrates another dot alignment where acentroid of alower resolution dot 136 may be alignedwith the centroid of ahigh resolution dot 132 oraligned between twohigh resolution dots 132. Thelower resolution dot 136 may print directly over ahighresolution dot 132 or partially over ahigh resolutiondot 132, as illustrated.
• In FIGS. 18-20, fourhigh resolution dots 132 areplaced around theircentroid 130 at 45° from the x andy axis lines. Fourhigh resolution dots 132 may alsobe placed along the 90° axis lines, as shown inFIG. 21. Such an arrangement ofhigh resolutiondots 132 may be created by either modifying thearrangement of nozzles in the nozzle array of an inkjetpen (or tilting the pen) to produce the dot arrangementof FIG. 21 in a single swath or by modifying theenergization speed of the inkjet firing resistors incombination with reducing the incremental steps of thepaper. The mixed resolution dot alignments of FIG. 21 present certain advantages in graphics applications. Acluster oflower resolution dots 136 may either havethe diamond pattern of FIG. 21 or the square pattern ofFIGS. 18-20.
• Other mixed dot resolutions are alsocontemplated, such as 3 to 1 resolutions or 4 to 1resolutions, producing either a nine dot cluster or asixteen dot cluster for every single lower resolutiondot.
• FIGS. 22-24 illustrate other alignments of highand lower resolution dots.
• In FIG. 22, adjacent columns ofhigh resolutiondots 132 are staggered, and a centroid of a cluster offourhigh resolution dots 132 is aligned with acentroid of alower resolution dot 136.
• In FIG. 23, a similar arrangement is shown exceptthat thelower resolution dots 136 are shifted downwardby one half of a higher resolution dot 132 diameter.
• In FIG. 24, variations of the high resolutiondot 132 patterns and lower resolution dot 136 patternsare shown to illustrate the various combinations ofalignments which may be obtained.
• Any combination of high resolution and lowerresolution dots may directly overlap to produce variouscolors or shades or more intense colors. The black,high resolution dots 132 may be printed during the samescan as thelower resolution dots 136 or during adifferent scan to reduce ink bleed and to otherwiseenhance print quality.
• The dot alignments of FIGS. 18-24, or acombination of the alignments, may be used to maximizethe ink coverage on a page while minimizing the amountof ink put down. Dot alignments may even be changedduring printing or between print jobs as desired. Theselection of a particular arrangement may depend on the expected ink bleed and ink characteristics as well asthe particular image being printed.

Claims (9)

1. A mixed resolution printer (10) comprising:

   a frame for holding a medium (18) for beingprinted upon in a print zone;

   a scanning carriage (20) supported on saidframe to be positioned proximate to said printzone;

   a first printhead (110) supported by saidcarriage (20) which prints dots (132) of a first sizeat a first print resolution along an x directionand a y direction, as said carriage (20) scans acrosssaid medium in said x direction, said y directionbeing perpendicular to said x direction; and

   a second printhead (112) supported by saidcarriage (20) which prints dots (136) of a second size,larger than said first size, at a second printresolution lower than said first print resolutionalong said x direction and said y direction, assaid carriage (20) scans across said medium in said xdirection,

   said first printhead (110) and said secondprinthead (112) printing said dots of said first sizeand dots of said second size so as to be alignedwith each other on said medium (18) in a predeterminedmanner along said x and y directions,

   wherein, said first printhead (110) prints black ink and said secondprinthead (112) prints colour ink.
2. The printer of Claim 1 wherein said dots(132) of said first size and said dots (136) of saidsecond size are aligned when printed on said medium(18) such that the centroids of said dots (132) of said firstsize in a line of dots along said x direction arealigned with the centroids of said dots (136) of said secondsize in said x direction.
3. The printer of Claim 1 or 2 wherein dots in acluster of four dots (132) of said first size arepositioned about the centroid of said cluster at 45° angles with respect to said x and y directions.
4. The printer of Claim 1 or 2 wherein dots(132) in a cluster of four dots of said first size arepositioned about the centroid of said cluster at 90°angles with respect to said x and y directions.
5. A method for printing using a mixedresolution printer (10) comprising the steps of:

   controlling a first printhead (110) to printdots (132) of a first size at a first printresolution along an x direction and a y direction,as said first printhead scans across a medium (18)in said x direction, said y direction beingperpendicular to said x direction; and

   controlling a second printhead (112) to printdots (136) of a second size, larger than saidfirst size, at a second print resolution lowerthan said first print resolution along said xdirection and said y direction, as said firstprinthead (110) and said second printhead (112) scan acrosssaid medium (18) in said x direction,

   said first printhead (110) and said secondprinthead (112) printing said dots (132) said first sizeand said dots (136) of said second size so as to bealigned with each other on said medium (18) in apredetermined manner along said x and ydirections,

   wherein the first printhead (110) prints black ink and thesecond printhead (112) prints colour ink.
6. The method of Claim 5 wherein said dots (132)of said first size and said dots (136) of said secondsize are aligned when printed on said medium (18) suchthat the centroids of said dots of said first size in aline of dots along said x direction are aligned withthe centroids of said dots of said second size in saidx direction.
7. The method of Claim 5 or 6 wherein dots (132)in a cluster of four dots of said first size arepositioned about the centroid of said cluster at 45°angles with respect to said x and y directions.
8. The method of Claim 5 or 6 wherein dots (132)in a cluster of four dots of said first size arepositioned about the centroid of said cluster at 90°angles with respect to said x and y directions.
9. The method of Claim 5, 6, 7 or 8 whereinsaid second printhead (112) prints ink including acolor component selected from a group consisting ofcyan, magenta, and yellow.

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