CA1278460C - Multitone ink jet printer and method of operation - Google Patents
Multitone ink jet printer and method of operationInfo
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- CA1278460C CA1278460C CA000534038A CA534038A CA1278460C CA 1278460 C CA1278460 C CA 1278460C CA 000534038 A CA000534038 A CA 000534038A CA 534038 A CA534038 A CA 534038A CA 1278460 C CA1278460 C CA 1278460C
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Abstract
ABSTRACT
This patent application discloses a method and apparatus useful for eight-level halftone thermal ink jet printing by printing with droplets of ink with volumes weighted in a binary sequence. Three (3) binary-weighted drop generators which are fired in sequence are useful in an eight-level, three color printing process and additionally may be employed with a clear ink vehicle drop generator in order to reduce optical density of single small dots in a given pixel area to thereby reduce grainyness This method and apparatus are also adapted for three (3) color number printing with a chosen number of rows and columns of binary-weighted drop generators, including untoned vehicle if desired, in order to achieve color printing of pixels having desired color and optical density.
This patent application discloses a method and apparatus useful for eight-level halftone thermal ink jet printing by printing with droplets of ink with volumes weighted in a binary sequence. Three (3) binary-weighted drop generators which are fired in sequence are useful in an eight-level, three color printing process and additionally may be employed with a clear ink vehicle drop generator in order to reduce optical density of single small dots in a given pixel area to thereby reduce grainyness This method and apparatus are also adapted for three (3) color number printing with a chosen number of rows and columns of binary-weighted drop generators, including untoned vehicle if desired, in order to achieve color printing of pixels having desired color and optical density.
Description
Z~4~
MULTITONE INK JET PRINTER AND METHOD OF OPERATION
Technical Fle~d This invention relates generally to thermal ink j~t printers and more particularly to a multitone ink ~et printer and method having an improvecl grey scale operation.
~k~
Thermal ink j et printing has baen described in many recent technical articles, such a~ an article by Kuhn &
Myers in Scie~ific Ame~ica~, 1985, at pages 162 through 15 178, and also in an article by J. B. Angell et al. also in Sc ~ e~ April 1983 a~ page~ 44 through 55.
In the art of multitone ink jet printing, one approach to printing a dot with one of eight grey scale 20 level~ i~ to e~ploy a ingle inX jet drop gen~rator and fire it from one (1) to ~ven ~7) ti~es at a gi:~n pixel in order to provide the pixel from on~ to seven levels of ink drop volume. ~owever, this approach suffers at least two dis-tinct disadvantage~ when used ln a thermal ink-jet printer.
The ~irst of th~ disadvantages is that the substantial repeated use o~ a 3ingle drop generator and its a~sociated heater resistor increa~e~ the wear and failure rate (decreacad lif~time) o~ the ther~al ink jet print head. As 30 used harain, th~ ter~ "wear" is defined as the accu~ulation of drop e;~ction cycle~ in a drop generator with ~inite liPeti~es. Such li~etimes are typically measured in tens of millions o~ cycles. Secondly, when Lnk i8 ejected in a drop sequence from a single drop generator, thare is a certain 35 recovery time relatad to the bubble collapse associated with each in~ drop e~ection from thQ drop generator~ This recovery time obviou31y imposes a limitation on the maximum achievable rate at which pixel9 are printed using this method of thermal inX jet printing.
Another approach to multitone ink jet printing ,~ ..
~2~
involvas the use of mul~iple inX jet drop generators and firing these drop generators simultaneously in different 5 numbers to achieva different corresponding ink jet drop volumes. To some ex~ent, the use of these multiple drop generators as contrasted to a single drop generator can increase the lifetime of the thermal ink jet printer. One such approach is disclosed fsr example by T. Kawanabe in U.
10 S. Patent ~,4~53,079 issued October 5, 1982. However, the thermal ink jet recorder apparatus of ~he Kawanabe patent identified above i8 possessed with certain other disadvan-tages related to the requirement for simultaneous firing of the multiple drop generators therein.
In particular, since these drop generators of the prior art are simultaneously fired at a single location, th~
nozzles must be critically aligned with respect to each other so that the ink drops will properly register within the pixel on the recording medium (paper). Furthermore, 20 this alignment is predicated upon a particular spacing between the nozzles and paper, and maintaining this distance is critical to achieving a simultaneous combination of these drop volumes on the pixel. In addition, since each drop generator in the Kawanabe recorder of U. S. Patent 4,353,07g produces only one uni volume of ink, then anywhere up to seven drop genera~ors must be fired simultanesusly to achieve the variation o~ one to seven levels on the grey scale. This requirement significantly increases the 30 complexity,cost and unreliability of printhead design, and it also increases the total drop generator~use time ~or the print head and, aqain, imposes a limitation on the useful print head lifetime.
Disc~Qsure of Invent~ion The general purpose of this invention is to pro-vide a new and improved thermal ink jet printer and method of operation which overcomes the a~oredescribed disadvan-tages of the prior art and consequentlv provides a print head of decreased drop generator design complexity and characterized by an extended lifetime.
To accomplish this purpose, I have discovered and developed an improved multitone ink jet printer and method wherein a plurality of ink drop volumes are provided in a drop generator structure and are weighted in a predetermined binary sequence. The drop generators which are each assigned a binary number corresponding to a specific ink drop volume are sequentially fired at a chosen pixel as they come into alignment with the pixel as the printhead moves with respect to the paper or vice versa. Thus, firing one to three binary-weighted drop generators produces 1 to 7 volume units of ink within the pixel. This process produces 1-8 levels of grey scale. The total number of drop generators required in the print head and the total drop generator use time is minimized to thereby maximize print head lifetime with a minimum of associated drop generator design complexity.
.:
In an alternative embodiment of the invention, there is disclosed and claimed a method for reducing the optical density of ink ejected into a given pixel area during a halftoning printing operakion. This method includes ejecting a drop of untoned li~uid, termed "ink vehicle" in the art, into a given area of a pixel and also ejecting one or more drops of ink with a fixed dye loading into khe same area of the pixel. In this manner, the dye is dispersed over a laryer area, and the objectionable optical characteristics of single, small, high-contrast dots standing alone are eliminated in favor of a more uniform gray tone.
~n aspect of the invenkion is as follows:
A scanning printhead for firing ink drops in a predetermined binary sequence including, in combination:
(a) a thin film resistor substrate having a plurality of thin-film heater resistors thereon for generating vapor bubbles in the ink to effect the generation of ink-droplets, ~;~7~
3a (b) a barrier layer disposed on said thin film resistor substrate and having a plurality of channels defining respectively a plurality of drop generators, (c) a drop generator orifice plate disposed on : 5 said barrier member and having respectively a plurality of different drop generator diameters representative of said predetermined binary sequence of drop volumes and disposed respectively over said plurality of heater resistors and barrier channels forming a drop generator, whereby said drop generators may be seguentially first by the application of electrical pulses to said heater resistors as said print head is provided with relative motion with respect to paper receiving ink droplets from said printhead.
A scanning printhead for firing ink drops in a predetermined binary sequence including, in combination:
: (a) a thin film resistor substrate having a ; plurality of thin film heater resistors thereon for generating vapor bubbles in the ink to effect the generation of ink-droplets, (b) a barrier layer disposed on said thin film resistor substrate and having a plurality of channels defining respectively a plurality of drop generators, (c) a drop generator orifice plate disposed on said barrier member and having respectively a plurality of different drop generator diameters representative of said predetermined binary sequence of drop volumes and disposed respectively over said plurality of heater resistor.s and barrier channels forming a drop generator, whereby said drop generators may be seguentially fired by the application of electrical pulses to said heater resistors as said printhead is provided with relative motion with respect to paper receiving ink droplets from said printhead.
B
7~
3b Brief Description of the_Drawin~s Figure lA - lD are sequential isometric views looking up through the paper at the bottom of a scanning printhead having the "1", 'l29' and 9-4l- binary volumes for ejecting ink onto a given pixel.
Figure 2 is a graph of optical dot density versus print volume for the binary drop generator depicted in Figures lA - lD.
Figures 3A and 3B illustrate isometrically, and in B
~L%7~
cross-section respectively, a print head structure consti-tuting a preferred embodiment of the invention.
Figures 4A-4E illustrate schematically an alterna-tive embodiment of tha inv~ntion wherein untoned ink vehicle is combined with an ink ~rop of fixed dye loading. This process is carried out in order to obtain a mixture of ink vehicle and ink on paper to produce a reduction in optical lOdensity o~ the fix d dye loading to thereby eliminate grairyness of small dots.
Figures 5A and 5B illustrate isometrically and in plan view, respectively, a three-color, eight-level halftone printer in accordance with the present invention.
Bes~Mode fQr~Ca~rying___t the Invention Re~erring now to Figures lA-lD, there is shown in sequence the firing of the binary-weighted "4", "2" and "l"
volume ink drops at the pixel p. The direction of scan for 20 a printhead lO is from left to right, and the "4" volume ink drop "a" has printed into the pixel at displacement xl As indicated in Figure lB, the "2" volume drop "b" is on its way toward the pixel ~here it ubsequently combines with the 1-4-1 volume drop to provide a "4" + "2" combined volume spot on the pixel at displacement x2 as indicated in Figure lC.
Also shown in Figure lC is the firing of the "l" volume ink "c" which combines with the already deposited ~'4" + "2"
volumes of ink to give a seven volume ink spot or level 30 eight on the grey scale and completely covering the pixel as indicated in Figuxe lD at displacement X3.
There i8 much less critical alignment with the drop generator scheme of ~he present in~ention than w.ith the approach of firing seven drop generators simultaneously.
35 Furthermore, since there are only three drop generators for the eight grey levsls rather than the seven drop generator scheme of the prior art, this feature results in a simpler electrical interconnect requirement for the printhead heater resistors, less complex driver electronics, a less complex plumbing scheme for feeding ink to the three drop genera-tors, and a more compact and reliable printhead.
Referring to Figure 2, the scheme wher~y combined 5 ink drops with total volume "1" through "7" produce eight grey levels is de~cribed. Thi~ figure shows how optical density of a pixel is increased fro~ the re~lectivity of the untoned paper ("white") to the reflectivi~y of ink covering the paper ("black") a~ succe~ively larger volume~ of ink 10 are applied to the region of a single pixel. The curve in the figure obeys a typical rela~ion between spot area and drop volume on a coatsd paper, and the total optical density of the pixel-is computed ~rom th2 reflectivities and areas of the toned and untoned re~ion~ within a pixel boundary.
15 Next to each print volume derived ~rom the ~ ', "2'l, and "4"
binary-weighted dot printars is shown schematically the co~bination of drops producing this volume.
Referring now to Figures 3A and 3~, the partially cut-away isometric vie~ of a printhead employing the three 20 drop generator sche~Q o~ the pre~ent invention includes a 9ilicon thin fil~ resiRtor sub~trate 30 which is fabricated u ing silicon planar processing and thin film deposition techniques which are w~ll known to thos~ skilled in the art.
The silicon ~bstrat~ 30 include~ a com~on ink feed-hole 32 25 in the form o~ a cylinder or ~lo~ throug~ substrate 30 and configured u~ing diamond saw blade or laser drilling tech~
riques. As i~ also well known, thQ thin film resistor silicon sub3trate 30 is constructed to have a plurality of heater ra~i~tor~ 34, 36 and 3~ thereon, and these resistors are configured to correspond to th~ different "1", '12" and "4" volume ink channels 40, 42 and 4~ in the barrier layer 46. This ~arrier layer 46 i~olates individual drop yenera-tor~ to reduc~ cros~talk and is i~portant to obtaining long 35 operating lifQ for the ~her~al lnk je~ re~i3tor~. Typically the barrier layer 46 i~ ~a~rica~ed ~rom a well known commer-cial polymer material with tha trade mark "VACREL", nickel, glass, or some o~her mater~al impgrviou~ to attack by the liquid ink contained therein.
The printhead in Figure 3A further includes a drop genexator orifice plate 48 typically constructed of nickel .2~
, and includes the plurality of orifices 50, s2 and 54 for ejecting tAe "1", "2" and "4" binary ink volumes, respec-5 tively. These orifices 50, 52 and 54 will emit the "1", "2"and ~ l volumes of ink when their corresponding thin-film resistors 34, 36 and 38 respectively are heated by the application thereto of current pulses. T~e means by which the ink bubble for~ on the heater resistor and provides the 10 energy to eject a droplet of ink is well known to those skilled in the thermal inX j~ printing art, and is des-cribed, ~or example, in the ~ewl et~ __rd Journal, Volume 36, Number 5, May 1985.
These current pulses are applied by way of 15 conventional surface metallization patterns (not shown), but typically consisting of very thin conductive traces of aluminum or gold on th~ upper ~urfac~ of the silicon sub-strate 30 and d~po~ited u~i~g ~tandard evaporation processes well known in the axt.
Although th~ substrat~ memher 30 is referred to herein as a "silicon sub3trate", it will be unders~ood by those s~ill2d in the art that the sub~trate 30 will ~ypical-ly by a thin film compo~it~ or layered s~ructure wherein a first layor of silicon dioxide Slo2, will be grown or depo ited on a ~ilicon ~ub~trata sur~ace to provide surface pasivation thereo~, and then a resistive layer such as tantalum-aluminum will b~ ~po~ited on the Slo2 layer. Next the conductivQ traca material will be evaporated on the tantalum-aluminu~ lay~r and lithographically defined so that opening~ in this trace mat~rial define ~he boundaries of the heater re~istora. Finally, a inert outer passivation or barrier layer ~at~rial su¢h as silicon carbide, SlCl, or silicon nitrid~, Si3N4, or tantalu~ pentoxide, Ta205, or combination thereo~ in succes~iv~ layex~ is for~ed on ~he sur~ace of the al~minu~ trace material and the exposed heater resistors in order to provide a good isolation bar-rier layer betwee~ the heater resistorq and the inX in the reservoirs above these heater resistors. This inert barrier layer is necessary due to the highly corrosive nature of the ink and al~o because of ther cavitation-produced wear during ., i ~I!l27~3~fi~l ink ejection from the drop generators. Therefore, as used herein, "silicon substrate'l is intendad to mean a thin film 5 re~is~or silicon sub~trate of the a~ove type of layered structure.
Referring now to Figures ~ through 4E, there is illustrated an alternative embodiment of my invention which includes an additional drop generator which is indicated as - 10 drop generator 60 in Figure 4A. This generator 60 produces untoned droplets of fluid which is the ink without toning dyes. This liquid is known in the art aa the ink vehicle.
The volu~ of the untoned drop will be betw2en the "1" and "4" volume. When a ~ingle drop 64 is ejected from the 15 printhead onto the paper 65 a~ indicatad in Figure 4B, it will typically exhibit an ~ptical density profile in the for~ indicated in Figure 4C. In this Figure, re~erence number 66 indicate~ th~ optical den ity profile acxoss the diameter of printed dot 67. A~ a result o the sharp steep 20 profile 66 of optical density at the edge, the dot 67 in FigurQ 4C, when se~n at a normal viewing distance, will produce a grainylik~ charactQri~tic a~ perceived by the eye and will consequently re ult in undesirable shading ~r grainyne~s for c~rtain image printing and background appli-25 cations - particulary in th~ reproduction of highlights in continuous tona imag~s. Thus, it is frequently de~irable to remove thi~ grainylike characteri~tic and thi~ may be accomplish~d by th~ utilization og an untoned liquit vehicle drop 68 as indicated in Ftguro 4D. This vehicle drop 68 is ejacted onto t~a same pixel area a~ the toned ink drop 64 and thi~ produces a certain quanti~y o~ vehicle volume plus "1" toned ink volum~ in area 69 a3 indicated in 4~ and having an optical density pro~ 70 which has a maximum 35 valu2 in the center portion 72 ther~of and then decreases out to the ~dges o~ the tonod area 69.
Referring now to Figures 5A and 5B, there i5 shown, in iso~etric and plan view~ respectively, a ~hree-color, eight-level halftone printhead 73 including three foam filled reservoir~ 74, 76 & 78 of the type disclosed and claimed in U.S. Patent No. 4,771,295 fiO
of Jeffrey Baker, assign d to the present assignee. These foam filled reservoirs 74, 76 and 78 are 5 filled with inks having dye colors of cyan, magenta and yellow, respectively for subtractive col3r printing. These reservoirs 74, 76 and 78 are connected using known fluid interconnect technique~ to an outer orifice plate 82 with the cyan, magenta and yellow orifice patterns 84, 86 and 88, respectively. The orifica pattern 84, 86 and 88 are shown in an enlarged plan view in Figure 5~ and include n-rows of the "4", "2", "1" binary drop generators in each of the cyan, magenta and yellow column8 a~ indicated. Thus, each of the cyan, magenta and yellow column~ may have a~ many n-15rows o~ "4", "2", "l" binary drop generators as may benecessa~y to provide a de~ired gua~tity oP these side -by side ink dispen ers for an eight-levol three-color halftoning printing operation. ~dditionally, each o~ the n-rows may be modifi2d to include a ~ingla clear fluid or ink 20 vehicle drop generator (no~ sh~wn) if it becomes desirable for some reason to di~fuse on~ or more of the colors produced in order to r~duGs edge sharpness of isolated, color printed dots. This may b2 d~sirable for example when printing color dot~ (in the ~anner described previously to provida a more uniform coverag~ of a colored region within a pixel).
Various ~odifications may be mad~ in the above-describ~d embodim~nts without departing from the spirit and 30 scop~ of thi~ invention. For example, the present invention is not limited ~pec~ically to tho "4", "2", -1t~ binary sequence indicated, and instead m~y employ vàriations of this binar,v sequence in accordance with tha particular type of grey level i~aging operation being performed. In 35 addition, multicolor printing may be produce~ by individual color pen~ (cyan, yellow, magenta, black) registered and aligned with respect to one another 90 a~ to print succes-sively within the boundary o~ a single pixel to produce mixing of drop~ of various volumes and color~. Furthermore, the present invention is not limited to the particular 3-color printhead of Figure 5 wherein th~ differen~ colors are ``` ~ 27~
all located in adj acent columr~s in an integrat~d ink storage - and orifice plate structure. In~tead, the cyan, magenta, 5 yellow and black inks may be spaced apart by a chosen distance compatible with a particular color printing appl ication .
MULTITONE INK JET PRINTER AND METHOD OF OPERATION
Technical Fle~d This invention relates generally to thermal ink j~t printers and more particularly to a multitone ink ~et printer and method having an improvecl grey scale operation.
~k~
Thermal ink j et printing has baen described in many recent technical articles, such a~ an article by Kuhn &
Myers in Scie~ific Ame~ica~, 1985, at pages 162 through 15 178, and also in an article by J. B. Angell et al. also in Sc ~ e~ April 1983 a~ page~ 44 through 55.
In the art of multitone ink jet printing, one approach to printing a dot with one of eight grey scale 20 level~ i~ to e~ploy a ingle inX jet drop gen~rator and fire it from one (1) to ~ven ~7) ti~es at a gi:~n pixel in order to provide the pixel from on~ to seven levels of ink drop volume. ~owever, this approach suffers at least two dis-tinct disadvantage~ when used ln a thermal ink-jet printer.
The ~irst of th~ disadvantages is that the substantial repeated use o~ a 3ingle drop generator and its a~sociated heater resistor increa~e~ the wear and failure rate (decreacad lif~time) o~ the ther~al ink jet print head. As 30 used harain, th~ ter~ "wear" is defined as the accu~ulation of drop e;~ction cycle~ in a drop generator with ~inite liPeti~es. Such li~etimes are typically measured in tens of millions o~ cycles. Secondly, when Lnk i8 ejected in a drop sequence from a single drop generator, thare is a certain 35 recovery time relatad to the bubble collapse associated with each in~ drop e~ection from thQ drop generator~ This recovery time obviou31y imposes a limitation on the maximum achievable rate at which pixel9 are printed using this method of thermal inX jet printing.
Another approach to multitone ink jet printing ,~ ..
~2~
involvas the use of mul~iple inX jet drop generators and firing these drop generators simultaneously in different 5 numbers to achieva different corresponding ink jet drop volumes. To some ex~ent, the use of these multiple drop generators as contrasted to a single drop generator can increase the lifetime of the thermal ink jet printer. One such approach is disclosed fsr example by T. Kawanabe in U.
10 S. Patent ~,4~53,079 issued October 5, 1982. However, the thermal ink jet recorder apparatus of ~he Kawanabe patent identified above i8 possessed with certain other disadvan-tages related to the requirement for simultaneous firing of the multiple drop generators therein.
In particular, since these drop generators of the prior art are simultaneously fired at a single location, th~
nozzles must be critically aligned with respect to each other so that the ink drops will properly register within the pixel on the recording medium (paper). Furthermore, 20 this alignment is predicated upon a particular spacing between the nozzles and paper, and maintaining this distance is critical to achieving a simultaneous combination of these drop volumes on the pixel. In addition, since each drop generator in the Kawanabe recorder of U. S. Patent 4,353,07g produces only one uni volume of ink, then anywhere up to seven drop genera~ors must be fired simultanesusly to achieve the variation o~ one to seven levels on the grey scale. This requirement significantly increases the 30 complexity,cost and unreliability of printhead design, and it also increases the total drop generator~use time ~or the print head and, aqain, imposes a limitation on the useful print head lifetime.
Disc~Qsure of Invent~ion The general purpose of this invention is to pro-vide a new and improved thermal ink jet printer and method of operation which overcomes the a~oredescribed disadvan-tages of the prior art and consequentlv provides a print head of decreased drop generator design complexity and characterized by an extended lifetime.
To accomplish this purpose, I have discovered and developed an improved multitone ink jet printer and method wherein a plurality of ink drop volumes are provided in a drop generator structure and are weighted in a predetermined binary sequence. The drop generators which are each assigned a binary number corresponding to a specific ink drop volume are sequentially fired at a chosen pixel as they come into alignment with the pixel as the printhead moves with respect to the paper or vice versa. Thus, firing one to three binary-weighted drop generators produces 1 to 7 volume units of ink within the pixel. This process produces 1-8 levels of grey scale. The total number of drop generators required in the print head and the total drop generator use time is minimized to thereby maximize print head lifetime with a minimum of associated drop generator design complexity.
.:
In an alternative embodiment of the invention, there is disclosed and claimed a method for reducing the optical density of ink ejected into a given pixel area during a halftoning printing operakion. This method includes ejecting a drop of untoned li~uid, termed "ink vehicle" in the art, into a given area of a pixel and also ejecting one or more drops of ink with a fixed dye loading into khe same area of the pixel. In this manner, the dye is dispersed over a laryer area, and the objectionable optical characteristics of single, small, high-contrast dots standing alone are eliminated in favor of a more uniform gray tone.
~n aspect of the invenkion is as follows:
A scanning printhead for firing ink drops in a predetermined binary sequence including, in combination:
(a) a thin film resistor substrate having a plurality of thin-film heater resistors thereon for generating vapor bubbles in the ink to effect the generation of ink-droplets, ~;~7~
3a (b) a barrier layer disposed on said thin film resistor substrate and having a plurality of channels defining respectively a plurality of drop generators, (c) a drop generator orifice plate disposed on : 5 said barrier member and having respectively a plurality of different drop generator diameters representative of said predetermined binary sequence of drop volumes and disposed respectively over said plurality of heater resistors and barrier channels forming a drop generator, whereby said drop generators may be seguentially first by the application of electrical pulses to said heater resistors as said print head is provided with relative motion with respect to paper receiving ink droplets from said printhead.
A scanning printhead for firing ink drops in a predetermined binary sequence including, in combination:
: (a) a thin film resistor substrate having a ; plurality of thin film heater resistors thereon for generating vapor bubbles in the ink to effect the generation of ink-droplets, (b) a barrier layer disposed on said thin film resistor substrate and having a plurality of channels defining respectively a plurality of drop generators, (c) a drop generator orifice plate disposed on said barrier member and having respectively a plurality of different drop generator diameters representative of said predetermined binary sequence of drop volumes and disposed respectively over said plurality of heater resistor.s and barrier channels forming a drop generator, whereby said drop generators may be seguentially fired by the application of electrical pulses to said heater resistors as said printhead is provided with relative motion with respect to paper receiving ink droplets from said printhead.
B
7~
3b Brief Description of the_Drawin~s Figure lA - lD are sequential isometric views looking up through the paper at the bottom of a scanning printhead having the "1", 'l29' and 9-4l- binary volumes for ejecting ink onto a given pixel.
Figure 2 is a graph of optical dot density versus print volume for the binary drop generator depicted in Figures lA - lD.
Figures 3A and 3B illustrate isometrically, and in B
~L%7~
cross-section respectively, a print head structure consti-tuting a preferred embodiment of the invention.
Figures 4A-4E illustrate schematically an alterna-tive embodiment of tha inv~ntion wherein untoned ink vehicle is combined with an ink ~rop of fixed dye loading. This process is carried out in order to obtain a mixture of ink vehicle and ink on paper to produce a reduction in optical lOdensity o~ the fix d dye loading to thereby eliminate grairyness of small dots.
Figures 5A and 5B illustrate isometrically and in plan view, respectively, a three-color, eight-level halftone printer in accordance with the present invention.
Bes~Mode fQr~Ca~rying___t the Invention Re~erring now to Figures lA-lD, there is shown in sequence the firing of the binary-weighted "4", "2" and "l"
volume ink drops at the pixel p. The direction of scan for 20 a printhead lO is from left to right, and the "4" volume ink drop "a" has printed into the pixel at displacement xl As indicated in Figure lB, the "2" volume drop "b" is on its way toward the pixel ~here it ubsequently combines with the 1-4-1 volume drop to provide a "4" + "2" combined volume spot on the pixel at displacement x2 as indicated in Figure lC.
Also shown in Figure lC is the firing of the "l" volume ink "c" which combines with the already deposited ~'4" + "2"
volumes of ink to give a seven volume ink spot or level 30 eight on the grey scale and completely covering the pixel as indicated in Figuxe lD at displacement X3.
There i8 much less critical alignment with the drop generator scheme of ~he present in~ention than w.ith the approach of firing seven drop generators simultaneously.
35 Furthermore, since there are only three drop generators for the eight grey levsls rather than the seven drop generator scheme of the prior art, this feature results in a simpler electrical interconnect requirement for the printhead heater resistors, less complex driver electronics, a less complex plumbing scheme for feeding ink to the three drop genera-tors, and a more compact and reliable printhead.
Referring to Figure 2, the scheme wher~y combined 5 ink drops with total volume "1" through "7" produce eight grey levels is de~cribed. Thi~ figure shows how optical density of a pixel is increased fro~ the re~lectivity of the untoned paper ("white") to the reflectivi~y of ink covering the paper ("black") a~ succe~ively larger volume~ of ink 10 are applied to the region of a single pixel. The curve in the figure obeys a typical rela~ion between spot area and drop volume on a coatsd paper, and the total optical density of the pixel-is computed ~rom th2 reflectivities and areas of the toned and untoned re~ion~ within a pixel boundary.
15 Next to each print volume derived ~rom the ~ ', "2'l, and "4"
binary-weighted dot printars is shown schematically the co~bination of drops producing this volume.
Referring now to Figures 3A and 3~, the partially cut-away isometric vie~ of a printhead employing the three 20 drop generator sche~Q o~ the pre~ent invention includes a 9ilicon thin fil~ resiRtor sub~trate 30 which is fabricated u ing silicon planar processing and thin film deposition techniques which are w~ll known to thos~ skilled in the art.
The silicon ~bstrat~ 30 include~ a com~on ink feed-hole 32 25 in the form o~ a cylinder or ~lo~ throug~ substrate 30 and configured u~ing diamond saw blade or laser drilling tech~
riques. As i~ also well known, thQ thin film resistor silicon sub3trate 30 is constructed to have a plurality of heater ra~i~tor~ 34, 36 and 3~ thereon, and these resistors are configured to correspond to th~ different "1", '12" and "4" volume ink channels 40, 42 and 4~ in the barrier layer 46. This ~arrier layer 46 i~olates individual drop yenera-tor~ to reduc~ cros~talk and is i~portant to obtaining long 35 operating lifQ for the ~her~al lnk je~ re~i3tor~. Typically the barrier layer 46 i~ ~a~rica~ed ~rom a well known commer-cial polymer material with tha trade mark "VACREL", nickel, glass, or some o~her mater~al impgrviou~ to attack by the liquid ink contained therein.
The printhead in Figure 3A further includes a drop genexator orifice plate 48 typically constructed of nickel .2~
, and includes the plurality of orifices 50, s2 and 54 for ejecting tAe "1", "2" and "4" binary ink volumes, respec-5 tively. These orifices 50, 52 and 54 will emit the "1", "2"and ~ l volumes of ink when their corresponding thin-film resistors 34, 36 and 38 respectively are heated by the application thereto of current pulses. T~e means by which the ink bubble for~ on the heater resistor and provides the 10 energy to eject a droplet of ink is well known to those skilled in the thermal inX j~ printing art, and is des-cribed, ~or example, in the ~ewl et~ __rd Journal, Volume 36, Number 5, May 1985.
These current pulses are applied by way of 15 conventional surface metallization patterns (not shown), but typically consisting of very thin conductive traces of aluminum or gold on th~ upper ~urfac~ of the silicon sub-strate 30 and d~po~ited u~i~g ~tandard evaporation processes well known in the axt.
Although th~ substrat~ memher 30 is referred to herein as a "silicon sub3trate", it will be unders~ood by those s~ill2d in the art that the sub~trate 30 will ~ypical-ly by a thin film compo~it~ or layered s~ructure wherein a first layor of silicon dioxide Slo2, will be grown or depo ited on a ~ilicon ~ub~trata sur~ace to provide surface pasivation thereo~, and then a resistive layer such as tantalum-aluminum will b~ ~po~ited on the Slo2 layer. Next the conductivQ traca material will be evaporated on the tantalum-aluminu~ lay~r and lithographically defined so that opening~ in this trace mat~rial define ~he boundaries of the heater re~istora. Finally, a inert outer passivation or barrier layer ~at~rial su¢h as silicon carbide, SlCl, or silicon nitrid~, Si3N4, or tantalu~ pentoxide, Ta205, or combination thereo~ in succes~iv~ layex~ is for~ed on ~he sur~ace of the al~minu~ trace material and the exposed heater resistors in order to provide a good isolation bar-rier layer betwee~ the heater resistorq and the inX in the reservoirs above these heater resistors. This inert barrier layer is necessary due to the highly corrosive nature of the ink and al~o because of ther cavitation-produced wear during ., i ~I!l27~3~fi~l ink ejection from the drop generators. Therefore, as used herein, "silicon substrate'l is intendad to mean a thin film 5 re~is~or silicon sub~trate of the a~ove type of layered structure.
Referring now to Figures ~ through 4E, there is illustrated an alternative embodiment of my invention which includes an additional drop generator which is indicated as - 10 drop generator 60 in Figure 4A. This generator 60 produces untoned droplets of fluid which is the ink without toning dyes. This liquid is known in the art aa the ink vehicle.
The volu~ of the untoned drop will be betw2en the "1" and "4" volume. When a ~ingle drop 64 is ejected from the 15 printhead onto the paper 65 a~ indicatad in Figure 4B, it will typically exhibit an ~ptical density profile in the for~ indicated in Figure 4C. In this Figure, re~erence number 66 indicate~ th~ optical den ity profile acxoss the diameter of printed dot 67. A~ a result o the sharp steep 20 profile 66 of optical density at the edge, the dot 67 in FigurQ 4C, when se~n at a normal viewing distance, will produce a grainylik~ charactQri~tic a~ perceived by the eye and will consequently re ult in undesirable shading ~r grainyne~s for c~rtain image printing and background appli-25 cations - particulary in th~ reproduction of highlights in continuous tona imag~s. Thus, it is frequently de~irable to remove thi~ grainylike characteri~tic and thi~ may be accomplish~d by th~ utilization og an untoned liquit vehicle drop 68 as indicated in Ftguro 4D. This vehicle drop 68 is ejacted onto t~a same pixel area a~ the toned ink drop 64 and thi~ produces a certain quanti~y o~ vehicle volume plus "1" toned ink volum~ in area 69 a3 indicated in 4~ and having an optical density pro~ 70 which has a maximum 35 valu2 in the center portion 72 ther~of and then decreases out to the ~dges o~ the tonod area 69.
Referring now to Figures 5A and 5B, there i5 shown, in iso~etric and plan view~ respectively, a ~hree-color, eight-level halftone printhead 73 including three foam filled reservoir~ 74, 76 & 78 of the type disclosed and claimed in U.S. Patent No. 4,771,295 fiO
of Jeffrey Baker, assign d to the present assignee. These foam filled reservoirs 74, 76 and 78 are 5 filled with inks having dye colors of cyan, magenta and yellow, respectively for subtractive col3r printing. These reservoirs 74, 76 and 78 are connected using known fluid interconnect technique~ to an outer orifice plate 82 with the cyan, magenta and yellow orifice patterns 84, 86 and 88, respectively. The orifica pattern 84, 86 and 88 are shown in an enlarged plan view in Figure 5~ and include n-rows of the "4", "2", "1" binary drop generators in each of the cyan, magenta and yellow column8 a~ indicated. Thus, each of the cyan, magenta and yellow column~ may have a~ many n-15rows o~ "4", "2", "l" binary drop generators as may benecessa~y to provide a de~ired gua~tity oP these side -by side ink dispen ers for an eight-levol three-color halftoning printing operation. ~dditionally, each o~ the n-rows may be modifi2d to include a ~ingla clear fluid or ink 20 vehicle drop generator (no~ sh~wn) if it becomes desirable for some reason to di~fuse on~ or more of the colors produced in order to r~duGs edge sharpness of isolated, color printed dots. This may b2 d~sirable for example when printing color dot~ (in the ~anner described previously to provida a more uniform coverag~ of a colored region within a pixel).
Various ~odifications may be mad~ in the above-describ~d embodim~nts without departing from the spirit and 30 scop~ of thi~ invention. For example, the present invention is not limited ~pec~ically to tho "4", "2", -1t~ binary sequence indicated, and instead m~y employ vàriations of this binar,v sequence in accordance with tha particular type of grey level i~aging operation being performed. In 35 addition, multicolor printing may be produce~ by individual color pen~ (cyan, yellow, magenta, black) registered and aligned with respect to one another 90 a~ to print succes-sively within the boundary o~ a single pixel to produce mixing of drop~ of various volumes and color~. Furthermore, the present invention is not limited to the particular 3-color printhead of Figure 5 wherein th~ differen~ colors are ``` ~ 27~
all located in adj acent columr~s in an integrat~d ink storage - and orifice plate structure. In~tead, the cyan, magenta, 5 yellow and black inks may be spaced apart by a chosen distance compatible with a particular color printing appl ication .
Claims (3)
1. A scanning printhead for firing ink drops in a predetermined binary sequence including, in combination:
(a) a thin film resistor substrate having a plurality of thin-film heater resistors thereon for generating vapor bubbles in the ink to effect the generation of ink-droplets, (b) a barrier layer disposed on said thin film resistor substrate and having a plurality of channels defining respectively a plurality of drop generators, (c) a drop generator orifice plate disposed on said barrier member and having respectively a plurality of different drop generator diameters representative of said predetermined binary sequence of drop volumes and disposed respectively over said plurality of heater resistors and barrier channels forming a drop generator, whereby said drop generators may be sequentially first by the application of electrical pulses to said heater resistors as said print head is provided with relative motion with respect to paper receiving ink droplets from said printhead.
(a) a thin film resistor substrate having a plurality of thin-film heater resistors thereon for generating vapor bubbles in the ink to effect the generation of ink-droplets, (b) a barrier layer disposed on said thin film resistor substrate and having a plurality of channels defining respectively a plurality of drop generators, (c) a drop generator orifice plate disposed on said barrier member and having respectively a plurality of different drop generator diameters representative of said predetermined binary sequence of drop volumes and disposed respectively over said plurality of heater resistors and barrier channels forming a drop generator, whereby said drop generators may be sequentially first by the application of electrical pulses to said heater resistors as said print head is provided with relative motion with respect to paper receiving ink droplets from said printhead.
2. The apparatus defined in Claim 1 wherein the volumes produced by said drop generators are weighted in an approximate "1", "2", "4" binary sequence.
3. The apparatus defined in Claim 2 wherein said printhead for producing multiple gray-levels is provided with an additional clear untoned ink vehicle drop generator positioned in the same row as said binary sequence for imparting to said print head an additional grey scale toning capability sufficient to remove grainyness in images formed from small high-contrast dots deposited on a print media.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000534038A CA1278460C (en) | 1987-04-07 | 1987-04-07 | Multitone ink jet printer and method of operation |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000534038A CA1278460C (en) | 1987-04-07 | 1987-04-07 | Multitone ink jet printer and method of operation |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1278460C true CA1278460C (en) | 1991-01-02 |
Family
ID=4135381
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000534038A Expired - Lifetime CA1278460C (en) | 1987-04-07 | 1987-04-07 | Multitone ink jet printer and method of operation |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1278460C (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6260939B1 (en) | 1991-06-05 | 2001-07-17 | Canon Kabushiki Kaisha | Tone recording method using ink jet recording head that records pixels using a plurality of liquid droplets |
| US6406114B1 (en) | 1991-06-05 | 2002-06-18 | Canon Kabushiki Kaisha | Tonal product recorded by ink and having a plurality of pixels with plural tonal levels |
-
1987
- 1987-04-07 CA CA000534038A patent/CA1278460C/en not_active Expired - Lifetime
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6260939B1 (en) | 1991-06-05 | 2001-07-17 | Canon Kabushiki Kaisha | Tone recording method using ink jet recording head that records pixels using a plurality of liquid droplets |
| US6406114B1 (en) | 1991-06-05 | 2002-06-18 | Canon Kabushiki Kaisha | Tonal product recorded by ink and having a plurality of pixels with plural tonal levels |
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