EP1361068A1 - Staggered multi-phase firing of nozzle heads for a printer - Google Patents

Abstract

The present invention describes a method for printing, with one typeof printhead, with a resolution that differs from the resolution of thetype of printhead used. In the method according to the presentinvention, the speed in the fast scan direction is changed withreference to a reference velocity which the printhead is intended to bedriven with, while preferably keeping the firing frequency of the setsof nozzles unchanged. The firing order of the nozzles may or may not be changed.

Description

FIELD OF THE INVENTION

The present invention relates to apparatus and methods for printingand in particular to drop-on-demand (DOD) inkjet printing methodsand apparatus.

BACKGROUND OF THE INVENTION

When DOD inkjet is considered, two main groups can be discerned:thermal inkjet and piezo inkjet.

With thermal inkjet technology, tiny resistors rapidly heat a thinlayer of liquid ink. The heated ink causes a vapour bubble to beformed, expelling or ejecting drops of ink through nozzles andplacing them precisely on a surface to form text or images. As thebubble collapses, it creates a vacuum that pulls in fresh ink. Thisprocess is repeated thousands of times per second. With thermalinkjet technology, water-based inks are used.

Piezoelectric printing technology - commonly called piezo - pumpsink through nozzles using pressure, like a squirt gun. A piezocrystal used as a very precise pump places ink onto the printingmedium. A wide range of ink formulations (solvent, water, UV) may beused.

A number of different piezo concepts exist.

A typical concept, as described in US-4887100,WO 96/10488, WO97/04963 and WO 99/12738, uses so called shared walls. The pressurechambers containing the ink are next to each other, while theirdividing walls are the actuators.

Because an actuator is always shared by two channels, it is notpossible to jet a drop out of two neighbouring channels at the sametime. InWO 96/10488 is described that the nozzles are divided inthree interlaced groups (A, B, C). Neighbouring nozzles are fired ina sequence ABC. Two solutions are possible to print dots on astraight line.

A first solution uses a complete nozzle array under a certain angle.By doing this, the resolution is increased, and by using the rightfast scan speed, dots fired in a sequence A, B, C are on a straightline.

A second solution uses a head perpendicular to the fast scandirection, in which the A, B, and C nozzles are staggered in thefast scan direction. Printing of a line of pixels is divided intothree cycles. In the first cycle, the dividing walls to either sideof the A channels are driven (if ink is to be ejected from them -depending on the image to be printed) with a pulsed signal. In thesecond cycle, the dividing walls to either side of the B channelsare driven (if ink is to be ejected from them - depending on theimage to be printed) with a pulsed signal. In the third cycle, thedividing walls to either side of the C channels are driven (if inkis to be ejected from them - depending on the image to be printed)with a pulsed signal. The pressure pulses developed in the channelsthat are not included in the current cycle are not larger than 1/2of those in the channels that are intended to eject ink. Theprinting apparatus is arranged so that such pulses with 1/2magnitude do not cause ink ejection.

A drawback of this concept is that, once the firing frequency isdefined, only one fast scan speed can be used to print ABC dots on astraight line, as explained hereinafter. In the fast scan direction,the head will e.g. print each 1/360-inch.

Fig. 1 shows apiezo printhead 10 according to the prior art, havingnozzles 12 which are divided into three sets, called a set of Anozzles, a set of B nozzles and a set of C nozzles, each setintended to be fired during different firing cycles. The differentsets of nozzles are staggered with respect to each other over astagger distance D1 in the fast scan direction. If the nozzles aredivided in groups G of three, every first nozzle is part of the setof A nozzles, every second nozzle is part of the set of B nozzlesand every third nozzle is part of the set of C nozzles. All nozzlesin one set A, B, C are positioned on a straight line in the slowscan direction S, which lines are located at the stagger distance D1with respect to each other in the fast scan direction F.

As an example,printhead 10 is considered to be a type 360 head.This means that theprinthead 10 is provided for printing 360 dpi (=pixels per inch) in the fast scan direction F. In this type 360printhead 10, the distance D1 betweennozzles 12 in the fast scandirection F is 1/360 inch / 3 = 70.56 µm / 3 = 23.52 µm.

If the firing frequency is 12.4 kHz, meaning that every set A, B, Cof nozzles can be fired every 80.65 µs, the speed of theprinthead10 in the fast scan direction F is 1/360 inch * 12.4 kHz = 0.875m/s. Thenozzles 12 are fired in an ABC sequence, with the A nozzlesat the leading edge of theprinthead 10 in the fast scan directionF.

The cycle frequency is 12.4 kHz * 3 = 37.2 kHz. Or formulated inanother way: the set of B nozzles fires 26.88 µs after the set of Anozzles, and the set of C nozzles fires 53.76 µs after the set of Anozzles. After 80.65 µs, the set of A nozzles fires again.

One type of printing may be called "mutually interstitial printing",also called shingling e.g. as in US-4,967,203, in which adjacentpixels on a raster line in the fast scan direction are not printedby the same nozzle in the printhead. Printing dictionaries, however,refer to "shingling" as a method to compensate for creep in book-making.The inventors are not aware of any industrially acceptedterm for the printing method wherein no adjacent pixels on a rasterline are printed by one and the same nozzle. Therefore, from here onand in what follows, the terms "mutually interstitial printing" or"interstitial mutually interspersed printing" are used. It is meantby these terms that an image to be printed is split up in a set ofsub-images, each sub-image comprising printed parts and spaces, andwherein at least a part of the spaces in one printed sub-image forma location for the printed parts of another sub-image, and viceversa.

When it would be desired to keep the same firing frequency, but toprint a 180 * 180 dpi image with the 360 type printhead of theexample given above, the printhead speed should theoretically doubleto 1.750 m/s. In the above case of printing a 180 * 180 dpi imagewith a 360 type printhead, where the printhead speed must double to1.750 m/s, the delays for firing B and C need to be shorter to make sure that dots are printed on the same line. Nozzle set B has to befired 13.44 µs after nozzle set A, and nozzle set C 26.88 µs afternozzle set A. These firing frequencies are too close one to theother, and therefore a 360 type printhead cannot be used to print a180 * 180 dpi image.

When it would be desired, on the other hand, to print a 720 * 720dpi image with the 360 type printhead, the firing delay between theset of A nozzles, set of B nozzles and set of C nozzles increases to53.76 µs. As, however, after 80.65 µs the set of A nozzles has tofire again, there is not enough time left to fire the set of Cnozzles, and therefore a 360 type printhead cannot be used to printa 720 * 720 dpi image neither.

It is an object of the present invention to provide a method forprinting, with one type of printhead, with a resolution whichdiffers from the design resolution of the type of printhead used.

SUMMARY OF THE INVENTION

The above objective is accomplished by a method of driving a printhead according to the present invention. A print head used has alongitudinal axis in a slow scan direction and has an array ofmarking elements comprising at least one group of marking elements.

Marking elements of one group are staggered with respect to eachother over a stagger distance in a fast scan direction, which isperpendicular to the slow scan direction. The print head is intendedto be driven with a reference velocity Vref, which is equal to thestagger distance, multiplied by a reference firing frequency Fref.

One marking element of a group is able to be fired at each referencefiring frequency pulse (whether it fires depends upon the image tobe printed). The marking elements of the print head are intended tobe fired according to a reference firing order to print an imagewith a first resolution. The method of the present invention ischaracterised in that it is operated at an operating velocity thatis different from the reference velocity so as to print the sameimage with a different resolution.

If there are n marking elements in one group, wherein theoperating velocity may be equal toreference velocity /nX+1 or toreference velocity /nX-1, X being an integer larger than 0. In the first case,the firing order of the marking elements equals the reference firingorder, in the second case it equals the inverse of the referencefiring order.

The above methods may be used for carrying out fast mutuallyinterstitial printing.

The present invention also includes a printing device with aprint head (10) having a longitudinal axis in a first direction (S)and having an array of marking elements (A, B, C; A, B, C, D)comprising at least one group (G) of marking elements (A, B, C; A,B, C, D), marking elements (A, B, C; A, B, C, D) of one group (G)being staggered with respect to each other over a stagger distance(D1) in a second direction (F) perpendicular to the first direction(S), the print head (10) being intended to be driven with areference velocity (Vref) equal to the stagger distance (D1)multiplied by a reference firing frequency (Fref), one markingelement of a group being firable at each reference firing frequencypulse, the marking elements (A, B, C; A, B, C, D) of the print head(10) being intended to be fired according to a reference firingorder to print an image at a first resolution, further comprisingmeans for driving the print head (10) at an operating velocity whichis different from the reference velocity to print the same image ata second resolution of printing. For this printing device there maybe n marking elements (A, B, C; A, B, C, D) in one group (G) and theoperating velocity for printing with the second resolution is equaltoreference velocity /nX+1, X being an integer larger than or equal to 0.,the firing order of the marking elements (A, B, C; A, B, C, D) toprint the second resolution being the same as the reference firingorder (ABC; ABCD). Alternatively, this printing device has n markingelements (A, B, C; A, B, C, D) in one group (G), wherein theoperating velocity to print the second resolution is equal toreference velocity /nX-1, X being an integer larger than 0, the firing orderof the marking elements (A, B, C; A, B, C, D) to print the secondresolution equalling the inverse of the reference firing order (CBA;DCBA).

For either of these arrangements the marking elements (A, B, C;A, B, C, D) of one group (G) may be staggered with respect to eachother over a stagger distance (D1) in a second direction (F)perpendicular to the first direction (S) to form a plurality of rowsof marking elements, and the printing device may be adapted tosupply printing data representing the image to the marking elementsof one row which is delayed with respect to the printing datasupplied to another row.

The present invention also includes a computer program productfor executing any of the methods of the present invention whenexecuted on a computing device associated with a printing head. Amachine readable data storage device may store the computer programproduct. The computer program product may be transmitted over alocal or wide area telecommunications network.

The present invention also includes a control unit for a printerfor printing an image on a printing medium using a print head (10)having a longitudinal axis in a first direction (S) and having anarray of marking elements (A, B, C; A, B, C, D) comprising at leastone group (G) of marking elements (A, B, C; A, B, C, D), markingelements (A, B, C; A, B, C, D) of one group (G) being staggered withrespect to each other over a stagger distance (D1) in a seconddirection (F) perpendicular to the first direction (S), the controlunit being adapted to control the driving of the print head (10)with a reference velocity (Vref) equal to the stagger distance (D1)multiplied by a reference firing frequency (Fref), and forcontrolling the firing of one marking element of a group at eachreference firing frequency pulse, and for controlling the firing ofthe marking elements (A, B, C; A, B, C, D) of the print head (10)according to a reference firing order to print the image at a firstresolution, further comprising means for controlling the driving ofthe print head (10) at an operating velocity which is different from the reference velocity to print the image at a second resolution ofprinting.

Although there has been constant improvement, change andevolution of devices in this field, the present concepts arebelieved to represent substantial new and novel improvements,including departures from prior practices, resulting in theprovision of more efficient devices of this nature.

Other features and advantages of the present invention willbecome apparent from the following detailed description, taken inconjunction with the accompanying drawings, which illustrate, by wayof example, the principles of the invention. This detaileddescription is given for the sake of example only, without limitingthe scope of the invention. The reference figures quoted below referto the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1

is a front view of a printhead with staggered markingelements as known in the prior art.

Fig. 2

schematically illustrates an ABC printing scheme of aprinthead according to Fig. 1.

Fig. 3

is a front view of a printhead with two arrays of markingelements, each having a first resolution, the nozzle arraysbeing placed so that the combined resolution equals twice thefirst resolution.

Fig. 4

schematically shows a printhead consisting of two staggerednozzle arrays.

Fig. 5

is a printing scheme for 12.5% mutually interstitial printingaccording to an embodiment of the present invention.

Fig. 6

schematically illustrates an ABCD printing scheme inaccordance with an embodiment of the present invention for aprinting head with four marking elements in one group.

Fig. 7

is a highly schematic representation of an inkjet printer foruse with the present invention.

Fig. 8

is a schematic representation of a printer controller inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described with reference tovarious embodiments and drawings but the present invention is notlimited thereto but only by the claims.

The term "printing" as used in this invention should beconstrued broadly. It relates to forming markings whether by ink orother materials or methods onto a printing substrate. Variousprinting methods which may be used with the present invention aredescribed in the book "Principles of non-impact printing", J. L.Johnson, Palatino Press, Irvine, 1998, e.g. thermal transferprinting, thermal dye transfer printing, deflected ink jet printing,ion projection printing, field control printing, impulse ink jetprinting, drop-on-demand ink jet printing, continuous ink jetprinting. Non-contact printing methods are particularly preferred.However, the present invention is not limited thereto. Any form ofprinting including dots or droplets on a substrate is includedwithin the scope of the present invention, e.g. piezoelectricprinting heads may be used to print polymer materials as used anddescribed by Plastic Logic (http://plasticlogic.com/) for theprinting of thin film transistors. Hence, the term "printing" inaccordance with the present invention not only includes marking withconventional staining inks but also the formation of printed 2-D or3-D structures or areas of different characteristics on a substrate.On example is the printing of water repellent or water attractiveregions on a substrate in order to form an off-set printing plate byprinting. Accordingly, the term "printing medium" or "printingsubstrate" should also be given a wide meaning including not onlypaper, transparent sheets, textiles but also flat plates or curvedplates which may be included in or be part of a printing press. Inaddition the printing may be carried out at room temperature or atelevated temperature, e.g. to print a hot-melt adhesive the printinghead may be heated above the melting temperature. Accordingly, theterm "ink" should also be interpreted broadly including not onlyconventional inks but also solid materials such as polymers whichmay be printed in solution or by lowering their viscosity at high temperatures as well as materials which provide some characteristicto a printed substrate such as information defined by a structure onthe surface of the printing substrate, water repellence, or bindingmolecules such as DNA which are spotted onto microarrays. Assolvents both water and organic solvents may be used. Inks as usedwith the present invention may include a variety of additives suchas ant-oxidants, pigments and cross-linking agents.

In the following the invention will be described with respectto one type of printing, e.g. ink jet printing in which a printheadtraverses with respect to a printing medium in a first direction(fast scan direction) while the print medium indexes forwardsrelative to the printhead in a direction perpendicular to this (slowscan direction). In a method according to the present invention,the speed in the fast scan direction is changed with reference to areference velocity which the printhead is intended to be drivenwith, while preferably keeping the firing frequency of the sets ofnozzles unchanged. This is done in order to be able to print, with aprinthead of a certain type, which is intended to print images witha certain resolution, images with other resolutions. If needed, thefiring sequence is changed as well.

FIRST EMBODIMENT: THREE MARKING ELEMENTS IN A GROUP

Aprinthead 10 used according to the first embodiment has threesets of marking elements or nozzles 12: a set of A-nozzles, a set ofB-nozzles and a set of C-nozzles. This means that there a threenozzles 12 in one group G, as represented in Fig. 1.

For aprinthead 10 intended to print images of a certain basicresolution, changing the firing sequence from ABC to CBA while usinghalf the fast scan speed used for the ABC sequence, makes itpossible to print images with a resolution which is the double ofthe basic resolution. For example a type 360 head, with a staggerdistance D1 of 23.52 µm between two neighbouring sets of nozzles,which head 10 is normally intended to be fired (in an ABC firingsequence) at a frequency of 12.4 kHz and moved with a speed of 0.875m/s, can be used for printing images with a resolution of 720 dpi by using half the fast scan speed (i.e. 0.4375 m/s) and by firing thenozzles in a sequence CBA.

If the example of the above type 360 head is worked outfurther, the following is obtained. If the set of C nozzles is firedfirst, the set of B nozzles is already 23.52 µm ahead in the fastscan direction F. At a speed of 0.875 m/s (at a firing frequency of12.4 kHz), the set of B nozzles would have travelled another 23.52µm in the fast scan direction F before actually firing. When,however, half the fast scan speed is used, the set of B nozzles willonly travel over 11.76 µm before it is fired, so that there is adistance of 35.28 µm in the fast scan direction between the dotsprinted by the set of C nozzles and the dots printed by the set of Bnozzles. This corresponds to the distance between dots in a 720 dpiimage.

With the CBA firing sequence, the dots printed by the sets ofA, B and C nozzles in one cycle are not printed on one straightline, with a pitch of 1/360 inch between lines printed duringdifferent cycles, but instead they are printed on three differentlines with a pitch of 1/720 inch between them.

Also other pitches or modes are possible with the same headtype at different fast scan speeds. The only difference with the"standard pitch" is that the dots printed during one CBA cycle arenot on one straight line, contrary to the dots printed during onenormal ABC cycle. With a "normal ABC cycle" is meant: firing thenozzles 12 in an ABC firing sequence, with a reference firingfrequency and driving thehead 10 with a reference driving speed forwhich thehead 10 is intended.

In general, the following relationship between the speeds isobtained:Vmode =VFFcwith v_mode the speed for the considered mode

v_FF the reference speed for the head type for use with apredetermined firing frequency FF. The speed V_FF is given by (phi) ϕ x nozzle stagger distance (D_I) x the firing frequency where ϕ (phi)is the number of staggered rows of nozzles.mode =c * headtype expressed in dpi,where,in casec = 3 i + 1, with i = integer ≥ 0   the firing sequence is ABCin casec = 3 i - 1, with i = integer > 0   the firing sequence is CBA
This means that, for the present embodiment it is impossible toprint in a mode that has a speed v_mode, which e.g. equals one thirdof the reference speed v_FF for the head type (as c is either 3i +1or 3i -1 and can never be a factor of 3). This also means that, forthis embodiment, it is impossible to print images with a resolutionthat equals a plurality of three times the resolution of the headused.

A more in depth analysis shows that a type 90 head offersfollowing possibilities:

Head type	Nozzle stagger	Firing frequency	Desired image resolution in fast scan direction	Head speed	Cycling direction
90	94.07 µm	12400 Hz	90 dpi	3.50 m/s	ABC
90	94.07 µm	12400 Hz	180 dpi	1.75 m/s	CBA
90	94.07 µm	12400 Hz	360 dpi	0.87 m/s	ABC
90	94.07 µm	12400 Hz	450 dpi	0.70 m/s	CBA
90	94.07 µm	12400 Hz	630 dpi	0.50 m/s	ABC
90	94.07 µm	12400 Hz	720 dpi	0.44 m/s	CBA
90	94.07 µm	12400 Hz	900 dpi	0.35 m/s	ABC
90	94.07 µm	12400 Hz	990 dpi	0.32 m/s	CBA
90	94.07 µm	12400 Hz	1170 dpi	0.27 m/s	ABC
90	94.07 µm	12400 Hz	1260 dpi	0.25 m/s	CBA
90	94.07 µm	12400 Hz	1440 dpi	0.22 m/s	ABC

As mentioned above, the pixels printed during one printingcycle are not printed in one row. The distance between the pixels printed by a B- or C-nozzle and an A-nozzle during the same cycle isgiven by (expressed in 1/mode pitch):pitch =1mode=1c*headtype [inches]

For ABC-cycling:

According to the above, if nozzle A prints dots on an imageline during cycle x, the B nozzles will print during cyclex+int(c/3) and the C nozzles during cycle x+int(2c/3) on the sameimage line.

Thus for a type 90 head printing in 360 mode,c = 4 andΔcycle_A-B = 1 and Δcycle_A-C = 2, so if nozzles A print dots on animage line during cycle x, nozzles B print dots on that image lineduring cycle x+1 and nozzles C print dots on that image line duringcycle x+2.

For CBA-cycling:

According to the above, if nozzle A prints dots on an imageline during cycle x, the B nozzles will print on the same image lineduring cycle x+int(c/3)+1 and the C nozzles will print on the sameimage line during cycle x+int(2c/3)+1.

Thus for a type 360 head printing in 720 mode, c = 2 andΔcycle_B-A = 1 and Δcycle_C-A = 2, so if nozzles A print dots on animage line during cycle x, nozzles B print dots on that image lineduring cycle x+1 and nozzles C print dots on that image line duringcycle x+2.

Fig. 2 shows an ABC firing case atc = 7, e.g. a type 90 headin 630 dpi mode. As shown in table 1, the normal speed or referencespeed for a 90 type head is 3.50 m/s. According to equation (1), thespeed in the 630 dpi mode is 3.50/7 = 0.50 m/s, as also shown inTable 1. Equation (3) shows that forc = 7, the nozzles are to bedriven in an ABC sequence.

During a first cycle, the set of A nozzles is driven first.Where necessary (according to the image) A nozzles eject a drop onlocations 14 on astraight line 16 in the slow scan direction S. Atthe moment of firing the set of A nozzles, the set of B nozzles islocated at a location 18 at a distance of 1/(headtype.3) = 1/90.3= 1/270 inches = 94.07 µm behind the set of A nozzles, and the setof C nozzles is located at alocation 20 at a distance of 188.15 µmbehind the set of A nozzles. Before firing the set of B nozzles, thehead 10 is moved over adistance 1/(c.headtype.3) = 1/1890 inches =13.44 µm in the fast scan direction F. During the first cycle, theset of B nozzles ejects a drop onlocations 22 on astraight line 24in the slow scan direction S, where necessary according to the imageto be printed. At the moment of firing the set of B nozzles, the setof C nozzles is located at alocation 26 at a distance of 94.07 µmbehind the set of B nozzles. Before firing the set of C nozzles, thehead 10 is moved over adistance 1/(c.headtype.3) = 1/1890 inches =13.44 µm in the fast scan direction F. During the first cycle, theset of C nozzles ejects a drop onlocations 28 on astraight line 30in the slow scan direction S, where necessary according to the imageto be printed.

At the moment of firing the set of C nozzles, the set of Anozzles is located at alocation 32 at a distance of 188.15 µm infront of the set of C nozzles, and the set of B nozzles is locatedat alocation 34 at a distance of 94.07 µm behind the set of A (or94.07 µm in front of the set of C nozzles). Before firing the set ofA nozzles during a second cycle, thehead 10 is moved over adistance of 13.44 µm in the fast scan direction F. During the secondcycle, the set of A nozzles eject a drop onlocations 36 on astraight line 38 in the slow scan direction S, where necessaryaccording to the image to be printed. At the moment of firing the set of A nozzles, the set of B nozzles is located at alocation 40at a distance of 94.07 µm behind the set of A nozzles. Before firingthe set of B nozzles, thehead 10 is moved over a distance of 13.44µm in the fast scan direction F. The set of B nozzles eject a droponlocations 42 on astraight line 43 in the slow scan direction S,where necessary according to the image to be printed.

The above printing scheme is continued in the same way. In thenext (third) ABC cycle, the drops of the B nozzles are ejected onlocations onstraight line 16, where necessary according to theimage to be printed, and the drops of the C nozzles are ejected onlocations onstraight line 24, where necessary according to theimage to be printed.

This corresponds to what is given in equations (6): for c=7 andABC cycling,

Thus if the set of A nozzles prints on a straight line during cyclex (e.g.straight line 16 during cycle 1), the set of B nozzles willprint on that same straight line during cycle x+2 (cycle 3 in theexample given), and the set of C nozzles will print on that samestraight line during cycle x+4 (cycle 5 in the example given).

Theprinthead 10 continues to move on in the fast scandirection F up to the end of the printing medium on which an imageis to be printed, according to the content of the image to beprinted. Dots are printed onstraight lines 16, 24, 30, 38, 43 andso on, in the slow scan direction S, each straight line comprisingdots printed by the set of A nozzles, the set of B nozzles and theset of C nozzles, if necessary for the image to be printed. Thedistance between two straight lines in the slow scan direction is1/(c.headtype) = 1/(7.90) inches = 40.32 µm, which shows that animage at 630 dpi is printed.

In Fig. 3, anozzle plate 50 of twonozzle arrays 52, 54 isshown, eachnozzle array 52, 54 having 225 npi (nozzles per inch),and placed so that the combined resolution is 450 dpi (i.e. whereby each nozzle of thesecond nozzle array 54 is always located in themiddle, in the slow scan direction S, between two nozzles of thefirst nozzle array 52). The distance between two adjacent nozzles ofone nozzle array in the slow scan direction S is 112.89 µm. Thenozzle stagger in the fast scan direction F is 94.07 µm (type 90head).

As an example, the type 90 head is used in 450 dpi mode toobtain an image with a resolution of 900 dpi in at least two passes.A type 90 head used in mode 450 follows a CBA printing cycle, asshown in Table 1.

During a first pass, at first during a first cycle, the sets ofC nozzles are fired. Where necessary (according to the image), Cnozzles eject a drop on the printing medium, whereby C nozzles ofthefirst nozzle array 52 eject drops onlocations 62, and C nozzlesof thesecond nozzle array 54 eject drops onlocations 64. At themoment of firing the sets of C nozzles, the set of B nozzles of thefirst array 52 is located atlocation 66 at a distance of1/(headtype.3) = 94.07 µm before the set of C nozzles of thefirstarray 52, and the set of B nozzles of thesecond array 54 is locatedatlocations 68 at a distance of 94.07 µm before the set of Cnozzles of thesecond array 54. Before firing the sets of B nozzles,thehead 50 is moved over adistance 1/(c.headtype.3) = 18.81 µm inthe fast scan direction F. During the first cycle, the set of Bnozzles of thefirst nozzle array 52 ejects a drop onlocations 70,where necessary according to the image to be printed, and the set ofB nozzles in thesecond array 54 ejects a drop onlocations 72,where necessary according to the image to be printed. At the momentof firing the sets of B nozzles, the set of A nozzles of thefirstarray 52 is located at alocation 74 at a distance of 94.07 µmbefore the set of B nozzles of thefirst array 52, and the set of Anozzles of thesecond array 54 is located at alocation 76 at adistance of 94.07 µm before the set of B nozzles of thesecond array54. Before firing the sets of A nozzles, thehead 50 is moved over adistance of 18.81 µm in the fast scan direction F. The set of Anozzles of thefirst array 52 ejects a drop onlocations 78, and the set of A nozzles of thesecond array 54 ejects a drop onlocation80, both where necessary according to the image to be printed.

When the sets of A nozzles are firing, the set of C nozzles ofthefirst array 52 is located atlocations 82, and the set of Cnozzles of thesecond array 54 is located atlocations 84. Beforefiring the sets of C nozzles during the second cycle, thehead 50 ismoved over a distance of 18.81 µm in the fast scan direction F. Theset of C nozzles of thefirst array 52 ejects a drop onlocations86, and the set of C nozzles of thesecond array 54 ejects a drop onlocations 88, both where necessary according to the image to beprinted.

At the moment of firing the sets of C nozzles, the set of Bnozzles of thefirst array 52 is located at location 90 at adistance of 94.07 µm before the set of C nozzles of thefirst array52, and the set of B nozzles of thesecond array 54 is located atlocations 92 at a distance of 94.07 µm before the set of C nozzlesof thesecond array 54. Before firing the sets of B nozzles duringthe second cycle, thehead 50 is moved over a distance of 18.81 µmin the fast scan direction F. The set of B nozzles of thefirstnozzle array 52 ejects a drop onlocations 94, where necessaryaccording to the image to be printed, and the set of B nozzles inthesecond array 54 ejects a drop onlocations 96, where necessaryaccording to the image to be printed. At the moment of firing thesets of B nozzles, the set of A nozzles of thefirst array 52 islocated at alocation 98 at a distance of 94.07 µm before the set ofB nozzles of thefirst array 52, and the set of A nozzles of thesecond array 54 is located at alocation 100 at a distance of 94.07µm before the set of B nozzles of thesecond array 54. Before firingthe sets of A nozzles during the second cycle, thehead 50 is movedover a distance of 18.81 µm in the fast scan direction F. During thesecond printing cycle, the set of A nozzles of thefirst array 52ejects a drop onlocations 102, where necessary according to theimage to be printed, and the set of A nozzles of thesecond array 54ejects a drop onlocation 104, where necessary according to theimage to be printed.

When the sets of A nozzles are firing, the set of C nozzles ofthefirst array 52 is located atlocations 106, and the set of Cnozzles of thesecond array 54 is located atlocations 108. Beforefiring the sets of C nozzles during a third printing cycle, thehead50 is moved over a distance of 18.81 µm in the fast scan directionF. The set of C nozzles of thefirst array 52 ejects a drop onlocations 110, where necessary according to the image to be printed,and the set of C nozzles of thesecond array 54 ejects a drop onlocations 112, where necessary according to the image to be printed.Drops printed by the set of C nozzles of thefirst array 52 onlocations 110 during the third printing cycle are printed on astraight line 111, on whichline 111 previously (during the firstprinting cycle) drops 70 have been printed by the set of B nozzlesof thefirst array 52. In the same manner, drops printed by the setof C nozzles of thesecond array 54 onlocations 112 during thethird printing cycle are printed on astraight line 113, on whichline 113 previously (during the first printing cycle) drops 72 havebeen printed by the set of B nozzles of thesecond array 54.

This printing scheme continues. The continuation of theprinting scheme is shown in Fig. 3 without further numbering of thedots. As can be seen, as fromstraight line 114 in the slow scandirection, drops are printed onlocations 116 by the set of Cnozzles of thefirst array 52, while on that samestraight line 114drops 118, 120, 122, 80, 124 have already been printed previously bythe set of C nozzles of thesecond array 54, the set of B nozzles ofthesecond array 54, the set of B nozzles of thefirst array 52, theset of A nozzles of thesecond array 54, and the set of A nozzles ofthefirst array 52, respectively.

Before starting a second pass, theprinthead 50 is moved in theslow scan direction S so as to make droplets fall in between alreadyprinted droplets in the slow scan direction S. For the example underconsideration, if the resolution is to be obtained in two passes,theprinthead 50 is moved in the slow scan direction S over a paperfeed distance of 28.22 µm or an odd multiple thereof. During thesecond and further printing passes, a CBA cycle is then applied asexplained for the first printing pass.

According to the above it is clear that it is only possible tohave dots from three phases printed during one cycle on one slowscan line using a normal print order for the data if the print headtype and mode are equal. Otherwise the print data must bereorganised or "shuffled" so that the correct data is presented tothe relevant nozzle at the right time.

The most convenient solution consists in shifting the pixellines along the fast scan direction (if different nozzle arrays arecombined resulting in pixel lines belonging to one phase one alsospeaks of image bands) related to the different phases over a numberof cycles as given byformula 6 or 7. In case a 3 phase system withphases ABC, the shift between pixel line A and B and between B and Cis equal to a number equal to the Δcycle as given by formula 6(formula 7 in case a CBA cycle is involved). It is necessary toreorganise the sequence of input data so that the final image iscorrectly printed. When data for pixels on a certain slow scan lineis printed by the A phase, the data for the same slow scan line butfor the B-phase nozzles will be presented to them later. AnotherΔcycle later the C-phase nozzles will receive the data related tothat slow scan line. When one cycle is considered, the B-phaseprints during that cycle a dot that is Δcycle dot positions behindthe A phase, while the C-phase is printing 2 Δcycle dot positionsbehind the A phase. For example, 2 or 4 dot positions as defined inequation 8. The data transformation needs to be done for each newfast scan because it is possible that when using mutuallyinterstitial printing, nozzles belonging to different phases print acertain pixel line in the fast direction.

This printing technique requires more pixel positions than thenumber of pixel positions in a fast scan pixel line to finish a fastscan than would be required if the nozzles were not staggered but ona straight line.

It is now explained in more detail how paper feeds in betweensuccessive printing passes are calculated and how wet-on-wetprinting or bleeding is avoided by enforcing boundary conditions onthe colour sequence.

The following is a general calculation scheme to obtain valuesfor a paper feed L₁ and a paper feed L₂, expressed in pixels (on thefinal image resolution). It will be explained, based on aprinthead130 as shown in Fig. 4, having n=764 nozzles. The printhead itselfconsists of 2nozzle arrays 132, 134, each having 382 nozzles witheach a nozzle pitch of 180 npi. By shifting bothnozzle arrays 132,134 over half a pitch, the complete 764nozzle head 130 has a nozzlepitch of 360 npi. Each of the twonozzle arrays 132, 134 consists of3 phases (A, B and C). The calculation given does not consider thestaggering of the nozzles in the different phases nor the phasesitself.

First an imaginary paper feed L_base is calculated by dividingthe length of the head 130 (expressed in pixels on the finalresolution) by the total number of required passes (equal to thenumber of sub-images to be printed). The length of thehead 130 is

   with nozzle pitch NP=(1/360) inch and pixel pitch DP=(1/720)inch. In fact, when the first pixel corresponding withnozzle 1 isalso labeledpixel number 1, the last pixel corresponding withnozzle 764 is pixel 1527. The image needed is 1527 xw_p x 720 (with720 dpi resolution andw_p the printing width). The number of passesneeded to print all pixels, is given by P(I/hs), where P is thenumber of mutually interstitial printing passes, I is the requirednumber of interlacing steps (normally given by dpi/npi or NP/DP).Interlacing is used to increase the resolution of a printing device.That is, although the spacing between nozzles on the printing headalong the slow scan direction S is a certain distance X, thedistance between printed dots in the slow scan direction S is lessthan this distance. The relative movement between the printingmedium (not shown) and theprinting head 130 is indexed by adistance given by the distance X divided by an integer. If thevalues of the example above are taken, the number of interlacingsteps equals I = dpi/npi = 720/360 = 2 and the number of mutuallyinterstitial printing steps P = 8. The parameter hs, the number of nozzle rows printing the same colour, is used when different nozzlearrays of a same colour are considered: in the current example n=764nozzles is taken at 360 npi and therefore hs = 1. In case the twonozzle arrays of n=382 nozzles (each at 180 npi) would have beentaken separately, hs = 2 must be taken, but also the number ofinterlacing steps I doubles (because 720/180 = 4) and the finalresult for L_base would be the same.

The result for L_base in the given example is the integer value

being 95 pixels. In this example, there is one line of non printedpixels in the fast scan direction F in between two consecutivenozzles in the slow scan direction S (as the number of interlacingsteps equals 2).

A parameter I' is then introduced, defined as:I'=Ihs,I being the number of interlacing steps needed and hs being thenumber of nozzle rows printing the same colour.

A paper feed is derived from L_base that is equal to a multipleof I' by doing L_base - L_basemod I', resulting in 94. Because I' = 2,and 94 is thus a multiple of I', paper feeds based on this valuewould always print in the same 360 dpi image, never addressing thepixels between the nozzles.

To avoid the above, the value of 94 is incremented byl₁ orl₂(respectively for a first paper feed L₁ and a second paper feed L₂).An odd value for one of the paper feeds guarantees that there willalso be printed on pixel lines not addressed before (the other paperfeed can be even).

The above formulae for the first paper feed L₁ and the secondpaper feed L₂ can generate a whole set of values depending on thechosenl₁, l₂ and j and i. By applying a number of boundaryconditions onl₁, l₂ for I'>2, this set can be limited.

if I'> 2thenl1 +l2 ≠kI'  k integer

Further, L₁ and L₂ must meet a set of two equations :

• a linear combination of L₁ and L₂ should equal the totallength of the head expressed in pixels
• the factors a and b, used to combine L₁ and L₂, should equalto the total number of passes P*I' (= 16 in this particularcase).

or written in symbols:

A different way for writing the above more explicitly as afunction ofl₁, l₂, i andj is:

For the above example, possible values for L₁ and L₂ could be: fori = 0,j = 0,l₁ = 1,l₂ = 1:

The above calculation scheme of equation (16) can find all L₁,L₂ and associated a and b based onl₁,l₂, i andj. Although this isthe most general method, it is often advantageous to restrict to asubset of the above. The above method allows any filling order.

When printing different colours, it is desired that thedifferent colours e.g. CMYK are printed in a same order on allpixels. To guarantee this, the image is being filled up in a regularway. This can be guaranteed by shifting nozzle arrays of a differentcolour over a distance of at least 3/P in the slow scan direction, Pbeing the number of mutually interstitial printing passes. The valueof 3 is derived as follows: a sub-image table counts N lines. Whenin a sub-image table three pixel rows are filled row by row, therecan be started with the next colour on the second row (also startingon the first row could result in bleeding towards row N of the subimage table), while the first colour is printed on the fourth row.As said, the distance two consecutive heads need to be shifted is atleast 3/P. The exact amount the printheads need to be shifted iscalculated as follows : if only I₁ and L₂ are used it is tried tomake a sequence as short as possible of formfeeds L₁ and L₂ that isrepeated during the printing process : e.g. if there is aP*I'=4x4=16 and L₁L₁L₁L₂, L₁L₁L₁L₂, L₁L₁L₁L₂, L₁L₁L₁L₂, ... eachperiod in the sequence has a length I'=4 which agrees with a row ofthe sub-image table. After 3 rows it is allowed to start the nextcolour. In this specific case the sum of the 3 periods is exactly3/P of the headlength. To make the distance between the heads asshort as possible a period equal to I' or I' being a multiple ofthis periodlength (ixperiod=I') is required. The minimum headshiftcan be written as follows :Δx = 3(I'-1)L1 + 3L2

When all L_i are different there are still needed 3xI' passesbefore the next colour is allowed to start. Because in this case allL_i are different, the following condition must be fulfilled:

It is of course possible in the above to add more types ofpaper feeds L₃, L₄, etc., in which case the above formulae can beamended correspondingly. It is possible to broaden the above theoryfor L₁ and L₂ towards as much L_i as there are passes P*I'. In thatcase, L_i should meet the following condition:

Now one concept for applying mutually interstitial printingwith the head configurations described above is explained in moredetail: shifting of image bands over Δcycle pixels..

One of the possibilities is to allow for shifting of imagebands over Δcycles using "redundant cycles" (mutually interstitialprinting) to print all pixels on a same line in the slow scandirection without omitting nozzles or reducing the number of activenozzles of the printhead. The print speed will be lower, related tothe amount of mutually interstitial printing but quality is higher.In Fig. 5 for a number of mutually interstitial printing passesP = 8, a type 90 head is used in 360 dpi mode resulting in Δcycle=1.This means that a fire pulse is available at half (360 dpi) of thepixels (720 dpi) in the fast scan direction. Doing this allows theclassical way of calculating L, and e.g. L₁ = 96 and L₂ = 95 isobtained.

When the set of A nozzles receive a fire pulse duringpass 1above a pixel indicated with a "1" in Fig. 5 the B and C nozzles arenot used during the same ABC cycle. At the next fire pulse or cycle,the A nozzles pass above pixels indicated with 5, but are not fired.Instead the B nozzles are fired during thispass 1 above thelocation indicated with 5. So the A and C nozzles are not firedduring this second ABC cycle. Finally, at the third fire pulse orcycle, the A-nozzles and the B-nozzles pass abovepixels 9 withoutbeing fired, while the C-nozzles are fired at pixels indicated witha 9. The next fire pulse is a fully redundant pulse: no nozzles arefired atposition 13.

Beforepass 2 is carried out, a paper feed of L₁=96 pixels iscarried out in the slow scan direction. When the set of A nozzlesreceive a fire pulse duringpass 2 above a pixel indicated with a 2in Fig. 5, the B and C nozzles are not used during the same ABCcycle. At the next fire pulse or cycle, the A nozzles pass abovepixels indicated with 6, but are not fired. Instead the B nozzlesare fired during thispass 2 above the location indicated with 6. Sothe A and C nozzles are not fired during this second ABC cycle.Finally, at the third fire pulse or cycle, the A-nozzles and theB-nozzles pass abovepixels 10 without being fired, while theC-nozzles are fired at pixels indicated with a 10. The next firepulse is a fully redundant pulse: no nozzles are fired atposition14.
In the next pass, a paper feed of L₂ = 95 pixels is used. From thenon, the paper feed is alternated between 96 and 95 pixels. Printinggoes on, and 16 passes are needed to print the complete image.

From the above, the following rule can be derived: during passX, the A-nozzles print at all pixel positions in Fig. 5 labelledwith the pass number X, the B-nozzles print at all pixel positionshaving the number X+4 and the C nozzles print at pixel positionshaving thenumber X+8.

For a number of mutually interstitial printing passes of P = 2,there is no redundancy (fast mutually interstitial printing), but itis possible to fill row-by-row by shifting the image bands under theB and C nozzles over respectively 2 and 4 pixels. This is basicallyalso what has been done for P = 4 and P = 8.

SECOND EMBODIMENT: ϕ MARKING ELEMENTS IN A GROUP

The above formulae can be formulated more generally for a systemusing ϕ phases as shown below:

An example of a printing scheme for a system with four markingelements in a group (number of phases ϕ is four) is given in Fig. 6,and is explained hereinafter. As an example, a type 90 head is usedin mode 450 dpi, i.e. c = 5, or thus, as can be seen from equation(18) the forward scheme or ABCD cycling is to be used.

As shown in Table 1, the normal speed or reference speed for a90 type head is 3.50 m/s. According to equation (1), the speed inthe 450 dpi mode is 3.50/5 = 0.70 m/s.

For ABCD cycling, first the set of A nozzles is driven. Wherenecessary, according to the image, A nozzles eject a drop onlocations 11. At the moment of firing the set of A nozzles, the setof B nozzles is located at alocation 13 at a distance of1/(headtype.4) = 1/90.4 = 1/360 inches = 70.56 µm behind the set ofA nozzles, the set of C nozzles is located atlocation 15 at adistance of 141.11 µm behind the set of A nozzles, and the set of D nozzles is located atlocation 17 at a distance of 211.67 µm behindthe set of A nozzles. Before firing the set of B nozzles, thehead10 is moved over adistance 1/(c.headtype.4) = 1/1800 inches = 14.11µm in the fast scan direction F. The set of B nozzles eject a droponlocations 19, where necessary according to the image to beprinted. At the moment of firing the set of B nozzles, the set of Cnozzles is located at alocation 21 at a distance of 70.56 µm behindthe set of B nozzles, and the set of D nozzles is located at alocation 23 at a distance of 141.11 µm behind the set of B nozzles.Before firing the set of C nozzles, thehead 10 is moved over adistance of 14.11 µm in the fast scan direction F. The set of Cnozzles eject a drop on locations 25 where necessary according tothe image to be printed. At the moment of firing the set of Cnozzles, the set of D nozzles is located at alocation 27 at adistance of 70.56 µm behind the set of C nozzles. Before firing theset of D nozzles, thehead 10 is moved over a distance of 14.11 µmin the fast scan direction F. The set of D nozzles eject a drop onlocation 29, where necessary according to the image to be printed.

At the moment of firing the set of D nozzles, the set of Anozzles is located at alocation 31 at a distance of 211.67 µm infront of the set of D nozzles, the set of B nozzles is located at alocation 33 at a distance of 141.11 µm in front of the set of Dnozzles, and the set of C nozzles is located atlocations 35 at adistance of 70.56 µm in front of the set of D nozzles. Before firingthe set of A nozzles, thehead 10 is moved over a distance of 14.11µm in the fast scan direction F. The set of A nozzles eject a droponlocations 37, where necessary according to the image to beprinted. At the moment of firing the set of A nozzles, the set of Bnozzles is located at alocation 39 at a distance of 70.56 µm behindthe set of A nozzles. Before firing the set of B nozzles, thehead10 is moved over a distance of 14.11 µm in the fast scan directionF. The set of B nozzles eject a drop onlocations 41, wherenecessary according to the image to be printed. At the moment offiring the set of B nozzles, the set of C nozzles is located atlocations 45 at a distance of 70.56 µm behind the set of B nozzles.Before firing the set of C nozzles, thehead 10 is moved over a distance of 14.11 µm in the fast scan direction F. The set of Cnozzles eject a drop onlocations 47 where necessary according tothe image to be printed. At the moment of firing the set of Cnozzles, the set of D nozzles is located atlocations 49 at adistance of 70.56 µm behind the set of C nozzles. Before firing theset of D nozzles, thehead 10 is moved over a distance of 14.11 µmin the fast scan direction F. The set of D nozzles eject a drop onlocations 51, where necessary according to the image to be printed.

The above printing scheme is continued in the same way. In thenext ABCD cycles, the drops are all put on parallel straight linesin the slow scan direction, as can be seen from Fig. 6, eachstraight line comprising dots printed with each of the sets ofnozzles A, B, C, D. The distance in the fast scan direction betweentwo straight lines in the slow scan direction is 1/(c.headtype) =1/(5.90) inches = 56.44 µm, which shows that a 450 dpi image isbeing printed.

Fig. 7 is a highly schematic general perspective view of aninkjet printer 20 which can be used with the present invention. Theprinter 20 includes abase 31, acarriage assembly 32, astep motor33, adrive belt 34 driven by thestep motor 33, and aguide railassembly 36 for thecarriage assembly 32. Mounted on thecarriageassembly 32 is aprint head 10 that has a plurality of nozzles. Theprint head 10 may also include one or more ink cartridges or anysuitable ink supply system. A sheet ofpaper 37 is fed in the slowscan direction over asupport 38 by a feed mechanism (not shown).Thecarriage assembly 32 is moved along theguide rail assembly 36by the action of thedrive belt 34 driven by thestep motor 33 inthe fast scanning direction.

Fig. 8 is a block diagram of the electronic control system of aprinter 20, which is one example of a control system for use with aprint head 10 in accordance with the present invention. Theprinter20 includes abuffer memory 40 for receiving a print file in theform of signals from ahost computer 30, animage buffer 42 forstoring printing data, and aprinter controller 60 that controls theoverall operation of theprinter 10. Connected to theprintercontroller 60 are afast scan driver 62 for a carriageassembly drive motor 66, aslow scan driver 64 for a paperfeed drive motor68, and ahead driver 44 for theprint head 10. Optionally, there isadata store 70 for storing parameters for controlling theinterlaced and mutual interstitial printing operation in accordancewith the present invention.Host computer 30 may be any suitableprogrammable computing device such as personal computer with aPentium III microprocessor supplied by Intel Corp. USA, forinstance, with memory and a graphical interface such asWindows 98as supplied by Microsoft Corp. USA. Theprinter controller 60 mayinclude a computing device, e.g. microprocessor, for instance it maybe a microcontroller. In particular, it may include a programmableprinter controller, for instance a programmable digital logicelement such as a Programmable Array Logic (PAL), a ProgrammableLogic Array, a Programmable Gate Array, especially a FieldProgrammable Gate Array (FPGA). The use of an FPGA allows subsequentprogramming of the printer device, e.g. by downloading the requiredsettings of the FPGA.

The user ofprinter 20 can optionally set values into thedatastore 70 so as to modify the operation of theprinter head 10. Theuser can for instance set values into thedata store 70 by means ofamenu console 46 on theprinter 20. Alternatively, these parametersmay be set into thedata store 70 fromhost computer 30, e.g. bymanual entry via a keyboard. For example, based on data specifiedand entered by the user, a printer driver (not shown) of thehostcomputer 30 determines the various parameters that define theprinting operations and transfers these to theprinter controller 60for writing into thedata store 70, e.g. the resolution. One aspectof the present invention is that theprinter controller 60 controlsthe operation ofprinter head 10 in accordance with settableparameters stored indata store 70. Based on these parameters, theprinter controller reads the required information contained in theprinting data stored in thebuffer memory 40 and sends controlsignals to thedrivers 62, 64 and 44. Inparticular controller 60 isadapted for a dot matrix printer for printing an image on a printingmedium, the control unit comprising, software or hardware means forcontrolling printing of the image as at least one set of monochromatic mutually interstitially printed images, and softwareor hardware means for setting the resolution. The controller may beused for independently setting the resolution. The controller isalso adapted to control the operation of theprinting head 10 sothat each mutually interstitial printing step and/or eachinterlacing step is a pass of theprinting head 10 at theappropriate resolution. As explained above the printing head has anarray of marker elements under the control of the controller. Forinstance the controller may be adapted so that for a specificresolution the speed of the head in the fast scan direction and thesequence of firing of the staggered nozzles is controlled.

For instance, the printing data is broken down into theindividual colour components to obtain image data in the form of abit map for each colour component which is stored in the receivebuffer memory 30. In accordance with control signals from theprinter controller 60, thehead driver 44 reads out the colourcomponent image data from theimage buffer memory 52 in accordancewith a specified resolution to drive the speed and the array(s) ofnozzles on theprint head 10 to achieve the required resolution.

As indicated above thecontroller 60 may be programmable, e.g.it may include a microprocessor or an FPGA. In accordance withembodiments of the present invention a printer in accordance withthe present invention may be programmed to provide differentresolutions. For example, the basic model of the printer may provideselection of one resolution only. An upgrade in the form of aprogram to download into the microprocessor or FPGA of thecontroller 60 may provide additional selection functionality, e.g. aplurality of resolutions. Accordingly, the present inventionincludes a computer program product which provides the functionalityof any of the methods according to the present invention whenexecuted on a computing device. Further, the present inventionincludes a data carrier such as a CD-ROM or a diskette which storesthe computer product in a machine readable form and which executesat least one of the methods of the invention when executed on acomputing device. Nowadays, such software is often offered on theInternet or a company Intranet for download, hence the present invention includes transmitting the printing computer productaccording to the present invention over a local or wide areanetwork. The computing device may include one of a microprocessorand an FPGA.

Thedata store 70 may comprise any suitable device for storingdigital data as known to the skilled person, e.g. a register or setof registers, a memory device such as RAM, EPROM or solid statememory.

While the invention has been shown and described with referenceto a preferred embodiment, it will be understood by those skilled inthe art that various changes or modifications in form and detail maybe made without departing from the scope and spirit of thisinvention. For instance, the preparation for the printing file tocarry out the above mentioned printed embodiments may be prepared bythehost computer 30 and theprinter 20 simply prints in accordancewith this file as a slave device of thehost computer 30. Hence, thepresent invention includes that the printing schemes of the presentinvention are implemented in software on a host computer and printedon a printer which carries out the instructions from the hostcomputer without amendment. Accordingly, the present inventionincludes a computer program product which provides the functionalityof any of the methods according to the present invention whenexecuted on a computing device which is associated with a printinghead, that is the printing head and the programmable computingdevice may be included with the printer or the programmable devicemay be a computer or computer system, e.g. a Local Area Networkconnected to a printer. The printer may be a network printer.Further, the present invention includes a data carrier such as a CD-ROMor a diskette which stores the computer product in a machinereadable form and which can execute at least one of the methods ofthe invention when the program stored on the data carrier isexecuted on a computing device. The computing device may include apersonal computer or a work station. Nowadays, such software isoften offered on the Internet or a company Intranet for download,hence the present invention includes transmitting the printing computer product according to the present invention over a local orwide area network.

Claims (10)

1. A method of driving a print head (10) having a longitudinal axisin a first direction (S) and having an array of marking elements(A, B, C; A, B, C, D) comprising at least one group (G) ofmarking elements (A, B, C; A, B, C, D), marking elements (A, B,C; A, B, C, D) of one group (G) being staggered with respect toeach other over a stagger distance (D1) in a second direction (F)perpendicular to the first direction (S), the print head (10)being intended to be driven with a reference velocity (Vref)equal to the stagger distance (D1) multiplied by a referencefiring frequency (Fref), each marking element of a group beingfirable at each reference firing frequency pulse, the markingelements (A, B, C; A, B, C, D) of the print head (10) beingintended to be fired according to a reference firing order toprint an image at a first resolution, wherein the print head (10)is operated at an operating velocity which is different from thereference velocity to print the same image at a differentresolution.
2. A method according to claim 1, there being n marking elements (A,B, C; A, B, C, D) in one group (G), wherein the operatingvelocity is equal toreference velocity /nX+1, X being an integer largerthan or equal to 0, the firing order of the marking elements (A,B, C; A, B, C, D) to produce the second resolution being the sameas the reference firing order (ABC; ABCD).
3. A method according to claim 1, there being n marking elements (A,B, C; A, B, C, D) in one group (G), wherein the operatingvelocity is equal to, X being an integer larger than 0, thefiring order of the marking elements (A, B, C; A, B, C, D) forprinting with the second resolution being the same as the inverseof the reference firing order (CBA; DCBA).
4. A method according to any previous claim, wherein the markingelements (A, B, C; A, B, C, D) of one group (G) are staggered with respect to each other over a stagger distance (D1) in asecond direction (F) perpendicular to the first direction (S) toform a plurality of rows of marking elements, and the methodincludes delaying printing data representing the image suppliedto the marking elements of one row with respect to the printingdata supplied to another row.
5. A method of any of the previous claims for carrying out fastmutually interstitial printing.
6. A computer program product for executing any of the methods asclaimed in claims 1 to 5 when executed on a computing deviceassociated with a printing head.
7. A machine readable data storage device storing the computerprogram product of claim 6.
8. A method of transmitting the computer product of claim 6 over alocal or wide area telecommunications network.
9. A printing device with a print head (10) having a longitudinalaxis in a first direction (S) and having an array of markingelements (A, B, C; A, B, C, D) comprising at least one group (G)of marking elements (A, B, C; A, B, C, D), marking elements (A,B, C; A, B, C, D) of one group (G) being staggered with respectto each other over a stagger distance (D1) in a second direction(F) perpendicular to the first direction (S), the print head (10)being intended to be driven with a reference velocity (Vref)equal to the stagger distance (D1) multiplied by a referencefiring frequency (Fref), each marking element of a group beingfirable at each reference firing frequency pulse, the markingelements (A, B, C; A, B, C, D) of the print head (10) beingintended to be fired according to a reference firing order toprint an image at a first resolution, further comprising meansfor driving the print head (10) at an operating velocity which isdifferent from the reference velocity to print the same image ata second resolution of printing.
10. A control unit for a printer for printing an image on a printingmedium using a print head (10) having a longitudinal axis in afirst direction (S) and having an array of marking elements (A,B, C; A, B, C, D) comprising at least one group (G) of markingelements (A, B, C; A, B, C, D), marking elements (A, B, C; A, B,C, D) of one group (G) being staggered with respect to each otherover a stagger distance (D1) in a second direction (F)perpendicular to the first direction (S), the control unit beingadapted to control the driving of the print head (10) with areference velocity (Vref) equal to the stagger distance (D1)multiplied by a reference firing frequency (Fref), and forcontrolling the firing of one marking element of a group at eachreference firing frequency pulse, and for controlling the firingof the marking elements (A, B, C; A, B, C, D) of the print head(10) according to a reference firing order to print the image ata first resolution, further comprising means for controlling thedriving of the print head (10) at an operating velocity which isdifferent from the reference velocity to print the image at asecond resolution of printing.

Images