WO2013176661A1

WO2013176661A1 - Printing with multiple printhead dies

Info

Publication number: WO2013176661A1
Application number: PCT/US2012/039055
Authority: WO
Inventors: Lluis ABELLO ROSELLO; Joan VIDAL FORTIA; Ronald Burns
Original assignee: Hewlett Packard Development Co LP
Current assignee: Hewlett Packard Development Co LP
Priority date: 2012-05-23
Filing date: 2012-05-23
Publication date: 2013-11-28
Anticipated expiration: 2014-11-23
Also published as: CN104245327B; CN104245327A; EP2852496B1; EP2852496A1; US9073312B2; EP2852496A4; US20150062218A1

Description

Printing with multiple printhead dies

BACKGROUND jOOOlj Many iakjet printers use multiple printhead dies to print multiple colors each pass. The multiple pf inthead dies may be mounted in a carriage that scans back- and-forth across the media or in a page wide array (PWA).

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] FIG. 1 is a top view of a printer 00 in an example embodiment of the invention.

[0003] FIG. 2 is a block diagram of printer 100 in an example embodiment of the invention.

[0004] FIG, 3 is a timing diagram for printing at 600 dpi, in an example embodiment of the i n ven tion.

[0005] FIG, 4 shows ink drops printed from two printhead dies in an example embodiment of the i n vention.

[0006] FiG. 5 is a flow chart for printing with multiple printhead dies m an example embodimen t of the invent ion.

DETAILED DESCRIPTION

[0007] FIGS. 1 - 5 and the following description depict specific examples to teach those skilled in the art how to make and use the best mode of the invention. For the purpose of teaching in venti ve principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall within the scope of the in vention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents. [0008) Inkjet printers typically have one or more printhead dies where each printhead die has an array of nozzles. The prinihead dies and media are moved relat e to each other. In page wide array printers, the media is moved past the page wide array of print dies. Other Inkjet printers have the print dies -mounted on a carriage that moves back and forth across the media width while printing swaths of ink. The media is then advanced between the different swaths. In both cases the direction of motion between the printhead dies and the media is called the print direction. The spacing or resolution, of the ink drops on the paper in the print direction is determined by the frequency of firing pulses sent to the prinihead die and the speed the media is moving with respect to the prinihead dies. The spacing or resolution of the ink drops on the paper in the axi perpendicular to the print axis is determined by the nozzle spacing on the priiithead die and the number of nozzles used,

[0009] Figure 1 is a top view of a printer 100 in an example embodiment of the invention. Printer 100 is a page wide array printer with a print bar 102 extending across the width of the media 104. Media .104 is moved in. the print direction shown by arrow PD, Print bar has multiple prinihead dies numbered I ~Ή. Each prinihead die may be used to print ink of one color onto media 104, for example cyan, yellow, magenta or black. There may be multiple printhead dies used to print the same color. Each printhead die has a row of nozzles numbered 1 ~ M Each nozzle can dispens ink drops onto media 104. A real printer would have more than one row of nozzles in each printhead die and may have -multiple colors, but for clarity the number of rows of nozzles has been reduced. A sensor 106 is attached to print bar 102 and can be moved in an axis (shown by arrow 108) perpendicular to the print direction. Sensor 10 can be used to measure the position of the drops of ink deposited on media 104. In other examples, an external sensor may be used to measure the position of ink drops on the media. jOOlOf The al ignment of ink drops on the media from different printhead dies is affected by the spacing between the rows of nozzles in the different printhead dies and the speed the media is moving with respect to the printhead dies. The spacing its the print direction between the nozzles in the different printhead dies is XI . Distance XI may vary due to manufacturing tolerance such that the spacing between the nozzles in the different printhead dies i non-uniform. For example, the spacing between the nozzles in prinihead die 2 and printhead die 3 may be Xi+delta, and the spacing between the nozzles in printhead die 3 and prinihead die 4 may he X 1 -delta. The alignment of i nk drops from different printhead dies can also he affected by medi stretch or shrinkage due to wetting by the ink, drying, media tension variations, media speed variations and the like. By measuring the ink drop location on the media from the different priMhead dies, the firing pulses for the nozzles in the different printhead dies can be aligned/calibrated, such that the drops from the different printhead dies align.

[0011 j figure 2 is a block diagram of printer 100 in an example embodi ment of the invention.. Printer 100 comprises a media positioning system 220, ink sensor 106, printhead dies 1 - N, an encoder 226, a controller 228, and communication bus 230. Media positioning system 220 may comprise drums, motors, sensors, teed rollers, take-up rollers and the like. Controller 228 may comprise one or more processors, an application specific integrated circuit (ASIC), memory, input/output circuitry and the like.

Communication bus 230 may be any type of communication bus, for example USB. Controller 228 is coupled to media positioning system 220, ink sensor 106, printhead dies I-N, and encoder 226 throug bus 230. Memory in controller 228 may comprise both volatile and non-volatile memory. Code, stored in the memory, when executed b a processor on controller 228, causes printer 100 to take actions, for example printing ink on media 104.

(0012] Encoder 226 ma be a .150 dpi quadrature encoder and output a 50 dpi encode signal. When using all 4 edges of the 150 dpi encoder signal, a 600 dpi encode signal is generated. The output from encode 226 is used to derive the firing pulses for the different printhead dies. Printers typically print at multiple resolutions. For high quality- jobs a printer may print at its native resolution, for example i 200 dots per inch (DPI). For high, speed or lower quality jobs, the printing resolution may be 600 DPI. For draft modes the printin resolution may only be 00 to Ϊ 50 DPI. The resolution for each print job is selected before t he start of the pr int job. Once the pr int job resolution has been selected, the encoder signal will be up-sampled to a h igher than, printing resolution signal . For example, when printing at 600 dpi the encode signal will be up-sampled by 4X t 2400 dpi. The up-sampled 2400 dpi signal will be used to align the firing betwee the different printhead dies to sub-pixel accuracy at the printing resolution. [0013) Figure 3 is a timing diagram for printing at 600 dpi, in an example embodiment of the invention. In figure 3, line 330 is the base encoder signal running a 600 dpt. Line 332 is an up-sampled encoder signal. In this example the base encoder signal has been up-sampled by 4X, so the up-sampled encoder signal 332 is at 2400 dpi. Lines 334, 336, 338 and 340 shows the firing pulses for printhead dies I, 2, 3 and 4 respectively. The firing pulses in lines 334, 336, 338 and 340 are the colum sync signal for printhead dies 1, 2, 3 and 4 respectively. The column syne for die i is aligned to phase 0 of the up-sampled encoder signal in line 332. The column sync for die 2 is aligned to phase 1 of the up-sampled encoder signal in line 332. This means die 2 will print dots of ink offset by 1 /2400^m of an inch rel tive to dots of ink pri ted by die 1. .1/2400* of an inch is ¼ of a pixel at the 600 dpi printing resolution, 00141 The column sync for die 3 is aligned to phase 3 of the up-sampled, encoder signal in line 332. This means die 3 will print dots of ink offset by 3/2400'¹' of an inc relative to dots of ink printed by die 1. The column syne for die 4 is aligned to phase 2 of the up-sampled encoder signal in line 332. This means die 4 will print dots of ink offset by 2/2400^,h of an inch relative to dots of ink printed by die 1. Using this method, the ink drops from each printhead die can be aligned to sub-pixel accuracy at the print resolution. In one example embod iment of the in vention, the up-samp le rate is fixed and is independent of the print resolution. For example the encoder signal is always up-sampled by a factor of 4 so that: the ink dots axe aligned to within ½ of the print: resolution.

[0015] In another example embodiment of the invention, the up-sample rate is variable and is dependent on the print resolution. In this example, the up-sample rate would increase with decreasing print resolution. This could maintain the ink drop alignment between printhead dies at a constant physical distance. For example, when printing at 600 dpi, the up-sample rate may be 4X and when printing at 300 dpi the up- sample rate would be 8X. In each case the alignment between drops of ink printed by two different printhead dies would be 1/2400* of an inch. This would be ¼ of a pixel at 600 dpi and 1/8 of a pixel at 300 dpi.

[00161 The sel ected phase of the up-sampled encoder signal for two printhead dies corresponds to a print offset between ink drops printed from the two printhead dies. The print offset between two printhead dies can be determined i the followin way. One or more ink drops are printed by each of ihe two printhead dies using the encoder signals for each printhead die that should align the ink drops deposited on the media. The distance between the nozzles in the two printhead dies and the media speed past the printhead dies affec t the alignment of the ink on the media. In some i nstances, t he encode r signal for each printhead die that should align ink drops from the two printhead dies may not be in the same phase. The ink drops that should align are printed and then the location or position of the ink drops on the media are measured. During a .long print job, conditions in the printer and/or the media may change such that the encoder signals that should a!ign the ink drops from the two printhead dies no longer align the ink drops from the two printhead dies. jOOl 7| The position of the ink drops are measured using an ink sensor. The print offset corresponds to the miss-alignment between the ink drops printed by the two printhead dies, .Figure 4 shows ink drops printed from two printhead dies in an example embodiment of the invention. Ink. drops 450 ha ve been printed from printhead die 1. Ink drops 452 have been printed from printhead die 2. Both printhead dies are printing at the same resolution which corresponds to a spacing between ink drops of distance . A time axis/print direction is running along the bottom of figure 4 with increments of ¼ R. The ink drops or dots from the two printhead dies should be aligned vertically. The ink drops from printhead die I are offset from printhead die 2 by distance PC). Distance PO is the print offset. In this example the prin offset (distance PC)) corresponds to approximately 3/8 R,

(0918) When the encoder signal is up-sampled by a factor of 4 from the print resolution, the miss-alignment between print dies can be corrected within ¼ of the print resolution. The print resolution in figure 4 is R, To align the ink drops in figure 4 the nozzles from die 1 (in figur 4) will be fired at phas 1 and the nozzles in die 2 will be fired at phase 0. T his will shift the positions of the drops from die 1 by ½ R to the right with respect to the ink drops from die 2. Once the ink drops have been shifted, the ink drops from die 1 will be aligned to within ¼ R to the ink drops from die 2. If the encoder signal in figure 4 was up-sampled by a factor of 8, the miss-alignment between print dies could be corrected to within 1/8 of the print resolution or 1/8 of R. In this case the nozzles from die 1 (in figure 4) will be fired at phase 3 and the nozzles in die 2 will be fired at phase 0. This will shift the positions of the drops from die i by 3/8 R to the right with respect to the ink drops from die 2. Once the ink drops have been shifted, the ink drops from die 1 will be aligned to within 1/8 of R to the ink drops front die 2

[0019] The print offset between two printhead dies can be measured by printing drops in a number of different locations. In some examples the ink drops are measured by looking at ink deposited in a page or image being printed, in other examples, the ink drops to be measured may be deposited between pages or in the margin alongside pages being printed. Because the ink drops can be measured in these different locations, the print offset between printhead dies can be updated dynamically during a print job. This allows the alignment between printhead dies to be adjusted on a per page bases, if needed, in some examples, the alignment between printhead dies ma be updated on a periodic time period or at the start of each print job. In other examples, the alignment between printhead dies may be updated whenever the print offset exceeds a threshold value.

(0020) Figure 5 is a flo chart for printing with multiple printhead dies in an example embodiment of the in vention. At step 570 a print resolution in a printing axis is determined. At ste 572 an encoder signal is up-sampled to a higher tha print resolution. At step 574 the firing phase in the up-sampled encode signal is selected for a first one of the two printhead dies t be aligned. And the firing phase in the up-sampled encode signal is selected for the second of the two printhead dies to be aligned. At step 576 the nozzles in the first printhead die are fired at the printing resolution, starting at the firing phase for the first die. The nozzles in the second printhead die are fired at the printing resolution, starting at the firing phase for the second die,

(0021 J The examples above describe adjusting the al ignment of printhead dies usnig a page wide array printer. Adjusting the alignment of printhead dies using this method may also be done for Inkjet printers that have printhead dies moving across the media in a carriage.

Claims

j0022J CLAIMS What is claimed is:

1. A printer, comprising:

at least two printhead dies in spaced apart relationship, where each printhead die compr ises a plurality of nozzles;

an encoder that provides an encoder signal;

a controlier coupled to the two printhead dies and the encoder, the controller to control the printer;

the controlier to up-sample the encoder signal to higher than a prim resolution in a print direction;

the controlier to select a first one of the up-sampled encoder signal phases for a first one of the at leas two printhead dies;

the controller io select a second one of the up-sampled encoder si gnal phases tor a second one of the at least two printhead dies, wherein the difference between the first one and the second one of the up-sampled encoder signal phases corresponds to a print offset between the first printhead die and the second printhead die;

the controller to fire nozzles in the first printhead die at the print resolution beginning at the first one of the up-sampled encoder signal phases;

the controller to fire nozzles in the second printhead die at the print resolution beginning at the second one of the up-sampled encoder signal phases.

2. The printer of claim I , further comprising:

an ink sensor, the ink sensor to sense the position of ink, deposited on media loaded in the printer, by the at least two printhead dies;

the controller coupled to the ink sensor the controller to determine the print offset from the position of the ink on the media,

3. The printer of claim 2, wherein the controller determines the print offset periodically.

4. The printer of claim 3, wherein the controller re-selects the first one and die second one of the αρ-sampled encoder signal, phases when the print offset exceeds a threshold value.

5. The printer of claim 2, wherein the controller uses ink drops printed in the margins of the page to determi e the print offset.

6. The printer of claim. 1„ wherein the controller uses an up-sample rate when the controller up-sampl.es the encoder signal to higher than the print resolution, and the up- sample rate is selected from the following group of up-sample rates: 4X, 6X, 8X, 10X, J 2X, 16X, 32X, 64X and 128X.

7. The printer of claim 1, wherein the controller uses an up-sample rate when the controller up-samples the encoder signal to higher than the print resolution, and the up- sample rate is dependent on the print resolution.

8. A method for printing, comprising

determining a print resolution in a print axis;

up-sampling an encoder signal to higher than the print resolution;

determining a print offset between a first prmthead die and a second prinihead die;

selecting a first one of the up-sampled encoder signal phases for the first prmthead die;

selecting a second one of the up-sampled encoder signal phases for the second prinihead die, wherein the difference between the first one and the second one of the up- sampled encoder signal phases corresponds to the print offset;

firing nozzles in the first prmthead die at the print resolution starting at the first one of die up-sampled encoder signal phases;

firing nozzles in the second prmthead die at the print resolution starting at the second one of the up-sampled encoder signal phases.

9. The method of claim 7, where the print resolution is less than a native resolution in the print axis.

10. The method of claim ?, wherein determining the print offset between the first priiithead die and the second priiithead die is done during a print job.

. 1. The method of claim 7, wherein determining the print offset between the first printhead die ami the second printhead die is done using ink printed between pages in a print job.

.12. The method of claim 7, further comprising:

determining a print offset between the second printhead die and a third printhead die;

selecting a third one of the up-sampled encoder signal phases for the third priiithead die, wherein the difference between the second one and the third one of the up- sampled encoder signal phases corresponds to the print offset between the second priiithead die and a third printhead die;

firing nozzles in the third printhead die at the print resolution starting at the third one of the up-sampled encoder signal phases.