GB2389080A - High accuracy swath advance paper positioning for printers - Google Patents

Abstract

Techniques for high accuracy media positioning in a swath printer. A high accuracy media positioning method (100) includes printing a first swath (102) and advancing the media for the second swath using the media advance system (104). The next step (106) includes determining zones of the swath that need high accuracy swath alignment based on the type of image and the print quality requested. Following this and during the printing of the swath(108), for zones which need high accuracy swath alignment (110), the alignment errors are determined and applied to effect compensation (112), and the appropriate error compensation values are stored in a memory (114). The process continues until the swath printing is completed (116).

Description

( HIGH ACCURACY SWATH ADVANCE PAPER

POSITIC)NINC, FOR PRINTERS

TECHNICAL_ElE!..D OF THE INVP.N'I'}ON This invention relates to swath printing systems, and more particularly to techniques for high accuracy swath advance media positioning.

s BACKGIkOUNn OF TIlis lNV_NTION Accurately advancing paper between print swaths is Recoining a greater awl greater challenge. In early inl;jet printers, the swath advances were short and 10 the allowable error large. With the push to improve print quality and speed, the swath advances are getting larger and at the same time the accuracy needs to be greater. This invention provides accurate pen/paper positioning regardless of the length of swath advance.

Early inkjet printers relied on stepper motor position through a gear train 15 to a drive shaft with rubber wheels to position the paper. This was adequate for the small advances and the coarse large dots. Subsequent inprovemenls in swath advances have been accomplished using higher precision gears, micro-stel)ping, and drive rollers with lower run-out.

( hive rccentl:' an encoder has been adUcd to the drive roller shaft to Act direct feedback of drive Aloft and reduce the requirement for precision gears.

A second encoder is typically needed to compensate for eccentricity of the encoder disk. In addition, the manufacturing variation in the drive tire diameter may require a calibration routine to measure the drive tire circurnDcrence. I his information is stored in nit e-volatile RAM and used to further improve the swath advance accuracy.

All these improvements have helled to meet the requirements for each new generation of printer With the precision required for the next gcneTution I O products, the existing technologies are again cxcecded.

Isle swath advance distances can be expected to increase substantial!,'.

At the same time the number of dots per inch is increasing, e.. from 600 dpi (15240 dots per mm) to 190() Hopi (.30480 Lots per rem). In the past, system paper swath a3vancc accuracies on the order of 1/2 to 1/4 Dot row have been 1 required. TO position paper to /- ().00()2 inches (0.(;)5 mm) for paper advances greater than one inch (95 mm) woLId be difOcu]t to achieve using conventional teclmiques.

SI]MIk ARY()I. FJIl,lNVENTION 9(1 Tecllniqucs are described for high accuracy media positioning in a swath printer.

According to one aspect of the invention there is provided a method for swath printing; as clcfincd in claim 1.

( The fine compensation needed to compensate positioning errors can be performed prior to printing a swath, or even Ion the fly '' curing the printing of a swath. Coarse positioning errors can be measured by the sensor and compensate by use of the printer media advance system, by increasing or decreasing as 5 appropriate the nominal commanded swath-toswath advance distance BRIEF DESCRIPTION OF THIS DRAWING

These and other features and advantages of the present invention will 1:] become more apparent from die following detailed description of an exemplary

embodimcut thereof, as illustrated in the accompanying drawings, in which: FIG. 1 is a diagrammatic view showing a printer carriage with sensors for detecting the edge of the prior swath.

FIGS. 2A-2C illustrate respective image examlls with low to high swath i-, alignment accuracy requirements.

FICI. 3 is a diagrammatic view illustrating how the carriage sensor detects the swath edge.

FIGS. 4A4C illustrate different types of swath errors.

FIGS. 5A-5C illustrate types of swath printing compensation techniques for o0 addressing swath errors.

FIG. 6 illustrates the partial image fill areas in which high swath accuracy is necessary.

FIG. 7 is a simplified diagrammatic side view of the media path and media advance elements of a printer embodying this invention.

25 FIG. 8 is a schematic block diagram of the printer of FIG. 7.

FIGS. DA-SIB and 10 illustrate an exemplary process flow diagram of an exemplary swath position correction technique in accordance with this invention.

FIG. 11 illustrates an exemplary sensor calibration mode for the printer.

FIG. 12 is a diagrammatic side view of an apparatus for effecting position 30 correction by moving the printer pens in relation to the printer carriage.

I7IG. 13 is a diagrammatic side view of an apparatus for collecting position correction by moving the carriage in relation to the carriage rod l lG. 14 is a diagrarTunatic side isometric view of an apparatus for effecting position correction by moving the carriage rod in relation to the printer frame.

FIG. 15 is a diagrammatic side view of an apparatus for efEccting position correction by moving the printer platen in relation to the printer frame.

Fly. 16 is a diagrammatic side view of an apparatus for effecting position correction by moving the print tneciium in relation to the printer platen.

FIG. 17 is a diagrammatic side view of act apparatus as in FIG. IN, 10 but allowing novemc',t of the platen during position correction.

DerAIl LD nips_ RIPTION OF THE PRE.PERREn EM]30DlhtENTS I his invention involves a major paradigm shift in the way a print medium I 5 is positioned for each swath. 1 his invention recog,niz.cs that a critical task in high accuracy alignment is not in moving the paper accurately, but rather in linin' Up the bottom oi the last swath with the top of the next swath. l Listing media advance technclo=,ies can readily position the print medium to within a/- 0.00l inch (0.05 mm). llic,her positioning accuracies would be desirable, e.g. to align -0 the bottom of the last swath to the top of tlc curTcut swath to within +/-

0.00()1 inch (0.0()25 mm).

High positioning accuracy can be achieved by measuring a the bottom of the last swath with a sensor located on to carriage. In carder to have bidirectional printing, a sensor is placed on h,th sides of the carriage. this arrangement is A:> illustrated in Ivies. l, which illustrates a carria,c 20 mounted for sliding movement along a carTiagc rod 22. The carriage supports a plurality of ink jet pens 24A-24D having no:.les arrays for e3ectirg droplets ot ink as the carriage is moved along the swath axis 30. Mounted at each side ol the carriage are respective sensors 26, 28. As the carriage is traveling across the page, in., along the X axis, the carriage 30 location along the Y axis can be adjusted on the fly to compensate for position errors of the media advance system, e. g. i/().001 inch (0.025 mm) positioning errors, to a much smaller range, e.g. to within +/- 0.0001 inches (0.0()25 mm). Of

( course, it is to be understood that the magnitudes of the particular positioning errors u ill be dependent on the particular system design.

Since the correction required in 'any applications is less than a few thousandths of an inch (0.001 inch - 0.02S mm), it can be accomplished, e. g. with a servo controlled piezoelcctnc apparatus, pneumatic cylinder, motor with cani actuator, or a solenoid weds actuator. l his final correction move can be clone by moving the carriage, the individual pens, the carriage rod, the carriage plate, the drive roller shaft, the paper path mo3ulc, or at other locations that affect pen to paper rclati e positions.

I O I he advantages of malting a final adjustment of pen to paper alignment on the By are several fold. I he error for "final positioning on the fly" is independent of the length of swath advance, llercas for all previous techniques; for swath advance, the error is directly proportional to the Jen{gah of swath advance.

(:onsidcr the example of a printer with a ().5 inch (12.7 mm) swath acivanee7 sued a 15 typical tolerance of -1- 0.001 incl1 (0.025 mm) for a 0.5 inch (10.7 Ann) move.

The maximum error is 0.2 % of a 0.5 inch (12.7 mm) move. Now consider a printer having a 2 inch (51 mm) swath advance and a positioning requirement of A/- ().0001 inch (0.0025 mill). The required maximum error is only 0.005% of a full swath move. For a 2 inch (51 mm) move, a 0.2% error would position the 20 paper within +/- 0.004 inch (0.1() mm), anal this could be achieved by knows merli:1 advance systems. The final 0.00 inch (0.10 mm) error can he compensated by the "final positioning on the By" techniuc. Ihis requires a foal positioning accuracy of only t /- 2.5%. For longer swath advances, there are not only error in Y position but also in l heta-.. I he "final positioning' on the fly" tcchnigue can 95 also compensate for this paper skew by adjusting liar the swaths not being parallel.

In zones where there is white space between swaths i.e. in which there are blank, unprinted spaces between swaths, the positioning accuracy requirements arc substantially reduced. Since the image to be printed is known, it is also known where it is critical to snatch top and bottom edge swaths. It is only critical to

( align where there is a match and thus a signal is available to do the match.

Ihis is illustrated in FIGS. 2A-2(: FIG 2A illustrated diagrammatically the case in which the swath boundary 40 falls between two blocks or lines of text, indicated as text 42 and 44, with space hetwcen the hountlary and ad Scent portions of tle text. or this case, the alip,runent of one swath (o tle next swath is not critical Fly. 2B illustrates the case ill which the swath boundary 40 passes through a block fir line of text 46. Ilere, the alignment between successive swaths is somcwlat critical. FIG 2C illustrates the case in which the swath boundary 40 passes through a graphical or solid image 48. For this case, the alignment 10 hetwe'n the adjacent svatis is very critical for high image quality.

In accordance with an asccl of the invcution, the edge of the last swath is sensed. and compensation is achieved by moving oiler the paper or the pcNs, using the position information regarding the edge of the last swath The preferred embodiment is lo move the peas by either moving the carriapc lS with rc:;pect to the carriage rod or the carriage raid with respect to the printing pla(en. Gross or accumulated errors can be compensated during leaper advances' i e by use of the media advance system, by commanding larger or smaller advanecs in comparison lo the nomiTlal advance distance. Minor errors can be 2') comlcnsatc<l via carriatc/pen.scrvoing The range ol 'on the fly" compen.sation is limited to some relatively small range, city for talc sake of cxanplc /-.11 incl, (HAS mix). If there is an error <if say 2 mils (().OS mm) in each swath aclvancc, it would only tal;e 5 advances to take up all of the "on (he fly" range of CornpcnsatiOn. I hercf<>rc' by knowin, an average error lor each advance, which 25 can be measured "on the fly" by the sensor, the next media advance could be commanded to be larger/smaller than the nominal advance distance to compensate.

FIG 3 illustrates the location on the image at which the sensor 28 carried by the carriage 20 will be activated to sense the edge, as the carriage transports the sensor in the direction inclicaled by arrow 40A. 'like sensor 28 will be 30 deactivated after the sensor- reaches location 4013, wlcre (he previously printed

( image ends. Since the printer controller knows the location of the edges (along the Y axis) of the just printed eclges, the locations at which the sensor needs to be activated and deactivated are known. Of course, the sensor could alternatively he activated continuously during a swath.

FIGS. 44-4C illustrate three Types of swath errors. FIG. 4A illustrates a linear swath error, wherein the second swath is offset from its nominal position relative to the first swath by an error AYI = AY2 across the width of the swath.

Linear swath errors can be compensated down tile page with a combination of pen servo and subsequent compensation during media advances.

10 Sltew or rotational error, illustrated in FIG. 4B, wherein AYI does not equal AY2, can accumulate down the page and compensation would be limiter to the range of the pen/carT.age servo. This type of error has been corrunon with previous irlcJet printers using a drive tire arrangement. Use of a belt drive would reduce this type of error.

15 Any remaining n,nlineariti across the page, such as those illustrated in FIG. 4C, c an be "straightened out" over several swaths. Since the swath should be straight, the tracking algorithm can aim to ninirnize deviations gradually enough to handle or minimize print defects.

One pass straightening, depicted in FIG. SA, would produce print defects.

20 tracking front one swath to the next, as shown in FIG. SB, could enhasze defects further down the page.}hybrid compensation, melding the techniques of FIG. 5A and SB, minimizes print defects and will tend to straighten swaths after several passes.

Swath tracking works well where there is continuous fill on:he previous 25 swath. Swath tracking works also on non-continuous previous swaths. Since it is known where the filled areas of the previous swath are, the tracking is turned on in those areas only. FIG. illustrates the case in which the image includes non continuous areas 1 and 2 of solid fill. Since the critical alignment areas are those of the solid fill areas, the tracking to detect the edge of the previous swath can 30 be turned on or activated only for these areas.

lucre arc several possible techniques for tracking. The preferrcti embodiment involves a pair of CCI) arrays, one on each side of the carriage for bi-directional printing as generally illustrated in}IT. 1. Consider the example in which the media positioning sy.stcm without tracking can position the media within a,proximatcly 5 ().001 inch (0.095 mm) for a one half inch (13 mm) swath, and can position the media uitllin approximately ().004 inch (0.10 mm) on a 2 inch (5I mm) swath. For this cxamplc, the C('l> array need only be about O.OIOinch (O.Q5 mm) tall and at a minimum one pixel wide An array as small as one by one hundred pixels would provitie adequate resolution lor tracking. Arrays wirier than one pixel could provided 10 better resolution and accuracy. Ale size of the array is therefore detenlined by, tile rccuired resolution and accuracy of a particular application.

Since the cnpensation for position is small, on the order of ().004 inch (0.10 mm) for this example, the "servo'' or actuating elcnent could be as simple and lig,htweiolt as a piczoclectric driver on tile carriage, or as sinplc as a no rector 15 driving a cam mounted to a carriage rod. Individual pen datums could also incorporate a piez.nelectric element. In general, the actuating clement could be a piezoelcctric element a pneumatic or hydraulic cylinder, a motor with a linear actuator or a cam actuator, a solenoid, a wedge actuated by any of these actic tiCViCCS, or other actuation structure.

() FIG. 7 is a simplified diagrammatic sicie view calf an exemplary printer 0 with one possible form of media advance apparatus. Ihe printer inclutlcs a frame 66 which supports the carriage tIrive and the carriage 2(). motor tirivcn pick roller 52 is activated lo pick a sheet of the print mcdi from an input source 54, and pass it into the nip between drive roller set 56. Ihc print media nay be any type of suitable 25 material, such a paper, cardstock, transparcncics, photogr,raphic patter, fabric, mvlari metalized media, and the like, but for convcnicnce, the illustrated embodiment is described using paper as the print medium. l he invention is also applicable to roll-

ted media as well. Lyle shcot is advanced onto an endless perforated belt 58, mounted for rotation on belt pulleys 60, 62. llc pulleys are driven to advance the sheet to the 30 print zone 25 under the

9 - pens 24A-241). A Vacuum plenum 62 holds the sheet tightly against the belt surface at the print zone. The exiting sheet is passed through the nip fonned by output roller set 64 to an output tray (not shown in I;IC. 7). Of course, the invention is not limited to the specific form of media advance apparatus.

5 Other media advance systems could be employed, e g. friction roller drives.

IG. 8 is a schematic block diagram of the control system for tle printer of Fly. 7. A controller 70 such as a microcomputer or ASIC receives print job commands and data from a print job source 72, wlich can lye a personal computer, digital camera or other known source of print jobs. The controller acts 0 on the received commands to activate the pick roller motor 74 to pick a sheet from the input tray 54, advance the sheet to the nip between the drive roller and pinch roller set 56, and activate the drive motor system 76 to advance the sheet onto the belt, and move tile belt to advance the sheer to the print zone.

11e carriage drive 78 is driven by the controller to position fete carriage 2() 1'> for coinmenceinent of a print job, ace to scan the carriage along the slider rod 28. As this is done firing pulses are sent to the printleads comprising the pens 24-24L?. The controller receives encoder signals from tle carriage encoder 80 lo provide position data for the carriage. The controller is programmed to advance incrementally the sheet to p<'siticn the sheet for successive swaths using 2() the media advance {'elf drive, and to finely position the print media anal perk in relation to one another using an error compensation positioning system 90.

The controller ejects the completed sheet into the output tray upon completion of printing.

Exemplary techniques for effecting the Fizz position compensation will be 25 discussed further below.

FIGS. 9A-9B illustrate steps of a flow diagram of an exemplary process 100 for high accuracy swath advances in a swath printer. The first swath is printed (102), and the media is advanced for the second swath using the media advance system (104). At 1()6, the zones that need high accuracy swath 30 alignment are detennned, based on the type of iznagc and the print quality

lo requested (e.g.,draft mode, high resolution, etc.). At 108, printing of the next swath is commenced. During the printing of the swath, if in a zone needing high accuracy swath alignment (l to), the error compensation needed is de(cmined arid applied to effect the compensation (112), and the compensation values are 5 stored irk memory (114). The process continues until Else swath printing is completed (116). Referring now to FIG. 9S, If the just completed swath is the last swath for the page (118), operation proceeds to print the next page (if any), whirls involves ejecting the sheet just printed to an output location, loading a fresh sheet, and positioning the new sheet to comnence printing the first swath, 10 at which tiruc talc process lOO is repeated.

Aim. 10 illustrates in further detail the process step 119 of FIG. 9.

AL 112A, the sensor is read to determine the position of the edge of the last swath. The error is determined at 11213, and at 112C, the appropriate compensation drive signal is generated and applied to the compcusation 1 5 apparatus.

Preferably, the printer will include a calibration mode for calibrating the swath edge sensors. An exemplary calibration process 150 is shown in PIG 11.

A blank sheet is fed to the print zone for use in the calibration process at 152.

A Blackout swath is printed across the sheet, from left to right, at 154; 20 the blackout swath has only a dark strip along, the top of the swath, say (.01 inch (0.25 rmn) thick. At step 156, the position of the trailing (left) sensor is recorded to cali hrate the top of the swath with the left sensor. Me sheet is advanced at 158, and second blackout swath is then printed, from right to left, at 160. 'lithe position of the trailing (right) sensor is then recorded at 162, calibrating the top of the swath 25 with the right sensor. Thus, the calibration process employs the trailing sensor.

During printing the leading sensor is typically used to align the bottom of the last swath printed with the top of the current swath For a multiple-pen printer, each pen could be calibrated relative to the sensor, thus repeating tile calibration steps (154-162) for each pen.

Several alternate means for effecting relative movement between the pens and the print media to provide fine position compensation are illustrated in I:;IGS. 12-17. FIG. 12 illustrates a technique for providing pen-tocaiage position compensation. Shown in cross-section is a carriage structure 102 holding 5 one or more ink jet pens 104, and mounted for sliding movement along slider rod 106. The pen position in the carriage is registered by pen datum surfaces 104A and 104B, and by piezoelectric device 104C which also acts as a datum. Spring contacts 108 bias the position of the pen away from the rod, bringing the device 104C against the carriage shoulder surface 102A. The device 104C is driven by IO the printer controller to modify the pen position along the Y axis. Typically, for a color printer there will be a plurality of pens held in the carriage, and each will have a piezoelectric element to modify its position within the carriage.

Alternatively, the element lWC could include another type of positioning element or apparatus, such as a solenoid, a pucumatic or hydraulic actuator, a cam, or 15 other commonly used positioning apparatus. Piezoelectric actuators suitable for flee purpose are l;nown in the art; by way of example only, piezoelectric actuators and translators are mariceted by Micro Pulse Systems, luc., Santa Barbara, California, and by PiezoMech Incorporated.

FlG. 13 illustrates a technique for providing carriage-to-carriage-rod fine 20 position compensation. This will effect movement for all pens mounted Lathe carriage Leo, shown in cross-section, with exemplary pen 112 visible in FIG. 13.

The carriage is mounted on rod 116 for sliding movement. The carriage includes a carriage stall portion llOA which is cantilevered from carriage rod portion I JOB; a gap I IOC is formed tetwecn the two portions. The pens include datums 25 112A, 112B and 112C. Spring contacts 118 urge the pen in registered position within the carriage as determined by the dawns against corresponding carriage surfaces. To achieve fine position compensation between the rod 116 arid flee carriage portion 1104, a position control device 114 such as a piezoelectric device is placed in the gap 110C. Driving the device will cause movement of the 30 carriage portion IlOA relative to the rod 116. FIG. 14 is a diagrammatic

illustration of a fine position compensation technique which achieves pen to media position control by providing relative movement of the carriage rod in relation to the printer frame 66. '1'he slider rod 124 is mounted at each rod end on a rod snort, one of which is shown in FIG. 14 as rod mount 122. Tile rod 5 mount is secured to frame portion MA, and includes thin flexible beam members 122A, 1223. spring struehire 126 exerts a bias force pushing the rod mount against an actuator element 128.

l'he rod 124 can be moved in the Y axis by actuating clement 128, to cause the beams to flex, moving the mount against the bias force. 'lie actuating element 10 could be a piezoelectrie element, a pneumatic or hydraulic cylinder, a motor with a linear actuator or a cam actuator, a solenoid, a wedge actuated by any of these active devices, or other actuation structure.

Another technique for providing fine position compensation in accordance with the invention is to position the printer platen relative to the printer frame.

1 ' This technique is illustrated ifs I<IG. 15, a simplified diagrammatic side view showing tle media advance system 130 including a drive belt 58 as in the system of FIG. 7, mounted on a slidable support table 132 which slides on bearings 136 relative to frame 134 along the Y axis. The position of the table is controlled by actuator 140, which can be a piezoeleetrie actuator, or another actuator type as 20 described above with respect to the embodiment of IG. 14. The print medians is located on the media advance system at the print zone 142 under the printer pens. In this embodiment, the printer platen 144, and its position and that of the print medium 146 held thereon, is movable in response to actuation of the element 1 40.

25 RIG. 16 shows an exemplary technique for providing relative movement between the print medium and the printer platen by moving the print medium relative 1O the platen. The media advance system includes a belt 58 and belt drive as described with respect to FiG. 7. With the print media held against the platen 154 at the print zone 152 by a vacuum hold- down, the media drive is 30 actuated to provide incremental rotation of the drive belt, thus moving the print

( L medium relative to the platen. For this embodiment, the fine compensation movement can be accomplished via a second drive motor system tlal has a very high, but precise gear reduction. Another technique is lo mount the main drive motor to a plate that rotates coarally relative the motor shaft. 'lathe main motor 5 moves a commanded position (say +/^ 5 mils (0.13 mm)) anti then its position is locked relative to the plate using a brake. The second motor then rotates the plate to achiev<: fme compensation.

In tile embodiment of FIG. 16, the platen is stationary. Alternatively, the platen can be mounted on a slide arrangement. This is illustrated in 1<1(. 17, 10 with the platen 162 moving with the belt 58 and tile print mcciium when the Delia advance system is incrementally advanced with the vacuum lold-down actuated, effecting the fine position compensation. 'I'll media advance system D has a snail motor which coarsely positions the l:clt with the llaten in a locked position. 'I'hc platen is titan unlocked, the main motor is cliseng,agcd, and the 15 platen is incrementally moved to actricvc zinc compensation, with a vacuum loldir:g tlc belt to the platen.

It is understood that tlic ahovc-lescribed embodiments are ncrcly illustrative of Ihc possible specific cmbodimouts which may rc,resent principles of the present invention Hitler arrangements may readily be devised in 20 accordance with these principles by those skilled in the art without departing foam hc scope ol the invention.

Claims (4)

À 1 CLAIMS:

1.S

2. A method as claimed in claiTll 1, wherein the step of deTer'. inir'= /tones of tile second swath which need high accuracy swath alig, nncnt is based on the type of image anal the print quality reque:tcd.

20

3. met according to claim l, wherein the prilltiT1 g clcncat includes Fin inkjet pCI1.

4. A ncthod for swath printing sulstarTtiaLly as hercinbcfore descriLcd with relcrencc to the accoTnpanying drawings

1. A method for swath printing, comprising,: printing a first swath of an ima:,c on a print medium with an inkjet printing 5 structure; advancing he print mcd,um to position the medium for printing a sccoTld swath; determining z.ones of the second swath which need hill accuracy swath alignment; beginning pi-inting tile second swath; during said pTiLIting of the scconl swath for those cones Nvl;icll nee<l high accuracy 10 swath alignment, dctcrmining the alignment errors and storing in memory appropriate error cotter nsation values; Tftcr completing, the printin g of said second swath. calculating the next mclium cTdVaTiCC diStaTlCC basso OT1 the stored coTI,lcnsalion values; arid advancing, the Tnedium for the next swath to be coTnpleted.