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EP1688262A1 - Druckverfahren für Farbstrahldrucker und Farbstrahldrucker geeignet zum Durchführen dieses Verfahrens - Google Patents

Druckverfahren für Farbstrahldrucker und Farbstrahldrucker geeignet zum Durchführen dieses Verfahrens Download PDF

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Publication number
EP1688262A1
EP1688262A1 EP06100828A EP06100828A EP1688262A1 EP 1688262 A1 EP1688262 A1 EP 1688262A1 EP 06100828 A EP06100828 A EP 06100828A EP 06100828 A EP06100828 A EP 06100828A EP 1688262 A1 EP1688262 A1 EP 1688262A1
Authority
EP
European Patent Office
Prior art keywords
printing
ink
ink chamber
strategy
image
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP06100828A
Other languages
English (en)
French (fr)
Other versions
EP1688262B1 (de
Inventor
Hubertus M.J.M. Boesten
Hans Reinten
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Canon Production Printing Netherlands BV
Original Assignee
Oce Technologies BV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from NL1028178A external-priority patent/NL1028178C2/nl
Application filed by Oce Technologies BV filed Critical Oce Technologies BV
Priority to EP20060100828 priority Critical patent/EP1688262B1/de
Publication of EP1688262A1 publication Critical patent/EP1688262A1/de
Application granted granted Critical
Publication of EP1688262B1 publication Critical patent/EP1688262B1/de
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/17—Ink jet characterised by ink handling
    • B41J2/19—Ink jet characterised by ink handling for removing air bubbles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/165—Prevention or detection of nozzle clogging, e.g. cleaning, capping or moistening for nozzles
    • B41J2/16579—Detection means therefor, e.g. for nozzle clogging
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/14—Structure thereof only for on-demand ink jet heads
    • B41J2002/14354—Sensor in each pressure chamber

Definitions

  • the invention relates to a method for application in an inkjet printer containing a substantially closed ink chamber comprising a nozzle, said ink chamber being operationally connected to an electro-mechanical converter, the method comprising: printing an image for the purposes of which the converter is actuated according to a predetermined printing strategy in order to eject ink drops from the nozzle for the formation of the image onto a carrier, detecting the presence of an obstruction, in particular a gas bubble, inside the ink chamber during printing, followed by interrupting the printing process.
  • the invention also relates to an inkjet printer which has been modified for this method to be automatically applied.
  • the printer in question comprises an ink chamber which is connected to a piezo-electrical converter. By actuating this converter, pressure waves are generated inside the ink chamber, said pressure waves in turn being able to cause ink drops to be ejected from the nozzle. By actuating the converter image-wise, an image, made up of individual ink drops, may be formed onto a carrier.
  • the printer comprises a calculation unit which determines an adequate printing strategy prior to printing the image. This printing strategy comprises information on the times at which and the actuation pulse with which the ink chamber is to be actuated for the correct ink drop to take on the required pixel on the carrier.
  • the inkjet printer comprises only one ink chamber, said ink chamber being part of a printhead which is a fixed arrangement in the printer.
  • the carrier is led along the printhead in a number of scanning movements, so that ultimately, the entire carrier may be provided with ink drops.
  • the printhead is a movable arrangement in the printer, so that it may make this scanning movement in an initial (main) scanning direction.
  • the carrier is usually moved along the printhead in a number of (sub) scanning directions. The combination of both scanning movements means that the entire carrier may be provided with ink drops, despite the limited dimensions of the printhead.
  • a strategy is thus determined with which the image may in principle - i.e. if no unforeseen problems occur- be printed.
  • a total image to be printed e.g. the image of a photograph in A3 format, is divided into a number of part images, where the printing strategy is determined per part image, prior to it being printed.
  • An example of such part image is a strip of the total image, said strip having a width that is equal to the width of an image that may be printed in one scan action of the printhead.
  • a detection circuit has been provided to determine whether an obstruction - i.e. anything that hinders the inkdrop formation process, in particular a gas bubble, is present in the chamber while an image is being printed (i.e. immediately after the piezo-electrical converter has been actuated in order to provide the first pixel on the carrier with an ink drop). If such an obstruction is detected, the printing process will be interrupted, as such obstructions usually have an adverse effect on the drop formation process: for example, ink drops are formed that are too small or which do not have the correct speed.
  • ink drops of an unintended size end up on the carrier or on an unintended location of the carrier, which may result in print artefacts.
  • an obstruction will usually produce ink chamber failure (i.e. a state in which the ink chamber is no longer able to eject an ink drop when the converter is actuated).
  • ink chamber failure i.e. a state in which the ink chamber is no longer able to eject an ink drop when the converter is actuated.
  • gas bubbles may grow quickly due to the pressure waves generated. From a certain size upwards, it will no longer be possible to eject ink drops from the ink chamber since their presence interferes too much with the acoustics in the chamber such that for example all acoustic energy is absorbed or reflected by the gas bubble.
  • the obstruction is removed from the ink chamber after the printing process has been interrupted, for example by purging the ink chamber with fresh ink, after which the printing process may be resumed.
  • the known method does have a number of major disadvantages. Interrupting the printing process is relatively time-consuming, which is considered a nuisance by any user of the printer. Furthermore, a relatively large amount of ink is required to ensure that the obstruction is indeed removed during the purge operation. Another important disadvantage is that joining errors often occur between the part of the image printed before the obstruction was detected and the part printed after the obstruction has been removed. This is because, to enable the ink chamber to be purged with fresh ink, it will move to a purge station, so that the purging ink cannot soil the carrier. After the purge operation, the printhead will need to be repositioned in the exact same place where it was when the printing process was interrupted. Here, it is virtually impossible to prevent positioning errors in the region of 20 to 200 ⁇ m, often producing visible joining errors.
  • the object of the invention is to obviate the problems described above.
  • a method has been invented according to the preamble, which is characterised in that it further comprises: modifying the printing strategy so that the obstruction will not produce ink chamber failure while the process of printing the image continues by actuation of the converter using the modified printing strategy, and continuing the printing process by application of this modified printing strategy.
  • This invention is partly based on the recognition that an obstruction inside the ink chamber does not necessarily need to produce visible print artefacts. Often, the ink chamber may still be used to eject ink drops despite the presence of an obstruction, without producing visible print artefacts.
  • the printing strategy is modified.
  • the modified printing strategy is chosen in such a way that the obstruction will not grow to a size that will cause the ink chamber to fail.
  • a gas bubble for example, will quickly grow to a size that will cause the chamber to fail. If previous research has shown, for example, that this gas bubble will take on a small equilibrium size at a frequency of 10kHz, at which size the ink chamber will still be available for printing, then it will be possible to modify the printing strategy in such a way that this ink chamber will only be loaded at a frequency of 10kHz maximum.
  • the presence of an obstruction has such a minor effect on the drop formation process that it will not usually produce visible print artefacts.
  • the printing process may be continued as normal using this ink chamber.
  • the printing strategy will have been modified, for example in such a way that a smaller number of ink drops may be ejected from the nozzle per time unit, but the major advantage of this method is that the ink chamber is still available for printing without a purge operation being required.
  • the modified printing strategy may be combined with another method of scanning the printhead relative to the carrier.
  • the printing strategy may be modified very quickly, for example by using modifications stored in the printer memory. It will also be possible for a powerful processor to calculate a new strategy very quickly, immediately after the obstruction has been detected, and said new strategy may usually be implemented within a few seconds. This then often eliminates the need for a noticeable interruption of the printing process.
  • the present invention allows the printing process to continue using an ink chamber in which an obstruction is present, without producing visible print artefacts. This invention implies knowing the correlation between the obstruction present, its effect on the drop formation process, and the behaviour of this obstruction (growing and thus causing the chamber to fail, shrinking, reaching equilibrium) as a function of the printing strategy. The knowledge required to apply the present invention may easily be determined by experiments. An example of this has been included in the further
  • the predetermined printing strategy is modified by changing the frequency at which the converter is actuated, i.e. the average number of actuations per second directed at the ejection of ink droplets.
  • the load on the ink chamber in this embodiment is modified by modifying the way in which the converter is actuated.
  • a lower amplitude of the actuation pulse may have the same effect, but this also leads to droplets of other sizes or speed which has to be taken into account when devising an alternative print strategy.
  • the printing process is automatically interrupted when it is detected that the process of printing the entire image by application of the predetermined printing strategy would produce ink chamber failure during this printing process.
  • it is first determined, before the printing process is interrupted, whether the present obstruction will actually produce ink chamber failure, if the printing process were continued using the original printing strategy. If the obstruction is, for example, a small gas bubble, and the ink chamber in question is only required to eject a few more drops of ink in order to complete the image, then this bubble will normally not grow to a size that will cause the ink chamber to fail. Interrupting the printing process and modifying the printing strategy will then not be required despite the presence of the obstruction inside the ink chamber.
  • the printing process will be interrupted and the strategy will be modified according to the present invention.
  • the advantage of this embodiment is that the printing process will not need to be interrupted if that is not required to prevent ink chamber failure.
  • the part of the image still to be printed using said ink chamber will be taken into account when modifying the printing strategy. It appears to be advantageous to take into account the information still to be printed as originally envisaged when modifying the printing strategy. Let us assume, for example, that at the moment of detecting a gas bubble inside the ink chamber, this chamber is still to be used to generate a maximum number of ink drops for the remainder of the image still to be printed (for example because this ink chamber is used to print a solid area of ink). This produces a completely different situation than when this chamber is still to be used to eject, on average, one ink drop every tenth pixel for the remainder of the image (for example to form accents in the background of a landscape photograph).
  • the load on the chamber in the event of an air bubble of equal size compared to the originally envisaged actuation (according to the predetermined strategy) will need to be reduced much less than in the second case.
  • it may suffice to leave out every fifth envisaged ink drop (20% fewer drops) whereas in the first case it may suffice to leave out every second drop (50% fewer drops) in the new printing strategy.
  • This more considerable reduction will obviously also depend on the time reduction between two actuations of the ink chamber in the first case. This is because this time reduction increases the intrinsic load of the ink chamber, which causes the gas bubble to be stimulated more strongly to grow to a critical size at which the chamber will fail. In order to prevent this, the load will need to be reduced relatively strongly.
  • the part image still to be printed may also give rise to a modification of the printing strategy where, given the nature of the information to be printed around the one pixel, barely any to no modification of the predetermined strategy takes place, whereas at a different pixel, the strategy will be modified strongly.
  • the printing strategy may be modified in such a way that the maximum load of the chamber is sought locally where the obstruction will just not produce ink chamber failure.
  • the obstruction is removed while the process of printing the image continues.
  • the possibility of removing the obstruction is used as soon as an opportunity presents itself. If the obstruction is, for example, a small contamination on the exterior of the nozzle, then this contamination may be removed between two scan actions (between which the ink chamber is at rest), for example by wiping the nozzle. If the obstruction is a gas bubble, then it may likely be possible to remove it at a time during the printing process where the ink chamber is not temporarily being used to generate ink drops (for example if there is a white area in the image). The removal will then most likely proceed passively (by the gas bubble dissolving) as known from European patent application EP 1 075 952. Once the obstruction has been removed, it is possible to continue the printing process using the printing strategy predetermined originally.
  • the frequency and/or amplitude will be modified in such a way that the gas bubble is actively removed from the ink chamber.
  • a gas bubble may be actively removed from an ink chamber by targeted actuation of the converter associated with this ink chamber. This has shown that under certain conditions, a gas bubble will take on a smaller equilibrium size at a lower actuation frequency. This may be used advantageously by exposing the ink chamber to an actuation pattern in which the frequency is decreased further and further. As such, the gas bubble may shrink until it is removed.
  • the presence of an obstruction inside the ink chamber is detected by application of the electro-mechanical converter as a sensor.
  • Application of the converter as a sensor is known from the prior art, for example as described in EP 1 013 453 or EP 1 378 360. This involves exploiting the fact that the pressure waves generated inside the ink chamber in turn deform the electro-mechanical converter. This deformation causes the converter to generate an electrical signal. By measuring this signal as a function of time, information may be obtained on the state of the ink chamber, as the pressure waves generated inside the ink chamber will be directly dependent on the state of the ink chamber. If, for example, there is a gas bubble inside the ink chamber, then a different pressure wave will be generated by actuation of the converter compared to when there is no gas bubble present. This difference in pressure wave produces a difference in deformation of the converter, which in turn produces a different electrical signal. By analysing this signal (as is also known from EP 1 013 453), it is possible to obtain information on the obstruction inside the ink chamber.
  • the inkjet printer comprises a plurality of ink chambers and where the application of the printing strategy produces a loss of printed pixels that would originally have been formed by the ink drops originating from the ink chamber in which the obstruction is present, this loss will at least partly be compensated by ink drops from one or more other ink chambers.
  • the inkjet printer comprises, for example, a printhead with some tens to hundreds of ink chambers and associated nozzles. If an obstruction is present inside one of these ink chambers, the printing strategy is modified according to the invention so that at least the load on this ink chamber will be modified to ensure that this ink chamber does not fail.
  • this modification will involve a lower load, for example by ejecting fewer ink drops from this ink chamber than originally envisaged when forming the image. This may cause part of the information on the image to be lost.
  • this information or at least some of it, is printed by ink drops originating from one or more of the other ink chambers. These will therefore be subject to a higher load than when using the predetermined printing strategy.
  • the extent to which the other ink chambers may be able to take over this function will, of course, depend to a large extent on the printhead configuration, the movement of the printhead relative to the carrier, the amount of loss to be compensated, the load originally envisaged for the other ink chambers, etc.
  • the method according to the invention is applied when printing a two-dimensional image onto the carrier where more than 50% of the carrier is covered with ink and, in particular where more than 70% of it is covered.
  • the inkjet printing process may be used to produce three-dimensional images, such as specimens prior to making final templates.
  • the present invention may be used for printing this type of image.
  • the method according to the present invention has been shown to be particularly suitable when printing flat images (i.e. relief images where the height differences in the image are typically less than 1 mm) with relatively high coverage rates, for example photographic images or displays, such as poly-LED displays, which may be formed onto a carrier by application of inkjet printers. This is because, with these high coverage rates, any failure of an ink chamber will virtually always produce print artefacts which are visible to the naked eye.
  • Application of the present invention obviates the above problem.
  • the method is applied when printing an image in one-pass mode.
  • a so-called one-pass mode as generally known from the prior art, there is only one nozzle (or chamber) is available for each pixel in which it may be provided with an ink drop. If, therefore, a certain pixel is not printed because its associated ink chamber has failed, it is not possible to still provide an alternative ink drop from a different chamber.
  • the invention can also be applied in a two (or multi-) pass mode, i.e. a mode wherein two (or multi-) nozzles are available for printing a pixel.
  • a printer which uses two printheads in a row is often used to print ink of the same colour.
  • both printheads are being used typically at half their maximum printfrequency. If in that case for example in the downstream printhead a gas bubble is detected, then this printhead could be operated at even a lower frequency which is compensated by increasing the print frequency of the upstream printhead.
  • the downstream printhead can take over partly. In the latter case, ideally the upstream printhead continues with its original print strategy until the position is reached where the downstream printhead has started printing with its alternative print strategy.
  • the invention also relates to an inkjet printer containing a substantially closed ink chamber comprising a nozzle, said ink chamber being operationally connected to an electro-mechanical converter, and a controller which has been programmed to control the printer to automatically carry out the method described above.
  • This controller does not need to form a designatable unit of the printer but may also be composed of several components, which may or may not be programmable, distributed across the printer and the printer's control units, in particular a control unit located at a distance from the printer itself.
  • Fig. 1 is a diagram showing an inkjet printer.
  • Fig. 2 is a diagram showing an ink duct assembly and its associated transducer.
  • Fig. 3 is a block diagram showing a circuit that is suitable for measuring the state inside the ink duct by application of the transducer used as a sensor.
  • Fig. 4 shows the correlation between the size of an air bubble and the actuation frequency in equilibrium.
  • Fig. 5 shows how an air bubble that is present inside an ink duct may be actively removed.
  • Fig. 6 is a diagram showing a number of images which have been printed onto a carrier by application of various methods.
  • FIG. 1 is a diagram showing an inkjet printer.
  • the printer comprises a roller 1 used to support a receiving medium 2, such as a sheet of paper or a transparency, and move it along the carriage 3.
  • This carriage comprises a carrier 5 to which four printheads 4a, 4b, 4c and 4d have been fitted.
  • Each printhead contains its own colour, in this case cyan (C), magenta (M), yellow (Y) and black (K) respectively.
  • the printheads are heated using heating elements 9, which have been fitted to the rear of each printhead 4 and to the carrier 5.
  • the temperature of the printheads is maintained at the correct level by application of a central control unit 10 (controller).
  • the roller 1 may rotate around its own axis as indicated by arrow A.
  • the receiving medium may be moved in the sub-scanning direction (often referred to as the X direction) relative to the carrier 5, and therefore also relative to the printheads 4.
  • the carriage 3 may be moved in reciprocation using suitable drive mechanisms (not shown) in a direction indicated by double arrow B, parallel to roller 1.
  • the carrier 5 is moved across the guide rods 6 and 7.
  • This direction is generally referred to as the main scanning direction or Y direction.
  • the receiving medium may be fully scanned by the printheads 4.
  • each printhead 4 comprises a number of internal elongated ink chambers (not shown). These ink chambers will be referred to as ink ducts in the remainder of the description.
  • Each of these ink ducts comprises a nozzle (an exit opening for jetting ink drops) 8.
  • the nozzles in this embodiment form one row per printhead perpendicular to the axis of roller 1 (i.e. the row extends in the sub-scanning direction).
  • the number of ink ducts per printhead will be many times greater and the nozzles will be arranged over two or more rows.
  • Each ink duct comprises a electro-mechanical converter, in this case a piezo-electric transducer (not shown) that may generate a pressure wave inside the ink duct so that an ink drop is ejected from the nozzle of the associated duct in the direction of the receiving medium.
  • the transducers may be actuated image-wise via an associated electrical drive circuit (not shown) by application of the central control unit 10.
  • an image made up of ink drops may be formed on receiving medium 2.
  • a receiving medium is printed using such a printer where ink drops are ejected from ink ducts, this receiving medium, or some of it, is imaginarily split into fixed locations that form a regular field of pixel rows and pixel columns.
  • the pixel rows are perpendicular to the pixel columns.
  • the individual locations thus produced (also referred to as pixels) may each be provided with one or more ink drops.
  • the number of locations per unit of length in the directions parallel to the pixel rows and pixel columns is referred to as the resolution of the printed image, for example indicated as 400x600 d.p.i. ("dots per inch").
  • Figure 2 shows an ink duct 19 comprising a piezo-electric transducer 16.
  • Ink duct 19 is formed by a groove in base plate 15 and is limited at the top mainly by piezo-electric transducer 16.
  • Ink duct 19 changes into an exit opening 8 at the end, this opening being partly formed by a nozzle plate 20 in which a recess has been made at the level of the duct.
  • actuation circuit 17 When a pulse is applied across transducer 16 by a pulse generator 18 via actuation circuit 17, this transducer bends in the direction of the duct. This produces a sudden pressure rise in the duct, which in turn generates a pressure wave in the duct.
  • the transducer first bends away from the duct, thus sucking in ink via an inlet opening (not shown), after which the transducer is moved back into its initial position. This also produces a pressure wave in the duct. If the pressure wave is strong enough, an ink drop is ejected from exit opening 8. After expiry of the ink drop ejection process, the pressure wave, or some of it, is still present in the duct, after which the pressure wave will damp fully over time. This pressure wave in turn results in a deformation of transducer 16, which then generates an electric signal. This signal depends on all the parameters that influence the generation and the damping of the pressure wave.
  • FIG. 3 is a block diagram showing the piezo-electric transducer 16, the actuation circuit (items 17, 25, 30, 16 and 18), the measuring circuit (items 16, 30, 25, 24, and 26) and control unit 33 according to one embodiment.
  • the actuation circuit comprising a pulse generator 18, and the measuring circuit, comprising an amplifier 26, are connected to transducer 16 via a common line 30.
  • the circuits are opened and closed by two-way switch 25. Once a pulse has been applied across transducer 16 by pulse generator 18, item 16 is in turn deformed by the resulting pressure wave inside the ink duct. This deformation is converted into an electric signal by transducer 16. After expiry of the actual actuation, two-way switch 25 is converted so that the actuation circuit is opened and the measuring circuit is closed.
  • the electric signal generated by the transducer is received by amplifier 26 via line 24.
  • the resulting voltage is fed via line 31 to A/D converter 32, which offers the signal to control unit 33. This is where analysis of the measured signal takes place. If necessary, a signal is sent to pulse generator 18 via D/A converter 34 so that a subsequent actuation pulse is modified to the current state of the duct.
  • Control unit 33 is connected to the central control unit of the printer (not shown in this figure) via line 35, allowing information to be exchanged with the rest of the printer and/or the outside world.
  • Figure 4 shows a correlation 100 for the inkjet printhead as described beneath figure 1, between the size of an air bubble (vertical axis, arbitrary units) and the frequency with which the transducer of the duct with the air bubble is actuated (horizontal axis in kilohertz), where an equilibrium exists and ink drops are ejected from the duct nozzle as a result of the actuation.
  • the size of an air bubble inside an ink duct of which the transducer is actuated at a certain frequency will normally increase to a certain equilibrium level due to said actuations.
  • the size of a bubble at this equilibrium depends i.a. on whether or not ink drops are ejected during actuation.
  • the exact position of the curves depends on many factors such as the geometries of the duct and the nozzle, the ink type, the temperature of the printhead, etc. and may be determined by experiments.
  • the size of the air bubble itself may, for example, be derived from analysing the signal generated by the transducer when the latter is used as a sensor (see figures 2 and 3). As the size of the air bubble is an important parameter for the acoustics in the duct, this size may be derived by application of a simple model for these acoustics by measuring a pressure wave present in the duct after the associated converter has been actuated. As is generally known, the pressure wave is directly dependent on the acoustics in the duct.
  • the present invention exploits the knowledge that, despite the presence of an obstruction, it may still be possible to reliably eject ink drops from the duct in many cases.
  • an air bubble is detected inside an ink duct
  • the predetermined printing strategy is such that this duct must be loaded at a 18,000Hz jet frequency for the next minute.
  • the duct will fail after approximately 20 seconds if the predetermined printing strategy is maintained (as 18,000Hz exceeds the critical frequency of 17,500Hz).
  • the duct will no longer be instantly available for printing, which will in all likelihood produce an unacceptable loss of information in the image.
  • an alternative strategy will be determined after the air bubble has been detected. As such a printing strategy will take less than 1 second to calculate, the printing process using the predetermined printing strategy will not need to be interrupted immediately after the air bubble has been detected (because it will take approximately 20 seconds for the air bubble to grow to a critical value). Therefore, prior to this interruption, an alternative strategy will first be determined, with which the printing process may be continued without the associated duct failing. In this case, the strategy may easily be modified by reducing the maximum jet frequency of the associated duct to for example 15,000 Hz (as the duct will not fail at this frequency according to correlation 100). It should be noted that 15,000 Hz is very near to the critical frequency of 17.500 Hz. This could mean that the ink droplet formation process is not optimal.
  • the frequency could be lowered to e.g. 10.000 Hz.
  • the necessity of this depends i.a. on the required image quality but also on the jetting characteristics of the printhead.
  • the printing process using the predetermined strategy will be interrupted. However, the printing process will immediately continue by application of the modified printing strategy. Therefore, there is no noticeable interruption of the printing process.
  • the printing strategy will be modified in such a way that the number of ink drops ejected from the duct will barely be reduced (in a solid area, for example, 1 in 18 ink drops will not be jetted). In the image, this reduction will produce little or no undesirable print artefact.
  • the printing strategy will be modified by applying, in addition to a minor reduction in frequency, a minor change in amplitude of the actuation pulses (providing this will not produce ink duct failure). This allows slightly larger ink drops to be jetted, which may offset the loss of ink caused by the reduction in frequency.
  • Figure 5 shows correlation 100 again.
  • This example describes a manner in which an air bubble present inside an ink duct may be actively removed by performing a targeted actuation of the converter associated with this ink chamber.
  • an ink duct of an inkjet printhead is actuated at a frequency of 20,000Hz.
  • an air bubble of a size between d 2 and d e is detected inside one of the ink chambers (in the area indicated by B). If the printing strategy were not modified, this air bubble would quickly grow until it reached the critical size and caused the duct to fail (as at a frequency of 20,000Hz, an air bubble as indicated in the figure will not be able to reach an equilibrium size according to curve 100).
  • the predetermined printing strategy will be interrupted and modified in such a way that the air bubble will not produce ink chamber failure while the process of printing the image continues, by actuation of the converter using this modified printing strategy.
  • the transducer of the associated duct will be actuated at a frequency of 8,000Hz for 20 seconds, where the amplitude of each pulse is such that an ink drop will be ejected from the duct. These ink drops will then be applied according to the invention to continue to print the image. These actuations will cause the air bubble to shrink to a size d 2 .
  • the transducer will be actuated for 10 seconds at a frequency of 2,000Hz, again at an amplitude high enough to ensure that ink drops are ejected from the duct. These drops too will form pixels of the image in question onto the carrier. This second series of actuations at an even lower frequency will cause the air bubble to further shrink to a size d 1 .
  • An air bubble of this size may be deemed to have been removed as it is so small that it will disappear during printing, for example by being ejected from the duct together with an ink drop.
  • the modified printing strategy may be abandoned and the printing process may be resumed by application of the predetermined printing strategy.
  • a major advantage of this embodiment is that the obstruction will quickly disappear so that only a very small part of the image needs to be printed by application of the modified printing strategy, which might involve a minor loss of information. Next, the remainder of the image may be printed again using the predetermined strategy.
  • Figure 6 shows a number of images which have been printed onto a carrier. In each of the images, a pixel that has been provided with an ink drop has been indicated by a little black square. The pixels that have not been printed and those that fall outside the image have been indicated by a little white square (so that they will disappear as a white area against the white background).
  • Figure 6a shows the image as it presented for printing. The image is made up of three part images, i.e. (from left to right) a solid square made up of 42 pixels (7 pixel columns x 6 pixel rows), a diagonal line made up of 6 pixels and the letter H made up of 17 pixels.
  • This image may easily be printed using a properly functioning printhead 4 containing a row of 6 nozzles (coinciding with the 6 pixel rows making up the image), by moving it along the carrier in the direction indicated by F once by actuating the associated ink chambers image-wise.
  • Figure 6b shows that one ink duct, i.e. the duct that corresponds to the third pixel row, contains an obstruction that has led to failure of this duct (shown by a cross of solid lines drawn through the nozzle associated with this duct). If this printhead is required to print the same image, it will not be possible for one entire line of the image to be provided with ink drops. This will produce a highly undesirable print artefact, particularly in the solid area and at letter H.
  • Figure 6c shows a solution provided for this problem as known from the prior art, for example from American patent US 6,270,187, where the information associated with pixels that cannot be printed due to failure of their associated ink duct will be transferred to adjacent ducts. This will not be an improvement for the solid area: as the adjacent ducts are already fully loaded, they will not be able to jet additional ink drops to compensate for the loss of information. At the diagonal line and letter H, there will be some improvement but the chance of producing a visible print artefact will continue to be relatively high here.
  • Figure 6d shows the image which may be printed by application of the method according to the present invention.
  • the diagonal line may in any case be printed without any print artefact as the pixel that is to be printed using the duct in which the air bubble is present, will not immediately follow or precede another pixel to be printed.
  • the letter H half of the pixels from the horizontal line may be provided with an ink drop. In the embodiment shown, part of the information missed will be transferred to the adjacent ink ducts. This letter H will show a print artefact that will be less noticeable in the image than the artefact of the letter H as described beneath figure 6c.

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  • Ink Jet (AREA)
  • Particle Formation And Scattering Control In Inkjet Printers (AREA)
EP20060100828 2005-02-03 2006-01-25 Druckverfahren für Farbstrahldrucker und Farbstrahldrucker geeignet zum Durchführen dieses Verfahrens Expired - Lifetime EP1688262B1 (de)

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Applications Claiming Priority (3)

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NL1028178A NL1028178C2 (nl) 2005-02-03 2005-02-03 Werkwijze voor het tegengaan van luchtbellen in een inkjetprinter en een inkjetprinter welke is aangepast voor toepassing van deze werkwijze.
EP05108188 2005-09-07
EP20060100828 EP1688262B1 (de) 2005-02-03 2006-01-25 Druckverfahren für Farbstrahldrucker und Farbstrahldrucker geeignet zum Durchführen dieses Verfahrens

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Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS59176056A (ja) * 1983-03-26 1984-10-05 Ricoh Co Ltd インクジエツト記録装置における励振方法
US4695852A (en) 1985-10-31 1987-09-22 Ing. C. Olivetti & C., S.P.A. Ink jet print head
EP1013453A2 (de) 1998-12-14 2000-06-28 Océ-Technologies B.V. Druckvorrichtung
EP1075952A2 (de) 1999-08-12 2001-02-14 Océ-Technologies B.V. Verfahren zur Erhöhung der Zuverlässigkeit eines Tintenstrahlkdruckers und Tintenstrahldrucker geeignet zur Durchführung des Verfahrens
US6270187B1 (en) 1998-12-14 2001-08-07 Hewlett-Packard Company Method and apparatus for hiding errors in single-pass incremental printing
EP1378360A1 (de) 2002-07-05 2004-01-07 Océ-Technologies B.V. Steuerungsverfahren für einen Tintenstrahldruckkopf, Tintenstrahldruckkopf der sich zur Anwendung des Verfahrens geeignet ist und Tintenstrahldrucker mit diesem Tintenstrahldruckkopf
EP1378359A1 (de) 2002-07-05 2004-01-07 Océ-Technologies B.V. Steuerungsverfahren für einen Tintestrahldruckkopf, Tintenstrahldruckkopf der sich zur Anwendung des Verfahrens geeignet ist und Tintenstrahldrucker mit diesem Tintenstrahldruckkopf

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS59176056A (ja) * 1983-03-26 1984-10-05 Ricoh Co Ltd インクジエツト記録装置における励振方法
US4695852A (en) 1985-10-31 1987-09-22 Ing. C. Olivetti & C., S.P.A. Ink jet print head
EP1013453A2 (de) 1998-12-14 2000-06-28 Océ-Technologies B.V. Druckvorrichtung
US6270187B1 (en) 1998-12-14 2001-08-07 Hewlett-Packard Company Method and apparatus for hiding errors in single-pass incremental printing
EP1075952A2 (de) 1999-08-12 2001-02-14 Océ-Technologies B.V. Verfahren zur Erhöhung der Zuverlässigkeit eines Tintenstrahlkdruckers und Tintenstrahldrucker geeignet zur Durchführung des Verfahrens
EP1378360A1 (de) 2002-07-05 2004-01-07 Océ-Technologies B.V. Steuerungsverfahren für einen Tintenstrahldruckkopf, Tintenstrahldruckkopf der sich zur Anwendung des Verfahrens geeignet ist und Tintenstrahldrucker mit diesem Tintenstrahldruckkopf
EP1378359A1 (de) 2002-07-05 2004-01-07 Océ-Technologies B.V. Steuerungsverfahren für einen Tintestrahldruckkopf, Tintenstrahldruckkopf der sich zur Anwendung des Verfahrens geeignet ist und Tintenstrahldrucker mit diesem Tintenstrahldruckkopf

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PATENT ABSTRACTS OF JAPAN vol. 009, no. 034 (M - 357) 14 February 1985 (1985-02-14) *
PATENT ABSTRACTS OF JAPAN vol. 013, no. 282 (M - 843) 28 June 1989 (1989-06-28) *

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