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WO2008004929A1 - Unité d'impression, imprimante couleur et procédé pour améliorer la qualité d'impression dans une imprimante couleur - Google Patents

Unité d'impression, imprimante couleur et procédé pour améliorer la qualité d'impression dans une imprimante couleur Download PDF

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Publication number
WO2008004929A1
WO2008004929A1 PCT/SE2007/000150 SE2007000150W WO2008004929A1 WO 2008004929 A1 WO2008004929 A1 WO 2008004929A1 SE 2007000150 W SE2007000150 W SE 2007000150W WO 2008004929 A1 WO2008004929 A1 WO 2008004929A1
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WO
WIPO (PCT)
Prior art keywords
sensor
print unit
print
target structure
printer
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.)
Ceased
Application number
PCT/SE2007/000150
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English (en)
Inventor
Bengt Bern
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.)
Individual
Original Assignee
Individual
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Filing date
Publication date
Application filed by Individual filed Critical Individual
Publication of WO2008004929A1 publication Critical patent/WO2008004929A1/fr
Anticipated expiration legal-status Critical
Ceased 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
    • B41J2/21—Ink jet for multi-colour printing
    • B41J2/2132—Print quality control characterised by dot disposition, e.g. for reducing white stripes or banding
    • B41J2/2135—Alignment of dots

Definitions

  • the present invention relates to a print unit for use in a color printer, a color printer and a method for improving print quality in a color printer.
  • color printers especially small and cost-efficient ink-jet printers, can be found in almost every office and home in the industrialized world. These color printers are increasingly being used to produce color documents ranging from business graphics to holiday snap shots. Regarding color printers, one of the most important factors for customer satisfaction is print quality. Consequently, development efforts are continuously made in order to improve print quality.
  • Color printers in general, have replaceable print units or print cartridges which need to be replaced by the user at intervals depending on the frequency of use of the printer.
  • a replaceable print unit typically consists of a container holding ink or another marking substance and a print head.
  • output from several of these print units typically need to interact in order to create a desired color on a printed document.
  • an output from a second print unit is printed on top of an output from a first print unit. Where these outputs overlap, the desired color is created. If the print units are perfectly aligned with each other, a flawless printed structure of the desired color can be created.
  • the traditional way of reducing misalignment is to let the user print special calibration patterns and provide the printer controller with feedback indicating a suitable misalignment compensation. This is cumbersome for the user, who wants to start printing right away. Furthermore, a satisfactory result is not guaranteed, since the average user typically is not used to assessing print quality and providing the correct feedback.
  • a general object of the present invention is to provide an improved print unit, color printer and method for improving print quality in a color printer.
  • a print unit for use in a color printer having a printer body which is adapted to receive the print unit, the print unit comprising a container for containing a marking substance, a print head configured to transfer the marking substance from the container to a print medium, and a target structure adapted to, following positioning of the print unit at a print unit reference position in the color printer, provide a stimulus to a sensor which is arranged on the printer body.
  • the print unit may be a mono-color print unit or a multi-color print unit having several containers containing marking substances of different colors, and one print head for each color in the print unit. Furthermore, the print unit is typically replaceable.
  • the color printer may function according to any marking technology.
  • the print unit according to the present invention is especially useful in various forms of direct printing, such as ink-jet printing.
  • the "marking substance” may be ink based on any solvent, including water, wax, organic and inorganic solvents, or it may be a dry substance, such as toner.
  • the "print medium” may be any kind of medium used for printing onto, such as paper, plastic film, textiles etc.
  • the print medium may, furthermore, be an intermediate member, such as a belt or a drum, onto which the marking substance is transferred by the print head. In this case, the marking substance is subsequently transferred to the final medium, such as paper, plastic film, textiles, etc.
  • the "print head” should be understood as a structure which is controllable to selectively transfer an amount of the marking substance to a given location on the print medium.
  • the print head typically includes a plurality of nozzles which are configured to restrict or allow passage of a controlled amount of marking material in order to produce a "dot" on the print medium.
  • the target structure adapted to, following positioning of the print unit at a print unit reference position in the color printer, provide a stimulus to a sensor which is arranged on the printer body, an accurate determination of a misalignment of the print unit following insertion of the print unit in the color printer is enabled.
  • This misalignment can then be automatically compensated for, without any user intervention.
  • improved print quality may be maintained without any tedious manual calibration operation.
  • the misalignment may be determined and compensated for following an exchange of print unit, or print cartridge, and/or at predetermined intervals thereinbetween. Of course, a misalignment compensation may also be prompted by the user.
  • the target structure may advantageously be formed by a portion of the print head.
  • the human eye is very sensitive to color variations at edges in particular. Therefore, also a very small misalignment must be detectable through a sensing of the target structure. Since the position of a printed dot is determined by the position of the print head, the positioning tolerance of the target structure in relation to the print head should preferably be kept as small as possible.
  • the positioning tolerance of the target structure with respect to the print head will be determined by the manufacturing tolerances of the print head, which are typically in the range of 0.1 ⁇ m to 5 ⁇ m.
  • the target structure may be conductive. By forming the target structure from a conductive material, a stimulus can be provided by the target structure to a variety of sensors employing different sensing mechanisms. Such sensor types, for example, include optical sensors, capacitive sensors and conductive sensors.
  • This conductive target structure may, furthermore, preferably be configured to be connected to a voltage source when the print unit is positioned at the print unit reference position in the color printer.
  • a voltage AC or DC
  • the sensor control circuitry may be provided within or outside the sensor itself and the voltage may be applied to the target structure directly by the sensor, or indirectly by means of an intermediate driving circuit.
  • an intermediate driving circuit capable of delivering a higher voltage and/or current than the sensor itself may advantageously be employed.
  • the print unit according to the present invention may advantageously be comprised in a color printer further comprising a printer body having print medium transportation means, a sensor capable of providing an output indicative of a position of a stimulus facing the sensor, the sensor being provided at a printer body reference position, and control circuitry for controlling operation of the printer.
  • the above-mentioned output from the sensor may indicate a position of the stimulus in one dimension, a two-dimensional in-plane position, or a three- dimensional position in space.
  • the sensor may preferably comprise a plurality of pixels.
  • certain sensors including one sensor element only such as the PSD- detector manufactured by the company SiTek AB (SE) are capable of outputting a signal indicative of a position of a stimulus facing the sensor
  • the provision of a plurality of pixels in the sensor may simplify position readout and enables use of several sensor technologies which are already utilized in other technology fields, such as image sensors in digital cameras or fingerprint sensors.
  • the sensor may, furthermore, be capable of, for each pixel, providing an output of a plurality of values within an output range.
  • a position of a stimulus may be determined with far greater accuracy than the pixel resolution of the sensor.
  • the location of the target stimulus may determined with high accuracy through a simple center-of-mass calculation, the gray scale value here representing mass.
  • the output from the sensor may preferably be digital.
  • the sensor may be a capacitive sensor.
  • the target structure can be designed without regard to the optical contrast, the only requirement being that there is a sufficient contrast in electric conductivity between the target structure and its surroundings.
  • a color printer comprising a printer body having a print medium transportation mechanism, at least one print unit attached to the printer body, a sensor capable of providing an output indicative of a position of a stimulus facing the sensor, the sensor being provided at a printer body reference position, and control circuitry for controlling operation of the printer, wherein the print unit has a target structure configured to provide a stimulus to the sensor, and wherein the control circuitry is adapted to position the print unit at a print unit reference position adjacent to the printer body reference position such that the target structure at least partly faces the sensor, acquire, by means of the sensor, a signal indicative of a position of the target structure in relation to the printer body reference position, determine, based on the acquired signal, a misalignment of the print unit, and compensate for the determined misalignment, thereby improving print quality of the color printer.
  • a method for improving print quality in a color printer having a printer body with at least one print unit attached thereto comprising the steps of providing, at a printer body reference position, a sensor capable of providing an output indicative of a position of a stimulus facing the sensor, positioning the print unit at a print unit reference position adjacent to the printer body reference position such that a target structure provided on the print unit at least partly faces the sensor, the target structure being adapted to provide a stimulus to the sensor, acquiring, by means of the sensor, a signal indicative of a position of the target structure in relation to the printer body reference position, determining, based on the acquired signal, a misalignment of the print unit, and compensating for the determined misalignment, thereby improving print quality in the color printer.
  • the step of acquiring may comprise the steps of activating the target structure such that a stimulus is provided to the sensor, and providing as an output from the sensor, in response to the stimulus, a signal indicative of a position of the target structure in relation to the printer body reference position.
  • the target structure By “activating” the target structure should here be understood influencing the target structure in such a way that the sensor becomes able to sense it.
  • the target structure may be activated in a number of ways including, for example, illuminating it, directly or indirectly, heating it, and applying a voltage to it.
  • the stimulus sensed by the sensor may be provided in the form of light generated or reflected by at least part of the target structure, heat generated or reflected by at least part of the target structure, or voltage or current emitted by at least part of the target structure.
  • the target structure may advantageously be activated by means of an activation signal which is triggered by a sensor output.
  • the activation of the target structure can be synchronized with the sensor operation and a better output signal from the sensor achieved.
  • the sensor output referred to above may preferably be a specific trigger output from the sensor.
  • This activation signal may be a voltage pulse train.
  • Fig 1 is a schematic plane view of a portion of a color printer according to a preferred embodiment of the present invention.
  • Figs 2a-b are schematic plane views illustrating misalignment in different directions of print units according to a preferred embodiment of the present invention.
  • Fig 3 a schematically illustrates the sensor comprised in the color printer of fig l.
  • Fig 3b schematically illustrates position determination according to a preferred embodiment of the method of the present invention, by means of the sensor in fig 3a
  • Fig 4 is a flow chart which schematically illustrates a preferred embodiment of the method according to the present invention.
  • a preferred embodiment of the present invention is described with reference to an ink-jet color printer having a capacitive sensor mounted on the printer body in order to sense a position of a target structure on a print unit attached to the printer body when the print unit is positioned at a print unit reference position.
  • the ink-jet printer described herein has 4 mono-color print units. It should be understood that this by no means limits the scope of the present invention, which is equally applicable to other color printers, such as so-called solid ink printers, laser printers and other types of color printers for direct and indirect printing.
  • the invention is, obviously, also applicable to color printers having different numbers of print units than 4.
  • the color printer may have 6 print units each intended for printing a particular different color.
  • a single print unit may consist of several print heads and several corresponding containers each containing a different color marking substance, such as ink.
  • Fig 1 schematically shows a portion of a color printer according to a preferred embodiment of the present invention.
  • an ink-jet color printer 1 is partly shown comprising a printer body 2 and four replaceable print units 3a-d.
  • the printer body comprises a carriage 4 to which the print units 3a-d are attached, the carriage 4 being arranged to move along an axis 12 extending in the x-direction, and an optical positioning strip 5 for determining the position in the x-direction of the carriage 4, a mechanism (not shown) for transporting a print medium 6 in the y-direction past the print units 3a-d, and a sensor 7, for sensing a location of a target structure provided on each of the print units, which is mounted in a printer body 2 reference position in the color printer 1.
  • Two of the print units 3a,d are shown to eject ink droplets 8a,d through nozzles (not shown, see fig 2b) in print heads 9a-d comprised in the print units towards the print medium 6.
  • the print medium 6 is held stationary while the carriage 4 moves the print units 3a-d across the surface of the print medium 6 in the x-direction. At locations determined by the image to be printed, the print units 3a-d eject ink droplets through selected print head nozzles to thereby form a strip of the image to be printed. After the carriage 4 has completed one (or several) such passages across the surface of the print medium 6, the print medium is forwarded one step in the y-direction.
  • the droplets will end up at unintended locations, leading to print defects, such as color mismatch and shadow images.
  • figs 2a-b misalignment in the three dimensions (x, y, and z) is illustrated.
  • the print unit 3c is shown to be located at the print unit reference position, with its print head 9c facing the sensor 7.
  • the distance from this print head 9c to the sensor surface is denoted Z 3 .
  • this distance is denoted Z 1 , Z 2 , and Z 4 , respectively.
  • these z-direction distances are typically different from each other.
  • the ink droplets ejected from the respective print heads 9a-d need different amounts of time to reach the print medium surface, that is, they have different times-of -flight. Since the print units 3a-d are not stationary during printing, but rather moving across the print medium 6 with the carriage 4, ink droplets which are intended for the same location on the print medium but are ejected through print heads having different distances Z 1-4 to the print medium 6 will end up on different locations on the print medium surface.
  • the print units 3a-d are viewed as seen from the print medium 6 and the sensor 7, and nozzles 10 (only one of which here being indicated by a reference numeral for the sake of clarity of drawing) as well as target structures 1 la-d, here in the form of small metallic, essentially pyramid-shaped structures are shown.
  • the target structures lla-d are connected to respective connection pads 12a-d for enabling connection of the target structure to a voltage source (not shown) which is triggered by the sensor 7 to supply a pulsed voltage to the target structure of the print unit currently being in the print unit reference position, facing the sensor 7.
  • the target structures lla-d are here provided on the print heads 9a-d.
  • the target structures lla-d are manufactured at the same time as the nozzles and other structures of the print heads 9a-d are formed, to thereby achieve very small positioning tolerances between target structure and nozzle (typically in the sub-micron range).
  • print units 3a-d are, in addition to the above described z- direction misalignment, typically misaligned in the x- and y-directions as well.
  • Fig 3 a schematically illustrates the sensor comprised in the above described color printer according to a preferred embodiment of the present invention.
  • a position determination sensor 7 is schematically shown including a plurality of pixels, or sensor elements 20.
  • the sensor elements 20 are arranged in a matrix with a pitch P, which is typically in the range of 50 ⁇ m, and a gray scale value for each sensor element 20 can be read from the sensor. These values can be acquired for discrete positions denoted by (X 1 , V 1 ) - (x n , y n ) in fig 3 a.
  • the useful gray scale range is typically determined by the signal-to-noise ratio of the sensor.
  • this ability to output gray scale values from a plurality of pixels, or sensor elements enables position determination with a far greater accuracy than the pitch P.
  • the ability to output sensor element gray scale values enables determination not only of position in the x-y-plane, but additionally of position in the z-direction, or in other words, the distance between sensor 7 and target structure lla-d.
  • Fig 3b schematically illustrates position determination according to a preferred embodiment of the method of the present invention, by means of the sensor in fig 3 a
  • fig 3b the output values of sensor elements 20 of the sensor 7 as a response to stimulus by a target structure is schematically shown.
  • the position of the target structure lla-d is schematically illustrated by the hatched area 30 in fig 3b, and the output gray scale values of selected sensor elements are indicated in diagrams along the x- and y-axis, respectively, of the sensor 7.
  • the output values from the sensor elements are dependent on the 3D-shape of the target structure providing the sensor stimulus.
  • the target structure is essentially pyramid shaped.
  • Fig 4 is a flow chart which schematically illustrates a preferred embodiment of the method according to the present invention. Referring to fig 4, a first step 41 of providing, at a printer body reference position, a sensor capable of providing an output indicative of a position of a stimulus facing the sensor is followed by a step 42 of positioning the print unit at a print unit reference position adjacent to the printer body reference position such that a target structure provided on the print unit at least partly faces the sensor, the target structure being adapted to provide a stimulus to the sensor.
  • a subsequent step 43 the target structure is activated such that the stimulus is provided to the sensor, and in a following step 44, a signal indicative of a position of the target structure in relation to the printer body reference position is providing as an output from the sensor, in response to the stimulus.
  • the misalignment of the print unit is determined by performing a centre-of-mass calculation on the pixel values output from the sensor, and finally, in step 46, compensating for the determined misalignment.
  • the print medium motion need not be stepped, but could be continuous.
  • the print units need not be carried on a carriage, but could be provided in the form of so-called page wide arrays. In this case, several sensors, one for each print unit may be provided in the printer body.

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  • Engineering & Computer Science (AREA)
  • Quality & Reliability (AREA)
  • Ink Jet (AREA)

Abstract

La présente invention concerne un procédé pour améliorer la qualité dans une imprimante couleur (1) comportant un corps d'imprimante (2) avec au moins une unité d'impression (3a-d) montée à celui-ci. Le procédé comprend les étapes de mise à disposition (40), au niveau d'une position de référence de corps d'imprimante, un capteur (7) capable de délivrer une donnée de sortie indiquant une position d'un stimulus en regard du capteur; le positionnement (41) de l'unité d'impression (3a-d) à une position de référence d'unité d'impression adjacente à la position de référence du corps d'imprimante de sorte qu'une structure cible (11a-d) disposée sur l'unité d'impression (3a-d) soit au moins en partie en regard du capteur, la structure cible (11a-d) étant apte à fournir un stimulus au capteur (7); l'acquisition, au moyen du capteur (7), d'un signal indiquant une position de la structure cible (11a-d) par rapport à la position de référence du corps d'imprimante; la détermination, en fonction du signal acquis, d'un mauvais alignement de l'unité d'impression (3a-d); et la compensation (46) du mauvais alignement déterminé, améliorant ainsi la qualité d'impression dans l'imprimante couleur (1).
PCT/SE2007/000150 2006-02-17 2007-02-19 Unité d'impression, imprimante couleur et procédé pour améliorer la qualité d'impression dans une imprimante couleur Ceased WO2008004929A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE0600348 2006-02-17
SE0600348-7 2006-02-17

Publications (1)

Publication Number Publication Date
WO2008004929A1 true WO2008004929A1 (fr) 2008-01-10

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PCT/SE2007/000150 Ceased WO2008004929A1 (fr) 2006-02-17 2007-02-19 Unité d'impression, imprimante couleur et procédé pour améliorer la qualité d'impression dans une imprimante couleur

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999015338A1 (fr) * 1997-09-24 1999-04-01 Olivetti Lexikon S.P.A. Systeme d'alignement de plusieurs tetes d'impression a jet d'encre couleur et tete d'impression presentant un detecteur de position optique integre
EP0775587B1 (fr) * 1995-11-21 2000-07-19 Hewlett-Packard Company Alignement d'une tête d'impression à jet d'encre par la mesure d'erreurs et une mémoire de données
US20020180821A1 (en) * 2001-05-31 2002-12-05 Cook William Paul Method and apparatus for detecting the position of an inkjet printhead

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0775587B1 (fr) * 1995-11-21 2000-07-19 Hewlett-Packard Company Alignement d'une tête d'impression à jet d'encre par la mesure d'erreurs et une mémoire de données
WO1999015338A1 (fr) * 1997-09-24 1999-04-01 Olivetti Lexikon S.P.A. Systeme d'alignement de plusieurs tetes d'impression a jet d'encre couleur et tete d'impression presentant un detecteur de position optique integre
US20020180821A1 (en) * 2001-05-31 2002-12-05 Cook William Paul Method and apparatus for detecting the position of an inkjet printhead

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