WO2002006051A1 - Method for monitoring a deflection distance, an image forming apparatus, means for producing a control signal and a control signal produced by said means - Google Patents

Method for monitoring a deflection distance, an image forming apparatus, means for producing a control signal and a control signal produced by said means Download PDF

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Publication number
WO2002006051A1
WO2002006051A1 PCT/SE2000/001489 SE0001489W WO0206051A1 WO 2002006051 A1 WO2002006051 A1 WO 2002006051A1 SE 0001489 W SE0001489 W SE 0001489W WO 0206051 A1 WO0206051 A1 WO 0206051A1
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WO
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Prior art keywords
means
dots
deflection
characterised
method according
Prior art date
Application number
PCT/SE2000/001489
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French (fr)
Inventor
Akira Ishida
Original Assignee
Array Ab
Matsushita Electric Industrial Co., Ltd.
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B41PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41JTYPEWRITERS; SELECTIVE PRINTING MECHANISMS, e.g. INK-JET PRINTERS, THERMAL PRINTERS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/385Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective supply of electric current or selective application of magnetism to a printing or impression-transfer material
    • B41J2/41Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective supply of electric current or selective application of magnetism to a printing or impression-transfer material for electrostatic printing
    • B41J2/415Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective supply of electric current or selective application of magnetism to a printing or impression-transfer material for electrostatic printing by passing charged particles through a hole or a slit
    • B41J2/4155Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective supply of electric current or selective application of magnetism to a printing or impression-transfer material for electrostatic printing by passing charged particles through a hole or a slit for direct electrostatic printing [DEP]

Abstract

Method for monitoring a deflection distance between a set of pixel locations on an image receiving member by an image forming apparatus including a print head having an array of print elements each print element arranged for producing dots at said set of pixel locations to form an interlaced pattern of dots, a deflection control element which is arranged for interacting with said print elements for enabling each print element to produce a dot at each pixel location in said set of pixel locations, means for restricting or permitting dot production at pixel locations and means for monitoring the distance between dots produced on an image receiving member. In an embodiment of the invention a repeated pattern is created such that one dot is printed and four pixel cells are not printed. The resulting pattern is C(1,1), R(1,1), L(2,1), C(2,1), R(2,1), L(1,2), C(1,2), R(1,2), L(2,2), C(2,2), R(2,2), L(1,3), C(1,3), etc, where X(n,n), indicates a printed dot and X(n,n), indicates a non-printed pixel. A corresponding image density as a function of the position along one row of pixel elements printed by the pattern exemplified in fig. 10d.

Description

Method for monitoring a deflection distance, an image forming apparatus, means for producing a control signal and a control signal produced by said means.

FIELD OF INVENTION

The invention relates to a method for monitoring a deflection distance between a set of pixel locations in an image forming apparatus including a print head having an array of print elements each print element arranged for producing dots at said set of pixel locations to form an interlaced pattern of dots, a deflection control element which is arranged for interacting with said print elements for enabling each print element to produce a dot at each pixel location in said set of pixel locations, means for restricting or permitting dot production at pixel locations and means for monitoring the distance between dots produced on an image receiving member.

The invention furthermore relates to an image forming apparatus being provided with means for performing such a method according to the preamble of claim 19, means for producing a control signal to an image forming apparatus being provided with means for performing such a method according to the preamble of claim 20 and a control signal produced by said means for producing a control signal.

h a specific embodiment the invention relates to a direct printing apparatus and a method for monitoring the deflection distance in such an apparatus, in which a computer generated image information is converted into a pattern of electrostatic fields, which selectively transport electrically charged particles from a particle source toward a back electrode through a printhead structure, whereby the charged particles are deposited in image configuration on an image receiving substrate caused to move relative to the printhead structure.

More specifically, the invention relates to a direct printing apparatus and a method for monitoring the deflection distance in such an apparatus, wherein the printhead structure causes at least some of the electrically charged particles to undergo a deflection prior to being deposited on the image receiving surface so as to increase the printable area of a receiving surface with a simplified printhead structure. The invention also relates to a method for improving the print quality and reducing manufacturing costs of such direct printing apparatus

BACKGROUND OF THE INVENTION

U.S Patent No. 5,036,341 discloses a direct electrostatic printing device and a method to produce text and pictures with toner particles on an image receiving substrate directly from computer generated signals. Such a device generally includes a printhead structure provided with a plurality of apertures through which toner particles are selectively transported from a particle source to an image-receiving medium due to control in accordance with an image information. The printhead structure is formed by a lattice consisting of intersecting wires disposed in rows and columns. Each wire is connected to an individual voltage source. Initially the wires are grounded to prevent toner passing through the mesh. As a desired print location on the image receiving medium passes below an intersection, adjacent wires in a corresponding column and row are set to back potential to produce an electric field that draws the toner particles from the particle source. The toner particles are propelled through the square apertures formed by four crossed wires and deposited on the image-receiving medium in the desired pattern. A drawback with this construction of printhead is that individual wires can be sensitive to the opening and closing of adjacent apertures, resulting in imprecise image formation due to the narrow wire border between apertures.

This effect is mitigated in an arrangement described in US patent No. 5 847 733 by the present applicant. This proposes a control electrode array formed on an apertured insulating substrate. A ring electrode is associated with each aperture and is driven to control the opening and closing of the apertures to toner particles. Each aperture is further provided with deflection electrodes. These are controlled to selectively generate an asymmetric electric field around the aperture, causing toner particles to be deflected prior to their deposition on the image-receiving medium. This process is referred to as dot deflection control (DDC). This enables each individual aperture to address several dot positions. The print addressability is thus increased without the need for densely spaced apertures.

However, the actual position of a deflected dot relative to a dot formed by undeflected toner particles on the image receiving medium is affected not just by the electric field profile around the aperture, but also by the distance between the aperture, or printhead, and the image receiving medium. Accordingly variations in this distance, for example resulting from unevenness in the image receiving medium or the back electrode supporting this medium, or unparallelity between the printhead and the image receiving medium, will result in the relative positions of dots varying across the surface of the image. Moreover inaccuracy in the deflection voltage will result in the relative positions of dots varying across the surface of the image. The print quality will thus be seriously degraded. Manufacturing measures designed to reduce unevenness or unparallelity are costly and furthermore not capable of eliminating the problem altogether. Similarly if paper is used as the image-receiving medium, significant differences in print quality will be observed for different paper thicknesses.

In prior art methods for providing a feed back signal to for adjusting deflection electrode voltage. An analysis of the optical density is made and the result is compared to an optimum value for creating said feed back signal. The analysis is made on a regular print or on a test patter in the shape of a line of predetermined length and width.

The method for providing a feed back signal disclosed thus requires a scanning apparatus with high resolution since the test pattern would normally be printed with 600 dpi.

SUMMARY OF THE INVENTION

A first object of the invention is to provide a method for monitoring a deflection distance between a set of pixel locations on an image receiving member by an image forming apparatus including a print head having an array of print elements each print element arranged for producing dots at said set of pixel locations to form an interlaced pattern of dots, a deflection control element which is arranged for interacting with said print elements for enabling each print element to produce a dot at each pixel location in said set of pixel locations, means for restricting or permitting dot production at pixel locations and means for monitoring the distance between dots produced on an image receiving member, where the requirement of the resolution of a measuring means for monitoring the distance included in the image forming apparatus is reduced. This object is achieved by a method for monitoring a deflection distance according to the characterising portion of claim 1. By restricting the production of dots at pixel locations in a repeated pattern such that neighbouring pixel cells are not printed while printing at remaining pixel locations thereby creating a set of parallel lines, the pixel density is reduced while information about deflection distance remains. Thereby, a scanner with relatively low resolution can be used.

An second object of the invention is to provide a method for monitoring a deflection distance in an image forming device, where the requirement of the resolution of a measuring means for monitoring the distance included in the image forming apparatus is reduced. This object is achieved by a method for monitoring a deflection distance according to the characterising portion of claiml. By restricting the transport of charged toner particles from the particle carrier through the apertures in a repeated pattern such that neighbouring pixel cells are not printed while printing at remaining pixel locations thereby creating a set of parallel lines, the pixel density is reduced while information about deflection distance remains. Thereby, a scanner with relatively low resolution can be used.

A third object of the invention is to provide an image forming apparatus including a control element arranged for performing said methods. This object is achieved by an image forming apparatus according to the characterising portion of claim 19.

A fourth object of the invention is to provide means for producing a control signal to an image forming apparatus being provided with means for performing such a method.

A fifth object of the invention is to provide a control signal produced by said means for producing a control signal.

Preferred embodiments are claimed in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail for explanatory, and in no sense limiting, purposes, with reference to the following drawings, wherein like reference numerals designate like parts throughout and where the dimensions in the drawings are not to scale, in which Figure 1 is a schematic section view across an image recording apparatus according to a preferred embodiment of the invention,

Figure 2 is a schematic section view across a particular print station of the image recording apparatus shown in Figure 1 ,

Figure 2a show a cross section along line I - 1 in fig 2.

Figure 3 is an enlargement of Figure 2 showing the print zone corresponding to a particular print station,

Figure 4 is a schematic plan view of the top side of part of a transfer belt showing a cleaning area,

Figure 5a is a schematic plan view of the top side of a printhead structure used in a print station such as that shown in Figure 2,

Figure 5b is a schematic section view along the section line I-I through the printhead structure shown in Figure 5a,

Figure 5c is a schematic plan view of the bottom side of the printhead structure shown in

Figure 5a,

Figure 6 is a schematic view of a single aperture and its corresponding control electrode and deflection electrodes,

Figure 7a illustrates a control voltage signal as a function of time during a print cycle having three subsequent development periods,

Figure 7b illustrates a first deflection voltage signal as a function of time during a print cycle having three subsequent development periods

Figure 7c illustrates a second deflection voltage signal as a function of time during a print cycle having three subsequent development periods Figure 8a illustrates the transport trajectory of toner particles through the printhead structure shown in Figures 5a,b,c according to a first deflection mode wherein

DK D2,

Figure 8b illustrates the transport trajectory of toner particles through the printhead structure shown in Figures 5a,b,c, according to a second deflection mode wherein Dl = D2,

Figure 8c illustrates the transport trajectory of toner particles through the printhead structure shown in Figures 5a,b,c, according to a third deflection mode wherein D1 > D2,

Figure 9a illustrates deposited toner particles and their density, trajected with a too small deflection voltage difference according to Figures 8a,b,c, from a printhead structure such as that shown in Figures 5a,b,c,

Figure 9b illustrates deposited toner particles and their density trajected with a too large deflection voltage difference according to Figures 8a,b,c, from a printhead structure such as that shown in Figures 5a,b,c,

Figure 9c illustrates deposited toner particles and their density, trajected with a substantially correct deflection voltage difference according to Figures 8a,b,c, from a printhead structure such as that shown in Figures 5a,b,c,

Figure 10a illustrates a print head structure having two rows of apertures,

Figure 10b illustrates a sequence of printed dots by the print head structure shown in fig 10a,

Figure 10c illustrates the variation of the image density of the sequence of dots shown in figure 10b, Figure 1 Od illustrates a print sequence according to the invention,

Figure 1 Oe illustrates the variation of the image density of the sequence of dots shown in figure lOd,

Figure lOf illustrates at its left part, the variation of image density, when two lines are positioned too close to each other, and the variation of image density, when two lines are positioned too far away from each other, at its right part,

Figure 11 illustrate means for providing a control signal for controlling an image forming apparatus communicating with an electronic control unit in a printer, and

Figure 12 illustrate a print medium having five different segments where a monitoring according to the invention is performed.

DESCRIPTION OF PREFERRED EMBODIMENTS

In order to clarify the methods and device according to the invention, some examples of its use will now be described in connection with Figures 1 to 9.

One aspect of the invention relates to a method for monitoring a deflection distance between a set of pixel locations on an image receiving member by an image forming apparatus including a print head having an array of print elements each print element arranged for producing dots at said set of pixel locations to form an interlaced pattern of dots, a deflection control element which is arranged for interacting with said print elements for enabling each print element to produce a dot at each pixel location in said set of pixel locations, means for restricting or permitting dot production at pixel locations and means for monitoring the distance between dots produced on an image receiving member.

In a preferred embodiment this method is used for monitoring a deflection distance between a set of pixel locations on an image receiving member by an image forming apparatus of direct printing type, in which a computer generated image information is converted into a pattern of electrostatic fields, which selectively transport electrically charged particles from a particle source toward a back electrode through a printhead structure, whereby the charged particles are deposited in image configuration on an image receiving substrate caused to move relative to the printhead structure.

A direct printing apparatus includes a printhead structure which causes at least some of the electrically charged particles to undergo a deflection prior to being deposited on the image receiving surface so as to increase the printable area of a receiving surface with a simplified printhead structure.

A preferred embodiment of the invention, wherein the image forming apparatus is constituted by an image fo-rming apparatus of the direct printing type, will be described in detail in connection with the appended figures.

In this embodiment the array of print elements is constituted by a printhead structure disposed between a particle carrier and a back electrode in a background electric field and including a plurality of apertures, control electrodes and deflection electrodes being associated with the apertures.

The deflection control element is formed by deflection voltage sources for selectively applying potentials to said deflection electrodes relative to a back electrode member to generate an asymmetric electrical field about said apertures to cause charged toner particles to be deflected when transported from a particle carrier towards said back electrode member.

Furthermore, the means for restricting or permitting dot production at pixel locations is formed by control voltage sources for supplying control potentials to said control electrodes in accordance with the image information to selectively permit or restrict the transport of charged toner particles from the particle carrier through the apertures.

Figure 1 is a schematic section view of an image recording apparatus according to a first embodiment of the invention, comprising at least one print station, preferably four print stations (Y, M, C, K), an intermediate image receiving member, a driving roller 11, at least one support roller 12, and preferably several adjustable holding elements 13. The four print stations (Y, M, C, K) are arranged in relation to the intermediate image receiving member. The intermediate image receiving member, preferably a transfer belt 10, is mounted over the driving roller 11. The at least one support roller 12 is provided with a mechanism for ma-ntaining the transfer belt 10 with at least a constant surface tension, while preventing transversal movement of the transfer belt 10. The preferably several adjustable holding elements 13 are for accurately positioning the transfer belt 10 at least with respect to each print station.

The driving roller 11 is preferably a cylindrical metallic sleeve having a rotational axis extending perpendicular to the belt motion and a rotation velocity adjusted to convey the transfer belt 10 at a velocity of one addressable dot location per print cycle, to provide line by line scan printing. The adjustable holding elements 13 are arranged for maintaining the surface of the transfer belt 10 at a predetermined distance from each print station. The holding elements 13 are preferably cylindrical sleeves disposed perpendicularly to the belt motion in an arcuated configuration for slightly bending the transfer belt 10 at least in the vicinity of each print station. The transfer belt 10 is slightly bent in order to, in combination with the belt tension, create a stabilization force component on the transfer belt 10. The stabihzation force component is opposite in direction and preferably larger in magnitude than an electrostatic attraction force component acting on the transfer belt 10. The electrostatic attraction forces at a print station are created by different electric potentials on the transfer belt 10 and on the print station in question.

The transfer belt 10 is preferably an endless band of 30 to 200 μm thick composite material as a base. The base composite material can suitably include thermoplastic polyamide resin or any other suitable material having a high thermal resistance, such as 260°C of glass transition point and 388°C of melting point, and stable mechanical properties under temperatures in the order of 250°C. The composite material of the tranfer belt 10 preferably has a homogeneous concentration of filler material, such as carbon or the like, which provides a uniform electrical conductivity throughout the entire surface of the transfer belt 10. The outer surface of the transfer belt 10 is preferably overlaid with a 5 to 30 μm thick coating layer made of electrically conductive polymere material such as for instance PTFE (poly tethra fluoro ethylene), PFA (tetra flouro ethylene, perflouro alkyl vinyl ether copolymer), FEP (tetra flouro ethylene hexaflouro, propylene copolymer), silicone, or any other suitable material having appropriate conductivity, thermal resistance, adhesion properties, release properties, and surface smoothness. To further improve for example the adhesion and release properties a layer of silicone oil can be applied to either the transfer belt base or preferably onto a coating layer if it is applied onto the transfer belt base. The silicone oil is coated evenly onto the transfer belt 10 preferably in the order of 0.1 to 2 μm thick giving a consumption of silicone oil in the region of 1 centiliter for every 1000 pages. Silicone oil also reduces bouncing/-scattering of toner particles upon reception of toner particles and also increases the subsequent transfer of toner particles to an information carrier. Making use of silicone oil and especially coating of the tiansfer belt with silicone oil is made possible in an electrostatic printing method according to the present invention as there is no direct physical contact between a toner delivery and a toner recipient, i.e. the transfer belt.

In some embodiments the transfer belt 10 can comprise at least one separate image area and at least one of a cleaning area and/or a test area. The image area being intended for the deposition of toner particles, the cleaning area being intended for enabling the removal of unwanted toner particles from around each of the print stations, and the test area being intended for receiving test patterns of toner particles for calibration purposes. The transfer belt 10 can also in certain embodiments comprise a special registration area for use of determining the position of the transfer belt, especially an image area if available, in relation to each print station. If the transfer belt comprises a special registration area then this area is preferably at least spatially related to an image area.

The transfer belt 10 is conveyed past the four different print stations (Y, M, C, K), whereby toner particles are deposited on the outer surface of the transfer belt 10 and superposed to form a toner image. Toner images are then preferably conveyed through a fuser unit 2, comprising a fixing holder 21 arranged transversally in direct contact with the inner surface of the transfer belt. In some embodiments of the invention the fuser unit is separated from the transfer belt 10 and only acts on an information carrier. The fixing holder 21 includes a heating element preferably of a resistance type of e.g. molybdemum, maintained in contact with the inner surface of the transfer belt 10. As an electric current is passed through the heating element, the fixing holder 21 reaches a temperature required for melting the toner particles deposited on the outer surface of the transfer belt 10. The fuser unit 2 further comprises a pressing roller 22 arranged transversally across the width of the transfer belt 10 and facing the fixing holder 21. An information carrier 3, such as a sheet of plain, untreated paper or any other medium suitable for direct printing, is fed from a paper delivery unit (not shown) and conveyed between the pressing roller 22 and the tiansfer belt 10. The pressing roller 22 rotates with applied pressure to the heated surface of the fixing holder 21 whereby the melted toner particles are fused on the information carrier 3 to form a permanent image. After passage through the fusing unit 2, the transfer belt is brought in contact with a cleaning element 4, such as for example a replaceable scraper blade of fibrous material extending across the width of the transfer belt 10 for removing all untransferred toner particles. If the transfer belt 10 is to be coated with silicone oil or the like, then after the cleaning element 4, and before the printing stations, the transfer belt 10 is brought into contact with a coating application element 8 for evenly coating the transfer belt with silicone oil or the like.

Furthermore the image recording device includes means 17 for monitoring the distance between dots produced on an image receiving member. In a preferred embodiment of the invention said means is constituted by a scanner device having a focus set for producing a signal with a modulation transfer function of preferable between 20 - 40 % at R*D dpi, where R = the resolution level of the printer, normally 300 or 600 dpi, and D is the dot density produced in a repeated pattern when restricting the production of dots at pixel locations. If in the repeated pattern, every fifth dot is printed, which is preferable under certain circumstances, the dot density is D=l/5. The definition of dot density is the number of dots printed at pixel locations/the number of pixels in a pattern.

Figure 2 is a schematic section view of a print station in, for example, the image recording apparatus shown in Figure 1. A print station includes a particle delivery unit 5 preferably having a replaceable or refillable container 50 for holding toner particles, the container 50 having front and back walls, a pair of side walls and a bottom wall having an elongated opening extending from the front wall to the back wall and provided with a toner feeding element (not shown) disposed to continuously supply toner particles to a developer sleeve 52 through a particle charging member. The particle charging member is preferably formed of a supply brush 51 or a roller made of or coated with a fibrous, resilient material. The supply brush 51 is brought into mechanical contact with the peripheral surface of the developer sleeve 52, for charging particles by contact charge exchange due to triboelectrification of the toner particles through frictional interaction between the fibrous material on the supply brush 51 and any suitable coating material of the developer sleeve 52. The developer sleeve 52 is preferably made of metal coated with a conductive material, and preferably has a substantially cylindrical shape and a rotation axis extending parallel to the elongated opening of the particle container 50. Charged toner particles are held to the surface of the developer sleeve 52 by electrostatic forces essentially proportional to (O/D)2, where Q is the particle charge and D is the distance between the particle charge center and the boundary of the developer sleeve 52. Alternatively, the charging unit may additionally comprise a charging voltage source (not shown), which supply an electric field to induce or inject charge to the toner particles. Although it is preferred to charge particles through contact charge exchange, the method can be performed by using any other suitable charge unit, such as a conventional charge injection unit, a charge induction unit or a corona charging unit, without departing from the scope of the present invention.

A metering element 53 is positioned proximate to the developer sleeve 52 to adjust the concentration of toner particles on the peripheral surface of the developer sleeve 52, to form a relatively thin, uniform particle layer thereon. The metering element 53 may be formed of a flexible or rigid, insulating or metallic blade, roller or any other member suitable for providing a uniform particle layer thickness. The metering element 53 may also be connected to a metering voltage source (not shown) which influence the triboelectrification of the particle layer to ensure a uniform particle charge density on the surface of the developer sleeve 52.

The developer sleeve 52 is arranged in relation with a support device 54 for supporting and ma taining the printhead structure 6 in a predetermined position with respect to the peripheral surface of the developer sleeve 52. The support device 54 is preferably in the form of a trough- shaped frame having two side walls, a bottom portion between the side walls, and an elongated slot arranged through the bottom portion, extending transversally across the print station, parallel to the rotation axis of the developer sleeve 52. The support device 54 further comprises means for maintaining the printhead structure in contact with the bottom portion of the support device 54, the printhead structure 6 thereby bridging the elongated slot in the bottom portion.

The transfer belt 10 is preferably slightly bent partly around each holding element 13 in order to create a stabihzation force component 30. The stabilization force component 30 is intended to counteract a field force component 31 which is acting on the transfer belt. The field force component 31 is a resultant of the electrostatic attraction forces acting on the transfer belt 10 due to different electric potentials on the transfer belt 10 and on the print station in question. The stabilization force component 30 is directed in a direction opposite the field force component 31 and preferably also at least slightly larger in magnitude than the magnitude of the field force component 31. If the field force component 31 is not counteracted it can cause distance fluctuations between the transfer belt 10 and the printhead structure 6 which can cause a degradation in print quality. The stabihzation force component 30 is created by the slight bending of the transfer belt 10 in combination with the tension of the transfer belt 10. The transfer belt 10 is bent around the holding element 13 in such a way that two angles 34, 35, at least one of which is greater than zero (i.e. at most one angle equal to zero), are created to the transfer belt 10 from a reference plane 39. The reference plane 39 being substantially perpendicular to an imaginary line/plane that extends between the center of the developer sleeve 52 and the holding element 13. Preferably the imaginary line/plane also separates the two angles 34, 35. The two angles 34, 35 are preferably both greater than zero and in the region between 0° and 10°.

In fig 2a is shown a cross section along line I - 1 in fig 2. The particle delivering unit 5 is supported at a frame 14 of the printer. The transfer belt 10 is positioned in close connection with the particle delivering unit. In a preferred embodiment of the invention the particle delivering unit is supported at the frame by means for adjusting the distance 15a and 15b between the particle delivering unit 5 and the transfer belt 10. The particle delivering unit is provided with one means at each end region 16a, 16b of the particle delivering unit 5, thereby providing possibility for tilting the particle delivering unit such that the transfer belt and particle delivery unit are positioned parallel to each other.

Figure 3 is an enlargement of the print zone in a print station of, for example, the image recording apparatus shown in Figure 1. The printhead structure 6 is preferably formed of an electrically insulating substrate layer 60 made of flexible, non-rigid material such as polyamide or the like. The printhead structure 6 is positioned between the peripheral surface of the developer sleeve 52 and the bottom portion of the support device 54. The substrate layer 60 has a top surface facing the toner layer 7 on the peripheral surface of the developer sleeve 52. The substrate layer 60 has a bottom surface facing the the bottom portion of the support device 54. Further, the substrate layer 60 has a plurality of apertures 61 arranged through the substiate layer 60 in the part of the substrate layer 60 overlying the elongated slot in the bottom portion of the support device 54. The printhead structure 6 further includes a first printed circuit arranged on the top surface on the substrate layer 60 and a second printed circuit arranged on the bottom surface of the substrate layer 60. The first printed circuit includes a plurality of control electrodes 62, each of which, at least partially, surrounds a corresponding aperture 61 in the substrate layer 60. The second printed circuit preferably includes a first and a second set of deflection electrodes 63 spaced around first and second portions of the periphery of the apertures 61 of the substrate layer 60. The apertures 61 and their surrounding area will under some circumstances need to be cleaned from toner particles which agglomerate there, hi some embodiments of the invention the transfer belt 10 advantageously comprises at least one cleaning area for the purpose of cleaning the apertures 61 and the general area of the apertures 61. The cleaning, according to these embodiments, works by the principle of flowing air (or other gas). A pressure difference, compared to the air pressure in the vicinity of the apertures, is created on the side of the transfer belt 10 that is facing away from the apertures 61. The pressure difference is at least created during part of the time when the cleaning area is in the vicinity of the apertures 61 of the print station in question during the transfer belt's 10 movement. The pressure difference can either be an over pressure, a suction pressure or a sequential combination of both, i.e. the cleaning is performed by either blowing, suction, blowing first then suction, suction first then blowing, or some other sequential combination of suction and blowing. The pressure difference is transferred across the transfer belt 10 by means of the cleaning area comprising at least one slot/hole 80 through the transfer belt 10. The cleaning area preferably comprises at least one row of slots 80, and more specifically two to eight interlaced rows of slots 80. The slots can advantageously be in the order of 3 to 5 mm across. The pressure difference appears on the holding element 13 side of the transfer belt 10 through a transfer passage 81 through an outer sleeve 85 of the holding element 13. The transfer passage 81 can advantageously suitably extend transversally across the printhead structure as an elongated slot with a width, in the direction of the transfer belt 10 movement, that is equal to or greater than the n-nnimum distance between the printhead structure 6 and the transfer belt 10. In some embodiments it can be advantageous to have a controllable passage 82 which by means of, for example, a movable inner sleeve 86 can open and close access of the pressure difference to the transfer passage 81. Thereby a suction pressure will not increase the transfer belt's friction on the holding element 13 more than necessary. The controllable passage 82 will preferably open and close in synchronization with the movement of the transfer belt 10 to thereby coincide its openings with the passage of the cleaning area of the transfer belt 10. The means for creating the pressure difference is not shown and can suitably be a fan, bellows, a piston, or some other suitable means for creating a pressure difference. In some embodiments according to the invention the transfer passage 81 is substantially located symmetrically in relation to the apertures. In other embodiments according to the invention the transfer passage 81 is shifted in the direction of movement of the transfer belt 10. Figure 4 shows an example of holes 80 in a plurality of interlaced rows within a cleaning area 85 of the transfer belt 10. The number of holes/slots, their size and design will depend on the specific application. A preferable design is elongated slots in at least two interlaced rows.

Although, a printhead structure 6 can take on various embodiments without departing from the scope of the present invention, a preferred embodiment of the printhead structure will be described hereinafter with reference to Figures 5a, 5b and 5c. A plurality of apertures 61 are arranged through the substrate layer 60 in several aperture rows extending transversally across the width of the print zone, preferably at a substantially right angle to the motion of the transfer belt. The apertures 61 preferably have a circular cross section with a central axis 611 extending perpendicularly to the substrate layer 60 and suitably a diameter in the order of 160μm. Each aperture 61 is surrounded by a control electrode 62 having a -ring-shaped part circumscribing the periphery of the aperture 61, with a symmetry axis coinciding with the cential axis 611 of the aperture 61 and an inner diameter which is equal or sensibly larger than the aperture diameter. Each control electrode 62 is connected to a control voltage source (IC driver) through a connector 621. As apparent in Figure 5a, the printhead structure further preferably includes guard electrodes 64, preferably arranged on the top surface of the substrate layer 60 and connected to a guard potential (Vguard) aimed to electrically shields the control electrodes 62 from one another, thereby preventing undesired interaction between the electrostatic fields produced by two adjacent control electrodes 62. Each aperture 61 is related to a first deflection electrode 631 and a second deflection electrode 632 spaced around a first and a second segment of the periphery of the aperture 61, respectively. The deflection electrodes 631, 632 are preferably semicircular or crescent-shaped and disposed symmetrically on each side of a deflection axis extending diametrically across the aperture at a predetermined deflection angle to the motion of the transfer belt, such that the deflection electrodes substantially border on a first and a second half of the circumference of their corresponding aperture 61, respectively. All first and second deflection electrodes 631, 632 are connected to a first and a second deflection voltage source Dl, D2, respectively.

Figure 6 is a schematic view of a single aperture 61 and its corresponding control electrode 62 and deflection electrodes 631, 632. Toner particles are deflected in a first deflection direction Rl when Dl < D2, and an opposite direction R2 when Dl > D2. The deflection angle δ is chosen to compensate for the motion of the transfer belt 10 during the print cycle, in order to be able to obtain two or more transversally aligned dots. A preferred embodiment of a dot deflection control function is illustrated in Figures 7a, 7b and 7c respectively showing the control voltage signal (Ncontrol), a first deflection voltage Dl and a second deflection voltage D2, as a function of time during a single print cycle. According to some embodiments of the invention and as illustrated in the figure, printing is performed in print cycles having three subsequent development periods for addressing three different dot locations through each aperture. In other embodiments each print cycle can suitably have fewer or more addressable dot locations for each aperture. In still further embodiments each print cycle has a controllable number of addressable dot locations for each aperture. During the whole print cycle an electric background field is produced between a first potential on the surface of the developer sleeve and a second potential on the back electiode, to enable the transport of toner particles between the developer sleeve and the transfer belt. During each development period, control voltages are applied to the control electrodes to produce a pattern of electrostatic control fields which due to control in accordance with the image information, selectively open or close the apertures by influencing the electric background field, thereby enhancing or inhibiting the transport of toner through the printhead structure. The toner particles allowed to pass through the opened apertures are then transported toward their intended dot location along a trajectory which is determined by the deflection mode.

The examples of control function shown in Figures 7a, 7b and 7c illustrates a control function wherein the toner particles have negative polarity charge. As is apparent from Figure 7a, a print cycle comprises three development periods tb, each followed by a recovering period tw during which new toner is supplied to the print zone. The control voltage pulse (Ncontrol) can be amplitude and/or pulse width modulated, to allow the intended amount of toner particles to be transported through the aperture. For instance, the amplitude of the control voltage varies between a non-print level Nw of approximately -50N and a print level N, in the order of +350N, corresponding to full density dots. Similarly, the pulse width can be varied from 0 to tb. As apparent from Figures 7b and 7c, the amplitude difference between Dl and D2 is sequentially modified for providing three different toner trajectories, i.e. dot positions, during each print cycle. The amplitudes of Dl and D2 are modulated to apply converging forces on the toner to obtain smaller dots. Utilizing this method enables, for example, 60μm dots to be obtained utilizing 160μm apertures. Suitably the size of the dots are adjusted in accordance with the dot density (dpi) and thus also dynamically with the number of dot locations each aperture is to address. Figures 8a, 8b and 8c illustrate the toner trajectories in three subsequent deflection modes. The figures 8a, 8b and 8c illustrate a cross section of a substrate layer 60 with apertures 61 with corresponding control electrodes 62. Also illustrated are deflection voltages Dl and D2 that are connected to respective deflection electrodes 631 , 632. During a first development period illustrated in Figure 8a, the modulated stream of toner particles is deflected to the left by producing a first amplitude difference (DKD2) between both deflection voltages. The amplitude difference is adjusted to address dot locations 635 located at a deflection length Ld to the left of the central axes 611 of the apertures 61. During a second development period illustrated in Figure 8b, the deflection voltages have equal amplitudes (D1=D2) to address undeflected dot locations 636 coinciding with the central axes 611 of the apertures 61. During a third development period illustrated in Figure 8c, the modulated stream of toner particles is deflected to the right by producing a second amplitude difference (D1>D2) between both deflection voltages. The amplitude difference is adjusted to address dot locations 637 located at a deflection length L to the right of the central axes 611 of the apertures 61.

Figure 9a, 9b, and 9c illustrate deposited toner particles and their density, trajected with a too small, too large and substantially correct deflection voltage difference respectively. The toner particles are trajected, for example, according to Figures 8a, 8b, 8c, from a printhead structure such as that shown in Figures 5a, 5b, 5c. Figure 9a illustrates toner particles 635, 636, 637 trajected onto, for example, a transfer belt and their resulting density distribution when a deflection voltage difference has been to small. According to the example three addressable dots per aperture are shown, as described previously, more or fewer dots per aperture are possible. As can be seen from the density diagram there is quite a large dip 41 in the density of the recorded toner particle dots 635, 636, 637 in comparison to an average density 91. The leftmost dot 635 leaves a gap to the rightmost dot 637 of the adjacent aperture resulting in the density dip 41. The rightmost dot 637 overlaps the center dot 636 as does the leftmost dot 635. It is the rightmost 637 and leftmost 635 that are in the wrong position, the center 636 dot will always be substantially along the center axis 611 where it should be. Figure 9b illustrates the situation when the deflection voltage difference has been to large, thus resulting in spreading out of the rightmost dots 637 and of the leftmost dots 635 to much away from the center dots 636 and actually resulting in an overlap of the leftmost dots 635 and the rightmost dots 637 of respective adjacent apertures and thereby leaving several density dips 42, 43 in comparison to an average density 92, 93, 94. Figure 9c illustrates the situation when the deflection voltage difference has been at its substantially optimal value leaving all of the dots 635, 636, 637 substantially at their predetermined places which results in a substantially even density 95 across the dots.

The smaller the deflection voltage difference is the greater the dip 41 according to figure 9a will become. An increase in the deflection voltage difference will decrease the size of the dip 41 until it has disappeared completely. The density across the dots will then have the appearance according to figure 9c, i.e. the deflection voltage difference is, at least, substantially correct. If the deflection voltage difference is increased even further, the density across the dots will break apart again, but this time according to figure 9b with two dips 42, 43 per aperture. The deflection voltage difference has to be decreased again so that a density 95 across the dots will have an appearance according to figure 9c again.

Figures 10a - 10 g illustrate the invention applied to a print head 5 having apertures arranged in a first and a second row 70, 71. The apertures are indexed for illustrating from which aperture an specific dot is provided in fig 10b. Each aperture is arranged for providing a dot at a position L deflected to the left, at a central non-deflected position C and at a position R deflected to the right. In figure 10b dots produced from all apertures in the first and second row are shown. These dots are indexed C i,i), R<ι,i), 2,i), C(2,i), R(2,ι L(i,2)5 C(i,2 R(i,2)? L(2,2). C(2,2 R( ,2)> L(W)J C^), etc, Where the first position in the vector indicates from which line the dot is produced and the second from which aperture in the row.

Fig 10c show the image density as a function of the position along one row of pixel elements. A dot is normally wider than a pixel in order to avoid unprinted lines to appear when printing. In a preferred embodiment the width of a dot is between 120 - 200 % of the width of a pixel cell. Therefore, when printing all dots in a line, the dots are partly covering each other. Therefore the variation of image density is small, which provides for good image quality, but also makes it difficult to monitor the deflection distance. The deflection distance is defined as the distance form the centre of a right or left dot to the centre of a central dot.

According to the invention means for restricting restrict the production of dots at pixel locations in a repeated pattern such that neighbouring pixel cells are not printed while printing at remaining pixel locations thereby creating a set of parallel lines. In figure lOd an example of the invention is provided, where the repeated pattern is such that one dot is printed and four pixel cells are not printed.

The resulting pattern is C(ljl), R(i,i), L(2>1), C(2)1), R 2ιl), L(1;2), C(ι,2), R(1)2), L(2j2), C(2>2), R(2,2), L(W), C(i)3), etc, where X(n,n)-> indicates a printed dot and X(n,n)5 indicates a non-printed pixel.

Fig lOe show the image density as a function of the position along one row of pixel elements printed by the pattern exemplified in fig. lOd. Since the dots are not positioned partly on top of each other the variation in image density is much greater than when dots are produced at neighbouring pixel cells as exemplified in fig. 10b.

When performing the method of monitoring, means for monitoring 17 monitors the distance between neighbouring lines by comparing peaks 73 of said signal with a parametric window 74 defined by a first and a second threshold value 75, 76, whereby two neighbouring lines are judged to be too close if said signal is above the first threshold value and two neighbouring lines are judged to be too distant if said signal is below the second threshold value.

In a prefeπed embodiment of the invention the first and second threshold values are dependent on the colour printed.

In figure lOf, left part it is shown the result of two dots being too close, whereby the signal representing the image density exceeds the first threshold value. In figure lOf, right part it is shown the result of two dots being too far from each other, whereby the signal representing the image density is below the second threshold value.

In the most preferred embodiment of the invention the repeated pattern is such that dots are printed from neighbouring print elements in the same row in a matrix of print elements, in groups of three where a first dot is deflected in one direction, a second dot is deflected in a second direction and a third dot is not deflected, without being interlaced by dots produced by printing elements in other rows.

According to the invention this difference in density is used to enable an automatic calibration of the deflection voltage difference. In a preferred embodiment of the invention, the result of the measurement is compared with an expected optimum value to thereby create a deflection feedback signal which can adjust the deflection voltage difference to an optimum value. In a further preferred embodiment of the invention the feed back signal can be used for adjusting the distance between a print head and the print medium.

I a further development of the invention signal processing of the output signal from the scanner could be used for detection of the variation of the deflection voltage within one row of apertures and variation of deflection voltages between different rows of apertures. At first the discrimination level is a R*D dpi, where R = the resolution level of the printer, normally 300 or 600 dpi, and D is the dot density produced in a repeated pattern when restricting the production of dots at pixel locations. The pattern produced by the discrimination gives easy access to determination of difference in right or left deflection by using a scanner and comparing the output signal to threshold values as explained above. The signal produced by the scanner is further analysed at frequencies of R*D N, where N = number of deflection possibilities, that is in the case of one left and one right deflection N=2. If the signal varies at this frequency, the deflection voltage for a particular row of apertures is either to large or too small. By varying the deflection voltage in the direction where the top to down value of the signal is at a minimum., the deflection voltage could be set to a correct value.

Furthermore, the signal could be analysed at frequencies of R*D/(N*M), where M= the number of rows in the printhead. If the signal varies at this frequency, the deflection voltage is different in the different rows. By varying the deflection voltage for each row in the direction where the top to down value of the signal is at a minimum, the deflection voltage for each row could be set to a correct value.

For performing this additional analysis of the signal the printer should be provided with means for performing frequency analysis of the signal produced by the scanner. These means could be in the form of an analogue or a digital filter.

The test can be performed at regular or irregular intervals, such as between every page, every 1000 pages, or every hour, or on demand from, for example, the user or a environmental sensor, or at every power on. According to two further aspects of the invention means for producing a control signal for controlling an image forming apparatus according to a method for monitoring the deflection distance in a printer and a control signal produced by said means for producing a control signal. These aspects are further explained in connection with figure 11, where 76 denotes a printer according to the invention. The printer includes a control circuit 77 capable of controlling the functions in a printer. The control circuit could include one processor running the different functions or several processors each running different functions in the printer. Typically the processor controls print elements arranged in a print head comprising an array of print elements each arranged for producing dots, a deflection control element which is arranged for interacting with said print elements for enabling each print element to produce a dot at each pixel location in said set of pixel locations, means for restricting or permitting dot production at pixel locations and means for monitoring the distance between dots produced on an image receiving member.

If a direct printing apparatus is used the control circuit would control at least one background voltage source coupled with a back electrode member for producing a background electric field, a printhead structure disposed between said particle carrier and said back electrode in said background electric field and including a plurality of apertures, control electrodes and deflection electrodes being associated with the apertures, control voltage sources for supplying control potentials to said control electrodes in accordance with the image information to selectively permit or restrict the transport of charged toner particles from the particle carrier through the apertures, deflection voltage sources for selectively applying potentials to said deflection electrodes relative to the back electrode member to generate an asymmetric electrical field about said apertures to cause said charged toner particles to be deflected when transported from said particle carrier towards said back electrode member; and measuring means for monitoring the distance from dots of deflected charged toner particles deposited on an image receiving member to a non-deflected pixel location.

The contiol circuit is arranged for communicating with means 78 for producing a control signal for controlling an image forming apparatus. These means carries the instructions needed for performing the method for monitoring according to the invention. The means could be integrated in the printer as a memory device or a processor or be separate from the printer. Typically the means for producing a control signal is a computer transferring an algorithm used when performing the method of monitoring. The tiansfer is made either via a carrying medium as a diskette or via a communication channel 79 which could be wireless or a wired communication.

Said means for producing a control signal for controlling an image forming apparatus transmits a signal which could be stored in the control circuit 77 of the printer.

The signal could optionally be compressed at said means for producing a control signal and be unpacked at the control circuit 77.

In one embodiment of the invention the means for restricting restrict the production of dots at pixel locations in a repeated pattern in one or several segments as said print medium whereby said means for monitoring obtains a signal including information about variations of image intensity from scanning said lines at said one or more segments. In a preferred embodiment of the invention the deflection voltage is individually controllable within each segment. The produced segments are distributed over the width of the image receiving member and originates from different parts of the print head. In fig 12 a print-medium 80 having five different segments 81 - 85 is shown

The invention is not limited to the embodiments described above but may be varied within the scope of the appended patent claims. The invention may for example be used on in jet printers having means for deflecting print elements arranged for providing a possibility of printing a set of different pixel locations from each position of a print element. Furthermore, the invention is not restricted to printers having transfer belts but could also be used on printers scanning any type of print medium. The scanning can be provided either by moving the print medium or by moving the print head.

Claims

1 Method for monitoring a deflection distance between a set of pixel locations on an image receiving member by an image forming apparatus including a print head (6) having an array of print elements (61) each print element arranged for producing dots at said set of pixel locations to form an interlaced pattern of dots, a deflection control element (631,632) which is arranged for interacting with said print elements for enabling each print element to produce a dot at each pixel location in said set of pixel locations, means (62) for restricting or permitting dot production at pixel locations and means (17) for monitoring the distance between dots produced on an image receiving member
characterised in that
said means for restricting (62) restrict the production of dots at pixel locations in a repeated pattern such that neighbouring pixel cells are not printed while printing at remaining pixel locations thereby creating a set of parallel lines and
said means for monitoring (17) obtains a signal including information about variations of image intensity from scanning said lines.
2) Method according to claim 1, characterised in that said means for momtoring monitors the distance between neighbouring lines by comparing peaks of said signal with a parametric window defined by a first and a second threshold value, whereby two neighbouring lines are judged to be too close if said signal is above the first threshold value and two neighbouring lines are judged to be too distant if said signal is below the second threshold value.
3) Method according to claim 2, characterised in that said first and second threshold values are dependent on the colour printed by said print head. 4) Method according to any of the preceding claims, characterised in that said means for momtoring includes a scanner device having a focus set for producing a signal with a modulation transfer function of 20 - 40 % at R*D dpi, where R = the resolution level of the printer, and D is the dot density produced in a repeated pattern when restricting the production of dots at pixel locations, dpi.
5) Method according to any of the preceding claims, characterised in that said means for momtoring the distance produces a feed back signal to a control unit in the image forming device, wherein said feed back signal is used for adjusting the distance between lines.
6) Method according to any of the preceding claims wherein said set of pixel locations consist of a first and a second deflected pixel locations and one non- deflected pixel location, characterised in that said repeated pattern is such that at least one group of three neighbouring lines are formed wherein said three lines includes one line composed of dots deflected in the first direction, one line composed of dots deflected in the second direction and one line composed of non-deflected dots.
7) Method according to claim 6, characterised in that said at least one group of lines is formed from three neighbouring apertures in the same row of the matrix.
8) Method according to any of the preceding claims, wherein said array of print elements includes a first and a second tiansverse row, wherein the print elements in the first and the second row are positioned in an interlaced manner in the transverse direction, characterised in that said repeated pattern is such that one pixel position is printed and four pixel positions are discriminated from printing.
9) Method according to any of the preceding claims, characterised in that said means for restricting restrict the production of dots at pixel locations in a repeated pattern in one or several segments as said print medium whereby said means for momtoring obtains a signal including information about variations of image intensity from scanning said lines at said one or more segments.
10) Method according to claim 9, characterised that a deflection voltage created by said deflection control element is individually controllable within each segment.
11) Method according to any of the preceding claims characterised in that said means for monitoring produces an output signal that is processed through frequency analysing means providing information of the level of a deflection voltage created by said deflection control element and/or variation of the deflection voltage between different rows in said array of print elements.
12) Method for momtoring a deflection distance from dots of deflected charged toner particles deposited on an image receiving member to a non-deflected pixel location, in an image forming apparatus including:
at least one background voltage source coupled with a back electiode member for producing a background electric field;
a printhead structure disposed between said particle carrier and said back electrode in said background electric field and including a plurality of apertures, control electrodes and deflection electrodes being associated with the apertures;
control voltage sources for supplying contiol potentials to said contiol electrodes in accordance with the image information to selectively permit or restrict the transport of charged toner particles from the particle carrier through the apertures;
deflection voltage sources for selectively applying potentials to said deflection electrodes relative to the back electrode member to generate an asymmetric electrical field about said apertures to cause said charged toner particles to be deflected when transported from said particle carrier towards said back electrode member; and measuring means for monitoring the distance from dots of deflected charged toner particles deposited on an image receiving member to a non-deflected pixel location
characterised in that
said control voltage sources restrict the transport of charged toner particles from the particle carrier through the apertures in a repeated pattern such that neighbouring pixel cells are not printed while printing at remaining pixel locations thereby creating a set of parallel lines and
said means for monitoring obtains a signal including information about variations of image intensity from scanning said lines
13) Method according to claim 11, characterised in that said means for monitoring monitors the distance between neighbouring lines by comparing peaks of said signal with a parametric window defined by a first and a second threshold value, whereby two neighbouring lines are judged to be too close if said signal is above the first threshold value and two neighbouring lines are judged to be too distant if said signal is below the second threshold value.
14) Method according to claim 12, characterised in that said first and second threshold values are dependent on the colour printed by said printhead structure.
15) Method according to any of claims 11-13, characterised in that said means for monitoring includes a scanner device having a focus set for producing a signal with a modulation transfer function of 20 - 40 % at R*D dpi, where R is the resolution level of the printer, and D is the dot density produced in a repeated pattern when restricting the production of dots at pixel locations.
16) Method according to any of claims 11-14, characterised in that said means for monitoring the distance produces a feed back signal to a control unit in the image forming device, wherein said feed back signal is used for adjusting the distance between lines.
17) Method according to claim 15, characterised in that said feed back signal is used for adjusting the potentials applied to said deflection electrodes:
18) Method according to claim 15 or 16,wherein said the distance from said printhead structure to the image receiving member is adjustable characteri s e d i n that said feed back signal is used for adjusting said distance.
19) Method according to any claims 11-17 wherein said apertures are arranged in a matrix including at least one transverse row and said deflection electrodes are arranged for creating a first and a second set of deflected dots, each set of dots deflected in a different direction, characterised in that said repeated pattern is such that at least one group of three neighbouring lines are formed wherein said three lines includes one line composed of dots deflected in the first direction, one line composed of dots deflected in the second direction and one line composed of non-deflected dots.
20) Method according to claim 18, characterised in that said at least one group of lines are formed from three neighbouring apertures in the same row of the matrix.
21) Method according to any of claims 11-19, wherein said apertures are arranged in a first and a second tiansverse row, wherein the transverse position of the apertures of the first and second row are interlaced, characterised in that said repeated pattern is such that one pixel position is printed and four pixel positions are discriminated from printing.
22) Method according to any claims 11 - 20, characterised in that said means for restricting restrict the production of dots at pixel locations in a repeated pattern in one or several segments as said print medium whereby said means for monitoring obtains a signal including information about variations of image intensity from scanning said lines at said one or more segments.
23) Method according to claim 21, characterised that the deflection voltage is individually controllable within each segment.
24) Method according to any of claims 11 - 22 characterised in that said means for momtoring produces an output signal that is processed through frequency analysing means providing information of the level of a deflection voltage created by said deflection contiol element and/or variation of the deflection voltage between different rows in said array of print elements.
25) Image forming apparatus including a print head having an array of print elements each print element aπanged for producing dots at said set of pixel locations to form an interlaced pattern of dots, a deflection control element which is arranged for interacting with said print elements for enabling each print element to produce a dot at each pixel location in said set of pixel locations, means for restricting or permitting dot production at pixel locations and means for momtoring the distance between dots produced on an image receiving member
c h a r a c t e r i s e d i n that said image forming apparatus further includes a control element arranged for performing the method according to any of claims 1 - 22.
26) Means for producing a contiol signal controlling an image forming apparatus according to the method of any of claims 1 - 22.
27) A control signal produced by a means for producing a control signal according to claim 24.
PCT/SE2000/001489 2000-07-14 2000-07-14 Method for monitoring a deflection distance, an image forming apparatus, means for producing a control signal and a control signal produced by said means WO2002006051A1 (en)

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PCT/SE2000/001489 WO2002006051A1 (en) 2000-07-14 2000-07-14 Method for monitoring a deflection distance, an image forming apparatus, means for producing a control signal and a control signal produced by said means
AU6195500A AU6195500A (en) 2000-07-14 2000-07-14 Method for monitoring a deflection distance, an image forming apparatus, means for producing a control signal and a control signal produced by said means

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5774159A (en) * 1996-09-13 1998-06-30 Array Printers Ab Direct printing method utilizing continuous deflection and a device for accomplishing the method
US5847733A (en) * 1996-03-22 1998-12-08 Array Printers Ab Publ. Apparatus and method for increasing the coverage area of a control electrode during direct electrostatic printing
WO1999032297A2 (en) * 1997-12-19 1999-07-01 Array Printers Ab Direct electrostatic printing method and apparatus
US5984456A (en) * 1996-12-05 1999-11-16 Array Printers Ab Direct printing method utilizing dot deflection and a printhead structure for accomplishing the method

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5847733A (en) * 1996-03-22 1998-12-08 Array Printers Ab Publ. Apparatus and method for increasing the coverage area of a control electrode during direct electrostatic printing
US5774159A (en) * 1996-09-13 1998-06-30 Array Printers Ab Direct printing method utilizing continuous deflection and a device for accomplishing the method
US5984456A (en) * 1996-12-05 1999-11-16 Array Printers Ab Direct printing method utilizing dot deflection and a printhead structure for accomplishing the method
WO1999032297A2 (en) * 1997-12-19 1999-07-01 Array Printers Ab Direct electrostatic printing method and apparatus

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