WO2001056799A1

WO2001056799A1 - Direct electrostatic printing method and apparatus

Info

Publication number: WO2001056799A1
Application number: PCT/SE2000/000213
Authority: WO
Inventors: Agneta Sandberg; Karin Bergman; Thomas Oskarsson
Original assignee: Matsushita Electric Industrial Co Ltd; Array Printers AB
Current assignee: Panasonic Holdings Corp; Array Printers AB
Priority date: 2000-02-03
Filing date: 2000-02-03
Publication date: 2001-08-09
Anticipated expiration: 2002-08-03
Also published as: AU3848500A

Abstract

A direct electrostatic printing device and method for printing an image to an information carrier with improved harmonization of the printed density when each aperture addresses more than one dot position. The harmonization of the printed density from different apertures is accomplished by a method of modifying at least one dot position, and not more than all but one dot positions, addressed by an aperture. A number of different options of which dot positions are modified and how they are modified, exists.

Description

DIRECT ELECTROSTATIC PRINTING METHOD AND APPARATUS

FIELD OF THE INVENTION

The present invention relates to direct electrostatic printing methods in which charged toner particles are transported under control from a particle source in accordance with an image information to form a toner image used in a copier, a printer, a plotter, a facsimile, or the like.

BACKGROUND TO 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 one or more rows with a plurality of apertures in each, through which apertures toner particles are selectively transported from a particle source to an image receiving medium due to control in accordance with an image information.

However, it can be considered a drawback of current single and multiple row direct electrostatic printing methods that there is a somewhat different perceived image density for the same desired image density, of dots printed by different apertures. SUMMARY OF THE INVENTION

An object of the present invention is to provide a method of and a device for diminishing perceived image density variations of dots printed by different apertures in direct electrostatic printing methods.

Another object of the present invention is to provide a method of and device for reducing or eliminating perceived uneven image density in direct electrostatic printing methods .

Said objects are achieved according to the invention by providing a direct electrostatic printing device and method for printing an image to an information carrier with improved harmonization of the printed density when each aperture addresses more than one dot position. The harmonization of the printed density from different apertures is accomplished by a method of modifying at least one dot position, and not more than all but one dot positions, addressed by an aperture. A number of different options of which dot positions are modified and how they are modified, exists.

Said objects are also achieved according to the invention by providing a direct electrostatic printing device including a pigment particle delivery, a voltage source, a printhead structure, and a control unit. The pigment particle delivery providing pigment particles. An image receiving member and the printhead structure are moving relative to each other during printing thereby creating a relative movement between the image receiving member and the printhead structure. The image receiving member having a first face and a second face. The printhead structure being placed in between the pigment particle delivery and the first face of the image receiving member. The voltage source being connected to the pigment particle delivery and the back electrode thereby creating an electrical field for transport of pigment particles from the pigment particle delivery toward the first face of the image receiving member. The printhead structure including control electrodes connected to the control unit to thereby selectively open or close apertures through the printhead structure to permit or restrict the transport of pigment particles. The printhead structure further including deflection electrodes connected to the control unit for controlling the deflection of pigment particles in transport by means of predetermined deflection voltages to thereby be able to deflect pigment particles against predetermined locations . Each aperture in question being arranged for placing pigment particles at at least two different dot positions adjacent each other in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member, to thereby enable the formation of a pigment image on the first face of the image receiving member. According to the invention the control unit in a predetermined manner modifies the control of the amount of pigment particles to be transported through at least one aperture when addressing at least one dot position and at most all but one dot position that an aperture in question can address.

Advantageously each aperture in question is arranged for placing pigment particles at two different dot positions adjacent each other in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member.

In some embodiments the apertures are aligned in at least two rows in a direction mainly perpendicular to the relative movement between the image receiving member and the printhead structure. In such embodiments the predetermined modification can preferably include one or more apertures that are in a row situated most upstream in relation to the pigment particle delivery. Preferably the predetermined manner in which the control of the amount of pigment particles to be transported is modified, of one or more apertures situated in a row most upstream in relation to the pigment particle delivery, is by reducing the amount. In certain cases it is suitable that the control of the amount of pigment particles to be transported is reduced by controlling the amount by a factor of less than one. In other cases it is suitable that the predetermined manner in which the control of the amount of pigment particles to be transported is modified, of one or more apertures situated in a row most upstream in relation to the pigment particle delivery, is by reducing the amount of pigment particles to be transported to zero.

In some embodiment the predetermined modification includes one or more apertures that are in a row situated downstream in relation to the pigment particle delivery. Suitably the predetermined manner in which the control of the amount of pigment particles to be transported is modified, of one or more apertures situated in a row downstream in relation to the pigment particle delivery, is by increasing the amount. Preferably the control of the amount of pigment particles to be transported is increased by controlling the amount by a factor greater than one .

In some embodiments according to the invention the predetermined modification is of one or more addressed dot positions of an aperture in question, which dot positions only have adjacent dot positions which are addressed by the same aperture in question.

In some versions each aperture in question is arranged for placing pigment particles at an odd number of different dot positions adjacent each other, and in that the predetermined modification is only done on one respective center dot position.

In some embodiments the predetermined modification is only done on one or more respective center dot positions addressed by each aperture in question. Preferably the predetermined modification is only done on one or more symmetrically placed respective center dot positions addressed by each aperture in question.

In some versions the dot positions with the predetermined modification are predetermined. In other versions the dot positions with the predetermined modification are determined by analysis of an image to be printed. Preferably the determined dot positions are from among dot positions which at least have adjacent dot positions in a direction substantially perpendicular and in a direction substantially parallel to the relative movement between the printhead structure and the image receiving member, which adjacent dot positions have, in view of an image to be printed, a density.

In some versions of the invention, which dot positions comprise the predetermined modification vary in a direction substantially parallel to the relative movement between the printhead structure and the image receiving member. Suitably which dot positions comprise the predetermined modification vary in such a way that dot positions comprising the predetermined modification are only adjacent unmodified dot positions in a direction substantially parallel to the relative movement between the printhead structure and the image receiving member. In some cases which dot positions comprise the predetermined modification vary systematically in a direction substantially parallel to the relative movement between the printhead structure and the image receiving member. In other cases which dot positions comprise the predetermined modification vary randomly in a direction substantially parallel to the relative movement between the printhead structure and the image receiving member. In some versions which dot positions comprise the predetermined modification vary systematically in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member. In other versions which dot positions comprise the predetermined modification vary randomly in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member .

Advantageously the control unit controls the control electrodes to thereby individually control the amount of pigment particles transported through each aperture. The control unit can control the selective opening and closing of the apertures to thereby control the amount of pigment particles transported through each aperture. The control unit can control a voltage potential of the control electrodes of the apertures during the respective selective opening and closing of the apertures to thereby control the amount of pigment particles transported through each aperture. The control unit can control the selective opening and closing of the apertures of each row and a voltage potential of the control electrodes of the apertures during the respective selective opening and closing of the apertures to thereby control the amount of pigment particles transported through each apertures. The image receiving member can be an information carrier. Preferably the image receiving member is a transfer belt comprised in the direct electrostatic printing device where the transfer belt is positioned at a predetermined distance from the printhead structure, the transfer belt being substantially of uniform thickness, whereby a pigment image is subsequently transferred to an information carrier. The transfer belt is Preferably supported by at least one holding element arranged on the side of the second face of the transfer belt adjacent to the print station. Suitably the first face of the image receiving member, the transfer belt, is substantially evenly coated with a layer of bouncing reduction agent thus providing a surface on the first face of the image receiving member that the pigment particles transported through the print head structure substantially adhere to substantially without bouncing.

Suitably the image printing device is capable of printing color images and includes four pigment particle deliveries. In other embodiments the printing device includes at least two pigment particle deliveries with corresponding control electrodes and apertures on and in at least one printhead structure. In still other embodiments the image printing device includes four pigment particle deliveries with corresponding control electrodes and apertures on and in at least one printhead structure.

Said objects are also achieved according to the invention by providing a direct electrostatic printing device including a pigment particle delivery, a voltage source, a printhead structure, and a control unit. The pigment particle delivery providing pigment particles. An image receiving member and the printhead structure are moving relative to each other during printing thereby creating a relative movement between the image receiving member and the printhead structure. The image receiving member having a first face and a second face. The printhead structure being placed in between the pigment particle delivery and the first face of the image receiving member. The voltage source being connected to the pigment particle delivery and the back electrode thereby creating an electrical field for transport of pigment particles from the pigment particle delivery toward the first face of the image receiving member. The printhead structure including control electrodes connected to the control unit to thereby selectively open or close apertures through the printhead structure to permit or restrict the transport of pigment particles. The apertures are aligned in at least two rows in a direction mainly perpendicular to the relative movement between the image receiving member and the printhead structure. The printhead structure further including deflection electrodes connected to the control unit for controlling the deflection of pigment particles in transport by means of predetermined deflection voltages to thereby be able to deflect pigment particles against predetermined locations . Each aperture in question being arranged for placing pigment particles at at least two different dot positions adjacent each other in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member, to thereby enable the formation of a pigment image on the first face of the image receiving member. According to the invention the control unit reduces the amount of pigment particles to be transported through at least one aperture in a row situated most upstream in relation to the pigment particle delivery when addressing at least one dot position and at most all but one dot position that an aperture in question can address, by controlling the amount by a factor of less than one. And that the control unit increases the amount of pigment particles to be transported through at least one aperture in a row situated downstream in relation to the pigment particle delivery when addressing at least one dot position and at most all but one dot position that an aperture in question can address, by controlling the amount by a factor greater than one.

Preferably each aperture in question being arranged for placing pigment particles at at least three different dot positions adjacent each other in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member, and in that the dot positions with a modified pigment particle transport are the respective center dot positions, center in view of the dot positions that are adressable by a single aperture.

Further variants are possible according to the invention as previously disclosed.

Said objects are also achieved according to the invention by providing a direct electrostatic printing device including a pigment particle delivery, a voltage source, a printhead structure, and a control unit. The pigment particle delivery providing pigment particles. An image receiving member and the printhead structure are moving relative to each other during printing thereby creating a relative movement between the image receiving member and the printhead structure. The image receiving member having a first face and a second face. The printhead structure being placed in between the pigment particle delivery and the first face of the image receiving member. The voltage source being connected to the pigment particle delivery and the back electrode thereby creating an electrical field for transport of pigment particles from the pigment particle delivery toward the first face of the image receiving member. The printhead structure including control electrodes connected to the control unit to thereby selectively open or close apertures through the printhead structure to permit or restrict the transport of pigment particles. The apertures are aligned in at least two rows in a direction mainly perpendicular to the relative movement between the image receiving member and the printhead structure. The printhead structure further including deflection electrodes connected to the control unit for controlling the deflection of pigment particles in transport by means of predetermined deflection voltages to thereby be able to deflect pigment particles against predetermined locations . Each aperture in question being arranged for placing pigment particles at at least two different dot positions adjacent each other in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member, to thereby enable the formation of a pigment image on the first face of the image receiving member. According to the invention the control unit restricts to zero the pigment particles to be transported through at least one aperture in a row situated most upstream in relation to the pigment particle delivery when addressing one dot position that an aperture in question can address, by controlling the amount by a factor of less than one. The dot position or dot positions in question are from among dot positions which at least have adjacent dot positions in a direction substantially perpendicular and in a direction substantially parallel to the relative movement between the printhead structure and the image receiving member, which adjacent dot positions have a density in view of an image to be printed. Further variants are possible according to the invention as previously disclosed.

Said objects are also achieved according to the invention by a method for printing an image to an information carrier. The method comprises a number of steps. In a first step pigment particles are provided from a pigment particle delivery. In a second step an image receiving member and a printhead structure are moved relative to each other during printing. In a third step an electrical field is created for transporting pigment particles from the pigment particle delivery toward the first face of the image receiving member . In a fourth step apertures through a printhead structure are selectively opened or closed to permit or restrict the transporting of pigment particles. In a fifth step the deflection of pigment particles in transport is controlled by means of predetermined deflection voltages to thereby be able to deflect pigment particles against predetermined locations, each aperture in question being arranged for placing pigment particles at at least two different dot positions adjacent each other in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member, to thereby enable the formation of a pigment image on the first face of the image receiving member. And in a final sixth step modifying in a predetermined manner the control of the amount of pigment particles to be transported through at least one aperture when addressing at least one dot position and at most all but one dot position that an aperture in question can address, to thereby enable an even flow of pigment particles through different apertures. Further variations of the method according to previously described enhancements are possible in view of the application of the invention.

The present invention satisfies a need for density harmonization not previously met.

The present invention relates to an image recording apparatus including an image receiving member conveyed past one or more, so called, print stations to intercept a modulated stream of toner particles from each print station. A print station includes a particle delivery unit, a particle source, such as a developer sleeve, and a printhead structure arranged between the particle source and the image receiving member. The printhead structure includes means for modulating the stream of toner particles from the particle source and means for controlling the trajectory of the modulated stream of toner particles toward the image receiving member. According to a preferred embodiment of the present invention, the image recording apparatus comprises four print stations, each corresponding to a pigment colour, e.g. yellow, magenta, cyan, black (Y,M,C,K), disposed adjacent to an image receiving member formed of a seamless transfer belt made of a substantially uniformly thick, flexible material having high thermal resistance, high mechanical strength and stable electrical properties under a wide temperature range. The toner image is formed on the transfer belt according to the invention and thereafter brought into contact with an information carrier, e.g. paper, in a fuser unit, where the toner image is simultaneously transferred to and made permanent on the information carrier upon heat and pressure. After image transfer, the transfer belt is brought in contact with a cleaning unit removing untransferred toner particles . Other objects, features and advantages of the present inventions will become more apparent from the following description when read in conjunction with the accompanying drawings in which preferred embodiments of the invention are shown by way of illustrative examples.

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

Figure 4a 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 4b is a schematic section view along the section line I -I through the printhead structure shown in Figure 4a, Figure 4c is a schematic plan view of the bottom side of the printhead structure shown in Figure 4a,

Figure 5 is a schematic view of part of a printhead structure and a pigment particle source,

Figure 6 is a diagram showing fixed and dynamic control areas,

Figure 7 is a schematic view of a single aperture and its corresponding control electrode and deflection electrodes,

Figure 8a illustrates a control voltage signal as a function of time during a print cycle having three subsequent development periods,

Figure 8b illustrates a first deflection voltage signal as a function of time during a print cycle having three subsequent development periods

Figure 8c illustrates a second deflection voltage signal as a function of time during a print cycle having three subsequent development periods

Figure 9a illustrates the transport trajectory of toner particles through the printhead structure shown in Figures 4a,b, c according to a first deflection mode wherein Dl > D2 ,

Figure 9b illustrates the transport trajectory of toner particles through the printhead structure shown in Figures 4a,b, c, according to a second deflection mode wherein Dl = D2 ,

Figure 9c illustrates the transport trajectory of toner particles through the printhead structure shown in Figures 4a,b, c, according to a third deflection mode wherein Dl < D2 ,

Figure 10A illustrates dot positions from a number of apertures and their corresponding aperture variation frequency,

Figure 10B illustrates dot positions from a number of apertures modified according to one embodiment of the invention and their corresponding aperture variation frequency,

Figure 11A illustrates dot positions with modifications according to another embodiment according to the invention,

Figure 11B illustrates overlapping area coverage of dot positions,

Figure 12 illustrates a control unit,

Figure 13 illustrates a high voltage control electrode driver .

DESCRIPTION OF PREFERRED EMBODIMENTS

In order to clarify the method and device according to the invention, some examples of its use will now be described in connection with Figures 1 to 11. Figure 1 is e 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 maintaining 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 stabilization 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 induction charging of the belt and by different electric potentials on the holding elements 13 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 transfer 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 this embodiment.

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. molybdenium, 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 transfer 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 preferably 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. In other embodiments toner particles are deposited directly onto an information carrier without first being deposited onto an intermediate image receiving member.

Figure 2 is a schematic section view of one embodiment 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 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 can preferably be formed of a supply brush 51 or a roller made of or coated with a fibrous, resilient material. The supply brush 51 can suitably in some embodiments be 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 which can, for example, be coated with a conductive material, and preferably have 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 (Q/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. In some embodiments the metering element 53 also suitably contributes to the charging of the toner particles. 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 distribution and mass 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 maintaining 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 stabilization force component 30. The stabilization force component 30 is intended to counteract, among other things, a field force component 31 which is acting on the transfer belt. 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.

Figure 3 is an enlargement of the print zone in a print station of, for example, the image recording apparatus shown in Figure 1. A 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 a peripheral surface of a developer sleeve 52 and a bottom portion of a support device 54. The substrate layer 60 has a top surface facing a toner layer 7 on the peripheral surface of the developer sleeve 52. The substrate layer 60 has a bottom surface facing the bottom portion of the support device 54. Further, the substrate layer 60 has a plurality of apertures 61 arranged through the substrate layer 60 in a part of the substrate layer 60 overlying a elongated slot in the bottom portion of the support device 54. The printhead structure 6 further preferably 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 at least 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. In 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 through the transfer belt 10. The cleaning area preferably comprises at least one row of slots, and more specifically two to eight interlaced rows of slots. 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 in the holding element 13. The transfer passage 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 minimum distance between the printhead structure 6 and the transfer belt 10. In some embodiments it can be advantageous to have a controllable passage which can open and close access of the pressure difference to the transfer passage. Thereby a suction pressure will not increase the transfer belt's friction on the holding element 13 more than necessary. The controllable passage 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 also 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 is substantially located symmetrically in relation to the apertures . In other embodiments according to the invention the transfer passage is shifted in relation to the direction of movement of the transfer belt 10.

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 4a, 4b and 4c. 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 lOOμm to 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 central 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 4a, 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, among other things, decrease the influence on the toner layer and to electrically shield 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.

As mentioned previously, an uneven supply of pigment particles to the apertures may arise. If different apertures have a different amount of pigment particles available, then the amount of toner/pigment particles transported, and thus a printed density, through these apertures will be different for the same desired density. Even if different apertures may have a sufficient amount of pigment particles available, the pigment particles might be of different qualities, i.e. the force and/or the time needed to release the pigment particles from a pigment particle source might differ. One possible reason for an uneven availability and quality of pigment particles to different apertures can be that the apertures commonly are arranged in two or more rows.

Figure 5 shows a very rough schematic of a printhead structure with two rows 231, 232 of apertures 230, a pigment particle source/delivery 210 having a first rotational direction 211, a back electrode 220 with a possible second rotational direction 221, and an image receiving member 240 such as an intermediate image receiving member, a transfer belt, or information carrier, having a directional movement 241.

The row 231 of apertures that the pigment particle source 210 reaches first, so to speak, will have a full nominal supply of pigment particles available, and of a high quality, i.e. easily releasable. This first row 231 can also be referred to as an upstream row 231, i.e. upstream in relation to the pigment particle source 210 and its rotational direction 211. The second 232 and further rows will have less pigment particles available if there has been some printing done by the first row 231, and the pigment particles that are left will usually be of a "lower" quality, i.e. it will be harder to use/release the pigment particles. The second row 232 can also be referred to as a downstream row 232, i.e. downstream in relation to the pigment particle source 210 and its rotational direction 211. The lower available amount of pigment particles is, at least in part, due to that the pigment particle pick-up area of an aperture is somewhat larger than the aperture, which in turn causes the first row 231 of apertures to "steal" pigment particles from the second 232 and further rows' supply of pigment particles. If the first row 231 of apertures has stolen pigment particles from the supply of the second 232 and possible further rows then the first row 231 has stolen the easy pigment particles, i.e. the most volatile pigment particles. What is left for the second 232 and possible further rows are less volatile pigment particles, pigment particles of a lower quality. The rotational speed, size and direction of the pigment particle source/delivery 210 in relation to the direction and speed of movement of the image receiving member 240 and the distance between the rows 231, 232 will only change the relative positions of printed dots that relate as to "stealth" of pigment particles.

Figure 6 is a diagram showing fixed and dynamic control areas. A vertical axis 800 indicates a desired optical density and a horizontal axis 801 indicates an aperture control electrode open time and/or an aperture control electrode control voltage. A desired optical density 810 of a dot to be produced by an aperture belonging to a first row being situated most upstream in relation to the pigment particle delivery, corresponds to a point 820 on a first row fixed function 840, which results in a specific first time 830. The first row fixed function 840 is formed in such a way that the amount of transported pigment particles is according to the previously mentioned constraints. On the other hand if the desired optical density 810 is to be produced by an aperture belonging to a row that is situated downstream in relation to the pigment particle delivery, then this will correspond to a point 820, 822, 824 somewhere within the dynamic control area 844 delimited by the first row fixed function 840 and least available pigment particles function 842 which is due to a first row maximum density. Figure 6 discloses three different cases for an aperture of a downstream row. A first point 820 located on the first row fixed function 840, which results in a first time 830, when no other aperture has taken pigment particles from the aperture in question. This corresponds to apertures of the first row upstream. A second point 822 is located somewhere in the middle of the dynamic control area, which results in a second time 832 which indicates that the aperture has to work harder to pull all the necessary pigment particles through it. This situation arises when some pigment particles has been stolen from the aperture in question, it also being that it is the most volatile pigment particles that are stolen first. A third point 824 is located on the least available pigment particles function 842, which results in a third time 834 which indicates that the aperture has to work even harder to pull all the necessary pigment particles through it. This situation arises when apertures of rows upstream have "stolen" as many pigment particles as are allowed.

Figure 7 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 8a, 8b and 8c respectively showing the control voltage signal (V_control) , 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 print sequences with corresponding 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 electrode, 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 8a, 8b and 8c illustrates a control function wherein the toner particles have negative polarity charge. As is apparent from Figure 8a, a print cycle comprises three development periods t_b, each followed by a recovering period t_w during which new toner is supplied to the print zone. The control voltage pulse (V_control) 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 V_w of approximately -50V and a print level V_b in the order of +350V, corresponding to full density dots. Similarly, the pulse width can be varied from 0 to t_b. As apparent from Figures 8b and 8c, 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 9a, 9b and 9c illustrate the toner trajectories in three subsequent deflection modes. The figures 9a, 9b and 9c 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 9a, the modulated stream of toner particles is deflected to the left by producing a first amplitude difference (Dl > D2 ) between both deflection voltages. The amplitude difference is adjusted to address dot locations 635 located at a deflection length L_d to the left of the central axes 611 of the apertures 61. During a second development period illustrated in Figure 9b, the deflection voltages have equal amplitudes (Dl = 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 9c, the modulated stream of toner particles is deflected to the right by producing a second amplitude difference (Dl < D2 ) between both deflection voltages. The amplitude difference is adjusted to address dot locations 637 located at a deflection length L_d to the right of the central axes 611 of the apertures 61. As is apparent from the Figures 9a-c, the toner particles in question are negatively charged.

Figure 10A illustrates dot positions from a number of apertures 330, 331, 332, 333 and their corresponding aperture variation frequency 315 with respect to resulting density 310 along/parallel 320 with the apertures. When printing a number of dot positions then there will be a variation in printed density in dependence of which aperture 330, 331, 332, 333 prints a dot position. When printing on an image receiving medium then there is a direction 301 of movement between a print structure and an image receiving medium, this will cause the aperture variations to propel in the direction 301 of movement and create stripes that extend in said direction 301. The invention can suitably be implemented on printing devices that comprise dot-deflection. According to the example of Figure 10A, each aperture can address three dot positions, all of these three dot positions will be influenced by a corresponding aperture that addresses them. The invention is not restricted to the number of deflections a printing device can perform, except that there is a minimum of two dot positions addressable per aperture, i.e. each aperture will be able to traject toner particles in at least two different paths, which can, in a two deflection embodiment, be accomplished by one deflected path and one un-deflected path or it can be accomplished by two deflected paths, all in dependence on the specific implementation. As can be seen, any variations between the apertures propagate in a direction parallel to the movement 301, and thus create long stripes. It has been discovered that the eye is unfortunately more sensitive to low frequency variations than to high frequency variations, i.e. the eye is more sensitive, and will thus more easily notice, the variations of apertures in a 600 dpi dot-deflection machine with three addressable dot positions per aperture giving an aperture variation of 200 apertures per inch, than in a 400 dpi machine with no dot-deflection giving an aperture variation of 400 apertures per inch. The variations between the apertures, or rather the different behaviour of the apertures, can be due to one or more factors. These factors can, for example, be due to manufacturing of individual apertures, difference in manufacturing of apertures in different rows, difference in position of apertures in relation to toner particle feed. A symmetrical difference between apertures, as shown in Figure 10A, is most likely due to apertures being placed in two or more rows.

Figure 10B illustrates dot positions 340, 341, 342, 343 from a number of apertures 330, 331, 332, 333 that are modified according to one embodiment of the invention. Figure 10B also illustrates the corresponding aperture variation frequency 316, with respect to density 310 along 320 the apertures. This embodiment is especially suitable for printhead structures with two or more aperture rows, see for example Figure 5. This embodiment will modify one or more dot positions 340, 341, 342, 343, up to all but one, addressable by an aperture 330, 331, 332, 333. Preferably dot positions 341, 343 addressed by apertures 331, 333 in an upstream row will be modified by lowering/restricting their density by a factor, and dot positions 340, 342 addressed by apertures 330, 332 in a downstream row will be modified by raising/increasing their density by a factor. As can be seen, the aperture variation frequency 316 will thus increase by a factor of three, all other conditions being the same, in relation to that of Figure 10A. This embodiment of the invention can be said to actually hide an original defect by introducing an additional defect, the additional defect being less visible than the original defect. Another advantage with the invention is that in two or more aperture row systems there is a toner particle redistribution from upstream row apertures to downstream row apertures .

In some embodiments it can be sufficient to only modify dot positions 341, 343 addressed by apertures 331, 333 in an upstream row by lowering/restricting their density by a factor. In still other embodiments it can be sufficient to only modify dot positions 340, 342 addressed by apertures 330, 332 in a downstream row by raising/increasing their density by a factor.

In embodiments with only one aperture row it can be equally beneficial to modify one or more dot positions, preferably by modifying dot positions 341, 343 addressed by every second apertures 331, 333 by lowering/restricting their density by a factor and dot positions 340, 342 addressed by every other apertures 330, 332 by raising/increasing their density by a factor. Equally well, by only modifying one or more dot positions 341, 343 addressed by every or every second aperture or apertures 331, 333 by lowering/restricting their density by a factor, or only by modifying one or more dot positions 340, 342 addressed by every or every second aperture or apertures 330, 332 by raising/increasing their density by a factor.

Figure 11A illustrates dot positions 350 with modifications according to another embodiment according to the invention. This embodiment is especially suitable for dot positions surrounded by other dot positions with a density. When printing an area with a density, one or more dot positions 350, up to all but one addressed by a single aperture, that are preferably addressed by apertures belonging to an upstream row, are modified by lowering/restricting their density by a factor. In some embodiments and/or situations it is preferable that the density of one or more modified dot positions is lowered to zero, i.e. the dot position will not receive any toner particles . By reducing the amount of toner particles used by apertures in an upstream aperture row then there will be more toner particles left over for apertures in one or more downstream aperture rows. Advantageously not the same dot position is modified in consequtive printed lines, to thus avoid creating any streaks or lines.

As is illustrated in Figure 11B, dot positions 350, 360, 361, 362, 363 overlap. By modifying the density of a dot position 350, the actual bare area 351 that is effected by this and not influenced by any other dot position 360, 361, 362, 363, is significantly smaller than the area a dot position covers. According to one embodiment of the invention only dot positions 350 that are overlapped by dot positions 360, 361, 362, 363 with a density separated from zero, are modified. Preferably adjacent dot positions which are parallel to the direction of movement and adjacent dot positions which are perpendicular to the direction of movement are checked with regard to a dot position which is processed to determine if the dot position in question should be modified or not.

The modification of dot positions can preferably be accomplished by the control by changing the opening and closing times of the apertures, changing the voltage potentials of the control electrodes during opening and closing, and/or by changing the electrical field created by i.a. the back electrode for the transportation of pigment particles. The control functions of a printer according to the invention is handled by a control unit which is schematically illustrated in Figure 12. The illustration of the control unit 900 is merely to give an example of one possible embodiment of the control unit 900. All the different parts may be separate as illustrated or more or less integrated. The memories 902, 903, 930 may be of an arbitrary type which will suit the embodiment in question. The control unit 900 comprises a computing part which comprises a CPU 901, program memory ROM 902, working memory RAM 903, a user I/O interface 910 through which a user will communicate 951 with the printer for downloading of commands and images to be printed, and a bus system 950 for interconnection and communication between the different parts of the control unit 900. The control unit 900 also suitably comprises a bitmap 930 for storage of the image to be printed and one or more I/O interfaces 911, 912 for control and monitoring of the printer. Further, if necessary, one or more power - high voltage drivers 921, 922, 923, 924, 925 are connected to the hardware of the printer illustrated by an interface line 999.

The one or more I/O interfaces 911, 912 for control and monitoring of the printer can logically be divided into one simple I/O interface 912 for on/off control and monitoring and one advanced I/O interface 911 for multilevel control and monitoring, speed control, and analog measurements. Typically the simple I/O interface 912 handles keyboard input 969 and feedback output 968, control of simple motors and indicators, monitoring of different switches and other feedback means. Typically the advanced I/O interface 911 will control 954, 955 the deflection voltages 964 and guard voltages 965 via high voltage drivers 924, 925. The advanced I/O interface 911 will typically

speed control 966 one or more motors with a control loop feedback 967.

A user, e.g. a personal computer, will download, through the user I/O interface 910, commands and images 951 to be printed. The CPU 901 will interpret the commands under control of its programs and typically load the images to be printed into the bitmap 930. The bitmap 930 will preferably comprise at least two logical bitmaps, one which can be printed from and one which can be used for download of the next image to be printed. The functions of the preferably at least two logical bitmaps will continuously switch when their previous function is finished.

In a preferred embodiment the bitmap 930 will serially 952 load a plurality of high voltage drive controllers 921, 922, 923 with the image information to be printed. The number of high voltage drive controllers 921, 922, 923 that are necessary will, for example, depend on the resolution and the number of apertures, i.e. control electrodes, each controller 921, 922, 923 will handle. The high voltage drive controllers 921, 922, 923 will convert the image information they receive to signals 961, 962, 963 with the proper voltage levels required by the control electrodes of the printer.

Figure 13 illustrates one possible schematic of a high voltage drive controller 940. The image information is received serially via a data input 971. The image information is clocked 972 into a serial to parallel register 941. When the serial to parallel register 941 is full the image information is latched 973 into a latch 942 at an appropriate time, thus enabling new image information to be clocked into the serial to parallel register. The controller preferably comprises high voltage drivers 943, 944, 945, 946, 947 for conversion of the image data in the latch to signals 983, 984, 985, 986, 987 with the appropriate voltage levels required by the control electrodes of the apertures. The high voltage drive controller can also suitably comprise a blanking input 974 to enable a higher degree of control of the outputs 983, 984, 985, 986, 987 to the control electrodes .

The invention is not limited to the embodiments described above but may be varied within the scope of the appended patent claims.

Claims

WHAT IS CLAIMED IS

1. A direct electrostatic printing device including a pigment particle delivery, a voltage source, a printhead structure, and a control unit, the pigment particle delivery providing pigment particles, an image receiving member and the printhead structure are moving relative to each other during printing thereby creating a relative movement between the image receiving member and the printhead structure, the image receiving member having a first face and a second face, the printhead structure being placed in between the pigment particle delivery and the first face of the image receiving member, the voltage source being connected to the pigment particle delivery and the back electrode thereby creating an electrical field for transport of pigment particles from the pigment particle delivery toward the first face of the image receiving member, the printhead structure including control electrodes connected to the control unit to thereby selectively open or close apertures through the printhead structure to permit or restrict the transport of pigment particles, the printhead structure further including deflection electrodes connected to the control unit for controlling the deflection of pigment particles in transport by means of predetermined deflection voltages to thereby be able to deflect pigment particles against predetermined locations, each aperture in question being arranged for placing pigment particles at at least two different dot positions adjacent each other in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member, to thereby enable the formation of a pigment image on the first face of the image receiving member, characterized in that the control unit in a predetermined manner modifies the control of the amount of pigment particles to be transported through at least one aperture when addressing at least one dot position and at most all but one dot position that an aperture in question can address .

2. A direct electrostatic printing device according to claim 1, characterized in that each aperture in question is arranged for placing pigment particles at two different dot positions adjacent each other in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member.

3. A direct electrostatic printing device according to claim 1 or 2 , characterized in that the apertures are aligned in at least two rows in a direction mainly perpendicular to the relative movement between the image receiving member and the printhead structure.

4. A direct electrostatic printing device according to claim 3, characterized in that the predetermined modification includes one or more apertures that are in a row situated most upstream in relation to the pigment particle delivery.

5. A direct electrostatic printing device according to claim 4, characterized in that the predetermined manner in which the control of the amount of pigment particles to be transported is modified, of one or more apertures situated in a row most upstream in relation to the pigment particle delivery, is by reducing the amount.

6. A direct electrostatic printing device according to claim 5, characterized in that the control of the amount of pigmer.t particles to be transported is reduced by controlling the amount by a factor of less than one.

7. A direct electrostatic printing device according to claim 4, characterized in that the predetermined manner in which the control of the amount of pigment particles to be transported is modified, of one or more apertures situated in a row most upstream in relation to the pigment particle delivery, is by reducing the amount of pigment particles to be transported to zero.

8. A direct electrostatic printing device according to any one of claims 3 to 7 , characterized in that the predetermined modification includes one or more apertures that are in a row situated downstream in relation to the pigment particle delivery.

9. A direct electrostatic printing device according to claim 8, characterized in that the predetermined manner in which the control of the amount of pigment particles to be transported is modified, of one or more apertures situated in a row downstream in relation to the pigment particle delivery, is by increasing the amount.

10. A direct electrostatic printing device according to claim 9 , characterized in that the control of the amount of pigment particles to be transported is increased by controlling the amount by a factor greater than one .

11. A direct electrostatic printing device according to any one of claims 1 to 10, characterized in that the predetermined modification is of one or more addressed dot positions of an aperture in question, which dot positions only have adjacent dot positions which are addressed by the same aperture in question.

12. A direct electrostatic printing device according to any one of claims 1 to 11, characterized in that each aperture in question being arranged for placing pigment particles at an odd number of different dot positions adjacent each other, and in that the predetermined modification is only done on one respective center dot position.

13. A direct electrostatic printing device according to any one of claims 1 to 11, characterized in that the predetermined modification is only done on one or more respective center dot positions addressed by each aperture in question.

14. A direct electrostatic printing device according to claim 13, characterized in that the predetermined modification is only done on one or more symmetrically placed respective center dot positions addressed by each aperture in question.

15. A direct electrostatic printing device according to any one of claims 1 to 14, characterized in that the dot positions with the predetermined modification are predetermined.

16. A direct electrostatic printing device according to any one of claims 1 to 14, characterized in that the dot positions with the predetermined modification are determined by analysis of an image to be printed.

17. A direct electrostatic printing device according to claim 16, characterized in that the determined dot positions are from among dot positions which at least have adjacent dot positions in a direction substantially perpendicular and in a direction substantially parallel to the relative movement between the printhead structure and the image receiving member, which adjacent dot positions have, in view of an image to be printed, a density.

18. A direct electrostatic printing device according to any one of claims 1 to 15, characterized in that which dot positions comprise the predetermined modification vary in a direction substantially parallel to the relative movement between the printhead structure and the image receiving member.

19. A direct electrostatic printing device according to claim 18, characterized in that which dot positions comprise the predetermined modification vary in such a way that dot positions comprising the predetermined modification are only adjacent unmodified dot positions in a direction substantially parallel to the relative movement between the printhead structure and the image receiving member.

20. A direct electrostatic printing device according to claim 18 or 19, characterized in that which dot positions comprise the predetermined modification vary systematically in a direction substantially parallel to the relative movement between the printhead structure and the image receiving member .

21. A direct electrostatic printing device according to claim 18 or 19, characterized in that which dot positions comprise the predetermined modification vary randomly in a direction substantially parallel to the relative movement between the printhead structure and the image receiving member .

22. A direct electrostatic printing device according to any one of claims 18 to 21, characterized in that which dot positions comprise the predetermined modification vary systematically in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member.

23. A direct electrostatic printing device according to any one of claims 18 or 21, characterized in that which dot positions comprise the predetermined modification vary randomly in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member.

24. A direct electrostatic printing device according to any one of claims 1 to 23, characterized in that the control unit controls the control electrodes to thereby individually control the amount of pigment particles transported through each aperture .

25. A direct electrostatic printing device according to any one of claims 1 to 23, characterized in that the control unit controls the selective opening and closing of the apertures to thereby control the amount of pigment. particles transported through each aperture.

26. A direct electrostatic printing device according to any one of claims 1 to 23, characterized in that the control unit controls a voltage potential of the control electrodes of the apertures during the respective selective opening and closing of the apertures to thereby control the amount of pigment particles transported through each aperture .

27. A direct electrostatic printing device according to any one of claims 1 to 23, characterized in that the control unit controls the selective opening and closing of the apertures of each row and a voltage potential of the control electrodes of the apertures during the respective selective opening and closing of the apertures to thereby control the amount of pigment particles transported through each apertures .

28. A direct electrostatic printing device according to any one of claims 1 to 27, characterized in that the image receiving member is an information carrier.

29. A direct electrostatic printing device according to any one of claims 1 to 27, characterized in that the image receiving member is a transfer belt comprised in the direct electrostatic printing device where the transfer belt is positioned at a predetermined distance from the printhead structure, the transfer belt being substantially of uniform thickness, whereby a pigment image is subsequently transferred to an information carrier.

30. A direct electrostatic printing device according to claim 29, characterized in that the transfer belt is supported by at least one holding element arranged on the side of the second face of the transfer belt adjacent to the print station.

31. A direct electrostatic printing device according to claim 29, characterized in that the first face of the image receiving member, the transfer belt, is substantially evenly coated with a layer of bouncing reduction agent thus providing a surface on the first face of the image receiving member that the pigment particles transported through the print head structure substantially adhere to substantially without bouncing.

32. A direct electrostatic printing device according to any one of claims 1 to 31, characterized in that the image printing device is capable of printing color images and includes four pigment particle deliveries.

33. A direct electrostatic printing device according to any one of claims 1 to 31, characterized in that the printing device includes at least two pigment particle deliveries with corresponding control electrodes and apertures on and in at least one printhead structure.

34. A direct electrostatic printing device according to any one of claims 1 to 31, characterized in that the image printing device includes four pigment particle deliveries with corresponding control electrodes and apertures on and in at least one printhead structure.

35. A direct electrostatic printing device including a pigment particle delivery, a voltage source, a printhead structure, and a control unit, the pigment particle delivery providing pigment particles, an image receiving member and the printhead structure are moving relative to each other during printing thereby creating a relative movement between the image receiving member and the printhead structure, the image receiving member having a first face and a second face, the printhead structure being placed in between the pigment particle delivery and the first face of the image receiving member, the voltage source being connected to the pigment particle delivery and the back electrode thereby creating an electrical field for transport of pigment particles from the pigment particle delivery toward the first face of the image receiving member, the printhead structure including control electrodes connected to the control unit to thereby selectively open or close apertures through the printhead structure to permit or restrict the transport of pigment particles, the apertures being aligned in at least two rows in a direction mainly perpendicular to the relative movement between the image receiving member and the printhead structure, the printhead structure further including deflection electrodes connected to the control unit for controlling the deflection of pigment particles in transport by means of predetermined deflection voltages to thereby be able to deflect pigment particles against predetermined locations, each aperture in question being arranged for placing pigment particles at at least two different dot positions adjacent each other in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member, to thereby enable the formation of a pigment image on the first face of the image receiving member, characterized in that the control unit reduces the amount of pigment particles to be transported through at least one aperture in a row situated most upstream in relation to the pigment particle delivery when addressing at least one dot position and at most all but one dot position that an aperture in question can address, by controlling the amount by a factor of less than one, and in that the control unit increases the amount of pigment particles to be transported through at least one aperture in a row situated downstream in relation to the pigment particle delivery when addressing at least one dot position and at most all but one dot position that an aperture in question can address, by controlling the amount by a factor greater than one.

36. A direct electrostatic printing device according to claim 35, characterized in that each aperture in question being arranged for placing pigment particles at at least three different dot positions adjacent each other in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member, and in that the dot positions with a modified pigment particle transport are the respective center dot positions, center in view of the dot positions that are adressable by a single aperture.

37. A direct electrostatic printing device according to claim 35, characterized in that each aperture in question is arranged for placing pigment particles at two different dot positions adjacent each other in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member .

38. A direct electrostatic printing device including a pigment particle delivery, a voltage source, a printhead structure, and a control unit, the pigment particle delivery providing pigment particles, an image receiving member and the printhead structure are moving relative to each other during printing thereby creating a relative movement between the image receiving member and the printhead structure, the image receiving member having a first face and a second face, the printhead structure being placed in between the pigment particle delivery and the first face of the image receiving member, the voltage source being connected to the pigment particle delivery and the back electrode thereby creating an electrical field for transport of pigment particles from the pigment particle delivery toward the first face of the image receiving member, the printhead structure including control electrodes connected to the control unit to thereby selectively open or close apertures through the printhead structure to permit or restrict the transport of pigment particles, the apertures being aligned in at least two rows in a direction mainly perpendicular to the relative movement between the image receiving member and the printhead structure, the printhead structure further including deflection electrodes connected to the control unit for controlling the deflection of pigment particles in transport by means of predetermined deflection voltages to thereby be able to deflect pigment particles against predetermined locations, each aperture in question being arranged for placing pigment particles at at least two different dot positions adjacent each other in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member, to thereby enable the formation of a pigment image on the first face of the image receiving member, characterized in that the control unit restricts to zero the pigment particles to be transported through at least one aperture in a row situated most upstream in relation to the pigment particle delivery when addressing one dot position that an aperture in question can address, by controlling the amount by a factor of less than one, the dot position or dot positions in question are from among dot positions which at least have adjacent dot positions in a direction substantially perpendicular and in a direction substantially parallel to the relative movement between the printhead structure and the image receiving member, which adjacent dot positions have a density in view of an image to be printed.

39. A direct electrostatic printing device according to claim 38, characterized in that each aperture in question is arranged for placing pigment particles at two different dot positions adjacent each other in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member .

40. A method for printing an image to an information carrier, characterized in that the method comprises the following steps:

- providing pigment particles from a pigment particle delivery; moving an image receiving member and a printhead structure relative to each other during printing;

- creating an electrical field for transporting pigment particles from the pigment particle delivery toward a first face of the image receiving member; selectively opening or closing apertures through the printhead structure to permit or restrict the transporting of pigment particles - controlling the deflection of pigment particles in transport by means of predetermined deflection voltages to thereby be able to deflect pigment particles against predetermined locations, each aperture in question being arranged for placing pigment particles at at least two different dot positions adjacent each other in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member, to thereby enable the formation of a pigment image on the first face of the image receiving member modifying in a predetermined manner the control of the amount of pigment particles to be transported through at least one aperture when addressing at least one dot position and at most all but one dot position that an aperture in question can address; to thereby enable an even flow of pigment particles through different apertures.