WO2001087628A1

WO2001087628A1 - Direct electrostatic printing method and apparatus

Info

Publication number: WO2001087628A1
Application number: PCT/SE2000/000990
Authority: WO
Inventors: Agneta Sandberg
Original assignee: Array Ab Publ.; Matsushita Electric Industrial Co., Ltd.
Priority date: 2000-05-18
Filing date: 2000-05-18
Publication date: 2001-11-22
Also published as: AU2000260309A1

Abstract

A direct electrostatic printing device and method for printing an image with improved printing speed without degradation in printing quality. A length of time of print sequences are restricted to be at least substantially equal a length of time a substantial part of a toner jet is travelling in a volume which comprise influential forces such as deflection forces above a predetermined value, to enable dot degradation due to increased printing speed to be eliminated or at least reduced. Refinements to enable the reduction of the volume are also disclosed. Preferably a length of time of the print sequences are also shorter than a length of time a toner jet is travelling from a pigment particle delivery to an image receiving medium to ensure high printing speeds.

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 row. 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.

According to such a method, each single aperture is utilized to address a specific dot position of the image in a transverse direction, i.e. perpendicular to print media motion. Thus, the transversal print addressability is limited by the density of apertures through the printhead structure. For instance, a print addressability of 300 dpi requires a printhead structure having 300 apertures per inch in a transversal direction.

A new concept of direct electrostatic printing, hereinafter referred to as dot deflection control (DDC) , is disclosed in U.S. Patent No. 5,847,733. According to the DDC method, each single aperture is used to address several dot positions on an information carrier by controlling not only the transport of toner particles through the aperture, but also their transport trajectory toward a paper, and thereby the location of the obtained dot. The DDC method increases the print addressability without requiring a larger number of apertures in the printhead structure. This is achieved by providing the printhead structure with at least two sets of deflection electrodes connected to variable deflection voltages which, during each print cycle, sequentially modify the symmetry of the electrostatic control fields to deflect the modulated stream of toner particles in predetermined deflection directions. For instance, a DDC method performing three deflection steps per print cycle, provides a print addressability of 600 dpi utilizing a printhead structure having 200 apertures per inch.

In direct electrostatic printing methods a plurality of apertures, each surrounded by a control electrode, are preferably arranged in parallel rows extending transversally across the print zone, i.e. substantially perpendicular to the motion of the image receiving medium. As a pixel position on the image receiving medium passes beneath a corresponding aperture, the control electrode associated with this aperture is set on a print potential allowing the transport of toner particles through the aperture to form a toner dot at that pixel position. Accordingly, transverse image lines can be printed by simultaneously activating several apertures of the same aperture row, and longitudinal image lines can be printed by sequentially activating at least one aperture when pixel positions in question passes beneath the at least one aperture.

However, it can be considered a drawback of current direct electrostatic printing methods that it is difficult to increase a printing speed, in particular when dot deflection control is used, and especially without degrading the print quality. Therefore, there seems to still exist a need to improve the current direct electrostatic printing method.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method of and a device for improving the printing speed when using direct electrostatic printing methods .

Another object of the present invention is to provide a method of and device for improving the printing speed in direct electrostatic printing methods when dot deflection control and/or size control is used.

A further object of the present invention is to provide a method of and device for enabling a high speed printing in deflection control and/or size control 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 with improved printing speed without degradation in printing quality. According to the invention it has been discovered that by restricting a length of time of the print sequences to be at least substantially equal a length of time a substantial part of a toner jet is travelling in a volume which comprise influential forces, such as deflection forces, above a predetermined value, dot degradation due to increased printing speed can be eliminated or at least reduced. Refinements to enable the reduction of the volume according to the invention are also disclosed. Preferably a length of time of the print sequences are also shorter than a length of time a toner jet is travelling from a pigment particle delivery to an image receiving medium to ensure high printing speeds, i.e. a subsequent print sequence is started and a subsequent toner jet's travelling is initiated before a present toner jet has arrived/landed at an image receiving medium.

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 during a print sequence in the form of toner jets, at least one print sequence is included in a print cycle, to thereby enable the formation of a pigment image on the first face of the image receiving member. And in a final fifth step controlling a length of time of each

■ print sequence to be at least substantially equal a length of time a substantial part of a toner jet is travelling in a volume which comprise influential forces, such as deflection forces, above a predetermined value, thereby enabling high speed printing.

In one preferred embodiment at least two print sequences are included in a print cycle and the method further comprises an optional step where the deflection of toner jets in transport is controlled by means of predetermined deflection voltages related to each one of the print sequences to thereby be able to deflect toner jets against predetermined locations, each aperture in question being arranged for placing toner jets at different dot positions in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member during each print sequence, to thereby enable the formation of a pigment image on the first face of the image receiving member, and the influential forces above a predetermined value comprise deflection forces .

In other embodiments, the method further comprises, alone or in combination with other embodiments, the step of controlling the focusing of toner jets in transport by means of predetermined focusing voltages related to each one of the print sequences to thereby be able to adjust a size of placed toner jets dot position, and the influential forces above a predetermined value comprise focusing forces .

Further variations of the method according to the invention will be described below. The enhancements are possible to mix arbitrarily in view of the specific embodiment .

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 during a print sequence in the form of toner jets, at least one print sequence is included in a print cycle. The printhead structure preferably also further including deflection electrodes connected to the control unit for controlling toner jets in transport by means of predetermined voltages, 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 controls a length of time of each print sequence to be at least substantially equal a length of time a substantial part of a toner jet is travelling in a volume which comprise influential forces, such as deflection forces, above a predetermined value, thereby enabling high speed printing.

In one preferred embodiment at least two print sequences are included in a print cycle, and the deflection electrodes connected to the control unit are for controlling the deflection of toner jets in transport by means of predetermined deflection voltages to thereby be able to deflect toner jets against predetermined locations, each aperture in question being arranged for placing toner jets at different dot positions in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member during each print sequence, to thereby enable the formation of a pigment image on the first face of the image receiving member, and where the influential forces above a predetermined value comprise deflection forces .

In other embodiments, alone or in combination, the deflection electrodes connected to the control unit are for controlling the focusing of toner jets in transport by means of predetermined focusing voltages to thereby be able to focus toner jets, and where the influential forces above a predetermined value comprise focusing forces.

Further variations of the device according to the invention will be described below. The enhancements can be mixed arbitrarily in view of the specific application of the invention.

The present invention satisfies a need for higher printing speeds not previously met, by enabling a toner jet to land at a predetermined dot location substantially without tailing.

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 color, e.g. yellow, magenta, cyan, black (Y,M,C,K), disposed adjacent to an intermediate image receiving member either 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 or formed of a drum. The toner image is formed on the intermediate image receiving member 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 transferred to and made permanent on the information carrier, preferably by means of heat and pressure. After image transfer, the intermediate image receiving member 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

Fig. 1 is a schematic section view across an image recording apparatus according to a preferred embodiment of the invention,

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

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

Fig. 4 is a schematic view of a single aperture and its corresponding control electrode and deflection electrodes,

Fig. 5a illustrates a control voltage signal as a function of time during a print cycle having three subsequent development periods,

Fig. 5b illustrates a first deflection voltage signal as a function of time during a print cycle aving three subsequent development periods

Fig. 5c illustrates a second deflection voltage signal as a function of time during a print cycle having three subsequent development periods Fig. 6a illustrates the transport trajectory of toner particles according to a first deflection mode wherein Dl > D2 ,

Fig. 6b illustrates the transport trajectory of toner particles according to a second deflection mode wherein Dl = D2 ,

Fig. 6c illustrates the transport trajectory of toner particles according to a third deflection mode wherein Dl < D2 ,

Fig. 7a illustrates a deflection horizontal E-field overlaid on a print zone,

Fig. 7b illustrates a toner jet,

Fig. 8a illustrates a first deflection field concentrator according to the invention,

Fig. 8b illustrates a second deflection field concentrator according to the invention,

Fig. 9 illustrates a control unit,

Fig. 10 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 10. 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, which preferably also acts as background electrodes . 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, another preferred embodiment uses a drum as an intermediate image receiving member. The at least one support roller 12 is provided with a mechanism for maintaining the transfer belt 10 in the described embodiment 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 arcuate 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 transfer 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 polymer 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 or drum 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 or drum can also in certain embodiments comprise a special registration area for use of determining the position of the transfer belt or drum, especially an image area if available, in relation to each print station. If the transfer belt or drum comprises a special registration area then this area is preferably at least spatially related to an image area.

The transfer belt 10 is conveyed, or a drum is rotated, 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. molybdenum, 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 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/toner 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 deflection electrodes can be used for deflection and/or focusing, i.e. size control of a printed dot.

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 or drum 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 or drum by means of the cleaning area comprising at least one slot/hole through the transfer belt 10 or drum. 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 .

Figure 4 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.

According to a preferred embodiment, an improved dot deflection control method provides a simultaneous dot size and dot position control . This method utilizes the deflection electrodes to influence the convergence of the modulated stream of toner particles thus controlling the dot size, also called focusing. Each aperture is surrounded by two deflection electrodes connected to respective deflection voltages Dl, D2, such that the electrostatic control field generated by the control electrode remains substantially symmetrical as long as both deflection voltages Dl, D2 have the same amplitude. The amplitude of Dl and D2 are modulated to apply converging forces on toner particles as they are transported toward the image receiving medium, thus providing smaller dots. The dot position is simultaneously controlled by modulating the amplitude difference between Dl and D2 to deflect the toner trajectory toward predetermined dot positions. In some embodiments the deflection electrodes only control dot size and are not used for dot position control.

A dot deflection control function is illustrated in Figures 5a, 5b and 5c respectively showing the control voltage signal (V_oontrol) , 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 5a, 5b and 5c illustrates a control function wherein the toner particles have negative polarity charge. As is apparent from Figure 5a, 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 5b and 5c, 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 6a, 6b and 6c illustrate the toner trajectories in three subsequent deflection modes. The figures 6a, 6b and 6c 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 6a, 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 6b, 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 6c, the modulated stream of toner particles is deflected to the right by producing 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 6a-c, the toner particles in question are negatively charged.

A problem of increasing a printing speed is that the time of the print sequences must be as short as possible. This has lead to problems with misalignment of desired dot locations 635, 636, 637 at worst, to only a degradation in dot quality by dot tailing or scattering at best. These problems with misalignments and dot quality degradation are at least partly due to a poor understanding of the mechanisms of toner jet flight. To gain a maximum print speed without the above mentioned deficiencies a length of time of each print sequence is, according to the invention, controlled to be at least substantially equal a length of time a substantial part of a toner jet is travelling in a volume which comprise influential forces, such as deflection forces, above a predetermined value. If a print sequence is not of such a length of time, then dot tails can appear due to deflection forces of a subsequent print sequence being able to influence a toner jet in question. Likewise scattering of dots can appear due to focusing forces of subsequent print sequences being able to influence a toner jet in question. The reason a toner jet in question could be influenced by subsequent influential forces is that the toner jet in question has not had time enough to exit a vlume within which the forces are above a predetemined level . According to the invention the time of print sequences is controlled in relation to the amount of time a toner jet Figure 7a illustrates a deflection horizontal E-field overlaid on a print zone. Illustrated is a toner layer 7, a substrate layer 60 with an aperture 61 for passage of toner jets and an intermediate image receiving member 10 such as a transfer belt for reception of toner jets. Overlaid is a deflection horizontal E-field 700 function 710 between the intermediate image receiving member 10 and the toner layer 7 along a distance axis 701. The E- field function 710 will create deflection forces above a predetermined level in a volume acting on toner jets passing through the volume. The volume will be defined by how the function 710 varies in different directions, i.e. as the function 710 turns around a, in an aperture 61 symmetrically placed, distance axis 701. The illustrated E-field function 710 is along a deflection direction Rl or R2 according to Figure 4. Marked in the figure is a maximum 719 E-field that influences a toner jet passing from the toner layer 7 through the aperture 61 towards the transfer belt 10. The predetermined value 711 which the deflection forces are above is also illustrated. The predetermined value will differ from application to application but can typically be 50% of the maximum deflection force 719 and preferably down to somewhere around 10% of the maximum deflection force 719. The predetermined value 711 will define a first point 712 where a toner jet enters the volume with a deflection force above the predetermined value 711, and a second point 713 where a toner jet exits the volume with deflection force above the predetermined value 711. These points 712, 713 will of course vary in dependence on how far from a center axis the toner jet exits the volume.

Figure 7b illustrates a toner jet 750 having just passed an aperture 61 of a substrate layer 60, travelling from a toner layer 7 to an intermediate image receiving member 10. As can be seen in the figure, the toner jet 750 is not an ideal sphere of toner particles but instead elongated and somewhat cigar-shaped. This is due to many different factors, such as the release properties of the toner layer 7.

As mentioned, a length of time of each print sequence is, according to the invention, controlled to be at least substantially equal a length of time a substantial part of a toner jet is travelling in a volume which comprise deflection forces above a predetermined value. Advantageously in some methods according to the invention the length of time of each print sequence is controlled to be substantially equal or less than a length of time a substantial part of a toner jet is travelling from the pigment particle delivery to the first face of the image receiving member. Then preferably the length of time a substantial part of a toner jet is travelling from the pigment particle delivery to the first face of the image receiving member, is the difference between a point in time when a bulk of the toner jet starts to leave the pigment particle delivery, and a point in time when the bulk of the toner jet has arrived at the first face of the image receiving member .

According to other methods the length of time of each print sequence is controlled to be substantially equal or less than a length of time a substantial part of a toner jet is travelling from an aperture in question to the first face of the image receiving member. Then preferably the length of time a substantial part of a toner jet is travelling from the pigment particle delivery to the first face of the image receiving member, is the difference between a point in time when a bulk of the toner jet starts to enter an aperture in question, and a point in time when the bulk of the toner jet has arrived at the first face of the image receiving member.

In still other methods the length of time of each print sequence is controlled to be substantially equal or equal a length of time a substantial part of a toner jet is travelling in a volume which comprise deflection forces above a predetermined value. Then preferably the length of time a substantial part of a toner jet is travelling in a volume which comprise deflection forces above a predetermined value, is the difference between a point in time when a bulk of the toner jet starts to enter the volume where the deflection forces are above a predetermined value, and a point in time when the bulk of the toner jet has left the volume.

Indicated in Figure 7b are two markings 751, 759 which indicate a begining 759 and an end 751 of a bulk of a toner jet 750. In some applications it is advantageous that the bulk of a toner jet is 50% or more of the pigment particles of the toner jet, in other applications it is preferable that the bulk of a toner jet is 80% or more of the pigment particles of the toner jet. In some applications it is preferable that the bulk of a toner jet starts 759 after at least 5% of the pigment particles of the toner jet, i.e. the point in time a bulk of a toner jet starts to enter the volume is when at least 5% of the pigment particles of the toner jet has entered. In other applications the point in time a bulk of a toner jet starts to enter the volume is when at most 5% of the pigment particles of the toner jet has entered.

According to some methods the deflection substantially only acts on a toner jet when the tonerjet in question is within a corresponding volume which influences the toner jet by deflection forces. In other methods the deflection only acts on a toner jet when the tonerjet in question is within a corresponding volume which influences the toner jet by deflection forces.

Preferably a length of time of the deflection of a tonerjet is substantially equal, equal, or less the length of time of a corresponding print sequence.

Advantageously in an application of the invention a start time of the deflection of a tonerjet is delayed in relation to a start time of its corresponding print sequence .

An enhancement of the invention to enable a quicker printing is by reducing the length of time a substantial part of a toner jet is travelling in a volume which comprise deflection forces which deflection forces will influence pigment particles of a toner jet within the volume. Advantageously the length of time a substantial part of a toner jet is travelling in a volume which comprise deflection forces which deflection forces will influence pigment particles of a toner jet within the volume is less than 200μs, preferably less than lOOμs.

In some methods according to the invention the length of time a substantial part of a toner jet is travelling in a volume which comprise deflection forces, which deflection forces will influence pigment particles of a toner jet within the volume, is reduced by reducing the length of the volume in a direction of toner jet travel. Advantageously the length of the volume in a direction of toner jet travel is less than 300μm, and in some embodiments less than 200μm, and in other embodiments less than lOOμm. According to some methods according to the invention the length of time a substantial part of a toner jet is travelling in a volume which comprise deflection forces, which deflection forces will influence pigment particles of a toner jet within the volume, is reduced by reducing the volume. Advantageously the volume, and also the length of the volume is reduced by shielding the deflection forces. Figure 8a illustrates a print zone with a first deflection field concentrator 850 according to the invention. Illustrated is a toner layer 7, a substrate layer 60 with an aperture 61 for passage of toner jets, control 62 and deflection 63 electrodes in association with the aperture 61 and an intermediate image receiving member 10 such as a transfer belt for reception of toner jets. According to a first method the shielding of the deflection forces is done on a face of the printhead structure facing the first face of the image receiving member 10. This is preferably accomplished according to the invention by adding a deflection field concentrator 850 as illustrated, on the substrate layer surface facing the intermediate image receiving member 10. As can be seen a first point 712 where a toner jet enters the volume with a deflection force above a predetermined value, and a second point 713 where a toner jet exits the volume with deflection force above the predetermined value are now much closer together, i.e. the volume has become smaller. To be observed is that these points 712, 713 will of course vary in dependence on how far from a center axis the toner jet exits the volume.

Figure 8b illustrates a print zone with a second deflection field concentrator 851 according to the invention. Illustrated is a toner layer 7, a substrate layer 60 with an aperture 61 for passage of toner jets, control 62 and deflection 63 electrodes in association with the aperture 61 and an intermediate image receiving member 10 such as a transfer belt for reception of toner jets. According to a second method the shielding of the deflection forces is done within the printhead structure. This is preferably accomplished according to the invention by adding a deflection field concentrator 851 as illustrated, within the substrate layer 60, and specifically between the control 62 and the deflection 63 electrodes. As can be seen a first point 712 where a toner jet enters the volume with a deflection force above a predetermined value, and a second point 713 where a toner jet exits the volume with deflection force above the predetermined value are now much closer together, i.e. the volume has become smaller. To be observed is that these points 712, 713 will of course vary in dependence on how far from a center axis the toner jet exits the volume.

Another method according to the invention of reducing the length of time a substantial part of a toner jet is travelling in a volume which is influenced by deflection forces, is by increasing the speed of the toner jet. In some application the speed of the toner jet is advantageously more than 1 m/s, in others the speed of the toner jet is more than 2 m/s, and in still others the speed of the toner jet is preferably more than 3 m/s. One method according to the invention of attaining an increased speed of the toner jet is by increasing a charge of the pigment particles. Advantageously the charge of the pigment particles is more than 5 μC/g. In some embodiments the charge of the pigment particles is preferably more than 10 μC/g. In other embodiments the charge of the pigment particles is preferably more than 15 μC/g or 20 μC/g. The speed of the toner jet can be achieved by increasing the electrical field. In some applications the electrical field is advantageously more than 1 V/μm, in other preferably more than 3 V/μm, in still other preferably more than 6 V/μm. However, in all applications it is preferable that the electrical field is less than 15 V/μm.

Other methods of reducing the length of time a substantial part of a toner jet is travelling in a volume which comprise deflection forces which deflection forces will influence pigment particles of a toner jet within the volume, is by decreasing the extension of the toner jet, i.e. concentrating the bulk of the toner jet. This can according to the invention advantageously be achieved by improving pigment particle release from the pigment particle delivery such that the pigment particles releases more simultaneously from the pigment particle delivery, thus creating a less elongated toner jet.

The control functions of a printer according to the invention is handled by a control unit which is schematically illustrated in Figure 9. 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 also 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 10 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 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 during a print sequence^ in the form of toner jets, at least one print sequence is included in a print cycle, to thereby enable the formation of a pigment image on the first face of the image receiving member;

- controlling a length of time of each print sequence to be at least substantially equal a length of time a substantial part of a toner jet is travelling in a volume which comprise influential forces above a predetermined value; thereby enabling high speed printing.

2. The method according to claim 1, characterized in that at least two print sequences are included in a print cycle and that the method further comprises the step of: - controlling the deflection of toner jets in transport by means of predetermined deflection voltages related to each one of the print sequences to thereby be able to deflect toner jets of pigment particles against predetermined locations, each aperture in question being arranged for placing toner jets at different dot positions in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member during each print sequence, to thereby enable the formation of a pigment image on the first face of the image receiving member; and the influential forces above a predetermined value comprise deflection forces.

3. The method according to claim 1 or 2 , characterized in that the method further comprises the step of: controlling the focusing of toner jets in transport by means of predetermined focusing voltages related to each one of the print sequences to thereby be able to adjust a size of placed toner jets dot position; and the influential forces above a predetermined value comprise focusing forces .

4. The method according to any one of claims 1 to 3 , characterized in that the step of controlling the length of time of each print sequence, controls the length of time of each print sequence to be substantially equal or less than a length of time a substantial part of a toner jet is travelling from the pigment particle delivery to the first face of the image receiving member.

5. The method according to claim 4, characterized in that the length of time a substantial part of a toner jet is travelling from the pigment particle delivery to the first face of the image receiving member, is the difference between a point in time when a bulk of the toner jet starts to leave the pigment particle delivery, and a point in time when the bulk of the toner jet has arrived at the first face of the image receiving member.

6. The method according to any one of claims 1 to 3 , characterized in that the step of controlling the length of time of each print sequence, controls the length of time of each print sequence to be substantially equal or less than a length of time a substantial part of a toner jet is travelling from an aperture in question to the first face of the image receiving member.

7. The method according to claim 6, characterized in that the length of time a substantial part of a toner jet is travelling from the pigment particle delivery to the first face of the image receiving member, is the difference between a point in time when a bulk of the toner jet starts to enter an aperture in question, and a point in time when the bulk of the toner jet has arrived at the first face of the image receiving member.

8. The method according to any one of claims 1 to 3 , characterized in that the step of controlling the length of time of each print sequence, controls the length of time of each print sequence to be substantially equal a length of time a substantial part of a toner et is travelling in a volume which comprise influential forces above a predetermined value.

9. The method according to any one of claims 1 to 3, characterized in that the step of controlling the length of time of each print sequence, controls the length of time of each print sequence to be equal a length of time a substantial part of a toner jet is travelling in a volume which comprise deflection forces above a predetermined value.

10. The method according to any one of claims 2, characterized in that the length of time a substantial part of a toner jet is travelling in a volume which comprise deflection forces above a predetermined value, is the difference between a point in time when a bulk of the toner jet starts to enter the volume where the deflection forces are above a predetermined value, and a point in time when the bulk of the toner jet has left the volume .

11. The method according to any one of claims 5, 7, or 10 characterized in that the bulk of a toner jet is 50% or more of the pigment particles of the toner jet.

12. The method according to claims 5, 7, or 10 characterized in that the bulk of a toner jet is 80% or more of the pigment particles of the toner jet.

13. The method according to any one of claims 10 to 12, characterized in that the point in time a bulk of a toner jet starts to enter the volume is when at least 5% of the pigment particles of the toner jet has entered.

14. The method according to any one of claims 10 to 12, characterized in that the point in time a bulk of a toner jet starts to enter the volume is when at most 5% of the pigment particles of the toner jet has entered.

15. The method according to any one of claims 1 to 14, characterized in that the predetermined value, which the deflection forces are above in the volume, is 50% of the maximum deflection force within the volume.

16. The method according to any one of claims 1 to 14, characterized in that the predetermined value, which the deflection forces are above in the volume, is 10% of the maximum deflection force within the volume.

17. The method according to any one of claims 1 to 16, characterized in that the deflection substantially only acts on a toner jet when the tonerjet in question is within a corresponding volume which influences the toner jet by deflection forces.

18. The method according to any one of claims 1 to 16, characterized in that the deflection only acts on a toner jet when the tonerjet in question is within a corresponding volume which influences the toner jet by deflection forces .

19. The method according to any one of claims 1 to 18, characterized in that a length of time of the deflection of a tonerjet is substantially equal the length of time of a corresponding print sequence.

20. The method according to any one of claims 1 to 18, characterized in that a length of time of the deflection of a tonerjet is less or equal the length of time of a corresponding print sequence.

21. The method according to any one of claims 1 to 20, characterized in that a start time of the deflection of a tonerjet is delayed in relation to a start time of its corresponding print sequence.

22. The method according to any one of claims 1 to 21, characterized in that to enable a quicker printing reducing the length of time a substantial part of a toner jet is travelling in a volume which comprise deflection forces which deflection forces will influence pigment particles of a toner jet within the volume.

23. The method according to claim 22, characterized in that the length of time a substantial part of a toner jet is travelling in a volume which comprise deflection forces which deflection forces will influence pigment particles of a toner jet within the volume is less than 200μs.

24. The method according to claim 22, characterized in that the length of time a substantial part of a toner jet is travelling in a volume which comprise deflection forces which deflection forces will influence pigment particles of a toner jet within the volume is less than lOOμs.

25. The method according to claim 22, characterized in that the length of time a substantial part of a toner jet is travelling in a volume which comprise deflection forces which deflection forces will influence pigment particles of a toner jet within the volume, is reduced by reducing the length of the volume in a direction of toner jet travel .

26. The method according to claim 25, characterized in that the length of the volume in a direction of toner jet travel is less than 300μm.

27. The method according to claim 25, characterized in that the length of the volume in a direction of toner jet travel is less than 200μm.

28. The method according to claim 25, characterized in that the length of the volume in a direction of toner jet travel is less than lOOμm.

29. The method according to claim 22, characterized in that the length of time a substantial part of a toner jet is travelling in a volume which comprise deflection forces which deflection forces will influence pigment particles of a toner jet within the volume, is reduced by reducing the volume.

30. The method according to claim 29, characterized in that the volume is reduced by shielding the deflection forces.

31. The method according to claim 30, characterized in that the shielding of the deflection forces is done within the printhead structure.

32. The method according to claim 30 or 31, characterized in that the shielding of the deflection forces is done on a face of the printhead structure facing the first face of the image receiving member.

33. The method according to claim 22, characterized in that the length of time a substantial part of a toner jet is travelling in a volume which is influenced by deflection forces, is reduced by increasing the speed of the toner jet.

34. The method according to claim 33, characterized in that the speed of the toner jet is more than 1 m/s.

35. The method according to claim 33, characterized in that the speed of the toner jet is more than 2 m/s.

36. The method according to claim 33, characterized in that the speed of the toner jet is more than 3 m/s.

37. The method according to claim 33, characterized in that the speed of the toner jet is achieved by increasing a charge of the pigment particles .

38. The method according to claim 37, characterized in that the charge of the pigment particles is more than 5 μC/g.

39. The method according to claim 37, characterized in that the charge of the pigment particles is more than 10 μC/g.

40. The method according to claim 37, characterized in that the charge of the pigment particles is more than 15 μC/g.

41. The method according to claim 37, characterized in that the charge of the pigment particles is more than 20 μC/g.

42. The method according to claim 33, characterized in that the speed of the toner jet is achieved by increasing the electrical field.

43. The method according to claim 42, characterized in that the electrical field is more than 1 V/μm.

44. The method according to claim 42, characterized in that the electrical field is more than 3 V/μm.

45. The method according to claim 42, characterized in that the electrical field is more than 6 V/μm.

46. The method according to any one of claims 1 to 45, characterized in that the electrical field is less than 15 V/μm.

47. The method according to claim 22, characterized in that the length of time a substantial part of a toner jet is travelling in a volume which comprise deflection forces which deflection forces will influence pigment particles of a toner jet within the volume, is reduced by decreasing the extension of the toner jet, i.e. concentrating the bulk of the toner jet.

48. The method according to claim 47, characterized in that decreasing the extension of the toner jet is achieved by improving pigment particle release from the pigment particle delivery such that the pigment particles releases more simultaneously from the pigment particle delivery, thus creating a less elongated toner jet.

49. 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 during a print sequence in the form of toner jets, at least one print sequence is included in a print cycle, the printhead structure further including deflection electrodes connected to the control unit for controlling toner jets in transport by means of predetermined voltages, to thereby enable the formation of a pigment image on the first face of the image receiving member, characterized in that the control unit controls a length of time of each print sequence to be at least substantially equal a length of time a substantial part of a toner jet is travelling in a volume which comprise influential forces above a predetermined value, thereby enabling high speed printing.

50. The device according to claim 49, characterized in that at least two print sequences are included in a print cycle, and where the deflection electrodes connected to the control unit are for controlling the deflection of toner jets in transport by means of predetermined deflection voltages to thereby be able to deflect toner jets against predetermined locations, each aperture in question being arranged for placing toner jets at different dot positions in a direction substantially perpendicular to the relative movement between the printhead structure and the image receiving member during each print sequence, to thereby enable the formation of a pigment image on the first face of the image receiving member, and where the influential forces above a predetermined value comprise deflection forces .

51. The device according to claim 49 or 50, characterized in that the deflection electrodes connected to the control unit are for controlling the focusing of toner jets in transport by means of predetermined focusing voltages to thereby be able to focus toner jets, and where the influential forces above a predetermined value comprise focusing forces .

52. The device according to any one of claims 49 to 51, characterized in that the control unit controls the length of time of each print sequence to be substantially equal or less than a length of time a substantial part of a toner jet is travelling from the pigment particle delivery to the first face of the image receiving member.

53. The device according to claim 52, characterized in that the length of time a substantial part of a toner jet is travelling from the pigment particle delivery to the first face of the image receiving member, is the difference between a point in time when a bulk of the toner jet starts to leave the pigment particle delivery, and a point in time when the bulk of the toner jet has arrived at the first face of the image receiving member.

54. The device according to any one of claims 49 to 51, characterized in that the control unit controls the length of time of each print sequence to be substantially equal or less than a length of time a substantial part of a toner jet is travelling from an aperture in question to the first face of the image receiving member.

55. The device according to claim 54, characterized in that the length of time a substantial part of a toner jet is travelling from the pigment particle delivery to the first face of the image receiving member, is the difference between a point in time when a bulk of the toner jet starts to leave an aperture in question, and a point in time when the bulk of the toner jet has arrived at the first face of the image receiving member.

56. The device according to any one of claims 49 to 51, characterized in that the control unit controls the length of time of each print sequence to be substantially equal a length of time a substantial part of a toner jet is travelling in a volume which comprise deflection forces above a predetermined value.

57. The device according to any one of claims 49 to 51, characterized in that the control unit controls the length of time of each print sequence to be equal a length of time a substantial part of a toner jet is travelling in a volume which comprise influential forces above a predetermined value.

58. The device according to any one of claims 49 to 57, characterized in that the length of time a substantial part of a toner jet is travelling in a volume which comprise influential forces above a predetermined value, is the difference between a point in time when a bulk of the toner jet starts to enter the volume where the deflection forces are above a predetermined value, and a point in time when the bulk of the toner jet has left the volume.