WO2002040276A1

WO2002040276A1 - Direct electrostatic printing method and apparatus

Info

Publication number: WO2002040276A1
Application number: PCT/SE2000/002225
Authority: WO
Inventors: Bo RYDSTRÖM
Original assignee: Matsushita Electric Industrial Co Ltd; Array AB
Current assignee: Panasonic Holdings Corp; Array AB
Priority date: 2000-11-14
Filing date: 2000-11-14
Publication date: 2002-05-23
Anticipated expiration: 2003-05-14
Also published as: AU2001219068A1

Abstract

A direct electrostatic printing device and method for printing an image with a simple printhead structure. According to the invention at least one control electrode of an aperture, is controlled in three different phases thereby removing the necessity of separate deflection control electrodes for deflection and size control of toner jets. A control unit controls at least one control electrode of each aperture in three phases during a print sequence which permits the transport of a toner jet, a first phase of creating a toner jet, a second phase of controlling the created toner jet, and a third phase of recovery, by means of predetermined voltages. Permission and restriction of transport of toner jets and toner jet tracetory control is according to the invention controlled by the same at least one control electrode. Further the one or more control electrodes of an aperture encompasses an aperture in question less than 100 %, preferably asymmetrically placed in relation to a relative movement between the printhead structure and an image receiving surface.

Description

DIRECT ELECTROSTATIC PRINTING METHOD AND APPARATUS

FIELD OF THE INVENTION

The present invention relates to direct electrostatic printing methods and devices 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 during a number print sequences to deflect the modulated stream of toner particles in predetermined deflection directions. For instance, a DDC method performing three deflection steps, print sequences, 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 resolution, in particular when dot deflection control is used, due to printed circuit restrictions of conductor widths and inter-conductor spacing. 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 resolution when using direct electrostatic printing methods.

Another object of the present invention is to provide a method of and device for improving the printing resolution 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 reducing the number of control electrodes of an aperture when printing in deflection control and/or size control direct electrostatic printing methods.

A still further object of the present invention is to provide a method of and device for reducing the number of conductors of a printhead structure for 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 a simple printhead structure. According to the invention at least one control electrode of an aperture, is controlled in three different phases thereby removing the necessity of separate deflection control electrodes for deflection and size control of toner jets. Permission and restriction of transport of toner jets and toner jet trajectory control is according to the invention controlled by the same at least one control electrode. This reduces the number of necessary connections and thus also the necessary number of driver integrated circuits, thus simplifying the manufacture of the printhead structure and also reducing costs by using fewer integrated circuits. Further the one or more control electrodes of an aperture encompasses an aperture in question less than 100%, preferably asymmetric in relation to a relative movement between the printhead structure and an image receiving surface.

Said objects are also achieved according to the invention by providing a direct electrostatic printing device including a toner particle delivery, an electrical field creator, a printhead structure, and a control unit. The toner particle delivery providing toner particles. An image receiving surface and the printhead structure are arranged for relative movement between each other during printing. The electrical field creator creating an electrical field between the toner particle delivery and the image receiving surface for transport of toner particles from the toner particle delivery toward the image receiving surface. The printhead structure being placed in the electrical field in between the toner particle delivery and the image receiving surface. 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 toner particles during a print sequence in the form of toner jets. At least one print sequence is included in a print cycle. Thereby the formation of an image on the image receiving surface is enabled. According to the invention each aperture comprises substantially one passage for one toner jet at a time and comprises at least one control electrode. The one or more control electrodes surrounds an aperture in question less than 100%. Further the control unit controls the at least one control electrode of each aperture in three phases during a print sequence which permits the transport of a toner jet, a first phase of creating a toner jet, a second phase of controlling the created toner jet, and a third phase of recovery, by means of predetermined voltages.

The one or more control electrodes which surrounds an aperture in question less than 100%), can advantageously surround an aperture in question either less than 75%, less than 50%, less than 30%, or approximately 50%.

In some embodiments the at least one control electrode is only one control electrode. Each print cycle preferably comprises either only one print sequence, two print sequences, three print sequences, or four print sequences. Suitably in some embodiments the second phase of at least one print sequence comprises a push back pulse to adjust a toner jet trajectory. In other embodiments the second phase comprises a push back pulse to adjust a toner jet trajectory in dependence of which print sequence within a print cycle the second phase in question belongs to. In still other embodiments the second phase comprises a push back pulse to adjust a toner jet trajectory. In still further embodiments the second phase comprises a push back pulse to adjust a toner jet trajectory in dependence of which print sequence within a print cycle the second phase in question belongs to and how long a kick pulse during the first phase of the print sequence in question was. Suitably the control electrode during the third phase is set to a field neutral potential.

In some ebodiments the at least one control electrode is two control electrodes. Then suitably each one of the two control electrodes surrounds an aperture in question less than 50%. Advantageously each one of the two control electrodes surrounds an aperture in question an equal amount. Each print cycle preferably comprises either only one print sequence, two print sequences, three print sequences, or four print sequences. Suitably in some embodiments the second phase of at least one print sequence of at least one control electrode of an aperture in question comprises a push back pulse to adjust a toner jet trajectory. In other embodiments the second phase comprises a push back pulse of an control electrode of an aperture in question to adjust a toner jet trajectory, in dependence of which print sequence within a print cycle the second phase in question belongs to. In still other embodiments advantageously during each print sequence the second phase of at least one control electrode of an aperture in question comprises a push back pulse to adjust a toner jet trajectory. Suitably the control electrodes during the third phase is set either to a field neutral potential, or to a focusing neutral potential.

In some embodiments the device further comprises a back electrode, and where the image receiving surface is a first face of the back electrode, the image subsequently being transferred from the back electrode to an information carrier.

In other embodiments the image receiving surface is a first face of an information carrier which also acts as a back electrode. In further embodiments the device further comprises an intermediate image receiving member and a back electrode, and where the image receiving surface is a first face of the intermediate image receiving member, and the back electrode being located facing a second face of the intermediate image receiving member, the image subsequently being transferred from the intermediate image receiving member to an information carrier. In still further embodiments the device further comprises a back electrode, and where the image receiving surface is a first face of an information carrier, and the back electrode being located facing a second face of the information carrier. Suitably the electrical field creator comprises a voltage source connected to the toner particle delivery and the back electrode. 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.

Said objects are also achieved according to the invention by a method for printing an image. The method comprises a number of steps. In a first step providing toner particles from a toner particle delivery. In a second step moving, relative to each other during printing, an image receiving surface and a printhead structure. In a third step creating an electrical field for transporting toner particles from the toner particle delivery toward the image receiving surface. In a fourth step selectively opening or closing apertures through the printhead structure to permit or restrict the transporting of toner particles during a print sequence in the form of toner jets by means of one or more control electrodes , at least one print sequence is included in a print cycle, to thereby enable the formation of an image on the image receiving surface. And in a final fifth step controlling one or more control electrodes, of an aperture in question, in three phases during a print sequence which permits transport of toner jets, a first phase of creating a toner jet, a second phase of controlling the created toner jet, and a third phase of recovery, by means of predetermined voltages, where the one or more control electrodes surrounds an aperture in question less than 100%.

In some embodiments the one or more control electrodes is only one control electrode, and in that the second phase comprises a push back pulse to adjust a toner jet trajectory. Then suitably at least two print sequences are included in a print cycle and the method further comprises an additional step. In the additional step controlling the trajectory of toner jets in transport by means of predetermined control electrode voltages on the one control electrode, the control electrode voltages being 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.

In some embodiments the one or more control electrodes are two control electrodes, a first control electrode and a second control electrode, and in that during at least one print sequence the first control electrode comprises a push back pulse during the second phase. Then suitably at least two print sequences are included in a print cycle and the method further comprises an additional step. The additional step controlling the trajectory of toner jets in transport by means of predetermined control electrode voltages on the first and second control electrodes during the second phase 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. The method can advantageously further comprise a further step. The further step controlling the focusing of toner jets in transport by means of predetermined focusing voltages during the third phase on the first and second control electrodes to thereby be able to adjust a size of placed toner jets. 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.

The present invention satisfies a need for simplifying a printhead structure not previously met, by enabling a toner jet to be controlled both as to transport and trajectory by the same at least one control electrode of an aperture in question.

The present invention relates to an image recording apparatus including an image receiving surface 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 toner sleeve, and a printhead structure arranged between the particle source and the image receiving surface. The printhead structure according to the invention includes combined means for modulating the stream of toner particles from the particle source and for controlling the trajectory of the modulated stream of toner particles toward the image receiving surface. 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 image receiving surface such as an intermediate image receiving member either formed of a seamless transfer belt or formed of a drum such as the back electrode. The toner image is formed on the intermediate image receiving surface according to the invention and thereafter brought into contact with an information carrier, e.g. paper, in e.g. a fuser unit, where the toner image is transferred to and made permanent on the information carrier. After image transfer, the intermediate image receiving surface is preferably 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 A to ID show step by step printing during sequential print sequences,

Fig.2 is a schematic view of a single aperture and its corresponding control electrode according to one embodiment of the invention,

Fig. 3 is a schematic section view across a print zone of an image recording apparatus with toner jet trajectories according to one embodiment of the invention, e.g. using a control electrode arrangement according to Figure 2,

Fig. 4A to 4C illustrate three different examples of control voltage signals according to the invention, e.g. using a control electrode arrangement according to Figure 2, each as a function of time during a print cycle having three subsequent print sequences,

Fig. 5A to 5D show different control electrode embodiments for print cycles with more than one print sequence, Fig. 6A to 6E show different control electrode and aperture embodiments for print cycles comprising only one print sequence,

Fig. 7 is a schematic view of a single aperture and its corresponding control electrodes according to an additional embodiment of the invention,

Fig. 8 is a schematic section view across a print zone of an image recording apparatus and toner jet trajectories according to an additional embodiment of the invention, e.g. using a control electrode arrangement according to Figure 7,

Fig. 9A & 9B illustrate control voltage signals of two control electrodes, e.g. a control arrangement according to Figure 7, as a function of time during a print cycle having three subsequent print sequences,

Fig. 10 illustrates a control unit,

Fig. 11 illustrates a high voltage control electrode driver.

DESCRIPTION OF PREFERRED EMBODIMENTS

An image recording apparatus according to the invention, comprises at least one print station, preferably four print stations (Y, M, C, K). The four print stations (Y, M, C, K) are arranged in relation to an image receiving surface, preferably an intermediate image receiving member. An intermediate image receiving member can either be a transfer belt mounted over driving rollers, or a drum. In other embodiments toner particles are deposited directly onto an information carrier without first being deposited onto an intermediate image receiving member. The image receiving surface and a print station move relative to each other at a velocity of one addressable dot location per print cycle, to provide line by line scan printing. Each print station comprises a printhead structure that has a plurality of apertures extending perpendicular to the relative motion. A transfer belt is conveyed, or a drum is rotated, past the four different print stations (Y, M, C, K), whereby toner particles are deposited on the image receiving surface and superposed to form a toner image.

Also a so-called multi-pass technique can be utilized. When utilizing such a technique, the image forming apparatus is provided with moving means causing the image receiving surface and the printhead structure to move in relation to each other, i.e. the image receiving surface or the printhead structure, or both, are movable. Thereby, the relative movement is so arranged that each line on the image-receiving surface that is transverse to the direction of the relative movement passes the printhead structure at least twice in order to form an image. Accordingly, the printhead structure prints only a part of each transverse line on each pass. When utilizing multi-pass technique, the moving means further includes means to move the printhead structure and the image receiving surface relative to each other (i.e. the printhead structure or the image receiving surface, or both, are moved) between consecutive passes or during a pass, so that each time that the image receiving surface passes the printhead structure, different parts of the image receiving surface are positioned to receive charged toner particles. The multi-pass technique increases the print addressability without requiring a larger number of apertures in the printhead structure which, if desired, can eliminate the need for special deflection electrodes or the like.

In many cases, the multi-pass technique results in an improved resolution and print quality in comparison to when an image is printed in one single printing pass.

Multi-interlacing (MIC) is a further developed technique where an image forming apparatus utilizing multi-pass techniques is so constructed and arranged that adjacent columns of print are not printed by the same aperture in different passes. When utilizing MIC-technique, columns of print from different passes (partial images) are "interlaced" with each order in order to form the completed image. It has been found that MIC-techniques can improve print resolution and print quality even further in comparison to conventional multi-pass techniques.

Also dot deflection techniques (DDC) can be utilized in an image forming apparatus of the types in question. According to the DDC-method, each single aperture is used to address several dot positions on an image receiving surface by controlling not only the transport of toner particles through the aperture, but also their transport trajectory towards the image receiving surface, 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.

By means of utilizing a combination of multipass-, MIC- and/or DDC- techniques, the print addressability/number of apertures, and the print resolution can be optimized.

In some embodiments the transfer belt 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 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.

Each print station comprises a particle delivery unit. The particle delivery unit preferably has a replaceable or refillable container for holding toner particles which is disposed to continuously supply toner particles to a surface of a particle carrier through a particle charging member. Toner particles are retained on the surface of the particle carrier by an adhesion force which essentially is related to the particle charge and to the distance between the particle and the surface of the particle carrier. The electrostatic field applied onto a control electrode to initiate toner transport through a selected aperture is selected to be sufficient to overcome the adhesion force in order to cause the release of an appropriate amount of toner particles from the particle carrier. The electrostatic field is applied during the time period required for these released particles to reach sufficient momentum to pass through the selected aperture, whereafter the transported toner particles are exposed to the attraction force from the back electrode and are intercepted by the image receiving surface.

Properties such as charge amount, charge distribution, particle diameter etc. of the individual toner particles have been found to be of particularly great importance to the print performance in a direct printing method. Accordingly, the size and size distribution of the toner particles affect the printing result, since larger toner particles have a tendency to cause clogging of the apertures in the control electrode array. In addition, the toner particles allowed to pass through selected "opened" apertures are accelerated towards the image receiving under the influence of a uniform attraction field from the back electrode. In order to control the distribution of the transported particles onto a printing surface, the particles may be deflected by the application of a deflection pulse, resulting in an increase in the addressable area on the image receiving surface. Thereby, small particles having a low surface charge exhibit poor deflection properties.

Normally, toner particles are produced by the so-called melt-crushed method, which involves crushing and classifying colored resin, such as polyester resin or the like, with dispersed coloring agents and other additives using a compounding process. However, this method is not ideally suited for producing small-particle toner since it has a relatively low yield, and tends to produce a great variety of particle sizes and toner particles with a non-uniform composition. A non-uniform toner results in a poor charge uniformity and may impair the print quality.

Toner particles can also be produced in a chemical polymerization process, which is better suited for producing small toner particles of a uniform size. There are three basic processes, i.e. the suspension polymerization method, the dispersion polymerization method, and the emulsion polymerization method. The suspension and dispersion polymerization methods produce full-shaped spherical toner particles with a size between a few and up to 10 microns. The emulsion polymerization method produces polymer particles of sub-micron size or smaller, which particles are aggregated by means of different methods, e.g. heat-welding or coagulation, in order to form micron-order particles. The shape of the aggregated particles can vary from grape cluster to spherical, depending on the conditions prevailing in the aggregation process.

Toner particles can comprise a number of ingredients, e.g. a binding resin based on a cyclic polyolefin e.g. a copolymer of an alicyclic compound with double bonds, such as cyclohexene or norbornene, and an alpha-olefin, such as ethylene, propylene or butylene. Accordingly, the toner particles can be of 2-component or multi-component type.

Advantageously, the toner particles have an irregular surface structure and an average diameter within the range of 3-8 microns. Depending on the application in question, electrically conductive, electrically non-conductive, or magnetic toner particles can be provided and utilized.

The printhead structure is preferably formed of an electrically insulating substrate layer made of flexible, non-rigid material such as polyamide or the like. The printhead structure is positioned between a peripheral surface of a particle carrier and a bottom portion of a support device. The substrate layer has a top surface facing a toner layer on the peripheral surface of the particle carrier, and a bottom surface facing the bottom portion of the support device. Further, the substrate layer has a plurality of apertures arranged through the substrate layer in a part of the substrate layer overlying a elongated slot in the bottom portion of the support device. The printhead structure further preferably includes a first printed circuit arranged on the top surface on the substrate layer. The first printed circuit includes a plurality of control electrodes, each of which, at least partially, surrounds a corresponding aperture in the substrate layer.

According to some embodiments of the invention printing is performed in print cycles having three subsequent print sequences for addressing three different dot locations through each aperture, i.e. a dot location is addressed during each print sequence. Each print sequence comprises a print period t_b followed by a recovering period t_w during which new toner is supplied to the print zone. 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 a surface of a particle carrier and a second potential on a back electrode, to enable the transport of toner particles between the particle carrier and an image receiving surface. During each print sequence, control voltages are applied to 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. The control voltage pulse ( _cont_roi) 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 -50N and a print level N_b in the order of +350N, corresponding to full density dots. Similarly, the pulse width can be varied from 0 to t_b.

The back electrode member or members utilized in an image forming apparatus can be of a number of different types, e.g. a stationary or rotating roll or sleeve, or a movable belt arranged in an endless loop by means of guide rolls. Depending on the application, the back electrode member can be made of different materials, e.g. a suitable metal alloy or another electrically conductive material. Furthermore, a back electrode member can be arranged behind a belt constituting an intermediate image receiving member. It is also conceivable with embodiments where a suitable information carrier, such as a printing paper, passes across the back electrode when printing so that an image is printed directly onto the information carrier, or where the information carrier also constitutes the back electrode by means of being electrically conductive.

In other applications, an intermediate image is formed directly onto the surface of the back electrode member, whereafter the image is transferred to a suitable image receiving substrate such as a printing paper. It is particularly advantageous to print directly onto the back electrode in applications utilizing so-called multi- interlacing (MIC) techniques.

Furthermore, it is conceivable with applications where the electrical field, by means of which the toner particles are transported, is generated by another means than a pair of electrodes, e.g. applications where the electrical field is generated by means of a suitable charge carrier which in itself is able to generate an electrostatic field.

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.

To clarify the concept of dot deflection Figures 1A to ID show step by step printing during sequential print sequences. Figures 1A to IC each illustrate a print sequence comprised in one print cycle and Figure ID illustrates a first print sequence of a subsequent print cycle. Illustrated is a matrix comprising six columns CI, C2, C3, C4, C5, and C6 and two rows LI and L2 on an image receiving surface that is moving 38 in relation to a printhead structure. The printhead structure in this example comprises two apertures 61 aligned with column C2 and column C5 respectively. Figure 1A illustrates a first print sequence of a print cycle. The first sequence will deflect a tonerjet in a direction Rl from a respective aperture to thereby fill intersection areas in row L2 and column CI and column C4. The illustrated print sequences all print black, i.e. a tonerjet is trajected to a desired fill area during each print sequence, in actual printing tonerjets are permitted or restrained in dependence of an image to be printed. Figure IB illustrate how tonerjets are trajected directly to intersection areas defined by row L2 and columns C2 and C5 in a second print sequence of the print cycle. Figure IC illustrates the final print sequence of the print cycle where tonerjets are deflected in a direction R2 to fill intersection areas on row L2 in columns C3 and C6. This process is repeated in further print cycles and Figure ID illustrates a first print sequence of a subsequent print cycle where tonerjets are deflected in a direction Rl to fill intersection areas on row LI and columns CI and C4.

The example according to Figures 1A to ID illustrates print cycles with three print sequences each, i.e three dots in a direction perpendicular to the relative movement are printed by each aperture. More or less print sequences per print cycle can be performed during a print cycle and the print sequences can be performed in another order, e.g. just the definition of which print sequence a print cycle begins with will change the sequence within a cycle.

Traditionally to achieve dot deflection each aperture comprised at least three different electrodes, one control electrode and two deflection electrodes. According to the invention, to among other things reduce the number of connections necessary to control and deflection electrodes, the functions of aperture control and deflection are combined. By reducing the number of connections, then the number of output drivers is reduced which results in fewer driver ICs and or driver ICs with fewer outputs. By fewer connections to driver ICs then there will be more room on a printhead structure, this unused real estate on the printhead structure may advantageously be used to provide wider connections. Wider connections are easier to manufacture and can carry higher currents. All in all, a higher reliability and a higher yield of printhead structures is attained.

Figure 2 is a schematic view of a single aperture 61 and its corresponding single control electrode 62 according to one embodiment of the invention. This first embodiment has a single control electrode 62 that is connected to a N_controi which provides the control electrode with necessary control voltages for aperture control and, according to this embodiment, deflection control for providing more than one addressable dot position during a print cycle. The deflection angle δ is chosen to compensate for the relative motion 38 between the image receiving surface and the printhead structure during a print cycle, in order to be able to obtain two or more transversally aligned dots, by deflection in a first deflection direction Rl and an opposite direction R2. According to the invention the control of a control electrode 62 during a print sequence by means of N_controi is divided into at least three different stages to attain desired tonerjet trajectories.

Figure 3 is a schematic section view across a print zone of an image recording apparatus with toner jet trajectories PI, P2, P3 according to one embodiment of the invention, e.g. using a control electrode arrangement according to Figure 2. 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 in some embodiments positioned between a peripheral surface of a toner particle delivery 52 and a bottom portion of a support device 54. The substrate layer 60 has a plurality of apertures 61 arranged through the substrate layer 60 for passage of toner jets from the toner layer 7 towards a back electrode 13, e.g. in the shape of a drum, intervened by an image receiving surface of the back electrode, or of an intermediate image receiving means such as a transfer belt 10, or directly onto an information carrier such as a printing paper or an overhead film. The printhead structure 6 further includes a printed circuit arranged on the top surface of the substrate layer 60. The printed circuit includes a plurality of control electrodes 62, each of which partially surrounds a corresponding aperture 61 in the substrate layer 60.

Each print sequence is divided into at least three phase by predetermined voltages applied to corresponding control electrodes 62. A first phase of creating a toner jet, a second phase of controlling the created toner jet, and a third phase of recovery, to thereby, among other things, replenish the toner layer 7. Figure 3 shows three different toner jet trajectories PI, P2, P3, which typically each represent the trajectory of a print sequence of a three print sequence print cycle. As can be seen all three trajectories PI, P2, P3 start at the toner layer and are pulled toward the control electrode. In a first trajectory PI, possibly during a first print sequence, a toner jet is suitably trajected in a direction Rl . It should be noted that the view according to Figure 3 is perpendicular to the relative movement 38 between the printhead structure and the image receiving surface, which means that the trajectories PI, P2, P3 are viewed at an angle. The first trajectory PI is pulled towards the control electrode 62, then it preferably steadies out before an optional push-back just before it reaches the image receiving surface such that it hits the image receiving surface at a right angle. The second trajectory P2, possibly a second print sequence, is first pulled towards the control electrode 62, then it is pushed back so that the resulting trajectory is equivalent with a toner jet travelling along a straight trajectory from the toner layer 7 straight through the aperture 61 to the image receiving surface. The third trajectory P3, possibly a third print sequence, is first pulled towards the control electrode 62 for a short time, a shorter time than for the second trajectory P2, and is then pushed back to attain a resulting direction R2. The control voltages are preferably such that all trajectories hit the image receiving surface at a right angle.

Figures 4A to 4C illustrate three different examples of control voltage signals according to the invention, e.g. using a control electrode arrangement according to Figure 2 to thereby attain trajectories such as those according to Figure 3, each as a function of time during a print cycle having three subsequent print sequences. Figure 4A illustrate a first basic manner in which to control a control electrode. First during a print sequence a kick pulse 701, 703, 705 is set in to release a toner jet from a toner layer and to start pulling the toner jet towards the control electrode. Thereafter there is a time period to steadily fraject a toner jet, the voltage level can then suitably be set such that it becomes field neutral, i.e. the voltage level of a confrol elecfrode is set such that a resulting field is equal the background field at the confrol elecfrode. To correctly fraject a toner jet to a desired dot position a push back pulse 711, 713, 715 of varying length in dependence of what trajectory is desired. If a desired dot position is in a direction Rl of the confrol electrode, then no push back pulse or only a small late push back pulse 711 is used to attain a perpendicular entry onto the image receiving surface. If a desired dot position is substantially directly beneath an aperture in question then a push back pulse 713 is set in to thereby straighten out the slanted trajectory. The push back pulse 713 is timed both as to start and length so that the toner jet arrives in the desired position. If a desired dot position is in a direction R2 opposite the confrol elecfrode then a push back pulse 715 is started early and of sufficient size to thereby change direction of the trajectory. After the push back pulses 711, 713, 715, a respective time period of recovery 707, 708, 709 is comprised in a print sequence before a subsequent print sequence starts. The voltage levels during the recovery 707, 708, 709 are suitably such that the resulting field is field neutral, i.e. the confrol elecfrodes could be said to be floating. The voltage levels depicted assumes a use of negatively charged toner particles and the exact amplitudes and times are dependent on many different factors. Positively charged toner particles may equally well be used with a corresponding change of control voltages.

Figure 4B shows an alternative confrol of the confrol elecfrodes. Here the kick pulses 721, 723, 725 are also modulated in dependence of where a desired dot position is located. A long pulse 721 is used if a desired dot position is in a direction Rl of the control electrode, possibly with a further extension 722 if a push back pulse 731 is utilized, i.e. a toner jet should be pulled toward the confrol elecfrode. A short kick pulse 725 is used with a long corresponding push back pulse 735 if a desired dot position is in a direction R2 opposite the confrol electrode, i.e. a toner jet should only be released from a toner layer and pulled towards the control electrode for this time and then be pushed away from the confrol electrod. A medium pulse 723 is used, suitably of a similar magnitude as a corresponding push back pulse 733, if a desired dot position is straight down, i.e. a toner jet should be pulled towards the confrol electrode the same amount it is pushed away from the control elecfrode.

Figure 4C shows an even further alternative confrol of the confrol elecfrodes with density confrol. The kick pulses 741, 743, 745 each comprise a variable density confrol extension 742, 744, 746. The extensions are a way of controlling the amount of toner that is included in a toner jet and thereby the resulting density, i.e. more toner gives more density. Since the confrol electrode is not symmetrically placed, the denser a desired resulting dot is the further its corresponding toner jet will be pulled toward the confrol elecfrode, this will then be compensated for by adding a variable push back extension 752, 754, 756 onto the corresponding ordinary push back pulses 751, 753, 755. The size of the variable push back extensions 752, 754, 756 will thus relate to the size of the corresponding variable density confrol extension 742, 744, 746.

Figures 5A to 5D show different confrol elecfrode 62 embodiments suitable for print cycles with more than one print sequence. The placement of the confrol electrodes 62 are at an angle in relation to the aperture and relative movement 38 between a print head structure and an image receiving surface, as disclosed in relation to Figure 2. For reasons of conductor spacing, it can be advantageous to combine the embodiments of Figures 5A and 5B by having every other aperture 61 and control elecfrode 62 arrangement come from the embodiment of Figure 5 A and every other come from Figure 5B. This will result in that the feeding conductors to the confrol electrodes 62 of adjacent apertures 61 go in opposite directions, i.e. are placed on opposite sides of the apertures 61. These different embodiments can also be used for print cycles with only one print sequence.

Figures 6 A to 6E show different confrol elecfrode 62 and aperture 61 embodiments for print cycles comprising only one print sequence. The confrol electrodes 62 can thus be aligned with the relative movement 38 between the print head structure and the image receiving surface. Suitably the confrol voltages applied during the single print sequence of each print cycle is equivalent to the middle print sequences 703, 713, 708, 723, 733, 743, 744, 753, 754 shown according to Figures 4A, 4B and 4C.

Figure 7 is a schematic view of a single aperture 61 and its corresponding two control elecfrodes 621, 622 according to an additional embodiment of the invention. This second major embodiment has two confrol elecfrodes 621, 622 each connected to a corresponding control voltage Nco_nt_roib V_controi₂ which provide the confrol electrodes 621, 622 with necessary confrol voltages for aperture control and, also according to this second major embodiment, deflection control for providing more than one addressable dot position during a print cycle. The deflection angle δ is chosen to compensate for the relative motion 38 between the image receiving surface and the printhead structure during a print cycle, in order to be able to obtain two or more fransversally aligned dots, by deflection in a first deflection direction Rl and an opposite direction R2. According to the invention the control of the confrol elecfrodes 621, 622 during a print sequence by means of Vco_ntroii, V_COnt_roi₂ is divided into at least three different stages to attain desired tonerjet trajectories.

Figure 8 is a schematic section view across a print zone of an image recording apparatus and toner jet trajectories P21, P22, P23 according to an additional embodiment of the invention, e.g. using a confrol elecfrode arrangement according to Figure 7. The illustrated build of the print zone of the image recording apparatus suitably comprises a printhead structure 6, a substrate layer 60 with apertures 61, a toner particle delivery 52 with a toner layer 7, a support device 54, a back electrode 13, an image receiving surface of the back electrode or an intermediate image receiving means such as a transfer belt 10, and are preferably at least similar to those described in relation to Figure 3. The printhead structure 6 further includes a printed circuit arranged on the top surface of the substrate layer 60. The printed circuit includes a plurality of control elecfrodes 621, 622, two of which partially surrounds a corresponding aperture 61 in the substrate layer 60.

Each print sequence is divided into at least three phases by predetermined voltages applied to corresponding confrol elecfrodes 621, 622. A first phase of creating a tonerjet, a second phase of controlling the created toner jet, and a third phase of recovery, to thereby, among other things, replenish the toner layer 7. Figure 8 shows three different toner jet trajectories P21, P22, P23, which typically each represent the frajectory of a print sequence of a three print sequence print cycle. In comparison with the trajectories PI, P2, P3 of Figure 3, the trajectories P21, P22, P23 of Figure 8 are symmetrical which is due to the use of two control elecfrodes 621, 622 around each aperture 61. The trajectories P21, P22, P23 does not have to be symtrical, but are most suitably so. As can be seen all three trajectories P21, P22, P23 start in common at the toner layer and are split up into three different trajectories suitably at or approximately at the aperture 61. In a first frajectory P21, possibly during a first print sequence, a tonerjet is suitably trajected in a direction Rl. It should be noted that the view according to Figure 8 is perpendicular to the relative movement 38 between the printhead structure and the image receiving surface, which means that the trajectories P21, P22, P23 are viewed at an angle. The first trajectory P21 is first directed sfraight down towards the image receiving surface by means of an equal pull from both confrol electrodes 621, 622. Then a tonerjet is pulled towards the confrol elecfrode 621, in a direction Rl, and preferably pushed by the other confrol elecfrode 622. Then the toner jet is preferably focused just before it reaches the image receiving surface. The second trajectory P22, possibly a second print sequence, is first pulled equally towards both control elecfrodes 621, 622, i.e. in a frajectory sfraight into the aperture. Then the toner jet is preferably focused before hitting the image receiving surface. The second frajectory P22 is thus substantially a sfraight path from the toner layer sfraight through the aperture 61 and towards the image receiving surface. The third trajectory P23, possibly a third print sequence, is first pulled towards both control elecfrodes 621, 622, then pulled towards the confrol electrode 622 in a direction R2. The other confrol elecfrode 621 can preferably at the same time push the toner jet in the direction R2. Finally the toner jet is preferably focused by means of both confrol electrodes 621, 622.

Figures 9A and 9B illustrate control voltage signals of two control elecfrodes, e.g. a confrol arrangement according to Figure 7, as a function of time during a print cycle having three subsequent print sequences to thereby attain trajectories such as those depicted in Figure 8. Figure 9 A illustrates suitable control voltages of a first confrol elecfrode, typically a confrol elecfrode 621 in a direction Rl as illustrated in Figures 7 and 8. Figure 9B illustrates suitable control voltages of a second confrol elecfrode, typically a control elecfrode 622 in a direction R2 as illustrated in Figures 7 and 8. As mentioned previously, a toner jet is controlled with three different phases during a print sequence, each print sequence of a print cycle being different to thereby create different trajectories. In a first print sequence a tonerjet is in a first phase created by means of a kick pulse 761, 781 on both control elecfrodes. The kick pulses 761, 781 attract toner particles from a toner particle layer. During a second phase the first confrol electrode is preferably kept at a kick pulse level 761 while at the same time a push pulse 791 is set in at the second electrode. This results in the toner jet being attracted towards the first control elecfrode and repelled from the second control electrode thus attaining a frajectory such as P21 towards Rl of Figure 8. In a final phase the confrol electrodes are either put in a field neufral state or as depicted subjected to focusing pulses 771, 792. The focusing pulses 771, 792 are suitably of an equal level and length and both will repel the toner jet slightly, thus concentrating, focusing, a toner jet. In a second print sequence, to attain a trajectory P22 as illustrated in Figure 8, kick pulses 763, 783 are set in on both confrol elecfrodes. In a second phase both confrol elecfrodes are preferably put in a field neufral state 764, 784. The voltage levels during the second phase of the second print sequence can be anywhere from the kick pulse level to a focusing level. During a third phase during the second print sequence focusing pulses 773, 793 are set in on both confrol elecfrodes. The pulses 763, 764, 773, 783, 784, 793 are suitably at least substantially equal on both control electrodes to attain a straight symmetrical frajectory during the second print sequence. During a third print sequence the confrol pulses 765, 775, 776, 785, 795 are the same as during the first print sequence, but are switched over between the confrol elecfrodes to thus obtain a toner jet frajectory in an opposite direction such as trajectory P23 of Figure 8 in a direction R2. As is apparent from the Figures 9 A and 9B, the toner particles in question are negatively charged.

The control functions of a printing unit according to the invention is handled by a confrol unit which is schematically illustrated in Figure 10. The illustration of the confrol 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 confrol 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 confrol and monitoring of the printer can logically be divided into one simple I/O interface 912 for on/off confrol and monitoring and one advanced I/O interface 911 for multilevel confrol and monitoring, speed confrol, 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 confrol 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 confrol 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 confrol electrodes of the printer. Figure 11 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 confrol elecfrodes.

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 toner particle delivery, an electrical field creator, a printhead structure, and a confrol unit, the toner particle delivery providing toner particles, an image receiving surface and the printhead structure are arranged for relative movement between each other during printing, the electrical field creator creating an electrical field between the toner particle delivery and the image receiving surface for transport of toner particles from the toner particle delivery toward the image receiving surface, the printhead structure being placed in the electrical field in between the toner particle delivery and the image receiving surface, the printhead structure including confrol electrodes connected to the confrol unit to thereby selectively open or close apertures through the printhead structure to permit or restrict the transport of toner 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 an image on the image receiving surface, characterized in that each aperture comprises substantially one passage for one toner jet at a time and comprises at least one confrol elecfrode, where the one or more confrol electrodes surrounds an aperture in question less than 100%, and in that the confrol unit controls the at least one confrol elecfrode of each aperture in three phases during a print sequence which permits the transport of a toner jet, a first phase of creating a toner jet, a second phase of controlling the created toner jet, and a third phase of recovery, by means of predetermined voltages.

2. The device according to claim 1, characterized in that the one or more confrol elecfrodes which surrounds an aperture in question less than 100%, surrounds an aperture in question less than 75%.

3. The device according to claim 1, characterized in that the one or more confrol elecfrodes which surrounds an aperture in question less than 100%, surrounds an aperture in question less than 50%).

4. The device according to claim 1, characterized in that the one or more control electrodes which surrounds an aperture in question less than 100%, surrounds an aperture in question less than 30%.

5. The device according to claim 1, characterized in that the one or more confrol elecfrodes which surrounds an aperture in question less than 100%), surrounds an aperture in question approximately 50%).

6 The device according to any one of claims 1 to 5, characterized in that the at least one confrol elecfrode is only one control elecfrode.

7. The device according to claim 6, characterized in that each print cycle comprises only one print sequence.

8. The device according to claim 6, characterized in that each print cycle comprises two print sequences.

9. The device according to claim 6, characterized in that each print cycle comprises three print sequences.

10. The device according to claim 6, characterized in that each print cycle comprises four print sequences.

11. The device according to any one of claims 6 to 11, characterized in that the second phase of at least one print sequence comprises a push back pulse to adjust a tonerjet frajectory.

12. The device according to any one of claims 6 to 11, characterized in that the second phase comprises a push back pulse to adjust a toner jet trajectory in dependence of which print sequence within a print cycle the second phase in question belongs to.

13. The device according to any one of claims 6 to 11, characterized in that the second phase comprises a push back pulse to adjust a toner jet frajectory.

14. The device according to any one of claims 6 to 11, characterized in that the second phase comprises a push back pulse to adjust a toner jet trajectory in dependence of which print sequence within a print cycle the second phase in question belongs to and how long a kick pulse during the first phase of the print sequence in question was.

15. The device according to any one of claims 6 to 14, characterized in that the confrol elecfrode during the third phase is set to a field neutral potential.

16. The device according to any one of claims 1 to 5, characterized in that the at least one confrol elecfrode is two confrol elecfrodes.

17. The device according to claim 16, characterized in that each one of the two confrol elecfrodes surrounds an aperture in question less than 50%).

18. The device according to claim 16 or 17, characterized in that each one of the two confrol electrodes surrounds an aperture in question an equal amount.

19. The device according to any one of claims 16 to 18, characterized in that each print cycle comprises only one print sequence.

20. The device according to any one of claims 16 to 18, characterized in that each print cycle comprises two print sequences.

21. The device according to any one of claims 16 to 18, characterized in that each print cycle comprises three print sequences.

22. The device according to any one of claims 16 to 18, characterized in that each print cycle comprises four print sequences.

23. The device according to any one of claims 16 to 22, characterized in that the second phase of at least one print sequence of at least one control elecfrode of an aperture in question comprises a push back pulse to adjust a toner jet frajectory.

24. The device according to any one of claims 16 to 22, characterized in that the second phase comprises a push back pulse of an confrol elecfrode of an aperture in question to adjust a toner jet trajectory, in dependence of which print sequence within a print cycle the second phase in question belongs to.

25. The device according to any one of claims 16 to 22, characterized in that during each print sequence the second phase of at least one confrol electrode of an aperture in question comprises a push back pulse to adjust a toner jet trajectory.

26. The device according to any one of claims 16 to 25, characterized in that the confrol elecfrodes during the third phase is set to a field neutral potential.

27. The device according to any one of claims 16 to 25, characterized in that the confrol electrodes during the third phase is set to a focusing neutral potential.

28. The direct electrostatic printing device according to any one of claims 1 to 27, characterized in that the device further comprises a back elecfrode, and where the image receiving surface is a first face of the back elecfrode, the image subsequently being transferred from the back electrode to an information carrier.

29. The direct electrostatic printing device according to any one of claims 1 to 27, characterized in that the image receiving surface is a first face of an information carrier which also acts as a back elecfrode.

30. The direct electrostatic printing device according to any one of claims 1 to 27, characterized in that the device further comprises an intermediate image receiving member and a back elecfrode, and where the image receiving surface is a first face of the intermediate image receiving member, and the back elecfrode being located facing a second face of the intermediate image receiving member, the image subsequently being fransferred from the intermediate image receiving member to an information carrier.

31. The direct electrostatic printing device according to any one of claims 1 to 27, characterized in that the device further comprises a back elecfrode, and where the image receiving surface is a first face of an information carrier, and the back electrode being located facing a second face of the information carrier.

32. The direct electrostatic printing device according to any one of claims 28 to 31, characterized in that the electrical field creator comprises a voltage source connected to the toner particle delivery and the back elecfrode.

33. A method for printing an image, characterized in that the method comprises the following steps:

- providing toner particles from a toner particle delivery;

- moving, relative to each other during printing, an image receiving surface and a printhead structure; - creating an electrical field for transporting toner particles from the toner particle delivery toward the image receiving surface;

- selectively opening or closing apertures through the printhead structure to permit or restrict the transporting of toner particles during a print sequence in the form of toner jets by means of one or more control elecfrodes , at least one print sequence is included in a print cycle, to thereby enable the formation of an image on the image receiving surface;

- controlling one or more control elecfrodes, of an aperture in question, in three phases during a print sequence which permits transport of toner jets, a first phase of creating a toner jet, a second phase of controlling the created toner jet, and a third phase of recovery, by means of predetermined voltages, where the one or more confrol electrodes surrounds an aperture in question less than 100%.

34 The method according to claim 33, characterized in that the one or more confrol elecfrodes is only one confrol elecfrode, and in that the second phase comprises a push back pulse to adjust a toner jet frajectory.

35. The method according to claim 34, 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 trajectory of toner jets in fransport by means of predetermined confrol electrode voltages on the one control elecfrode, the confrol elecfrode voltages being 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.

36. The method according to claim 33, characterized in that the one or more confrol electrodes are two control elecfrodes, a first confrol elecfrode and a second confrol elecfrode, and in that during at least one print sequence the first confrol elecfrode comprises a push back pulse during the second phase.

37. The method according to claim 36, 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 trajectory of toner jets in transport by means of predetermined confrol elecfrode voltages on the first and second confrol electrodes during the second phase 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.

38. The method according to claim 36 or 37, characterized in that the method further comprises the step of:

- controlling the focusing of toner jets in transport by means of predetermined focusing voltages during the third phase on the first and second confrol electrodes to thereby be able to adjust a size of placed tonerjets.