WO2001049501A1 - Direct printing device and method - Google Patents

Direct printing device and method

Info

Publication number
WO2001049501A1
WO2001049501A1 PCT/SE2000/000016 SE0000016W WO2001049501A1 WO 2001049501 A1 WO2001049501 A1 WO 2001049501A1 SE 0000016 W SE0000016 W SE 0000016W WO 2001049501 A1 WO2001049501 A1 WO 2001049501A1
Authority
WO
Grant status
Application
Patent type
Prior art keywords
image
particle
control
structure
particles
Prior art date
Application number
PCT/SE2000/000016
Other languages
French (fr)
Inventor
Filip Alm
Original Assignee
Array Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date

Links

Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B41PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41JTYPEWRITERS; SELECTIVE PRINTING MECHANISMS, e.g. INK-JET PRINTERS, THERMAL PRINTERS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/385Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective supply of electric current or selective application of magnetism to a printing or impression-transfer material
    • B41J2/41Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective supply of electric current or selective application of magnetism to a printing or impression-transfer material for electrostatic printing
    • B41J2/415Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective supply of electric current or selective application of magnetism to a printing or impression-transfer material for electrostatic printing by passing charged particles through a hole or a slit
    • B41J2/4155Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective supply of electric current or selective application of magnetism to a printing or impression-transfer material for electrostatic printing by passing charged particles through a hole or a slit for direct electrostatic printing [DEP]
    • GPHYSICS
    • G03PHOTOGRAPHY; CINEMATOGRAPHY; ELECTROGRAPHY; HOLOGRAPHY
    • G03GELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G2217/00Details of electrographic processes using patterns other than charge patterns
    • G03G2217/0008Process where toner image is produced by controlling which part of the toner should move to the image- carrying member
    • G03G2217/0025Process where toner image is produced by controlling which part of the toner should move to the image- carrying member where the toner starts moving from behind the electrode array, e.g. a mask of holes

Abstract

The present invention relates to an image forming method in which an image information is converted to a pattern of control voltage pulses which modulate a transport of charged toner particles from a particle source to an image receiving member, said method comprising the steps of: providing a background voltage source for producing a background electric field between said particle source and said image receiving member, for enabling a transport of charged particle therebetween; providing a printhead structure between said particle source and said image receiving member, said printhead structure having a plurality of apertures arranged in said background electric field, and a plurality of control electrodes arranged in conjunction to the apertures; and connecting the control electrodes to control voltage sources which supply control voltage pulses in accordance with the image information, each control voltage pulse being dimensioned to open a corresponding aperture for permitting the transport of an appropriate amount of charged particles therethrough, said transported charged particles being thereby attracted towards the image receiving member under influence of said background electric field. The invention is characterized in that each of said control voltage pulse has a duration which is shorter than the time period required for said appropriate amount of charged particles to be transported from said particle source past said corresponding aperture. The invention also relates to an image forming device.

Description

Direct printing device and method

TECHNICAL FIELD

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

BACKGROUND

US Patent 5,036,341 discloses a direct electrostatic printing device and a method to produce text and pictures with toner particles on an image receiving substrate directly from computer generated signals. Such a device generally includes a printhead structure provided with a plurality of apertures through which toner particles are selectively transported from a particle source to the image receiving substrate due to control in accordance with an image information. The printhead structure is formed by a lattice consisting in intersecting wires disposed in rows and columns. Each wire is connected to an individual voltage source. Initially the wires are grounded to prevent toner from passing through the wire mesh. As a desired print location on the image receiving substrate passes below an intersection, adjacent wires in a corresponding column and row are set to a print potential to produce an electric field that draws the toner particles from the particle source. The toner particles are propelled through the square aperture formed by four crossed wires and deposited on the image receiving substrate in the desired pattern.

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

The ring electrodes are individually connected to control voltage sources which, in non-print conditions, supply a white potential preventing the transport of toner. As a dot location on the image receiving member passes beneath an aperture, a control voltage pulse is supplied to its corresponding ring electrode in order to open the aperture for toner transport during a predetermined transport period, thus permitting an appropriate amount of toner to be transported through the aperture to form a dot. Generally, the aperture is opened during the entire transport time required for toner particles to be propulsed from the particle source to the image receiving member.

In order to obtain faster print sequences, there is still a need for improving a method and device in which the print process is achieved with shorter control voltage pulses.

SUMMARY OF THE INVENTION

The invention relates to an image forming method in which an image information is converted to a pattern of control voltage pulses which modulate a transport of charged toner particles from a particle source to an image receiving member, said method comprising the steps of: providing a background voltage source for producing a background electric field between said particle source and said image receiving member, for enabling a transport of charged particle therebetween; providing a printhead structure between said particle source and said image receiving member, said printhead structure having a plurality of apertures arranged in said background electric field, and a plurality of control electrodes arranged in conjunction to the apertures; connecting the control electrodes to control voltage sources which supply control voltage pulses in accordance with the image information, each control voltage pulse being dimensioned to open a corresponding aperture for permitting the transport of an appropriate amount of charged particles therethrough, said transported charged particles being thereby attracted towards the image receiving member under influence of said background electric field, characterized in that: each of said control voltage pulse has a duration which is shorter than the time period required for said appropriate amount of charged particles to be transported from said particle source past said corresponding aperture.

The invention also relates to an image forming device in which an image information is converted to a pattern of control voltage pulses which modulate a transport of charged toner particles from a particle source to an image receiving member, said device comprising: a printhead structure arranged between said particle source and said image receiving member, said printhead structure having a plurality of apertures and a plurality of control electrodes arranged in conjunction to the apertures; control voltage sources for supplying control voltage pulses in accordance with the image information, each control voltage pulse being dimensioned to open a corresponding aperture for permitting the transport of an appropriate amount of charged particles therethrough, characterized in that: each of said control voltage pulse has a duration which is shorter than the time period required for said appropriate amount of charged particles to be transported from said particle source past said corresponding aperture.

According to the invention, the duration of a control voltage pulse, i.e. the pulse width, is chosen to be sufficiently large to initiate the particle transport, i.e. to allow an appropriate amount of particles to reach sufficient momentum to be propulsed through an aperture. Before the particles have past through the aperture, the control pulse is shut off, such that only the particles that have reached sufficient momentum continue their path through the aperture, the other particles being repelled back to the particle source.

It can be observed in high-speed camera films of the particle transport, that the time needed for particles to reach an aperture varies from one particle to another depending on mass and charge variations.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic view of an image forming apparatus according to the invention.

Fig. 2 is a schematic section view across a print station of the image forming apparatus.

Fig. 3 is a schematic perspective view of a positioning device in accordance with the invention.

Fig .4 is a section view of across the section line l-l of Figure 3.

Fig. 5 illustrate the adjustment of the curvature of the printhead structure in the positioning device of Fig. 3 and 4

Fig. 6 illustrates the position of the toner delivery unit on the positioning device of Fig. 3 and 4.

Fig. 7 is a partial view of a printhead structure showing the part of the substrate facing the toner delivery unit. • Fig. 8 is a partial view of a printhead structure showing the part of the substrate facing the belt unit.

Fig. 9 is a partial section view across the section lines ll-ll or Ill-Ill in Fig. 7 or 8.

Fig. 10 is an enlargement of a part of Fig.9 showing an aperture in the printhead structure. • Fig. 11 is a partial exploded view of the printhead structure illustrating its different layers.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT As shown in Fig.1, an image forming apparatus in accordance with a preferred embodiment of the invention comprises four print stations (Y, M, C, K) arranged in cooperation with a belt unit. However, it will be understood that an image forming apparatus in accordance with the invention comprises at least one print station, and an image receiving member. Allthough the illustrated embodiment is a four color printer, the present invention is neither restricted to a particular number of print stations nor a particular arrangement of the image receiving member. For instance toner particles could be projected directly on paper or any other material suitable for direct printing, without the need for an intermediate transfer belt. Alternatively, a solid drum could be provided for receiving the image and subsequently transferring this to paper or other final medium.

1. Belt Unit

The image forming apparatus illustrated in Fig.1 comprises a belt unit including a driving roller 10, at least one support roller 11 and several adjustable holding elements 12. The support roller 11 is provided with a mechanism for maintaining the transfer belt 1 with a constant tension, while preventing transversal movement of the transfer belt 1. The holding elements 12 are for accurately positioning the transfer belt 1 with respect to each print station. The driving roller 10 is preferably a cylindrical metallic sleeve having a rotation axis extending perpendicular to the motion direction (arrow 15) of the transfer belt 1 and a rotation velocity adjusted to convey the transfer belt at a velocity of one addressable dot location per print cycle to provide line by line scan printing. The adjustable holding elements 12 are arranged for maintaining the surface of the belt 1 at a predetermined gap distance from each print station. The holding elements 12 are preferably cylindrical sleeves disposed perpendicularly to the belt motion 15 in an arcuated configuration so as to slightly bend the belt 1 at least in a vicinity of each print station in order to create a stabilization force component on the belt in combination with the belt tension. That stabilization force component is opposite in direction to, and preferably larger in magnitude than an electrostatic attraction force component acting on the belt due to interaction with the different electric potentials applied on the corresponding print station.

The transfer belt 1 is preferably an endless band of 30 to 200 microns thickness having composite material as a base. The base composite material can suitably include thermoplastic polyimide 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 has preferably a homogeneous concentration of filler material, such as carbon or the like, which provides a uniform electric conductivity throughout the entire surface of the transfer belt. The outer surface of the transfer belt is preferably coated with a 5 to 30 microns thick coating layer made of electrically conductive polymer material having appropriate conductivity, thermal resistance, adhesion properties, release properties and surface smoothness.

The transfer belt 1 is conveyed past the four print stations, whereas toner particles are deposited on the outer surface of the transfer belt and superposed to form a four color toner image. Toner images are then conveyed through a fuser unit 16 comprising a fixing holder 161 arranged transversally in direct contact with the inner surface of the transfer belt 1. The fixing holder 161 includes a heating element 162 preferably of a resistance type of e.g. molybdenium, maintained in contact with the inner surface of the transfer belt 1. As an electric current is passed through the heating element 162, the fixing holder 161 reaches a temperature required for melting the toner particles deposited on the outer surface of the transfer belt 1. The fusing unit 16 further includes a pressure roller 163 arranged transversally across the width of the transfer belt 1 and facing the fixing holder 161. An information carrier 170, such as a sheet of plain untreated paper or any other medium suitable for direct printing, is fed from a paper delivery unit 17 and conveyed between the pressure roller 163 and the transfer belt 1. The pressure roller 163 rotates with applied pressure to the heated surface of the fixing holder 161 whereby the melted toner particles are fused on the information carrier 170 to form a permanent image. After passage through the fuser unit 16, the transfer belt 1 is brought in contact with a cleaning element 18, such as for example a replaceable scraper blade of fibrous material extending across the width of the transfer belt for removing all untransferred toner particles from the outer surface.

2. Toner delivery unit

As shown in Fig. 2, a print station in the image forming apparatus illustrated in Fig. 1, includes a particle delivery unit 2 preferably having a replaceable or refillable container 20 for holding toner particles T, the container having front and back walls (not shown), 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 22 disposed to continuously supply toner particles to a developer sleeve 21 through a particle charging member 23.

A particle charging member 23 is preferably formed of a supply brush or roller made of or coated with a fibrous, resilient material. The supply brush 23 is brought into mechanical contact with the peripheral surface of the developer sleeve 21 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 and any suitable coating material of the developer sleeve 21. The developer sleeve 21 is preferably made of metal coated with a conductive material, and preferably has a substantially cylindrical shape and a rotation axis extending parallel to the elongated opening of the particle container 20. Charged toner particles are held on the surface of the developer sleeve 21 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. Alternatively, the charge unit may additionally includes 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 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 invention.

A metering element 24 is positioned proximate to the developer sleeve 21 to adjust the concentration of toner particles on the peripheral surface of the sleeve 21 , to form a relatively thin, uniform particle layer thereon. The metering element 24 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 24 may also be connected to a metering voltage source (not shown) to produce an electric potential which influences the triboelectrification of the particle layer to ensure a uniform particle charge density on the sleeve surface.

A spacer element 5 is arranged proximate to the developer sleeve 21 to space the peripheral surface of the sleeve 21 from the printhead structure when the particle delivery unit 2 is secured on the positioning device 3. The spacer element 5 has a portion that is fastened to one of the side walls of the container 20, and a free portion made of flexible material, which is guided to a predetermined fixed position between the sleeve 21 and the printhead structure 4 as the particle delivery unit 2 is secured on the positioning device 3. 3. Positioning device

The developer sleeve 21 is arranged in relation to a positioning device 3 for accurately supporting and maintaining the printhead structure 4 in a predetermined position with respect to the peripheral surface of the developer sleeve 21. As shown in Fig. 3 and Fig. 4, the positioning device 3 is formed of a frame 30 having a front portion 301, a back portion 302 and two transversally extending side rulers 303, 304 disposed on each side of the developer sleeve 21 parallel with its rotation axis. The first ruler 303, positioned at a upstream side of the developer sleeve 21 with respect to its rotation direction, is provided with fastening means 31 to secure the printhead structure 4 along a transversal fastening axis 32 extending across the entire width of the printhead structure 4. The second side ruler 304, positioned at a downstream side of the developer sleeve 21 , is provided with a support element 33, or pivot, for supporting the printhead structure 4 in a predetermined position with respect to the peripheral surface of the developer sleeve 21. The support element 33 and the fastening axis 32 are so positioned with respect to one another, that the printhead structure 4 is maintained in an arcuated shape along at least a part of its longitudinal extension. As illustrated in Fig. 5, that arcuated shape has a curvature radius determined by the position of the support element 33 which can be adjusted by moving the support element in a longitudinal direction. The bending curvature of the printhead structure 4 is dimensioned to maintain a part of the printhead structure 4 curved around a corresponding part of the peripheral surface of the sleeve 21. The support element 33 is arranged in contact with the printhead structure 4 at a fixed support location on its longitudinal axis so as to allow a slight variation of the printhead structure position in both longitudinal and transversal direction about that fixed support location, in order to accommodate a possible eccentricity or any other undesired variations of the developer sleeve 21. That is, the support element 33 is arranged to made the printhead structure 4 pivotable about a fixed point to ensure that the distance between the printhead structure 4 and the peripheral surface of the developer sleeve 21 remains constant along the whole transverse direction at every moment of the print process, regardless of undesired mechanical imperfections of the developer sleeve 21. Preferably, parts of the printhead structure 4 are reinforced by stiffening element 41 , and only a central portion of the printhead structure is bendable. The front and back portions 301 , 302 of the positioning device 3 are provided with securing members 34 on which the particle delivery unit 2 can be removably secured in a predetermined print position, which is illustrated in Fig. 6. As the particle delivery unit 2 is secured in its print position, the free portion of the spacer element 5 is pressed against the curvated part of the printhead structure 4.

4. Printhead structure

As shown in Fig. 7-11, a printhead structure 4 in an image forming apparatus in accordance with the invention comprises a substrate 40 of flexible, electrically insulating material such as polyimide or the like, having a predetermined thickness, a first surface facing the developer sleeve 21 (Fig. 7), a second surface facing the transfer belt 1 (Fig. 8), a transversal axis 46 extending parallel to the rotation axis of the developer sleeve 21 across the whole print area, and a plurality of apertures 42 arranged through the substrate 40 from the first to the second surface thereof. The first surface of the substrate 40 is coated with a first printed circuit, comprising a plurality of control electrodes 43 disposed in conjunction with the apertures 42, and, in some embodiments, shield electrode structures (not shown) arranged in conjunction with the control electrodes 43. The second surface of the substrate is coated with a second printed circuit, including a plurality of deflection electrodes 44. The printhead structure 4 further includes a layer of antistatic material (not shown), preferably a semiconductive material, such as silicium oxide or the like, arranged on at least a part of the second cover layer, facing the transfer belt 1. The printhead structure 4 is brought in cooperation with a control unit (not shown) comprising variable control voltage sources connected to the control electrodes 43 to supply control potentials which control the amount of toner particles to be transported through the corresponding aperture 42 during each print sequence. The control unit further comprises deflection voltage sources (not shown) connected to the deflection electrodes 44 to supply deflection voltage pulses which controls the convergence and the trajectory path of the toner particles allowed to pass through the corresponding apertures 42. In some embodiments, the control unit, in some embodiments, even includes a shield voltage source (not shown) connected to the shield electrodes to supply a shield potential which electrostatically screens adjacent control electrodes from one another, preventing electrical interaction therebetween.

In a preferred embodiment of the invention, the substrate is a flexible sheet of polyimide having a thickness on the order of about 50 microns. The first and second printed circuits are copper circuits of approximately 8-9 microns thickness etched onto the first and second surface of the substrate, respectively, using conventional etching techniques. The printed circuits are insulated with cover layers 45 (shown in Fig. 10). Cover layers are preferably parylene films of 5 to 10 microns thickness, laminated onto the substrate 50 using vacuum deposition techniques. The apertures 42 are made through the printhead structure 4 using conventional laser micromachining methods. The apertures 42 have preferably a circular or elongated shape centered about a central axis 420 (shown in Fig. 11). The aperture diameter is in a range of 80 to 120 microns. Alternatively, elongated apertures have a transversal minor diameter of about 80 microns and a longitudinal major diameter of about 120 microns. Although the apertures have preferably a constant shape along their central axis, for example cylindrical apertures, it may be advantageous in some embodiments to provide apertures whose shape varies continuously or stepwise along the central axis, for example conical apertures.

In a preferred embodiment of the invention, the printhead structure 4 is dimensioned to perform 600 dpi printing utilizing three deflection sequences in each print cycle, i.e. three dot locations are addressable through each aperture 42 of the printhead structure 4 during each print cycle. Accordingly, one aperture is provided for every third dot location in a transverse direction, that is, 200 equally spaced apertures per inch aligned parallel to the transversal axis of the printhead structure. The apertures 42 are generally aligned in one or several rows, preferably in two parallel rows each comprising 100 apertures per inch. Hence, the aperture pitch, i.e. the distance between the central axes of two neighbouring apertures of a same row is 0,01 inch or about 254 microns. The aperture rows are preferably positioned on each side of the transversal axis 46 of the printhead structure 4 and transversally shifted with respect to each other such that all apertures 42 are equally spaced in a transverse direction. The distance between the aperture rows is preferably chosen to correspond to a whole number of dot locations.

As can be seen in Fig. 11, the first printed circuit comprises control electrodes 43 each of which having a ring-shaped structure 431 surrounding the periphery of a corresponding aperture 42 and a connector 432 preferably extending in the longitudinal direction, connecting the ring-shaped structure 431 to a corresponding control voltage source. Although a ring-shaped structure is preferred, the control electrodes 43 may take on various shape for continuously or partly surrounding the apertures 42, preferably shapes having symmetry about the central axis 420 of the apertures 42. In some embodiments, particularly when the apertures 42 are aligned in one single row, the control electrodes 43 are advantageously made smaller in a transverse direction than in a longitudinal direction.

The second printed circuit comprises a plurality of deflection electrodes 44, each of which is divided into two semicircular or crescent-shaped deflection segments 441 , 442 spaced around a predetermined portion of the circumference of a corresponding aperture 42. The deflection segments 441 , 442 are arranged symmetrically about the central axis 420 of the aperture 42 on each side of a deflection axis 443 extending through the center of the aperture at a predetermined deflection angle d to the longitudinal direction. The deflection axis 443 is dimensioned in accordance with the number of deflection sequences to be performed in each print cycle in order to neutralize the effects of the belt motion during the print cycle, to obtain transversally aligned dot positions on the transfer belt. For instance, when using three deflection sequences, an appropriate deflection angle is chosen to arctan(1/3), i.e. about 18,4°.

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

Claims

1. An image forming method in which an image information is converted to a pattern of control voltage pulses which modulate a transport of charged toner particles from a particle source to an image receiving member, said method comprising the steps of: providing a background voltage source for producing a background electric field between said particle source and said image receiving member, for enabling a transport of charged particle therebetween; providing a printhead structure between said particle source and said image receiving member, said printhead structure having a plurality of apertures arranged in said background electric field, and a plurality of control electrodes arranged in conjunction to the apertures; connecting the control electrodes to control voltage sources which supply control voltage pulses in accordance with the image information, each control voltage pulse being dimensioned to open a corresponding aperture for permitting the transport of an appropriate amount of charged particles therethrough, said transported charged particles being thereby attracted towards the image receiving member under influence of said background electric field, c h a r a c t e r i z e d i n that: each of said control voltage pulse has a duration which is shorter than the time period required for said appropriate amount of charged particles to be transported from said particle source past said corresponding aperture.
2. An image forming device in which an image information is converted to a pattern of control voltage pulses which modulate a transport of charged toner particles from a particle source to an image receiving member, said device comprising: a printhead structure arranged between said particle source and said image receiving member, said printhead structure having a plurality of apertures and a plurality of control electrodes arranged in conjunction to the apertures; control voltage sources for supplying control voltage pulses in accordance with the image information, each control voltage pulse being dimensioned to open a corresponding aperture for permitting the transport of an appropriate amount of charged particles therethrough, c h a r a c t e r i z e d i n that: each of said control voltage pulse has a duration which is shorter than the time period required for said appropriate amount of charged particles to be transported from said particle source past said corresponding aperture.
3. An image forming method as defined in claim 1, in which said image receiving member is caused to move relative said apertures, at a predetermined velocity corresponding to one pixel location per print sequence, wherein each print sequence includes at least one development period Tb during which control voltage pulses are applied, and at least one recovery period Tw during new particles are supplied on the particle source, c h a r a c t e r i z e d i n that Tb corresponds to the time required for an average particle to be released from the particle source and reach sufficient momentum to be transported through an aperture, and Tw corresponds to the time required for an average particle to be transported through the aperture to the image receiving member.
4. An image forming method as defined in claim 3, in which Tb is ended prior to that an average particle has reached an aperture.
5. An image forming method as defined in claim 3, in which Tb is ended prior to that an average particle has past through an aperture.
6. An image forming method as defined in claim 3, in which Tb is ended prior to that an average particle has reached a control electrode corresponding to an aperture.
7. An image forming method as defined in claim 3, in which Tb is shorter than 150 microseconds, preferably shorter than 80 microseconds.
8. An image forming method as defined in claim 1 , in which said control voltage pulse has a variable amplitude.
9. An image forming method as defined in claim 8, in which said control voltage pulse has a first amplitude level dimensioned to initiate the release of charged particles from the particle source and a second amplitude level dimensioned to provide an average particle with sufficient momentum to be transported through an aperture.
10. An image forming method as defined in claim 1 , in which any average particle released from the particle source is still located in a gap between the particle source and the aperture as the control voltage pulse is shut off, said any average particle having, at that moment, sufficient momentum to continue its trajectory toward the image receiving member.
1 . An image forming method as defined in claim 1 , in which any average particle released from the particle source is still located within an aperture as the control voltage pulse is shut off, said any average particle having, at that moment, sufficient momentum to continue its trajectory toward the image receiving member.
12. An image forming device as defined in claim 2, in which said printhead structure includes a substrate having a predetermined thickness, a first surface facing the particle source, a second surface facing the image receiving member, and apertures arranged through said substrate, from said first surface to said second surface, wherein said control voltage pulse has a duration corresponding to the time required for an average particle to be transported a distance approximately corresponding to the distance between the particle source and said first surface of said substrate.
13. An image forming device as defined in claim 2, in which said printhead structure includes a substrate having a predetermined thickness, a first surface facing the particle source, a second surface facing the image receiving member, and apertures arranged through said substrate, from said first surface to said second surface, wherein said control voltage pulse has a duration which does not exceed the time required for an average particle to be transported a distance corresponding to the distance between the particle source and said second surface of said substrate.
14. An image forming device as defined in claim 2, in which said printhead structure includes a substrate having a predetermined thickness, a first surface facing the particle source, a second surface facing the image receiving member, and apertures arranged through said substrate, from said first surface to said second surface, said printhead structure further including control electrodes arranged on said first surface of the substrate, wherein said control voltage pulse has a duration corresponding to the time required for an average particle to be transported a distance approximately corresponding to the distance between the particle source and one of said control electrodes.
15. An image forming method as defined in claim 3, in which, for any amount of particles released from said particle source during a development period Tb, that development period Tb is ended prior to that a first particle has past through an aperture.
PCT/SE2000/000016 2000-01-07 2000-01-07 Direct printing device and method WO2001049501A1 (en)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998040218A1 (en) * 1997-03-10 1998-09-17 Array Printers Ab Direct printing method with improved control function
US5847733A (en) * 1996-03-22 1998-12-08 Array Printers Ab Publ. Apparatus and method for increasing the coverage area of a control electrode during direct electrostatic printing
EP0884190A2 (en) * 1997-06-09 1998-12-16 Array Printers Ab Direct printing method with improved control function

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5847733A (en) * 1996-03-22 1998-12-08 Array Printers Ab Publ. Apparatus and method for increasing the coverage area of a control electrode during direct electrostatic printing
WO1998040218A1 (en) * 1997-03-10 1998-09-17 Array Printers Ab Direct printing method with improved control function
EP0884190A2 (en) * 1997-06-09 1998-12-16 Array Printers Ab Direct printing method with improved control function

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