Patent Publication Number: US-7583918-B2

Title: Electrographic printing or copying device, and method for operating one such printing or copying device

Description:
BACKGROUND 
   The preferred embodiment concerns an electrographic printing or copying device and in particular the cleaning of an applicator element that feeds toner to a photoconductor element. The preferred embodiment also concerns a method for operation of such a cleaning device. 
   A known device for cleaning of carrier elements in printers or copiers (DE 101 52 892 A1) comprise applicator rollers, photoconductor drums, transfer belts or photoconductor belts that are cleaned with magnetic roller arrangements. The surfaces of the rollers, drums or belts should be cleaned of toner with these magnetic roller arrangements. 
   In the known device a toner mixture made up of carrier particles and toner particles is supplied to an applicator roller via a magnetic roller arrangement. The applicator roller then transfers the toner particles onto a photoconductor corresponding to the characters to be printed. The toner remaining on the applicator roller and not transferred onto the photoconductor is removed from the surface of the applicator roller with a second magnetic roller arrangement. For this what is known as a magnetic brush is generated by the second magnetic roller arrangement, which magnetic brush brushes the still-remaining toner from the surface of the applicator roller with the aid of magnetic carrier particles arranged like beads. The toner mixture is then directed away from the applicator roller via rotation of the outer magnetic roller and fed again to a reservoir for toner mixture. 
   A device for transport of toner is known from the U.S. Pat. No. 4,647,179. The toner should thereby be applied on a photoconductor element in a developer station. For this charged toner particles are transported from a reservoir vessel to a traveling field device. The traveling field device comprises a plurality of spaced, linear electrodes that are connected with an alternating voltage source. Phase offset voltages are applied to the successive electrodes such that a progressive alternating electrostatic field arises. Toner particles are moved along the progression direction to the photoconductor element via this alternating field and the toner particles are drawn onto the photoconductor element via the corresponding oppositely charged photoconductor element. 
   For cleaning of the photoconductor element a vacuum sucker is provided that sucks the toner particles from the photoconductor element. In the known devices the toner is significantly damaged upon cleaning of the applicator elements since it is severely mechanically stressed in the cleaning, either due to the suction or by the brushing. 
   In a further known electrographic printing or copying device (DE 197 30 729 A1), toner is removed from a photoconductor belt by means of a cleaning device. The toner is thereby electrically and mechanically removed by the cleaning device. The cleaning device is a roller that rotates. The cleaning device is additionally connected to a direct voltage source whose voltage is set between 200 and 1000 V dependent on the toner quantity on the photoconductor belt. The transport of the toner away thereby occurs via rotation of the cleaning device, whereby the transfer onto the roller is assisted by the voltage. 
   The cleaning device comprises a cylindrical fur brush that rotates counter to the rotation direction of the photoconductor drum and thereby mechanically removes the toner from the photoconductor drum. A cleaning blade supports the removal of the toner from the photoconductor drum. A beating rod removes the toner from the fur brush and allows it to fall into a toner discharge screw. From there the toner is mechanically transported away. 
   Here an electromechanical cleaning also occurs, which is disadvantageous due to the wear. 
   SUMMARY 
   It is an object to achieve an electrographic printing or copying device given which no mechanical load or only a slight mechanical load is present for the toner in the cleaning of a carrier element and which exhibits no mechanically moving parts. 
   In a method or device for operation of an electrographic printing or copying device, at least toner particles are accumulated on a surface of a first carrier element. After a transfer of toner particles onto a further carrier element, toner particles still remaining on the first carrier element are removed by generating a traveling field between the first carrier element and the cleaning device which transports the toner particles. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is section through electrographic printing or copying device of the preferred embodiment; 
       FIG. 2  shows a cleaning device of the printing or copying device according to  FIG. 1 ; 
       FIG. 3  shows a traveling field generation element of the cleaning device according to  FIG. 2 ; and 
       FIGS. 4 through 6  are further exemplary embodiments of the cleaning device in a respective electrographic printing or copying device (respectively shown in parts and in a section image). 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the preferred embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, and such alterations and further modifications in the illustrated device and such further applications of the principles of the invention as illustrated as would normally occur to one skilled in the art to which the invention relates are included. 
   The printing or copying device in the preferred embodiment thereby comprises a cleaning element that is arranged at a distance from a carrier element to be cleaned. An electrical and/or magnetic field by which the toner particles are drawn to the cleaning device exists between the carrier element and the cleaning device. The cleaning element comprises a traveling field generation element via which the attracted toner particles are transported away along the traveling field. 
   Such a traveling field device has the advantage that the toner particles are transported away in the direction of the progressing traveling field without being mechanically stressed. The toner particles thereby do not abrade on the cleaning device but rather are moved by the field forces. The abrasion of the particles on one another is also relatively slight. Various transport directions can be realized via simple control. The traveling field can also be utilized to draw the toner particles from the carrier element to the cleaning device. 
   Various carrier elements (such as a toner feed element, an inking element, a developer element or a photoconductor element) can thus be cleaned of remaining toner with such a cleaning device. 
   The cleaning device advantageously comprises a plurality of electrodes spaced from one another that are controlled by a control unit in the sense of a traveling field generation. An electrical field is generated by the electrodes. Instead of the electrodes, magnetic field generation elements can naturally also be used via which a traveling magnetic field is then generated via which magnetic toner particles can be transported away. 
   The cleaning device with the electrodes is advantageously designed as a circuit board with conductor traces, whereby the conductor traces are designed as a plurality of electrodes arranged parallel to one another. If a flexible circuit board (conductor traces on a flexible, electrically insulating intermediate layer) is used, the circuit board can be attached on a shaped, largely rigid carrier element. The toner can then be better directed in the direction of a toner mixture container and be directed back again into the printing system. 
   It is also advantageous to control a plurality of groups of electrodes with an alternating voltage. The voltage can thereby change cyclically in a sinusoidal, stepped or also linear manner from a small amplitude to a large amplitude and vice versa. It can thereby be achieved in a simple manner that traveling fields are generated in corresponding desired directions in that the various groups of electrodes are activated correspondingly. It is also possible to simultaneously generate different directions of traveling fields in that other groups of electrodes are activated in a different direction. 
   A section from an electrographic printing or copying device is shown in a section image in  FIG. 1 . In the present exemplary embodiment only the developer station  10  is shown via which toner is fed to a photoconductor belt of an electrographic printing system. The exposure station and the fixing station are not shown, nor are the printing substrate feed and post-processing. 
   Given the electrophotographic printing principle electrically-charged toner particles  11  (also designated as toner in the following) are mixed with magnetic or ferromagnetic carrier particles  12  and form what is known as a two-component mixture (also designated as a toner mixture  13 ). This mixture  13  is supplied to a bucket roller  16  via a merging screw  15 . Toner consumed by the printing is replenished by the toner transport coil  14 . The bucket roller  16  rotates and thereby triboelectrically charges the toner  11 . The bucket roller  16  comprises buckets (not shown) arranged distributed over its length, which buckets convey toner mixture from the bucket roller  16 . Due to a helical design a portion of the mixture  14  is transported along the entire length of the bucket roller  16  so that toner mixture can be conveyed away by the buckets all along the bucket roller  16 . At the end the remaining mixture  13  is conveyed to the front again by the merging screw  15  or transport screw and resupplied to the bucket roller  16 . 
   The toner mixture  13  is supplied to an inking roller  18  over the entire length via the bucket roller  16 . This inking roller  18  comprises a rotating hollow roller  19  with a magnetic roller stator  20  located inside it. 
   The magnetic roller stator  20  comprises permanent magnets or electromagnets  21  that are arranged stationary along the inner circumference of the hollow roller  19 . The magnets  21  attract the carrier particles  12  (and therewith the toner particles  11  adhering to the carrier particles  12 ) towards the surface of the hollow roller  19 . Due to the rapidly rotating hollow roller  19  the toner mixture  13  (which adheres slightly to the surface) is transported into proximity of an applicator roller (designated as a jump roller  25  in the following). 
   Given the electrophotographic principle, an electrical field that is generated via application of distinctly different electrical potentials (for example −1000 V or −300 V) exists between the inking roller  18  and the jump roller  25 . The electrically-charged toner particles  11  are drawn towards the jump roller  25  by the electrical field when the toner is located near enough to the jump roller  25  and the field forces on the toner are greater than the adhesion forces on the carrier particles  12  as well as the hollow roller  19  and the magnetic forces. The region of the transition or of the application of toner onto the jump roller  25  is designated here as an accumulation point  26  since the toner is accumulated in a laminar manner (optimally without gaps) on the jump roller  25 . 
   The carrier particles  12  are magnetically or ferromagnetically designed (for example, they are produced from iron). They are not electrostatically charged and are therefore not drawn to the jump roller  25  (only in an undesirable manner when the toner  11  adheres too strongly to the carrier particles  12  and the electrical field is strong enough), but rather react to magnetic fields due to their magnetic properties. The carrier particles  12  are transported further along the surface of the hollow roller  19  due to the fast rotation of the hollow roller  19  and the attraction force of the magnets  21 . Due to the centrifugal force and gravity, the carrier particles  12  drop off from the surface of the inking roller  18  after the accumulation point  26  and fall downwards (due to gravity) into a reservoir for toner  11  and carrier particles  12 . The carrier particles  12  can thus be fed again to the bucket roller  16  and therewith to the printing process. 
   The goal of the accumulation of toner  11  at the jump roller  25  is that the jump roller  25  is coated with a thick layer of toner particles  11  without gaps on its surface between the accumulation point  26  and a subsequent transfer point  27 . 
   For instance, still-present carrier particles  12  that have likewise attached to the jump roller  25  in an undesirable manner are removed by a carrier capture roller  30 . This carrier capture roller  30  is likewise provided as a magnetic roller with a rotating hollow roller  31  and a stationary magnetic roller stator  32 . Only toner particles  11  thus arrive at the transfer point  27  where toner  11  is transferred onto a photoconductor at those points at which a print character should also be. 
   The photoconductor here is designed as a photoconductor belt  34 . This photoconductor belt  34  is initially electrostatic charged (for example to −550 V) and discharged at points (for example −30 V) via an optical unit corresponding to the points/characters to be printed or not to be printed. Toner  11  is drawn to the photoconductor belt  34  only at these points via a correspondingly directed electrical field between the jump roller  25  and the discharged points of the photoconductor belt  34 . The toner  11  is then fed to a transfer printing station (not shown) in the further course of the photoconductor belt  34 . The toner is then transferred onto a printing substrate, recording medium or final image medium (for example paper or plastic film) and subsequently fixed. 
   Since only a small portion of the toner particles  11  normally jump over onto the photoconductor belt  34  (dependent on the respective print image), many toner particles  11  remain adhered to the jump roller  25 . In order to again obtain a uniformly thick toner particle carpet after the accumulation point  26  of the inking roller  18 , the remaining toner particles  11  should initially be removed from the jump roller  25 . This occurs via a cleaning device  35 . 
   The cleaning device  35  exhibits on its surface distinctly different voltage potentials relative to the surface of the jump roller  25 . An electrical field (see arrow  33  in  FIG. 2 ) thereby arises between the jump roller  25  and the cleaning device  35 , via which toner particles  11  jump over from the jump roller  25  onto the cleaning device  35  when the toner particles  11  arrive close enough to the cleaning device  35 . The typical smallest distance between jump roller  25  and cleaning device  35  is approximately 0.2 to 0.3 mm so that (given the existing voltage potentials) toner particles  11  can jump this distance as a consequence of the electrical field and thus are attracted. 
   The cleaning device  35  additionally comprises a traveling field generation element via which an electrostatic and/or magnetic traveling field is generated that transports the toner particles  11  along the propagation direction (see arrow  36  in Figures) of the traveling field. The toner particles  11  can thus be transported in a targeted manner to desired points corresponding to the direction of the traveling field. It is advantageous when the electrical field for attracting the toner particles  11  is generated as well by the traveling field. 
   In the exemplary embodiment according to  FIG. 1  the toner particles  11  are transported in the direction of the carrier particles  12  falling from the inking roller  18  and mix with these. The mixture then sinks in the direction of the bucket roller  16  and is thus fed again to the printing process. 
   According to  FIG. 2  an exemplary embodiment of a traveling field generation element of a cleaning device  35  comprises a plurality of electrodes  37  arranged approximately parallel to one another, which electrodes  37  are designed as conductor traces on a circuit board  38 . The individual conductor traces or electrodes  37  are provided (via an alternating voltage source  39 ) with different voltage potentials (here the three voltage potentials U 1 , U 2  and U 3 ). If the electrodes  37  are provided with the voltage potentials consecutively and in cyclical rotation (i.e. are consecutively and alternately activated in a phase-shifted manner in one direction), a traveling field arises transverse to the electrodes  37  (traveling field direction  36  in  FIG. 2 ). 
   According to  FIG. 2 , a plurality of groups of electrodes  37  are provided (each group there comprises three electrodes  37 ), whereby within a group the various electrodes  37  are supplied with different voltages that are varied cyclically such that an electrical field (traveling field) progressing transverse to the electrodes  37  arises. 
   When the jump roller  25  exhibits on its surface a voltage potential of, for example, approximately −300 V and the voltage potentials of the electrodes  37  are distinctly deviating from this (distinctly more positive in the exemplary embodiments), a negatively-charged toner particle  11  is thus attracted from the jump roller  25  to the electrodes  37 . Since the electrical field is inversely proportional to the distance between the respective parts, the cleaning device  35  must approach the jump roller  25  up to approximately 0.2 to 0.3 mm when the voltage potentials of the cleaning examination volume  35  are greater than/equal to 0 V and the jump roller  25  exhibits a potential of −300 V. 
   When the voltage potentials of the various electrodes  37  are all greater than, for example, 0 V, the electrodes  37  also already act in an attractive manner on the negatively-charged toner particles  11 . To generate the traveling field, groups with three electrodes  37  can be present, whereby a voltage potential of U 1 =0 V can be present at the first electrode, a voltage potential of U 2 =+700 V can be present at the second electrode and a voltage potential of U 3 =+1400 V can be present at the third electrode. This is equivalent to a step-like alternating voltage with the three voltage values U 1 , U 2  and U 3  that are applied phase-shifted to the electrodes  37 . 
   No separate field generation device is then necessary in order to draw the toner particles  11  from the jump roller  25  to the cleaning device  35 ; rather, the different voltage potentials of the electrodes  37 , all of which are distinctly higher than the voltage potential of the jump roller  25 , are sufficient here. 
   The toner particles  11  attracted by the electrodes  37  are then transported forward along the direction of the traveling field by the traveling field of the electrodes  37 . Since the movement of the toner particles  11  is generated by electrical fields, barely any mechanical load is exerted on the toner particles  11 . The toner particles  11  can therefore be used without further measures for the further printing process and be resupplied to the toner mixture  13 , from where they arrive on the surface of the jump roller  25  via the bucket roller  16  and the inking roller  18 . 
   An exemplary embodiment for a circuit board  38  of the cleaning device  35  is shown in  FIG. 3 . A plurality of electrodes  37  are thereby arranged parallel to one another. The distance a from electrode to electrode is, for example, a=0.2 mm and the width d of an electrode is likewise d=0.2 mm, The thickness of the electrodes  37  can be a typical thickness of conductor traces on a circuit board  38 , for example from 20 to 400 μn. 
   Due to the small distances a and the very slight thickness, it is possible that the toner particles  11  are drawn from one electrode to another (as a consequence of an electrical field between the electrodes  37 ) without remaining attached to the electrodes  37 . 
   When (as schematically indicated in  FIG. 3 ) the voltage potentials U 1  to U 3  are now switched along from one electrode to the adjustment electrode from time to time (cross-over switching points in time t 1  through t 7  are plotted to the left in  FIG. 3 ), a voltage difference thus always arises between two adjacent electrodes  37  that changes continuously and cyclically transverse to the electrodes  37  and advances in the traveling field direction  36 . A traveling electrical field is thereby created via which negatively-charged toner particles  11  are drawn along and are consequently moved and transported in the direction of the traveling field. 
   As in the example according to  FIG. 2 , the voltage potentials of the electrodes  37  can thereby be cyclically changed in stages from U 1 =0 V to U 2 =+700 V and further to U 1 =+1400 V as well as then back to U 1 =0 V. Finer stepped sub-divisions for the voltage potentials can also be effected, which then also leads to a higher number of electrodes  37  within a group. It is thereby essential that the potential differences between two electrodes  37  is great enough in order to draw the toner particles  11  from electrode to electrode in order to thereby create a traveling field via which the toner particles  11  are transported forward along the circuit board  37 . 
   Instead of staged or stepped changes of the voltage potentials, a sinusoidal or continuous linear change of the voltage potentials can also be cyclically effected. 
   The direction of the traveling field thereby depends on the activation of the field generation elements (here the electrodes  37 ) by the alternating voltage source  39 . The circuit board  38  is located at one end in proximity to the jump roller  25  and leads approximately tangentially away from the jump roller  25  in the direction of the bucket roller  16  in which the toner mixture  13  is prepared (see  FIG. 1 ). The circuit board  38  can also be arranged with the other end in proximity to the jump roller  25  and leads approximately tangentially away, however in the opposite direction as before (see  FIG. 4 ). The respective traveling field is then designed proceeding (in Figures) either from right to left ( FIG. 1 ) or from left to right ( FIG. 4 ) corresponding to the activation of the electrodes  37 . 
   It is likewise possible in a simple manner to generate two or more traveling fields via which (as shown in  FIG. 5 ) traveling fields arise in different proceeding directions. For example, the toner can thus be transported away to both sides of the cleaning device  35 . When the toner is moved in the direction of the inking roller  18  and therewith in the direction of the carrier particles  12  transported away from the inking roller  81  the toner particles  11  can already admix with the carrier particles  12  and again be supplied mixed to the entire process via the bucket roller  16  and the inking roller  18 . 
   It is advantageous when the beginning of the toner transport (at the electrode where the toner particles  11  are drawn from the jump roller  25  to the cleaning device  35 ) by the traveling field lies in the region of the nearest approach of the cleaning device  35  to the jump roller  25 . It is thereby ensured that the toner cannot arrive back on the jump roller  25  and is transported away from the jump roller  25  by the traveling field. 
   The circuit board  38  does not necessarily have to be designed flat. It can also be curved convexly or concavely or be spatially shaped otherwise. At the point that comes nearest to the jump roller surface, the toner particles are drawn to the circuit board  38  and then transported away corresponding to the traveling field and its direction  36 . At the end of the circuit board  38 , the toner particles fall away from the circuit board  38  due to gravity. The falling away from the circuit board  38  could also be achieved via corresponding electrical fields that act in a repulsive manner on the toner particles  11 . 
   As shown in  FIG. 6 , the circuit board  38  can also be designed as a three-dimensional circuit board  38 . For this a flexible circuit board  38  can be attached on a shaped, rigid carrier  40 . In this exemplary embodiment the cross-section of the carrier  40  is arced with a small space at one end from which the toner is transported away in the direction of the other end due to the traveling field. The electrodes  37  thereby run approximately parallel to one another and extend in the axial direction of the jump roller  25  over the entire length of the jump roller  25 . It is thereby ensured that the toner is removed from the jump roller  25  over the entire length. The shape of the carrier  40  is thereby designed such that the toner  11  moving along the traveling field is transported away from the jump roller  25 . 
   The outer surface of the first carrier element (jump roller  25 ) exhibits a roughness in the range from 1 to 5000 μm. The toner particles  11  thereby remain well attached in order to transport them from the accumulation point  26  to the transfer point  27 . On the other hand, the surface is then not too rough to remove the toner particles  11  remaining on the surface from this by the cleaning device  35 . 
   The surface of the second carrier element (this is the photoconductor belt  34  in the described exemplary embodiments) comprises at least the components aluminum, chromium, nickel, copper, conductive plastic and/or plastic with a conductive layer. The toner can thereby accumulate well there. 
   As in the previous exemplary embodiments, the cleaning device  35  with electrodes  37  can be designed such that a traveling electrical field is created. The traveling electrical field is then used when electrostatically-charged toner  11  is to be transported away. Magnetic or ferromagnetic toner can be transported away via a magnetic field. For this the cleaning device must exhibit magnetic field generation elements that are activated such that a traveling magnetic field is created. The cleaning device can likewise be designed as an electromagnetic traveling field generation element in order to transport both electrically-charged particles and magnetic or ferromagnetic particles away. 
   In the method for operation of an electrographic printing or copying device, to clean a first carrier element the toner particles  11  are removed from the first carrier element by a field-generating device in that a first field is generated. According to the preferred embodiment, an electrical, magnetic or electromagnetic field in the manner of a traveling field is generated to transport the toner away, in that a field-generating unit of the cleaning device  35  is cyclically activated. The toner particles  11  are transported along by this traveling field. 
   It is advantageous when the traveling field is simultaneously used as well to transfer the toner from the first carrier element onto the cleaning device  35 . Given the electrostatically-charged toner  11 , this can occur due to the voltage potentials U 1 , U 2 , U 3  of the participating elements. For this the first carrier element exhibits a distinctly different voltage potential relative to all voltage potentials of the field-generating unit with its electrodes  37 . Additional necessary parts are thereby spared. 
   Due to the transport of the toner away via the traveling field, no mechanically moving parts are necessary. No element of the cleaning device  35  contacts the first carrier element. Also, no spatula that abrades the toner from the first carrier element is therefore necessary. 
   The toner particles  11  are thereby transported virtually without contact, and in fact only by means of electrical, magnetic or electromagnetic fields, which leads to a significantly lower mechanical stressing of the toner particles  11 . The mutual abrasion of the particles on one another is likewise less. 
   Different directions  36  of traveling fields or also a plurality of traveling fields with different directions can then be generated via simple activation of the field-generating unit (alternating voltage source  39 ). The carrier elements to be cleaned can be inking elements, toner feed elements, developer elements, photoconductor elements or other toner-transporting elements that are designed as cylindrical rollers or in the form of endless belts. The toner  11  or also the toner mixture  13  can be transferred from the carrier element to further carrier elements (such as, for example, photoconductor elements) or to recording media to be printed. That element from which the toner  11  or the toner mixture  13  is transferred to another carrier element must subsequently be cleaned so that new toner  11  or toner mixture  13  can therewith be cleanly applied. This increases the quality of the generated print image. 
   The preferred embodiment depends not on whether the printing or copying devices operate according to the electrophotographic, electromagnetic or other printing principles, but rather on toner particles  11  being cleanly removed from a carrier element fur the purposes of cleaning and being supplied to a reservoir. The cleaning device  35  thereby provides the corresponding field in order to attract and then to also transport away the electrically-charged or magnetic toner particles  11 . The electrophotographic principle, given which the toner is electrostatically charged and transported by means of electrical fields, is advantageously used. The cleaning device  35  then comprises electrodes  37  for generation of a traveling electrical field. 
   While a preferred embodiment has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention both now or in the future are desired to be protected.