Abstract:
A cleaning unit is provided for cleaning of a transport belt for transport of recording media in a electrographic printer or copying device. An abration element is positioned to avoid toner located on the transport belt. A toner capture reservoir captures abraded toner.

Description:
BACKGROUND  
       [0001]     The present disclosed preferred embodiment concerns a cleaning unit and a method for cleaning a transport belt for transport of recording media in the transfer printing region of an electrographic printing or copying device, as well as an abrasion element and a capture reservoir for such a cleaning unit.  
         [0002]     In electrographic printers or copiers, the transfer of a toner image from an intermediate carrier (for example a photoconductor drum or a photoconductor ribbon) onto a recording medium is designated as transfer printing. The section of the printing or copying device at which the intermediate carrier and the recording medium are brought into contact with one another is designated as a transfer printing region. In the transfer printing region, the intermediate carrier (meaning, for example, the generated surface of a photoconductor drum) and the recording medium move in the same direction with the same speed while the toner is transferred from the intermediate carrier onto the recording medium. A print image of high quality can only be achieved on the recording medium when a uniform contact between recording medium and intermediate carrier is produced in the transfer printing region and when the recording medium and the intermediate carrier actually move with exactly the same speed in the transfer printing region.  
         [0003]     In order to ensure this, transport belts are proposed on which the recording media (for example electrostatically adhering) are transported through the transfer printing region. With such a transport belt, the transport speed of the recording medium in the transfer printing region can be predetermined exactly and without interference, and a uniform arrangement of the recording medium on the intermediate carrier can be achieved. Since the transport belt moves through the transfer printing region, it can easily be contaminated with toner. When, for example, individual paper sheets are used as recording media, toner can arrive on the intermediate regions between successive sheets and in the boundary regions outside of the paper dimension. In the event that the recording medium is printed on both sides, toner can moreover loosen from an already-printed side with which the recording medium lies on the transport belt and contaminate this. A transport belt contaminated with toner in turn contaminates subsequent recording media, which is not acceptable.  
         [0004]     A cleaning unit is known from DE 198 31 786 A1 that has an abrasion element (arranged transverse to the running direction of the transport belt and lying on this) that is set to abrade toner located on a transport belt and that has a toner capture reservoir for capture of the abraded toner.  
         [0005]     An abrasion element for a photoconductor drum is known from JP 03-200191. The abrasion element is comprised of a synthetic rubber that is admixed with 1 weight percent aluminum oxide as a polishing agent. A further abrasion element for a photoconductor drum is known from EP 0 691 594 A1. Rubber, plastic, metal and ceramic are cited therein as materials for the abrasion element. The material rubber is thereby preferred.  
         [0006]     A cleaning unit with a mounting device for an abrasion element that is rotatable by 180° is known from EP 0 546 751 A2. Various edges of the abrasion element can thereby be used for cleaning. Toner capture reservoirs are disclosed in U.S. Pat. No. 4,730,205, U.S. Pat. No. 6,405,016 B1, U.S. Pat. No. 5,581,342, U.S. Pat. No. 4,500,196 and U.S. Pat. No. 5,383,011.  
       SUMMARY  
       [0007]     It is an object to specify a cleaning unit for cleaning of a transport belt with which the transport belt can be thoroughly cleaned of toner.  
         [0008]     A cleaning unit is provided that has an abrasion element that is positioned to abrade toner located on the transport belt and a toner capture reservoir to capture the abraded toner. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a schematic representation of a cleaning unit for cleaning of a transport belt for transport of recording media in the transfer printing region of an electrographic printer;  
         [0010]      FIG. 2 a  schematic representation of the transport belt of  FIG. 1  that is pressed by an abrasion element against the felt of a support element;  
         [0011]      FIG. 3 a  bottom view of the transport belt of  FIG. 1  with abrasion bar lying thereon;  
         [0012]      FIG. 4  is a plan view of the abrasion bar of  FIG. 1  through  3  in its mounting;  
         [0013]      FIG. 5  is a side view of the abrasion bar of  FIG. 1  through  4  in its mounting;  
         [0014]      FIG. 6  is a section along the line A-B of  FIG. 4 ;  
         [0015]      FIG. 7 a  perspective view of a toner capture reservoir with partially inserted cover;  
         [0016]      FIG. 8 a  perspective view of the toner capture reservoir of  FIG. 7  without cover; and  
         [0017]      FIG. 9  is an enlarged section of  FIG. 8 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]     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, such alterations and further modifications in the illustrated device, and/or method, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur now or in the future to one skilled in the art to which the invention relates.  
         [0019]     In tests, the use of very hard materials for the abrasion element has proven to be advantageous, both concerning the thoroughness of the cleaning and the wear of the transport belt and of the abrasion element itself. Abrasion elements made from ceramic, whose wear was by far less (due to their hardness) than, for example, that of a likewise tested abrasion element made of spring steel, have proven to be particularly advantageous. In a particularly advantageous embodiment, the abrasion element is made from an aluminum oxide ceramic that represents a very good compromise between high wear durability and advantageous production costs.  
         [0020]     In the production of the ceramic it is advantageous to grind the initial materials to a grain size that is smaller than or equal to that of the toner particles. In the event that individual grains loosen from the ceramic abrasion element, the cavities created are small enough that no toner particles pass through them and therefore possibly remain on the transport belt in spite of the cleaning unit.  
         [0021]     In an advantageous development of the present preferred embodiment, the abrasion element is designed as a cuboid-shaped abrasion bar. The cleaning unit also preferably has a mounting device in which the abrasion bar can be used in four different positions, whereby the four positions differ from one another by a rotation of the abrasion bar by respectively 180° around its longitudinal axis and/or its transverse axis. Via these four positions, all four longitudinal edges of the abrasion bar can be used in succession for abrasion of the toner, which quadruples the lifespan of the abrasion bar.  
         [0022]     In order to conserve the longitudinal edges, the mounting preferably has recesses that prevent a contact of the longitudinal edges of the abrasion bar with the mounting. Longitudinal edges of the abrasion bar not yet used for abrasion thus remain sharp.  
         [0023]     The mounting preferably has a receptacle in which the abrasion bar is inserted with a positive fit and a clamping plate with which the abrasion bar is clamped fast in the receptacle. The change of the position of the abrasion bar in the mounting device can thereby be implemented simply and quickly. In particular the alignment of the abrasion bar with regard to the transport belt thereby does not have to be readjusted, since the abrasion bar is placed in the mounting with a positive fit and therefore in an explicit position, and the position of the mounting does not vary upon changing the position of the abrasion bar.  
         [0024]     A flexible support element for the transport belt is preferably provided on the side of the transport belt opposite the abrasion element. The transport belt can then be pressed against the flexible support element by the abrasion element, whereby a consistent contact results between transport belt and abrasion element.  
         [0025]     The support element preferably comprises a felt lying on the transport belt. Such a felt offers a sufficient flexibility and at the same time serves to clean the side of the transport belt facing away from the abrasion element. In an advantageous development, the felt is arranged with a positive fit in a metal receptacle. It is thereby prevented that the felt is loosened or shifted by the transport belt.  
         [0026]     As mentioned above, the cleaning unit of the preferred embodiment comprises a toner capture reservoir to capture the abraded toner. The captured toner can, for example, be transported with a screw transport from the toner capture reservoir into a waste toner reservoir present anyways in an electrographic printer or copier. The transport device necessary for placing the captured toner into the waste toner reservoir present anyway, is, however, relatively elaborate and costly. Therefore, in the present preferred development, such a transport is foregone and instead of this the capture reservoir is designed such that it can be removed from the printing or copying device. The capture reservoir thus simultaneously serves as an independent waste toner reservoir.  
         [0027]     The toner capture reservoir can preferably be sealed in the printer or copying device. Upon removal of the capture reservoir from the printer or copying device, no toner can then be spilled.  
         [0028]     In a preferred development, the toner capture reservoir is electrically conductive. The toner (normally electrostatically charged) can thereby be discharged in the toner capture reservoir and does not tend to accumulate at components located in the environment of the capture reservoir and charged opposite to the toner.  
         [0029]     When the toner conveyance system is simultaneously used as a waste reservoir, it is important that it can be produced particularly cost-effectively. The toner capture reservoir is preferably comprised of plastic that can be cost-effectively processed. The toner capture reservoir is thereby preferably produced in a vacuum deep-draw method which enables a small material consumption and low production costs.  
         [0030]     Guide grooves into which a cover to seal the toner capture reservoir can be inserted are preferably designed on the toner capture reservoir. The guide grooves are preferably formed by down-turned sections of the edge of the toner capture reservoir. The toner capture reservoir also preferably has an engagement section at which the toner capture reservoir can be engaged upon its removal from the printer or copying device and that is height-displaced relative to the guide grooves, such that it undercuts the inserted cover.  
         [0031]     Longitudinal and/or transverse ribs that prevent a flow movement of the toner in the toner capture reservoir are preferably designed in the toner capture reservoir.  
         [0032]     In a preferred development, the cleaning unit comprises a microswitch that scans whether the toner capture reservoir is correctly arranged in the printer or copier.  
         [0033]     The transfer printing of a toner image from the generated surface  10  of a photoconductor drum  12  onto a sheet of paper  14  is schematically shown in  FIG. 1 . The transfer of the toner from the photoconductor drum  12  onto the paper sheet  14  occurs in the transfer printing region  16 , in which the generated surface  10  of the photoconductor drum  12  and the sheet  14  contact one another. The toner located on the generated surface  10  of the photoconductor drum  12  is electrostatically charged and is transferred onto the sheet  14  in a known manner with the aid of electrostatic field forces.  
         [0034]     The sheet  14  electrostatically adheres to the transport belt  18  that revolves counterclockwise with a revolution speed V U  in the representation of  FIG. 1 , as is indicated by corresponding speed arrows. The photoconductor drum  12  rotates clockwise in the representation of  FIG. 1 , whereby the generated surface  10  moves with a tangential speed V U  of the transport belt  18 . The exact coincidence of V T  and V U  is a precondition of the toner image being transfer printed without distortion and without smearing.  
         [0035]     In addition to the sheet  14  located in the transfer printing region  16  in  FIG. 1 , an already-printed sheet  20  is shown. The transport belt  18  is contaminated with toner particles  22  (schematically shown) between these two successive sheets. The toner particles  22  may, for example, have been transferred from the photoconductor drum  12  onto the transport belt  18  when this was not completely cleaned of residual toner.  
         [0036]     Furthermore, a cleaning unit  24  for cleaning of the transport ribbon  18  is shown in  FIG. 1 . The cleaning unit  24  comprises an abrasion bar  26  that is arranged transverse to the running direction of the transport belt  18 , a support element  28 , and a toner capture reservoir  30 . The support element  28  is likewise arranged transverse to the running direction of the transport belt  18  and has a flexible felt  32  that is arranged with a positive fit in a metal receptacle  34 .  
         [0037]     With the transport belt  18 , the abrasion bar  26  encloses an angle of 30° and, with its first longitudinal edge  36   a , presses the transport belt  18  against the felt  32  of the support element  28  with a pressure force F d  represented in  FIG. 1  by a force arrow. The pressure force F d  is generated by a spring (not shown in  FIG. 1 ) with which the abrasion bar  26  is pressed with its first longitudinal edge  36   a  against the transport belt  18  such that it acts in an impinging manner counter to the belt running direction. When the transport belt passes the cleaning unit  24 , toner  22  adhering on the transport belt remains hanging on the longitudinal edge  36   a  of the abrasion bar  26  and, due to gravity, falls into the toner capture reservoir  30 .  
         [0038]     The abrasion bar  26 , the transport belt  18  and the felt  32  of  FIG. 1  are shown in an enlarged view in  FIG. 2 . As is to be seen therein, due to the pressure force F d  the transport belt  18  travels closely around the longitudinal edge  36   a  such that no toner particles  22  pass this.  
         [0039]     In the shown exemplary embodiment, the abrasion bar  26  is comprised of an aluminum oxide ceramic and the transport belt  18  is comprised of polyvinylidenfluoride (PVDF). The combination of the very hard ceramic with the soft transport belt enables a very thorough cleaning with very low wear, both of the transport belt  18  and of the abrasion bar  26 . The ceramic allows a very smooth, even and precise production of the abrasion bar, which contributes to the thoroughness of the cleaning and to the lifespan of the transport belt  18 . The friction forces occurring between PVDF belt  18  and ceramic bar  26  are so slight that the belt speed is barely affected by the abrasion bar.  
         [0040]     The surface quality of the ceramic abrasion bar  26  is tuned to the grain size of the toner. In particular, in its production the initial materials of the ceramic are milled to a grain size that is smaller or equal to that of the toner particles. When individual grains loosen from the ceramic, the cavities thereby created in the abrasion bar are so small that no toner particles  22  pass through and thus can remain on the transport belt  18 .  
         [0041]     A bottom view of the transport belt  18  and a part of the abrasion bar  26  are shown in  FIG. 3 . The abrasion bar  26  is arranged with positive fit in a mounting  38  and extends transverse to the running direction of the transport belt  18  over its entire width. For reasons of clarity, the mounting  38  was left out in the schematic representation of  FIG. 1 . The mounting  38  is set once transverse to the transport belt  18 , such that a uniform pressure force F d  results over the entire width of the transport belt  18 . Since the abrasion bar  26  is arranged with a positive fit in the mounting  38 , neither the abrasion bar  26  nor the mounting  38  have to be readjusted when the abrasion bar  26  is exchanged or, as is described in detail below, when the abrasion bar  26  is rotated around one of its axes of symmetry.  
         [0042]     As is furthermore shown in  FIG. 3 , the toner  22  can adhere both to the edges of the transport belt and in a middle region of the same. It is therefore necessary to ensure a uniform pressure force F d  over the entire width of the transport belt  18 , as is the case in the shown exemplary embodiment.  
         [0043]     The mounting device  38  and the abrasion bar  26  are shown in  FIGS. 4, 5  and  6 .  FIG. 4  is a plan view and  FIG. 5  is a side view of the mounting device  38 , which has a receptacle  40  in which the abrasion bar  26  is arranged with positive fit. As is likewise shown in  FIGS. 4 and 5 , the abrasion bar  26  is clamped fast in the recess  40  with the aid of a clamping plate  42  that is attached to the mounting  38  in a detachable manner with the aid of a knurled screw  44 .  
         [0044]     As is to be seen in  FIGS. 4 and 5 , the abrasion bar  26  is cuboid-shaped. The abrasion bar can thereby be uniformly used in four different positions in the recess  40  of the mounting  38 , whereby the positions differ from one another by a rotation of the abrasion bar of respectively 180° around its longitudinal axis and/or is transverse axis, thus its axes of symmetry. In each of these four positions, another of the four longitudinal edges  36   a  through  36   d  of the abrasion bar  26  comes to rest on the transport belt  18 . By changing these positions, the lifespan of the abrasion bar  26  is quadrupled.  
         [0045]     A cross-section along the line A-B of  FIG. 4  is shown in  FIG. 6 . A recess  46  in the receptacle  40  of the mounting  38  is to be seen therein that extends over the entire length of the receptacle  40  and prevents a contact of the longitudinal edges of the abrasion bar  26  with the mounting  38 . The longitudinal edges  36   a  through  36   d  of the abrasion bar  26  are thereby prevented from damage. Similar recesses  48  for the transverse edges of the abrasion bar  26  are likewise shown in  FIG. 4 .  
         [0046]     The toner capture reservoir  30  shown only schematically in  FIG. 1  is shown in detail in  FIGS. 7 and 8 . The toner capture reservoir  30  simultaneously serves as a waste reservoir and is therefore designed as a cost-effective disposable part that can be simply removed from the printer or copying device and replaced by a new one. The toner capture reservoir  30  is produced from plastic and in a vacuum deep-draw method. Its longitudinal edges  50  and its rear transverse edge  51  are recurved inwards, such that guide grooves  52  result in which a pasteboard  52  ( FIG. 7 ) can be inserted from the front while the toner capture reservoir  30  is still located in the printer or copier such that it no toner spills upon its removal.  
         [0047]      FIG. 9  shows the section characterized by a dashed circular arc in  FIG. 8  in enlarged representation. In  FIG. 9 , the guide grooves  2  are easily recognizable. The recurved edge  50  of the toner capture reservoir  30  has a section  56  drawn slanted downwards. This section exerts a light pressure on the inserted cover  54  ( FIG. 7 ), such that this seals the toner capture reservoir