Cleaning apparatus

Abstract: An electrically biased cleaning belt brush (110) removes oppositely biased particles from a surface (10). The belt brush (110), which is entrained about supporting members (112,114,116), includes a substrate to which is attached a multiplicity of conductive brush fibers. Electrical biasing means electrically biases the belt brush (110) with alternating regions (181,183) of points and negative polarity. Particles adhering to the conductive fibers are removed from the brush fibers at a detoning station (118).

Description: This invention relates generally to an electrostatographic printer or copier, and more particularly concerns a flexible belt cleaning apparatus used therein. In an electrophotographic application such as xerography, a charge retentive surface (i.e., photoconductor, photoreceptor or imaging surface) is electrostatically charged and exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. Contacting the latent image with a finely divided electrostatically attractable powder referred to as "toner" develops the image. Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. This process is well known, and useful for light lens copying from an original, and printing applications from electronically generated or stored originals, where a charged surface may be image-wise discharged in a variety of ways. Ion projection devices where a charge is image-wise deposited on a charge retentive substrate operate similarly. Although a preponderance of the toner forming the image is transferred to the paper during transfer, some toner invariably remains on the charge retentive surface, it being held thereto by relatively high electrostatic and/or mechanical forces. Additionally, paper fibers, Kaolin and other debris have a tendency to be attracted to the charge retentive surface. It is essential for optimum operation that the toner remaining on the surface be cleaned thoroughly therefrom. A commercially successful mode of cleaning employed on automatic xerographic devices utilizes a brush with soft conductive fiber bristles or with insulative soft bristles which have suitable triboelectric characteristics. While the bristles are soft for the insulative brush, they provide sufficient mechanical force to dislodge residual toner particles from the charge retentive surface. In the case of the conductive brush, the brush is usually electrically biased to provide an electrostatic force for toner detachment from the charge retentive surface. The fixed radius of commonly used brushes can limit cleaning applications. Toner particles adhere to the fibers (i.e. bristles) of the brush after the charge retentive surface has been cleaned. The process of removing toner from these types of cleaner brushes can be accomplished in a variety of ways. Typically, brush cleaners use flicker bars to provide the detoning function which may not sufficiently clean the particles from the brush fibers. Although electrostatic brush cleaners have proved quite successful, high volume electrostatographic printer or copier applications require higher process speeds and the ability to clean with production color requirements. These requirements include high process speeds, higher toner input masses into the cleaner, better cleaning in a color process than in black and white, and the production printing desire to print to the edge of the page, which leaves untransferred toner densities around the edge of the document which must be cleaned in a single pass through the cleaner. The cleaning ability of an electrostatic brush cleaner is a function of the number of fibers which are available to clean toner from the photoreceptor and the quantity of toner which can be held by each fiber, as well as the charge on the toner particles and the bias on the fibers. The toner charge and the brush bias can be controlled by preclean corona treatment and brush bias power supplies. The number of fibers available to clean toner from the photoreceptor, known as fiber strikes, is a function of brush speed, brush interference to the photoreceptor, brush size, weave density and pile height. The amount of toner which can be held on the tip of a fiber during the cleaning process is a function of the fiber diameter, interference to the photoreceptor, toner charge and fiber bias. As a patch of toner enters the cleaning nip the brush fibers mechanically dislodge the toner from the photoreceptor and electrostatically attract and adhere the toner particles to the fibers. As the fiber proceeds through the cleaning nip, more toner particles are cleaned and electrostatically adhere to the fiber forming what is known as a match head. As the thickness of the match head increases, the electrostatic forces available to hold additional charged toner particles decreases. This is due to the physical spacing of the particles from the biased fiber and the like charge of the toner particles already adhered to the fiber. The match head will cease to increase in size when the electrostatic attractive forces are no longer strong enough to hold dislodged toner particles. At this point the fiber has reached its toner capacity and no further cleaning takes place. Additional toner remaining on the photoreceptor surface will pass through the cleaning nip creating a cleaning failure if all of the available fibers have reached their toner holding capacity. For an electrostatic brush cleaner which has been optimized for toner charge and brush bias, and which has exceeded the capacity of the fibers to clean toner due to the level of the toner input to the cleaner, the only remaining remedy is to increase the number of fibers available for cleaning. This may be accomplished by adding additional electrostatic brushes biased to the appropriate polarity. Although a multiple brush cleaner would, with enough brushes, be able to clean any desired toner input, such a cleaner would require more space along the photoreceptor belt than would be available and would create additional drag on the photoreceptor belt. To meet high volume printer and copier applications, an electrostatic belt cleaner, which will provide enhanced cleaning capability within available space requirements and without imposing excessive photoreceptor belt drag is needed. US-A-4,457,615 discloses a belt brush constructed of alternate conductive and non-conductive segments, which causes one conductive segment which is being used for charging to be electrically isolated from another conductive segment which is being used for cleaning. Different voltages can be simultaneously applied to each of the segments without adversely affecting the operation of the other. A single detoning roller is provided to remove toner particles from the brush. US-A-3780391 discloses a belt brush constructed of alternate positively and negatively charged segments depending on whether the segment is near the cleaning position or at the detoning position. Briefly stated, and in accordance with one aspect of the present invention, there is provided an apparatus for cleaning particles from a surface. The apparatus includes a flexible belt brush, which includes a substrate and a multiplicity of conductive brush fibers extending outwardly therefrom with the fibres contacting a surface for removal of particles therefrom. A supporting device movably supports the flexible belt brush in extended contact with the surface, the belt brush parting contact with the surface at a cleaning nip. A detoning device cooperates with the belt brush to remove particles therefrom. The belt brush is characterised by electrically biasing means for electrically biasing said belt brush to alternating regions of positive and negative polarity at the cleaning nip. Particular embodiments in accordance with this invention will now be described with reference to the accompanying drawings; in which:- FIG. 1 is a schematic illustration of a printing apparatus incorporating the inventive features of the present invention; FIG. 2 is an elevational view of a first embodiment of the present invention; FIG. 3 shows a section of a first embodiment of cleaning belt; FIG. 4 shows a section of a second embodiment of cleaning belt; and, FIG. 5 is a elevational view of a second embodiment. For a general understanding of an electrophotographic printer or copier, in which the present invention may be incorporated, reference is made to FIG. 1, which depicts schematically the various components thereof. Hereinafter, like reference numerals will be employed throughout to designate identical elements. Although the dual polarity electrostatic belt cleaner apparatus of the present invention is particularly well adapted for use in an electrophotographic printing machine, it should become evident from the following discussion that it is equally well suited for use in other applications and is not necessarily limited to the particular embodiment shown herein. Referring now to the drawings, the various processing stations employed in the reproduction machine illustrated in FIG. 1 will be described briefly hereinafter. It will no doubt be appreciated that the various processing elements also find advantageous use in electrophotographic printing applications from an electronically stored original, and with appropriate modifications, to an ion projection device which deposits ions and image configuration on a charge retentive surface. A reproduction machine, in which the present invention finds advantageous use, has a photoreceptor belt 10, having a photoconductive (or imaging) surface 11. The photoreceptor belt 10 moves in the direction of arrow 12 to advance portions of the belt 10 sequentially through the various processing stations disposed about the path of movement thereof. The belt 10 is entrained about a stripping roller 14, a tension roller 16, and a drive roller 20. Drive roller 20 is coupled to a motor 21 by suitable means such as a belt drive. The belt 10 is maintained in tension by a pair of springs (not shown) resiliently urging tension roller 16 against the belt 10 with the desired spring force. Both stripping roller 14 and tension roller 16 are rotatably mounted. These rollers are idlers, which rotate freely as the belt 10 moves in the direction of arrow 12. With continued reference to FIG. 1, initially a portion of the belt 10 passes through charging station A. At charging station A, a corona device 22 charges a portion of the photoreceptor belt 10 to a relatively high, substantially uniform potential, either positive or negative. At exposure station B, an original document 30 is positioned face down on a transparent platen 26 for illumination with flash lamps 32. Light rays reflected from the original document are reflected through a lens 33 and projected onto the charged portion of the photoreceptor belt 10 to selectively dissipate the charge thereon. This records an electrostatic latent image, which corresponds to the informational area contained within the original document, onto the belt. Alternatively, a laser may be provided to image-wise discharge the photoreceptor in accordance with stored electronic information. Thereafter, the belt 10 advances the electrostatic latent image to developing station C. At development station C, either developer housing 34 or 36 is brought into contact with the belt 10 for the purpose of developing the electrostatic latent image. Housings 34 and 36 may be moved into and out of developing position with corresponding cams 38 and 40, which are selectively driven by motor 21. Each developer housing 34 and 36 supports a developing system such as magnetic brush rolls 42 and 44, which provides a rotating magnetic member to advance developer mix (i.e. carrier beads and toner) into contact with the electrostatic latent image. The electrostatic latent image attracts toner particles from the carrier beads, thereby forming toner powder images on the photoreceptor belt 10. If two colors of developer material are not required, the second developer housing may be omitted. The photoreceptor belt 10 then advances the developed image to transfer station D. At transfer station D, a sheet of support material such as paper copy sheets is advanced into contact with the developed images on the belt 10. A corona generating device 46 charges the copy sheet to the proper potential so that it becomes tacked to the photoreceptor belt 10 and the toner powder image is attracted from the photoreceptor belt 10 to the sheet. After transfer, the corona generator 48 charges the copy sheet to an opposite polarity to de-tack the copy sheet from the belt 10, whereupon the sheet is stripped from the belt 10 at stripping roller 14. Sheets of support material 49 are advanced to transfer station D from a supply tray 50. Sheets are fed from tray 50, with sheet feeder 52, and advanced to transfer station D along conveyor 56. After transfer, the sheet continues to move in the direction of arrow 60, to fusing station E. Fusing station E includes a fuser assembly indicated generally by the reference numeral 70, which permanently affixes the transfer toner powder images to the sheets. Preferably, the fuser assembly 70 includes a heated fuser roller 72 adapted to be pressure engaged with a backup roller 74 with the toner powder images contacting the fuser roller 72. In this manner, the toner powder image is permanently affixed to the sheet, and such sheets are directed via a chute 62 to an output 80 or finisher. Residual particles, remaining on the photoreceptor belt 10 after each copy is made, may be removed at cleaning station F. The cleaning apparatus of the present invention is represented by the reference numeral 92, which will be described in greater detail in FIG. 2. Removed residual particles may also be stored for disposal. A machine controller 96 is preferably a known programmable controller or combination of controllers, which conventionally control all of the machine steps and functions described above. The controller 96 is responsive to a variety of sensing devices to enhance control of the machine, and also provides connection diagnostic operations to a user interface (not shown) where required. As thus described, a reproduction machine in accordance with the present invention may be any of several well-known devices. Variations may be expected in specific electrophotographic processing, paper handling and control arrangements without effecting the present invention. However, it is believed that the foregoing description is sufficient for purposes of the present application to illustrate the general operation of an electrophotographic printing machine, which exemplifies one type of apparatus employing the present invention therein. Reference is now made to FIGS. 2-4, where the showings are for the purpose of illustrating preferred embodiments of the present invention and not for limiting the same. Removal of charged dielectric particles adhered to a dielectric surface can be accomplished by mechanical, electrical or electro-mechanical means. The electrostatic belt brush cleaner employs a combination of electrical and mechanical forces to detach and remove toner particles from the photoreceptor surface. Reference is now made to FIG. 2, which shows an elevational view of the preferred embodiment of the present invention. The flexible belt brush 110 is shown in operable condition in contact with photoreceptor belt 10 through extended cleaning nip 150. Flexible belt brush 110 is electrically biased to suitable magnitude and polarity and is comprised of a continuous loop of conductive backing material (e.g. urethane or polyester) to which conductive brush fibers are attached. The flexible belt brush 110 is entrained about three rollers 112, 114, and 116, one of which is a drive roller, and moving in direction 130 opposed to the movement of photoreceptor belt 10. The two rollers 112 and 114 support the belt 110 in brushing contact with photoreceptor belt 10. The third roller 116 supports belt 110 as the conductive brush fibers are brought into contact with electrostatic detoning roll 118, which is biased to a greater polarity than the belt brush and is rotating in direction 160 opposed to movement of belt 110. Although entraining the belt brush about three rollers is suitable for many applications, it is understood that some applications may require a different number of support rollers. In order to exert an electrostatic force on the toner particles, the toner particles are charged using a preclean corona device and an electric potential is applied to the conductive fibers of the brush. This potential creates an electric field between the fibers and the ground plane of the photoreceptor. The force experienced by the toner particles must exceed the adhesion force between the toner particles and the photoreceptor surface in order to detach the particles. The electrical force, when combined with the mechanical (deflection) forces of the fibers, detaches and removes charged toner particles from the photoreceptor surface. Although biasing the brush belt to a single polarity is suitable for some applications, high volume printing or copying applications require that the belt be produced such that there are regions of reversing polarization along the length of the belt. In such applications both positive and negative polarities are applied to the alternating regions of polarity along the length of the belt. Reference is now made to FIG. 3, which shows a section of belt 110 with such regions of alternating positive and negative polarity. The ability to bias multiple sections of the cleaning belt independently enables replacement of two oppositely biased brushes with a single belt brush. Due to the narrow cleaning nip of a brush, it is very difficult to provide enough fiber strikes of each polarity within the constraints of a reasonably small diameter brush. In contrast to the narrow cleaning nip of a brush, the belt brush of the present invention provides an extended cleaning nip 150 which enables adequate fibers of each polarity to be present in the cleaning nip. Space between the oppositely biased regions of the belt may also be provided for electrical isolation. As illustrated in FIG. 3, an electrical source biases section 181 of belt 110 to a negative polarity through connecting bias strip 180 and a similar source biases section 183 of belt 110 to a positive polarity through connecting bias strip 182. Section 184 electrically isolates sections 181 and 183 from each other. Alternatively, the connecting edge bias strip may be eliminated as illustrated in FIG. 4. Sections of negative polarity 188 and sections of positive polarity 186 have offset ends, which may be independently biased by any known means. Section 184 electrically isolates sections 186 and 188 from each other. The pattern of alternating positive and negative biases illustrated in FIGS. 3 and 4 are intended as examples of possible patterns for biasing a belt brush. Referring again to FIG. 2, in operation, as a negative toner particle enters the cleaning nip 150 it is dislodged from the photoreceptor belt 10 and adheres to a positive biased fiber attached to belt 110. The positive biased fibers transport the toner particles to the more positively biased detoning roll 118. As the brush fibers of belt 110 come into contact with detoning roll 118, the negative toner particles then transfer from the belt 110 to detoning roll 118. The rotating detoning roll 118 then transports the toner particles to the detoning blade 122 that scrapes the toner particles off the detoning roll 118 and into an auger 120. The auger 120 transports the toner particles to a waste container. Reference is now made to FIG. 5, which shows an alternate embodiment of the present invention. As in the first embodiment, the flexible belt brush 110 is in operable contact with photoreceptor belt 10 through extended cleaning nip 150. Flexible belt brush 110 is electrically biased to suitable magnitude and polarity and is comprised of a continuous loop of conductive backing material to which conductive brush fibers are attached. The flexible belt brush 110 is entrained about three rollers 112, 114, and 116, one of which is a drive roller, and moving in direction 130 opposed to the movement of photoreceptor belt 10. The two rollers 112 and 114 support the belt 110 in brushing contact with photoreceptor belt 10. A backer bar 152, which may be electrically biased, may apply pressure to the belt to maintain constant brushing contact between the photoreceptor belt 10 and belt brush 110 through the cleaning nip 150. The third roller 116 supports belt 110. In operation, as a toner particle enters the cleaning nip 150 it is dislodged from the photoreceptor belt 10 and adheres to a fiber attached to belt 110. The fibers transport the toner particles past an acoustic transducer and horn 124, which apply high frequency vibrational energy to the fibers of the belt brush 110 to dislodge toning particles. Although it is possible to dislodge the toner particles through the use of acoustic vibrational energy alone, a flicker bar, which is not shown, may assist in dislodging toner particles. The dislodged toner particles are collected by auger 120 or a vacuum device, which is not shown but is known in the art, and transported to waste container 140. Alternatively, the toner particles loosened by acoustic transducer 124 may transfer to a detoning roll 118, which transports the toner particles to a detoning blade that scrapes the particles off the detoning roll and into an auger 120, which transports the toner particles to a waste container, as illustrated in FIG.2.

Claims: An apparatus for cleaning particles from a surface (10), comprising: a flexible belt brush (110) including a belt substrate and a multiplicity of conductive fibers extending outwardly therefrom with the fibers contacting a surface (10) for removal of particles therefrom; a supporting device (112,114,116) for movably supporting said belt brush (110) in extended contact with the surface (10), the belt brush (110) parting contact with the surface (10) at a cleaning nip (150); and, a detoning device (118,124), cooperating with said belt brush (110), to remove particles from said belt brush (110) to ensure sufficient cleaning of said belt brush (110), characterized by electrical biasing means for electrically biasing said belt brush (110) to alternating regions (181,183) of positive and negative polarity at the cleaning nip (150). An apparatus according to claim 1, wherein said supporting device comprises a plurality of supports (112,114,116), said belt brush (110) being entrained about said plurality of supports (112,114,116). An apparatus according to claim 1 or 2, wherein said detoning device comprises: a detoning roll (118); a detoning blade (122) adjacent to said detoning roll (118) to remove particles from said detoning roll (118); an auger (120) to collect the particles removed from said detoning roll; and a waste toner chamber (140) positioned to receive the particles being transported by said auger (120). An apparatus according to claim 3, further including means for electrically biasing said detoning roll. An apparatus according to any one of the preceding claims, further including an acoustic transducer and horn (124). An apparatus according to claim 1 or 2, wherein said detoning device comprises: an acoustic transducer; a horn (124) adjacent to said acoustic transducer; an auger (120) to collect the particles loosened from said flexible belt brush (110); and, a waste toner chamber (140) positioned to receive the particles being transported by said auger (120). An apparatus according to claim 6, further comprising a flicker bar which contacts said conductive fibers of said belt brush (110) as said belt brush moves past said acoustic transducer (124). An electrostatographic printing machine comprising: a photoreceptor (10) having a photoconductive charge retentive surface (11); a charging station (A) for charging said photoconductive surface (11) to a predetermined potential; an exposure station (B) for exposing said photoconductive surface to produce a latent image thereon; a development station (C) for depositing development material on said charge retentive surface (11); a transfer station (D) for transfer of said development material adhered to said latent image onto print media (49); a fusing station (70) for fusing of said latent image onto said print media (49); and a cleaning apparatus (F) in accordance with any one of the preceding claims for removal of said development material remaining on said charge retentive surface (11) after fusing.

Inventors: THAYER BRUCE E, THAYER, BRUCE E.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 2000
Main classification: G03G21
IPC codes: G03G21