Developer apparatus for a printing machine

Abstract: A developing system (200a,200b) for a color electrophotographic printing machine prints documents in at least two different colors. The developing system includes a first toner carrying piezoelectric polymer belt (205) for conveying toner of a first color to the latent image on the photoconductive member (10) and a second toner carrying piezoelectric polymer belt (205') for conveying toner of a second color to the latent image. A first developer activation stylus (215) selectively vibrates toner carrying surface areas of the first piezoelectric polymer belt to develop a first portion of the latent image with the first color. A second developer activation stylus (215') selectively vibrates toner carrying surface areas of the second piezoelectric polymer belt to develop a second portion of the latent image with the second color.

Description: This invention relates generally to an electrophotographic printing machine, and more particularly concerns a developer apparatus for a color printing machine which prints a document in at least two different colors. Recently, electrophotographic printing machines had been developed which produce highlight color copies. A typical highlight color printing machine records successive electrostatic latent images on the photoconductive surface. When combined, these electrostatic latent images form a latent image corresponding to the entire original document being printed. One latent image is usually developed with black toner particles. The other latent image is developed with color highlighting toner particles, e.g. red toner particles. These developed toner powder images are transferred sequentially to a sheet to form a color highlighted document. A color highlighting printing machine of this type is generally a two-pass machine. Single pass highlight color printing machines using tri-level printing have also been developed. Tri-level electrophotographic printing is described in greater detail in US-A-4,078,929. As described in this patent, the latent image is developed with toner particles of first and second colors. The toner particles of one of the colors are positively charged and the toner particles of the other color are negatively charged. In tri-level electrophotographic printing, the photoconductive surface is charged and exposed imagewise such that one image corresponds to the charged areas and remains at the full charged potential. Another image, which corresponds to discharged image areas, is exposed to discharge the photoconductive surface to its residual potential. The background areas are exposed to reduce the photoconductive surface potential to about halfway between the charged and discharged potentials. A developer unit arranged to develop the charged images is typically biased to a potential between the background potential and the full potential. The developer unit arranged to develop the discharged imaged areas is typically biased to a level between the background potential and the discharged potential. The single pass nature of this system dictates that the electrostatic latent image passes through the developer unit in a serial fashion. Another type of printing machine which may produce highlight color copies initially charges the photoconductive member. Thereafter, the charged portion of the photoconductive member is discharged to form an electrostatic latent image thereon. The latent image is subsequently developed with black toner particles. The photoconductive member is then recharged and imagewise exposed to record the highlight color portions of the latent image thereon. A highlight latent image is then developed with toner particles of a color other than black, e.g. red, then develop the highlight latent image. Thereafter, both toner powder images are transferred to a sheet and subsequently fused thereto to form a highlight colour document. US-A-4,403,848 discloses a multi-colour printer wherein the photoconductive member is charges, exposed and developed with toner particles of the first colour. Thereafter, the photoconductive member is reexposed, developed with toner particles of a second colour and the toner particles of both colours transferred to a sheet. After transferring the toner particles to the sheet, the toner particles are fused thereto. US-A-4,660,059 describes an apparatus on which ta document is printed in two different colours. Ions are projected onto a dielectric surface to record a first electrostatic latent image thereon. The first electrostatic latent image is developed with toner particles of a first colour. Thereafter, the first electrostatic latent image recorded on the dielectric member is substantially neutralized. A second ion projector then projects ions onto a dielectric surface to a record another electric latent image. This second electrostatic latent image is then developed with toner particles of a second colour. The toner particles of the first colour and the second colour are transferred from the dielectric member to a sheet and subsequently fused thereto forming a highlight colour document. US-A-5,282,005 discloses a monochrome printer having an imaging surface for carrying an electrostatic image, a donor surface for transporting marking particles to a location against the imaging surface, and means for vibrating the donor surface to develop the latent image on the imaging surface. Pursuant to one aspect of the present invention, there is provided a developer apparatus for developing a selected area of an electrostatic latent image recorded on an imaging member, comprising a donor surface for transporting marking particles to a location adjacent the imaging member, and means for vibrating the donor surface, characterised in that the means only vibrates selected portions of said donor surface to develop selected areas of the latent image with the marking particles, with unselected portions of said donor surface being substantially non-vibrating so that an area other than the selected area of the latent image is not developed. Pursuant to another aspect of the present invention, there is provided a printing machine for developing an electrostatic latent image on an imaging member, comprising: a donor surface for transporting marking particles to a location adjacent the imaging member, and means for vibrating said donor surface to develop a latent image with marking characterised in that said donor surface comprises a first donor surface for transporting first marking particles to a first location and a second donor surface for transporting second donor particles to a second location, and in that the machine includes means for selecting either a first area or a second area of the latent image and, in response to selecting the first area the means vibrates the first donor surface to develop the first selected area if the latent image with the first marking particles during development with the first donor surface with the second donor surface being substantially non-vibrating in the first area of the latent image during development by the second donor surface; and the means in response to the selection of the second area vibrates the second donor surface to develop the second selected area of the latent image with the second marking particles, with said first donor surface being substantially non-vibrating in the second area of the latent image during development by the first donor surface. The present invention will now be described by way of example with reference to the accompanying drawings, in which: Figures 1A-1C illustrates exemplary modes of development of a latent image employing the teaching of the present invention; Figure 2A illustrates the (ideal) step in acoustic motion desired at the edge of a development area along with envisioned actual motion without employing active damping; FIG. 2B illustrates the application of phase shifted voltages to electrodes in the vicinity of the edge which then act as active damping electrodes rather then primary driving electrodes; FIG. 3 illustrates the development stylus of the present invention; FIG. 4 is an enlarged portion of figure 3 showing details of a single styli of the development stylus; and Figure 5 is a schematic elevational view depicting an illustrative portion of an electrophotographic printing machine incorporating the features of the present invention therein. In Figure 5, a known photoconductive belt 10 for a typical electrophotographic printing machine is shown. Belt 10 moves in the direction of arrow 12 to advance successive portions of the photoconductive surface sequentially through the various processing stations disposed about the path of movement thereof. Belt 10 is entrained about stripping roller 14, tensioning roller 16, idler rollers 18, and drive roller 20. Drive roller 20 is rotated by a motor coupled thereto by suitable means such as a belt drive. A portion of the photoconductive surface passes through charging station A. At charging station A, two corona generating devices 22,24 charge photoconductive belt 10 to a relatively high, substantially uniform potential. Corona generating device 22 places all the required charge on photoconductive belt 10. Corona generating device 24 acts as leveling device, and fills in any areas missed by corona generating device 22. Next, the charged portion of the photoconductive surface is advanced through imaging station B. At imaging station B, the uniformly charged photoconductive surface is exposed by an imager, such as a laser based input and/or output scanning device 26, which causes the charged portion of the photoconductive surface to be discharged in accordance with the output from the scanning device. The scanning device is a laser raster output scanner (ROS). The ROS performs the function of creating the output image copy on the photoconductive surface. An electronic subsystem (ESS) 28 is the control electronics which prepare and manage the image data flow between the data source and the ROS. It may also include a display, user interface and electronic storage functions. The ESS is typically a self-contained, dedicated mini computer. The photoconductive surface, which is initially charged to a high charge potential, is discharged imagewise in the background areas and remains charged in the image areas in the black parts of the image. Alternatively, the photoconductive surface be can discharged in the image areas while in the background areas remains charged. As understood by those skilled in the xerographic arts, color developing materials normally consist of a suitable carrier material with relatively smaller color material (referred to as toner). Toner is drawn to the image areas while being repelled in the background areas. The toners employed for mulit-color toner images are charged to have the same polarity, and preferrably the toner is non-magnetic. Development apparatus 200a,200b of the present invention is shown at development station C and provides sonic toner release in a non-interactive development process having minimal interactive effects between deposited (developed) toner and subsequently presented toner. Each development apparatus 200a,200b provides a means to achieve multicolor single transfer systems without cross-color contamination of images and/or developer materials (scavenging effects). Each development apparatus comprises a peizoelectric polymer belt 205 or 205' as a donor member having a portion thereof closely spaced with respect to photoconductive member 10 in what is commonly known as touchdown development. Each piezoelectric belt 205,205' is entrained around roller 210,210' and development stylus 215,215'. Roller 210 or 210' is the driver and is positioned adjacent a magnetic brush toner loading device 212 or 212'. Each belt 205,205' has a D.C. bias applied to its outside surface by a D.C. source (not shown). The outside surface of the belt includes a conductive coating thereon. An A.C. source 230 applies a bias to development activation stylus 215 or 215'. Thus, the basic concept of sonic toner release is achieved by locally reducing the net force of adhesion of toner to the loaded donor surface by acoustic agitation of the donor surface by A.C. source 230. Sufficient reduction of the net force of adhesion of toner to the donor surface enables q E electrostatic forces to selectively remove toner from the donor and transport it to desired areas of development on the photoconductive belt. In sonic toner release development, use is made of motions of a charged particle bearing surface (donor) to controllably counter forces adhering the particles to the surface. These motions can be adjusted in magnitude such that particles continue to adhere to the donor surface unless they are additionally affected by an electric field of appropriate direction and magnitude to remove them from the donor. In the case wherein the electric field is due to proximity of an electrostatic image, the released toner will selectively traverse to the image, thereby developing it. The selective toner removal characteristics of sonic toner release development distinguish it from powder cloud (and jumping) development where airborne toner is presented to the entire receptor regardless of its potential. This distinction provides an important copy quality advantage with sonic toner release since wrong sign and un-charged toner deposition is inhibited. In addition, interaction effects between successive developments with different toners (colors) are minimal. Development system advantages obtained with single transfer and enabled by non-interactive development include simplified (on the photoconductive belt) registration of images, increased throughput, and reduced system complexity. Development activated stylus 215 or 215' of the present invention is activated by the ESS in both the process direction and the direction orthogonal to process direction by controlling both the timing and the inboard/outboard locations of acoustic motions imparted to multiple development activation styluses. Localized areas of development are defined to selectively develop a single latent electrostatic image with selected highlight colors. Development stylus 215 or 215' has only relatively low resolution development area addressability in the cross process direction of order 0.25mm (0.010 inch), for example, for typical highlight colored business documents. It should be evident that, if higher cross process resolution was desired, one could increase the number of addressable styli. Addressability in the process direction depends upon the precision of timing and the time response of the acoustic excitation of the donor surface. The addressability of the development stylus determines how close adjacent image areas of different colors may be. The development stylus of the present invention employs an electrode array which is incorporated to enable the desired control of areas of acoustic motion of the donor belt. An advantage of this electrode array is the ability to introduce "active damping" of motion at the edges of development areas by applying appropriately phase shifted voltages to electrodes in the vicinity of the edges. This technique is used to suppress/reduce noise at audio frequencies, and it should be applicable to ultrasonic frequencies as well. FIG. 2A shows the (ideal) step in acoustic motion desired at the edge of a development area along with envisioned actual motion without employing active damping. FIG. 2B illustrates the application of phase shifted voltages to electrodes in the vicinity of the edge which then act as active damping electrodes rather then primary driving electrodes. The electrode array also provides control of acoustic motion locations orthogonal to the process direction. With reference to FIGs. 3 and 4, passive acoustic damping material 5 is positioned upstream and downstream of each individual electrode 6 to limit the active donor area in that direction. Height "d" of electrodes 6 determines the minimum length of developed area in the process direction while timing and driving voltage applications to electrodes 6 controlled by the ESS determine the actual location of developed area edges. FIG. 4 is an enlarged drawing showing details of a single electrode of the development stylus engaged with the donor belt. Referring to FIGs. 1A-C which illustrates sequential development of a single latent electrostatic image (FIG. 1A) by two development apparatuses. As the latent image passes by development apparatus 200a, the ESS controls each individual electrode of development stylus 215 so that toner (i.e. black toner) is only released in area 8 (FIG. 1B). As the partial developed latent image passes by development apparatus 200b, the ESS controls each individual electrode of development stylus 215' so that different color toner (i.e. red toner) is only released in area 4 (FIG. 1C). It is preferred that ESS has a color controller to control the development stylus so that reproduced (output) images have the same color as scanned input image. Alternatively, an edit pad can be employed with the ESS to select areas on the original to be copied in a desire color. After the latent image is selectively developed with black toner particles and with toner particles of a color other than black, belt 10 advances the resultant toner powder image to transfer station D as shown in FIG.5. At transfer station D, a sheet or document (not shown) is moved into contact with the toner powder image on the photoconductive belt from a tray (not shown) by transport rollers 66. Photoconductive belt 10 is exposed to a pre-transfer light from a lamp (not shown) to reduce the attraction between the photoconductive belt and the toner powder image. Next, a corona generating device 41 charges the sheet to the proper magnitude and polarity as the sheet is passed thereby on photoconductive belt 10. The toner powder image is attracted from photoconductive belt 10 to the sheet. After transfer, a corona generator 42 charges the sheet to the opposite polarity to detack the sheet from belt 10. Conveyor 44 advances the sheet to a fusing station E (not shown). After the sheet is separated from photoconductive belt 10, some residual toner particles remain adhering thereto. After transfer, photoconductive belt 10 passes beneath corona generating device 94 which charges the residual toner particles to the proper polarity. Thereafter, the pre-charge array lamp (not shown), located inside photoconductive belt 10 discharges the photoconductive belt in preparation for the next imaging cycle. Residual particles are removed from the photoconductive surface at cleaning station G, which includes an electrically biased cleaner brush 88 and two de-toning rolls 90 and 92, i.e. waste and reclaim de-toning rolls.

Claims: A developer apparatus for developing a selected area of an electrostatic latent image recorded on an imaging member (10), comprising a donor surface (205) for transporting marking particles to a location adjacent the imaging member, and means (215) for vibrating the donor surface (205), characterised in that the means (215) only vibrates selected portions of said donor surface (205) to develop selected areas (4,8) of the latent image with the marking particles, with unselected portions of said donor surface (205) being substantially non-vibrating so that an area other than the selected area of the latent image is not developed. A printing machine for developing an electrostatic latent image on an imaging member (10), comprising: a donor surface (205) for transporting marking particles to a location adjacent the imaging member, and means (215) for vibrating said donor surface to develop a latent image with marking particles, characterised in that said donor surface comprises a first donor surface for transporting first marking particles to a first location and a second donor surface (205') for transporting second donor particles to a second location, and in that the machine includes means (28) for selecting either a first area or a second area of the latent image and, in response to the selection of the first area, the means (215) vibrates the first donor surface (205) to develop the first selected area of the latent image with the first marking particles during development with the first donor surface and the second donor surface being substantially non-vibrating in the first area of the latent image during development by the second donor surface, and, in response to the selection of the, second area, the means (215') vibrates the second donor surface to develop the second selected area of the latent image with the second marking particles, and the first donor surface being substantially non-vibrating in the second area of the latent image during development by the first donor surface. A printing machine according to claim 2, wherein the first marking particles are of a different colour from the second marking particles. A printing machine according to claim 2 or 3, further comprising: means (41,42) for transferring the first and second marking particles from said imaging member to a document; and means for substantially permanently fusing the first and second marking particles to the document. A developer apparatus according to claim 1 or printing machine according to any one of claims 2 to 4, wherein the, or each, donor surface (205,205') comprises a piezoelectric polymer belt spaced from said imaging member. A developer apparatus or printing machine according to claim 5, wherein the, or each, means (215,215') for vibrating said piezoelectric polymer belt comprises a developer stylus adjacent to the latent image. A developer apparatus or printing machine according to claim 6, wherein the, or each, stylus comprises an array of individually addressable electrodes (6). A developer apparatus or printing machine according to claim 7, wherein the individual electrodes in said array or arrays are selectively actuated in response to movement of said imaging member in a predetermined direction of movement, so that the, or each, selected area of the latent image is developed orthogonally and in the direction of movement of said imaging member. A developer apparatus or printing machine according to claim 7 or claim 8, wherein said array comprises a damping material (5) interposed between the electrodes (6) thereof.

Inventors: SNELLING CHRISTOPHER, SNELLING, CHRISTOPHER
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1995
Main classification: G03G15
IPC codes: G03G15, G03G13