Patent Application
20110033209
The claimed invention relates in general to electrophotographic imaging systems, and more particularly to an electrophotographic development apparatus having a feed roller with one or more take-off magnets.
In a typical commercial reproduction apparatus (electrographic copier/duplicators, printers, or the like), a latent image charge pattern is formed on a uniformly charged charge-retentive or photoconductive member having dielectric characteristics (hereinafter referred to as the dielectric support member). Pigmented marking particles (for example, toner) are manipulated into close proximity with the latent image charge pattern by a one or more development stations, allowing the pigmented marking particles to be attracted to the latent image charge pattern in order to develop such image on the dielectric support member. A receiver member, such as a sheet of paper, transparency or other medium, is then brought directly, or indirectly via an intermediate transfer member, into contact with the dielectric support member, and an electric field is applied to transfer the marking particle developed image to the receiver member from the dielectric support member. After transfer, the receiver member bearing the transferred image is transported away from the dielectric support member, and the image is fixed (fused) to the receiver member by heat and/or pressure to form a permanent reproduction thereon.
The development system of an electrophotographic reproduction apparatus is ideally designed to provide a uniform toner concentration to the passing dielectric support member so that a uniformly charged latent image on the dielectric support member will be developed with a proportionally uniform density of toner. Unfortunately, many existing electrophotographic development stations have undesirable toner concentration uniformity due to the influence of depleted developer of a first toner concentration mixing with fresh developer of a second toner concentration on a toning roller. The resultant toner non-uniformity can produce objectionable “depletion streaks” on output images.
Therefore, it would be beneficial if there were an inexpensive, yet reliable, apparatus for reducing depletion streaks that could easily be implemented.
In view of the above, the claimed invention is directed towards a feeding apparatus. The feeding apparatus has a feed roller, one or more feed magnets within the feed roller, and one or more take-off magnets within the feed roller. The feed roller is rotatable around the one or more feed magnets and the one or more take-off magnets.
The claimed invention is also directed towards a development station. The development station has a rotating shell, a rotating magnetic core within the rotating shell, and a sump region. The development station also has a feeding apparatus configured to supply fresh developer from the sump region to the rotating shell. The feeding apparatus has a feed roller, one or more feed magnets within the feed roller, and one or more take-off magnets within the feed roller. The feed roller is rotatable around the one or more feed magnets and the one or more take-off magnets.
The claimed invention is also directed towards an electrophotographic imaging system. The electrophotographic imaging system has a dielectric support member (DSM), a primary charging station configured to form a charge layer on the DSM, and an exposure station configured to selectively discharge the charge layer formed on the DSM, thereby producing a latent image on the DSM. The electrophotographic imaging system also has a development station configured to develop the latent image on the DSM with toner. The development station has a rotating shell, a rotating magnetic core within the rotating shell, and a sump region. The development station also has a feeding apparatus configured to supply fresh developer from the sump region to the rotating shell. The feeding apparatus has a feed roller, one or more feed magnets within the feed roller, and one or more take-off magnets within the feed roller. The feed roller is rotatable around the one or more feed magnets and the one or more take-off magnets.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below.
It will be appreciated that for purposes of clarity and where deemed appropriate, reference numerals have been repeated in the figures to indicate corresponding features, and that the various elements in the drawings have not necessarily been drawn to scale in order to better show the features.
One or more of the rollers 34a-34g are driven by a motor 36 to advance the DSM 32. Motor 36 preferably advances the DSM 32 at a high speed, such as 20 inches per second or higher, in the direction indicated by arrow P, past a series of workstations of the print engine 30, although other operating speeds may be used, depending on the embodiment. In some embodiments, DSM 32 may be wrapped and secured about only a single drum. In further embodiments, DSM 32 may be coated onto or integral with a drum.
Print engine 30 may include a controller or logic and control unit (LCU) (not shown). The LCU may be a computer, microprocessor, application specific integrated circuit (ASIC), digital circuitry, analog circuitry, or an combination or plurality thereof. The controller (LCU) may be operated according to a stored program for actuating the workstations within print engine 30, effecting overall control of print engine 30 and its various subsystems. The LCU may also be programmed to provide closed-loop control of the print engine 30 in response to signals from various sensors and encoders. Aspects of process control are described in U.S. Pat. No. 6,121,986 incorporated herein by this reference.
A primary charging station 38 in print engine 30 sensitizes DSM 32 by applying a uniform electrostatic corona charge, from high-voltage charging wires at a predetermined primary voltage, to a surface 32a of DSM 32. The output of charging station 38 may be regulated by a programmable voltage controller (not shown), which may in turn be controlled by the LCU to adjust this primary voltage, for example by controlling the electrical potential of a grid and thus controlling movement of the corona charge. Other forms of chargers, including brush or roller chargers, may also be used.
An image writer, such as exposure station 40 in print engine 30 projects light from a writer 40a to DSM 32. This light selectively dissipates the electrostatic charge on photoconductive DSM 32 to form a latent electrostatic image of the document to be copied or printed. Writer 40a is preferably constructed as an array of light emitting diodes (LEDs), or alternatively as another light source such as a Laser or spatial light modulator. Writer 40a exposes individual picture elements (pixels) of DSM 32 with light at a regulated intensity and exposure, in the manner described below. The exposing light discharges selected pixel locations of the photoconductor, so that the pattern of localized voltages across the photoconductor corresponds to the image to be printed. An image is a pattern of physical light which may include characters, words, text, and other features such as graphics, photos, etc. An image may be included in a set of one or more images, such as in images of the pages of a document. An image may be divided into segments, objects, or structures each of which is itself an image. A segment, object or structure of an image may be of any size up to and including the whole image.
After exposure, the portion of DSM 32 bearing the latent charge images travels to a development station 42. Development station 42 includes a rotating shell 44 in juxtaposition to the DSM 32. The rotating shell 44 surrounds a rotating magnetic core 46 that helps magnetic toner (not shown in this view) adhere to the rotating shell 44. Development station 42 is shown with a feeding apparatus including a feed roller 90 which is discussed in one embodiment, in conjunction with
Upon the imaged portion of DSM 32 reaching development station 42, the LCU selectively activates development station 42 to apply toner to DSM 32 by moving backup roller 42a and DSM 32, into engagement with or close proximity to the rotating shell 44. Alternatively, the development station 42 and/or the rotating shell 44 may be moved toward DSM 32 to selectively engage DSM 32. In still other embodiments, neither the development station 42, the rotating shell 44, the DSM 32, nor the backup roller 42a are moved. Instead, the development station may be activated by switching electrical biases on/off. In any of the above cases, charged toner particles on the rotating shell 44 are selectively attracted to the latent image patterns present on DSM 32, developing those image patterns. As the exposed photoconductor passes the developing station, toner is attracted to pixel locations of the photoconductor and as a result, a pattern of toner corresponding to the image to be printed appears on the photoconductor. As known in the art, conductor portions of development station 42, such as conductive applicator cylinders, are biased to act as electrodes. The electrodes are connected to a variable supply voltage, which is regulated by a programmable controller in response to the LCU, by way of which the development process is controlled.
Development station 42 may contain a two component developer mix which comprises a dry mixture of toner and carrier particles. Typically the carrier preferably comprises high coercivity (hard magnetic) ferrite particles. As a non-limiting example, the carrier particles may have a volume-weighted diameter of approximately 30μ. The dry toner particles are substantially smaller, on the order of 6μ to 15μ in volume-weighted diameter. The rotating magnetic core 46 and the rotating shell 44 may be rotatably driven by a motor or other suitable driving means. Relative rotation of the core 46 and shell 44 moves the developer through a development zone in the presence of an electrical field. In the course of development, the toner selectively electrostatically adheres to DSM 32 to develop the electrostatic images thereon and the carrier material remains at development station 42. As toner is depleted from the development station due to the development of the electrostatic image, additional toner may be periodically introduced by a toner auger into development station 42 to be mixed with the carrier particles to maintain a uniform amount of development mixture. This development mixture is controlled in accordance with various development control processes.
A transfer station 48 in printing engine 30 moves a receiver sheet 50 into engagement with the DSM 32, in registration with a developed image to transfer the developed image to receiver sheet 50. Receiver sheets 50 may be plain or coated paper, plastic, or another medium capable of being handled by the print engine 30. Typically, transfer station 48 includes a charging device for electrostatically biasing movement of the toner particles from DSM 32 to receiver sheet 50. In this example, the biasing device is roller 52, which engages the back of sheet 50 and which may be connected to a programmable voltage controller that operates in a constant current mode during transfer. Alternatively, an intermediate member may have the image transferred to it and the image may then be transferred to receiver sheet 50. After transfer of the toner image to receiver sheet 50, sheet 50 is detached from DSM 32 and transported to fuser station 54 where the image is fixed onto sheet 50, typically by the application of heat and/or pressure. Alternatively, the image may be fixed to sheet 50 at the time of transfer.
A cleaning station 56, such as a brush, blade, or web is also located beyond transfer station 48, and removes residual toner from DSM 32. A pre-clean charger (not shown) may be located before or at cleaning station 56 to assist in this cleaning. After cleaning, this portion 32a of DSM 32 is then ready for recharging and re-exposure. Of course, other portions of DSM 32 are simultaneously located at the various workstations of print engine 30, so that the printing process may be carried out in a substantially continuous manner.
A controller provides overall control of the apparatus and its various subsystems with the assistance of one or more sensors which may be used to gather control process input data. One example of a sensor is belt position sensor 58.
In this embodiment, the print engine 60 also has an intermediate image-transfer drum 72 to which toner images formed on the DSM 62 are transferred prior to being re-transferred to a receiver sheet 74. Following transfer to the intermediate transfer drum 72, residual toner on the DSM 62 may be removed by the combination of an optional pre-clean corona charger 76 and a cleaning station 78.
A feed roller 90, as part of a feeding apparatus, may house one or more feed magnets to pull developer from the sump region 60 and deliver it to the rotating shell 82. The developer adheres to the rotating shell 82 due to the magnetic fields created by the rotating magnetic core 84 located within the rotating shell 82. A metering blade 92 may be provided in proximity to the rotating shell 82 to assist in controlling the height of developer on the rotating shell 82.
An embodiment of the feed magnets 96 and the take-off magnets 98 are schematically illustrated on their own in
The feed magnets 96 and the take-off magnets 98 are illustrated as defining, or being separated by, two gaps: a post-feed gap 104, and a post-take-off gap 106. The magnetic field lines are schematically sketched in
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The advantages of an electrostatic development station having a feed roller with one or more take-off magnets have been discussed herein. Embodiments discussed have been described by way of example in this specification. It will be apparent to those skilled in the art that the foregoing detailed disclosure is intended to be presented by way of example only, and is not limiting. Various other alterations, improvements, and modifications will occur and are intended to those skilled in the art, though not expressly stated herein. These alterations, improvements, and modifications are intended to be suggested hereby, and are within the spirit and the scope of the claimed invention. Additionally, the recited order of processing elements or sequences, or the use of numbers, letters, or other designations therefore, is not intended to limit the claims to any order, except as may be specified in the claims. Accordingly, the invention is limited only by the following claims and equivalents thereto.
