Abstract:
An apparatus and method for dispensing toner in an electrostatographic printer includes apparatus for drawing ambient air in a vertical direction, preferably upwards, through a relatively large toner container (e.g., 10-225 liters in volume). The air-flow is sufficient to fluidize the toner in the container and thereby prevent compaction. Such fluidization is optionally supplemented by the action of an auger or propeller mechanism mounted within the container. During rotation of the auger/propeller, the toner is lifted and thereby further prevents toner compaction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    Reference is made to the commonly assigned U.S. patent application Ser. No. ______, filed concurrently herewith and entitled “Apparatus and Method for Fluidizing Toner in a Storage Container”. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to improvements in methods and apparatus for dispensing fresh toner to an image development station in an electrostatographic copier/printer or the like.  
         BACKGROUND OF THE INVENTION  
         [0003]    In electrostatographic copiers and printers, pigmented thermoplastic particles, commonly known as “toner,” are applied to latent electrostatic images to render such images visible. Often, the toner particles are mixed with and carried by somewhat larger particles of magnetic material. During the mixing process, the magnetic carrier particles serve to triboelectrically charge the toner particles to a polarity opposite that of the latent charge image. In use, the development mix is advanced, typically by magnetic forces, from a sump to a position in which it contacts the latent charge image. The relatively strong electrostatic forces associated with the charge image operate to strip the toner from the carrier, causing the toner to remain with the charge image. Thus, it will be appreciated that, as multiple charge images are developed in this manner, toner particles are continuously depleted from the mix and a fresh supply of toner must be dispensed from time-to-time in order to maintain a desired image density. Usually, the fresh toner is supplied from a toner supply bottle mounted upside-down, i.e., with its mouth facing downward, at one end of the image-development apparatus. Under the force of gravity, toner accumulates at the bottle mouth, and a metering device, positioned adjacent the bottle mouth, operates to meter sufficient toner to the developer mix to compensate for the toner lost as a result of image development. Usually, the toner-metering device operates under the control of a toner concentration monitor that continuously senses the ratio of toner to carrier particles in the development mix.  
           [0004]    It is well known that toner is a powdery substance that exhibits a considerable degree of cohesiveness and, hence, relatively poor flowability. Since the force of gravity alone does not usually suffice in causing toner to flow smoothly from the mouth of an inverted toner bottle, other supplemental techniques have been used to “coax” the toner from the bottle. For example, flow additives, such as silica and the like, have been added to the mix to reduce the troublesome cohesive forces between toner particles. See, e.g., the disclosure of U.S. Pat. No. 5,260,159 in which a “fluidization” agent is added to a developer mix in a development sump to assist the movement of developer therein. While beneficial to a more consistent flow of developer, such substances influence other performance attributes of the development process and their effectiveness is therefore constrained. Automatically operated stirring devices or augers mounted within a horizontally oriented toner container, and thumping or vibrating devices connected to such containers have also been used to urge toner from its rest position towards an outlet or exit port. Such mechanical techniques work well when the toner container is relatively small (e.g., 2 to 5 liters) and the height of the toner column above the exit port is relatively low (e.g., lower than about 15 cm.) so as to avoid gravity-assisted compaction of the toner which further compromises flowability. But, as the size of the toner bottle or container increases, e.g., to accommodate high speed and wide format printing in which toner is consumed at extraordinarily fast rates, the above-noted flow-enhancing techniques have been found to be inadequate. In such high toner-consumption situations, toner sumps of the order of tens of liters are desirable in order to eliminate the need for frequent toner bottle replacements. The weight of the toner in these large volume containers is too great for conventional rappers and vibrators to keep the toner flowing through the outlet, and most of these devices only exacerbate the toner-packing problem.  
           [0005]    In U.S. Pat. No. 5,570,170, there is disclosed an apparatus for dispensing single-component, electrically conductive magnetic toner particles from a pair of inverted toner bottles mounted above a conventional development station in an electrostatic printing apparatus. A screen positioned at the mouth of each bottle serves to prevent toner flow from the bottle whenever the toner is piled up atop the screen. The toner-dispensing apparatus includes a pair of gas-permeable, but toner-impermeable, tubes that extend upwardly, into each bottle, a distance of about 30-60% of the height of the bottles. On command, pressurized gas is introduced into the tubes. As the gas passes through the tubes and into the toner bottles, it acts to fluidize the toner in the bottle in the vicinity of the bottle&#39;s outlet, thereby enabling the toner to flow smoothly through the screen mesh and into the development station of the printer, as needed. In effect, the screen acts as a gate to prevent toner flow into the development station until the toner above the screen is fluidized. A microprocessor controls the application of pressurized gas to each of the bottles, switching from one bottle to the other as one-bottle empties. By using two bottles, the machine operator can replace an empty bottle without shutting down the machine.  
           [0006]    While the apparatus disclosed in the above patent may be advantageous in some respects in selectively dispensing magnetic toner to an image-development station, it is disadvantageous in that it requires one or more sources of compressed gas in order to effect the necessary fluidization of the toner mass in order to achieve passage of the toner through the metering screen at the mouth of each toner bottle. Further, to prevent toner dust from being blown out of the development station during toner dispensing, a vacuum must be created in the mouth of the development station. This dusting problem can be especially problematic as the size of the toner bottle increases to accommodate high speed and large format printing.  
         SUMMARY OF THE INVENTION  
         [0007]    In view of the foregoing discussion, an object of this invention is to provide an improved method and apparatus for dispensing toner from high tower sumps or hoppers of the type used in high speed and/or high volume printing applications.  
           [0008]    In accordance with a preferred embodiment of the invention, there is provided a toner-dispensing apparatus comprising a relatively large (e.g. 25-50 liters), vertically oriented container adapted to receive a fresh supply of toner. The toner container is adapted to be permanently installed within the framework of an electrostatographic printer or the like, and it is shaped somewhat like a funnel, having a lower portion with walls that converge towards a relatively small toner-outlet port in the container&#39;s lowest-most portion. The toner-outlet port is positioned directly above an auger that serves, when rotating, to transport toner from the outlet port of the toner container to the housing of a conventional image-development station of the printer. One or more toner-impervious air-inlet port(s), as provided, for example, by a screened opening, is provided in the container wall in the vicinity of the toner-outlet port. The upper portion of the toner container is operatively coupled to a vacuum source, preferably via a toner-impermeable, air-permeable filter. The upper portion of the container defines a normally closed toner-refill port through which fresh toner can be added manually to the container. When activated, the vacuum source serves to draw air from the container through the aforementioned filter, thereby lowering the pressure in the container and causing air to be drawn into the container through the air inlet port at the base of the container. Thus, as the air entering the container through the air-inlet port rises towards the vacuum source at the top of the container, it acts to lift and tumble the intervening toner particles, thereby fluidizing or aerating the entire toner mass within the container. Such fluidization serves to prevent any compaction of the toner within the container, as would normally occur in a toner container of the size contemplated for use in the invention, allowing the toner to flow uninterrupted through the container&#39;s toner outlet port and onto the underlying toner-transport auger. Preferably, the filter through which the air is evacuated from the container is vibrated, either continuously or intermittently, to prevent the build-up of any toner deposit occurring while the toner-fluidizing vacuum is applied. In accordance with another preferred embodiment, the air entering the air-inlet port(s) at the base of the toner container is supplied from the housing of the image-development station. By this arrangement, any toner dusting that might occur for any reason at the toner applicator/image-recording element interface is minimized.  
           [0009]    According to alternate embodiments, toner fluidization within the container via the vacuum applied to the container as described above is supplemented by either a vertically oriented rotatable auger that, when rotating, acts to convey toner upwardly, towards the top of the aforementioned container, or by a vertically oriented rotatable shaft that supports a plurality of outwardly-extending propellers that serve, while the support shaft is rotating, to drive the toner upwardly within the container and thereby assist in the toner fluidization process.  
           [0010]    In accordance with another aspect of the invention, a method is provided for enhancing the flowability of toner particles through an exit port located in the base of a vertically oriented toner storage hopper. Such method comprises the steps of fluidizing the toner mass above the port by either by directing a gas in a vertical direction, either upwards or downwards, through the toner mass while dispensing toner from the hopper outlet, and optionally by simultaneously mechanically agitating the mass with propellers or augers that rotate about a vertical axis within the toner container.  
           [0011]    An advantageous technical effect of the invention is that fresh toner can be dispensed with enhanced reliability from a relatively large storage container in which the toner, but for the invention, would most certainly compact from its weight and from internal machine vibrations, and thereby resist movement from the container&#39;s outlet port.  
           [0012]    The invention and its advantages will become better understood from the ensuing detailed description of preferred embodiments, reference being made to the accompanying drawings in which like reference characters denote like parts. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    FIGS.  1 - 5  are schematic illustrations of various preferred embodiments of the invention; and  
         [0014]    [0014]FIGS. 6 and 7 are enlarged views showing certain details of the embodiments of FIGS. 3, 4, and  5 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    Referring now to the drawings, FIG. 1 schematically illustrates a preferred embodiment of a toner dispensing apparatus  10  adapted for use with an electrostatographic printer P. The latter is of conventional design comprising, for example, an endless photoconductive recording element  12 , typically in the form of a drum, on which electrostatic images are formed by the well known electrostatographic process. Briefly, such process comprises the steps of uniformly charging the outer surface of recording element at a primary charging station  14  as the recording element moves therepast, and then, at an exposure station  16 , imagewise exposing the uniformly charged surface to actinic radiation adapted to imagewise discharge the charged surface. The charge image thus formed is subsequently rendered visible via the application of toner particles at an image-development station  18 . The toned image is then transferred to a receiver sheet at a transfer station  19  and the image-forming process is repeated. The image-development station  18  commonly comprises a rotating “magnetic brush”  20  that operates, in a well known manner, to transport a development mixture of toner and carrier particles from a sump to the surface of the charge image borne by the outer surface of the recording element. As noted earlier herein, as the development mixture contacts the charge image, the toner is stripped from the carrier and applied to the charge image. Thus, toner is continuously depleted from the developer and must be replenished.  
         [0016]    Still referring to FIG. 1 , the toner dispensing apparatus of the invention comprises a relatively large volume (e.g. 25-50 liters), vertically oriented container  30  adapted to receive a fresh supply of toner T. As will be appreciated, such a container is considerably larger (e.g. by a factor of 10 or more) than the volume of conventional toner bottles that are used to replenish toner to conventional document printers and copiers, such bottles being disposable after the contents has been emptied into the developer station sump. In contrast, the toner container  30  is designed to be permanently installed within the housing or frame F of the electrostatographic printer and, as illustrated, is preferably shaped somewhat like an elongated funnel, having a cylindrical upper portion  30 B and lower portion  30 A that converges towards a relatively small toner-outlet port  32  in the container&#39;s lowest-most portion. Port  32  is preferably positioned directly above a rotatable auger  40  that serves, when rotated by an auger motor AM, to transport toner from the outlet port  32  of the toner container to the sump housing of image-development station  18 . One or more toner-impervious air-inlet port(s)  34  is provided in the container wall  36  in the vicinity of the toner-outlet port  32 . Air can enter the outlet port(s) through a conduit  38  connected to air inlet plenum  38  having an air-pervious filter screen  39  that serves to filter out air-borne particles and other contaminants.  
         [0017]    The cylindrically shaped upper portion  32 B of toner container  30  is operatively coupled to a vacuum source V, such as a vacuum pump or the like, preferably via a toner-impermeable, air-permeable screen or filter  49 . The vacuum source is electrically operated and is selectively energizeable via a switch S connected to a voltage source VS. The upper portion of the container defines a normally closed toner-refill port  36  through which fresh toner can be added manually to the container to establish a desired initial toner level TL. Normally, port  36  is closed by a cap  36 A. When activated by switch S, the vacuum source serves to draw air from the container through filter  49 . As air in the container is evacuated, filtered clean air is drawn into the container through the air inlet port  34  and filter  39 . Thus, as the air entering the container through the air-inlet port rises towards the vacuum source at the top of the container, it acts to lift and tumble the intervening toner particles, thereby fluidizing or aerating the entire toner mass within the container. Such fluidization serves to prevent any compaction of the toner within the container, as would normally occur in a toner container of the size contemplated for use in the invention, allowing the toner to flow uninterrupted through the container&#39;s toner outlet port and onto the underlying toner-transport auger mechanism  40 . Preferably, the filter  49  through which the air is evacuated from the container is vibrated via a vibrating actuator of a suitable motor M 1 , the latter being operated either continuously or intermittently, to prevent the build-up of any toner deposit occurring while the toner-fluidizing vacuum is applied.  
         [0018]    As a result of the above-described construction, the aforementioned disadvantages of the prior art are avoided. Specifically, fresh toner can be dispensed with enhanced reliability from a relatively large storage container in which the toner, but for the invention, would most certainly compact from its weight and from internal machine vibrations, and thereby resist movement from the container&#39;s outlet port. Further, fluidization of the toner is achieved without the use of any external sources of compressed gas, as is required by the aforementioned prior art apparatus, and the apparatus of the invention requires no auxiliary vacuum source at the mouth of the development station to prevent toner dust from being blown out of the development station during toner dispensing.  
         [0019]    Referring now to FIG. 2, the FIG. 1 apparatus is shown to be modified by the inclusion of a dust shield  50  that surrounds the development station  18 . As shown, the interior of the dust shield is pneumatically coupled to the intake of inlet plenum  38  via an air duct or conduit  52 . Thus, when the vacuum source V is energized, ambient air in the vicinity of the development brush  20  enters the dust shield and is directed to the entrance of plenum  38 . Preferably, the screen filter  39  is connected to the actuator of a vibrating motor M 2 ; the vibrating motion of the filter operates to rid the filter of toner dust particles that will accumulate on the filter when the vacuum source is applied. Toner particles T′ that fall from the filter screen as a result of its vibration accumulate in a tray  54  that is releasably mounted on the printer housing directly beneath the filter  39 . By this arrangement, any tendency for toner particles or dust to escape the confines of the development station will be minimized.  
         [0020]    Referring now to FIG. 3, the toner fluidization effect achieved by the FIG. 1 apparatus is illustrated as being enhanced by a vertically disposed rotating auger RA. The latter comprises a helical auger blade  60  supported by a rotatably mounted shaft  62 . Details of this auger mechanism are better shown in FIG. 6. Shaft  62  is supported at opposite ends by a pair of bearings B 1 , B 2  mounted by a spider support  63  mounted within the container  30 . Operation of the auger mechanism is controlled by a drive motor M that serves to rotate the auger blade so that toner is lifted vertically within the toner container. A series of holes  60 A formed in the auger blade enable the lifted toner to be fall, under the force of gravity, downward into the container to maintain the toner level substantially constant, at a level determined by the toner consumption of the printer. As shown in FIG. 6, the auger shaft  62  terminates in a flange or skirt  62 A that surrounds and protects the bearing B 2 . Further, it is preferred that the ambient air drawn into the container through entrance port(s)  34  be filtered by a cylindrically shaped screen  65  that concentrically surrounds shaft  62 . Further preferred is that the auger blade  60  has a screen-sweeping paddle portion  66  that operates, while the auger blade is rotating, to sweep particulate material from the surface of screen  65  and thereby maintain the screen relatively clean at all times.  
         [0021]    In an alternative embodiment shown in FIG. 4, the auger mechanism of FIG. 3 is replaced by a propeller arrangement  70  in which a series of propellers  72  extend radially outward from a rotatably mounted and driven drive shaft  74 . Each of the propellers is suitably shaped to lift and propel toner particles slightly upwards within the container, thereby supplementing the fluidizing effect of the above-described vacuum system.  
         [0022]    [0022]FIGS. 5 and 7 illustrate yet another embodiment of the invention in which fluidizing air is drawn through the toner container from the top down, rather than from the bottom up, as is the case of the FIGS.  1 - 4  embodiments. As shown, an air manifold  75  is provided atop toner container  30 , and a vacuum source V is positioned between the toner container&#39;s outlet port  32  and toner entrance to the development station  18 . A pair of gates G 1  and G 2 , operating under the control of a suitably programmed control unit  80  and responsive to the actuators of motors M 3  and M 4  (also controlled by control unit  80 ), operate to control the flow of toner from container  30  to the development station  18 . When no toner is being dispensed, gate G 1  is closed. When the control unit receives information from the toner concentration monitor TM indicating that toner is fresh required, it operates to close or adjust the position of gate G 2  to prevent excessive suction from being applied to the dust shield and activates the vacuum source while opening gate G 1 . The downwardly flowing air through the toner container acts to fluidize the toner in the container. To determine the extent to which gate G 2  needs to be closed, the control unit compares the pressures sensed by a pair of pressure sensors P 1  and P 2  located on opposite sides of gate G 2 . Thus, the toner dispensed from container  30  is contained between gates G 1  and G 2  until the vacuum source is deactivated, at which time gate G 1  is closed and gate G 2  is opened to release the dispensed toner to the development station. The released toner may be applied directly to the toner sump of the development station, as shown, or it may be applied to a toner-transport auger mechanism, as described above, operating under control of the control unit. Each of the gates G 1  and G 2  may take the form of pivotally mounted plate, as shown in FIG. 7, or they may take the form of a fine screen that is toner-impermeable unless the fluidizing vacuum is applied. Preferably, the vacuum source is isolated from the dispensed toner by a filter or screen  81  that is vibrated or thumped by the vibrating actuator a motor M 5  to prevent toner from accumulating. In this embodiment, the dust shield  50  is still used to draw toner dust from the vicinity of the development brush/recording element interface. As in the FIG. 2 embodiment, air-borne toner particles in conduit  52  are captured by the vibrating screen filter  39  and deposited in container  54 .  
         [0023]    While the invention has been described in detail with reference to preferred embodiments, it will be understood that changes can be made without departing from the spirit of the invention. Such changes are intended to fall within the scope of the following claims.