Abstract:
An apparatus and method for dispensing toner in an electrostatographic printer includes apparatus for agitating toner contained by a relatively large toner container (e.g., 10-25 liters in volume). Such apparatus includes a substantially vertically-oriented shaft supporting s blade member that operates, as the blade rotates, to drive the contained toner mass upwardly, thereby aerating the mass and preventing compaction during toner dispensing.

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 Dispensing Tone”.  
         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. More particularly, it relates to apparatus for maintaining toner in a fluidized state to facilitate toner dispensing from relatively large storage containers.  
         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. Rotatably supported within the toner container is a vertically oriented mechanical agitator that, during rotation, is adapted to break-up any agglomerations or compactions of toner particles in the container and to lift the toner vertically upwards, allowing such particles to settle in the container under the force of gravity. By such an arrangement, the contained toner is maintained in a fluidized or aerated state while toner is dispensed through the toner outlet port. In accordance with a first preferred embodiment, such mechanical agitator comprises auger blade having a plurality of apertures formed therein. The auger blade has a helical configuration and is shaped to advance toner substantially vertically upwards as the blade rotates. Preferably, the apertures are equally spaced apart along the length of the blade and are of a size to enable the lifted toner to easily drop downwardly, through the blade openings in order to maintain the level of toner in the container substantially constant. The auger blade is configured so that its outer edges are closely spaced from the container wall over the effective portion of the container that holds toner. According to a preferred embodiment, the axis of rotation of the auger is slightly displaced from the container&#39;s central axis to facilitate break-up of compacted toner particles and to avoid any tendency for a large “slug” of toner to be advanced by the auger rotation.  
           [0009]    According to another preferred embodiment, the above-noted mechanical agitator takes the form of a rotatably mounted substantially vertically oriented shaft having a series of radially-extending propeller blades. The blades are shaped so that, during rotation of the shaft, the toner particles are driven upwardly within the container.  
           [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 substantially vertically oriented toner storage hopper. Such method comprises the steps of fluidizing the toner mass above the port by mechanically agitating the mass with propellers or an auger that rotate(s) about a substantially 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]    [0013]FIGS. 1 and 2 are schematic illustrations of preferred embodiments of the invention; and  
         [0014]    [0014]FIG. 3 is an enlarged view showing certain details of the FIG. 1 embodiment. 
     
    
     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), substantially 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. Also, the orientation may be at some relatively small angle to the vertical as long as the main component of flow is vertical. In contrast, the toner container  30  is designed to be permanently installed within the housing or frame F of the electrostatographic printer. As illustrated, it is preferred that at least the container&#39;s interior wall is shaped somewhat like an elongated funnel, having a cylindrical upper portion  30 B and conical lower portion  30 A that converges towards a relatively small toner-outlet port  32  in the container&#39;s lowest-most portion. Preferably, the container has a substantially circular transverse cross-section. 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 . 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.  
         [0017]    Now, in accordance with the invention, compaction of the toner contained by container  30  as a result of the relatively high vertical column of toner within the container is prevented by a mechanical, toner agitator  50  positioned within the container. Preferably, such agitator comprises a substantially vertically disposed auger mechanism comprising a rotatably driven, helical auger blade  52  supported by a shaft  54 . Details of this auger mechanism are better shown in FIG. 3. Shaft  54  is supported for rotation at opposite ends by a pair of bearings B 1 , B 2  and is rotatably driven by a drive motor M. Bearing B 1  is supported by a spider mount that enables toner to flow around and into the container&#39;s outlet port  32 . Bearing B 2  is supported by a lid  31  atop the container  30 , the shaft passing through the lid to engage the drive mechanism of drive motor M. Auger blade  52  is contoured such that, as its associated drive shaft rotates, the blade acts to lift the toner within container substantially vertically upwards. A series of suitably sized apertures  56  are formed in the auger blade to enable the lifted toner to fall, under the force of gravity, downwardly into the container, thereby maintaining the toner level TL therein substantially constant, at a level determined by the toner consumption of the printer. Preferably, the respective axes A and A′ of the auger shaft  52  and container  30  are not coincident; rather, these axes, though extending parallel to each other, are displaced by a relatively small distance D of up to about 2 or 3 mm. Such a spacing represents a trade-off that serves to maintain a sufficiently close relationship between the container wall and the outer edge of the auger blade to prevent a significant portion of toner from stagnating within the container while, at the same time, preventing any tendency for the rotating auger blade to advance the toner upwardly as a sizable “slug” of non-aerated material within the container. This non-concentric relationship assures that the auger blade constantly mixing the toner mass as it elevates it.  
         [0018]    As shown in FIG. 3, it is preferred that the auger shaft  54  terminates in a flange or skirt  54 A that surrounds and protects the bearing B 2 . Further preferred is that the auger blade  52  has a surface-sweeping paddle portion  52 A that operates, while the auger blade is rotating, to sweep particulate material from the wall of outlet port  32  and thereby maintains the port relatively clean at all times.  
         [0019]    In an alternative embodiment shown in FIG. 2, the auger mechanism of FIG. 1 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 and pitched to lift and propel toner particles upwardly within the container.  
         [0020]    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.  
         [0021]    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. For example, while it is preferred that the respective axes of shaft  54  be offset from each other for reasons expressed above, it is contemplated that the same effect can be achieved by employing a container having a slightly elliptical cross-section, in which case the container and shaft axes may coincide. Such changes are intended to fall within the scope of the following claims.