Magnetic Shielding Apparatus

Abstract

A device in which a magnetic flux field forms a shield of magnetic granules about a shaft member journaled for rotary movement. The shield is arranged to prevent contamination of the shaft member. The foregoing abstract is neither intended to define the invention disclosed in the specification nor is it intended to be limiting as to the scope of the invention in any way.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to a development apparatus of an electrostatographic printing machine, and more particularly concerns a device for preventing contamination of the development apparatus.

In the process of electrostatographic printing, an electrostatic charge pattern corresponding to an original document to be reproduced is recorded on an insulating medium. A viewable record is produced by developing the electrostatic charge pattern with particles to form a powder image thereof. Thereafter, the visible powder image is fused to the insulating medium, or transferred to a suitable support material and fused thereto.

The electrostatic charge pattern or latent image is developed by bringing a developer mix into contact therewith. Various types of developer mixes may be employed. However, generally, the developer mix comprises dyed or colored thermoplastic particles, known in the art as toner particles, which are mixed with coarser carrier granules, such as ferromagnetic granules. The carrier granules charge the toner particles to the correct polarity by triboelectrification. As the developer mix is brought into contact with the electrostatic latent image, the electric field exerts a force on the charged toner particles. When this force is large enough to break the carrier-to-toner bond, the toner particles then attach themselves to the electrostatic latent image.

Development systems utilize suitable rotary impeller systems or bucket conveyor systems to transport the developer mix from a sump storing a supply thereof to the electrostatic latent image. Impeller systems or conveyor systems generally include shaft members journaled for rotary movement in suitable rolling contact bearings, i.e., roller or ball bearings, to achieve the requisite movement of developer mix.

The dynamic load characteristics of the bearing generally determine its life expectancy. Defects in the bearings, mounting, lubrication, or contamination may accelerate failure and shorten bearing life. Magnetic carrier granules frequently enter the bearing and act as a contaminant thereof. In this manner, the carrier granules contaminate the bearings supporting the shaft for rotary movement resulting in a reduction in the life expectancy thereof. This substantially reduces the life expectancy of the conveyor or impeller system and, in turn, that of the development apparatus.

Accordingly, it is a primary object of the present invention to improve the development apparatus by substantially reducing contamination thereof.

SUMMARY OF THE INVENTION

Briefly stated, and in accordance with the present invention, there is provided a device arranged to prevent contamination of a shaft member journaled for rotary movement.

In the particular device illustrated, bearing means rotatably support the shaft member with magnetic means being interposed between the bearing means and a flow of magnetic granules. A magnetic flux field produced by the magnetic means entraps and aligns the magnetic granules into a shield. Thus, in accordance with the present invention, the shield of granules located between the shaft member and the magnetic means prevents subsequent granules from contaminating the bearing means. Moreover, the present invention also includes means for impelling the granules entrapped by the shield in a direction substantially away from the bearing means.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which:

FIG. 1 is a sectional elevational view of a development apparatus having the present invention therein and adapted for usage in an electrostatographic printing machine; and

FIG. 2 is a partial, fragmentary sectional view of the shielding device used in the development apparatus depicted in FIG. 1.

While the present invention will hereinafter be described in connection with a preferred embodiment, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

For a general understanding of the illustrated development apparatus in which the present invention may be incorporated, reference is had to the drawings wherein like reference numerals have been used throughout to designate like elements. FIG. 1 schematically illustrates the development apparatus used in an electrostatographic printing machine for producing copies from an original document. As in all electrostatographic machines, an electrostatic latent image is formed on an insulating medium. Developer mix is brought into contact with the latent image and toner particles deposited thereon to form a powder image thereof. Thereafter, the powder image is transferred to a sheet of support material to which it may be permanently adhered by a suitable fusing device. This concept was originally disclosed in U.S. Pat. No. 2,297,691 issued to Carlson in 1942.

The development unit depicted in FIG. 1 is of the type referred to in the art as a "magnetic brush development system." In a magnetic brush development system, a magnetizable developer mix having carrier granules and toner particles is continually moved through a directional flux field to form a brush of developer material. The brush comprises a magnetic member with a mass of developer mix adhering thereto by magnetic attraction. This chain-like arrangement of developer mix simulates the fibers of a brush. Development is achieved by bringing the brush of developer mix into contact with the electrostatic latent image.

Referring once again to FIG. 1, the principle components of the development unit depicted therein are developer housing 10, conveyor means or paddle wheel 12, transport means or roll 14, and developer means or roll 16. Paddle wheel 12 is a cylindrical member with scoops or buckets 20 mounted around the periphery thereof. As paddle wheel 12 rotates, it elevates developer mix 18 from the lower region or sump of housing 10 to the upper region thereof. When developer mix 18 reaches the upper region of housing 10, it is lifted from buckets 20 to transport roll 14 by the magnetic flux field produced by fixed magnets 22 disposed interiorly thereto. Preferably, alternate buckets 20 of paddle wheel 12 have apertures in the root diameters thereof enabling developer mix 18 carried in those areas to fall back to the sump of developer housing 10. As developer mix 18 falls back to the sump, it cascades over shroud 24 which is preferably a tubular member having an aperture or longitudinally extending slot 26 in the lower region thereof. In this way, developer mix 18 is recirculated such that the carrier granules thereof are continually agitated to mix with fresh toner particles and generate a strong triboelectric charge therebetween. As developer mix 18, in buckets 20 of paddle wheel 12, approach transport roll 14 the magnetic flux field produced by magnets 22 mounted fixedly therein attract developer mix 18 thereto. Transport roll 14 moves developer mix 18 in an upwardly direction by the frictional force exerted between the roll surface and developer mix 18. Metering blade 28 is provided to control the amount of developer mix 18 carried over the top of transport roll 14. The surplus developer mix is sheared from transport roll 14 and falls in a downwardly direction toward paddle wheel 12. Surplus developer mix falls through the apertures of paddle wheel 12 in a downwardly direction into the sump of developer housing 10.

Developer mix 18, which passes metering blade 28, is carried over transport roll 14 to developer roll 16 and into development zone 30 located between photoconductive surface 32 of drum 34 and developer roll 16. The electrostatic latent image recorded on photoconductive surface 32 is developed by contact with moving developer mix 18. The charged areas of photoconductive surface 32 electrostatically attract toner particles from the carrier granules of developer mix 18. At the exit of development zone 30, magnetic fields in a direction generally tangential to developer roll 16 continue to secure thereto denuded carrier granules (carrier granules which had toner particles stripped therefrom) and unused developer mix. Upon passing from development zone 30, the denuded carrier granules and unused developer mix enter a region relatively free from magnetic forces and fall from developer roll 16 in a downwardly direction into the lower region of developer housing 10. As the denuded carrier granules and unused developer mix descend, mixing baffle 36 diverts the flow from the ends toward the center of developer housing 10 to provide mixing in this direction. Paddle wheel 12 includes a shaft member or hub 38 rotatably mounted on frame member or developer housing 10. Buckets 20 are secured fixedly to hub member 38.

Cylindrical shroud 24 serves to control the fall of unused developer mix and denuded carrier granules such that they mix with toner particles rather than simply falling into the sump of developer housing 10. Furthermore, shroud 24 isolates, from developer mix 18, an interior cylindrical enclosure which is used to house toner dispenser 40. Toner dispenser 40 contains a fresh supply of toner particles 42 arranged to pass through slot 26 in shroud 24 and into the stream of developer mix 18. Having toner particles introduced into the developer mix at this location insures that the particles cannot be carried into development zone 30 without some degree of mixing with the carrier granules. Additional toner particles are added to developer mix 18 in order to replace the particles used in forming images so as to maintain the concentration thereof substnatially constant providing substantially uniform image developability.

Development begins when clutch gear 44 meshes with gear 46 which is secured to paddle wheel 12. Clutch gear 44 rotates in the direction of arrow 48 to drive gear 46 in the direction of arrow 50, thereby causing paddle wheel 12 to also revolve in the direction of arrow 50. In operation, the development unit positions developer roll 16 adjacent the photoconductive surface 32 in operative communication therewith to develop the electrostatic latent image formed thereon with toner particles. Thereafter, toner particles are transferred to the support material forming a toner powder image of the original document thereon. In the preferred embodiment thereof, development roll 16 includes stationary magnets 52 disposed interiorly and arranged to attract developer mix 18 thereto from transport roll 14.

As hereinbefore indicated paddle wheel 12 is journaled for rotary movement by suitable bearing means such as roller bearings or ball bearings mounted on opposed end portions of hub member 38 providing support therefore. Carrier granules may contaminate the bearing member and reduce the life expectancy of the paddle wheel assembly. In order to preclude the occurrence of the aforementioned carrier granule contamination, magnetic means are mounted on shroud 24 and developer housing 10. The aforementioned relationship between the magnetic means and bearing means is indicated more clearly in FIG. 2.

As shown in FIG. 2, developer housing 10 includes a generally cylindrical interior surface for housing roller bearing 54. Outer race 56 of roller bearing 54 is mounted on the cylindrical interior surface of developer housing 10, while inner race 58 of bearing 54 is mounted on hub member 38 of paddle wheel 12. A pair of such bearing members are mounted on hub member 38 in the region of opposed end portions to provide a simple support therefore. Hence, in this manner, paddle wheel 12 is journaled for rotary movement to raise developer mix 18 from the lower region of developer housing 10 to the upper region thereof. Preferably, paddle wheel 10 is interposed between shroud 24 and developer housing 10 and is substantially concentric about the longitudinal axis of shroud 24. In order to permit the addition of toner particles to toner dispenser 40 or the replacement thereof, end cap 60 is removably mounted on developer housing 10. As developer mix 18 is advanced in an upwardly direction, magnetic carrier particles tend to move toward bearing members 54 resulting in contamination thereof. However, in the present invention, a shield of magnetic carrier particle granules is formed via the utilization of magnetic means operatively associated with impelling means to prevent carrier granules from contaminating bearing 54. Magnetic means or ring magnet 62 has the exterior circumferential surface thereof mounted on developer housing 10 and is spaced axially from bearing member 54 by arcuate spacer 64. The interior circumferential surface of magnetic means 62 is spaced from hub member 38. Hub member 38 includes a threaded portion 66 aligned so as to be opposed from magnetic means 62. By way of example, threaded portion 66 may be a suitable pipe thread. As carrier granules 68 advance toward bearing member 54 they are attracted to magnetic means or ring magnet 62 via the magnetic flux field formed thereby. The magnetic flux field is arranged to form a shield of carrier granules between hub member 38 and ring magnet 62. As hub member 38 rotates the exterior threaded portion 66 thereof is arranged to impel carrier granules 68 in a direction substantially away from bearing member 54.

In order to further protect bearing member 54 from carrier granule contamination an interior magnetic member 72 is mounted on shroud 24 in operative communication with internal threaded portion 74 e.g., a suitable pipe thread, of hub member 38. The magnetic means or ring magnet 72 has the interior circumferential surface thereof mounted on shroud 24. The exterior circumferential surface of ring magnet 72 is spaced from hub member 38. The interior threaded portion 74 of the hub member 38 is spaced from and aligned with the exterior circumferential surface of ring magnet 72. As carrier granules 68 advance toward bearing member 54, they are attracted to ring magnet 72. Ring magnet 72 is arranged to form a magnetic flux field which aligns and entraps carrier granules 68 to form shield 71 between the interior circumferential surface of hub member 38 and ring magnet 72. Hub member 38 includes an interior threaded portion 74 substantially aligned with the exterior circumferential surface of ring member 72. Threaded portion 74 is adapted to impel carrier granules 68 away from bearing member 54 as hub member 38 rotates.

From the foregoing, it is apparent that the shielding arrangement of the present device substantially improves the development apparatus of an electrostatographic printing machine by reducing contamination thereof. Furthermore, the carrier granules are prevented from entering the bearing members supporting the paddle wheel in rotary movement, thereby improving its life expectancy.

It is, therefore, evident that there has been provided in accordance with this invention, a device for substantially reducing contamination of the development apparatus of an electrostatographic printing machine that fully satisfies the objects, aims and advantages set forth above. While this invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

Claims

What is claimed is:

1. A device for preventing magnetic granules from contaminating a tubular shaft member journaled for rotary movement, including:

bearing means mounted on the shaft member; and

magnetic means disposed externally of and internally of said tubular member, each said magnetic means being interposed between said bearing means and the flow of magnetic granules, said magnetic means producing a magnetic flux field entrapping and aligning the granules into a shield located between the shaft member and said magnetic means to prevent granules from contaminating said bearing means.

2. A device as recited in claim 1, further including means for impelling the granules entrapped by the shield formed by said magnetic means in a direction substantially away from said bearing means.

3. A device as recited in claim 2, further including a frame member adapted to support said bearing means so as to enable the shaft member to rotate relative thereto.

4. A device as recited in claim 3, wherein said magnetic means includes a magnet member mounted on the shaft member spaced from said frame member.

5. A device as recited in claim 4, wherein said impelling means includes a threaded portion on said frame member aligned generally opposed from said magnetic member and spaced therefrom, said threaded portion being adapted to move the entrapped granules in a direction substantially away from said bearing means as the shaft member rotates.

6. A device as recited in claim 3, wherein said magnetic means includes a magnet member mounted on said frame member spaced from the shaft member.

7. A device as recited in claim 6, wherein said impelling means includes a threaded portion on the shaft member aligned generally opposed from said magnet member and spaced therefrom, said threaded portion being adapted to move the entrapped granules in a direction substantially away from said bearing means as the shaft member rotates.

8. A development apparatus for an electrostatographic printing machine of the type having conveyor means for transporting a developer mix comprising magnetic carrier granules and toner particles into contact with an electrostatic latent image to create a toner powder image thereof, wherein the improvement includes:

a tubular rotary driven shaft member;

bearing means for rotatably supporting said shaft member; and

magnetic means disposed externally of and internally of said tubular member, each said magnetic means being interposed between said bearing means and the flow of carrier granules, said magnetic means producing a magnetic flux field entrapping and aligning the carrier granules into a shield located between said shaft member and said magnetic means to prevent granules from contaminating said bearing means.

9. An apparatus as recited in claim 8, further including means for impelling the granules entrapped by the shield formed by said magnetic means in a direction substantially away from said bearing means.

10. An apparatus as recited in claim 9, further including a frame member adapted to support said bearing means so as to enable said shaft member to rotate relative thereto.

11. An apparatus as recited in claim 10, wherein said magnetic means includes a magnet member mounted on said shaft member spaced from said frame member.

12. An apparatus as recited in claim 11, wherein said impelling means includes a threaded portion on said frame member aligned generally opposed from said magnetic member and spaced therefrom, said threaded portion being adopted to move the entrapped granules in a direction substantially away from said bearing means as said shaft member rotates.

13. An apparatus as recited in claim 10, wherein said magnetic means includes a magnetic member mounted on said frame member spaced from said shaft member.

14. An apparatus as recited in claim 13, wherein said impelling means includes a threaded portion on said shaft member aligned generally opposed from said magnetic member and spaced therefrom said threaded portion being adapted to move the entrapped granules in a direction substantially away from said bearing means as said shaft member rotates.