Residual powered developer homogenizer for electrophotographic device

Abstract

A cleaner for removing residual powdered developer from an applicator which applies the developer to a photoconductive electrostatic image-forming member. The cleaner has a flat inclined surface down which the residual developer slides into a reservoir. The homogenizer is mounted above the flat surface perpendicular to the gradient thereof and comprises a rotary shaft carrying a plurality of elliptical plates. The minor axes of the plates perpendicularly intersecting the axis of the shaft and the major axes intersecting the axis of the shaft at an acute angle equal to the arc sine of the ratio of the lengths of the minor axis of the plates and the major axis so that the edges of the plates just touch the flat surface at all rotational positions of the shaft. The plates deflect the residual developer in various directions along the length of the shaft to homogenize the same.

Description

The present invention generally relates to an electrophotographic device having means for recycling residual powdered developer, and more particularly to a homogenizer to homogenize the residual developer prior to returning the same to a reservoir.

In an electrophotographic device such as a copying machine to which the present invention is directed, an image of a document is projected onto a photoconductive element to form a latent electrostatic image of the document, and the latent image is converted into a visible image by a wet or dry development process. In a dry development process, a powdered developer comprising toner and carrier particles is applied by an applicator onto the photoconductive member. The toner particles are transferred to a sheet of paper and fixed thereto by means such as thermal fixing, and the carrier particles are returned to a developer reservoir. Light areas of the electrostatic image on the photoconductive member have no electrostatic charge, whereas dark areas of the image have, for example, a positive electrostatic charge. The toner particles are dark in color and have a charge opposite to that of the dark portions of the electrostatic image, or in this case a negative charge, so that they will be attracted by and adhere to the dark image areas of the photoconductive member. The carrier particles have the same polarity as the dark areas of the electrostatic image, in this example positive, so that they will attract and carry the toner particles and be repelled by the positive charge of the photoconductive member. The charge of the photoconductive member is stronger than that of the carrier particles so that the carrier particles will be separated from the toner particles when the toner particles adhere to the photoconductive member and drop away from the photoconductive member. The development process is thereby based on the Coulomb attraction between the dark areas of the electrostatic image on the photoconductive member and the toner particles.

In another known method, the applicator is a rotary magnetic brush and the carrier particles are of a magnetic material. As the magnetic brush sweeps the photoconductive member, toner particles are transferred to the dark areas of the electrostatic image, but the carrier particles remain adhered to the magnetic brush. Residual toner particles resulting from lack of transfer to light areas of the electrostatic image will also remain adhered to the magnetic brush. This method represents an improvement in that scattering of the residual developer particles is largely prevented. A drawback of this method is that continuous prolonged development will progressively reduce the darkness and contrast of the developed image since toner particles are consumed and the carrier particles are capable of attracting only a limited amount of toner particles.

As an example, if the copy paper onto which the image is transferred is in the form of an elongated strip, one side of the strip being dark and the other side being light, and the magnetic brush development method is applied along the length of the strip, the dark areas will continuously consume toner particles whereas the light areas will not, and the darkness of the developed dark side of the strip will progressively decrease. It is clear, however, that toner particles are present in the half of the magnetic brush corresponding to the light side of the image, and if utilized can maintain the dark side of the developed image at a satisfactory level of darkness for a greater period of time. Although this example is extreme, it points out the desirability of removing the residual developer particles from the magnetic brush, homogenizing them so that the ratio of the concentrations of the toner and carrier particles is uniform, and recycling the developer particles to a reservoir for re-use.

A prior art arrangement to accomplish this object involves a cleaner for the magnetic brush which comprises an inclined flat plate having its upper edge engaging with the magnetic brush to scrape residual developer particles therefrom. Deflecting plates or baffles are arranged above the plate to deflect the residual developer particles sliding down the plate in different directions to mix or homogenize the same. Although simple in construction, the practical performance of this arrangement has not been satisfactory.

It is therefore an important object of the present invention to provide a homogenizer to effectively homogenize residual developer particles removed from a magnetic brush of an electrophotographic device such as a copying machine.

The above and other objects, features and advantages of the present invention will become more clear from the following detailed description taken with the accompanying drawings, in which:

FIG. 1 is a plan view of a homogenizer embodying the present invention;

FIG. 2 is a plan view of a plate of the homogenizer shown in FIG. 1;

FIG. 3 is a schematic view of a portion of an electrophotoconductive device incorporating the homogenizer shown in FIG. 1;

FIG. 4 is a plan view of the homogenizer shown in FIG. 1 in operative engagement with a flat surface of a part of the device shown in FIG. 2;

FIG. 5 is a plan view of a modified form of the homogenizer shown in FIG. 1;

FIG. 6 is a view illustrating the profile of a modified form of a shaft of the homogenizer shown in FIG. 1; and

FIG. 7 is a view illustrating a modified form of a plate of the homogenizer shown in FIG. 1 fixed to a sleeve by which the plate is adapted to be mounted on the shaft shown in FIG. 6.

Referring now to FIG. 1, a homogenizer 10 embodying the present invention comprises a shaft 12. Elliptical plates 14 are mounted on the shaft 12 by means of sleeves 16 respectively. Referring also to FIG. 2, the major axis of each plate 14 has a length a and the minor axis has a length b. The minor axis of each plate 14 perpendicularly intersects the axis of the shaft 12, and the major axis of each plate 14 intersects the axis of the shaft 12 at an acute angle .theta.. The relationship is such that b = a (sin .theta.). .theta. = arc sin (b/a), and is shown in the drawings as 45.degree..

Referring now to FIG. 3, a copying machine 18 includes a casing 20, the bottom portion of which defines a reservoir 22 containing powdered developer in the form of carrier and toner particles. Fresh developer is fed into the reservoir 22 through a hopper 24. A photoconductive drum 26 is provided on which an electrostatic image of a document being copies is formed by an optical system (not shown), and which rotates counterclockwise. An applicator in the form of a rotary drum 28 having a brush (not shown) provided on its circumference has its lower portion immersed in the developer in the reservoir 22 and rotates counterclockwise. Although not shown, the brush of the drum 28 is arranged to slidably contact the surface of the drum 26 as the drums 26 and 28 are simultaneously rotated. Magnets 28a, 28b, 28c and 28d are fixedly mounted within the drum 28 adjacent to the inner surface thereof near the contact area of the drums 26 and 28.

The shaft 12 of the homogenizer 10 is rotatably supported within the casing 20 above a cleaner 30 in the form of a flat plate. The cleaner 30 is rotatably supported by the shaft 12 by means of hangers 32, one of which is shown. The cleaner 30 is inclined as shown, and the upper edge of the cleaner 30 engages with the brush of the drum 28 to remove residual developer therefrom. The residual developer slides down the flat upper surface of the cleaner 30, passes through the homogenizer 10 and drops down into the reservoir 22 for recycling. Toner and/or carrier particles may be continuously or periodically introduced into the hopper 24 at a fixed concentration ratio of carrier/toner particles. A feed rotor 34 is also provided to move the developer particles into the area of the reservoir 22 under the drum 28.

In operation, the optical system projects an image of the document onto the drum 26 to form a latent electrostatic image. The brush of the drum 28 picks up developer from the reservoir 22 due to the effect of the magnets 28a, 28b, 28c and 28d and transfers the same to the drum 26 to develop the latent image. Toner particles are attracted by and adhere to dark areas of the image on the drum 28, and carrier particles and some toner particles corresponding to light areas of the image remain adhered to the brush of the drum 28. Upon further rotation of the drum 28, the toner particles adhered thereto are transferred and fixed to a sheet of copy paper to provide the desired copy.

Upon further rotation of the drum 28, the residual toner and carrier particles are detached from the brush of the drum 28 by the upper edge of the cleaner 30, and slide down the upper surface of the cleaner 30 through the homogenizer 10 and drop down into the reservoir 22. The residual developer particles may be easily removed from the brush of the drum 28 because there are no magnets arranged inside the drum 28 near the cleaner 30, and the magnetic attraction of the drum 28 and brush for the developer particles near the cleaner 30 is very low.

The purpose of the homogenizer 10 is to throughly mix or homogenize the residual developer particles passing therethrough so that the ratio of the concentration of carrier particles to toner particles will be the same for particles emerging from all points of the homogenizer 10 to provide a homogenious powdered developer for recycling.

The detailed operation of the homogenizer 10 will now be described with reference to FIG. 4. As shown, the bottom edges of the plates 14 are closely adjacent to the upper flat surface of the cleaner 30; either the plates 14 just touch the cleaner 30 or the clearance therebetween is very small. The residual developer particles move through the homogenizer 10 perpendicular to the plane of FIG. 4, or down the gradient of the flat surface of the cleaner 30. As will be understood by one skilled in the art, due to the relationship .theta. = arc sin(b/a), the edges of the plates 14 will just touch the surface of the cleaner 30 at all rotational positions of the shaft 12. If desired, the projections of the major axes of the plates 14 on a plane perpendicular to the axis of the shaft 12 may coincide, as shown in FIG. 5, so that the orientation of all of the plates 14 is the same. In a preferred form of the present invention, however, the projections of the major axes of the plates 14 on a plane perpendicular to the axis of the shaft 12 do not coincide, but are equiangularly spaced about the axis of the shaft 12. For example, as shown in FIG. 4, if the projection of the major axis of the leftmost plate 14 as shown is oriented vertically in a plane perpendicular to the shaft 12, the projection of the major axis of the second plate 14 from the left will appear as rotated by 90.degree.. The projections of the major axes of the third plate 14 from the left and the rightmost plate 14 will appear in said plane as rotated by 180.degree. and 270.degree. respectively from the vertical position of the first plate 14, and will be symmetrical to the first and second plates 14 from the left respectively.

In the embodiment shown in FIG. 4, the homogenizer 10 is freely rotatably mounted within the casing 20 and will be rotated by the developer particles passing therethrough. Since the plates 14 are arranged at 90.degree. angles to each other along the length of the shaft 12, the plates 14 will deflect the developer particles in different directions as the particles pass through the homogenizer 10, and particles deflected by one plate 14 will mix with particles deflected in an intersecting direction by another plate 14 along the length of the shaft 12 so that the residual developer particles will be effectively and efficiently homogenized as they slide down the upper surface of the cleaner 30 and drop into the reservoir 20.

In FIG. 5 the plates 14 are shown as all having the same orientation as mentioned above, and the shaft 12 is rotatably driven from drive means (not shown) through a drive shaft 40, pulley 42 and belt 44.

FIGS. 6 and 7 illustrate an accurate, simple and inexpensive method of assembling and aligning plates 14' on a shaft 12'. The shaft 12' is shown as having a hexagonal profile, and the bore of a sleeve 16' is also hexagonal and has the same size and profile as the shaft 12'. Each plate 14' may be assembled onto the shaft 12' simply by sliding the attached sleeve 16' onto the shaft 12'. In this example, the angular spacing between the major axes of two adjacent plates 14' may be accurately provided as 60.degree., 120.degree., 180.degree., 240.degree., 300.degree. or 360.degree. as desired. Naturally, the profile of the shaft 12' may be in the form of a polygon having any number of sides to provide any desired equiangular relationship between the major axes of the plates 14'. Also, if the round shaft 12 is utilized, the plates 14 may be welded or otherwise secured thereto so that the relationships between the major axes of the various plates 14 is not equiangular, and may be random if desired.

Claims

What is claimed is:

1. In an electrophotographic device having a photoconductive member adapted to produce an electrostatic image of a document, an applicator for applying powdered developer to the photoconductive member to develop the image and a cleaner for removing residual developer from the applicator, the cleaner having an inclined flat surface down which residual developer moves after being removed from the applicator, wherein the improvement comprises a homogenizer to homogenize the residual developer as the same moves down the flat surface, said homogenizer comprising:

a shaft rotatably mounted above and in a plane parallel to the flat surface the axis of said shaft being substantially transverse to the direction of movement of the residual developer; and

a plurality of substantially elliptical plates mounted for rotation with said shaft, the minor axes of said plates perpendicularly intersecting the axis of said shaft and the major axes of said plates intersecting the axis of said shaft at an acute angle, the edges of said plates being closely adjacent to the flat surface at all rotational positions of said shaft; whereby

residual developer moving down the flat surface is deflected by said plates and thereby homogenized.

2. A homogenizer according to claim 1, in which projections of the major axes of said plates on a plane perpendicular to the axis of said shaft are equiangularly spaced about the axis of said shaft.

3. A homogenizer according to claim 1, in which said acute angle between the major axes of said plates and the axis of said shaft is equal to the arc sine of the ratio of the lengths of the minor axis of said plates to the major axis of said plates.

4. A homogenizer according to claim 1, in which the electrophotographic device has drive means, and said shaft is rotatably driven by the drive means.

5. A homogenizer according to claim 1, which is rotated by the moving residual developer.

6. A homogenizer according to claim 1, in which the electrophotographic device has a reservoir for the developer, the applicator being operative to pick up developer from the reservoir, and in which said homogenizer is arranged to recycle the residual developer into the reservoir.

7. A homogenizer according to claim 1, in which said shaft has a polygonal profile, and which further comprises sleeves to mount the plates respectively on said shaft, the bores of said sleeves having substantially the same profile as said shaft.

8. A homogenizer according to claim 1, in which projections of the major axes of said plates on a plane perpendicular to the axis of said shaft coincide.