US3678897A

US3678897A - Developer mixing apparatus

Info

Publication number: US3678897A
Application number: US110489A
Authority: US
Inventors: Robert E Hewitt
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1971-01-28
Filing date: 1971-01-28
Publication date: 1972-07-25
Anticipated expiration: 1989-07-25
Also published as: BE778426A; JPS5423255B1; IT946909B; CA951113A; GB1377151A; NL7200932A; FR2124988A5; DE2204082A1

Abstract

Improved cascade apparatus for developing electrostatic images wherein a latent electrostatic image supported on a moving member is developed by cascading a flow of developer material including a magnetic carrier component and an electroscopic toner component through a development zone. A toner dispenser dispenses toner material to supplement that portion consumed during development. The dispensed toner material is received onto a chute which directs the toner material into a predetermined location in the sump of the developer housing. A bucket conveyor moves developer material upwardly in the housing and spillage from the buckets is directed along the chute to combine with the dispensed toner material and also to prevent the dispensed toner material from clinging on the chute. A magnetic field producing member is positioned on the chute adjacent the path of the bucket conveyor to control the direction of flow of the spillage and to pull excess developer material from the buckets.

Description

United States Patent Hewitt 21 Appl. No.: 110,489

[52] U.S.Cl ..ll8/637,l17/l7.5,355/l5 [51] Int. Cl. ..G03g 13/00 [58] Field of Search ..1 18/637, DIG. 24; ll7/l7.5

[56] References Cited UNITED STATES PATENTS 3,348,521 10/1967 Hawk ..118/637 3,367,307 2/l968 Lawes et a1. 18/637 3,572,289 3/1971 Maksymiak... 118/637 3,611,982 10/1971 Coriale ..1 18/4 Primary Examiner-Morris Kaplan Assistant Examiner-Leo Millstein Attorney-James .l. Ralabate, Norman E. Schrader and Melvin A. Klein [151 3,678,897 [4 1 July 25,1972

[57] ABSTRACT improved cascade apparatus for developing electrostatic images wherein a latent electrostatic image supported on a moving member is developed by cascading a flow of developer material including a magnetic carrier component and an electroscopic toner component through a development zone. A toner dispenser dispenses toner material to supplement that portion consumed during development. The dispensed toner material is received onto a chute which directs the toner material into a predetermined location in the sump of the developer housing. A bucket conveyor moves developer material upwardly in the housing and spillage from the buckets is directed along the chute to combine with the dispensed toner material and also to prevent the dispensed toner material from clinging on the chute. A magnetic field producing member is positioned on the chute adjacent the path of the bucket conveyor to control the direction of flow of the spillage and to pull excess developer material from the buckets.

4 Claims, 3 Drawing Figures Patented July 25, 1972 2 Sheets-Sheet 1 INVENTOR. ROBERT E. HEWITT W A m ATTORNEY Patented July 25, 1972 2 Sheets-Sheet 2 DEVELOPER MIXING APPARATUS This invention relates to an improved cascade development apparatus which increases the uniformity of mix of two component developer material loaded from a sump and unloaded from a bucket conveyor to an entrance chute leading to a cascade development zone for a more efficient development.

In the process of xerography as described, for example, in U.S. Pat. No. 2,297,691 to Chester F. Carlson, a xerographic plate formed of a conductive backing material upon which is placed a conductive insulating material is charged uniformly in the surface of the plate exposed to a light image of an original to be reproduced. The photoconductive coating is caused to become conductive under the influence of the light image so as to selectively dissipate the electrostatic charge found thereon thus producing an electrostatic latent image. The latent image is then developed by means of a variety of finely divided pigmented resins which have been specifically developed for this purpose. The pigmented resin material or toner is electrostatically attracted to the latent image on the photoconductive surface in proportion to the ion charge found thereon that is areas of small charge concentration become areas of low toner density whileareas of greater charge concentration become proportionately more dense, the fully developed images generally transferred to a support material, as for example, paper and the image fixed thereto to form a permanent record of the original document.

One of the most widely used methods of developing a latent electrostatic image is by means of cascade development in which a two component developer material is caused to flow down over the moving image bearing photoconductive surface to effect image development. The toner and carrier material are triboelectrically charged to opposite polarities and the particulate toner material adheres to the carrier in a charged state. As the toner laden carrier beads flow over the photoconductive surface, the toner is electrostatically stripped from the carrier and attracted to the plate surface by the relatively stronger force fields associated with the imaged areas. Cascade development has a high development latitude and is particularly noteworthy in freedom from background deposition. Further, the process is dependable and operates with high efficiency under extreme humidity conditions and is easily converted to give either positive or reverse reproduction of the original document to be copied.

There are, however, certain problems which may result with cascade development, as for example, solid areas and tonal patterns may not develop well especially if the proper mixture of carrier to toner is not maintained as toner is consumed. Also, cascade development under certain conditions, such as high electrostatic contrast, may result in carrier beads sticking to the photoconductive surface.

Heretofore efforts to develop electrostatic images by a technique different from cascade development has centered largely on magnetic brush development in which the granular carrier is selected which has ferromagnetic properties as well as having a triboelectric relationship to impart the desired electrostatic property to the toner as in the cascade development. On inserting a magnet into such a mixture of toner and magnetic granular material, the carrier particles align themselves along the lines of force of the magnet to assume a brushlike array with the toner particles electrostatically coated on the surface of the magnetic carrier to affect the desired development as described, for example, in U.S. Pat. No. 2,892,446 and U.S. Pat. No. 2,910,964. While magnetic development is suitable for machine application, there are certain disadvantages. Thus, in magnetic development, only part of the brush contacts the xerographic surface. In addition, the magnetic field restricts the motion of the carrier particles interferring with the individual toner particles rolling across the image surface. As a consequence of this, a higher concentration of toner is generally essential in magnetic development.

A recent tendency has been to use a cascade development process for development of the electrostatic images using a high density developer material including a magnetic carrier component with the electroscopic toner component and it is the purpose of the present invention to improve cascade development in this sense.

It is therefore an object of the invention to improve cascade development of electrostatic latent images.

It is another object of the invention to enable high print quality at very high development speeds.

It is still a further object of the present invention to maintain a proper mixture of two component developer material from the sump portion of a developer housing to the development zone in a manner more efficient to heretofore.

It is still a further object of the present invention to enable more efficient dispensing of toner materials to a developer mix to replenish that consumed during development.

These and other objects of the present invention are attained by positioning a chute to direct dispensed toner material and catch developer spillage from a bucket conveyor. A magnetic field in close proximity to the path of the bucket conveyor serves to pull excess developer from buckets towards the path of dispensed toner as well as control the flow of spillage. For a better understanding of the present invention as well as other objects and further features thereof reference is had to the following detailed description of the invention to be read in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic side elevation of a continuous automatic xerographic reproducing machine having a cascade development zone and incorporating development apparatus constructed in accordance with the instant invention;

FIG. 2 is an enlarged partial sectional view of cascade developing apparatus according to the present invention; and

FIG. 3 is an enlarged portion of FIG. 2 illustrating certain details of the present invention.

Referring now to the drawings, there is shown in FIG. 1 an embodiment of the subject invention in a suitable environment such as an automatic xerographic reproducing machine employing a drum shaped xerographic plate 10 comprising a photoconductive layer which is placed on a conductive backing and is moved in an uphill direction in the development zone on a shaft 12 journaled in the machine frame. The rotation causes the plate surface to sequentially pass a series of xerographic processing stations. For the purposes of the present disclosure, the several xerographic processing stations in the path of moving of the plate surface may be described functionally as follows:

A charging station A at which a uniform electrostatic charge is deposited on the photoconductive plate;

An exposure station B at which light radiation pattern of copy to be reproduced is projected onto the plate surface, dissipate the charge in the exposed areas thereof to thereby form a latent electrostatic image of the copy to be reproduced;

A developing station C at which xerographic developing material including electroscopic toner particles and a magnetic interior component is cascaded over the plate surface whereby the toner particles adhere to the latent electrostatic image to form a toner powder image in the configuration of the copy being reproduced in a manner as will be described more fully hereinafter;

A transfer station D at which the toner powder image is electrostatically transferred from the plate surface to a support material such as paper; and

A drum cleaning and discharge station E at which the plate surface is crushed to remove residual toner particles remaining thereon after image transfer and exposed to a relatively bright light source to affect substantially complete discharge of any residual electrostatic charge remaining thereon.

For a more detailed description of the processing stations which have been only briefly described above, reference is made to copending application Ser. No. 838,914 filed on July 3, 1969, now U.S. Pat. No. 3,61 1,992, and commonly assigned with the instant application.

In accordance with the present invention, the development station includes a conveyor assembly 14 for transporting developer material from a sump 16 to an elevated location. The developer material comprises a mixture of any suitable magnetic carrier particles and an electroscopic toner powder with the toner powder adhering to the carrier as a result of the triboelectric effect. Typical carrier materials comprise powdered iron including the types known commercially as alcoholized iron and carboxal iron, steel nickel, alloys of magnetic iron such as nickel-iron alloys, nickel-cobalt iron alloys, and magnetic oxides, such as iron oxide, hematite (F6 and magnetite (Fe-p and ferromagnetic ferrites.

Where the ferromagnetic material does not have the desired triboelectric relationship to the toner, the ferromagnetic material may be used as a core covered with a resinous coating having the desired triboelectric properties as described, for example, in U.S. Pat. No. 2,618,551 to Walkup and U.S. Pat. No. 2,874,063 to Greog. Typical'electroscopic toner powders are described in U.S. Pat. No. 2,618,551 to Walkup, U.S. Pat. No. 2,618,552 to Wise, and U.S. Pat. No. 2,638,416 to Walkup and Wise.

The conveyor assembly 14 includes a plurality of buckets stapled or otherwise suitably secured to endless belts 22 mounted on upper pulleys 24 and lower pulleys 26 for movement in a path of travel indicated by the arrow. The lowermost pulleys are located so that the buckets can pass through the sump 16 of development material beneath the cascade development zone 28. The sump is continually reloaded with developer falling from the cascade development zone and captured and directed by a pickoff baffle 30. Above the development zone is an input chute 32 receiving the conveyed developer material as it is unloaded or dumped from the buckets and gravity dropped for cascading through the development zone. Due to the fact that toner particles are lost from the development system through the development of the electrostatic images on the xerographic drum, a toner dispenser 36 is employed to replenish that consumed from the system.

In accordance with the invention a chute member 40 is positioned to receive toner material dispensed and direct the flow of the material towards one side of sump 16 adjacent to the path of bucket conveyor 14. Because the toner material is a very fine powder there is a tendency for clumps to form on the chute 40. It will be noted that chute 40 is positioned to receive developer spillage from buckets 20. A magnet member 45 is positioned in close proximity to the chute member with pole faces N and S arranged at right angles to the surface of the chute member. By this arrangement the chute member which is made out of magnetic material serves as an extended pole face of the magnet member. Due to the magnetic field established from magnet member 45 and chute member 40 developer material spilled is directed across the chute member 40 where it combines with toner material being dispensed. Additionally, excess developer material from the buckets is pulled across chute member 40 by virtue of the magnetic field as best shown in FIG. 3. In this manner, toner material being dispensed which might otherwise clump together is continuously mixed with developer material and directed into a sump location .easily accessible to the conveyor moving fresh developer to the development zone. It should be noted that since chute member 40 is made of a magnetic material, the magnetic lines of force will be shielded from the top surface of the chute member to prevent sticking of developer material along the upper surface of the chute members.

Heretofore it has been necessary to stir or otherwise mix two component developer to be used for cascade development. By virtue .of the present invention, newly added toner material is continuously mixed with remaining developer such that a proper mixture results. Thus, there is a higher quality development of images.

While the present invention as to its objects and advantages have been described as carried out in the specific embodiment thereof, it is not intended to be so limited but is intended to be protected broadly within the scope of the appended claims.

What is claimed is:

1. An apparatus dispensing toner to a cascade development station wherein a latent electrostatic image is developed by cascade flow of developer material including a magnetic component and an electroscopic toner component moving through a development zone, the improvement comprising a housing including a sump portion containing developer material including a magnetic component and an electroscopic component,

conveyor means including buckets disposed in the housing for moving developer material from the sump portion to an upper portion of the housing for downward cascade flow onto a latent electrostatic image moving in a development zone,

toner dispenser means positioned in said housing for dispensing toner material at predetermined intervals, chute means disposed below said toner dispenser means for directing the flow of the toner material towards a predetermined location of said sump portion,

said chute means extending towards said bucket path to receive back spillage of developer material being dropped from said upwardly moving buckets and having a magnetic field producing means associated therewith to pull excess developer material from said buckets and direct the excess developer material and spilled developer material along a predetermined path intersecting with the path of dispensed toner material whereby toner material being dispensed is continuously supplied into said sump portion for uniform mixing with developer material therein.

2. The apparatus of claim 1 wherein said chute means comprises a magnetic member.

3. Apparatus according to claim 2 wherein the magnetic field producing means is a magnet member positioned with its poll faces extending at right angles to the magnetic member.

4. Apparatus according to claim 3 wherein said magnet member is positioned adjacent to and below said magnetic member.

Claims

1. An apparatus dispensing toner to a cascade development station wherein a latent electrostatic image is developed by cascade flow of developer material including a magnetic component and an electroscopic toner component moving through a development zone, the improvement comprising a housing including a sump portion containing developer material including a magnetic component and an electroscopic component, conveyor means including buckets disposed in the housing for moving developer material from the sump portion to an upper portion of the housing for downward cascade flow onto a latent electrostatic image moving in a development zone, toner dispenser means positioned in said housing for dispensing toner material at predetermined intervals, chute means disposed below said toner dispenser means for directing the flow of the toner material towards a predetermined location of said sump portion, said chute means extending towards said bucket path to receive back spillage of developer material being dropped from said upwardly moving buckets and having a magnetic field producing means associated therewith to pull excess developer material from said buckets and direct the excess developer material and spilled developer material along a predetermined path intersecting with the path of dispensed toner material whereby toner material being dispensed is continuously supplied into said sump portion for uniform mixing with developer material therein.