US3667427A

US3667427A - Improved cascade apparatus

Info

Publication number: US3667427A
Application number: US110488A
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: 1972-06-06
Anticipated expiration: 1989-06-06
Also published as: JPS5146609B1; DE2204081B2; GB1377152A; DE2204081C3; CA951112A; DE2204081A1

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 component and an electroscopic component through a development zone. A chute receives a sufficient quantity of the developer material from a conveyor which moves the developer material in buckets from a sump and unloads a developer material at the inlet side of the chute. A magnetic member is positioned at the inlet side of the chute in close proximity to the path of the conveyor to affect the buildup of the magnetic developer material in the path of the conveyor buckets such that a sufficient quantity of the developer material is directed along the chute into the development zone instead of a certain portion being returneed into the sump as the buckets are inverted by their movement to dump the conveyed developer at the inlet of the chute leading into the development zone.

Description

United States Patent Hewitt 211 Appl. No.: 110,488

[52] US. Cl ..ll8/637, ll7/17.5, 118/636 [51] Int. Cl. ..G03g 13/00 [58] Field of Search ..1 18/637, 636, DIG. 24;

[56] i References Cited UNITED STATES PATENTS 3,4l5,224 12/1968 Hudson ..1 18/637 3,105,770 10/1963 Lehmann et a1. ....1 18/637 3,303,817 2/1967 Cranch et a1. ....l18/637 3,117,891 1/1964 Lehmann ..-.1l8/637 Primary Examiner-Mervin Stein Assistant Examiner-Leo Millstein Attorney-James J. Ralabate, Norman E. Schrader and Melvin A. Klein 1 June6, 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 component and an electroscopic component through a development zone. A chute receives a sufficient quantity of the developer material from a conveyor which moves the developer material in buckets from a sump and unloads a developer material at the inlet side of the chute. A magnetic member is positioned at the inlet side of the chute in close proximity to the path of the conveyor to affect the buildup of the magnetic developer material in the path of the conveyor buckets such that a sufficient quantity of the developer material is directed along the chute into the development zone instead of a certain portion being returneed into the sump as the buckets are inverted by their movement to dump the conveyed developer at the inlet of the chute leading into the development zone.

3 Claims, 3 Drawing Figures PATENTUJUH 6 m2 SHEET 1 OF 2 INVENTOR. ROBERT E. HEWITT it A Q ATTORNEY 1' CASCADE APPARATUS This invention relates to an improved cascade development apparatus which increases the flow of developer material 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 place 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 while areas 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 US. Pat. No. 2,892,446 and US. 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 another object of the invention to present developer material in a relatively high flow rate of a development zone.

It is still a further object of the present invention to transport 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 direct substantially all the developer material conveyed by a bucket conveyor assembly to a cascade development zone with a minimum of spillage.

These and other objects of the present invention are attained by means of establishing a magnetic field in close proximity to the path of a bucket conveyor in the area of the development zone such that developer material unloaded from the buckets is substantially directed along an input chute to the cascade development rather than having spillage back into the sump of the developer housing.

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 without the present invention; and

FIG. 3 is an enlarged partial sectional view of cascade developing apparatus illustrating the features 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 4 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 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 particles 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-colbalt iron alloys, and magnetic oxides, such as iron oxide, hematite R and magnetite (Fe O 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 move ment in a path of travel indicated by the arrow, The lowermost pulleys are located so that the buckets can pass through a sump 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 supplement that toner consumed from the system.

What would normally result in the case of a cascade development system in the absence of the instant invention is illustrated in FIG. 2. As shown in this Figure, the developer material carried by the buckets upwardly at a slight angle with respect to the vertical are then moved around the upper reaches of the upper pulleys 24 causing the buckets sequentially to tip and then dump the developer material toward the input chute 32. As a consequence of this, some of the developer material is caused to fall back into the sump through a gap 35 thereby detracting from the flow of developer material presented to the development zone.

In order to alleviate this situation and improve cascade development of the electrostatic latent images by presenting sufiicient developer material in the development zone, a magnetic field is established across the gap 35 through which the buckets 20 of the conveyor are passed such that developer spillage from the buckets 20 as they are tipped is pulled into the magnetic field to form a bridge 40 across the gap. The magnetic field is effected by positioning a magnet member 50 on the lower surface of the inlet side of chute 32 adjacent to the gap 35. In this manner, substantially all of the developer material unloaded from the buckets is directed onto the chute and is prevented from falling into the sump area thereby increasing the flow of the developer material being conveyed by the bucket conveyor to the development zone. If, in fact, contact is made by the edge of the buckets with bridge 40 formed with the developer material, the bridge will be peeled away sufi'iciently for the desired clearance but will quickly reform as additional developer material is unloaded from succeeding buckets.

While the present invention as to its ob ects 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. Apparatus for use in a cascade developing station wherein a latent electrostatic image supported on a moving member is developed by a flow of developer material including a magnetic component and an electroscopic 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 for developing electrostatic images, chute means disposed in the housing for receiving a predetermined quantity of the developer material and directing the flow of the developer material onto a latent electrostatic image moving through a development zone,

conveyor means including buckets for loading developer material from the sump portion and unloading the developer material onto the chute means, and

magnetic field producing means positioned on the inlet side of said chute means and coextensive therewith in close proximity to the path of said conveyor means to effect a buildup of the developer material therebetween whereby any gap between the chute means and conveyor means is minimized and sufficient developer material is directed along said chute means towards the development zone.

2. The apparatus of claim 1 wherein said magnetic field producing means comprises a magnet member with pole faces oriented at right angles to the surface ofthe chute means.

3. Apparatus according to claim 2 wherein the magnitude of the magnetic field producing means is sufficient to effect rapid accumulation of the developer material on the chute means in the path of the conveyor means.

Claims

2. The apparatus of claim 1 wherein said magnetic field producing means comprises a magnet member with pole faces oriented at right angles to the surface of the chute means.
3. Apparatus according to claim 2 wherein the magnitude of the magnetic field producing means is sufficient to effect rapid accumulation of the developer material on the chute means in the path of the conveyor means.