US3901187A

US3901187A - Developer retoning apparatus

Info

Publication number: US3901187A
Application number: US397020A
Authority: US
Inventors: Frederick W Hudson
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1971-10-14
Filing date: 1973-09-21
Publication date: 1975-08-26
Anticipated expiration: 1992-08-26

Abstract

Xerographic apparatus for the cascade development of latent electrostatic images with a two-component ferromagnetic developer. The apparatus includes a rotating magnetic transport belt having a lower portion positioned across the photoconductive surface adjacent the lower end of the development zone to magnetically attract the cascaded developer away from the photoconductive surface. Positioned downstream of the transport belt, there is provided a scraper assembly for removing a portion of the detoned developer mass from the belt and directing such removed portion into contact with a stream of toner with the combined mass passing downwardly to a sump zone to effect intimate admixing thereof. A scraper blade is disposed at the upper portion of the transport belt above the upper end of the development zone to remove developer from the transport belt and to guide the developer onto the photoconductive surface at the upper end of the development zone for cascade developing latent electrostatic images formed on the photoconductive surface.

Description

United States Patent 11 1 Hudson 1 DEVELOPER RETONING APPARATUS Frederick W. Hudson, West Henrietta, NY.

[75] Inventor:

[73] Assignee: Xerox Corporation, Stamford,

Conn.

22 Filed: Sept. 21, 1973 21 App1.No.:397,020

Related US. Application Data [63] Continuation of Scr. No. 189,313, Oct. 14, 1971,

Primary ExaminerRonald Feldbaum 57 ABSTRACT Xerographic apparatus'for the cascade development of latent electrostatic images with a two-component ferromagnetic developer. The apparatus includes a rotating magnetic transport belt having a lower portion positioned across the photoconductive surface adjacent the lower end of the development zone to magnetically att'ractthe cascaded developer away from the photoconductive surface. Positioned downstream of the transport belt, there is provided a scraper assembly for removing a portion of the detoned developer mass from the belt and directing such removed portion into contact with a stream of toner with the combined mass passing downwardly to a sump zone to effect intimate admixing thereof. A scraper blade is disposed at the upper portion of the transport belt above the upper end of the development zone to remove developer from the transport belt and to guide the developer onto the photoconductive surface at the upper end of the development zone for cascade developing latent electrostatic images formed on the photoconductive surface.

4 Claims, 8 Drawing Figures -Emwmm 3,901,187

SHEET 1 BF INVENTOR Frederick W. Hudson BY ATTORNEYS INVENTOR.

Frederick W. Hudson BY DEVELOPER RETONING APPARATUS This application is a continuation of application Scr. No. 189.313, lilcd Oct. 14., 1971, now abandoned.

BACKGROUND OF THE INVENTION This invention relates in general to xerographic dcvclopment, and in particular, relates to apparatus for cascade developing Iatcnt electrostatic images with a ferromagnetic two-component developer mixture.

In the practice of xerography as described in US. Pat. No. 2,297,691 to Chester F. Carlson, a xerographic surface comprising a layer of photoconductive insulation material affixed to a conductive backing is used to support electrostatic images. In the usual method of carrying out the process, the xerographic plate is electrostatically charged uniformly over its surface and then exposed to a light pattern of the image being reproduced to thereby discharge the charge in the areas where light strikes the layer. The undischarged areas of the layer thus form an electrostatic charge pattern in conformity with the configuration of the original light pattern.

The latent electrostatic image may then be developed by contacting it with a finely divided electrostatically attractable material, such as a resinous powder. The powder is held in the image areas by the electrostatic fields on the layer. Where the field is greatest, the greatest amount of material is deposited; and where the field is least, little or no material is deposited. Thus, a powder image is produced in conformity with the light image of the copy being reproduced. The powder is subsequently transferred to a sheet of paper or other surface and suitably affixed to thereby form a permanent print.

The electrostatically attractable developing material commonly used in xerography consists of a pigmented resinous powder hereinafter referred to as a toner, and a carrier of larger granular beads formed with glass, sand or steel cores coated with a material removed in the triboelectric series from the toner so that a triboelectric charge is generated between the toner powder and the granular carrier. The carrier also provides mechanical control so that the toner can be readily handled and brought into contact with the exposed xerographic surface. The toner is then attracted to the electrostatic image from the carrier to produce a visible powder image on the xerographic surface.

The most common technique employed today for bringing the developer into contact with a latent electrostatic image-bearing surface for its development is the cascade system. In the cascade system, the developer is cascaded or poured across a segment of a rotating xerographic drum. During the time of contact between the developer and the xerographic surface, the toner-coated carrier moves across the surface while toner particles are electrostatically pulled away from the carrier by the charged areas of the surface and are selectively deposited thereon to form a visible powder image. The partially detoned carrier granules then move beyond the xerographic surface. As toner images are formed, additional toner powder is generally supplied to the developer mixture in proportion to the amount of toner deposited on the xerographic surface to maintain the proper amount of toner in the developer mixture.

Typical of the cascade development systems employed today is that disclosed in US. Pat. No. 3,062,109 to Mayo et al. According to that disclosure, the developer mixture is moved from a sump region to an area elevated with respect to the photoconductive surface by means of conveyor buckets. The developer is then dropped onto a portion of the xerographic surface for its development. After reaching an area on the xcrographic surface which is below the horizontal center line of the xerographic drum, a fixed mechanical pick-off baffle located slightly removed from the drum directs the developer back into the sump region for the recirculation by the conveyor system.

In US. Pat. No. 3,415,224, there is disclosed a eascade development system employing two-component ferromagnetic developer wherein the apparatus includes a rotating magnetic transport belt having a lower portion positioned across the photoconductive surface adjacent the lower end of the development zone to magnetically attract the cascade developer away from the photoconductive surface. The upper portion of the transport belt is positioned above the upper end of the development zone. The apparatus includes a scraper blade to remove developer from the transport belt and to guide it onto the photoconductive surface at the upper end of the development zone for the cascade development of latent electrostatic images formed on the photoconductive surface. Ferromagnetic developers have been known in the art per se and have been described, for example, in US. Pat. No. 2,618,551 to Walkup and US. Pat. No. 2,874,063 to Grieg.

During use of a compact developing system, the developer mass becomes deplete with toner and it is necessary to add toner to maintain a proper ratio of toner to carrier beads in the developer mass. While the toner was added in proportion to the amount used, the toner was not uniformly admixed in the developer mass resulting in a reproduction of varied intensity.

OBJECTS OF THE INVENTION It is, therefore, an object of the present invention to develop latent electrostatic images with twocomponent ferromagnetic developer.

Another object-of the invention is to provide an apparatus and method for retoning a developer mass as the mass becomes detoned during use.

Still another object of the present invention is to provide an apparatus and method for retoning a developer mass as the mass becomes detoned during use whereby the added toner is more uniformly admixed with the detoned developer mass.

BRIEF DESCRIPTION OF THE INVENTION These and other objects of the invention are obtained in a compact development system employing twocomponent ferromagnetic developer wherein the apparatus includes a rotating magnetic transport belt having a lower portion positioned across the photoconductive surface adjacent the lower end of the development zone to magnetically attract the cascade developer away from the photoconductive surface with the upper portion of the transport belt being positioned above the upper end of the development zone. A scraper assembly is provided to remove a portion of developer mass from the transport belt and to direct such portion into a stream of toner whereby the developer mass and added toner become uniformly admixed during downward passage to the sump region. The developer rnass remaining on the belt after passing the scraper assembly may be redistributed thereon by a leveling blade prior to passage to a section of the apparatus having a scraper blade for removal of the redistributed developer mass from the transport belt whereby the developer mass is guided onto the photoconductive surface at the upper end of the development zone.

A better understanding of the present invention as well as other objects and further features thereof will be had by reference to the following detailed description of the invention when taken in conjunction with the accompanying drawings wherein:

DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic sectional view illustrating a xerographic machine adapted for continuous and automatic use employing a development system of the instant invention;

FIG. 2 is an isometric view of one embodiment of a scraper assembly of the present invention;

FIG. 3 is a top elevational view of the scraper blade assembly of FIG. 2 disposed within the developer mass;

FIG. 4 is a side elevational view of the scraper blade of FIG. 2 including a leveling blade mounted thereon;

FIG. 5 is a partial isometric view of another embodiment of a scraper assembly of the present invention;

FIG. 6 is an elevational side-sectional view of still another embodiment of a scraper assembly of the present invention disposed within a layer of developer mass;

FIG. 7 is a bottom sectional view of the scraper assembly of FIG. 6 taken along the lines 77 of FIG. 6; and

FIG. 8 is a rear view of the scraper assembly of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 1, there is illustrated a xerographic machine employing a developer conveyor assembly constructed in accordance with the present invention. The elements of this machine, which are constructed for continuous and automatic operation, are all conventional in the xerographic arts except for the novel apparatus and method for retoning a lean developer mass forming the basis of the instant application. For the purpose of the present disclosure the several xerographic processing stations in the path of movement of the xerographic surface for each machine may be briefly described as follows:

A charging station A, at which a uniform electrostatic charge is deposited on the photoconductive layer of the xerographic drum;

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

A developing station C, at which a xerographic development material, including toner particles having an electrostatic charge opposite to that of the electrostatic latent image, are cascaded across the drum surface, whereby the toner particles adhere to the electrostatic latent image to form a xerographic powdered image in the configuration of the copy being reproduced;

A transfer station D, at which the xerographic pow der image is electrostatically transferred from the drum surface to a transfer material or a support surface; and

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

The latent electrostatic images to be developed are formed on a xerographic surface 10 formed in the shape of a drum or other cylinder. The drum is adapted to be rotated about its axis by a main drum drive shaft 12 by any conventional power source (not shown). The movement of the drum permits its surface to be moved past the various processing stations including the development zone.

The developing instrumentalities include a conveyor assembly, generally indicated as 14, confined with a housing 16 adjacent one of the upper quadrants of the xerographic drum. The conveyor assembly 14 includes an endless rotatable belt 18 trained around

rollers

20, 22 and 24, for rotation in the direction of the arrow as shown with at least one of the rollers connected to a suitable source of power (not shown) to drive the belt 18.

Adjacent an inner surface of the belt 18 is a magnetic plate 25 to assist in creating a magnetic field adjacent the flat portion of the belt remote from the xerographic drum. This plate assists in holding the magnetic developer adjacent the belt in this area against the action of gravity to permit the belt to raise the developer mass to an elevated position. Positioned adjacent the roller 24, there is provided a developer scraper assembly, generally indicated as 26, to remove a portion of the devel oper mass from the belt 18, as more fully hereinafter described. Adjacent the roller 20 of the conveyor assembly 14, there is provided a scraper blade 28 which functions to scrape developer from the belt 18 and to guide the developer into the upper portion of the cascade development zone 30.

Referring to FIGS. 2, 3 and 4, there is illustrated one embodiment of a developer scraper assembly 26 of the present invention wherein the assembly 26 is comprised of a plurality of alternating long and short square-shaped

conduits

32 and 34, respectively. In FIG. 3, the scraper assembly 26 of FIG. 2 is illustrated as being positioned within the conveyor assembly 14 and disposed to intercept the developer mass (greatly exaggerated) 36 magnetically entrained on the belt 18. That portion of the detoned developer mass entrained on the belt 18 having a thickness greater than the dis tance between the belt 18 and the upper edge portions of the

conduits

32 and 34 is scraped from the mass and is forced through the conduits for discharge from the other end thereof. The detoned developer mass leaving the

conduits

32 and 34 is contacted with toner being added from a dispenser, generally indicated as 38 (FIG. 1), such as disclosed in my US. Pat. No. 3,324,291, with the combined mass cascading downwardly along the inner side wall 40 of the housing 16 to the sump zone 42 in the lower portion of the housing 16. During such downward passage the added toner and the toner depleted developer mass intimately admix to form a more uniform admixture entering the development stream.

In FIG. 4, there is illustrated a generally L-shaped leveling blade 44 suitably affixed, such as by welding, to the top of the assembly 26 to essentially level the developer mass retained on the belt 18 after passage by the

conduits

32 and 34. It will be understood that any configuration of the scraper assembly 26 may be used provided that the configuration thereof removes only a portion of the developer mass, i.e., a device extending into the developer mass magnetically retained on the belt 18 to remove a portion of such developer mass.

FIG. 5 illustrates another embodiment of a scraper assembly 26 of the present invention wherein the assembly 26 is comprised of plurality of alternating long and

short tubes

44 and 46, respectively. Use of the scraper assembly of FIG. 5 in a xerographic apparatus is essentially the same as that described with reference to the embodiment of FIGS. 2, 3 and 4.

In FIGS. 6, 7 and 8, there is illustrated a further embodiment of a developer scraper assembly 26 the present invention wherein the assembly 26 is comprised of an elongated tubular member formed by top wall 48 side walls 50 and bottom wall 52 and includes a leveling blade 44, suitably affixed to the top wall 48, such as by welding. The top wall 48 and bottom wall 52 diverge outwardly from that portion of the assembly 26 which is disposed in contact with the developer mass 36 magnetically retained on the belt 18. The top wall 48 is provided with a serrated section, generally indicated as 54, as seen in FIG. 7, which serrated section 54 contacts the developer mass on the belt 18 to remove a portion of the mass and to cause such removed portion to fall to the bottom wall 52 from which the mass is directed into a toner stream (not shown) as discussed with reference to FIG. 1.

In operation, a two-component ferromagnetic developer is cascaded across the xerographic surface 10 through the development zone and enters the magnetic field of the lower roller 22. When this occurs, the developer will be entrained by the field into contact with the rotating belt 18. Since the system relies on the magnetic properties between the developer mass and the conveyor assembly 14 to remove it from the xerographic surface, it is not necessary that the lower portion of the cascade development zone be located adjacent the horizontal center line of the xerographic drum. Once the cascaded developer has been entrained on the magnetic field adjacent the belt 18, the movement of the rollers and belt continuously moves the developer mass about the lower roller 22 and up the segment of the belt adjacent the plate 25 into contact with the developer scraper assembly 26 where a portion of the developer mass is removed and admixed with toner being added from the dispenser 38. The removed portion of the developer mass and toner then cascades downwardly to the sump zone 42 whereby intimate mixing is achieved therebetween. The uneven developer mass retained on the belt 18 after passage by the scraper assembly 26 is levelled, such as by the leveling blade of FIG. 4 and is passed around the upper roller 24. During this time, the developer is transferred from the magnetic field of the plate 25 into the field of the upper roller 24 in a continuous fashion whereby no developer is lost from the belt 18 other than that removed by the assembly 26.

As the stream of developer mass on the belt 18 is moved to the nine Oclock position of roller 20, it is contacted by a scraper blade 28 which functions to scrape the developer mass from the belt 18. The blade 28 after scrapping the developer mass from the belt 18, guides it along a path into the development zone 30 adjacent the upper end thereof. At this point, the developer mass directly falls across the rotating xerographic surface until it is again entrained by the magnetic fields adjacent the lower roller 22. When moved from the xerographic surface 10 into entrainment with the belt 18, the magnetic property of the developer carrier is employed to move the developer to the belt, with the toner particles attached to the carrier by the triboelectric attraction therebetween. To insure total development, the plate 25, conveyor belt 18, and

rollers

20, 22 and 24 extend across the development Zone a length at least equal to the length of the photoconductive drum.

While the instant invention as to its objects and advantages has been described herein as carried in specific embodiments thereof, it is not desired to be limited thereby; but it is intended to cover the invention broadly within the scope of the appended claims.

What is claimed is:

1. A development system for developing latent electrostatic images carried by a photoconductively coated surface, said system comprising the combination of a sump for storing a supply of developer including ferromagnetic carrier particles having toner particles triboelectrically attracted thereto;

an endless member rotatable in a predetermined direction through said sump and past said surface for presenting developer to said surface;

means for magnetically entraining developer on said endless member;

scraper means located between said sump and said surface, said scraper means having at least two transversely offset scraping portions extending toward said endless member for scraping developer from respective transverse sections of said endless member, one of said scraping portions being closer to said endless member than the other, whereby one of said sections of said endless member presents a thicker layer of developer to said surface than the other; and

means between said scraper means and said sump for returning developer scraped from said endless member to said sump, the last mentioned means including means for adding toner to the developer being returned to said sump.

2. The development system of claim 1 wherein said scraper means is comprised of a plurality of alternating long and short tubular members.

3. The development system of claim 2 wherein said tubular members are right circular cylinders.

4. The development system of claim 1 wherein said scraper means is an elongated tubular member having top wall formed with a serrated contact surface.

Claims

1. A development system for developing latent electrostatic images carried by a photoconductively coated surface, said system comprising the combination of a sump for storing a supply of developer including ferromagnetic carrier particles having toner particles triboelectrically attracted thereto; an endless member rotatable in a predetermined direction through said sump and past said surface for presenting developer to said surface; means for magnetically entraining developer on said endless member; scraper means located beTween said sump and said surface, said scraper means having at least two transversely offset scraping portions extending toward said endless member for scraping developer from respective transverse sections of said endless member, one of said scraping portions being closer to said endless member than the other, whereby one of said sections of said endless member presents a thicker layer of developer to said surface than the other; and means between said scraper means and said sump for returning developer scraped from said endless member to said sump, the last mentioned means including means for adding toner to the developer being returned to said sump.