US3665891A

US3665891A - Magnetic brush development apparatus

Info

Publication number: US3665891A
Application number: US13543A
Authority: US
Inventors: Carl R Pitasi
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1970-02-24
Filing date: 1970-02-24
Publication date: 1972-05-30
Anticipated expiration: 1989-05-30
Also published as: JPS4940300B1; DE2108722A1; GB1347138A

Abstract

An apparatus for developing a latent electrostatic image with developer material wherein development is effected by utilizing a rotating magnetic brush mechanism. The axis of rotation of the magnetic brush extends in a skewed relationship with respect to the axis of rotation of the image bearing surface. The developer material attracted to the magnetic brush is doctored to form a concave outer surface of developer on the member for effective development of the latent image without streaking. Alternatively, the magnetic member carrying developer possesses a concave-like exterior surface to transport developer into uniform stroking contact with the image bearing surface similarly to prevent streaking defects in the developed image. Similarly the magnetic field of the brush may be shaped so as to be weakest in the middle of the brush creating, automatically, a concave shaped surface of developer.

Description

United States Patent Pitasi I [54] MAGNETIC BRUSH DEVELOPMENT APPARATUS Carl R. Pitasi, Rochester, N.Y.

[72 Inventor:

[73] Assignee: Xerox Corporation, Rochester, NY.

[22] Filed: Feb. 24, 1970 211 Appl. 190.; 13,543

Hider 18/637 3,169,887 2/1965 3,207,050 9/ l 965 v 3 241,466 3/ l 966 Clark ..95/1 7 [151 3,665,891 1 51 May 30, 1972 Primary Examiner-Henry S. Jaudon Attorney-James J. Ralabate, Donald F. Daley and R. W. Mulcahy [57] ABSTRACT An apparatus for developing a latent electrostatic image with developer material wherein development is effected by utilizing a rotating magnetic brush mechanism. The axis of rotation of the magnetic brush extends in a skewed relationship with respect to the axis of rotation of the image bearing surface. The developer material attracted to the magnetic brush is doctored to form a concave outer surface of developer on the member for effective development of the latent image without streaking. Alternatively, the magnetic member carrying developer possesses a concave-like exterior surface to transport developer into uniform stroking contact with the image bearing surface similarly to prevent streaking defects in the developedimage. Similarly the magnetic field of the brush may be shaped so as to be weakest in the middle of the brush creating, automatically, a concave shaped surface of developer.

12 Claims, 6 Drawing Figures 2 Sheets-$heet 1 INVENTOR. CARL R. PITASI ika y/ ATTORNEY Patented May 30, 1972 3,665,891

2 Sheets-Sheet 2 1 MAGNETIC BRUSH DEVELOPMENT APPARATUS BACKGROUND OF THE INVENTION This invention relates in general to developing a latent electrostatic image and in particular to an improved magnetic brush development apparatus.

the photosensitive surface bearing an image to be developed.

The positioning of the magnetic brush in such a manner is found to produce enhanced development results and, in particular, reduces streaking in the developed image.

Although not intended to be so limited, for convenience of illustration the present invention is described as a develop ment apparatus for use in xerography. In the process of xerography, a xerographic plate comprising a layer of photoconductive material on a conductive backing is given a uniform electric charge on its surface and then is exposed to the subject matter to be reproduced by various projection techniques. This exposure discharges the plate in accordance with the light intensity reaching it thereby creating a latent electrostatic image on or in the plate. Development of the image is effected by developers which may comprise, in general, a mixture of suitable pigmented or dyed resin base powder herein referred to as toner, which is brought into contact with the plate by various well-known development techniques. During such development of the image the toner powder is brought into surface contact with the photoconductive coating and is held there electrostatically in a pattern corresponding to the latent electrostatic image. Thereafter, the developed xerographic image may be transferred to a support material to which it may be fixed by any suitable means, such as, heat fusmg.

An example of one of the aforementioned techniques for developing the latent image is disclosed in US. Pat. No. 3,! 76,652 to Mott et al., wherein developer material is carried on a magnetic element into contact with a latent electrostatic image bearing surface. Generally, in such a system, the developer material comprises a two component developer consisting of toner and a powdered magnetic carrier such as a ferro-magnetic material. The developer material is supported as an attracted mass on the exterior of a rotating cylinder having interiorly mounted magnetic means to carry the material into brush-like contact with the image bearing surface for development.

A magnetic brush device utilizes a two component developer including a ferro-magnetic carrier material because it is readily attracted by the magnetic field of the'brush. Also, as in other development systems utilizing a two component developer, the'toner powder and carrier particles of a magnetic brush system are selected so that a triboelectric relationship exists between-them to effect an opposite charging of toner and carrier when in contact as well as providing a mutual attraction of the two components. Therefore, as the triboelectrically attracted toner carried by the magnetic carrier particles is brought into the vicinity of the image, the electrostatic lines of force of the latent image attracts the toner for development. Alternatively, in the prior art magnetic brush development has utilized a single component developer wherein the developer comprises a ferro-magnetic material which acts both as carrier and toner.

A magnetic brush development system has proven to be an effective technique for developing latent electrostatic images. The latent image is developed by a magnetic brush in a reliable manner whereby the toner is applied to the image bearing surface in a gentle manner. Further, such a development system readily develops large dark areas and also achieves high resolution in development of an image. However, prior art magnetic brush techniques are deficient by producing streaking in the developed image to mar the quality of reproductions produced therefrom. Such streaking is caused generally by the tendency of the magnetic brush to wipe toner from already developed areas off the surface of the drum and be reattracted to the ferrite carrier forming the brush as it is stroked across the surface to be developed. In the prior art one cause of streaking in the development of image results because the direction of movement of developeron the magnetic cylinder is identical to the direction of motion of the image bearing surface. Accordingly, it is desirable to provide a magnetic brush development apparatus which prevents or minimizes the aforementioned streaking of a developed image and still produces the major advantages inherent in a magnetic brush system.

SUMMARY OF THE INVENTION It is, therefore, an object of this invention to improve the apparatus for developing a latent electrostatic image.

Another object of this invention is to develop a latent electrostatic image with an improved magnetic brush development apparatus.

A further object of this invention is to prevent streaking defects in developing latent electrostatic images.

Still another object of this invention is to transport developer on a magnetic brush element in a direction other than the path of movement of the surface to be developed.

A still further object of this invention is to apply developer material with a magnetic brush as a non-cylindrical surface to contact with the image to be developed.

These and other objects are attained in accordance with the present invention wherein there is provided amagnetic brush development apparatus which develops a latent electrostatic image without the aforementioned streaking defects as encountered when utilizing prior art magnetic development devices. The present invention achieves the elimination of streaking by orienting the magnetic element of the development device herein disclosed in a skewed relationship with respect to the image bearing surface thereby to eliminate a single point on the brush being moved along the path of movement of the image. For example, if the brush of the invention includes a rough surface of developer at any location thereon, the movement of the developer in a skewed relation across the image bearing surface overcomes the tendency of the rough portion to wipe the image off the drum during development to produce streaking.

In order to accomplish effective developing of an image when utilizing the skewed or cooked magnetic brush of the present invention, it has been found advantageous to use a non-cylindrical surface of developer being stroked by the magnetic brush into contact with the image bearing surface when developing a surface other than a flat plate. By shaping the surface of the developer on the brush in such a manner, uniform contact is achieved between the image bearing surface and developer for effective development results despite the skewed positioning of the magnetic brush. Therefore, the magnetic brush development apparatus of the present invention achieves improved development of a latent image by moving developer in a different direction than the path of movement of the image bearing surface. Such a technique of development has been found to overcome the problem of streaking normally associated with the prior art magnetic brush development methods.

Further objects of the invention, together with additional features contributing thereto and advantages accruing therefrom, will be apparent from the following description of several embodiments of the invention when read in conjunction with the accompanying drawings. conjunction BRIEF DESCRlPTlON OFTHE DRAWINGS FIG. 1 is a schematic illustration of a xerographic apparatus utilizing the development device of the present invention.

FIG. 2 is a schematic illustration of the positioning of the magnetic brush apparatus of the present invention.

FIG. 3 is an end illustration of one embodiment of the magnetic brush development apparatus of the present invention.

FIG. 4 is a front schematic illustration of the magnetic brush apparatus taken along line 4--4 of FIG. 3.

FIG. 5 is a front schematic illustration of another embodiment of the magnetic brush development apparatus of the present invention.

FIG. 6 is a schematic side illustration of the magnetic brush apparatus of the present invention taken along line 6-6 of FIG. 5.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIG. I there is shown a schematic view of a drum type automatic xerographic reproducing machine utilizing the development apparatus of the present invention. The central element of the apparatus is a drum I mounted for rotation and drivable in a conventional direction by a motor M. The drum 1 comprises an outer surface with a layer of photoconductive insulating material, such as, vitreous selenium or other suitable surface. A uniform electrostatic charge is placed on the photoconductive surface of the drum by means of a conventional corona charging device 2. The uniformly charged surface on the drum is then moved to an exposure means 3 which may be any well known device which will expose the charged surface to copy to be reproduced to thereby form a latent electrostatic image of the copy on the photoconductor drum surface in a manner well known in the art.

Following the formation of the latent electrostatic image of the copy to be reproduced, the image on the drum moves to a development device according to the present invention (to be hereinafter described in detail) to bring the charged image into contact with developer material, comprising charged toner, to develop the latent image. After development, the visible image moves to transfer means 4 and is transferred from the drum to a web 5 of the paper or other suitable sup port medium which is positioned in contact with the drum by rollers 6. A second corona charging device 7 applies a charge to the side of the web opposite the image to facilitate transfer of the toner powder in image form. The toner image on the web moves past the heating element 8 which permanently affixes the toner to the paper web to form a duplicate of the original copy. A cleaning device 9 contacts the photoreceptor surface after it moves past the transfer device to remove any residual image material on the surface prior to subsequent reproduction cycles. It should be clear that other modes of charging, exposing, transfer, and fusing may be utilized in connection with the present invention.

Referring now to FIGS. 3 and 4 there is illustrated an embodiment of the development apparatus 10 according to the present invention. The development apparatus 10 is positioned adjacent the photoconductor drum 1 to bring developer material into contact with the charged electrostatic image lying thereon. The developer material is conveyed into development contact with the drum surface by being attracted to a magnetic brush element 11 which is rotatably mounted adjacent the drum in development housing 12. The magnetic brush element 11 comprises a hollow cylinder 13 or the like which is mounted in suitable bearings 14 to be rotated in a clockwise direction as shown in FIG. 3. The cylinder 13 may comprise, for example, any suitable non-magnetic material having a stationary magnetic means 15 mounted therein (to be described in detail later). The cylinder 13 is rotated by a suitable motor 16 through a conventional motion transmitting means 17.

The development housing 12 supports a supply of developer material in a sump 18 to be utilized in development of the latent electrostatic image lying on the photosensitive surface of the drum. The developer may comprise, for example, suitable toner powder and a carrier material of magnetically attractable material, such as, magnetic ferrites or other suitable carrier particles. The carrier and toner are selected so that a triboelectric relationship exists between them whereby the toner and carrier are attracted to each other and acquire an opposite charge in contact. The developer supported within the developer housing 12 in sump I8 is attracted to the cylinder 13 through the influence of the magnetic field emanating from the magnet means 15 whereby a layer of developer adheres to surface 17 of the cylinder 13 to be brought into contact with the drum by rotation of the cylinder by the motor 16. Because of the magnetic force emanating from the magnet means 15 within the cylinder, the developer attracted to the cylinder adheres in the form of a brush so that the developer is stroked against the drum surface and toner is attracted to the latent image for development thereof. Thereafter, the unused developer is carried on the cylinder to a point where it drops off the cylinder 13 since the magnetic field in that particular area is sufficiently weak to allow the developer to fall back into the sump. Alternatively, a suitable scraper means or the like (not shown) may be utilized to remove unused developer from the cylinder 13 to effect tonerization of the carrier in the sump 18. The sump may include any suitable tonerization means such as mixing device 19 illustrated in FIG. 3 to add and mix toner with the carrier to insure optimumly toner-ized developer is attracted to the cylinder.

The shaft supporting the cylinder for rotation in the embodiment illustrated in FIGS. 3 and 4 extends at a skewed angle with respect to the axis of rotation of the drum 1 as best shown in FIG. 2. By skewing the axis of rotation of the magnetic brush, developer moves in a slightly different direction across the image bearing surface than the direction of movement of the drum. Such a deviation in the direction of movement of the brush surface with respect to the drum surface reduces the streaking effects heretofore encountered in utilizing prior art magnetic brush development devices. It is within the scope of the present invention to skew the brush in the opposite direction than as shown in FIG. 2 and any angle of skewing may be selected depending on the desired develop ment results. Further, the axis of rotation of the magnetic brush is shown to be skewed or tilted in a plane parallel to the direction of motion of the image past the magnetic brush, but the brush may be rotated around other axes tilted in other planes, if desired.

It is advantageous in magnetic brush development for the developer to contact the surface of the drum uniformly across the entire width thereof. In order to achieve uniform contact of the tilted brush of the present invention with the surface to be developed, a non-cylindrical shaped surface is applied into contact with the image bearing surface, if the image bearing surface is not a flat plate. The developer material on the brush is illustrated in FIGS. 3 and 4 in the shape of a dog bone" wherein the surface of developer on the cylinder is slightly concave in appearance. The degree of the concavity of the surface depends on the selected angle of skewing of the brush and desired development results. The shape of the developer is achieved by a doctor blade 20 mounted beneath the cylinder comprising a scraping element 21 of any suitable material which doctors off the surface of developer on the cylinder to provide the dog bone appearance of the magnetic brush. The shape of the doctor blade is best shown in FIG. 4 wherein the contact edge 21 of the blade with the developer is complimentary to the desired shape of the surface of the brush. Therefore, the doctor blade 20 both smooths off the developer carried by the magnetic brush to insure uniform contact with the drum and further creates the desired shape of the developer after it is attracted to the cylinder from the sump. The blade is illustrated as being a flat member, but it is within the scope of the present invention to utilize other suitable members, such as, fixed or moving surfaces of revolution and the like.

Still referring to FIG. 4 it is apparent that the developer attracted in the center portions of the cylinder after doctoring is less in height that at the end portions. Therefore, it is desirable to mount within the cylinder a magnetic field producing means 15 which varies in magnetic flux intensity from the center to the ends. Therefore, a series of permanent magnets 30 are mounted in a stationary manner by suitable means (not shown) within the cylinder 13 to create the desired magnetic field around the exterior thereof. The magnets 30 located near the end portions have greater magnetic properties than the magnets located in the center portion, wherein the strength of each magnet is selected to achieve the desired magnetic field for effective development. THe number of magnets utilized depends on the required magnetic field, selected development results and the like, and moreover a single magnet may be used, if desired. From the foregoing, it should be apparent that a non-cylindrical shape of developer adhering to the cylinder may be achieved by omitting the doctor blade 20 and utilizing a variable strength magnetic field in the brush whereby the varying field automatically attracts a concave surface of developer to the cylinder. In such a case, the magnets within the brush possess the weakest strength in the middle portion of the cylinder and increase in strength toward the end portions thereof.

Therefore, the skewed magnetic brush of the present invention brushes developer across the drum surface in a different direction of movement than the drum whereby the concavity of the surface produces uniform contact of developer on the drum for efficient development results. If other planes of skewing the brush than as illustrated in FIG. 2 are selected, the developer would be doctored in other shapes than those illustrated in FIG. 4 for the provision of uniform contact between brush and drum. Therefore, the embodiment of FIGS. 3 and 4 of the present invention effects magnetic brush development in an efficient manner without streaking as produced by prior art magnetic brush development techniques.

Referring nowto FIGS. 5 and 6 there is illustrated another embodiment of the development-device 10 according to the present invention. The development device 10 of the embodiment illustrated in FIGS. 5 and 6 includes a housing 12 having a brush member 40 mounted for rotation in a similar manner as described in reference to the embodiment of FIGS. 3 and 4. The axis of rotation of the brush member 40 is further skewed, similarly as illustrated in FIG. 2, to produce movement of the brush in a different direction than the direction of movement of the image lying on the photoconductor drum 1. However, the present embodiment of FIG. 5 utilizes a brush member 40 having a non-cylindrical shape to effect the uniform contacting of the brush and drum. The non-uniform shape of the cylinder thereby allows the developer to be picked up and carried into uniform stroking contact along the entire width of the drum. Magnets 41 are stationarily mounted by suitable means (not shown) within the member and comprise a series of magnets having a magnetic strength sufiicient to pick up a uniform layer of developer of constant height on the noncylindrical member.

Therefore, as the magnetic brush member rotates, developer is attracted from the sump to create a surface of developer having substantially the same shape as the brush member. After being attracted, the developer passes a conventional doctoring means to insure a smooth surface for development contact. Therefore, when developing a drum surface, the magnetic brush strokes the image bearing surface with a shape similar to that described in reference to the embodiment of FIGS. 3 and 4, wherein the developer has a concave form to approximate a dog bone in appearance. Other 7 forms of the brush member 40 may be utilized for uniform contact in the development of other shaped surfaces or when the member 40 is tilted around other axes than in FIG. 2. Further, any number of magnets having desired magnetic strength may be utilized in conjunction with the embodiment of FIGS. 5 and 6 depending on the selected intensity of the magnetic field and the amount of toner attracted to the brush. Alternatively, a single magnet may be employed in the invention, if desired.

In the above description there has been disclosed an improved apparatus for effectively developing a latent electrostatic image supported no a xerographic photoconductive surface. The surface to be developed is described for convenience of illustration as being that of a xerographic drum,

but the invention may be used to develop other well known photoconductive members in the form of plates, belts, webs or coated papers. It should be apparent that when utilizing the invention to develop a surface other than the drum herein disclosed, the particular shape of the skewed magnetic brush would comprise other forms than as illustrated which would produce the desired uniform contact of developer across the entire width of the image bearing surface. Further, the magnetic brush development method and apparatus of the present invention was described utilizing a two component developer comprising toner and a suitable magnetic carrier, but it is within the scope of the present invention to utilize a single component developer material comprising a magnetic material which acts both as carrier and toner. To further achieve a reduction of streaking of the image, the magnetic brush herein disclosed may be vibrated or oscillated in a direction transverse to the direction of the movement of the image bearing surface.

While the invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes maybe made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teaching of the invention without departing from its essential teachings.

What is claimed is: 1. Apparatus for developing latent electrostatic images comprising I I a support .member adapted for rotation about an axis skewed in relation to the direction of movement of the image to be developed,

magnetic field producing means for attracing magnetically attractable developer material to the surface of said support member and for supporting the attracted developer material thereon in a non-cylindrical surface configuration, and

means for rotating said support member about said skewed axis to produce a relative movement between said noncylindrical surface and the image to be developed to bring successive areas of said non-cylindrical surface into contact with the image to be developed.

2. Apparatus according to claim 2 further including shaping means for contacting developer material supported 'on said support member and for creating said non-cylindrical surface configuration of the developer material on said support member.

3. An apparatus for developing a relatively moving surface bearing a latent electrostatic image to be developed comprising a support member comprising a surface of revolution mounted on an axis extending in a skewed relationship to an axis extending perpendicular to the direction of movement of the image bearing surface and adapted to support developer material adjacent a relatively moving image bearing surface to be developed,

said support member including magnetic field producing means to retain developer material on said support member,

means to create a non-cylindrical surface of developer for adherence on said support member to effect development of the image bearing surface, and

means to move said support member to effect moving contact of the developer material on the image bearing surface in a different direction than the direction of movement of the image bearing surface for development thereof.

4. The apparatus of claim 3 wherein said means to create a non-cylindrical surface is a shaping means in contact with adher-ing developer.

5. The apparatus of claim 3 wherein said surface of revolution is non-cylindrical whereby a non-cylindrical surface of developer retains thereto.

6. In an apparatus for developing a surface bearing a latent electrostatic image including means to rotate a magnetic element supporting a surface of developer material for contact with the image bearing surface for development thereof, the improvement therein comprising means to create a non-cylindrical surface of revolution of developer material on said magnetic element for contact with the image bearing surface.

7. The apparatus of claim 6 wherein said means to create the non-cylindrical surface is a non-cylindrical outer surface on said magnetic element.

8. The apparatus of claim 6 wherein said means to create the non-cylindrical surface includes a shaping element to contact the developer on said magnetic element and create a noncylindrical surface of developer.

9. An apparatus for developing a surface bearing a latent electrostatic image to be developed comprising a support member having an outer support surface adapted to support developer material adjacent an image bearing surface to be developed,

said support member including a varying magnetic field producing means to create a varying magnetic field along said surface to retain developer thereon, and

means coupled to said support member to effect diagonal movement of developer material relative to the image bearing surface for development contact therewith.

10. The apparatus of claim 9 wherein said magnetic field producing means includes a plurality of magnets.

11. The apparatus of claim 10 wherein said magnets are mounted in tandem within said support member to extend across the image bearing surface.

12. The apparatus of claim 9 wherein said varying magnetic field producing means retains varying levels of developer on said support member.

$33 2 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION June 9, 1972 Patent No. 3 I 665 I 891 Dated Inventor(s) Carl R. Pitasi It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 1, column 6, line 34, the word "attracing" should read attracting.

Signed and sealed this 3rd day of October 1972. I

(SEAL) Attest: I

EDWARD M.FLETCHER,JR. I ROBERT GQITSCHALK Commissioner oi Patents Attesting Officer 22 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 665 ,891 Dated June 9, 1972 Inventor(s) Carl R. Pitasi It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 1,- column 6, line 34, the word v "attracing" should read 'attractin'g. i

Signed and sealed this 3rd day of October 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents

Claims

1. Apparatus for developing latent electrostatic images comprising a support member adapted for rotation about an axis skewed in relation to the direction of movement of the image to be developed, magnetic field producing means for attracing magnetically attractable developer material to the surface of said support member and for supporting the attracted developer material tHereon in a non-cylindrical surface configuration, and means for rotating said support member about said skewed axis to produce a relative movement between said non-cylindrical surface and the image to be developed to bring successive areas of said non-cylindrical surface into contact with the image to be developed.

2. Apparatus according to claim 2 further including shaping means for contacting developer material supported on said support member and for creating said non-cylindrical surface configuration of the developer material on said support member.

3. An apparatus for developing a relatively moving surface bearing a latent electrostatic image to be developed comprising a support member comprising a surface of revolution mounted on an axis extending in a skewed relationship to an axis extending perpendicular to the direction of movement of the image bearing surface and adapted to support developer material adjacent a relatively moving image bearing surface to be developed, said support member including magnetic field producing means to retain developer material on said support member, means to create a non-cylindrical surface of developer for adherence on said support member to effect development of the image bearing surface, and means to move said support member to effect moving contact of the developer material on the image bearing surface in a different direction than the direction of movement of the image bearing surface for development thereof.

4. The apparatus of claim 3 wherein said means to create a non-cylindrical surface is a shaping means in contact with adhering developer.

8. The apparatus of claim 6 wherein said means to create the non-cylindrical surface includes a shaping element to contact the developer on said magnetic element and create a non-cylindrical surface of developer.

9. An apparatus for developing a surface bearing a latent electrostatic image to be developed comprising a support member having an outer support surface adapted to support developer material adjacent an image bearing surface to be developed, said support member including a varying magnetic field producing means to create a varying magnetic field along said surface to retain developer thereon, and means coupled to said support member to effect diagonal movement of developer material relative to the image bearing surface for development contact therewith.