US3640248A

US3640248A - Electrostatic magnetic developing apparatus

Info

Publication number: US3640248A
Application number: US830285A
Authority: US
Inventors: William B Nielander
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1969-06-04
Filing date: 1969-06-04
Publication date: 1972-02-08
Anticipated expiration: 1989-02-08
Also published as: CA929337A; ZA703774B

Abstract

An arrangement of spaced magnetic brushes for developing latent electrostatic images wherein the magnetic fields associated with the brushes overlap so that magnetizable carrier particles are carried from one brush to the other across the space therebetween thereby presenting a continuous magnetic blanket of developing material during development.

Description

United States Patent Nielander Feb. 8, 1972 [54] ELECTROSTATIC MAGNETIC DEVELOPING APPARATUS 21 Appl. No,: 830,285

[52] US. Cl ..l18/637 [51] Int. Cl ..B05b 5/00 [58] Field of Search ..118/637,623,602,636, 603; 117/17.5, 37 L X; 198/41; 209/216, 219

[56] References Cited UNITED STATES PATENTS 3,543,720 12/1970 Drexler et al ..1 18/637 2,745,549 5/1956 Syodig 209/219 3,113,042 12/1963 Hall 118/637 3,133,834 5/1964 Sowiak ..1 18/637 3,457,900 7/1969 Drexler ..117/l7.5 X 3,472,205 l0/l965 Tsuchiya et al ..1l7/17.5 X

WWW/W 1 /z 57 y/ 1 FOREIGN PATENTS OR APPLICATIONS 17,228 8/1966 Japan ..1 18/637 OTHER PUBLICATIONS TBM Technical Disclosure Bulletin. Cross et all. 37 38 Magnetic Brush Developer". Vol. 9, No. 9 (Feb. 1967) pp.

1090.1091-C0pyin 346/74 ESX Primary Examiner-Morris Kaplan AttorneyNorman E. Schrader, James J. Ralabate and Bernard A Chiama [5 7] ABSTRACT An arrangement of spaced magnetic brushes for developing latent electrostatic images wherein the magnetic fields as- 'sociated with the brushes overlap so that magnetizable carrier particles are carried from one brush to the other across the space therebetween thereby presenting a continuous magnetic blanket of developing material during development.

7 Claims, 3 Drawing Figures PATENTEU FEE 8 i972 SHEET 1 BF 3 INVENTOR WILLIAM B. NIELANDER KM J QA .4 T TORNEY ELECTROSTATIC MAGNETIC DEVELOPING APPARATUS This invention relates to a developing apparatus of the type employing magnetic fields for forming brush bristles that are carried into contact with a latent electrostatic image to be developed.

Generally, for magnetic bnrsh development, there is employed a single magnetic brush arranged in close spaced relationship relative to a surface carrying a latent electrostatic image. Since the speed of development, especially for solid area images is quite limited with the use of a single brush, there have been attempts to utilize two magneticbrushes, each having a mechanism for introducing developing material individually. For still higher speeds, and better solid area coverage, the use of two brushes are not adequate. Utilizing more than two brushes, while being effective for high-speed developing, involves the need for relatively large spaces to contain development equipment and complex tonerdispensing equipment.

Therefore, it is a principal object of the present invention to arrange magnetic brushes so that a maximum development zone is provided for any particular amount of developing to be acquired. I

Another object of the invention isto conserve machine space bymini mizing or eliminating the need for extra developing material supplies and accessories for multiple magnetic brush units.

Still another object of the invention is to arrange multiple magnetic brushes so as to allow more rapid activation and deactivation of the unit during its programming sequence.

The foregoing objects are attained by an arrangement which includes at least two magnetic brushes spaced apart to such an extent that magnetic bristles are adapted to be carried from one brush to the succeeding brush, thereby supplying this brush with material. The resultant flow of development material spans the top portions of the two brushes and the space therebetween with the development material being in contact with an image to be developed throughout this travel. While in this space and during movement from one brush to another, the development material is in the state of agitation and in good developing condition. More uniform mixture of the ingredients of the material is also available before being applied to the second brush.

For a better understanding of the 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'in which:

FIG. 1 is a schematic view of a reproduction machine show ing various electrostatic processing components;

FIG. 2 is an enlarged cross-sectional view of one of the developing units taken along a line parallel to the path of movement of a photoconductor element; and

FIG. 3 is a cross-sectional view of the developing unit taken along a line normal to the path of movement of the photoconductor.

For a general understanding of the illustrated copier/reproducfion machine, in which the invention may be incorporated, reference is had to FIG. 1 in which the various components for the machine are schematically illustrated. As in all electrostatic systems as well as'a xerographic machine of the type illustrated, a light image of a document to be reproduced is projected onto the sensitized surface of a xerographic plate to form an electrostatic latent image thereon. Thereafter, the latent image is developed to fonn a xerog aphic powder image, corresponding to the latent image on the plate surface. The powder image is then electrostatically transferred to a support surface to which it may be fixed by a fusing device whereby the powder image is caused permanently to adhere to the support surface.

In the illustrated machine. an original D to be copied is placed upon a transparent support platen fixedly arranged relative to an illumination lamp assembly positioned at the upper end of the machine as viewed in FIG. 1. While upon the platen, a programming system for the machine introduces a lamp control circuit to cause successive energization of the lampsiirithe lamp assembly 10 for impinging light rays upon the original thereby producing image rays which when acted upon by separation filters correspond to the color informational areas on the original. The image rays are projected by means of an optical lens system 11 for exposing the photosensitive surface of a xerographic plate at the exposure station A, the plate being in the form of a flexible photoconductive belt 12 arranged on a belt assembly generally indicated by the reference numeral 13.

The .photoconductive belt assembly 13 may be mounted upon the frame of the machine and is adapted to drive the selenium belt 12 at a constant rate in the direction of the arrow as shown in FIG. 1. During this movement of the belt,

the light-imaging rays of an original are successively flashed.

The flash exposure of the belt surface to the light image discharges the photoconductive layer in the areas struck by' light, whereby there remains on the belt an electrostatic latent image for each exposure, each being in image configuration corresponding to the light image projected from the original D on the supporting platen through the corresponding separation filter. As the belt surface continues its movement, the latent electrostatic images pass through a developing station B at which there is positioned a developer assembly generally indicated by the reference numeral 15 and where the belt is maintained in a flat condition. The developer assembly 15 comprises a plurality of developing devices 16, l7, l8 and 19 each of which contains a different color-developing material to provide individual development of the electrostatic images.

The successively developed electrostatic images are transported by the belt to a transfer station C whereat a sheet of copy paper is moved at a speed in synchronism with the moving belt in order to accomplish transfer of the developed images. There is provided at this station a sheet transport mechanismin the form of a transfer drum 20 adapted to support a sheet of paper and to carry the same into image transfer relationship with the belt 12 once for each image transfer operation. A sheet of paper S from a paper-handling mechanism, generally indicated by the reference numeral 21, is transported into position upon the drum 20 where it is supported during the image transfer function. The transfer of the developed image from the selenium belt surface to sheet material is effected by means of an electrical bias of the oppositepolarity as the triboelectric charge on the developing particles utilized in image development being applied to the transfer drum 20 at the point of contact between the sheet and selenium belt as the sheet passes the transfer station C.

After the sheet is stripped from the transfer drum 20, it is conveyed by conveyor 22 into a fuser assembly generally indicatedby the reference numeral 23 wherein the developed and transferred powder image on the sheet material is permanently affixed thereto. After fusing, the finished copy is discharged from the apparatus at a suitable point for collection externally of the apparatus.

It is believed that the foregoing description is sufficient for the purposes of this application to show the general operation of an electrostatic copier constructed in accordance with the present invention.

As shown in FIGS. 2 and 3, the unit 17 comprises a boxlike structure 35 having a rectangular cross section and a length extending'beyond the width of the belt 12. Within the boxlike structure 35, there is suitably mounted a developer container formed with a thin walled developer housing 36 closed at its ends, end walls 37 and 38. The housing 36 contains developing material comprising carrier beads made from magnetizable material and color toner particles which adhere electrostatically in great numbers to the carrier beads. Mounted for rotation within the developer housing 36 are two

magnetic brushes

39 and 40 positioned with their axes in parallel and below the selenium belt 12.

The magnetic brush 40, comprising outer cylinder 41 made of nonmagnelizable material and extending almost the length of the housing 36, is mounted for rotation within the structure 35. One end of the cylinder 41 is closed by a cap 42 which supports a drive shaft 43 in axial alignment with the cylinder and is mounted in bearings 44 on the end plate wall 38. The other end of the cylinder is provided with a cap 45 having a central opening therein. Within the cylinder 41 there is positioned an elongated magnet bar 46 extending nearly the full length of the cylinder and being mounted therein by means of a stub shaft 47 rotatably supported in the end cap 42 and a drive shaft 48 extending through and rotatably mounted in bearings held within the central opening formed in the cap 45. The shaft 48 extends through and is suitably joumaled in the end wall 37 so as to be rotated by an external control device as will be described hereinafter. In operation during a development cycle, the brush cylinder 41 is rotated by way of the drive shaft 43 and the magnet 46 remains stationary.

The second magnetic brush 39 comprises a cylinder 50 having a length and diameter equal to the cylinder 41. Within the brush cylinder 50 there is mounted a main magnet bar 51 which is supported in fixed position relative to its enclosing rotatable cylinder. This is accomplished by the use of shafts (not shown) mounted at both ends of the magnet bar 51 and projecting through openings in end caps (not shown) that are used to close and support the ends of the cylinder 50. Such caps and shafts are similar to the cap 42 and the shaft 47 at one end and the cap 45 and shaft 48 at the other end. One of the shafts would be fixed in order to maintain the magnet bar 51 in a fixed position during rotation of the cylinder 50. A second elongated magnet bar 52 is mounted within the cylinder 50 and is attached to a spacer bar 53 secured to the lower surface of the magnet bar 51. The polar orientation of the

magnets

46 and 51 are indicated in FIG. 2 and are arranged so that magnetic lines of flux project through the walls of the respective cylinders 41, 50 and across the surface of the belt 12 as it moves adjacent the

brushes

39, 40.

As shown in FIG. 2, the peripheral walls of the brush cylinders 41 and 51 are relatively close to each other. During a development cycle when both cylinders are rotating in unison and with the

magnets

46 and 51 held stationary, the brush bristles produced by the sue of magnetizable carrier beads in the developing material used in the unit 117 will form on the upper region of the cylinder 50 between this region and the undersurface of the selenium belt 12. These bristles remain formed during the developing cycle, being produced by the magnetic field of the magnet 51 beginning slightly before reaching the closest distance between the cylinder 50 and the belt 12. When the bristles are moved out of the influence of this magnet beyond the closest distance between the belt and the cylinder, they are picked up by the magnetic field of the magnet 46 which is stronger at this point than the diminished strength of he magnetic field attributed to the magnet 51 and carried therealong during rotation of the cylinder 41 until they reach a point beyond the development zone Z when the carrier beads and toner particles drop off the cylinder and back into the housing 36.

During movement of the carrier beads and toner through the development zone Z, the magnetic bristles and, therefore, the development material, is in the form of a magnetic blanket" extending the entire width of the zone Z wherein the material is disposed or available for developing purposes. It will be apparent that the width of the development zone Z is larger than the sum of the individual development zones for each of the

magnetic brushes

39, 40. One or two additional brushes may be added in the same arrangement in order to extend the dimensions of the magnetic blanket and therefore Also mounted within the development housing 36 and below the magnetic brush 39 is an impeller 54 having a plurality of blades 55 radially extending therefrom and having one end rotatably mounted in the end wall 37 and its other end terminating in a drive shaft 46 which in turn is rotatably mounted on and extends through the end wall 38. During a development cycle the impeller 54 is rotated in the direction shown by the arrow in FIG. 2 and serves to carry and throw development material toward the lower surface of the magnetic brush 39. The development material so thrown is picked up by the pickup magnet 52 which commences the formation of bristles on the cylinder 50. As this cylinder rotates, the newly formed bristles come under the influence of the main magnet 51.

A clipping blade 57 is secured to the upper wall of the housing 36 and extends radially toward the cylinder 41 being spaced from the periphery thereof a short distance equal to the length of the bristles to be formed on this magnetic brush. Upon rotation of the cylinder 50 for carrying the magnetic bristles toward the development zone Z, the blade 57 clips the tops of the magnetic bristles for presenting optimum lengths of the bristles to the belt 12. A curved baffle plate 58 is secured interiorly of the housing 36 and extends along for a length equal to the length of the impeller 54 with the center of curvature coincident with that of the impeller. The baffle assists the paddle blades of the impeller in forming large increments of developing material to be moved from the lower region of the housing 36 to the vicinity of the pickup magnet 52 whereat some of the material is formed into magnetic brush bristles.

A pair of augers 60, 61 are mounted in the lower region of the housing 36 for insuring continual mixing of the particles that comprise the developed material and for insuring proper quantities at all times. Each of the augers is suitably mounted at one end on the wall 37 while the other ends terminate in a drive shaft 62 which extends through and supported on the end wall 38. A suitable drive mechanism (not shown) may be connected to the shaft 62 and be activated when the machine is in its operative condition.

The magnetic developer unit 17 is also provided with devices which will control the developing action of the unit, and in such a way that the action may be switched on and off as rapidly as possible. Since the development zone Z is relatively wide and more than one magnetic brush is being controlled, the time period in which it takes the magnetic blanket" over both brushes to become inoperative is shortened by having both brushes controlled separately. To this end, the first of the magnetic brushes; namely, the brush 39 is provided with a gate element 64 fixed to a shaft 65 for rotation therewith. The gate 64 is formed with an edge 66 extending radially relative to the cylinder 50, and upon the rotation of the shaft 65, is adapted to engage the adjacent periphery of this cylinder. This action serves to scrape off instantly any magnetic bristles on the cylinder 50 thereby preventing the transport of development material beyond the edge 66 and consequently terminating the development action by the magnetic brush 39 except for the developing material still on the brush the instant before gating. This control action of the shaft 65 is made effective by the overall machine-programming system.

Gating action of the other magnetic brush 40 is provided by the quick rotation of the magnet 46 for approximately from its illustrated position. As previously stated, the magnet 46 is provided with a shaft 48 that extends externally of the developer housing 36. As shovm in FIG. 2, the shaft 48 is rotatably connected to a rocker arm 67 which has a pin 68 extending therefrom at one end to be engaged by a rocker arm 69 arranged to be swung in either direction upon activation of a rotary solenoid SOL-l. This solenoid is suitably mounted on the end wall 37 and connected electrically to the programming system for the machine. Upon energization of the solenoid SOL-l when it is desired to inactivate the unit 17, the rocker arm 69 is rocked in one direction to producing rocking of the rocker arm 67 with corresponding rotation of the shaft 47. This complete action involves only a very small increment of time. Rotation of the magnet 46 will remove its magnetic influence upon the magnetic carrier beads attempting to bridge across the gap between the

magnetic brushes

39, 40. A suitable machine-programming system may be arranged to efi'ect simultaneously activity of the shaft 65 and the shaft 48 for causing near simultaneous gating of the two magnetic brushes. In this event, only that developing material which forms on the brush 39 beyond the edge 66 will be involved in further development before most of the material falls through the space between the cylinders 41, 50 and, for the brush 40, that development material which was conveyed from the magnetic brush 39 just prior to gating requirement will be involved in further development. In this manner, the length of time needed to remove all residual developing material from the magnetic blanket on and between the

brushes

39 and 40 when gating is programmed is effectively that time needed to remove the material from just one of the brushes. As opposed to the use of a magnetic conveyor belt between two rollers, an arrangement which cannot be effectively gated to on-off conditions in acceptable short periods of time, the present magnetic blanket" concept, especially with the employment of many individual magnetic brushes, has the advantage that the gating periods for the entire coverage of the blanket is effectively the same for only one of the brushes utilized.

While the invention has been described with reference to the structure disclosed herein, it is not confined to the details set forth; but is intended to cover such modifications, or changes as may come within the scope of the following claims.

What is claimed is:

1. An apparatus for developing a movable surface bearing a latent electrostatic charge image including:

a plurality of rotatable cylindrical members mounted in spaced relation with an open space therebetween, said members having their axes generally in parallel and being arranged in spaced tangential relationship to the surface,

each of said members having associated therewith means for producing a magnetic field across a portion of the periphery thereof and across said surface as the same moves, said last-named means being arranged to produce bristles of magnetizable particles on each of the members during rotation thereof,

means for supplying a mixture of developing material having magnetizable particles and developing powder electrostatically carried by the particles to at least one of the members thereby initiating the formation of bristles thereon,

said means for producing magnetic fields being arranged wherein the magnetic influence upon one member diminishes within a stronger magnetic influence of the other thereby causing the movement of bristles from said one member to said other member across said open space therebetween upon rotation of said members.

2. An apparatus for developing a latent electrostatic image on a moving photoconductive insulating surface including:

a housing for containing a supply of developing material comprising magnetizable carrier particles and electrostatically adhering developing particles,

a plurality of cylindrical members mounted in spaced relation in the housing with an open space therebetween and arranged adjacent to and in spaced tangential relationship with said photoconductive insulating surface with their longitudinal axes generally normal to the path of movement of said surface,

means for rotating said members,

means supported within the cylindrical members for producing a magnetic field across at least a portion of the periphery of each of the members, and wherein the magnetic fields produced overlie one another whereby upon rotation thereof causing the formation of bristles of developing material upon said portion of each member arranged to contact said surface during movement thereof,

said means for producing a magnetic field being cooperable with said rotating members for producing movement of bristles along said portion of one of the members across said open space between the same and an adjacent member and along said portion of the adjacent member with the developing material remaining in contact with said surface thereby presenting a partially unsupported magnetic developing blanket during development of the latent electrostatic image.

3. An apparatus for developing a movable surface bearing a latent electrostatic charge image including: 7

each of said members having supported therein means for producing a magnetic field across a portion of the periphery thereof and across said surface as the same moves, said last named means being arranged to produce bristles of magnetizable particles on each of the members during rotation thereof,

at least one of said members being positioned to receive a supply of developing material having magnetizable particles and developing powder electrostatically carried by the particles thereby initiating the formation of bristles thereon,

said means for producing magnetic fields being arranged wherein the magneticv influence upon one member diminishes within a stronger magnetic influence of the other thereby causing the movement of bristles from said one member to said other member across said open space therebetween upon rotation of said members.

4. An apparatus for developing a movable surface bearing a latent electrostatic charge image including:

a plurality of rotatable elongated members mounted in spaced relation with an open space therebetween, said members having their longitudinal dimension generally in parallel and being arranged in spaced relationship to the surface,

each of said members having associated therewith means for producing a magnetic field over a portion of and along said surface as the same moves, said last-named means being arranged to produce bristles of magnetizable particles on each of the members,

5. An apparatus for developing a latent electrostatic image on a moving photoconductive insulating surface including:

a plurality of rotatable elongated members mounted in spaced relation in the housing an open space therebetween and arranged adjacent to and in spaced relationship with said photoconductive insulating surface with their longitudinal axes generally normal to the path of movement of said surface,

means supported within the members for producing a magnetic field over at least a portion of each of the members and causing the formation of bristles of developing material upon said portion of each member the bristles being arranged to contact said surface during movement thereof, said members being disposed in close parallel relationship whereby the magnetic fields associated with said members overlap,

said means for producing a magnetic field being cooperable with said members upon rotation of said members for producing movement of bristles along said portion of one of the members across said open space between the same and an adjacent member and along said portion of the adjacent member with the developing material remaining in contact with said surface thereby presenting a partially unsupported magnetic developing blanket during development of the latent electrostatic image.

6. In an electrostatic reproduction machine having means for producing latent electrostatic images on an element supporting latent images and for processing the images into copies of an original including:

a first magnetic developing brush arranged for contacting and applying developing material upon the images being processed,

a second magnetic developing brush arranged for contacting and applying developer material upon the images after the same have been contacted by said first brush,

said first and second magnetic brushes comprising a pair of rotatable roll members having an open space therebetween and means to establish a magnetic field over at least a portion of each member,

the magnetic fields associated with said members overlapping across said open space,

said second brush exerting a stronger magnetic influence, at a point in said open space, than said first brush, for

receiving developing material therefrom.

whereby said second brush is arranged to receive its supply of developing material from said first brush across the space therebetween upon rotation of said members.

7. In an electrostatic reproduction machine having means for producing latent electrostatic images on an element supporting latent images and for processing the images into copies of an original including:

a first magnetic developing brush arranged for contacting and applying magnetizable developing material upon the images being processed,

said second brush exerting a stronger magnetic influence, at a point in said open space, than said first brush, for receiving developing material therefrom.

whereby the magnetizable material is transported across said open space from one brush to another upon rotation of said members.

Claims

1. An apparatus for developing a movable surface bearing a latent electrostatic charge image including: a plurality of rotatable cylindrical members mounted in spaced relation with an open space therebetween, said membeRs having their axes generally in parallel and being arranged in spaced tangential relationship to the surface, each of said members having associated therewith means for producing a magnetic field across a portion of the periphery thereof and across said surface as the same moves, said lastnamed means being arranged to produce bristles of magnetizable particles on each of the members during rotation thereof, means for supplying a mixture of developing material having magnetizable particles and developing powder electrostatically carried by the particles to at least one of the members thereby initiating the formation of bristles thereon, said means for producing magnetic fields being arranged wherein the magnetic influence upon one member diminishes within a stronger magnetic influence of the other thereby causing the movement of bristles from said one member to said other member across said open space therebetween upon rotation of said members.

2. An apparatus for developing a latent electrostatic image on a moving photoconductive insulating surface including: a housing for containing a supply of developing material comprising magnetizable carrier particles and electrostatically adhering developing particles, a plurality of cylindrical members mounted in spaced relation in the housing with an open space therebetween and arranged adjacent to and in spaced tangential relationship with said photoconductive insulating surface with their longitudinal axes generally normal to the path of movement of said surface, means for rotating said members, means supported within the cylindrical members for producing a magnetic field across at least a portion of the periphery of each of the members, and wherein the magnetic fields produced overlie one another whereby upon rotation thereof causing the formation of bristles of developing material upon said portion of each member arranged to contact said surface during movement thereof, said means for producing a magnetic field being cooperable with said rotating members for producing movement of bristles along said portion of one of the members across said open space between the same and an adjacent member and along said portion of the adjacent member with the developing material remaining in contact with said surface thereby presenting a partially unsupported magnetic developing blanket during development of the latent electrostatic image.

3. An apparatus for developing a movable surface bearing a latent electrostatic charge image including: a plurality of rotatable cylindrical members mounted in spaced relation with an open space therebetween, said members having their axes generally in parallel and being arranged in spaced tangential relationship to the surface, each of said members having supported therein means for producing a magnetic field across a portion of the periphery thereof and across said surface as the same moves, said last named means being arranged to produce bristles of magnetizable particles on each of the members during rotation thereof, at least one of said members being positioned to receive a supply of developing material having magnetizable particles and developing powder electrostatically carried by the particles thereby initiating the formation of bristles thereon, said means for producing magnetic fields being arranged wherein the magnetic influence upon one member diminishes within a stronger magnetic influence of the other thereby causing the movement of bristles from said one member to said other member across said open space therebetween upon rotation of said members.

4. An apparatus for developing a movable surface bearing a latent electrostatic charge image including: a plurality of rotatable elongated members mounted in spaced relation with an open space therebetween, said members having their longitudinal dimension generally in parallel and being arranged in spaced relationship to the surface, each of said members having associatEd therewith means for producing a magnetic field over a portion of and along said surface as the same moves, said last-named means being arranged to produce bristles of magnetizable particles on each of the members, means for supplying a mixture of developing material having magnetizable particles and developing powder electrostatically carried by the particles to at least one of the members thereby initiating the formation of bristles thereon, said means for producing magnetic fields being arranged wherein the magnetic influence upon one member diminishes within a stronger magnetic influence of the other thereby causing the movement of bristles from said one member to said other member across said open space therebetween upon rotation of said members.

5. An apparatus for developing a latent electrostatic image on a moving photoconductive insulating surface including: a housing for containing a supply of developing material comprising magnetizable carrier particles and electrostatically adhering developing particles, a plurality of rotatable elongated members mounted in spaced relation in the housing with an open space therebetween and arranged adjacent to and in spaced relationship with said photoconductive insulating surface with their longitudinal axes generally normal to the path of movement of said surface, means supported within the members for producing a magnetic field over at least a portion of each of the members and causing the formation of bristles of developing material upon said portion of each member the bristles being arranged to contact said surface during movement thereof, said members being disposed in close parallel relationship whereby the magnetic fields associated with said members overlap, said means for producing a magnetic field being cooperable with said members upon rotation of said members for producing movement of bristles along said portion of one of the members across said open space between the same and an adjacent member and along said portion of the adjacent member with the developing material remaining in contact with said surface thereby presenting a partially unsupported magnetic developing blanket during development of the latent electrostatic image.

6. In an electrostatic reproduction machine having means for producing latent electrostatic images on an element supporting latent images and for processing the images into copies of an original including: a first magnetic developing brush arranged for contacting and applying developing material upon the images being processed, a second magnetic developing brush arranged for contacting and applying developer material upon the images after the same have been contacted by said first brush, said first and second magnetic brushes comprising a pair of rotatable roll members having an open space therebetween and means to establish a magnetic field over at least a portion of each member, the magnetic fields associated with said members overlapping across said open space, said second brush exerting a stronger magnetic influence, at a point in said open space, than said first brush, for receiving developing material therefrom. whereby said second brush is arranged to receive its supply of developing material from said first brush across the space therebetween upon rotation of said members.

7. In an electrostatic reproduction machine having means for producing latent electrostatic images on an element supporting latent images and for processing the images into copies of an original including: a first magnetic developing brush arranged for contacting and applying magnetizable developing material upon the images being processed, a second magnetic developing brush arranged for contacting and applying developer material upon the images after the same have been contacted by said first brush, said first and second magnetic brushes comprising a pair of rotatable roll members having an open space therebetween and means to esTablish a magnetic field over at least a portion of each member, the magnetic fields associated with said members overlapping across said open space, said second brush exerting a stronger magnetic influence, at a point in said open space, than said first brush, for receiving developing material therefrom. whereby the magnetizable material is transported across said open space from one brush to another upon rotation of said members.