US3908037A

US3908037A - Image developing techniques

Info

Publication number: US3908037A
Application number: US452152A
Authority: US
Inventors: John T Bickmore
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1971-09-14
Filing date: 1974-03-18
Publication date: 1975-09-23
Anticipated expiration: 1992-09-23

Abstract

Image developing methods are provided in accordance with teachings of the present invention. According to one embodiment of this invention, a surface traverses a uniformly varying electric field whereby electrophotographic developer particles adhering to said surface are removed therefrom in accordance with a first portion of said electric field and further electrophotographic developer particles are uniformly deposited on said surface in accordance with a second portion of said electric field. Said surface may comprise a donor member for selectively transferring the uniformly deposited electrophotographic developer particles to an electrostatic latent image. In another embodiment of the present invention said surface may comprise a photoconductive plate whereby the electrophotographic developer particles are selectively deposited on said photoconductive plate in conformity with the distribution of electrostatic charges thereon. The uniformly varying electric field is produced by variably biassed electrode means.

Description

United States Patent [191 Bickmore Sept. 23, 1975 [73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Mar. 18, 1974 [21] Appl. No.: 452,152

Related US. Application Data [62] Division of Ser. No. 180,426, Sept. 14, 1971, Fat.

['75] Inventor:

[52] U.S. C1. 427/14; 427/25; 96/1 SD; 355/3 DD [51] Int. Cl. G03G 13/08 [58] Field of Search 117/175, 19; 118/621, 118/637; 355/3, 3 DD; 96/1 R, 1 SD; 427/14, 25

[56] References Cited UNITED STATES PATENTS 3,147,147 9/1964 Carlson 118/637 3,328,193 6/1967 Oliphant et a1. 117/37 LE 3,331,355 7/1967 Donalies et al. 1 17/17.5 3,411,482 11/1968 Brodie 118/637 3,412,710 11/1968 Robinson 118/637 3,416,494 12/1968 Hudson 118/637 3,443,517 5/1969 Gundlach 101/219 3,601,092 8/1971 Satomi 118/637 3,638,610 2/1972 Lyles et a1. 118/637 3,696.785 10/1972 Andrus 118/637 3,818,864 6/1974 Bickmore... 117/l7.5 3,825,421 7/1974 Tamai 1l7/17.5

Primary Examiner-Michael Sofocleous [57] ABSTRACT Image developing methods are provided in accordance with teachings of the present invention. According to one embodiment of this invention, a surface traverses a uniformly varying electric field whereby electrophotographic developer particles adhering to said surface are removed therefrom in accordance with a first portion of said electric field and further electrophotographic developer particles are uniformly deposited on said surface in accordance with a second portion of said electric field. Said surface may comprise a donor member for selectively transferring the uniformly deposited electrophotographic developer particles to an electrostatic latent image. In another embodiment of the present invention said surface may comprise a photoconductive plate whereby the electrophotographic developer particles are selectively deposited on said photoconductive plate in conformity with the distribution of electrostatic charges thereon. The uniformly varying electric field is produced by variably biassed electrode means.

9 Claims, 3 Drawing Figures US Patent Sept. 23,1975 Sheet 2 of2 3,908,037

IMAGE DEVELOPING TECHNIQUES This is a division, of application Ser. No. 180,426, filed Sept. 14, 1971, now US. Pat. No. 3,818,864.

This invention relates to image developing techniques and more particularly to a method of uniformly developing an electrostatic latent image.

In the art of electrophotography such as described in US. Pat. No. 2,297,691 which issued to Chester F. Carlson, a uniform electrostatic charge is deposited on a surface of an electrophotographic plate which is comprised of a layer of photoconductive insulating material overlying a conductive backing. Upon exposure to a light pattern or image projected thereto, the electrostatic charge is electively dissipated in accordance with said light pattern so as to form an electrostatic latent image on the photoconductive insulating material. The electrostatic latent image is then normally developed by depositing electrophotographic developer particles, such as a powder or fine liquid droplets, onto the surface of the photoconductive insulating material whereby the elctrophotographic developer particles are held in image areas by the electrostatic charges. The greatest amount of electrophotographic developer particles are deposited in image areas including the greatest charge density and conversely little or no electrophotographic developer particles are deposited in image areas where the charge density is least. Consequently a developed image is produced in conformity with the distribution of electrostatic charges on the surface of the photoconductive insulating material. The

developed image may be subsequently transferred to a support surface to form a permanent copy. The photoconductive insulating material is then prepared for reuse and the foregoing operation is repeated.

The electrophotographic developer particles conventionally utilized to develop an electrostatic latent image may comprise charged toner particles such as a charcoal powder or any of a number of various carbon or lampblck materials, finely divided materials having added pigment such as resins containing pigment or dyes, metallic particles and generally all xerographic developer materials. Such toner particles may be deposited on the electrostatic charges as by cascading a two-component developing material consisting of the toner particles which adhere to a coarse granular material, such as a glass, sand or steel bead commonly known as the carrier, over the surface of the photoconductive insulating material. Other conventional developing systems direct a cloud of toner particles toward the surface of the photoconductive insulating material. Still other image developing systems employ a donor member adapted to receive the toner particles and to transfer said toner particles to the electrostatic latent image such as described in US. Pat. No. 3,166,419 which issued to R. W. Gundlach and assigned to Xerox Corporation, the assignee of the present invention. Further image developing systems well known to those skilled in the prior art employ toner particles suspended in an insulating liquid.

It has been found that proper development of an electrostatic latent image by developing systems employing a donor member requires a uniform deposit of toner particles on the surface of said donor member. A non-uniform deposit of toner particles on said surface results in the non-uniform development of portions of the photoconductive insulating material, which portions should be uniformly developed. Thus, for example, traces of a previous simage on a donor member, formed by the selective transfer of the toner particles therefrom, will rsult in a ghost image of the previous image superimposed on the subsequently developed image, if toner particles are not uniformly deposited onto the donor member. Consequently toner particles adhering to the surface of the donor member subsequent to the development of the electrostatic latent image must be removed therefrom prior to the deposition of further toner particles to said surface. Although a large portion of such adhering toner particles is removed by the well-known scavenging effect of carrier material cascading over the surface of said donor member thos toner particles remaining on said surface are sufficient to interfere with the uniform toning of the donor member. Conventional cleaningdevices such as rotating brushes or the like can be utilized for removing all the adhering toner particles from the surface of the donor member but these devices are generally not effective in removing dense layers of toner particles. Moreover, since the quantity of toner particles that remain on the donor member afterdevelopme'nt is generally ten to fifty times the quantity of toner particles actually deposited on the electrostatic latent image, it would be highly inefficient to remove all the adhering toner particles after each development cycle if the removed toner particles were to be discarded. The removed toner particles should be returned for subsequent reuse. Accordingly, a conventional blade cleaning device has been advantageously utilized. In addition, the techniques heretofore employed by the prior art to deposit toner particles on the surface of the doner member as described in aforementioned US. Pat. No. 3,166,419 do not readily provide a uniform layer of toner particles on said surface.

The foregoing disadvantages inherent in the transfer development of an electrostatic latent image are applicable to the direct development of an electrostatic latent image. For example, if a plurality of copies is to be produced from the electrostatic charges distributed on the surface of photoconductive insulating material, the photoconductive insulating material must be cleaned of adhering toner particles subsequent to each transfer of the developed image and the lectrostatic latentimage must again be developed.

Therefore it is an object of the present invention to provide a method of uniformly applying electrophotographic developer particles to a surface.

It is another object of the present invention to provide a method for developing an electrostatic latent image.

It is a further object of the present invention to provide a method for repeatedly developing an original electrostatic latent image for producing a plurality of copies therefrom.

It is yet another object of this invention to provide a method for suppressing background development of an electrostatic latent image.

Various other objects and advantages of the invention will become clear from the following detailed description of exemplary embodiments thereof and the novel features will be particularly pointed out in connection with the appended claims.

In accordance with this invention, a method of uniformly applying electrophotographic developer particles to a surface is provided wherein said surface traverses a uniformly varying electrostatic field such that electrophotographic developer particles adhering to said surface are removed therefrom in accordance with a frist portion of said electrostatic field; and as said surface continues to traverse said electrostatic field, further electrophotographic developer particles are uniformly deposited on said surface in accordance with a second portion of said electrostatic field. The uniformly varying electrostatic field is produced by resistive electrode means supplied with biassing voltages such that a uniformly varying potential is provided along said electrode means.

The invention will be more clearly understood by reference to the following detailed description of exemplary embodiments thereof in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a first embodiment of apparatus in accordance with the present invention for uniformly depositing electrophotographic developer particles to a surface;

FIG. 2 illustrates another embodiment of the present invention for developing an electrostatic latent image comprised of selectively distributed electrostatic charges; and

FIG. 3 illustrates a further embodiment of the apparatus that may be utilized in accordance with the present invention for applying electrophotographic developer particles to an electrostatic latent image comprised of selectively distributed electrostatic charges.

Referrring now to the drawings wherein like reference numerals are used throughout, and in particular to FIG. 1, there is illustrated a diagrammatic representation of the present invention comprising electrode means 10, donor member and photoconductive plate 30. The donor member 20 is adapted to be rotated about an axis in the direction indicated by the arrow A and to receive a uniform layer of electrophotographic developer particles 124 on the surface 20] thereof and to transfer said electrophotographic developer particles to the surface of photoconductive plate 30. The electrophotographic developer particles 124 comprise charged toner particles conventionally utilized in xerographic developing techniques. Accordingly the donor member 20 may be electrically conductive and may comprise a sheet of material such as steel,

' stainless steel, aluminum or the like; or donor member 20 may comprise non-conductive material such as a sheet of glass, plastic, paper or any other support base, the surface of which maybe coated with a conventional electrically conductive material. The voltage potential at the surface 201 of the donor member 20 is maintained at a constant value by applying a reference potential such as ground potential thereto. For convenience the donor member 20 is illustrated in drum configuration, however, as will soon become apparent, the donor member 20 may adopt any convenient configuration such as an endless belt or a reciprocating twodimensional planar surface. The surface 201 of donor member 20 is adapted to be disposed in spaced registration from the surface of photoconductive plate at a transfer station 31. Alternatively, the donor member may contact the photoconductive plate.

Photoconductive plate 30 may comprise a conventional xerographic plate including a photoconductive insulating surface 301 overlying a conductive backing 302. The photoconductive plate 30 may assume any convenient configuration, such as the illustrated drum configuration whereby the photoconductive plate 30 is adapted to rotate about an axis in the direction mdicated by the arrow B. Alternatively, the photoconductive plate 30 may assume an endless belt configuration, or the photoconductive plate 30 may be a planar member. The surface 301 of photoconductive plate 30 may be comprised of photoconductive insulating material, such as selenium or any other conventional xerographic photoreceptor. The conductive backing 302 is adapted to be supplied with a reference potential such as a biassing potential and a uniform electrostatic charge is adapted to be deposited on the surface 301 of the photoconductive plate 30. A description of the apparatus that may be utilized in depositing a uniform electrostatic charge on surface 301 may be found in US. Pat. No. 2,77,957 which issued to L. E. Walkup and assigned to Xerox Corporation. The uniform electrostatic charge deposited on surface 301 is adapted to be dissipated in accordance with the exposure thereof to a light image projected thereto resulting in an electrostatic latent image comprised of selectively distributed electrostatic charges 303. It is of course understood that the potential appearing at the surface 301 is a function of the density of the electrostatic charges 303 which in turn is dependent upon the intensity of light projected thereon. Typically, the potential appearing at exposed areas on the surface 301 may be on the order of volts and the potential appearing at non-exposed areas on the surface 301 may be on the order of 800 volts. Accordingly, the bias potential supplied to the conductive backing 302 should be somewhat larger than background potential to suppress the deposition of developer particles on background areas. A suitable bias potential might be 200 volts. The electrostatic latent image comprised of the selectively distributed electrostatic charges 303 is adapted to be developed at developing station 31. A more complete description of the development of the electrostatic latent image is set forth in US. Pat. No. 3,166,419 which issued to R. W. Gundlach and assigned to Xerox Corporation. At the transfer station 31 the electrophotographic developer particles 124 carried on the surface 201 of donor member 20 are transferred to the surface 301 of photoconductive plate 30 to form a developed image comprised of selectively deposited electrophotographic developer particles 304. Although the polarity of the electrostatic charges 303 is not critiical per se, it should be understood that in the image developing system of the type illustrated in FIG. 1 the polarity of the electrostatic charges 303 should be opposite to the polarity of the electrophotographic developer particles 124 to facilitate electrostatic transfer of said particles to develop a photographically positive image. The converse, of course, obtains if a photographically negative image is to be developed. Accordingly the polarity of electrostatic charges 303 as illustrated in FIG. 1 admits of positive polarity and the polarity of the electrophotographic developer particles 124 admits of negative polarity. However, if desired the polarity of the electrostatic charges 303 may be negative and the polarity of the electrophotographic developer particles 124 may be positive. The developed image may be transferred to a support surface such as paper in a well-known manner, not shown herein.

The manner in which a uniform layer of electrophotographic developer particles 124 is deposited on the surface 201 of donor member 20 is the subject matter of theh present invention. Apparatus that may be utilized in accordance with the present invention is illustrated as electrode means 10. Electrode means is fixedly disposed relative to donor member and is in spaced registration from the surface 201. The electrode means 10 is adapted to be coextensive with at least a portion of the surface 201 of donor member 20 and accordingly, if the donor member 20 is of a drum configuration the surface of the electrode means 10 may lie in a cylindrical plane concentric with the surface 201. The longitudinal dimension of the electrode means 10 is at least equal to the axial length of the donor member 20. Consequently, the sruface of the electrode means 10 and the surface 201 admit of a face to face relationship such that a given point on the surface 201 is adapted to be rotated past the electrode means 10 from an upper portion of said electrode means, as viewed in FIG. 1, to a lower portion thereof. The terminology upper portion and lower portion, as applied to electrode means 10, is used merely for convenience in describing the apparatus of FIG. 1 and should not be interpreted as limiting the configuration of the illustrated apparatus to pre-established vertical or horizontal planes. It is of course recognized that if donor member 20 is of an endless belt configuration the electrode means 10 may lie in a plane parallel to the surface of said donor member. The electrode means 10 is adapted to produce an electrostatic field between the electrode means 10 and the surface 201 of donor member 20. The electrostatic field is characterized by a uniformly varying magnitude from the upper portion of electrode means 10 to the lower portion thereof. In addition the direction of the electrostatic field is reversible over the illustrated dimension of the electrode means 10. Accordingly, a first portion 120 of said electrostatic field may emanate from the electrode means 10 toward surface 201 of donor member 20; and a second portion 121 of said electrostatic field may emanate from the surface 20] toward the electrode means 10.

The electrode means 10 may be comprised of conductive material having a relatively high resistance. Accordingly electrode means 10 may be comprised of glass, or ceramic material having a resistivity on the order of 10 ohm-centimeters. Alternatively, the electrode means 10 may comprise glass or ceramic material having a resistivity on the order eorder of 10 ohmcentimeters and include thin layers of metal, carbon or conductive plastic coated thereon. If desireu the electrode means 10 may comprise a grid of fine parallel wires. The relatively high resistivity of the electrode means is preferred so that a smoothly varying potential may be obtained on the surface thereof thereby inducing the aforementioned uniformly varying electrostatic field, and significant heat dissipation does not occur. Consequently, the electrode means 10 is divided into discrete portions represented as 101, 102, 103, 104, 105 and 106, adjacent portions being separated by an insulating strip such as 107. Each of said discrete portions of the electrode means 10 is supplied with a selected d.c. potential so that the potential differences between adjacent portions of the electrode means 10 are uniform. Hence a d.c. voltage source 11 is connected to a voltage divider network comprised of series connected

resistances

111, 112, 114, 115 and 116 whereby said selected d.c. potentials are produced by respective resistances. Accordingly, the junction between the d.c. voltage source 11 and resistance 111 is coupled to portion 101 of electrode means 10. Similarly, the junction between resistances 111 and 112 is coupled to portion 102. In a like manner the junction between

resistances

112 and 114 is coupled to portion 103. And the junction between resistances 114 and 115 is coupled to portion 104. Likewise the junction between resistances IIS and 116 is coupled to portion and the junction between resistance 116 and the d.c. voltage source 11 is coupled to portion 106. To effectuate a reversal in the direction of the uniformly varying electrostatic field produced by electrode means 10, the d.c. voltage source 11 may be comprised of two oppositely poled d.c. supplies. Alternatively one of the discrete portions of electrode means 10 may be coupled to the reference potential supplied to the donor member 20. FIG. 1 illustrates that portion 103 is supplied with the aforementioned reference potential by applying a ground potential to the junction 113 between

resistances l

12 and 114. It may thus be observed that the relative potential of portion 101 is greater than the relative potential at the surface 201 of donor member 20. Similarly the potential of portion 102 is less than the potential of portion 101 but greater than the potential at the surface 201. It has been assumed that portion 103 is supplied with a potential equal to the potential at surface 201. The potential at portion 104 is less than the potential at the surface 201 and the potential at portion 105 is less than the potential at portion 104. As is expected the potential at portion 106 is less than that at portion 105. The selected potentials applied to the discrete portions 101 106 of electrode means 10 may be produced by other conventional means such as a plurality of Zener diodes connected to a common source of voltage, or a plurality of individual d.c. voltage supplies, or the like.

An alternative embodiment of electrode means 10 adapted to produce the aforementioned uniformly varying electrostatic field may comprise a unitary structure having a resistive cermet coated surface such that a uniformly varying voltage potential is provided along the surface of said electrode means 10 from the upper portion thereof to the lower portion thereof in accordance with a d.c. voltage applied thereto.

The electrophotographic developer particles 124 deposited on the surface 201 of donor member 20 may be supplied by a source of developer material 12. Source of developer material 12 is adapted to be compatible with conventional xerographic developing techniques. Accordingly, if electrophotographic developer particles are to be cascaded across the surface 201 the source of developer material 12 may comprise a housing filled with a quantity of two-component developer material. Those skilled in the art will recognize that such developer material consists of a pigmented resinous powder known as toner particles and coarse granular material known as carrier particles. The carrier particles may comprise glass, sand or plastic coated steel beads so situated in the triboelectric series that charges are imparted to the toner particles of a polarity opposite to the polarity of the electrostatic charges comprising the electrostatic latent image to be developed. Thus for the embodiment illustrated in FIG. 1 the toner particles are formed of a material which is nearer to the negative end of the triboelectric series then the material comprising the carrier particles. Consequently, the toner particles adhere to the carrier particles. The twocomponent developer material is adapted to drop from the housing 12 and to cascade over the surface 201 under the action of gravity. A sump, not shown, may be provided to recover the carrier particles and those toner particles not deposited on the surface 201.

The operation of the apparatus illlustrated in FIG. 1 will now be described. For purposes of simplification it will be assumed that donor member 20 and photoconductive plate 30 admit of a rotatable drum configuration. However, it should be clearly understood that either the donor member 20 or the photoconductive plate 30 or both may be an endless belt, a movable rectangular member or the like. When the surface 201 of the donor member 20 rotates into proximity with the surface 301 of photoconductive plate 30 the developer particles 124 on the surface 201 are selectively transferred to the surface 301 in conformity with the electrostatic charges 303 distributed on surface 301 to thereby develop the electrostatic latent image. This transfer of developer particles occurs because of the electrostatic forces exerted on said particles by the electrostatic charges 303. In some cases, improved development of the electrostatic latent image may be achieved if the donor member 20 is skidded across the surface 301 of photoconductive plate 30. Accordingly, the angular velocity of donor member 20 may be slightly greater than the angular velocity of the photoconductive plate 30. Generally, however, the donor member and the photoconductive plate rotate in synchronism. It is recognized that the electrostatic forces exerted on developer particles 124 by the areas of surface 301 wherein electrostatic charges have been dissipated are not adequate to remove the developer particles from the surface 201. Consequently, some developer particles 123 adhere to the surface 201 and must be removed to enable a uniform coating of developer particles to be deposited on surface 201.

A uniformly varying d.c. potential is provided along the surface of electrode means 10 in response to the voltages supplied thereto. The d.c. potential varies from a maximum of a positive polarity at portion 101 to a maximum of negative polarityat portion 106. Since the electrode means 10 is comprised of resistive material the d.c. potential provided along the surface thereof varies smoothly so that high electrostatic fields are not created across adjacent portions. It is noted however, that the potential difference between the portion 101 of electrode means 10 and the surface 201 is relatively high so that the magnitude of the electro static field 120 emanating from the portion 101 toward the surface 201 is correspondingly high. The magnitude of the electrostatic field emanating from portion 102 toward surface 201 is less than that of the electrostatic field 120 in response to the decreased potential difference between the portion 102 and the surface 201. Since the voltage applied to portion 103 is substantially equal to the reference potential at the surface 201 a neglible electrostatic field is produced there between. Continuing along electrode means 10, it may be observed that the d.c. voltages applied to portions 104, I05 and 106 are effective to produce an electrostatic field emanating from the surface 201 toward the electrode means of uniformly increasing magnitude. Thus the electrostatic field 121 exhibits a maximum value in the direction shown. It is now readily apparent that a uniformly varying potential is provided along the surface of the electrode means 10 whereby a uniformly varying electrostatic field is established transversely of said electrode means 10 and the surface 201 of donor member 20. It is recalled that the uniformly varyin;v go tential may be provided along the surface of the electrode means 10 by supplying the discrete portions 101 106 thereof with selected d.c. potentials or by supplying a constant d.c. voltage across opposite ends of an electrode means including a cermet resistive coated surface. To facilitate the flow of developer material across the surface 201 of donor member 20, to be described, it is preferred that the upper and lower portions of electrode means 10 assume the geometric configuration illustrated.

The surface 201 of the donor member 20 is rotated past the electrode means 10 by conventional driving means, such as a motor, not shown, whereby the surface 201 successively traverses the uniformly varying electrostatic field. Developer material is introduced at the upper portion of the electrode means 10. Thus the source of developer material 12 comprises a housing for two-component developer. The two-component developer, which is comprised of carrier particles having toner particles adhering thereto, is cascaded over the surface 201 under the action of gravity. The flowing two-component developer collides with residual developer particles 124 adhering to the surface 201 of donor member 20, thereby dislodging said developer particles. The electrostatic field exerts corresponding electrostatic forces on the disloged developer particles 123 sufficient to sweep said dislodged developer particles into the flowing developer stream and to direct the particles toward the electrode means 10. Although some dislodged developer particles will be deposited on the surface of the electrode means 10, only a relatively thin layer will accumulate because of the action of the flowing developer stream. Thus it is seen that the surface 201 of donor member 20 is electrostatically cleaned as it is translated past a first portion of the electrode means 10.

The electrostatic forces exerted on the developer particles adhering to the carrier) particles of the twocomponent developer inhibit the transfer of such developer particles to the surface 201 as the two-component developer falls through the uniformly varying electrostatic field. Likewise, developer particles that are jarred loose from their associated carrier particles while cascading across surface 201 are urged toward the electrode means 10 and therefore are not transferred to the surface 201. However, when the twocomponent developer, the unassociated developer particles and the dislodged developer particles 123 pass through that portion of the electrostatic field that is uniformly increasing in magnitude and emanates from the surface 201 toward the electrode means 10, the resulting electrostatic forces are sufficient to deposit a uniform coating of developer particles 124 onto said surface. It should be noted that the uniformly increasing electrostatic field tends to insure a uniform deposit of developer particles onto the surface 201 of donor member 20.

Another embodiment of the present invention is illustrated in FIG. 2 which comprises photoconductive plate 30 and electrode means 40. The photoconductive plate 30 of FIG. 2 is identical to the aforedescribed photoconductive plate 30 of FIG. 1 and is herein illustrated in rectangular configuration. Said photoconductive plate 30 is adapted to be translated with respect to electrode means 40 in the direction indicated by the arrow B. It is understood that electrode means 40 may be translated in the opposite direction.

Electrode means 40 is similar to aforedescribed electrode means 10 and may be formed from highly resis tive material. As illustrated, the electrode means 40 is divided into discrete portions 401 405 wherein adjacent portions are separated by highly insulating material 406. Each of said discrete portions is provided with a selected d.c.' voltage which may be supplied thereto from a plurality of dc. voltage sources, or as indicated in the drawings, by a conventional voltaage divider network connected to a d.c. supply 11. The voltage divider network is comprised of series connected resistances 212 215. Each junction formed by the series connection of resistances is coupled to one of the discrete portions 401 405 of the electrode means 40. An additional resistance 216 is connected between resistance 215 and a reference potential such as ground potential such that the voltage supplied to portion 405 of electrode means 40 is maintained above said reference potential. The electrode means 40 is disposed in spaced registration from the surface of photoconductive plate 30 and is substantially coextensive with at least a portion of said photoconductive plate. Accordingly, the electrode means 40 is parallel to the photoconductive plate 30 and admits of a dimensional characteristic normal to the plane of the paper of the drawings herein at least equal to the corresponding dimensional characteristic of the photoconductive plate 30. It should now be readily apparent from the description set forth hereinabove with respect to FIG. 1 that the electrode means 40 is adapted to have a uniformly varying potential provided along the surface thereof. If the dc. voltage supply 11 is assumed to be a conventional d.c. battery having a positive terminal coupled to portion 401 of the electrode means 40 it is understood that the potential provided along the surface of the electrode means 40 varies uniformly from a maximum value of approximately 1000 volts to a minimum value of approximately 150 volts in the direction of translation B of the photoconductive plate 30. Therefore an electrostatic field of uniformly varying magnitude is capable of being produced transversely of the electrode means 40 and the surface of photoconductive plate 30.

The apparatus illustrated in FIG. 2 is particularly adapted to treat the surface of the photoconductive plate 30 whereby an original electrostatic latent image thereon may be repeatedly developed and a plurality of copies of graphic information corresponding to said electrostatic latent image may be produced. In operation the developed image may be Ira] sferred to a support surface in a manner resulting in negligible distortion of the electrostatic charge pattern as described in U.S. Pat. No. 3,244,083 which issued to R. W. Gund- Iach and assigned to Xerox Corporation. Although photoconductive plate 30 may be translated to a conventional cleaning station, such as the type described in U.S. Pat. No. 2,751,616 which issued to M. I. Turner .Ir., et al. and assigned to Xerox Corporation, or a conventional blade cleaning device, for the purpose of removing toner particles that have not been transferred to the support surface, it is clear that some toner particles 423 may still adhere to the surface of the photoconductive plate 30. If two-component developer material is introduced at the rightmost portion (or, in an alternative embodiment, the leftmost portion) of electrode means 40 when the surface of the photoconductive plate 30 traverses the uniformly varying electrostatic field produced by the electrode means 40, electrostatic forces are exerted on toner particles 423 dislodged from the surface of photoconductive plate 30. If the dc. voltage supplied to portion 401 of electrode means 40 is of sufficient magnitude, such as 1000 volts, the potential induced on the surface of said portion 401 exceeds the potential at the surface of photoconductive plate 30 attributable to the distribution of the electrostatic charges 303. Consequently, electrostatic forces are exerted on the dislodged toner particles 423 to urge said toner particles toward the surface of the electrode means 40. The magnitude of the electrostatic field produced in the vicinity of the portion 402 of electrode means 40 is slightly less than the magnitude of the electrostatic field produced in the vicinity of portion 401. However, the former may still be sufficient to urge toner particles toward the surface of the electrode means 40. It is recalled that uniformly varying electrostatic fields are preferred so that high fields are not created between adjacent portions of the electrode means 40, such as

portions

401 and 402, which result in the deposition of toner particles on the surface of the electrode means.

The additional toner particles 422 of the twocomponent developer material introduced into the space between the electrode means 40 and the surface of the photoconductive plate 30 in the manner previously described with respect to FIG. 1, will likewise be urged toward the electrode means 40. It is recognized that since a uniformly decreasing potential is provided along the surface of the electrode means 40 there exists a position at the surface of the electrode means whereat the potential is less than the potential of the distributed electrostatic charges 303. At this position the electrostatic forces exerted on the toner particles 422 by the selectively distributed electrostatic charges 303 exceed the electrostatic forces exerted on said toner particles by the electrode means 40. Consequently, the toner particles are urged toward and deposited on the surface of the photoconductive plate 30 in conformity with the distribution of the electrostatic charges 303, thereby forming a developed image 304. It is observed that as the photoconductive plate 30 is translated in direction B the electrostatic forces exerted on the toner particles 422 by the electrostatic charges 303 increase because the potential provided along the surface of the electrode means 40 decreases. It is a feature of the illustrated embodiment however, that the magnitude of the potential provided along the surface of the portion 405, although a minimum value, exceeds the potential at the surface of photoconductive plate 30 in the non-image areas to thereby inhibit the deposit of toner particles 422 on said nonimage areas. Hence, the potential provided at portion 405 will be approximately l50 volts if the background potential is equal to volts. It should therefore be understood that the major change in the uniformly decreasing potential provided along the surface of electrode means 40 occurs between

portions

402 and 404 thereof.

A further ennbodiment of the present invention is illustrated in FIG. 3 which comprises electrode means 50 and photoconductive plate 30. The apparatus illustrated in FIG. 3 is adapted to develop an electrostatic latent image comprised of electrostatic charges 303 selectively distributed on the surface of the photoconductive plate 30, which photoconductive plate has previously been cleaned by conventional means. Accordingly, the removal of toner particles that might adhere to the surface of the photoconductive plate 30 is merely incidental to the principal function of development as performed by the electrode means 50. The photoconductive plate 30 is illustrated in drum configuration, however it is apparent that said photoconductive plate may comprise a rectangular member as illustrated in FIG. 2 or an endless belt. The electrode means 50 is similar to aforedescribed electrode means and is disposed in spaced registration from the surface of the photoconductive plate 30 and is substantially coextensive therewith for at least a portion of said photoconductive plate. Thus the longitudinal dimension of the electrode means 50 is at least equal to the longitudinal dimension of the photoconductive plate 30. Discrete portions 501 506 of the electrode means 50 are adapted to be supplied with selected d.c. potentials whereby a uniformly varying potential is induced across the surface of said electrode means 50. Accordingly, a singular voltage supply may be coupled to each of said discrete portions 501 506. In the illustrated configuration a single voltage source 1 1 is connected to a conventional voltage divider network comprised of series connected resistances 311 through 315.

The voltage produced at each junction formed by the series connection of resistances is supplied to a corresponding portion 501 506 of electrode means 50. It should now be readily apparent that the electrode means 50 is adapted to produce an electrostatic field transversely of the electrode means 50 and the surface of the photoconductive plate 30. The magnitude of said electrostatic field exhibits a decreasing characteristic in the direction of rotation B of the photoconductive plate 30. A source of developer material 12 identical to the aforedescribed source of developer material illustrated in FIG. 1 is disposed to introduce toner particles 122 into the space between the electrode means 50 and the surface of the photocondutive plate 30.

In operation, the photoconductive plate 30 is driven by conventional driving means, such as a motor, not shown, to transport an electrostatic latent image comprised of electrostatic charges 303 selectively distributed on the surface of the photoconductive plate past electrode means 50. It is understood that the distribution of the electrostatic charges 303 corresponds to a light image that has been projected onto the surface of the photoconductive plate 30. The non-image areas on the surface of the photoconductive plate 30 correspond to the highlights of the projected image and may have a voltage potential not much less than the reference potential such as the bias potential that is applied to the conductive backing of the photoconductive plate 30. Accordingly, the non-image areas may exhibit a voltage potential of approximately 100 volts. Areas of moderate electrostatic charge distribution exhibit a correspondingly moderate potential, and those areas of maximum electrostatic charge distribution exhibit a maximum potential of, say, 800 volts. If the potential along the surface of portion 501 of electrode means 50 is greater than the maximum potential at the surface of the photoconductive plate 30, for example, if portion 501 exhibits a potential of approximately 2000 volts, it is apparent that charged toner particles 122 will not be deposited on the non-image areas or the areas having moderate electrostatic charge distribution thereat. However, as the potential across the surface of the electrode means 50 decreases, electrostatic forces are exerted on the toner particles 122 to urge them toward the surface of the photoconductive plate 30. Hence if it is assumed that the potential on the surface of portion 501 of electrode means 50 is greater than the potential at the surface of the photoconductive plate 3-) in the areas of maximum electrostatic charge distribution, the charged toner particles will not be deposited on the surface of photoconductive plate 30 in the vicinity of portion 501. If the potential on the surface of portion 502 of electrode means 50 is approximately 500 volts and the potential on the surface of the remaining portions is approximately 200 volts, then it is seen that the electrostatic field emanating from the surface of the photoconductive plate 30 toward the electrode means 50 uniformly increases in the direction of rotation B of the photoconductive plate. Hence, the density of the toner particles applied to the surface of the photoconductive plate 30 increases in the direction of rotation B so that maximum development of the electrostatic latent image occurs in the vicinity opposite portion 506 of electrode means 50. It of course should be clearly understood that the density of the toner particles deposited on the surface of the photoconductive plate 30 and, therefore, the degree of development of the latent image is dependent upon the selected d.c. voltages supplied to the discrete portions 501 506 of electrode means 50. Accordingly, if the dc voltage supplied to portion 506 for example, is increased, the intensity of the electrostatic field emanating from the surface of photoconductive plate 30 toward the portion 506 of electrode means 50 is correspondingly decreased and the deposition of toner particles on areas having little or no electrostatic charge distribution thereat is further suppressed. Alternatively, the portion 506 may be supplied with a negative d.c. voltage thereby resulting in a deposit of toner particles on non-image areas. It is recognized that a smoothly varying d.c. potential is induced along the surface of the electrode means 50 thereby preventing high electrostatic fields from being established across adjacent portions of the electrode means 50 which could result in the deposition of toner particles on the surface of the electrode means.

It should be clear from the foregoing description that the present invention is effective to remove toner particles adhering to a surface and to subsequently deposit a uniform layer of toner particles on said surface. Although the electrostatic charges have been described as exhibiting positive polarity and the toner particles have been described as exhibiting negative polarity, it should be readily apparent that the respective polarities may be interchanged. It is merely required that electrostatic attraction be obtained between the toner particles and the selectively distributed electrostatic charges. In addition, the development of the electrostatic latent image on photoconductive plate 30 may be photographically positive or negative depending upon the contemplated application of the present inveniton. It is further noted that the resistive electrode means described herein has been provided with discrete portions so that a smoothly varying potential may be obtained on the surface thereof. As has been pointed out hereinabove, the electrode means may comprise a unitary structure including a cermet resistive coated surface. The precise magnitude of the uniformly varying electrostatic field produced by the electrode means is suitable to induce electrostatic forces that are sufficient to clean toner particles from a surface and to uniformly deposit toner particles on said surface.

While the invention has been particularly shown and described with reference to a plurality of exemplary embodiments thereof, it will be obvious to those skilled in the art that the foregoing and various other changes and modifications in form and details maybe made without departing from the spirit and scope of the invention. It is therefore, intended that the appended claims be interpreted as including all such changes and modifications.

What is claimed is:

l. A method for removing and applying charged toner particles from and to, respectively, a surface; said method comprising the steps of maintaining said surface in spaced apart relationship with respect to an electrode means;

establishing a uniformly varying electrostatic field between said electrode means and said surface, said field being selected to define a first region having electrostatic forces which tend to urge toner particles toward said electrode means, a second region having electrostatic forces which tend to urge toner particles toward said surface, and a transistion between said first and second regions; translating said surface relative to said electrode means so that points on said surface sequentially advance through said first and second regions; and projecting developer containing toner into the space between said electrode means and said surface proximate said first region to dislodge any residual toner particles adhering to said surface and to supply toner particles for application to said surface.

2. The method of claim 1 wherein said surface is translated in a predetermined direction; and the electrostatic forces in said first and second regions decrease and increase, respectively, in said direction.

3. The method of claim 2 wherein residual toner particles are removed from said surface in said first region, and said surface is uniformly coated with toner particles in said second region.

4. The method of claim 1 further including the step of transferring toner particles carried by said surface to a photoconductor in accordance with a latent electrostatic image borne by said photoconductor.

5. The method of claim 4 wherein the electrostatic forces in said first and second regions decrease and increase, respectively, in a predetermined direction, and said surface is translated through said first and second regions in said direction so that residual toner particles are removed from said surface in said first region and said surface is uniformly recoated with toner particles in said second region.

6. A method for developing latent electrostatic images carried by a photoconductor, said method comprising the steps of maintaining a donor member in spaced apart relationship relative to an electrode means and in contact with said photoconductor;

establishing a uniformly varying electrostatic field between said electrode means and said doner member, said field being selected to define a first region having electrostatic forces which tend to urge toner particles having a charge of a predetermined polarity toward said electrode means, a second region having electrostatic forces which tend to urge toner particles having a charge of said polarity toward said doner member, and a transistion between said first and second regions;

advancing said doner member past said electrode means in a direction running from said first region toward said second region;

introducing toner particles having a charge of said polarity into the space between said doner member and said electrode means, whereby said doner member is freed of residual toner particles while advancing through said first region and uniformly reloaded with toner particles while advancing through said second region.

7. The method of claim 6 whererin said doner member is advanced at the same rate as said photoconductor and makes nonskidding contact with said photoconductor.

8. The method of claim 6 wherein said doner member is advanced at a higher rate than said photoconductor and makes skidding contact with said photoconductor.

9. A method for developing a latent electrostatic image defined by electrostatic charges of a predetermined polarity selectively distributed on a substrate, said method comprising the steps of maintaining said substrate in spaced apart relationship relative to an electrode means;

establishing a uniformly varying electrostatic field between said electrode means and said substrate, said field being selected to urge toner particles having a charge opposing the charge of said image away from and toward said substrate in first and second regions, respectively, of the space between said electrode and said substrate;

translating said substrate relative to said electrode means to sequentially subject points on said substrate to the electrostatic forces within said first and second regions; and

introducing developer containing toner particles into said space at a point proximate said first region and remote from said second region.

Claims

1. A METHOD FOR REMOVING AND APPLYING CHARGED TONER PARTICLES FROM AND TO, RESPECTIVELY, A SURFACE, SAID METHOD COMPRISING THE STEPS OF MAINTAINING SAID SURFACE IN SPACED APART RELATIONSHIP WITH RESPECT TO AN ELECTRODE MEANS: ESTABILISHING A UNIFORMLY VARYING ELECTROSTATIC FIELD BETWEEN SAID ELECTRODE MEANS AND SAID SURFACE, SAID FIELD BEING SELECTED TO DEFINE A FIRST REGION HAVING ELECTROSTATIC FORCES WHICH TEND TO URGE TONER PARTICLES TOWARD SAID ELECTRODE MEANS, A SECOND REGION HAVING ELECTROSTATIC FORCES WHICH TEND TO URGE TONER PARTICLES TOWARD SAID SURFACE, AND A TRANSISTION BETWEEN SAID FIRST AND SECOND REGIONS, TRANSLATING SAID SURFACE RELATIVE TO SAID ELECTRODE MEANS SO THAT POINTS ON SAID SURFACE SEQUENTIALLY ADVANCE THROUGH SAID FIRST SECOND REGIONS, AND

6. A method for developing latent electrostatic images carried by a photoconductor, said method comprising the steps of maintaining a donor member in spaced apart relationship relative to an electrode means and in contact with said photoconductor; establishing a uniformly varying electrostatic field between said electrode means and said doner member, said field being selected to define a first region having electrostatic forces which tend to urge toner particles having a charge of a predetermined polarity toward said electrode means, a second region having electrostatic forces which tend to urge toner particles having a charge of said polarity toward said doner member, and a transistion between said first and second regions; advancing said doner member past said electrode means in a direction running from said first region toward said second region; introducing toner particles having a charge of said polarity into the space between said doner member and said electrode means, whereby said doner member is freed of residual toner particles while advancing through said first region and uniformly reloaded with toner particles while advancing through said second region.

9. A method for developing a latent electrostatic image defined by electrostatic charges of a predetermined polarity selectively distributed on a substrate, said method comprising the steps of maintaining said substrate in spaced apart relationship relative to an electrode means; establishing a uniformly varying electrostatic field between said electrode means and said substrate, said field being selected to urge toner particles having a charge opposing the charge of said image away from and toward said substrate in first and second regions, respectively, of the space between said electrode and said substrate; translating said substrate relative to said electrode means to sequentially subject points on said substrate to the electrostatic forces within said first and second regions; and introducing developer containing toner particles into said space at a point proximate said first region and remote from said second region.