US3661118A

US3661118A - Electrostatic development

Info

Publication number: US3661118A
Application number: US104269A
Authority: US
Inventors: Stephen F Royka
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1971-01-06
Filing date: 1971-01-06
Publication date: 1972-05-09
Anticipated expiration: 1989-05-09
Also published as: DE2200138A1; GB1359234A; CA951107A

Abstract

Electrostatographic development apparatus in which developer is stored in the interior of a movable recording member, such as a rotatable drum. The interior of the drum is provided with buckets which are rotated therewith and scoop developer from the lower portion of the drum and convey the developer to an upper portion of the drum at which point the developer is removed from the interior of the drum and cascaded over the recording surface. The developer which has cascaded over the surface is then returned to the interior of the drum.

Description

United States Patent Royka Stephen F. Royka, Fairport, NY.

[52] U.S. Cl. ..1l8/636, 1l8/D1G. 24

[51] Int. Cl. ..G03g 13/00 [58] Field of Search ..1 18/637; 117/175; 96/1 R; 101/D1G. 13

[56] References Cited UNITED STATES PATENTS 2,761,416 9/1956 Carlson ..1 18/51 3,117,030 1/1964 .lons et al... ..l18/637 3,173,805 3/1965 Robinson t ..118/637 3,245,341 4/1966 Childress et a]. 101/122 51 May9, 1972 3,265,522 8/1966 Games ..l17/25 Primary E.\aminerMorris Kaplan Assistant Examiner-Leo Millstein Attorney-James J. Ralabate, Donald F. Daley, Thomas J. Wall and Marn & Jangarathis [57] ABSTRACT cascaded over the surface is then returned to the interior of the drum.

11 Claims, 5 Drawing Figures PATENTEDHAY 9:972 3,661,118

sum 1 0r 3 INVENTOR.

Stephen F. Royku ATTORNEYS PATENTEDMAY 9 I972 8.661.118

sum

2 or 3 INVENTOR. Stephen F. Royko ATTORNEYS PATENTEDMAY 91922 3,661.1 18

SIHH 3111' 3 INVFINIOR.

Stephen F. Royko Fig. 5.

Maw

ATTORNEYS ELECTROSTATIC DEVELOPMENT BACKGROUND OF THE INVENTION This invention relates to electrostatography and more particularly to a new and improved apparatus for developing a latent electrostatic image.

Electrostatography is exemplified by the basic electrophotographic process taught by C. F. Carlson in U.S. Pat. No. 2,297,691, which involves placing a uniform electrostatic charge on a photoconductive insulating layer, exposing the layer to a light and shadow image to dissipate the charge on the areas of the layer exposed to the light and developing the resulting latent electrostatic image by depositing on the image a finely-divided electroscopic material referred to in the art as toner. The toner is normally attracted to those areas of the layer which retain a charge, thereby forming a toner image corresponding to the latent electrostatic image, which may then be transferred to a support surface, such as paper. The transferred image is generally permanently affixed to the support surface by heating, although other suitable fixing means, such as solvent or overcoating treatment, may be substituted for the foregoing heat fixing step.

One method for applying the electroscopic material to a latent electrostatic image is the cascade process disclosed by L. E. Walkup in U.S. Pat. No. 2,618,551 and E. N. Wise in U.S. Pat. No. 2,618,552. In the cascade process, the developer is basically a two component system comprised of a finely divided electroscopic material (toner) and a carrier. The carrier is generally comprised of a core material, such as glass or sand, and a triboelectric resinous coating with the toner particles being loosely held on the coating by triboelectric action. The carrier and toner are chosen so that the toner assumes a charge of an opposite polarity to the latent electrostatic image, whereby upon rolling or cascading the developer over the surface bearing the electrostatic image, the toner particles are attracted to the image being developed. Conversely, if the toner particles have a charge of identical polarity to the latent electrostatic image, the toner particles accumulate on the background portions.

In automatic electrophotographic equipment, it is conventional to employ a photoconductive plate in the form of a cylindrical drum which is continuously rotated through a cycle of sequential operations including charging, exposure, developing, transfer and cleaning. The plate is usually charged with corona with positive polarity by means of a corona generating device of the type disclosed by L. E. Walkup in U.S. Pat. No. 2,777,957 which is connected to a suitable source of high potential and the charged plate is then exposed to a light and shadow image to dissipate the charge on the areas exposed to the light thereby forming a latent electrostatic image. A developer comprised of toner loosely held on a coated carrier is conveyed from a reservoir to a point above the drum bearing the latent electrostatic image and is allowed to fall and roll by gravity over the image-bearing surface thereby forming a powder image. The carrier along with any unused toner is returned to the reservoir for recycle through the development system. After forming a powder image on the electrostatic image during the development step, the powder image is electrostatically transferred to a support surface by means of a corona generating device such as the corona device mentioned above. In automatic equipment employing a rotating drum, a support surface to which a powdered image is to be transferred is moved through the equipment at the same rate as the periphery of the drum and contacts the drum in the transfer position interposed between the drum surface and the corona generating device. Transfer is effected by the corona generating device which imparts an electrostatic charge to attract the powder image from the drum to the support surface. The polarity of charge required to effect image transfer is dependent upon the visual form of the original copy relative to the reproduction and the electroscopic characteristics of a developing material employed to effect development. For example, where a positive reproduction is to be made of a positive original, it is conventional to employ a positive polarity corona to effect transfer of a negatively charged toner image to the support surface. When a positive reproduction from a negative original is desired, it is conventional to employ a posi tive charged developing material which is repelled by the charged areas on the plate to the discharge areas thereon to form a positive image which may be transferred by negative polarity corona.

The machines utilizing such a cascade development technique are generally quite large as the result of the large area encompassed by the development system which includes a reservoir and conveyor positioned externally to the drum. In addition, the system requires a multiplicity of components including separate drive means for the developer conveyor in order to effect such development. Consequently, this develop ing technique is not particularly suitable for low cost and/or compact machines.

SUMMARY OF THE INVENTION Accordingly, an object of this invention is to provide for the development of latent electrostatic images.

Another object of this invention is to provide for development of a latent electrostatic image by the cascade development technique which is particularly suitable for low cost and/or compact machines.

These and other objects of the invention should be readily apparent from the following detailed description thereof when read with reference to the accompanying drawings.

The objects of this invention are broadly accomplished by developing a latent electrostatic image formed on the exterior surface of a movable electrostatographic recording member with developer stored within the interior of the movable electrostatographic member, thereby eliminating the necessity for a developer reservoir and conveying mechanism exteriorly to the electrostatographic recording member which increases the overall size of the machine. The electrostatographic recording member is provided with an exit port and inlet port for withdrawing and returning, respectively, developer from and to the interior thereof, and a conveying means is also provided within the interior of the electrostatographic recording member for conveying developer stored therein to the exit port. The exit port is in communication with a suitable conveying means, such as a ramp, chute or the like which conveys developer material, by gravity, to the latent image bearing exterior surface of the electrostatographic recording member. The developer released from the chute orramp cascades over the exterior surface to effect development of the latent image, and the developer which has cascaded, by gravity, over the exterior surface is transported, by gravity, by a suitable conveying means, such as a ramp, chute, or the like, to the inlet port for return to the interior of the electrostatographic recording member.

The conveying means within the interior of the electrostatographic recording member is preferably of the type which is movable therewith, such as buckets or the like connected thereto, whereby there is no necessity for separate drive means for driving the conveying means which transports developer from the reservoir or sump within the interior of the electrostatographic recording member to the exit port for subsequent cascading over the latent image bearing surface.

In carrying out the development of the present invention, any suitable conventional two-component type developing material comprising carrier and toner particles may be used. Representative patents in which these developer compositions are disclosed include U.S. Pat. No. 2,618,551 to Walkup, US. Pat. No. 2,618,552 to Wise, U.S. Pat. No. 2,633,415 to Walkup and Wise, U.S. Pat. No. 2,659,670 to Copley, U.S. Pat. No. 2,788,288 to Rheinfrank and Jones and U.S. Reissue Pat. No. 25,136 to Carlson. Generally, the toners have an average particle diameter between about 1 and about 30.microns, and the relatively larger carrier beads have an average particle diameter from about 30 to about 1,000 microns in diameter.

Typical toner concentrations include a range .from about 0.5 to about 10 percent by weight based on the total weight of the two-component developer composition.

The invention is particularly applicable to electrophotographic processes having an imaging surface formed of a photoconductive material such as vitreous selenium or selenium alloys, organic or inorganic photoconductors embedded in a non-photoconductive matrix, organic or inorganic photoconductors embedded in a photoconductive matrix and the like. Representative patents in which photoconductive materials are disclosed include U.S. Pat. No. 2,803,542 to Ullrich, U.S. Pat. No. 2,970,906 to Bixby, U.S. Pat. No. 3,121,006 to Middleton, U.S. Pat. No. 3,121,007 to Middleton and U.S. Pat. No. 3,151,982 to Corrsin. Generally, photoconductive materials are supported by conductive substrates. Typical conductive substrates include brass, aluminum, gold, platinum, steel, glass coated with conductive oxides, metallized non-conductive substrates, laminated sheets of metal and plastic and the like. The conductive substrate may be in the form of a cylinder, belt or the like. Preferably, the photoconductive surface comprises vitreous selenium, selenium alloys or mixtures of selenium and other inorganic materials because superior copy quality is maintained for a greater number of copying or duplicating cycles.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial schematic, elevational view, with portions broken away, of an embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along the line 2-2 of FIG. 1;

FIG. 3 is a side elevational view taken along the line 3-3 of FIG. 1;

FIG. 4 is an isometric view, with portions broken away, of the embodiment of FIG. I; and

FIG. 5 is an isometric view with portions broken away of the embodiment of FIG. I with modified drive means.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIGS. 1-4 of the drawings, there is illustrated an electrostatographic machine employing one embodiment of this invention. The machine includes an image forming member such as, for example, an electrophotographic cylindrical drum designated and generally comprising a photoconductive insulating layer, such as vitreous selenium or an alloy of selenium disposed on a conductive backing. Preferably the drum I0, and in particular its conductive backing, is electrically grounded. The image forming or image receiving surface of the electrophotographic cylinder 10 is adapted to be rotated past appropriate electrophotographic processing stations disposed and positioned to form an electrostatic image on the cylinder surface. For example, when used with a photoconductive insulating electrophotographic image surface, the electrophotographic processing stations may include means for charging or sensitizing, exposure means, and cleaning means. Illustrated in the figure is a charging station generally designated 14 at which is positioned a corona discharge electrode 15, desirably one or more high voltage corona discharge wires 16 mounted within a grounded shield 17 and adapted to be connected to a high voltage source such as, for example, a positive polarity direct current source of several thousand volts. In general the voltage applied to the corona discharge electrode will be sufficient to cause air ionization surrounding the corona wires and it is understood that such a corona discharge potential is generally in the order of several thousand volts and usually 5 to 10 thousand volts as disclosed, for example, in Walkup US. Pat. No. 2,777,957.

Positioned next adjacent to the charging station is an exposure station generally designated 18 and including suitable means for projecting or otherwise directing a light or optical image onto the surface of the electrophotographic drum. The exposure station may include a slit projection mechanism for exposing onto the drum surface a moving projected image of microfilm or the like, and may include means for projecting onto the surface documentary or other information or an image corresponding to the face of a cathode ray tube or the like. As is disclosed in Carlson U.S. Pat. No. 2,297,691, the combination of electric field and exposure to activating radiation forms on the drum surface an electrostatic image capable of being developed or made visible by deposition of finely divided charged particles.

A development station for developing the latent electrostatic image, generally designated as 21, is positioned at a subsequent location around the circumference of the drum, the structure and operation of which is hereinafter described.

Positioned subsequently around the surface of the electrophotographic drum is an image transfer station generally designated 27 including for example a supply roll 28 of transfer material such as, for example, a roll of paper and a take-up roll 29 together with guide means and the like to feed the image transfer material into contiguous relationship with the electrophotographic drum. As illustrated in the figure, suitable guide rolls 30 may guide and optionally drive the transfer web into contact with the electrophotographic drum, and transfer means such as, for example, a corona discharge electrode 31 is positioned to transfer the developer image to the image web at the transfer station. Preferably, the transfer means is a corona discharge electrode of substantially the same construction as is located at the charging station 14 although other transfer means may be employed such as the means disclosed in U.S. Pat. No. 2,807,233. For the usual case of direct or positive-to-positive photographic copy the charging electrode 15 and the transfer electrode 31 are of the same polarity and for the opposite situation of photographic reversal the electrodes are of opposite polarity. Optionally positioned near the transfer station and along the line of travel of the transfer web subsequent to the transfer station is a fusing station generally designated 32 and including a plurality of heating elements 33 suitably contained within a housing 34 and adapted to fuse onto the web surface the image that has been transferred thereto. ltis understood that suitable vapor fixing means may be employed as disclosed for example in Carlson U.S. Pat. No. 2,776,907.

Disposed next adjacent to the transfer station and between the transfer station and the charging station is a cleaning station generally designated 36 and comprising for example a cloth or, preferably, rotatable brush 37 operated by suitable drive means to brush against the electrophotographic drum surface and remove residual powder therefrom. Suitable brush cleaning apparatus is illustrated in Turner et al U.S. Pat. No. 2,751,616.

The various processing stations, except for the development station, are conventional in the electrophotographic art and,

therefore, only the hereinabove brief description thereof is deemed necessary for a full understanding of the present invention.

The electrostatographic drum I0 is an open ended hollow drum having support rings 51 and 52 rigidly secured thereto at each end for driving and supporting the drum 10. The open ends of the drum 10 are provided with fixed end plates 53 to seal the ends thereof and the rim of the drum 10, at each end, defines a journal surface with a corresponding bearing surface on the end plates 53, whereby the drum 10 may be rotated relative to and in contact with the end plates 53 to provided a closed compartment 57 in the interior of the drum 10, the bottom portion of which contains a supply of a two component electrostatographic developer. Thus, the bottom interior portion of the drum 10 functions as a reservoir or sump for developer material. It is to be understood, however, that the end plates 53 may be spaced from the rim of drum 10 provided that the space therebetween is smaller than the carrier of the two component developer to thereby prevent developer from falling out of the interior compartment 57 in drum 10.

The inner peripheral surface 58 of drum 10 has fixedly mounted thereto for rotation therewith a conveying means comprised of a plurality of longitudinally extending, circumferentially spaced buckets 61 having a generally triangularly shaped cross-section. The buckets 61 are comprised of a fixedly mounted longitudinal baffle or plate 62 which extends radially inwardly from the inner surface 58 of drum at an acute angle, in the direction of rotation of drum 10, with the interior surface of drum 10, with the radial free ends 63 of the baffle 62 being spaced from the interior surface 58 of drum 10. The length of baffle 62 is coextensive with the length of the drum 10, and the longitudinal ends 64 thereof are contiguous with the inner surfaces of end plates 53, with the longitudinal ends 64 of baffles 62 defining a journal surface with corresponding bearing surfaces on the end plates 53, whereby the baffles 62 are rotated with the drum 10 relative to and in contact with the end plates 53. The end plates 53 confine developer within buckets 61 at the longitudinal ends thereof. It is to be understood, however, that the longitudinal ends of the buckets 61 may be spaced from end plates 53, provided the spacing therebetween is smaller than the developer carrier to thereby prevent developer from falling off the buckets 61 at its longitudinal ends.

The inner surface 65 of the baffles 62 is formed in the shape of an inverted V, thereby defining

inclined surfaces

66 and 67 which extend from the center axis of the baffle 63 toward the longitudinal ends thereof. Thus, the interior of the buckets 61 is defined by the two end plates 53; the inverted V-shaped surface 65 of baffle 62 and the inner surface 58 of the drum 10, with the radial free end 63 of the baffle 62, which is spaced from the inner surface 58 of drum l0 defining the opening which places the interior of the buckets 61 in communication with the compartment 57in the interior ofdrum 10.

The end plates 53, at the upper ends, have rigidly secured thereto, an upper chute, generally indicated as 68, for transporting developer removed from the interior of the drum through exit ports defined by apertures 71 in each of the end plates 53 to the portion of the electrophotographic surface of the drum 10 rotated through the developing station 21. The apertures 71 are preferably positioned on each of the end plates 53 at a point which is immediately prior to the vertical axis of the drum 10, in the direction of rotation thereof, and which is also aligned with the rotational path of the surface 65 of baffles 62, whereby during rotation thereof, developer material on the outwardly

inclined surfaces

66 and 67 flows through the apertures 71 in the end plates 53 onto the upper chute 68.

The upper chute 68 is comprised of two outwardly extending and downwardly inclined outer ramps 72 which extend over the outer surface of each of the end plates 53 from the apertures 71 therein to beyond the outer periphery of the drum 10; and an inwardly extending and downwardly inclined inner ramp 73 which is coextensive with the electrophotographic surface of drum 10 and extends from the outer terminus of the outer ramp 72 to a point above the horizontal axis of the drum 10 closely adjacent to, but not contiguous with the electrophotographic surface of the drum 10. The upper chute 68 further includes upwardly extending side walls 74 for each of the outer ramps 72 spaced from each of the end plates 53, which along with the end plates 53 confines the developer to the outer ramps 72; and an upwardly extending end wall 75 which is coextensive with the outer ramps 72 and the inner ramp 73 to direct developer from the outer ramps 72 to the inner ramp 73. Thus, the upper chute 68 defines a U- shaped path which directs the developer downwardly to beyond the outer perimeter of the drum 10 along the ends thereof, and then directs the developer downwardly toward and over the portion of the electrophotographic surface of the drum 10 which is rotated through the development station 21. Similarly, the lower ends of end plates 53 have rigidly secured thereto a lower chute, generally indicated as 76, for transporting developer which has cascaded over the electrophotographic surface of drum 10 to apertures 77 in each of the plates 53 which function as inlet ports for returning developer to the interior of drum 10. The apertures 77 of end plates 53 are not necessarily aligned with the buckets 61 in that such apertures merely return developer to the interior of the drum. The chute 76 is comprised of an outwardly extending inner ramp 78 which is coextensive with the electrophotographic surface of drum 10 and is inclined downwardly and outwardly from a point below the horizontal axis of drum l0 closely adjacent to, but not contiguous with the electrophotographic surface of the drum l0; and two downwardly inclined, and inwardly extending outer ramps 79 which extend over the outer surface of end plates 53 from the outer terminus of the inner ramp 78 to the apertures 77 in each of the end plates 53. The lower chute 76 further includes: upwardly extending side walls 81 for each of the outer ramps 79, spaced from the end walls 53, with the side walls 81 and end plates 53 confining the developer flow to the outer ramps 79; an upwardly extending outer end wall 82 which is coextensive with the outer ramps 79 and inner ramp 78 to direct developer from the inner ramp 78 to the outer ramps 79; and an upwardly extending inner end wall 83 positioned between each of the side walls 81 and its respective end plate 53 to prevent developer from rolling off the outer ramp 79 beyond the apertures 77.

A development electrode 84 positioned adjacent to, and preferably concentric with the drum 10, is coextensive with the portion of the electrophotographic surface of drum 10 rotated within the developing station 21. The development electrode 84 is mounted at the upper end to the chute 68 and at the lower end to the chute 76 through suitable insulating strips (not shown). The development electrode 84 is suitably biased, as known in the art, to aid in the development process, and further functions to confine developer within the development station 21.

The drive mechanism of the drum, as shown in FIGS. 1 and 2, is comprised of a drive roller 91, containing a drive portion 93 and positioning portions 94 of a diameter greater than the diameter of the drive portion 93. The drive portion 93 of the drive roller 91 is in driving engagement with the peripheral surface of support ring 51 and the positioning portions 94 of the drive roller 91 abuts against the outer surface of the support ring 51 to prevent the drum 10 from moving in a horizon tal direction. The drive roller 91 is rigidly mounted on a shaft 97 which is rotatably mounted in journal support members 98, supported by a pedestal 99. The shaft 97 is rotated by a motor 102 through a speed reduction gear train generally indicated as 103.

The drum 10 is further supported by three idler rollers 104 (only two are illustrated) on which the support rings 51 and 52 are received. Similar to the drive roller 91, the idler rollers 104 contain an idler portion 105 and positioning portions 106 having a diameter greater than the diameter of the idler portion 105. The idler rollers are rotatably mounted in journal support members 108, supported by pedestals 109. Thus, the drum 10 has a four-point support structure.

In operation, the motor 102 rotates the shaft 97 and the drive roller 91 in the direction of the arrow. The drive roller 91 drivingly engages the support ring 51 which is rigidly mounted on the drum 10 thereby rotating the drum 10 in the direction of the arrow (FIG. 1). The electrophotographic surface of the drum 10 is provided with a uniform charge at the charging station 14 and the charged drum 10 is rotated past the exposure station 18 wherein the charged electrophotographic surface is exposed to light and shadow images corresponding to the document to be reproduced, thereby providing a latent electrostatic image on the electrophotographic surface of the drum 10, as generally known in the art.

The compartment 57 of the drum 10 contains a suitable two component developer, comprised of toner electrostatically coated on the surface ofa suitable carrier, with the developer being confined in the lower portion of the interior of the drum 10 by the end plates 53. Thus, the lower portion of the interior of the drum 10 functions as a reservoir or sump for the electrostatographic developer.

The buckets 61 on the interior surface 58 of the drum 10 are rotated therewith and are passed through the developer material in the lower portion of the interior of the drum 10, whereby the developer is scooped into the buckets through the open ends thereof. In the bottom portion of the rotational path of the buckets 61, the interior surface 58 of the drum 10 functions as the bottom of the buckets 61 with the developer being confined at the ends by the end plates 53. As the drum 10 is rotated, the buckets 61 are moved from the bottom of their rotational path toward the top thereof and at a point in their rotational path which is at about the horizontal axis of the drum 10, the surface 65 of baffle 62 becomes the lower portion of the bucket 61, and the developer material in the bucket 61 is supported by the surface 65. The surface 65, as hereinabove noted, is comprised of two

inclined surfaces

66 and 67, which are inclined away from the axis of the buckets toward the respective ends of the drum 10 and, therefore, as the buckets 61 rise, the developer supported by the surface 65 is forced to the respective ends of the bucket 61, where the developer is confined by the end plates 53. At a point immediately prior to or at the highest point in the rotational path of the buckets 61, i.e., at a point immediately prior to or at the vertical axis of the drum 10, the surface 65 of the buckets 61 is aligned with the apertures 71 in the end plates 53 and developer at each end of surface 65 flows out of the aperture 71 and onto the outer ramps 72 of upper chute 68. The developer on the outer ramps 72 flows by gravity downwardly and outwardly from the drum l and then flows by gravity on the inner ramp 73 downwardly and inwardly toward the electrophotographic surface of drum which bears the latent electrostatic image.

The developer released from the inner ramp 73 cascades down the arcuate path of the drum l0, and as known in the art, toner is attracted to the latent electrostatic image bearing areas thereby rendering the latent electrostatic image visible. As the developer material falls past the horizontal center line of the drum 10, the developer drops by gravity onto the inner ramp 78 of the lower chute 76. The. developer flows on the inner ramp 78 downwardly and outwardly from the drum 10, and then the developer is directed downwardly and inwardly toward the drum 10 along the ends thereof over the outer ramps 79. The developer is returned from the outer ramps 79 into the interior of drum 10 through the apertures 77 in each of the end plates 53.

The development electrode 84 aids in confining the developer released from upper chute 68 to the portion of the rotational path of drum 10 within development station 21 and is also suitably biased to aid the development process, as known in the art. Thus, the development electrode 84 may be biased to a polarity the same as that on the image and nonimage areas of the electrophotographic surface for conventional development; i.e., the electrode is biased to a polarity which is opposite to the polarity of the charge which the toner assumes. The charge on the electrode is preferably of slightly greater magnitude than that on non-image areas of the latent electrostatic image bearing surface for attracting toner away from the non-image areas to thereby reduce background. Alternatively, the development electrode 84 may be grounded with respect to the electrophotographic surface in which case the development electrode would strengthen large area portions of the image.

The developed image on the electrophotographic surface is then rotated past the transfer station 27 at which point the image is transferred, as known in the art. The electrophotographic surface is then rotated past cleaning station 36 at which point residual toner is removed from the surface, as known in the art, and the surface may now be reemployed for the formation and development of a latent electrostatic image, as previously described.

Numerous modifications and variations of the present invention are possible in light of the above teachings and such modifications are within the spirit and scope of the invention. Thus, for example, the means for conveying developer from the reservoir in the interior of the electrostatographic recording member may be other than as particularly described. Thus,

for example, the interior of the recording member may be provided with scoop buckets of a type known in the art, with the end surfaces of the buckets being provided with apertures which would align with exit apertures formed in the plates enclosing the ends of the recording member. The apertures in the end surfaces of the buckets would be sealed by the fixed end plate during rotation of the buckets, with developer flowing from the buckets to the exterior of the drum upon alignment of the bucket apertures with the apertures in the end plates of the drum. The buckets are preferably inclined toward the ends. of the drum, as hereinabove described. Alternatively, the drum 10 could be provided with end plates which are rotatable therewith and are in rotational engagement with the fixed end plates 53. The movable end plates, in the area of each of the baffles defining a bucket, would be provided with an aperture which would be rotated into alignment with the exit apertures in the fixed end plates 53 for withdrawal of the developer. The design of the hereinabove described conveying means and various others should be apparent to those skilled in the art from the teachings herein.

As another modification, as shown in FIG. 5, the drum 10 may be provided with a central drive means. The embodiment of FIG. 5 is identical to the embodiment illustrated in FIGS. 1 4, except for the replacement of the external drive means with a central drive means and, therefore, like parts are designated by like prime numerals. Referring to FIG. 5, the interior of drum 10' is provided with longitudinally spaced sleeves 201 aligned with the axis of rotation of drum 10, each of which is supported by three circumferentially spaced radial arms 202 rigidly secured to the interior surface of drum 10' between adjacent baffles 62'. A rigid drive shaft 203 extending along the axis of rotation of drum 10 is telescopically received in the spaced sleeves 201, with one end of the drive shaft 203 extending through an aligned aperture (not shown) in one of the end plates (not shown); the one end of the drive shaft 203 being drivingly connected to a suitable drive means, such as a motor (not shown), for rotation thereby and the other end of drive shaft 203 being unsupported. The spaced sleeves 201 are in frictional driving contact with the drive shaft 203, and the drum 10' is supported by the drive shaft 203. In operation, the rotation of the drive shaft 203 which frictionally engages the aligned sleeves 201 effects rotation of the drum 10'. The operation of this modified embodiment is similar to the embodiment described with reference to FIGS. 1

Similarly, although the invention has been particularly described with reference to an electrostatographic recording member in the form of a rotatable drum, the invention is equally applicable to electrostatographic recording members having other designs and shapes. Thus, for example, the electrostatographic recording member could be in the form of a movable belt, of a type known in the art, in which case the ends of the belt would be suitably closed to provide a compartment for storing developer in the interior of the belt. The interior of the movable belt would be provided with suitable conveying means, for example, as described with reference to the embodiment illustrated in the drawings, for conveying developer to an exit port in the confined ends of the belt. The developer withdrawn from the exit port would then be conveyed, for example by chutes of the type hereinabove described, to the exterior recording surface of the belt to develop a latent electrostatic image formed thereon. The developer which has cascaded over the exterior surface of the belt could then be returned to the interior compartment, for example, by chutes of the type hereinabove described.

As still another modification, the developer withdrawn from the interior of the recording member may be directed to a hopper from which the developer is then cascaded over the latent image bearing surface of the recording member.

The hereinabove described modifications and others should be apparent to those skilled in the art from the teachings herein.

The present invention is particularly advantageous in that an electrostatographic machine incorporating the principles of the present invention would not require a large area for the development station which would permit a reduction in the overall size of the machine or result in more space for other components of the machine. In addition, the overall system is less complex and eliminates the necessity for separate drive means for conveying developer to a position for cascading thereof over a latent image bearing surface.

These advantages and others should be apparent to those skilled in the art from the teachings herein.

The present invention, as should be apparent from the hereinabove description is subject to numerous modifications within the spirit and scope thereof and, therefore, within the scope of the appended claims, the invention may be practiced in a manner other than as particularly described.

What is claimed is:

l.' Apparatus for developing a latent electrostato-graphic image, comprising: I

a movable electrostatographic recording member having an exterior surface on which a latent electrostatic image is formed and developed, said recording member having an interior compartment in which developer is stored;

outlet means for withdrawing developer from the interior compartment of said recording member;

first conveying means positioned in the interior compartment of said recording member for transporting developer therein to said outlet means;

second conveying means positioned exteriorly of said recording member for directing developer from said outlet means to and over said exterior surface of the recording member on which the electrostatic latent image is formed to effect development thereof;

inlet means for returning developer to said compartment in said recording member; and

third conveying means positioned exteriorly of said recording member for returning developer which has passed over said exterior surface to said inlet means.

2. The apparatus as defined in claim 1 wherein the first conveying means is attached to the interior surface of the recording member and is movable therewith.

3. The apparatus as defined in claim 1 wherein the first con veying means comprises a plurality of buckets connected to the interior surface of the recording member.

4. Apparatus for developing latent electrostatographic images comprising:

a hollow rotatable drum having an electrostatographic recording surface on the exterior thereof on which a latent electrostatic image is formed and then developed, the interior of the drum defining a compartment for an electrostatographic developer;

outlet means for withdrawing developer from the upper interior portion of the drum;

first conveying means connected to the interior surface of the drum and rotatable therewith for transporting developer from the lower interior portion of the drum to the outlet means;

second conveying means positioned exteriorly of the drum for directing developer from said outlet means to and over the exterior surface of said drum to develop an electrostatic latent image thereon;

inlet means for returning developer to the interior of the and a lower aperture defining the inlet means.

7. The apparatus as defined in claim .6 wherein said second conveying means comprises a first inclined chute positioned at the end plates adjacent the upper apertures for directing developer, by gravity, from the aperture to the exterior surface of the drum; and said third conveying means comprises a second inclined chute positioned below the first chute for directing developer, by gravity, which has cascaded over the exterior surface of the drum to said lower aperture for return to the interior of said drum.

8. The apparatus as defined in claim 7, wherein said buckets comprise: a radial baffle fixedly mounted to the interior of the drum, said baffle being coextensive with the length of the drum and rotatable therewith, said baffle extending radially inwardly at an acute angle, in the direction of rotation, with respect to the interior surface of the drum, the radial free end of the baffle defining an open space between the interior surface of the drum to define said bucket, the surface of the baffle facing the surface of the drum being in alignment at its longitudinal ends with the upper apertures of said end plates dur ing rotation of said baffle past said apertures, whereby during rotation of said buckets, in the lower portion of the drum, developer is scooped into the buckets and carried by the buckets to the upper portion of the drum, and in the upper portion of the drum, developer flows from the bucket at its longitudinal ends through the upper aperture onto the first chute upon alignment of said surface of the baffle with the upper aperture. 7

9. The apparatus as defined in claim 8, wherein said surface of said baffle is inclined away from the center thereof toward its longitudinal ends.

10. The apparatus as defined in claim 9, wherein said first and second chutes are fixedly mounted to said end plates, said first chute comprising: outer ramps extending along the end plates downwardly and outwardly from the upper apertures in the end plates to beyond the outer surface of said drum and an inner ramp coextensive with the exterior surface of the drum extending downwardly and inwardly from the outer ramps to a point closely adjacent the external surface of said drum and above the horizontal axis of said drum, said second chute comprising an inner ramp coextensive with the outer surface of said drum and extending outwardly and downwardly from a point closely adjacent the external surface of the drum which is below the horizontal axis thereof and outer ramps extending along the end plates downwardly and inwardly from the inner ramp of said second chute to the lower apertures in said end plates.

11. The apparatus as defined in claim 10, and further comprising: a development electrode mounted between the first and second chutes adjacent the exterior surface of said drum and coextensive therewith.

Claims

1. Apparatus for developing a latent electrostato-graphic image, comprising: a movable electrostatographic recording member having an exTerior surface on which a latent electrostatic image is formed and developed, said recording member having an interior compartment in which developer is stored; outlet means for withdrawing developer from the interior compartment of said recording member; first conveying means positioned in the interior compartment of said recording member for transporting developer therein to said outlet means; second conveying means positioned exteriorly of said recording member for directing developer from said outlet means to and over said exterior surface of the recording member on which the electrostatic latent image is formed to effect development thereof; inlet means for returning developer to said compartment in said recording member; and third conveying means positioned exteriorly of said recording member for returning developer which has passed over said exterior surface to said inlet means.

3. The apparatus as defined in claim 1 wherein the first conveying means comprises a plurality of buckets connected to the interior surface of the recording member.

4. Apparatus for developing latent electrostatographic images comprising: a hollow rotatable drum having an electrostatographic recording surface on the exterior thereof on which a latent electrostatic image is formed and then developed, the interior of the drum defining a compartment for an electrostatographic developer; outlet means for withdrawing developer from the upper interior portion of the drum; first conveying means connected to the interior surface of the drum and rotatable therewith for transporting developer from the lower interior portion of the drum to the outlet means; second conveying means positioned exteriorly of the drum for directing developer from said outlet means to and over the exterior surface of said drum to develop an electrostatic latent image thereon; inlet means for returning developer to the interior of the drum; and third conveying means positioned exteriorly of said recording member for returning developer which has passed over said exterior surface of the drum to said inlet means.

5. The apparatus as defined in claim 4 wherein said conveying means comprises a plurality of circumferentially spaced buckets.

6. The apparatus as defined in claim 5 and further comprising fixed end plates at each end of the drum, said fixed end plates including an upper aperture defining the outlet means and a lower aperture defining the inlet means.

7. The apparatus as defined in claim 6 wherein said second conveying means comprises a first inclined chute positioned at the end plates adjacent the upper apertures for directing developer, by gravity, from the aperture to the exterior surface of the drum; and said third conveying means comprises a second inclined chute positioned below the first chute for directing developer, by gravity, which has cascaded over the exterior surface of the drum to said lower aperture for return to the interior of said drum.

8. The apparatus as defined in claim 7, wherein said buckets comprise: a radial baffle fixedly mounted to the interior of the drum, said baffle being coextensive with the length of the drum and rotatable therewith, said baffle extending radially inwardly at an acute angle, in the direction of rotation, with respect to the interior surface of the drum, the radial free end of the baffle defining an open space between the interior surface of the drum to define said bucket, the surface of the baffle facing the surface of the drum being in alignment at its longitudinal ends with the upper apertures of said end plates during rotation of said baffle past said apertures, whereby during rotation of said buckets, in the lower portion of the drum, developer is scooped into the buckets and carried by the buckets to the upper portion of the drum, and in the uPper portion of the drum, developer flows from the bucket at its longitudinal ends through the upper aperture onto the first chute upon alignment of said surface of the baffle with the upper aperture.