US2786441A - Apparatus for applying electrostatic developer powder by means of a magnetic brush - Google Patents

Description

March 26, 1957 c J YOUNG 02,786,441

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APPARATUS FOR APPLTIN'G ELECTROSTATIC DEVEL POWDER BY MEANS OF A MAGNETIC BRUSH Filed July 20, 1953 2 Sheets-Sheet l @di fj" Z; l I INVENTOR. A id Marla; (fl 5317 f; 43 66 BY .11 TTOR NE 1 March 26, 1957 c, J YOUNG 2,786,441

APPARATUS FOR APPLYING ELECTROSTATIC DEVELOPER POWDER BY MEANS OF A MAGNETIC BRUSH 2 Sheets-Sheet 2 Filed July 20, 1953 INVENTOR.

cl Yzzag )1 TTOR NE Y United States Patent Ofice 2,786,441 iatented Mar. 26, 1957 APPARATUS FOR APPLYENG ELECTROSTATIC DEVELOPER PGWDER BY MEANS OF A MAG- NETIC BRUSH Charles J. Young, Princeton, N. J., assigncr to Radio Corporation of America, a corporation of Delaware Application July 20, 1953, Serim No. 369314 11 Claims. (Cl. lid-51) This invention relates to electrostatic printers, and more particularly to a novel means for continuously sweeping a brush or brushes composed of filaments or bristles of a ferromagnetic type of developer mix across the record receiving surface of a recording member such, for example, as a continuously moving sheet or web of paper having a light sensitive or photoconductive surface.

Light projected through frames of film or drawings on tracing paper will impose a latent charge image upon the previously charged photoconductive sheet or web of an electrostatic printer. This web is in continuous motion in printers of the continuously operating type. Pigmented electroscopic powder, for example, may be supplied to the web so that the charge image can attract the powder coating which maltes it visible. A developer powder mix and method of application using a ferromagnetic carrier is set forth in the copending application for Letters Patent of the United States of Harold G. Greig, Serial No. 344,123, filed lvlarch 23, 1953.

An improved ferromagnetic brush arrangement having magnet poles above and below the photoconductive sheet or web is set forth in the copending application for Letters Patent of the United States of Edward C. Giaimo, In, Serial No. 365,152, filed June 30, l53.

A ferromagnetic brush which drops and reforms its bristles to provide uniform mixing of carrier and developer is set forth in the copending application for Letters Patent of the United States of Edward C. Giaimo, IL, Serial No. 365,151, filed June 30, 1953.

In continuously operating electrophotographic apparatus to achieve rm production speed the web must move very rapidly. The method and equipment for applying developer powder must be highly efficient to uniformly coat color the image consistently, especially where the web is ery wide. Reproduction of large sheets of mechanical drawing is a particularly demanding type of service.

An object of this invention is to provide a continuously sweeping brash of ferromagnetic developer mix for an electrostatic printer which will have an even powder distribution bristle formation completely across the entire record receiving surface. A closely related object is to provide plity of spaced moving brushes to perform a similar auction.

Another object of this invention is to provide an improved carrier for a ferromagnetic brush which will thoroughly shed and reform its bristles.

Another object of this invention is to provide a developer powder applicator brush for a continuous electrostatic printer which will provide even coloration completely across extremely wide webs of paper.

A further object of this invention is to provide a continuously sweeping electrostatic printer developer brush applicator of the ferromagnetic type which will provide substantially equal flux paths through all points of the brush so that bristle formation will be uniform throughout.

Still another object of the present invention is to pro- 2 vide continuousl sweeping developer powder applicator brush for a. printer of the electrostatic type using ferromagnetic bristles which drop and reform with a renewed supply of electroscopic powder supplying an even toner to powder ratio providing even coloration completely across a moving web.

A still further object of the present invention is to provide a. developer powder applicator brush of the ferromagnetic type for an electrostatic printer which will sweep completely across the surface of the moving web with bristles of uniform stifiness and size which contain a uniform toner to powder ratio giving even streak-free col on of tie image on the moving web of the photoconductive web.

A still further object of the present invention is to provide a ferromagnetic developer powder applicator brush for an electrostatic printer which will reliably, uniformly, and evenly color the image on a photo conductive sheet.

In one illustrative embodiment of the present invention, the sheet of photo conductive paper bearing the latent charge image passes between two magnets of opposite polarity. One of the magnets is above the sheet and the other of the magnets below the sheet. Two vertically mounted pulleys are mounted in the same plane at the ends of the lower magnets. An endless non-magnetic belt of thin hr 55, paper, or plastic passes around both these pulleys passes over the top of the lower magnet. The upper surface of the belt is adjacent the lower surface of the moving photo-conductive paper. The charge image is inprirted upon this lower surface. A horizontally rota tray carries a mixture of ferromagnetic powder and toner under and adjacent to these pulleys.

As the belt rotates from a position near the bottom or close to the surface of this rotating tray it enters the magnetic field between the two magnets. It, therefore, picks up bristles of the ferromagnetic powder which triboelectrically hold the toner.

A continuous brush of these ferromagnetic bristles passes across the moving surface of the web upon which the latent charge image is imposed. The higher potential charge image attracts the toner from the ferromagnetic bristles. A continuous brush, therefore, sweeps in a relatively narrow path across the entire surface of the paper. As this endless belt brush passes out of the magnetic field between the upper and lower magnets it drops the mixture of ferromagnetic powder and toner onto the rotating tray once more.

The supply of electroscopic powder or toner on the brush is depleted while it is passing across the paper. Toner is added to the mixture while the powder is upon the tray. The tray rotates carrying a replenished mixture of toner and ferromagnetic powder to the originating or picking-up pulley.

To provide even coloration completely across the page, two oppositely directed belts are used on extremely wide sheets. This insures that the portion of the web on the far side of the first brush stroke, which might receive an insufficient supply of toner, will be darkened by the freshly renewed toner in the second oppositely directed brush.

in the double belt arrange rent the web and belts pass within the gap between the ends of two abutting U-shaped magnets. The magnetic lines of flux pass twice through the web and belts in flux paths of uniform length across the width of the web. This provides a perfectly uniform distribution of lines of flux across the width of the web. As a result the bristles of ferromagnetic powder will therefore be uniform in stiffness and size completely across the width of the paper. A uniform powder coating is, therefore, applied no matter how wide a sheet is used.

Other objects and advantages of the present invention will become apparent to one skilled in the art from a reading of the Specification in conjunction. with the following drau ing'whercinf Figure l is a view in sectional elev t on of one form of apparatus in accordance with the cation providing a doublebelt continuous sweep developer powder applicator brush;

Figure 2 is a section in elevation taken through Figure 1 on the line 2-2 in thedirection of the arrows;

Figure 3 is a section in elevation taken through Figure 1 on the line 3-3 in the direction of the arrows;

Figure 4 is a plan view of another form of apparatus providing a double belt continuous sweep developer powder applicator brush; and

Figure 5 is a section in elevation taken through Figure 4 on the line 55 in'the direction of the arrows.

In Figures 1, 2, and 3 is illustrated one embodiment of the present invention. Reference to these figures will show pole pieces and 11 above the photo conductive web or sheet of paper 12. Permanent magnets 15 of Alnico, for example, join the pole pieces it) and 11.

The structure including the pole pieces 16 and 1% is supported in any suitable manner, as by brackets 91 secured to any static-nary part 92. Below the web 12 are located pole pieces 17 and 18. Magnets 2! connect the pole pieces 17 and 1-8. A suitable support such as T shaped pedestal 93 extending from the base 42 carries the pole pieces 17 and 13. The polarity of magnets 15 and 28 is so directed. that pole pieces 19 and 17 will be respectively of opposite polarity and 11 and 13 will also be respectively of opposite polarity.

Extensions 21 and 22 are mounted at the ends of pole pieces 17. Similar extensions (not shown) are provided at the ends of the pole piece 18. Shafts 24 and 25 are fixed within these extensions. These extensions are made of iron as are the pole pieces.

Iron pulleys 27 and 28 rotate on shafts 24 and 25 respectively. The circumference of the pulleys tits closely within the cutout ends of the pole pieces so that the lines of flux in the pole pieces continue across the short gap and through the pulleys and the pulleys are included in the flux path circuit. An endless flexible belt 3% made of a non-magnetic material through which lines of flux will pass, such, for example asplastic or brass, is looped around pulleys 27 and 28. Idler pulleys 31 and 32 on brackets 33 and 34 keep the belt 3% tight on the pulleys.

A similar arrangement of pulleys and a belt 35 provided'for the pole piece 18, one of these pulleys, namely pulley 23, appears. in Figure 3. A pole piece extension 36 is secured to the end of polepiece It? and carries an adjustable arm 14 on a pivot screw 83. approaches the far side of pulley 27. A similar pole piece extension 37 is secured to the other end of pole piece 11 and its'adjustable arm 84 on pivot screw 36 approaches the far side of pulley 23. Brass facing strips 16 and 2d are secured to the side and ends of arms 14 and 34.

Tray 40 rotating on a centrally located bearing ring 41 is supported on the base 42, by suitable supports such as the pedestals 8%. A supply of ferromagnetic developer. such as finely divided iron mixed with developer powder or toner is carried in depression 43 annularly disposed on tray 40.

In operation, the paper 12 moves continuously through the magnetic field in the direction shown.

Lines of flux pass in a closed circuit from the north polarity pole pieces through the web into t e south polarity pole: pieces. As the. pulleys rotate, the upward rotating pulleys 27 and 23 pick up or attract magnetically the ferromagnetic mix in the high flux density gap between the pulleysv 27 and 23 and the arms 14 and 84 respectively. The brass facing strips 16 and 26 prevent the mixfrom sticking to the iron arms 14 and 34.

The coated paper 12. is provided with a distributed electrostatic charge over one of its surfaces which. is exposed to the influence of an; electrostatic charging device .6; The" charging device may comprise a plurality of The arm 14 fine wires 9-8 carried by a pa of spaced insulating membe'rs99 only one of the latter appearing in Fig. 2 of the drawing. It will be understood that the insulating members are spaced in such a manner that the wires 98 span the width of the paper sheet 12. It will be understood that light is preferably excluded during the charging step. A source of high voltage D. C. (not shown) is connected to the wires 98 so as to give them a negative charge with respect to a ground plate or platen 102.

The charged paper is exposed to a light image from a luminous image projector'104 of any known kind. The paper bearing the charge-image or latent image in the form of an electrostatic charge then passes through the magnetic field or fields of the developer powder applying apparatus described previously in detail. A guide plate 1% guides the paper web 12' so that it is drawn through the magnetized zone at the proper level and past a heater or fuser 108 where the developer powder is'melted and fused to the paper surface to form a permanent image.

Reference character 109 indicates an electric motor of any suitable kind or type which drives a feed roller 112. A pressure roller 116 serves to press the paper against the roller 112 so that it may be drawn through the several recording stages or stations described above.

The pulley 28 is driven by suitable means such as a motor 118. As shown, the pulley rotates on the shaft 25. The belt 36 is driven and passes over the pulley 27 which serves as the driven pulley. The pulley 23 is driven for rotation in the opposite direction by a motor 119. be understood that the feed roller 112, the pulley 28 and the pulley 23 may be driven from a single motor and any power transmission system known to the art.

The ferromagnetic powder will be arranged in a bristle like array and form a continuous brush sweeping across the lower face of the photo-conductive web. This lower face carries the latent charge image. The charge of the image will attract toner powder from the lower potential ferromagnetic bristles. The pigmented toner will color the charge image so that, on the application of heat, a permanent picture of the image will be fused to the paper.

As the brush sweeps across the moving web, the supply of toner will be steadily depleted. As the belts move on to the downward rotating pulleys 23 and the pulley (not shown) beside the pulley 27 and out of the high flux density region the toner depleted ferromagnetic powder will start dropping into the tray 40. When the belt leaves the pulley circumference to travel under the pole piece to the pick-up pulley it has passed out of the flux region and has shed all its ferromagnetic bristles. The tray 4%) rotates on bearing 41, and may be turned by hand or be driven. The tray 40 thus comprises a transporting means for the developer mix. The powder will therefore be carried from one pulley to the other. As the tray 4% rotates, a supply of toner powder is added to the mixture. Toner powder may be supplied from a hopper 5 having a spout 6 disposed to discharge toner powder onto the tray 46. This picking up and dropping operation mixes the toner with the ferromagnetic carrier component so that a uniform ratio mixture will be supplied to the brush.

Since the belts are made of a nonmagnetic material, a very thorough dropping and reforming will occur. In brushes where the ferromagnetic carrier bristles are suspended from a magnetic substance like soft iron, which may retain a quantity of residual magnetism, the reformation of the brush may not be complete.

By nonmagnetic material. is meant herein. nonsferromagnetic materials. Paramagnetic and diamagnetic materials where the magnetic effect is very slight are herein as a matter of convenience considered to be nonmagnetic because they will function similar to nonmagnetic materials when used as conveyor belts to carry ferromagnetic bristle brushes of this type.

Since the pulleys 27 and 28 rotate in one direction, conveyor belt. 30 will. rotate as shown. The conveyor It will.

belt 35 rotating on pulleys 23 and on the pulley beside the pulley 27 will move across the web in the opposite direction. The concentration of toner will be maximum as the brush first starts to move across the web. If there were only one conveyor moving across extremely wide sheets of paper such as large sheets of mechanical drawing, the coating on the side of the paper where the brush first contacts could possibly be heavier and darker than on the far side. By use of the two counter-directed bristle conveyor belts or brushes, coloration will be of even darkness completely across the moving web with depletion in each brush counter-balancing the initial concentration in the other.

A closed fiux path is provided through pole piece to pole piece 17 to magnets 20, to pole piece 18, to pole piece 11 and back to pole piece it through magnets 15 across the entire length of the belts. Equal length flux paths assure uniform flux distribution completely across the web. The moving brush, therefore, has bristles which are uniform in height and stiffness at any point in its traverse of the web. Even brushing action helps provide even coloration.

Brass plates 123 to 126 are provided on lower pole pieces 17 and 18 and brass sides on plates 121, 122, 127 and 128 are provided on all of the pulleys to prevent the bristles from overlapping around the edges of the pole pieces and pulleys. Since the lines of flux do not travel through these brass pieces, the bristles cling only to the central portion of the belt over the iron leaving clean edges on the pulleys and pole pieces and at the edges of the belts as stated above. Proper concentration of bristles toward the center of the pole pieces and pulleys is therefore provided. This prevents wasteful loss of toner over the edges of the belt and pulleys.

Where a web of lesser width is fed through the developer brush, a developer brush which only has one of these endless conveyor belt brushes might be utilized. In a short traverse the brush would not be so depleted of toner in a single traverse at the end of its travel. A practically even distribution of toner across the face of narrow webs will be achieved Without the necessity of having two such opposed moving belts. With relatively narrow paper a magnetic flux return path around the side of the paper would affect the uniformity in flux distribution to a lesser degree.

Another embodiment of the invention is illustrated in Figures 4 and 5. In this illustrative example a magnet 50 is placed above the paper 52 while a pole piece 51 is located below the paper. The magnet 50 is of an elongated horse shoe shape and its polar edges are oppositely disposed with respect to the elongated upstanding projections 161 and 162 of the pole piece 51. The pole piece 51 is suitably supported from any stationary part 163. The charged latent image is on the upper surface of the paper 52. Shafts 53 and 54 support sprocket wheels 55 and 56. The sprocket wheels and shafts are made of a nonmagnetic material to prevent attraction of the mix. The shafts are mounted in any suitable stationary hearing (not shown). These sprocket wheels carry a flexible belt 60 which may be of the type known as timing belt. Small iron pole pieces 61 are fixed to the outer surface of the belt on by rivets s2. The shaft 53 is rotated by a motor 63 through any suitable mechanical coupling device (not shown in detail). Shoes 57 and 58 of a suitable bearing metal such as, for example, bronze are secured to the lower edges of the magnet. The pole pieces 51 are attracted by the magnet and slide against these shoes. Circular trays 65 and 66 rotate with the sprocket wheels 55 and 56 as the paper 52 carrying the latent charge image on its upper face moves through the magnetic field. The paper 52 may be supported and moved as described above. The belt moves across the paper in one direction and then retraces its way across the paper in the opposite direction. Ferromagnetic developer mix is suspended from the pole pieces 61 on the belt and form a bristle-like array or brush of developer mix which sweeps across the surface of the paper.

The pole pieces will enter the magnetic field before they start to sweep across the paper. This is accomplished by diagonally, shaping the ends 171 and 172 of the magnet 50 and, correspondingly, the ends of the pole piece 51. A mixture of ferromagnetic component and toner powder held triboelectrlcally within the ferromagnetic mix is picked up by the pole pieces 61 from the trays 55 and 56. It is picked up at regions 68 and 69 W e the ieces 61 start to pass within the magnetic field existing in the gap between magnet 50 and pole pieces 51. The mixture is dropped at 7'3 and 71 regions after the pole pieces leave the magnetic field in the gap. The magnets cover more of the trays on the pick up cycle than at the drop points to assure that an adequate supply of developer mix is picked up before the pole pieces 61'. start to sweep across the moving surface of the paper.

The flux path will be continuous through the paper or web completely across the length of magnet 50 and pole piece 51 providing even distribution of flux and even bristle formation completely across the surface of the paper. Double belt counter-sweeping action is also provided. Coloration of uniform texture even on very wide webs will be achieved by the uniform bristle formation as well as the compensating depletion of the counter-moving brushes.

On very narrow Webs a sweep type of brush with only one traversing belt might be desired. if so, in either the nonmagnetic belt or ma netic belt embodiment one of the conveyor belt transverses might be eliminated or routed away from the web surface and the respective brushless north and south poles of the magnet and pole piece brought extremely close to the surface of the paper forming a very narrow gap through which the paper moves. This gap would be located in the direction to allow the paper to move through the gap before it moves through the brush, such as for example between pole pieces 11 and in Figure 2 or between the south pole of magnet 50 and end 162 on pole piece 51 in Figure 5. This prevents the gap from becoming clogged with bristles of ferromagnetic powder. A perfectly uniform flux distribution across a single traversing conveyor would be provided in this form of the invention.

The nonmagnetic belt type of moving brush illustrated in Figures 1, 2, and 3 might be equipped with two small rotating trays similar to the ones in Figures 4- and 5. This would allow a more compact arrangement since the tray it? might occupy a prohibitive amount of space.

What is claimed is:

l. Electrostatic printing apparatus comprising means for moving a photoconductive web having a latent charge image imposed thereon along a predetermined path, an endless belt, means for supporting and driving said belt whereby one run thereof traverses along a path at right angles to the path of said web and with on run of said belt in close proximity to the charged surface of said web, a magnet structure for produ a ma netic flux throughout the width of said Web and cngtnv of said belt, one run of said belt being within said magnetic flux and the remaining run being outside of said magnetic flux, transporting means disposed in cooperative relation with two regions of said one run of said belt, said magnet structure having an extension for developing a magnetic flux a. one of said regi for formation of a ferromagnetic developer mix into a bristle-l array on said one run of said belt, supply means for said transporting means for adding developer powder to the ferromagnetic mix in makeup quantity, and means whereby in the other of said regi .5 said ferromagneg mix and unused developer power are released onto said transporting means for transport to said first mentioned region.

2. The combination set forth in claim 1 wherein the belt is comprised of a nonmagnetic material.

3. The combination set forth in claim 1 wherein guide greater;

means -are providedifor said endlessbelt, saidguide meansdisposed for direeting'said belt in its path across means located adjacent to one surface of said web and substantially spanning the width thereof, magnetic pole means of polarity opposite to saidfirst pole means located adjacentto the opposite surface of said web substan tially spanningthe width thereof forming together with said-liirst pole means a gap through which'lines of 'flux emanating from one of said poles pass through the web into the other of said poles, an endless conveyor a portion of which is located between said poles traversing substantially the length of said gap and passing across the moving surface of said-web carrying a charge of a latent image, ferromagnetic powder held to the surface of the conveyor adjacent said web formed in a bristle-lil e array extending from said conveyor by said lines of flux, said bristles 'tribo-electrically holding a quantity of pigmented eieotroscopic developer powder, said bristles brushing continuously across the charge of a latent image on the surface of said web whereby developer powder is supplied tor attraction to said latent image on said web.

5. The combination set forth in claim 4 wherein said endless conveyor is comprised of nonmagnetic material.

6. A magnet structure for establishing throughout the width of a moving photoconductive web of a continuous operating electrostatic printer a uniform distribution of lines of magnetic flux comprising magnet means for providing said lines of magnetic flux, said magnet'means having one portion disposed for creating in close proximity to'the surface of said web across the width of said web a relatively narrow region of one polarity, said magnet means having a second portion disposed in close proximity to said web creating a similar relatively narrow region of polarity opposite to that of said first region, said second region being substantially parallel to said first region across the width of said web, return path means of magnetic material provided on the opposite side of said web from said magnet means providing a conductive return path whereby lines of flux emanating from apole of said magnet means will pass through one of said pole regions on sai web into said return path means through said return path means through the other pole region on said web back into the other pole of said magnet means.

' 7. In an electrostatic printing apparatus, means for supporting and moving a photoconductive web bearing a latent electrostatic charge image, means for providing a developer powder applicator brush which continuously sweeps over a photoconductive web supported and moved by said first named means comprising magnetic means for emanating lines of fiux disposed in close proximity to said surface, said magnetic means creating narrow band regions of opposite polarity across said web, a; structure of magnetic material disposed adjacent to the opposite side of said web from said magnetic means providing a path for lines of flux emanating from one of said regions topass through the web into the structure back through the web into another of said regions, an endless conveyor means passing within said polar regions across the surface of said web, means to provide a ferromagnetic developer mix to be formed in a bristle-like array extending-from said conveyor by said line of flux, said array brushing developer mix in intimate contact with the record carrying surface of said web.

8.'The combination set forth in claim, 7 wherein said endless conveyor means is comprised of non-magnetic material,

9 -ln an electrostatic printer, means to support a sheet bearing an-T electrostatic charge. image, means to: provide. a 'movingxbrushrofi ferromagnetic powder arranged in. bristle-.likearray for traversing asheet supported by said.

sheet'supportingmeans, said second uamedmeanscom: prisinga magnet means providing a gap through which lines ofmagnetic fluxpass, a circulating endlessbelt of: nonmagnetic materiaha: portion of said belt circuit being.

positioned within said gap, said sheet supporting means presenting said sheet adjacent saidportion of said belt circuit, and means for supplying ferromagnetic powder to.-

a surface of. said belt at a region within said gap.

10; Means for providing a developer powder applicator. brush which continuously sweeps the moving photoconductive web of an electrostatic printer having a charge of a latent-image, imposed thereon comprising magnetic:

pole'means located-adjacent to one surface of said web and substantially spanning the width thereof, magnetic pole means of polarity opposite to said first pole means located adjacent to the opposite surface of said websub- I stantiaily spanning the width thereof forming together withsaidfirstpolemeansa gap through which'linesof.

flux emanating from one of said poles pass through the webinto the other ofsaid poles, an endless conveyor a portion of which is located between said poles traversing. substantially the length of said gap and passing across the moving surface of said web carrying a charge of a latent image, ferromagnetic powder held to the surface of the conveyoradjacent said. web formed in a bristlelike array extending'from said conveyor by said lines of it flux,- said bristles tribo-electrically' holding a quantity of pigmented electroscopic developer powder, said bristles brushing continuously across the charge of a latent'image on the surface of said web whereby developer powder is supplied for. attraction to said latent image on said 1 web, and guide means for directing said conveyor across said web in two separate oppositely directed traversals' across said web, a structure of magnetic material disposed-adjacentto the opposite side of said web from said magnetic means providing a path for lines of flux emanating from-one-of said regions to pass through the web into the structure back through the web into another of saidregions, an endless conveyor means passing within said polar regions across the surface of said Web, ferromagnetic developer mixformed in a bristle-like array extending from said conveyor bysaid line of flux, said bristles brushing developer mix in intimate contact with the record carrying surface of said web, and said con veyor passing across the web in one direction within one of said narrow band polar regions and sweeping back across the web in its return traverse within another of said narrow band, regions.

References Cited in the file of this patent 'UNITED STATES PATENTS 573,485 Sanders et al. Dec. 22, 189.6 1,094,125 Cousins Apr. 21, 1914 1,140,642 Weingartner et al. May 25, 1916 1,828,958 Canton, Oct. 27, 1931 2,239,970 Osborne Apr. 29, 1941 2,357,809 Carlson .a Sept. 12, 1944 2,591,121 Blind Apr. 1, 1952' 2,618,551 Walkup Nov. 18, 1952 2,624,652 Carlson Jan. 6, 1953 2,705,199 Clark Mar. 29, 1955 FOREIGN BATENTS 4455137 France Aug. 27; 1912'

Claims (1)

1. ELECTROSTATIC PRINTING APPARATUE COMPRISING MEANS FOR MOVING A PHOTOCONDUCTIVE WEB HAVING A LATENT CHARGE IMAGE IMPOSED THEREON ALONG A PREDETERMINED PATH, AN ENDLESS BELT, MEANS FOR SUPPORTING AND DRIVING SAID BELT WHEREBY ONERUN THEREOF TRAVERSES ALONG A PATH AT RIGHT ANGLES TO THE PATH OF SAID WEB AND WITH ONE RUN OF SAID BELT IN CLOSE PROXIMITY TO THE CHARGED SURFACE OF SAID WEB, A MAGNET STRUCTURE FOR PRODUCING A MAGNETIC FLUX THROUGHOUT THE WIDTH OF SAID WEB AND LENGTHWISE OF SAID BELT, ONE RUN OF SAID BELT BEING WITHIN SAID MAGNETIC FLUX AND THE REMAINING RUN BEING OUTSIDE OF SAID MAGNETIC

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