US2684902A - Image transfer mechanism for electrostatically adhering images - Google Patents

Description

July 27, 1954 Filed Nov. 23, 1951 FIGZ C. IMAGE TRANSFER MECHANISM FOR ELECTROSTATICALLY R MAYO ET AL 2,684,902

ADHERING IMAGES 3 Sheets-Sheet l POTENTIAL S U P PLY LOW VOLTAGE HIGH TAGE

25 27 32 4 l6 l8 l3 INVENTORS CLYDE R. MAYO WILLIAM G. LEWlS FWMQ ATTORNEY July 27, 1954 MAYO ET AL 2,684,902

C. IMAGE TRANSFER MECHANISM FOR ELECTROSTATICALLY ADHERING IMAGES Filed Nov. 25, 1951 3 Sheets-Sheet 2 l NVE N TO R S CLYDE-R. MAYO WILLIAM G. LEWIS EMA. Y L

ATTORNEY July 27, 1954 MAYO ET AL 2,684,902

C. IMAGE TRANSFER MECHANISM FOR ELECTROSTATICALLY ADHERING IMAGES Filed Nov. 25, 1951 3 Sheets-Sheet 3 GLYDE R.MAYO WILLIAM G. LEWIS BY SH LQI ATTORNEY Patented July 27, 1954 IMAGE TRANSFER MECHANISM FOR ELEC- TROSTATICALLY ADHERING IMAGES Clyde R. Mayo and Willi N. Y., assignors to The ester, N. Y.,

am G. Lewis, Rochester, Haloid Company, Rocha corporation of New York Application November 23, 1951, Serial No. 257,872

2 Claims. 1

This invention relates to paper or sheet feeding, placing or advancing mechanisms, and to the combination of such mechanisms with plates or surfaces can'ying pigment or powder images to be transferred and electrostatic transfer elements to effect transfer of such images to paper or other sheet material.

An important application. of the mechanisms herein disclosed resides in their use in equipment for electrophotography, now commonly called xerography, in which an electrostatic latent image is formed on a sensitized photoconductive surface, the image is developed with a finely-divided material, such as a pigmented powder, and then the powder or other material is transferred to paper or other sheet material Where it can then be affixed, if desired, to form a permament image.

One transfer mechanism used in xerography includes an ion source, such as a high voltage corona electrode. The transfer sheet, i. e., a sheet of paper or other material, is placed on the photoconductive surface carrying the image ma.- terial, such as powder, pigment or other material, and the assembly is passed under the ion source, such as a grid of corona wires, which is spaced a short distance above the transfer sheet and is held at a high potential with respect to the support for the photoconductive surface. The transfer sheet is thus charged by the ion source to a potential sufficient to attract the image material and cause it to adhere electrostatically to the transfer sheet. The sheet is then stripped off the plate and carries the image with it.

During transfer by this method the electrostatic charge applied to the transfer sheet produces a fairly strong adhesion between the sheet and the image-bearing surface. In fact, once the leading edge of the sheet is pinned to the surface by the charge, the attractive force is adequate to pull the sheet along with the surface even if a substantial amount of drag or backpull is present in the feeding device for the sheets. It is of importance, however, that the sheet material be accurately and smoothly placed against the image surface so that there will be no subsequent shifting or slippage to produce smudging. If bulges or wrinkles are present when the sheet is first placed in position, such slippage and smudging may occur as the sheet is flattened against the surface. More serious than this is the situation in which a transfer sheet contains bulges and wrinkles which cannot be fiattened down by the electrostatic forces. This results in a deletion of part of the image since substantially direct contact is necessary to effect good transfer of the powder or other material.

Rollers pressed against the sheet during transfer have been successfully used in some applications. However, they do not completely eliminate the smudging and deletion problem. Thus, as the roller passes over the transfer sheet, it may sometimes cause a shifting of the sheet or some areas of it as they are flattened out. Moreover, since the ion source ordinarily does not charge the sheet until it has passed out from under the roller there is an opportunity for bulges and wrinkles to re-form after the sheet i released by the roller and before it is pinned down by the electrostatic charge. Another disadvantage of contact rollers resides in their tendency to pick up image material from the margins or from the image area when a transfer sheet is accidentally not fed into position. Such material will then be offset onto the back of a subsequent sheet. Very precise control of roller pressure is also required with contact rollers, since light pressure may fail to iron out all the bulges and wrinkles and heavy pressure may produce compression and ad hesion of the image material to the original surface and defeat electrostatic transfer to the overlying sheet, making cleaning of the plate difficult. Damage to the plate may also result.

The present invention contemplates novel sheet feeding mechanisms and combinations including such mechanisms in which the feeding mechanisms are spaced from an image surface from which an electrostatic transfer is to be made, and sheet material is fed against the surface in a curved condition, whereby wrinkles and bulges are eliminated prior to and during electrostatic transfer of an image material, and the problem of accurate matching of the sheet feeding to the image surface speed is reduced.

The preferred embodiment of the invention comprises mechanisms for feeding transfer sheets against surfaces carrying electrostatically deposited powder images preparatory to electrostatic transfer of such images to the sheets. Such surfaces may comprise electrophotographic or xerographic plate surfaces, xeroprinting plate surfaces and the like.

The invention comprises the features of construction, combination of elements, arrangement of parts, and methods of operation referred to above or which will be brought out and exemplified in the disclosure hereinafter set forth, including the illustrations in the drawing.

In the drawings:

Figure 1 is a vertical section showing a portion 3 of a xerographic processing unit embodying features of the present invention;

Figure 2 is a fragmentary section on the line 2-2 of Figure 1;

Figure 3 is a vertical section through another form of transfer device for transferring powder or pigment images from electrostatic image plates;

Figure e is a top view of the device of rigure 3 with parts broken away for illustration;

Figure 5 illustrates the invention applied to a cylindrical drum machine;

Figure 6 is a vertical section through a further modified form of the invention; and

Figure '7 illustrates preferred features of the invention.

While a preferred embodiment of the invention is described herein, it is contemplated that considerable variation may be made in the construction and arrangement of parts and in the method of operation without departing from the spirit of the invention. in the following description and in the claims, parts will be identified by specific names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit.

Referring to Figures 1 and 2 of the drawings, the invention is illustrated in connection with a xerographic processing unit in which a xerographic plate is is mounted in a sloping position on a stationary base plate H. The xerographic plate is arranged to be charged in the dark, then exposed to a light image projected onto its surface, then developed by cascading a developing powder composition over its surface to leave a powder image deposited upon the electrostatic latent image formed during the exposure. mechanisms for performing the exposing and developing steps are not here illustrated since they form no part of the present invention.

Ihe present invention contemplates mechanisms for effecting a transfer of the powder image formed on the plate l and such mechanisms are illustrated in the drawings wherein the moving carriage assembly i2 is arranged to travel up and down over the surface 'of the plate and to feed a sheet of transfer material, such as paper,

against he plate for the purpose of making a transfer of the powder image.

The carriage i2 comprises a pair of parallel vertical side plates is rigidly spaced by frame members such as L-shaped members I l and i to straddle the plate. A pair of stationary gear racks iii are mounted in spaced parallel relation along the sloping edges of base plate ll so that lower edges of side plates is extend down between the edge of the base plate and gear racks A pair of smooth tracks 5'! are provided along the inner sides of gear racks H5 and spaced pairs of idling rollers 58 and is mounted on pintles in side plates is are arranged to ride on the top and bottom faces of tracks H to guide the carriage assembly and keep it accurately positioned with respect to the face of the xerographic plate.

Carriage E2 is moved up and down over the plate by a drive mechanism comprising reversible electric motor as and a drive chain 2!, which drives a pair of endless chains 22, running on spaced sprockets 23 on shafts 2 which extend across the machine underneath the plane of the plate and beyond the upper and lower ends of the plate. The chains 22 are bolted to the lower edges of side plates 53 of the carriage so that travel of the chains 22- raises or lowers carriage 52 along its tracks, depending upon whether chains 22 are rotated in a counterclockwise or a clockwise direction (as viewed in Figure 1). Motor 28 may be controlled by a manual switch, or an automatic cycling circuit, and travel-limiting switches may be provided at the top and bottom of the tracks to deenergize the motor when the carriage reaches the end of the track.

Carriage 52 carries a corona discharge electrode comprising a grid of fine wires so which are stretched across the plate is in a horizontal direction, the grid being parallel to the plate surface and spaced from it a short distance, such as Grid 3%! is connected to a high voltage source 35 such as a transformero'ectifier system capable of supplying several thousand volts potential, for example, 7,090 volts, to the grid wires 39. The wires are supported at their ends on a pair of spaced insulating blocks 32 mounted under a flange of frame member I l. The grid 81! consists of three parallel corona emission wires uniformly spaced from the plate ill and a fourth parallel corona wire 33 is also connected to the high voltage source but is mounted slightly closer to the plate surface. A control grid of wires 313 which is formed of larger diameter wires, is supported from blocks 32 between grid at and the plate. Grid 3 does not however, extend in front of corona wire 33. Control grid 3 is connected to a lower voltage terminal 35 of the high voltage supply so that grid Ed is held at a potential between that of corona wires to and ground. Thus a potential of about 400 or 560 volts may be used on grid This effects a measure of control over the potential of charge appliedto the photoconductive insulating coating on xerographic plate is by corona wires 36. Thus when the potential of the coating reaches substantially the voltage of grid the flow of charged ions to the plate substantially ceases. A grounded conductive shield 3% is mounted behind the corona wires 38 and 33 in order to improve the characteristic of the corona discharge.

The corona discharge assembly just described may be used for charging xerographic plate 59 preparatory to exposure to a light image and the same corona may subsequently be used for effecting electrostatic transfer of the image to a sheet of transfer material. During charging of the plate the carriage is preferably advanced upward over the plate surface so that corona wire 33 precedes wires 3% and the control grid 34 over the plate.

Since corona wire 33 is not shielded by grid 34 its rate of charging the plate is rapid and it serves to charge the plate up to substantially the desired potential. The rate of travel of the carriage is sufiiciently great so that there is no danger of overcharging from the single corona wire. Following wire 33 the shielded corona wires 33 add further charge to the plate surface under control of grid 55 1 so that a uniform and controlled potential is thus applied to plate.

After exposure and development of the image, carriage I2 is again brought to the bottom of the plate is in preparation for transferring the powder image to a sheet of paper or other transfer material.

The transfer mechanism, embodying features of the present invention, comprises a pair of sheet feed rollers 37 and 38 for receiving and feeding a sheet of paper or other transfer material against the xerographic plate and the powder image carried by it and under the corona discharge assembly. The sheet feed rollers are spaced from the plate surface and are arranged to feed the sheet against the plate at a substantial angle so that the sheet is bowed into a substantial curve just preceding its point of contact with the plate and just prior to its passage under the corona discharge assembly. The rollers are driven by gears cooperating with gear racks it at a surface speed at least equal to the rate of travel of the carriage and preferably slightly in excess of it so that the bow in the sheet eing fed against the plate is increased slightly during carriage travel, all of which has the beneficial effect of pressing the transfer sheet more firmly against the plate as travel proceeds.

Feed roller 3's is in the form of a sleeve on a horizontal shaft 25 which runs in bearings 26 located in side plates is of the carriage at a position above the corona assembly. A spur gear '27 is keyed to each end of shaft 25. A pair of pinion gears 28 are suported on pintles 29 on the carriage in positions to mesh with gear racks l6 and with spur gears 27. As carriage i2 is driven up and down the tracks by motor 28, shaft 25 is rotated at a speed which is arranged to give a surface speed to roller 31 which is at least equal to, and preferably 0.5 to 5% greater than the speed of the carriage. This is accomplished by making the diameter of feed roller 3! equal to or slightly larger than the pitch diameter of spur gears 2?.

Roller 38 is mounted parallel to roller 31 with surface in contact with roller 3'! so as to be driven by it. The tangent plane at the line of contact is substantially vertical so that it intersects the surface of plate ill at an acute angle, and at a position just ahead of corona wire 33. Shield 36 is preferably bent downward and bevelled inward along its upper margin, as shown, to terminate at an edge just above the plate surface providing a small clearance, such as ,4 at substantially the line of intersection between the tangent plane and the plate surface. Rollers 3'! and are preferably surfaced with rubber layers 39 and 4e respectively, although in some cases other surfacing materials may be used or rubber may be applied to one of the rollers and the other may be provided with a knurled metal surface.

In the transfer operation, when a powder imag has been produced on plate as and carriage i2 is at the lower end of its path oftravel, the operator inserts the end of a sheet of paper down between rollers 3'! and 38 and energizes motor as to start the travel of the carriage upward over the plate. As travel begins rollers and 38 grip the leadingedge of the sheet and feed it downward into contact with plate it at an acute angle with the plate surface. As travel continues, the leading edge of the sheet is fed under the turned-down flange of shield 35 and comes under the influence of the corona discharge from corona wire 33 and subsequently from corona wires As soon as the transfer sheet passes into the corona discharge zone an electrostatic charge is deposited on the back of the sheet by the electric discharge from the corona wires and the sheet is attracted tightly against the of plate is by electrostatic attraction. Fhis brings the section of the transfer sheet which is between rollers 3i and 38 and the surface of the plate into the form of a curve or channel which effectively smooths out wrinkles bulges which may be present in the sheet material and brings the sheet against the plate surface smoothly and uniformly along a line extending across the width of the plate just ahead of the corona assembly. At the same time, or immediately thereafter, the corona discharge deposits a charge on the sheet to pin it smoothly to the plate surface and also to effect a transfer of the powder image to the transfer sheet.

As the carriage i2 continues to advance upwardly, the entire transfer sheet is fed progressively against the plate and adhesion of the powder or other transfer material to the sheet is effected. The carriage is preferably arranged to continue its travel above the top edge of the plate for a sufiicient distance to enable the top edge of the transfer sheet, which finally lies flat, on the plate surface, to be reached by the operator. It is then possible for the operator to grasp the upper edge of the sheet and peel the sheet from the plate with its attached powder image. The sheet may then be placed in an oven or fed through a suitable fusing device to affix the powder to the sheet by fusion and form a permanent fixed image. The plate may be subsequently cleaned of any residual powder by any suitable method and the cycle repeated to produce further copies by recharging, exposure, development and transfer.

Figures 3 and 4 illustrate a transfer apparatus suitable for making transfers from movable plates which can be fed through the machine along with paper or other transfer material. This transfer device comprises a frame 4i having a pair of vertical end plates 42 between which the operating parts are mounted. The frame is mounted in a generally rectangular op ning in a top panel 33 of a box-like base J3 in which are mounted a drive motor 44 and a high voltage corona power supply 55. Panel 53 forms a horizontal feed plate with its upper surface substantially midway between the top and bottom edges of frame it. is surfaced with sheet metal plates it which run lengthwise of the surface. Guide strips f ll; of L-shaped cross-section are mounted along the outer edges of plates 56 to guide an image plate through the transfer device a the operator slides it into the feed rollers and the rollers carry it through the transfer mechanism.

The operating parts mounted between plates 42 include a pair of input feed rollers and 48, a paper feed chute 49, paper edge guides his, paper feed roll 5:}, paper feed idling roller 5i, corona discharge assembly 52, and output feed rollers 53 and 54. All the feed rollers preferably comprise rubber cover-ed metal rolls. Upper output roller 54, as shown in Figure 4 (and likewise upper input roller 48) comprises a central shaft provided near its ends with a metal sleeve which is surfaced with the rubber covering, so that the roller engages only the edges of the top surface of an image plate fed through the machine and does not roll on the image-bearing central area of the plate or ride on the transfer sheet which is fed against the plate by the paper feed rollers. The remainder of the rollers are of uniform diameter and are rubber-surfaced throughout their working length.

Lower input and output feed rollers ll and 53 run in hearings in end plates 32 and are positioned near the input and output edges, respectively, of the frame ll and below the plane of the feed plates it with their surfaces substantially tangent with that plane, or slightly above the tangent position. It is thus possible to slide an image plate along plates 46 smoothly onto the input roller 4?, and for output roller 53 to feed the plate out onto plates '46 at the output side not we a in as i Fi u e A metal slide plate 55 is adjustably mounted between walls s2 by" flanges .55 to provide a table portion having its upper surface substantially in the plane of the feed plates 5.5 to provide a sliding surface and eleotric'al grou nd for image plates as they pass under 'Ithe corona asseinbly 52 betweenthe inputand output rollers. The frame'lli i itself mounted in the opening in the baselbox by moun in brackets to which the end plates fl are secured by heig htadjusting sc ews 53 to perrnit accurate adjustiner'it of the height of the'enti-re inecchanisrn with respect to .toppanel -33 as the'base box.

Lower input roller iii ca ries a sprocket on" one end of its shaft byivhich is driven by geared-downrnotor through chain iioller t? carries a spurgear'ei on th san e end of its shaft oiitside plate and re r 48 has a meshing gear '32 to drive it at sa ne speed as H. A chain of genres, 54, and 55 are also driven by gear '55 an gents" drives a spur gear 66 on the end of 'ti q haapr output roller 5-5 which is therbydr'iven"atthe san e peripheral speed as roller e7. Roller 54 is driven by a gear 51 on its shaft, which meshes with gear Eli. Paper feed 'r'oller carries a gear \38 which inesheswith gear'tfff Gear 53 is slightly smaller iiipitch diameter than gear iii while roller 55 is" the saine "size'as'rollerfil, so that the paper feed roller'advances eta slightly faster rate than thEDlate fee'd roller, such as 0.5 to 5% taster. Idling roller 5! is' surface-driven by roller 58 and is held against it'by 'plu'ng'ers Z35. Upperinput and output feed roll s l5 and 54 travel inhearings rnoun'ted in sw,' ging arms 69 and "iii, respectively, pivoted on end plates 42 to allow th'eonto be raised away the lower rollers to"admit an image plate between the rolls. The upper rollers are norrnally held against the lower feed rollers by spring-pressed plunge'r'sl which press against swinging arms 59 and li Arms scare- 51- ecl with upward extensions ll" having circul r earn openings in the upper endsth rough which a con 12 extends. Shaft '52 carries a handl V e'rid'and a pair or cani pins l4 wh v ride against the inside ofthe caiii openings. When handle i3 is in one position, the carnpins allow plungers i5 tohold the input rollers contact butwhen handle '53 isrnanually. rotated the pins l4 ill lift'the upper roller 43 away frorn the lowerroller by "a distance'sufiicient to provide. easy sliding clearance for the ehdfof'an irr 'g e plate as it isiiiSertedfintO the machine. The" control arm can 'then rower the roller. 432mm thegtop surface of the plate Whereit is held by. plungers 15.

An indexing stop arni i's slipporlted on shaft TI to be swung upward'int'o the pathof an'irnage plate which hasjbeen slid between rollers 4i and 48. 'Ar'm'i'fi is adjustable by a screw and slot combination to enable'the starting position of the leading edge; of the image 7 plate to, be. set. An arm 19 'is'fixedonlone e'ndiojf shafti'il and itsend is pivotally e nnegteai 1 e; end of a link 8i) which meson an eccentric ca n' portion orshart 1250' that whenjhandle 7-3 is turned to raise roller lathe stop' arm is also raisedinto operative'posit ion Corona discharge assembly 5;} comprises. a grid of fine wires 8 strung on pins mounteqin P r, i. nsulat n l ks, ssu s near slide plate 55 to aifford a sloping guide ins gthat the transfer paper will pass under the I grid without striking it.

operation of the device of Figures 3 and 4 an image plate, such as a rectangular flat lir erographic plate, carrying an image material to betransferred, such as an electrostatically adhering powder image, is laid on top panel 43 and handle is is turned to raise roller 53 and stop it. The plate is then slid between rollers A! and $3 until its front end engages stop i5 after which the handle is again turned to remove stop it and to drop roller against the margins of the image plate outside the image area. A sheet of transfer material, such as paper or an ofiset duplicator mat of the desired size is laid in paper feed chute 29 with its leading end in the wedgeshaped spaced formed by lead rollers 55 and 5|. The tangent plane of contact between paper feed rollers and Si intersects the path of the image plate at an acute angle, such as i5 degrees, and at a point just beneath the curved lower edge of corona shield 8 The operator now closes a switch to energize the power sup-ply and motor M and the rollers thereupon will advance the image plate alongthe top of slide plate 55. At the same time the paper feed rollers advance the transfer sheet down into contact with the plate where it bends into a curved channel as it passes under shield 8% and into the corona discharge now being produced by grid 8i. The sheet is attracted to the image plate by the electric charge, and due to the curve in the sheet, all wrinkles or bulges are remoyed prior to contact with the image plate and uniform contact with the plate results as the sheet enters the corona zone where it is then held fiat by the electrostatic attraction. Due to, the slightly higher speed of the transfer sheet the curve in the sheet moves back slowly as the sheet advances toform a cloublebow or S.- shape as indicated by the dashed line 83.. This tends to increase the pressure with which the sheet is fed against the plate and, alsoinsures that there will be no tension applied to. the sheet and that it will not rub against shield 84. After the sheetancl image plate have passed under the corona assembly incontactand they have issued from between rollers 5-3, as the machine is stoppedby openin switch 86 manually-or by a control lever actuated by the plate and the transfor sheet with adhering image is manually stripped cit the image plate.

Figure 5 shows: a drum copying machine embodying ieaturesof the invention and comprising a cylindrical drum as which is surfaced with a. coating or photoconductive insulating mate.- rial. Thedrurn is rotated in a clockwise direction by a drive motorand means are provided within housing 85 for charging its surface, ex-

and whose tangent plane of contact intersects the surface of the drum at an angle of approximately 45 degrees. Roller so is driven intermittently at the same surface speed, or a slightly higher speed than drum 86. by a drive gear $32 which meshes with gear attached to the end of roller cc. Gear 92 is attached to a smaller gear E92 which meshes with a segment gear 593 on the shaft of drum 88. A paper feed plate supports a stack of paper 94 to be fed between the rollers, one sheet at a time, by pusher arm 95 which is oscillated by lever 96 attached to earn following rod er which is oscillated by cam 88 on the shaft of drum so. A sheet is brought be tween the rollers by the pusher arm and the roll ers feed the sheet against the drum as a powder image on the drum passes the transfer station. As a sheet of paper is fed against the drum it passes above corona discharge assembly as and the paper is electrostatically charged and thereby held against the drum and the powder image transferred. Further advance of the drum brings the paper to a suitable stripper 98 which peels it from the drum and feeds it through a fusing oven or other fixing device ltil to fix the powder image on the sheet.

Figure 6 shows manual transfer arrangement comprising a base plate Iili over which a corona discharge assembly I32 is bridged. A paper feed chute lilt is also bridged across the plate. This comprises a feed plate I84. supported at an angle of 45 degrees to the top of base plate 565, and a shorter upper plate I 85 spaced above plate Illa to provide a paper feed slot I55 between them along the lower portion of plate i634. For making a transfer the operator energizes the corona discharge grid and slides an image plate as? under chute its and under corona shield lI-il into the zone of the corona discharge. At the same time he manually feeds a sheet of paper ltd down feed plate I M and through the feed slot i until it strikes the top of plate 551. The motions are manually co-ordinated to locate the end of the paper in the desired position on plate It? and then the assembly is pushed on through the corona zone. The sheet N33 is pushed with the hand just enough to maintain the desired curvature at the point where the paper enters the corona zone.

Figure 7, which refers to Figure 6, but applies to the other forms as well, shows the preferred relationship of paper Ice and image plate it] during transfer, although these conditions can be departed from to some extent without serious loss of image transfer. The paper approaches the plate at an acute angle, of which 45 degrees is a satisfactory example, although the angle may vary from about degrees to 90 degrees depen ing on the nature of the transfer material and other conditions. For most applications it is preferred to keep the angle between 5 and 85 degrees.

Near the plate the transfer sheet is bent into a curve or channel I09 which merges with the leading portion of the sheet which lies fiat on the image plate and is held firmly in position. by the electrostatic charge applied to it by the ion source, such as the corona wire grid In the preferred form, the channel I69 merges with the plate Ill? at margin of the corona zone. This margin can be rather sharply determined by shield plate II a so the initial line of merging may be closely determined. However, if shield is not used, or the lower edge of the shield is spaced quite far from the plate there may be a zone of decreasing corona intensity and generally speaking contact anywhere in this zone, or even slightly 'in advance of it, will be satisfactory. As soon as theleading edge of the sheet is pinned down by the corona the electrostatic forces will tend to draw the sheet down against the plate and shift the line of merging to the left as viewed in Figure '7.

Since the sheet is confined by a feed slot Figure 6) or the feed rollers (other figures) as indicated by arrows II! in Figure 2, the curvature of the channel is increased by this action thus improving, if anything, the beneficial straightening of bulges and wrinkles. If feed rollers, or other means, are provided to advance the sheet at a speed slightly greater than the plate speed the curvature gradually increases as the plate advances until the channel H39 may assume a form such as indicated by the dashed line by which more pressure is brought to bear against the plate.

It is preferred that the speed of the sheet advance be such as to keep the channel Hi9 close to the corona zone since bulges in the transfer sheet may have a tendency to re-forrn if a flat portion is allowed to develop between channel I09 and the start of the corona zone. However, the present arrangement greatly reduces the criticality in the rate of paper feed as the channel I69 can take up the slack. The problem of precise matching of the paper speed and plate speed is thereby reduced or eliminated.

In the claims, the reversal of parts is contemplated, and the parts which are movable and those which are stationary may be interchanged without exceeding the scope of the claims.

While the present invention, as to objects and advantages, has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby but it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. An image transfer mechanism for electrostatically adhering images comprising a corona discharge electrode for attaching a transfer sheet and transferring a powder image, a plate feed mechanism for feeding an image plate under said electrode, and a sheet feed mechanism for feeding separate sheets of transfer material against an image plate in a sheet feed plane which makes a substantial angle at least greater than 5 with said plate and intersects plate in a line substantially perpendicular to the direction of travel of said image plate and immediately in advance of said electrode, said sheet feed mechanism being spaced from the path or" said image plate and including sheet guiding and advancing members, said sheet guiding advancing members Comprising a pair of parallel rollers which are in tangent coirtact said sheet feed plane, and in which a common drive means is provided for image plate feed mechanism and said parallel rollers to advance said image plate mechai at a linear speed to advance parallel rollers at a higher linear speed.

2. An image transfer mechanism for electrostatically adhering images comprising a corona discharge electrode for electrostatically attaching a transfer sheet and transferring a powder image, a plate feed mechanism for feeding an image plate under said elec rode, and a sheet feed mechanism for feeding separate sheets or" transfer material against an image plate in a sheet

Claims (1)

1. AN IMAGE TRANSFER MECHANISM FOR ELECTROSTATICALLY ADHERING IMAGES COMPRISING A CORONA DISCHARGE ELECTRODE FOR ATTACHING A TRANSFER SHEET AND TRANSFERRING A POWDER IMAGE, A PLATE FEED MECHANISM FOR FEEDING AN IMAGE PLATE UNDER SAID ELECTRODE, AND A SHEET FEED MECHANISM FOR FEEDING SEPARATE SHEETS OF TRANSFER MATERIAL AGAINST AN IMAGE PLATE IN A SHEET FEED PLANE WHICH MAKES A SUBSTANTIAL ANGLE AT LEAST GREATER THAN 5* WITH SAID PLATE AND INTERSECTS SAID PLATE IN A LINE SUBSTANTIALLY PERPENDICULAR TO THE DIRECTION OF TRAVEL OF SAID IMAGE PLATE AND IMMEDIATELY IN ADVANCE OF SAID ELECTRODE, SAID

Images