US2942573A

US2942573A - Xerographic developing apparatus

Info

Publication number: US2942573A
Application number: US725702A
Authority: US
Inventors: Herbert E Crumrine
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1958-04-01
Filing date: 1958-04-01
Publication date: 1960-06-28
Anticipated expiration: 1977-06-28
Also published as: GB930072A

Description

June 28, 1960 H. E. CRUMRINE 2,942,573

XEROGRAPHIC DEVELOPING APPARATUS Filed April 1, 1958 2 Sheets-Sheet 1' mvzzmozz Herbert E.Crumr|ne ATTORNEY June 28, 1960 H. E. CRUMRINE XEROGRAPHIC DEVELOPING APPARATUS 2 Sheets-Sheet 2 Filed April 1, 195a INVENTOR.

KOPUUJJOU FWDO Herbert E.Crumrine ywflwo ATTORNEY United States Patent 2,942,573 XEROGRAPHIC DEVELOPING APPARATUS Herbert E. Crumrine, Rochester, N.Y., a'ssiguor to Haloid Xerox Inc., a corporation of New York Filed Apr. 1, 1958, Ser. No. 725,702 9 Claims. (Cl. 118'637) This invention relates to the held of xer'o'gra'phy and in particular to an improved device for use in the development of xerographic images. l V

In the art of xerograpny an electrostatic latent image is formed on an insulating surface, such as, for example, a hotoeonductive insulating layer or electrophotographic surface by the combined action of an electric field applied through a photoconductive material and action of light or suitable activating radiation on the photoconductive material "to cause selective conductivity in accordance with the pat-tern of radiation to which the material is exposed. The result of this combined exposure and field is to form a pattern of electric charge on the photoco'nductive layer that is known in the art as an electrostatic latent image which is capable of utilization, for example, by deposition thereon of finely divided material, such deposition being known in the art as development.

It has been found by others in the art of xerography, as disclosed in Landrigan Patent 2,725,304 and Hayford Patents 2,808,023 and 2,817,598 that an electrostatic latent image can be developed very satisfactorily by presentihg to the image surface a cloud of charged powder particles with a conductive surface or development electrode positioned closely adjacent to the image surface, preferably at a distance therefrom in the order of about to A of an inch or in some instances even closer than 0 inch. It has also been found by others in the art of Xerography that one effective way of preparing a cloud of substantially uniformly charged particles is to form a powder cloud in a suitable cloud generator and to pass the cloud under conditions of turbulence through a restricted opening, such as, for example, a capillary tube.

Basic to the use of the development electrode is the desire to reproduce copies of the original image of high quality and Without distortion. Electrostatic lines of force exist between the electrostatic charges on the photoconductive insulating layer and areas of different charge potential. When large area carrying electrostatic charges exist, the lines of force which are present due to charges in the central area of the large area tend to run inward through the photoconductive insulating layer to the conductive backing member which is the nearest surface carrying a different potential. Lines of force running from electrostatic charges near the external boundaries of this large area will tend to extend outward and around the outside border of the large area at which point their paths will extend inward through the photoconductive insulatim layer .to the conductive backing member. .Development of such an electrostatic :latent image creates deposition which relates to the paths taken by the electrostatic lines of force or development of the electrostatic fields. Therefore, development of a large area as has just been described tends to reproduce copies with hollow centers and emphasized edges. To prevent such development a surface is positioned at a slight distance the photoconductive insulating layer during development. surface, the development electrode, is composed of a conductive material and, in the case of positive-to-posi- 2,942,573 Patented June 28, 1960 tive reproductions, is usually maintained at about the same potential as the lowest charge on the photoconductive layer; whereas, in negative-to-positive reproduction, is usually maintained at a potential equal to the highest charge on the photoconductive layer. In this manner, a surface is formed that causes an increase in the lines of force extending outwardly from the plate member, thereby creating electrostatic fields which when developed produces distortion-free and fringe-free high quality copy.

In Xerographic development according to these methods there are many inherent problems caused, among other things, by the need for working in an extremely confined space and with extremely fine tolerances, this need being brought about by the narrow space between the image surface and the development electrode. For example, the usual development of a xerographic image involves uniform deposition of powder particles or other finely divided particulate material, across an area of normal picture size which may, for example, be an area whose smallest dimension is several inches or an area Whose smallest dimension is a foot or more. The introduction of a cloud uniformly across this entire area in :1 development space in the order of eg to inch thick has obviously presented many serious problems.

Many of .the devices used heretofore for powder cloud development have been characterized by various shortcomings. For example, when the powder cloud in its flow travels over an area that should be white and then over an area that should be dark, the leading edge of the dark area is not always properly developed. Frequently on the developed image the dark area appears to be torn so that a white background shows through. Because of this appearance the flaw is referred to as tearing. Another difliculty occurs when the powder cloud travels over a large, dark area and then over a large area that should remain white. Although the white area is void of charge, it does not always remain free of powder. De veloper particles may deposit in streaks through this area in amounts roughly proportional to the length of the dark area that immediately precedes the white area. This diificulty is termed streaking. Still another difiiculty is that developed images are not always uniformly developed end-.to-end nor does extending the development time remedy this defect as, apparently, part of the charge in the image areas at one end of the plate are erased in the development process. Another difficulty encountered is that powder particles, striking the surface of the Xerographic plate as a result of mechanical forces, will not only adhere .to the plate regardless of the charge on the plate, but the powder particles will also abrade the surface of the plate thereby reducing the life of the Xerographic plate in terms of the number of quality reproductions that can be made by the plate.

It is therefore an object of this invention to improve xerographic developing apparatus for reproducing copies of the original image of high quality and without distontion.

Another object of the invention is to improve xerographic developing apparatus to attain a uniformly distributed flow of powder particles carried by an air stream over a moving electrophotographic plate surface in a man ner free from localized concentrations or powder-starved zones or streaks, and free from agglomerations of powder particles.

These and other objects of the invention are attained by means of a xerographic developing apparatus in the form of .a manifold assembly positioned in closely spaced relation to the path of movement of a Xerographic plate whereby a development zone is formed bet-ween the manifold assembly and the xero-graphic plate, tl e manifold assembly containing a pair of oppositely directed entrance slots for flowing developing material into the developmen-t zone, and multiple exhaust slots for withdrawing excess developing material from the development zone. For a better understanding of the invention as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be'read in connection with the accompanying drawings, wherein:

Fig. l is a perspective view of the developing apparatus, partially broken away to illustrate the various elements of the device, and

Fig. 2 is a detail vertical sectional view of the developing apparatus taken along line 2-2 of Fig.1.

JFigures 1 and 2 show the developing apparatus and related parts with a xerographic plate in position for development. The xerographic plate 10, which forms no part of the subject invention, consists of a photoconductive insulating layer coated on a conductive backing, and is supported on carrier block 11 which in turn rests on drive rolls r12 for movement relative to the developing apparatus. The developing apparatus is mounted to maintain a, uniform close spacing between its lower surface and that of the xerographic plate whereby to form a development zone 13.

The developing apparatus, generally made of metal or other conductive material, is essentially a manifold or manifold assembly which contains two entrance slots, through each of which a stream of fine, electrostatically charged development powder particles suspended in air are directed into the development zone in substantially laminar, parallel flow to the xerographic plate, and which also contains three exhaust slots through which any excess powder particles are removed from the development zone.

In theembodiment disclosed, the manifold or manifold assembly, generally designated 14, includes a development wall portion or electrode element 15 consisting of plate 16 having deflector plates 17 fastened to the undercut portions 18 of the plate '16, for reasons which will be explained in more detail hereinafter. To prevent warping of the bottom of the plate 16 during machining, the plate is a casting having three

vertical risers

19, 20 and 21 and the reinforcement ribs 22 formed integral therewith, the ribs 22 being perforated at 23 to permit mounting the plate 16 to a structural element (not shown) of a xerographic device.

A pair of riser blocks 25 are attached to the top of plate 16, the gaskets 26 being positioned between the plate 16 and the riser blocks 25.

The electrode element .15 contains a pair of entrance slots 27, through each of which a stream of fine, electrostatically charged development powder particles suspended in a fluid, commonly called a powder cloud, is directed into the development zone 13. The walls of each of the slots 27 are formed by the beveled surface of the undercut portions 18 of the plate 16, and the tapered portions of the deflector plates 17. Each entrance slot 27 extends transversely across the electrode element 15, terminating just short of the outer margins of the electrode element so that the powder cloud is retained in the development zone. Each entrance slot forms an acute angle with the plane of the bottom surface of the plate 16, and each slot is inclined toward the center of the plate. Preferably, this angle'should approach zero, but as a practical matter it is usually on the order of from 2 to 5 because the deflector plates must be made of suflicient thickness to minimize excessive wear.

' Each of the entrance slots'27 is supplied with 'a powder cloud by a conventional type powder cloud generator 28,- such as those described in Hayford Patent 2,812,883 and Andrus et al. Patent 2,815,330. The powder cloud, by whatever means produced, is then charged. Where a cloud of dry powdered developing material is used, any method of generating the cloud will almost necessarily produce a charge thereon. For some purposes, the charge so produced will be adequate. If it is desired to produce a more uniform charge, however, other charging devices 29, such as triboelectric charging (as by passing the electroscopic powder through a narrow tube of suitable material in turbulent flow), corona charging or other charging device, may be used.

Although any convenient means may be employed to deliver developing material to the developing zone, the preferred construction for this purpose, as disclosed herein, is similar to the system disclosed and claimed in copending application, Serial No. 725,558, filed April 1, 1958, in the names of Richard E. Hayford and Carl B. Kaiser. In this system, the charged powder cloud is delivered to each entrance slot 27 by means of conduit 30, elbow 31, inlet conduit 32 and expansion chamber 33. The inlet conduits 32 and expansion chambers 33 are formed both in the plate 16 and riser blocks 25.

An exhaust slot 35 is formed in the center of the plate 16, between the entrance slots 27, the exhaust slot 35 as well as the later described auxiliary exhaust slots 42, extends transversely across the plate 16, terminating just short of the outer margins of the plate 16. The exhaust slot 35 communicates with a bored passage 36 extending transversely across the full width of the riser block 20, the passage 36 being closed by end plates 37 secured by fasteners 38. a In Fig. 1, an end plate 37 is shown secured to the riser 21, while the end plate has been removed .from the riser 20, and riser 19 and the corresponding portion of the plate 16 has been broken away, to more clearly illustrate the configuration of the various elements.

Communicating with the passage 36 is an exhaust outlet passage 39 that is connected by means of conduit or vacuum line 40 to a convenient form of dust collector 41 which may comprise a suction pump connected to a dust filter.

A pair of auxiliary exhaust slots 42, similar to exhaust slot 35, is formed outboard of the entrance slots 27. Each auxiliary exhaust slot 42 communicates with an auxiliary passage 43, similar to passage 36, and these passages 43 are also closed at their outer ends by end plates 37. Communicating with each auxiliary passage 43 is an auxiliary outlet passage 44 that is connected by conduit or vacuum line 45 to dust collector 41.

The passage 36 and each of the auxiliary passages 43 are each connected to damper openings 46 which can be closed by damper plates 47 movably secured to the risers by screw fasteners 48.

In operation, assume that the photoconductive insulati-ng layer of the xerographic plate 10 bears an electrostatic image. The drive rolls 12, actuated by a power means (not shown) will transport the carrier block 11 with the xerographic plate 10 relative to the developing apparatus. As the xerographic plate passes the developing apparatus, a powder cloud, supplied by the powder cloud generator 28, is introduced into the development zone formed by the xerographic plate and the developing apparatus through the entrance slots 27. The powder cloud delivered through the entrance slots 27 is continuous and from opposite directions. The center exhaust slot 35 connected to a souce of negative pressure, dust collector 41, draws in most of the powder cloud from each entrance slot, and in so doing causes the powder cloud streams to travel across the xerographic plate in a substantial laminar flow, and before the opposed flows can collide and thereby cause turbulence, the powdercloud is withdrawn from the development zone.

No powder cloud should near a plate bearing a latent image where there is no electrode because reversal development is effected by virtue of the bias, field between the xerographic plate and .the development electrode. Powder which would therefore develop a charged and exposed plate without an electrode present would be damaging to the sensitometric quality of the resultant dust image. If, therefore, a long xerographic plate is passed over a relatively short electrode element, escaping powder must be disposed of before it can deposit on a mil 5..

charged surface of the xerographic plate. This powder, if not caught, causes peculiar reversed reversal effects, whereby powder is deposited in areas that should be free of powder. Thus, the auxiliary exhaust slots 42 connected to the dust collector 41 are used to trap and remove all excess powder which could deposit on the plate.

With the xerographic plate moving past the developing apparatus and therefore past each entrance slot which introduces a flow of powder cloud from separate directions, a uniform distributed amount of powdered developing material is applied over the xerographic plate. Since the flow of powdered developing material is substantially parallel to the xerographic plate, only electrical forces attract the powdered developing material to the xerographic plate and not mechanical forces.

The resultant dust images, developed by the subject developing apparatus, are uniformly developed end-toend with no streaks or tears, because the simultaneous introduction of two streams of powdered developing material from opposite directions over the moving xerographic plate eliminates streaking and tearing, the buildup of powder on one edge of a dark area due to developing material flowing from one direction being counteracted by a buildup on the other edge of the dark area by developing material flowing from the opposite direction.

The xerographic plate and the development wall portion or electrode element may be in the shape of flat members, as shown, or, if desired, they may be curved to fit on a drum for continuous operation. Although not shown, it is obvious that the development apparatus may be positioned within a container of suitable design so as to prevent loss of developer powder to external areas or merely to improve the appearance of the apparatus. Since the image-bearing member has a light-sensitive surface, it is desirable that the apparatus be positioned in a light-tight enclosure prior to development.

While there have been shown and described the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device and in its operation may be made by those skilled in the art, without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

l. A developing apparatus for use in a xerographic machine wherein a xerographic plate carrying an electrostatic latent image is moved relative to the developing apparatus during a developing operation, said developing apparatus including a manifold assembly having an electrode element in closely spaced relation to the path of movement of a xerographic plate whereby a development zone is formed between the electrode element and a xerographic plate during a developing operation, three exhaust slots, for Withdrawing excess developing material from the development zone, in said electrode element extending transversely thereof, each of said exhaust slots being connectable to a vacuum line, and two entrance slotsin said electrode element for flowing developing' material into the developing zone, one of said exhaust slots being located between said entrance slots, the other two of said exhaust slots being positioned, one each, on opposite sides of and outboard of said entrance slots, each of said entrance slots forming an acute angle with the plane of said electrode element and each of said entrance slots being inclined toward the center of said electrode element, each of said entrance slots being connectable to a source of powdered developing material.

2. A developing apparatus for use in a xerographic machine wherein a xerographic plate carrying an electrostatic latent image is positioned in closely spaced relationship to the developing apparatus, said developing apparatus including a manifold assembly having an electrically conductive development wall portion conformable with the surface of the xerographic plate, at least three exhaust slots in said development wall portionextending transversely thereof, each of said exhaust slots being connectable to a vacuum line, at least two oppositely directed entrance slots, one each of said entrance slots being positioned between each grouping of said exhaust slots in said development wall portion, each of said entrance slots forming an acute angle with the plane of said development wallportion, and each of said entrance slots being connectable to a source of powdered developing material.

3. A developing apparatus for use in a xerographic machine wherein a xerographic plate carrying an electrostatic latent image is positioned in closely spaced relationship to the developing apparatus, and wherein the electrostatic latent image is developed by a powdered developing material delivered through said developing apparatus, said development apparatus including a manifold assembly having an electrically conductive development wall portion conformable with the surface of the xerographic plate, an exhaust conduit means in said manifold, one end of said exhaust conduit means extending transversely of and across the center of said development wall portion of said manifold, the other end of said exhaust conduit means being connectable to a vacuum line, and a first inlet conduit means and a second inlet coduit means in said manifold located on opposite sides of said exhaust conduit means, one end of said first inlet conduit means and one end of said second inlet conduit means extending transversely of said development wall portion of said manifold and at opposed angles with the plane of said Wall portion to form oppositely directed inlets for a powdered developing material, the other end of said first inlet conduit means and the other end of said second inlet conduit means being connectable to a source of powdered developing material.

4. A developing apparatus for use in a xerographic machine wherein a xerographic plate carrying an electrostatic latent image is positioned in closely spaced relationship to the developing apparatus for relative movement therewith, said developing apparatus including a manifold having an electrically conductive development wall portion, a center exhaust slot in said development wall portion extending transversely of said development Wall portion, conduit means in said manifold connected at one end to said center exhaust slot and being connectable at its other end to a vacuum line, a first entrance slot and a second entrance slot in said develop ment wall portion located on opposite sides of and parallel to said center exhaust slot and in oppositely inclined position with respect to each other, said first and second entrance slots being connectable to a source of powdered developing material, a first auxiliary exhaust slot and a second auxiliary exhaust slot in said development wall portion positioned outboard of said first entrance slot and said second entrance slot, first and second auxiliary conduit means connected to said first and second auxiliary exhaust slots for connecting said first and second exhaust slots to a vacuum line, and damper means connected to each of said first and second auxiliary conduit means and to said conduit means for regulating the flow of additional air through said last mentioned means.

5. A developing apparatus for use in a xerographic machine wherein a xerographic plate carrying an electrostatic latent image is positioned in closely spaced relationship to the developing apparatus for development by a powdered developing material, said developing apparatus including a manifold having an electrically conductive development wall portion, an exhaust means in said manifold, said exhaust means including a narrow exhaust slot extending transversely of and in the center of said development wall portion and an outlet passage connectable to a vacuum line, and at least one powder cloud conduit means on each side of said exhaust means, each said powder cloud conduit means including a narrow entrance slot in said development wall portion inclined toward said exhaust slot so that flow from said entrance slot is toward said exhaust slot, and a powder cloud inlet conduit connectable to a source of powdered developing material.

6. A developing apparatus for use in a xerographic machine wherein a xerographic plate carrying an electrostatic latent image is positioned in closely spaced movable relationship to the developing apparatus, and wherein the electrostatic latent image is developed by a powdered developing material delivered through said development apparatus, said developing apparatus including an electrically conductive manifold having a development wall portion conformable in shape with the surface of the xerographic plate, an exhaust conduit means in said manifold, one end of said exhaustconduit means having a narrow exhaust slot extending transversely of and across the center of said development wall portion of said manifold,vthe other end ofsaid exhaust conduit means being connectable to a vacuum line, a first inlet conduit means and a, second inlet conduit means in said manifold located on opposite sides ofsaid exhaust conduit means, one end of said first inlet conduit means having .an inclined first entrance slot and one end of said second inlet conduit means having an inclined second entrance slot extending transversely of said development Wall portion of said manifold said second entrance slot being inclined in an opposite direction from said first entrance slot, the other end of said first inlet conduit means and the other end of said second inlet conduit means being connectable to a source of powdered developing material, and a first auxiliary exhaust conduit means and a second auxiliary exhaust conduit means in said manifold outboard of said first inlet conduit means and said second inlet conduit means, respectively, one end of said first auxiliary exhaust conduit means and one end of said second auxiliary exhaust conduit means each terminating in an auxiliary exhaust slot extending transversely of said development wall portion of said manifold, the other end of said first auxiliary exhaust conduit means and the other end of said second auxiliary exhaust conduit means being connectable to a vacuum line.

7. A developing apparatus for use in a xerographic machine wherein a xerographic plate carrying an electrostatic latent image is positioned in closely spaced movable relationsihp to the developing apparatus for development by a powdered developing material, said developing apparatus including a manifold having an electrically conductive development wall portion, an exhaust means in said manifold, said exhaust menas including a narrow exhaust slot extending transversely of said development portion and an outlet passage connectable to a vacuum line, a pair of powder cloud conduit means in said manifold, each said powder cloud conduit means including an entrance slot in said development wall portion, said entrance slots being located on opposite sides of, inclined toward, and parallel to said exhaust slot, and a powder cloud inlet conduit connectable to a source of powdered developing material, and a pair of auxiliary exhaust means in said manifold, each of said auxiliary exhaust means including an auxiliary exhaust slot extending trans versely of said development wall portion, one each of said auxiliary exhaust slots being located outboard of each of said entrance slots, and each said auxiliary exhaust means including an auxiliary outlet passage connectable to a vacuum line. 7

j 8. A developing apparatus for use in a xerographic machine wherein a xerographic plate carrying an electrostatic latent image is positioned in closely spaced movable relation to the developing apparatus, said developing ap: paratus including an electrically conductive manifold having a development wall portion conformable to the xerographic plate, a pair of oppositely directed entrance slots in saidwall portion positioned adjacent opposite ends of said development wall portion, each of said entrance slots being connectable to a source of powdered developing material, a first exhaust slot in said wall portion positioned between one of said entrance slots and the respective end of said development wall portion, a second exhaust slot in said wall portion positioned between the other said entrance slot and its respective end of the development wall portion, and a third exhaust slot in said wall portion positioned intermediate said entrance slots,

, each of sai drexhaust slots being connectable to a vacuum line.

9. A developing apparatus for use in a xerographic machine wherein a xerographic plate carrying an electrostatic latent image is positioned in closely spaced movable relation to the developing apparatus, and wherein the electrostatic latent image is developed by a powdered developing material delivered through said developing apparatus, said development apparatus including a manifold assembly having an electrically conductive wall portion conformable with the surface of the xerographic plate to permit uniform close spacing of the said wall portion therewith, said manifold assembly including an exhaust conduit means, one end of said exhaust conduit means forming an exhaust slot extending transversely of and across the approximate center of said wall portion of said manifold assembly, a first inlet conduit means and a second inlet conduit means in saidmanifold, one end of said first inlet conduit means and one end of said second inlet conduit means extending transversely of said wall portion of said manifold assembly on opposite sides of said exhaust conduit means, and at opposed angles with respect to each other to form oppositely directed inlets for a powdered developing material; a powdered developing source means, the other end of said first inlet conduit means and the other end of said second inlet conduit means being connected to said powdered developing source means, and a vacuum means, the other end of said exhaust conduit means being connected to said vacuum means.

References Cited in the file of this patent UNITED STATES PATENTS Hayford July-15, 1958'