US3349750A

US3349750A - Xerographic development apparatus

Info

Publication number: US3349750A
Application number: US516646A
Authority: US
Inventors: Daniel J Donalies
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1965-12-27
Filing date: 1965-12-27
Publication date: 1967-10-31
Anticipated expiration: 1984-10-31
Also published as: DE1522715A1; GB1165377A; FR1516053A

Description

D. J. DONALIES XEROGRAPHIC DEVELOPMENT APPARATUS Oct. 31, 1967 Filed Dec. 27, 1965 2 Sheets-Sheet 1 Jim MB. 5 TL N NA R 9 0 V T N ID A Oct. 31, 1967 D. .1. DONALIES XEROGRAPHI C DEVELOPMENT APPARATUS 2 Sheets-Sheet Filed Dec. 2 1965 INVENTOR. DANIEL J. DONALIES United States Patent ice York Filed Dec. 27, 1965, Ser. No. 516,646 9 Claims. (Cl. 118637) This invention relates to apparatus for developing images and particularly to apparatus for developing an image on an electrostatically sensitive member. More specifically, the invention relates to a xerographic development system which produces powder images on a moving xerographic plate by bringing a two-component developer material into contact with the moving xerographic plate.

In the process of xerography, a xerographic plate comprising a layer of photoconductive insulating material on a conductive backing is given a uniform electrostatic charge over its surface and is then exposed to the subject matter to be reproduced, usually by conventional projection techniques. This exposure discharges the plate areas in accordance with the light intensity that reaches them and thereby creates an electrostatic latent image on or in the photoconductive layer. Development of the latent image is effected with an electrostatically charged, finely divided material such as an electroscopic powder that is brought into surface contact with the photoconductive layer and is held thereon electrostatically in a pattern corresponding to the electrostatic latent image. Thereafter, the developed xerographic powder image is usually transferred to a support surface'to which it may be fixed by any suitable means.

A variety of types of finely divided electroscopic powders may be employed for developing electrostatic latent images. However, as the art of xerography has progressed, it has been found preferable to develop line copy images with a two-component type of developing material such as that disclosed in Walkup Patent No. 2,618,551, issued Nov. 18, 1952, which may include a powder or toner of any of a variety of pigmented resins that has been specifically developed for the purpose, and a granular carrier material, such as glass, encased in a suitable covering such as, for example, a polymer capable of establishing a desired triboelectric relationship with the toner. A number of such developing materials are manufactured and marketed commercially, being specifically compounded for producing dense images of high resolution and to have characteristics to permit convenient storage and handling.

Generally, in a xerographic reproduction system a latent electrostatic image is developed into a powder image by cascading the developing material over the surface of the xerographic plate. Carrier beads and toner powder are mixed together and agitated so that a triboelectric charge is formed on the carrier beads and toner particles to attract and hold toner particles to the carrier beads. The combination of carrier beads and toner powder is referred to herein as developer. The developer material is then elevated to a position where it may be allowed to freely fall or cascade over the surface of a xerographic plate. This is generally referred to in the art as cascade development.

In automatic xerographic machines, the xerographic plate is usually in the form of a cylindrical drum, and the developer material is allowed to cascade over the surface of the drum as the drum rotates. While the developer material is in moving contact with the surface of the xerographic plate, the electrostatic charge on the plate is greater than the triboelectric charge holding the toner on the carrier beads so that toner particles are attracted to the plate surface away from the carrier beads. The powder remains on the areas of the plate that have the 3,349,750 Patented Oct. 31, 1967 electrostatic charge in image configuration, and the carrier falls from the plate surface and is remixed With toner and recirculated.

Conventional cascade development has been one of the most effective forms of developing systems used in the xerographic process. However, even though conventional cascade development produces excellent powder images and has been commercially successful, there are limitations which restrict the speed at which the xerographic plates may be moving. For example, in convention-a1 cascade development the velocity of the developer material while it is cascading over the plate surface is limited by the gravitational effect on a freely falling body. In order to increase the velocity of the carriers, it is necessary to extend the point at which the carriers are allowed to fall before encountering the xerographic plate. It has been found that to produce optimum development, the speed of the carriers relative to the speed of the plate should be approximately 32 inches per second. In order to increase the number of feet of xerographic plate developed in a given time and still maintain the optimum relative speed between the developer and the plate, it is necessary to increase the speed of the developer. As pointed out above, under a gravity system the speed can be increased only by increasing the size of the developing unit to give the developer a longer fall before encountering the xerographic plate. Since the movement of the developer is dependent on gravity, the position of the development unit is restricted to areas of the drum where gravity will carry the material over the drum surface.

The impingement developer apparatus is capable of use in any system where a developer must be brought in contact or close relation with an image to be developed. It may therefore be used in xero-printing, as described in Schaffert Patent No. 2,576,047, issued Nov. 20, 1951. The apparatus may also be used where the image pattern of electrostatic charges is transferred from the photoconductor to the final copy surface and then developed with powders or suitable developers. Whether the image to be developed is formed on a xerographic plate or drum or the final support surface, or has been transferred to a final copy surface, that member or surface holding such image shall be hereinafter referred to as image member or image surface.

It is an object of this invention to develop electrostatic images.

It is an object of this invention to develop electrostatic images using two-component developer.

It is an object of this invention to improve electrostatic development systems to allow increased surface speeds of a moving electrostatic plate.

Further objects of this invention are to reduce the size of electrostatic developer systems, to attain a greater flexibility in the speed of developer material and to provide a two-component developer system that is not dependent on gravity feed.

These and other objects of this invention are attained by means of a rotatable perforated housing containing a supply of developer material and positioned to impinge developer material against the surface of a xerographic plate.

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. 1 schematically illustrates an embodiment of a xerographic apparatus adapted for continuous and automatic operation, and incorporating the subject matter of the invention;

FIG. 2 is a partial perspective view of the schematic embodiment ofvan impingement developing apparatus in J a container in conjunction with a xerographic drum with portions of the container broken away to show internal construction;

FIG. 3 is a partial perspective view of another schematic embodiment of an impingement developer apparatus in conjunction with a container and xerographic drum with portions of the container and developer housing broken away to show the internal construction;

FIG. 4 is a partial perspective view of another schematic embodiment of the impingement developing apparatus in conjunction with a conventional lifting device.

As shown in FIG. 1, the xerographic apparatus comprises a xerographic plate including a photoconductive layer or light-receiving surface on a conductive backing and formed in the shape of a drum, generally designated by numeral which is journaled in a frame to rotate in the direction indicated by the arrow to cause the drum surface sequentially to pass a plurality of xerographic processing stations.

For the purpose of the present disclosure, the several xerographic processing stations in the path of movement of the drum surface may be described functionally as follows:

A charging station, at which a uniform electrostatic charge is deposited on the photoconductive layer of the xerographic drum;

An exposure station, at which a light or radiation pattern of copy to be reproduced is projected onto the drum surface to dissipate the drum charge in the exposed areas thereof and thereby form a latent electrostatic image of the copy to be reproduced; A developing station, at which a xerographic developing material including toner particles having an electrostatic charge opposite to that of the electrostatic latent image are impinged upon the drum surface, whereby the toner particles adhere to the electrostatic latent image to form a xerographic powder image in the configuration of the copy to be reproduced;

A transfer station, at which the xerographic powder image is electrostatically transferred from the drum surface to a transfer material or support surface; and

A drum cleaning and discharge station, at which the drum surface is first charged and then brushed to remove residual electrostatic charge remaining thereon.

The charging station is located as indicated by reference character A in the schematic illustration of the apparatus.

In general, the charging apparatus or corona charging device 21 includes a corona discharge array of one or more discharge electrodes that extend transversely across the drum surface and are energized from a high potential source and are substantially enclosed within a shielding member.

Next subsequent thereto in the path of motion of the xerographic drum is an exposure station B. This exposure station may be one of a number of types of mechanisms or members such as desirably an optical scanning or projection system or the like designed to project a line copy image onto the surface of the photoconductive xerographic drum from a suitable original.

The optical scanning or projection assembly consists of a copyboard in the shape of a drum, hereinafter referred to as copy drum 22, which is adapted to support copy to be reproduced and arranged to rotate in lightprojection relation to the moving light-receiving surface of the xerographic plate. Uniform lighting is provided by suitable lamps attached to a slotted light reflector 23 mounted adjacent to the copy drum.

A light shield 24 adapted to protect the xerographic plate from extraneous light is positioned adjacent to the surface of the xerographic plate. A slot aperture 25 in the light shield extends transversely to the path of movement of the light-receiving surface of the xerographic drum 20 to permit reflected rays from the copy drum to be directed against a limited transverse area of the lightreceiving surface as it passes therebeneath,

4- To enable the optical system to be enclosed within a relatively small cabinet, a folded optical system including an object mirror 26, a lens 27, and an image mirror 28 is used in the preferred embodiment of the apparatus. Copy fed through paper guides 31 to the copy drum is removably secured thereon by a suitable gripper mechanism for movement therewith in timed relation to the movement of the xerographic drum whereby a flowing image of the copy is projected onto the xerographic drum. The copy is held against the surface of the copy drum by means of guides 32. and 33, the latter also preventing the trailing edge of the copy from contacting the web cleaner 54. After the copy is scanned, it can be released from the copy drum to be transported out of the machine by copy feed out roller 34 coacting with the peripheral surface of the copy drum to forward the copy through copy guide 30. Adjacent to the exposure station is a developing station C in which there is positioned a developer apparatus encased in container 1 which is formed to include a lower sump portion for accumulating developer material 2. Mounted within the container is a lifting device in the form of a conical truncated housing 3 with a perforated upper portion positioned approximately opposite to xerographic drum 20. The conical housing is made to rotate by motor 5 at speeds sufiicient to lift the developer material in the sump of the container up along the walls of the conical housing to be forced out through the perforations 6 to impinge upon the xerographic drum. As the toner powder, which comprises part of the developer material in a two-component developer is depleted, more is added by toner dispenser 7.

Within the conical housing and in intimate contact therewith are slats 8 which agitate the developer material in the sump and cause it to enter the conical housing.

' The slats also function to maintain the developer material in mechanical contact with the housing so the forces generated by the rotation of the housing may act upon the material causing it to ascend the sides of the conical housing to be dispersed through the perforations in the upper portion thereof.

This apparatus may form a combination of impingement and cascade development by designing a container, such as that in FIG. 1, which has a cascade trap 9 for guiding a portion of the developer along the path of the drum surface to be pulled by the force of gravity, or cascaded, over that portion of the surface opposed by the cascade trap in a normal cascade relation, eventually to be delivered to the sump at the bottom of container 1. Such trap may be formed of any suitable material and placed in cooperative relation with the image carrying drum.

Positioned next adjacent to the developing station is the image transfer station D which includes suitable sheet feeding mechanism adapted to feed sheets of paper successively to the xerographic drum in coordination with the presentation of the developed image on the drum at the transfer station. The sheet feeding mechanism includes a sheet source such as tray 41 for supplying a plurality of sheets of suitable support material, that is, sheets of paper or the like, a separator roller 42 adapted to feed the top sheet of the stack of support material to a sheet conveyor mechanism 43 having paper grippers 44 thereon which carry the sheet support material into contact with the rotating xerographic drum in coordination with the appearance of a developed image at the transfer station.

The transfer of the xerographic powder image from the drum surface of the support mate-rial is effected by means of a corona transfer device 45 that is located at or immediately after the point of contact between the support material and the rotating xerographic drum. The

corona transfer device 45 is substantially similar to the corona discharge device that is employed at the charging station in that it also includes an array of one or more corona discharge electrodes that are energized from a suitable high potential source and extend transversely across the drum surface and are substantially enclosed with a shielding member. In operation, the electrostatic field created by the corona transfer device is effective to tack.the transfer material electrostatically to the drum surface and simultaneously with the tacking action, the electrostatic field is effective to attract the toner particles comprising the xerographic powder image from the drum surface and cause them to adhere electrostatically to the surface of the support material.

As the paper gripper mechanism continues to move forward in its closed circuit, it will strip the support material from the xerographic drum and carry it to a fixing device, such as, for example, heat fuser 46, whereat the developed and transferred xerographic powder image on the support material is permanently fixed thereto.

After fusing, the finished copy is preferably discharged from the apparatus at a suitable point for collection externally of the apparatus. To accomplish this, there is provided a pair of delivery rolls 47 and 48 by means of which the copy is delivered to a copy holder after it is released by the gripper mechanism. Suitable cam means are provided at the receiving and delivery stations of the conveyor mechanism to actuate the paper gripper at these stations to receive or discharge a sheet of support material. I

The next and final station in the device is a drum cleaning station E whereat any powder remaining on the xerographic drum after the transfer step is removed and whereat the xerographic drum is flooded with light to cause dissipation of any residual electrical charge remaining on the xerographic drum.

To aid in the removal of any residual powder remaining on the xerographic drum there is provided a corona precleaning device 51 that is substantially similar to the corona discharge device that is employed at charging station A. Removal of residual powder from the xerographic drum is effected by means of a web cleaner device 54 adapted to continuously feed a clean fibrous web material into wiping contact with the xerographic drum. As shown, the web material 55 is taken from a supply roll 56 and transported around a cleaning roll 57, preferably made of rubber, to be wound on a take-up or rewind roll 61.

Any residual electrical charge remaining on the xerographic drum is dissipated by light from a fluorescent lamp 62 mounted in a suitable bracket above the xerographic drum, a suitable starter being provided for energizing the fluorescent lamp 62 mounted in a suitable bracket above the xerographic drum, a suitable starter being provided for energizing the fluorescent lamp.

Suitable drive means drive the xerographic drum, the copy drum, and the sheet conveyor mechanism at predetermined speeds relative to each other, and to effect operation of the paper separator roll, and the web cleaner mechanism, the latter being driven at a speed whereby relative movement between the xerographic drum and the web material is effected. Suitable drive means are also providing for effecting operation of the developing ap paratus assembly.

FIGS. 2, 3, and 4 more specifically point out the invention in several of its embodiments. In FIGS. 2 and 3 centrifugal force is used both to lift developer material 2 from the lower sump portion of the container enclosing the developer apparatus to a position within the perforated developer housing where it can be dispersed through the perforations 6, by the centrifugal force of the rotating perforated housing, to be impinged upon the image carrying member 20 wherever such drum surface is received by an opening in the container of the developer system. The quantum of drum surface avail able for impingement by the developer material may be varied according to the design of the developer container. A greater amount of image surface, such as in FIG. 2, may be exposed for impingement by container 18, or a lesser amount of image surface, such as that of FIG. 3, may be made available by a container such as container 19.

In FIGS. 2 and 3 centrifugal force is used both to lift -the developer material to a position within the housing to be impinged upon the image member and also for the actual functioning of the apparatus to cause development of the image. The rotation applied to the housing by motor 5 must be suflicient to cause the developer material not only to rise along the sides of the lower portion of the conical housing but to be dispersed throughout the upper portion of the housing where the perforations are located. The developer material is prevented from escaping over the top of the housing by cap 11 which is securely fastened thereon.

In operation, the impingement housing is rotated such that the developer is captured by slats 8 from the sump portion of the container and scooped into the lower, lifting portion of the developer housing where, by a component of centrifugal force and friction, the developer is caused to rise along the inner wall of the housing to the upper portion which is perforated. When the developer reaches this portion, it is dispersed through the perforations along the upper portionof the housing because of the forces exerted by the rotational motion of such housing. The developer is then caused to impinge upon that portion of the image surface which is received through the container. Any developer not striking the image surface, or striking the surface and leaving same, or falling against the container is returned to the sump of developer material by gravity.

As the toner portion of the developer is depleted through development of the images, more is added to the developer material sump by any conventional toner dispenser 7. This toner is then attracted to the carrier beads of the developer material by a triboelectric force generated through friction which is supplied by the agitation of the developer material by the slats and any lower portion of the rotating housing disposed within the reservoir of developer material.

The impingement developer apparatus housing may be in any shape along any axis provided that the spinning of such housing around such axis will cause developer to be forced to the walls of the housing and through the perforations therein, to contact any portion of an image member such as .a xerographic drum. Any means or mechanism may be used to lift developer material from any convenient sump or reservoir to a position where it can be distributed into the impingement developer housing, there to be acted upon by forces generated by the rotation of the housing for impingement on a receptive surface. The conveyor or lifting means may be incorporated in the impingement apparatus as shown in FIGS. 1-3 or it may be a separate mechanical feature.

FIG. 4 illustrates another embodiment of an impingement developer housing 12 in conjunction with a conventional xerographic development lifting device such as, for example, .an endless conveyor 15 with a multitude of trays 16. The lifting device brings developer material into a chute 51 for gravitational delivery to the developer housing which is caused to rotate around center shaft 17 by motor 5. The rotational speed of the developer housing around axis 17 causes the developer contained therein to be thrust against the inner wall and through perforations 6 to impinge upon an image member 20. The annular cap 13 covers a portion of the developer housing forming a lip from the outer wall of'said housing inward toward center shaft 17 thereby preventing developer material within the impingement developer housing from escaping over the top of said housing. The developer housing is mechanically connected to center shaft 17 which is journaled through an upper portion of container 14 for action with motor 5. Braces 50, adapted to permit rotation of the housing, support it within the container. Any lifting device can be used in conjunction with this impingement 7 developer housing, such as that disclosed in copending application, Ser. No. 516,528, filed Dec. 27, 1965 in the name of Daniel J. Donalies, so long as such lifting device eventually deposits developer material into the impingement developer housing.

Development speeds can be increased or decreased by varying the rotational speed of the developer housing, varying the diameters of the perforations in the housing, varying the amount of image surface available for impingement by the developer material, or varying the size or number of the impingement developer housings. Development within a given system can be varied as to the amount of developer reaching any given part of a receptive surface with a latent image thereon by increasing the rotational speed of the impingement developer housing thereby increasing the amount of developer dispersed through the perforations of such housing and reaching the image member to be developed. The speed of the entire system may be increased by proportionally increasing the drum speed and the rotational speed of the impingement housing. This is not possible in the conventional cascade method development since the amount of developer reaching the drum and cascading over it is limited by the pull of the force of gravity creating relative movement between the developer material and the drum.

While the invention has been described with reference to the structure disclosed herein, it is not confined to the details set forth; and this application is intended to include such modifications or changes as may come within the purpose and spirit of the improvements or the scope of the following claims.

What is claimed is:

1. A developer apparatus for use in developing electrostatic images on an image member comprising a perforated housing adapted to contain developer material, said perforation approximately opposite to an image member to be developed,

a means to cause a developer material to enter said housing and be maintained in mechanical contact therewith, and

a means for rotating the housing at a sutficient speed to cause developer material therein to be thrust to the housing walls by centrifugal force and dispersed through the perforations therein to impinge the image member.

2. The apparatus of claim 1, said housing including a lower portion having tapered outer walls and a cylindrical upper portion, said upper portion being perforated and sealed at the top thereof and placed approximately opposite to said image member.

3. The apparatus of claim 1, wherein said housing is an inverted truncated conical shape with an upper portion containing perforations, said perforated portion opposite to said image member.

4. The apparatus of claim 1, wherein said housing is cylindrical in shape and is approximately opposite a xerographic drum image member and is caused to rotate around an axis approximately perpendicular to the longitudinal axis of said drum image member.

5. The apparatus of claim 1 wherein said means to cause developer to enter said housing and to remain in mechanical contact therewith comprises slats in intimate contact with the inner wall of said housing along a substantial portion of its length and extending below said housing.

6. The apparatus of claim 5 further including a cap in association with the upper portion of said perforated housing such that the top thereof is sealed whereby any developer material therein is dispersed through the perforations of said housing by the centrifugal force.

7. The apparatus of claim 6 including a container, adapted with an opening to receive an image member, enclosing said housing, said container including a sump portion adapted to receive and hold developer material to be delivered to said housing.

8. The apparatus of claim 7, said container further including a cascade trap causing a portion of a developer material to remain in cooperative contact with an image member which it first impinged.

9. The apparatus of claim 7 further including a lifting member within said container adapted to bring developer material from the sump to the perforated housing, said housing being cylindrical with an opening to receive developer material and sealed such that developer material therein escapes through said perforations.

References Cited UNITED STATES PATENTS CHARLES A. WILLMUTH, Primary Examiner.

PETER FELDMAN, Examiner.

Claims

1. A DEVELOPER APPARATUS FOR USE IN DEVELOPING ELECTROSTATIC IMAGES ON AN IMAGE MEMBER COMPRISING A PERFORATED HOUSING ADAPTED TO CONTAIN DEVELOPER MATERIAL, SAID PERFORATION APPROXIMATELY OPPOSITE TO AN IMAGE MEMBER TO BE DEVELOPED, A MEANS TO CAUSE A DEVELOPER MATERIAL TO ENTER SAID HOUSING AND BE MAINTAINED IN MECHANICAL CONTACT THEREWITH, AND A MEANS FOR ROTATING THE HOUSING AT A SUFFICIENT SPEED TO CAUSE DEVELOPER MATERIAL THEREIN TO BE THRUST TO THE HOUSING WALLS BY CENTRIFUGAL FORCE AND DISPERSED THROUGH THE PERFORATIONS THEREIN TO IMPINGE THE IMAGE MEMBER.