Electric Charging Device For Electrophotography

Abstract

Method and apparatus for uniformly charging the surface of a curved insulating member. A carrier member has a plurality of joining members disposed at substantially equal intervals thereon. Each of a plurality of needle electrodes is retained respectively by an associated joining member. When a force of sufficient magnitude is exerted on the needle electrodes, the tips of the electrodes are forced into contact with the member, the tips forming an envelope which conforms to the curved surface of the member. The needle electrodes are subsequently withdrawn to a predetermined position above the surface and an electric discharge potential is applied thereto, whereby a uniform electric charge is deposited on the surface of the insulating member.

Description

BACKGROUND OF THE INVENTION

The charging devices heretofore used in charging insulative members such as those utilized in electrophotography are designed to accomplish electric charging of electrophotographic sensitive layers in the form of flat or cylindrical members and therefore fail to provide electric charging for sensitive layers in complicatedly rugged forms. With the advancement of electrophotography, electrophotographic sensitive layers have become all the more complicated in shape, making it necessary to develop an electric charging device usable therewith. Where a given sensitive layer happens to have the shape of corrugated plate, for example, electric charging made by suing conventional electric charging devices enables the portion of the corrugated plate in corresponding to ridges of the corrugation to be charged to a higher potential because of the smaller distance from the corona discharge electrode and the portion corresponding to grooves to be charged to lower potential because of the greater distance from the corona discharge electrode. From the nature of electrophotographic equipment, however, it is necessary that the portion corresponding to ridges and the portion corresponding to grooves be charged to equal potential.

SUMMARY OF THE INVENTION

The present invention provides method and apparatus for uniformly charging the surface of a curved insulating member. In particular, a carrier member has a plurality of joining members disposed at substantially equal intervals thereon. Each of a plurality of needle electrodes is retained respectively by an associated joining member. When a force of sufficient magnitude is exerted on the needle electrodes, the tips of the electrodes are forced into contact with the member, the tips forming an envelope which conforms to the curved surface of the member. The needle electrodes are subsequently withdrawn to a predetermined position above the surface and an electric discharge potential is applied thereto, whereof a uniform electric charge is deposited on the surface of the insulating member.

It is an object of the present invention to provide method and apparatus for uniformly charging the surface of a curved insulating member.

It is a further object of the present invention to provide method and apparatus for uniformly charging an electrophotographic sensitive layer formed on the surface of a curved conductive member.

It is still a further object of the present invention to provide method and apparatus for uniformly charging the surface of a curved insulating member wherein a plurality of needle electrodes joined to a carrier member are forced into contact with the insulating surface and subsequently withdrawn, the tips of the electrodes forming an envelope conforming to the curved insulating surface.

BRIEF DESCRIPTION OF THE DRAWING

For a better understanding of the invention as well as other objects and further features thereof, reference is made to the following description which is to be read in conjunction with the accompanying drawing wherein:

FIG. 1 is a schematic sectional view of the electric charging apparatus of the present invention;

FIG. 2 is a sectional view of the apparatus shown in FIG. 1 in the state assumed when the apparatus is lowered until the tips of the needle electrodes thereof come into contact with the surface of the curved plate,

FIG. 3 is a sectional view illustrating the apparatus as elevated from the state in FIG. 2 up to a desired position;

FIG. 4 is a sectional view illustrating one mode of returning the needle electrodes of the apparatus to their original state;

FIG. 5 is a schematic oblique view of another embodiment of the apparatus according to the present invention;

FIGS. 6 (a)-6 (c) are enlarged sectional views illustrating various preferred embodiments of the joining member for fixing a needle electrode on a carrier plate;

FIG. 7 is a partially enlarged sectional view illustrating another embodiment of the joining member;

FIG. 8 is a sectional view illustrating an embodiment having an auxiliary carrier plate incorporated for needle electrode parallelism; and

FIG. 9 is a schematic oblique view illustrating an embodiment having a cylindrical guard disposed around every other needle electrode.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 represents apparatus for providing uniform electric charging a curved insulating member. For example, an electrophotographic sensitive layer is disposed on the surface of a curved conductive plate 102 mounted on base 101. Typical electrophotographic materials include cadmium sulphide, zinc oxide, selenium, sulphur selenium, etc. Numeral 103 denotes the electric charging apparatus of the present invention. Numeral 104 denotes needle-shaped charging electrodes of a fixed length; a multiplicity of such charging electrodes are arranged substantially uniformly two-dimensionally. A carrier plate 105 is provided for the needle electrodes 104, with the joining of the needle electrodes to the carrier plate being accomplished by means of joining members 106. The joining members 106 are either fixed onto the carrier plate 105 or formed inseparably therewith. The needle electrodes 104 are held in position by the joining members 106 in such way that, when exposed to a force of sufficient magnitude exerted in the axial direction thereof, they will slide in that direction but otherwise will be prevented from sliding. In other words, the retaining force of joining members 106 is limited within a certain level, so that, when the retaining force is overcome by a force of sufficient magnitude exerted in the axial direction, the joining members will allow the needle electrodes to slide. Examples of joining member 106 will be described hereinafter with reference to FIGS. 6(a)-6(c). FIG. 2 is a view of the electric charging device portion 103 of FIG. 1 in the state to be assumed when it has been pushed downward (or the base 101 is pushed upward) until the tips of the needle electrodes reach the lowermost point of the curved plate 102. Since the needle electrodes are movable by external force overcoming the retaining force, or power, of the joining members 106 and exerted in the axial direction, those needles electrodes which have reached the elevated portion of the curved plate are pushed back above the carrier plates 105. As shown in FIG. 2, therefore, an envelope 201 is formed by the heads of the needle electrodes conforming to, or in correspondence with, the shape of the curved plate.

When the electric charging apparatus is removed from the surface of the curved plate (or the base 101 is lowered downward) and brought to a stop at a desired position or height, as illustrated in FIG. 3, the tips of these needle electrodes and the curved plate are spaced by a substantially equal interval and the needle tips contacting the surface form an envelope conforming to the shape of the curved plate. When these needle electrodes are joined electrically and a high electric potential is applied between the needle electrodes and the curved plate, corona discharge is produced from the tips of these needle electrodes the surface of the curved plate being charged substantially uniformly. According to the present invention, therefore, uniform electric charging can be accomplished on any curved member no matter how complex the shape may be.

When another curved plate is to be charged, a flat plate 401 may be pushed down upon the electric charging apparatus as illustrated in FIG. 4 of the electric charging apparatus may be pushed up against the flat plate 401 so as to cause the heads of the needle electrodes to be aligned. In this way, the electric charging apparatus can be brought back to its original state shown in FIG. 1. For subsequent cycles of charging, this procedure has only to be repeated.

The foregoing description presumes a case in which the surface of the curved plate has a three-dimensionally varied shape. Where the surface of the curved plane has a two-dimensionally varied shape, namely, when the curved plate is something like a corrugated plate, the device of this invention becomes much simpler. FIG. 5 is a schematic representation of the apparatus of the invention which is usable in such case. For the purpose of electrically charging a corrugated plate 502 on the base 501, the electric charging apparatus 503 comprises a row of needle electrodes 504, a supporting bar 505 and joining members 506. Similarly to the apparatus described hereinabove, the needle electrodes and the joining members are retained by a limited magnitude of force. When the tips of the needle electrodes are so arranged as to conform to the shape of the corrugated plate 502 and electric potential is applied thereto while they are moved to scan the surface in the direction of the arrow mark 507 (the direction in which the sectional shape of the corrugated plate remains unchanged) the surface of the corrugated plate is charged substantially uniformly.

FIG. 6 shows a few specific examples of the joining member. FIG. 6 (a) represents an example utilizing a rubber bushing 603, in which a needle electrode 601 is retained in the hole of the bushing while the bushing is fixed on the carrier plate 602. When the hole in the rubber piece is given a diameter slightly smaller than that of the needle electrode, the electrode is made to slide by a force of sufficient magnitude applied in the axial direction of the needle electrode to overcome the retaining force of rubber bushing 603. FIG. 6 (b) represents an example making use of a leaf spring 613. One end of this leaf spring is fixed on the carrier plate 602 and the other end holds the needle electrode in position together with the corresponding end of another leaf spring 613'. The object of the invention can be fulfilled by selecting the strength of the leaf spring suitable. FIG. 6 (c) represents an example utilizing the resiliency of the carrier plate 602 itself. A portion of the carrier plate is bent as illustrated so as to function as a spring, with the resiliency produced thereby utilized for supporting the needle electrode. The joining member suffices so long as it has a construction such that the needle electrode is moved by a force of sufficient magnitude to overcome the retaining force of the joining member. FIG. 7 shows another preferred embodiment of the device of the present invention. FIG. 7 represents a device so designed that the needle electrodes can be moved freely only when the envelope formed by the tips of needle electrodes is arranged to conform to the shape of the curved plate, while they are immobilized at any other time. The needle electrode 601 can fall freely by gravitational pull through the guide 604 which is provided at one portion of the carrier plate 602. When the electromagnet 605 is functioning, however, the needle electrode is attracted by the electromagnet and therefore is prevented from falling. When the envelope is desired to be formed, therefore, the electromagnet is not energized, enabling the needle electrode to fall until it reaches the curved plate. The envelope conforming to the curved plate can be obtained by energizing the electromagnet at the time the needle electrode reaches the curved plate and then lifting the electric charging apparatus. Any suitable device which can take the place of electromagnet 605 and which produces the same effect as mentioned above may be utilized.

Although the carrier plates are maintained horizontally in all the illustrated examples, they may be inclined by a desired angle, of course. This angle is determined by the case with which the surface being charged can be retained.

The needle electrodes 804 joined by joining member 806 to carrier plate 805 may be maintained in exact parallelism with one another by utilizing an auxiliary carrier plate 807, as shown in FIG. 8.

The intervals between the needle electrodes are determined by the shape of the surface to be charged, the distance from the surface for charging to the tips of the needle electrodes, and the required degree of uniformity of electric charging and therefore cannot be fixed absolutely.

Generally speaking, uniform electric charging can be obtained by selecting the intervals such that the shape of individual sections of the material falling between two adjacent needle electrodes can be nearly approximated by a straight line or a plane.

The individual needle electrodes are maintained at an equal electric potential. If they are placed too close to one another, therefore, they may be affected by those positioned in the immediate neighborhood. Accordingly, they may fail to produce equal discharging. To avoid this, a grounded conductor arranged close to each needle electrode may be provided. According to one conceivable method, charging apparatus 903 and curved plate 905 may be arranged to include a cylindrical guard, or shield 908, disposed around every other needle electrode 904 as illustrated in FIG. 9, for example. The guard 908 may be disposed as to be moved up and down synchronously with the movement of the electrode or it may be fixed at a given height.

Although the member to be charged has been characterized as including an electrophotographic layer, the present invention may be utilized with equal facility with an electrically insulating layer formed on a curved substrate. For example, a latent electrostatic image may be formed on a layer of plastic formed on a curved substrate.

While the invention has been described with reference to its preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teaching of the invention without departing from its essential teachings.

Claims

What is claimed is:

1. A method for uniformly charging the surface of a curved insulating member comprising the steps of:

positioning a carrier member having a plurality of joining members disposed at substantially equal intervals thereon above said insulating surface, a plurality of needle electrodes being retained respectively by means of said joining members substantially vertical with reference to the plane of said carrier member,

applying a force of sufficient magnitude to said needle electrodes to overcome the retaining force of said joining members, whereby said needle electrodes are caused to contact said insulating surface, the tips of said needle electrodes forming an envelope which conforms to the shape of the insulating surface,

separating said needle electrodes and said insulating surface a predetermined distance, and

applying an electric discharge potential to said needle electrodes whereby the corona discharge emitted by said needle electrodes deposits substantially uniformly on said insulating surface.

2. The method as set forth in claim 1 wherein said insulating member comprises an electrophotographic layer overlying a conductive substrate.

3. The method as set forth in claim 1 further including the step of realigning the tips of said needle electrodes.

4. A method for uniformly charging the surface of a curved insulating member comprising the steps of:

positioning a carrier member having a plurality of joining members disposed at substantially equal intervals thereon above said insulating surface, a plurality of needle electrodes being retained respectively by means of said joining members substantially vertical with reference to the plane of said carrier member,

releasing the retaining force of said joining members on said needle electrodes, whereby said needle electrodes are caused to contact said insulating surface, the tips of said needle electrodes forming an envelope which conforms to the shape of the insulating surface reapplying the retaining force of said joining members on said needle electrodes,

separating said needle electrodes and said insulating surface a predetermined distance, and

applying an electric discharge potential to said needle electrodes whereby the corona discharge emitted by said needle electrodes deposits substantially uniformly on said insulating surface.

5. The method as set forth in claim 1 wherein said insulating member comprises an electrophotographic layer overlying a conductive substrate.

6. Apparatus for uniformly charging the surface of a curved insulating member comprising:

a carrier member having a plurality of joining members disposed at substantially equal intervals on said carrier member and a plurality of needle electrodes retained respectively by said joining members substantially vertical with reference to the plane of said carrier member, said carrier member being positioned above said insulating surface,

means for applying a force to said needle electrodes of sufficient magnitude to overcome the retaining force of said joining members whereby said needle electrodes are caused to contact said insulating surface, the tips of said needle electrodes forming an envelope which conforms to the shape of the insulating surface,

means for separating said needle electrodes and said insulating surface a predetermined distance, and

means for applying an electric discharge potential to said needle electrodes, whereby the corona discharge produced by said needle electrodes deposits substantially uniformly on said insulating surface.

7. The apparatus as set forth in claim 6 wherein said insulating member comprises an electrophotographic layer overlying a conductive substrate.

8. The apparatus as set forth in claim 6 further including an additional carrier member for supporting said needle electrodes, whereby said needle electrodes are maintained substantially in parallelism.

9. The apparatus as defined in claim 6 further including means for shielding said needle electrodes from the effect of the discharge produced by adjacent needle electrodes.

10. Apparatus for uniformly charging the surface of a curved insulating member comprising:

a carrier member having a plurality of joining members disposed at substantially equal intervals on said carrier member and a plurality of needle electrodes retained respectively by said joining members substantially vertical with reference to the plane of said carrier member, said carrier member being positioned above said insulating surface,

means for releasing the retaining force of said joining member on said needle electrodes whereby said needle electrodes are caused to contact said insulating surface, the tips of said needle electrodes forming an envelope which conforms to the shape of the insulating surface,

means for reapplying the retaining force of said joining members on said needle electrodes,

means for separating said needle electrodes and said insulating surface a predetermined distance, and

means for applying an electric discharge potential to said needle electrodes, whereby the corona discharge produced by said needle electrodes deposits substantially uniformly on said insulating surface.

11. The apparatus as set forth in claim 10 wherein said insulating member comprises an electrophotographic layer overlying a conductive substrate.

12. The apparatus as set forth in claim 10 further including an additional carrier member for supporting said needle electrodes, whereby said needle electrodes are maintained substantially in parallelism.

13. The apparatus as defined in claim 10 further including means for shielding said needle electrodes from the effect of the discharge produced by adjacent needle electrodes.