US3897750A

US3897750A - Electrophotographic apparatus

Info

Publication number: US3897750A
Application number: US317123A
Authority: US
Inventors: Klaus Gunder
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1971-12-24
Filing date: 1972-12-21
Publication date: 1975-08-05
Anticipated expiration: 1992-08-05
Also published as: NL7217012A; DE2250703A1; GB1420762A; FR2170549A5

Abstract

An electrophotographic apparatus including a developing station for developing an electrostatic charge pattern and a rotatable drum for moving a carrier having such a pattern thereon past the station. The developing station comprising a developing electrode at the station which is adjustable in relation to the path of the carrier and a developer feeder which supplies developer to the space between the electrode and the carrier for adherence to the charge zones of the pattern. The electrode adjusting apparatus providing for each lateral edge of the developing electrode to be adjusted independently of the other in its relation with the path of the carrier may be constituted of an electrode being pivotally mounted on a shaft which extends across the path of the carrier, is parallel thereto, and is at right angles to the direction of movement of the carrier. The electrode is provided with a projection which extends beyond the respective side of the path of the carrier, each projection having an internally threaded bore therethrough for receiving an adjusting screw which contacts a stop forming a portion of the housing. The electrode adjusting apparatus may also be constituted of an electrode being pivoted or axially displaced by at least one spacing element which contacts and moves over the surface of the carrier.

Description

United States Patent [191 Gunder 1 1 ELECTROPHOTOGRAPHIC APPARATUS [75] Inventor: Klaus Gunder, Darmstadt, Germany [73] Assignee: Hoechst Aktiengesellschatt,

Wiesbaden-Biebrich, Germany 22 Filed: Dec. 21, 1972 [21] App]. No.: 317,123

[30] Foreign Application Priority Data Dec. 24, 1971 Germany 2164494 Oct. 16, 1972 Germany 2250703 [52] US. Cl. 118/637 [51] Int. Cl. G03G 13/00 [58] Field of Search 117/175; 118/2, 6, 637; 355/3 DD, 14; lOl/DlG. 13

[56] References Cited UNITED STATES PATENTS 2,952,241 9/1960 Clark et a1 118/637 3,011,474 12/1961 Ulrich 1. 118/637 3,105,426 10/1963 Bickmore et al.... 355/3 DD 3,147,147 9/1964 Carlson 118/637 3,357,399 12/1967 Fisher.,,. 118/637 3,416,494 12/1968 Hudson 118/637 3,662,711 5/1972 Hudson 118/637 Primary ExaminerMorris Kaplan Attorney, Agent, or FirmStevens, Davis, Miller & Mosher 1 Aug. 5, 1975 5 7 ABSTRACT An electrophotographic apparatus including a developing station for developing an electrostatic charge pattern and a rotatable drum for moving a carrier having such a pattern thereon past the station. The developing station comprising a developing electrode at the station which is adjustable in relation to the path of the carrier and a developer feeder which supplies developer to the space between the electrode and the carrier for adherence to the charge zones of the pattern. The electrode adjusting apparatus providing for each lateral edge of the developing electrode to be adjusted independently of the other in its relation with the path of the carrier may be constituted of an electrode being pivotally mounted on a shaft which ex tends across the path of the carrier, is parallel thereto. and is at right angles to the direction of movement of the carrier. The electrode is provided with a projection which extends beyond the respective side of the path of the carrier, each projection having an internally threaded bore therethrough for receiving an adjusting screw which contacts a stop forming a portion of the housing. The electrode adjusting apparatus may also be constituted of an electrode being pivoted or axially displaced by at least one spacing element which contacts and moves over the surface of the carrier.

8 Claims, 7 Drawing Figures SHEET PATENTED 51975 SHEET PATENTEU 5W5 Q on mm R w 0 m wN W 3 ELECTROPHOTOGRAPHIC APPARATUS The present invention relates to electrophotographic apparatus.

Electrostatic charge patterns are widely produced nowadays, especially in electrophotographic reproduction machines, and may be rendered visible with, for example, the aid of a two-component developer. In a developing process of this kind, color-producing components of the developer are preferentially deposited at the zones where the differences in charge are greatest and in some cases it is difficult to develop grey tones and larger dark areas. Thus, for example, the large areas are usually developed only at the edges, remaining bright in the middle. Attempts have been made to overcome these difficulties by the use of so-called developing electrodes.

The use of developing electrodes, however, causes numerous other difficulties. Thus, for example, it is particularly difficult to keep the field distribution produced by a developing electrode constant in the case of a relatively wide photoconductor. Furthermore, when photoconductor drums are changed in electrophotographic reproduction machines, there is a danger that the geometric arrangement will no longer be exact and that development will take place unevenly over the width of the imagev The present invention provides electrophotographic apparatus which comprises a developing station for de veloping an electrostatic charge pattern and means for moving a carrier having such a pattern thereon over a predetermined path past the station, the station comprising a developing electrode which can be connected to a voltage source and beneath which the pattern can be developed by means ofa developer of which at least a part adheres to the charged zones of the pattern, the position of the developing electrode in relation to the path of the carrier being adjustable.

The present invention makes it possible to obtain good development over the entire surface and good development of grey tones. These good results can be obtained over long periods, and even when the material carrying the charge pattern (the carrier) is changed.

More particularly, the adjustable arrangement of the developing electrode enables problems relating to the fitting of the electrode to be solved and allows account to be taken of variations in dimensions occurring during manufacture of the electrodes. It is also possible by varying the adjustment to obtain different qualities of copy and, for example, to set the apparatus to suit particular originals, for example those exhibiting slight contrast. Finally, it may also be possible to use a slightly twisted developing electrode without the quality of the copy suffering, by adjusting the position of the electrode to compensate for the twist,

In the simplest case the developing electrode is secured in the copying machine with the aid of adjusting means permitting fine adjustment of the position of the electrode in relation to the path of travel of the record carrier. The adjusting means are preferably so designed and arranged in the copying machine that the distances of the two lateral edges of the developing electrode from the path of the record carrier can be adjusted independently of each other. By means of this arrangement, the distance between the developing electrode and the path of the record carrier can be adjusted, and

unintentional inclination of the electrode relative to the path of the carrier can be corrected.

In the embodiment of the present invention described above the developing electrode is preferably pivotally mounted on a shaft which extends across the path of the carrier, is parallel thereto, and is at right angles to the direction of movement of the carrier. Each lateral edge of the developing electrode is advantageously provided with a projection which extends beyond the respective side of the path of the carrier, each projection having an internally threaded bore therethrough for receiving an adjusting screw and the housing of the apparatus comprising a stop for the end of each adjusting screw. The apparatus may also comprise locking means for securing the adjusting means against unintended movement. The locking means advantageously comprises two screws, one positioned on each side of the path of the carrier, each screw passing through a respective bore in the developing electrode and being received in a respective internally threaded recess in the housing of the apparatus.

According to the present invention, for all those cases in which a rigid arrangement of the developing electrode is not required, the electrode is so formed and arranged in the apparatus that it is in mechanical engagement with a support for the record material, so that the distance between the developing electrode and the carrier of the electrostatic pattern and their position relative to each other are automatically kept constant. Accordingly, the apparatus of the present invention may, instead of comprising the adjusting means described above, comprise support means for moving the carrier and determining its path past the developing electrode, the developing electrode being such that it can be pivoted and/or axially displaced and being provided with at least one distance piece which can contact, and move over, the surface of the support.

The developing electrode may be pivotally mounted on a shaft which extends across the path of the carrier, is parallel thereto, and is at right angles to the direction of movement of the carrier, the shaft being positioned either upstream or downstream of the zone in which developing takes place; in this case, a distance piece is preferably provided at each lateral edge of the developing electrode.

Alternatively, the developing electrode may be pivotally mounted on a shaft which extends across the path of the carrier above the zone in which developing takes place, the shaft being parallel to the carrier at right angles to its direction of movement. In this case, the developing electrode is such that it can be moved along a line at right angles to the portion of the carrier located beneath the shaft and there are at least two distance pieces, the two lateral edges, and the leading and trailing edges, of the developing electrode each being provided with at least one distance piece. If there are only two distance pieces these are disposed at diametri cally opposite corners of the developing electrode, Preferably, however, there are four distance pieces arranged at the corners of a square or rectangle, one distance piece being disposed at each corner of the developing electrode. In a preferred form of the abovedescribed apparatus, each end of the shaft projects through a slot in the shaft mounting, the slot extending at right angles to the surface of the support,

The distance piece or each distance piece in the ap paratus of the invention is advantageously biased against the surface of the support. Each distance piece preferably comprises a roller mounted on a spindle which is parallel to the carrier and is at right angles to its direction of movement.

In the apparatus of the present invention, the support means preferably comprises a drum and the carrier 3 photoconductor. The drum may include a lock for the photoconductor. If it does, the surface of the drum preferably has a raised portion of such a length that it subtends substantially the same angle at the center of the drum as does the developing zone, the raised portion being so disposed in relation to the lock that it remains in contact with the distance piece(s) as long as the lock is moving beneath the developing electrode. and the amount by which the raised portion extends beyond the surface of the drum being at least equal to the amount by which the lock projects beyond the surface of the drum.

The position of the developing electrode can also be controlled by hydraulic or electromagnetic means.

In the developing zone, the developing electrode preferably has a bright surface finish. It may be made of aluminum.

The apparatus may also comprise guide means for dividing the developer into two partial streams of different sizes, the smaller partial stream passing between the developing electrode and the carrier and the larger partial stream contacting the portion of the carrier that has passed beneath the developing electrode. The amount of developer that flows beneath the developing electrode is preferably 2 to 12%, advantageously of the total amount of developer. The apparatus advantageously also comprises a cascade feed device for supplying developer to the developing zone, a reservoir for developer being provided upstream of the developing zone and the magnitude of the smaller partial stream being determined only by the movement of the carrier and the developing electrode.

The particular advantages of the non-rigid apparatus of the present invention are as follows. As a result of the self-adjustment of the distance between the developing electrode and the photoconductor (carrier), a single setting of the guide means for the electrode suffices, so that the desired conditions are maintained even when the photoconductor or its drum is changed, or when other maintenance operations are carried out. Damage to the developing electrode and in particular to its polished surface is prevented. The apparatus can be incorporated in electrophotographic reproduction machines without high costs being incurred.

The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. I is a diagrammatic representation of an electrophotographic reproduction machine;

FIG. 2a is a diagrammatic representation of a developing electrode;

FIG. 2b is a side elevational view of the electrode of FIG. 22;

FIG. 3 shows a developing electrode and a photoconductor drum with control surfaces and distance pieces;

FIG. 4 shows yet another form of developing electrode;

FIG. 5 illustrates a form of construction of the apparatus of the invention comprising a fixed but adjustable arrangement for setting the position of the developing electrode; and

FIG. 6 is a front elevation view of the apparatus of FIG. 5.

Referring now to FIG. I of the drawings, a photoconductor 2, fitted on a drum 1, can be charged uniformly by a corona-discharge unit 3. The charged photoconductor 2 can be exposed to provide an image at an exposure station 4, and can be developed in a developing station 5, the latter comprising two zones. The developed charge pattern can be transferred in the transfer station 6 to a copy carrier 7, for example, paper. The apparatus of the invention can of course also be used if zinc oxide paper (ZnO paper) is employed instead of a photoconductor 2 that can be repeatedly used. In this case there is of course no transfer station 6, since the zinc oxide paper constitutes the photoconductor and the material for carrying the copy.

Developing of the electrostatic charge pattern produced in the exposure station 4 takes place in the following manner. Developer 10 is passed from a supply container 8 with the aid of a bucket conveyor system 9 and is allowed to trickle over a developing electrode II. Part of the developer I0 passes into the reservoir 12 from which it is carried beneath the developing electrode II by the photoconductor 2. The main mass of the developer 10, however, flows past the outer face of the electrode 11 and trickles over that zone of the photoconductor 2 that has been previously developed below the developing electrode 11. The developing electrode II has a projection 13, the purpose of which is to control the quantity of developer that can pass below the actual developing zone b c of the electrode 11.

The distance between the electrode 11 and the photoconductor 2 at the point c is approximately 2.4 mm and at the point b about 1.6 mm. In some of the Figures these distances are not shown to scale in order to render the Figures in question clearer. The mean thickness of the carrier material is approximately 0.4 mm.

Since the distance between the electrode II and the photoconductor in the developing zone c b is extremely critical, the electrode 11 is mounted to pivot about spindle 14 (see FIG. 2b). To enable the electrode 1 1 always to remain at the same constant distance from the carrier 2 of the electrostatic charge pattern, freely rotatable and preferably insulated rollers or small wheels 15 are fitted at its sides, and these can run on the surface of the photoconductor or on the surface of the drum (see FIG. 2a). The developing electrode 11 may be pressed against the photoconductor drum 1 by a spring 16 (See FIG. 2b). The spindles 14 on which the developing electrode 11 can pivot are mounted to rotate in arms 17.

It has been found that with the aid of a single setting of the arms 17 in the above-described apparatus, copies of uniformly high quality can always be obtained without, for example. the changing of the photoconductor or of the drum therefor resulting in any trouble.

A modified form of photoconductor drum which can be used in the apparatus of the present invention is il lustrated in FIG. 3. To secure the photoconductor 2 on the drum 1 and at the same time to prevent penetration of developer into the interior of the drum, there is provided a lock 18 which extends over the entire width of the strip of photoconductive material 2. This lock 18 is not precisely flush with the surface of the drum 1, but for the most part projects slightly above said surface. The present invention makes it possible to ensure that the developing electrode 11 is not permanently displaced from its set position or damaged by the projecting lock 18. For this purpose, a projection 19 is provided at each side of the photoconductor 2 and over an angular zone a which corresponds to the actual developing zone of the electrode. that is, to the angle between b and c. Each of these projections 19 projects beyond the surface of the drum to an extent at least equal to the extent by which the lock 18 projects beyond the surface of the drum.

The projections 19 are so arranged, that when the drum 1 is turning, they move into contact with the rollers when the lock 18 moves below the developing electrode 11. The electrode I1 is lifted from the surface of the drum by the projections and the lock 18 does not come into contact with it. When the lock 18 has passed below the electrode 11, the wheels 15 roll over the rearward end of the projection 19, and the electrode 11 is again brought into the original spaced relationship with the photoconductor 2. This arrangement offers the particular advantage that the lock 18 can be of relatively uncomplicated construction without it being necessary to forego the use of an electrode 11 that lies close to the photoconductor 2.

A further embodiment of the apparatus of the invention is illustrated in FIG. 4. In this example the developing electrode 11 is not only adapted to swing about a spindle 14 but is also movable perpendicularly as a whole towards and away from the photoconductor 2. For this purpose arms 37 are each provided with a slot 20 in which the spindle 14 can move. In this embodiment, the developing electrode 11 has two wheels 15, and two wheels 15', only two of which are shown in FIG. 4.

The developing electrode 11 is pressed against the photoconductor drum 1 by

springs

21 and 21 which are compressed between the electrode and a backing element 22 mounted on the arms 17. This arrangement offers the additional advantage that even if the photoconductor drum 1 is positioned off-center, this has no effect on the conditions of the developing process. The developing electrode 11 always remains in the same specific position in relation to the photoconductor drum 1, Le, it always remains at the desired distance from the drum.

In the case of the embodiment of the present inven tion illustrated in FIGS. 5 and 6, the position of the developing electrode is not adjusted automatically in the manner described with reference to FIGS. 1 to 4; instead. the apparatus is provided with an adjusting unit to which the developing electrode is secured.

In the apparatus shown in FIGS. 5 and 6, the distance between the developing electrode 11 and the photo conductor 2 is about 2 mm. The mean thickness of the carrier material is about 0.4 mm. In general, a distance between the electrode 11 and the charge pattern that is approximately 4 to 6 times as great as the mean thickness of the carrier is preferred. The electrode 11 has a projection 13 which serves the purpose of measuring out the quantity of developer passing below the actual electrode. To vary the quality of the copies and in particular to eliminate a poor quality of copy, the developing electrode 11 is connected to an adjusting device.

The electrode 11 is firmly connected to two U- section bars 24 mounted on either side of the electrode. These bars 24 are mounted with the aid of bearings 25 on shafts 26 in retaining elements 27 which are firmly connected to the housing of the copying machine.

Projections 28 extend outwards from the U-section bars 24, these projections each having a fine female screw-thread 29. Cooperating with the screw-threads 29 are screws 30 the ends of which bear against backing elements 31 which are firmly connected to the retaining elements 27. By turning the screws 30 the dis tance of the developing electrode II from the photoconductor 2 can be adjusted independently at each side.

To avoid unintentional displacement of the finethreaded screws 30, there are provided counter-screws 32. These counter-screws cooperate with screwthreads 33 in the retaining elements 27 and extend through bores 34 in the U-section bars 24. Tightening of the counter-screws 32 after the adjusting screws 30 have been set causes a pressure to be exerted on the fine screw-threads and this is sufficient to prevent the screws 30 from being unintentionally turned.

The longitudinal axes of the adjusting screws 30 and also of the counter-screws 32 do not intersect the shafts 26. This is necessary in order to enable the position of the developing electrode 11 to be adjusted by its being swung about the shafts 26 and to enable the electrode 11 to be locked in position.

What is claimed is:

1. Electrophotographic apparatus which comprises a developing station for developing an electrostatic charge pattern and means for moving a carrier having such a pattern thereon over a predetermined path past the station, the station comprising a developing electrode which can be connected to a voltage source and beneath which the pattern can be developed by means of a developer of which at least a part adheres to the charged zones of the pattern, the position of said developing electrode in relation to the path of the carrier being adjustable, said developing electrode being pivotally mounted on a shaft which extends across the path of the carrier, is parallel to said shaft, is at right angles to the direction of movement of the carrier, and is connected to two bars mounted on either side of the developing electrode, each bar being provided with a projection which extends outwards from the bar and beyond the respective side of the path of the carrier, each projection having an internally threaded bore therethrough for receiving an adjusting screw and the housing of the apparatus comprising a stop for the end of each adjusting screw.

2. The apparatus of claim 1 also comprising locking means for securing the adjusting means against unin tended movement.

3. The apparatus of claim 2 wherein the locking means comprises two screws, one positioned on each side of the path of the carrier, each screw passing through a respective bore in the developing electrode and being received in a respective internally threaded recess in the housing of the apparatus.

4. The apparatus of claim I wherein the means for moving the carrier and determining its path comprises a rotatable drum.

5. The apparatus of claim 1 also comprising guide means for dividing the developer into two partial streams of different sizes, the smaller partial stream passing between the developing electrode and the carrier and the larger partial stream contacting the portion oping zone, a reservoir for developer being provided upstream of the developing zone and the magnitude of the smaller partial stream being determined only by the movement of the carrier and the developing electrode.

8. The apparatus of claim 1 wherein the developing electrode has a bright surface in the developing zone. 1K

Claims

2. The apparatus of claim 1 also comprising locking means for securing the adjusting means against unintended movement.

4. The apparatus of claim 1 wherein the means for moving the carrier and determining its path comprises a rotatable drum.

5. The apparatus of claim 1 also comprising guide means for dividing the developer into two partial streams of different sizes, the smaller partial stream passing between the developing electrode and the carrier and the larger partial stream contacting the portion of the carrier that has passed beneath the developing electrode.

6. The apparatus of claim 5 wherein the smaller partial stream comprises from 2 to 12% of the total amount of developer.

7. The apparatus of claim 5 also comprising a cascade feed device for supplying developer to the developing zone, a reservoir for developer being provided upstream of the developing zone and the magnitude of the smaller partial stream being determined only by the movement of the carrier and the developing electrode.

8. The apparatus of claim 1 wherein the developing electrode has a bright surface in the developing zone.