US3736424A

US3736424A - Corona discharge device

Info

Publication number: US3736424A
Application number: US00204464A
Authority: US
Inventors: T Cecil; R Davidge
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1971-12-03
Filing date: 1971-12-03
Publication date: 1973-05-29
Anticipated expiration: 1990-05-29
Also published as: FR2164155A5; IT967751B; JPS5121797B2; GB1398024A; CA1001219A; DE2257930B2; JPS4864937A; DE2257930A1

Abstract

The continued performance of a charge corona for an electrostatic copy machine is enhanced by the provision of specially configured corona wire support blocks that minimize current leakage through hygroscopic salts accumulating on the support block surface. The support blocks are configured to include a surface interruption that provides a cul-de-sac including surface which is shielded from the path of corona current and ionized gas thereby preventing accumulation of salts on the shielded portion.

Description

United States Patent 11 1 Cecil, II et al. 1 May 29, 1973 541 CORONA DISCHARGE DEVICE 2,070,307 2/1937 Nicholls ..2s/49.s cc 3,369,152 2/l968 Spengler... ....250/49.5 0c [75] mentorss i fig gg i g 3,114,377 12/1963 Dunham ..2s0/49.s 0c 9 v [73] Assignee: International Business Machines Examiner1ames Lawrence I Corporation, Armonk, NY. Assistant Examiner-B. C. Anderson Attorney-E. Ronald Coffman, C. E McTiernan, [22] Filed; l)ec. 3, 1971 Y J JancinJL c aL [21] Appl. No.: 204,464

[57] v ABSTRACT 521 US. (:1. ..2s0/49.5 zc, 250/495 0c The continued Performance of a charge coma for 511 1111.01 .1101, 37/00 elecmsmm is enhamd by the P [58] Field of Search ...2s0/495zc 4950c Specially blocks that minimize current leakage through hygroscopic salts accumulating on the support block sur- [56] References Cited face. The support blocks are configured to include a a v surface interruption that provides a cul-de-sac includ- UNITED STATES PATENTS ing surface which is shielded from the path of corona current and ionized gas thereby preventing accumula- 3;

tion of salts on the shielded portion.

r 12 Claims, 3 Drawing Figures 15 L J L a V l I \d l 4124 44 44 k 42/3? 1 1 55 p 1 1 1 I 1 v(25 7/0 '1: I li I777 n I II 22 55, 23 1 I L 22 31 L U J 56 V/ M 38| l I Sl'fl j 1 CORONA DISCHARGE DEVICE BACKGROUND OF THE INVENTION Electrostatic document copying machines commonly employ a photoconductive copy surface capable of selectively discharging a uniformly applied initial electrostatic charge in response to a light image.

embodiment of our inventive concepts wherein refer- A latent electrostatic image remains following the discharge which can be developed by the application of charged electroscopic powder through any of several techniques. The more sophisticated techniques employ a magnetic brush or powder cloud with a development electrode and are capable of developing half-tones and solid areas as well as line copy.

Since the latent image is in the form of differential charge levels on the copy surface to which the charged electroscopic powder is attracted, it is important that these differences represent the intended image as accurately as possible. The charge corona is one possible source of non-image variations in charge which can interfere with the accurate reproduction of a document. Uniform operation of a charge corona is achieved through the selection of relatively large corona current flow which, by its very magnitude, reduces the significance of potential non uniformities.

It can be appreciated thatloss of current through leakage paths thus, would reduce the quality and efficiency of corona performance. Where leakage paths develop through continued use or through use under varying conditions, the performance of the entire copying process will suffer accordingly.

It has thus been an object of our invention to eliminate a major source of corona current leakage caused by the accumulation of conductive salts on the surface of necessary electrode support structure. A further object of our invention has been to provide a corona discharge unit having a sustained high quality performance that is achieved by the simple configuration of the electrode support parts.

DISCLOSURE OF THE INVENTION It has been determined that the ionization of gases in the air characteristic of a corona discharge result in the precipitation of hygroscopic electrically conductive salt on surfaces over which ionized gases pass. The corona discharge operation itself creates a gas movement in the direction of ion flow. The gases brush against the surfaces adjacent to their path and deposit salts thereon. These salts can form a conductive path along the surface of various supporting members from the corona wire to other conductive structure such as a control grid, a current receiving shield, or even the machine frame. Our invention provides an interruption in the surface of corona wire support structure such as end-blocks, to prohibit a continuous path of conductive salts from being developed through corona operation. The interruption comprises a shielded surface portion that is substantially out of the path of ionized gases and can preferably be in the form of an elongated cul-desac having a restricted entrance that is inherently nonreceptive to gaseous flows. Thus, in a corona unit designed in accordance with our invention, all paths from the point of corona electrode contact with support structure to adjacent conductive structure, must traverse a shielded non-conductive surface.

Our invention will be more completely understood from the following description of a specific illustrative ence is made to the accompanying drawings, of which:

FIG. 1 is an elevational schematic view of a xerographic type electrostatic copy reproducing machine; FIG. 2 is a cross-sectional view of a charging corona unit constructed in accordance with our invention and taken along the line of its longitudinal axis; and

FIG. 3 is a side cross-sectional view of the corona unit shown in FIG. 2 taken along axis III III thereof. Referring now more specifically to the drawings, in FIG. 1 there is showna xerographic type electrostatic copy reproducing mechanism 10 having a corona discharge assembly or charge corona unit 20 for placing a uniform electrostatic charge on a copy drum surface 1 l. The charged copy surface 11 is passed under an imaging station 12 where the original charge is selectively discharged by a light image from an original document 13. The resultant latent image is moved to a development station 14 which for example could be like that described in U. S. Pat. No. 3,599,605. After the image is developed, it is passed to a transfer station 15 where plain paper is fed into superimposition therewith and the image is transferred to the paper. The paper then is separated from the drum surface 11 and passed to a heat fixing station 16 while the drum surface 11 continues to move to a cleaning station 17 for preparation for further copying. As discussed above, the ability of the copy machine 10 to faithfully reproduce an image of the original document 13 depends, in part, upon the uniformity of the initial charge received by surface 11 from the charge corona unit 20.

One preferred form of corona construction is shown in FIGS. 2 and 3. The corona unit 20 includes three elongated corona emitting electrode wires 21 that are suspended in spaced relation from the copy surface 11 between hooks 22 carried by a pair of electrically insulative end blocks 30 best shown in FIG. 2. The end blocks 30 are connected to suitable frame-work 18 through an electrically conductive shield 40 by screws 41. The shield 40 is slideably mounted by a track member 42 on dovetail frame part 19 connected to the machine frame part I8 to permit removing of the corona unit 20 for repair or cleaning.

The hooks 22 are connected to the electrode wire ends 23 by tensioning springs 24. Conductor rod 25 extends through the end block 30 and is electrically connected with the books 22 at one end and projects outwardly of a tapered plug portion 31 for connection to a suitable power'supply 26, see FIG. 1.

The charge corona unit 20 also includes a wire con trol grid 50 positioned between the corona wires 21 and the drum surface 11 for limiting the corona current received by the drum surface 11. The wires 51 of grid 50 are also supported by the end blocks 30 as best shown in FIG. 2.

One end of each grid wire 51 is connected through tensioning springs 52 to a tab 53 of a mounting plate 54. A screw 55 anchors the mounting plate 54 to the end block 30. Aconductor rod 56 is connected to the mounting plate 54 to provide for connection of the grid 50 to a suitable potential source such as power supply 26, see FIG. 1.

In operation, the electrode wires 21 are connected to a high potential line 27 of power supply 26. Also, the shield 40 and grid 50 are connected to a lower potential line 28 of the power supply 26, through

conductors

43 and 56a respectively. Alternatively, the shield 40 can be connected to ground if desired. The difference in potential between the electrode wires 21 and the shield 40 and grid 50 causes the air therebetween to become ionized and a so-called corona current discharge or flow occurs. Since the copy surface 11 is at a different potential than the corona electrode wires 21, a potential exists for causing a portion of the corona current flow to go past the grid' 50 and deposit charge on the copy surface 11. The path of the corona discharge current flow is shown by the lines 32 in FIGS. 1 and 2.

The flow of current in a corona discharge is accompanied by a movement of the gases that are ionized and these gases also move along the path of corona discharge 32. As seen in FIG. 2 these gases will brush against inwardly facing external surface 33 of the supporting end blocks 30. While all of the end blocks 30 are made of electrically insulated material and thereby provide no conductive path for current flow between v the corona electrode wires 21 and other conductive parts connected thereto, such as the grid wires 50 or the shield 40, the inwardly facing external surface 33 which is generally exposed to the path of corona cur rent flow can become conductive due to the deposition of salts from the corona gas movement.

The corona exposed surface region 33 of the end block 30 of our corona includes an interrupted configuration in the form of a long and narrow cul-de-sac 34 that is positioned between the point of corona wire suspensing connection 22 and the point of contact such as 57 between the end block 30 and the grid wire 50 or the point 44 between the end block 30 and the shield 40. The cul-de-sac 34 includes a shielded surface portion 35 including an overhanging lip 36 that faces outwardly away from the corona wire 21 and extends at a substantial angle 37, greater that 45 and preferably 90 from the path 32 of corona discharge flow. The culdesac 34 further, is preferably formed with a narrow inlet 38 and is relatively long with respect to the inlet 38 to substantially eliminate any regular flow of ionized gases therewithin.

In operation, corona discharge from electrode wires 21 produces ionized gases which precipitate salts on the exposed inwardly facing surface 33 of the corona end block 30. While the surfaces thus become conductive, a complete electrical path is not formed, however, due to the presence of the shielded surface 35 of the cul-de-sac 34 which does not receive corona generated salts. Thus, surface portion 35 remains an electrically insulated interruption lying in any path that can be traced on the corona exposed surface 33 from the corona wires 21 to a conductive member such as grid wires 50 or shield 40 that is also in contact with the end blocks 30. The performance of the charge corona unit' 20 thus will not deteriorate with time due to the accumulation of corona generated salts on its necessary supporting end blocks 30.

While we have described a preferred illustrative embodiment of our invention to illustrate certain principals of our inventive concepts, those skilled in the art will recognize that various modifications, deletions and additions can be made to the embodiment shown without departing from the spirit and resultant benefits of our invention. For example, our invention can be beneficially employed in corona units having electrodes other than wire electrodes and in corona units that do not have a control grid. Accordingly, it is to be understood that the protection sought by Letters Patent is to be defined and limited solely by the appended claims.

We claim:

1. A corona discharge assembly of the type having electrode means, means for suspending said electrode means in spaced relation to a corona current receiving member whereby a corona current flow path is defined between said electrode means and said corona current receiving member, said suspending means comprising at least one electrically insulative member supportively connected to said electrode means and including an external surface having a region that is generally exposed to the path of corona current flow, and electrically conductive means engaging said insulative member at a location spaced from said electrode means wherein the improvement comprises:

means forming an interruption in said corona exposed external surface region positioned between said electrode means and said electrically conductive means whereby substantially all paths on said corona exposed external surface region of said insulative member between said electrode means and said electrically conductive means cross said interruption, said interruption including a shielded surface portion that lies out of the path of corona current flow.

2. The corona discharge assembly as defined in claim 1 wherein said shielded surface portion extends in a direction making a substantial angle with the path of corona current flow and faces outwardly away from said electrode means.

3. The corona discharge assembly as defined in claim 1 wherein said shielded surface portion extends in a direction making an angle in excess of 45 with the path of corona current flow and faces outwardly away from said electrode means.

4. The corona discharge assembly as defined in claim 1 wherein said shielded surface portion extends in a direction that is substantially normal to the path of corona current flow and faces outwardly away from said electrode means.

5. The corona discharge assembly as defined in claim 1 wherein said interruption comprises a cul-de-sac configuration formed in said insulative member and having at least a restricted external opening to minimize gaseous movement therethrough.

6. The corona discharge assembly as defined in claim 5 wherein said cul-de-sac configuration long relative to said restricted external opening.

7. A corona discharge assembly of the type having at least one elongated electrode means, means for suspending said electrode means in spaced relation to a corona current receiving member whereby a corona current flow path is defined between said electrode means and said corona current receiving member, said suspending means comprising at least a pair of electrically insulative members supportively connected to opposed ends of said elongated electrode means, and each including an external surface region that is generally exposed to the path of corona current flow and electrically conductive means engaging said insulative members at points spaced from said electrode means, wherein the improvement comprises:

means forming an interruption in said corona exposed external surface region of each of said insulative members positioned between said electrode means and said electrically conductive means whereby substantially all paths on said corona exposed external surface region of said insulative members between said electrode means and said electrically conductive means cross said interruption, said interruptions each including a shielded surface portion that lies out of the path of corona current flow. 8. The corona discharge assembly as defined in claim 7 wherein said electrically conductive means comprises a control grid positioned in'the path of corona current flow and supportedly mounted on said insulative members.

9. The corona discharge assembly as defined in claim 7 wherein said electrically conductive means comprises a conductive shield partially surrounding said electrode means and being supportingly connected to said insulative members.

10. The corona discharge assembly as defined in claim 8 wherein said electrically conductive means comprises a conductive shield partially surrounding said electrode means and being supportingly connected to said insulative members. I

11. A corona discharge assembly of the type having at least one elongated electrode wire, means for suspending said electrode wire in spaced relation to a corona current receiving member whereby a corona current flow path is defined between said electrode wire and said corona current receiving member, said suspending means comprising at least a pair of electrically insulative members supportively connected to opposed ends of said electrode wire and each including an external surface region that is generally exposed to the path of corona current flow, and electrically conductive control grid means supportedly connected to said electrically insulative members and positioned between said electrode wire and said corona current receiving member for limiting corona current flow, wherein the improvement comprises:

means forming an interruption in said corona exposed external surface region of each of said insulative members, said interruption including a surface portion extending a substantial distance generally normal to the path of corona current'flow and facing outwardly away from said electrode wire, and positioned between said electrode wire and said conductive grid whereby substantially all paths on said corona exposed external surface regions of said insulative members between said electrode wire and said conductive grid cross said interruptions.

12. An electrostatic copy reproducing mechanism having a copy surface, for receiving an electrostatic charge and comprising the improvement of a corona discharge assembly as defined in claim 11 wherein said copy surface comprises said corona current receiving member andfurther comprising high voltage power supply means for delivering corona generating potential to said electrode wire,

and

means connected with said conductive grid for controlling the potential thereon.

Claims

1. A corona discharge assembly of the type having electrode means, means for suspending said electrode means in spaced relation to a corona current receiving member whereby a corona current flow path is defined between said electrode means and said corona current receiving member, said suspending means comprising at least one electrically insulative member supportively connected to said electrode means and including an external surface having a region that is generally exposed to the path of corona current flow, and electrically conductive means engaging said insulative member at a location spaced from said electrode means wherein the improvement comprises: means forming an interruption in said corona exposed external surface region positioned between said electrode means and said electrically conductive means whereby substantially all paths on said corona exposed external surface region of said insulative member between said electrode means and said electrically conductive means cross said interruption, said interruption including a shielded surface portion that lies out of the path of corona current flow.

3. The corona discharge assembly as defined in claim 1 wherein said shielded surface portion extends in a direction making an angle in excess of 45* with the path of corona current flow and faces outwardly away from said electrode means.

6. The corona discharge assembly as defined in claim 5 wherein said cul-de-sac configuration is long relative to said restricted external opening.

7. A corona discharge assembly of the type having at least one elongated electrode means, means for suspending said electrode means in spaced relation to a corona current receiving member whereby a corona current flow path is defined between said electrode means and said corona current receiving member, said suspending means comprising at least a pair of electrically insulative members supportively connected to opposed ends of said elongated electrode means, and each including an external surface region that is generally exposed to the path of corona current flow and electrically conductive means engaging said insulative members at points spaced from said electrode means, wherein the improvement comprises: means forming an interruption in said corona exposed external surface region of each of said insulative members positioned between said electrode means and said electrically conductive means whereby substantially all paths on said corona exposed external surface region of said insulative members between said electrode means and said electrically conductive means cross said interruption, said interruptions each including a shielded surface portion that lies out of the path of corona current flow.

8. The corona discharge assembly as defined in claim 7 wherein said electrically conductive means comprises a control grid positioned in the path of corona current flow and supportedly mounted on said insulative members.

10. The corona discharge assembly as defined in claim 8 wherein said electrically conductive means comprises a conductive shield partially surrounding said electrode means and being supportingly connected to said insulative members.

11. A corona discharge assembly of the type having at least one elongated electrode wire, means for suspending said electrode wire in spaced relation to a corona current receiving member whereby a corona current flow path is defined between said electrode wire and sAid corona current receiving member, said suspending means comprising at least a pair of electrically insulative members supportively connected to opposed ends of said electrode wire and each including an external surface region that is generally exposed to the path of corona current flow, and electrically conductive control grid means supportedly connected to said electrically insulative members and positioned between said electrode wire and said corona current receiving member for limiting corona current flow, wherein the improvement comprises: means forming an interruption in said corona exposed external surface region of each of said insulative members, said interruption including a surface portion extending a substantial distance generally normal to the path of corona current flow and facing outwardly away from said electrode wire, and positioned between said electrode wire and said conductive grid whereby substantially all paths on said corona exposed external surface regions of said insulative members between said electrode wire and said conductive grid cross said interruptions.

12. An electrostatic copy reproducing mechanism having a copy surface, for receiving an electrostatic charge and comprising the improvement of a corona discharge assembly as defined in claim 11 wherein said copy surface comprises said corona current receiving member and further comprising high voltage power supply means for delivering corona generating potential to said electrode wire, and means connected with said conductive grid for controlling the potential thereon.