US 3708661 A
Apparatus for charging an insulating layer comprising an ion source for simultaneously producing a corona discharge of positive and negative ions and an acceleration electrode for extracting negative ions to uniformly charge the insulating layer. The ion source comprises at least one main electrode, an auxiliary electrode and a counter electrode coaxial to the main and auxiliary electrodes, and the accelerating electrode is arranged at the remote side of the layer to be charged. The apparatus further comprises deflecting electrodes and a plate electrode further acting upon the distribution of charge across the insulating layer.
Claims available in
Description (OCR text may contain errors)
United States Patent 1191 Hansen et a1.
1 Jan. 2, 1973  CORONA DISCHARGE FOR ELECTRO- STATIC CHARGING  Inventors: Norbert Ernst Fritz Hansen, Roetgen; Dieter Wadow, Aachen, both of Germany  Assignee: U.S. Philips York,'N.Y.
22 Filed: Jan. 25, 1971 211 Appl.No.: 109,120
 Foreign Application Priority Data.
Feb. 21, 1970 Netherlands ..7002477  U.S. Cl... ..250/49.5 ZC, 317/262 A s 1 Int. Cl. ..G03g 15/02  Field of Search ..250/49.5 ZC, 49.5 TC; 317/262 A  References Cited UNITED STATES PATENTS 7/1967 Gundlach ..250/49.5 X
3,358,289 12/1967 Lee.. ..250/49.5 X 3,489,895 1/1970 3,163,753 12/1964 3,196,270 7/1965 Rosenthal ..250/49.5
Primary Examiner-William F. Lindqu ist Attorney-Frank R. Trifari  ABSTRACT Apparatus for charging an insulating layer comprising an ion source for simultaneously producing a corona discharge of positive and negative ions and an acceleration electrode for extracting negative ions to uniformly charge the insulating layer. The ion source comprises at least one main electrode, an auxiliary electrode and a counter electrode coaxial to the main and auxiliary electrodes, and the accelerating electrode is arranged at the remote side of the layer to be charged. The apparatus further comprises deflecting electrodes and a plate electrode further acting upon the distribution of charge across the insulating layer.
10 Claims, 3 Drawing Figures PA TENT ED 2 I975 3. 7 08 661 sum 1 or 2 NOR BERT E.F. MKEQII DIETER WADOW BYWZ AGENT CORONA DISCHARGE FOR ELECTRO-STATIC CHARGING The invention relates to a device for charging an insulating layer, particularly for electro-photography, said device comprising an ion source having .at least one main electrode for coronadischarge and at least one counter-electrode and comprising furthermore a acceleration electrode on the side of the layer remote from the ion source. It is important for the charge applied by such a device to the insulating layer to be uniformly distributed across said layer. In known devices it is endeavored to achieve this by moving the insulating layer relatively to the corona electrodes, for example, by using a layer in the form of a belt passing along a roller see U. S. Pat. No. 2,701,764 or by moving to and fro the suction electrode in the form of a flat plate supporting the layer beneath the electrodes as described in British Pat. Specification 696,515. This British Patent Specification also discloses measures for improving the reproduceability of the charging process with the aid of a grid between the electrodes and the insulating layer. In this embodiment the layer can be charged fairly uniformly up to a comparatively high potential, for example, a few hundred volts. However, with some types of layers better results are obtained when the layer is charged only up to a potential of a few tens of volts. With these charging devices this is only possible at the expense of uniformity. Moreover, it is sometimes undesirable for the layer to be moved during the charging process, for example, if it is desired to charge and expose simultaneously.
An important cause of the non-uniform charge distribution resides in that the corona discharge is strongly localized so that the ions formed migrate from a few separate areas towards the layer. This gives rise to the formation of a few ion channels between the electrodes and the layer, which are filled with space charges having the same polarities and hence repelling one another; separate charge region therefore being formed on the layer. The object of the invention is to avoid the formation of these channels, so that a continuous charge distribution is produced on a stationary plate, which distribution can then be further smoothed by additional measures. According to the invention this is achieved by providing means for producing simultaneously positive and negative ions.
The invention will be described more fully with reference to the drawing, in which:
FIG. 1 is a sectional view of a charging device embodying the invention,
FIG. 2 is an enlarged plan view of the ion source of FIG. 1 and FIG. 3 illustrates the distribution of the ion flow across the insulating layer.
The charging device shown in FIG. 1 comprises an ion source 1 comprising needle-shaped main electrodes 3 see also FIG. 2 a cylindrical counter-electrode 5 and a needle-shaped auxiliary electrode 7, mounted in an insulating block 9. In-the embodiment shown the main electrodes 3, as is clearly shown in FIG. 2, are uniformly distributed along the sheath of a cylinder, which is coaxial to the counter-electrode 5, while the auxiliary electrode 7 coincides with the axes of the two cylinders. As will be apparent from FIG. 1, the dimensions of the ion source 1 are preferably considerably smaller than its distance from a acceleration electrode 11, which is provided on its side facing the source with an insulating layer not shown for the sake of clarity Also by this large distance the operation of the ion source 1 is not affected by the potential of the acceleration electrode 11. The electrodes are fed from highvoltage sources not shown for the sake of clarity which are all connected on one side to a common earth-connection point 13, to which is also connected the counter-electrode 5. The main electrodes 3 receive from point 15 a negative voltage of, for example, 10 kV and the auxiliary electrode 7 receives a positive voltage of, for example, 8.5 kV from point 17. The value of these voltages is chosen so that a corona discharge occurs at all needle-shaped electrodes, so that negative ions emerge from the main electrodes 3 and positive ions from the auxiliary electrode 7. It is thus avoided that relatively repelling space charge concentrations of identical ions are produced; a homogeneous ion cloud is formed which contains both positive and negative ions. Since the acceleration electrode 11 receives a positive voltage of, for example, 13 kV from point 19, it is capable of extracting negative ions from the cloud so that the insulating layer is charged negatively. This charge is continuously distributed across the layer and it is not, as in said known devices, concentrated in a number of discrete charge regions. In the arrangement shown in FIG. 1, comprising one ion source which is small as compared with the transverse dimension of the acceleration electrode, a greater charge is produced at the center of the layer than at the sides. This might be improved by using more ion sources, but a simpler and cheaper solution consists in the provision of a'plurality of annular deflection electrodes 21, which receive from point 23 a preferably variable positive voltage of, for example, 10.5 kV so that they cause the ion beam to spread in fan-shaped fashion on its path from the source to the layer. This permits further smoothing of the already continuous charge distribution on the insulator to obtain a more uniform distribution. If desired, a further improvement may be obtained by arranging a plate electrode 25 on the side of the plate-shaped acceleration electrode 11 remote from the ion source, said electrode 25 also receiving a preferably variable positive voltage of, for example, 1 1 kV from point 27.
In order to obtain full effect of these control-possibilities it should be possible to measure the ion flow to different parts of the insulating layer. For this purpose probes 29 are provided, which are connected to point 19 through measuring instruments 31 for very low currents, for example, electrometers.
FIG. 3 is a graph made by means of said probes 29, in which the probe current is plotted as a function of the distance from the center of a circular suction electrode having a diameter of 36.5 cms. The ion source was at a distance of 28 cms from the suction electrode and had a diameter of 12 cms. It will be apparent that practically throughout the layer the ion flow and hence the charge substantially does not change.
By varying the charging time it is now possible to charge uniformly the layer to any desired potential up wards of a few volts.
What is claimed is:
1. Apparatus for charging an insulating layer comprising an ion source for simultaneously producing a homogeneous ion cloud of positive and negative ions adjacent to but spaced from one side of said insulating layer, said ion source comprising at least two electrodes for producing a corona discharge of negative and positive ions, respectively, means for supplying potentials to said electrodes, an accelerating electrode on the side of said insulating layer remote from said ion source, and means to supply a potential to said accelerating electrode at which only negative ions are extracted from said ion cloud thereby uniformly distributing negative charges on said insulating layer.
2. Apparatus as claimed in claim 1 wherein said two electrodes for producing a corona discharge of negative and positive ions comprises at least one main electrode for producing a corona discharge of negative ions and an auxiliary electrode for producing a corona discharge of positive ions within said corona discharge of negative ions.
3. Apparatus as claimed in claim 1 wherein said ion source is of given dimensions and further comprises a counter electrode for forming said corona discharge into an ion cloud, the distance between said ion source and said acceleration electrode being substantially greater than the dimensions of said ion source so that the potential of said acceleration electrode has no effect on said ion source, the potential supplied to said accelerating electrode being positive relative to said counter electrode.
4. Apparatus as claimed in claim 3 wherein said two electrodes for producing a corona discharge of negative and positive ions comprises at least one main electrode for producing a corona discharge of negative ions and an auxiliary electrode for producing a corona discharge of positive ions within said corona discharge of negative ions, said main electrode and said auxiliary electrode comprising needle-shaped,.parallel conductors and said counter-electrode being shaped as a tube surrounding said conductors.
5. Apparatus as claimed in claim 4 wherein said counter-electrode has a cylindrical shape, said auxiliary electrode lying along the longitudinal axis of. said cylinder and said main electrodes being evenly distributed along a cylindrical surface coaxial to said counter-electrode.
6. Apparatus as claimed in claim 5 wherein said main electrode is located at the center of a straight line between the auxiliary electrode and thecounter-electrode.
7. Apparatus as claimed in claim 1 further comprising at least one deflecting electrode positioned between said ion source and said insulating layer outside of the paths of the ions from said ion source for influencing the distribution of charge across said layer.
8. Apparatus as claimed in claim 7 wherein said deflecting electrodes are parallel to each other and are spaced apart from the insulating layer by different distances, the further the deflection electrodes are spaced from the insulating layer, the greater the distances between the deflection electrodes and the connecting line between the ion source andthe insulating layer.
9. Apparatus as claimed in claim 1 further comprising a flat plateelectrode positioned on the side of the acceleration electrode remote from the ion source, said plate electrode having lateral dimensions substantially larger than those of said accelerating electrode and extending parallel to said acceleration electrode for mfluencing the charge distribution across the insulating layer.
10. Apparatus as claimed in claim 1 further comprising probes coupled to said acceleration electrode to measure very low currents indicative of the ion HOW to different parts of said insulating layer.