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Publication numberUS3699388 A
Publication typeGrant
Publication dateOct 17, 1972
Filing dateMay 17, 1971
Priority dateJul 6, 1967
Also published asDE1771684A1
Publication numberUS 3699388 A, US 3699388A, US-A-3699388, US3699388 A, US3699388A
InventorsTakeshi Ukai
Original AssigneeRicoh Kk
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Apparatus for electrostatic charging of paper in electrophotographic reproduction
US 3699388 A
Abstract
A corona discharge electrode is supplied with voltage from a high frequency power source to produce a corona discharge which strikes a sheet of reproducing paper to charge the same electrostatically. A detection electrode is positioned in the field of the corona discharge and is connected via a resistor and amplifier to the power source to control the same in accordance with the detected corona discharge to maintain the magnitude of the discharge field constant. A switch is connected in the power supply to interrupt connection thereof with the discharge electrode if a spark discharge is produced between the discharge electrode and the paper.
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Description  (OCR text may contain errors)

United States Patent Ukai 1 Oct. 17, 1972 [54] APPARATUS FOR ELECTROSTATIC 2,868,989 1/1959 Haacke ..317/262 A CHARGING OF PAPER IN 3,390,266 6/1968 Epping ..3l7/262 A ELECTROPHOTOGRAPHIC FOREIGN PATENTS OR APPLICATI NS REPRODUCTION O Inventor: Takeshi Ukai, Tokyo, Japan 748,015 12/1966 Canada ..3l7/262A [73] Assignee: Kabushiki Kaisha Ricoh, Tokyo, Primary Examiner-L. T. I-lix Japan Attorney-Waters, Roditi, Schwartz & Nissen [22] Filed: May 17, 1971 [57] ABSTRACT 2 App! 1 a A corona discharge electrode is supplied with voltage Related A fi fi Data from a high frequency power source to produce a corona discharge which strikes a sheet of reproducing [63] commuatlonlrlpart of 5 June paper to charge the same electrostatically. A detection l 1968' electrode is positioned in the field of the corona discharge and is connected via a resistor and amplifier [30] Fomg Apphcam Pnomy Data to the power source to control the same in accordance July 6, 19 7 j n 42/43571 with, the detected corona discharge to maintain the magnitude of the discharge field constant. A switch is [52] U.S. Cl ..317/4, 317/262 A nn c in th power supply to interrupt connection 51 Int. Cl. ..G03g 15/02, HOlt 19/00 thereof with the discharge electrode if a spark [58] Field of Search ..3 1 7/262 R, 262 A, 4 discharge is produced between the discharge electrode and the paper. [56] References Cited UNITED STATES PATENTS Larsen et a]. ..317/262 R 5 Claims, 1 Drawing Figure BRIEF SUMMARY OF THE INVENTION The invention relates to apparatus and methods for controlling high voltage current supplied to a corona discharge electrode in electrophotographic reproduction apparatus. 7

Heretofore it has been difficult to stabilize the operation of a corona discharge electrode as its charging ac- .tion is substantially affected by changes in power voltage, loads or atmospheric conditions.

An object of the present invention is to provide a charging device incorporating means for stabilizing the charging action and obviate any variations thereof.

According to the invention a corona current detecting means is incorporated in the charging device for controlling the change of corona current for eliminating instability and for maintaining a uniform that a uniform copy may be obtained.

According to a specific embodiment of the invention there is provided a charge control circuit for electrophotographic reproducing apparatus which comprises a high voltage power source, a corona discharge electrode electrically connected to said source for producing a corona discharge current, a target plate for supporting a sheet of reproducing paper, said target plate being grounded and facing said discharge electrode to expose the sheet of reproducing paper to the coronadischarge current from said corona discharge electrode whereby said sheet is electrostatically charged, a detection electrode positioned adjacent said discharge electrode to detect corona discharge current from said discharge electrode, and feedback means connected to said discharge electrode and to said high charge so voltage power source to control said power source in accordance with the detected corona discharge current to maintain the value of said current constant.

The discharge electrode and detection electrode are placed adjacent one, another in a hollow, grounded guide member which has an opening facing the target plate. Thus, the discharge between the discharge electrode and the detection electrode is substantially constant regardless of the presence or absence of a copy sheet on the target plate.

A further object of the invention is to provide a safety device which is operative to interrupt supply of power to the discharge electrode if a spark discharge should be produced between the discharge electrode and the paper due to contact therebetween, or the like, which could produce a fire.

In further accordance with the invention the safety device is operative when the detection electrode detects the absence of a corona discharge field upon the production of a spark discharge between the discharge electrode and the copy paper.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a circuit diagram of the charge control apparatus according to the invention; and

FIG. 2 is a perspective view, partly broken away, of a portion of the apparatus of FIG. 1.

DETAILED DESCRIPTION Referring to the drawing, therein is seen a corona discharge electrode 1 constituted as a tungsten wire. Mounted adjacent electrode 1 is a detection electrode 2 also in the form of a tungsten wire. The detection electrode 2 is intended to detect the magnitude of the corona discharge field developed by the electrode 1. The electrodes 1 and 2 are mounted in a hollow guide member 3. which is connected to ground and is pro vided with an opening facing a grounded target plate 10 on which a sheet of reproducing paper 11 can be placed. The hollow member 3 servesto confine the corona discharge and direct the discharge to the paper 11 to charge the paper electrostatically. The intensity of the corona field is the same at the detection electrode 2 as at the plate 10 with the exception that the electrode 2 is not subject to the variable effects of the paper 11 as is the plate 10. Thus, the current detected in the electrode 2 is an accurate representation of the intensity of the corona field produced by the electrode 1. As will be seen hereafter the current in the electrode 2 will serve as a means to control the voltage applied to electrode 1 in order to stabilize the corona discharge and render the charge on the copy paper 1 l uniform.

The detection electrode 2 is connected to a variable resistor 4 across which a voltage is produced related to the current in detection electrode 2. The resistor 4 is connected to the input of an amplifier 5 which produces an amplified output signal of the voltage in resistor 4. The output of the amplifier produced at the plate of a triode V is connected to the control grid of an oscillating vacuum tube 6 which serves to control the voltage input to the discharge electrode 1 by virtue of its connection via resonance condenser 7 to the primary winding of a high frequency transformer 8. The secondary of the transformer is connected to a high voltage rectifier 9 which is connectedto discharge electrode l.

In an oscillation circuit consisting of the oscillating vacuum tube 6, the resonance condenser 7 and the transformer 8, when resonance current is caused to flow in the primary winding of the transformer 8 through its output, sine wave high voltage is simultaneously induced in the secondary winding of the transformer 8. This sine wave high voltage is changed to negative high voltage by the high voltage rectifier 9 and applied to the discharge electrode 1. Thereby, a corona field isproduced and corona current flows between the discharge electrode 1, the detection electrode 2, the corona guide member 3 and the paper 11. The corona current which flows from the electrode 1 to the paper 11 is approximately proportional to the corona current which flows from the electrode 1 to ground through the detection electrode 2 and the variable resistor 4.

When the negative corona current which flows from the discharge electrode 1 to the paper 11 is increased excessively due to changes of power voltage, changes in the paper and atmospheric conditions, the negative corona current which flows from the electrode 1 to ground through electrode 2 and the variable resistor 4 is also increased and the electric potential at the point flowing from the electrode 1 is decreased, a similar ac-.

tion is produced, namely, the corona current is increased contrary to the above-mentioned case and the balance is maintained. In this way, the corona current is always kept at a fixed value, and the charging operation is stabilized withoutany unevenness so that a uniform copy can be obtained by the electrophotographic reproduction apparatus. Thus, the resistor 4, amplifier 5 and oscillation circuit constitute a feedback meansto control the power source of transformer 8 and rectifier 9 to maintain the value of the corona discharge current constant.

The same object is obtainable by providing the oscillation circuit of the invention with a pulse generator, thereby changing-the pulse interval by using the detected voltage of the variable resistor 4 and controlling the high voltage applied to the discharge electrode 1. The detection electrode 2 need not be arranged adjacent to the electrode 1 and for example, a shielding box (similar to corona guide member 3) can be employed for electrode 1, but the shielding box is normally grounded directly. Preferably, however, the electrodes l and 2 are mounted in hollow guide member 3 with the electrode 2 remote from paper 11 and spaced further therefrom than is the electrode 1, in order to eliminate any effect of the paper 11 on the current detected in detection electrode 2.

From the above it is seen that a corona current detection produces a signal which is employed as a feedback to the corona generating power supply to maintain the corona current constant without any change so that a uniform copy may be obtained.

The circuit of the invention is also constructed to eliminate the possibility of a fire in the event that the copy paper should contact the discharge electrode 1 to produce a spark discharge therebetween.

Accordingly, a safety device is provided which detects the presence of a spark discharge to open a switch 40 connected between the primary winding of trans former 8 and the voltage source. As seen in the circuit in FIG. 1, a grid of a triode V is connected to the plate of triode V, through a Zener diode Zn. A coil of a holding type relay 40' is connected to the plate of triode V Any holding type relay can be used if the open state of its contacts is maintained until the relay once operated is reset by hand.

A time constant circuit comprising a diode 30, a resistor 31, a condenser 32 and a resistor 33 is connected between the plate of the triode V and the Zener diode Zn. If a button is pushed to supply the charging device with power, a discharge will be effected in the discharge electrode 1 after a short delay of time during which the heater of the vacuum tube is heated. Herein, if there is not provided this time lag mechanism, the triode V is operated to open the switch contacts 40 of the relay 40'. In the state of normal use, the potential of the plate of the triode V, is lower than that of the Zener diode and the triode V is cut off. If a sheet of paper is caught in the charging device and a spark discharge is produced, the discharge between the discharge electrode 1 and the detecting electrode 2 will be interrupted and the voltage of the resistor 4 will become zero. With the increase of the potential of the grid of the triode V the'potential of the plate of the triode V will be lowered, and the triode V will be cut off and the potential of its plate will be increased, the Zener diode Zn will be operated,

the triode V will become conductive, and the normally closed switch contacts 40 of the relay coil 40' will be opened. These contacts can be closed by resetting them by hand after the trouble has been corrected.

Although the invention has been described with reference to a specific embodiment thereof, the invention is not limited thereto and modifications and variations will become evident to those skilled in the art without departure from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

l. A charge control circuit for electrophotographic reproducing apparatus, said charge control circuit comprising a high voltage power source, a corona discharge electrode electrically connected to said. source for producing a corona discharge current, a tar-.

get plate for supporting a sheet of reproducing paper, said target plate being grounded and facing said discharge electrode to expose the sheet of reproducing paper to the corona discharge current from said corona discharge electrode whereby said sheet is electrostatically charged, a detection electrode positioned adjacent said discharge electrode to detect corona discharge current from said discharge electrode, feedback means connected to said discharge electrode and to said high voltage power source to control said power source in accordance with the detected corona discharge current to maintain the value of said current constant, and means connected to said power source to interrupt the connection thereof to said discharge electrode upon elimination of discharge current betweenthe discharge electrode and the detection electrode when a spark discharge is produced between the discharge electrode and the reproducing paper, said power. source comprising a high voltage transfonner with primary and secondary windings, and a high voltage rectifier connected to the secondary winding of the transformer and to the discharge electrode, said means to interrupt the connection of the power source to the discharge electrode comprising a switch means for interrupting power supply to the primary winding of the transformer, a relay controlling said switch means, and means including a timer circuit connected to said feedback means and to said relay to operate said relay and open said switch means if said feedback means detects lack of corona discharge current.

2. A circuit as claimed in claim 1 comprising a hollow grounded guide member having an opening facing said target plate, said discharge electrode and detection electrode being adjacent one another within said guide member.

3. A circuit as claimed in claim 2 wherein said discharge electrode is closer to said target plate than is said detection electrode.

4. A circuit as claimed in claim 1 wherein said feedback means comprises a variable resistor connected to said detection electrode, amplifier means having an input connected to said variable resistor, control means connected to the amplifier means at the output thereof and to the power source to adjust the latter in accurrent to render said triode conductive whereupon the relay is activated and said switch means is opened.

5. A circuit as claimed in claim 4 wherein said timer circuit comprises a diode, a resistor means and a condenser connected between said Zener diode and said amplifier means.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2767359 *Jun 29, 1951Oct 16, 1956Gen Motors CorpHigh voltage current control
US2868989 *Jan 3, 1956Jan 13, 1959Haloid Xerox IncElectrostatic charging method and device
US3390266 *Oct 19, 1965Jun 25, 1968Epping Reinhold HermannApparatus for charging the surface of photoelectric layers using corona discharge
CA748015A *Dec 6, 1966Canadian Kodak Co LtdElectrostatic charging methods and apparatus
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3809955 *Mar 26, 1973May 7, 1974Graco IncSafety circuit for electrostatic spray gun
US3909614 *Sep 30, 1974Sep 30, 1975Xerox CorpScorotron power supply circuit
US3976880 *Oct 29, 1975Aug 24, 1976Xerox CorporationCorona stabilization arrangement
US3976881 *Oct 29, 1975Aug 24, 1976Xerox CorporationArrangement for stabilizing corona devices
US4189642 *Apr 3, 1978Feb 19, 1980International Business Machines CorporationMethod and apparatus for drum corona current measurement and alignment
US4346986 *Feb 3, 1981Aug 31, 1982Canon Kabushiki KaishaImage formation method and apparatus
US4417804 *Jun 19, 1981Nov 29, 1983Xerox CorporationHigh voltage comparator for photoreceptor voltage control
US4423134 *Feb 17, 1978Dec 27, 1983Ricoh Company, Ltd.Development, electrodes, floating, potentials, variations
US5164771 *Mar 25, 1991Nov 17, 1992Canon Kabushiki KaishaImage forming apparatus which adjusts illumination levels independently for test samples and for originals
US5164776 *Sep 19, 1991Nov 17, 1992Xerox CorporationApparatus and method for correcting the voltage on a photoconductive device
US5317155 *Dec 29, 1992May 31, 1994The Electrogesic CorporationCorona discharge apparatus
US6034368 *Jul 6, 1998Mar 7, 2000Xerox CorporationAC corona current regulation
US7457096May 3, 2006Nov 25, 2008Taser International, Inc.Systems and methods for ARC energy regulation
US7821766Apr 19, 2007Oct 26, 2010Taser International, Inc.Systems and methods for pulse delivery
US7986506Nov 20, 2007Jul 26, 2011Taser International, Inc.Systems and methods for arc energy regulation and pulse delivery
US8154845Dec 17, 2010Apr 10, 2012Taser International, Inc.Systems and methods for arc energy regulation and pulse delivery
US8456793Mar 15, 2012Jun 4, 2013Taser International, Inc.Systems and methods for ionization using adjusted energy
US8743527Mar 14, 2012Jun 3, 2014Taser International, Inc.Systems and methods for arc energy regulation using binary adjustment
DE2550846A1 *Nov 12, 1975May 13, 1976Ricoh KkEntwicklungseinrichtung fuer ein elektrophotographisches kopiergeraet
DE3401445A1 *Jan 17, 1984Aug 2, 1984Sharp KkElektrophotographischer kopierer
EP0207554A1 *Jun 19, 1986Jan 7, 1987OcÚ-Nederland B.V.Method of and device for determining a measure of the surface potential of a medium charged by means of a corona charging device
Classifications
U.S. Classification361/229, 361/235, 250/324
International ClassificationG03G15/02, H02H7/00
Cooperative ClassificationH02H7/003, G03G15/0266, G03G15/0291
European ClassificationG03G15/02C, H02H7/00D