US3778690A - Electrostatic copying machine - Google Patents

Electrostatic copying machine Download PDF

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Publication number
US3778690A
US3778690A US00235346A US3778690DA US3778690A US 3778690 A US3778690 A US 3778690A US 00235346 A US00235346 A US 00235346A US 3778690D A US3778690D A US 3778690DA US 3778690 A US3778690 A US 3778690A
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US
United States
Prior art keywords
sleeve
improvement
rollers
copy paper
roller
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US00235346A
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English (en)
Inventor
F Rothacker
D Bujese
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
COPY RES CORP
Original Assignee
COPY RES CORP
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Filing date
Publication date
Application filed by COPY RES CORP filed Critical COPY RES CORP
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Publication of US3778690A publication Critical patent/US3778690A/en
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G15/00—Apparatus for electrographic processes using a charge pattern
    • G03G15/02—Apparatus for electrographic processes using a charge pattern for laying down a uniform charge, e.g. for sensitising; Corona discharge devices
    • G03G15/0208—Apparatus for electrographic processes using a charge pattern for laying down a uniform charge, e.g. for sensitising; Corona discharge devices by contact, friction or induction, e.g. liquid charging apparatus
    • G03G15/0216—Apparatus for electrographic processes using a charge pattern for laying down a uniform charge, e.g. for sensitising; Corona discharge devices by contact, friction or induction, e.g. liquid charging apparatus by bringing a charging member into contact with the member to be charged, e.g. roller, brush chargers
    • G03G15/0233—Structure, details of the charging member, e.g. chemical composition, surface properties

Definitions

  • ABSTRACT In a copying machine employing two conductive rollers to which zinc oxide coated copy paper is fed, the power source provides a DC voltage between the rollers that is derived from a frequency (of 25 kilocycles, for example) which is relatively high compared to line frequency. The relatively high frequency ripple that is on the DC output eliminates much of the problem with discernible lines on the end product.
  • One of the two rollers has a rubber sleeve which is selected to provide a low capacitance such as 75 micromicrofarads.
  • the resistance of the sleeve is such that a current flow of 50 microamperes is obtained with a 3,000 volt potential between the two rollers.
  • the low capacitance means that when a sheet of copy paper is fed between the rollers, the change in the potential across the rubber sleeve and the change in current flow will occur very rapidly so that an even charge is applied on the copy paper. Because of the relatively high frequency employed, the ripple factor is kept low and the voltage magnitude applied is kept down to a point where the amount of ozone generated is minimized.
  • corona is essentially two sets of spaced apart parallel wires across which 15,000 volts are applied.
  • the paper is passed between the two sets of wires and a discharge across the gap between the two sets of wires carries an electric charge that is picked up in part by the paper.
  • the discharge is of a sort that is known as a corona discharge.
  • this part of the equipment has been termed the corona.
  • the two roller design has required a sufficiently high voltage that some ozone is generated.
  • the rate of ozone generation may be considerably less than when a corona is employed, it is sufficient to deteriorate the high resistance, rubber-type sleeve employed on one of the two rollers.
  • the even and repeatable application of a charge across the entire sheet of copy paper is a problem when a tworoller design is employed particularly when relatively high copy paper feeding speeds are employed.
  • this invention provides an improved two-roller design from which superior performance will be obtained, and by which improvements will be achieved in the areas of cost, weight, evenness with which charge is applied, repeatability of charge application and limiting of ozone generation. More particularly, it is a purpose of this invention to provide a design in which lower voltages and lower currents are required and in which a much more efficient use of the power supply is effected.
  • this invention is an improvement in a tworoller type of copier.
  • the di-electric sleeve on one of the two rollers is selected to have a capacitance and resistance that will provide a sufficiently low time constant that when paper is introduced between the rollers,
  • the change in the voltage distribution across the dielectric sleeve will occur quickly and will thus avoid a gradually varying magnitude of charge laid down on the copy paper.
  • the resistance of the sleeve is high enough that a very low level of DC current is provided.
  • the DC power supply has a high frequency ripple that permits easy filtering so that the amplitude of the ripple can be kept at a low level.
  • the frequency of the ripple is sufficiently high that a series of discernable lines in the end product, that are a result of a varying level of charge laid down on the copy paper, are avoided.
  • FIG. 1 is a perspective, fragmentary view, illustrating copy paper feeding through two rollers, one of which is provided with a rubber sleeve.
  • FIG. 2 is an elevation view of one embodiment of this invention.
  • FIG. 3 is a left side view of FIG. 2.
  • FIG. 4 is a right side view of FIG. 2.
  • FIG. 5 is a longitudinal cross sectional view of FIG. 2.
  • FIG. 6 is a schematic representation of the invention.
  • FIG. 7 is an electrical schematic of the power supply.
  • FIG. 1 passes copy paper 10 between two rollers 12, 14.
  • the machine can be designed to employ either sheet or roll fed copy paper.
  • the rollers 12 and 14 are electrically conductive, preferably made of metal.
  • the roller 14 is surrounded by a high resistivity di-electric sleeve 16 which in one embodiment is a one-sixteenth inch thick, 10 inch long, rubber sheet.
  • Two springs 18 bias'the two rollers 12, 14 toward one another so that when in operation, the sheet 10 is in physical contact with the periphery of the roller 12 and the sleeve 16.
  • a DC power supply 20 provides a positive voltage to the roller 12 and a negative voltage to the roller 14.
  • the roller 12 is preferably held at zero potential and the roller 14 has a negative potential. What counts is that the rollers l2, 14 have a DC potential between them. As a consequence when copy paper is passed between the rollers, a small leakage current flows between the two rollers through the high resistance rubber sleeve 16.
  • the amount of current flow is in the range of 50 microamperes.
  • the paper 10 is a standard zinc oxide coated copy paper in which the coated surface We is in contact with the rubber sleeve 16 of the negative roller 14.
  • the rubber sleeve is Buna N with a thickness of approximately onesixteenth of an inch and provides a very high resistance and a low capacitance between the roller 12 and the roller 14.
  • the resulting 50 microampere leakage current provides an adequate electron supply to negatively charge the coated surface 100 of the copy paper 10.
  • this invention not only substantially reduces the voltage level required but also greatly reduces the amount of current required.
  • the embodiment illustrated in the Figures shows a inch diameter metal roller 12 and a l/16th inch diameter metal roller 14, both mounted for rotational movement about their respective axes in bearings 21a, 21b, respectively.
  • the bearings 21a are directly mounted in electrical insulating end plates 22R, 22L which in turn are connected to supporting framework (not shown).
  • the bearings 21b which support the lower roller 14, float in the end plates 22R, 22L and are supported by the springs 18.
  • the ends of each spring 18 are connected 'to respective projections 22p of the end plates 22L, 22R.
  • the springs 18 hold the roller 14 and tend to cause the rubber sleeve 16 to bear against the roller 12.
  • a gear 26 on a shaft extension 28 of the upper roller 12 provides coupling to a mechanical drive mechanism (not shown) so that the roller 12 can be rotated. Because of the frictional contact, due to the rubber sleeve 16 and copy paper 10, rotation of the roller 12 will result in rotation of the sleeve 16 and thus rotation of the roller 14. Thus it may be seen that the rubber sleeve 16 provides riot only the electrical function of limiting the current flow between rollers 12 and 14, but also traction that aids in pulling the copy paper between the two rollers 12, 14. This rubber sleeve 16 also provides a cushioning contact against the coated surface 10c of the paper 10 to avoid damage to the coating.
  • the DC power supply has its positive terminal connected through a lead 30 and terminal 32 to the right bushing 21a which is in contact with the upper roller.
  • the negative terminal of the DC power supply 20 is connected through lead 34 and contact 36 tothe right bushing 21a, which bushing is in contact with the lower metal roller 14.
  • this background voltage level for the copy paper 10 will mean a minimum background shading of the copy paper 10 when it is inked.
  • FIG. 6 is a schematic representation of how the invention operates and provides an explanation of some of the more significant operating aspects of the invention that result in the objectives stated above.
  • the power supply 20 provides 3,000 volts which is applied to the inner surface of the di-electric sleeve 16.
  • the di-electric sleeve 16 presents a resistive parameter R and a capacitive parameter C to the circuit.
  • the outer part of the di-electric sleeve is in direct contact with the coated upper surface 100 of the paper 10.
  • the lower surface 10b of the paper 10 is'in direct electrical contact, through the roller 12, with the other side of the power supply 20.
  • the power supply 20 and roller 12, 14 combination is electrically substantially isolated from the rest of the chassis.
  • the capacitive and resistive parameters of the sleeve 16 are represented as a resistor R and capacitor C in parallel between the negative terminal of the power supply 20 and the upper surface 100 of the paper 10. Assuming an ideal DC power supply 20 (and thus no ripple) there will be a current flow to and from the two surfaces of the paper 10 in much the same fashion as there is when the plates of a battery are being charged from a power supply. The DC current will flow through the resistor R from the top surface We to charge the top surface 10c negative and will flow to the lower surface 10b from the power supply 20 to charge the lower surface 10b positive. As the copy paper 10 is moved, as to the right, the portion of the surfaces 10c and 10b in contact with the di-electric sleeve and lower roller, respectively, continuously changes and new charge is laid down on the paper so that there is a continuous current flow.
  • the DC current flow is 50 microamperes and the voltage at the positive surface of the paper 10 is approximately 500 volts.
  • the resistance of the sleeve 16 is 50 megohms.
  • the capacitor C becomes effectively charged to a voltage level of 3,000 volts.
  • a sheet of copy paper 10 is introduced between the rollers, that sheet of paper is equivalent to applying another capacitor in series with the capacitance C.
  • the charge and thus the voltage drop is divided between the capacitance C and the effective capacitance of the paper 10.
  • the transient conditions that will exist until a stable charging condition is obtained will produce a non-uniform charge on the paper 14.
  • the sleeve in one'embodiment has a micro-microfarad capacitance parameter, this discharge occurs very rapidly and permits rapid movement of the paper through the rollers while applying a uniform charge on the paper.
  • a linear speed of 275 inches per minute is employed in this embodiment.
  • the rubber sleeve 16 is molded onto the roller 14 from a butadiene acrylonitrile rubber, commonly known as Buna N, a material which may be purchased from the Dyco Rubber Company of Belleville, NJ.
  • Buna N a material which may be purchased from the Dyco Rubber Company of Belleville, NJ.
  • a number of materials can be employed as long as they provide the required resistive and capacitive properties.
  • the sleeve 16 be resilient so that a surface rather than a line contact between rollers is established and so that the tension of the spring 18 can be adjusted to obtain the amount of area contact which will provide the required current flow.
  • a resilient sleeve 16 has the advantage of providing traction to assure proper feed through of the copy paper 10.
  • the DC power supply 20 is preferably variable to some extent so that once a machine has been set up and adjusted, the voltage can be varried to adjust the current flow and thus adjust the charge on the copy paper to affect the intensity of the image.
  • the sleeve 16 resistance is preferably in order of magnitude greater than the copy paper 10 used so that most of the voltage drop is across the sleeve 16 and it is the resistance of the sleeve 16 that primarily controls charging current magnitude.
  • FIG. 7 illustrates one embodiment of a power supply that constitutes part of this invention.
  • the FIG. 7 power supply converts a 50 or 60 Ben, 110 volt AC line input to a 3,000 volt DC output that has a relatively low level of ripple (2 percent) at a relatively high frequency (KHz.). Furthermore, the FIG. 7 design for a power supply provides an impedance output (specifically, sufficiently low capacitance) from power supply to the roller system so that meaningful efficiency is obtained.
  • the 100 ohm variable resistor R1 is a dropping resistor that provides the ability to manually adjust the output voltage level.
  • the diode D1, resistor R2 and capacitor Cl constitute a rectifying circuit.
  • the capacitor C2 and small inductor Ll tune the primary PI of the transformer TI to 25 KHz.
  • the capacitor C3 is selected to tune the secondary of the transformer T1 to 25 KHZ.
  • the capacitor C2, inductor L1 and transformer primary PI constitute the tank circuit for the transistor Q1, thereby providing an oscillator at 25KHZ.
  • a few turns of primary winding P 2 are connected to the base of transistor O1 to provide regenerative feedback. The number of turns of this feedback coil P2 are selected as a trade-off between degree of regulation and magnitude of DC output.
  • the diode bridge 40 provides full wave rectification of the 25,000 Hz. output of the step-up transformer T1. Because of the high impedance of the load consisting of the sleeve 16 and paper 10 between the two rollers, efficient operation of this power supply 20 requires that the output impedance of this bridge must also be high. Accordingly, diodes were selected that have a 4,000 peak inverse voltage rating; and thus a peak inverse voltage rating above that of the DC output voltage. Furthermore, in order to provide an efficient impedance match, it is important that the capacitance of the diodes be small as possible. However, a small capacitor C5 of about 5,000 micro-microfarads is employed in order to reduce the magnitude of the ripple.
  • FIG. 7 power supply design arises out of a recognition that the capacitance as well as the resistance of the di-electric sleeve must be considered in designing an efficient, fast operating copying device.
  • the device of this invention provides a very substantial increase in the frequency of the signal that is rectified to produce the DC output. Accordingly, as shown in FIG. 7, a 25 KHz input is applied to the rectifier 40 so that the ripple output is at a high frequency.
  • This high frequency alone means that the lines mentioned above that are created in the copy paper tend to be much more closely spaced and thus that the copy paper can be run through more quickly than otherwise might be the case.
  • this high (25 KHZ) frequency makes it much easier to filter the output so that the magnitude of the ripple is very substantially reduced. In one embodiment, this ripple is as low as 2 per-cent of the DC level.
  • FIG. 7 does not show a ground connection in the power supply.
  • the device of this invention makes possible isolating the power supply output from the chassis of the copying machine.
  • the potential charge between paper and chassis is minimized and the electrostatic charge that causes the paper to hang up in the machine and makes the paper more difficult to handle is minimum.
  • This advantage is made possible only because of the very low current level required by the device of this invention. Since the power supplys output current capacity is in the range of 50 to I00 microamperes, physical contact by a user with the roller having the sleeve 16 is in effect a contact through a very high impedance. The resultant voltage drop and current level in the body of the person making such contact is completely harmless.
  • the preferred ripple frequency range is from 10 KHz to KHz.
  • the preferred power supply output voltage range is from 1,500 volts to 4,000 volts.
  • the preferred range of sleeve 16 capacitance is from 25 micro-microfarads to micro-microfarads.
  • a preferred RC time constant for the sleeve 16 in use is less than 5 milli-seconds.
  • a preferred current level is one that is less than 60 microamperes.
  • pressure means to apply pressure between said first roller and said sleeve
  • the material of said sleeve being such that substantial area contact is established between said sleeve and whatever paper is fed between said sleeve and said first roller under said pressure established by said pressure means
  • said area of contact being sufficiently great to provide a current path that substantially eliminates the generation of ozone
  • said sleeve being mounted on said second roller such that said second roller applies a uniform potential at any one moment to the surface of said sleeve in contact with said second roller.
  • the improvement of claim 1 further comprising: a DC power supply having its output across the rollers and having a relatively high frequency ripple current on its DC output, the relationship between a. the output capacity of said power supply, b. the capacity of the di-electric sleeve when subject to said pressure and c. the amplitude and frequency of the ripple providing a substantially even charge density along the surface of copy paper introduced between the rollers.
  • the frequency of said ripple current is at least 10 kilohertz.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • General Physics & Mathematics (AREA)
  • Electrostatic Charge, Transfer And Separation In Electrography (AREA)
US00235346A 1972-03-16 1972-03-16 Electrostatic copying machine Expired - Lifetime US3778690A (en)

Applications Claiming Priority (1)

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US23534672A 1972-03-16 1972-03-16

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US00235346A Expired - Lifetime US3778690A (en) 1972-03-16 1972-03-16 Electrostatic copying machine

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US (1) US3778690A (enrdf_load_stackoverflow)
JP (1) JPS4914132A (enrdf_load_stackoverflow)
CA (1) CA980406A (enrdf_load_stackoverflow)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4309737A (en) * 1980-08-27 1982-01-05 Pitney Bowes Inc. Charge roller system for an electrophotographic copier
US4379630A (en) * 1980-04-01 1983-04-12 Olympus Optical Company Limited Transfer roller for electrophotographic apparatus
US4386395A (en) * 1980-12-19 1983-05-31 Webster Electric Company, Inc. Power supply for electrostatic apparatus
US4556795A (en) * 1982-11-19 1985-12-03 Ensign-Bickford Industries, Inc. Corona discharge device
US4636640A (en) * 1983-07-01 1987-01-13 Pillar Corporation Corona discharge electrode assembly
EP0308185A3 (en) * 1987-09-14 1989-08-23 Canon Kabushiki Kaisha A charging device
US5146280A (en) * 1990-02-17 1992-09-08 Canon Kabushiki Kaisha Charging device
WO1994011791A1 (en) * 1992-11-09 1994-05-26 American Roller Company Charge donor roller with blended ceramic layer
EP0762230A1 (en) * 1995-09-05 1997-03-12 Canon Kabushiki Kaisha Charging member and process cartridge having same
USRE35698E (en) * 1992-10-02 1997-12-23 Xerox Corporation Donor roll for scavengeless development in a xerographic apparatus

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5849960A (ja) * 1981-09-21 1983-03-24 Toshiba Corp ロ−ラ−帯電器
JPS6141233U (ja) * 1985-08-01 1986-03-15 キヤノン株式会社 電気回路の接続装置

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2965755A (en) * 1958-06-04 1960-12-20 West Maxwell George Method of and means for producing a corona discharge
US2980834A (en) * 1956-04-26 1961-04-18 Bruning Charles Co Inc Charging of photo-conductive insulating material
US3684364A (en) * 1971-06-24 1972-08-15 Xerox Corp Lift off electrode

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3172024A (en) * 1960-03-17 1965-03-02 Xerox Corp Charge induction

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2980834A (en) * 1956-04-26 1961-04-18 Bruning Charles Co Inc Charging of photo-conductive insulating material
US2965755A (en) * 1958-06-04 1960-12-20 West Maxwell George Method of and means for producing a corona discharge
US3684364A (en) * 1971-06-24 1972-08-15 Xerox Corp Lift off electrode

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4379630A (en) * 1980-04-01 1983-04-12 Olympus Optical Company Limited Transfer roller for electrophotographic apparatus
US4309737A (en) * 1980-08-27 1982-01-05 Pitney Bowes Inc. Charge roller system for an electrophotographic copier
US4386395A (en) * 1980-12-19 1983-05-31 Webster Electric Company, Inc. Power supply for electrostatic apparatus
US4556795A (en) * 1982-11-19 1985-12-03 Ensign-Bickford Industries, Inc. Corona discharge device
US4636640A (en) * 1983-07-01 1987-01-13 Pillar Corporation Corona discharge electrode assembly
US5126913A (en) * 1987-09-14 1992-06-30 Canon Kabushiki Kaisha Charging device with contactable charging means and an image forming apparatus having the charging means and a detachable process unit
EP0308185A3 (en) * 1987-09-14 1989-08-23 Canon Kabushiki Kaisha A charging device
US5146280A (en) * 1990-02-17 1992-09-08 Canon Kabushiki Kaisha Charging device
USRE35698E (en) * 1992-10-02 1997-12-23 Xerox Corporation Donor roll for scavengeless development in a xerographic apparatus
WO1994011791A1 (en) * 1992-11-09 1994-05-26 American Roller Company Charge donor roller with blended ceramic layer
US5600414A (en) * 1992-11-09 1997-02-04 American Roller Company Charging roller with blended ceramic layer
EP0762230A1 (en) * 1995-09-05 1997-03-12 Canon Kabushiki Kaisha Charging member and process cartridge having same
US5790927A (en) * 1995-09-05 1998-08-04 Canon Kabushiki Kaisha Charging member and process cartridge having same

Also Published As

Publication number Publication date
JPS4914132A (enrdf_load_stackoverflow) 1974-02-07
DE2306420A1 (de) 1973-10-04
CA980406A (en) 1975-12-23
DE2306420B2 (de) 1977-05-26

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