US3918395A - Continuous bias control for electrographic development apparatus - Google Patents

Continuous bias control for electrographic development apparatus Download PDF

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Publication number
US3918395A
US3918395A US447717A US44771774A US3918395A US 3918395 A US3918395 A US 3918395A US 447717 A US447717 A US 447717A US 44771774 A US44771774 A US 44771774A US 3918395 A US3918395 A US 3918395A
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United States
Prior art keywords
pattern
development
toner
bias
applying
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Expired - Lifetime
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US447717A
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English (en)
Inventor
William T Fearnside
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Eastman Kodak Co
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Eastman Kodak Co
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Priority to US447717A priority Critical patent/US3918395A/en
Priority to CA220,655A priority patent/CA1046268A/fr
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Expired - Lifetime legal-status Critical Current

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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
    • G03G15/06—Apparatus for electrographic processes using a charge pattern for developing
    • G03G15/065—Arrangements for controlling the potential of the developing electrode

Definitions

  • the apparatus continuously senses an electrostatic charge pattern and applies an electrical bias to the development station which corresponds to the intensity of the sensed charge.
  • the application of the bias is delayed until the charge pattern passes the last development portion of the zone. for example. the second magnetic brush.
  • the charge pattern is sensed by an induction plate coupled to an amplifier which provides a signal to a Pade pure time delay circuit.
  • the delayed signal drives a high voltage bias amplifier which accordingly biases the development station.
  • the delay is chosen to correspond to the time it takes the sensed pattern to pass the later portion of the development zone.
  • This invention relates to electrographic development and more particularly to an apparatus for automatically adjusting the electrical bias applied to a development electrode to compensate for variations in an electrostatic image being developed.
  • the surface can be contacted with a magnetic developer brush, the bristles of which comprise a mixture of toner and metallic carrier particles.
  • the toner particles which are charged to a polarity to be attracted to the electrostatic charge pattern, are selectively deposited on the surface in accordance with the charge pattern.
  • a development electrode is an at least partially conductive member arranged in close proximity to the recording element during the development process. It is generally equipotential and biased, as described below.
  • the primary function of the development electrode is to assist development of large solid areas of electrostatic image by creating electric fields from the electrode toward such areas. The strength of such fields is proportional to the charge intensity in such areas and the electrical potential of the electrode relative to the recording element. These fields cause toner particles to move toward and adhere to the recording element during the development period.
  • the development electrode In a magnetic brush, the development electrode is generally the brush itself, that is, the carrier particles.
  • the bias voltage can be applied in many cases to the container for the carrier particles.
  • the art has carefully adjusted the electrical potential of the electrode so that the background areas of the electrostatic image can be made electrostatically unattractive and even repulsive to toner particles, while the image is attractive to toner.
  • the result is copies having low density background areas, i.e., background areas substantially free of toner.
  • the bias would be slightly above the lowest potential portion; if the lowest potential portion is to be toned, the bias would be slightly below the highest potential portion.
  • US. Pat. No. 2,956,487 discloses apparatus for continuously sensing the charge associated with a latent electrostatic image upstream from a single magnetic brush development station.
  • a signal derived from such sensing continually biases a development electrode in accordance with the level of sensed charge at a time when that portion of the charge image responsible for such sensed charge passes the development electrode.
  • the electrode is spaced opposite the magnetic brush on the other side of the photoconductor bearing the sensed charge.
  • an induction plate occupies a closely spaced relationship with respect to the path along which an electrostatic image-bearing element travels. At least a portion of the electrostatic image induces a proportional charge on the plate.
  • Circuitry continuously samples the charge induced on the plate and applies a corresponding electrical bias to a two magnetic brush development station, of the type described above, The bias corresponding to the sensed charge is applied at a time when that portion of the electrostatic image which induced such charge passes the last point of toner application, for example, the last point of contact with the second magnetic brush. Pure time delay circuitry is provided to delay the application of the electrical bias to the development electrode until that portion of the electrostatic image responsible for such biasing signal is passing the last part of the development electrode.
  • an object of the invention is to minimize retention of toner in background areas in developing electrostatic images, thereby giving toned images or patterns having high contrast and clean background.
  • a further object is to obtain such clean backgrounds despite variations in charge density in the background areas of the electrostatic image and despite the use of a developing mechanism having a lengthy development zone and a lengthy equipotential development electrode.
  • the present invention relates to an apparatus for developing or toning an electrostatic image or charge pat tern.
  • the invention is not restricted to use with any particular mechanism for obtaining the charge pattern, it is particularly useful with apparatus in which the patterns are produced by electrophotography. Accordingly, electrophotographic apparatus is shown, in part, in the drawing. Because electrophotographic apparatus is well known, the present description will be directed in particular to elements forming part of, or cooperating more directly with, the present invention, and elements not specifically shown or described may take various forms well known to those skilled in the art.
  • an electrographic recording element 2 is driven through a series of electrophotographic stations by a suitable drive means, here depicted illustratively as rollers 3.
  • the recording element 2 includes a support 8, a conductive layer 5, and a photoconductive layer 6.
  • the photoconductive layer has a surface 7 capable of holding a charge in the dark.
  • the element 2 is driven by rollers 3 to move surface 7 through a path in which it passes charging station 10 where a portion of the surface 7 receives a uniform electrostatic charge 11 (shown, for the purposes of illustration, as a negative charge) from a corona discharge source or the like.
  • a uniform electrostatic charge 11 shown, for the purposes of illustration, as a negative charge
  • the charge-bearing surface is advanced past an exposure station 12 where it is imagewise exposed to actinic radiation in accordance with the light and dark areas of an original document.
  • imagewise ex posure serves to selectively dissipate the uniform charge on the photoconductive surface to form an electrostatic latent image 13 corresponding to the original document.
  • Development of the electrostatic image is accomplished as that portion of the recording element bearing the image passes the development station 14 where it is subjected to an electrographic developer.
  • Such a developer commonly comprises a mixture of toner and carrier particles, the latter serving to carry the toner particles by triboelectric forces between them.
  • the toner particles are separated from the carrier particles by the stronger forces associated with the electrostatic image and are deposited on the surface of the photoconductive belt to form a toner image 15.
  • the toner image can be used in a number of ways, for example, it can be transferred to a paper receiving sheet on which the toner can be permanently fixed, or can be fixed directly to the charge carrying surface 7, by appropriate means, not shown.
  • Development station 14 includes a trough 33 for containing a development mix 34, and conventional magnetic development brushes 36 and 38 which are rotatably mounted in trough 33 and serve to apply the development mix to surface 7 to form a developed or toned image 15.
  • Each of the development brushes 36 and 38 can be constructed in a manner well known in the art, see, for example, US. Pat. No. 3,543,720, Drexler et al.
  • each of brushes 36 and 38 include a rotatable, non-magnetic cylinder with a fixed magnetic field producing means inside. The field producing means attracts magnetic carrier particles to the cylinder to form bristles. Rotation of the cylinder brushes the bristles across the charge pattern 13.
  • Toner triboelectrically coated on the carrier particles is then deposited on the charge pattern according to the relative attraction of the carrier and the pattern.
  • Trough 33 is arranged adjacent the path along which the recording element 2 travels, being spaced therefrom such that the bristles of the development brushes contact the surface 7 at all times.
  • a magnetic development brush in addition to functioning as a means for applying toner to an electrostatic image, can also function as a development electrode and thereby assist in the development of large solid image areas.
  • Development electrodes have a tendency to permit deposition of toner in background areas,
  • by controlling the electrical potential or bias of a development electrode it is possible to effectively neutralize the charge in the background areas of the electrostatic image while, at the same time, providing a field between the solid image areas requiring development and the develop ment brush which is sufficient to attract toner particles to such solid areas.
  • the charge density in the background may vary by as much as several hundred volts.
  • the exposure of the recording element to a document of high density little of the uniform charge previously applied to the recording element is dissipated.
  • a green background original will give a much higher background voltage or charge density than will a white background original.
  • the development electrode bias must be high to neutralize such charge.
  • the optimum electrode bias is directly proportional to the background voltage, the denser the background of the original, the higher the electrode bias.
  • an offset bias e.g., 50 volts
  • the background areas of the charge image tend to be repulsive to toner particles.
  • an induction plate 40 which is positioned in close proximity to the path along which the recording element travels, upstream from the developing stations.
  • Induction plate 40 comprises a plate of highly conductive material, such as copper or aluminum, preferably having dimensions smaller than the overall dimensions of the electrostatic image.
  • the induction plate size is not critical and could very reasonably be made to extend the full width of the recording surface.
  • Plate 40 is positioned parallel to the photoconductive surface of the recording element and spaced sufficiently close thereto to receive an induced charge from the electrostatic charge pattern borne by such surface as it passes by.
  • plate 40 is located between the lateral edges of the recording element.
  • the charge induced on plate 40 is, at any given time, proportional to the average instantaneous charge borne by the portion of the recording element which is directly opposite the induction plate.
  • the voltage induced on induction plate 40 is continuously sensed during the passage of the electrostatic image past the induction plate, and a biasing voltage, proportional to the instantaneous level of sensed charge, is applied to the development brushes. Obviously, the bias voltage will have to be delayed until the sensed charge is passing the development station.
  • the charge pattern 13 is first contacted by the toner applying means at an upstream position 51. It is continuously or intermittently contacted by toner and carrier until it reaches a downstream position 52 giving a lengthy development zone.
  • the carrier being conductive will be substantially equipotential throughout. But the image will vary in character over the portion being toned. For example, a green background document may be copied immediately after a white background document. I have found that good results can be obtained if the delay is timed so that the bias adjustment corresponds to the last contact area between the toner applying mechanism and the photoconductive surface.
  • the biasing voltage can be timed to be applied when the electrostatic charge pattern which produced the induced charge is passing the last brush in a two magnetic brush development station, downstream position 52.
  • This delayed bias voltage produced better copies than those obtained from development electrodes biased in a conventional manner.
  • the final touch of development over the second brush 38 has a profound effect on the quality of the final copy.
  • the second brush 38 with bias timed to be applied thereon, essentially fine tunes the development process. If black image areas are too light, it adds toner to them, and if the background has picked up toner it cleans it off.
  • the voltage induced on plate 40 due to the passage of electrostatic image 13 in close proximity thereto is amplified by an amplifier 42.
  • Amplifier 42 can be of any conventional type suitable for the purpose of amplifying the output from induction plate 40, for example, an FET input operational amplifier.
  • the output of amplifier 42 is used to control the output voltage of a bias amplifier 44 which is directly connected to the magnetic brush 38 or to housing 33.
  • the output of amplifier 42 is passed through a pure time delay circuit.
  • the embodiment shows a pure time delay circuit 46 based on Pade' approximants. Other suitable approximants may also be used.
  • Bias amplifier 44 drives the developer brushes to a bias level which is proportional to its input signal coming from pure time delay circuit 46.
  • the bias amplifier 44 can be 4 of any suitable conventional design, for example, an operational amplifier driving high voltage control transistors which connect between the bias supply voltage and the bias amplifier output.
  • controlling means for instantaneously varying the electrical potential applied to said brushes to correspond uniquely to the charge characteristics of the individual charge pattern portion instantaneously passing the last contact area between the magnetic brushes and the surface.
  • sensing means for continuously sensing charge characteristics of each of the transverse segments of the electrostatic charge pattern passing a predetermined location upstream of the development station and for generating successive electrical signals respectively proportional to the charge characteristics of each of the transverse segments;
  • time delay means for receiving an electrical signal 10 downstream position.
  • Electrographic apparatus including:
  • Bald develop' sensing means comprises: mam Zone I 4 an induction plate for generating said signal, which Electrogrlphlc zlpparatus gplate is mounted in close proximity to the surface; mean? for advancmg a Surface bearmg an gleam and static charge pattern through a path; amplifier means, having an input connected to said mfians for applymg toner tothe Pf as the surface induction plate and an output connected to said advanced- Sald tneans lncludlng I time delay means, for amplifying said signal. at least two magnetic brushes arranged in tandem, 6.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Developing For Electrophotography (AREA)
US447717A 1974-03-04 1974-03-04 Continuous bias control for electrographic development apparatus Expired - Lifetime US3918395A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US447717A US3918395A (en) 1974-03-04 1974-03-04 Continuous bias control for electrographic development apparatus
CA220,655A CA1046268A (fr) 1974-03-04 1975-02-24 Commande continu de polarisation pour appareil de developpement electrographique

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Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4021112A (en) * 1975-06-23 1977-05-03 Xerox Corporation Photoreceptor dark current leakage detecting apparatus for xerographic machines
US4111152A (en) * 1976-05-17 1978-09-05 Ricoh Co., Ltd. Electrostatographic apparatus comprising improved development bias means
WO1983003149A1 (fr) * 1982-03-08 1983-09-15 Eastman Kodak Co Dispositif a brosse magnetique pour le developpement d'images electrostatiques
EP0117533A1 (fr) * 1983-02-26 1984-09-05 Mita Industrial Co. Ltd. Dispositif de régulation automatique du potentiel de développement
US4610528A (en) * 1983-03-30 1986-09-09 Sharp Kabushiki Kaisha Electrophotographic copying machine with delayed development bias voltage application
WO1988003670A1 (fr) * 1986-11-06 1988-05-19 Eastman Kodak Company Commande predictive dynamique pour machines electrophotographiques
WO1988008156A1 (fr) * 1987-04-06 1988-10-20 Eastman Kodak Company Commande de traitement dynamique pour machines electrostatographiques
DE4336690A1 (de) * 1993-10-27 1995-05-04 Henning Dipl Phys Dr Frunder Einrichtung zum Messen von elektrischen Potentialkontrasten (Potentialunterschieden)
US5537329A (en) * 1994-06-30 1996-07-16 At&T Corp. Apparatus and method for analyzing circuits
DE102007009070A1 (de) 2007-02-23 2008-08-28 OCé PRINTING SYSTEMS GMBH Verfahren und Vorrichtung zum Erfassen eines elektrischen Potentials sowie von elektrischen Ladungen ein einem Drucker oder Kopierer

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3554161A (en) * 1968-11-14 1971-01-12 Addressograph Multigraph Developing apparatus
US3611982A (en) * 1969-08-29 1971-10-12 Xerox Corp Development electrode control apparatus
US3654893A (en) * 1970-05-01 1972-04-11 Eastman Kodak Co Automatic bias control for electrostatic development
US3674532A (en) * 1970-07-23 1972-07-04 Eastman Kodak Co Control for bias of magnetic brush and method
US3779204A (en) * 1972-08-14 1973-12-18 Eastman Kodak Co Toner concentration and auto bias control apparatus

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3554161A (en) * 1968-11-14 1971-01-12 Addressograph Multigraph Developing apparatus
US3611982A (en) * 1969-08-29 1971-10-12 Xerox Corp Development electrode control apparatus
US3654893A (en) * 1970-05-01 1972-04-11 Eastman Kodak Co Automatic bias control for electrostatic development
US3674532A (en) * 1970-07-23 1972-07-04 Eastman Kodak Co Control for bias of magnetic brush and method
US3779204A (en) * 1972-08-14 1973-12-18 Eastman Kodak Co Toner concentration and auto bias control apparatus

Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4021112A (en) * 1975-06-23 1977-05-03 Xerox Corporation Photoreceptor dark current leakage detecting apparatus for xerographic machines
US4111152A (en) * 1976-05-17 1978-09-05 Ricoh Co., Ltd. Electrostatographic apparatus comprising improved development bias means
WO1983003149A1 (fr) * 1982-03-08 1983-09-15 Eastman Kodak Co Dispositif a brosse magnetique pour le developpement d'images electrostatiques
US4465356A (en) * 1982-03-08 1984-08-14 Eastman Kodak Company Magnetic brush developer apparatus
EP0117533A1 (fr) * 1983-02-26 1984-09-05 Mita Industrial Co. Ltd. Dispositif de régulation automatique du potentiel de développement
US4607954A (en) * 1983-02-26 1986-08-26 Mita Kogyo Kabushiki Kaisha Automatic developing bias control device
US4610528A (en) * 1983-03-30 1986-09-09 Sharp Kabushiki Kaisha Electrophotographic copying machine with delayed development bias voltage application
US4806980A (en) * 1986-11-06 1989-02-21 Eastman Kodak Company Dynamic feedforward process control for electrographic machines
WO1988003670A1 (fr) * 1986-11-06 1988-05-19 Eastman Kodak Company Commande predictive dynamique pour machines electrophotographiques
WO1988008156A1 (fr) * 1987-04-06 1988-10-20 Eastman Kodak Company Commande de traitement dynamique pour machines electrostatographiques
DE4336690A1 (de) * 1993-10-27 1995-05-04 Henning Dipl Phys Dr Frunder Einrichtung zum Messen von elektrischen Potentialkontrasten (Potentialunterschieden)
DE4336690C2 (de) * 1993-10-27 1999-04-15 Henning Dipl Phys Dr Frunder Vorrichtung zum Messen von elektrischen Potentialunterschieden an elektrografischen Aufzeichnungsmaterialien
US5537329A (en) * 1994-06-30 1996-07-16 At&T Corp. Apparatus and method for analyzing circuits
US5689685A (en) * 1994-06-30 1997-11-18 Lucent Technologies Inc. Apparatus and method for analyzing circuits using reduced-order modeling of large linear subscircuits
DE102007009070A1 (de) 2007-02-23 2008-08-28 OCé PRINTING SYSTEMS GMBH Verfahren und Vorrichtung zum Erfassen eines elektrischen Potentials sowie von elektrischen Ladungen ein einem Drucker oder Kopierer
US20100321047A1 (en) * 2007-02-23 2010-12-23 Alfred Zollner Method and device for detecting electric potential and electric charges in a printer or copier
US8384403B2 (en) 2007-02-23 2013-02-26 OCé PRINTING SYSTEMS GMBH Method and device for detecting electric potential and electric charges in a printer or copier

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Publication number Publication date
CA1046268A (fr) 1979-01-16

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