US3321307A - Exposure control in xerographic printing - Google Patents

Exposure control in xerographic printing Download PDF

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Publication number
US3321307A
US3321307A US295143A US29514363A US3321307A US 3321307 A US3321307 A US 3321307A US 295143 A US295143 A US 295143A US 29514363 A US29514363 A US 29514363A US 3321307 A US3321307 A US 3321307A
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United States
Prior art keywords
exposure
field
photoconductor
potential
sensing electrode
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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
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US295143A
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English (en)
Inventor
Urbach Franz
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.)
Eastman Kodak Co
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Eastman Kodak Co
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Publication date
Application filed by Eastman Kodak Co filed Critical Eastman Kodak Co
Priority to US295143A priority Critical patent/US3321307A/en
Priority to FR981072A priority patent/FR1404770A/fr
Priority to BE650336D priority patent/BE650336A/xx
Priority to GB28296/64A priority patent/GB1055696A/en
Priority to FR981411A priority patent/FR1404027A/fr
Priority to DEE27393A priority patent/DE1188426B/de
Priority to BE650516A priority patent/BE650516A/xx
Priority to GB29066/64A priority patent/GB1018290A/en
Application granted granted Critical
Publication of US3321307A publication Critical patent/US3321307A/en
Anticipated expiration legal-status Critical
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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
    • G03G15/04—Apparatus for electrographic processes using a charge pattern for exposing, i.e. imagewise exposure by optically projecting the original image on a photoconductive recording material
    • G03G15/043—Apparatus for electrographic processes using a charge pattern for exposing, i.e. imagewise exposure by optically projecting the original image on a photoconductive recording material with means for controlling illumination or exposure
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G17/00—Electrographic processes using patterns other than charge patterns, e.g. an electric conductivity pattern; Processes involving a migration, e.g. photoelectrophoresis, photoelectrosolography; Processes involving a selective transfer, e.g. electrophoto-adhesive processes; Apparatus essentially involving a single such process
    • G03G17/02—Electrographic processes using patterns other than charge patterns, e.g. an electric conductivity pattern; Processes involving a migration, e.g. photoelectrophoresis, photoelectrosolography; Processes involving a selective transfer, e.g. electrophoto-adhesive processes; Apparatus essentially involving a single such process with electrolytic development

Definitions

  • the present invention relates to xerography and particularly to a method and apparatus for controlling the exposure of a charged photoconductor sheet.
  • Optimum quality of an electrostatic image is that distribution of charges which, when developed with a suitable toner, produces prints whose quality is the optimum obtainable with the particular photoconductor and toner being used.
  • the quality in a print refers to the minimum and maximum densities and to the contrast of the print. High quality prints have extremely low minimum density (clean highlights), fairly high maximum density and a contrast which approximates or slightly exceeds that of the original subject being reproduced.
  • the present invention is also particularly useful in the copying of documents.
  • a further object of the invention is to provide method and apparatus for controlling the termination of the exposure time. It is a particular object of the invention to provide such control independent of the intensity of the exposure over a wide range of intensities, including all or practically all intensities found in light transmitted through commonly over-exposed and under-exposed transparencies (negatives or positives). It is also a particular object of the invention to provide a system which corrects for variations in sensitivity of the recording material at the same time as it corrects for the density of the transparency being printed.
  • the present invention is applicable to the various forms of xerography including those in which the toner adheres to the charged areas and those in which the toner adheres to the discharged areas of the electrostatic image. It is equally applicable to systems in which the toner image remains on the photoconductor (zinc oxide in resin on paper base is sufiiciently inexpensive) and those in which the image is transferred from a reusable photoconductor (which may be relatively expensive) to a separate receiving sheet.
  • the invention utilizes the change in an average electric field adjacent to the photoconductor as the charge on the photoconductor changes from a uniform, relatively high-density charge to an imagewise distribution of charge with a lower average density. The proper average electric field is attained by an exposure time which depends on the intensity of the exposing image and the sensitivity of the photoconductor.
  • the electric field, or more exactly the change in the electric field, adjacent to a substantially uniformly charged photoconductor is measured during the exposure to an image.
  • the exposure is started either manually or by the measuring system.
  • the exposure efiectively removes charges in the exposed areas, causing the field to change, and the exposing is terminated when the measured field or the change in field reaches a predetermined value.
  • excellent quality prints are obtained from a wide range of negatives and a wide range of photoconductor sensitivities when such a control system is used.
  • the term effectively removes charges is used herein to include movements of charges from the surface, move ments of opposing charges to or nearer the surface and what is sometimes referred to as a disorientation of dipoles.
  • the present invention is not concerned with the theory or convention adopted, but uses the term in its commonly accepted sense.
  • the charging of the surface must be terminated before or at the moment exposure starts.
  • the surface is charged uniformly and brought to the position for exposure before the measuring electrometer or field meter is rendered operative.
  • the electrometer may have its field-sensing electrode shorted to ground or shielded from the charged photoconductor until the photoconductor is in place and ready for exposure.
  • the shield is used and then removed, the sensing electrode of the electrometer or field meter is immediately subjected to a high electric field.
  • the grounded electrode is used and then ungrounded, it remains at ground potential until the field of the charged photoconductor surface changes either through spontaneous decay or exposure.
  • the exposing light is then turned on or the shutter in the projection printer is opened either manually or by a relay operated by the output of the electrometer or field meter. Then, as the field falls (causing, in the case of the removed shield, a decrease of potential on the sensing electrode and in the case of an unground electrode an increase of the potential thereof) the measuring is used to terminate the exposure at a predetermined value of the average electric field or at a predetermined change in the field, namely that corresponding approximately to an optimum quality electrostatic image. It should be noted, at this point, that one of the advantages of the present invention arises from the fact that it takes into account any reasonable amount of natural leaking away of the electrostatic charges as well as the discharging due to the image exposure. While excessive natural leakage of charge will tend to degrade the image, the present invention still assures the optimum available among such degraded images.
  • the type of development may determine whether the meter should be set to terminate the exposure at a predetermined value or at a predetermined change from the initial value.
  • the latter is particularly useful for any type of development which takes place with no grounded electrode near the recording surface at the time of development; this includes fringe development by powder cloud, liquid development or cascade development with insulating carrier for the toner.
  • the exposure is terminated substantially at a fixed field value when the development is to be in the presence of a grounded electrode as for example with magnetic brush development or some forms of liquid or powder cloud development with a grounded electrode adjacent the image surface.
  • sensing electrode used therewith is a transparent one held immediately in front of the charged surface of the photoconductor being measured.
  • One form of electrometer useful with this type of sensing electrode is the General Radio D.C. Amplifier and Electrometer, Type 1230A. The sensing electrode being transparent does not obscure the printing beam.
  • a second type of meter commonly used employs a mechanical chopper between the source of the field and the sensing electrode.
  • the chopper and sensor constitute two sectored discs or vanes, one of which is stationary and the other rotating behind or preferably in front of the stationary one.
  • a steady field creates an alternating signal in the sensing electrode.
  • the front vane (either the chopper or the fixed one) is grounded, or biased to a fixed potential, and the other one acts as the sensing electrode supplying an AC. signal to the field meter amplifier. Since such a sensing electrode with chopper is normally opaque, it is positioned, in the present invention, to one side of the image-forming beam so as not to obscure the beam.
  • the sensing electrode in this case faces the surface to be measured, obliquely.
  • Electrometers or field meters of the rotating electrode type are described in many publications. An elementary description appears, for example, in Measurements of Electrical Polarization in Thin Dielectric Materials by Tyler, Webb and York, Journal of Applied Physics, vol. 26, pp. 61-68, January 1955. Also, the five references listed in a footnote on page 56 of this Tyler et al. article describe useful forms of such electrometers. The various known forms of electrometers have, of course, different ranges of current values in their output or measuring circuits. If these values are not sufficient to operate the relays or the equivalent involved in initiating and terminating the exposure, various degrees or stages of amplification are introduced.
  • FIG. 1 schematically illustrates a preferred embodiment of the invention.
  • FIG. 2 similarly illustrates the field meter or electrometer employed in FIG. 1.
  • FIG. 3 illustrates a modification of one part of the arrangement shown in FIG. 1 to incorporate a different embodiment of the invention.
  • a sensing electrode is positioned to one side of the printing beam and is arranged to face the charged surface of the photoconductor 15 obliquely.
  • the sensing electrode 25 is stationary behind a rotating sector blade or chopper 26 of an electrometer of the above-discussed type.
  • the chopper 26 is biased slightly above or below ground by a battery,
  • the rotating chopper alternately shields and exposes the stationary elect-rode 25. This mechanical chopping of the field produces an AC. potential across a high resistance 28.
  • a metal shield 31 is placed across the illuminating beam and in front of the sensing electrode 25 of the field meter, until a fully charged photoconductor 15 is in place, as shown, and ready for exposure.
  • This shield 31 maintains the field meter inoperative, i.e. prevents the field meter from measuring the average field adjacent to the photoconductor 15 until the photoconductor sheet is ready to receive the exposure.
  • the shield 31 is then removed manually by grasping the extension 32 and withdrawing the shield from the metal housing 33 which is grounded and which shields the whole unit.
  • mechanical means can be provided for removing the shield or for moving it to an inoperative position, rendering it ineffective.
  • the electrometer sensing electrode becomes operative, and a signal acnoss the resistor 28 is amplified in the field meter amplifier 36 and impressed across a resistance 37 which in this case is a 500-0hm resistance.
  • Standard field meter amplifiers such as 36 are provided with output connectors, one of which is grounded and across which the variable resistance 37 is connected.
  • the output With a field meter of the type described below having a final rectifier (such as 57, FIG. 2) which may be connected with either polarity, the output can be a negative, negative-going signal for an increasing positive surface potential, or with a reverse arrangement, the output can be a negative, negative-going signal for an increasing negative surface potential.
  • a SOD-ohm resistor at 37 the output of the field meter 36 produces for example a potential acnoss this resistor 37 between zero and approximately 0.5 volt as the magnitude of the surface potential under measurement is increased.
  • the 6 BH6 tube 40 With no input signal, the 6 BH6 tube 40 has its control grid at +0.04 volt from ground. The cathode is also above ground by the potential drop across the cathode resistor. In this condition the tube 40 is conducting fairly heavily. The potential at the plate is +62 volts which is dropped to +35 volts by the Zener diode (IN205). This potential drop plus the potential drop across a portion of the resistor 44 puts the grid of the 6C4 tube 43 at 16 volts which is sufficient to keep the tube 43 cut off and no current flowing through the relay 20.
  • a negative, negative-going output current from the field meter amplifier is produced as a sensed field strength from the photoconductor 15 increases.
  • the potential on the grid of tube 40 becomes more negative. I-ts plate current then decreases, causing the plate potential to rise.
  • the grid of tube 40 reaches -0.5 volt from ground, the plate of this tube 40 is at +84- volts.
  • the diode 42 drops this to +56 volts and tube 43 grid is then at 2.0 volts, as determined by the ad justment of the contact on resistor 44.
  • This grid voltage permits sufficient current to flow in the plate circuit to actuate the relay 20, closing the relay contact 19 and starting the exposure if switch 18 is already closed.
  • This energized condition of relay 20 is reached immediately after the shield 32 is removed, thus exposing the sensing electrode 25, 26 to the field adjacent to the charged photoconductor 15.
  • the surface potential on the photoconductor 15 starts to decrease, which causes the potential on the grid of the tube 40 to rise, increasing the plate current and causing the plate potential to drop, causing the grid on tube 43 to be come more negative reducing the plate cur-rent through relay 20 until it releases.
  • the sensing electrode 25 may be grounded until the sheet 15 is ready for exposure. Opening the ground connection renders the sensing electrode 25, 26 operative, starting the exposure which, as described above, terminates when the potential on the grid of the tube 43 reaches -2.0 volts. It is customary to use a vacuum plate of the type commonly used in process photography, to hold the plate 15 flat on the shielded easel of the projection printer illustrated schematically in FIG. 1. After the exposure is terminated, the photoconductor sheet 15 is developed or toned by any standard xerographic method; the toner image may be fused to the photoconductor or transferred to a receiving sheet.
  • the lamp may remain on, and the exposure may be controlled by opening and closing the shutter 13 by means of a shutter control actuated by the closing and opening of the switch 19.
  • this instrument not only corrects for various densities of the transparency 11 or intensities of the lamp 10, but also corrects for sensitivities in the layer 15.
  • photoconduc-tors whose sensitivities vary by as much as 7 to l were used.
  • Each coating was charged to a surface potential of -400 volts under a --9 kv. corona, before exposure.
  • the optimum exposure time was determined for one of the coatings.
  • a series of prints were run on the various coatings and another series were run with a 1.0 neutral density filter inserted in the printer beam. Without interference on the part of the operator, the apparatus was allowed to monitor each of the exposures. When the same average surface potential had been reached, the exposure was automatically terminated.
  • the resulting prints with all of these variations were essentially identical and for practical purposes were indistinguishable. They were all developed with a standard magnetic brush toner, by magnetic :brush development.
  • FIGS. 1 and 2 are merely for illustration of a suitable circuit, since any field meter may be used, and any of the many known circuits for operating a relay from the output of a field meter may be used without departing from the spirit of this invention.
  • FIG. 2 essential features of one particular field meter 36 are illustrated.
  • the input potential from a point or tap on the l-megohm resistor 28 is fed to two stages of amplification in tubes 50 and 51 (l2AU7) and the output of the last stage is impressed across a 110,000-ohm resistor 52.
  • a voltage signal tapped off this resistor 52 is then fed to the grid of tube 54 (6C4) which is tuned by the tuned circuit 53, the output of which is fed to the control grid of 6AK6 pentode 55
  • Whose output current is sufficient through a transformer 56 and a rectifier 57 to give a substantial signal across a SOD-ohm resistor 37. From this point on, as shown in FIG. 1, there is further amplification to obtain sufficient current to operate the relay 20.
  • the value of the impedance of the load resistor 37 is selected to match the particular electrometer or field meter being used.
  • the easel of the projection printer holding the charged photoconductive surface 15 is shielded by a shield 70.
  • the sensing electrode 71 of the electrometer 72 is transparent.
  • a different type of field meter is used, and hence the output is across a resistor 74 which is equivalent to resistor 37 of FIG. 1 but is selected to have proper impedance value.
  • the potential at a selected point on the resistor 74 is fed to an amplifier tube such as 40 in FIG. 1.
  • the sensing electrode 71 is placed within a fraction of a millimeter of the photooonductor surface and uniformly covers the whole surface.
  • the field meter is maintained inoperative by closing the grounding switch 73 until the charged plate 15 is in position ready for exposure.
  • the present invention requires the average of the field over a substantial area of image to be measured. Accordingly, the preferred embodiments of the invention expose the whole of the exposure areas of the photoconductor, at one time. Scanning exposure of this area complicates the operation of the present invention and is therefore to be avoided.
  • the closing and opening of the relay contact 19 can be manual or relay contact 19 can be omitted. That is, the exposure is initiated manually and when the operator (reading the field value on the miliiammeter which is a part of commercially available field meters, in series with the load impedance 37) notes that the field has dropped to the optimum image value, he opens the switch 19 or 18, terminating the exposure.
  • the preferred embodiments are the automatic ones illustrated, however.
  • a xerographic process for controlling the exposure of a substantially uniformly charged photoconductor the steps which comprise: exposing said photoconductor image'wise while simultaneously measuring the changes in the electric field as charges are effectively removed in exposed areas, and terminating said exposing when the measured change in the electric field reaches a predetermined value.
  • a projection printer for imagewise exposing a substantially uniformly charged surface of a photoconductor sheet comprising means for projecting a light beam onto said surface with an image in focus,
  • a field meter with its sensing electrode facing said surface but not obscuring said beam for measuring the average electric field adjacent to the surface, and means controlled by said field meter for terminating said projecting means when the field decreases to a value equal to that of an electrostatic image of approximately optimum quality.
  • a printer including means for maintaining said field meter inoperative to measure said average field until said photoconductor sheet is ready to receive said exposure, and means for rendering said maintaining means ineffective and hence said field meter operative.
  • a printer according to claim 5 in which said maintaining means is an electric ground connected to said sensing electrode and disconnectable therefrom by said rendering means.
  • a printer according to claim 5 in which said maintaining means is a shield removably located between the sensing electrode and said surface and removable by said rendering means.
  • a projection printer for imagewise exposing a substantially uniformly charged surface of a photoconductor sheet comprising means for projecting a light beam onto said surface with an image in focus,

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Molecular Biology (AREA)
  • Electrophotography Using Other Than Carlson'S Method (AREA)
  • Control Or Security For Electrophotography (AREA)
US295143A 1963-07-15 1963-07-15 Exposure control in xerographic printing Expired - Lifetime US3321307A (en)

Priority Applications (8)

Application Number Priority Date Filing Date Title
US295143A US3321307A (en) 1963-07-15 1963-07-15 Exposure control in xerographic printing
FR981072A FR1404770A (fr) 1963-07-15 1964-07-08 Procédé de réglage de la durée d'exposition et compte-pose pour appareil de reproduction xérographique de documents
GB28296/64A GB1055696A (en) 1963-07-15 1964-07-09 Electro-photographic reproduction
BE650336D BE650336A (xx) 1963-07-15 1964-07-09
FR981411A FR1404027A (fr) 1963-07-15 1964-07-10 Nouveau procédé de reproduction d'images par couche photoconductrice
DEE27393A DE1188426B (de) 1963-07-15 1964-07-14 Verfahren zur Steuerung der Belichtung beim xerographischen Kopieren und Vorrichtung zur Durchfuehrung dieses Verfahrens
BE650516A BE650516A (xx) 1963-07-15 1964-07-14
GB29066/64A GB1018290A (en) 1963-07-15 1964-07-15 Electrophotographic reproduction

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US295143A US3321307A (en) 1963-07-15 1963-07-15 Exposure control in xerographic printing

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Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3406334A (en) * 1964-07-27 1968-10-15 Nuclear Corp Of America Apparatus for testing electrostatic copy material
US3449658A (en) * 1966-11-17 1969-06-10 Eastman Kodak Co Method and apparatus for sensitometrically testing photoconductive insulators
US3880512A (en) * 1973-05-21 1975-04-29 Coulter Information Systems Image recording apparatus for electrophotographic film
JPS511132A (xx) * 1974-06-24 1976-01-07 Canon Kk
US3973956A (en) * 1973-09-14 1976-08-10 Coulter Information Systems, Inc. Electrophotographic process employing signal comparison
US4144539A (en) * 1975-12-23 1979-03-13 International Business Machines Corporation Feedback control for laser discharge system
US4236812A (en) * 1979-03-07 1980-12-02 Coulter Systems Corporation Image recording method for electrophotographic film
US4261660A (en) * 1977-11-09 1981-04-14 Canon Kabushiki Kaisha Surface potentiometer for use in an electrostatic copier
US4284344A (en) * 1978-07-27 1981-08-18 Minolta Camera Kabushiki Kaisha Electrophotographic density control
US4326796A (en) * 1979-12-13 1982-04-27 International Business Machines Corporation Apparatus and method for measuring and maintaining copy quality in an electrophotographic copier
US4470691A (en) * 1981-10-22 1984-09-11 Tetras, S.A. Illuminating means for electrophotographic copier apparatus
EP0156217A1 (de) * 1984-03-16 1985-10-02 Hoechst Aktiengesellschaft Verfahren und Anordnung zum Einhalten eines vorgegebenen Potentialverhältnisses bei der Belichtung von elektrostatisch aufgeladenen lichtempfindlichen Schichten
US4613228A (en) * 1977-12-21 1986-09-23 Canon Kabushiki Kaisha Surface potentiometer
US4684239A (en) * 1984-08-22 1987-08-04 Canon Kabushiki Kaisha Image forming apparatus with automatic regulation in response to image density
US5164771A (en) * 1978-08-24 1992-11-17 Canon Kabushiki Kaisha Image forming apparatus which adjusts illumination levels independently for test samples and for originals
US20040228777A1 (en) * 2001-04-11 2004-11-18 The Kansai Electric Power Co., Inc. Gas-liquid contact plate and gas-liquid contactor

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2297691A (en) * 1939-04-04 1942-10-06 Chester F Carlson Electrophotography
US2781705A (en) * 1953-10-29 1957-02-19 Herbert E Crumrine Paper handling mechanism for xerographic copying machine
US3013203A (en) * 1958-07-01 1961-12-12 Xerox Corp Xerographic electrometer apparatus
US3251685A (en) * 1959-10-19 1966-05-17 Xerox Corp Method of controlling contrast in a xerographic reproduction process

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2297691A (en) * 1939-04-04 1942-10-06 Chester F Carlson Electrophotography
US2781705A (en) * 1953-10-29 1957-02-19 Herbert E Crumrine Paper handling mechanism for xerographic copying machine
US3013203A (en) * 1958-07-01 1961-12-12 Xerox Corp Xerographic electrometer apparatus
US3251685A (en) * 1959-10-19 1966-05-17 Xerox Corp Method of controlling contrast in a xerographic reproduction process

Cited By (20)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3406334A (en) * 1964-07-27 1968-10-15 Nuclear Corp Of America Apparatus for testing electrostatic copy material
US3449658A (en) * 1966-11-17 1969-06-10 Eastman Kodak Co Method and apparatus for sensitometrically testing photoconductive insulators
US3880512A (en) * 1973-05-21 1975-04-29 Coulter Information Systems Image recording apparatus for electrophotographic film
US3973956A (en) * 1973-09-14 1976-08-10 Coulter Information Systems, Inc. Electrophotographic process employing signal comparison
JPS598830B2 (ja) * 1974-06-24 1984-02-27 キヤノン株式会社 電子写真法
JPS511132A (xx) * 1974-06-24 1976-01-07 Canon Kk
US4144539A (en) * 1975-12-23 1979-03-13 International Business Machines Corporation Feedback control for laser discharge system
US4261660A (en) * 1977-11-09 1981-04-14 Canon Kabushiki Kaisha Surface potentiometer for use in an electrostatic copier
US4613228A (en) * 1977-12-21 1986-09-23 Canon Kabushiki Kaisha Surface potentiometer
US4284344A (en) * 1978-07-27 1981-08-18 Minolta Camera Kabushiki Kaisha Electrophotographic density control
US5164771A (en) * 1978-08-24 1992-11-17 Canon Kabushiki Kaisha Image forming apparatus which adjusts illumination levels independently for test samples and for originals
US4236812A (en) * 1979-03-07 1980-12-02 Coulter Systems Corporation Image recording method for electrophotographic film
US4326796A (en) * 1979-12-13 1982-04-27 International Business Machines Corporation Apparatus and method for measuring and maintaining copy quality in an electrophotographic copier
US4470691A (en) * 1981-10-22 1984-09-11 Tetras, S.A. Illuminating means for electrophotographic copier apparatus
EP0156217A1 (de) * 1984-03-16 1985-10-02 Hoechst Aktiengesellschaft Verfahren und Anordnung zum Einhalten eines vorgegebenen Potentialverhältnisses bei der Belichtung von elektrostatisch aufgeladenen lichtempfindlichen Schichten
US4616923A (en) * 1984-03-16 1986-10-14 Hoechst Aktiengesellschaft Potential control on photosensitive layers in electrostatic charging processes
AU570307B2 (en) * 1984-03-16 1988-03-10 Hoechst A.G. Exposure control of electrostatically charged light-sensitive layers
US4684239A (en) * 1984-08-22 1987-08-04 Canon Kabushiki Kaisha Image forming apparatus with automatic regulation in response to image density
US20040228777A1 (en) * 2001-04-11 2004-11-18 The Kansai Electric Power Co., Inc. Gas-liquid contact plate and gas-liquid contactor
US20070039182A1 (en) * 2001-04-11 2007-02-22 The Kansai Electric Power Co., Inc. Gas-liquid contact plate and gas-liquid contactor

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GB1055696A (en) 1967-01-18
BE650516A (xx) 1964-11-03

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