CA1149154A - Automatic development electrode bias control system - Google Patents
Automatic development electrode bias control systemInfo
- Publication number
- CA1149154A CA1149154A CA000222749A CA222749A CA1149154A CA 1149154 A CA1149154 A CA 1149154A CA 000222749 A CA000222749 A CA 000222749A CA 222749 A CA222749 A CA 222749A CA 1149154 A CA1149154 A CA 1149154A
- Authority
- CA
- Canada
- Prior art keywords
- electrode
- potential
- image
- developing
- biasing
- 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
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Classifications
-
- 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
-
- 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
- G03G15/10—Apparatus for electrographic processes using a charge pattern for developing using a liquid developer
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Developing For Electrophotography (AREA)
- Wet Developing In Electrophotography (AREA)
- Control Or Security For Electrophotography (AREA)
Abstract
Title of the Invention AUTOMATIC DEVELOPMENT ELECTRODE
BIAS CONTROL SYSTEM
Abstract of the Disclosure An automatic control system for the bias on a development electrode in which a plurality of ground-insulated, narrow floating electrodes are spaced along a line adjacent the entrance of a liquid developer applicator unit. the floating electrodes relatively scan image areas of the surface of an organic photoconductor carried by a conductive support moving through the developer unit.
Owing to conduction of a charge from the photoconductive surface through the developer liquid to the floating electrodes, they assume potentials each of which is a function of the average potential of the image area subtended by the floating electrode. The potential of each floating electrode is sensed by a high input impedance measuring circuit which selects the potential of the low-est value, amplifies the selected potential and applies the amplified voltage to the biasing electrode or electrodes of the developer system.
A fully charged and unexposed area of the surface following the image area produces a reverse bias which cleans the biasing electrodes as the fully charged area passes through the developer system.
BIAS CONTROL SYSTEM
Abstract of the Disclosure An automatic control system for the bias on a development electrode in which a plurality of ground-insulated, narrow floating electrodes are spaced along a line adjacent the entrance of a liquid developer applicator unit. the floating electrodes relatively scan image areas of the surface of an organic photoconductor carried by a conductive support moving through the developer unit.
Owing to conduction of a charge from the photoconductive surface through the developer liquid to the floating electrodes, they assume potentials each of which is a function of the average potential of the image area subtended by the floating electrode. The potential of each floating electrode is sensed by a high input impedance measuring circuit which selects the potential of the low-est value, amplifies the selected potential and applies the amplified voltage to the biasing electrode or electrodes of the developer system.
A fully charged and unexposed area of the surface following the image area produces a reverse bias which cleans the biasing electrodes as the fully charged area passes through the developer system.
Description
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Background o~ the Invention In the art of electrostatic copying in which the surface of a photoconductor carried by a conduc-tor su~port first is charged, then exposed to a light image and then subjected to the action of a developer, organic photoconductors have recently come into relatively wide use.
While pho~oconductors of this type have many advantages over inorganic photoconductors, they have one significant disadvantage. Upon exposure to light the charge on the photoconductor does not leak off as rapidly as is desirable.
Thus, in any co~ying apparatus whlch is to operate at a reasonable rate of speed, an organic photoconductor retains a significant charge in background or non-image areas after normal exposure to the copy to be reproduced.
This background level may be in the range of from about 100 to about 200 voltsO
~any attempts have been made in the prior art to overcome the problem of deposit of developer upon background areas owing to the residual potential -thereon.
For example, it has been suggested that the developer station be provided with a biasing electrode to which a potential is applied to counteract the effect of the residual potential in background areas. One problem in using a fixed biasing potential is that the background potential varies over a relatively wide range so that ms/~
either deve:Lopment of background areas takes place :if the biasin~ po-tential is not large enough or toner is deposited on the biasing el~ctrode if -too large a biasing potential is employed. ~-t will be apprecla-ted further that a biasing po-ten-tial should be applied to the electrode only durlng the period oE time durinq which the latent image is passing through the developer system. If the biasing potential is not switched off~ relatively great amounts of toner will be deposited on the biasing electrode when uncharged areas of the drum pass through the deve].oper stationO
Attempts have been made in the prior art to provide systems which vary the biasing potential in response to variations in the potential of bac~ground areas. For example, Coriale Patent 3,611,982 shows an arrangement in which a capacitive probe, located outside and just before t:he developer unit, is exposed by a shutter to a charged and fulIy exposed strip at the edge of the photo-conductor drum. The sensed potential is amplified and is used to control a variable power source which provides the biasing potential for the electrode located in the developer system. Another example of a bias voltage con-trol system is shown in Coriale Patent 3,788,739, in which a capacitive probe, located outside and just ahead of the developer system, senses the potential of a part of an oversize exposed area outside the image area to control the bias potential applied to an electrode in the de~elo~er unit. A further example of the use of a ms/ ~
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:, :
capacitance probe to regulate the bias applied by a source to a biasing electrode is shown in Smith Patent 3,782,818. The probe of Smith, like those of Coriale, is located just ahead of and outside of the developer applicator unit in which the biasing electrode is disposed.
Parmigiani Patent 3,575,505 shows an arrangement in which the developer system bias voltage is changed in response ; to the number of`copies made in an attempt to compensate ~or changes in the characteristics of the photoconductor over a period of time.
The systems of the prior art discussed herein~
above sense photoconductor voltage by the use of delicate and sensitive instruments such as elec-trometers for measuring the charge in residual areas of the photoconductor.
Such instruments are not only expenslve, but also involve critical factors such as the particular geometry of the probe and the critical distance of the probe from the surface carrying the potential to be sensed. The arrange-ments of the prior art, moreover, employ switching arrange~
: 20 ments for rendering the bias , '~}
~ ms/~
~9154 effec-tive only for the period o:E time during which the image passes through the developer system. In addi-tionl owing to the deposition of toner particles on the biasing electrode, unless some means is provided for cleaning this electrode, it will rapidly become so contaminated as to render the system inoperative.
We have invented an automatic development ele~trode . .
bias control system for inhibiting deposit of toner on back-ground areas which overcomes the defects of systems o the 1~ prior art. The parameters of our system are non-criticalO
Our assembly is relatively inexpensive to construct. Our construction is such as to insure that the bias will at all ti.mes be sufficient to prevent deposition of toner on back-ground areas. We provide our system with automatic means for removing toner deposited on the biasing electrode without the use of mechanical cleaning means.
SUMMARY OF THE INVENTION
An object of the invention is to provide an automatic development electrode bias control system.
In one particular aspect of the present invention there is provided a method of electrically biasing a developing electrode disposed closely adjacent to a photo-conductive member of an electrophotographic device after the photoconductive member has been charged and exposed to a light image. The electrophotographic aevice is of the wet-type having a developer unit utilizing a developing solution.
The method comprisiny the s-teps of a) automatically sensing through the developing solution the potential remaining on the photoconductive member by means of electrostatic induction and the electrical conductivitv of the developing solu-tion; b) computing biasing voltage in accordance with a predetermined value of the sensed potential; and c) automatically applying the biasing voltage to the developing electrode.
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g~54 In a further particulax aspect the presen-t invention provides a development apparatus for an electrostatic copier including in combination, a drum having an arcuate surface, a photoconductor comprising at least a portion of the arcuate surface of said drum, means for electrastatically charging said photoconductor, means for exposing a portion of the charged photoconductor to a pattern o~ light and shade to produce an electrostatic image, said image occupying a region of the arcuate surface of said drum of less than 360 angular extent, the arcuate surface of said drum including a non-image area of appreciable angular extent, development means for applying to said image a developer liquid containing dispersed toner particles~ means for rotating the drum to carr-y sequentially said image and said non-lmage area past the development means, the development means comprising an electrode and means for electrically bia~ing said electrode to provide adjacent said electrode a first electric field which attracts toner particles to said electrode, and means operable during passage of a non-image area past said development means for providing adjacent said electrode a second electric field which repels toner particles from said electrode.
BRIEF DES~RIPTION OF THE DRAWINGS
.~
In the accompanying drawings to which reference - is made in the accompanying specification and in which like reference characters indicate like parts in the various views:
~ igure 1 is a partially schematic end elevation of an electrostatic copying machine which may be provided with our automatic development electrode bias control system.
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Figure 2 ls a perspeetive view with parts removed, with other parts broken away, and with parts shown ln ~ection, illustrating our automatic development - jl/ . -7-., P~
electrode bias control s~stem.
FIGUI~E 3 is a schematic view of one form of an electrical circuit which may.be employed in our automatic development electrode bias control s~stem.
Description of the Preferred Embodiment Referring now to FIGURES 1 and 2, a machine indicated generally by the reference character 10, with which our system ma~ be used, includes a drum indicated generally by the reference character 12 made up of a conducti1ve cylinder 14, the outer surface of whi.ch carries a layer 16 of organic photoconductive material well known to the art. Drum 12 includes respective end plates 18 and 20 carrying stub shafts 22 and 24 by means of which the drum is mounted for rotary movement in a manner known to the artu A corona discharge unit 26 is adapted to be connected to a suitable source of power 28 ~hrough a switch 30 to provide a corona discharge for applying a uniform electrostatic charge to -the photoconductor 16 as the drum 12 rotates. After having been charged, the photoconductor surEace moves past an exposure unit 32 of any type known to the art, adapted to be connected to a control unit 34 upon the closure of a switch 36.
After having been exposed to an original of the image to be copied, the photoconductive surface moves ir.to : cooperative relationship with a developer unit indicated generally by the reference character 38. Developer unit 38 may, for example, be of -the t~pe which includes an applicator tank 40 di.sposed within a return tray 42. As is known in the art, developer made up of charged toner m c. / (~
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particles disPosed in a carrier li~uid having a ~e]ativelY
high volume resistivity is ~ed into the tan~ 40 through a pipe 44. The tank 40 fills -to a point at which ~he liquid developer comes into contact with the surface of the drum 12 and then overflows into the tray 42, from whence it is re-turned to the supply ~not shown) through a pipe 46.
It will readily be a~preciated that any means may be employed to control the operation of the various units of the machine 10. For reasons which will be explained more fully hereinbelow, we wish to provide a region on the photoconductive surface 16 following the image area, ~hich region is fully charged but not exposed. By way of example, in order to achieve this result we may mount a cam 48 on shaft 22 for rotation therewith, so as to actuate a follower 50 to close switch 30 so that a predetermined region around the drum is fully charged. A second cam 54 ~-on shaft 22 is adapted to operate a follower 56 to close swItch 36 to place the ex~osure unit 32 into operation.
It will be seen from FIGURE 1 that the angular extent of the cam 48 is greater than that of cam 54, so that a greater region of the surface layer 16 is charged than is exposed. Moreover, -the arrangement is such that exposure starts at the beginning of the charged region, so that the fully charged and unexposed region 60 follows the image in the directlon of movement of the drum. It will further be appreciated by those skilled in t'ne art that such an arrangement could, if desired, readily be adapted to a system in which the controls are so set as to permit of the making of co~ies of different lengths In our automatic development electrode bias control system, we dispose a small centrally located `~ ms/ ~
., .
electrode 62, and edge electrodes 64 and 66 of conductive material in the developer tank ~0 adjacent to the entrance thereof. We so locate the electrodes 62, 64 and 66 as to insure that the image area on -the drum passes over the electrodes as the image area moves through the developer uni-t 38. Moreover, the electrodes 62, 64 and 66 are so located that developer liquld flows between the electrodes and the drum and contacts the surfaces of both the electrodes and the drum. Our electrodes 62, 64 and 66 are completely insulated from ground or "floating" so that they are permitted to assume their own potentials. When developer is disposed between and contacting both surfaces of the electrodes and of the drum, charged toner particles are attracted to the surface of the photoconducbor resulting in charges on the electrodes 62, 64 and 66 such that ea~h electrode assumes a potential which is a measure of that of an -area on the surface of layer 16. The resistance of the toner is high but not a comPlete insulatorO In the particular orientation shown, each electrode 62, 64 and 66 will assume a potential which is a measure oE the average potential over that portion of the image area which registers with the electrode. The potential the electrode assumes is nearly independent of the elec-trode-to-photoconductor spacing owing to conductive interconnection by the toner liquid. It is also reasonably independent of the electrode capacity-to-ground and resistive capcity-to-ground, providing that the capacities are small and that the resistances are fairly high. It will thus be seen that our sensing electrodes 62, 64 and 66 operate on the principle of conduction, rather than capacitance.
In order to utilize the potentials sensed by electrodes 62, 64 and 66, we connect the electrodes to a m c~
high input imp~dancc- measurin~ circui-t 68 which selec-ts as its ou-tput the lowest potential sensed. An amPliEier 70, which recelves ; ts input from the measuring circuit 68 applies a biasing potential -to biasing electrodes 72, 7~, 76 and 78 in a manner to be described. The average voltage of each electrode 62, 64 and 66 over the image area being sensed thereby will be equal -to -the residual or background potential in clear areas with no printing and greater than the residual potential in areas with printing.
~s indicated in Figure 3, each of the development electrodes 72, 74, 76 and 78 extends across substantially the entire width W of a copy to be ~roduced. Moreover, dimensioning of the sensing electrodes 62, 64 and 66 and ~the positioning thereof across the width of the copy to be produced are so selected that the electrode 62 scans the central portion oi~ the image which normally corresponds to that part of the original, such as a typewritten page, which contains printing, while the electrodes 64 and 66 scan areas corresponding to margin or border areas of the original which normally are devoid of printing. By virtue of this arrangement of multiple electrodes, one on each edge and one in the middle of the image area, we are able to, and our circuit 78 does, select the biasing voltage from the sensing electrode having the lowest reading.
Since, as is pointed out hereinabove, mos-t originals include one or more clear border areas, our arrangement ensures that a minimum bias is provided for most copies. Our circuit 68 also permits of the insertion o E a small additional bias to the development electrode to provide an overall bias which is slightly greater than the potential value sensed in a clear area, thus ensuring that no develop-ment will take place in the background areas. In the course of our investigation, we discovered that the resistance of ,~ - 11 -ms/ r ~
the liquid developer between a scnsing electrode and the drum is of the order oE 109 ohms. Our high impedance measuring circuit 68 has an in~ut impedance of more than 1012 ohms, or at least three orders of magnitude greater than the resistance be-tween the e:lectrode and the drum surEace. In this way we are ab]e to obtain a good reading of the average potential along the region of the image area in registry with the electrodes 62.
When the fully charged and unexposed area 60 of the drum 12 arrives at the developer unit at a location in registry with the biasing electrodes, the high potential o~
this area produces a reverse bias. It will readily be appreciated that, even with the amplifier 70 putting out its deliberately limited maximum value, the potential of the development electrodes will be well below that of the unexposed area 60. Consequently, toner particles which may have been deposited on the biasing electrodes in the course of the developing o~eration, are drawn toward the surface of the drum. In the course of that operation, many of the developer particles return to suspension in the carrier liquid. It is, of course, true that the area 60 will be to some extent developed by the toner Particles. This does not present a serious problem in most commerical app]ications, however, since such units are provided with mechanical means for cleaning the surface of the photoconductor 16 in the course of each operation of the machine.
Alternatively to providing the fully charged and unexposed region for cleaning the biasing electrodes, we may provide a section of the drum with a thin plastic coating rather than a conductor, or we may switch a reverse polarity voltage onto the development electrodes during passage of non-image-areas of the drum through the ms/~
developer system.
Referriny now to FIGURE 3, we have shown one example of a high input impedance measuring circuit indicated generally by the reference character 68, including a sample-and-hold portion to be described hereinbelow and an amplifier indicated generally by the reference character 70, which w~e may employ in our automatic developer electrode bias control s~stem. In the arrange-ment shown, we provide respective shields 80, 82 and 84 for the conductors leading from the sensing electrodes 66, 62 and 64. Res~ective resistors 86, 88 and 90 connect the sensing electrodes 66, 62 and 64 to insulated gate field effect transistors 92, 9~ and 96 having a common drain line 98 and a common source line 100 connected by a resistor 102 to the terminal ln4 of a source of potential having a value of, for example.-600 volts. ~he high input impedance of the measuring circuit 68 is provided by the transistors 92, 94 and 96. These transistors, in - res~onse to the sensed voltages, serve to shunt current away from the base emitter junction of a transitor 106.
The common source line 100, which is connected to -the base of transistor 106, supplies the base current for the transistor through the resistor 102. A transistor.1~8 forms a current source for providing the emitter current for transistor 106. Owing to this arrangement, the emitter of transistor 1~6 normally is a few volts more positive ; than the input to the field effect transistors 92, 94 and 96, assuming that all of these transistors were fed from the same source. As a matter of fact, however, as is indicated in FIGURE 3, the field effect transistors 92, 94 and 96 are fed with in~ut voltages from the respective sensing electrodes 66, 62 and 64O In the arrangement shown, the circuit responds to the least negative of the m~
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sensed voltages ignoring the o-ther sensed voltages. It will readily be aPparent that -the least negative voltage is produced on the probe which is sensing the most discharged area of the photoconductor which normally would be in the margin of the original. A parallel RC circui-t, indicated generally by the reference character 109, couples the emitter of transistor 106 to the shields 80, 82 and 84, so that the capacitance between the input conductor and the shield does not load the sensing electrode.
The negative voltage source of the sensing circuit is a Zener diode 110 connected to the source of -600 volts by a resistor 112.
: .Our measuring circuit 68 includes a sample-and-hold circu1t which is respons~ve to the potential at the common terminal of diode 110 and resistor 112. This signal is applied to the base of a transistor 114 which . base is connected to the emitter by means of.a diode llÇo The collector of transistor 114 is connected to a source :: of, for example, -300 volts. The transistox 114 forms a low impedance c1ri~er which is adapted to appl~ a potential .
to a storage capacitor 124. The sample-and-hold circuit ~: includes back-to-back diodes 118 and 120, the common terminal of which is connected to ground and to one terminal of the storage capacitor 124 by a resistor 122.
A pair of microswitches 126 and 130 are adapted to be closed to control the charging of the capacitor 124. A
- resistor 128 connects one terminal of switch 126 to the common terminal of diodes 116 and 118. We connect the common terminal of the two switches 126 and 130 to the diode 120. The other terminal of switch 130 is connected to capacitor 124. From the circuit it can be seen that with switch 126 closed transistor 114 is ~ermitted to ~ - 14 -ms/ ~
~' charge the storage capacl-tor 124 very rapidly in either direction. Operation of microswi-tch 130 with switch 126 open permits the capacitor to charge only in the positive direction.
We so arrange our circuit that swi-tch 126 is closed during the first two or -three centime-ters of the copy image and switch 130 is closed for about the first twelve centimeters of the copy image. In order to achieve this result, we may, for example, mount a first cam 132 on shaft 22 for rotation therewith. A follower 134, positioned at a location around shaft 22 corresponding to that at which the latent image is entering the developer system 38, is adapted to be actuated by the cam 132 to close switch 126 and to hold the switch closed for approximately two to three centimeters of the copy.
Another cam 136 on shaft 22 is adapted to actuate a follower 138 located at a position corresponding to that o~
fo~ower 134 to close switch 130 for approximately the first twelve centimeters of the copy ~ength. Thus, during the first -two to three centimeters of the image, transistor 114 is permitted to charge capacitor 124 rapidly in either direction. During the next portion of the copy image up to approxlmately twelve centimeters, transistor 114 can charge capacitor 124 only in the positive direction and at a ` controlled charging rate which is a compromise among a number of factors.
A resistor 140 ap~lies the stored voltage to the amplifi~r 70, which is made up of a pair of transistors 142 and 144, to provide the development electrode biasing voltage on a conductor 146. We apply the voltage on line 146 to the various development electrodes 72, 74, 76 and 78 by means of a string of diodes 148, 150, 152 and a ms/~
resistor 154, all connected in series between the line 146 and ground. In the arrangement shown, the electrode 72, which is the first electrode adjacent to which the copy passes as it moves through the developer system, receives the full biasing potential. The second electrode 74 receives the potential at the common -terminal of diodes 148 and 150. Electrode 76 receives the potential at the common terminal of diodes 150 and 152, while the last development electrode 78 receives the potential at the common terminal of diode 152 and resistor 154.
It is desirable that no voltage be applied to the development electrodes during times when no development ,r"
- is to take place, in order to prevent excessive deposit of toner on the development electrodes. This result may be accomplished in any convenient manner. For ; example, as we have indlcated schematically in FIGURE 3, the power supply 156, which supplies the -600 volt potential and the -300 volt potential to various points in the circuit, may be disconnected from the sensing ci~uit by any ; 20 convenient means. By way of example, we have indicated a .
switch 158 in the output line of supply 156. A cam follower 160 is adapted to be operated to close switch 158 to apply po~er to the sensing cirucit. Follower 160 may be operated in any convenient manner. For example, we may position the follower 160 in line with followers 134 and 138 and at a position at which it is actuated by the exposure ca~ 54 which will cause switch 158 to be closed ; all during the period of time when the latent image is passing -through the developer system~ It will readily be appreciated that an~ other suitable means might be employed to control the application of power to the sensing circuit~
In operation of our automatic develop~en-k electrode bias control system, when the machine 10 is set m c: ~ rl .
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in operation, drum 12 rotates in the direction ~f -the arro~s shown in FIGURES 1 and 2. Cam ~8 actuates follower 50 to apply power from the source 28 to the corona 26 so that the surface of layer 16 receives a uniform charge over the period o~ time for which the cam ~8 actuates the follower 50.
After the drum has rotated to a point at which the leading edge of the charged area is adjacent to the optical system 32, cam 54 actuates follower 56 to close switch 36 to connect the control arrangement 34 to the optical system 32 to begin the exposure step. This exposure step lasts for the extent of cam 54 so that, as can be seen from FIGURE l, there is a fully charged but unexposed area 60 following the image area. ~s the image area enters the develo~er system 38, cam 54 closes switch 158 to apply power to the sensing circuit 68. As the image passes electrodes 62, 64 - and 66, the electrodes sense the potentials of areas of - the image covered thereby. The sensing circuit selects the least negative of the potentials which is sampled and held. The resultant signal is amplified and applied to ~o the development electrodes 72, 7g, 76 and 78. It will readily be appreciated that this potential will be equal to or somewhat greater than the actual residual potential in background areas of the image so that we ensure that no development of these background areas takes place.
It will further be appreciated, as is pointed - out hereinabove, that in the course of this development operation some toner particles will collect on the biasing electrodes. However, as the area 60 moves over the development electrodes, there is produced a reverse bias owing to the fact that the fully charged but unexposed area 60 is at a much greater potential than the maximum biasing potential provided by the circuit including amplifier 70. This reverse bias causes toner X
ms/~
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to migra~e from the development electrodes 6~ and 66 toward the surface of the drum. In the course of this operation some of the toner particles coming off the electrodes will go back into suspension in the developer carrier liquid. It is true that, in the course of this operation, the area 60 will be developed at least to some extent. As is further pointed out hereinabove, however, this presents no great problem in a commerical machine, since some means already is provided for cleaning the surface of the drum 12 on each operation of the machine.
It will be seen that we have accomplished the ob]ects of our invention. We have provided an automatic development electrode biaslng control system. Our biasing system overcomes the defects of systems of the prior art intended to inhibit background development. Our s~stem provides a variable bias which produces the effect of automatic e~posure control. The parameters of our system are not critical~ We provide our svstem with means for cleaning the biasing electrodes without the necessity of employing mechanical cleaners. Our system is appreciably less expensive than are systems of the prior art employing instruments such as electrometersO
It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations.
This is contemplated by and is within the scope o~ our claims. It is further obvious that various changes may be made in details within the scope of our claims without depar-ting from the spirit of our inventionO
It is, therefore~ to be understood that our invention is not to be limited to the specific details shown and described.
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Background o~ the Invention In the art of electrostatic copying in which the surface of a photoconductor carried by a conduc-tor su~port first is charged, then exposed to a light image and then subjected to the action of a developer, organic photoconductors have recently come into relatively wide use.
While pho~oconductors of this type have many advantages over inorganic photoconductors, they have one significant disadvantage. Upon exposure to light the charge on the photoconductor does not leak off as rapidly as is desirable.
Thus, in any co~ying apparatus whlch is to operate at a reasonable rate of speed, an organic photoconductor retains a significant charge in background or non-image areas after normal exposure to the copy to be reproduced.
This background level may be in the range of from about 100 to about 200 voltsO
~any attempts have been made in the prior art to overcome the problem of deposit of developer upon background areas owing to the residual potential -thereon.
For example, it has been suggested that the developer station be provided with a biasing electrode to which a potential is applied to counteract the effect of the residual potential in background areas. One problem in using a fixed biasing potential is that the background potential varies over a relatively wide range so that ms/~
either deve:Lopment of background areas takes place :if the biasin~ po-tential is not large enough or toner is deposited on the biasing el~ctrode if -too large a biasing potential is employed. ~-t will be apprecla-ted further that a biasing po-ten-tial should be applied to the electrode only durlng the period oE time durinq which the latent image is passing through the developer system. If the biasing potential is not switched off~ relatively great amounts of toner will be deposited on the biasing electrode when uncharged areas of the drum pass through the deve].oper stationO
Attempts have been made in the prior art to provide systems which vary the biasing potential in response to variations in the potential of bac~ground areas. For example, Coriale Patent 3,611,982 shows an arrangement in which a capacitive probe, located outside and just before t:he developer unit, is exposed by a shutter to a charged and fulIy exposed strip at the edge of the photo-conductor drum. The sensed potential is amplified and is used to control a variable power source which provides the biasing potential for the electrode located in the developer system. Another example of a bias voltage con-trol system is shown in Coriale Patent 3,788,739, in which a capacitive probe, located outside and just ahead of the developer system, senses the potential of a part of an oversize exposed area outside the image area to control the bias potential applied to an electrode in the de~elo~er unit. A further example of the use of a ms/ ~
5~
:, :
capacitance probe to regulate the bias applied by a source to a biasing electrode is shown in Smith Patent 3,782,818. The probe of Smith, like those of Coriale, is located just ahead of and outside of the developer applicator unit in which the biasing electrode is disposed.
Parmigiani Patent 3,575,505 shows an arrangement in which the developer system bias voltage is changed in response ; to the number of`copies made in an attempt to compensate ~or changes in the characteristics of the photoconductor over a period of time.
The systems of the prior art discussed herein~
above sense photoconductor voltage by the use of delicate and sensitive instruments such as elec-trometers for measuring the charge in residual areas of the photoconductor.
Such instruments are not only expenslve, but also involve critical factors such as the particular geometry of the probe and the critical distance of the probe from the surface carrying the potential to be sensed. The arrange-ments of the prior art, moreover, employ switching arrange~
: 20 ments for rendering the bias , '~}
~ ms/~
~9154 effec-tive only for the period o:E time during which the image passes through the developer system. In addi-tionl owing to the deposition of toner particles on the biasing electrode, unless some means is provided for cleaning this electrode, it will rapidly become so contaminated as to render the system inoperative.
We have invented an automatic development ele~trode . .
bias control system for inhibiting deposit of toner on back-ground areas which overcomes the defects of systems o the 1~ prior art. The parameters of our system are non-criticalO
Our assembly is relatively inexpensive to construct. Our construction is such as to insure that the bias will at all ti.mes be sufficient to prevent deposition of toner on back-ground areas. We provide our system with automatic means for removing toner deposited on the biasing electrode without the use of mechanical cleaning means.
SUMMARY OF THE INVENTION
An object of the invention is to provide an automatic development electrode bias control system.
In one particular aspect of the present invention there is provided a method of electrically biasing a developing electrode disposed closely adjacent to a photo-conductive member of an electrophotographic device after the photoconductive member has been charged and exposed to a light image. The electrophotographic aevice is of the wet-type having a developer unit utilizing a developing solution.
The method comprisiny the s-teps of a) automatically sensing through the developing solution the potential remaining on the photoconductive member by means of electrostatic induction and the electrical conductivitv of the developing solu-tion; b) computing biasing voltage in accordance with a predetermined value of the sensed potential; and c) automatically applying the biasing voltage to the developing electrode.
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g~54 In a further particulax aspect the presen-t invention provides a development apparatus for an electrostatic copier including in combination, a drum having an arcuate surface, a photoconductor comprising at least a portion of the arcuate surface of said drum, means for electrastatically charging said photoconductor, means for exposing a portion of the charged photoconductor to a pattern o~ light and shade to produce an electrostatic image, said image occupying a region of the arcuate surface of said drum of less than 360 angular extent, the arcuate surface of said drum including a non-image area of appreciable angular extent, development means for applying to said image a developer liquid containing dispersed toner particles~ means for rotating the drum to carr-y sequentially said image and said non-lmage area past the development means, the development means comprising an electrode and means for electrically bia~ing said electrode to provide adjacent said electrode a first electric field which attracts toner particles to said electrode, and means operable during passage of a non-image area past said development means for providing adjacent said electrode a second electric field which repels toner particles from said electrode.
BRIEF DES~RIPTION OF THE DRAWINGS
.~
In the accompanying drawings to which reference - is made in the accompanying specification and in which like reference characters indicate like parts in the various views:
~ igure 1 is a partially schematic end elevation of an electrostatic copying machine which may be provided with our automatic development electrode bias control system.
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...
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Figure 2 ls a perspeetive view with parts removed, with other parts broken away, and with parts shown ln ~ection, illustrating our automatic development - jl/ . -7-., P~
electrode bias control s~stem.
FIGUI~E 3 is a schematic view of one form of an electrical circuit which may.be employed in our automatic development electrode bias control s~stem.
Description of the Preferred Embodiment Referring now to FIGURES 1 and 2, a machine indicated generally by the reference character 10, with which our system ma~ be used, includes a drum indicated generally by the reference character 12 made up of a conducti1ve cylinder 14, the outer surface of whi.ch carries a layer 16 of organic photoconductive material well known to the art. Drum 12 includes respective end plates 18 and 20 carrying stub shafts 22 and 24 by means of which the drum is mounted for rotary movement in a manner known to the artu A corona discharge unit 26 is adapted to be connected to a suitable source of power 28 ~hrough a switch 30 to provide a corona discharge for applying a uniform electrostatic charge to -the photoconductor 16 as the drum 12 rotates. After having been charged, the photoconductor surEace moves past an exposure unit 32 of any type known to the art, adapted to be connected to a control unit 34 upon the closure of a switch 36.
After having been exposed to an original of the image to be copied, the photoconductive surface moves ir.to : cooperative relationship with a developer unit indicated generally by the reference character 38. Developer unit 38 may, for example, be of -the t~pe which includes an applicator tank 40 di.sposed within a return tray 42. As is known in the art, developer made up of charged toner m c. / (~
5~
particles disPosed in a carrier li~uid having a ~e]ativelY
high volume resistivity is ~ed into the tan~ 40 through a pipe 44. The tank 40 fills -to a point at which ~he liquid developer comes into contact with the surface of the drum 12 and then overflows into the tray 42, from whence it is re-turned to the supply ~not shown) through a pipe 46.
It will readily be a~preciated that any means may be employed to control the operation of the various units of the machine 10. For reasons which will be explained more fully hereinbelow, we wish to provide a region on the photoconductive surface 16 following the image area, ~hich region is fully charged but not exposed. By way of example, in order to achieve this result we may mount a cam 48 on shaft 22 for rotation therewith, so as to actuate a follower 50 to close switch 30 so that a predetermined region around the drum is fully charged. A second cam 54 ~-on shaft 22 is adapted to operate a follower 56 to close swItch 36 to place the ex~osure unit 32 into operation.
It will be seen from FIGURE 1 that the angular extent of the cam 48 is greater than that of cam 54, so that a greater region of the surface layer 16 is charged than is exposed. Moreover, -the arrangement is such that exposure starts at the beginning of the charged region, so that the fully charged and unexposed region 60 follows the image in the directlon of movement of the drum. It will further be appreciated by those skilled in t'ne art that such an arrangement could, if desired, readily be adapted to a system in which the controls are so set as to permit of the making of co~ies of different lengths In our automatic development electrode bias control system, we dispose a small centrally located `~ ms/ ~
., .
electrode 62, and edge electrodes 64 and 66 of conductive material in the developer tank ~0 adjacent to the entrance thereof. We so locate the electrodes 62, 64 and 66 as to insure that the image area on -the drum passes over the electrodes as the image area moves through the developer uni-t 38. Moreover, the electrodes 62, 64 and 66 are so located that developer liquld flows between the electrodes and the drum and contacts the surfaces of both the electrodes and the drum. Our electrodes 62, 64 and 66 are completely insulated from ground or "floating" so that they are permitted to assume their own potentials. When developer is disposed between and contacting both surfaces of the electrodes and of the drum, charged toner particles are attracted to the surface of the photoconducbor resulting in charges on the electrodes 62, 64 and 66 such that ea~h electrode assumes a potential which is a measure of that of an -area on the surface of layer 16. The resistance of the toner is high but not a comPlete insulatorO In the particular orientation shown, each electrode 62, 64 and 66 will assume a potential which is a measure oE the average potential over that portion of the image area which registers with the electrode. The potential the electrode assumes is nearly independent of the elec-trode-to-photoconductor spacing owing to conductive interconnection by the toner liquid. It is also reasonably independent of the electrode capacity-to-ground and resistive capcity-to-ground, providing that the capacities are small and that the resistances are fairly high. It will thus be seen that our sensing electrodes 62, 64 and 66 operate on the principle of conduction, rather than capacitance.
In order to utilize the potentials sensed by electrodes 62, 64 and 66, we connect the electrodes to a m c~
high input imp~dancc- measurin~ circui-t 68 which selec-ts as its ou-tput the lowest potential sensed. An amPliEier 70, which recelves ; ts input from the measuring circuit 68 applies a biasing potential -to biasing electrodes 72, 7~, 76 and 78 in a manner to be described. The average voltage of each electrode 62, 64 and 66 over the image area being sensed thereby will be equal -to -the residual or background potential in clear areas with no printing and greater than the residual potential in areas with printing.
~s indicated in Figure 3, each of the development electrodes 72, 74, 76 and 78 extends across substantially the entire width W of a copy to be ~roduced. Moreover, dimensioning of the sensing electrodes 62, 64 and 66 and ~the positioning thereof across the width of the copy to be produced are so selected that the electrode 62 scans the central portion oi~ the image which normally corresponds to that part of the original, such as a typewritten page, which contains printing, while the electrodes 64 and 66 scan areas corresponding to margin or border areas of the original which normally are devoid of printing. By virtue of this arrangement of multiple electrodes, one on each edge and one in the middle of the image area, we are able to, and our circuit 78 does, select the biasing voltage from the sensing electrode having the lowest reading.
Since, as is pointed out hereinabove, mos-t originals include one or more clear border areas, our arrangement ensures that a minimum bias is provided for most copies. Our circuit 68 also permits of the insertion o E a small additional bias to the development electrode to provide an overall bias which is slightly greater than the potential value sensed in a clear area, thus ensuring that no develop-ment will take place in the background areas. In the course of our investigation, we discovered that the resistance of ,~ - 11 -ms/ r ~
the liquid developer between a scnsing electrode and the drum is of the order oE 109 ohms. Our high impedance measuring circuit 68 has an in~ut impedance of more than 1012 ohms, or at least three orders of magnitude greater than the resistance be-tween the e:lectrode and the drum surEace. In this way we are ab]e to obtain a good reading of the average potential along the region of the image area in registry with the electrodes 62.
When the fully charged and unexposed area 60 of the drum 12 arrives at the developer unit at a location in registry with the biasing electrodes, the high potential o~
this area produces a reverse bias. It will readily be appreciated that, even with the amplifier 70 putting out its deliberately limited maximum value, the potential of the development electrodes will be well below that of the unexposed area 60. Consequently, toner particles which may have been deposited on the biasing electrodes in the course of the developing o~eration, are drawn toward the surface of the drum. In the course of that operation, many of the developer particles return to suspension in the carrier liquid. It is, of course, true that the area 60 will be to some extent developed by the toner Particles. This does not present a serious problem in most commerical app]ications, however, since such units are provided with mechanical means for cleaning the surface of the photoconductor 16 in the course of each operation of the machine.
Alternatively to providing the fully charged and unexposed region for cleaning the biasing electrodes, we may provide a section of the drum with a thin plastic coating rather than a conductor, or we may switch a reverse polarity voltage onto the development electrodes during passage of non-image-areas of the drum through the ms/~
developer system.
Referriny now to FIGURE 3, we have shown one example of a high input impedance measuring circuit indicated generally by the reference character 68, including a sample-and-hold portion to be described hereinbelow and an amplifier indicated generally by the reference character 70, which w~e may employ in our automatic developer electrode bias control s~stem. In the arrange-ment shown, we provide respective shields 80, 82 and 84 for the conductors leading from the sensing electrodes 66, 62 and 64. Res~ective resistors 86, 88 and 90 connect the sensing electrodes 66, 62 and 64 to insulated gate field effect transistors 92, 9~ and 96 having a common drain line 98 and a common source line 100 connected by a resistor 102 to the terminal ln4 of a source of potential having a value of, for example.-600 volts. ~he high input impedance of the measuring circuit 68 is provided by the transistors 92, 94 and 96. These transistors, in - res~onse to the sensed voltages, serve to shunt current away from the base emitter junction of a transitor 106.
The common source line 100, which is connected to -the base of transistor 106, supplies the base current for the transistor through the resistor 102. A transistor.1~8 forms a current source for providing the emitter current for transistor 106. Owing to this arrangement, the emitter of transistor 1~6 normally is a few volts more positive ; than the input to the field effect transistors 92, 94 and 96, assuming that all of these transistors were fed from the same source. As a matter of fact, however, as is indicated in FIGURE 3, the field effect transistors 92, 94 and 96 are fed with in~ut voltages from the respective sensing electrodes 66, 62 and 64O In the arrangement shown, the circuit responds to the least negative of the m~
5~
sensed voltages ignoring the o-ther sensed voltages. It will readily be aPparent that -the least negative voltage is produced on the probe which is sensing the most discharged area of the photoconductor which normally would be in the margin of the original. A parallel RC circui-t, indicated generally by the reference character 109, couples the emitter of transistor 106 to the shields 80, 82 and 84, so that the capacitance between the input conductor and the shield does not load the sensing electrode.
The negative voltage source of the sensing circuit is a Zener diode 110 connected to the source of -600 volts by a resistor 112.
: .Our measuring circuit 68 includes a sample-and-hold circu1t which is respons~ve to the potential at the common terminal of diode 110 and resistor 112. This signal is applied to the base of a transistor 114 which . base is connected to the emitter by means of.a diode llÇo The collector of transistor 114 is connected to a source :: of, for example, -300 volts. The transistox 114 forms a low impedance c1ri~er which is adapted to appl~ a potential .
to a storage capacitor 124. The sample-and-hold circuit ~: includes back-to-back diodes 118 and 120, the common terminal of which is connected to ground and to one terminal of the storage capacitor 124 by a resistor 122.
A pair of microswitches 126 and 130 are adapted to be closed to control the charging of the capacitor 124. A
- resistor 128 connects one terminal of switch 126 to the common terminal of diodes 116 and 118. We connect the common terminal of the two switches 126 and 130 to the diode 120. The other terminal of switch 130 is connected to capacitor 124. From the circuit it can be seen that with switch 126 closed transistor 114 is ~ermitted to ~ - 14 -ms/ ~
~' charge the storage capacl-tor 124 very rapidly in either direction. Operation of microswi-tch 130 with switch 126 open permits the capacitor to charge only in the positive direction.
We so arrange our circuit that swi-tch 126 is closed during the first two or -three centime-ters of the copy image and switch 130 is closed for about the first twelve centimeters of the copy image. In order to achieve this result, we may, for example, mount a first cam 132 on shaft 22 for rotation therewith. A follower 134, positioned at a location around shaft 22 corresponding to that at which the latent image is entering the developer system 38, is adapted to be actuated by the cam 132 to close switch 126 and to hold the switch closed for approximately two to three centimeters of the copy.
Another cam 136 on shaft 22 is adapted to actuate a follower 138 located at a position corresponding to that o~
fo~ower 134 to close switch 130 for approximately the first twelve centimeters of the copy ~ength. Thus, during the first -two to three centimeters of the image, transistor 114 is permitted to charge capacitor 124 rapidly in either direction. During the next portion of the copy image up to approxlmately twelve centimeters, transistor 114 can charge capacitor 124 only in the positive direction and at a ` controlled charging rate which is a compromise among a number of factors.
A resistor 140 ap~lies the stored voltage to the amplifi~r 70, which is made up of a pair of transistors 142 and 144, to provide the development electrode biasing voltage on a conductor 146. We apply the voltage on line 146 to the various development electrodes 72, 74, 76 and 78 by means of a string of diodes 148, 150, 152 and a ms/~
resistor 154, all connected in series between the line 146 and ground. In the arrangement shown, the electrode 72, which is the first electrode adjacent to which the copy passes as it moves through the developer system, receives the full biasing potential. The second electrode 74 receives the potential at the common -terminal of diodes 148 and 150. Electrode 76 receives the potential at the common terminal of diodes 150 and 152, while the last development electrode 78 receives the potential at the common terminal of diode 152 and resistor 154.
It is desirable that no voltage be applied to the development electrodes during times when no development ,r"
- is to take place, in order to prevent excessive deposit of toner on the development electrodes. This result may be accomplished in any convenient manner. For ; example, as we have indlcated schematically in FIGURE 3, the power supply 156, which supplies the -600 volt potential and the -300 volt potential to various points in the circuit, may be disconnected from the sensing ci~uit by any ; 20 convenient means. By way of example, we have indicated a .
switch 158 in the output line of supply 156. A cam follower 160 is adapted to be operated to close switch 158 to apply po~er to the sensing cirucit. Follower 160 may be operated in any convenient manner. For example, we may position the follower 160 in line with followers 134 and 138 and at a position at which it is actuated by the exposure ca~ 54 which will cause switch 158 to be closed ; all during the period of time when the latent image is passing -through the developer system~ It will readily be appreciated that an~ other suitable means might be employed to control the application of power to the sensing circuit~
In operation of our automatic develop~en-k electrode bias control system, when the machine 10 is set m c: ~ rl .
~9:~5~
in operation, drum 12 rotates in the direction ~f -the arro~s shown in FIGURES 1 and 2. Cam ~8 actuates follower 50 to apply power from the source 28 to the corona 26 so that the surface of layer 16 receives a uniform charge over the period o~ time for which the cam ~8 actuates the follower 50.
After the drum has rotated to a point at which the leading edge of the charged area is adjacent to the optical system 32, cam 54 actuates follower 56 to close switch 36 to connect the control arrangement 34 to the optical system 32 to begin the exposure step. This exposure step lasts for the extent of cam 54 so that, as can be seen from FIGURE l, there is a fully charged but unexposed area 60 following the image area. ~s the image area enters the develo~er system 38, cam 54 closes switch 158 to apply power to the sensing circuit 68. As the image passes electrodes 62, 64 - and 66, the electrodes sense the potentials of areas of - the image covered thereby. The sensing circuit selects the least negative of the potentials which is sampled and held. The resultant signal is amplified and applied to ~o the development electrodes 72, 7g, 76 and 78. It will readily be appreciated that this potential will be equal to or somewhat greater than the actual residual potential in background areas of the image so that we ensure that no development of these background areas takes place.
It will further be appreciated, as is pointed - out hereinabove, that in the course of this development operation some toner particles will collect on the biasing electrodes. However, as the area 60 moves over the development electrodes, there is produced a reverse bias owing to the fact that the fully charged but unexposed area 60 is at a much greater potential than the maximum biasing potential provided by the circuit including amplifier 70. This reverse bias causes toner X
ms/~
9~
to migra~e from the development electrodes 6~ and 66 toward the surface of the drum. In the course of this operation some of the toner particles coming off the electrodes will go back into suspension in the developer carrier liquid. It is true that, in the course of this operation, the area 60 will be developed at least to some extent. As is further pointed out hereinabove, however, this presents no great problem in a commerical machine, since some means already is provided for cleaning the surface of the drum 12 on each operation of the machine.
It will be seen that we have accomplished the ob]ects of our invention. We have provided an automatic development electrode biaslng control system. Our biasing system overcomes the defects of systems of the prior art intended to inhibit background development. Our s~stem provides a variable bias which produces the effect of automatic e~posure control. The parameters of our system are not critical~ We provide our svstem with means for cleaning the biasing electrodes without the necessity of employing mechanical cleaners. Our system is appreciably less expensive than are systems of the prior art employing instruments such as electrometersO
It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations.
This is contemplated by and is within the scope o~ our claims. It is further obvious that various changes may be made in details within the scope of our claims without depar-ting from the spirit of our inventionO
It is, therefore~ to be understood that our invention is not to be limited to the specific details shown and described.
ms/~
Claims (9)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Development apparatus for an electrostatic copier including in combination a drum having an arcuate surface, a photoconductor comprising at least a portion of the arcuate surface of said drum, means for electrostatically charging said photoconductor, means for exposing a portion of the charged photoconductor to a pattern of light and shade to produce an electrostatic image, said image occupying a region of the arcuate surface of said drum of less than 360° angular extent, the arcuate surface of said drum including a non-image area of appreciable angular extent, development means for applying to said image a developer liquid containing dispersed toner particles, means for rotating the drum to carry sequentially said image and said non-image area past the development means, the development means comprising an electrode and means for electrically biasing said electrode to provide adjacent said electrode a first electric field which attracts toner particles to said electrode, and means operable during passage of a non-image area past said development means for providing adjacent said electrode a second electric field which repels toner particles from said electrode.
2. Apparatus as in claim 1 wherein said second electric field means includes a charged but unexposed portion of said photoconductor.
3. Apparatus as in claim 1 wherein said second electric field means includes means for varying the bias on said electrode.
4. A method of electrically biasing a developing electrode disposed closely adjacent to a photoconductive member of an electrophotographic device after the photo-conductive member has been charged and exposed to a light image, said electrophotographic device being of the wet-type having a developer unit utilizing a developing solution, comprising the steps of:
(a) automatically sensing through the developing solution the potential remaining on the photoconductive member by means of electrostatic induction and the electrical conductivity of the developing solution;
(b) computing biasing voltage in accordance with a predetermined value of the sensed potential; and (c) automatically applying the biasing voltage to the developing electrode.
(a) automatically sensing through the developing solution the potential remaining on the photoconductive member by means of electrostatic induction and the electrical conductivity of the developing solution;
(b) computing biasing voltage in accordance with a predetermined value of the sensed potential; and (c) automatically applying the biasing voltage to the developing electrode.
5. The method of Claim 4, in which step (a) is characterized by sensing through the developing solution the potential remaining on image areas of the photoconductive member.
6. The method of claim 5, in which step (a) is characterized by serially sensing through the develop-ing solution with a single sensor the potentials remaining at a plurality of respective portions of the image area of the photocondutive member and step (b) is characterized by automatically selecting the lowest value of the sensed potentials.
7. In an electrophotographic device having a photoconductive member, charging means for charging the photoconductive member, imaging means for radiating a light image of an original document onto a photoconductive member, a developing electrode disposed adjacent to the photoconductive member after the photoconductive member has been charged by the charging means and radiated with the light image by the imaging means, and developing means utilizing a developing solution for developing the electrostatic image, the apparatus comprising:
sensing means disposed at least partially in said developing solution for automatically sensing through the developing solution the potential remaining on the photo-conductive member by means of electrostatic induction and the electrical conductivity of the developing solution;
computing means for automatically computing the biasing voltage to be applied to the developing electrode in accordance with the value of the sensed potential; and biasing means for applying said biasing voltage to the developing electrode.
sensing means disposed at least partially in said developing solution for automatically sensing through the developing solution the potential remaining on the photo-conductive member by means of electrostatic induction and the electrical conductivity of the developing solution;
computing means for automatically computing the biasing voltage to be applied to the developing electrode in accordance with the value of the sensed potential; and biasing means for applying said biasing voltage to the developing electrode.
8. The apparatus of claim 7, in which the sensing means is arranged at a position corresponding to image areas of the photoconductive member.
9. The apparatus of claim 7, in which the photoconductive member is movable relative to the developing electrode and the developing electrode is formed in sections disposed in the developing solution along the path of movement of the photoconductive member, the biasing means being operative to apply biasing voltages tote sections of the developing electrode which are respectively predetermined in accordance with both the lowest value of the sensed potential and the positions of the sections along the path of the photoconductive member.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000412994A CA1154950A (en) | 1974-06-17 | 1982-10-06 | Automatic development electrode bias control system |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US479,659 | 1974-06-17 | ||
| US479659A US3892481A (en) | 1974-06-17 | 1974-06-17 | Automatic development electrode bias control system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1149154A true CA1149154A (en) | 1983-07-05 |
Family
ID=23904891
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000222749A Expired CA1149154A (en) | 1974-06-17 | 1975-03-21 | Automatic development electrode bias control system |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US3892481A (en) |
| JP (1) | JPS6158829B2 (en) |
| CA (1) | CA1149154A (en) |
| DE (1) | DE2516012A1 (en) |
| FR (1) | FR2280117A1 (en) |
| GB (1) | GB1483400A (en) |
| IT (1) | IT1034714B (en) |
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| US3835380A (en) * | 1973-08-14 | 1974-09-10 | Xerox Corp | Electrometer system |
-
1974
- 1974-06-17 US US479659A patent/US3892481A/en not_active Expired - Lifetime
-
1975
- 1975-03-21 CA CA000222749A patent/CA1149154A/en not_active Expired
- 1975-03-28 IT IT21838/75A patent/IT1034714B/en active
- 1975-04-01 GB GB13269/75A patent/GB1483400A/en not_active Expired
- 1975-04-04 FR FR7510654A patent/FR2280117A1/en active Granted
- 1975-04-12 DE DE19752516012 patent/DE2516012A1/en active Granted
- 1975-04-15 JP JP50044879A patent/JPS6158829B2/ja not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPS511144A (en) | 1976-01-07 |
| FR2280117A1 (en) | 1976-02-20 |
| DE2516012A1 (en) | 1976-01-02 |
| GB1483400A (en) | 1977-08-17 |
| US3892481A (en) | 1975-07-01 |
| IT1034714B (en) | 1979-10-10 |
| JPS6158829B2 (en) | 1986-12-13 |
| DE2516012C2 (en) | 1987-08-13 |
| FR2280117B1 (en) | 1977-04-15 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |