CA1036654A - Image density control apparatus - Google Patents
Image density control apparatusInfo
- Publication number
- CA1036654A CA1036654A CA193,290A CA193290A CA1036654A CA 1036654 A CA1036654 A CA 1036654A CA 193290 A CA193290 A CA 193290A CA 1036654 A CA1036654 A CA 1036654A
- Authority
- CA
- Canada
- Prior art keywords
- sample
- latent image
- electrostatic latent
- potential
- neutral density
- 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
Links
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
- G03G15/01—Apparatus for electrographic processes using a charge pattern for producing multicoloured copies
- G03G15/0105—Details of unit
- G03G15/0121—Details of unit for developing
-
- 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
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Color Electrophotography (AREA)
- Control Or Security For Electrophotography (AREA)
- Magnetic Brush Developing In Electrophotography (AREA)
- Developing For Electrophotography (AREA)
- Dry Development In Electrophotography (AREA)
Abstract
IMAGE DENSITY CONTROL APPARATUS
ABSTRACT OF THE DISCLOSURE
An apparatus in which the potential of a sample electrostatic latent image recorded on a photoconductive surface is detected for controlling the density of toner particles deposited on a single color electrostatic latent image recorded thereon.
The foregoing abstract is neither intended to define the invention disclosed in the specification, nor is it intended to be limiting as to the scope of the invention in any way.
ABSTRACT OF THE DISCLOSURE
An apparatus in which the potential of a sample electrostatic latent image recorded on a photoconductive surface is detected for controlling the density of toner particles deposited on a single color electrostatic latent image recorded thereon.
The foregoing abstract is neither intended to define the invention disclosed in the specification, nor is it intended to be limiting as to the scope of the invention in any way.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to a multi-color electrophotographic printing machine, and more particularly concerns an apparatus for controlling the density of toner particles deposited on a single color electrostatic latent image recorded on a charged photoconductive surface.
In the process of electrophotographic printing, a photoconductive surface is uniformly charged and exposed to a light image of an original document. Exposure of the photoconductive surface records thereon an electrostatic latent image corresponding to the original document. The electrostatic latent image is then rendered visible by depositing thereon toner particles which adhere electro-statically, in image configuration, thereto. Thereafter, the toner powder image may be transferred to a sheet of support material. The toner powder image is, then, permanently affixed to the support material to provide a copy of the original document. The foregoing process was originally disclosed in U. S. Patent No. 2,297,691 issued to Carlson in 1942.
Multi-color electrophotographic printing is slmilar to the heretofore discussed process with the following exceptions. Rather than forming a total light image of the original document, the light image is filtered producing a single color light image which is a partial light image of the original. The foregoing single color light image exposes the charged photoconductive surface to record thereon a single color electrostatic latent image. This single color electrostatic latent image is developed with toner particles of a color complementary to the single color light image.
This invention relates generally to a multi-color electrophotographic printing machine, and more particularly concerns an apparatus for controlling the density of toner particles deposited on a single color electrostatic latent image recorded on a charged photoconductive surface.
In the process of electrophotographic printing, a photoconductive surface is uniformly charged and exposed to a light image of an original document. Exposure of the photoconductive surface records thereon an electrostatic latent image corresponding to the original document. The electrostatic latent image is then rendered visible by depositing thereon toner particles which adhere electro-statically, in image configuration, thereto. Thereafter, the toner powder image may be transferred to a sheet of support material. The toner powder image is, then, permanently affixed to the support material to provide a copy of the original document. The foregoing process was originally disclosed in U. S. Patent No. 2,297,691 issued to Carlson in 1942.
Multi-color electrophotographic printing is slmilar to the heretofore discussed process with the following exceptions. Rather than forming a total light image of the original document, the light image is filtered producing a single color light image which is a partial light image of the original. The foregoing single color light image exposes the charged photoconductive surface to record thereon a single color electrostatic latent image. This single color electrostatic latent image is developed with toner particles of a color complementary to the single color light image.
- 2 -.. . . .
~ . . . .
Subsequently, the single color toner powder image is transferred to the sheet of support material. The foregoing process is repeated a plurality of cycles with differently colored light images and the respective complementary colored toner particles. Each single color toner powder image is transferred ~ the support material superimposed in registration with the prior toner powder image to form a composite multi-layer powder image thereon.
This multi-layered toner powder image is coalesced and permanently affixed to the support material forming a composite image corresponding in color to the original document.
It is apparent that in multi-color electro-photographic printing machines, the characteristics of the photoconductive surface are critical. Preferably, the electrical characteristics of the photoconductive surface should remain substantially constant. However, it has been found that the electrical characteristics of the photoconductive surfaces will vary with temperature changes or with continuous usage thereof. Hence, it is extremely difficult to maintain substantially the same potential on the photoconductive surface for light images projected thereon having substantially identical intensities.
Moreover, electrophotographic printing machines frequently utilize magnetic brushes to produce viewable toner powder images on the electrostatic latent image recorded on the photoconductive surface. Toner particles are attracted from the magnetic brush to the charged photoconductive surface.
In multi-color electrophotographic printing, the ~(~36ti5~
imaged areas are developed with the toner particles whereas -~
the non-image areas remain substantially devoid of toner particles. However, it is evident that some toner particles -will be attracted to the non-image areas inasmuch as a residual charge remains thereon. Hence, it is desirable to electrically ~ ~ :
bias the magnetic brush to a potential intermediate that of the non-image areas respective single color electrostatic latent image.
Accordingly, it is an object of an aspect of the present invention to improve the development system utilized in a multi-color electrophotographic printing maching by sensing changes in the electrical characteristics of the photocon-ductive surface and varying the potential of the development system in response thereto.
SUMMARY OF THE INVENTION
Briefly stated, and in accordance with one aspect of the present invention, there i5 provided an apparatus for -controlling the density of toner particles deposited on a single color electrostatic latent image recorded on a charged photoconductive surface.
In an embodiment, the apparatus includes at least one neutral density sample, illuminating means, toner particle depositing means, and sensing and electrical biasing means.
Preferably, the neutral density sample has a pre-selected density corresponding to substantially about a predetermined cut-off density for the single color electrostatic la~ent image recorded on the photoconductive surface. The illuminating means irradiates the neutral density sample and projects the light image formed thereof onto the charged photoconductive surface. In this way, a sample electrostatic latent image is recorded on the photoconductive surface. The sample electro-static latent image has a potential intermediate that of the ~ -, . .
- . . : - . . . :. -1~3665~
single color electrostatic latent image and the non-image regions of the charged photoconductive surface. The potential of the sample electrostatic latent image recorded on the charged photoconductive surface is detected by the sensing and electrical biasing means. Pursuant to an aspect of the present invention, the sensing and electrical biasing means electrically bias the toner particle depositing means to a potential corres-ponding to that of the sample electrostatic latent image recorded on the charged photoconductive surface. Hence, toner particles are deposited on regions of the photoconductive surface having a potential greater than the potential of the sample electrostatic latent image.
In accordance with another aspect of this invention there is provided an apparatus for controlling the cut-off density of toner particles deposited on a single color electro-static latent image recorded on a charged photoconductive surface, including: at least one neutral density sample having a pre-selected density corresponding to substantially about the predetermined cut-off density of the single color electrostatic latent image; means for illuminating said neutral density sample and projecting the light image formed thereof onto the charged photoconductive surface to record thereon a sample electrostatic latent image having a potential intermediate the single color electrostatic latent image and the non-image regions of the charged photoconductive surface; means for depositing toner particles, complementary in color to the single color electrostatic latent image, on the charged photo-conductive surface; and means for sensing the potential of the sample electrostatic latent image recorded on the charged photoconductive surface and electrically biasing said toner particle depositinq means to a potential correspondinq to the sample electrostatic latent image potential so that toner particles are deposited on regions of the photoconductive surface Q ~ - 5 ~
1~36tj`54 having a potential substantially greater than the potential , -of the sample electrostatic latent image.
In accordance with another aspect of this invention there is provided an electrophotographic printing machine of the type having a photoconductive surface, including: means for charging the photoconductive surface to a substantially uniform potential; at least one neutral density sample having ~' a pre-selected density corresponding to substantially about ~:
the predetermined cut-off density of the single color electro- '~
static,latent image; means for,exposing the charged photo-conductive surface to a single color light image of an original ' document to record thereon a single color electrostatic latent ' image, said exposing means being arranged to illuminate said neutral density sample and project a light image thereof onto . ::
the charged photoconductive surface to record thereon a sample eleetrostatic latent image having a potential intermediate the single color electrostatic latent image and the non- ~., image regions of the charged photoconduetive surface; means ' for depositing toner particles, complementary in color to the ~ :
20 'single color electrostatic latent image, on the charged ~' photoconductive surface; and means for sensing the potential ..
of the sample eleetrostatic latent image recorded on the charged photoconduetive surfaee and eleetrieally biasing said toner particle depositing means to a potential corresponding to the sample electrostatie latent image potential so that toner particles are deposited on regions of the photoconductive surface having a potential substantially greater than the potential of the sample electrostatic latent image.
In accordance with another aspect of this invention there is provided apparatus for controlling the cut-off density of toner particles deposited by a developer means on a single color latent electrostatic image recorded on a charged photo-~ - 5a -- ,.
~ .
1~3665~
conductive surface, said developer means including potential means for biasing the toner particles, the bias on said devel-oper means being controlled in response to variations in the electrical characteristics of the photoconductive surfaces which the single color electrostatic latent image is formed, at least one neutral density sample having a pre-selected density corresponding substantially to the predetermined cut-off density of the single color electrostatic latent image, means to illuminate the sample and pro]ect the light image.
thereof onto a charged photoconductive surface, a sensor located in proximity of the charged photoconductive surface for detecting the potential level of the sample image on the charged photoconductive surface prior to the deposition of toner particles on the surface, the sensor coupled to said developer potential means to bias the toner particles to a potential corresponding to the potential of the sample image.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and advantages of the present inven-tion will become apparent upon reading the following detailed description and upon reference to the drawings, in which Figure 1 is a schematic perspective view of a multi-color electrophotographic printing machine having the present invention incorporated therein;
Figure 2 is a schematic illustration of the light source and disc of neutral density samples utilized in the Figure 1 printing machine.
Figure 3 is a partial elevational view of the development system and the probe utiliæed therein to sense `.
the potential of the sample electrostatic latent :.:
.,: ,~, ... '.,:
- ~ -, .
~6)36654 image recorded on the photoconductive surface; and eeO~ s~e~ F~;~e~
Figure 4nis a schematic circuit diagram for periodically sampling the sensed sample electrostatic latent image potential.
While the present invention will be described in connection with a preferred embodiment, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
With continued reference to the drawings, Figure 1 schematically illustrates a multi-color electro-photographic printing machine employing the present invention. In the drawings, like reference numerals have been used throughout to designate like elements.
The multi-color electrophotographic printing machine shown schematically in Figure 1, illustrates the various components used to produce multi-color copies from a colored original. Although the apparatus of the present invention is particularly well adapted for use in an electrophotographic printing machine, it will become evident from the following description that it is equally well suited for use in a wide variety of electrophoto-graphic printing machines, and is not necessarily limited to the particular embodiment shown therein.
As shown in Figure 1, the printing machine employs a drum 10 having a photoconductive surface 12 secured thereto and entrained about the exterior circum-- . . ~ . :
. - - . - : . . :
~()366S4 ferential surface thereof. Drum 10 is mounted rotatably ' within the machine frame (not shown). A series of processing stations are positioned such that as drum 10 rotates in the direction of arrow 14, photoconductive surface 12 passes sequentially therethrough. Drum 10 is driven at a predetermined speed relative to the other machine operating mechanisms by a common drive motor (not shown). One type of suitable photoconductive material is disclosed in U. S. Patent No. 3,655,377, issued to Sechak in 1972. A timing wheel is mounted in the region of one end of drum 10 and adapted to trigger the logic circuitry of the printing machine.
This coordinates the various machine operations with one another to produce the proper sequence of the events at the appropriate processing stations.
Initially, drum 10 moves photoconductive surface 12 through charging station A. Charging station A has positioned thereat a corona generating device, indicated generally at 16. Corona generating device 16 extends in a generally longitudinal direction transversely across photoconductive surface 12. This readily enables corona generating device 16 to charge photoconductive surface 12 to a relatively high substantially uniform potential.
Preferably, corona generating device 16 is of the type described in U. S. Patent No. 2,778,946 issued to Mayo in 1957.
Drum 10, thereafter, is rotated to exposure station B. Exposure station B includes thereat a moving lens system, generally designated by the reference number 18, and a color filter mechanism shown generally at 20.
~S~3f~4 :~
A suitable moving lens system is disclosed in U.5. Patent No. 3,062,108 issued to Mayo in 1962, and a suitable color filter mechanism is described in Canadian patent ~15,490 issued November 28, 1972. Disc 22 has a plurality of neutral density samples (in this case 3) disposed thereon. Disc 22 is mounted rotatably in the printing machine and is disposed beneath transparent platen 24 within the half angle of the optical system. Before the light source lamps indicated generally by the reference numeral 26, begin to scan, they will be actuated to illuminate one of the neutral density samples. In this way, a sample electrostatic latent image is recorded, on photoconductive surface 12 as drum 10 rotates.
Lamps 26 are stationary and the appropriate filter is posi-tioned in filter 20 forming a sample electrostatic latent image on photoconductive surface 12 which is a strip dis-charged to the desired potential. The potential of the sam-ple electrostatic latent image recorded on photoconductive surface 12 is detected by probe 28, i.e. a suitable elec-trometer disposed adjacent to photoconductive surface 12 intermediate exposure station B and development station C.
The electrical output signal from probe 28 is processed by circuit elements 30 which regulate voltage source or power supply 84 adjusting the bias voltage of the respective developer unit having toner particles complementary in color ~-to the filter of filter mechanism 20. Preferably, disc 22 includes three equally spaced neutral density samples located about the periphery thereof. Sample 32 is a neutral density sample for green separation, sample 34 is a neutral density sample for red separation and -: : . .
.
1(~36654 sample 36 is a neutral density sample for blue separation.
Preferably the green separation sample has a density of 0.32, the blue separation sample a density of 0.35, and the red separation sample a density of 0.15. The appro-priate neutral density sample is illuminated by light source 26 to produce a sample electrostatic image corresponding to a predetermined development density for the filter being used, i.e. a green filter will have neutral density sample 32 illuminated forming a sample electrostatic latent image corresponding to the predeter-mined development density for the green separation.
In multi-color electrophotographic printing, a single color light image exposes the charged photoconductive surface. The potential on the charged photoconductive surface in the area irradiated by the single color light image is reduced. The potential of the charged photo-conductive surface in the non-irradiated areas remain substantially unchanged. During development, toner particles, complementary in color to the single color light image, are deposited on the photoconductive surface.
The irradiated areas remain substantially devoid of toner particles. The development system is biased such that the potential thereof is intermediate the irradiated and non-irradiated areas. In this way, toner particles are attracted to the non-irradiated areas from the development system since the potential of the non-irradiated areas is greater than the potential of the development system, whereas toner particles are not attracted to the irradiated areas inasmuch as the charge thereof if less thin than that of the development system. Each of the neutral density g samples form a sample electrostatic latent image. The charge of the sample electrostatic latent image is greater than that of the irradiated areas and less than that of the non-irradiated areas. The developer unit is adjusted to the potential of the sample electrostatic latent image.
Thus, toner particles are attracted to all regions of the charged photoconductive surface having a potential greater than that of the sample electrostatic latent image. The potential of the sample electrostatic latent image corre-sponds to the washout density of the single color toner powder image, i.e. the potential beneath which development of the single color electrostatic latent image does not occur. However, if the potential of the single color electrostatic latent image is greater than that of the sample electrostatic latent image development will occur.
With continued reference to the Figure 1, after the sample electrostatic latent image is formed on the charged photoconductive surface, an original document 25, such as a book, sheet of paper, or the like, disposed upon transparent viewing platen 24 is scanned. Lamps 26 and lens 18 move in a timed relation with drum 10 to scan successive incremental areas of original document 25 disposed upon platen 24. This creates a flowing light image of original document 25 which is projected onto charged photoconductive surface 12. Filter mechanism 20 is adapted to interpose selected color filters into the optical light path. The appropriate color filter operates on the light rays passing through lens 18 to record an electrostatic latent image on photoconductive surface 12 corresponding to a pre-selected spectral region of the ~ - , 1~)36654 electromagnetic wave spectrum, heretofore referred to as a single color electrostatic latent image.
After exposure, drum 10 rotates the sing~e color electrostatic latent image recorded on photoconductive surface 12 to development station C. Development station C includes thereat three individual developer units, generally indicated by the reference numerals 38, 40, and 42. A suitable develop-ment system employing a plurality of developer units is dis-closed in Canadian patent 982,886 issued February 3, 1976.
Preferably, the developer units are all of a type generally referred to as magnetic brush developer units. A typical magnetic brush developer unit utilizes a magnetizable developer mix having carrier granules and toner particles. The developer ;
mix is continually brought through a directional flux field to form a brush thereof. Each developer unit includes a develop-er roll ~6, 88 and 90 (Figure 3) electrically biased to the appropriate potential such that toner particles are attracted to the image areas (non-irradiated areas) rather than the non-image areas (irradiated areas) of the photoconductive surface 12. The potential applied to the developer roll is substan-tially equal to that of the sample electrostatic latent image recorded on photoconductive surface 12 and detected by probe 28. The single color electrostatic latent image recorded on photoconductive surface 12 is developed by bringing the brush of developer mix into contact therewith. Each of the respec-tive developer units contain discretely colored toner particles corresponding to the complement of the spectral region of the wavelength of light transmitted through filter 21, e.g. a green filtered -1~- . ~
electrostatic latent image is rendered visible by depositing green absorbing magenta toner particles therein, blue and red latent images are developed with yellow and cyan toner particles, respectively.
Drum 10 is, next, rotated to transfer station D
where the toner powder image adhering electrostatically to photoconductive surface 12 is transferred to a sheet of final support material 44. Support material 44 may be plain paper, or a sheet of transparent, thermoplastic material. A
transfer roll, shown generally at 46, rotates support material 44 in the direction of arrow 48. Transfer roll 46 is electrically biased to a potential of sufficient magnitude and polarity to electrostatically attract toner particles from photoconductive surface 12 to support material 44. U. S. Patent No. 3,612,677, issued to Langdon et al. in 1972, discloses a suitable electrically biased transfer roll. Transfer roll 46 is arranged to rotate in synchronism with drum 10, i.e. transfer roll 46 and drum 10 rotate at substantially the same angular velooity and have substantially the same outer diameter.
Inasmuch as support material 44 is secured to transfer roll 46 for movement therewith in a recirculating path, successive toner powder images may be transferred from photoconductive surface 12 to support material 44, in superimposed registration with one another. Hence, a multi-color toner powder image corresponding in color to the original document is formed on support material 44.
With continued reference to Figure 1, the sheet feeding path for advancing support material 44 to transfer roll 46 will be briefly described hereinafter. A stack 50 of support material 44 is supported on tray 52. Feed roll 54, operatively associated with retard roll 56, separates and advances the uppermost sheet from stack 50. The advancing sheet moves into chute 58 and is directed into the nip of register rolls 60. ~ext, gripper fingers 62, mounted on transfer roll 46, releasably secure thereto support material 44 for movement therewith in a recirculating path.
After all of the discretely colored toner powder images have been transferred to support material 44, gripper fingers 62 space support material 44 from transfer roll 46.
This enables stripper bar 64 to be interposed between support material 44 and transfer roll 46 separating support material 44 therefrom. After support material 44 is stripped from transfer roll 46, it is moved on endless belt conveyor 66 to fixing station E.
At station E, a suitable fuser, indicated generally at 68, coalesces and permanently affixes the toner powder image to support material 44. A typical fuser is described in U. S. Patent ~o. 3,498,592 issued to Moser et al. in 1970. After the multi-layer toner powder image is fixed to support material 44, endless belt conveyors 68 and 70 advance support material 44 to catch tray 72. Catch tray 72 is readily accessible so that an operator may remove the final multi-color copy from the printing machine.
Invariably, residual toner particles remain on photoconductive surface 12 after the transfer of the toner powder image therefrom to support material 44.
These residual toner particles are removed from photo-conductive surface 12 as it passes through cleaning station F. At cleaning station F, residual toner particles are initially brought under the influence -16~36~54 of a cleaning corona generating device (not shown) adapted to neutralize the electrostatic charge remaining on the residual toner particles and photoconductive surface.
The neutralized toner particles are then removed from photoconductive surface 12 by rotatably mounted brush 76. A suitable brush cleaning device is described in U. S. Patent No. 3,590,412 issued to Gerbasi in 1971.
Brush 76 is positioned at cleaning station F and main-tained in contact with photoconductive surface 12. Thus, the residual toner particles remaining on photoconductive surface 12, after each successive transfer operation, are readily removed therefrom.
Turning now to Figure 2, there is shown lamp carriage 78 supporting a pair of light sources or lamps 26 thereon. Lamp carriage 78 is arranged to traverse platen 24 illuminating incremental widths of original document 25disposed therein. A suitable belt drive system advances lamp carriage 78 in the direction of arrow 80 to scan successive incremental areas of the original document 25 and returns lamp carriage 78 in the direction of arrow 82 to the initial position. Disc 22 is mounted rotatably on the printing machine frame and is interposed between lamp carriage 78 and platen 24.
Thus, when lamp carriage 78 is in the initial position, prior to the initiation of the scan cycle, disc 22 is indexed so that light source 26 illuminates one of the neutral density samples disposed thereon. For example, in Figure 1, neutral density sample 32 is shown in position to be illuminated. Light source 26 remains stationary as drum 10 rotates so that a sample electro-1~36654 static latent lmage corresponding in density to the neutral density sample is recorded on photoconductive surface 12.
Referring now to Figure 3, there is shown developer units 38, 40 and 42, probe 28 and drum 10.
Probe 28 is secured in the machine frame and positioned between exposure station B and development station C.
Probe 28 is seated within the machine's support housing and arranged to detect the sample electrostatic latent image recorded on photoconductive surface 12. A light image of the neutral density sample is projected onto the charged photoconductive surface recording a sample electrostatic latent image thereon. The sample electro-static latent image is detected by probe 28. The machine logic is arranged to generate a signal during each print cycle initiating the formation of the sample electrostatic latent image. In practice, the signal is generated when light source 26 is in the initial position prior to scanning of original document 25. A voltage indicative of the sample electrostatic latent image is sensed by probe 28 and processed by electrical circuitry 30 to produce an electrical output signal regulating voltage source or variable power supply 84. Power supply 84 is operati.vely connected to developer rolls 86, 88 and 90, respectively, of the corresponding developer units 38, 40, and 42. Power supply 84 regulates the electrical potential applied to the respective developer rolls 86, 88 and 90. In this way, each of the developer rolls is selectively biased to a potential substantially identical to that of the appropriate sample electrostatic latent image potential recorded on photoconductive surface :
12. Thus, the developer roll potential is intermediate -1~)36654 the potential of the irradiated and non-irradiated areas in photoconductive surface 12. The signal generated by the machine logic has a pulse of sufficient duration to de-energize the drive of lamp carrlage 78 when light source 26 is in the initial position. This enables disc 22 to index such that a neutral densi~ty sample is illuminated by light source 26. The resulting light image thereof is projected onto the moving photoconductive surface forming the sample electrostatic latent image thereon. After the sample electrostatic latent image is formed, a second pulse of sufficient duration is generated -by the machine logic actuating the drive system of lamp carriage 78 so that light source 26 illuminates incremental portions of original document 25 as it moves thereacross.
This creates a single color electrostatic latent image on photoconductive surface 12 after the corresponding sample electrostatic latent image is recorded thereon. As drum 10 rotates the sample electrostatic latent image recorded thereon, it passes adjacent to probe 28. Probe 28 senses the potential of the sample electrostatic latent image and develops a voltage signal indicative thereof.
As shown in Figure 4, the voltage signal from probe 28 is processed by unity gain amplifier 92. A
suitable amplifier having a high impedance can be utilized in conjunction with the probe of the present invention.
The electrical output from amplifier 92, is transmitted through two successive amplifier stages 94 and 96, and then applied to a hold circuit including a high impedance unity gain amplifier 98 and a capacitor 100. However, the signal is initially prevented from passing to the 1~36654 hold circuit by normally open contact 102.
Referring once again to Figure 4, probe 28 includes a sensing element 104 surrounded by an insulator 106. Insulator 106 is preferably fabricated from a material which is electrically insensitive to humidity changes and functions to maintain a high probe-to-ground resistance.
Conductive shield 108 is disposed around insulator 106 and the output from amplifier 92 is fed back to shield 108. This maintains shield 108 at the same potential as amplifier 92 reducing current leakage from sensing element 104 to the surrounding electrical ground. The machine logic, preferably, includes suitable circuitry adapted to close contact 100 at the appropriate time.
Thus, the sample voltage is applied across the high impedance unity gain amplifier 98. Closing contact 102 causes two discrete conditions to occur. Initially, the sensed sample electrostatic latent image potential is applied across the high impedance amplifier 98 and secondarily, capacitor 100, in the hold circuitry, is charged to the sample electrostatic latent image potential. Termination of the signal from the machine logic after the sample electrostatic latent image has passed probe 28 permits contact 102 to return to its normally open position.
However, the sample electrostatic latent image potential is stored on capacitor 100 and continues to be impressed across amplifier 98. Because of the high impedance of amplifier 98, a relatively constant output is maintained during the hold periods until the subsequent reclosing of contacts 102 provides a new sample electrostatic latent image potential. This output voltage is applied . . .. ~ . - .
1~36654 to power supply 84 ( Figure 3 ) holding the output voltage therefrom substantially constant until the next sample signal is received thereby. If the potential level of the next sample electrostatic latent image differs from that of the first sample electrostatic latent image, capacitor 100 is allowed to recharge to the new potential through contact 102 and through the circuitry of amplifier 96.
The new sample electrostatic latent image potential is impressed across the high-impedance hold amplifier 98 and capacitor 100 is recharged to this new voltage. The output voltage is supplied to power supply high-voltage operational amplifier 110 which holds the voltage output from power supply 84 substantially constant until the next signal is received. At the end of the sample period, contact 102 is again open and the hold circuit waits for the next sample.
It is evident, therefore, that this type of arrangement permits the present apparatus to detect both increases and decreases in the potential of the sample electro-static latent image recorded on photoconductive surface 12 while, substantially simultaneously therewith, generating a continuous control signal for regulating the potential applied to developer rolls 86, 88 and 90 of developer units 38, 40 and 42, respectively.
While the present invention has been described in connection with a single set of three neutral density samples, one skilled in the art will appreciate that the invention is not necessarily so limited and that a plurality of such sets may be utilized, each set corresponding to a prescrihed set of conditions and having specified densities to achieve desired copy characteristics. Furthermore, - ~
while the present invention has been described as utilizing a disc, it will be apparent to one skilled in the art that the neutral density samples may be mounted on any suitable support arranged to be appropriately indexed, e.g. and endless conveyor belt.
In recapitulation, it is apparent that the apparatus of the present invention controls the cut-off density of toner particles deposited on a single color electrostatic latent image recorded on a charged photoconductive surface.
This is achieved by exposing the charged photoconductive surface to a neutral density sample having a pre-selected density corresponding to substantially about the predeter-mined cut-off density of the single color electrostatic latent image. In this way, a sample electrostatic latent image is recorded on the photoconductive surface. The potential of the sample electrostatic latent image is employed to electrically bias the developer roll of the corresponding magnetic brush developer unit to substan-tially the same potential. Thus, toner particles are attracted to those regions of the photoconductive sur-face having a potential greater than that of the sample electrostatic latent image. Inasmuch as the potential of the non-image region is substantially less than that of the image region, toner particles are not attracted thereto and the image region of photoconductive surface 12 has toner particles deposited thereon.
It is, therefore, evident that there has been provided, in accordance with the present invention, an apparatus for controlling the cut-off density of toner particles deposited on a single color electrostatic latent : . . : . .~ . , -1~36654 image recorded on a photoconductive surface that fully satisfies the objects, aims, and advantages set forth above. While this invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled iIl the art. Accordingly, it is intended to embrace all alternatives, modifications, and variations that fall within the spirit and broad scope of the appended claims.
- 2~ -. . . : . . : ~ . . --
~ . . . .
Subsequently, the single color toner powder image is transferred to the sheet of support material. The foregoing process is repeated a plurality of cycles with differently colored light images and the respective complementary colored toner particles. Each single color toner powder image is transferred ~ the support material superimposed in registration with the prior toner powder image to form a composite multi-layer powder image thereon.
This multi-layered toner powder image is coalesced and permanently affixed to the support material forming a composite image corresponding in color to the original document.
It is apparent that in multi-color electro-photographic printing machines, the characteristics of the photoconductive surface are critical. Preferably, the electrical characteristics of the photoconductive surface should remain substantially constant. However, it has been found that the electrical characteristics of the photoconductive surfaces will vary with temperature changes or with continuous usage thereof. Hence, it is extremely difficult to maintain substantially the same potential on the photoconductive surface for light images projected thereon having substantially identical intensities.
Moreover, electrophotographic printing machines frequently utilize magnetic brushes to produce viewable toner powder images on the electrostatic latent image recorded on the photoconductive surface. Toner particles are attracted from the magnetic brush to the charged photoconductive surface.
In multi-color electrophotographic printing, the ~(~36ti5~
imaged areas are developed with the toner particles whereas -~
the non-image areas remain substantially devoid of toner particles. However, it is evident that some toner particles -will be attracted to the non-image areas inasmuch as a residual charge remains thereon. Hence, it is desirable to electrically ~ ~ :
bias the magnetic brush to a potential intermediate that of the non-image areas respective single color electrostatic latent image.
Accordingly, it is an object of an aspect of the present invention to improve the development system utilized in a multi-color electrophotographic printing maching by sensing changes in the electrical characteristics of the photocon-ductive surface and varying the potential of the development system in response thereto.
SUMMARY OF THE INVENTION
Briefly stated, and in accordance with one aspect of the present invention, there i5 provided an apparatus for -controlling the density of toner particles deposited on a single color electrostatic latent image recorded on a charged photoconductive surface.
In an embodiment, the apparatus includes at least one neutral density sample, illuminating means, toner particle depositing means, and sensing and electrical biasing means.
Preferably, the neutral density sample has a pre-selected density corresponding to substantially about a predetermined cut-off density for the single color electrostatic la~ent image recorded on the photoconductive surface. The illuminating means irradiates the neutral density sample and projects the light image formed thereof onto the charged photoconductive surface. In this way, a sample electrostatic latent image is recorded on the photoconductive surface. The sample electro-static latent image has a potential intermediate that of the ~ -, . .
- . . : - . . . :. -1~3665~
single color electrostatic latent image and the non-image regions of the charged photoconductive surface. The potential of the sample electrostatic latent image recorded on the charged photoconductive surface is detected by the sensing and electrical biasing means. Pursuant to an aspect of the present invention, the sensing and electrical biasing means electrically bias the toner particle depositing means to a potential corres-ponding to that of the sample electrostatic latent image recorded on the charged photoconductive surface. Hence, toner particles are deposited on regions of the photoconductive surface having a potential greater than the potential of the sample electrostatic latent image.
In accordance with another aspect of this invention there is provided an apparatus for controlling the cut-off density of toner particles deposited on a single color electro-static latent image recorded on a charged photoconductive surface, including: at least one neutral density sample having a pre-selected density corresponding to substantially about the predetermined cut-off density of the single color electrostatic latent image; means for illuminating said neutral density sample and projecting the light image formed thereof onto the charged photoconductive surface to record thereon a sample electrostatic latent image having a potential intermediate the single color electrostatic latent image and the non-image regions of the charged photoconductive surface; means for depositing toner particles, complementary in color to the single color electrostatic latent image, on the charged photo-conductive surface; and means for sensing the potential of the sample electrostatic latent image recorded on the charged photoconductive surface and electrically biasing said toner particle depositinq means to a potential correspondinq to the sample electrostatic latent image potential so that toner particles are deposited on regions of the photoconductive surface Q ~ - 5 ~
1~36tj`54 having a potential substantially greater than the potential , -of the sample electrostatic latent image.
In accordance with another aspect of this invention there is provided an electrophotographic printing machine of the type having a photoconductive surface, including: means for charging the photoconductive surface to a substantially uniform potential; at least one neutral density sample having ~' a pre-selected density corresponding to substantially about ~:
the predetermined cut-off density of the single color electro- '~
static,latent image; means for,exposing the charged photo-conductive surface to a single color light image of an original ' document to record thereon a single color electrostatic latent ' image, said exposing means being arranged to illuminate said neutral density sample and project a light image thereof onto . ::
the charged photoconductive surface to record thereon a sample eleetrostatic latent image having a potential intermediate the single color electrostatic latent image and the non- ~., image regions of the charged photoconduetive surface; means ' for depositing toner particles, complementary in color to the ~ :
20 'single color electrostatic latent image, on the charged ~' photoconductive surface; and means for sensing the potential ..
of the sample eleetrostatic latent image recorded on the charged photoconduetive surfaee and eleetrieally biasing said toner particle depositing means to a potential corresponding to the sample electrostatie latent image potential so that toner particles are deposited on regions of the photoconductive surface having a potential substantially greater than the potential of the sample electrostatic latent image.
In accordance with another aspect of this invention there is provided apparatus for controlling the cut-off density of toner particles deposited by a developer means on a single color latent electrostatic image recorded on a charged photo-~ - 5a -- ,.
~ .
1~3665~
conductive surface, said developer means including potential means for biasing the toner particles, the bias on said devel-oper means being controlled in response to variations in the electrical characteristics of the photoconductive surfaces which the single color electrostatic latent image is formed, at least one neutral density sample having a pre-selected density corresponding substantially to the predetermined cut-off density of the single color electrostatic latent image, means to illuminate the sample and pro]ect the light image.
thereof onto a charged photoconductive surface, a sensor located in proximity of the charged photoconductive surface for detecting the potential level of the sample image on the charged photoconductive surface prior to the deposition of toner particles on the surface, the sensor coupled to said developer potential means to bias the toner particles to a potential corresponding to the potential of the sample image.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and advantages of the present inven-tion will become apparent upon reading the following detailed description and upon reference to the drawings, in which Figure 1 is a schematic perspective view of a multi-color electrophotographic printing machine having the present invention incorporated therein;
Figure 2 is a schematic illustration of the light source and disc of neutral density samples utilized in the Figure 1 printing machine.
Figure 3 is a partial elevational view of the development system and the probe utiliæed therein to sense `.
the potential of the sample electrostatic latent :.:
.,: ,~, ... '.,:
- ~ -, .
~6)36654 image recorded on the photoconductive surface; and eeO~ s~e~ F~;~e~
Figure 4nis a schematic circuit diagram for periodically sampling the sensed sample electrostatic latent image potential.
While the present invention will be described in connection with a preferred embodiment, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
With continued reference to the drawings, Figure 1 schematically illustrates a multi-color electro-photographic printing machine employing the present invention. In the drawings, like reference numerals have been used throughout to designate like elements.
The multi-color electrophotographic printing machine shown schematically in Figure 1, illustrates the various components used to produce multi-color copies from a colored original. Although the apparatus of the present invention is particularly well adapted for use in an electrophotographic printing machine, it will become evident from the following description that it is equally well suited for use in a wide variety of electrophoto-graphic printing machines, and is not necessarily limited to the particular embodiment shown therein.
As shown in Figure 1, the printing machine employs a drum 10 having a photoconductive surface 12 secured thereto and entrained about the exterior circum-- . . ~ . :
. - - . - : . . :
~()366S4 ferential surface thereof. Drum 10 is mounted rotatably ' within the machine frame (not shown). A series of processing stations are positioned such that as drum 10 rotates in the direction of arrow 14, photoconductive surface 12 passes sequentially therethrough. Drum 10 is driven at a predetermined speed relative to the other machine operating mechanisms by a common drive motor (not shown). One type of suitable photoconductive material is disclosed in U. S. Patent No. 3,655,377, issued to Sechak in 1972. A timing wheel is mounted in the region of one end of drum 10 and adapted to trigger the logic circuitry of the printing machine.
This coordinates the various machine operations with one another to produce the proper sequence of the events at the appropriate processing stations.
Initially, drum 10 moves photoconductive surface 12 through charging station A. Charging station A has positioned thereat a corona generating device, indicated generally at 16. Corona generating device 16 extends in a generally longitudinal direction transversely across photoconductive surface 12. This readily enables corona generating device 16 to charge photoconductive surface 12 to a relatively high substantially uniform potential.
Preferably, corona generating device 16 is of the type described in U. S. Patent No. 2,778,946 issued to Mayo in 1957.
Drum 10, thereafter, is rotated to exposure station B. Exposure station B includes thereat a moving lens system, generally designated by the reference number 18, and a color filter mechanism shown generally at 20.
~S~3f~4 :~
A suitable moving lens system is disclosed in U.5. Patent No. 3,062,108 issued to Mayo in 1962, and a suitable color filter mechanism is described in Canadian patent ~15,490 issued November 28, 1972. Disc 22 has a plurality of neutral density samples (in this case 3) disposed thereon. Disc 22 is mounted rotatably in the printing machine and is disposed beneath transparent platen 24 within the half angle of the optical system. Before the light source lamps indicated generally by the reference numeral 26, begin to scan, they will be actuated to illuminate one of the neutral density samples. In this way, a sample electrostatic latent image is recorded, on photoconductive surface 12 as drum 10 rotates.
Lamps 26 are stationary and the appropriate filter is posi-tioned in filter 20 forming a sample electrostatic latent image on photoconductive surface 12 which is a strip dis-charged to the desired potential. The potential of the sam-ple electrostatic latent image recorded on photoconductive surface 12 is detected by probe 28, i.e. a suitable elec-trometer disposed adjacent to photoconductive surface 12 intermediate exposure station B and development station C.
The electrical output signal from probe 28 is processed by circuit elements 30 which regulate voltage source or power supply 84 adjusting the bias voltage of the respective developer unit having toner particles complementary in color ~-to the filter of filter mechanism 20. Preferably, disc 22 includes three equally spaced neutral density samples located about the periphery thereof. Sample 32 is a neutral density sample for green separation, sample 34 is a neutral density sample for red separation and -: : . .
.
1(~36654 sample 36 is a neutral density sample for blue separation.
Preferably the green separation sample has a density of 0.32, the blue separation sample a density of 0.35, and the red separation sample a density of 0.15. The appro-priate neutral density sample is illuminated by light source 26 to produce a sample electrostatic image corresponding to a predetermined development density for the filter being used, i.e. a green filter will have neutral density sample 32 illuminated forming a sample electrostatic latent image corresponding to the predeter-mined development density for the green separation.
In multi-color electrophotographic printing, a single color light image exposes the charged photoconductive surface. The potential on the charged photoconductive surface in the area irradiated by the single color light image is reduced. The potential of the charged photo-conductive surface in the non-irradiated areas remain substantially unchanged. During development, toner particles, complementary in color to the single color light image, are deposited on the photoconductive surface.
The irradiated areas remain substantially devoid of toner particles. The development system is biased such that the potential thereof is intermediate the irradiated and non-irradiated areas. In this way, toner particles are attracted to the non-irradiated areas from the development system since the potential of the non-irradiated areas is greater than the potential of the development system, whereas toner particles are not attracted to the irradiated areas inasmuch as the charge thereof if less thin than that of the development system. Each of the neutral density g samples form a sample electrostatic latent image. The charge of the sample electrostatic latent image is greater than that of the irradiated areas and less than that of the non-irradiated areas. The developer unit is adjusted to the potential of the sample electrostatic latent image.
Thus, toner particles are attracted to all regions of the charged photoconductive surface having a potential greater than that of the sample electrostatic latent image. The potential of the sample electrostatic latent image corre-sponds to the washout density of the single color toner powder image, i.e. the potential beneath which development of the single color electrostatic latent image does not occur. However, if the potential of the single color electrostatic latent image is greater than that of the sample electrostatic latent image development will occur.
With continued reference to the Figure 1, after the sample electrostatic latent image is formed on the charged photoconductive surface, an original document 25, such as a book, sheet of paper, or the like, disposed upon transparent viewing platen 24 is scanned. Lamps 26 and lens 18 move in a timed relation with drum 10 to scan successive incremental areas of original document 25 disposed upon platen 24. This creates a flowing light image of original document 25 which is projected onto charged photoconductive surface 12. Filter mechanism 20 is adapted to interpose selected color filters into the optical light path. The appropriate color filter operates on the light rays passing through lens 18 to record an electrostatic latent image on photoconductive surface 12 corresponding to a pre-selected spectral region of the ~ - , 1~)36654 electromagnetic wave spectrum, heretofore referred to as a single color electrostatic latent image.
After exposure, drum 10 rotates the sing~e color electrostatic latent image recorded on photoconductive surface 12 to development station C. Development station C includes thereat three individual developer units, generally indicated by the reference numerals 38, 40, and 42. A suitable develop-ment system employing a plurality of developer units is dis-closed in Canadian patent 982,886 issued February 3, 1976.
Preferably, the developer units are all of a type generally referred to as magnetic brush developer units. A typical magnetic brush developer unit utilizes a magnetizable developer mix having carrier granules and toner particles. The developer ;
mix is continually brought through a directional flux field to form a brush thereof. Each developer unit includes a develop-er roll ~6, 88 and 90 (Figure 3) electrically biased to the appropriate potential such that toner particles are attracted to the image areas (non-irradiated areas) rather than the non-image areas (irradiated areas) of the photoconductive surface 12. The potential applied to the developer roll is substan-tially equal to that of the sample electrostatic latent image recorded on photoconductive surface 12 and detected by probe 28. The single color electrostatic latent image recorded on photoconductive surface 12 is developed by bringing the brush of developer mix into contact therewith. Each of the respec-tive developer units contain discretely colored toner particles corresponding to the complement of the spectral region of the wavelength of light transmitted through filter 21, e.g. a green filtered -1~- . ~
electrostatic latent image is rendered visible by depositing green absorbing magenta toner particles therein, blue and red latent images are developed with yellow and cyan toner particles, respectively.
Drum 10 is, next, rotated to transfer station D
where the toner powder image adhering electrostatically to photoconductive surface 12 is transferred to a sheet of final support material 44. Support material 44 may be plain paper, or a sheet of transparent, thermoplastic material. A
transfer roll, shown generally at 46, rotates support material 44 in the direction of arrow 48. Transfer roll 46 is electrically biased to a potential of sufficient magnitude and polarity to electrostatically attract toner particles from photoconductive surface 12 to support material 44. U. S. Patent No. 3,612,677, issued to Langdon et al. in 1972, discloses a suitable electrically biased transfer roll. Transfer roll 46 is arranged to rotate in synchronism with drum 10, i.e. transfer roll 46 and drum 10 rotate at substantially the same angular velooity and have substantially the same outer diameter.
Inasmuch as support material 44 is secured to transfer roll 46 for movement therewith in a recirculating path, successive toner powder images may be transferred from photoconductive surface 12 to support material 44, in superimposed registration with one another. Hence, a multi-color toner powder image corresponding in color to the original document is formed on support material 44.
With continued reference to Figure 1, the sheet feeding path for advancing support material 44 to transfer roll 46 will be briefly described hereinafter. A stack 50 of support material 44 is supported on tray 52. Feed roll 54, operatively associated with retard roll 56, separates and advances the uppermost sheet from stack 50. The advancing sheet moves into chute 58 and is directed into the nip of register rolls 60. ~ext, gripper fingers 62, mounted on transfer roll 46, releasably secure thereto support material 44 for movement therewith in a recirculating path.
After all of the discretely colored toner powder images have been transferred to support material 44, gripper fingers 62 space support material 44 from transfer roll 46.
This enables stripper bar 64 to be interposed between support material 44 and transfer roll 46 separating support material 44 therefrom. After support material 44 is stripped from transfer roll 46, it is moved on endless belt conveyor 66 to fixing station E.
At station E, a suitable fuser, indicated generally at 68, coalesces and permanently affixes the toner powder image to support material 44. A typical fuser is described in U. S. Patent ~o. 3,498,592 issued to Moser et al. in 1970. After the multi-layer toner powder image is fixed to support material 44, endless belt conveyors 68 and 70 advance support material 44 to catch tray 72. Catch tray 72 is readily accessible so that an operator may remove the final multi-color copy from the printing machine.
Invariably, residual toner particles remain on photoconductive surface 12 after the transfer of the toner powder image therefrom to support material 44.
These residual toner particles are removed from photo-conductive surface 12 as it passes through cleaning station F. At cleaning station F, residual toner particles are initially brought under the influence -16~36~54 of a cleaning corona generating device (not shown) adapted to neutralize the electrostatic charge remaining on the residual toner particles and photoconductive surface.
The neutralized toner particles are then removed from photoconductive surface 12 by rotatably mounted brush 76. A suitable brush cleaning device is described in U. S. Patent No. 3,590,412 issued to Gerbasi in 1971.
Brush 76 is positioned at cleaning station F and main-tained in contact with photoconductive surface 12. Thus, the residual toner particles remaining on photoconductive surface 12, after each successive transfer operation, are readily removed therefrom.
Turning now to Figure 2, there is shown lamp carriage 78 supporting a pair of light sources or lamps 26 thereon. Lamp carriage 78 is arranged to traverse platen 24 illuminating incremental widths of original document 25disposed therein. A suitable belt drive system advances lamp carriage 78 in the direction of arrow 80 to scan successive incremental areas of the original document 25 and returns lamp carriage 78 in the direction of arrow 82 to the initial position. Disc 22 is mounted rotatably on the printing machine frame and is interposed between lamp carriage 78 and platen 24.
Thus, when lamp carriage 78 is in the initial position, prior to the initiation of the scan cycle, disc 22 is indexed so that light source 26 illuminates one of the neutral density samples disposed thereon. For example, in Figure 1, neutral density sample 32 is shown in position to be illuminated. Light source 26 remains stationary as drum 10 rotates so that a sample electro-1~36654 static latent lmage corresponding in density to the neutral density sample is recorded on photoconductive surface 12.
Referring now to Figure 3, there is shown developer units 38, 40 and 42, probe 28 and drum 10.
Probe 28 is secured in the machine frame and positioned between exposure station B and development station C.
Probe 28 is seated within the machine's support housing and arranged to detect the sample electrostatic latent image recorded on photoconductive surface 12. A light image of the neutral density sample is projected onto the charged photoconductive surface recording a sample electrostatic latent image thereon. The sample electro-static latent image is detected by probe 28. The machine logic is arranged to generate a signal during each print cycle initiating the formation of the sample electrostatic latent image. In practice, the signal is generated when light source 26 is in the initial position prior to scanning of original document 25. A voltage indicative of the sample electrostatic latent image is sensed by probe 28 and processed by electrical circuitry 30 to produce an electrical output signal regulating voltage source or variable power supply 84. Power supply 84 is operati.vely connected to developer rolls 86, 88 and 90, respectively, of the corresponding developer units 38, 40, and 42. Power supply 84 regulates the electrical potential applied to the respective developer rolls 86, 88 and 90. In this way, each of the developer rolls is selectively biased to a potential substantially identical to that of the appropriate sample electrostatic latent image potential recorded on photoconductive surface :
12. Thus, the developer roll potential is intermediate -1~)36654 the potential of the irradiated and non-irradiated areas in photoconductive surface 12. The signal generated by the machine logic has a pulse of sufficient duration to de-energize the drive of lamp carrlage 78 when light source 26 is in the initial position. This enables disc 22 to index such that a neutral densi~ty sample is illuminated by light source 26. The resulting light image thereof is projected onto the moving photoconductive surface forming the sample electrostatic latent image thereon. After the sample electrostatic latent image is formed, a second pulse of sufficient duration is generated -by the machine logic actuating the drive system of lamp carriage 78 so that light source 26 illuminates incremental portions of original document 25 as it moves thereacross.
This creates a single color electrostatic latent image on photoconductive surface 12 after the corresponding sample electrostatic latent image is recorded thereon. As drum 10 rotates the sample electrostatic latent image recorded thereon, it passes adjacent to probe 28. Probe 28 senses the potential of the sample electrostatic latent image and develops a voltage signal indicative thereof.
As shown in Figure 4, the voltage signal from probe 28 is processed by unity gain amplifier 92. A
suitable amplifier having a high impedance can be utilized in conjunction with the probe of the present invention.
The electrical output from amplifier 92, is transmitted through two successive amplifier stages 94 and 96, and then applied to a hold circuit including a high impedance unity gain amplifier 98 and a capacitor 100. However, the signal is initially prevented from passing to the 1~36654 hold circuit by normally open contact 102.
Referring once again to Figure 4, probe 28 includes a sensing element 104 surrounded by an insulator 106. Insulator 106 is preferably fabricated from a material which is electrically insensitive to humidity changes and functions to maintain a high probe-to-ground resistance.
Conductive shield 108 is disposed around insulator 106 and the output from amplifier 92 is fed back to shield 108. This maintains shield 108 at the same potential as amplifier 92 reducing current leakage from sensing element 104 to the surrounding electrical ground. The machine logic, preferably, includes suitable circuitry adapted to close contact 100 at the appropriate time.
Thus, the sample voltage is applied across the high impedance unity gain amplifier 98. Closing contact 102 causes two discrete conditions to occur. Initially, the sensed sample electrostatic latent image potential is applied across the high impedance amplifier 98 and secondarily, capacitor 100, in the hold circuitry, is charged to the sample electrostatic latent image potential. Termination of the signal from the machine logic after the sample electrostatic latent image has passed probe 28 permits contact 102 to return to its normally open position.
However, the sample electrostatic latent image potential is stored on capacitor 100 and continues to be impressed across amplifier 98. Because of the high impedance of amplifier 98, a relatively constant output is maintained during the hold periods until the subsequent reclosing of contacts 102 provides a new sample electrostatic latent image potential. This output voltage is applied . . .. ~ . - .
1~36654 to power supply 84 ( Figure 3 ) holding the output voltage therefrom substantially constant until the next sample signal is received thereby. If the potential level of the next sample electrostatic latent image differs from that of the first sample electrostatic latent image, capacitor 100 is allowed to recharge to the new potential through contact 102 and through the circuitry of amplifier 96.
The new sample electrostatic latent image potential is impressed across the high-impedance hold amplifier 98 and capacitor 100 is recharged to this new voltage. The output voltage is supplied to power supply high-voltage operational amplifier 110 which holds the voltage output from power supply 84 substantially constant until the next signal is received. At the end of the sample period, contact 102 is again open and the hold circuit waits for the next sample.
It is evident, therefore, that this type of arrangement permits the present apparatus to detect both increases and decreases in the potential of the sample electro-static latent image recorded on photoconductive surface 12 while, substantially simultaneously therewith, generating a continuous control signal for regulating the potential applied to developer rolls 86, 88 and 90 of developer units 38, 40 and 42, respectively.
While the present invention has been described in connection with a single set of three neutral density samples, one skilled in the art will appreciate that the invention is not necessarily so limited and that a plurality of such sets may be utilized, each set corresponding to a prescrihed set of conditions and having specified densities to achieve desired copy characteristics. Furthermore, - ~
while the present invention has been described as utilizing a disc, it will be apparent to one skilled in the art that the neutral density samples may be mounted on any suitable support arranged to be appropriately indexed, e.g. and endless conveyor belt.
In recapitulation, it is apparent that the apparatus of the present invention controls the cut-off density of toner particles deposited on a single color electrostatic latent image recorded on a charged photoconductive surface.
This is achieved by exposing the charged photoconductive surface to a neutral density sample having a pre-selected density corresponding to substantially about the predeter-mined cut-off density of the single color electrostatic latent image. In this way, a sample electrostatic latent image is recorded on the photoconductive surface. The potential of the sample electrostatic latent image is employed to electrically bias the developer roll of the corresponding magnetic brush developer unit to substan-tially the same potential. Thus, toner particles are attracted to those regions of the photoconductive sur-face having a potential greater than that of the sample electrostatic latent image. Inasmuch as the potential of the non-image region is substantially less than that of the image region, toner particles are not attracted thereto and the image region of photoconductive surface 12 has toner particles deposited thereon.
It is, therefore, evident that there has been provided, in accordance with the present invention, an apparatus for controlling the cut-off density of toner particles deposited on a single color electrostatic latent : . . : . .~ . , -1~36654 image recorded on a photoconductive surface that fully satisfies the objects, aims, and advantages set forth above. While this invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled iIl the art. Accordingly, it is intended to embrace all alternatives, modifications, and variations that fall within the spirit and broad scope of the appended claims.
- 2~ -. . . : . . : ~ . . --
Claims (17)
1. An apparatus for controlling the cut-off density of toner particles deposited on a single color electrostatic latent image recorded on a charged photo-conductive surface, including:
at least one neutral density sample having a pre-selected density corresponding to substantially about the predetermined cut-off density of the single color electrostatic latent image;
means for illuminating said neutral density sample and projecting the light image formed thereof onto the charged photoconductive surface to record thereon a sample electrostatic latent image having a potential intermediate the single color electrostatic latent image and the non-image regions of the charged photoconductive surface;
means for depositing toner particles, complementary in color to the single color electrostatic latent image, on the charged photoconductive surface; and means for sensing the potential of the sample electrostatic latent image recorded on the charged photoconductive surface and electrically biasing said toner particle depositing means to a potential corresponding to the sample electrostatic latent image potential so that toner particles are deposited on regions of the photocon-ductive surface having a potential substantially greater than the potential of the sample electrostatic latent image.
at least one neutral density sample having a pre-selected density corresponding to substantially about the predetermined cut-off density of the single color electrostatic latent image;
means for illuminating said neutral density sample and projecting the light image formed thereof onto the charged photoconductive surface to record thereon a sample electrostatic latent image having a potential intermediate the single color electrostatic latent image and the non-image regions of the charged photoconductive surface;
means for depositing toner particles, complementary in color to the single color electrostatic latent image, on the charged photoconductive surface; and means for sensing the potential of the sample electrostatic latent image recorded on the charged photoconductive surface and electrically biasing said toner particle depositing means to a potential corresponding to the sample electrostatic latent image potential so that toner particles are deposited on regions of the photocon-ductive surface having a potential substantially greater than the potential of the sample electrostatic latent image.
2. An apparatus as recited in Claim 1, wherein said sensing and biasing means includes;
a probe positioned adjacent to the photoconductive surface and arranged to detect the potential of the sample electrostatic latent image recorded thereon prior to toner particles being deposited on the photoconductive surface;
a voltage source for electrically biasing said toner particle depositing means; and means, in electrical communication with said probe and said voltage source, for generating an electrical output signal indicative of the sample electrostatic latent image potential detected by said probe to regulate the output voltage of said voltage source.
a probe positioned adjacent to the photoconductive surface and arranged to detect the potential of the sample electrostatic latent image recorded thereon prior to toner particles being deposited on the photoconductive surface;
a voltage source for electrically biasing said toner particle depositing means; and means, in electrical communication with said probe and said voltage source, for generating an electrical output signal indicative of the sample electrostatic latent image potential detected by said probe to regulate the output voltage of said voltage source.
3. An apparatus as recited in Claim 2, wherein successive distinguishable single color electrostatic latent images are recorded on the charged photoconductive surface, including an indexable support member having a plurality of discrete neutral density samples disposed thereon, said support member being mounted in a light-receiving rela-tionship with said illuminating means, each of said neutral density samples having a pre-selected density substantially about the cut-off density of the respective single color electrostatic latent image corresponding thereto.
4. An apparatus as recited in claim 3, wherein the neutral density samples disposed on said support member include:
a first neutral density sample for a green electro-static latent image;
a second neutral density sample spaced from said first neutral density sample for a blue electrostatic latent image; and a third neutral density sample spaced from said first and second neutral density samples for a red electro-static latent image.
a first neutral density sample for a green electro-static latent image;
a second neutral density sample spaced from said first neutral density sample for a blue electrostatic latent image; and a third neutral density sample spaced from said first and second neutral density samples for a red electro-static latent image.
5. An apparatus as recited in Claim 2, wherein said electrical signal generating means includes:
means for periodically sampling the sample electro-static latent image potential detected by said probe; and circuit means for analyzing the periodically detected sample electrostatic latent image potential and forming a continuous electrical output signal indicative thereof.
means for periodically sampling the sample electro-static latent image potential detected by said probe; and circuit means for analyzing the periodically detected sample electrostatic latent image potential and forming a continuous electrical output signal indicative thereof.
6. An electrophotographic printing machine of the type having a photoconductive surface, including:
means for charging the photoconductive surface to a substantially uniform potential;
at least one neutral density sample having a pre-selected density corresponding to substantially about the predetermined cut-off density of the single color electro-static latent image;
means for exposing the charged photoconductive surface to a single color light image of an original document to record thereon a single color electrostatic latent image, said exposing means being arranged to illuminate said neutral density sample and project a light image thereof onto the charged photoconductive surface to record thereon a sample electrostatic latent image having a potential intermediate the single color electrostatic latent image and the non-image regions of the charged photoconductive surface;
means for depositing toner particles, complementary in color to the single color electrostatic latent image, on the charged photoconductive surface; and means for sensing the potential of the sample electrostatic latent image recorded on the charged photo-conductive surface and electrically biasing said toner parti-cle depositing means to a potential corresponding to the sample electrostatic latent image potential so that toner particles are depositied on regions of the photoconductive surface having a potential substantially greater than the potential of the sample electrostatic latent image.
means for charging the photoconductive surface to a substantially uniform potential;
at least one neutral density sample having a pre-selected density corresponding to substantially about the predetermined cut-off density of the single color electro-static latent image;
means for exposing the charged photoconductive surface to a single color light image of an original document to record thereon a single color electrostatic latent image, said exposing means being arranged to illuminate said neutral density sample and project a light image thereof onto the charged photoconductive surface to record thereon a sample electrostatic latent image having a potential intermediate the single color electrostatic latent image and the non-image regions of the charged photoconductive surface;
means for depositing toner particles, complementary in color to the single color electrostatic latent image, on the charged photoconductive surface; and means for sensing the potential of the sample electrostatic latent image recorded on the charged photo-conductive surface and electrically biasing said toner parti-cle depositing means to a potential corresponding to the sample electrostatic latent image potential so that toner particles are depositied on regions of the photoconductive surface having a potential substantially greater than the potential of the sample electrostatic latent image.
7. A printing machine as recited in Claim 6, wherein said sensing and biasing means includes:
a probe positioned adjacent to the photoconductive surface and arranged to detect the potential of the sample electrostatic latent image recorded thereon prior to toner particles being deposited on the photoconductive surface;
a voltage source for electrically biasing said toner particle depositing means; and means, in electrical communication with said probe and said voltage source, for generating an electrical output signal indicative of the sample electrostatic latent image potential detected by said probe to regulate the output voltage of said voltage source.
a probe positioned adjacent to the photoconductive surface and arranged to detect the potential of the sample electrostatic latent image recorded thereon prior to toner particles being deposited on the photoconductive surface;
a voltage source for electrically biasing said toner particle depositing means; and means, in electrical communication with said probe and said voltage source, for generating an electrical output signal indicative of the sample electrostatic latent image potential detected by said probe to regulate the output voltage of said voltage source.
8. A printing machine as recited in claim 7, wherein successive distinguishable single color electro-static latent images are recorded on the charged photocon-ductive surface, including an indexable support member having a plurality of discrete neutral density samples disposed thereon, said support member being mounted on the printing machine in a light-receiving relationship with said exposing means, each of said neutral density samples having a pre-selected density substantially about the cut-off density of the respective single color electro-static latent image corresponding thereto.
9. A printing machine as recited in Claim 8, wherein the neutral density samples disposed on said support member include:
a first neutral density sample for a green electro-static latent image;
a second neutral density sample spaced from said first neutral density sample for a blue electrostatic latent image;
a third neutral density sample spaced from said first and second neutral density samples for a red electro-static latent image.
a first neutral density sample for a green electro-static latent image;
a second neutral density sample spaced from said first neutral density sample for a blue electrostatic latent image;
a third neutral density sample spaced from said first and second neutral density samples for a red electro-static latent image.
10. A printing machine as recited in claim 7, wherein said electrical signal generating means includes means for periodically sampling the sample electro-static image potential detected by said probe; and circuit means for analyzing the periodically detected sample electrostatic latent image potential and forming a con-tinuous electrically output signal indicative thereof.
11. Apparatus for controlling the cut-off density of toner particles deposited by a developer means on a single color latent electrostatic image recorded on a charged photo-conductive surface, said developer means including potential means for biasing the toner particles, the bias on said devel-oper means being controlled in response to variations in the electrical characteristics of the photoconductive surfaces which the single color electrostatic latent image is formed, at least one neutral density sample having a pre-selected density corresponding substantially to the predetermined cut-off density of the single color electrostatic latent image, means to illuminate the sample and project the light image thereof onto a charged photoconductive surface, a sensor located in proximity of the charged photoconductive surface for detecting the potential level of the sample image on the charged photoconductive surface prior to the deposition of toner particles on the surface, the sensor coupled to said developer potential means to bias the toner particles to a potential corresponding to the potential of the sample image.
12. The apparatus according to claim 11 wherein a plurality of discrete neutral density samples are provided, each of said samples having a preselected density.
13. The apparatus according to claim 12 wherein succes-sive discrete single color electrostatic latent images representing each sample are recorded on the charged photo-conductive surface.
14. The apparatus according to claim 12 or 13 wherein there is provided an indexable support member to which each of the samples is attached and successively indexable into said illuminating and projecting means.
15. The apparatus according to claim 12 or 13 wherein the plurality of neutral density samples include a first neutral density sample for a green electrostatic latent image, a second neutral density sample spaced from the first neutral density sample for a red electrostatic latent image and a third neutral density sample spaced from the first and second neutral density samples for a blue electrostatic latent image.
16. The apparatus according to claim 1 wherein means are electrically coupled to said developer biasing means and said sensor for generating an electrical output signal indic-ative of the sample potential detected by said sensor to regulate said developer biasing means.
17. The apparatus according to claim 16 wherein the signal generating means includes means for periodically sampling the sample image potential on the charged photo-conductive surface detected by the sensor and circuit means for forming a continuous electrical output signal indicative of the sample image potential.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US00361112A US3815988A (en) | 1973-05-17 | 1973-05-17 | Image density control apparatus |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1036654A true CA1036654A (en) | 1978-08-15 |
Family
ID=23420693
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA193,290A Expired CA1036654A (en) | 1973-05-17 | 1974-02-22 | Image density control apparatus |
Country Status (12)
| Country | Link |
|---|---|
| US (1) | US3815988A (en) |
| JP (1) | JPS5536144B2 (en) |
| AR (1) | AR205710A1 (en) |
| BE (1) | BE815209A (en) |
| BR (1) | BR7403928D0 (en) |
| CA (1) | CA1036654A (en) |
| DE (1) | DE2411855C3 (en) |
| FR (1) | FR2230003B1 (en) |
| GB (1) | GB1458707A (en) |
| IT (1) | IT1012346B (en) |
| NL (1) | NL166805C (en) |
| ZA (1) | ZA743132B (en) |
Families Citing this family (47)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5926957B2 (en) * | 1973-12-28 | 1984-07-02 | キヤノン株式会社 | Color electrophotographic method |
| US4045218A (en) * | 1974-03-29 | 1977-08-30 | Xerox Corporation | Method for electrostatically producing a color accented photocopy |
| USRE31964E (en) * | 1974-06-17 | 1985-08-06 | Savin Corporation | Automatic development electrode bias control system |
| US3892481A (en) * | 1974-06-17 | 1975-07-01 | Savin Business Machines Corp | Automatic development electrode bias control system |
| US3936182A (en) * | 1974-08-12 | 1976-02-03 | Xerox Corporation | Control arrangement for an electrostatographic reproduction apparatus |
| US3960444A (en) * | 1974-08-14 | 1976-06-01 | Xerox Corporation | Electrophotographic printing machine |
| JPS5243439A (en) * | 1975-10-03 | 1977-04-05 | Ricoh Co Ltd | Generator for the bias voltage for the electrophotographic copying machine |
| JPS5939742B2 (en) * | 1975-10-03 | 1984-09-26 | キヤノン株式会社 | Copy machine control device |
| US4093457A (en) * | 1976-06-10 | 1978-06-06 | Xerox Corporation | Method of transfer |
| DE2759637C2 (en) * | 1976-10-19 | 1986-01-30 | Ricoh Co., Ltd., Tokio/Tokyo | Device for setting the development voltage and / or the exposure intensity for an electrophotographic copier |
| US4226525A (en) | 1976-10-19 | 1980-10-07 | Ricoh Company, Ltd. | Electrostatic copying machine |
| GB1561923A (en) * | 1976-12-31 | 1980-03-05 | Xerox Corp | Control system for an electrostatogrophic copying machine |
| JPS5393030A (en) * | 1977-01-27 | 1978-08-15 | Ricoh Co Ltd | Copying process control method of electrophotographic copying machine |
| JPS5398834A (en) * | 1977-02-09 | 1978-08-29 | Canon Inc | Controller for electrostatic device |
| DE2807317C3 (en) * | 1977-02-23 | 1982-02-11 | Ricoh Co., Ltd., Tokyo | Procedure for maintaining optimal conditions in electrophotography |
| JPS53106129A (en) * | 1977-02-28 | 1978-09-14 | Canon Inc | Recording electrostatic device |
| JPS53136838A (en) * | 1977-05-04 | 1978-11-29 | Ricoh Co Ltd | Automatic controlling method of image quality in transfer type electrostatic copier |
| JPS543546A (en) * | 1977-06-10 | 1979-01-11 | Canon Inc | Exposure device |
| JPS543540A (en) * | 1977-06-10 | 1979-01-11 | Canon Inc | Automatic exposure device |
| JPS5486347A (en) * | 1977-12-21 | 1979-07-09 | Canon Inc | Development stabilizing system |
| JPS5497044A (en) * | 1978-01-17 | 1979-07-31 | Konishiroku Photo Ind Co Ltd | Toner concentration controller for zerographic copier |
| CA1128114A (en) * | 1978-04-10 | 1982-07-20 | Clement C. Wilson | Test cycle quality control system for an electrophotographic machine |
| JPS54141645A (en) * | 1978-04-26 | 1979-11-05 | Ricoh Co Ltd | Copy image adjusting method |
| US4277162A (en) * | 1978-07-13 | 1981-07-07 | Ricoh Company, Ltd. | Electrophotographic apparatus comprising density sensor means |
| US4348099A (en) * | 1980-04-07 | 1982-09-07 | Xerox Corporation | Closed loop control of reproduction machine |
| JPS57100449A (en) * | 1980-12-16 | 1982-06-22 | Canon Inc | Color copying device |
| DE3149668A1 (en) * | 1980-12-16 | 1982-07-15 | Canon K.K., Tokyo | "COLOR COPIER" |
| JPS57102670A (en) * | 1980-12-19 | 1982-06-25 | Canon Inc | Color copying machine |
| JPS57100448A (en) * | 1980-12-16 | 1982-06-22 | Canon Inc | Color copying device |
| GB2111674B (en) * | 1981-10-30 | 1985-09-25 | Konishiroku Photo Ind | Monitoring in electrostatic reproducing apparatus |
| US4403848A (en) * | 1982-02-17 | 1983-09-13 | Xerox Corporation | Electronic color printing system |
| JPS5844451A (en) * | 1982-07-12 | 1983-03-15 | Canon Inc | Stabilizing method for surface potential |
| JPS5925545U (en) * | 1982-08-11 | 1984-02-17 | 株式会社リコー | double-sided copy machine |
| US4600294A (en) * | 1983-04-01 | 1986-07-15 | Canon Kabushiki Kaisha | Image forming apparatus with detector and control |
| DE3526878C2 (en) * | 1984-07-27 | 1997-10-02 | Konishiroku Photo Ind | Device for generating a multicolor image |
| US4803514A (en) * | 1984-10-22 | 1989-02-07 | Konishiroku Photo Industry Co., Ltd. | Multi-color image forming method and apparatus |
| JPS61166558A (en) * | 1985-01-18 | 1986-07-28 | Konishiroku Photo Ind Co Ltd | Image forming device |
| US4607944A (en) * | 1985-06-07 | 1986-08-26 | Eastman Kodak Company | Apparatus for controlling toner replenishment in electrographic copier |
| DE3530011C3 (en) * | 1985-08-22 | 1994-09-29 | Aeg Sensorsysteme Gmbh | Method and device for suppressing the influence of stray light in a measuring light barrier |
| GB2180947B (en) * | 1985-08-31 | 1989-08-09 | Ricoh Kk | Image recording device |
| US4772920A (en) * | 1985-12-24 | 1988-09-20 | Kabushiki Kaisha Toshiba | Image forming apparatus |
| US4806980A (en) * | 1986-11-06 | 1989-02-21 | Eastman Kodak Company | Dynamic feedforward process control for electrographic machines |
| US4780744A (en) * | 1987-02-18 | 1988-10-25 | Eastman Kodak Company | System for quality monitoring and control in an electrophotographic process |
| US5124750A (en) * | 1989-09-05 | 1992-06-23 | Minolta Camera Kabushiki Kaisha | Toner density detecting method, and image forming method and apparatus employing the toner density detecting method |
| US5153658A (en) * | 1991-08-09 | 1992-10-06 | Xerox Corporation | Mac cleaner brush film control |
| JPH0553422A (en) * | 1991-08-29 | 1993-03-05 | Minolta Camera Co Ltd | Image forming device |
| US5328787A (en) * | 1993-05-24 | 1994-07-12 | Eastman Kodak Company | Method for assessing and controlling the sensitometric characteristics of photographic products |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2956487A (en) * | 1955-03-23 | 1960-10-18 | Rca Corp | Electrostatic printing |
| BE755383A (en) * | 1969-08-29 | 1971-03-01 | Xerox Corp | APPARATUS FOR THE CONTROL OF DEVELOPMENT ELECTRODES |
| US3674532A (en) * | 1970-07-23 | 1972-07-04 | Eastman Kodak Co | Control for bias of magnetic brush and method |
-
1973
- 1973-05-17 US US00361112A patent/US3815988A/en not_active Expired - Lifetime
-
1974
- 1974-01-01 AR AR253772A patent/AR205710A1/en active
- 1974-02-22 CA CA193,290A patent/CA1036654A/en not_active Expired
- 1974-03-12 DE DE2411855A patent/DE2411855C3/en not_active Expired
- 1974-04-16 NL NL7405155.A patent/NL166805C/en not_active IP Right Cessation
- 1974-05-10 JP JP5216374A patent/JPS5536144B2/ja not_active Expired
- 1974-05-14 IT IT22689/74A patent/IT1012346B/en active
- 1974-05-14 FR FR7416693A patent/FR2230003B1/fr not_active Expired
- 1974-05-15 BR BR3928/74A patent/BR7403928D0/en unknown
- 1974-05-16 ZA ZA00743132A patent/ZA743132B/en unknown
- 1974-05-16 GB GB2177074A patent/GB1458707A/en not_active Expired
- 1974-05-17 BE BE144468A patent/BE815209A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| BE815209A (en) | 1974-09-16 |
| NL166805B (en) | 1981-04-15 |
| NL166805C (en) | 1981-09-15 |
| AR205710A1 (en) | 1976-05-31 |
| DE2411855C3 (en) | 1979-06-21 |
| FR2230003B1 (en) | 1976-12-24 |
| US3815988A (en) | 1974-06-11 |
| GB1458707A (en) | 1976-12-15 |
| JPS5020730A (en) | 1975-03-05 |
| ZA743132B (en) | 1975-05-28 |
| JPS5536144B2 (en) | 1980-09-18 |
| NL7405155A (en) | 1974-11-19 |
| IT1012346B (en) | 1977-03-10 |
| DE2411855A1 (en) | 1974-12-05 |
| BR7403928D0 (en) | 1975-01-21 |
| FR2230003A1 (en) | 1974-12-13 |
| DE2411855B2 (en) | 1978-10-12 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA1036654A (en) | Image density control apparatus | |
| US5160946A (en) | Image registration system | |
| EP0360484B1 (en) | Densitometer for measuring specular reflectivity | |
| US4113371A (en) | Color development system | |
| US5717978A (en) | Method to model a xerographic system | |
| US5019859A (en) | Process control for highlight color with developer switching | |
| US4251154A (en) | Electrophotographic color copier | |
| EP0414504A2 (en) | Densitometer for measuring developability | |
| EP0311359B1 (en) | Sheet transport | |
| US5749019A (en) | Look up table to control non-linear xerographic process | |
| CA1066354A (en) | Corona generator for multicolor electrocopier | |
| US3970042A (en) | Color development apparatus | |
| EP0375432B1 (en) | Method and apparatus for creating images | |
| EP0492451A2 (en) | A densitometer for measuring marking particle density on a photoreceptor having a compensation ratio which adjusts for changing environmental conditions and variability between machines | |
| US3805069A (en) | Regulated corona generator | |
| US3778146A (en) | Illuminating apparatus | |
| US4847657A (en) | Electrophotographic apparatus for depositing developer only on the image area of the image bearing member | |
| US3998539A (en) | Illumination system | |
| US4509850A (en) | Two-color electrophotographic printing machine | |
| US4045219A (en) | Method of reproducing color highlighted documents | |
| US4227795A (en) | Half-tone imaging system | |
| US4922298A (en) | Automatic color separation system | |
| US4066351A (en) | Variable illumination optical system | |
| US4959286A (en) | Two-pass highlight color imaging with developer housing bias switching | |
| US4025182A (en) | Transfer apparatus for a color electrophotographic printing machine |