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Description  |
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BACKGROUND OF THE INVENTION
This invention relates generally to an electrostatographic printing
machine, and more particularly concerns an improved development system for
use therein.
An electrostatographic printing process forms an electrostatic latent image
of an original document and reproduces the image in viewable form on a
copy sheet. Electrostatography includes electrophotography and
electrography. As is well known, electrophotography employs a
photosensitive medium to form, with the aid of electromagnetic radiation,
the electrostatic latent image. Contrawise, electrography utilizes an
insulating medium to form, without the aid of electromagnetic radiation,
the electrostatic latent image. Both of the foregoing processes render the
latent image viewable by the process of development, i.e. depositing
particles thereon. Frequently, the particles are transferred from the
latent image to a copy sheet. Alternatively, the recording sheet on which
the latent image is produced may also serve as the copy sheet after the
particles have been deposited thereon. In both of the foregoing cases, the
resultant toner powder image deposited on the copy sheet is permanently
affixed thereto by the application of heat and/or pressure. Hereinafter,
an electrophotographic printing machine will be described as an
illustrative embodiment.
Electrophotographic printing employs a photoconductive manner which is
charged to sensitize the surface thereof. The charged portion of the
photoconductive member is exposed to a light image of the original
document being reproduced. Exposure of the sensitized portion of the
photoconductive member discharges the charge therein selectively in the
irradiated areas in accordance with the intensity of the light transmitted
thereto. This creates an electrostatic latent image on the photoconductive
member corresponding to the original document being reproduced.
Development of the electrostatic latent image recorded on the
photoconductive member is achieved by bringing a developer material into
contact therewith. Generally, the developer material comprises dyed or
colored heat settable plastic powders, known to the art as toner
particles, which adhere triboelectrically to coarser carrier granules,
such as ferromagnetic granules. The toner particles and carrier granules
are selected such that the toner particles have the appropriate charge
relative to the electrostatic latent image recorded on the photoconductive
member. Thus, when the developer material is brought into contact with the
latent image recorded on the photoconductive member, the greater
attractive force thereof causes the toner particles to transfer from the
carrier granules and adhere to the electrostatic latent image. This
process was disclosed originally by Carlson in U.S. Pat. No. 2,297,691 and
is further amplified and described by many related patents in the art.
The process of electrophotographic printing was significantly advanced with
the advent of multi-color electrophotographic printing. In color
electrophotographic printing, filters form single color light images from
the colored original document. Each single color light image records a
single color electrostatic latent image on the photoconductive member. The
single color electrostatic latent image is developed with toner particles
of a color complementary to the color of the filtered light image.
Thereafter, each differently colored toner powder image is transferred to
the copy sheet in superimposed registration with one another. This results
in a multi-layered toner powder which is subsequently permanently affixed
to the copy sheet. In this manner, the copy sheet has a transparent
multi-layered toner powder image formed thereon. Each layer is of a
different color. Light rays pass through the multi-layered powder image
and reflected from the copy sheet back through the layers to the eye of
the observer. Each layer acts as an optical colored filter so that the
observer sees an image having a composite color. This results in the
observer seeing a copy corresponding in color substantially to the
original document being reproduced. U.S. Pat. No. 3,854,449 issued to
Davidson in 1974 describes this process in greater detail.
Recently, it has been highly desirable to create flat color, i.e. a copy
containing colored information formed as a single layer rather than a
multiple layer. This may be achieved by utilized colored toner particles
corresponding to all desired colors. This requires that the developer
housing storing the toner particles be replaced or differently colored
toner particles placed therein to change copy colors. Alternatively,
subtractive primary color toner particles may be blended in the developer
housing. The ratios of toner particles defines the resultant color of the
mixture. In order to vary the color of the mixture, the ratios of the
substractive primary color toner particles must be suitably adjusted.
Thus, the development system comprises a mixture of cyan, magenta, and
yellow toner particles. The ratios of respective toner particles produces
a resultant mixture of toner particles having the desired color.
A development control system which regulates the concentration of toner
particles in each developer housing of a multi-color electrographic
printing machine is described in U.S. Pat. No. 3,754,821 issued to Whited
in 1973. This patent describes a control system for regulating the
concentration of toner particles in each developer housing employed in a
multi-color electrophotographic printing machine. Each developer housing
is controlled independently and contains only single color toner particles
therein.
Another multi-color electrophotographic printing machine is described in
U.S. Pat. No. 3,910,232 issued to Kondo et al in 1975. This patent teaches
that developing agents employed in a multi-color development system may be
re-used as a black color developing agent. This is achieved by mixing the
developing agents in a recovery unit. These differently colored developing
agents are mixed with a black colored developing agent so as to be
suitable for monochromatic reproduction. The combined developing agent may
be utilized for a monochromatic reproduction that is not necessarily
black.
Accordingly, it is a primary object of the present invention to improve the
development apparatus employed in an electrophotographic printing machine
so as to be able to form a mixture of differently colored particles to
achieve a resultant pre-selected color therein.
SUMMARY OF THE INVENTION
Briefly stated, and in accordance with the present invention, there is
provided a development apparatus.
Pursuant to the features of the present invention, the development
apparatus includes means for storing a supply of particles. Means are
provided for dispensing a plurality of differently colored particles into
the storing means. The dispensing means discharges the particles therefrom
in a pre-selected ratio to form a mixture of particles in the storing
means having a pre-selected color.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and advantages of the present invention will become apparent
upon reading the following detailed description and upon reference to the
drawings, in which:
FIG 1 is a schematic elevational view depicting an electrophotographic
printing machine incorporating the features of the present invention
therein;
FIG. 2 is a sectional elevational view showing the development apparatus
employed in the FIG. 1 printing machine; and
FIG. 3 is a block diagram illustrating the controller employed in the FIG.
2 development apparatus.
While the present invention will hereinafter be described in connection
with a preferred embodiment thereof, 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
For a general understanding of the illustrative electrophotographic
printing machine, in which the features of the present invention may be
incorporated, reference is had to the drawings. In the drawings, like
reference numerals have been used throughout the designate identical
elements. FIG. 1 schematically illustrates the various components of a
printing machine having the development system of the present invention
incorporated therein. Although the development system is particularly well
adapted for use in the electrophotographic printing machine depicted
hereinafter, it will become evident from the following discussion that it
is equally well suited for use in a wide variety of electrostatographic
printing machines and is not necessarily limited in its application to the
particular embodiment shown herein.
Inasmuch as the art of electrophotographic printing is well known, the
various processing stations depicted in the FIG. 1 printing machine will
be shown hereinafter schematically. There operation will only be described
briefly with reference to FIG. 1.
Referring now to FIG. 1, the electrophotographic printing machine employs a
belt 10 having a photoconductive surface 12. By way of example,
photoconductive surface 12 is a suitable selenium alloy deposited on a
conductive substrate, such as aluminum. Belt 10 moves in the direction of
arrow 14 to advance sequentially through the various processing stations
disposed thereabout. Rollers 16, 18 and 20 support belt 10. A drive
mechanism, i.e. a suitable motor is coupled to roller 16 so as to advance
belt 10 in the direction of arrow 14.
Initially, a portion of belt 10 passes through charging station A. At
charging station A, a corona generating device, indicated generally by the
reference numeral 22, charges photoconductive surface 12 of belt 10 to a
relatively high substantially uniform potential. A suitable corona
generating device is described in U.S. Pat. No. 2,836,725 issued to
Vyverberg in 1958.
Thereafter, the charged portion of photoconductive surface 12 is advanced
by belt 10 to exposure station B. At exposure station B, an original
document 24 is placed face down upon a transparent support platen 26. An
illumination system flashes light rays upon original document 24 to
produce image rays corresponding to the informational areas contained
therein. The image rays are projected by means of an optical system 28
onto the charged portion of photoconductive surface 12. In this manner,
the charged portion of photoconductive surface 12 is exposed to a light
image of the original document. Irradiation of photoconductive surface 12
to the light image selectively discharges the charge thereon in accordance
with the intensity of the light image projected thereto. This records an
electrostatic latent image on photoconductive surface 12.
Next, the electrostatic latent image recorded on photoconductive surface 12
is advanced by belt 10 to development station C. At development station C,
a developer unit, indicated generally by the reference numeral 30, employs
a plurality of magnetic brush rollers to deposit toner particles on the
electrostatic latent image. The toner particles are formed from a mixture
of differently colored toner particles. These toner particles are mixed in
a pre-selected ratio so as to form a pre-selected color. Thus, the
electrostatic latent image is developed with a mixture of toner particles
having a desired pre-selected color. The color of the toner particle
mixture may be suitably adjusted by changing the ratio of the toner
particles within the mixture. By way of example, the toner particle
mixture comprises cyan toner particles, magenta toner particles and yellow
toner particles. Depending upon the ratio of these toner particles to one
another, the color of the resultant mixture will vary. For example, a
combination of equal parts of yellow and magenta will produce red.
Similarly, a combination of equal parts of yellow and cyan will produce
green. Finally, a combination of equal parts of magenta and cyan will
produce blue. Variations and intermediate shades of these colors may be
produced by adjusting the ratio of the differently colored toner particles
to one another. For example, equal parts of yellow, magenta, and cyan will
result in black. Controller 32 regulates the ratio of differently colored
toner particles employed by developer unit 30 and maintains the
concentration of toner particles within the developer mix substantially
constant. However, the ratio between differently colored toner particles
may be suitably varied to obtain a mixture having a desired preselected
color. Sensing unit 34 detects the density of the toner powder image
recorded on photoconductive surface 12. A sample electrostatic latent
image is formed on photoconductive surface 12 and rendered visible by
developer unit 30. The density of the toner particles deposited in the
sample electrostatic latent image is detected by sensing unit 30.
Controller 32, responsive to an electrical signal from sensing unit 34,
regulates the dispensing of additional toner particles into developer unit
30 to maintain the concentration of the toner particles within the mixture
substantially constant. The developer material contained within developer
unit 30 comprises differently colored toner particles and carrier granules
having the toner particles triboelectrically attracted thereto. Controller
32 regulates the concentration of toner particles within the developer mix
and the ratio of differently colored toner particles with respect to each
other. The detailed structure of developer unit 30, controller 32 and
sensing unit 34 will be discussed hereinafter with reference to FIGS. 2
and 3. As in all electrophotographic printing processes, the electrostatic
latent image attracts electrostatically the toner particles from the
carrier granules forming a toner powder image on photoconductive surface
12 of belt 10. The resultant color of the toner particle mixture depends
upon the ratio of differently colored toner particles therein.
The toner powder image is transported by photoconductive surface 12 to
transfer station D. Transfer station D is located at point of tangency on
belt 10 as it moves around roller 16. Transfer roller 36 is disposed at
transfer station D with the copy sheet being interposed between transfer
roll 38 and photoconductive surface 12 of belt 10. Transfer roller 36 is
electrically biased to a suitable magnitude and polarity so as to attract
the toner powder image to the surface of the copy sheet in contact
therewith. After transferring the toner powder image to the copy sheet,
conveyor 38 advances the copy sheet in the direction of arrow 40 to fixing
station E.
Fixing station E includes a fuser assembly, indicated generally by the
reference numeral 42. Fuser assembly 42 comprises a heated fuser roll and
a back-up roll. The surface of the copy sheet having the toner powder
image thereon passes between the fuser roll and back-up roll with the
toner powder image contacting the fuser roll. In this manner, the toner
powder image is permanently affixed to the copy sheet. After fusing,
conveyers 44 and 46 advance the copy sheet to catch tray 48.
Briefly referring to the sheet feeding path, sheet transport 50 advances,
in seriatum, successive copy sheets from stack 52 or, in lieu thereof,
stack 54. The machine programming permits the operator to select the
desired stack from which the copy sheet is advanced. In this manner, the
selected copy sheet advances to transfer station D where the toner powder
image is transferred thereto.
It is believed that the foregoing description is sufficient for purposes of
the present application to illustrate the general operation of an
electrophotographic printing machine incorporating the features of the
present invention therein. Referring now to the specific subject matter of
the present invention, FIGS. 2 and 3 depict the developer unit and the
associate controller and sensor therefor.
Referring now to FIG. 2, there is shown in detailed structure of developer
unit 30. As shown therein, housing 56 has a chamber 58 for storing a
supply of developer mix therein. Toner particles are added to the
developer mix, as required, from toner cartridges 60, 62 and 64. Each of
these toner cartridges is a hollow cylindrical member extending the length
of housing 56 with perforations in the lower portion thereof. Toner
particles are dispensed from the cartridge during oscillation about the
longitudinal axis thereof. Toner cartridge 60 comprises cyan toner
particles, toner cartridge 62 has magneta toner particles therein, and
toner cartridge 64 has yellow toner particles therein. The ratio of the
toner particles dispensed from each of the cartridges is regulated so that
the resultant toner particle mixture within the developer material is at a
pre-selected ratio forming a pre-selected color. Augers 66 mix the toner
particles dispensed from cartridges 60, 62 and 64 with the unused
developer material and denuded carrier granules dropping from developer 80
to obtain a homoegenous developer material. Baffle plate 68 isolates the
transport rollers and developer rollers from sump 58. Transport rollers 70
and 72 advance the developer mix in an upwardly direction to developers
rollers 74, 76, 78 and 80. Each transport roller 70 and 72 includes an
outer cylinder or tubular member 82 made of non-magnetizable material and
extending almost the length of housing 56. Tubular members 82 are mounted
for rotation in housing 56. Disposed within each tubular member 82 is a
magnet 84. Tubular member 82 of transport roller 70 rotates in the
direction of arrow 86. Tubular member 82 of transport roller 72 rotates in
the direction of arrow 88. Mounted for rotation within chamber 58 of
housing 56 are four magnetic brush developer rollers 74, 76, 78 and 80
positioned with their axis in parallel and adjacent to photoconductive
surface 12 of belt 10. Each magnetic brush developer roller comprises an
outer cylinder or tubular member 90 made of a non-magnetizable material
and extending almost the length of housing 56. Tubular members 90 are
mounted for rotation in housing 56. Disposed within each tubular member 90
is a magnet 92. During a development cycle, tubular members 90 rotate in
unison with the respective magnets 92 being held substantially stationary.
The magnetic field emanating from magnets 92 causes the developer mix to
be attracted to the outer surface of tubular members 90. As the tubular
members rotate in the direction of arrows 94, the developer material
advances across the outer surface of each tubular member 90. In this
manner, a brush or bristles of developer material extend in an outwardly
direction from housing 56 in contact with the electrostatic latent image
recorded on photoconductive surface 12 of belt 10. After passing developer
roller 80, the unused developer material is guided by baffle 68 onto auger
66 and is mixed once again with the toner particles dispensed from
cartridges 60, 62 and 64. The resultant material falls into chamber 58 of
housing 56 for subsequent reuse.
The ratio of differently colored toner particles is regulated by controller
32. In addition, controller 32 maintains the total concentration of toner
particles within the developer material substantially constant. Sensing
unit 34 detects the density of the sample toner powder image 96 formed on
photoconductive surface 12. Sensing unit 34 comprises a light source 98
and a photodetector or photodiode 100. Differently colored optical filters
102 are disposed in front of light source 98 to optimize the color of the
light rays transmitted therethrough onto the toner powder image 96.
Thus, an optical filter of a color complimentary to the color of the toner
particles being controlled is inserted between light source 98 and toner
powder image 86. By way of example, if cartridge 60 having cyan toner
particles is being regulated, a red filter is inserted between toner
powder image 96 and light source 98. The red light rays are reflected by
the cyan toner particles in toner powder image 96 while the yellow and
magenta toner particles therein absorb the red light rays. Thus, the
intensity of the light rays reflected to photodiode 100 from toner powder
image 96 correspond to the density of the cyan toner particles in toner
powder image 96. Similarly, if cartridge 62 having magenta toner particles
is being regulated, a green filter is inserted between toner powder image
96 and light source 98. Finally, if cartridge 64 having yellow toner
particles is being regulated, a blue filter is inserted between toner
powder image 96 and light source 98.
Intensity of the light rays reflected from toner powder image 96 are
detected by photodiode 100. Photodiode 100 develops an electrical output
signal indicative of the density or light absorbing mass of the toner
powder image. This electrical signal is processed by controller 32.
Controller 32 actuated cartridges 60, 62 and 64 to dispense toner
particles, in the proper ratio, therefrom into chamber 58 of housing 56.
Thus, by controlling the ratio of differently colored toner particles with
respect to one another in the developer material, the color thereby may be
suitably selected. Though it is readily simple to proceed from a light
color to a dark color, in returning from a dark color to a light color, it
may be necessary to purge the developer housing of the darker material.
This may be achieved by draining the developer material from housing 56
and passing unprocessed magnetite therethrough. The foregoing is described
more fully in co-pending application Ser. No. 728,101, filed in 1976, the
relevant portions thereof being hereby incorporated into the present
application.
Referring now to FIG. 3, the detailed circuitry of controller 32 will be
hereinafter described. Controller 32 comprises three substantially
identical channels. One channel is associated with each toner particle
cartridge. Each channel is controlled by a signal from photodiode 100. An
appropriately colored optical filter is interposed between toner powder
image 96 and light source 98, depending upon the cartridge being
controlled.
Turning initially to the channel for controlling cartridge 64, a blue
filter is interposed between light source 98 and toner powder image 96.
This channel includes a logic circuit for converting the analog signal
from photodiode 100 to a digital signal. The digital signal from logic
circuit 104 is transmitted to logic circuit 106 which compares it with a
reference signal. The reference signal is produced by a variable voltage
source 108. Voltage source 108 includes a constant voltage source
connected to a potentiometer. Changes in potentiometer resistance adjust
the reference signal. The output from voltage source 108 is processed by
logic circuit 110 which converts the analog signal to a digital signal.
Logic Circuit 106 develops an error signal. The error signal from logic
circuit 106 corresponds to the difference between the signal from
photodiode 100 and the reference signal generated by variable voltage
source 108. When this signal is nulled, i.e. zero or beneath a prescribed
level, power supply 112 remains unactuated. Excitation of power supply 112
energizes motor 114 which oscillates cartridge 64 to dispense toner
particles therefrom into the developer material in chamber 58 of housing
56. In this way, additional toner particles from cartridge 64 are added to
the developer material.
Turning now to cartridge 62, cartridge 62 is controlled in a similar manner
to cartridge 64 with a green filter being interposed between toner powder
image 96 and light source 98. Logic circuit 116 converts the analog signal
from photodiode 100 to a digital signal. Variable voltage source 118
produces a reference signal. Voltage source 118 also includes a constant
voltage source connected to a potentiometer. Similarly, changes in
potentiometer resistance adjusts the reference signal. Thus, the ratio of
the reference voltages from variable voltage source 118 and variable
voltage source 108 are in the same ratio as the quantity of toner
particles dispensed from their respective cartridges 64 and 62. The analog
signal from variable voltage source 118 is processed by logic circuit 120
and converted to a digital signal. Logic circuit 122 compares the
reference signal to the signal from photodiode 100 and generates an error
signal. The error signal from logic circuit 122 is transmitted to power
supply 124. Excitation of power supply 124 energizes motor 126 which
oscillates cartridge 62 to dispense toner particles into the developer
material.
Referring now the channel for regulating the discharging of toner particles
from cartridge 60, a red filter is interposed between toner powder image
96 and light source 98. This channel also includes a logic circuit 128 for
processing the analog signal from photodiode 100 and converting it to a
digital signal. The reference signal is produced by variable voltage
source 130. Variable voltage source 130 comprises a constant voltage
source connected to a potentiometer. Changes in potentiometer resistance
adjust the reference signal. The reference signal is processed by logic
circuit 132 and coverted from an analog signal to a digital signal. Logic
circuit 134 compares the digital reference signal to the digital signal
from photodiode 100 and develops an error signal therefrom. The error
signal is transmitted to power supply 136. Excitation of power supply 136
energizes motor 138 which oscillates cartridge 60 to dispense toner
particles into the developer material.
In this manner, the concentration of toner particles of each color is
controlled within the developer mixture. By regulating the concentration
of toner particles within the developer material for each of the
differently colored toner particles, the total concentration of toner
particles within the developer material is also controlled. Thus, the
total concentration of toner particles within the developer material is
maintained substantially constant as long as the sum of the reference
voltages remains constant.
It is evident that the ratio of toner particles in the developer material
is controlled by adjusting the ratios of the reference voltages with
respect to one another. The foregoing is achieved by adjusting the
potentiometers associated with the respective constant voltage sources. In
this way, the reference voltages are suitably adjusted and the ratios
between each of the reference voltages corresponds to the ratios of the
toner particles dispensed into the developer material. However, the sum of
the reference voltages must remain constant so that the total
concentration of toner particles within the developer material remains
constant independent of the ratios.
In recapitulation, the development system of the present invention is
capable of forming differently colored mixtures of toner particles within
the developer housing by controlling the ratios of toner particles
dispensed therein. Thus, the ratios of the cyan, magenta and yellow toner
particles with respect to one another forms a resultant toner particle
mixture having a pre-selected color. This mixture of toner particles is
then employed to develop the electrostatic latent image recorded on the
photoconductive surface. The colors of the toner particle mixture may be
readily changes adjusting the ratios of cyan, magenta and yellow within
the developer material while maintaining the total concentration of toner
particles within the developer material constant.
It is, therefore, evident that there has been provided in accordance with
the present invention, a development system which has the capability of
forming a mixture of differently colored toner particles. The apparatus of
the present invention fully satisfies the objects, aims and advantages
hereinbefore set forth. While this invention has been described in
conjunction with a specific embodiment thereof, it is evident that many
alternatives, modifications and variations will be apparent to those
skilled in the art. Accordingly, it is intended to embrace all such
alternatives, modifications and variations that fall within the spirit and
broad scope of the appended claims.
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