Note: Descriptions are shown in the official language in which they were submitted.
16 Background o~ t]~e Invention
17 1. Field of the In~ention
18 The invention xelates to an electrophoto-
19 graphic copylng device and more specifically,
to an improvement over the charging and
21 cleaning of the support surface on which
22 the latent image of an original is developed.
23 2. Prior Art
24 The following U. S. Patents are
representative of the prior a'~t: V. S. Patents -
26 3,647,293; 3,637,306; and 3,736,055.
27 Numerous prior art teachings in
the field of electrophotographic or xerographic
BO974050
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1 copying teaches various methods and devices
2 for prep~ring the surface of a photoconductor
3 so as to obtain a latent image from an original
4 copy. Prints are then transferred from
the latent image on the surface of the photo-
6 conductor, to a transferring media.
7 To enable the development of the
8 latent image on the photoconductor and the
g transferring of said latent image to a trans-
ferring media, several stations are arranged
11 in proximity to and to cooperate with the
12 photoconductor to perform certain functions.
13 At the charging station, the photoconductor
- 14 is charged negatively. rrhe photoconductor
then moves to the exposing or imaging station
16 where a latent image-is copied from an original.
17 Next, the electrostatic :Latent image is
18 developed at a developer s~ation to form
19 a t~ner image on the photoconductor. The
; 20 toner image is then transferred from the
photoconductor to another media at ~he transferring
22 station. To complete the cycle~ the photoconductor
- 23 is erased, precleaned, and cleaned and is
24 then ready for another cycle.
Although the prior art electrophotographic
26 devices function adequately for the intended
27 purpose, several problems plague the systems.
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1 Probably one of the pressing problems is the Fact that the charging,
transferring and precleaning functions are all performed by separate
corona units at separate stations. With this type of prior art design,
the cost of the electrophotographic device is relatively high, due to
the individual cost of each corona unit. Since the general trend is to
minimize the cost of electrophotographic devices without sacrificing
efficiency, any reduction in the number of component counts in the prior
art devices will be welcome.
Another problem relating to the separate processing station is the
fact that each of the separate corona units require a separate power
supply. The aggregate cost of these power supplies further augments the
overall cost of the unit. As such, any reduction in the number of power
supplies will result in cost reduction oF the unit.
It is common knowledge, that conventional electrophotographic devices
may be either a single cycle process or a two-cycle process. In the typi-
cal two-cycle process, the photoconductor is charged, imaged and developed
during the first cyclei while the image is transferred and the photo-
conductor is cleaned in the
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B09-74-050 _ 3 _
DLM/F32
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1 second cycle. For satisfactory op~rations,
2 some of the stations which render necessary
3 functions during the copying process are
4 active during the first cycle, while others
are inactive and vice versa. On account
6 of the rapid speed at which the photoconductor
7 would access each of the stations, it is
8 therefore necessary for high speed switching
9 to occur at these stations. The conventional
60 cycle power supply which is used for
11 supplying power to these stations cannot
12 withstand high speed switching, With these
13 drawbacks, it is clear that a more efficie~t
14 device is needed.
Several attempts have been made
16 to improve the prior art electrophotographi¢
17 devices by solving some of the above-identified `~
18 problems. For example, attempts have been
19 made to combine the charge and the transfer
corona station. At first blush, this combination
21 seems to be workable and logical; since
i 22 the function of both stations is to supply
23 negative charges. However, the combination
24 instead of solving the above described problems
creates additional problems.
.
26 One of the additional problems
27 stem from the fact that the combined charge
28 transfer station is designed with a grid
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1 structure to enhance the charge operation. However, transferring media
which is fed into the machine at the charge/transfer station for trans-
ferring the latent image from the photoconductor jams into the grid
wires. This jam results in machine breakdown.
For proper operation, a negative charge has to be deposited onto
the transferring media so that the positively charged toner particles
will be attracted. With the presence of the grid assembly in the com-
bined charge/transfer station, the negative charge cannot be uniformly
distributed onto the transfer media. With an uneven distribution of
charges, the quality of the final copy is less than satisfactory.
Objects of the Invention
It is, therefore, the object of the invention to design a more
efficient, low cost electrophotographic device than has heretoFor been
possible.
It is another object of the present invention to build an electro-
photographic device with fewer corona units than has heretofor been
possible.
It is a Further object of this invention to combine the preclean
and charge corona units into a single unit.
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DLM/F33
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1 It is still a further object of the present invention to use the
transfer corona station to render the precharging and the transferring
functions.
~ummary of the Invention
The present invention overcomes the aforementioned drawbacks in
the prior art by means of a unique structural combination of processing
stations within the copying process. More specifically, the invention
discloses a unique two-cycle process for an electrophotographic copying
device. In one feature of the invention during the first cycle, the
photoconductor is overcharged to a first polarity by the combined pre- -
charge transfer corona unit (Corotron), the overcharge is then reduced
by an opposite polarity combined chargejpreclean corona unit (Scorotron).
Imaging and developing also occurs during this first cycle.
During the second cycle, the toned image is transferred to the
transferring media using the same precharge transfer corona unit (Corotron).
Following transfer, the drum is charged by the charge/preclean corona
unit to a second potential for cleaning. In order to place the second
charge level or potential on the photoconductor drum,
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DLM/F34
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1 the grid of the charge/preclean corona unit is switched to a different
voltage (either the same or opposite polarity or ground as required to
obtain best cleaning). The drum is then (optionally) erased by the
erase lamp, and cleaned by the developer.
In another feature of the invention, the photoconductor is over-
charged by a first or auxilliary corona unit at a precharged station.
The charge is then reduced to a uniform value by a second corona unit
of opposite polarity at a final charge station. The photoconductor is
then ready for imaging and developing.
In another feature of the invention, the photoconductor is charged
to a very uniform negative value by means of a positive final charge
corona unit which yields more uniform emission than a negative corona -
unit.
Another feature of the invention is the use of a gridded corona
unit (Scorotron~. to perform the preclean function. The increased
control of the preclean photoconductor voltage because of the grid
structure may eliminate the need for the preclean erase lamp function.
The improved cleaning action has reduced the hole and electron carrier
intensities in the photoconductor which also reduces the fatigue effects
of the photoconductor.
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The foregoing and other objects, features and advantages of the
invention will be apparent From the following more particular descrip-
tion of the preferred embodiment of the invention, as illustrated in
the accompanying drawings.
Brief Description of the Drawings
FIGURES 1 and 3 are a schematic diagram of a two-cycle process
electrophotographic machine showing a plurality of processing stations
which incorporates the present invention.
FIGURE 2 is a schematic diagram showing the control circuit which
changes the voltage of the control grid in the combined charge/preclean
station.
Detailed Description
` The term corotron as used in this application means a type of
corona unit having either limited or no grid structure. In effect the
corotron may be cons;dered analogous to a current source.
The term scorotron as used in this application means a type of
corona unit having a grid structure. The scorotron may be considered as
a voltage source.
For explanation purposes, the photoconductor in the preferred
embodiment
B09-74-050 _ 8 _
DLM/F36
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1 of the present invention will be described
2 as a rota~ing drum. Elowever, this should
3 not be cons-trued as a limitation on the
4 scope of the invention; since it is well
known in the art to design a pho-toconductor
having a different shape, size and mechanical
7 configuration. For example, the photo-
8 conductor may be a continuous belt or a plate
9 rather than a rotating drum structure.
Although the preferred embodiment
11 of the invention is described in association
12 with a two-cycle copying process, this should
13 be interpreted as only illustrative rather
14 than restrictive, since it would be obvious
for one skilled in the art to modify the
16 inventive feature as disclosed hereinafter
17 to malse said concept operable in a one-cycle
18 copying process.
19 Referring now to FIGURE lf a pictorial
view of an electrophotographic copying system
21 10 which embodies the present invention
22 is shown. A cylindrical drum 12 herein-
23 after called a photoconductor is mounted
24 for rotation on shaft 14 and having on its
ouker periphery a photoconductive insulating
26 layer which contains an organic ox inorganic
27 photoconductor material. The drum 12 is
i Z8 ro~ated to bring the photoconductive layer
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1 -to various stations associa-ted with the
2 electrophot'ographic process; each of said
3 stations being positioned in proximity to
4 the rotating drum.
A negative corotron 18 is positioned
6 within the orbit of cylindrical drum 12
7 to define the so-called precharge/transfer
8 station 32. Negative corotron 18 of the
9 precharge/transfer station serves two functions,
namely: to deposit an excess of negative
11 ions on the surface of the photoconductor
12 (for example, -1300 volts) and to deposit
13 negative ions-on a transferring media, for
14 example, paper so as to transEer a latent
- 15 toner image from the surEace ofl the photoconductor.
16 As will be explained subsequently, the negative
17 charge which is deposited on the photoconductor
' 18 by nega~ive corotron 18 is rough; i.e.,
19 the charge is unevenly distxibuted on the '
surface of the photoconductor.
21 After precharge/transfer station
22 32, the next sta-tion in'order is the combined
23 final charge/preclean station 20. Finally,
24 charge/preclean station 20 is the facility
which supplies the final charge to the surface
26 of the photoconductor'and renders the preclean
27 function. This final charge is referred
28 to as smooth due to the fact that the charge
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1 is evenly distributed over the surface of the photoconductor because
of the cut-off characteristic produced by the control grid. As will
be explained subsequently5 the polarity of the emission wires in the
final charge/preclean corona is opposite to the voltage applied to the
precharge/transfer corona unit. In the preferred embodiment, a posi-
tive emission voltage is used so that positive ions are generated.
Final charge/preclean station 20 comprises a positive scorotron 22.
Scorotron 22 supplies positive ions at station 20. The positive ions
reduce the rough charge on the photoconductor surface to a smooth charge.
Grid structure 24 is positioned between scorotron 22 and the photocon-
ductor 12. The function of grid structure 24 is to control the flow of
positive ions which are deposited on photoconductor 12 and hence, the
resulting photoconductor voltage.
As will be expl~ined subsequently, and as shown in FIGURE 2, a
switching circuit is connected to grid 24 to control the voltage on
the grid. For example, in one instance the voltage on the gris is very
negative (approximately -700 volts), while in another instance the
grid is slightly positive
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1 (approximately +50 volts). Still in another
2 ins-tance, the voltage may be slightly negative
3 (approximately -50 volts) or ground.
4 The other station in order is
the so-called interimage 26. The interimage
6 stati~n comprises high intensity lamp 28
7 and the function is to erase images on the
8 sides of the photoconductor depending on
9 the size of the document to be copied. During
the second cycle, this lamp can be option-
11 ally turned on to erase the photoconductor
12 to aid in the cleaning process.
13 The next station in order is the
14 image station 30. Imàge station 30 COmpriSQS
a conventional optical system Ihich functions
16 to transfer a latent image of a document
17 onto the photoconductor. With the latent
18 image on the photoconductor, the next station
19 in line is the developer cleaner station 60.
; 20 Developer cleaner sta~ion 60 is conventional.
21- For example, the developer cleaner station
22 is analogous to the developer cleaner station
23 as disclosed in ~he above-identified U. S. Patent
24 3,637,306, entitled "Copying System Featuring
Alternate Developing and Cleaning of Successive
26 Image Areas for Photoconductor" and assigned
27 to the same assignee o~ the present invention.
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1 Referring now -to FIGURE 2, the
2 controlled means which controls the negative
3 corotron 18 of precharged station 32 is
4 disclosed. Also the control means for switching
the polarity of grid structure 24 from a
first potential to a second potential is
7 disclosed.
8 As was mentioned previously, negative
9 corotron 18 of precharge/transfer station 32
supplies negative ions to the photoconductor
11 in one cycle and in another cycle supplies
12 negative ions to a transfer medium (not
. 13 shown). In order to supply negative ions,
14 a negative high voltage power supply 34
. 15 is connected to corotron 18. Il
16 In one embodiment of precharge/transfer
. 17 station 32 the same amount of negative ions
~ 18 (negative charge) was applied to the photoconductor
: 19 and the.transfer media. With this design
~ there is no need for a switching mechanism.
- 21 In an alternative embodiment, the negative
22 charge which is applied to the photoconductor `
23 and the trans-Eer media was different. This
: 24 design requires a switching means analogous
to he one which will be subsequently described.
26 Still re~erring to FIG~RE 2, grid
27 structure 24 functions as a limiting means
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; 28 for controlling the positive ion (positive
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1 charge) which is deposite~ on the surface
2 of photoconductor 12 from scorotron 22. Tne
3 resultlng photoconductor voltage is a strong
4 function of the grid voltage. In order
S to effectuate this limiting or controlling
6 function, a switching means is operably
7 connected to the grid for switching its
8 voltage between two (or more) levels.
9 Switching means 36 comprises a
diode 38 hereinaf~er called unidirectional
11 device 38. One terminal of the unidirectional
12 device is connected to grid 24 while the
13 other terminal is connected to positive
14 terminal 40 hereinafter called third reference
voltage source 40. Third reference voltage
16 source 40 may be any positive value, negative
17 value or ground. For example, in ~he prQferred
18 embodiment of this inven~ion the value was
19 ground.
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ResistQr 42 hereinafter called
21 third resistor means 42 connects third reference
22 voltage source 40 to a lower or equal potential.
23 In the preferred embodiment of this invention,
24 the low potential is ground. Likewise,
another resistor 44 herainafter called second
26 resistor means 44 connects third referenae
27 vol~age mean~ 40 to a higher potential.
28 In the preferred embodiment o~ the invention,
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1 the higher potential was chosen to be 120
2 volts.
3 In an alternate embodiment of
4 the invention, third reference voltage source 40
was connected to a switchable preclean level
6 suppl~. The preclean level supply can be
7 adjusted to one of a plurality of voltage
8 potentials. For example, typical voltage
9 levels would be ~100 volts to -100 volts
or ground.
11 Reference voltage source 46 hereinaftar
12 called first reference voltage source 46
13 is positioned in parallel with third reference
14 voltage source 40. The potential of first
reference voltage source 46 is negative.
16 In the preferred embodiment of this invention,
17 a 1000 volts negative potential was chosen.
18 First reference voltage source 46 was established
19 by a conventional bank of neon tubes 48.
Of course, it would be obvious to one skilled
21 in the art to substitute conventional devices
22 to establish first reference voltage source 46
23 without departing from the scope of this
24 invention.
Resistor 50 hereinafter called
26 first resistor means 50 is connected in
27 series with first reference volta~e source 46
` 28 ~so as to establish second voltage source 52.
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1 In -the preferred embodiment of this invention,
2 source 52 is chosen to be 1500 volts negative.
3 In an alternate embodiment, second voltage
4 source 52 was connected to a negative grid
supply means. The negative grid supply
means has a typical value of approximately
7 -1500 volts. Switching means 54 interconnects
8 unidirectional device 38 and first reference
9 voltage source 46. The connection is such
that by activating switching means 54 either
11 the voltage at third reference voltage source 40
12 or the voltage at first reference voltage
13 means 46 is rendered operative. Of course,
14 several conventional switching devices may
be used for switching means 54 ! However,
16 in the preferred embodiment of this invention,
17 switching means 54 was a high voltage read
18 relay switch. Positive high vol-tage supply 58
19 supplies power to scorotron 22 via terminal 56.
This completes the detailed description
21 of the preferred embodiment of -the invention.
- 22 In the preferred embodiment, high
23 voltage corona supplies 34 and 54 are current
24 regulated so that they deliver a constant
total current to the corona emission wires.
~l 26 Operation
27 In describing the operation of
28 the two-cycle process, the position of the
,
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BO974050 -16-
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1 processing station in relation with rotating cylindrical drum 12 will
be equated with positions on the face of a clock (see FIGURES 1 and 3).
In operation, cylindrical drum 12 rotates in the direction shown by
arrow 16. During the first cycle of the two-cycle process, step lA
occurs at 6:00. At 6:00, the precharge/transfer constant current nega-
tive corona unit 18 of precharge/transfer station 32 will precharge
the photoconductor of cylindrical drum 12 to a rough negative voltage.
For example, the overcharge voltage is -1300 volts.
The second step lB occurs at 11:00 where the final charge/preclean
scorotron 22 of final charge/preclean station 20 reduces the photocon- `
ductor charge to approximately -800 volts as controlled by grid 24. At
2:00 step 2 occurs; lamp 28 of interimage station 26 performs the inter-
image erase. At 3:00, step 3 occurs; the photoconductor is imaged at
image station 30, such that the photoconductor charge i~ a black image
is approximately -720 volts, the photoconductor charge in a gray image
is approximately -400 volts, and the erase background and white charge
is from -170 to -200 volts.
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B09-74-050 - 17 -
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1 At approximately ~:00 step 4 occurs;
2 the latent image is developed by magnetic
3 brush 58 of developer/cleaner station 60.
4 The bias of magnetic brush 58 is approximately
-300 volts. Thus, magnetic brush 58 is
6 positive relative to the latent image and
7 negative relative to the erased background.
8 This completes the first drum cycle.
9 - At 6:00 during the second drum
cycle step 5 occurs; transfer media 62 is
11 gated so that it moves between the corona
12 and the drum. Negative corotron 18 of precharge/
13 transfer station 3? provides the electrostatic
14 force causing the toned image on cyclindrical
drum 12 to be transferxecl to transfer media 62.
- 16 The transfer media for example, paper, is
17 held against drum 12 by electrostatic force
; 18 only. In one embodiment of the invention,
19 the same corotron current setting was used
for both precharge and transfer functions
21 so that switching the current level was
22 not necessary except at the end of a multi-
23 copy run when the unit must be turned oEf .!
~ 24 for the final clean cycle. Of course, one.
- 25 alternative embodiment would be to switch
26 the current setting depending on whether
27 the precharge function or the transfer function
28 was being performed.
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1 ~t approximately 11:00 during the second drum cycle step 6 occurs;
switching means 36 switches grid 2~ so that the voltage from third re-
ference source 40 appears on the photoconductor surface of rotating drum
12 so that the charge on said drum is reduced to a voltage near ground.
This change in voltage accomplishes the preclean function.
At approximately 1:00 step 7 occurs, lamp 28 of interimage station
26 is energized to illuminate the entire photoconductor surface of rota-
ting drum 12 which changes the voltage to approximately O volts. This
is an optional step and may be eliminated because of the improved con- -
trol of the preclean photoconductor voltage achieved with the gridded
preclean corona unit. At 3:00 during the second cycle, imaging station
30 may be on or off. The photoconductor then rotates to developer/
cleaner station 60 where`magnetic brush 58 removes residual toner from
the photoconductor surface. This completes the two-cycle process. ~-
This unique configuration as described above has distinct advantages ~ -
over prior art configurations, in that the requirement of high voltage
ferro switching in short time intervals is eliminated. In addition,
the combination of the two corona units
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1 requires one less power supply and one less corona unit for a sizable
cost reduction.
Another advantage of this configuration is the fact that the trans-
fer corona unit can be made smaller than would have been possible if
the combined charge and transfer corona units had been used. This is
important in that significant reduction in the overall machine dimension
is achieved.
While the invention has been particularly shown and described with
reference to a preferred embodiment thereof, it will be understood by
those skilled in the art that various changes in form and details may
be made therein without departing from the spirit and scope of the in-
vention.
B09-74-050 - 20 -
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