Information
-
Patent Grant
-
6650851
-
Patent Number
6,650,851
-
Date Filed
Tuesday, January 22, 200222 years ago
-
Date Issued
Tuesday, November 18, 200320 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 399 50
- 399 89
- 399 168
- 399 170
- 399 171
- 250 324
- 250 325
- 250 326
- 361 225
- 361 229
- 361 230
- 361 234
-
International Classifications
-
Abstract
A combined charge/recharge xerographic power supply is provided that utilizes one power supply to drive the charge pin scorotron and recharge discorotron grids of a electrophotographic or xerographic system. The power supply uses recycled power from the pin scorotron grid to drive the discorotron grid. In particular, the power supply uses power that is dissipated in the traditional shunt regulator attached to the pin scorotron grid terminal to drive and provide active current to the discorotron grid through a series-pass regulation circuit. Thereby providing reduced electromagnetic emissions and reduced unit manufacturing costs.
Description
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to systems and apparatus for recycling scavenged power from a pin scorotron grid to drive a discorotron grid in an electrophotographic or xerographic system.
2. Description of Related Art
The xerographic imaging process is initiated by charging a charge retentive surface, such as that of a photoconductive member, to a uniform potential. The charge retentive surface is then exposed to a light image of an original document, either directly or via a digital image driven laser. Exposing the charged photoconductor to light selectively discharges areas of the charge retentive surface while allowing other areas to remain unchanged. This creates an electrostatic latent image of the document on the surface of the photoconductive member.
Developer material is then brought into contact with the surface of the photoconductor material to develop the latent image into a visible reproduction. The developer typically includes toner particles with an electrical polarity that is the same as, or that is opposite to, the polarity of the charges remaining on the photoconductive member. The polarity depends on the image profile.
A blank image receiving medium is then brought into contact with the photoreceptor and the toner particles are transferred to the image receiving medium. The toner particles forming the image on the image receiving medium are subsequently heated, thereby permanently fixing the reproduced image to the image receiving medium.
Electrophotographic or xerographic laser printers, scanners, facsimile machines and similar document reproduction devices must be able to maintain proper control over the systems of the image forming apparatus to assure high quality output images. For example, the level of electrostatic charge on the photographic member must be maintained at a certain level to be able to attract the charged toner particles.
FIG. 1
shows an exemplary embodiment of an image forming apparatus
100
having a photoreceptor
120
. The image forming apparatus
100
can be a xerographic printer or other known or later developed xerographic device. It should be appreciated that the specific structures of the image forming apparatus are not relevant to this invention and thus are not intended to limit the scope of this invention.
As shown in
FIG. 1
, one or more latent images can be generated on the photoreceptor
120
in any well known manner, by controlling one or more of a number of different developer units
150
A,
150
B,
150
C and
150
D using controller
110
.
In many xerographic machines, where high image quality targets are desired, the photoreceptor is first charged using a pin scorotron device, and then recharged, or charge leveled, by a discorotron device. For example, as shown in
FIG. 1
, in the direction of movement of the photoreceptor
120
, as indicated by the arrows, to lay a first level of toner onto the photoreceptor, the photoreceptor
120
is charged by charge/recharge device
130
E having a pin scorotron and a discorotron device. Next, the charge laid by the charging device is exposed by exposing unit
140
E and finally, the toner is developed by developing unit
150
E. The process continues in the direction of movement of the photoreceptor until all layers of toner are laid to complete an image-on-image full-color image forming process. Once the full-color image is finished, the completed image is transferred to a sheet of image recording media
160
.
The charging procedure of the charge/recharge device is performed to produce a very uniform charge on the photoreceptor. This uniform charge is especially important in the image-on-image type xerographic color machines, as shown in
FIG. 1
, where the photoreceptor may be buried under multiple layers of toner. Typically, the pin scorotron device is set to charge the photoreceptor to a voltage slightly higher than the final voltage, and the discorotron is then used to discharge the photoreceptor uniformly to the desired voltage.
FIG. 2
represents a typical configuration of a charge/recharge system
200
that is usable in a xerographic system. The left side of the configuration represents the pin scorotron device
270
, while the right side of the configuration represents the discorotron device
210
. In the pin scorotron device
270
, a high-voltage DC signal is applied to the pins
240
by a pin current supply
250
. The applied voltage is sufficiently high to cause corona discharge at the pins
240
. This discharge provides a path for a pin current to be applied to a pin scorotron grid
245
. The pin scorotron grid
245
is located between the photoreceptor
120
and the pins
240
so that the majority of the pin current is absorbed by the pin scorotron grid
245
. The grid is held at a constant voltage by the pin scorotron grid voltage control circuit
260
, which is a simple shunt regulator type circuit. The pin scorotron grid voltage control circuit
260
operates in a linear manner to achieve a variable resistance network to ground. The resistance of the pin scorotron grid voltage control circuit
260
can be controlled to either increase or decrease its voltage drop to achieve the desired grid voltage.
The discorotron device comprises a shield
225
formed of aluminum or the like and having an open lower end, a corona discharge electrode
230
, such as a glass coated tungsten wire or the like, extending within the shield
225
, and a discorotron grid
235
disposed opposite the opening of the shield
235
and between the shield
225
and the photoreceptor
120
. The discorotron device
210
operates in much the same manner as the pin scorotron device
270
. The discorotron grid
235
is typically driven by an active power source, such as the grid voltage active control circuit
215
. The discorotron high-voltage AC source
220
is connected to the corona discharge electrode
230
to produce a corona discharge.
SUMMARY OF THE INVENTION
As shown in
FIG. 2
, the pin scorotron device
270
and the discorotron device
210
are driven by separate power supplies. However, there is available power in the pin scorotron grid voltage control circuit
260
that can be recycled and used to drive and control the discorotron grid
235
.
The inventors have discerned that the power that is dissipated in the pin scorotron grid voltage control circuit
260
can be used to drive the discorotron grid
235
.
This invention provides systems and apparatus that provide reduced power dissipation in the high voltage power supply.
This invention separately provides possible direct programming of the voltage applied to the photoreceptor and the voltage between the pin scorotron grid and the discorotron grid rather than by indirect programming of the voltage applied directly to the pin scorotron grid and the discorotron grid.
This invention separately provides reduced electromagnetic emissions and increased arc immunity of the discorotron due to a better controlled xerographic current path. The reduced emissions is achieved because the discorotron grid is not driven by an active power supply.
In various exemplary embodiments of the systems and apparatus of this invention, the active power source that is typically used to drive the discorotron grid is removed. According to the systems and apparatus of this invention, the discorotron grid instead utilizes a combined circuit which uses the power dissipated in the traditional shunt regulation circuit that drives the pin scorotron grid to drive the discorotron grid through a series pass regulation circuit. The current flow of the combined circuit naturally flows in a direction to allow shunt regulation of the pin scorotron grid while also providing an active drive voltage for the discorotron grid.
These and other features and advantages of this invention are described in or are apparent from the following detailed description of the apparatus and systems according to this invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Various exemplary embodiments of this invention will be described in detail with respect to the following drawings, in which like reference numerals indicate like elements, and wherein:
FIG. 1
depicts an exemplary embodiment of a xerographic image forming apparatus in which an exemplary combined charge/recharge xerographic power supply according to this invention may be used to charge a photoreceptor;
FIG. 2
depicts an exemplary representation of a typical configuration of a charge/recharge device;
FIG. 3
depicts an exemplary representation of a typical pin scorotron grid voltage control circuit;
FIG. 4
depicts an exemplary embodiment of a charge/recharge circuit using a combined charge/recharge xerographic power supply according to this invention; and
FIG. 5
is a schematic diagram of one exemplary embodiment of the circuit elements of the combined charge/recharge xerographic power supply of
FIG. 4
according to this invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
FIG. 3
depicts in greater detail an exemplary representation of a typical grid voltage control circuit
260
. The grid voltage control circuit
260
, which is a simple shunt regulation circuit, contains seven cascaded pnp bipolar transistors that would be connected directly to the pin scorotron grid
245
. This circuit, while effective in providing adequate power to drive the pin scorotron grid
245
, is ineffective in providing reduced power dissipation in the high voltage power supply, which will improve electromagnetic emission profiles.
FIG. 4
depicts an exemplary embodiment of the charge/recharge xerographic power supply
400
according to this invention. As shown in
FIG. 4
, the charge/recharge xerographic power supply
400
comprises the pin scorotron device
270
and the discorotron device
210
. In the pin scorotron device
270
, as in conventional systems, a high-voltage DC signal is applied to the pins
240
by the pin current supply
250
. The pin scorotron grid
245
is located between the photoreceptor
120
and the pins
240
.
The discorotron device
210
, as in conventional systems, comprises the shield
225
formed of aluminum or the like and having the open lower end, the corona discharge electrode
230
, such as a glass coated tungsten wire or the like, extending within the shield
225
, and the discorotron grid
235
disposed opposite the opening of the shield
225
and between the shield and the photoreceptor
120
. The discorotron high-voltage AC source
220
is connected to the corona discharge electrode
230
to produce the corona discharge.
However, as shown in
FIG. 4
, the separate pin scorotron grid voltage control circuit
260
and the separate grid voltage active control circuit
215
of the conventional system are replaced by a single combined charge/recharge power supply
500
. That is, the pin scorotron grid
245
is held at a constant voltage and the discorotron grid
235
is driven by the combined charge/recharge power supply
500
. This configuration recycles the power provided from the pin scorotron grid
245
to drive the discorotron grid
235
through a series pass regulation circuit.
FIG. 5
shows the current flow direction and demonstrates that the current from a shunt regulation circuit naturally flows in a proper direction to allow shunt regulation of the pin scorotron grid
245
while also providing an active drive voltage for the discorotron grid
235
.
FIG. 5
shows in greater detail a schematic diagram of one exemplary embodiment of the circuit elements of the combined charge/recharge xerographic power supply
500
. The combined charge/recharge power supply
500
has two main sections
501
and
502
. The first main section
502
is a pin scorotron grid voltage control circuit
502
. The second main section
501
is a high side gate drive circuit
501
.
In
FIG. 5
, the pin current supply
250
, pins
240
and the pin scorotron grid
245
are represented by current source
554
and resistors
551
and
553
, respectively. Also in
FIG. 5
, the discorotron grid is represented by resistor
555
. The discorotron high voltage AC source
220
and corona discharge electrode
230
are not shown in
FIG. 5
because they have no particular bearing on the invention.
As shown in
FIG. 5
, the pin scorotron grid voltage control circuit
502
includes a positive terminal of a voltage source
503
connected to a first node
505
through a first resistor
504
. The negative terminal of the voltage source
503
is connected to ground
556
. Also connected at the first node
505
are a gate of a first p-channel MOSFET
507
and a second resistor
506
. A drain of the first p-channel MOSFET
507
is connected to the common ground
556
. A source of the first p-channel MOSFET
507
is connected to the drain of a second p-channel MOSFET
509
.
The second resistor
506
is connected at a second node
508
to a gate of the second p-channel MOSFET
509
and a third resistor
510
. Similarly, a source of the second p-channel MOSFET
509
is connected to a drain of a third p-channel MOSFET
511
.
A third resistor
510
is connected at a third node
512
to the gate of the third p-channel MOSFET
511
and a fourth resistor
513
. Similarly, the source of the third p-channel MOSFET
511
is connected to the drain of a fourth p-channel MOSFET
514
.
The fourth resistor
513
is connected at node
515
to the gate of the fourth p-channel MOSFET
514
and a fifth resistor
516
. Similarly, the source of the fourth p-channel MOSFET
514
and the other end of the fifth resistor
516
are connected to a fifth node
517
. Also connected at the fifth node
517
are a sixth resistor
519
, the source of a first n-channel MOSFET
520
and a first pull-up resistor
518
.
The sixth resistor
519
is connected at a sixth node
521
to the gate of the first n-channel MOSFET
520
and a seventh resistor
522
. Similarly, the drain of the first n-channel MOSFET
520
is connected to the source of a second n-channel MOSFET
523
.
An eighth resistor
527
is connected at a seventh node
524
to the seventh resistor
522
, a ninth resistor
525
and the gate of the second n-channel MOSFET
523
. Similarly, the drain of the second n-channel MOSFET
523
is connected to the ninth resistor
525
at an eighth node
526
. Also connected at the eighth node
526
is a second pull-up resistor
550
and a tenth resistor
529
, which is a part of the high side gate drive
501
. This configuration makes up the pin scorotron grid voltage control circuit
502
.
The high side gate drive circuit
501
includes the positive terminal of a variable voltage source
549
, which is connected to a ninth node
547
through an eleventh resistor
548
. The negative terminal of the variable voltage source
549
is connected to ground
556
. Also connected at the ninth node
547
is the gate of a fifth p-channel MOSFET
546
and a twelfth resistor
543
. The drain of the fifth p-channel MOSFET
546
is connected to ground
556
. Similarly, the source of the fifth p-channel MOSFET
546
is connected to a tenth node
544
. Also connected at the tenth node
544
is a first tap terminal
545
and the drain of a sixth p-channel MOSFET
542
.
A thirteenth resistor
538
is connected at an eleventh node
541
to the gate of the sixth p-channel MOSFET
542
and the twelfth resistor
543
. Similarly, the source of the sixth p-channel MOSFET
542
is connected to a twelfth node
539
. Also connected at the twelfth node
539
is a second tap terminal
540
and the drain of a seventh p-channel MOSFET
536
.
A fourteenth resistor
535
is connected at a thirteenth node
537
to the gate of a seventh p-channel MOSFET
536
and the thirteenth resistor
538
. Similarly, the source of the seventh p-channel MOSFET
536
is connected to a fourteenth node
532
. Also connected at the fourteenth node
532
is a third tap terminal
533
and the drain of the eighth p-channel MOSFET
531
.
The fourteenth resistor
535
is connected at a fourteenth node
530
to the gate of the eighth p-channel MOSFET
531
and the other end of the tenth resistor
529
. Similarly, the source of the eighth p-channel MOSFET
531
is connected to a fifteenth node
528
. Also connected at the fifteenth node
528
is a fourth tap terminal
534
and the other end of the eighth resistor
527
.
As shown in
FIG. 5
, the high side gate drive circuit
501
is connected to the pin scorotron grid voltage control
502
at the eighth and fifteenth nodes
526
and
528
, respectively.
Active current is supplied to the discorotron grid through the first pull-up resistor
518
. The first pull-up resistor
518
is connected to ground
556
through the discorotron grid terminal load resistance. In this instance, the discorotron grid terminal load of the discorotron grid
235
is shown as a fifteenth resistor
555
.
In operation of the combined charge/recharge power supply
500
, as the voltage of the variable voltage source
549
is varied, the gate-to-source voltage of the first and second n-channel MOSFETs
520
and
523
is varied through the cascaded configuration of the high side gate drive circuit
501
. Additionally, the voltage of voltage source
503
serves as the discorotron analog error voltage. The voltage supplied by the voltage source
503
serves to bias and stabilize the current supplied to the fifteenth resistor
555
.
The second pull-up resistor
550
is connected between the eighth node
526
and a sixteenth node
552
to provide a path for current flow and shunt regulation of the pin scorotron grid
245
. A sixteenth resistor
551
and the pin scorotron grid terminal load of the pin scorotron grid
245
, which is shown in
FIG. 5
as a seventeenth resistor
553
, are connected at the sixteenth node
552
. The seventeenth resistor
553
is also connected to ground
556
. A current source
554
is connected to the sixteenth resistor
551
. The current source
554
serves to drive the pin scorotron grid
245
.
There are two constraints in the circuit shown in FIG.
5
. The first constraint is that the voltage at the discorotron grid terminal load, i.e., at the fifteenth resistor
555
, cannot exceed the voltage at the pin scorotron grid terminal load, i.e., the voltage at the seventeenth resistor
553
. In this instance this means that the voltage at node
517
cannot be made more negative than the voltage at node
526
. This constraint arises because the voltage supply for the discorotron grid
235
is derived from the pin scorotron grid
245
. The second constraint stems from the same instance, in that the current flow into the terminal of the discorotron grid
235
cannot exceed the current flow from the terminal of the pin scorotron grid
245
.
The first constraint can be overcome by adding a small transformer coupled DC to DC converter in series with resistor
550
, with the positive terminal connected nearest to node
552
. This source would allow the pin scorotron grid voltage to be maintained at a less negative voltage than required at the discorotron grid terminal. Using this method, several tens of volts are capable of being added to the output of the discorotron grid
235
.
The second constraint does not particularly affect the operation of a system using this invention. This is true because, as previously discussed, the majority of the pin current is collected by the grid in the pin scorotron device
270
. Thus, only a small portion is actually used to charge the photoreceptor
120
. Similarly, only a small amount of DC current is required at the discorotron grid terminal to recharge the photoreceptor
120
.
While this invention has been described in conjunction with the exemplary embodiment outlined above, it is evident that many alternative modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiment of the inventions as set forth above, are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and the scope of the invention.
Claims
- 1. An image forming apparatus comprising:a photoreceptor; and at least one charging unit that charges and recharges the photoreceptor to produce a uniform charge on the photoreceptor, comprising: a pin scorotron device that charges the photoreceptor, and a discorotron device that recharges the charged photoreceptor, wherein a voltage from a grid of the pin scorotron device is recycled to drive a grid of the discorotron device.
- 2. The image forming apparatus of claim 1, wherein the voltage from the grid of the pin scorotron is supplied to the discorotron grid using a combined power supply circuit.
- 3. The image forming apparatus of claim 2, wherein the combined power supply circuit comprises a grid voltage control circuit that provides shunt regulation of the voltage supplied by the grid of the pin scorotron device.
- 4. The image forming apparatus of claim 2, wherein the combined power supply circuit comprises an active drive circuit that supplies an active drive voltage to the grid of the discorotron device.
- 5. The image forming apparatus of claim 2, wherein the combined power supply circuit comprises a variable voltage source that biases the voltage applied to the grid of the discorotron device.
- 6. The image forming apparatus of claim 2, wherein the combined power supply circuit comprises a voltage source that supplies a discorotron analog error voltage, wherein the discorotron analog error voltage biases and stabilizes the voltage supplied to the discorotron grid.
- 7. The image forming apparatus of claim 1, further comprising at least one controller that controls the image forming apparatus to produce a visible image.
- 8. The image forming apparatus of claim 7, further comprising at least one exposing unit usable to expose the photoreceptor based on an original document to produce a latent image on the photoreceptor.
- 9. The image forming apparatus of claim 8, further comprising at least one developing unit controlled by the at least one controller to apply a developing material to the latent image to develop the latent image on the photoreceptor into the visible image.
- 10. The image forming apparatus of claim 9, wherein the image forming apparatus brings at least one image receiving member into contact with the visible image to transfer the visible image to the at least one image receiving member.
- 11. The image forming apparatus of claim 1, further comprising at least one controller that controls the image forming apparatus to produce multi-layer images.
- 12. The image forming apparatus of claim 11, further comprising at least one exposing unit usable to expose the photoreceptor based on an original document to produce at least one latent image on the photoreceptor.
- 13. The image forming apparatus of claim 12, further comprising at least one developing unit controlled by the at least one controller to apply a developing material to the at least one latent image to develop the at least one latent image on the photoreceptor into a visible image.
- 14. The image forming apparatus of claim 13, wherein the image forming apparatus brings at least one image receiving member into contact with the visible image to transfer the visible image to the at least one image receiving member.
- 15. A charging unit that charges and recharges a photoreceptor to produce a uniform charge on the photoreceptor, comprising:a pin scorotron device that charges the photoreceptor, and a discorotron device that recharges the charged photoreceptor, wherein a voltage from a grid of the pin scorotron device is recycled to drive a grid of the discorotron device.
- 16. The charging unit of claim 15, wherein the voltage from the grid of the pin scorotron is supplied to the discorotron grid using a combined power supply circuit.
- 17. The charging unit of claim 16, wherein the combined power supply circuit comprises a grid voltage control circuit that provides shunt regulation of the voltage supplied by the grid of the pin scorotron device.
- 18. The charging unit of claim 16, wherein the combined power supply circuit comprises an active drive circuit that supplies an active drive voltage to the grid of the discorotron device.
- 19. The charging unit of claim 16, wherein the combined power supply circuit comprises a variable voltage source that biases the voltage applied to the grid of the discorotron device.
- 20. The charging unit of claim 15, wherein the combined power supply circuit comprises a voltage source that supplies a discorotron analog error voltage, wherein the discorotron analog error voltage biases and stabilizes the voltage supplied to the discorotron grid.
US Referenced Citations (1)
Number |
Name |
Date |
Kind |
4141648 |
Gaitten et al. |
Feb 1979 |
A |