Information
-
Patent Grant
-
6466764
-
Patent Number
6,466,764
-
Date Filed
Monday, March 19, 200123 years ago
-
Date Issued
Tuesday, October 15, 200221 years ago
-
Inventors
-
Original Assignees
-
Examiners
-
CPC
-
US Classifications
Field of Search
US
- 399 361
- 399 381
- 399 388
- 399 390
- 399 401
- 399 402
-
International Classifications
-
Abstract
Electrophotographic printers are provided with a roller type, sheet pretreatment device for providing successive sheets with substantially the same moisture content and, hence, substantially the same electrostatic properties.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to electrophotographic printers. More particularly, it relates to apparatus and techniques for improving the print quality of such printers by preconditioning the print media with heat and/or pressure.
2. Prior Art
Electrophotographic printing processes generally comprise the steps of using a laser beam to form an electrical latent image on a charged photoconductor drum, developing that latent image with a toner, transferring the resultant toner image onto a transfer substrate such as a sheet of paper and then fusing the toner image to the transfer substrate by means of heat, pressure and the like. Those skilled in this art will appreciate that the toner can be particulate or liquid in nature. In either case the toner fusing operation becomes especially involved in the case of electrophotographic color printing processes wherein images employing various colors, e.g., cyan, yellow, magenta and black (C, Y, M, K) toner particles are successively printed on a photoconductive drum and then transferred from the drum to a print media. In such processes, each successive color image printed on the sheet of print media (e.g., paper) is usually individually fused thereon.
It is well known that the quality of electrophotographic printing processes can vary with changes in ambient temperature and relative humidity. Print quality also can vary as the electrophotographic printer itself heats up during periods of extended use. These variations are generally related to the moisture content of the individual sheets of print media undergoing electrophotographic printing. For example, it is well known that the physical size of a sheet of paper (and especially bond paper) can vary with the paper's moisture content. A standard sheet of 8½×11 inch bond paper, for example, can shrink as much as a quarter of an inch in either dimension as it goes through an electrophotographic printer's pressure/fuser assembly. Such changes in paper size are sometimes annoying to a reader. They can be especially annoying in duplex printing situations where a sheet of paper receives printed information on a first side and then undergoes a heating and pressing operation that fuses the toner to the paper. This heating and pressing operation shrinks the paper. The sheet of paper then undergoes a duplex printing operation wherein the second side of the sheet receives printed information. In this circumstance the printed information on the second side of some kinds of paper will tend to “show through” the paper at the borders of the first side. This condition can create visual effects that vary from reader annoyance, to unprofessional appearance, to commercial unacceptability.
Those skilled in this art also will appreciate that, in order to carry out a toner transfer, the print media passes between a toner transfer roller and the photoconductor drum. During the toner transfer, the transfer roller electrostatically attracts toner away from the surface of the photoconductor drum and onto the surface of the print media (e.g., a sheet of paper). The electrical resistivity of the print media is one of the many factors involved in this electrostatic transfer of the toner from the drum to the media. The sheet's electrical resistivity is, in turn, especially effected by the moisture content of the media. Therefore, one of the primary objects of this invention is to precondition each sheet of print media (e.g., each sheet of paper) in a substantially uniform manner so that successive sheets of that print media will have virtually the same moisture content (and hence virtually the same electrical resistivity and hence the same electrostatic properties) as they pass between the transfer roller and the photoconductor drum. This uniformity of electrostatic properties of each successive sheet of print media helps to provide more uniform and, hence better, electrophotographic printing results.
SUMMARY OF THE INVENTION
This invention is particularly concerned with the use of pressure/heater devices to pretreat successive sheets of media (e.g., successive sheets of paper) that undergo electrophotographic printing processes. This pressure/heat pretreatment can be introduced into an otherwise conventional electrophotographic printing process. It takes place prior to the point in such a process where the toner image is transferred to the paper. The herein described pretreatment process serves two purposes. It preshrinks successive sheets of print media (e.g., paper) to a uniform size. Thus, it serves to minimize subsequent sheet shrinkage after the toner has been applied to one side of the paper and then duplexed. Applicant's pressure/heat pretreatment also serves to provide successive sheets passing through an electrophotographic printing apparatus with substantially the same moisture content—and hence substantially the same electrostatic properties. This is especially useful in uniformly transferring successive toner images from the photoconductor drum to successive sheets of paper as said sheets of paper pass between the photoconductor drum and the transfer roller.
The electrophotographic printing apparatus of this patent disclosure is especially characterized by the fact that it is provided with a pressure/heater device that is preferably comprised of two opposing rollers that roll over each other in pressured, rolling contact. In some of the preferred embodiments of this invention, at least one of the two opposing rollers will contain a heating device such as an inductive heater element or a halogen tube. Use of two opposing rollers wherein each of the two opposing rollers contains a heating device is also contemplated in the practice of this invention. Use of a powered heater roller also is contemplated. Use of two separately powered rollers is also possible, but not preferred.
The temperature and pressure conditions existing in the pressure/heater devices of this patent disclosure (e.g., pressure heater device
54
/
56
of FIG.
2
and/or pressure heater device
46
/
48
of
FIG. 3
) can vary considerably. They can vary with respect to each other and they can vary with respect to the residence time of a sheet of print media (e.g., a sheet of 8½×11 inch paper) in said pressure/heater devices. Generally speaking, the temperature of the roller surface of the heater roller should serve to soften (but not melt) a toner material. Generally speaking, such temperatures may vary between about 150 and about 350° F. Temperatures between about 250 and 350° F. are however somewhat preferred in those cases where polymer based toner particles are being employed in the inkjet printing process. The pressure conditions experienced by a sheet of media, and especially a sheet of paper, will generally range between about 232 and about 472 psi. Pressures between about 400 and about 472 psi are preferred, especially when the heater roller temperature is between about 329° F. and about 374° F.
The residence time of a sheet of media in a pressure/heater device of this patent disclosure is largely determined by the angular velocity of a powered drive roller. Typical residence times for an 8½×11 inch sheet of paper will be from about 2 to about 8 seconds. Residence times of about 3 to about 6 seconds are more preferred. These preferred residence times generally correspond to 8½×11 inch paper processing rates of about 16 to about 32 sheets per minute. Generally speaking, the shorter residence times will be used as the operating temperature is raised. For example, the lower end of the residence time range (e.g., 2-3 seconds) will generally be preferred as the temperature is raised to the upper regions of its range (e.g., 250-350° F.).
Thus, the electrophotographic printing apparatus of this patent disclosure will preferably comprise: (1) a laser printing device for creating a latent image on a photoconductor drum, (2) a sheet transport system leading to a toner transfer zone, (3) a photoconductor drum whose outside circumferential surface defines a top side of the toner transfer zone, (4) a transfer roller whose outside circumferential surface defines a bottom side of the toner transfer zone, and wherein the sheet transfer system leading to the toner transfer zone further comprises a (5) sheet pretreatment device for providing pressure and heat to successive sheets in order to provide said sheets with substantially the same moisture content and, hence, substantially the same electrostatic properties. Such an electrophotographic printing apparatus will preferably have two opposing rollers that create a nip and wherein at least one of the two opposing rollers contains a heating device such as an inductive heater element or halogen tube. In other, less preferred, embodiments of this invention, the electrophotographic printing apparatus pretreatment device may have two opposing rollers that each contain a heating device and its own means of powered rotation.
The apparatus and methods of this patent disclosure are especially well suited to electrophotographic printing processes wherein the sheet pretreatment process and the toner fixing step are carried out by the same pressure/heater (fuser) device. For example, such an electrophotographic apparatus might comprise: (1) a laser device for creating an image on a photoconductor drum, (2) a toner hopper for storing and dispensing toner particles on to the photoconductor drum, (3) a first sheet transport system that leads from a sheet dispenser tray to the pressure/heater device and then to an internal sheet collection tray (which may also help perform a duplexing function), (4) a second sheet transport system that carries a sheet from the internal sheet collection tray to the toner transfer zone, (5) a photoconductor drum whose outside surface defines a first or top end of the toner transfer zone, (6) a transfer roller whose outside surface defines a second or bottom end of the toner transfer zone, (7) a second sheet transport system that leads from the toner transfer zone to the pressure/heater (fuser) device and (8) a pressure/heater (fuser) device having a first mode of operation for providing successive sheets with substantially the same moisture content and a second mode of operation for fixing the toner to the sheet.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a cross sectional view of a generalized, prior art electrophotographic printer.
FIG. 2
is a cross sectional view of an electrophotographic printer provided with a sheet pretreatment device made and positioned in accordance with the teachings of a first embodiment of this invention.
FIG. 3
is a cross sectional view of an electrophotographic printer made according to a second embodiment of this invention wherein said printer employs a prior art fuser assembly as the electrophotographic printer's sheet pretreatment device and a sheet duplexing tray.
FIG. 4
is a cross sectional view of an electrophotographic printer made according to a third embodiment of this invention wherein said printer employs a prior art fuser assembly as the electrophotographic printer's sheet pretreatment device and uses a sheet dispensing tray and sheet collection tray, but does not employ a duplexing tray such as that shown in FIG.
3
.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1
shows a cross sectional view of a highly generalized prior art electrophotographic printer
10
. This prior art electrophotographic printer
10
contains a photoconductor drum
12
upon which a latent electrostatic image is placed, and thereafter removed, by methods well known to the electrophotographic printing arts. For example, a charge roller
14
can be used to charge the surface of the photoconductor drum
12
to a predetermined voltage. A laser scanner
15
emits a laser beam
16
which is pulsed on and off as it is swept across the surface of the photoconductor drum
12
and thereby discharging select portions of said surface according to a computer program. The selectively discharged portions of the surface of the drum
12
constitute a latent electrostatic image. The photoconductor drum
12
rotates (e.g., in the clockwise direction suggested by arrow
18
) into contact with a developer roller
20
.
The developer roller
20
is used to develop the latent electrostatic image in those places where the surface of the photoconductor drum
12
has been selectively discharged by the laser beam
16
. Charged toner particles
22
having magnetic properties, stored in a toner hopper
24
of an electrophotographic print cartridge
26
, are moved from within the toner hopper
24
to the developer roller
20
. For example, a magnet (not shown) located within the developer roller
20
can be used to magnetically attract charged toner particles
22
to the surface of the developer roller
20
. As the developer roller
20
rotates (e.g., in the counterclockwise direction
25
shown in FIG.
1
), the charged toner particles
22
on the surface of the developer roller
20
are electrostatically drawn across a gap between the surface of the photoconductor drum
12
and the surface of the developer roller
20
and thereby develop the latent electrostatic image in those areas of the photoconductor drum
12
that were not discharged by the laser beam
16
. This developed electrostatic image is then ready to be transferred to a print medium such as a sheet of paper.
To this end, the printer
10
is shown provided with a stack of print media such as a stack of sheets of paper. Individual sheets
28
of the print media (paper) are individually unloaded from a media holding tray
30
by a pickup roller
32
. Such a sheet of paper
28
then follows a media path
29
defined within the electrophotographic printer
10
by an array of media handling and guiding devices such as rollers, belts, side plate guides and the like. Thus, a sheet of paper
28
is taken from tray
30
and made to traverse the electrophotographic printer
10
via media path
29
. It is ultimately delivered to an output tray
33
. Such a media path
29
may, however, vary somewhat. For example, after being introduced into the printer
10
, the print media
28
may move through drive rollers
34
A and
34
B in a manner such that arrival of the leading edge of the print media
28
at a predetermined place below the photoconductor drum
12
is synchronized with rotation of that drum. Thus, a region on the surface of the photoconductor drum
12
carrying a latent electrostatic image can be associated with a specific region on the print media
28
. As the photoconductor drum
12
continues to rotate (e.g., in a clockwise direction
18
), those portions of the photoconductor drum
12
having toner particles
22
adhering to the discharged areas of the drum's surface are transferred to select regions of the print media
28
.
In order to accomplish this toner transfer, the print media
28
passes over a transfer roller
36
and under the photoconductor drum
12
. That is to say that the print media passes between the transfer roller
36
and the photoconductor drum
12
. Thus, the vertical space between the bottom of the drum
12
and the top of the transfer roller
36
may be regarded as a vertical, toner transfer zone. In this circumstance, the transfer roller
36
electrostatically attracts toner particles
22
away from the surface of the photoconductor drum
12
and onto the top surface of the print media
28
. Among the many factors involved, this toner transfer from the photoconductor drum
12
to the top of the paper
28
is effected by the electrical resistivity of the paper. This electrical resistivity is, in turn, effected by the moisture content of the paper. This electrical resistivity of the paper effects its electrostatic properties. Thus, one of the primary objects of this invention is to precondition each sheet of paper in a uniform manner so that successive sheets of paper will have the same moisture content—and hence the same electrical resistivity—and hence the same electrostatic properties—as they pass between the transfer roller
36
and the photoconductor drum
12
. This uniformity of the electrostatic properties of each successive sheet of paper helps to provide more uniform, and hence better, print results. And, as previously noted, this pressure/heater pretreatment also serves to shrink each successive sheet to a size that does not vary as much as unshrunken sheets during subsequent printing and fusing operations. Again, this advantage is especially useful in electrophotographic color printing operations where a sheet of print media experiences several successive toner laydown operations that each have a tendency to shrink a sheet of paper.
Transfer of toner particles
22
from the surface of photoconductor drum
12
to the surface of the print media
28
does not, however, occur with one hundred percent efficiency. Therefore, some toner particles will remain on the surface of photoconductor drum
12
. As photoconductor drum
12
continues to rotate, those untransferred toner particles that continue to adhere to the surface of the drum
12
are removed by a cleaning blade
38
and deposited in a toner waste hopper
40
. Having had the untransferred toner particles wiped from its surface, the photoconductor drum
12
is again ready to be charged by charge roller
14
to complete the photoconductor drum's rotation cycle.
Meanwhile, as the print media
28
moves further along the media path
29
(i.e., past photoconductor drum
12
and transfer roller
36
), a conveyer belt
42
receives and delivers the print-carrying media
28
to an inlet guide or ramp
44
that leads to a fuser roller
46
and pressure roller
48
. The print media
28
passes between the fuser roller
46
and pressure roller
48
under conditions of both pressure and heat. Preferably, the pressure roller
48
provides a powered, pressured rolling interface relationship between the two rotating roller surfaces. It also provides the motive force needed to pull the print media
28
through the fuser roller
46
and pressure roller
48
.
This pressure/fusing step is essential to virtually all electrophotographic printing processes. In it, the toner that was transferred, in imagewise fashion, from the photoconductor drum
12
onto the print media
28
is fixed, by a combination of heat and pressure, to form a permanent image on the print media. The heater or fuser component (fuser roller)
46
of the pressure/fuser roller system serves to soften toner particles so that the fusing of the toner to the paper can occur at relatively low pressures. As was previously noted, the temperature, pressure and residence time conditions can vary within certain ranges that can be established by those skilled in the electrophotographic printer manufacturing arts.
Again, only the most basic architecture of such a fuser device is shown in FIG.
1
. For the sake of simplicity, it is depicted as being comprised of a fuser roller
46
and a pressure roller
48
. Preferably, the pressure roller
48
is powered and rolls against (and thereby drives) the fuser roller
46
. Regardless of which roller is serving as a powered driver roller, the image-bearing sheet of print media passes through a nip produced between the two rollers. A heat source, such as an induction heater element or a halogen lamp, is preferably mounted in a hollow shaft of such a fuser roller
46
. Thus, a combination of heat from the fuser roller and pressure from the pressure roller serve to fix the toner to form a permanent image on the media
28
. Thereafter, an output roller system
50
/
52
(comprised of a top roller
50
turning in a clockwise manner and a bottom roller
52
turning in a counterclockwise manner) nips and pulls the print media
28
further along the media path
29
and eventually helps deposit said sheet in the output tray
33
. Preferably, the output tray
33
lies outside the housing of the printer
10
for easy manual access to the finished print product.
FIG. 2
shows an electrophotographic printer
10
A that is similar to the prior art electrophotographic printer
10
shown in FIG.
1
. The main difference is that the printer
10
A of
FIG. 2
is provided with a heater/pressure roller device
54
/
56
. For the purposes of this patent disclosure such devices also may be referred to as “roller type” pretreatment devices. They are positioned to pretreat a sheet of paper or other print media before it passes through a toner transfer zone located between the bottom outside or circumferential surface of a photoconductor drum
12
and the top or outside or circumferential surface of a transfer roller
36
. The temperature, pressure and sheet residence time conditions under which this heater/pressure roller device
54
/
56
operates are as previously described. In any case, this heater/pressure roller device
54
/
56
has a heater roller
54
and a pressure roller
56
. These two rollers also contact each other to create a nip into which a sheet of media, such as a sheet of paper
28
, is pulled. The heater roller
54
turns in a counterclockwise direction while the pressure roller
56
turns in a clockwise direction. Thus a sheet of paper
28
is nipped and pulled through the heater roller
54
, pressure roller
56
interface by the powered roller action delivered by the heater/pressure roller device
54
/
56
. In a particularly preferred embodiment of this invention, the heater/pressure roller device
54
/
56
is of the same type as the prior art fuser roller
46
and pressure roller
48
device described with respect to FIG.
1
. This circumstance will serve to lower the cost of applicant's printer
10
A since separate and distinct heater/pressure roller devices need not be designed and constructed.
In any case, the heater roller
54
depicted in
FIG. 2
is shown provided with a heat source
58
such as a halogen tube, induction heater element and the like. It also should be appreciated that either or both of the rollers
54
and
56
can have such a heater device. Thus, the pressure roller
56
is shown provided (in phantom lines) with a heater
60
as well. Similarly, either or both of the rollers
54
and
56
can supply the pressured rolling action that pulls the media sheet
28
through the roller
54
, roller
56
interface. Thus, each sheet in a series of sheets taken from tray
30
will be subjected to the same heat, pressure and residence time in the heater/pressure device
54
/
56
. Consequently, the moisture content of each successive sheet will be made more uniform relative to successive sheets taken from a stack of that media. Thereafter, an output roller system
50
/
52
delivers the sheet to the output tray
33
.
FIG. 3
shows a preferred embodiment of this invention wherein an electrophotographic printer
10
B is provided with a fuser roller
46
/pressure roller
48
device (such as that shown in
FIG. 1
) that performs two distinct functions. First, the fuser roller
46
/pressure roller
48
device is used to precondition each successive sheet of paper that is fed into the electrophotographic printer
10
B. In order to feed a series of paper sheets into said printer, a tray
33
will have to be properly positioned to perform this paper feeding function. Thus,
FIG. 3
shows a tray
33
that is capable of being placed in a feed mode or in a receiving mode. The feed mode is shown by drawing the tray
33
in solid lines. In this mode, the tray
33
is positioned such that a sheet of paper is picked from the top of a stack of such papers by a pick roller
58
. The sheet is inserted into the printer
10
B by virtue of the fact that an input/output roller system
50
/
52
is rotated in a manner that nips a sheet of paper and transfers it from the tray
33
and into the printer
10
B.
Once inside the printer
10
B, a given sheet of paper follows a media path that includes passage through the printer's fuser/pressure device
46
/
48
. Thus each sheet is subjected to virtually the same heat and pressure conditions before any toner is placed on said sheet. These heat and pressure conditions tend to provide each successive sheet with the same moisture content—and hence the same electrostatic properties. As was previously noted, this leads to more uniform print results as a series of sheets of paper undergo electrophotographic printing. After passing through the fuser/pressure device,
46
/
48
the sheet is sent along a first part MP
1
of a media path in the direction of arrow
63
and delivered to a duplexing tray
62
. After a defined series of sheets of paper have been delivered to the duplexing tray
62
, the electrophotographic printer
10
B is switched to its printing mode.
In this printing mode, a top sheet of paper is taken from the duplexing tray
62
(e.g., by a pick roller
64
) and, in the direction generally indicated by arrow
65
, delivered via a second media path part MP
2
to a powered roller
66
which, in turn, delivers the sheet of paper to the previously described toner transfer space between the photoconductor drum
12
and the transfer roller
36
. This sheet movement takes place in the direction generally indicated by arrow
67
, along a third part MP
3
of the media path. This third part MP
3
of the media path may, or may not, include the sheet's passage through guide rollers
34
. In any case, because each sheet has been recently subjected to the same pressure and heat conditions in the fuser roller and pressure roller
48
, each sheet arriving at the space between the transfer roller
36
and photoconductor drum
12
will have virtually the same moisture content—and hence virtually the same electrostatic properties. As was previously noted, successive sheets of paper having the same electrostatic properties will produce more uniform toner transfers between the photoconductor drum
12
and successive sheets of paper.
After receiving a toner image from the photoconductor drum
12
in the toner transfer zone, a sheet of paper is sent in the direction indicated by arrow
69
along a fourth part MP
4
of the media path. For example, it can be sent, via a belt
42
, and a ramp
44
, to the same combined action fuser roller
46
and pressure roller
48
that processed the incoming sheet. In this second or printing mode of operation, however, the rollers
46
and
48
are turning in the opposite direction that said rollers were turning when these same rollers
46
and
48
processed the incoming sheets. The general ability of this printer device
10
B to change the media flow direction in this roller system is indicated by the respective two-headed arrows in fuser roller
46
and pressure roller
48
. In this second mode of operation, the image on the paper is fused to said paper by the heat and pressure conditions created by the combined action of the fuser or heater roller
46
and the pressure roller
48
. The pressure, heat and residence time conditions existent when the toner is being fused to the paper may be the same as, or different from, the heat, pressure and residence conditions existing in the heater/pressure device
46
/
48
when the paper was originally taken into the printer
10
. In either case these pressure, heat and residence times will still generally fall within the ranges previously described in this patent disclosure. It might also be noted that in this second mode of operation the tray
33
can be moved to a position
33
A where it can better serve as a sheet collection tray.
FIG. 4
is a cross sectional view of an electrophotographic printer
10
C made according to another embodiment of this invention wherein said printer employs the same fuser roller/pressure roller device
46
/
48
as the electrophotographic printer's sheet pretreatment device and as its toner fuser. This printer
10
C also uses a sheet dispensing tray
70
and a sheet collection tray
76
. In this embodiment, the printer may or may not employ a duplexing tray such as that shown in
FIG. 3
(as duplexing tray
62
). Be that as it may, the fuser roller
46
/pressure roller
48
device receives a sheet of print media from a dispensing tray
70
. Such a sheet may be picked up by a pickup roller
72
and directed (in the direction suggested by arrow
61
) over a first part MP
1
of a media path through the printer
10
C by a sheet handling system that may include a roller
74
. Such a sheet then passes through a first or left side nip of an input/output roller system
50
/
52
. That is to say that said roller system
50
/
52
is operating in a first operating mode wherein the top roller
50
is turning in a counterclockwise direction while the bottom roller
52
is turning in a clockwise direction. Hence a first nip is formed on the left side of the roller system
50
/
52
. Thus, a sheet traveling over media path MP
1
is fed into this first nip.
The sheet is then fed into the fuser roller
46
/pressure roller
48
device while it too is in its first mode of operation. That is to say that the fuser roller
46
is turning clockwise while the pressure roller
48
is turning counterclockwise. The heat and pressure conditions are as previously described. After passing through this
46
/
48
roller device the sheet follows a media path MP
2
, MP
3
and MP
4
(e.g., over rollers
64
(A),
64
(B) and
66
) that leads up to the printer's toner transfer zone. This path may or may not include a duplexing tray
62
. Thus each sheet is subjected to virtually the same heat and pressure conditions (by passage through the fuser roller/pressure roller device
46
/
48
) before any toner is placed on said sheet. Here again, these uniform heat and pressure conditions tend to provide each successive sheet with the same moisture content—and hence the same electrostatic properties. As was previously noted, these uniform electrostatic properties leads to more uniform print results as a series of sheets of paper undergo electrophotographic printing.
After receiving a toner image from the photoconductor drum
12
in the toner transfer zone, a sheet of print media is sent (in the direction indicated by arrow
69
) along a fifth part MP
5
of the media path (via belt
42
, and ramp
44
), to the same fuser roller
46
and pressure roller
48
device that processed the incoming sheet. In this second mode of operation, the rollers
46
and
48
are turning in the opposite direction that said rollers were turning when these same rollers
46
and
48
were pretreating the incoming sheets. The general ability of this printer device
10
C to change the media flow direction is indicated by the respective two-headed arrows in fuser roller
46
and pressure roller
48
.
Thus, in this second mode of operation, the image on the paper is fused to said paper by the pressure/heat conditions created by the combined action of the fuser or heater roller
46
and the pressure roller
48
. Here again, the pressure, temperature and residence time conditions existent when the toner is being fused to the paper in this second mode of operation may be the same as, or different from, the heat, pressure and/or residence conditions existing in the fuser roller/pressure roller device
46
/
48
when the paper was originally taken into the printer
10
C and preconditioned. In any case these pressure, temperature and residence times will still generally fall within the ranges previously described in this patent disclosure. Thereafter the sheet is delivered (via the MP
6
part of the media path) to the sheet collection tray
76
via the sheet input/output roller system
50
/
52
by virtue of its being in second or sheet exit mode of operation (i.e., roller
50
turning clockwise and roller
52
turning counterclockwise).
Although specific embodiments of this invention have been disclosed herein in detail, it is to be understood that this was for purposes of illustration. This patent disclosure is not to be construed as limiting the scope of the invention, since the described electrophotographic printer and printing methods may be changed in several details by those skilled in the art in order to adapt these printers to particular applications without departing from the scope of the following claims and equivalents of the claimed elements.
Claims
- 1. An electrophotographic printing apparatus comprising:(1) a laser printing device for creating a latent image on a photoconductor drum whose outside surface defines a first side of a toner transfer zone; (2) a transfer roller whose outside surface defines a second side of the toner transfer zone; (3) a roller type heat pressure device having a first mode of operation for pretreating successive sheets and a second mode of operation for fixing toner to said sheets; (4) a first sheet transport system that leads through the roller type heat/pressure device while it is in the first mode of operation and then to a sheet duplexing tray; (5) a sheet duplexing tray for receiving sheets from the heat/pressure device and subsequently transferring said sheets to a second sheet transport system; (6) the second sheet transport system leads from the sheet duplexing tray to the toner transfer zone and turns the sheet over; and (7) a third sheet transport system that leads from the toner transfer zone back through the heat/pressure device in the second mode of operation and then out of said printing apparatus.
- 2. The electrophotographic printing apparatus of claim 1 wherein the roller type heat/pressure device has two opposing rollers and wherein one of the two opposing rollers contains a heating device and the other is a powered roller.
- 3. The electrophotographic printing apparatus of claim 1 wherein the roller type heat/pressure device has two opposing rollers and wherein one of the two opposing rollers contains an inductive heater element.
- 4. The electrophotographic printing apparatus of claim 1 wherein the roller type heat/pressure device has two opposing rollers and wherein one of the two opposing rollers contains a halogen tube.
- 5. The electrophotographic printing apparatus of claim 1 wherein the roller type heat/pressure device has two opposing rollers that each contain a heating device.
- 6. The electrophotographic printing apparatus of claim 1 wherein the roller type heat/pressure device operates at the same temperature, pressure and sheet residence time conditions when a sheet is dispensed from the apparatus as existed when the sheet was fed into said apparatus.
- 7. The electrophotographic printing apparatus of claim 1 wherein the roller type heat/pressure device operates at a different condition when a sheet is dispensed from the apparatus as existed when the sheet was fed into said apparatus.
- 8. An electrophotographic printing apparatus comprising:(1) a laser printing device for creating a latent image on a photoconductor drum whose outside surface defines a first side of a toner transfer zone; (2) a transfer roller whose outside surface defines a second side of the toner transfer zone; (3) a roller type heat/pressure device having a first mode of operation for pretreating successive sheets and a second mode of operation for fixing toner to said sheets; (4) a first sheet transport system that leads from a sheet dispensing tray, through the roller type heat/pressure device while it is in the first mode of operation and then to the toner transfer zone; and (5) a second sheet transport system that leads from the toner transfer zone back through the heat/pressure device while it is in the second mode of operation.
- 9. The electrophotographic printing apparatus of claim 8 wherein the roller type heat/pressure device has two opposing rollers and wherein at least one of the two opposing rollers contains a heating device and the other is a powered roller.
- 10. The electrophotographic printing apparatus of claim 8 wherein the roller type heat/pressure device has two opposing rollers and wherein at least one of the two opposing rollers contains a heating device employing an inductive heater element.
- 11. The electrophotographic printing apparatus of claim 8 wherein the roller type heat/pressure device has two opposing rollers wherein at least one of the two opposing rollers contains a heating device employing a halogen tube.
- 12. The electrophotographic printing apparatus of claim 8 wherein the roller type heat/pressure device has two opposing rollers that each contain a heating device.
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Number |
Name |
Date |
Kind |
5099281 |
Bhagat |
Mar 1992 |
A |
5412459 |
Borsuk et al. |
May 1995 |
A |
6128465 |
Castelli |
Oct 2000 |
A |