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Claims  |
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I claim:
1. An apparatus for fusing an image to a sheet during a copy run,
including:
means for counting the number of sheets having images fused thereto during
the copy run;
means for applying heat to at least the images on successive sheets of the
copy run; and
means, responsive to the number of sheets counted by said counting means,
for controlling said heat applying means.
2. An apparatus according to claim 1, wherein said heat applying means
includes:
a fusing member adapted to contact at least the images on successive sheets
of the copy run; and
means, in communication with said counting means, for heating said fusing
member.
3. An apparatus according to claim 2, wherein said heating means includes:
a first heating element disposed interiorly of said fusing member; and
a second heating element disposed interiorly of said fusing element, said
first heating element and said second heating element being arranged to
extend across the sheet contacting said fusing member with said first
heating element extending a greater distance than said second heating
element.
4. An apparatus according to claim 3, wherein said first heating element
generates greater heat than said second heating element.
5. An apparatus according to claim 4, further includes means for detecting
the size of each of the sheets of the copy run.
6. An apparatus according to claim 5, wherein said controlling means
regulates said heat applying means in responsive to the size of the sheet
sensed by said detecting means.
7. An apparatus according to claim 6, wherein said controlling means
deenergizes said first heating element in response to said detecting means
sensing a sheet having a size less than a preselected size.
8. An apparatus according to claim 7, wherein said controlling means
energizes said first heating element in response to said detecting means
sensing a sheet having a size greater than the preselected size.
9. An apparatus according to claim 8, wherein size controlling means
deenergizes said first heating element and energizes said second heating
element in response to said counting means indicating that the number of
sheets having images fused thereto during a copy run is greater than a
first preselected number of sheets.
10. An apparatus according to claim 9, wherein said controlling means
deenergizes said second heating element and energizes said first heating
element in response to said counting means indicating that the number of
sheets having images fused thereto during a copy run is greater than a
second preselected number of sheets with the second preselected number of
sheets being greater than the first preselected number of sheets.
11. An apparatus according to claim 10, wherein said fusing member is a
fuser roll.
12. An apparatus according to claim 11, wherein:
said first heating element includes a first heating lamp positioned
interiorly of said fuser roll extending in a direction substantially
parallel to the longitudinal axis of said fuser roll from one end of said
fuser roll to the other end thereof; and
said second heating element includes a second heating lamp spaced from said
first heating lamp and positioned interiorly of said fuser roll extending
in a direction substantially parallel to the longitudinal axis of said
fuser roll from one end of said fuser roll to the other end thereof.
13. An apparatus according to claim 12, further including a back-up roll
engaging said fuser roll to define a nip through which the sheet with the
image thereon passes.
14. An apparatus according to claim 13, wherein said first heating lamp
includes a first heating filament disposed interiorly thereof and
extending a distance substantially equal to the size of the largest sheet.
15. An apparatus according to claim 14, wherein said second heating lamp
includes a first heating filament disposed interiorly thereof and
extending a distance less than the distance that said first heating
filament extends.
16. An electrophotographic printing machine of the type having a fusing
apparatus for fusing an image transferred to a copy sheet during a copy
run of the printing machine, wherein the improved fusing apparatus
includes:
means for counting the number of copy sheets having images fused thereto
during the copy run;
means for applying heat to at least the images on successive copy sheets of
the copy run; and
means, responsive to the number of copy sheets counted by said counting
means, for controlling said heat applying means.
17. A printing machine according to claim 16, wherein said heat applying
means includes:
a fusing member adapted to contact at least the images on successive copy
sheets of the copy run; and
means, in communication with said counting means, for heating said fusing
member.
18. A printing machine according to claim 17, wherein said heating means
includes:
a first heating element disposed interiorly of said fusing member; and
a second heating element disposed interiorly of said fusing element, said
first heating element and said second heating element being arranged to
extend across the copy sheet contacting said fusing member with said first
heating element extending a greater distance than said second heating
element.
19. A printing machine according to claim 18, wherein said first heating
element generates greater heat than said second heating element.
20. A printing machine according to claim 19, further including means for
detecting the size of each of the copy sheets of the copy run.
21. A printing machine according to claim 20, wherein said controlling
means regulates said heat applying means in responsive to the size of the
copy sheet sensed by said detecting means.
22. A printing machine according to claim 21, wherein said controlling
means deenergizes said first heating element in response to said detecting
means sensing a copy sheet having a size less than a preselected size.
23. A printing machine according to claim 22, wherein said controlling
means energizes said first heating element in response to said detecting
means sensing a copy sheet having a size greater than the preselected
size.
24. A printing machine according to claim 23, wherein said controlling
means deenergizes said first heating element and energizes said second
heating element in response to said counting means indicating that the
number of copy sheets having images fused thereto during a copy run is
greater than a first preselected number of copy sheets.
25. A printing machine according to claim 24, wherein said controlling
means deenergizes said second heating element and energizes said first
heating element in response to said counting means indicating that the
number of copy sheets having images fused thereto during a copy run is
greater than a second preselected number of copy sheets with the second
preselected number of copy sheets being greater than the first preselected
number of copy sheets.
26. A printing machine according to claim 24, wherein said fusing member is
a fuser roll.
27. A printing machine according to claim 26, wherein:
said first heating element includes a first heating lamp positioned
interiorly of said fuser roll extending in a direction substantially
parallel to the longitudinal axis of said fuser roll from one end of said
fuser roll to the other end thereof; and
said second heating element includes a second heating lamp spaced from said
first heating lamp and positioned interiorly of said fuser roll extending
in a direction substantially parallel to the longitudinal axis of said
fuser roll from one end of said fuser roll to the other end thereof.
28. A printing machine according to claim 27, further including a back-up
roll engaging said fuser roll to define a nip through which the copy sheet
with the toner powder image thereon passes.
29. A printing machine according to claim 28, wherein said first heating
lamp includes a first heating filament disposed interiorly thereof and
extending a distance substantially equal to the size of the largest copy
sheet.
30. A printing machine according to claim 29, wherein said second heating
lamp includes a first heating filament disposed interiorly thereof and
extending a distance less than the distance that said first heating
filament extends. |
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Claims |
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Description |
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This invention relates generally to a fuser used in an electrophotographic
printing machine, and more particularly concerns a system for controlling
the fuser to provide a substantially uniform temperature distribution
thereacross during the fusing of various size copy sheets.
Generally, the process of electrophotographic printing includes charging a
photoconductive member to a substantially uniform potential so as to
sensitize the surface thereof. The charged portion of the photoconductive
surface is exposed to a light image of an original document being
reproduced. This records an electrostatic latent image on the
photoconductive surface. After the electrostatic latent image is recorded
on the photoconductive surface, the latent image is developed by bringing
a developer mixture into contact therewith. A common type of developer
comprises carrier granules having toner particles adhering
triboelectrically thereto. This two-component mixture is brought into
contact with the photoconductive surface. The toner particles are
attracted from the carrier granules to the latent image. This forms a
toner powder image on the photoconductive surface which is subsequently
transferred to a copy sheet. Finally, the toner powder image is heated to
permanently fuse it to the copy sheet in image configuration.
A high speed commercial printing machine of this type uses a fuser having a
heated roll and a back-up roll pressed thereagainst. The copy sheet passes
through the nip defined by the heated roll and back-up roll to heat the
toner powder image and fuse it to the copy sheet. Typically, the heated
roll is centrally heated. While most centrally heated rolls use a single
internal heat lamp, some fusers have two internal heat lamps. Two internal
heat lamps are generally required when there is a large variation in the
size of the copy sheets being handled. In this type of fuser, the main
heat lamp is typically used to maintain the roll surface at the
appropriate temperature during standby with the other heat lamp being used
to maintain the heat roll at the appropriate temperature to fuse the toner
powder image to the smaller size copy sheets. Although the purpose of
using two heat lamps is to minimize temperature variations that are
experienced when the copy sheets vary greatly in size, excessive gradients
still occur. The main heat lamp extends across the length of the largest
copy sheet to provide enough energy to fuse a toner powder image thereon.
However, when a smaller copy sheet is being used, a thermal hump is
produced outside the length of the smaller sheet. Thereafter, when the
larger copy sheet is used, there is a temperature variation along the
length of the roll which degradates copy quality. Various approaches have
been devised to control the temperature variations along the length of a
fuser roll, the following disclosures appear to be relevant:
______________________________________
US-A-4,551,007
Patentee: Elter
Issued: November 5, 1985
US-A-4,585,325
Patentee: Euler
Issued: April 29, 1986
US-A-4,588,281
Patentee: Elter
Issued: May 13, 1986
US-A-4,673,283
Patentee: Hisajima et al.
Issued: June 16, 1987
______________________________________
The relevant portions of the foregoing disclosures may be briefly
summarized as follows:
U.S. Pat. No. 4,551,007 discloses a controller which utilizes time
derivatives of a sensor measuring the surface temperature of a fuser roll
to control the output energy from a fuser heat lamp.
U.S. Pat. No. 4,585,325 describes a heated fixing roller having two heating
elements located inside the roller. The heating elements are connected to
a control system and a sensor to control the current being supplied to the
heating elements.
U.S. Pat. No. 4,588,281 discloses a fuser roll having a heat lamp disposed
interiorly thereof. The heating filament of the heat lamp extends along
the longitudinal axis of the fuser roll and is asymmetrical with respect
to a reference axis extending through the center of the fuser roller and
normal to the longitudinal axis thereof.
U.S. Pat. No. 4,673,283 describes a copying machine having a fixed
standstill time when larger size copy sheets are being used to achieve
good heating and fusing of the image.
In accordance with one aspect of the present invention, there is provided
an apparatus for fusing an image to a sheet during a copy run. The
apparatus includes means for counting the number of sheets having images
fused thereto during the copy run. Means are provided for applying heat to
at least the images on successive sheets of the copy run. Means,
responsive to the number of sheets counted by the counting means, control
the heat applying means.
Pursuant to another aspect of the present invention, there is provided an
electrophotographic printing machine of the type having a fusing apparatus
for fusing a toner powder image transferred to a copy sheet during a copy
run of the printing machine. The improved fusing apparatus includes means
for counting the number of copy sheets having toner powder images fused
thereto during the copy run. Means are provided for applying heat to at
least the toner powder images on successive copy sheets of the copy run.
Means, responsive to the number of copy sheets counted by the counting
means, control the heat applying means.
Other features of the present invention will become apparent as the
following description proceeds and upon reference to the drawings, in
which:
FIG. 1 is a graph showing the temperature variation of the fuser roll
surface when the control scheme of the present invention is not used.
FIG. 2 is a schematic elevational view of an illustrative
electrophotographic printing machine incorporating a fusing apparatus
having the features of the present invention therein;
FIG. 3 is a side elevational view, partially in section, showing the fusing
apparatus used in the FIG. 2 printing machine;
FIG. 4 is a block diagram illustrating the control system regulating the
energy output of the FIG. 3 fusing apparatus;
FIG. 5 is a flow diagram showing the control scheme used by the FIG. 4
control logic; and
FIG. 6 is a graph showing the fuser roll surface temperature variaton along
the length of the fuser roll when the FIG. 5 control scheme is employed.
While the present invention will 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.
Referring initially to FIG. 1, there is shown a graph illustrating the
temperature variation across the surface of the fuser roller when the
control scheme of the present invention is not used. Since the main heat
lamp must provide sufficient energy to fuse an image on a 11 inch by 16.5
inch copy sheet, the filament in this lamp must extend the entire length
of the sheet which passes through the fuser. In the case of a printing
machine that is capable of handling sheets long edge feed, this distance
is approximately 16.5 inches. The main heat lamp is also used for 14 inch
sheets. The temperature profile across the surface of the fuser roller
shown in FIG. 1 develops when a 14 inch sheet is used. As shown, there is
a temperature rise of approximately 25.degree. F. beyond the 14 inch
length of sheet. This temperature jump represents a high thermal stress at
the 14 inch edge which may cause hot offsetting of the toner particles.
If, after a 14 inch sheet is used, a 16.5 inch sheet is used, this thermal
hump may cause uneven fusing across the 16.5 inch sheet. Thus, it is clear
that it is highly desirable to have a substantially constant temperature
profile across the surface of the fuser roll without a temperature rise of
the type shown in FIG. 1.
Inasmuch as the art of electrophotographic printing is well known, the
various processing stations employed in the FIG. 2 printing machine will
be shown hereinafter schematically and their operation described briefly
with reference thereto.
Referring now to FIG. 2, the electrophotographic printing machine employs a
belt 10 having a photoconductive surface 12 deposited on a conductive
substrate 14. Preferably, photoconductive surface 12 is made from a
selenium alloy. Conductive substrate 14 is made preferably from an
aluminum alloy which is electrically grounded. Belt 10 moves in the
direction of arrow 16 to advance successive portions of photoconductive
surface 12 sequentially through the various processing stations disposed
about the path of movement thereof. Belt 10 is entrained about stripping
roller 18, tensioning roller 20 and drive roller 22. Drive roller 22 is
mounted rotatably in engagement with belt 10. Motor 24 rotates roller 22
to advance belt 10 in the direction of arrow 16. Roller 22 is coupled to
motor 24 by suitable means, such as a drive belt. Belt 10 is maintained in
tension by a pair of springs (not shown) resiliently urging tensioning
roller 20 against belt 10 with the desired spring force. Stripping roller
18 and tensioning roller 20 are mounted to rotate freely.
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 26 charges photoconductive surface 12 to a relatively
high, substantially uniform potential. High voltage power supply 28 is
coupled to corona generating device 26. Excitation of power supply 28
causes corona generating device 26 to charge photoconductive surface 12 of
belt 10. After photoconductive surface 12 of belt 10 is charged, the
charged portion thereof is advanced through exposure station B.
At exposure station B, an original document 30 is placed face down upon a
transparent platen 32. Lamps 34 flash light rays onto original document
30. The light rays reflected from original document 30 are transmitted
through lens 36 to form a light image thereof. Lens 36 focuses this light
image onto the charged portion of photoconductive surface 12 to
selectively dissipate the charge thereon. This records an electrostatic
latent image on photoconductive surface 12 which corresponds to the
informational areas contained within original document 30.
After the electrostatic latent image has been recorded on photoconductive
surface 12, belt 10 advances the latent image to development station C. At
development station C, a magnetic brush development system, indicated by
the reference numeral 38, advances developer material into contact with
the latent image. Preferably, magnetic brush development system 38
includes two magnetic brush developer rollers 40 and 42. Rollers 40 and 42
advance developer material into contact with the latent image. These
developer rollers form a brush of carrier granules and toner particles
extending outwardly therefrom. The latent image attracts toner particles
from the carrier granules forming a toner powder image thereon. As
successive electrostatic latent images are developed, toner particles are
depleted from the developer material. A toner particle dispenser,
indicated generally by the reference numeral 44, dispenses toner particles
into developer housing 46 of developer unit 38.
With continued reference to FIG. 1, after the electrostatic latent image is
developed, belt 10 advances the toner powder image to transfer station D.
A copy sheet 48 is advanced to transfer station D by sheet feeding
apparatus 50. Preferably, sheet feeding apparatus 50 includes a feed roll
52 contacting the uppermost sheet of stack 54. Feed roll 52 rotates to
advance the uppermost sheet from stack 54 into chute 56. Chute 56 directs
the advancing sheet of support material into contact with photoconductive
surface 12 of belt 10 in a timed sequence so that the toner powder image
formed thereon contacts the advancing sheet at transfer station D.
Transfer station D includes a corona generating device 58 which sprays
ions onto the back side of sheet 62. This attracts the toner powder image
from photoconductive surface 12 to sheet 48. After transfer, sheet 48
continues to move in the direction of arrow 60 onto a conveyor (not shown)
which advances sheet 48 to fusing station E.
Fusing station E includes a fuser assembly, indicated generally by the
reference numeral 62, which permanently affixes the transferred powder
image to sheet 48. Fuser assembly 60 includes a heated fuser roller 64 and
a back-up roller 66. Sheet 48 passes between fuser roller 64 and back-up
roller 66 with the toner powder image contacting fuser roller 64. In this
manner, the toner powder image is permanently affixed to sheet 48. After
fusing, sheet 48 advances through chute 70. As sheet 48 advances through
chute 70, a copy sheet sensor, indicated generally by the reference
numeral 68, detects the presence or absence of the copy sheet in fusing
apparatus 62 and indicates the status thereof to the control logic. By way
of example, copy sheet sensor 68 may be a switch or a photosensor. The
control logic counts the number of sheets passing through fusing apparatus
62. Chute 70 advances sheet 48 to catch tray 72 for subsequent removal
from the printing machine by the operator. Further details of fusing
apparatus 62 and the control system associated therewith will be described
hereinafter with reference to FIGS. 3 through 5, inclusive.
After the copy sheet is separated from photoconductive surface 12 of belt
10, the residual toner particles adhering to photoconductive surface 12
are removed therefrom at cleaning station F. Cleaning station F includes a
rotatably mounted fibrous brush 74 in contact with photoconductive surface
12. The particles are cleaned from photoconductive surface 12 by the
rotation of brush 74 in contact therewith. Subsequent to cleaning, a
discharge lamp (not shown) floods photoconductive surface 12 with light to
dissipate any residual electrostatic charge remaining thereon prior to the
charging thereof for the next successive imaging cycle.
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 FIG. 3, there is shown fusing apparatus 62 in greater
detail. As shown thereat, fuser 62 includes a heated fuser roller 64 and a
back-up roller 66. Fuser roller 64 is composed of a hollow tube 76 having
a thin covering thereon. Heating elements 78 and 80 are disposed
interiorly of tube 76. A thin layer of silicone oil is metered onto the
fuser roller during fusing. Tube 76 is made from a metal material having
the desired heat conductivity characteristics. By way of example,
aluminum, copper and other metals having a high thermal conductivity are
suitable for use as a tube. The thin layer coating tube 76 is made
preferably from silicone rubber. Back-up roller 66 is mounted pivotable
and is pressed against fuser roller 64. Back-up roller 66 has a relatively
thick layer of silicone rubber on a metal tube 82. When fusing is
occurring roller 66 pivots to press against roller 64. Back-up roller 66
and fuser roller 64 are adapted to rotate during the fusing operation so
as to advance the copy sheet therethrough. Heating element 78 comprises a
fuser lamp 82 having a filament 84 disposed interiorly thereof. As shown,
fuser lamp 82 extends substantially along the longitudinal axis of fuser
roller 64. Similarly, lamp filament 84 extends along the longitudinal axis
of fuser lamp 82 disposed interiorly thereof. Filament 84 extends from one
end 86 of fuser roller 64 to the other end 88 thereof. Heating element 80
comprises a fuser lamp 90 having a filament 92 disposed interiorly
thereof. As shown, fuser lamp 90 extends substantially along the
longitudinal axis of fuser roller 64. Similarly, lamp filament 92 extends
along the longitudinal axis of fuser lamp 90 disposed interiorly thereof.
Filament 92 extends from one end 88 of fuser roller 64 to a preselected
location intermediate end 86 and reference axis 94. Fuser lamp 82 is
designed to generate a greater energy output than fuser lamp 90. All copy
sheets passing through fusing apparatus 62 are registered or aligned such
that one edge thereof is substantially aligned with reference mark 96 on
fuser roller 64. Thus, filament 84 extends a distance of about 16.5 inches
from registration mark 96 with filament 92 extending a distance of about
14 inches from registration mark 96. Preferably registration mark 96 is
about 0.3 inches from end 88 of fuser roller 64. By way of example,
heating elements 78 and 80 may be halogen lamps having lamp filaments
disposed interiorly thereof.
Turning now to FIG. 4, copy sheet sensor 68 develops a voltage output
signal which indicates the presence of a copy sheet. Copy sheet sensor 68
may be a conventional sheet path sensor, such as a photosensor of a
switch, and is used for keeping track of the number of sheets that have
passed through fusing apparatus 62. The voltage signal from sensor 68 is
transmitted to control logic 98. Control logic 98 is preferably a
programmable microprocessor which controls all the machine functions. In
particular, the control logic 98 provides the storage and comparison of
counts of the copy sheets and the number of copy sheets that have passed
through the fusing apparatus. The decision whether or not to energize
lamps 82 and 90 is made by control logic 98. The output from control logic
98 regulates the power output from high voltage power supply 100 and high
voltage power supply 102. High voltage power supply 100 is coupled to
fuser lamp 82 and, dependent upon the input thereto, regulates the heat
output therefrom. High voltage power supply 102 is coupled to fuser lamp
90 and, dependent upon the input thereto, regulates the heat output
therefrom. In the event the length of the copy sheet is less than 14
inches, lamp 90 is energized, and lamp 82 deenergized. Alternatively, if
the length of the copy sheet is greater than 14 inches, the control scheme
determines the energization of the appropriate fuser lamp. If the copy
sheets being used have a length greater than 14 inches, fuser lamp 82 is
energized and fuser lamp 90 deenergized for the first 100 copy sheets
passing through fusing apparatus 62 as counted by the control logic.
Thereafter, for the next 50 copies, fuser lamp 90 is energized and fuser
lamp 82 deenergized. This cycle is repeated for every 150 copy sheets
passing through fusing apparatus 62.
FIG. 5 more clearly depicts the flow diagram describing the operation of
the control scheme. As shown thereat, the copy job is initiated. Sensors,
such as photosensors or switches, associated with the tray supporting the
stack of copy sheets 54 therein (FIG. 2) determine the size of the copy
sheet and transmit a signal indicative thereof to control logic 98.
Control logic 98 compares the signal from the sensors associated with the
tray supporting the stack of sheets (FIG. 2) with a preselected constant
corresponding to a copy sheet length of 14 inches. If the copy sheet
length is less than 14 inches, fuser lamp 90 is energized and fuser lamp
82 is deenergized. Alternatively, if the length of the stack 54 of copy
sheets is greater than 14 inches, fuser lamp 90 is deenergized and fuser
lamp 82 is energized. Control logic 98 counts the number of of copy sheets
passing through fusing apparatus 62. When the count equals 100 copy
sheets, fuser lamp 82 is deenergized and fuser lamp 90 is energized. When
the control logic counts another 50 copy sheets, the foregoing cycle is
repeated.
Turning now to FIG. 6, there is shown the change in fuser roll temperature
along its length when the control scheme of the present invention is used.
As shown, no thermal hump is produced and the temperature profile remains
substantially constant increasing from the ends there to the midpoint by
about 10.degree. F.
One skilled in the art will appreciate that while fusing of a dry toner
powder image has been described, the control scheme of the present
invention is also applicable to fusing a liquid image. Hence, the image
being fused to the copy sheet may either be a liquid image or a dry powder
image.
In recapitulation, it is evident that by controlling the energization of
different length fusing lamps disposed interiorly of the fuser roller as a
function of the number of copy sheets that have been fused and the size of
the copy sheet, the temperature profile along the length of the fuser
roller can be maintained substantially constant. In this manner, fusing is
optimized for various size copy sheets.
It is, therefore, apparent that there has been provided in accordance with
the present invention, a control system for a fusing apparatus of an
electrophotographic printing machine that fully satisfies the 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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