Method and apparatus for fusing envelopes

An electrophotographic printer is disclosed wherein the fusing of a toner image to an envelope by the use of a roll fuser causes the fusing nip to open early, i.e. the fusing nip opens a predetermined and controlled time/distance before the trailing edge of the envelope exits the fusing nip. As a result, creasing, wrinkling and the like of the envelope is minimized.

FIELD OF THE INVENTION 
This invention relates to the field of photocopying, i.e. 
electrophotographic copying and printing, and to a roll fusing method and 
apparatus having utility in an electric photography device, an 
electrophotographic device or a xerographic device. 
BACKGROUND OF THE INVENTION 
In an electrophotographic process or reproduction device such as a copier 
or a printer, a toner image is formed on the latent electrostatic image of 
a moving photoconductor. This photoconductor is reusable, and is used to 
sequentially carry many such toner images. The major portion of each toner 
image is transferred to the surface of transfer material, as this material 
and the photoconductor move in close proximity and synchronism through a 
toner transfer station. The toner image thereafter carried on the surface 
of the transfer material must now be fused to this surface. In this fusing 
process the toner image is permanently bound to the transfer material's 
surface. 
Reproduction devices of this type are usually classified as copiers or 
printers. In a copier the reproduced image is usually provided by scanning 
an original document's image. In a printer a data processing system, or 
computer system, usually provides an electronic image that is reproduced 
into a human readable image. 
The present invention will be described relative an electrophotographic 
printer. However, the scope and spirit of the invention is not to be 
limited thereto. 
A fusing station that has found wide acceptance in the art is the pressure 
roll fuser. This type of fuser, without limitation thereto, usually 
includes a pair of circular cylinder rollers that are mounted or supported 
in generally line contact, to thereby form a fusing nip through which the 
generally flat transfer material and its toner passes as the toner is 
fused to the transfer material. 
The two rollers of such a roll fuser are conventionally forced or spring 
biased toward each other so that the transfer material has a force applied 
thereto as the material passes through the fusing nip. Two types of roll 
fusers are known in the art, i.e. cold pressure fusers and hot pressure 
fusers. In a hot pressure fuser the toner being fused is subjected to both 
heat and pressure. In conventional practice, the fusing nip of such a 
pressure fuser is maintained closed during passage of the entire length of 
the transfer material. 
Preferred embodiments of the invention include hot pressure fusers, but the 
invention is not to be limited thereto. Hot pressure fusers may be of the 
dry release or the wet release type. U.S. Pat. No. 3,912,901, incorporated 
herein by reference for the purpose of indicating the background of the 
invention and illustrating the state of the art, is of the wet release 
type, and also shows a solenoid operated nip opening/closing mechanism. 
As electrophotographic reproduction devices such as printers find greater 
and greater utility, users thereof wish to produce toner images on various 
types of transfer material, including edge-bound multi-ply transfer 
material, of which envelopes are a typical example. 
Envelopes and other such bound multi-ply transfer material are available in 
a variety of structural designs and configurations. Variations include 
envelope construction quality, the type of paper used to form the 
envelope, the envelope size, the manner in which a single sheet is folded 
to form the multi-ply envelope, and the paper grain direction of the sheet 
from which the envelope is formed. In conventional practice, envelopes are 
manufactured with one surface or panel usually the back panel,of a 
somewhat larger surface dimension than the opposite panel. In this way, 
the envelopes interior may expand to form a pocket for holding documents, 
etc. 
We have discovered that roll pressure fusing of multi-ply transfer 
material, such as envelopes, tends to cause wrinkling of the material by 
the fusing process. This effect is thought to be caused by the formation 
of excess material upstream of the fusing nip. Usually, the envelope 
carries toner to be fused to only one side thereof, and in this case such 
excess material tends to build up on the non-toner side of the envelope. 
This excess material moves as a wave toward the envelope's trailing edge 
(i.e. the last edge of the envelope to pass through the fusing nip). The 
application of fusing pressure/heat to this excess material can produce an 
unsightly wrinkled area at the envelope's trailing edge. 
We have also noted that standard office practice does not provide or 
require address or other toner image data to be fused in the region of the 
trailing edge portion of an envelope. 
In accordance with the present invention, an electrophotographic printer 
fuses a toner image to an envelope by the use of a pressure fuser, and 
causes the fusing pressure to be released early, i.e. the roll fusing nip 
opens a predetermined and controlled time/distance before the trailing 
edge of the envelope exits the fusing nip. As a result, creasing, 
wrinkling and the like of the envelope is minimized. 
Within the knowledge of the inventors hereof, the concept of early fuser 
roll opening is not known by those skilled in the art. 
However, for other purposes, the art teaches early roll closing of a fuser 
nip. For example, U.S. Pat. No. 4,162,847 discloses a roll fuser wherein 
the fusing nip is closed before a sheet of transfer material arrives at 
the fusing nip. This early roll closure is used to cool the hot roll, the 
hot roll directly engages the relatively cool backup roll during the 
period of early closure. The effect is to improve performance of the fuser 
when the transfer material and its toner image subsequently arrives at the 
fusing nip. 
U.S. Pat. No. 4,429,987 is also of this general type having an early roll 
closure feature. 
The problem of fusing envelopes has been recognized in the art. For 
example, U.S. Pat. No. 4,814,819 attempts to solve the problem of fusing 
envelopes by providing a heated roller and a pressure roller, each having 
a resilient layer of critical thermal conductivity, as well as other 
critical parameters. 
SUMMARY OF THE INVENTION 
The present invention provides an electrophotographic reproduction device, 
such as a printer, wherein the fusing of a toner image to edge-bound, 
multi-ply, transfer material, such as envelopes, by the use of a pressure 
fuser, causes the fusing pressure to be released early, i.e. the fusing 
pressure is released a predetermined and controlled time/distance before 
the trailing edge of the transfer material exits the pressure fuser. As a 
result, creasing, wrinkling and the like of the transfer material is 
minimized. 
The term edge bound transfer material as used herein is intended to mean 
any construction and arrangement of the transfer material that produces 
multiple plies, the plies being attached to each other at one or more 
borders of the transfer material, including fold attachment as in well 
known envelope construction. 
An object of the invention is to provide a method and apparatus for fusing 
multiple-ply transfer material wherein toner bearing multiple-ply transfer 
material is fed to a fusing nip for fusing of the toner to the transfer 
material, including sensing the trailing edge of the transfer material as 
the transfer material moves toward the fusing nip, and controlling the 
fusing nip as a function of the trailing edge sensing, to open the fusing 
nip, and thereby release pressure from the transfer material, before the 
trailing edge exits the fusing nip. 
As a feature of the invention, the transfer material comprises an envelope, 
and the pressure fuser operates to fuse toner to an envelope as a result 
of the application of both heat and pressure. 
Another object of the invention is to provide a method and an apparatus for 
fusing xerographic toner to the flat surface of paper and paper-like 
envelopes by the use of an electrophotographic reproduction device having 
a roll fuser pressure nip, the envelopes being fed through the 
reproduction device in a manner to have a leading edge and a trailing 
edge. A determination is made as to whether toner images are in fact being 
reproduced on envelopes, and if toner images are being reproduced on 
envelopes, the pressure of the pressure nip is released after the majority 
of the envelope, extending from the leading edge toward the trailing edge, 
has passed through the pressure nip, and pressure is released before the 
trailing edge of the envelope has passed through the pressure nip, to 
thereby release pressure from the envelope before the trailing edge and 
its possible wave of excess envelope material exits the pressure nip. 
As a feature of the present invention, a nip opening device is provided 
which is sensitive to the detection of the position of the envelope as the 
envelope approaches the fuser. 
As a further feature of the invention, a nip opening device comprises a 
wedge shaped or eccentric cam that is driven between the two rolls that 
comprise the pressure fuser. This cam is driven into and through the nip, 
or is driven into an area adjacent the nip but axially displaced from the 
nip, by the rotational force of the fuser rolls. This cam operates to open 
the fusing nip so long as the cam is between the rolls. The cam allows the 
nip to close as the cam exits the fusing nip area, thus resetting the roll 
fuser to fuse the next transfer material. 
These and other objects and advantages of the invention will be apparent to 
those of skill in the art upon reference to the following detailed 
description of preferred embodiments of the invention wherein reference is 
made to the drawing.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention will be described with reference to a xerographic 
printer wherein the visual image to be formed on transfer material is 
supplied to the printer by a data processing system in the form of an 
electronic image signal. However, the spirit and scope of the invention is 
not to be limited thereto. 
Such an exemplary printer 10 is shown in FIG. 1. By way of example, but 
without limitation thereto, the printer of FIG. 1 may be of the type 
described in U.S. Pat. Nos. 4,664,507, 4,752,805 and 4,757,471, 
incorporated herein by reference for the purpose of indicating the 
background of the invention and illustrating the state of the art. 
This printer is a desk top device that includes two input cassettes or 
trays 11 and 12. Tray 11 holds sheets of blank transfer material such as 
letter size or legal size bond or bond-like paper. Tray 12 holds paper or 
paper-like envelopes. Many different types of envelopes are used in 
contemporary offices, and the present invention finds utility when forming 
a toner image on any type of envelope. Each tray 11,12 includes a paper 
feeding means 13,14 of conventional construction. The paper feeding means 
of each tray is selectively operable to feed either one sheet at a time 
from cassette 11, or one envelope at a time from cassette 12, to the 
printer's toner transfer station 15. 
By way of example, but without limitation thereto, the cassettes of FIG. 1 
may be of the type described in U.S. Pat. No. 4,780,740, incorporated 
herein by reference for the purpose of indicating the background of the 
invention and illustrating the state of the art. 
As is well known by those of skill in the art, a data processing system 
(not shown) provides electronic, binary, image data to printer 10 by way 
of input line or bus 16. This data is used to control a printhead or 
imaging station 27 that forms an electrostatic latent image on 
photoconductor drum or belt 17. 
By way of example, but without limitation thereto, the printer of FIG. 1 
may include an light emitting diode (LED) printhead 27 of the type 
described in U.S. Pat. No. 3,952,311, incorporated herein by reference for 
the purpose of indicating the background of the invention and illustrating 
the state of the art. 
The photoconductor's latent image is then toned by a developer station 28. 
The toned image then moves on to transfer station 15. A major portion of 
the photoconductor's toner image is transferred to a piece of transfer 
material at transfer station 15, as the photoconductor and the transfer 
material move in synchronism through the transfer station. After leaving 
transfer station 15, the photoconductor is discharged, cleaned of residual 
toner at a cleaning station 29, and recharged at a charging station 37, 
all in preparation for the formation of another latent image thereon as 
the photoconductor again passes through the printhead image station. This 
basic electrophotographic process is well known, and for purposes of 
simplicity these various processing stations will not be described herein. 
The transfer material and its toner image is separated from the 
photoconductor at transfer station 15, and substantially immediately 
thereafter the transfer material enters fusing station 18. At station 18 
the toner on the transfer material is subject to a pressure nip that is 
formed by a pair of parallel axis pressure engaged rollers 19 and 20. In a 
preferred form of the invention, the roller 19 that engages the toner on 
the bottom side of the transfer material is heated by an internal heater. 
Such a hot roll fuser is well known in the art. The toner is subjected to 
the pressure/heat of fusing station 18, and as a result the toner is 
permanently bound to the lower surface of the transfer material. 
Within the teachings of this invention fuser 18 may take many forms. For 
example, cold pressure fusers comprise two metal circular cylinders that 
are mounted in pressure contact. Usually the axes of these two cylinders 
are slightly skewed. In a hot pressure fuser, one or both of the rolls are 
heated, and the two cylinders are usually mounted with their axes 
parallel. Hot pressure fusers, also called hot roll fusers, usually have 
one or both of the rolls covered with an elastomer having toner release 
properties. Within the scope and spirit of this invention, any type of 
pressure fuser may be used. 
By way of example, but without limitation thereto, pressure fuser 18 of 
FIG. 1 may be of the type described in above mentioned U.S. Pat. No. 
4,814,819, incorporated herein by reference for the purpose of indicating 
the background of the invention and illustrating the state of the art. 
In accordance with the invention, when the user selected transfer material 
comprises an envelope, or generically a multi-ply transfer medium, the 
fusing nip formed by rolls 19,20 is opened, i.e. the nip pressure is 
released, just prior to the time that the envelope's trailing edge exits 
the fusing nip. When sheet material is selected for use, the fusing nip 
formed by rolls 19,20 remains closed for the entire length of the transfer 
material. 
After the transfer material has exited fuser 18, the reproduction process 
of printer 10 has been completed, and the finished product is fed to 
output tray 21 for retrieval by the operator. 
One of the control signals provided to printer 10 by the data processing 
system is an indication of the type of transfer material to be used when 
reproducing the electronic image data that is supplied to the printer by 
bus 16. This control signal is presented to printer 10 by way of line 22. 
For example, line 22 inactive may be the default condition, and this 
condition may result in the use of paper feeder 13 to feed a sheet of 
transfer material from tray 11, for example a sheet of letter or legal 
size blank paper. However, when line 22 is active, sheet feeder 14 is 
operable to feed an envelope from tray 12. 
This transfer material selection operation is represented by broken line 
23, and may be accomplished by a variety of well known 
electronic/mechanical means, all of which are to be considered within the 
present invention. 
Operation of the invention to feed an envelope from tray 12 is shown by 
broken line 24, i.e. by line 22 being active. An active line 22 activates 
an early nip opening means 25 only when an envelope is to be fused. Within 
the spirit and scope of the invention, nip opening means 25 may be of any 
type. It is essential however that the fuser nip formed by rolls 19,20 
open before the envelope's trailing edge reaches the nip, to thereby 
relieve the wave of envelope material that may have accumulated upstream 
of the fusing nip, as the leading portion of the envelope was fused. For 
example, it is usually sufficient to open the fusing nip for passage of 
the last inch or so of the envelope. While a variety of means can be used 
to control the time of opening of the fusing nip, such as the passage of 
time based upon the speed at which the envelope is being fed and based 
upon the size of the envelope, as a feature of the invention, the sheet's 
trailing edge is sensed by sensor 26, and the signal developed as a result 
of sensing the envelope' s trailing edge is used to open the fusing nip. 
The art provides for opening of the fusing nip of a roll fuser for 
different reasons. For example, many times the fusing nip is maintained 
open so long as the reproduction device is not in use, and the nip is 
closed when an operator indicates the need to use the device. In this 
case, the fusing nip usually remains closed throughout the entire 
reproduction job. In other devices, the fusing nip may open before arrival 
of each sheet of transfer material, and may open after each sheet of 
transfer material has left the fusing nip. The present invention finds 
utility with all such prior roll fusers. 
Many different roll fusers of detailed mechanical construction are known in 
the art. In some cases the fuser nip is opened by operation of a solenoid, 
a motor, or the like. In other cases a cam may operate to open the fusing 
nip. Again, the present invention finds utility with all such prior roll 
fusers. 
The present invention can be clearly understood by those skilled in the art 
upon reference to FIG. 2. This figure comprises a flow chart that will 
enable those skilled in the art to apply the invention in any of the well 
known types of pressure fusers. 
As shown in this figure, the beginning of the process or method of the 
invention is a determination of whether envelopes or like multi-ply 
material is to be fused, for example, is FIG. 1 line 22 active see 
decision block 30. If this type of transfer material is not being used in 
the printing cycle of printer 10, a program end occurs at 31. 
Assuming that envelope type transfer material is in fact in use, decision 
block 32 next monitors arrival of the envelope's trailing edge at a 
predetermined position relative the fusing nip. As stated previously, this 
function can be accomplished by actual sensing the trailing edge of the 
envelope, as at 26 in FIG. 1, or alternatively, this function may comprise 
the time-out of a timer that operates with knowledge of how fast the 
envelope is moving, how long the envelope is in the direction of its 
movement, and when the envelope enters the fusing nip, and assumes that 
the envelope is now at the predetermined position relative the fusing nip. 
When block 32 determines that the trailing edge of the envelope is at this 
predetermined position, action block 33 operates to open the fusing nip, 
so that the last inch or so of the envelope is not subjected to the force 
of the closed fusing nip. While not shown in FIG. 2, block 33 may operate 
a predetermined and operator-variable time period after operation of 
decision block 32, or in the alternative block 33 may operate immediately 
after operation of decision block 32. Since envelopes are of variable 
length, as measured in the direction in which the envelopes move through 
the printer, the time of nip opening will be variable relative the 
envelope's leading edge. 
When the fusing nip opens, a short period of time is required for the 
envelope's trailing edge, for example the last inch of the envelope, to 
clear or move through the fusing nip. This time is represented in FIG. 2 
by time delay function block 34. After the envelope has cleared the fusing 
nip, the fusing nip may be closed in preparation for the next 
reproduction/fusing cycle, as seen at block 35. While the time delay 34 of 
FIG. 2 is desirable, those skilled in the art may find that in a 
particular reproduction device it is only necessary to momentarily open 
the fusing nip, to release the wave of transfer material that has built up 
as a result of the pressure fusing of the envelope, and to then reclose 
the fusing nip on the envelope's trailing edge. While this operation is 
not a preferred operation, it is to be considered within the invention. 
FIG. 3 shows an embodiment of the invention that employs trailing edge 
sensing and a time delay to implement opening of the fusing nip to thereby 
allow the envelope's trailing edge to clear the fusing nip with no 
pressure being applied thereto. In this figure rolls 19,20 are shown in a 
closed condition, and an envelope 50 is shown as it is being fed to the 
closed fusing nip 51 formed by rollers 19,20. As will be appreciated, the 
size of envelope 50 and rollers 19,20 is not shown to scale. 
A sensor 26 in the form of a light source 52 and a photocell 53 is located 
in the feeding path upstream of fusing nip 51. When envelope 50 moves to 
the position shown in FIG. 3, a signal from photocell 53 activates time 
delay network 54. Network 54 is constructed and arranged to implement a 
time delay t1, this being the time required for envelope 50 to move to its 
dotted line position 55. As will be appreciated, by this time the majority 
of the envelope has passed through fusing nip 51, and the toner thereon, 
which toner may be on either the upper or the lower surface of the 
envelope, has been fused. 
After the t1 time delay, network 54 provides an operating signal to nip 
opening mechanism 56. As represented by broken line 58, nip opening 
mechanism 56 now operates on one or both of the rollers 19,20 to open 
fusing nip 51, i.e. to move rollers 19,20 apart so that the trailing edge 
or portion of the envelope (see dotted line position 55) may be fed 
through fusing nip 51 with no pressure being applied thereto. 
As shown by line 57, nip opening mechanism 56 is enabled only when 
envelopes or the like are to be fused. 
As a feature of the present invention, fusing nip 51 is opened by a unique 
arrangement that uses the rotational force of fuser rolls 19,20 to drive a 
wedge shaped, nip-opening cam between the two axial ends of the fuser 
rolls, in an area that is not used for fusing. This construction and 
arrangement of the invention is shown in FIGS. 4 and 5. 
In FIG. 4 the bottom fuser roll 19 is a heated roll, whereas the top fuser 
roll 20 is an unheated roll. Roll 20 is also called a backup roll. 
Preferably, but without limitation thereto, roll 19 is a driven roll, and 
roll 20 in an idler roll that rotates by virtue of friction engagement 
with roll 19. These two rolls are of a circular cylinder configuration, 
and are mounted on parallel axes Rolls are an exemplary 30 millimeters 
(mm) in diameter. Both rolls comprise an inner metal core and an 
elastomeric coating that is about 2 mm thick. 
The rolls are spring biased toward each other to form a pressure/heat 
fusing nip 62. In the standby condition of the fuser, the fusing nip is 
closed. While nip 62 of FIG. 4, as well as the nip shown in other figures 
hereof, is shown as comprising a substantially line contact between the 
rolls, as those skilled in the art will appreciate, when one or both of 
the rolls 19,20 includes an elastomer-like outer covering, fusing nip 62 
in fact has a finite width that extends in the direction of the movement 
of the transfer material. 
Since at least one of the rolls 19,20 is resiliently biased toward the 
other roll, the application of a nip-opening force to one or both of the 
rolls 19,20 in a direction away from nip 62 and generally through axes 
60,61 will operate to open the nip. Such an exemplary nip-opening force is 
about 80 pounds. The transfer material to be fused approaches fusing nip 
62 while moving generally left to right in FIG. 4. An exemplary feeding 
speed for the transfer material is about 6.7 inches per second. This speed 
also constitutes the surface speed of rolls 19,20. 
The nip opening mechanism of this embodiment of the invention comprises a 
roller powered roll separating cam member 70 that is mounted to freely 
rotate about axis 61 by way of arm 71. Cam 70 is lightly loaded against 
the rotating backup roll 20, by means of a spring portion 80 of arm 71. 
Cam member 70 thus tends to rotate with roll 20. Arm 71 engages the end 
surface of roll 20, and this engagement also applies a CCW drive force to 
arm 71 and cam member 70. 
Arm 71 is constrained against such CCW rotation by operation of catch 
member 72. Catch member 72 is formed as an extension of release lever 73. 
Lever 73 is controlled by a nip opening mechanism, such as 56 of FIG. 3, 
to cause lever 73 to rotate CW about stationary rod 74 (see arrow 75) when 
a signal is received to open the fusing nip during the passage of the last 
inch or so of an envelope that is being fused. 
Note that the opposite end of release lever 73 includes a like catch member 
72 that cooperates with a like cam member 70 and arm 71. That is, when a 
signal is received to open fusing nip 62, a cam member 70 is driven 
through both axial ends of the nip. 
When lever 73 momentarily rotates CW, catch 72 moves out of engagement with 
arm 71, thereby allowing cam member 70 and arm 71 to rotate CCW under the 
friction drive force provided by rotation roll 20. As stated, this event 
occurs at each end of fusing nip 62. 
Substantially immediately thereafter, the lower tapered portion 77 of cam 
member 70 is trapped in nip 62. Driven roll 19 then operates to feed cam 
member 70 through the fusing nip. The presence of cam member 70 at each 
axial end of nip 62 operates to move rolls 19,20 apart, thereby opening 
fusing nip 62 and releasing pressure from the trailing edge of the 
envelope. 
Note that catch 72 is substantially immediately reset by the CCW rotation 
represented by arrow 76. The length of cam member 70, measured in the 
direction of CCW cam movement, is such that the cam's trailing end will 
clear fusing nip 62, and allow nip 62 to reclose, after the trailing edge 
of the envelope has moved downstream of nip 62. In an exemplary 
construction, cam member 70 was constructed of metal, extended about 120 
degrees around the circumference of roll 20, was about 4 mm thick (measure 
radially of roll 20), and was about 3 mm wide (measured axially of roll 
20). 
The trailing end of cam member 70 includes a tapered surface much like its 
leading edge surface 77. These two surfaces are arranged to allow nip 62 
to both open and close with a minimum of mechanical shock or vibration. An 
exemplary taper provides a surface 77 at both ends of cam member 70 such 
that a gradual slope is provided to both open and close nip 62. A slope of 
about 10 degrees has proven to open the nip without mechanical shock to 
the fuser and its drive train. 
The width of cam member 70, that is the cam dimension measured in the 
direction of axes 60,61 is such that the cam does not extend into the area 
of rolls 19,20 that is used for fusing transfer material. Thus, passage of 
cam member 70 through fusing nip 62, as above described, does not 
interfere with the concurrent passage of an envelope through the nip. 
After cam member 70 has exited fuser nip 62, the CCW rotational force of 
roll 20 operates to return arm 71 and cam member 70 to the position shown 
in FIG. 4, where arm 71 is again arrested by operation of catch 72, which 
catch has been reset by CCW rotation of the catch about post 74, see arrow 
76. 
As stated previously while not shown in FIG. 4, it is to be understood that 
the opposite end of rolls 19,20 from that shown in FIG. 4 includes a 
similar nip opening mechanism. 
In those reproduction devices where it is desirable to maintain nip 62 in 
an open condition during standby and during an off period of the printer, 
those skilled in the art will readily appreciate that cam member 70 can be 
stopped with a mid portion thereof between the rolls. In this way, nip 62 
is maintained open during a standby/off period. 
A variation of the device of FIG. 4 that is to be considered within the 
invention provides a construction and arrangement wherein the elastomer is 
removed in a ring area directly under cam member 70. In this way cam 
member 70 is frictionally driven by engagement with the exposed metal core 
of roll 20 rather than its elastomer surface. 
FIG. 5 is a simplified showing of another embodiment of the invention 
having a cam for forcing the fuser rolls apart for passage of the trailing 
edge portion of an envelope being fused. 
FIG. 5 is an end perspective view of a pressure fuser in which transfer 
material approaches the fusing nip formed by hot roll 19 and backup roll 
20 while the transfer material moves left to right in the figure. Roll 19 
is a driven roll, and roll 20 is an idler roll that rotates by virtue of 
friction engagement with roll 19. These two rolls are of a circular 
cylinder configuration, and are mounted on generally parallel axes 60,61. 
Rolls 19,20 are spring biased toward each other to form a pressure/heat 
fusing nip 62. Without limitation thereto, in the standby condition of the 
fuser, fusing nip 62 is closed. 
Roll 20 is resiliently based toward roll 19. Thus the application of a 
nip-opening force to roll 20, in a direction away from nip 62 and 
generally through axis 61, operates to open the nip. 
The nip opening mechanism of this embodiment of the invention comprises a 
roller powered, eccentric, roll separating cam member 90 that is mounted 
to rotate with shaft 91. Note that roll 20 freely rotates about the center 
of shaft 91, i.e. roll 20 is not coupled to shaft 91. 
Cam member 90 is latched in the position shown by a cam latch mechanism 
diagrammatically shown at 92. In this latch condition of cam member 90, 
fusing nip 62 is closed, hot roll 19 is driven in a CW direction by well 
known drive means, and backup roll 20 is driven CCW by virtue of friction 
engagement with roll 19. 
Cam member 90 is a 360 degree eccentric cam. A first uniform radius cam 
portion 93, comprising about 90 degrees of cam member 90 and bounded by 
dotted lines 94 and 95, is constructed with a uniform radius about the 
center of shaft 61, for example a 15 mm radius. The remaining portion 96 
of cam member 90, i.e. the remaining 270 degrees of the cam, has a cam 
surface that is eccentric relative the center of shaft 91. In a preferred 
embodiment, this portion 96 of cam member 90 uniformly increased from a 15 
mm radius at dotted line 94, to a 17 mm radius halfway through portion and 
back to a 15 mm radius at dotted line 95. 
The external circumferential surface of the portion 93 of cam member 90 is 
spaced from a circular metal disk 99 that is carried at the end of roll 
19, i.e portion 93 does not engage the circumferential surface of disk 99. 
The external circumferential surface of the portion 96 of cam member 90 is 
adapted to ride on the circular metal disk 99 that is carried at the end 
of roll 19. Disk 99 is driven CW, as roll 19 is so driven. Disk 99 is of 
generally equal diameter to roll 19, and is mounted concentric with roll 
19. As can be seen in FIG. 5, in the FIG. 5 position of cam member 90, cam 
member 90 does not touch the circumferential surface of disk 99. 
Cam member 96 carries a pin 100 to which one end of an extension spring 101 
is attached. The other end of spring 101 is connected to a fixed-position 
post 102. For example, post 102 may comprise a portion of the fuser frame. 
In the position shown in FIG. 5, spring 101 is in a stretched condition, 
and a CCW rotational force is thus applied to cam member 96 by spring 101. 
However, since cam member 96 is latched in the position shown, by 
operation of cam latch mechanism 92, cam member 90 and shaft 91 will not 
rotate at this time. 
When a signal is received to open fusing nip 62 during the passage of the 
last inch or so of an envelope that is being fused, cam latch 92 is 
operated to release cam 90 for CCW rotation under the force bias provided 
by spring 101. As this rotation continues, the cam surface past the dotted 
line portion 94 of cam member 90 engages disk 99. When cam member 90 
engages disk 99, cam member 90 now no longer relies upon the bias force of 
spring 101, but rather cam member 90 is then driven CCW by CW rotation of 
disk 99. 
At this time an upward force is applied to shaft 61. This upward force 
moves shaft 61 and backup roll 20 upward, and fusing nip 62 begins to 
open, i.e. rolls 19,20 begin to separate. 
As rotation of cam member 90 continues, pin 100 is brought to dotted line 
position 103. This is the position of least stretching of spring 101. Cam 
90 continues to rotate CCW as it is driven by disk 99, until pin 100 is 
brought to dotted line position 104. This is the point of maximum 
extension of spring 101. 
As the surface of cam member 90 recedes radially inward toward the center 
of shaft 61, and fusing nip 62 begins to reclose, spring 101 is brought to 
an over center position relative to stationary post 102. Spring 101 now 
begins to shorten, and to provide a force bias causing cam member 90 to 
return to the latched position as shown in FIG. 5. By the time cam member 
so returns, cam latch mechanism has been reset, and cam member 90 is 
arrested at the position shown in FIG. 5. The fuser is then ready to fuse 
the next piece of transfer material. Cam latch 92 will be operated only 
when this next piece of transfer material is an envelope or the like. 
Note that the opposite end of the fuser includes similar arrangement to 
that shown in FIG. 5. That is, when a signal is received to open fusing 
nip 62, a cam latch 92 operates and a cam member 90 rotates through 360 
degrees, as above described, to open and then close fusing nip 62. 
The length of cam member portion 96, measured in the direction of CCW cam 
movement, is such that cam member 90 will allow nip 62 to reclose only 
after the trailing edge of the envelope has moved downstream of nip 62. 
The gradual increase and then decrease in radial size of portion 96 of cam 
member 90, from and exemplary 15 mm, to 17 mm, and then back down to 15 
mm, allows fusing nip 62 to both open and close with a minimum of 
mechanical shock or vibration. 
As stated previously while not shown in FIG. 5, it is to be understood that 
the opposite end of rolls 19,20 from that shown in FIG. 5 includes a 
similar nip opening mechanism. 
In those reproduction devices where it is desirable to maintain nip 62 in 
an open condition during standby and during an off period of the printer, 
those skilled in the art will readily appreciate that cam member 90 can be 
stopped with a mid portion thereof between the rolls. In this way, nip 62 
is maintained open during a standby/off period. 
While the present invention has been described in detail with reference to 
preferred embodiments of the invention, it is recognized that this 
teaching will enable those skilled in the art to originate other 
embodiments of the invention that are within the scope and spirit of the 
invention. Thus, the scope and spirit of the invention is to be as is 
defined in the claims hereof.