Note: Descriptions are shown in the official language in which they were submitted.
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PNEUMATIC/SPRING ACTUATION MEC~IANISM
FOR ROLL FUSER
BACKGROUND OF THE INVENTION
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The present invention relates to roll :Euser
apparatus for fixing toner images to copy substrates
and more particularly to mechanism for effecting pressure
engagement between a pair of rolls forming the roll fuser.
In the process o xerography, a light image
o~ an original to be copied is typically recorded in
the form of a latent electrostatic image upon a photo-
sensitive member with subsequent rendering of the latent
image visible by the application of electroscopic marking
particles, commonly referred to as toner. The visual
toner image can be either fixed directly upon the photo-
sensitive member or transferred rom the member t.o an-
other support, such as a sheet of plain paper~ with sub-
se~uent affixing of the image thereto in one oE various
ways, for example, as by heat and pressure~
~n order to affix or fuse electroscopic toner
material onto a support member by heat and pressure,
it is necessary to elevate the temperature of the toner
material to a point at which the constituents of the
toner material coalesce and become tacky while simul-
taneously applying pressure. This action causes the
toner to flow to some extent into the fibers or pores
of support members or otherwise upon the surfaces there-
of. Therea~ter, as the toner material coolsr solidifica-
tion of the toner material occurs causing the toner mater-
ial to be bonded firmly to the support member. In both
the xerographic as well as the electrographic recording
arts, the use of thermal energy and pressure for fixing
toner images onto a support member is old and well known~
One approach to heat and pressure fusing of
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electroscopic toner images onto a support has been to
pass the support with the toner images thereon between
a pair of opposed roller members~ at least one of which
is heated. During operation of a fusing system of this
type~ the support member to which the toner images are
electrostatically adhered is moved through the nip Eormed
between the rolls with the toner image contacting the
fuser roll thereby to effect heating of the toner images
within the nip. Conventionally one or the other of the
rolls is softer than the other so that where the rolls
are forced into pressure engagement the softer roll is
deformed thereby orminy a nip through which the support
or copy substrates pass. Formation of the nip enables
the toner images to contact the heated surface of the
roll for a period of time sufficient to effect fusing~
In order to effect pressure engagement of the
rolls a force applying mechanism is provided which usually
takes the form of a cam and lever arrangement. In some
instances the cam has been replaced by a pneumatic ac-
tuator as for example, as in U. S. Patent 3,256,002.Such mechanisms yield satisfactory results, but re~uire
complex and expensive pressure controls in order to main-
tain a constant nip pressure, assuming the roll dimen-
sions are exact.
25 BRIEF SUMMARY OF THE INVENTION AND PRIOR ART
Accordingly, it is the purpose of the present
invention to incorporate in a heat and pressure roll
fusing apparatusl pneumatically actuated mechanism for
effecting pressure engagement of a pair of rolls which
30 mechanism is substantially insensitive to fluctuations
in air pressure and which compensates for roll dimension
variations in the same roll as well as between different
rolls.
To this end, the mechanism contemplated com-
35 prises a pair of pivot arms which are pivotally suppor-
ted by a frame means forming a part of the xerographic
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machine in which the fuser is to be employed. The arms,
in turn, support one of the rolls such that when the
arms are pivoted in a predetermined direction the rolls
are forced into pressure engagement. A pneumatically
actuated diaphragm is operatively connected to the pivot
arms via an elongated load bar and a compression spring
interposed between each of the actuator arms and the
load bar.
When air pressure ls applied to the diaphragm
the displacement is transmitted first through the load
bar then through the compression springs, then the ac-
tuator arms and finally to the rolls.
Initial setting up o~ the mechanism requires
pressurizing the diaphragm to 4.3 psi and adjusting a
pair of stops which limit the travel of the load bar.
During operation, however, 6.0 psi are supplied so that
normally expected downward fluctuation of air pressure
will not affect the nip pressure, the maximum nip
pressure being limited to 4.3 psi due to the position
of the adjustable stops.
The mechanism disclosed dif~ers from that illus-
trated in U. S. Patent 3,256,no~, in that, the structure
disclosed in the pa~ent does not incorporate the compress-
ion springs.
During the initial setup with air at 4.3 psi.
the air system compensates for the manufacturing tol-
erances in the loading system resulting in the loading
bar being not parallel to the roll axis. The loading
bar is made to maintain this compensating po~ition by
stop screws. After this setup any load change due to
roll runouts and diametrical changes is minimized by
the presence of compression springs which respond to
those changes. A low k (load/deflection) value for
the spring would ensure a small change in load.
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Thus, according to one aspect of this invention
there is provided in a roll fuser apparatus for fixing
toner images to a support material wherein a pair of rolls
are orced into pressure engagement by a pneumatic actuator
comprising an air displaceable diaphragm operatively
coupled to a pair of pivot arm assemblies via a load bar
displaceable by said diaphra~m, said pivot arm assemblies
being operatively connected to the ends of one of said
rolls and wherein adjustable stops are provided for the
pressure that can be applied, whereby said one of the rolls
is deformed by the other the improvement comprising:
constant load applying means interposed between said air
displaceable diaghragm and said pivot arm assemblies and
bias means for effecting separation of said rolls, when
said pneumatic actuator is in operation.
According to another aspect of this invention
there is provided a method of fusing toner images wherein
a pair of rolls are provided one of which is mounted such
that it can be moved into and out of pressure engagement
with the other, by a pneumatic actuator for effecting such
pressure engagement of said rolls, and including adjust-
able stop means for limiting the degree of travel of said
pneumatic actuator, wherein a predetermined pressure is
applied to said pneumatic actuator for setting said adjust-
able stops, the improvement comprising: providingconstant load applying means intermediate said pneumatic
actuator and one of said rolls to which said actuator is
operatively connected; applying a second predetermined
pressure to said pneumatic actuator and passing copy sub-
strates between said rolls to thereby fix toner imagescarried by said copy substrates thereto.
DESC_IPTION OF THE DRAWINGS
Fig. 1 is a side elevational view of a roll
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fuser apparatus including mechanism for effecting pres-
sure engagement between the two rolls of the apparatus
representing the invention.
Fig. 2 is a cross sectional view taken sn the
line II-II of Fig. 1.
Fig. 3 is a top plan view of the apparat~s
of Fig. 1.
Fig. 4A is a cross sectional view taken along
lines IVA-IVA of Fig. 3.
Fig~ 4C is a view taken along the lines IVC-
IVC of Fig. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMEMT
As illustrated in Fig. 1, the fuser apparatus
representing the invention is designated by the reEerence
character 10.
The fuser apparatus comprises a heated Euser
roll 12 comprising a relatively thick (i. e. 70 mils.)
layer of conductive (i. e. 15 x 10 4 cal/cm. sec C.)
silicone rubber 14 adhered to a cylinder 16 fabricated
23 from a thermally conductive ma~erial, for example, alum
inum and haviny a wall thickness on the order of 0.375".
The fuser roll is preferably 15.75 in. long and has a
nominal diameter of 30 inches~ A conventional type heat
; source 18 (Fig. 2) is stationarily supported within the
hollow of the cylinder 16 and spaced equidistant from
the internal surface thereof.` The capacity of the heat
source is such that its output equals 1600 watts at 120
volts. The fuser roll is rotatahly journalled in a ma-
chine frame 20, rotation thereof being effected by means
of a drive arrangement 22 illustrated in Fig. 2~
As illustrated in Fig. 2, the drive arrangement
22 comprises a plurality of cylindrical gears 24, 26
and 28. As can be seen the gear 24 is attached to an
end cap 30 forming a part of the fuser roll while the
gears 26 and 28 are carried hy the machine frame 20.
Motive power to the drive arrangement is provided by
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a drive motor 32 (Fig. 2).
A pressure roll 34, as shown in Figs. 1 and
3 is supported for pressure engagement with the fuser
roll 12 by means of a pair of pivot arm assemblies 36,
36' which are, in turn, pivotally supported by stub
shafts 38 3~' carried by the machine frame 20. The
pressure roll comprises a rigid core 40 having a r~la-
tively thin 41 layer of PFA (a trademark oE E. I. du
Pont) material adhered to the outer surface thereof,
the PFA layer thickness being on the order of several
mils. The pressure roll structure is thus harder than
the fuser roll, therefore, when 300 pounds of pressure
is applied between the rolls, as will be discussed here-
inafte.r, the silicone rubber layer is deformed thereby
providing a nip 42 on the order of 0.175 inch~ Tt should
be appreciated that alternatively ~he user roll 12
could be supported by the pivot arm assemblies 36, 36'.
The ends of the arm assemblies 36, 36' remote
from ends supportin~ the pressure roll are displaced
during pressure enga~ement of the rolls by a pair of
compression openings 44, 44' which encircle shoulder
screws 46 (only one shown) and are thereby retained in their
operative positions. The spring rate is on the order
of 150#/IN. and the spring, free length is one inch,
the springs being in a pre-compressed state to 0O84 inch
of their free length. The opposite ends of the springs
are operatively connected to an elongated load bar 48
which, in turn, is operatively connected to a diaphragm
assembly 50 (Figs. 1 and 3).
The diaphragm assembly 50 (Figs. 4A, 4B, 4C)
comprises an elastomeric member 52 overcoated with a
nylon fabric which elastomer is attached to a rigid plate
54. The diaphragm is secured to a base 56 by means oE
a retaining ring 58, the base being supported by the
machine frame 20.
An elbow 60 secured to the underside of the
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base 56 and communicating with a bore 62 provided therein
serves as means for introducing air under pressure to
the diaphragm assembly to thereby displace the elastom-
eric member 5~ which, in turn, causes displacement of
the load bar 48, the displacement being transmitted to
the springs 44, 44', then to the pivot arms assemblies
resulting in loading of the pressure roll against the
fuser roll.
The effective area of the elastomer 52 is 16
in.2 and a desired working pressure has been established
as 4.3 psi. Conse~uently, in order to produce a total
of 300 pounds of pressure between the rolls 12 and 34
the pivot arm assemblies 36, 36' are designed t:o produce
a mechanical advantage of 4.32~
Roll load set-up is accomplished by applying
a 4.3 psi. loading on the diaphragm and adjusting adjus-
table stops 64 which are secured in the diaphragm support
56 (Fig. 3) and extend through apertures 65 (Fig. 4B)
in the load bar 48 such that when adjustment has been
made and the stops have been locked in place, the load
corresponding to 4.3 psi. is maintained when the pressure
is increased beyvnd 4.3 psi. During operakion of the
fuser, a pressure of 6.0 psi. is applied to allow for
downward fluctuations in the applied pressure without
a corresponding decrease in load between the rolls.
As will be appreciated, the compression springs maintain
a near constant load for roll dimension variations, either
with the same roll or from roll to roll when a new roll
is installed for a worn roll.
As viewed in Fig. 1, bias springs 66 are pro-
vided for returning the pressure roll to a non-operative
position ~i. e. rolls are out of contact). To this end,
the bias springs are attached to the fuser frame and
pivot arm assemblies 36, 36' r
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