Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
This invention relates generally to electrostatographic
copying apparatus and, more particularly, to radiant energy appara-
tus for fixing toner images to a support member.
In the process of electrostatography, latent electro-
static images are formed on a support member, for example, plain
paper with the subsequent rendering of the latent images visible
by the application of electroscopic marking particles, commonly
referred to as toner. The toner or powder images so formed vary
in density in accordance with the magnitude of electrostatic char-
ges forming the individual images. The toner images can be fixed
directly upon the support member on which they are formed or they
may be transferred to another support member with subsequent fixing
of the images thereto.
Fixing of toner images can be accomplished by various
methods one of which is by the employment of thermal energy. In
order to permanently fix or fuse toner images onto a support mem-
ber by means of thermal energy it is necessary to elevate the tem-
perature of the toner material to a point at which the constituents
of the toner coalesce and become tacky or melt. This action causes
the toner to be absorbed to some extent into the fibers of the
paper. Thereafter as the toner cools, solidification of the toner
material occurs causing it to be firmly bonded to the support
member. In the process of electrostatography, the use of thermal
energy for fixing toner images is old and well known.
One approach to thermal fusing of toner images onto a
support member is to pass the support with the toner images there-
on past a source of radiant energy such that the image bearing side
of the support is opposite the source of radiation while the re~
verse side thereof is moved in contact with a heated platen. In
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the foregoing arrangement, for reasons understood by those skilled
in the art, the radiant energy source is so constructed and func-
tions such that it radiates energy at short wave lengths (i.e.,
0.5-2.0 microns) which satisfactorily fuses high density images
by means of the energy being directly absorbed by the toner. The
heated platen provides thermal energy for elevating the temperature
of the copy paper so that the paper does not act as a heat sink
which would rob the toner images of heat provided by the radiant
source. While the foregoing arrangement has been found to operate
satisfactorily, it is possible for the low density images not to
be fused satisfactorily due to either, the lack of intimate con-
tact between the reverse side of the paper and the platen or the
platen not being at the proper fusing temperature when the copy
paper passes thereover. Moreover, in a duplex mode of operation
the heated platen which operates above the softening point of the
toner causes offsetting of toner to the platen.
BRIEF SUMM~RY OF THE INVENTION
In accordance with this invention there is provided
apparatus for heat fuser toner images to a substrate on which
they are supported, said apparatus comprising a first source of
radiant energy capable of emitting energy having wave lengths
on the order of 0.5-2.0 microns, a second source of radiant
energy capable of emitting energy having wave lengt~s over 2.0
microns, means for transporting said substrate past said sources
of radiant energy such that said toner images are directly
c~. s~
exposed to said radiant sources, and ~a~s interpose~d between
said radiant sources and said substrate, said ~e~ea2~-me~n~
being substantially transparent to the energy emitted from both
of said energy sources.
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In one embodiment of the invention the radiation sources
comprise a quartz lamp which emits the short wave length energy
and a reflector which absorbs energy emitted from the quartz lamp
and re-radiates long wave length energy for heating the copy paper
to ~hereby fuse the lower density images. As will be appreciated,
the short wave length energy is directly absorbed by the toner
images having a high density of toner particles.
In another embodiment of the invention, a resistance
heater operating at a much lower surface temperature than the
quartz lamp it is substituted for the reflector.
This invention will become more apparent from the
detailed description to follow when read in conjunction with the
accompanying drawings wharein:
DESCRIPTION OF THE DRAWINGS
_
Figure 1 is a schematic representation of a reproducing
apparatus incorporating the invention;
Figure 2 illustrates a sectional view in elevation of a
radiant fuser incorporated in the apparatus of Figure l;
Figure 3 illustrates a modified embodiment of the radiant
fuser illustrated in Figure 2; and
Figure 4 is a perspective view of a shield and support
therefore incorporated in the fuser of Figures 2 and 3.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODI~ENTS
Referring now to Figure 1, there is shown by way of
example an automatic xerographic reproducing machine 1 which in-
corporates the improved fusing apparatus 15 of the present inven-
tion. The reproducing machine 1 depicted in Figure 1 illustrates
the various components utilized therein for producing copies rom
an original. Although the fusing apparatus 15 of the present in-
vention is particularly well adapted for use in an automatic xero-
graphic reproducing machine 1, it should become evident from the
following description that it is equally well suited for use in a
wide variety of machines where an image is fused to a sheet of
final support material and it is not necessarily limited in its
application to the particular embodiment shown herein.
The reproducing machine 1 illustrated in Figure 1 employs
an image recording drum-like member 10 the outer periphery of which
is coated with a suitable photoconductive material 11. One type of
suitable photoconductive material is disclosed in U.S. Patent No.
2~970,906 issued to Bixby in 1961. The drum 10 is suitab]y jour-
naled for rotation within a machine frame (not shown) by means of
a shaft 12 and rotates in the direction indicated by arrow 13, to
bring the image retaining surface thereon past a plurality of
xerographic processing stations. Suitable drive means (not shown)
are provided to power and coordinate the motion of the various
cooperating machine components whereby a faithful reproduction of
the original input scene information is recorded upon a sheet 14
of final support material such as paper or the like.
Since the practice of xerography is well-known in the
art, the various processing stations for producing a copy of an
original are herein represented in Figure 1 as blocks A to E.
Initially, the drum 10 moves photoconductive surface 11 through
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charging station A. At charging station A an electrostatic
charge is placed uniformly over the photoconductive surface 11
of the drum 10 preparatory to imaging. The charging may be
provided by a corona generating device of a type described in
U.S. Patent No. 2,836,725 issued to Vyverberg in 1958.
Thereafter, the drum 10 is rotated to exposure
station B where the charged photoconducti~e surface 11 is ex-
posed to a light image of the origi 1 input scene information,
whereby the charge is selectively dissipated in the light
exposed regions to record the original input scene in the form
of a latent electrostatic image. A suitable exposure system
may be the type described in U.S. Patent ~o. 3,832,057, issued
August 27, 1974, D.K. Shogren.
After exposuref drum 10 rotates the electrostatic
latent image recorded on the photoconductive surface 11 to
development station C wherein a conventional developer mix is
applied to the photoconductive surface 11 of the drum 10
rendering the latent image visible. A suitable development
station is disclosed in Canadian Patent Application, Serial
No. 145,905 filed June 28, 1972. The application describes a
magnetic brush development system utilizing magnetizable
developer mix having carrier granules and toner colorant. The
developer mix is continuously brought through a directional
flux field to form a brush thereof. The electrostatic latent
image recorded on photoconductive surface 11 is developed by
bringing the brush of developer mIx into contack therewith.
The devoloped image on the photoconductive surface
11 is then brought into contact with a sheet 14 of final
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support material within a transfer station D and the toner
image is transferred from the photoconductive surface 11 to
the contacting side of the final support sheet 14. The final
support material may be paper, plastic, etc., as desired.
After the toner image has been transferred to the sheet of
final support material 14, the sheét with,the image thereon
is advanced to a fuser assembly 15, which fixes the transfer-
red powdered image thereto. After the fusing process, the
sheet 14 is advanced through a snuffing apparatus 2 then by
rolls 16 to a catch tray 17 for subse~uent removal therefrom
by the machine operator.
Although a preponderence of the toner powder is
transferred to the final support material 14, invariably
some residual toner remains on the photoconductive surface 11
ater the transfer of the toner powder image to the final
support material 14. The residual toner particles remaining
on the photoconductive surface 11 after the transfer operation
are removed from the drum 10 as it moves through cleaning
station E. Here the residual toner particles are first
brought under the influence of a cleaning coron~ generating
d~vice ~not shown) adapted to neutralize the electrostatic
charge remaining on the toner particles. The neutralized
- toner particles are than mechanically cleaned fr~m the photo-
conductive surface 11 by conventional means as for example
the use of a resiliently biased knife blade as set forth in
U.S. Patent No. 3,660,863 issued to Gerbasi in 1972.
If desired, in accordance with the invention, the
sheets 14 of final support material processed in the automa-
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tic xerographic reproducing device can be stored in themachine within a removable paper cassette 18. A suitable
paper cassette is set forth in Canadian Patent Application,
Serial No. 148,892 filed August 8, 1972.
The reproducing apparatus in accordance with this
invention can also have the capability of ~ccepting and pro-
cessing copy sheets 14 of varying lengths. The length of the
copy sheet 14, of
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course, being dictated by the size of the original input scene or
infoxmation recorded on the photoconductive surface 11. To this
end the paper cassette 18 is preferably provided with an adjust-
able feature whereby sheets of varying length and width can be
conveniently accommodated. In operation the cassette 18 is filled
with a stack of final support material 19 of pre-selected size and
the cassette 18 is inserted into the machine by sliding along a
base plate (not shown) which guides the cassette into operable re-
lationship with a pair of feed rollers 20. When properly positioned
in communication with the feed rollers 20, the top sheet of the
stack 19 is separated and forwarded from the stack 19 into the
transfer station D by means of registration rolls 21.
It is believed that the foregoing description is suffi-
cient for purposes of the present application to illustrate the
general operation of the automatic xerographic reproducing machine
1 which can embody the teachings of the present invention.
Referring now to Figure 2, that portion of the reproduc-
ing machine 1 of Figure 1 embodying the fusing apparatus 15 of this
invention is shown in greater detail. The image bearing sheet 14
after passing through the transfer station D of Figure 1 upon
separation from the photoconductive surface 11 is allowed to fall
into contact with a vacuum belt transport system 22 which conveys
the sheet directly to the fusing station 15.
The fusing station 15 comprises a radiant type fuser.
The fusing station 15 comprises a heated platen 30 mounted to en-
gage the non-image bearing side of the copy sheet 14 which moves
in sliding contact therewith as it is transported through the
fusing zone. The heated platen 30 is designed so that an efficient
heat flow is established between the platen and the copy sheet 14
to raise the temperature of the sheet rapidly to a level somewhat
below the sheet's scorch temperature. By controlling the tempera-
ture of the sheet 14 in this manner the ability of the sheet to act
as a heat sink during image fixing is minimized.
The radiant energy for fusing is provided by an infrared
S quartz lamp 31 which is mounted in a reflector assembly 32 in oppos-
ing relationship to the hea~ed platen 30 and in a position to ther-
mally communicate with the image side of the copy sheet 14. The
operating temperature of the lamp is on the order of 2400K. Pre-
ferably the spectral output of the lamp 31 is within a range at
which the imaging material which may be toner for a xerographic
machine 1 is highly absorptive and at which the support material
14 which may be paper is relatively non-absorptive. As a result,
the toner images are rapidly raised to the desired fusing tempera-
ture while the support sheet 14 remains at a relatively lower tem-
perature. A forced air cooling chamber 33 is provided about the
backside of the reflector assembly 32 to cool the fuser 15 in
operation.
A heating element 34 i9 provided in the platen 30 to
maintain it at the desired temperature during standby periods.
When the quartz lamp 31 is operated the preheat element is dis-
connected and the platen 30 receives its heat input directly from
the quartz lamp.
The reflector assembly 32 is so constructed that it both
reflects the short wave length energy emitted from the quartz lamp
31 and absorbs the long wave length energy with the subsequent re-
radiation thereof, the temperature of the reflector being on the
order of 1000K. To this end the reflector 32 is a low mass con-
struction and an air insulating barrier is provided between the
reflector and the cooling chamber 33. The re-radiated long wave
length energy is effective to raise the temperature of the paper 14
._ g _
to thereby assist the heating element 34 in providing the energy
necessary for fusing low density images. It will be appreciated
that the reflected short wave length energy is absorbed by -the
high density images to thereby effect fusing thereof.
A shield assembly 50 as best illustrated in Figure 4 is
provided to preclude physical contacting of the quartz lamp 31 and
the reflector 32 by the copy paper 14. The assembly 50 comprises
a radiant energy transparent film 51 which has a thickness on the
order of 5 mils. Typical materials which are useful as a film
such as 51 are tetrafluoroethylene, flourinated ethylene-propylene
and polyimide polymers. The film 51 is attached to a pair of frame
or support members 52 and 53 the former of which is provided with
a pair of pins 54 which are received in recesses or bores 55 of the
frame member 53. This arrangement allows relative movement of the
frame members by virtue of a pair of bias members in the form of
coil springs 56. Temperature variations of the film will cause
it to sag, consequently, the specific construction of the shield
assembly provides for a constant planar orientation of the film
over the operating temperatures of the fuser 15.
The frame members each have a flange 57 which is received
in one of a pair of opposed recesses 58 provided in the reflector
assembly 32. The space between the bottoms of the recesses 58 is
such as to allow for relative movement of the frame members in a
horizontal direction.
In the modified embodiment of the fuser assembly 15,
illustrated in Figure 3, the source of long wave length radia-tion
is provided by means of a resistance heater 59 operated at a tem-
perature on the order of 1000K which may be fabricated from any
suitable material, for example, nicrom wire.
While the invention has been described with respect to
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two preferred embodiments it will be apparent that certai.n modi-
fications and changes can be made without departing from the
spirit and the scope of the invention and it is therefore intended
that the foregoing disclosure be limited only by the claims ap-
pended hereto.
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