Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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1 COANDA EFFECT PAPER TRANSPORT
2 This invention relates to document copier machines,
3 and more particularly to methods and apparatus which make
4 use of the Coanda effect to move copy paper from the transfer
station to the fuser.
6 Background of the Invention
_
7 In document copier machines, rotating drums are
8 frequently used to support a photoreceptive material onto
9 which an e]ectrostatic image of an original document is
placed. That electrostatic image is then developed by the
11 application of developing material to the image and in the
12 continued rotation of the drum that developed image is
13 transferred to receiving material, typically a sheet of copy
14 paper. After transfer of the developed image, the photorecep-
tive material is cleaned and charged in order to be ready to
16 receive the next image of an original document.
17 The paper path for the copy paper begins with a
18 paper supply area which may be a paper bin holding cut
19 sheets of copy paper or a large roll of paper which is cut
as it is unwound. In either case, the sheet of copy paper
21 is fed from the supply area to the transfer station and
22 placed in direct contact with the developed image. A corona
23 is provided which attracts the developing material from the
24 drum to the paper so that when the paper is stripped from
contact with the drum, the image remains on the paper. The
26 paper is then transported to a fusing apparatus which,
27 through application of heat, joins the developer material to
28 the paper. Developing materials in current use include
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1 toner powders which rest on the copy paper after transfer
2 and can be easily dislodged before fusing with resultant
3 destruction of the image with the slightest jar of the copy
4 paper or physical contact with the unfused side of the
paper. As a consequence, one of the problems of document
6 copier machines is to provide a mechanism for transporting
7 the copy paper with the developed image thereon from the
8 transfer station to a fusing station without jarring the
9 copy paper or physically contacting the side of the paper
with the developed image.
11 Prior art apparatus devised for transporting copy
12 paper with unfused images have typically included the vacuum
13 transport, i.e., an endless belt moving across a plenum to
14 which the paper is attracted by a vacuum. Other means have
included the electrostatic attraction available between a
16 metal plenum and a sheet of copy paper and currently there
17 is some experimentation with the use of starwheels which
18 direct the copy paper toward the fuser by acting on the
19 unfused but developed side of the copy paper. All of the
above techniques have disadvantages relating to cost, size,
21 contamination of the copy sheet, or reliability. The
22 current invention, therefore, has as a primary object the
23 provision of a paper transport for unfused copy paper which
24 is reliable, compact, and economical.
It is a further object of this invention to provide
26 apparatus for transporting paper in which vibrational jarring
27 is kept to a minimum through the use of air cushions as
28 shock absorbers for the paper.
29 In a compact document copier machine utilizing a
hot roll fuser, a copy quality problem develops where the
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1 trailing edge of the copy paper is still in the process of
2 receiving an image in a transfer station when the leading
3 edge of the copy paper enters the nip of the hot roll fuser.
4 The problem appears as a mark on the copy paper since, when
the leading edge enters the hot roll fuser, a jar is trans-
6 mitted down the paper from the leading edge to the transfer
7 station and causes a smearing of the image at that point.
8 It is, therefore, another primary object of this invention to
9 eliminate such a mark by providin~ a paper transport which
absorbs the vibrational jars of entering the nip of a hot
11 fuser prior to the transmission of that jar to the transfer
12 station.
13 Summary of the Invention
14 This invention involves the use of the Coanda
effect, i.e., that moving air adheres to a smooth surface
16 and tends to follow the contour of that surface to provide a
17 transport which accomplishes the above-stated objects.
18 - In a first preferred embodiment of the invention,
19 air is blown along a deflector plate such that the developed
but unfused side of the copy paper is carried toward the nip
21 of a hot roll fuser along an air cushion which follows the
22 contour of the deflector. The deflector is positioned such
23 that the paper assumes an "S" shape for absorbing jars upon
24 fuser entrance.
In a second preferred embodiment of the invention,
26 air is blown along a smooth surfaced transport leaving a low
27 pressure area in and near the airstream, causing the under-
28 side of the paper to adhere to the airstream and follow the
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1 surface contour of the transport from the transfer station
2 to the hot roll fuser. The contour takes an "S" shape for
3 absorbing jars upon fuser entrance.
4 Brief Description of the Drawin~s
The above-mentioned and other features and objects
6 of this invention and the manner of attaining them will
7 become more apparent and the invention itself will best be
8 understood by reference to the following description of
9 embodiments of the invention taken in conjunction with the
accompanying drawings, the description of which follows.
11 FIGURE 1 is a perspective view of the paper path
12 of a document copier machine incorporating one embodiment of
13 the instant invention.
14 FIGURE 2 is a planar view showing one embodiment
lS of the instant invention.
16 FIG~E 3 is a planar view showing another embodi-
17 ment of the instant invention.
18 Detailed Description
19 FIGURE 1 shows the paper path of a typical document
copier such as that described above under background of the
21 invention, showing a drum 10, a developer 11, a transfer
22 station 12 with its associated corona 13, a charging corona
23 14, and a preclean corona 15. The drum 10 rotates in the
24 direction A and carries a photoreceptive material thereon
which receives an electrostatic charge from the corona 14.
26 An image of an original document is placed on the charged
27 photoreceptive material by apparatus not shown prior to the
28 arrival of the photoreceptive material at the developer 11.
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1 The developer deposits developing material such as a powder
2 on the surface of the photoreceptor to develop the electro-
3 static image thereon. The continued rotation of the drum 10
4 in the direction A carries the developed electrostatic image
to the transfer station 12 where the image is mated with a
6 copy paper 17, and the developing material is transferred to
7 the copy paper 17 under the influence of an electrostatic
8 field generated by the corona 13. The continued rotation of
9 the drum carries the photoreceptive material through a
preclean corona 15 and a cleaning station which may be
1l combined with the developer 11. In that manner the photorec-
12 eptive material is made ready for the application of the
13 next image. FIGURE 1 shows a compact document copier machine
14 in which the copy paper 17 is receiving a developed image at
transfer station 12, while at the same time the developed
16 image is being fused to the copy paper 17 in the nip of the
17 fuser rolls 18 and 19, wherein the hot roll is 18 and the
18 backup roll is the roll l9.
19 One embodiment of this invention is shown in
FIGURE 1 for transporting the paper from the transfer station
21 12 to the fuser rolls 18 and 19. In this case a deflector
22 plate 20 is positioned as shown and air is blown over the
23 deflector by the fan 21. The moving surface of air provides
24 an air cushion to guide the paper along the deflector into
the nip of the fuser rolls. Guide 20a acts on the underside
26 of the paper to prevent a deflection of the paper downwardly
27 into backup roll 19. This embodiment of the invention will
28 be explained further with respect to FIGURE 2.
29 In FIGURE 2 the drum 10 is shown with transfer
station 12. Copy paper 17 is shown with the trailing edge
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1 extending just beyond transfer station 12 and the leading
2 edge far beyond the fuser rolls 18 and 19 just entering a
3 pair of pinch rolls 22 and 23, A mechanical sheet stripplng
4 finger 24 is shown in its rest position and in phantom in
the position it takes before the leading edge of the copy
6 paper 17 strikes it. The finger 24 is positioned against or
7 closely adjacent to drum 10 in the position shown in phantom
8 so that as the leading edge of the copy paper 17 leaves
g transfer station 12, it is captured in the notch 25 of
finger 24, and thus drives the finger back around its pivot
11 32. In that manner the leading edge of the paper is stripped
12 away from drum 10 and pushes finger 24 in an arcuate path to
13 a position shown approximately at 26. At that point the
14 finger 24 is accelerated away from the leading edge of the
copy paper, for example, by an overcenter spring, not shown,
16 and the guidance of the leading edge of the copy paper is
17 taken over by the influence of an airstream shown by dotted
18 lines adjacent to the deflector plate 20. As discussed
19 above, this airstream moves along the surface of the deflector
plate 20 according to the Coanda effect and guides the paper
?.1 17 while keeping that paper apart from contact with the
22 deflector 20. In actuality, the air acts as a bearing or
23 cushion to guide the paper along the deflector surface but
24 does not allow the paper to come into contact with the
deflector surface. In that manner, the leading edge of the
26 copy paper is guided by the deflector 20 and the associated
27 airstream into the nip of the rollers 18 and 19. The
28 actual path of the leading edge of the paper may be guided
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1 by guide 20a to strike the backup roller 19 just ahead of
2 entrance into the nip of the rollers, so as to form a gentle
3 curve in the paper as part of an "S" shape. It is the
4 entrance into the nip of the rollers 18 and 19 which can
create a mark on the paper at transfer station 12 by virtue
6 of the driving effect on the paper which takes place when
7 the rollers 18 and 19 grasp the paper and begin to move it.
8 Any jarring effect of that entrance into the nip is dissipated
9 in the curves of an "S" shape in the length of the copy
paper between the nip of the fuser rolls and transfer station
11 12 due to the fact that the paper is at no point solidly
12 attached to any transport mechanism. The "S" shape is
13 formed in the paper by properly positioning the deflector
14 ~ 20.
1~ FIGURE 3 shows another embodiment of the invention
wherein the plate over which air is blown is placed on the
17 underside of the copy paper rather than on the toned but
18 unfused side as shown in FIGURE 2. In FIGURE 3 the copy
19 paper 17 once again is positioned with the trailing edge
still to reach transfer station 12 but with the leading edge
21 already beyond the fusing rolls 18 and 19 and entering pinch
22 rolls 22 and 23. A sheet stripping finger 24 is provided
23 and operates, as discussed above, to strip the copy paper
24 from the drum 10 and guide that paper in an arcuate path
into proximity with the airstream. At that point the finger
26 24 is accelerated away from the leading edge of the paper
27 and the paper is held to the airstream by forces produced in
,~8 accordance with the Bernoulli principle, and carried by the
29 airstream along the surface of the plate 20 into the nip of
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1 the fuser rolls. Note that in this embodiment of the inven-
2 tion, the deflector plate 20 imparts an "S" shape to the copy
3 paper so that when the leading edge of the paper enters the
4 nip of the fuser rolls any shock from that entrance is
dissipated in the bends of the "S" and does not reach backward
6 to the transfer station 12.
7 In both FIGURES 2 and 3 a centrifugal fan or
8 centrifugal blower 21 is shown feeding a plenum 30. A tube
o 31 extends out of the plenum 30 to carry the airflow to the
deflector plate 20. In referring to FIGURE 1 it can be seen
11 that the plenum 30 and the tube 31 extend across the width
12 of the paper such that a uniform distribution of airflow is
13 present from one side of the paper path to the other.
14 An interesting aspect of the Coanda effect phenom-
enon is that by virtue of the moving airstream a low pressure
16 area is present in and near the airstream such that the
17 paper "adheres" to the airstream by virtue of the Bernoulli
18 principle. Thus, the transport of this invention takes
19 advantage of both the Coanda effect and the Bernoulli princi-
ple to move paper across the surface of the deflector without
21 contacting it. Very small air pressures are suitable, for
22 example, as low as 0.04 inches water pressure appears adequate
23 but optimally over 0.08 inches. These low air pressures
~4 correspond approximately to a minimum required airstream
velocity of 50 inches-per-second. The thickness of the air-
26 stream is a function of the width of the tube 31 and it has
27 been found that if the thickness of the airstream drops
28 under 0.05 inches there will be insufficient viscous forces
29 to the airstream to keep the paper out of contact with the
deflector plate. Similarly, if the width of the airstream
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1 is increased above 0.25 inches the internal viscous forces
2 weaken and the airstrea~ does not follow the plate, i.e,,
3 the Coanda effect breaks down, Thus, it appears that the
4 best range of values is betweqn those two extremes and
optimally somewhat less than 0.15 inches thick.
6 While the invention has been particularly shown
7 and described with reference to a preferred embodiment
8 thereof, it will be understood by those skilled in the art
9 that the foregoing and other changes in form and details may
be made therein without departing from the spirit and scope
11 of the invention.
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