U.S. patent number 3,920,329 [Application Number 05/508,953] was granted by the patent office on 1975-11-18 for background removal apparatus.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to Richard H. Dennie, Michael R. Stanley.
United States Patent |
3,920,329 |
Dennie , et al. |
November 18, 1975 |
Background removal apparatus
Abstract
Improved background removal apparatus includes a magnetic brush
for removing background toner from the photoreceptor of an
electrostatic reproduction machine, and a reclaim roller for
removing the toner from the magnetic brush. The background removal
apparatus is neatly integrated into the developer of the machine so
as to form a developer/background removal apparatus unit. The
reclaim roller is positioned so as to both dispense the reclaimed
toner back into the main sump of the developer, and to serve as a
"doctor blade" for the magnetic brush. To promote mixing and
increase carrier life, the magnets within the magnetic brush are
arranged so as to allow the carrier beads of the brush to fall
freely into the sump of the background removal apparatus after
sweeping the photoreceptor surface. To provide for easy
maintenance, the background removal apparatus includes an opening
in the top thereof for loading carrier into the apparatus, and an
opening in the bottom thereof for unloading the carrier into the
main sump of the developer.
Inventors: |
Dennie; Richard H. (Walworth,
NY), Stanley; Michael R. (Pittsford, NY) |
Assignee: |
Xerox Corporation (Stamford,
CT)
|
Family
ID: |
24024739 |
Appl.
No.: |
05/508,953 |
Filed: |
September 25, 1974 |
Current U.S.
Class: |
399/264; 15/1.51;
399/273; 430/119.81 |
Current CPC
Class: |
G03G
15/095 (20130101); G03G 15/09 (20130101) |
Current International
Class: |
G03G
15/095 (20060101); G03G 15/09 (20060101); G03G
021/00 () |
Field of
Search: |
;355/15,3DD ;118/637
;117/17.5 ;15/1.5 ;222/DIG.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Greiner; Robert P.
Attorney, Agent or Firm: Ralabate; James J. Chiama; Bernard
A. Reichert; Earl T.
Claims
What is claimed is:
1. The combination of a developer having a first sump with a
background removal apparatus having a second sump, the background
removal apparatus being positioned above the first sump, and
including (a) means for transporting magnetic carrier beads into
sweeping contact with a photoreceptor to remove background toner,
the transporting means including a rotatably mounted non-magnetic
cylinder and magnet means positioned within the cylinder so as to
permit the carrier beads to drop freely from the cylinder into the
second sump after sweeping the photoreceptor and then to be
reattracted to the cylinder again after being mixed within the
second sump, and (b) reclaim means for reclaiming the toner from
the carrier beads which are being transported into sweepingg
contact with the photoreceptor.
2. The combination set forth in claim 1, and further including
means for opening the second sump to allow its contents to drop
into the first sump.
3. The combination set forth in claim 1, wherein the reclaim means
is positioned so as to allow the reclaimed toner to be dropped into
the first sump when removed from the reclaim means, and further
including means for removing the reclaimed toner from the reclaim
means.
4. The combination set forth in claim 3, wherein the reclaim means
is positioned so as to trim excess carrier beads from the transport
means and drop the excess carrier beads back into the second
sump.
5. The combination set forth in claim 4, and further including
means for opening the second sump to allow its contents to drop
into the first sump.
6. The combination set forth in claim 5 wherein the reclaim means
comprises a non-magnetic roller and means for electrically biasing
the non-magnetic roller, and wherein the removing means comprises a
plastic scraper blade.
Description
BACKGROUND OF THE INVENTION
This invention relates to an improvement in an electrostatic
reproduction machine, but more particularly to an electrostatic
reproduction machine having an improved apparatus for removing
background particles from a photoreceptor prior to image
transfer.
In the practice of xerography as described in U.S. Pat. No.
2,297,691 to Chester F. Carlson, a xerographic surface comprising a
layer of photoconductive insulating material affixed to a
conductive backing is used to support electrostatic images. In the
usual method of carrying out the process, the xerographic plate is
electrostatically charged uniformly over its surface, and then
exposed to a light pattern of the image being reproduced to thereby
discharge the charge in the areas where light strikes the layer.
The undischarged areas of the layer thus form an electrostatic
charge pattern or latent electrostatic image in conformity with the
configuration of the original pattern.
The latent electrostatic image is developed by contacting it with a
finely divided electrostatically attractable material, such as a
resinous powder. The powder is held in the image areas by the
electrostatic fields on the layer. Where the field is greatest, the
greatest amount of material is deposited, and where the field is
least, little or no material is deposited. Thus, a powder image is
produced in conformity with the image of the original being
produced. The powder image is subsequently transferred to a sheet
of paper or other transfer member, and suitably affixed thereto to
form a permanent copy.
The latest concept for electrostatic reproduction machines utilizes
high speed flash exposure of a document, and a moving
photoconductive material in the form of an endless belt which is
continuously charged. Additionally, such reproduction machines are
provided with a developing system which supplies toner particles in
relatively large quantities for solid area coverage, such as a
magnetic brush developing apparatus. Thus, after the belt passes
the magnetic brush assembly for example, a xerographic powder image
is formed on the belt which corresponds to the electrostatic latent
image. This powder image is then transferred to a support surface
(e.g., a sheet of paper) to which it is fused by a fusing assembly
whereby the powder image is caused to adhere to the support surface
permanently.
The latest electrostatic reproduction machines are high speed
machines which print copies at a rate substantially in excess of
any previous electrostatic reproduction machines, and are intended
to compete with other types of printing machines, e.g., offset
printing machines. Because of this, it is desired that the quality
of the copies made, be extremely high. Important to high quality
copies is the removal of all or substantially all of the background
particles (i.e., toner in non-image areas) from the photoreceptor
before transfer of the developed image to a support member. As
stated above, large amounts of toner are used in these high speed
electrostatic reproduction machines to develop the latent
electrostatic image, and to produce high quality copies, a very
efficient background removal apparatus is necessary to remove any
background particles which may be present after development. This
apparatus must be superior to previous means used to reduce the
background (e.g., lamps or pre-transfer corona charging devices
used to prevent or reduce transfer of background particles) on
copies in that it must eliminate all or substantially all of the
background from the copies; the apparatus must also not
detrimentally affect the developed image on the photoreceptor to
any great degree as did some of the previous means.
It is also highly desirable that the life of the developer (carrier
plus toner) be extended, and the life of the developer is directly
related to background, the less the background, the longer the life
of the developer. By efficiently removing all or substantially all
of the background, developer life will be substantially increased,
possibly doubled or even quadrupled. Also, this apparatus should be
integrated into a machine so as to occupy minimal space, and
cooperate with other elements of the machine, be accessible, and be
designed for easy maintenance by the machine operator.
SUMMARY OF THE INVENTION
The present invention is directed to background removal apparatus
having a magnetic brush for contacting a photoreceptor to remove
background toner particles, and at least one reclaim roller located
so as both to remove the particles from the magnetic brush roller
and discharge them into the main developer sump of the machine, and
to serve as a doctor blade for the bristles (formed by magnetic
carrier beads) of the magnetic brush roller. A grounded or properly
biased charge bar is located so as to contact the bristles of the
magnetic brush roller after they have been contacted by the reclaim
roll, but before they contact the photoreceptor once again; the
purpose of the charge bar is to discharge or substantially
discharge any charge placed on the magnetic carrier beads as a
result of their contact with the reclaim roller. The background
removal apparatus has openings for easy loading of carrier beads
into and unloading of carrier beads from the apparatus; when the
apparatus is unloaded, the carrier beads drop into the main
devloper sump.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic sectional view of an electrostatic
reproduction machine embodying the principles of the invention.
FIG. 2 is an enlarged schematic view showing the developer, the
background removal apparatus, and their interrelationship.
FIG. 3 is a plot of fractional decrease in background density
versus charging bar bias.
FIGS. 4 and 5 are enlarged views of the background removal
apparatus showing the magnetic brush roller, the reclaim roller,
the charge bar, and a detailed view of the means for unloading the
apparatus.
DETAILED DESCRIPTION OF THE INVENTION
For a general understanding of an electrostatic reproduction
machine in which the invention may be incorporated, reference is
made to FIG. 1 in which the various system components for the
machine are schematically illustrated. As in all electrostatic
systems of the type illustrated, a light image of a document to be
reproduced is projected onto the sensitized surface of a
xerographic plate to form an electrostatic latent image thereon.
Thereafter, the latent image is developed with an oppositely
charged developing material to form a xerographic powder image,
corresponding to the latent image on the plate surface. The powder
image is then electrostatically transferred to a support surface to
which it may be fused by a fusing device whereby the powder image
is caused permanently to adhere to the support surface.
In the illustrated machine 10, an original document D to be copied
is placed upon the transparent support platen P fixedly arranged in
an illumination assembly generally indicated by the reference
numeral 11, arranged at the left end of the machine; a platen cover
(not shown) is then lowered onto the original D to cover the same.
While upon the platen P, an illumination system flashes light rays
upon the original thereby producing image rays corresponding to the
informational areas on the original. The image rays are projected
by means of an optical system for exposing the photosensitiive
surface of a xerographic plate or photoreceptor in the form of a
flexible photoconductive belt 12. The surface of the belt was made
photosensitive by the previous step of uniformly charging the same
by means of a corona generating device 13. In order to effect image
processing, the belt 12 is arranged on a belt assembly generally
indicated by the reference numeral 14.
The photoconductive belt assembly 14 is slideably mounted upon two
support shafts, one of which is secured to the frame of the
machine, and is adapted to drive a belt 12 in the direction of the
arrow at a constant rate. During this movement of the belt, the
reflected light image of an original on the platen is flashed upon
the surface of the belt to produce electrostatic latent images
thereon at an exposure station A.
As the belt surface continues its movement, the electrostatic
latent image passes through a developing station B in which there
is positioned a developer/background removal assembly generally
indicated by the reference numeral 15, and which provides
development of the electrostatic latent image by means of a
developer 16 having multiple magnetic brush 17. The developed
electrostatic image then moves past a background removal apparatus
18 which removes background particles from the belt 12 prior to
transfer of the developed image.
The developed electrostatic image (without background particles) is
then transported by the belt to a transfer station C where a sheet
of copy paper is moved between a transfer roller 19 and the belt at
a speed in synchronism with the moving belt in order to effect
transfer of the developed image. There is provided at this station
a sheet transport mechanism indicated generally at 20 adapted to
transport sheets of paper from a paper handling mechanism generally
indicated by the reference numeral 21 to the developed image on the
belt at the station C.
After the developed image is transferred to the sheet, the latter
is stripped from the belt 12 and conveyed into a fuser assembly
indicated generally by the reference numeral 22 where the developed
and transferred xerographic powder image on the sheet material is
permanently affixed thereto. After each copy is thus produced, it
is delivered via sheet transport mechanism 23 into an output tray
24.
Additional details regarding the subject electrostatic reproduction
machine are set forth in a copending U.S. patent application Ser.
No. 312,411 assigned to the same assignee. Although not
specifically discussed herein, it is understood that the present
invention may also be utilized in other types of electrostatic
copying or duplicating machines, and is not limited to the high
speed duplicating machine disclosed herein.
Referring to FIG. 2, an enlarged schematic view of an embodiment of
the invention is shown. The latent electrostatic image is developed
by a plurality of magnetic brushes 17 which move developing
material (toner particles and magnetic carrier beads) up an
inclined plane as shown. The developing material is then directed
through a cross-mixing baffle 26, and returned to the main
developer sump 28. Toner is periodically dispensed into the
developer sump via a toner dispenser 30 having a porous dispensing
roller 32. Further details of the developer 16 are described in
U.S. Pat. No. 3,724,422, the disclosure of which is hereby
incorporated by reference.
For purposes of illustration only, it is assumed herein that the
belt 12 is initially charged to a positive polarity of
approximately 900 volts or more by the corona charging device 13.
After being exposed to a light pattern of the image being
reproduced, the image areas are approximately 700-900 volts, but
the background (non-image) areas are discharged or substantially
discharged; the background areas may still have a slight positive
charge of approximately 200 volts or less. Magnetic carrier beads
or particles which will place a negative charge (via
triboelectricity) on the toner particles are used in the developer
16. When the negatively charged toner is used to develop the image,
the toner will be strongly attracted to the highly charged positive
image areas. Some toner particles, however, may become loosely
attached to the weakly charged background areas also.
The belt 12 with the developed image thereon then moves past the
background removal apparatus 18 where it is contacted by the
bristles of a detoned magnetic brush 36, detoned meaning that the
amount of toner as compared to carrier within this apparatus is
preferably less than 0.1 percent by weight. The brush 36 has a
rotatably mounted cylinder 38 made out of any suitable non-magnetic
material, e.g., brass, aluminum, copper, or stainless steel.
Arranged within the cylinder 38 are two permanent bar magnets 40
and 42, the magnets having a magnetic strength and being arranged
substantially as shown so that the bristles formed by magnetic
carrier beads 44 on the periphery of the cylinder 38 are stiff
enough to remove substantially all of the background toner
particles from the belt 12 without substantially affecting the
developed image thereon; other suitable magnet arrangements may
also be used.
The bristles formed on the cylinder 38 adjacent to the belt 12 are
formed by magnetic carrier beads 44 which can be coated or
uncoated. It will be appreciated that bristles are formed from the
outer surface of cylinder 38 due to the lines of force from magnets
40 and 42 which are oriented in polar paths as indicated by the
letters N and S which illustrate north and south poles,
respectively (see FIG. 5). The magnetic beads comprise any suitable
material. The magnetic material may be "soft" i.e., retaining very
little residual magnetism, or the permanent magnet type. Typical
magnetic materials comprise powdered iron including types known
commercially as alcoholized iron and carboxal iron, steel, nickel,
alloys of magnetic iron, such as nickel-iron alloys,
nickel-cobalt-iron alloys, and magnetic oxides, such as, iron
oxide, hematite (Fe.sub.2 O.sub.3) and magnetite (Fe.sub.3 O.sub.4)
and magnetic ferrites. The magnetic beads can be coated with an
electrically insulating material. Typical coating materials are
described in U.S. Pat. No. 2,618,551 to Walkup, U.S. Pat. No.
2,618,552 to Wise, U.S. Pat. No. Re 25,136 to Carlson and U.S. Pat.
No. 2,874,063 to Greig. The materials disclosed in these patents as
well as many of the magnetic materials mentioned above, also have a
triboelectric attraction for the toner particles which serves to
further facilitate removal of the toner particles onto the
beads.
As the bristles of the brush 36 sweep over the surface of the belt
12, background toner particles are removed by the bristles and
adhere thereto. Although in absolute terms much more toner is
removed from the image areas than from the background areas of the
belt, percentage-wise, a much greater portion of toner is removed
from the background area (approximately 80-90 percent) than from
the image areas (approximately 10- 20 percent); the image areas are
not detrimentally affected. To assist in removing toner from the
belt 12, the magnetic brush 36 is electrically biased to a positive
polarity of approximately 150 volts (see FIG. 5). As the carrier
beads leave the magnetic field of magnet 40, they fall freely into
the sump 48 of the background removal apparatus. Arranging the
magnets substantially as shown allows the carrier beads to fall
freelly into the sump 48 rather than remain captured all the way
around the cylinder 38. This improves mixing and increases the life
of the carrier since each carrier bead is used less often, and the
impaction rate will consequently be less. Impaction of toner onto
the carrier beads shortens the useful cleaning life of the carrier
beads.
The carrier beads 44 then enter the magnetic field of the second
magnet 42 and are again attracted to the cylinder 38. As the
cylinder 38 continues to rotate, the carrier beads 44 pass the
reclaim roller 50 which is electrically biased to a positive
polarity of approximately 1,150 volts (see FIG. 5). The reclaim
roller 50 serves not only to attract the negatively charged toner
particles from the magnetic brush 36, but also serves as a doctor
blade so as to trim excess carrier beads from the cylinder 38 which
then fall back into the sump 48. The reclaim roller 50 rotates in a
counter-clockwise direction as shown, and the negative toner
particles 51 attracted thereto are removed by a plastic scraper
blade 52 and dropped into the main sump 28 of the developer
housing. It has been found that a plastic scraper blade reduces the
torque requirements necessary to rotate the roller 50. An
elastomeric lip seal 54 serves to prevent any of the material
within the sump 48 from escaping. The reclaim roller 50 may be made
of any suitable non-magnetic material, e.g., non-magnetic stainless
steel.
To discharge any charge placed upon the carrier beads by the
electrically biased reclaim roller 50, a conductive charging bar 56
is located between the reclaim roller 50 and the belt 12. The
charging bar 56 may also be made of any suitable nonmagnetic
stainless steel. The charging bar 56 may either be grounded or
electrically biased to a polarity opposite that of the reclaim roll
(see FIG. 5). This charging bar serves to discharge the carrier
beads prior to the time the carrier beads reach the belt 12. It has
been determined that charging bar 56 is necessary for the effective
removal of background particles. Referring to FIG. 3, it can be
seen that the background removal efficiency changes when the
polarity of the charging bar 56 changes from positive to
negative.
To make it easier for the magnetic brush 36 to remove background
particles, a corona charging device 60 may be incorporated into the
system as shown in FIG. 2. This corona charging device will place
an appropriate charge on the background so that the background
particles are more readily removed by the magnetic brush 36. In
other words, by using a corona charging device 60 as shown, it can
be seen that the charge on the background particles can all be made
approximately the same.
Another novel feature of this invention is the arrangement of the
developer 16 and the background removal apparatus 18 into a single
integrated unit. When it is desired to load carrier into the
background removal apparatus 18, a loading door 62 located above
the magnetic brush 36 may be removed and the carrier loaded into
the apparatus. This provides for easy maintenance of the apparatus.
When the carrier has been spent, and it is desired to remove or
unload the same from the sump 48, an unloading door 64 is provided
in the bottom of the sump as can be seen more clearly in FIGS. 4
and 5. This unloading door 64 is in the form of a circular rod, one
end of the door having a bent rod 66 which rides in a slotted ramp
68. When the door 64 is in its closed position a lip 70 rests upon
the upper end of the slotted ramp 68. The door 64 is held in its
closed position by a latch 72 on the other end thereof, the latch
72 being supported by a slot in bracket 74. When the door 64 is so
latched, it is held in place against the gasket 76. Thus, it can be
seen that the present arrangement provides for easy loading and
unloading of the background removal apparatus 18. The overall
arrangement is such that a minimum of space is occupied by the
developer/background removal apparatus 15 and a cooperative
relationship is provided between the developer 16 and the
background removal apparatus 18.
While the invention has been described with reference to the
structure disclosed, it is not confined to the details set forth,
but is intended to cover such modifications or changes as may come
within the scope of the following claims.
* * * * *