Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~ ii.l5332
BACKGROUND OF THE IN~E~TION
The invention xelates to an apparatus for cleaning
a photosensitive member, employed in the electro-photographic
process, and more particularly, for removal of any residual
powder attaching to the surface of such a member subsequent
to the image transfer step.
In the electrophotographic process, an electrostatic
latent image formed on a photosensitive member is developed
with a powder material, called a toner, which can be electro-
statically attracted, thereby producing a powder image whichis then transferred onto a copy sheet such as an ordinary
paper to provide an ultimate image. When the transfer step
is completed, a portion of the powder material which has not
been transferred remains on the surface of the photosensitive
member. It is necessary to remove such residue before recycling
the photosensitive member in the process. A cleaning apparatus
for the photosensitive member is used to this end. In the prior
art, the removal of such residual powder has been accomplished
by using a cleaning apparatus which incorporates a cylindrical
brush, called a fur brush, formed of rabbit fur. However, the
current trend is toward the use of a roller formed of foamed
resin instead of such a fur brush.
A roller formed of foamed resin has a high wiping
effect due to the unevenness formed by the pores in the surface,
and is flexible enough to avoid damage to the photosensitive
member In addition, such a roller has an abrasion resistance,
and is inexpensive. However, a difficul~y is exp~~ienc2d in
such rollers that powder wiped off by the roller finds its way
into the surface pores and cannot be easily removed therefrom.
Therefo~e, when a cleaning apparatus incorporating such a
roller is to be used, there must be provided some means which
-
1-- ~, b
11~5;~32
removes powder from the roller.
To provide such means, Japanese Patent Publication
No. 20227/1974 and Japanese Laid-Open Utility Model Application
~o. 699a2/1975 disclose the use of a recovering roller to
which an electrical bias is applied and which is disposed in
contact with the resin roller for absorbing powder from the
latter. Alternatively, Japanese Patent Publication No. 37547/
1975 discloses the use of a fur brush in contact with the resin
roller to scrape the powder off the latter. However, the use
of the bias results in a complex arrangement while the use of
the fur brush results in a dispersion Gr scattering of the
powder, causing a contamination of the overall system.
SUMMARY OF THE INVENTI ON
In accordance with the invention, there is p ovided
a cleaning apparatus including a cleaning roller formed of
a high resilient material such as foamed resin. The cleaning
roller scrapes any residual powder from the surface of the
photosensitive member, and the scraped powder is driven or
expelled by a pressure plate which is disposed in abutment
against the roller so as to extend in the direction of its
forward rotation. Because the roller material such as foamed
resin has elasticity, it is compressed when disposed in abut-
ment with the pressure plate. Durirg the rotation of the
cleaning roller, the compressed portion of the roller surface
is impulsively restored as it is disengaged or released from
the pressure plate, thereby expelling the powder by the resil-
ience which has been retained in the pores in the surface of
the cleaning roller. The cleaning apparatus also comprises a
recovering roller which is disposPd adjacent the pressure plate
for receiving powder that is expelled by the action of the
latter. In addition, the cleaning apparatus comprises means
~ S332
for charging the surface of the recovering roller to a degree
sufficien~ to attract the toner. The residual powder prin-
cipally comDrises the toner, which is at the electrical po-
tential of substantially zero when it passes by the neutrali2-
ing station of the process, so that when the surface of ,he
recovering roller is sufficiently charged, the powder expelled
~y the action of the pressure plate can be caused to adhere
to the surface of the recovering roller in a reliable manner.
In addition, the apparatus may include a rotatable helical
coil disposed in a ~ath for conveying removed powder for
preventing solidiLication of the removed powder and for
facilitating the conveyance.
Therefore, it is an object of the invention to provid~
an apparatus for cleaning a photosensitive-member which in-
cludes a cleaning roller formed of foamed resin or the like
resilient material and which facilitates the removal of powder
from the cleaning roller.
It is another object of the invention to provide such
apparatus which includes means for recovering powder that is ~-
removed by the cleaning roller.
It is a further object o~ the invention to provide
such apparatus including means which assures the removal of
the powder from the cleaning roller.
It lS still another object of the invention to provid~
such apparatus which includes means for preventing the solidi-
fication of and facilitating the conveyance of removed powder.
In accordance with the foregoing objects, there
is provided:
An apparatus for cleaning a photosensitive
3~ member to remOve any residual powder which may remain attached
to the Surface of the photosensitive member after a transfer
step, the apparatus comprising:
, . . .
332
a cleaning means having a surface with a high
restoring resilience and rotatably disposed in contact with
the surface of the photosensitive member for cleaning residual
powder therefrom;
a powder recovering means rotatably disposed
immediately adjacent a point on the surface of the cleaning
means for receiving powder expelled therefrom; and
a pressure plate having an end disposed in forced
abutment against the surface of the cleaning means at a point
which immediately precedes said point of adjacency between
the cleaning means and the recovering means in the direction of -~
rotation of the cleaning means, the pressure plate end ~.
compressing the surface of the cleaning means and extending
in a forward direction with respect to the direction of
rotation of the cleaning means, whereby the residual powder
is expelled from the surface of said cleaning means by the
resilient restoration of said surface after compression. ~ :
There is also provided:
An apparatus for cleaning a photosensitive
member to remove any residual powder which may remain attached
to the surface of the photosensitive member after a transfer
step, the apparatus comprising:
a cleaning means having a surface formed of
foamed resin and rotatably disposed in contact with the surface
of the photosensitive member for cleaning residual powder
therefrom;
a powder recovering means rotatably disposed
immediately adjacent a point on the surface of the cleaning
means for receiving powder expelled therefrom;
a pressure plate having an end disposed in
forced abutment against the surface of the cleaning means at
a point which immediately precedes said point of adjacency
between the rotating cleaning means and ~he recovering means
: in the direction of rotation of the cleaning means, tne
-3a-
'"
11 lS33Z
.
pressure plate end compressing the surface of the cleaning
means and extending in a forward direction with respect to
the direction of rotation of the cleaning means, whereby the
residual powder is expelled from the surface of said cleaning
means by the resilient restoration of said surface after
compression;
a scraping means arranged in contact with the
surface of the recovering means for removing the powder
received thereon;
a guide means located adjacent the scraping ,
means for guiding and transporting the powder removed there-
from; and
a rotatable helical coil disposed above the guide
means in close proximity thereto for dispersing the powder
transported thereby.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic view showing an exa~ple of
an electrophotographic system which includes a cleaning appa-
ratus for a photosensitive m~mber in accordance wi.th the
present invention;
-3~-
533Z
Fig. 2 is a schematic view in greater detail of one
embodiment of the invention; -
Fig. 3 is a schematic view of another embodiment
of the invention;
Fig. 4 is a schematic view of a further embodiment of
the invention; and
Fig. 5 is a perspective view of a helical coil of the
type used in the embodiment shown in Fig. 4.
DESCRIPTION OF PREFERRED EMBODI~IENTS
Referring to Fig. 1, there is shown a photosensitive
member in the form of a drum 1 having a photoconductive in-
sulating layer on its surface. The drum 1 is adapted to be
driven in the direction indicated by an arrow, and is initially
charged by a corona discharger 2 before it is imagewise exposed
to the image of an original through an exposure system 3. The
charge on the drum surface is neutralized in the exposed
region and is retained in the dark region which is free from
the influence of the exposure. In this manner, an electro-
static latent image corresponding to the image of the original
is formed on the drum surface. The latent image is converted
into a visual image by a developing unit 4. In the example
shown, the developing unit 4 is of a magnetic brush type
wherein a magnetic brush of powder developer comprising a
toner and a carrier is formed and maintained on the surface
of a developing roller under the influence of the magnetic
attraction exerted by the magnets contained internally within
the roller. By rotating the developing roller, the magnetic
brush is brought into contact with the latent image, which
electrostatically at*racts the toner in the magnetic brush,
thus producing a visual image. The developed powder image
on the drum is brought into superimposed relationship with a
i~S332
copy sheet 5 during a further rotation of the drum 1. The
copy sheet 5 is charged from the rear side by a corona dis-
charger 6. The electric charge applied to the copy sheet 5
is great enough to overcome the electrostatic attraction of
the latent image upon the powder image, thus transferring
the powder image onto the copy sheet 5. Subsequently, the
copy sheet 5 is separated from the drum surface, and the
powder image fixed to the sheet in a fixing unit 7. Subse-
quent to ~he transfer step, the drum surface is exposed to a
corona discharge by an a.c. corona discharger 8, whereby the
surface charge of the drum which maintains residual powder
thereon is neutralized, weakening the attaction upon the
residual powder. Thus, the residual powder can be removed
from the drum surface by a cleaning unit 9.
Referring to Fig. 2, which shows the cleaning appara-
tus 9 according to the invention in greater detail, it will
be seen that it comprises a cleaning roller 10 formed of
foamed urethane and disposed in gentle contact with the drum
surface. The roller 10 is rotated in a direction to run in
the opposite direction from the direction of rotation of the
drum 1 at the point of contact therebetween, and may be
driven at a peripheral speed of 250 mm/sec when the peripheral
speed of the drum 1 is 140 mm/sec. ~he apparatus also com-
prises a recovering roller 11 which is disposed close to or
in gentle contact with the surface of the cleaning roller 10.
The recovering roller 11 comprises a metallic roller 13 having
a surface coating 12 of Teflon (registered trademar~ of Du Pont
Company). The recovering roller 11 is rotated at substan-
tially the same speed as the cleaning roller lO but in a
direction such that these rollers move in opposite directions
at the point of contact therebetween or where they are most
332
closely located to each other. A pressure plate 14 is disposed
in forced abutment against a region of the surface of the
cleaning roller lO which immediately precedes the point of
contact with or minimum spacing from the recovering roller ll,
as viewed in the direction of rotation of the roller lO. It
will be noted that the pressure plate 14 is disposed to extend
generally in the same direction as the direction of rotation
of the cleaning roller 10, but it is preferred that the pres- -
sure plate 14 forms an angle ~ between 10 and 60 with respect
respect to the tangent at the point on the surface of
direction of the cleaning roller lO engaged by the end of the
plate. The pressure plate 14 is supported by a support member
15, and though it may comprise either a rigid or resilient
body, it is preferred that it have a relatively small thickness.
In the present embodiment, a stainless steel plate having a
thickness on the order of 0.5 mm is used.
A scraping blade 16 is disposed on the opposite side
of the recovering roller ll with its free end placed in gentle
contact with the surface thereof in a direction which is
opposite from the direction of rotation of the roller 11. The
scraping blade 16 is carried by a holder 17 which is integrally
formed with a guide plate 18 for conveying the removed powder.
A rotatable conveyor coil l9 is disposed below the free end
of the guide plate 18 for conveying the powder in a horizontal
direction to the exterior of the cleaning apparatus 9. The
entire apparatus 9 is enclosed in a cover 20.
In operation, the adhesion of the residual powder 21
to the surface of the drum 1 is diminished by the a.c. corona
discharger 8, and powder is then scraped by the cleaning roller
10 to be retained in the pores formed in the surface thereof.
As the cleaning roller lO rotates it carries the surface region
--6--
332
in which the remo~ed toner is retained to a position
corresponding to the free end of the pressure plate 14, at
which point the surface region is compressed by the pressure
plate 14. At the next moment when the surface region has
moved past the free end of the pressure plate 14 and is
released therefrom, the resilience of the roller material causes
the surface region to be restored impulsively to its original
configuration and at the same time to expel the retained powder
externally. Since the recovering roller 11 is rotating
immediately adjacent the pressure plate 14, the expelled
powder attaches to the surface of the recovering roller to be
carried thereby onto the scraping blade 16, and thence to the
guide plate 18 and conveyer coil 19, which conveys it to a
given l~cation.
In the embodiment described above, where both
the rollers 10, 11 maintain the contact therebetween during
their rotation, the cleaning roller 10 is triboelectrically
charged to a level of about positive 2400 volts while the
recovering roller 11 is charged to a negative level of the
same magnitude. After passing by the neutralizing charger,
the slectric charge remaining on the toner is substantially
reduced, so that the toner which is expelled by the pressure
plate 14 toward the recovering roller 11 can be easily
attracted and collected by the latter. In addition to the
triboelectric charging by the cleaning roller 10, the
recovering roller 11 can be charged (1) by triboelectric
charging by scraping blade 16, (2) by charging with a
charger, or (3) by the application of a bias voltage to the
metallic roller portion. The powder remaining on the drum
surface which is to be removed with the apparatus of the
invention may comprise a toner in a two-component developer,
or a magnetic or non-magnetic toner in a single component
332
developer.
Where a two-component developer is used in the
magnetic brush developing unit 4 as shown in Fig. 1, the
carrier usually comprises an iron powder or magnetic powder.
The carrier having a relatively large particle diameter forms
the tuft of a brush under the magnetic influence of the
magnets, and a toner having a relatively small particle
diameter is attached to the brush by triboelectricity which
results from the friction with the carrier. For example,
when an iron powder is mixed with a resin toner which is
situated at a higher rank in the triboelectric series, the
toner is charged to the positive polarity and the iron powder
to the negative polarity. The developing process takes place
by rubbing the carrier- and toner- brush against the drum
surface on which an electrostatic latent image is formed.
Where the latent image is formed by a negative charge, the
positively charged toner can be easily attached thereto while
the negatively charged iron powder is repelled. However,
1 if the adhesion between the iron powder and the toner is
~0 greater than the force of repulsion, the iron powder attaches
to the latent image while it is attached by the toner. In
this manner, there may be a small amount of iron powder
admixed with the developed powder image. When the cleaning
roller is used to remove any residual powder from the drum
surface subsequent to the transfer of the powder image onto
a copy sheet, the powder attaching to the cleaning roller
must be sufficiently recovered, otherwise the iron powder may
be brought into contact with the drum surface again, thereby
damaging it. In particular, when the cleaning roller is
formed of foamed resin, recovery of the removed powder is
difficult to achieve. In accordance with the invention, a
recovery means as shown in Fig. 3 is provided to this end.
lilt~33~
Fig. 3 shows another form of the recovering means.
Specifically, there is shown a recovering roller 31 which
comprises a rotatable metallic roller 33 having a surface
coatlng 32 of Teflon. A stationary magnet 34 is disposed
inside the metallic roller 33. The roller 31 is rotated sub-
stantially at the same speed as the cleaning roller 10, but
in a direction so that they move in opposite directions at
the point of contact therebetween. The orientation of the
magnet 34 is chosen such that one of its poles is situated
near the circumference of the cleaning roller 10 at a point
immediately preceding the point of contact with the recovering
roller 31. The pressure plate 14 has its free end disposed
in forced abutment against the surface of the cleaning roller
10 at a corresponding position. With this arrangement, the
iron powder contained in the removed powder which is expeiled
by the pressure plate 14 is attracted by the recovering roller
31 under its magnetic influence, together with the toner.
The recovering roller 31 may be entirely formed as a magnet.
The powder is removed from the recovering rollers
11, 31 shown in Figs. 2 and 3 by means of scraping blade 16.
The use of the scraping blade for removal generally tends to
produce a solidification of removed powder during its
conveyance. To avoid such solidification, it has been the
practive heretofore to impart oscillations to removed powder
in its path of conveyance for disintegrating it. An
' alternative has been to dispose the scraping blade in a nearly
vertical position for contact with the cleaning roller. How-
ever, imparting oscillations to the removed powder results in a
scattering or dispersion of the powder, thereby producing an
adverse influence upon the overall system. On the other hand,
the vertical disposition of the scraping blade imposes a
restriction on the layout of other devices.
332
In accordance with the invention, the cleaning
apparatus includes a rotatable helical coil disposed in a
path of conveyance of powder that is removed by the scraping
blade, for preventing a solidification of removed powder and
facilitating its conveyance. ~eferring to Fig. 4, the
scraping blade 16 is disposed on the side of the recovering
roller ll which is away from the cleaning roller, and
has its free end disposed in gentle contact with the surface
of the recovering roller 11 in a direction opposite from the
direction of rotation thereof. The scraping blade 16 is
carried by a holder 17 which is integrally provided with a
guide plate 18 for conveying removed powder. A rotatable
auxiliary helical coil 41 (see Fig. 5) of a large diameter
is disposed above the guide plate 18 and is closely spaced
therefrom while a rotatable helical coil l9 of a reduced
diameter is disposed below the free end of the guide plate 18.
The recovery of powder from the recovering roller ll by the
scraping blade 16 tends to solidify the powder. However, the
solidified powder is disintegrated by the helical coil ~l .
while moving down the guide plate 18. As it falls down from
the tip of the guide plate 18, the powder is laterally
conveyed by the helical coil 19 to a given position for recovery.
In carrying out the present invention, a number
of modifications and changes may be made in the embodiments
described above. By way of example, melton cloth (Molleton
for tradename) or a fur brush having a hair length on the order
of 1 to 1.5 mm may be substituted for the foamed resin material
of the cleaning roller with similar effect. Both of these
materials exhibit a high resilience. Where the drum runs at
a high peripheral speed, the single cleaning roller used will
have to be operated at a higher peripheral speed, causing a
scattering of the toner. This can be avoided by providing a
--10--
3~Z
plurality of cleaning rollers. In addition, the drum, the
cleaning and recovering rollers may be replaced by endless
belts. Therefore it is intended that the scope of the
invention be solely defined by the appended claims.
