U.S. patent number 3,634,077 [Application Number 04/755,265] was granted by the patent office on 1972-01-11 for method and apparatus for removing a residual image in an electrostatic copying system.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to William A. Sullivan.
United States Patent |
3,634,077 |
Sullivan |
January 11, 1972 |
METHOD AND APPARATUS FOR REMOVING A RESIDUAL IMAGE IN AN
ELECTROSTATIC COPYING SYSTEM
Abstract
A method and apparatus for recovering the residual image from an
electrostatic recording surface in an electrostatic copying system
which is accomplished by presenting a wiping element in pressure
contact with the residual image on the recording surface whereby
the residual image is substantially removed therefrom, moving a
conductive member in close proximity to the toner particles being
removed from the recording surface, applying a DC voltage opposite
in polarity to that of the toner particles and of sufficient
magnitude to the conductive member whereby the toner particles are
attracted onto the surface of the conductive member, and
continuously removing the toner particles from the conductive
member into a collection zone for reuse in the copying system.
Inventors: |
Sullivan; William A. (Webster,
NY) |
Assignee: |
Xerox Corporation (Rochester,
NY)
|
Family
ID: |
25038403 |
Appl.
No.: |
04/755,265 |
Filed: |
August 26, 1968 |
Current U.S.
Class: |
430/119.82;
15/100; 427/469; 399/359; 15/1.51; 15/256.5 |
Current CPC
Class: |
G03G
21/0047 (20130101); G03G 21/0011 (20130101); G03G
21/10 (20130101); G03G 2221/0005 (20130101) |
Current International
Class: |
G03G
21/00 (20060101); G03G 21/10 (20060101); G03g
013/16 (); G03g 013/22 () |
Field of
Search: |
;96/1,1.4
;117/17.5,19,93.41,102 ;118/637,70,104 ;15/1.5,256.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Van Horn; Charles E.
Claims
What is claimed is:
1. A method of cleaning and recovering a residual image from an
electrostatic recording surface for reuse in an electrostatic
copying system in which an electrostatic charge is placed on a
recording surface, then the charged surface is exposed to a
radiation image of copy to be reproduced to form an electrostatic
latent image thereon, then electroscopic toner particles are
applied to form a powder image, then electrostatically transferring
the powder image of the recording surface to a support material
whereby after transfer there remains on the recording surface a
residue of toner particles, the improved cleaning and recovering
method comprising the steps of placing a wiping blade in pressure
contact with the residual toner particles on the recording surface
whereby the residual toner particles are substantially removed
therefrom, moving a conductive member in close proximity to the
toner particles being removed from the recording surface, applying
a DC voltage opposite in polarity to that of the toner particles
and of sufficient magnitude to the conductive member to collect
substantially all the toner particles onto the surface of the
conductive member removed by the wiping blade and continuously
wiping the surface of the moving conductive member to remove the
toner particles from the conductive member into a collection zone
for reuse in the copying system.
2. A method according to claim 1 including the step of applying a
charge of the same polarity as said toner particles to said
recording surface before said toner particles are contacted by said
wiping element.
Description
This invention relates to electrostatic imaging systems and more
particularly, to an improved apparatus for cleaning electrostatic
recording surfaces.
The formation and development of images on the surface of recording
materials by electrostatic means is well known. One basic process,
as taught by Chester F. Carlson, in U.S. Pat. No. 2,297,691,
involved placing a uniform electrostatic charge on a
photoconductive insulating layer, exposing the layer to a
light-and-shadow image to dissipate the charge on the areas of the
layer exposed to the light and developing the resulting latent
electrostatic image by depositing on the image a finely divided
electroscopic powder material referred to in the art as "toner."
The toner is normally attracted to those areas of the layer which
retain a charge, thereby forming a toner image corresponding to the
latent electrostatic image. This powder image may then be
transferred to a support surface such as paper. The transferred
image may subsequently be permanently affixed to a support surface.
After cleaning, the layer is ready for another imaging cycle.
As is well known in recent years, the steadily increasing size of
various industries has required an enormous increase in the amount
of paper work that must be accomplished, maintained and made
available for wide interplant circulation. In the present day
commercial automatic copier/reproduction machines, the
electrostatic recording surface is in the form of a drum or belt
which moves at high rates in timed unison relative to a plurality
of processing stations. This rapid movement of the electrostatic
recording surface has required vast amounts of toner particles
during development resulting in greater difficulty in removing the
residual image remaining on the recording surface after
transfer.
Several techniques are known for cleaning the residual image from
the recording surfaces such as the "brush"-type apparatus as
described in U.S. Pat. No. 2,832,977 and the "web"-type apparatus
as described in U.S. Pat. No. 3,186,838. The present invention is
an improvement over the existing techniques and is also intended as
an improvement over the cleaning technique described in copending
application Ser. No. 702,306 filed on Feb. 1, 1968 for cleaning a
recording surface.
It is, therefore, an object of this invention to improve the
cleaning of recording surfaces used in electrostatic reproduction
machines.
It is a further object of this invention to reduce toner
consumption in automatic electrostatic imaging machines.
It is also an object of this invention to utilize cleaning
apparatus in reproduction equipment which does not require
extensive alignment or adjustment.
It is still another object of this invention to remove residual
toner which is immediately reusable in an electrostatic imaging
system.
It is a further object of this invention to provide simple,
inexpensive and reusable apparatus for cleaning electrostatic
recording surfaces.
It is still a further object of this invention to provide cleaning
apparatus for an electrostatic imaging system which is more
efficient than existing cleaning devices.
It is still a further object of this invention to prevent powder
cloud formation at the cleaning station of copier/duplicator
machines.
It is still a further object of this invention to reduce the noise
level of copier/duplicator machines.
These and other objects of the invention are attained, generally
speaking, by wiping the electrostatic recording surface with a
cleaning blade in pressure contact with the surface to mechanically
remove the toner particles from the surface. At the same time, an
electrical potential of a polarity opposite that of the toner
particles and of sufficient magnitude is applied to roll means
positioned adjacent the cleaning blade to attract the toner
particles from the vicinity of the blade onto the roll means
thereby recovering substantially all of the toner particles removed
from the recording surface and also preventing the formation of a
cloud. The toner particles are then removed from the electrically
biased roll means and collected for reuse in the copying
system.
For a better understanding of the invention as well as other
objects and further features thereof, reference is had to the
following detailed description of the invention to be read in
conjunction with the accompanying drawing, the single FIG. of which
is a partly schematic, cross-sectional side elevational view of a
reproduction machine incorporating cleaning apparatus according to
the present invention.
Referring to the drawing, an automatic copier machine is shown
employing a cleaning apparatus 10 for cleaning a residual image
from an electrostatic recording member 11. Recording member 11 is
formed in the shape of a drum having an outer layer 12 of suitable
photoconductive insulating material, such as, vitreous selenium,
and is mounted on a shaft 13 to move in the direction indicated by
the arrow past several processing stations.
As in most electrostatic recording machines, the surface of
photoconductive insulating layer 12 is uniformly charged by a
corona charging device 14. Next the drum surface is exposed to a
pattern of activating electromagnetic radiation as by an optical
projector 16 to form an electrostatic latent image.
The latent electrostatic image formed is then developed in any
suitable manner as by a developing apparatus 18. Developer
apparatus 18 comprises a developer housing 20 having a lower
reservoir or sump portion for accumulating developer material 22.
Any suitable developer material containing electroscopic toner
particles can be used such as that described, for example, in the
copending application referred to above or in U.S. Pat. No.
2,618,551 to Walkup, U.S. Pat. No. 2,618,552 to Wise, U.S. Pat. No.
2,638,416 to Walkup and Wise, and U.S. Pat. No. Re. 25,136 to
Carlson. For positive to positive reproduction, a negatively
charged toner is used, whereas in a negative to positive
reproduction, a positively charged toner is used. Mounted within
the developer housing 20 is a driven bucket-type conveyor 24 used
to carry the developer material from the sump to the upper portion
of the developer housing 20 from where the developer material is
cascaded over a hopper chute 28 onto the surface of the
photoconductive layer 12.
As the developer material cascades over the drum, toner particles
in the developer material adhere electrostatically to the
previously formed electrostatic latent image areas on the surface
of the photoconductive layer 12 to form a visible xerographic
powder image; the remaining developer material falling off the
peripheral surface of the drum into the sump of the developer
housing 20. Toner particles consumed during the developing
operation to form the xerographic powder images are replenished by
a toner dispenser 19, such as, the dispenser described in U.S. Pat.
No. 3,013,703 to Hunt.
The developed image emerging from the developing apparatus is
transferred to a moving web 30 made of any suitable material, such
as, paper by a corona charging device 31. The transferred image may
be permanently fixed to the web 30 by any suitable means such as by
a heat fuser 32. After transfer, the drum surface is cleaned of
residual toner particles by cleaning apparatus 10 as will be
explained completing the recording cycle and readying the surface
for another cycle in the manner already described. The cleaning
apparatus of this invention is adapted to remove the residual toner
material in such a manner that it can be reused with the developer
material and at the same time be effective for continuous cleaning
whereby replacement of the cleaning apparatus is not a concern.
Cleaning apparatus 10 comprises a substantially rectangular
cleaning blade member 36 suitably secured to a blade holder 38 as
by means of a shoulder screw 40. The cleaning blade 36 normally
rests in pressure contact with the surface of photoconductive layer
12 due to the combined weight of the blade itself, the blade holder
38, and spring-biasing assembly 46 which desirably is adjustable to
vary the contact pressure. Cleaning blade 36 may be made of any
suitable, nonmetallic flexible material. Typical materials include
polysiloxane rubber, polyurethane rubber, polytetrafluoroethylene
resin, polytrifluorochloroethylene resin, styrene butadiene rubber,
nitrile-silicone rubber, flexible polyurethane foam, polyethylene
resin and blends, mixtures and copolymers thereof. The blade should
be sufficiently soft to minimize abrasion of reusable imaging
surfaces, particularly selenium-type imaging surfaces. Preferably,
the blade material should have a Short hardness of less than about
D65. Considerable latitude in blade thickness is permissible.
However, the blade should be sufficiently thick to avoid collapse
of the blade on the imaging surface under the blade pressure
conditions employed.
As the leading edge or face of blade member 36 contacts the drum
surface 12 the residual toner particles are continuously removed
from the surface by a scraping action. To collect these particles
for reuse in the system, there is positioned in close proximity
with the blade member and drum surface a bias roll member 60
adapted for rotation on a shaft 62 driven to obtain about the same
peripheral speed between the roll and drum surface in the direction
indicated by the arrow. Bias roll member 60 is made out of a
suitable conductive material and is connected to a variable source
of DC voltage 64 which is of a polarity opposite to that of the
toner particles and of sufficient magnitude to attract toner
particles removed by blade 36 onto the roll surface. DC voltage 64
desirably ranges from about 500 volts to about 5,000 volts to
achieve efficient removal of the toner particles and to prevent any
undesirable cloud formation in the vicinity of the drum
surface.
In order to further enhance the electrostatic attraction of the
toner particles onto the bias roll member 60, corona generating
device 50 is positioned in the path of the drum after the transfer
step but before the cleaning blade to place a charge on the
residual toner particles of the same polarity as the particles
which in this case would be negative. This charge desirably reduces
the attraction of the toner particles to the surface of the drum
and ensures that the toner particles are properly negatively
charged so that they will be attracted to the positive potential
applied by DC voltage 64. It has been found that a current ranging
from about 2 to about 10 microamperes for the corona device is
sufficient for this purpose. Corona device 50 is suitably powered
as by a variable source of DC voltage 52.
To enable continuous cleaning action and to recover the toner
particles so that they may be returned and reused in the
development system of the machine, a scraper member 65 is
positioned in the path of bias roll member 60 to remove the
particles for collection in sump 66 in the lower portion of a
housing 68. Scraper member 65 is made of any suitable metallic or
nonmetallic material and is connected to housing 68 by one or more
insulating block members 71 as by screws 79. If desired, contact
pressure of the scraper member 65 with the surface of roll member
60 may be adjustable in any suitable manner as by a spring.
As the toner particles are collected in sump 66 they are desirably
removed by an auger member 81 mounted for rotation on a shaft 83
journaled in housing 68. Auger member 81 rotates through the toner
material collected in the tray in a direction shown by the arrow to
move the toner toward one or more conduits 85 from which the toner
particles are discharged either by gravity or any other suitable
means for reuse at the development station.
Above is described a new and novel cleaning apparatus capable of
removing substantially all of the residual toner particles on the
surface of an electrostatic recording member and for collecting the
toner for reuse in the copier/duplicating machine. Heretofore,
cleaning of the recording surface was accomplished by a rotating
brush or web which has to be discarded and replaced after periodic
use and which prevented the toner from being reused in the
development system again. With the present invention, the toner
particles are removed from the recording surface in such a manner
that objectionable filming of the toner does not occur and hence
the toner is adapted for reuse in the system repeatedly.
Furthermore, no powder cloud is formed at the cleaning station
which undesirably can cause a malfunction of the machine. Also, the
cleaning apparatus of the present invention does not require
extensive repair or adjustment as in the case of the prior art
cleaning devices. Thus, the apparatus of the invention not only
provides very efficient cleaning but is also inexpensive and
reusable while permitting toner collected to be used repeatedly in
the copying system. Hence the invention is greatly desirable for
producing high-quality prints in automatic copying machines at very
high rates.
This application specifically describes one form which the
invention may assume in practice. It will be understood that this
form is the same as shown for purposes of illustration and that the
invention may be modified and embodied in various other forms
without departing from the scope of the appended claims.
* * * * *