U.S. patent number 3,739,748 [Application Number 05/098,373] was granted by the patent office on 1973-06-19 for donor for touchdown development.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to Joseph Fantuzzo, Alfred J. Rittler, Raymond G. Williams.
United States Patent |
3,739,748 |
Rittler , et al. |
June 19, 1973 |
DONOR FOR TOUCHDOWN DEVELOPMENT
Abstract
Apparatus for developing a latent electrostatic image carried on
an image retaining member comprising A member including an
electrically conductive layer and a dielectric layer having a
generally continuous surface for carrying toner particles for the
development of the latent image, A plurality of stylii supported
for relative movement with the donor member spaced from each other
and positioned to contact the donor member enabling electrostatic
charge to be deposited onto separate, discrete areas of the toner
carrying surface of the donor member corresponding in size to the
surface area of the tips of the stylii creating an electrostatic
charge pattern comprising a plurality of lines on the donor member
upon coupling the donor member conductive layer and stylii to an
electrical energy source and upon moving the stylii and donor
member relative to one another and Means to move the donor member
relative to a supply of toner particles for loading toner particles
onto the donor member in areas associated with the charge pattern
of lines created by the plurality of stylii and to move the toner
loaded donor member relative to the image retaining member for the
development of the latent electrostatic image.
Inventors: |
Rittler; Alfred J. (Webster,
NY), Fantuzzo; Joseph (Webster, NY), Williams; Raymond
G. (Rochester, NY) |
Assignee: |
Xerox Corporation (Stamford,
CT)
|
Family
ID: |
22269003 |
Appl.
No.: |
05/098,373 |
Filed: |
December 15, 1970 |
Current U.S.
Class: |
399/313 |
Current CPC
Class: |
G03G
15/0815 (20130101); G03G 15/0806 (20130101) |
Current International
Class: |
G03G
15/08 (20060101); G03g 015/08 () |
Field of
Search: |
;117/17.5 ;96/1R,1SD
;118/637 ;355/3 ;346/74MP,74ES |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Katz; Murray
Assistant Examiner: Sofocleous; M.
Claims
What is claimed is:
1. Apparatus for developing a latent electrostatic image carried on
an image retaining member comprising
a donor member including an electrically conductive layer and a
dielectric layer having a generally continuous surface for carrying
toner particles for the development of the latent image,
a plurality of stylii supported for relative movement with the
donor member spaced from each other and positioned to contact the
donor member enabling electrostatic charge to be deposited onto
separate, discrete areas of the tonor carrying surface of the donor
member corresponding in size to the surface area of the tips of the
stylii creating an electrostatic charge pattern comprising a
plurality of lines on the donor member upon coupling the donor
member conductive layer and stylii to an electrical energy source
and upon moving the stylii and donor member relative to one another
and
means to move the donor member relative to a supply of tonor
particles for loading tonor particles onto the donor member in
areas associated with the charge pattern of lines created by the
plurality of stylii and to move the tonor loaded donor member
relative to the image retaining member for the development of the
latent electrostatic image.
2. The apparatus of claim 1 including oscillating means for
imparting relative movement between the stylii and donor member in
a lateral coordinate generally transverse to the direction of
movement between the donor member and the image retaining
member.
3. The apparatus of claim 1 including an electrical energy source
coupled to said stylii to maintain them at substantially the same
potential.
4. The apparatus of claim 1 including an electrical energy source
coupled to said stylii by means to maintain some stylii at
different potentials from other stylii.
5. The apparatus of claim 1 wherein the dielectric layer of the
donor member includes glass.
6. The apparatus of claim 1 wherein said donor member includes a
metal drum having an outermost coating of glass comprising the
dielectric layer.
Description
BACKGROUND OF THE INVENTION
This method and apparatus relates to electrostatic image
development and more particularly to an improved xerographic method
and apparatus for the development of electrostatic images by which
a toner layer is presented to the latent image for development
thereof.
In the reproduction process of xerography, a photoconductive
surface is charged and then exposed to a light pattern of the
information to be reproduced, thereby forming an electrostatic
latent image on the photoconductive surface. Toner particles, which
may be finely divided, pigmented, resinous material are presented
to the latent image where they are attracted to the photoconductive
surface. The toner image can be fixed and made permanent on the
photoconductive surface or it can be transferred to another surface
where it is fixed.
One known method of developing latent electrostatic images is by a
process called transfer development. Transfer development broadly
involves bringing a layer of toner to an imaged photoconductor
where toner particles will be transferred from the layer to the
imaged areas. In one transfer development technique, the layer of
toner particles is applied to a donor member which is capable of
retaining the particles on its surface and then the donor member is
brought into close proximity to the surface of the photoconductor.
In the closely spaced position, particles of toner in the toner
layer on the donor member, are attracted to the photoconductor by
the electrostatic charge on the photoconductor so that development
takes place. In this technique the toner particles must traverse an
air gap to reach the imaged regions of the photoconductor. In two
other transfer techniques the toner-laden donor actually contacts
the imaged photoreceptor and no air gap is involved. In one such
technique, the toner-laden donor is rolled in non-slip relationship
into and out of contact with the electrostatic latent image to
develop the image in a single rapid step. In another such
technique, the toner-laden donor is skidded across the xerographic
surface. Skidding the toner by as much as the width of the thinnest
line will double the amount of toner available for development of a
line which is perpendicular to the skid direction and the amount of
skidding can be increased to achieve greater density or greater
area coverage.
It is to be noted, therefore, that the term "transfer development"
is generic to development techniques where (1) the toner layer is
out of contact with the imaged photoconductor and the toner
particles must traverse an air gap to effect development, (2) the
toner layer is brought into rolling contact with the imaged
photoconductor to effect development, and (3) the toner layer is
brought into contact with the imaged photoconductor and skidded
across the imaged surface to effect development. Transfer
development has also come to be known as "touchdown
development."
In a typical transfer development system, a cylindrical or endless
donor member is rotated so that its surface can be presented to the
moving surface of a photoconductive drum bearing an electrostatic
latent image thereon. Positioned about the periphery of the donor
member are a number of processing stations including, a donor
loading station, at which toner is retained on the donor member
surface; an agglomerate removal station at which toner agglomerates
are removed from the toner layer retained on the surface of the
donor member; a charging station at which a uniform charge is
placed on the particles of toner retained on the donor surface; a
clean up station at which the toner layer is converted into one of
uniform thickness and at which any toner agglomerates not removed
by the agglomerate removal station are removed; a development
station at which the toner particles carried by said donor member
are presented to the imaged photoconductor for image development;
and a cleaning station at which a neutralizing charge is placed
upon the residual toner particles and that which a cleaning member
removes residual toner from the peripheral surface of the toner. In
this manner, a continuous development process is carried out.
Among the donor members employed in the prior art are those
embodying the principles described in U.S. Pat. No. 3,203,394. Such
a donor includes, an electrically conductive support member in the
form of a cylinder, a thin electrically insulating layer overlying
support member, and a continuous, electrically conductive screen
pattern overlying the insulating layer. The screen pattern is
provided with an electrical connection to slip ring so that its
potential may be varied between ground potential and a charge
potential at different stages of process. A multitude of high
fringe fields or microfields are created at the surface of this
type of donor member. When this type of donor member is brought
into contact with toner particles, it is in this manner loaded with
toner.
A donor member of this type is quite expensive to manufacture, it
is quite fragile in the screen regions and is subject to being
electrically disabled, e.g., through shorting of the screen to the
conductive substrate, unless considerable care is taken during its
manufacture and use.
The art of xerographic development, and in particular transfer
development, would be significantly advanced if a simpler and more
reliable donor member were available.
Accordingly, it is an object of the invention to improve donor
member apparatus for developing latent electrostatic images.
It is a further object of the invention to simplify the
construction of a donor member apparatus for developing latent
electrostatic images.
It is still an object of this invention to improve upon known
transfer development processes.
SUMMARY OF THE INVENTION
The invention is directed to an apparatus for developing a latent
electrostatic image formed on the surface of an image retaining
surface. The apparatus includes a means for developing a latent
image and the means includes: (a) a donor member adapted to
transport toner particles to the latent image comprising, an
endless electrically conductive support member carrying on the
outer surface thereof a continuous dielectric layer; (b) means to
maintain the conductive support member at a reference potential;
(c) means to cause electrical discharge at least at the surface of
defined regions of said dielectric layer to collect an electrical
charge pattern on the surface of said dielectric layer; (d) means
to continuously advance said donor member past a plurality of
treating stations, said treating stations including; (1) a toner
loading station including a supply of toner particles at which said
toner particles are contacted by said donor member and toner
particles retained on said donor member in response to the force of
said charge pattern; (2) a developing station at which the retained
toner particles are presented in developing relation to a latent
electrostatic image on an image retaining element.
In a preferred embodiment, the means to cause electrical discharge
at the surface of the defined regions of the dielectric layer is at
least one electrically conductive member, e.g., a stylus, in a
small area-contact with the surface of the dielectric layer and a
voltage source in electrical communication with the conductive
member. It is also preferred that this means includes a plurality
of uniformly spaced electrically conductive members each in small
area-contact with the surface of the dielectric layer. The same or
different voltages may be applied to the conductive members.
The present invention is also directed to a latent electrostatic
image developing method. The latent image is formed on the surface
of an image retaining member, e.g., a xerographic plate. A layer of
toner particles is retained on the surface of an endless donor
member, said donor comprising an electrically conductive support
member carrying on the outer surface thereof a continuous
dielectric layer, by (1) maintaining said conductive support member
at a reference potential (2) bringing at least one electrically
conductive member into small area-contact with the surface of the
dielectric layer, (3) causing relative motion between the
conductive member and the surface of the dielectric layer, (4)
causing electrical discharge between the surface of the dielectric
layer and the contact surface of the conductive member so as to
collect an electrical charge in the regions defined by the small
area-contact, and (5) bringing the so-charged surface of the donor
member into contact with the supply of toner particles to permit
toner particles to adhere to the surface of the donor member; and
presenting the adhered toner particles to the latent image to
effect development thereof.
Other treating stations and processing steps may be added to the
apparatus and process. For example, a toner agglomerate removal
station may follow the toner loading station, a uniform charging
station may follow the toner agglomerate removal station, a
clean-up station may follow the uniform charging station and a
residual or ghost image removal station may follow the developing
station.
BRIEF DESCRIPTION OF THE DRAWING
For a better understanding of the invention as well as other
objects and further features thereof, reference is made to the
accompanying drawing, wherein:
FIG. 1 is a sectional view of xerographic apparatus in accordance
with the present invention; and
FIG. 2 is an isometric view of a preferred donor member in
accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a transfer development system and method
in which toner particles are applied to an electrostatic latent
image on the photoconductive plate to develop the image. Although
the system and method is described herein as part of the
xerographic copier, it can be utilized in conjunction with any
reproduction system wherein a latent image is to be developed by
applying toner thereto, e.g., a latent image in an electrographic
system.
Referring to FIG. 1, there is shown a xerographic reproduction
system utilizing the concept of the present invention. In this
apparatus a xerographic plate is in the form of a drum 10 which
passes through stations A-E in the direction shown by the arrow.
The drum has a suitable photosensitive surface, such as one
including selenium overlying a layer of conductive material, on
which a latent electrostatic image can be formed. The various
stations about the periphery of the drum which carry out the
reproduction process are: charging station A, exposing station B,
developing station C, transfer station D, and cleaning station E.
Stations A, B, D, and E represent a conventional means for carrying
out their respective functions. Apart from their association with
the novel arrangement to be described with respect to station C
they form no part of the present invention.
At station A, a suitable charging means 12, e.g., a corotron,
places a uniform electrostatic charge on the photoconductive
material. As the drum rotates, a light pattern, via a suitable
exposing apparatus 14, e.g., a projector, is exposed onto the
charged surface of drum 10. The latent image thereby formed on the
surface of the drum is developed or made visible by the application
of a finely divided pigmented, resinous powder called toner at
developing station C, which is described in greater detail below.
After the drum is developed at station C, it passes through
transfer station D, comprising copy sheet 16, corona charging
device 18 and fuser device 20. Following transfer and fixing of
developed image to the copy sheet, the drum rotates through
cleaning station E, comprising cleaning device 22, e.g., a rotating
brush.
At developing station C, the apparatus includes a donor member 24
(more particularly described below) rotatably mounted adjacent a
toner reservoir 26 containing a supply of toner 28. The donor roll
24 is positioned so that a portion of its periphery comes into
contact with toner 28. The donor roll is also located so as to
provide a small gap between the surface of drum 10 and the outer
surface of a toner layer carried by donor roll 24. This gap can be
approximately 1 mil.
Located between the toner reservoir 26 and the developing region is
a charging means, such as a corona charging device 36, which is
adapted to place a uniform charge on the toner particles of a
polarity opposite to the polarity of the latent image on the
photoconductive drum in those instances where non-uniformly charged
toner particles are present in the toner reservoir.
Referring now also to FIG. 2 of the drawing, there is shown a donor
member of the type contemplated by the present invention. Donor
member 24 comprises a conductive drum 42, for example a metal drum
such as aluminum, copper, etc, over the surface of which is coated
a dielectric layer 44 which can be for example an organic plastic,
glass, ceramic, etc. As indicated above donor member 24 is
positioned so that a portion of its periphery may be rotated into
contact with a mass of toner particles 28 in a toner reservoir 26.
The metallic drum 42 is maintained at a reference potential, e.g.,
at ground potential, via contact member 34. In contact with the
surface of dielectric layer 44 are a plurality of conductive styli
46. These styli 46 are connected via conductive members 30 to a
common electrical lead 48 which in turn is in electrical
communication with a voltage source 32, e.g., a battery. It is to
be understood that instead of a single voltage source, individual
voltages may be applied to the conductive styli to facilitate gray
scale rendition during development.
In operation, as donor member 24 rotates in the direction shown by
the arrow in FIG. 1, and voltage source 32 is applied to the
system, a discharge occurs between the tips of styli 46 and the
surface of dielectric layer 44. This discharge causes an electrical
charge to be collected on the surface of the dielectric 44. The
charge is represented by dash lines 50 and are approximately as
wide as the small contact area of the tips of the styli. As the
drum continues to rotate into contact with the toner particles in
reservoir 26, toner is attracted to the charged lines on the drum.
The donor member then continues to rotate so as to present the
adhered toner particles into developing relation with the imaged
portion of drum 10.
It is to be understood that the individual styli can be connected
to different voltage sources of the same polarity, so that a
different magnitude of charge can be collected on the surface of
the donor member. By this means, gray scale development can take
place at the development region of the system. The styli may be
conveniently separated by a spacing of from 1 to 5 mils. During
rotation of the donor, a suitable oscillating means 52 can be
employed to impart a lateral or oscillating motion to the
conducting styli. This will give a zig-zag design to the charge
pattern and permit a larger amount of a single polarity toner to be
adhered to the donor surface.
Following development, the donor roll is prepared for toner
reloading by discharging the surface of the drum at a point just
beyond the developing region. The drum may be discharged by a
number of techniques, e.g., a conductive rubber roller or an AC
corona, for example, corona device 38, as shown in FIG. 1. After
discharge of the surface of the donor member, residual toner may be
removed by any cleaning means, for example brush 40, as shown in
FIG. 1. Instead of the toner loading station shown in the drawing,
other toner loading means may be employed, for example, fur brush,
magnetic brush, etc.
In addition to the several stations described in the apparatus of
the present invention it is to be understood that other stations
may be strategically located about the periphery of the donor
member, for instance, a toner agglomerate removal station may be
located between toner reservoir 26 and charging means 36. This
agglomerate removal station may conveniently be a vacuum means
adapted to remove large toner agglomerates from the surface of the
retained toner particles.
It is to be understood while for purposes of illustration the donor
member has been described basically as a cylinder, it may be an an
endless belt adapted to deliver toner from the toner source to the
several stations.
Conventional drive means, e.g., motors, belts, etc. are employed to
drive the several movable members all in a manner within the skill
of the art.
Since many changes can be made in the above construction and many
apparently widely different embodiments of this invention can be
made without departing from the scope thereof it is intended that
all matter contained in the drawing and specification should be
interpreted illustratively and not in a limited sense.
* * * * *