U.S. patent number 3,647,292 [Application Number 04/880,576] was granted by the patent office on 1972-03-07 for transfer apparatus.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to Donald J. Weikel, Jr..
United States Patent |
3,647,292 |
Weikel, Jr. |
March 7, 1972 |
TRANSFER APPARATUS
Abstract
An apparatus and method for efficiently transferring a toner
image from a rotatable electrostatic drum to a copy sheet while the
copy sheet remains in a substantially flat position without
degrading the quality of the latent image on the drum by imposing
an electrical field between the copy sheet and drum as the sheet
moves away from the drum surface after the toner image has been
transferred to the copy sheet. In one embodiment of the invention,
a movable, endless, two-layer belt having an inner layer of
conductive material and an outer layer of relatively nonconductive
material carries the copy sheet through the transfer station in a
plane substantially tangent to the surface of the drum. An
electrical bias is applied to the inner layer of the belt which
attracts toner from the electrostatic drum to the copy sheet, but
charge is prevented from reaching the copy sheet and drum by the
relatively nonconductive layer of the belt. Small holes can be made
in the belt and a vacuum placed on the copy sheet through the holes
to insure there is no relative motion between the copy sheet and
belt during the transfer step. In a second embodiment of the
invention, a movable, endless, relatively nonconducting belt
carries the copy sheet through the transfer station in a
substantially flat position. Directly under the belt, adjacent the
transfer area and that area through which the copy sheet travels as
it leaves the drum surface after transfer has taken place, is a
stationary conductive means having an electrical bias thereon. In a
third embodiment, the stationary conductive means is constructed so
that the electrical bias placed on it can be increased as a given
portion of the copy sheet increases its distance from the surface
of the drum.
Inventors: |
Weikel, Jr.; Donald J.
(Rochester, NY) |
Assignee: |
Xerox Corporation (Rochester,
NY)
|
Family
ID: |
25376579 |
Appl.
No.: |
04/880,576 |
Filed: |
November 28, 1969 |
Current U.S.
Class: |
399/315; 399/313;
399/398 |
Current CPC
Class: |
G03G
15/167 (20130101) |
Current International
Class: |
G03G
15/16 (20060101); G03g 015/00 (); G03g
015/08 () |
Field of
Search: |
;355/3,14,17 ;96/1.4
;117/17.5 ;118/637 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
IBM Technical Disclosure Bulletin, Vol. 12, No. 2 July
1969.
|
Primary Examiner: Peters, Jr.; Joseph F.
Assistant Examiner: Greiner; Robert P.
Claims
What is claimed is:
1. In a reproduction system having a rotatable electrostatic drum,
means to rotate the drum at a predetermined speed, means to form a
toner image on the surface of the drum with toner particles having
a predetermined polarity, and means to transfer the toner image
from the surface of the drum to a copy sheet, or the like, at a
transfer station, a transfer apparatus comprising:
a. an endless, flexible, movable belt of relatively nonconducting
material;
b. means to support the belt in a substantially flat plane in the
transfer station;
c. means to move successive portions of the belt through the
transfer station at a predetermined speed;
d. means to load the copy sheet on the belt so that the copy sheet
is carried through the transfer station by the belt in registration
with a toner image on the drum;
e. first conducting means located in the transfer station adjacent
the belt on the side thereof opposite the drum;
f. means to impose a first electrical potential on the first
conducting means having a polarity opposite to the predetermined
polarity on the toner particles adapted to transfer a toner image
from the surface of the drum to the copy sheet;
g. second conducting means located adjacent the belt on the side
thereof opposite the drum in the area where the copy sheet is
separated from the surface of the drum after a toner image is
transferred to the copy sheet; and
h. means to concurrently impose a plurality of different potentials
on the conducting means having a polarity opposite to the
predetermined polarity on the toner particles, each different
potential in said plurality being of greater value than first
potential and increasing in value in the direction towards which
the belt moves, whereby the retransfer of toner from the copy sheet
to the drum is prevented as the copy sheet is separated from the
surface of the drum.
2. The apparatus in claim 1 wherein the second conducting means is
a plate having sections of conducting and nonconducting material
alternately arranged and each conducting section has one of the
different potentials in said plurality of potentials imposed
thereon.
3. In an automatic reproducing apparatus having a movable image
retaining member, means to move said member at a predetermined
rate, means to formulate a charged toner image upon said member,
and means to transfer the toner image from said member to a sheet
of final support material within a transfer zone, the transfer
apparatus including
an endless belt having at least an outer coating thereon formulated
of a relatively nonconductive material,
means to support a portion of said belt in a substantially flat
position adjacent to said moving image retaining member within the
transfer zone,
means to move said belt over an endless path of travel at a rate
substantially equal to said predetermined rate,
means to secure a sheet of final support material upon the belt
whereby the sheet is transported through the transfer zone in
registration with a toner image on said image retaining member,
electrical means positioned within the transfer zone to
electrically transfer the toner image from said image retaining
member onto said support sheet, and
control means to create a regulated electrical force field within a
sheet separating region located subsequent to said transfer zone,
in the direction of sheet movement, said force field being of a
strength and polarity to hold the toner image to said sheet as said
sheet is separated from said member thereby preventing the toner
image from being repelled away from said sheet back toward said
image retaining member.
4. The apparatus of claim 3 wherein said means to secure a sheet to
said belt is adapted to place said sheet in moving contact with
said image retaining member within said transfer zone.
5. An automatic xerographic reproducing device of the type having a
rotatable xerographic plate arranged to move at a predetermined
rate through a circular path of travel, means to formulate a
charged toner powder image of an original upon said plate, means to
transfer the toner image to a sheet of final support material
within a transfer zone, the transfer apparatus further
including
a movable belt formulated of a relatively nonconductive material
being arranged to move at said predetermined rate over an endless
path of travel through said transfer zone, that portion of said
belt moving through the transfer zone being supported in a
substantially flat plane that is adjacent to and substantially
tangential with said xerographic plate within the transfer
zone,
means to secure a sheet of final support material to at least the
flat portion of said belt wherein the sheet is transported through
the transfer zone in registered synchronous moving contact with a
toner image on said xerographic plate,
electrical means positioned within the transfer zone to
electrically transfer the toner image from said plate onto said
support sheet, and
control means to create a regulated electrical force field within a
separation region located subsequent to said transfer zone in the
direction of belt movement said force field being of a strength and
polarity to retain the toner image on said sheet as said sheet is
separated from said plate.
6. The apparatus of claim 5 wherein said regulated force field
increases as the separation distance between the sheet and the
plate increases.
7. The apparatus of claim 5 wherein a means to secure said sheet to
said belt comprises a vacuum means operatively associated with said
belt and being arranged to hold said sheet to the flat portion of
said belt wherein the sheet is maintained in a relatively flat
condition as it is moved through the transfer zone.
Description
BACKGROUND OF THE INVENTION
This invention relates to electrostatic transfer apparatus and,
more particularly, to a transfer apparatus having a movable belt
which carries a copy sheet through the transfer station adjacent an
electrostatic drum and means to maintain an electrical field
between the drum and copy sheet in the transfer area and that area
adjacent the transfer area through which the copy sheet passes as
it moves away from the drum surface.
In reproduction processes, such as in the process of xerography,
wherein a latent image is first formed on an electrostatic member
and then made visible, or developed, with a powderous material, the
electrostatic member can be used repeatedly to form additional
powder images in successive cycles if the developed image is
transferred from it to another substrate such as a copy sheet
during each cycle. When the xerographic process is employed, the
electrostatic member can take the form of a photoconductive layer
over a conductive backing material. The photoconductive layer is
given a uniform electrostatic charge and then exposed to a light
image conforming to the information to be reproduced to form a
latent electrostatic image on the member. The member is then
developed with a finely divided, pigmented, electroscopic, resinous
powder called toner and the toner image is then electrostatically
transferred to a copy sheet. After transfer is complete, the
surface of the electrostatic member can be cleaned and then used
for another latent image which is developed with toner and the
toner image transferred in a similar manner.
If more than one copy of given information is to be made by the
process described above, the latent image formation steps can be
eliminated by using an electrostatic member having good latent
image preservation characteristics. In this mode of operation, a
latent image is formed on the electrostatic member by placing a
uniform charge on it and then exposing it to a light image of the
information to be reproduced during the formation of the first
copy. The latent image is then developed, the toner image
transferred from the electrostatic member to a copy sheet and the
surface of the electrostatic member cleaned. Then, when the second
copy and all succeeding copies are to be made, the charging and
exposing steps can be eliminated since the latent image retention
qualities of the electrostatic member maintain the latent image
intact. As a result, in the image preservation mode of operation,
the second and all subsequent copy cycles include only the steps of
developing the latent image, transferring the toner image from the
electrostatic member to a copy sheet and cleaning the electrostatic
member. It is obvious that this type of reproduction mode is faster
than the more conventional xerographic process described beforehand
since two steps, the steps of charging and exposing, are eliminated
during making of all copies after the first copy.
When a reproducing system is used in the image preservation mode,
special attention must be given to the technique and apparatus
utilized in transferring the toner image from the electrostatic
member to the copy sheet to assure that the latent image on the
member does not deteriorate. A common apparatus used for the
transfer step is a corona charging device. This device is widely
used in electrostatic copiers, but has serious disadvantages when a
copier functions in the image preservation mode. The non-image
device tends to electrostatically tack the copy sheet to the
electrostatic member during transfer since the copy sheet acquires
a charge during the transfer step. In addition, when the copy sheet
is stripped from the electrostatic member after transfer has taken
place, charges on the copy sheet tend to be conducted to nonimage
areas of the member due to air breakdown between it and the copy
sheet. Both types of charging either add or subtract charge from
the electrostatic member leaving a distorted latent image thereon
which is reflected in subsequent copies. When such charges are
placed in the non-image areas of the electrostatic member, they are
consequently developed with toner in succeeding cycles and result
in background in all subsequent copies. This situation is
undesirable since distorted toner images and background toner cause
noticeable degradation to copy quality.
Corona charging devices are also sensitive to humidity and altitude
and under certain conditions transfer efficiency; i.e., the amount
of toner transferred to the copy sheet, is considerably lessened.
In some cases a large part of the toner image is prevented from
transferring to the copy sheet and the resulting reproduction
becomes unintelligible. Corona devices normally require a
high-electrical potential; e.g., in the order of 4,000 volts, to
effect good transfer even under the most favorable operating
conditions, and this necessitates the use of a large power supply
in the copier. In addition, since a copy sheet is tacked to the
electrostatic member with the aid of a corona device when transfer
takes place, sheet removal apparatus is necessary to strip the copy
sheet from the member.
Another transfer device used with better success than the corona
device in the image preservation mode is a biased roller. This
device consists of a rotatable conductive core having a relatively
nonconductive surface layer. Although adequate transfer occurs when
approximately 2,000 volts is placed on the roller, the roller does
not efficiently effect transfer of the toner image at significantly
lower voltages due to back transfer. At low voltages toner which is
transferred to the copy sheet at the transfer area is retransferred
back to the photosensitive member when the copy sheet is separated
from the member.
Transfer efficiency can be increased by imposing a higher
electrical bias on the roller, however, a higher bias will cause
air breakdown as the copy sheet is removed from the electrostatic
member. This condition results in charging the nonimage areas of
the electrostatic member which distorts the quality of the latent
electrostatic image on the member and renders it undesirable for
use in the image preservation mode of operation. There has been no
value found for the electrical bias placed on a transfer roller at
which both poor transfer efficiency and background charging are
eliminated.
The present invention is a transfer apparatus having a movable belt
which carries the copy sheet through the transfer station in a
substantially flat position while an electrical field is maintained
between the copy sheet and electrostatic member in the transfer
area and the adjacent area through which the copy sheet passes as
it is separated from the surface of the member. Reliable, efficient
transfer takes place with the present device when a potential in
the vicinity of 1,000 volts is placed between the copy sheet and
electrostatic member, and the problems of charging of the
electrostatic member and stripping the copy sheet from the member
encountered in the prior art are avoided. In addition, the copy
sheet is removed from the transfer area in a plane tangent to the
surface of the electrostatic member which eliminates the
undesirable condition of back transfer. The present apparatus
operates at relatively low transfer voltages in a wide range of
environmental conditions and is particularly adaptable to copiers
operating in the image preservation mode.
Accordingly, it is an object of the invention to improve apparatus
for transferring toner images from an electrostatic member to a
copy sheet.
It is a further object of the invention to improve transfer
apparatus so that degradation of the latent image on an
electrostatic member is prevented during the transfer step and the
latent image remains suitable to be reused to form another toner
image.
It is a further object of the invention to improve transfer
apparatus so that back transfer of the toner from the copy sheet to
the electrostatic member is prevented.
It is a further object of the invention to improve transfer
apparatus so that transfer of toner images from an electrostatic
member to a copy sheet can be carried out efficiently at relatively
lower voltages than known previously.
It is a further object of the invention to improve transfer
apparatus so that transfer of a toner image is carried out in a
uniform, efficient manner regardless of relative humidity and
altitude.
It is a further object of the invention to improve transfer
apparatus by utilizing a belt to transport the copy sheet adjacent
an electrostatic member in the shape of a drum in a plane
substantially tangent to the surface of the drum.
SUMMARY
The present invention is a transfer apparatus comprising a movable
belt which carries a copy sheet, or the like, through a transfer
station of an electrostatic copier having an electrostatic drum in
a substantially flat position and a means to impose an electrical
field between the copy sheet and drum in the transfer area and that
area adjacent the transfer area through which the copy sheet passes
as it is removed from the drum surface. In one embodiment of the
invention, a movable, endless belt having an inner layer of
conductive material which is electrically biased and an outer layer
of relatively nonconductive material is used to carry out transfer
of a toner image from an electrostatic drum to a copy sheet. The
belt, which is supported and driven by rollers, carrier the copy
sheet in a plane that is tangent to the surface of the drum while a
toner image on the drum is transferred under the electrical
potential placed on the conductive layer of the belt. The belt
contains a plurality of holes through which a vacuum can be placed
on the copy sheet to prevent relative movement between the copy
sheet and belt while being transported through the transfer
station.
In a second embodiment, a belt of relatively nonconducting material
is used to carry the belt through the transfer station while an
electrical field is created by a stationary conducting means
adjacent the belt extending from the transfer area to the area
adjacent the transfer area through which the copy sheet passes as
it is being removed from the drum surface. In a third embodiment,
the stationary conducting means is constructed so that an
increasing electrical potential influences the copy sheet as it
increases its distance from the drum surface after transfer of the
toner image has occurred.
BRIEF DESCRIPTION OF THE DRAWINGS
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 used in
conjunction with the accompanying drawings, wherein:
FIG. 1 is a schematic illustration of the invention.
FIG. 2 is a detailed view of a first embodiment of the
invention.
FIG. 3 is a detailed view of a second embodiment of the
invention.
FIG. 4 is a detailed view of a third embodiment of the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention can be adapted to any reproduction apparatus
wherein an electroscopic, pigmented powder used to develop an
electrostatic latent image on an electrostatic member is
transferred from the member to a copy sheet. For the purpose of
this disclosure, however, the invention will be described within
the environment of a xerographic reproduction apparatus.
Referring to FIG. 1, there is shown a continuous xerographic copier
having a photosensitive member in the shape of drum 13 on which a
latent electrostatic image of the information to be reproduced is
formed. The rotatable drum 13 is driven by shaft 14 by any suitable
drive means (not shown). The peripheral surface of the drum is
covered by layer 12, an electrically conductive material, which, in
turn, is covered on its outer surface with layer 11, a conducting
material such as vitreous selenium. The drum has five processing
stations located about its periphery which carry out the steps of
the xerographic process. These stations include charging station A,
exposing station B, developing station C, transfer station D, and
cleaning station E.
A latent electrostatic image is formed on the drum by passing its
surface through charging station A and exposing station B. The
charging station includes any suitable means for placing a uniform
charge on layer 11 such as a corona charging device. Exposing
station B can include any suitable device which projects and
focuses a light pattern on the drum conforming to the image to be
reproduced by the xerographic system. The light image projected
onto the charge conductive layer of the drum is synchronized with
the movement of the drum and causes selective charge dissipation on
elemental areas of layer 11 to form a latent electrostatic image
thereon.
After the formation of the latent electrostatic image by passing
the drum through stations A and B, the drum carrier the latent
image to developing station a pigmented, resinous, electroscopic
powder called toner is deposited on the drum in imagewise
configuration in any suitable manner to develop, or make visible,
the latent image. Following the development step, the drum carrier
the toner image through a transfer station D where the toner image
is transferred from the drum surface to any suitable support
material such as copy sheet 15 which can be made of paper. In
addition to sheets, a continuous web or any other form of substrate
may be used to receive the toner image.
Transfer of the toner image onto the copy sheet is carried out by
belt 20. The copy sheet 15 is fed onto the surface of the belt by
any suitable device such as feeding device 30 which may include
tray 31 to hold a supply of copy sheets and feed roller 32 which
feeds the sheets one at a time as needed onto the belt. The belt 20
has an inner layer 22 of any suitable conductive material and an
outer layer 21 of any suitable relatively nonconductive material.
The belt is supported by rollers 23 and 24 and driven in the
clockwise direction by motor M. An electrical potential is placed
on layer 22 through roller 24 which is also made of a conductive
material. The belt may contain a plurality of holes, if desired,
shown only in FIG. 2, through which a vacuum can be imposed on the
copy sheet 15 by vacuum chamber 14.
A sheet is fed onto the belt by feeding device 30 and is carried
through transfer station D adjacent photosensitive drum 10. As it
passes through the transfer station, a toner image on the drum
surface adjacent the copy sheet is transferred to the copy sheet
due to the electrical field created between the copy sheet and drum
by the bias on layer 22 of the belt.
After the toner image have been transferred to the copy sheet and
the copy sheet has passed through the transfer station, the copy
sheet passes onto belt 40 which is supported by rollers 41 and 42
and driven by motor M. Any suitable fixing device 42 makes the
toner image permanent on the copy sheet. The copy sheet then moves
off the belt 40 as the belt turns about roller 41 and falls into
collection device 50 where it is stored in tray 31.
The final station shown in the drawing is cleaning station E which
can include any suitable cleaning device such as a fur brush which
contacts the photoconductive surface of the drum. The cleaning
station is utilized to remove any residue toner particles from the
photosensitive surface after transfer occurs and before another
cycle is begun. It is intended that the various moving elements
mentioned above be driven by any suitable means to allow the copier
to function as described; for instance, a single motor such as
motor M can drive drum 10 and the other moving elements in the
copier as well as the belts 20 and 40.
It is within the confines of the transfer station D that the
present invention is utilized. FIG. 2 showns a more detailed view
of the transfer station, but it should be kept in mind that the
various elements shown in FIG. 2 are not necessarily to scale. Belt
20 has an inner layer 22 of any suitable conductive material; e.g.,
a flexible steel band, and an outer layer 21 of any suitable
relatively nonconductive material; e.g., a dielectric material. The
belt moves in a clockwise direction around rollers 23 and 24 while
the drum rotates in a counterclockwise direction bringing
successive portions of the developed image, shown by grossly
enlarged toner particles on the surface of the drum, through the
transfer station, at the same speed as a copy sheet carried by the
belt.
The belt contains a plurality of holes 16 through which a vacuum
can be imposed on the copy sheet to prevent it from slipping. The
holes in the belt and the chamber 14 which supplies the vacuum are
optional to the transfer belt assembly, especially if the transfer
station is located as shown in FIG. 2 and the copy sheet is
conveyed in a substantially horizontal plane. However, if the
transfer station were so that the copy sheet had to be conveyed in
a plane other than a horizontal plane, the vacuum force of the copy
sheet would be desirable to prevent relative movement between the
copy sheet and belt.
The belt is driven at a speed which is substantially equal to the
surface speed of the drum and a suitable electrical potential is
placed on layer 22 to effect transfer of the toner image from the
drum to the copy sheet. The dielectric material actually used in
testing the invention was a 0.002 inch thick polyester resin
material and the conductive material was a rubber which was
impregnated with graphite. Using these materials, it was found that
transfer was carried out efficiently when the potential on the belt
was between 500 volts and 1,500 volts. The polarity of the
potential placed on the inner layer of the belt is determined by
the polarity of the toner particles to be transferred. For
instance, if the toner particles bear a negative charge, as
indicated in FIG. 2, a positive potential would be placed on the
belt. If, on the other hand, the toner particles were to bear a
positive charge, a negative potential would be placed on the layer
22 of the belt.
The proximity of the belt relative to the surface of the drum is
depended upon the thickness of the copy sheet. In FIG. 2, the belt
is located so that the top surface of the copy sheet is adjacent
the surface of the belt, however, the copy sheet can be placed into
intimate contact with the drum surface during the transfer step
also. Although the copy sheet is shown as an individual sheet, it
can take any other suitable form such as a continuous web and can
be made of any suitable material such as paper, plastic, fabric,
etc.
The path of the copy sheet through the transfer station is in a
plane which is substantially tangent to the surface of the drum.
This arrangement has been found to be the most preferrable to
prevent back transfer of toner to the drum as the copy sheet is
separated from the drum. Since the potential placed on the inner
layer of the belt is relatively low and the copy sheet is conveyed
in a path that is tangent to the surface of the drum, uncontrolled
charging of the drum due to conduction through the belt and copy
sheet is prevented. Both of these aspects, low potential and
tangentral path, enhance the value of the present system when it is
utilized in a reproduction system which is operated in the image
preservation mode, and the quality of succeeding copies is always
maintained at a high level.
Another embodiment of the invention is seen in FIG. 3. In this
apparatus the belt 31 which carries the copy sheet 15 through the
transfer station is made of a relatively, nonconductive material
and the electrical field imposed in the transfer area to effect
transfer of the toner image from the electrostatic member to the
copy sheet and the area adjacent the transfer area through which
the copy sheet travels as it is separated from the drum is
generated by a stationary plate 30. Plate 30 is located adjacent
the path of belt 31 and, in addition to being next to the transfer
area; i.e., where the belt is closest to the surface of the drum
and the toner image is transferred to the copy sheet, extends to
the right of the transfer area.
As the copy sheet exits from the transfer area, it is separated
from the photoconductive layer 11 of the drum and continues in the
same plane as belt 15. During the time that the copy sheet is being
separated from the drum, a field is maintained between the copy
sheet and drum to prevent back transfer of toner on the copy sheet.
Plate 30 is made of a conducting material and is biased by a
suitable power supply shown schematically in FIG. 3. The plate is
separated at all times from the copy sheet 15 by belt 31 to prevent
any conduction of charge to the copy sheet and/or drum during the
time that the transfer of the toner image is being carried out or
the time the copy sheet is being separated from the drum. The plate
30 also serves to support the belt 31 and hence the copy sheet in a
plane tangent to the drum while the two are within the transfer
station.
FIG. 4 shows another embodiment of the invention. When the
electrical field between the copy sheet and drum is stepped up as a
given portion of the copy sheet is increasingly separated from the
drum, back transfer is further eliminated. The apparatus shown in
FIG. 4 accomplishes this result. Segmented plate 30 has both
conducting portions 35a-35f and relatively nonconducting portions
34a-34e which extend across the belt 31 parallel to the axis of the
drum.
If an appropriate bias is placed on conductive section 35a of the
plate 30 to carry out transfer of the toner image from the drum to
the copy sheet, then the potential placed on conductive sections
35b-35f can be stepped up in successive degree to intensify the
fields as the copy sheet is increasingly separated from the drum to
eliminate back transfer. Of course, relatively nonconductive
sections 34a-34e will remain electrically inert. Any suitable
control apparatus 36 can be used to step the voltages to the
various conductive sections, the apparatus being joined to each
conductive section by wire 37.
As an example of the stepping technique, section 35a can have a
voltage of 1,000 volts to carry out the transfer of the toner image
to the copy sheet in the transfer area. Then, conductive sections
35b, 35c, 35d, 35e, and 35f can have voltages of 1,800 volts, 2,600
volts, 3,200 volts, 4,000 volts and 4,800 volts, respectively. It
is pointed out at this juncture, that the voltages mentioned
immediately above are illustrative only, and it is not intended
that the stepping technique be limited to these values or the
difference between the values. Ultimately, the actual values of the
various sections will depend on the diameter of the drum, width of
the conductive sections, width of the copy sheet, relative humidity
and other characteristics of the system.
In addition to the apparatus outlined above, many other
modifications and/or additions to this invention will be readily
apparent to those skilled in the art upon reading this disclosure,
and these are intended to be encompassed within the invention
disclosed and claimed herein.
* * * * *