U.S. patent number 3,574,301 [Application Number 04/812,798] was granted by the patent office on 1971-04-13 for developing apparatus.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to John S. Bernhard.
United States Patent |
3,574,301 |
Bernhard |
April 13, 1971 |
DEVELOPING APPARATUS
Abstract
An apparatus for developing an electrostatic image on an
insulating plate with toner particles including a brushlike
developing member, means to generate a cloud of toner particles, a
conductive donor member, and means to selectively place electrical
biases on the donor member.
Inventors: |
Bernhard; John S. (Pittsford,
NY) |
Assignee: |
Xerox Corporation (Rochester,
NY)
|
Family
ID: |
25210656 |
Appl.
No.: |
04/812,798 |
Filed: |
April 2, 1969 |
Current U.S.
Class: |
399/287;
399/290 |
Current CPC
Class: |
G03G
15/0805 (20130101) |
Current International
Class: |
G03G
15/08 (20060101); G03g 013/08 () |
Field of
Search: |
;118/637 ;117/17.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Stein; Mervin
Claims
I claim:
1. An apparatus for developing a surface bearing a latent
electrostatic image with toner particles comprising:
means for containing a quantity of toner particles adjacent said
surface;
a fibrous developing brush supported for rotation in the toner
container means with the fibers of said brush extending into
contact with said surface;
means to rotate said developing brush;
means to form a cloud of toner particles in said toner container
means;
a conductive donor member supported for rotation in said toner
container means, a portion of said donor member being in contact
with said developing brush;
means to rotate said donor member to bring successive portions of
said donor member in contact with said developing brush; and
means to bias said successive portions of said donor member before
they are brought in contact with said developing brush to attract
toner particles from the toner cloud to said successive portions of
the donor member,
the the periphery of said donor member having a collection zone in
which toner cloud are attracted to the periphery of the donor
member and a release zone in which toner particles attracted to
said donor member are transferred from said donor member to said
developing brush;
said release zone encompassing said portion of said donor member
which is in contact with said developing brush and said collection
zone encompassing the remainder at said donor member.
2. The apparatus in claim 1 further including means to bias said
portion of said donor member in contact with said developing brush
to urge toner particles from said donor member to said developing
brush.
3. The apparatus in claim 2 wherein the donor member is a hollow
cylinder having individual elements of conducting and relatively
nonconducting material placed adjacent one another in alternate
fashion, and means to separately bias said portion of said donor
member in contact with said developing brush and said successive
portions of said donor member including a source of electrical
power operatively connected to a conductive brush which contains
electrical contact with the internal surface of said donor member
as it rotates.
4. The apparatus in claim 1 wherein the developing brush is a fur
brush having elongated fibers extending therefrom.
5. An apparatus for developing a surface bearing a lent latent
electrostatic image with toner particles having a positive charge
comprising:
means for containing a quantity of toner particles adjacent said
surface;
a fibrous developing brush supported for rotation in the toner
container means with the fibers of said brush extending into
contact with said surface;
means to rotate said developing brush;
means to form a cloud of toner particles in said toner container
means;
an intermediate roller supported for rotation in said toner
container means, said intermediate roller being in contact with
said developing brush and being made of a material adapted to carry
toner particles having a positive charge;
means to rotate said intermediate roller;
a conductive donor member supported for rotation in said toner
container means, a portion of said donor member being in contact
with said intermediate roller;
means to rotate said donor member to bring successive portions of
said donor member in contact wit said intermediate roller; and
means to bias said successive portions of said donor member before
they are brought in contact with said intermediate roller to
attract toner particles from the toner cloud to said successive
portions of the donor member;
the periphery of said donor member having a collection zone in
which toner particles in said cloud are attracted to the periphery
of the donor member and a release zone in which toner particles
attracted to said donor member are transferred from said donor
member to said intermediate roller,
said release zone encompassing said portion of said donor member
which is in contact with said intermediate roller and said
collection zone encompassing the remainder of said donor
member.
6. The apparatus in claim 5 wherein the intermediate roller
material is rayon.
Description
This invention relates to apparatus for developing electrostatic
images, and, in particular, to an apparatus for placing toner
particles on a brushlike developing member used to develop an
electrostatic image on an insulating surface.
In xerography, as well as other reproduction processes, a latent
electrostatic image is formed on an insulating plate and made
visible by developing the image with marking particles such as
finely divided pigmented resinous powders called toner. One method
of developing electrostatic images is by depositing toner particles
on the plate in a pattern conforming to the latent image by a
developing member carrying toner particles. In this developing
technique, a brushlike material is loaded with toner particles and
brought into contact with the insulating plate bearing the
electrostatic image. As the toner-laden brush fibers contact the
plate, the electrostatic fields on the plate attract the particles
to the plate in imagewise configuration. A problem with brush
development is the difficulty encountered in attempting to load the
brush with toner particles and in replenishing toner particles
depleted from the brush during development. This problem is
especially acute in a continuous reproduction system where the
brush must be constantly reloaded with toner as development takes
place.
There are two known loading techniques which exhibit particular
difficulties. One method of loading a developing brush is to pass
the brush through a toner container in such a manner that the toner
particles adjacent the brush fibers are triboelectrically attracted
to the fibers. Although a relatively simple technique, this method
does not continuously load the brush satisfactorily since a cavity
of packed toner is formed in the toner container which eliminates
the necessary contact between the brush and toner. Mechanical
agitators of various types have been placed in the toner container
to keep the toner in a loose consistency, but it has been found
that cavities still occur especially at high humidities resulting
in inefficient loading of the brush.
A second method of loading is to cause toner to fall from a
vibrating hopper onto the brush. The hopper is usually placed over
the brush so that toner particles in it fall through a fine-mesh
screen to the periphery of the brush. This loading technique has a
metering problem resulting in nonuniform quantities of toner being
placed on the brush which impairs the quality of development. In
addition, it is important that a charge of desirable polarity and
uniform intensity be placed on the toner particles before they
reach the plate and this is difficult to achieve in a
hopper-loading system.
The invention described herein overcomes the problems encountered
in loading a developing brush which existed in presently known
systems. The present system avoids the problem of packed toner in
the toner container and can be adapted to load a developing brush
at a high rate of speed. In addition, the rate of toner loading can
be accurately metered and the toner polarity can be selected as
desired.
The invention includes a selectively biased donor member which
feeds toner to a developing brush as it rotates adjacent the brush.
The donor member is located within a toner container having
agitators which create a toner cloud. The donor member has
alternate sections of conductive and relatively nonconductive
material and means to selectively bias the conductive portions so
that toner in the cloud adjacent the donor member adheres to the
periphery of the donor member until it is adjacent the developing
brush. When the toner on the donor member reaches the developing
brush it is transferred from the donor member onto the brush due to
a repulsive bias placed on the donor member and the sweeping action
of the brush. The brush then deposits the toner on the insulating
plate to develop the electrostatic image thereon.
Accordingly, it is an object of the present invention to improve
the development of an electrostatic image with a brushlike
developing member.
It is another object of the invention to improve apparatus for
loading a developing brush by feeding toner to the brush from a
toner-laden, selectively biased, donor member.
It is a further object of the invention to improve development of
latent images by increasing the rate at which toner particles are
loaded onto a developing brush.
It is a further object of the invention to improve development of
latent images by loading a developing brush with positively or
negatively charged toner particles as desired.
It is a further object of the invention to improve development of
latent images by accurately metering the rate at which toner is
placed on the developing brush.
The present invention is an apparatus for developing a latent
electrostatic image on an insulating plate. A cylindrical donor
member having alternate sections of conductive and relatively
nonconductive material is placed in a cloud of toner particles
adjacent to and in contact with the developing brush. The donor
member is selectively biased in such a manner that a first
electrical bias is applied to the conductive sections which are
immediately adjacent the developing brush and a second electrical
bias is applied to the other conductive sections in the member. The
first bias repels toner particles from the donor member and the
second bias attracts toner particles to the donor member. As the
donor member rotates, toner particles in the cloud are attracted to
the donor member by the second bias and brought adjacent the
developing brush as the member rotates. When these toner particles
are positioned in the vicinity of the brush, the first bias urges
them from the donor member into the developing brush. The
developing brush then deposits the toner particles on the
insulating plate as it rotates in interference therewith to develop
the latent electrostatic image on it.
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 a xerographic machine
incorporating the invention.
FIG. 2 is a detailed view of the donor member with a portion
removed to show the internal structure.
FIG. 3 is a schematic illustration of a high-speed developing
system incorporating the invention.
FIG. 4 is a schematic illustration of an alternative embodiment of
the invention.
FIG. 1 illustrates a continuous xerographic machine incorporating
the present invention. The principal element of the machine is
photosensitive plate 60 which is shown as a rotatable drum. The
drum has five stations arranged about its periphery which carry out
the various steps of the xerographic process. These stations
include charging station 10, exposing station 20, developing
station 30, transfer station 40, and cleaning station 50. Drum 63,
which is driven about shaft 64 by a suitable drive means (not
shown), includes layer 62, an electrically conductive material, and
layer 61, a photoconductive insulating material such as vitreous
selenium.
A latent electrostatic image is formed on the surface of the drum
by passing it through charging station 10 and exposing station 20.
The charging station includes any suitable means for placing a
uniform charge on layer 61 such as corona charging device 11.
Exposure station 20 includes projector 21 which projects and
focuses a light pattern conforming to the image to be reproduced on
the drum in synchronism with the surface movement of the drum. The
projected light pattern causes selective charge dissipation on
elemental areas of layer 61 thus forming a latent electrostatic
image. Other means for forming an electrostatic latent image
including means for forming images or ordinary insulating surfaces
can be used and these are known in the art and may be used instead
of the one shown.
After the information of the latent electrostatic image the drum
passes through developing station 30. The developing station
includes developing brush 31, donor member 32, and means for
producing a toner cloud 36, all contained within housing 33 along
with a quantity of toner particles 34. The operation of developing
station 30 will be described in greater detail below.
Following the developing step, the drum passes through transfer
station 40 where the developed image can be transferred to support
material 41. Transfer of the image onto the support material is
aided by corona charging device 42 which applies an electrostatic
charge to the support material having a polarity opposite that of
the toner particles. Transfer of the developed image from the
photosensitive surface to the support material takes place between
guide rollers 45 which act to position the support material
adjacent the photosensitive drum while it is within the transfer
station.
Support material 41 is fed from reel 43 before transfer and is
rewound on reel 44 after transfer takes place. If the support
material is the permanent substrate upon which the image is to be
fixed, as shown in FIG. 1, fusing device 46 is desirable and should
be placed along the path of the support material between the point
where the developed image is transferred to the support material
and the point where the support material is wound on reel 44. The
fusing device is positioned to heat the toner particles and
permanently bond them to the support material. The final station in
the system shown in FIG. 1 is cleaning station 50. This station
includes fibrous brush 51 which contacts the photosensitive surface
of the drum and removes any toner particles remaining on the drum
after transfer is completed and before a new cycle is begun.
The above-described process and apparatus, with the exception of
the developing station, are commercially known in the art, as
evidenced in U.S. Pat. No. 3,117,891, and any of the many known
equivalents of process or apparatus may be employed in connection
with the invention. It is intended that appropriate drive
mechanisms and control circuits be part of the general disclosure
herein which would enable the continuous xerographic process to
operate, however, such apparatus is not shown or described in
detail since the elements can be of any suitable design to
accomplish the operational movement of the system as described
above.
Referring to the developing station 30 shown in FIG. 1, toner is
loaded onto brush 31 by donor member 32, and development of the
image is carried out thereafter by the brush as it rotates in
interference with drum 60. A quantity of toner 34 is placed at the
bottom of the housing 33 and agitated by agitators 36 to form a
cloud of toner particles within the lower portion of the housing.
Donor member 32 is selectively biased so that the portions of its
surface adjacent the brush; that is, in the release zone, are
electrically repulsive to the toner while the other portions of its
surface; that is, the collection zone, are electrically attractive
to the toner. As a result, the toner particles in the cloud
surrounding the donor member are attracted to and adhere to the
surface of donor member in the collection zone and are then carried
into the transfer zone as the donor member rotates. When the toner
is carried through the transfer zone it is urged from the surface
of the donor member to the developing brush due to the presence of
the repulsive bias on the donor member and a sweeping action by the
brush. After toner is transferred from the donor member to the
brush, the surface of the donor member is reloaded with new toner
particles as it again passes through the collection zone. In this
manner toner is constantly attracted to the donor member in the
collection zone and transferred to the brush in the transfer
zone.
The rate at which toner is loaded onto the brush can be varied by
varying the speed of rotation of the donor member, the faster the
speed of rotation of the donor member, the greater the amount of
toner that can be transferred to the brush during a given period of
time. This aspect of the loading system becomes significant when
the toner requirements change in a continuous developing process.
In a situation where an occasional image being developed requires a
greater amount of toner to be fully developed than others in the
same reproduction run, the speed of the donor member can be
increased to supply additional amounts of toner when needed. The
speed of the donor member can also be decreased to accommodate
development cycles where little toner is used.
FIG. 2 shows a more detailed view of the donor member used to load
the developing brush. The donor member is shown as a hollow
cylinder having conductive elements 202 and relatively
nonconductive elements 201 oriented in alternate fashion. As the
donor member is rotated adjacent the brush the conductive elements
are selectively biased by electrical connectors 203 and 205.
Electrical connector 203 applies an electrical bias to those
conductive elements within the collection zone, depicted as zone A.
The bias is generated by a suitable power source 204 which makes
the donor member attractive to the toner particles in toner cloud
212. Electrical connector 205, on the other hand, applies an
electrical bias to those conductive elements in the release zone,
depicted as zone B. This bias is generated by any suitable power
source 206 which makes the donor member repulsive to the toner
particles on the donor member.
In the developing mode where negatively charged toner particles are
used to develop the insulating plate, a bias which is positive
relative to the toner particles is imposed on the conductive
elements in zone A of the donor member. The toner is attracted to
the periphery of the donor member and is conveyed to the vicinity
of developing brush 209 as the donor member rotates in a clockwise
direction as shown in FIG. 2. The donor member brings the toner
within zone B as it rotates where a second bias is imposed on the
toner through the donor member. The bias placed on the conductive
elements of the zone B is negative relative to the negatively
charged toner particles and has the effect of urging the particles
from the donor member onto bristles 208 of the brush. As a result
of the bias in zone B the toner particles are transferred to or
swept onto the developing brush.
If on the other hand, positively charged toner particles were used
to develop the insulating plate, the biases of the release and
collective zones of the donor member can be modified to achieve the
same results as described above in conjunction with loading
negative toner onto the developing brush. It has been found,
however, that when positively charged toner particles are used to
develop the insulating plate, best results are realized when an
intermediate roller is placed between the developing brush and the
selectively biased donor member. This embodiment can be seen in
FIG. 4 wherein the insulating plate shown as drum 60 is developed
by brush 31. The toner 34 forms a toner cloud due to the action of
agitators 36 and is attracted to donor member 32 as described
above. The toner on the donor member is then transferred to
intermediate roller 35 with the aid of the release zone bias placed
on the donor member. The intermediate roller can be made of any
suitable material such as rayon which will feed the toner to the
developing brush. The advantages of using the intermediate roller
with positively charged toner are that the roller tends to maintain
the developing brush at its toner saturation level and the system
consistently produces good developed image at low humidities.
The developing brush used to carry the toner from the donor member
to the drum can be made of any suitable material such as brush
material 207 having elongated fibers 208 used as toner carriers as
shown in FIG. 2. It is desirable to use a material which has a
triboelectric characteristic which enhances the carrying of toner
to the insulating plate. Examples of such material are rayon,
dynel, fox fur, rabbit fur and other suitable natural and synthetic
materials. Similarly, the configuration of the developing member
can be any suitable one adaptable to the developing system such as
the cylindrical brush shown in FIG. 2. Examples of other various
configurations are rotary brushes, endless belts, and oscillating
brushes. The examples cited immediately above for brush materials
and brush configurations are intended only as exemplary of the
group that can be used for in the present invention and are not
intended as an exhaustive list.
The donor member can be rotated at any convenient speed and in any
desired direction depending upon the desired rate at which toner
particles are to be placed on the brush. As mentioned above, the
release zone, zone B, encompasses the vicinity of the interface
between the developing brush and donor member. Zone A, on the other
hand, can be any convenient portion of the periphery of the donor
member as long as its bias in zone B. As shown in FIG. 2, zone B
occupies approximately the entire periphery of the donor member
which is outside zone B.
FIG. 3 shows an apparatus which employs the donor member in
combination with a number of development brushes which can be used
in a high-speed reproducing system. Drum 101 which rotates in the
counterclockwise direction about shaft 103 bears a latent
electrostatic image. The developing station is contained within
housing 102 which has a reserve supply of toner particles in
compartment 104 which are allowed to pass into the housing as
needed. In the lower part of the housing are several agitators 106
which maintain the toner particles in a cloud about donor members
109, 111, and 113. Donor members 109, 111 and 113 have an
attraction zone in their lower regions and a release zone in the
vicinity of roller 108, and brushes 110, and 112, as described in
conjunction with FIG. 2.
A collection zone bias on each donor member attracts toner
particles to the periphery of the donor member. The donor member
rotates carrying the tone particles to roller 108 and brushes 110
and 112 where an other bias urges the toner to transfer to the
roller and brushes. Roller 108, an intermediate roller, in turn,
passes the toner particles from donor member 109 to brush 107.
Brushes 107, 110, and 112 develop the latent image on drum 101. The
use of more than one brush is desirable in a high-speed system in
order to assure that the amount of toner delivered to the drum is
sufficient for good development when the drum surface is moving at
relatively high speeds. It has been found that the bulk of the
toner is laced on the latent image by brush 107; that is, the first
brush which the drum contacts in the development station. Brushes
110 and 112 deposit additional amounts of toner on the latent image
as needed and also act to clean up the background areas of the
image thereby improving copy quality.
In addition to brushes 110 and 112 acting as background removal
brushes, fur brush 114 is intended for the specific purposes of
cleaning the background areas of the developed image. The fibers of
this fur brush actually contact the surface of drum 101 and sweep
any toner particles in the background areas or off the drum. Those
toner particles swept from the drum surface by the brush 114 are
removed from the brush by flicker bar 116 and fall into housing 115
surrounding it.
Appropriate drive mechanisms for driving the various moving parts
shown in FIG. 3 are to be understood as part of the system
shown.
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 spirit of the
invention.
* * * * *