U.S. patent number RE31,371 [Application Number 06/297,931] was granted by the patent office on 1983-09-06 for developing system.
This patent grant is currently assigned to Ricoh Co., Ltd.. Invention is credited to Masami Emoto, Tsuguo Kimura, Shoji Kuroishi, Shiro Yamamoto.
United States Patent |
RE31,371 |
Kuroishi , et al. |
September 6, 1983 |
Developing system
Abstract
A developing system is provided for a copying process such as an
electrophotographic copying process in which a developer is
supplied to the surface of a member which is formed with an
electrostatic latent image to provide developing thereof. An
electrode is disposed opposite the surface of the member with the
developer interposed therebetween, and the induction potential of
the electrode is maintained below a given value by means of a
constant voltage element. The potential of the electrode is induced
by either the image portion of the member's surface having the
electrostatic latent image or by an unexposed, separate charged
portion thereof.
Inventors: |
Kuroishi; Shoji (Yokohama,
JP), Kimura; Tsuguo (Zushi, JP), Emoto;
Masami (Yokohama, JP), Yamamoto; Shiro (Tokyo,
JP) |
Assignee: |
Ricoh Co., Ltd. (Tokyo,
JP)
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Family
ID: |
26345192 |
Appl.
No.: |
06/297,931 |
Filed: |
August 31, 1981 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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435270 |
Jan 21, 1974 |
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Reissue of: |
593293 |
Jul 7, 1975 |
04052127 |
Oct 4, 1977 |
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Foreign Application Priority Data
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Jan 24, 1973 [JP] |
|
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48-10033 |
May 7, 1973 [JP] |
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48-51007 |
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Current U.S.
Class: |
399/56;
399/237 |
Current CPC
Class: |
G03G
15/10 (20130101); G03G 15/065 (20130101) |
Current International
Class: |
G03G
15/10 (20060101); G03G 15/06 (20060101); G03G
015/06 (); G03G 015/10 () |
Field of
Search: |
;355/10,3DD
;118/647,648,659 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Braun; Fred L.
Attorney, Agent or Firm: Wyatt, Gerber, Shoup, Scobey &
Badie
Parent Case Text
This is a continuation of application Ser. No. 435,270 filed Jan.
21, 1974 .Iadd., now abandoned. .Iaddend.
Claims
What is claimed is:
1. A developing system for electrophotographic copying apparatus
for the type comprising:
a member having a surface of photosensitive material; and
means for forming an electrostatic latent image on said
photosensitive surface by successive charging and exposure
steps;
wherein the improvement comprises:
developing means for supplying a developer to said member to
develop the latent image, said developing means comprising an
electrode disposed in opposing relationship with the surface of
said member with the developer interposed therebetween; and
means for .[.permitting.]. .Iadd.enabling .Iaddend.the induced
potential on the electrode from said electrostatic latent image to
float below a given value, said .[.permitting.]. .Iadd.enabling
.Iaddend.means comprising constant voltage means connected between
said electrode and ground for preventing said induced potential
from exceeding said given value.
2. A developing system as in claim 1 further comprising means for
charging an area on at least one end portion of said member
adjacent said image surface during the charging step and for
keeping said area unexposed during the exposure step, such that
said area on the end portion of said member induces a potential on
said electrode.
3. A developing system according to claim 1 wherein said electrode
comprises a plurality of .[.electode.]. .Iadd.electrode
.Iaddend.elements disposed along a direction of travel of the
member relative to said developing means, the plurality of
electrode elements having a unidirectional conductive
characteristic in a direction opposite to said direction of travel
of said member.
4. A developing system according to claim 3 further comprising a
plurality of diodes respectively connected between adjacent
electrode elements to provide the unidirectional conducting
characteristic.
5. A developing system according to claim 2 wherein said electrode
comprises a plurality of electrode elements, each arranged along
the direction of travel of the member of photosensitive material,
the plurality of electrode elements having a unidirectionally
conducting characteristic in a direction opposite to the travel of
the member.
6. A developing system according to claim 5 in which diodes are
connected between the adjacent electrode elements of the plurality
to provide the unidirectionally conducting characteristic.
7. A developing system according to claim 1 wherein said constant
voltage means comprises a constant voltage diode having a threshold
value corresponding to said given value.
8. A developing system for an electrophotographic copying apparatus
of the type comprising:
a member having a photosensitive surface;
means for forming an electrostatic latent image on said
photosensitive surface by successive charging and exposure
steps;
wherein the improvement comprises:
developing means for supplying a developer to said surface while
moving relative thereto to develop said latent image, said
developing means comprising:
an electrode disposed in opposing relationship with said surface
with the developer interposed therebetween, said electrode
comprising:
a plurality of electrode elements disposed along the direction of
travel of said member relative to said developing means and having
a unidirectional conducting characteristic in a direction opposite
to said direction of travel of said member; and
the foremost element of said plurality of electrode elements in
said direction of travel of said member having its potential
additionally increased.
9. A developing system for electrophotographic copying apparatus of
the type comprising:
a member having a surface of photosensitive material;
means for charging said photosensitive surface; and
means for exposing said charged photosensitive surface to form an
electrostatic latent image thereon;
wherein the improvement comprises:
developing means for supplying a developer to said photosensitive
surface while it is moving relative thereto to develop the latent
image, said developing means comprising:
an electrode disposed in opposing relationship with said
photosensitive surface with the developer interposed therebetween,
said electrode comprising a plurality of electrode elements, each
arranged along the direction of travel of the member relative to
said developing means, said elements having a unidirectionally
conducting characteristic in a direction opposite to said direction
of travel of said member;
a plurality of diodes respectively connected between adjacent
electrode elements for providing the unidirectionally conducting
characteristic; and
the electrode element which is foremost in said direction of travel
of said member having its potential additionally increased;
means for maintaining the induced potential on the electrode from
said electrostatic latent image below a given value, said
maintaining means comprising:
a constant voltage element connected between said electrode and
ground and having a threshold value corresponding to said given
value; and means for charging an area on at least one end portion
of said member adjacent said image surface during the operation of
said charging means and for maintaining said area unexposed during
the operation of said exposure means such that said area on the end
portion of said member induces a potential on said electrode.
10. A developing system for electrophotographic copying apparatus
of the type comprising:
a member having a surface of photosensitive material;
means for charging said photosensitive surface; and
means for forming an electrostatic latent image on said charged
photosensitive surface;
wherein the improvement comprises:
developing means for supplying a developer to said photosensitive
surface to develop said latent image, .[.and.]. .Iadd.said
.Iaddend.developing means comprising:
an electrode disposed in opposing relationship with said
photosensitive surface with the developer interposed therebetween;
and
means for maintaining the induced potential on the electrode from
said electrostatic latent image .[.below.]. .Iadd.above .Iaddend.a
given value, said maintaining means comprising:
a constant voltage element operatively connected to both said
electrode and said means for charging said photosensitive surface
and connected between said electrode and ground and having a
threshold value corresponding to said given value.
Description
BACKGROUND OF THE INVENTION
The invention relates to a developing system for use in a copying
process such as an electrophotographic copying process, and more
particularly to such a system for developing an electrostatic
latent image on a member capable of retaining an electric
charge.
In a copying process such as an electrophotographic copying
process, an electrostatic latent image is formed on a member such
as a copying sheet which is capable of retaining an electric
charge, and this latent image is subsequently developed. For
example, in the electrophotographic copying process, the prior
practice has been to charge a photosensitive material, which is
subsequently exposed to an image of an article to be copied to have
an electrostatic latent image thereof formed thereon. The latent
image is then developed and transferred onto a transfer sheet,
followed by the fixing thereof. The developing step comprises
supplying a developer to the surface of the photosensitive material
to develop the electrostatic latent image.
As one of the developing techniques of this kind, a self-bias
developing technique has been proposed in which a developer is
supplied onto a member on which an electrostatic latent image is
formed and which is opposed to an electrically floating, conductive
plate (hereinafter referred to as developing electrode). In the
self-bias developing technique, the developing electrode is
maintained electrically floating so that a potential is induced on
the developing electrode by the charge on the image portion of the
member in order to attract the toner on the non-image portion of
the member to the developing electrode, thereby preventing the
background smearing and improving the contrast of the image.
However, where the contrast in the image of an original itself is
low or where the area of the image portion is small as compared to
that of the non-image portion, a sufficiently high potential may
not be induced on the developing electrode from the image portion
of the member to achieve the self-bias effects, that is, preventing
the background smearing and improving the contrast of the image. In
addition, the potential of the developing electrode varies
depending upon the potential and the size of the image portion, and
this results in a disadvantage that the toner on an image area of
low density may be attracted toward the developing electrode to
cause the loss of such image area when the potential of the
developing electrode is too high. While the application of a
constant bias voltage from a d.c. source to the developing
electrode has been proposed, too high a potential of the developing
electrode causes a disadvantage of removing an image area of low
density, while too low a potential of the developing electrode can
not prevent the background smearing and improve the contrast in the
image.
The present inventors have previously proposed a developing system
for the electrophotographic copying process in which the potential
of the developing electrode is induced by the potential of a part
of a photosensitive material which is maintained free from image
formation and which is maintained at a constant potential when
charged during the charging step. However, such system still
suffered from the disadvantages that the induced potential may
happen to be too high and that where a plurality of developing
electroes are provided, the potential may vary from electrode to
electrode, thus precluding a uniform image characteristic over the
entire surface of the photosensitive material.
SUMMARY OF THE INVENTION
It is a principal object of the invention to maintain the induced
potential of the developing electrode below a given value to
thereby eliminate the background smearing and to improve the
contrast in the image while avoiding the loss of an image area of
reduced density.
It is another object of the invention to use an end portion of a
photosensitive material which is charged to a constant potential
during the charging step and which is left unexposed in the
electrophotographic copying process so that the potential of the
developing electrode can be induced principally from this end
portion and maintained below a given value, thereby assuring a
uniform image developing characteristic over the entire system of
the photosensitive material.
It is a further object of the invention to provide a plurality of
developing electrodes along the direction of travel of a member
having an electrostatic latent image formed thereon, thereby
improving the rising characteristic of the induced potential of the
developing electrodes.
It is an additional object of the invention to enhance the effect
of the developing electrode by additionally increasing the
potential of the developing electrode.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic elevation of one exemplary
electrophotographic copying apparatus to which the invention can be
applied;
FIGS. 2 to 7 are schematic sections of several embodiments of the
liquid developing system according to the invention;
FIG. 8 is an elevation of one exemplary photosensitive material
used in the apparatus of FIG. 1; and
FIGS. 9(a) and 9(b) are perspective views showing examples of the
developing electrode shown in FIG. 1.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Referring to FIG. 1, there is shown an apparatus for carrying out
an electrophotographic copying process in accordance with the
invention. The apparatus comprises a body, having a peripheral
surface of photosensitive material 11, in the form of a drum which
is driven by a suitable drive means, not shown, for rotation in the
direction indicated by an arrow with a constant speed. During its
rotation, the body's surface 11 is adapted to be entirely charged
by a charger 12, and then exposed to the image of an article to be
copied by an exposure unit 13 to form an electrostatic latent image
thereon, which latent image is developed with a developing solution
in a liquid developing system 14. In all embodiments of this
specification, it is to be assumed that the electrostatic latent
images are formed by a negative high voltage. The polarity of the
electrostatic latent image is determined generally in connection
with the specific character of the photosensitive material. A
transfer sheet 15 is supplied from a paper feeder, not shown, into
the space between the drum surface 11 and a transfer unit 16 in
synchronism with the movement of the drum surface 11 in order to
transfer a toner image from the drum surface 11 onto the transfer
sheet 15. While the transfer unit 16 is shown as comprising a
transfer roller, it will be understood that it may be replaced by
an electrostatic transfer unit. Subsequent to the transfer of the
toner image thereto at the transfer unit 16, the transfer sheet 15
has its toner image fixed in a fixing unit, not shown, thereby
providing a copy sheet, which is discharged externally of the
apparatus. Subsequent to the transfer step, the drum surface 11 is
cleaned by a cleaning unit 17.
In the electrophotographic copying process above described, the
developing step is effected by the liquid developing system 14. In
the embodiment shown in FIG. 2, the system 14 comprises a vessel of
developing solution 18 located below the drum surface 11, and a
counter-electrode 19 disposed within the vessel 18 so as to be
opposed to the drum surface 11 with a given space, preferably a
spacing between 0.5 to 2 mm. The counter-electrode 19 constitutes
an electrically conductive developing electrode, and is formed
therein with a liquid inlet 20 and a liquid outlet 21 at positions
advanced and retracted with respect to the direction of rotation of
the drum surface 11. A developing solution within the vessel 18 is
pumped by a pump 22 through the liquid inlet 20 into the space
between the drum surface 11 and the counter-electrode 19 for
contact with a latent image on the drum surface 11, end is
subsequently returned into the vessel 18 through the liquid outlet
21. The counter-electrode 19 is connected to the ground through a
constant voltage element, for example, a bidirectional constant
voltage element 23, thus allowing a potential to be induced on the
electrode by the charge on the drum surface 11. It will be
appreciated that the constant voltage element 23 may be a
unidirectional constant voltage diode. The potential of the
counter-electrode 19 is lower than the potential of the image
portion in the latent image on the drum surface 11 and is higher
than that of the non-image portion thereof, and is maintained below
the threshold value of the constant voltage element 23. As a
consequence, the electrostatic latent image on the drum surface 11
is developed by the developing solution supplied, and the toner on
the non-image portion is electrically attracted to the
counter-electrode 19 to prevent the background smearing and improve
the contrast in the image, thus producing the so-called electrode
effect. By the arrangement according to the invention, it will be
appreciated that the potential of the counter-electrode 19 varies
depending upon the electrostatic latent image on the drum surface
11, so that even with an image of lower density, the background
smearing is eliminated and the contrast in the image is improved,
and further that the potential of the counter-electrode 19 can not
increase beyond the threshold value of the constant voltage element
23, thereby preventing the loss of an image area of reduced
density.
Another embodiment of the liquid developing system according to the
invention is shown in FIG. 3 wherein the counter-electrode 19 is
divided into a plurality of segments 19-1, 19-2 . . . 19-8 which
are disposed along the direction of rotation of the drum 11 with a
given spacing therebetween and which are carried on an insulating
member 24 having a liquid inlet 20' and a liquid outlet 21' formed
therein. A constant voltage element 23 is electrically connected
between the segment 19-1 and the ground. A plurality of diodes
25-1, 25-2, . . . 25-7 have their anodes connected with the
segments 19-1 to 19-7, respectively, and have their cathodes
connected with the segments 19-2 to 19-8, respectively. Potentials
are successively induced on the segments 19-1 to 19-8 by the
electrostatic latent image on the drum surface 11, and their
induced potentials are suitably held below a given value by the
constant voltage element 23 and through the diodes 25-1 to 25-7.
The division of the counter-electrode into a plurality of segments
19-1 to 19-8 reduces the capacitance of the respective segments,
thereby improving the leading edge of the induced potential and
hence the electrode effect. The segment 19-8 constitutes an
auxiliary counter-electrode which is disposed at a position
advanced in the direction of travel of the drum with respect to the
location where the developing solution is supplied to the image on
the drum 11. This results in the advantage that the potential of
the segments 19-1 to 19-7 is increased by the induced potential on
the counter-electrode 19-8 through the diodes 25-1 to 25-7, thus
assuring an electrode effect in the event sufficient potential is
not induced on these segments by the electrostatic latent image on
the drum 11. Specifically, if the induced voltage caused by the
electrostatic latent image on the drum surface 11 to the respective
segments 19-1 to 19-7 is not sufficient by itself, their potential
is increased by the induced potential of the segment located at an
advanced position, as transmitted through the respective diodes, to
a value enough to provide a satisfactory electrode effect. This
permits a compensation for the phenomenon that a sufficient induced
potential may not be produced within the developing solution.
In FIG. 4, the segment 19-8 of FIG. 3 is replaced by a roller 26,
which serves to remove residual developing solution after the
electrostatic latent image on the drum surface 11 has been
developed. The developing solution which has been taken off by the
roller 26 is scraped by a developing solution removal member 27 to
fall into the vessel 18. Both the roller 26 and the member 27 are
formed of an insulating material and are held in abutment against
each other. The roller 26 is driven by suitable drive means, not
shown, to rotate in the direction indicated by an arrow and is
charged to the same polarity as the drum surface 11 by friction
with the member 27. A conductive finger 28 contacts the roller 26
and is connected with the cathode of the diode 25-7. As a
consequence, the segment 19-7 has its potential increased by the
charged potential of the roller 26 as transmitted through the
finger 28 and the diode 25-7, thereby assuring a satisfactory
electrode effect.
FIG. 5 shows a modification of the embodiment shown in FIG. 4 in
that a constant voltage element contained in the charger serves
also as the constant voltage element in the liquid developing
system. In the example shown, the charger 12 comprises an electrode
29 which is disposed in opposition to the drum 11 with a grid 30
interposed therebetween and which is mounted within a shielding
frame 31. A d.c. source 32 is connected between the electrode 29
and the ground, and the shielding frame 31 is connected to the
ground through a chain of constant voltage elements 33 to 36, with
the grid 30 connected to the junction between the constant voltage
elements 34 and 35. The electrode 29 serves to charge the drum 11
by corona discharge through the grid 30. The junction between the
constant voltage elements 35 and 36 is connected with the junction
between the diode 25-7 and the finger 28, whereby the potential of
the segments 19-1 to 19-7 and the roller 26 is maintained
.[.below.]. .Iadd.above .Iaddend.a given value.
In another electrophotographic copying process, it is known that a
photosensitive paper is entirely charged, followed by an imagewise
exposure to form an electrostatic latent image, which is developed
by a developing solution and finally fixed. The invention can be
applied to such a process. Referring to FIG. 6, there is shown a
vessel 37 of developing solution within which a guide member 38 is
disposed, and a counter-electrode 39 is disposed above the guide
member 38 with a given spacing therebetween. A photosensitive paper
40 having an electrostatic latent image formed thereon is passed
between a pair of rollers 41 and 42 and is guided by the guide
member 38 to advance through the developing solution within the
vessel 37 in order to have its latent image developed. Subsequently
the photosensitive paper is delivered to a fixing unit. The
counter-electrode 39 is connected to the ground through a constant
voltage element 43, and produces the similar electrode effect as
mentioned above.
It should be understood that the invention can also be applied to
an electrophotographic process using a powder developer rather than
a developing solution, for example, a cascade developing process.
Furthermore, the invention can equally be applied to an
electrophotographic process in which the developing takes place by
means of a magnetic brush, as shown in FIG. 7. In the developing
system shown, a plurality of magnets 44 to 47 are fixed to an arbor
48 which is driven by suitable means, not shown, for rotation
within a hollow cylinder 49. The hollow cylinder 49 is disposed at
a position opposite to the drum 11 and is received within a
container 50. A developer 51 comprising a mixture of carrier and
toner is received within the container 50, and forms a magnetic
brush 52 as a result of the attraction acting between the carrier
and the magnets 44 to 47. As the magnets 44 to 47 rotate, the
magnetic brush 52 also rotates around the cylinder 49 to carry the
toner toward the surface of the drum 11 for the purpose of
developing. In accordance with the invention, a plurality of
counter-electrode segments 53-1, 53-2 . . . 53-n are secured on the
inner surface of the cylinder 50 and function in the same manner as
mentioned previously to provide an electrode effect. As shown, the
container 50 is provided with a brush length adjusting member 54
and a scraper 55 which scrapes off the magnetic brush 52.
While in the above description, the invention has been illustrated
with reference to an electrophotographic copying process, it should
be understood that the invention can also be applied to copying
processes other than the electrophotographic copying process in
which a member having an electrostatic latent image formed thereon
is to be developed with a developer. It will also be noted that the
constant voltage element for maintaining the potential of the
counter-electrode below a given value may comprise a plurality of
such elements connected in series to provide any desired threshold
value.
While the above embodiments relate to the induction of the
potential of the developing electrode 19 from the image portion on
the drum surface 11, it is also possible to induce a potential on
the developing electrode 19 from a portion of the drum 11 which is
charged to a constant potential and remains unexposed. In contrast
to the electrophotographic copying process in which the drum
surface 11 is entirely charged by the charger as mentioned
previously, FIG. 8 shows a modified body with a surface of
photosensitive material 11-2 having an area 11-1 which remains
unexposed by the exposure unit 13. Such area may be provided at one
end or both ends of the body and may be in the form of a band
having a width in the range from 5 to 50 mm, for example. A
potential of a given magnitude is induced on the developing
electrode 19 by the charged potential on the area 11-1, and is
maintained below the threshold value of the constant voltage
element 23. The supply of a developing solution to the modified
surface 11-2 produces a developing of the electrostatic latent
image thereon in the usual manner, and the toner on the non-image
portion is electrically attracted by the developing electrode 19 to
prevent the background smearing and to improve the contrast in the
image, thus producing the electrode effect. The potential of the
developing electrode 19 is effectively induced by the potential of
the blank area 11-1 to assure a high contrast in the image, and is
held below the threshold value of the constant voltage element 23,
so that the loss of an image area of reduced density is avoided.
Such area 11-1 may comprise an insulating material such as an
insulating film or the like. The area 11-1 is kept clear of contact
with the transfer sheet, and this may result in overloading the
cleaning unit 17. Such an overload can be avoided by providing the
developing electrode 19 with a protective member 126 which
comprises sponge or felt and is aligned with the area 11-1, as
shown in FIG. 9(a), or by providing the developing electrode 19
with a blade 127 comprising an elastomer such as polyurethane
rubber, as shown in FIG. 9(b), the member 126 or blade 127 cleaning
the area 11-1 of the modified body.
* * * * *