U.S. patent number RE30,535 [Application Number 06/035,897] was granted by the patent office on 1981-03-03 for developing device in electrophotographic copying apparatus.
This patent grant is currently assigned to Ricoh Co., Ltd.. Invention is credited to Shoji Kuroishi, Manabu Mochizuki.
United States Patent |
RE30,535 |
Kuroishi , et al. |
March 3, 1981 |
Developing device in electrophotographic copying apparatus
Abstract
An improved developing device in electrophotographic copying
apparatus in which a plurality of developing electrodes are
disposed along a path of movement of a photosensitive drum surface.
The electrodes are applied with voltages in a graded manner which
conforms to the damping characteristic of the potential on the
photosensitive surface at a developing station. The values of
voltages applied can be controlled in accordance with the value of
potential formed by an imaging area of the drum surface while
maintaining the graded potential to thereby achieve an excellent
developing effect. Further, the drum surface is provided with an
unexposed and hence high potential portion which serves to remove
toner which accumulates on the electrodes.
Inventors: |
Kuroishi; Shoji (Yokohama,
JP), Mochizuki; Manabu (Yokohama, JP) |
Assignee: |
Ricoh Co., Ltd. (Tokyo,
JP)
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Family
ID: |
13295154 |
Appl.
No.: |
06/035,897 |
Filed: |
May 3, 1979 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
584294 |
Jun 6, 1975 |
04021111 |
May 3, 1977 |
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Foreign Application Priority Data
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Jun 10, 1974 [JP] |
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49-65721 |
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Current U.S.
Class: |
399/56;
399/264 |
Current CPC
Class: |
G03G
15/047 (20130101); G03G 15/10 (20130101); G03G
15/065 (20130101) |
Current International
Class: |
G03G
15/045 (20060101); G03G 15/10 (20060101); G03G
15/047 (20060101); G03G 15/06 (20060101); G03G
015/10 () |
Field of
Search: |
;355/10
;118/647,648,662,DIG.23 ;430/117-119 |
References Cited
[Referenced By]
U.S. Patent Documents
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3707943 |
January 1973 |
Matsumoto et al. |
3778148 |
December 1973 |
Fujitsuka et al. |
3892481 |
July 1975 |
Schaefer et al. |
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Primary Examiner: Moses; R. L.
Attorney, Agent or Firm: Dunne; Gerard F. Shoup; Guy W.
Claims
What is claimed is:
1. In an electrophotographic copying apparatus comprising a movable
member having a photosensitive surface and adapted to be moved
along a predetermined path during which said surface is subject to
charging, exposing to an image of an original to be copied to form
an electrostatic latent image of the original thereon, developing
of the latent image with a developing agent having toner, transfer
printing of the developed image onto copy sheets, and cleaning of
residual toner thereon, the improvement comprising:
a. a plurality of developing electrodes disposed along the path of
movement of said surface in opposing relation thereto at a
developing station,
b. means for supplying the developing agent between said electrodes
and said surface,
c. voltage source means for providing a constant voltage .[.source
for.]. .Iadd.to .Iaddend.said electrodes,
d. means for distributing the supplied voltage from said source
means to said respective electrodes in a graded manner which
substantially conforms to that of a reference damping
characteristic of potential on said surface along the path of
movement thereof at the developing station, and
e. means for .[.varying the values.]. .Iadd.changing the level
.Iaddend.of .[.voltages.]. .Iadd.voltage .Iaddend.applied to said
respective electrodes without influence to said graded manner
therebetween .[.in accordance with the value of potential of an
electrostatic latent image on said surface to be developed.]..
2. An improvement as in claim 1 wherein said voltage source means
comprises a portion of a charger for said charging which normally
presents a constant voltage.
3. An improvement as in claim 1 wherein said distributing means
comprises constant voltage diodes connected in series to each other
and between said constant voltage source and ground and having
junctions therebetween connected to said respective electrodes.
4. An improvement as in claim 3 wherein said varying means
comprises a pair of variable voltage dropping means each connected
between the series of said diodes and said control voltage source
and said ground respectively.
5. An improvement as in claim 1 further comprising means for
setting a portion to be unexposed on said photosensitive surface to
maintain the unexpected portion at a high potential, whereby
removing toner placed on said electrodes therefrom by the
attraction of the high potential portion.
6. An electrophotographic copying apparatus comprising a movable
member having a photosensitive surface, an electrostatic charger
adjacent said member and located along the path of motion of said
member, for imparting an electrostatic charge to said surface, an
exposure unit adjacent said member and spaced away from said
charger in the direction of motion of said member, having means to
impart an electrostatic image to said surface, developer means
adjacent said member and spaced away from said exposure unit in the
direction of motion of said member, said developer means having a
reservoir containing a developing agent which is attractable to
said electrostatic image and forms a visual image corresponding to
said electrostatic image on said surface, means for moving a copy
sheet into pressing engagement with said member spaced away from
said developer means in the direction of motion of said member,
cleaning means adjacent said member and spaced away from said
moving means in the direction of motion of said member, for
cleaning away the developing agent from said surface, and a
constant light source adjacent said member and spaced away from
said cleaning means in the direction of motion of said member, for
discharging said electrostatic charge by exposing said surface to
light, said developer means comprising a plurality of electrodes
spaced away from and facing said surface and disposed along the
path of said surface, voltage source means connected to said
electrodes for providing a constant voltage to said electrodes,
pump means within said reservoir for supplying developing agent
from said reservoir to the space between said electrodes and said
surface, grading means connected to said electrodes for
distribution the supplied voltage from said source means to said
electrodes in a manner substantially conforming to the damping
characteristic of the said electrostatic charge on said surface as
said surface passes said electrodes, and .[.varying.].
.Iadd.changing .Iaddend.means connected between said voltage source
means and said grading means to change the .Iadd.level of constant
.Iaddend.voltage applied to said electrodes .[.in accordance with
the value of said electrostatic image,.]. without influencing the
graded relationship between said electrodes.
7. A copying apparatus according to claim 6, wherein said voltage
source means comprises a portion of said charger having a constant
voltage.
8. A copying apparatus according to claim 6, wherein said grading
means comprises a plurality of constant voltage diodes connected in
series to each other and having junctions therebetween connected to
said electrodes.
9. A copying apparatus according to claim 8, wherein said varying
means comprises a plurality of pairs of voltage dropping means
connectable on one side to each end of said diode series, one pair
at a time, and on the other side to said voltage source and ground
respectively.
10. A copying apparatus according to claim 6, wherein said
photosensitive surface has a portion charged by said charger and
unexposed to light, thus forming a high potential area situated on
said surface behind said electrostatic image, switching means
connected to said electrodes and to said moving member to cut the
voltage supply from said voltage source means to said electrodes at
the time when said high potential area passes said electrodes, the
difference in potential causing any excess developing agent left on
said electrodes after said visual image forming to be
electrostatically attracted to said high potential area.
11. An electrophotographic copying apparatus comprising a movable
member having a photosensitive surface, means along the path of
motion of said member for imparting an electrostatic image to said
surface, developer means along the path of motion of said member
and spaced from said former means in the direction of motion of
said member, said developer means having a plurality of electrodes
spaced from and facing said surface and disposed along said surface
in the direction of motion of said member, a constant voltage
source connected to said electrodes, a reservoir disposed below
said electrodes containing a developing agent which is attractable
to said electrostatic image and which forms a visual image
corresponding with said electrostatic image, a pump in said
reservoir for pumping said developing agent to the space between
siad electrodes and said surface, grading means connected between
said electrodes and said constant voltage source, for supplying
voltages to said electrodes in a manner corresponding to the damage
characteristic of said electrostatic image, said grading means
having a plurality of constant voltage diodes equal to the number
of electrodes, connected in series, said electrodes being connected
individually between said diodes, at least one first multi-position
switch being connected to one end of said series, and at least one
second multi-position switch being connected to the other end of
said series, said first and second multi-position switches being
mechanically connected to each other and simultaneously operable, a
first plurality of diodes, individually engageable with said first
multiposition switch at one end and connected to a common point at
the other end, a second plurality of diodes being individually
engageable with said second multiposition switch at one end and
connected to a common ground at the other end, said common point
being connected to said constant voltage source, said multi-purpose
switches being positionable to select a pair of diodes, one from
said first plurality and one from said second plurality, to vary
the potential applied to said diode series.
12. An electrophotographic copying apparatus, for making copies
from the light image, comprising a moving member having a
photosensitive surface, a charger adjacent said member and on the
path of motion of said member for imparting an electrostatic charge
to said surface, an exposure unit adjacent said member and spaced
from said charger in the direction of motion of said member, for
imparting an electrostatic image to said surface corresponding to
said light image, a constant light source spaced from said surface
in said exposure unit, shutter means in said exposure unit for
selectively exposing said surface to light from said constant light
source as said member moves past said exposure unit, developer
means adjacent said member and spaced from said exposure unit in
the direction of motion of said member, a plurality of electrodes
in said developer means spaced from and facing said surface and
disposed along said surface in the direction of motion of said
member, a developing agent in said developer means attractable to
said electrostatic image, and suppliable to the space between said
electrodes and said surface, a portion of said surface being
unexposed to light by said shutter means and retaining said charge
imparted by said charger, said unexposed portion of said surface
being formed on said surface at a location adjacent to and behind
said electrostatic image, and passing said developer means after
said electrostatic image and effective to attract excess developing
agent from said electrodes.
13. An apparatus according to claim 12, wherein said exposure unit
comprises said constant light source spaced from said movable
member, said shutter means disposed between said member and said
light source, and a scanner unit spaced from said member for
supplying said light image, said shutter means disposed between
said scanner and said member.
14. An apparatus according to claim 13, wherein said shutter means
comprises a first mirror affixed to said exposure unit and facing
said scanner unit at an angle to said scanner unit so as to reflect
said light image into said surface, a door, pivotally mounted in
said exposure unit between said first mirror and said surface, said
door having an open position allowing said light image to be
projected onto on said surface, and a closed position to block said
light image, a second mirror pivotally mounted in said exposure
unit between said constant light source and said surface, said
second mirror having an open position which allows light from said
constant light source to be reflected onto said surface by said
second mirror, and a closed position which blocks said constant
light source, said door and said second mirror being in respective
closed positions to form said unexposed surface portion.
Description
BACKGROUND OF THE INVENTION
The invention relates to an improved developing device in
electrophotographic copying apparatus.
In a wet developing process, a developing solution is supplied
across a photosensitive member to develop an electrostatic latent
image thereon. It is known to dispose a developing electrode within
the developing solution in opposing relationship with the
photosensitive member and to apply a bias voltage to the developing
electrode in accordance with a residual potential on the
photosensitive member, thereby preventing a background smearing.
However, in the known process, the bias voltage applied to the
developing electrode is, by several tens of volts, higher than the
residual potential on the photosensitive member, so that an
adhesion of toner to the electrode may occur, thereby reducing the
intended electrode effect.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved developing
device in electrophotographic copying apparatus which permits the
abovementioned disadvantage, namely, the adhesion of toner to the
developing electrode, to be eliminated.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is schematic view of an electrophotographic copying machine
to which the invention is applied;
FIG. 2 is a circuit diagram of an electrical circuit used in the
arrangement of FIG. 1;
FIG. 3 is a schematic view of a portion of the machine shown in
FIG. 1 which includes an exposure unit;
FIG. 4 is a fragmentary view of FIG. 3;
FIG. 5 is a schematic view of a portion of the arrangement shown in
FIG. 1 which includes a developing unit;
FIG. 6 is a perspective view of a cam and a switch which are used
in the arrangement of FIG. 1;
FIG. 7 is a perspective view of a photosensitive member used in the
arrangement of FIG. 1, illustrating the potential distribution
thereon; and
FIG. 8 graphically shows the damping characteristic of the
potential of non-image areas on the photosensitive member in the
region of the developing unit shown in FIG. 5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, there is shown a photosensitive member 11
which may be in the form of a drum arranged for rotation in the
direction indicated by an arrow at a uniform speed by means of a
suitable driving device. As the photosensitive member 11 rotates a
sequential operation is effected. Specifically, the member 11 is
charged by a charger 12, and then exposed to an image of an
original to be copied which is formed by an exposure unit 13,
thereby forming an electrostatic latent image thereon.
Subsequently, the latent image is developed by a developing unit
14, and the developed image is transferred onto a transfer paper 16
at a transfer unit 15. Thereafter, the photosensitive member 11 is
cleaned by a cleaning unit 17 and discharged by irradiation from a
light source 18. The transfer sheet 16 which has an image
transferred at the transfer unit 15 is fixed in a fixing unit (not
shown) to be subsequently discharged as a copy.
Describing the copying process more specifically, subsequent to the
flash charging of the photosensitive member 11 by the charger 12, a
non-imaging area 11b, except at an imaging area 11a which is
exposed to an image of the original through the exposure unit 13,
includes a non-exposed area 11c which is unexpected and hence
charged to a high potential, as shown in FIG. 7. Referring to FIG.
3, the exposure unit 13 includes a main body 19 which scans an
original in synchronism with the photosensitive member 11 and
exposes the photosensitive member 11 through a reflecting mirror 20
and an open shutter 21 which is pivotally mounted at its one end.
Light from the light source 18 is projected onto the photosensitive
member 11 through a movable reflecting mirror 22 which is also
pivotally mounted at its one end, thereby discharging the electric
charge on the photosensitive member 11. As indicated in FIG. 4, the
main body 19 includes an original receptacle 23 adapted to place an
original 24 thereon, which is illuminated by light from a light
source 25, and reflected light therefrom is directed toward the
reflecting mirror 20 through other reflecting mirrors. The original
24 is scanned by driving the light source 25, in the direction
indicated by an arrow, in synchronism with the movement of the
photosensitive member 11. A switch 26 is disposed below the
receptacle 23 at a position corresponding to the initial or
terminal end of the original 24, and the switch is operated by a
portion of a light shield member (not shown) which is integral with
the light source 25. As shown in FIG. 2, a control circuit 27
responds to the signal from the switch 26 by energizing a pair of
electromagnets 28, 29 at a proper timing, thereby operating the
shutter 21 and the movable reflecting mirror 22. The shutter 21 is
opened as the main body 19 scans the original 24 from its initial
to its terminal end, thereby projecting the image of the original
24 onto the imaging area 11a of the photosensitive member 11. The
movable reflecting mirror 22 is opened at a proper timing except
when the image of the original 24 is focussed onto the imaging area
11a. This occurs, during the time when the shutter remains closed
as shown in phantom lines 21', whereby the light from the light
source 18 is projected onto portion of the photosensitive member
except the high potential portion 11c of the non-imaging area 11b
for the purpose of discharge. During the time the image of the
original 24 is projected onto the imaging area 11a, the light
directed from the light source 18 is blocked from projection onto
the imaging area 11a by means of the closed mirror 22'.
Referring to FIG. 5, the developing unit 14 includes a plurality of
developing electrodes 301 to 305 which are supported by an
insulating plate 31 in opposing relationship with the
photosensitive member 11. The unit 14 also includes a vessel 32 for
containing a supply of developing solution, which is supplied by a
pump 34 through an inlet 33 into the space between the
photosensitive member 11 and the insulating plate 31. The solution
is returned to the vessel 32 through a drain port 35. A plurality
of constant voltage diodes 361 to 364 are connected between
adjacent pair of electrodes 301 to 305, and the junction between
the electrode 301 and the constant voltage diode 361 is connected
through a switch 37 with the movable arm of a switch 38. The
junction between the electrode 305 and the diode 364 is connected
with the movable arm of a switch 39 which has a plurality of
stationary contacts 391 to 39n, which are in turn connected with
one terminal of a plurality of constant voltage diodes 401 to 40n,
the other terminal of which is connected with the ground. A
plurality of constant voltage diodes 431 to 43n are connected
between the respective stationary contacts 381 to 38n of the switch
38 and a point of a given potential, which is shown as the junction
between a pair of bidirectional varistors 41 and 42. The
bidirectional varistors 41, 42 are connected in series with another
bidirectional varistor 45 across a shield member 44 of the charger
and the ground, and the junction between the bidirectional
varistors 41, 45 is connected with a grid 46 of the charger 12
which has its corona wire 47 connected with a d.c. source 48. As
indicated in FIG. 3, the corona wire 47 is disposed within the
shield member 44 so as to be opposite to the photosensitive member
11 through the interposition of the grid 46, thereby charging the
member 11 by means of corona discharge. A discharge will also occur
between the corona wire 47 on one hand and the shield member 44 and
the grid 46 on the other, thereby causing a current flow through
the bidirectional varistors 41, 42 and 45, thus establishing a
given potential on each of the shield member 44 and the grid 46. A
voltage of given magnitude developed across the varistor 42 is
supplied to the developing electrodes 301 to 305 through one of the
diodes 431 to 43n and through one of the diodes 401 to 40n which
are selected by the respective switches 38 and 39. It will be
appreciated that the diodes 361 to 364 function to apply
differential voltages to the respective electrodes 301 to 305 in a
graded manner which corresponds to the damping characteristic of
the residual potential on the photosensitive member 11.
FIG. 8 shows a family of curves representing the damping
characteristic of the potential of the non-image area of the
photosensitive member 11 which is exposed to the white portion of
the original. The switches 38 and 39 are ganged. The diodes 401 to
40n have a descending order of voltage drop while the diodes 431 to
43n have an ascending order of voltage drop. Assume now that the
movable arms of the switches 38 and 39 are connected with the
stationary contacts 381 and 391, respectively, so that the voltage
distribution and gradient of the electrodes 301 to 305 conform to a
curve 1. Under this condition, when the movable arms of the
switches 38 and 39 are thrown to the adjacent contacts 382 and 392,
the potential applied to the respective electrodes 301 to 305 will
be shifted to the voltage distribution conforming to a damping
curve 2 of FIG. 8 which is spaced by .DELTA.E from the initial
damping curve 1, without changing the overall profile, since the
diode 402 has a voltage drop which is by .DELTA.E reduced from that
of the diode 401 and the diode 432 has a voltage drop which is by
.DELTA.E increased over that of the diode 431. As a consequence, by
manually operating the switches 38 and 39 in accordance with the
level of the residual potential on the photosensitive member 11, it
is possible to apply an optimum bias potential to the developing
electrodes 301 to 305. An image area of the photosensitive member
11 which is charged to a higher potential than the bias potential
will be developed by attraction of toner thereto while a non-image
area will not be developed because the tone will be attracted
toward the developing electrodes 301 to 305. This prevents an
adhesion of the toner to an area of the photosensitive member 11
which corresponds to the white background of the original, thus
avoiding a background smearing. The toner which is attracted to the
developing electrodes 301 to 305 will be attracted to the high
potential area portion 11c of the photosensitive member 11, whereby
the developing electrodes 301 to 305 are cleaned.
As shown in FIG. 6, the switch 37 is driven at a given timing by
means of a cam 49 which is coupled with the shaft associated with
the photosensitive member 11. Specifically, the d.c. source 48 of
the charger 12 is turned on before the leading edge of the imaging
area 11a enters the coverage of the charger 12, and the switch 37
is turned on before the imaging area 11a comes opposite to the
electrode 301. The source 48 is turned off after the high potential
portion 11c has passed the charger 12, but at this time, such
portion 11c moves opposite to the electrode 301, and the switch 37
is subsequently turned off. After the source 48 is turned off, the
electrodes 301 to 305 are supplied with a bias potential by the
electrostatic induction from the high potential portion 11c.
With the invention described above, a graded distribution of the
bias potentials applied to the respective electrodes can be
achieved in a manner corresponding to the potential damping
characteristic of the photosensitive member, and the level of the
bias potentials can be changed, thus permitting the bias potentials
to be applied to the respective electrodes in accordance with the
pattern of the non-image area so as to prevent a background
smearing or the excessive attraction of toner to the electrodes,
thus achieving an excellent electrode effect. By providing a high
potential portion in the non-imaging area of the photosensitive
member, the electrodes are cleaned by such high potential area,
further contributing to the electrode effect.
* * * * *