Information
-
Patent Grant
-
6343200
-
Patent Number
6,343,200
-
Date Filed
Monday, July 24, 200023 years ago
-
Date Issued
Tuesday, January 29, 200222 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Chen; Sophia S.
- Ngo; Hoang
Agents
-
CPC
-
US Classifications
Field of Search
US
- 222 167
- 222 DIG 1
- 399 119
- 399 254
- 399 255
- 399 256
- 399 258
- 399 263
- 399 260
- 399 262
- 399 272
- 399 273
- 399 274
- 399 281
- 399 283
- 399 284
- 430 120
-
International Classifications
-
Abstract
A developing device for use in an image forming apparatus includes a developing agent supply unit which supplies a developing agent to a photoreceptor, a first mixing unit provided near the developing agent supply unit to convey the developing agent in a first conveyance direction while mixing the developing agent, a second mixing unit provided underneath the first mixing unit to receive the developing agent at a downstream end along the first conveyance direction so as to supply the developing agent to the developing agent supply unit while mixing and conveying the developing agent in a second conveyance direction, and a developing agent scoop-up unit provided substantially in the middle in a height direction between the first mixing unit and the second mixing unit along the second conveyance direction to receive the developing agent from the second mixing unit and draw up the received developing agent to the first mixing unit.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a developing device for use in an image forming apparatus such as copier and printer to supply a developing agent to a photoreceptor so as to develop a latent image into a toner image, and more particularly to a developing device which uses a two-component developing agent consisting of toner and carrier.
2. Description of the Related Art
Heretofore, there has been known a developing device for use in an image forming apparatus to develop an electrostatic latent image formed on the surface of a photosensitive drum into a toner image with use of a two-component developing agent consisting of toner and carrier.
Such a developing device is provided with a housing for accommodating a developing agent, developing agent supplier means for supplying the developing agent in the housing to the surface of the photosensitive drum to develop a latent image into a toner image, developing agent mixing means for mixing the developing agent in the housing while at the same time feeding the developing agent in a certain direction, and toner replenishing means for replenishing toner into the housing.
The developing agent supplier means supplies toner on a certain area (developing area) of the drum surface to develop the latent image into a toner image within the area. As the toner in the housing is used up in accordance with progress of the image formation, the toner replenishing means replenishes toner into the housing. The developing agent mixing means agitates the developing agent, namely mixes the toner particles with the carriers which are electrically charged to convey the toner particles together with the charged carriers owing to electrostatic friction.
A known technology relating to agitation and transport of developing agent is disclosed in, for example, Japanese Unexamined Patent Publication No. 10-142942. The publication discloses a four-membered tandem type developing device for use in a color copier comprising: developing agent supplier means for supplying a developing agent onto the surface of a photosensitive drum; first mixing/transporting means disposed near the developing agent supplier means to agitate the developing agent while transporting the developing agent in a first direction thereof; second mixing/transporting means disposed underneath the first mixing/transporting means to agitate the developing agent while transporting the developing agent in a second direction opposite to the first direction; and feeder means coaxially provided along with the longitudinal direction of the developing agent supplier means to feed the developing agent transported by the second mixing/transporting means toward the first mixing/transporting means in response to driving of the developing agent supplier means.
The above-mentioned conventional developing device has room for improvement in the aspect of agitation and transport of developing agent, prevention of undesired stay of developing agent, and reducing the dimensions of the developing device itself. Particularly, as for the dimensions of the device itself, since the feeder means is provided coaxially with the developing agent supplier means (magnet roller) to feed the developing agent from the second mixing means (lower mixing means) to the first mixing means (upper mixing means), the device itself is inevitably large in the axial direction of the magnet roller by a dimension corresponding to the axial length of the feeder means which axially protrudes beyond the developing area.
SUMMARY OF THE INVENTION
In view of the above problems residing in the prior art, it is an object of the present invention to provide a developing device of a compact size particularly in the axial length thereof that enables to ensure sufficient agitation of a developing agent and prevention of undesired stay of the developing agent.
In one aspect of this invention, a developing device for use in an image forming apparatus comprises: a developing agent supply unit which supplies a developing agent to a photoreceptor; a first mixing unit provided near the developing agent supply unit to convey the developing agent in a first conveyance direction while mixing the developing agent; a second mixing unit provided underneath the first mixing unit to receive the developing agent from the first mixing unit at a downstream end along the first conveyance direction so as to supply the developing agent to the developing agent supply unit while mixing and conveying the developing agent in a second conveyance direction; and a developing agent scoop-up unit provided substantially in the middle in a height direction between the first mixing unit and the second mixing unit and at a downstream end of the second mixing unit along the second conveyance direction to receive the developing agent from the second mixing unit and draw up the received developing agent to the first mixing unit.
With this arrangement, the developing agent is sufficiently mixed while conveyed in the first and second conveyance directions by the first and second mixing units. Further, this arrangement enables to provide an image forming apparatus of a compact size, particularly in the axial direction of the developing device while preventing stagnation of the developing agent.
These and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a schematic diagram showing an overall construction of an image forming apparatus incorporated with a developing device according to this invention.
FIG. 2A
is a diagram showing an internal mechanism of the developing device.
FIG. 2B
is a cross-sectional view taken along the line
2
B—
2
B in FIG.
2
A.
FIG. 3
is a cross-sectional view taken along the line
3
—
3
in FIG.
2
A.
FIG. 4
is a cross-sectional view taken along the line
4
-
4
in FIG.
2
A.
FIG. 5
is a schematic diagram showing essential elements of the developing device.
FIG. 6
is a diagram showing an interlocked state of gears viewed from rear side of the image forming apparatus.
FIG. 7
is a diagram showing an interlocked state of gears viewed from front side of the image forming apparatus.
FIG. 8
is an explanatory diagram showing as to how a developing agent is delivered through the developing device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1
is a schematic diagram showing an overall construction of a color printer as an embodiment of an image forming apparatus according to this invention.
The construction of the color printer is described with reference to FIG.
1
. The color printer
2
includes a sheet feeder section
4
for feeding a sheet member
3
on which an image is to be copied one by one, a sheet transport section
6
for transporting the sheet member
3
fed from the sheet feeder section
4
in a certain direction, an imaging assembly
5
for forming an toner image which is to be transferred onto the sheet member
3
, an image transfer section
7
for transferring the toner image onto the sheet member
3
, an image fixing section
8
for fixing the transferred toner image on the sheet member
3
, a sheet discharge section
10
which receives the sheet member
3
after the image fixation, and an optical unit
11
.
Specifically, the sheet feeder section
4
includes a first feeder unit
15
and a second feeder unit
18
. The first feeder unit
15
is constructed in such a manner that sheet members
3
stacked on a first sheet tray
12
are fed one by one by a feed roller (drive roller)
13
and a retard roller (driven roller)
14
toward downstream of the sheet transport direction. The second feeder unit
18
is constructed in such a manner that sheet members
3
stacked on a manual insertion tray
16
are fed one by one by a feed roller
17
toward downstream of the sheet transport direction.
The sheet transport section
6
includes a transport path
20
along which the sheet member
3
is fed from the first sheet feeder unit
15
or the second sheet feeder unit
18
toward the imaging assembly
5
, a transport roller
21
disposed at a certain position on the transport path
20
, a registration roller pair
22
which temporarily suspends transport of the sheet member
3
as timed with nipping of the lead end of the sheet member
3
and resumes transport of the sheet
3
toward the imaging assembly
5
while correcting a skew transport of the sheet member
3
, and a manual transport path
23
which is connected to the transport path
20
at an upstream position from the registration roller pair
22
with respect to the sheet transport direction.
The imaging assembly
5
includes a first imaging section
24
adapted to form a black color image, a second imaging section
25
adapted to form a cyan color image, a third imaging section
26
adapted to form a magenta color image, and a fourth imaging section
27
adapted to form a yellow color image. The first, second, third, and fourth imaging sections
24
,
25
,
26
,
27
each is provided with a cylindrical photosensitive drum
28
, a developing unit
30
for forming individual color toner image on the surface of the photosensitive drum
28
, a cleaning unit
33
provided with a brush
31
for removing toner residues on the surface of the photosensitive drum
28
and a cleaning blade
32
for scraping off toner residues on the surface of the photosensitive drum
28
, and a charger
34
which supplies electric charges on the photosensitive drum surface to uniformly charge the surface of the photosensitive drum
28
.
The image transfer section
7
includes an endless belt
37
composed of a resin material containing fluorine compound, a drive roller
38
and a tension roller (driven roller)
40
for circulating the belt
37
, and transfer rollers
41
a
,
41
b
,
41
c
,
41
d
respectively disposed at certain positions opposing the corresponding photosensitive drums
28
. The image transfer section
7
is constructed in such a manner that the sheet member
3
is conveyed further downstream of the sheet transport direction over the endless belt
37
which is driven between the transfer roller
41
a
(
41
b
,
41
c
,
41
d
) and the corresponding photosensitive drum
28
. Guide rollers
42
,
43
are provided at respective appropriate positions on an inner circumference of the transfer belt
37
.
In the case where the image transfer section
7
is adapted to form a monochromatic image, the transfer roller
41
a
is driven while the other transfer rollers
41
b
,
41
c
,
41
d
being set apart from the surface of the corresponding photosensitive drums
28
.
The image fixing section
8
includes a heater roller
44
built-in with a heater (not shown), a fixing roller
45
, a metallic endless belt
46
which is wound around the heater roller
44
and the fixing roller
45
, and a presser roller
47
which is pressed against the fixing roller
45
. The image transfer section
7
further includes an oil supply roller
48
for applying silicone oil onto the outer surface of the endless belt
46
, an oil replenish roller
50
for replenishing silicone oil to the oil supply roller
48
, and a cleaning roller
51
for wiping off oil residue on the surface of the oil replenish roller
50
.
The sheet discharge section
10
includes a first discharge unit
52
for receiving the sheet members
3
discharged from the fixing section
8
one by one to stack the sheet members
3
one over another with the surface thereof formed with an image facing upward, and a second discharge unit
54
for guiding the sheet members
3
discharged from the fixing section
8
one by one toward an upper part of a main body
36
of the image forming apparatus via a discharge path
53
to stack the sheet members
3
one over another with the surface thereof formed with an image facing downward. In the case where the first discharge unit
52
is not used, it is accommodated in the apparatus main body
36
.
The optical unit
11
is constructed in such a manner that a set of a polygonal mirror
55
, lenses
56
,
57
, and a mirror
58
is arranged at a certain position in correspondence with the corresponding photosensitive drum
28
. A laser beam is irradiated onto the surfaces of the photosensitive drums
28
via slits
61
each of which is formed in an optical unit support plate
60
at a certain position corresponding to the photosensitive drum
28
.
In the color printer
2
having the above construction, when a sheet member
3
is fed from the first feeder unit
15
or the second feeder unit
18
, the sheet member
3
is guided first between the photosensitive drum
28
of the first imaging unit
24
and the transfer belt
37
via the sheet transport section
6
. Wile the sheet member
3
is conveyed over the transfer belt
37
between the transfer rollers
41
a
,
41
b
,
41
c
,
41
d
and the corresponding photosensitive drums
28
in this order sequentially, toner images of respective colors (black, magenta, cyan, yellow) formed by the respective photosensitive drums
28
are sequentially transferred onto the sheet member
3
.
When the sequential color image transfer is completed, the sheet member
3
is guided between the fixing roller
45
and the presser roller
47
while conveyed by the transfer belt
37
to thereby fix the color image. After the color image fixation, the sheet member
3
is discharged onto the first discharge unit
52
or the second discharge unit
54
.
Next, the developing device for use in an image forming apparatus according to this invention is described in detail with reference to
FIGS. 2
to
4
.
FIG. 2A
is a diagram showing an internal mechanism of the developing unit
30
viewed from top of the apparatus main body
36
,
FIG. 3
is a cross-sectional view taken along the line
3
—
3
in
FIG. 2A
, and
FIG. 4
is a cross-sectional view taken along the line
4
—
4
in FIG.
2
A.
The developing unit
30
has a developing housing
144
. The housing
144
is made of a synthetic resin material, and generally includes a bottom wall
132
, a first side wall
134
generally extending upward perpendicularly from the bottom wall
132
over the entire length thereof (axial direction of the developing unit
30
), a second side wall
136
formed on left side of the first side wall
134
in
FIG. 2A
, a front wall
138
formed at a left end of the first side wall
134
in
FIG. 2A
, a rear wall
140
formed at a right end of the first side wall
134
in
FIG. 2A
, and a top wall
142
formed at a top part of the housing
144
as shown in
FIGS. 3 and 4
. The second side wall
136
constitutes part of a developing agent scoop-up section of the developing unit
30
which is described below.
Note that the axial direction of the developing unit
30
corresponds to the depthwise direction of the apparatus main body
36
, and the left side and the right side of the developing unit
30
in
FIGS. 2A and 5
respectively correspond to front side and rear side of the apparatus main body
36
. Further, left and right directions in
FIG. 1
corresponds to widthwise directions of the apparatus main body
36
.
As shown in
FIG. 3
, the housing
144
is provided with a developing agent supply unit
146
at a left end thereof. The developing agent supply unit
146
includes a cylindrical sleeve
148
composed of a non-magnetized material such as aluminum and extending axially to generally cover a developing area by the developing device for image formation, and an inner member
150
provided inside the developing sleeve
148
and composed of a magnetic material.
The sleeve
148
is rotatably connected to a driver system which is described below, and the inner member
150
is fixed to the sleeve
148
. As shown in
FIG. 2A
, a rotary shaft
151
fixed to the developing sleeve
148
protrudes in depthwise directions of the apparatus main body
36
and passes through the rear wall
140
. An input gear
152
is fixed to a protruding end of the rotary shaft
151
. When a drive source (not shown) of the driver system is driven, a driving force thereof is transmitted to the input gear
152
by way of an output gear
154
and an idle gear
156
, thereby rotating the rotary shaft
151
in a direction shown by the arrow R
1
in
FIG. 3. A
developing agent
100
consisting of toner particles and carriers is conveyed on the outer surface of the developing sleeve
148
due to magnetic attraction of the carriers toward the magnetic member
150
provided inside the developing sleeve
148
. The manner of conveying the developing agent
100
is described below in detail.
Hereinafter, specifications of toner and carrier as main components of a developing agent used in the present invention, but not limited thereto, are described.
(1) Carrier:
Carrier medium grain size (diameter): 0.6 μm;
Shape: Spherical;
Material: Ferrite;
Saturation Magnetization: 65 emu;
(2) Toner:
Toner medium grain size: 8.5 μm;
Resin composition: Polyester;
Toner Density: fluctuates in a range of 4-5 wt % under normal condition and fluctuates in a range of 3.5 to 6 wt % under non-ordinary condition such as a shortage of toner or a change in environmental factor.
Note that the above specifications for the carrier and the toner are one of the examples, thus inducing no limitations to the application of the present invention.
As shown in
FIG. 3
, a developing agent scraper
160
is provided above the developing agent supply unit
146
. The scraper
160
includes a blade
62
with a pointed edge portion at a lowermost part thereof and a holder
64
for holding the blade
62
. The holder
64
is fixedly supported at a certain position on an upper front part of a partition wall
66
which is adapted to accommodate a first mixing unit
68
. The edge portion of the blade
62
extends substantially over an entire axial length of the developing unit
30
at a slightly downstream position from an uppermost part of the developing sleeve
148
with respect to the rotating direction R
1
of the developing sleeve
148
.
The edge portion of the blade
62
is set generally in the middle between a magnetic field of north pole and a magnetic field of south pole at an upper part of the magnetic member
150
(see FIG.
3
). Residue of the developing agent
100
which has deposited on the circumferential surface of the developing sleeve
148
is scraped off by the edge portion of the blade
62
, subjected to agitation/mixing by a second mixing unit
70
, and then reused for next image formation by magnetic attraction of the carriers of the developing agent
100
toward the surface of the developing sleeve
148
again.
Next, an operation of a developing agent mixing device of the developing unit
30
is described in detail with reference to FIG.
5
.
FIG. 5
is an expansion view showing a view of the developing unit
30
taken along a line extending through a center of the developing agent supply unit
146
, a center of the second mixing unit
70
, a center of the first mixing unit
68
, and a center of a scoop-up unit. The first and second mixing units
68
,
70
constitute the developing agent mixing device.
The first mixing unit
68
is constructed in such a manner that a rotary shaft
72
is rotatably mounted between the front wall
138
and an inner wall
141
formed on the inner side (left side in
FIG. 5
) of the rear wall
140
. The rotary shaft
72
is formed with an impeller
74
generally over the axial length thereof except an area A
1
at a downstream end with respect to a first conveyance direction of the developing agent
100
shown by the arrow C
1
in FIG.
5
. The rotary shaft
72
extends outwardly from the front wall
138
by a certain length, and a gear
80
is attached to the distal end thereof. A gear
75
is fixed to the rotary shaft
72
between the rear wall
140
and the inner wall
141
.
The second mixing unit
70
is constructed in such a manner that a rotary shaft
76
is rotatably mounted between the front wall
138
and the rear wall
140
. Similar to the rotary shaft
72
, the rotary shaft
76
is formed with an impeller
78
generally over the axial length thereof except an area A
2
at a downstream end with respect to a second conveyance direction of the developing agent
100
shown by the arrow C
2
in FIG.
5
. The output gear
154
is fixed to a right end of the rotary shaft
76
, and a gear
81
is mounted to the rotary shaft
76
between the inner wall
141
and the rear wall
140
. The gear
81
is interlocked with the gear
75
.
Next, the developing agent scoop-up unit
82
is described in detail. As shown in
FIG. 4
, the developing agent scoop-up unit
82
is provided at a substantially middle position vertically between the first mixing unit
68
and the second mixing unit
70
on the right side of the first and second mixing units
68
,
70
.
Referring back to
FIG. 5
, the developing agent scoop-up unit
82
is provided on the front side (left side in
FIG. 5
) of the housing
144
, namely, beyond the developing area of the developing sleeve
148
in the axial direction of the developing unit
30
. The developing agent scoop-up unit
82
is constructed in such a manner that a rotary shaft
84
is rotatably mounted between the front wall
138
and a second rear wall
83
. The rotary shaft
84
is fixedly mounted with a scoop-up roller
86
composed of a magnetic material generally over the axial length thereof. The rotary shaft
84
protrudes forward (leftward in
FIG. 5
) from the front wall
138
, and a gear
88
is fixed at the protruding end. The gear
88
is interlocked with the gear
80
. The scoop-up roller
86
is in the shape of a cylinder with a continued surface and made of a ferrite material. The scoop-up roller
86
is magnetized in such a manner that a magnetic field generates in eight equi-sectioned areas circumferentially with each field having a magnetic force of about 800 gauss and that north pole and south pole appear alternately in the eight fields.
As shown in
FIGS. 2A
,
5
and
8
, a toner supply unit TS having a toner supply opening TSO is provided in an area vertically above the merging area between the first mixing unit
68
and the scoop-up roller
86
so that the toner can be directly supplied onto the merging area. More specifically, the toner supply opening TSO is preferably provided on a downstream side in the merging area along the developing agent delivering direction by the first mixing unit
68
. By positioning the toner supply opening TSO as described in the above, the supplied toner from the toner supply opening TSO is subject to both a scoop-up force derived by the scoop-up roller
86
and a delivering (propelling) force derived by the first mixing unit
68
so that the supplied toner is well blended with the existing developing agent. Furthermore, there is a slight clearance between a lead end
112
e of a separation wall
112
and an external surface of the scoop-up roller
87
, thus the supplied toner from the toner supply opening TSO may not easily fall through the clearance. Note that the lead end
112
e
of the separation wall is also referred to as a scraping portion that scrapes off the excessive amount of the developing agent attracted to around the scoop-up roller
86
.
FIG. 6
is a diagram showing an interlocked state of the gears viewed from the rear side of the developing unit
30
, and
FIG. 7
is a diagram showing an interlocked state of the gears viewed from the front side of the developing unit
30
. The developing unit
30
is described further with reference to
FIGS. 6 and 7
.
When a driving force of the drive source (not shown) is transmitted to the output gear
154
, the driving force is transmitted to the gears
81
,
75
via the rotary shaft
72
. The driving force which has been transmitted to the gear
75
is then transmitted to the gears
80
,
88
via the rotary shaft
72
.
On the other hand, when the driving force of the drive source is transmitted to the output shaft
154
, the driving force is also transmitted to the idle gear
156
and the input gear
152
. Thus, as the driving force is transmitted to the gears, the first mixing unit
68
rotates in the direction shown by the arrow R
2
in
FIGS. 3 and 4
, and the second mixing unit
70
rotates in the direction shown by the arrow R
3
in
FIGS. 3 and 4
. The developing agent scoop-up unit
82
rotates in the direction shown by the arrow R
4
in FIG.
4
.
Referring back to
FIG. 3
, the developing agent
100
is stored in the developing housing
144
. More specifically, the developing agent
100
is distributed in a first mixing section
102
, a second mixing section
104
, and a third mixing section
106
of the developing unit
30
. The first mixing section
102
is defined by the partition wall
66
and the top wall
142
in which part of the first mixing unit
68
is accommodated. The second mixing section
104
is defined by a lower surface of the partition wall
66
, the first side wall
134
, and the bottom wall
132
in which the developing agent supply unit
146
and part of the second mixing unit
70
are accommodated. The third mixing section
106
is defined by the second side wall
136
(see FIG.
4
), the bottom wall
132
, and the top wall
142
in which part of the first mixing unit
68
, part of the second mixing unit
70
and the scoop-up unit
82
are accommodated.
In the above construction where the developing agent
100
is distributed in each section, as the rotary shaft
72
of the first mixing unit
68
rotates in the direction of arrow R
2
, the developing agent
100
in the first mixing section
102
is conveyed along the axial direction of the rotary shaft
72
, namely, in the first conveyance direction C
1
shown in
FIG. 5
while being mixed well homogeneously during its conveyance.
The developing agent
100
in the second mixing section
104
is conveyed in the second conveyance direction C
2
as the rotary shaft
76
of the second mixing unit
70
rotates in the direction of arrow R
3
. The developing agent
100
is mixed well homogeneously during its conveyance. At this time, part of the developing agent
100
is supplied from the second mixing unit
70
to the developing agent supply unit
146
, and then supplied to the developing area of the surface of the photosensitive drum
28
to develop a latent image into a toner image. The photosensitive drum
28
rotates in the direction of arrow R
5
in
FIGS. 3 and 4
.
Next, with reference to
FIGS. 5 and 8
, how the developing agent
100
circulates while mixed and conveyed along the predetermined directions is described. First, the developing agent
100
in the first mixing section
102
is conveyed in the first conveyance direction C
1
, namely, from front to rear of the apparatus main body
36
by the operation of the first mixing unit
68
. At this time, since the first mixing section
102
is not formed with the partition wall
66
at the area A
1
and the impeller
74
is not formed on the first mixing unit
68
at the area A
1
, the developing agent
100
that has reached the area A
1
is restrained from being conveyed further rearward in the first conveyance direction C
1
and falls down from the first mixing section
102
into the second mixing section
104
by its weight at the area A
1
(see an arrow D in FIG.
8
).
Then, the developing agent
100
that has fallen off from the first mixing section
102
into the second mixing section
104
is conveyed in the second conveyance direction C
2
in FIG.
5
and
FIG. 8
by the operation of the second mixing unit
70
toward the area A
2
at the left end in FIG.
5
. Since the impeller
78
is not formed on the second mixing unit
70
at the area A
2
, there is no possibility that the developing agent
100
is conveyed further forward in the second conveyance direction C
2
. In addition, there is no possibility that the developing agent
100
stagnates on the area A
2
and agglomerates thereat for the following reason.
When the developing agent
100
reaches the area A
2
, the scoop-up roller
86
of the developing agent scoop-up unit
82
magnetically attracts the developing agent
100
(carriers along with the toner particles) toward the circumferential surface thereof by its magnetic force and guides the developing agent
100
into the third mixing section (scoop-up section)
106
(see an arrow U in FIG.
8
).
In the scoop-up section
106
, the partition wall
112
(see
FIG. 4
) extends transversely from a side wall of the housing
144
in
FIG. 4
at a vertically middle position between the first mixing unit
68
and the second mixing unit
70
. The lead end
112
e
(or scraping portion) of the partition wall
112
is formed into an acute angular shape with a clearance of e.g., about 1.0 mm from the outer surface of the scoop-up roller
86
.
The developing agent
100
magnetically attracted to the surface of the scoop-up roller
86
constitutes a magnetic heap as shown in FIG.
4
. More specifically, the magnetic heap of the developing agent
100
deposits on the surface of the scoop-up roller
86
in such a manner that the deposited developing agent
100
forms a sharp peak corresponding to a high-magnetized region of the magnetic field of N- or S- pole and forms a moderate recess corresponding to a low-magnetized region defined circumferentially in the middle between the magnetic fields of N- and S- poles.
More specifically, the scoop-up roller
86
has the following specifications.
The length of the scoop-up roller
86
can be set in a range of 15 mm to 50 mm and is preferably set in a range of 20 mm to 35 mm, which is more than a pitch of a blade of an impeller
78
for the second mixing unit
70
. Setting the length longer than the upper limit of the specified range will cause an unnecessary enlargement of the apparatus as a whole whereas lowering the length beyond the lower limit of the specified range will result in an insufficient scoop-up force derived by the scoop-up roller
86
. The peripheral speed of the scoop-up roller
86
can be set in a range of 100 to 250 mm/min and is preferably set in a range of 150 to 200 mm/min. Raising the peripheral speed beyond the upper limit of the specified range will rapidly scrape off the developing agent around the scoop-up roller
86
by the lead end
112
e
of the partition wall, causing the developing agent to deteriorate more easily. On the other hand, lowering the peripheral speed beyond the lower limit of the specified range will result in an insufficient scoop-up capability derived by the scoop-up roller
86
. Furthermore, the magnetic force for the scoop-up roller
86
is set in a range of 500 to 1200 Gauss. Exceeding the upper limit of the specified range may increase the possibility to deteriorate the developing agent whereas lowering beyond the lower limit of the specified range will result in an insufficient scoop-up capability of the scoop-up roller
86
. The clearance between the circumference of the scoop-up roller
86
and the lead end (scraping portion)
112
e
of the separation wall
112
is set to be in a range of 0.3 mm-3 mm, and preferably in a range of 0.5 mm to 2 mm. Having the clearance larger than the upper limit of the specified range will cause an insufficient supply of the developing agent to the first mixing unit
68
. On the other hand, the clearance smaller than the lower limit of the specified range will increase the chance of deteriorating the developing agent.
In this embodiment, since the magnetic field generates in such a state that the field of N-pole and the field of S-pole generate alternately in the circumferential direction of the scoop-up roller
86
, a field having a magnetic force of 0 gauss does not exist in the scoop-up roller
86
. Therefore, the scoop-up force (conveyance force) of the developing agent
100
by the scoop-up unit
82
can be varied according to needs.
As the scoop-up roller
86
rotates in the direction of arrow R
4
, the magnetic heap of the developing agent
100
deposited in the aforementioned manner on the surface of the scoop-up roller
86
is scraped off therefrom by the lead end
112
e
of the separation wall
112
. The thus collected developing agent
100
is conveyed to the first mixing section
102
while carried over the transversely extending upper surface of the separation wall
112
. When the developing agent
100
reaches the first mixing section
102
, the developing agent
100
is conveyed in the first conveyance direction C
1
by the rotation of the rotary shaft
72
of the first mixing unit
68
while mixed well. In this way, the developing agent
100
circulates while conveyed back and forth in the axial direction of the developing unit
30
in such a manner that the developing agent
100
is homogeneously mixed during the back and forth conveyance.
The developing agent mixing device is described in detail. The developing agent conveyance forces of the impeller
74
of the first mixing unit
68
and that of the impeller
78
of the second mixing unit
70
are set generally at the same level. Parameters to adjust the conveyance force include sizes of the impellers
74
,
78
, and shape thereof (twisting direction), spiral pitch thereof, and rotational speed, which enables to set the conveyance forces of the first and second mixing units
68
,
70
in a desired relation. As one example for the present invention, an external diameter of the impeller of the second mixing unit
70
is set smaller than that of the first mixing unit
68
. On the other hand, the rotational speed of the second mixing unit
70
is set greater than that of the first mixing unit
68
. As a result, the conveyance capability (amount of developing agent per a given time) of the developing agent by the second mixing unit
68
is set substantially equal to that by the first mixing unit
68
. Note that in this embodiment, a diameter of a shaft on which impeller wings are mounted for the first mixing unit
68
and that for the second mixing unit
70
are substantially the same so that when the external diameter of the impeller is greater than the other, the radial length of the impeller is longer than that of the other. With this feature, the developing agent supply unit
146
can be positioned further rightward direction (in FIG.
3
). As a result, the width (a left to right dimension in
FIG. 3
) of the developing device as a whole can be made smaller, thereby enabling to make a space between the imaging sections
24
,
25
,
26
,
27
small as well, which eventually contributes downsizing the printer
2
as a whole.
Furthermore, as shown in
FIGS. 2A
,
2
B, and
5
, a separation plate
190
having a U-shape cross section is provided in the downstream portion of the first mixing unit
68
. More specifically, the separation plate
190
is provided on the downstream side of the impeller
74
at the most downstream side along the first mixing unit
68
so that the developing agent accumulates in an area immediately upstream side of the separation plate
190
. With this construction, the developing agent accumulates beyond the amount held by the separation plate
190
overflows from the separation plate
190
. Accordingly, the overflowed developing agent from the separation plate
190
is supplied to the second mixing unit
70
.
The upper edge of the separation plate
190
is so set as to come to a position as high as approximately eighty percent (0.8φ) of the diameter (φ) of the impeller
74
as shown in FIG.
2
B.
In addition, the conveyance capability (amount of developing agent per a given time) derived by the scoop-up roller
86
is set larger than that by the impeller
74
of the first mixing unit
68
and that by the impeller
78
of the second mixing unit
70
. Specifically, the conveyance capability of the developing agent by the scoop-up roller
86
is set in a range of 1.0 to 1.5 times of the conveyance capability by the second mixing unit
70
.
More specifically, the conveyance force of the first and second mixing units
68
,
70
is set at 1,120 g/min, and that of the developing agent scoop-up unit
82
is set at 1,350 g/min. Note that the present invention is not necessarily limited to the specified numerals.
When the image forming apparatus stops its operation, the developing agent tends to accumulate in downstream portion of the second mixing unit
70
and if the usual amount of the developing agent is delivered upon resuming the operation when the accumulated agent was not yet removed, it may adversely affect the conveyance performance of the developing agent. However, since the conveyance capability by the scoop-up roller
86
in the present invention is set greater than that by the second mixing unit
70
, the agent accumulation in the downstream area of the second mixing unit
70
is scooped up to the first mixing unit
68
faster than the developing agent being transferred from the upstream side of second mixing unit
70
. As a result, with the above described arrangement, the likely occurring problem, i.e., excessive accumulation of the agent in the downstream side of the second mixing unit
70
, will be prevented. Furthermore, the amount of the developing agent delivered from the downstream side of the first mixing unit
68
to the upstream side of the second mixing unit
70
may fluctuate because of the presence of the separation plate
190
. However, even if it fluctuates, conveyance of the developing agent throughout the entire passage will be well balanced because of the greater conveyance ability given to the scoop-up roller
86
than the second mixing unit
70
. Moreover, the greater conveyance ability of the scoop-up roller
86
functions as a buffer to cope with the changes in conveyance capability of the each component of the developing agent due to the variation of the toner density or other environmental factors such as temperature and humidity. With this arrangement, when the developing agent
100
reaches the downstream end with respect to the second conveyance direction C
2
, namely, the area A
2
in
FIG. 5
after conveyed in the second conveyance direction C
2
by the second mixing unit
70
while being homogeneously mixed in the second mixing section
104
, the scoop-up roller
86
magnetically draws up the developing agent
100
that has reached the area A
2
of the second mixing unit
70
into the third mixing section
106
by the operation of the scoop-up unit
82
. Then, the developing agent
100
is securely and speedily supplied to the leftmost end of the first mixing unit
68
(see
FIG. 5
) located above the area A
2
of the second mixing unit
70
after carried over the upper surface of the separation wall
112
. With this arrangement, there can be prevented stagnation and agglomeration of the developing agent
100
in the developing unit
30
because the developing agent
100
is conveyed in a well-mixed manner in the predetermined directions back and forth, and a desirable image formation is carried out.
Referring back to the arrangement of the housing
144
, a toner density detector (not shown) is provided at an appropriate position inside the housing
144
to detect the toner density of the developing agent
100
. The toner density detector detects the toner density by sensing permeability of the developing agent
100
.
Further, the toner supply unit TS is provided in the housing
144
which is operable in response to a detection output from the toner density detector
180
. The toner supply unit TS automatically replenishes toner particles when the output of the toner density detector
180
falls below a predetermined level and suspends the replenishment when the output reaches the predetermined level. With this arrangement, the toner density in the housing
144
can be maintained in a certain range to develop a latent image into a toner image at a desirable toner density.
As an embodiment of this invention, but not limited thereto, the toner density detector
180
is provided near the separation plate
190
on its upstream side as shown in FIG.
2
A. More specifically speaking, the toner density detector
180
has a sensing portion
181
, generally a cylindrical form, which is provided at substantially the same level as the center axis of the first rotary shaft
72
and immediately upstream of the separation plate
190
such that the sensing portion can be maintained in contact with the accumulated developing agent in the downstream area of the first mixing unit
68
. Furthermore, the sensing portion
181
has a sensing surface
181
s
which is cleaned up by a horizontally extended edge
74
s
of the impeller
74
as it rotates over the sensing surface
181
s
. As a result, the sensor
181
does not usually surface over the accumulated developing agent so that the sensor
181
does not likely sense the density of something other than the developing agent, thereby improving an accuracy in measurement. Furthermore, the place immediately upstream side of the separation plate
190
is where the developing agent has been well-mixed. Thus the sensor
181
can detect the toner density accurately.
As mentioned above, in one aspect of this invention, the developing device is constructed in such a manner that the developing agent is conveyed from upstream to downstream with respect to the first conveyance direction while being agitated by the first mixing unit and reaches the downstream end. Then, the developing agent is conveyed from upstream to downstream with respect to the second conveyance direction while being agitated by the second mixing unit. When the developing agent reaches the downstream end with respect to the second conveyance direction, the developing agent scoop-up unit magnetically draws up the developing agent to carry the developing agent up to the first mixing unit. In this way, the developing agent can be sufficiently mixed/agitated by the first and second mixing units aided by a speedy draw-up operation of the scoop-up unit.
This invention is advantageous in preventing stagnation of the developing agent in the downstream end with respect to the first and second conveyance directions. Therefore, an agglomeration-free developing device is provided to ensure a clear image formation supplied with well-mixed and sufficiently-charged toner particles.
Further, in another aspect of this invention, the developing device is constructed in such a manner that the first and second mixing units are vertically stacked one over the other with the second mixing unit located below the first mixing unit, and the developing agent scoop-up unit is provided with its axial direction aligned with the axial direction of the first and second mixing units at a substantially middle position vertically between the first and second mixing units. Furthermore, the rotary member (scoop-up roller) of the developing agent scoop-up unit is magnetized to magnetically draw up the developing agent. With this arrangement, scoop-up unit can be made smaller and the axial length of the developing device itself can be shortened, thereby enabling to provide a developing device and image forming apparatus of a compact size.
An embodiment of the developing device for use in an image forming apparatus according to this invention has been described in the above section. The developing device is not limited to the above embodiment, and the following modifications and alterations are applicable.
(1) In the embodiment, the developing agent scoop-up unit
82
is provided on right side of the first and second mixing units
68
,
70
on the plane of FIG.
4
. Alternatively, the scoop-up unit
82
may be provided on left side of the first and second mixing units
68
,
70
. In the altered arrangement, the scoop-up unit
82
can be installed in a space axially extending from the developing sleeve
148
where the developing sleeve
148
is not provided. Thereby, the transverse length (left and right directions in
FIG. 4
) of the developing unit
30
can be reduced. This altered arrangement makes it possible to shorten the overall width of the apparatus main body
36
even if the developing device is utilized in an image forming apparatus provided with a four-membered tandem type developing device as a color printer.
(2) In the embodiment, a sleeve is not provided on the scoop-up roller
84
of the developing agent scoop-up unit
82
, which reduces the transverse size of the developing unit
30
(namely, the width of the apparatus main body
36
). A sleeve may be mounted on the scoop-up roller
84
since mounting of the sleeve does not substantially influence the overall width of the apparatus main body
36
.
(3) In the embodiment, the photosensitive drum
28
is used as a photoreceptor. A photosensitive belt may be used as a photoreceptor.
This application is based on patent application No. 11-216466 filed in Japan, the contents of which are hereby incorporated by references.
As this invention may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiment is therefore illustrative an not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds are therefore intended to embraced by the claims.
Claims
- 1. A developing device for applying a developing agent to a photoreceptor in an image forming apparatus comprising:a developing agent supply unit which supplies the developing agent to the photoreceptor; a first mixing unit to convey the developing agent in a first conveyance direction along a first axis of the first mixing unit to a downstream end thereof while mixing the developing agent; a second mixing unit provided underneath the first mixing unit to receive the developing agent from the first downstream end of the first mixing unit and to convey the developing agent in a second conveyance direction, opposite to said first conveyance direction, along a second axis of the second mixing unit to a downstream end thereof while mixing the developing agent and delivering the developing agent to the photoreceptor; a developing agent scoop-up unit provided substantially in the middle in a height direction between the first mixing unit and the second mixing unit and at said downstream end of the second mixing unit to receive the developing agent from the second mixing unit and draw up the received developing agent to the first mixing unit; and said developing agent scoop-up unit including a rotary member, and an even number of magnetic fields having a certain magnetic pole and formed in a circumferential direction of the rotary member.
- 2. The developing device according to claim 1, wherein said rotary member is formed with the magnetic fields generated by alternating north poles and south poles so as to have alternating directions.
- 3. The developing device according to claim 2, wherein the number of magnetic fields is any one of the numbers 4, 6, 8, 10, and 12.
- 4. The developing device according to claim 3, wherein said magnetic fields have substantially the same magnetic force.
- 5. The developing device according to claim 1, wherein a developing agent conveyance force of said developing agent scoop-up unit is set equal to or greater than the developing agent conveyance force of said first mixing unit and said second mixing unit.
- 6. The developing device according to claim 5, wherein a conveyance capability of the developing agent per a given time by the developing agent scoop-up unit is in a range of 1.0 to 1.5 times of that by the second mixing unit.
- 7. The developing device according to claim 1, wherein a conveyance capability of the developing agent per a given time by the developing agent scoop-up unit is in a range of 1.0 to 1.5 times of that by the second mixing unit.
- 8. The developing device according to claim 1, further comprising a toner supply unit having a toner supply opening which is positioned in a merging area between the first mixing unit and the developing agent scoop-up unit in a top view.
- 9. The developing device according to claim 8, wherein the toner supply opening is on the downstream side in the merging area along the first conveyance direction of the first mixing unit.
- 10. A developing device for applying a developing agent to a photoreceptor in an image forming apparatus comprising:a developing agent supply unit which supplies the developing agent to the photoreceptor; a first mixing unit to convey the developing agent in a first conveyance direction along a first axis of the first mixing unit to a downstream end thereof while mixing the developing agent; a second mixing unit provided underneath the first mixing unit to receive the developing agent from the first downstream end of the first mixing unit and to convey the developing agent in a second conveyance direction, opposite to said first conveyance direction, along a second axis of the second mixing unit to a downstream end thereof while mixing the developing agent and delivering the developing agent to the photoreceptor; and a developing agent scoop-up unit provided substantially in the middle in a height direction between the first mixing unit and the second mixing unit and at said downstream end of the second mixing unit to receive the developing agent from the second mixing unit and draw up the received developing agent to the first mixing unit.
- 11. A developing device for applying a developing agent to a photoreceptor in an image forming apparatus, the developing device comprising:a developing agent supply unit which supplies the developing agent to the photoreceptor; a first mixing unit for conveying the developing agent in a first conveyance direction along a first axis of the first mixing unit to a downstream end thereof while mixing the developing agent; a second mixing unit receiving the developing agent from the first downstream end of the first mixing unit and conveying the developing agent in a second conveyance direction, opposite to said first conveyance direction, along a second axis of the second mixing unit to a downstream end thereof while mixing the developing agent and delivering the developing agent to the photoreceptor; and a developing agent transfer device disposed adjacent the first mixing unit and the second mixing unit and at said downstream end of the second mixing unit to receive the developing agent from the second mixing unit and transfer the received developing agent to the first mixing unit.
- 12. The developing device of claim 11 wherein said first mixing unit includes a trough containing the developing agent and an agitator for effecting conveyance of the developing agent in the first conveyance direction along said trough.
- 13. The developing device of claim 12 wherein said agitator is helical.
- 14. The developing device of claim 11 wherein said developing agent transfer device is localized at said downstream end of the second mixing unit and transfers the received developing agent to said upstream end of the first mixing unit.
- 15. The developing device of claim 11 wherein said second mixing unit includes a trough containing the developing agent and an agitator for effecting conveyance of the developing agent in the second conveyance direction along said trough and said agitator extends adjacent to and along a length of said developing agent supply unit for delivering the developing agent to the developing agent supply unit.
- 16. The developing device of claim 15 wherein said agitator is helical.
- 17. The developing device of claim 11 wherein:said first mixing unit includes a first trough containing the developing agent and a first agitator for effecting conveyance of the developing agent in the first conveyance direction along said first trough; and said second mixing unit includes a second trough containing the developing agent and a second agitator for effecting conveyance of the developing agent in the second conveyance direction along said second trough and said second agitator extends adjacent to and along a length of said developing agent supply unit for delivering the developing agent to the developing agent supply unit.
- 18. The developing device of claim 17 wherein said first and second agitators are helical.
Priority Claims (1)
Number |
Date |
Country |
Kind |
11-216466 |
Jul 1999 |
JP |
|
US Referenced Citations (3)
Number |
Name |
Date |
Kind |
4914481 |
Yoshikai et al. |
Apr 1990 |
A |
5020471 |
Yoshikai |
Jun 1991 |
A |
5355199 |
Bray |
Oct 1994 |
A |