Title: Developing apparatus configured to prevent splashing of toner and carrier
Abstract: A developing apparatus prevents or reduces splashing of toner and carrier caused by abnormal outward airflows generated at downstream positions of a developing unit casing thereof through interactions between behaviors of magnetic brushes and local portions of the developing unit casing. The developing apparatus includes a developer carrying member, a first permanent magnet, a developing unit casing, a second permanent magnet, which is built in the developer carrying member at a fixed position at the downstream side from the first permanent magnet with respect to the rotational direction of the developer carrying member. The developing unit casing has a concave structure to form a low pressure area at a position facing the second permanent magnet. The low pressure area suppresses an increase in the speed of the airflow therein that causes the abnormal outward airflows.
Patent Number: 6,941,090 Issued on 09/06/2005 to Uchida, et al.
| Inventors:
|
Uchida; Keisuke (Tokyo, JP);
Hatori; Satoshi (Kanagawa, JP)
|
| Assignee:
|
Ricoh Company, Ltd. (Tokyo, JP)
|
| Appl. No.:
|
460409 |
| Filed:
|
June 13, 2003 |
Foreign Application Priority Data
| Jun 14, 2002[JP] | 2002-173876 |
| Current U.S. Class: |
399/98; 399/99; 399/103; 399/267 |
| Intern'l Class: |
G03G 015/09 |
| Field of Search: |
399/92,93,98,102,103,267,273,275-277
|
References Cited [Referenced By]
U.S. Patent Documents
| 5070812 | Dec., 1991 | Yamaji.
| |
| 5103765 | Apr., 1992 | Owada et al.
| |
| 5129357 | Jul., 1992 | Yamaji.
| |
| 5784669 | Jul., 1998 | Miura et al.
| |
| 5881338 | Mar., 1999 | Armstrong et al.
| |
| 5913092 | Jun., 1999 | Bisaiji et al.
| |
| 5915155 | Jun., 1999 | Shoji et al.
| |
| 6122469 | Sep., 2000 | Miura et al.
| |
| 6125243 | Sep., 2000 | Shoji et al.
| |
| 6597881 | Jul., 2003 | Hatori et al.
| |
| Foreign Patent Documents |
| 5-119626 | May., 1993 | JP.
| |
| 10-26861 | Jan., 1998 | JP.
| |
| 10-247042 | Sep., 1998 | JP.
| |
Primary Examiner: Royer; William J.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier & Neustadt, P.C.
Claims
1. A developing apparatus for developing a latent image on a latent image carrying
member with a magnetic brush made of developer comprising toner and magnetic carrier, comprising:
a developer carrying member being rotated in a state where said magnetic brush
is being formed thereon so as to develop said latent image;
a first permanent magnet being built in said developer carrying member at a fixed
position facing said latent image carrying member, said first permanent magnet
serving as a main pole and generating a magnetic field of said main pole so as
to form a first magnetic brush of the developer on said developer carrying member;
a developing unit casing covering said developer carrying member, said developing
unit casing having an aperture to expose said developer carrying member at the
position facing said latent image carrying member; and
a second permanent magnet being built in said developer carrying member at a
fixed position near said aperture at a downstream side from said first permanent
magnet with respect to a rotational direction of said developer carrying member,
said second permanent magnet serving as an auxiliary pole and generating a magnetic
field of said auxiliary pole so as to form a second magnetic brush of the developer
on said developer carrying member,
wherein said developing unit casing has a concave structure to form a low pressure
area at a position facing said second permanent magnet, and said concave structure
is concave toward an extension of said second magnetic brush so as to have a larger
gap there between said developer carrying member and said developing unit casing
than a gap at a tip part of said aperture between said developer carrying member
and said latent image carrying member.
2. The developing apparatus as claimed in claim 1, wherein said concave structure
comprises a concave part formed on an inner surface of said developing unit casing
at a position facing said second permanent magnet.
3. The developing apparatus as claimed in claim 1, wherein said concave structure
comprises a curvature of said developing unit casing.
4. The developing apparatus as claimed in claim 1, wherein at said position facing
the second permanent magnet, a distance between a surface of said developer carrying
member and a bottom of said concave structure is greater than or equal to a height
of said second magnetic brush.
5. The developing apparatus as claimed in claim 1, wherein said developing unit
casing has a passage to communicate between said low pressure area and an exterior
of said developing unit casing through a porous breathable sheet.
6. The developing apparatus as claimed in claim 5, wherein said porous breathable
sheet comprises a high-density polyethylene nonwoven fabric sheet.
7. The developing apparatus as claimed in claim 5, wherein said porous breathable
sheet is disposed such that a surface thereof is not orthogonal to a gravitational direction.
8. The developing apparatus as claimed in claim 5, further comprising a splashing
toner inhaling cover being disposed close to said developer carrying member at
a downstream side from said first permanent magnet with respect to a rotational
direction of said developer carrying member, adjacent to said aperture of the developing
unit casing, a splashing toner inhaling duct being disposed at a downstream position
from said splashing toner inhaling cover along an axial direction of said developer
carrying member and being connected to a ventilator so that air flows in a predetermined
direction through said splashing toner inhaling duct, said splashing toner inhaling
duct including a narrow part having a smaller diameter, and a plurality of pressure
inlet pipes communicating between said splashing toner inhaling duct and said splashing
toner inhaling cover at a plurality of positions including a position of said narrow part.
9. The developing apparatus as claimed in claim 8, further comprising a second
pressure inlet pipe communicating between said narrow part of the splashing toner
inhaling duct and said passage, and an interrupting part interrupting communication
between said splashing toner inhaling duct and said passage.
10. The developing apparatus as claimed in claim 1, further comprising a splashing
toner inhaling cover being disposed close to said developer carrying member at
a downstream side from said first permanent magnet with respect to a rotational
direction of said developer carrying member, adjacent to said aperture of the developing
unit casing, a splashing toner inhaling duct being disposed at a downstream position
from said splashing toner inhaling cover along an axial direction of said developer
carrying member and being connected to a ventilator so that air flows in a predetermined
direction through said splashing toner inhaling duct, said splashing toner inhaling
duct including a narrow part having a smaller diameter, and a plurality of pressure
inlet pipes communicating between said splashing toner inhaling duct and said splashing
toner inhaling cover at a plurality of positions including a position of said narrow part.
11. A developing apparatus for developing a latent image on a latent image carrying
member with a magnetic brush made of developer comprising toner and magnetic carrier, comprising:
a developer carrying member being rotated in a state where said magnetic brush
is being formed thereon so as to develop said latent image;
a first permanent magnet being built in said developer carrying member at a fixed
position facing said latent image carrying member, said first permanent magnet
serving as a main pole and generating a magnetic field of said main pole so as
to form a first magnetic brush of the developer on said developer carrying member;
a developing unit casing covering said developer carrying member, said developing
unit casing having an aperture to expose said developer carrying member at the
position facing said latent image carrying member;
a second permanent magnet being built in said developer carrying member at a
fixed position at a downstream side from said first permanent magnet with respect
to a rotational direction of said developer carrying member, said second permanent
magnet serving as an auxiliary pole and generating a magnetic field of said auxiliary
pole so as to form a second magnetic brush of the developer on said developer carrying
member;
a splashing toner inhaling cover being disposed close to said developer carrying
member at a downstream side from said first permanent magnet with respect to a
rotational direction of said developer carrying member, adjacent to said aperture
of the developing unit casing;
a splashing toner inhaling duct being disposed below said splashing toner inhaling
cover along an axial direction of said developer carrying member and being connected
to a ventilator so that air flows in a predetermined direction through said splashing
toner inhaling duct, said splashing toner inhaling duct including a narrow part
having a smaller diameter; and
a plurality of pressure inlet pipes communicating between said splashing toner
inhaling duct and said splashing toner inhaling cover at a plurality of positions
including a position of said narrow part.
12. The developing apparatus as claimed in claim 11, wherein at least one of
said pressure inlet pipes communicates between a position of said splashing toner
inhaling cover to which one of the toner and the magnetic carrier on said developer
carrying member is likely to splash and said narrow part of the splashing toner
inhaling duct.
13. The developing apparatus as claimed in claim 11, wherein at least one of
said pressure inlet pipes communicates between a middle position of said splashing
toner inhaling cover with respect to the axial direction of said developer carrying
member and said narrow part of the splashing toner inhaling duct and at least one
of said pressure inlet pipes communicates between an end position of said splashing
toner inhaling cover with respect to the axial direction of said developer carrying
member and a thick part of said splashing toner inhaling duct whose diameter is greater.
14. The developing apparatus as claimed in claim 11, wherein each of said pressure
inlet pipes includes a first interrupting part separately interrupting communication
between said splashing toner inhaling cover and said splashing toner inhaling duct.
15. An image forming unit, comprising:
a latent image carrying member on which a latent image is formed; and
a developing apparatus developing said latent image on said latent image carrying
member with a magnetic brush made of developer comprising toner and magnetic carrier,
comprising: a developer carrying member being rotated in a state where said magnetic
brush is being formed thereon so as to develop said latent image; a first permanent
magnet being built in said developer carrying member at a fixed position facing
said latent image carrying member, said first permanent magnet serving as a main
pole and generating a magnetic field of said main pole so as to form a first magnetic
brush of the developer on said developer carrying member; a developing unit casing
covering said developer carrying member, said developing unit casing having an
aperture to expose said developer carrying member at the position facing said latent
image carrying member; and a second permanent magnet being built in said developer
carrying member at a fixed position near said aperture at a downstream side from
said first permanent magnet with respect to a rotational direction of said developer
carrying member, said second permanent magnet serving as an auxiliary pole and
generating a magnetic field of said auxiliary pole so as to form a second magnetic
brush of the developer on said developer carrying member,
wherein said developing unit casing has a concave structure to form a low pressure
area at a position facing said second permanent magnet, and said concave structure
is concave toward an extension of said second magnetic brush so as to have a larger
gap there between said developer carrying member and said developing unit casing
than a gap at a tip part of said aperture between said developer carrying member
and said latent image carrying member.
16. An image forming unit, comprising:
a latent image carrying member on which a latent image is formed; and
a developing apparatus developing said latent image on said latent image carrying
member with a magnetic brush made of developer comprising toner and magnetic carrier,
comprising: a developer carrying member being rotated in a state where said magnetic
brush is being formed thereon so as to develop said latent image; a first permanent
magnet being built in said developer carrying member at a fixed position facing
said latent image carrying member, said first permanent magnet serving as a main
pole and generating a magnetic field of said main pole so as to form a first magnetic
brush of the developer on said developer carrying member; a developing unit casing
covering said developer carrying member, said developing unit casing having an
aperture to expose said developer carrying member at the position facing said latent
image carrying member; a second permanent magnet being built in said developer
carrying member at a fixed position at a downstream side from said first permanent
magnet with respect to a rotational direction of said developer carrying member,
said second permanent magnet serving as an auxiliary pole and generating a magnetic
field of said auxiliary pole so as to form a second magnetic brush of the developer
on said developer carrying member, a splashing toner inhaling cover being disposed
close to said developer carrying member at a downstream side from said first permanent
magnet with respect to a rotational direction of said developer carrying member,
adjacent to said aperture of the developing unit casing; a splashing toner inhaling
duct being disposed below said splashing toner inhaling cover along an axial direction
of said developer carrying member and being connected to a ventilator so that air
flows in a predetermined direction through said splashing toner inhaling duct,
said splashing toner inhaling duct including a narrow part having a smaller diameter;
and a plurality of pressure inlet pipes communicating between said splashing toner
inhaling duct and said splashing toner inhaling cover at a plurality of positions
including a position of said narrow part.
17. An image forming apparatus, comprising:
a latent image carrying member being rotationally driven;
an optical writing part forming a latent image on said latent image carrying
member; and
a developing apparatus being disposed near said latent image carrying member,
said developing apparatus developing said latent image on said latent image carrying
member with a magnetic brush made of developer comprising toner and magnetic carrier,
comprising: a developer carrying member being rotated in a state where said magnetic
brush is being formed thereon so as to develop said latent image; a first permanent
magnet being built in said developer carrying member at a fixed position facing
said latent image carrying member, said first permanent magnet serving as a main
pole and generating a magnetic field of said main pole so as to form a first magnetic
brush of the developer on said developer carrying member; a developing unit casing
covering said developer carrying member, said developing unit casing having an
aperture to expose said developer carrying member at the position facing said latent
image carrying member; and a second permanent magnet being built in said developer
carrying member at a fixed position near said aperture at a downstream side from
said first permanent magnet with respect to a rotational direction of said developer
carrying member, said second permanent magnet serving as an auxiliary pole and
generating a magnetic field of said auxiliary pole so as to form a second magnetic
brush of the developer on said developer carrying member,
wherein said developing unit casing has a concave structure to form a low pressure
area at a position facing said second permanent magnet, and said concave structure
is concave toward an extension of said second magnetic brush so as to have a larger
gap there between said developer carrying member and said developing unit casing
than a gap at a tip part of said aperture between said developer carrying member
and said latent image carrying member.
18. The image forming apparatus as claimed in claim 17, further comprising a
plurality of said latent image carrying members, a plurality of said developing
apparatuses, and a tandem type image carrying member on which a plurality of developed
images on respective said latent image carrying members are sequentially transferred.
19. An image forming apparatus, comprising:
a latent image carrying member being rotationally driven;
an optical writing part forming a latent image on said latent image carrying
member; and
a developing apparatus being disposed near said latent image carrying member,
said developing apparatus for developing said latent image on said latent image
carrying member with a magnetic brush made of developer comprising toner and magnetic
carrier, comprising: a developer carrying member being rotated in a state where
said magnetic brush is being formed thereon so as to develop said latent image;
a first permanent magnet being built in said developer carrying member at a fixed
position facing said latent image carrying member, said first permanent magnet
serving as a main pole and generating a magnetic field of said main pole so as
to form a first magnetic brush of the developer on said developer carrying member;
a developing unit casing covering said developer carrying member, said developing
unit casing having an aperture to expose said developer carrying member at the
position facing said latent image carrying member; a second permanent magnet being
built in said developer carrying member at a fixed position at a downstream side
from said first permanent magnet with respect to a rotational direction of said
developer carrying member, said second permanent magnet serving as an auxiliary
pole and generating a magnetic field of said auxiliary pole so as to form a second
magnetic brush of the developer on said developer carrying member; a splashing
toner inhaling cover being disposed close to said developer carrying member at
a downstream side from said first permanent magnet with respect to a rotational
direction of said developer carrying member, adjacent to said aperture of the developing
unit casing; a splashing toner inhaling duct being disposed below said splashing
toner inhaling cover along an axial direction of said developer carrying member
and being connected to a ventilator so that air flows in a predetermined direction
through said splashing toner inhaling duct, said splashing toner inhaling duct
including a narrow part having a smaller diameter; and a plurality of pressure
inlet pipes communicating between said splashing toner inhaling duct and said splashing
toner inhaling cover at a plurality of positions including a position of said narrow
part.
20. The image forming apparatus as claimed in claim 19, further comprising a
plurality of said latent image carrying members, a plurality of said developing
apparatuses, and a tandem type image carrying member on which a plurality of developed
images on respective said latent image carrying members are sequentially transferred.
21. An image forming apparatus, comprising:
an image forming unit, comprising: a latent image carrying member on which a
latent image is formed; and a developing apparatus developing said latent image
on said latent image carrying member with a magnetic brush made of developer comprising
toner and magnetic carrier, comprising: a developer carrying member being rotated
in a state where said magnetic brush is being formed thereon so as to develop said
latent image; a first permanent magnet being built in said developer carrying member
at a fixed position facing said latent image carrying member, said first permanent
magnet serving as a main pole and generating a magnetic field of said main pole
so as to form a first magnetic brush of the developer on said developer carrying
member; a developing unit casing covering said developer carrying member, said
developing unit casing having an aperture to expose said developer carrying member
at the position facing said latent image carrying member; and a second permanent
magnet being built in said developer carrying member at a fixed position near said
aperture at a downstream side from said first permanent magnet with respect to
a rotational direction of said developer carrying member, said second permanent
magnet serving as an auxiliary pole and generating a magnetic field of said auxiliary
pole so as to form a second magnetic brush of the developer on said developer carrying
member; and
an optical writing part forming said latent image on said latent image carrying
member,
wherein said developing unit casing has a concave structure to form a low pressure
area at a position facing said second permanent magnet, and said concave structure
is concave toward an extension of said second magnetic brush so as to have a larger
gap there between said developer carrying member and said developing unit casing
than a gap at a tip part of said aperture between said developer carrying member
and said latent image carrying member.
22. The image forming apparatus as claimed in claim 21, further comprising a
plurality of said latent image carrying members, a plurality of said developing
apparatuses, and a tandem type image carrying member on which a plurality of developed
images on respective said latent image carrying members are sequentially transferred.
23. An image forming apparatus, comprising:
an image forming unit, comprising: a latent image carrying member on which a
latent image is formed; and a developing apparatus developing said latent image
on said latent image carrying member with a magnetic brush made of developer comprising
toner and magnetic carrier, comprising: a developer carrying member being rotated
in a state where said magnetic brush is being formed thereon so as to develop said
latent image; a first permanent magnet being built in said developer carrying member
at a fixed position facing said latent image carrying member, said first permanent
magnet serving as a main pole and generating a magnetic field of said main pole
so as to form a first magnetic brush of the developer on said developer carrying
member; a developing unit casing covering said developer carrying member, said
developing unit casing having an aperture to expose said developer carrying member
at the position facing said latent image carrying member; a second permanent magnet
being built in said developer carrying member at a fixed position at a downstream
side from said first permanent magnet with respect to a rotational direction of
said developer carrying member, said second permanent magnet serving as an auxiliary
pole and generating a magnetic field of said auxiliary pole so as to form a second
magnetic brush of the developer on said developer carrying member; a splashing
toner inhaling cover being disposed close to said developer carrying member at
a downstream side from said first permanent magnet with respect to a rotational
direction of said developer carrying member, adjacent to said aperture of the developing
unit casing; a splashing toner inhaling duct being disposed below said splashing
toner inhaling cover along an axial direction of said developer carrying member
and being connected to a ventilator so that air flows in a predetermined direction
through said splashing toner inhaling duct, said splashing toner inhaling duct
including a narrow part having a smaller diameter; and a plurality of pressure
inlet pipes communicating between said splashing toner inhaling duct and said splashing
toner inhaling cover at a plurality of positions including a position of said narrow
part; and
an optical writing part forming said latent image on said latent image carrying
member.
24. The image forming apparatus as claimed in claim 23, further comprising a
plurality of said latent image carrying members, a plurality of said developing
apparatuses, and a tandem type image carrying member on which a plurality of developed
images on respective said latent image carrying members are sequentially transferred.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a magnetic brush development type
developing apparatus, an image forming unit and an image forming apparatus.
2. Description of the Related Art
Conventionally, a magnetic brush development type developing apparatus
develops a latent image on a photoconductor in the following process. A developing
sleeve, which is disposed in an aperture of a developing unit casing, serves as
a developer carrying member to form a magnetic field with a permanent magnet thereof.
This magnetic field forms a magnetic brush of a two-component developer containing
a toner and a carrier. The latent image is developed by the magnetic brush between
the photoconductor, which serves as an image carrying member, and the developing sleeve.
FIG. 1 is a front view of a conventional magnetic brush development type developing
apparatus for performing the above process. Referring to FIG. 1, a developing sleeve
101 is disposed to closely face a drum-shaped photoconductor
102.
The developing sleeve
101 is rotated clockwise, and, in contrast, the photoconductor
102 is rotated counterclockwise. For example, six permanent magnets, three
of which are illustrated in FIG.
1 and designated as
103a,
103b, and
103c, respectively, are fixed in a radial
pattern in the interior of the developing sleeve
101. Here, the permanent
magnet
103a, which faces the photoconductor
102 as illustrated,
is called a main pole. When the permanent magnet
103a creates a magnetic
field, the magnetic field forms a magnetic brush of a two-component developer whose
components are a toner and a magnetic carrier. The magnetic brush develops a latent
image on the photoconductor
102. The permanent magnets other than the main
pole permanent magnet
103a are called auxiliary poles and are used
to form adequate magnetic brushes at the main pole. The developing sleeve
101
is accommodated in a developing unit casing
105. The developing unit casing
105 has an aperture
104 at a position opposite to the photoconductor
102 such that the circumferential surface of the developing sleeve
101
is partially exposed through the aperture
104. As shown in FIG. 1, developer
carrying screws
106 and
107 are disposed at the bottom of the developing
unit casing
105 such that the developer carrying screws
106 and
107
are located below the developing sleeve
101. The developer carrying screws
106 and
107 work to deliver toners supplied from a toner supplying
part, which is not illustrated, to the circumferential surface of the developing
sleeve
101 and mix collected toners and supplied developers. Additionally,
a doctor blade
108 is provided in the developing unit casing
105
as illustrated. The doctor blade
108 works to maintain the am t of the developer
provided to the photoconductor
102 by each magnetic brush at a constant amount.
According to such a conventional magnetic brush development type developing
apparatus, however, there is a risk that the toner and the carrier may easily splash
from the aperture
104 of the developing unit casing
105. In this
case, most of the toner and the carrier fall under the developing apparatus. If
the developing apparatus is accommodated in an image forming apparatus such as
a copier and a printer, the toner and the carrier are accumulated in the interior
of the image forming apparatus and make the interior unclean. In this condition,
there are some problems. For instance, if an operator tries to eliminate a paper
jam, the operator is likely to dirty his/her hands with the toner or the carrier
accumulated in the image forming apparatus. Also, if the toner and the carrier
are attached to inner electric parts of the image forming apparatus, there is a
risk of noise occurrence. Additionally, if the image forming apparatus is a tandem
type full-color image forming apparatus, which has an intermediate transfer belt
as a second image carrying member below the photoconductor
102 and the developing
apparatus, there is a risk that the splashing toner and carrier fall on the intermediate
transfer belt or a transfer paper carried by the intermediate transfer belt.
In order to eliminate the above-mentioned problems, some related art applications
are presented below.
Japanese Laid-Open Patent Application No. 05-119626 discloses a developing
device that incorporates filters for preventing toner splashes at both ends of
an aperture of a developing unit casing thereof.
Additionally, Japanese Laid-Open Patent Application No. 10-026861 discloses
a technique that makes use of a phenomenon that splashing of toner and carrier
occurs in a contact region (which is referred to as a nip part hereinafter) between
a photoconductor and a magnetic brush formed on a developing sleeve. According
to the disclosure, carrier collecting means are disposed at a position below the
nip part such that the carrier collecting means are separated from the photoconductor
and the developing sleeve at respective predetermined intervals.
Additionally, Japanese Laid-Open Patent Application No. 10-247042 discloses
a technique for collecting splashing toner and splashing carrier by using airflow
caused in a developing apparatus. According to the disclosure, airflow generation
means are disposed between a photoconductor and carrier collecting means so as
to cause an air to flow from the exterior to the interior of the developing apparatus.
However, the above-mentioned conventional developing apparatuses have some
problems. For instance, if the filter or the carrier collecting means are disposed
only at ends of a developing unit casing or only at a portion of a developing sleeve
so as to prevent the toner splash, toner and carrier can still splash due to airflow
from the interior of the developing unit casing, that is, outward airflow. Thus,
the above-mentioned conventional techniques cannot sufficiently overcome the toner
and carrier splash problems.
In particular, as the conventional developing apparatus operates at higher speeds
and the size thereof becomes smaller, the outward airflow becomes more problematic.
The generation mechanism of the outward airflow has not been clearly explained.
In order to prevent the toner and carrier splash, it is indispensable to demonstrate
the generation mechanism and design a developing apparatus that can control the
entrance and the exit of the airflow.
Herein, the above-mentioned toner splash problem is investigated in more
detail. Although it is known that the toner splash problem is caused by nonuniform
developer characteristics, for instance, nonuniformity of the Q/M value where Q
represents an amount of electrostatic charge and M represents a toner mass, toner
also splashes due to the physical design of the developing apparatus.
A part of the developer carried by the developing sleeve
101 escapes from
an electric attractive force with a latent image or a carrier on the photoconductor
102 due to physical contact with the photoconductor
102 and the up-and-down
motion of magnetic brushes, and then the escaping developer floats on the airflow
in the image forming apparatus.
While the photoconductor
102 and the developing sleeve
101 are
rotated, an accompanying airflow arises on the boundary between the surfaces thereof,
resulting in the toner being carried along by the airflow. The accompanying airflow
hits the developing unit casing
105 at a downstream position with respect
to the rotational direction of the developing sleeve
101, or a portion of
the accompanying airflow flows out of the developing apparatus there. The separated
airflow becomes the above-mentioned outward airflow and causes the floating toner
to splash out of the developing unit casing
105. The above-mentioned toner
splash mechanism is referred to as the first factor hereinafter. For instance,
the above-mentioned developing apparatus according to Japanese Laid-Open Patent
Application No. 10-247042 challenges only the first factor.
In addition, there is another factor that has not been conventionally taken into
account. This factor focuses attention on viscosity of the air, which cannot be
neglected in a small region where a magnetic brush is formed. A mass of air is
trapped in an inner space in a plurality of magnetic brushes, and the trapped air
passes through a narrow gap between the developing sleeve
101 and the developing
unit casing
105. The narrow gap is referred to as a casing gap hereinafter.
Although the developer is collected by the developing unit casing
105, the
trapped air hits the developing unit casing
105 and is likely to physically
cause the toner to flake away. Consequently, the outward airflow is generated from
the casing gap. This toner splash mechanism is referred to as the second factor hereinafter.
When the first factor and the second factor are combined, an abnormal outward
airflow is generated at the downstream side of the developing unit casing
105.
Namely, the interaction between the behavior of magnetic brushes and the portion
of the developing unit casing
105 causes the outward airflow from the developing
unit casing
105.
Furthermore, the toner splash mechanism due to the second factor is
investigated below with reference to FIG.
2 and FIG. 3 in more detail.
FIG. 2 is an enlarged view of a developing part of the conventional magnetic
brush development type developing apparatus in FIG.
1. This conventional
developing apparatus uses a two-component developer. Referring to FIG. 2, when
the permanent magnet
103a, which serves as the main pole, is fixed
at a position corresponding to the aperture
104 of the developing unit casing
105, a magnetic field due to the main pole forms a magnetic brush
110
of the two-component developer
109. When a latent image on the photoconductor
102 is in contact with the magnetic brush
110, the latent image is developed.
As previously mentioned, toner has the tendency to splash more frequently at
the
downstream side of the nip part with respect to the rotational direction of the
developing sleeve
101.
FIG. 3 is an enlarged view of the downstream side of the nip part wherein the
gap between the developing sleeve
101 and the developing unit casing
105
and the height of a magnetic brush
111 are highlighted. In general, the
developing apparatus includes the permanent magnets
103b,
103c
as the auxiliary poles to maintain the magnetic field in the vicinity of the
main pole of the permanent magnet
103a that forms the magnetic brush
110 in the contact point between the photoconductor
102 and the developing
sleeve
101. As a result, magnetic brushes
111 are also formed at
positions corresponding to the auxiliary poles on the developing sleeve
101.
However, since the developing unit casing
105, which has the aperture
104
as an end part thereof, is located around the permanent magnet
103b at
the downstream position of the nip part, the magnetic brush
111 and the
developing unit casing
105 can physically interact, for example, a collision
can occur between the magnetic brush
111 and the developing unit casing
105.
Referring to FIG. 3, an amount of two-component developer
109 prescribed
by the doctor blade
108 is accumulated on the circumferential surface of
the developing sleeve
101, resulting in forming the magnetic brush
111
due to the permanent magnet
103b. At this time, an air layer
112
of a predetermined height H is trapped in the inner space of the magnetic brush
111 and then is carried to an area
113 on the developing unit casing
105. In particular, if the magnetic brush
111 is formed, a greater
amount of air is trapped therein. This phenomenon is caused because the two-component
developer
109 includes an extremely fine carrier whose grain diameter is
dozens of micrometers and the viscosity of the air has considerable influence.
Since the developing unit casing
105 is closed at the inner side from the
area
113 and has no outlet for the air, the trapped air has nowhere to go
and is released to the exterior of the developing unit casing
105 through
the upper side of the magnetic brush
111 as illustrated. The released air
becomes an outward airflow
114. The outward airflow
114 can be observed
by means of a high-speed camera and an image processing technique.
The outward airflow
114 has the most significant influence on the toner
and carrier splash. When the magnetic brush
111 collides with the developing
unit casing
105 or the developer carrying screws
106 and
107
mix the two-component developer
109 in the developing unit casing
105,
the outward airflow
114 directly blows out floating toner and carrier from
the developing unit casing
105.
By using image measuring means to make visible the outward airflow
114,
it was observed that the boundary layer (the air layer
112) has the following
thicknesses under the conditions as follows;
- thickness with the two-component developer 109: 0.07 (mm)
- thickness without two-component developer 109: 0.2 (mm)
- condition:
- diameter of the developing sleeve 101: 60 (mm)
- rotational speed of developing sleeve 101: 5 (rad/s)
- angle between the nip part and the permanent magnet 103b:
π/4 (rad)
The above measurement result shows that the two-component developer
109
traps air on the surface of the developing sleeve
101. In order to eliminate
the toner and carrier splash problem, it is necessary to improve such a structure
of the developing apparatus where the outward airflow
114 is generated.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide a developing apparatus,
an image forming unit and an image forming apparatus in which the above-mentioned
problems are eliminated.
A more specific object of the present invention is to provide a developing apparatus
that can prevent or reduce splashes of toner and carrier caused by an abnormal
outward airflow generated from a downstream side of a developing unit casing due
to the combination with the above-mentioned first and second factors.
In order to achieve the above-mentioned objects, there is provided according
to
one aspect of the present invention a developing apparatus for developing a latent
image on a latent image carrying member with a magnetic brush made of developer
comprising toner and magnetic carrier, including: a developer carrying member being
rotated in a state where the magnetic brush is being formed thereon so as to develop
the latent image; a first permanent magnet being built in the developer carrying
member at a fixed position facing the latent image carrying member, the first permanent
magnet serving as a main pole and generating a magnetic field of the main pole
so as to form a first magnetic brush of the developer on the developer carrying
member; a developing unit casing covering the developer carrying member, the developing
unit casing having an aperture to expose the developer carrying member at the position
facing the latent image carrying member; and a second permanent magnet being built
in the developer carrying member at a fixed position near the aperture at a downstream
side from the first permanent magnet with respect to a rotational direction of
the developer carrying member, the second permanent magnet serving as an auxiliary
pole and generating a magnetic field of the auxiliary pole so as to form a second
magnetic brush of the developer on the developer carrying member, wherein the developing
unit casing has a concave structure to form a low pressure area at a position facing
the second permanent magnet, and the concave structure is concave toward an extension
of the second magnetic brush so as to have a larger gap there between the developing
carrying member and the developing unit casing than a gap at a tip part of the
aperture between the developing carrying member and the latent image carrying member.
According to the above-mentioned invention, since a magnetic brush of an
auxiliary pole traps air in the interior thereof around the auxiliary pole due
to rising and falling motions thereof, the flow speed of the air increases in a
thin air layer in the developing unit casing. However, the developing unit casing
has a concave structure, which is concave toward the extension of the magnetic
brush, at a position corresponding to the auxiliary pole such that the concave
structure is optimized to form an effective low pressure area. In this configuration,
it is possible to prevent increase in the flow speed there and suppress an amount
of outward airflow that blows toward the aperture of the developing unit casing
due to the first and the second factors. As a result, it is possible to prevent
splashes of released toner and released carrier.
In the above-mentioned developing apparatus, the concave structure may include
a concave part formed on an inner surface of the developing unit casing at a position
facing the second permanent magnet.
According to the above-mentioned invention, it is possible to easily implement
the above-mentioned developing apparatus by partially processing the developing
unit casing.
In the above-mentioned developing apparatus, the concave structure may include
a curvature of the developing unit casing.
According to the above-mentioned invention, it is possible to easily implement
the above-mentioned developing apparatus by processing the shape of the developing
unit casing.
In the above-mentioned developing apparatus, at the position facing the second
permanent magnet, a distance between a surface of the developer carrying member
and a bottom of the concave structure may be greater than or equal to a height
of the second magnetic brush.
According to the above-mentioned invention, even if the distance between
the surface of the developer carrying member and the bottom of the concave structure
is less than the height of the second magnetic brush, it is possible to obtain
the prevention effect on the outward airflow. However, if the distance is set as
more than or equal to the height of the second magnetic brush, it is possible to
prevent toner and carrier from flaking away from the magnetic brush due to physical
impacts such as a collision of the magnetic brush with the inner wall of the developing
unit casing. Therefore, it is possible to more effectively prevent splashing of
the toner and the carrier.
In the above-mentioned developing apparatus, the developing unit casing may have
a passage to communicate between the low pressure area and an exterior of the developing
unit casing through a porous breathable sheet.
According to the above-mentioned invention, when the inner pressure of
the developing unit casing increases, the developing apparatus can partially release
the pressure in the low pressure area in the developing unit casing to the exterior
thereof through the passage. Since the porous breathable sheet is disposed on the
passage, the developing apparatus can collect toner and carrier that are to splash
from the passage by means of the porous breathable sheet. As a result, it is possible
to prevent splashing of the toner and the carrier.
In the above-mentioned developing apparatus, the porous breathable sheet may
be
a high-density polyethylene nonwoven fabric sheet.
According to the above-mentioned invention, if a high-density polyethylene
nonwoven fabric sheet is used as the porous breathable sheet, it is possible to
improve the capability of collecting toner and carrier. As a result, it is possible
to reliably prevent toner splashes and carrier splashes from the passage.
In the above-mentioned developing apparatus, the porous breathable sheet may
be
disposed such that a surface thereof is not orthogonal to a gravitational direction.
According to the above-mentioned invention, when the developing apparatus
is being used in a long time period, splashing toner and splashing carrier tend
to be accumulated in the low pressure area in the gravitational direction because
of insufficient air evacuation. However, since the porous breathable sheet is disposed
such that the sheet surface is not orthogonal to the gravitational direction, it
is possible to reduce clogging of the porous breathable sheet due to the accumulation
of the toner and the carrier. As a result, it is possible to maintain air permeability
over a long time interval.
Additionally, there is provided according to another aspect of the
present invention a developing apparatus for developing a latent image on a latent
image carrying member with a magnetic brush made of developer comprising toner
and magnetic carrier, including: a developer carrying member being rotated in a
state where the magnetic brush is being formed thereon so as to develop the latent
image; a first permanent magnet being built in the developer carrying member at
a fixed position facing the latent image carrying member, the first permanent magnet
serving as a main pole and generating a magnetic field of the main pole so as to
form a first magnetic brush of the developer on the developer carrying member;
a developing unit casing covering the developer carrying member, the developing
unit casing having an aperture to expose the developer carrying member at the position
facing the latent image carrying member; a second permanent magnet being built
in the developer carrying member at a fixed position at a downstream side from
the first permanent magnet with respect to a rotational direction of the developer
carrying member, the second permanent magnet serving as an auxiliary pole and generating
a magnetic field of the auxiliary pole so as to form a second magnetic brush of
the developer on the developer carrying member; a splashing toner inhaling cover
being disposed close to the developer carrying member at a downstream side from
the first permanent magnet with respect to a rotational direction of the developer
carrying member, adjacent to the aperture of the developing unit casing; a splashing
toner inhaling duct being disposed below the splashing toner inhaling cover along
an axial direction of the developer carrying member and being connected to a ventilator
so that air flows in a predetermined direction through the splashing toner inhaling
duct, the splashing toner inhaling duct including a narrow part having a smaller
diameter; and a plurality of pressure inlet pipes communicating between the splashing
toner inhaling duct and the splashing toner inhaling cover at a plurality of positions
including a position of the narrow part.
Additionally, the above-mentioned developing apparatus may further
include a splashing toner inhaling cover being disposed close to the developer
carrying member at a downstream side from the first permanent magnet with respect
to a rotational direction of the developer carrying member, adjacent to the aperture
of the developing unit casing, a splashing toner inhaling duct being disposed at
a downstream position from the splashing toner inhaling cover along an axial direction
of the developer carrying member and being connected to a ventilator so that air
flows in a predetermined direction through the splashing toner inhaling duct, the
splashing toner inhaling duct including a narrow part having a smaller diameter,
and a plurality of pressure inlet pipes communicating between the splashing toner
inhaling duct and the splashing toner inhaling cover at a plurality of positions
including a position of the narrow part.
According to the above-mentioned invention, the developing apparatus can
use the splashing toner inhaling cover to collect splashing toner and splashing
carrier that blow out of the developing unit casing and then incorporate the collected
toner and the collected carrier in airflows that are blowing in the splashing toner
inhaling duct in a predetermined direction via the pressure inlet pipes. Also,
the splashing toner inhaling duct includes the narrow part having the smaller diameter
and some of the pressure inlet pipes are connected to the narrow part. These pressure
inlet pipes have lower pressures than those of the pressure inlet pipes connected
to the other positions, resulting in stronger inhaling power there. As a result,
it is possible to effectively inhale toner and carrier from the narrow part. Hence,
it is possible to effectively prevent splashing of the toner and the carrier by
devising the shape of the splashing toner inhaling duct and partially strengthening
the inhaling power at the narrow part.
In the above-mentioned developing apparatus, at least one of the pressure inlet
pipes may communicate between a position of the splashing toner inhaling cover
to which one of the toner and the magnetic carrier on the developer carrying member
is likely to splash and the narrow part of the splashing toner inhaling duct.
According to the above-mentioned invention, some of the pressure inlet
pipes are connected by priority between the narrow part of the splashing toner
inhaling duct and positions to which toner and carrier are empirically likely to
splash with respect to the axial direction of the developer carrying member, for
example, an end part of the developing apparatus and a rib part of the developing
unit casing. As a result, it is possible to effectively inhale the toner and the
carrier in airflows in the splashing toner inhaling duct.
In the above-mentioned developing apparatus, at least one of the pressure inlet
pipes may communicate between a middle position of the splashing toner inhaling
cover with respect to the axial direction of the developer carrying member and
the narrow part of the splashing toner inhaling duct and at least one of the pressure
inlet pipes may communicate between an end position of the splashing toner inhaling
cover with respect to the axial direction of the developer carrying member and
a thick part of the splashing toner inhaling duct whose diameter is greater.
According to the above-mentioned invention, since it is empirically known
that toner splashes are likely to be generated at an end part of the developing
apparatus, some of the pressure inlet pipes are provided to communicate between
the middle point of the splashing toner inhaling cover with respect to the axial
direction and the narrow part of the splashing toner inhaling duct and some of
the pressure inlet pipes are provided to communicate between ends of the splashing
toner inhaling cover and the thick part of the splashing toner inhaling duct. As
a result, pressure differences between the narrow part and the thick part cause
an air in the splashing toner inhaling cover to flow from the ends to the middle
point. In this configuration, it is possible to shift splashing toner and splashing
carrier from the ends of the splashing toner inhaling cover to the middle point
and effectively inhale the splashing toner and the splashing carrier in airflows
in the splashing toner inhaling duct with minimal use of the pressure inlet pipes.
In the above-mentioned developing apparatus, each of the pressure inlet-pipes
may include a first interrupting part separately interrupting communication between
the splashing toner inhaling cover and the splashing toner inhaling duct.
According to the above-mentioned invention, if the developing apparatus
cannot sufficiently exhibit the expected capability of collecting toner and carrier
depending on conditions of an image forming apparatus in which the developing apparatus
is installed, it is possible to modify airflows to collect the toner and the carrier
after installation by switching connection conditions of the pressure inlet pipes
or selecting the pressure inlet pipes by the interrupting part.
Additionally, the above-mentioned developing apparatus may further
include a second pressure inlet pipe communicating between the narrow part of the
splashing toner inhaling duct and the passage, and a second interrupting part interrupting
communication between the splashing toner inhaling duct and the passage.
According to the above-mentioned invention, while the developing apparatus
is not used, the second interrupting part opens the second pressure inlet pipe
so as to communicate between the narrow part of the splashing toner inhaling duct
and the passage. As a result, it is possible to force outward airflows to blow
in the low pressure area by changing the air in the low pressure area to positive
pressure with respect to the atmosphere. The developing apparatus can collect toner
and carrier accumulated on the porous breathable sheet in the splashing toner inhaling
duct via the splashing toner inhaling cover because of the forced outward airflows.
Accordingly, it is possible to maintain the function of the porous breathable sheet
for a long time period.
Additionally, there is provided according to another aspect of the
present invention an image forming unit, including: a latent image carrying member
on which a latent image is formed; and a developing apparatus developing the latent
image on the latent image carrying member with a magnetic brush made of developer
comprising toner and magnetic carrier, including: a developer carrying member being
rotated in a state where the magnetic brush is being formed thereon so as to develop
the latent image; a first permanent magnet being built in the developer carrying
member at a fixed position facing the latent image carrying member, the first permanent
magnet serving as a main pole and generating a magnetic field of the main pole
so as to form a first magnetic brush of the developer on the developer carrying
member; a developing unit casing covering the developer carrying member, the developing
unit casing having an aperture to expose the developer carrying member at the position
facing the latent image carrying member; and a second permanent magnet being built
in the developer carrying member at a fixed position near the aperture at a downstream
side from the first permanent magnet with respect to a rotational direction of
the developer carrying member, the second permanent magnet serving as an auxiliary
pole and generating a magnetic field of the auxiliary pole so as to form a second
magnetic brush of the developer on the developer carrying member, wherein the developing
unit casing has a concave structure to form a low pressure area at a position facing
the second permanent magnet, and the concave structure is concave toward an extension
of the second magnetic brush so as to have a larger gap there between the developing
carrying member and the developing unit casing than a gap at a tip part of the
aperture between the developing carrying member and the latent image carrying member.
Additionally, there is provided according to another aspect of the
present invention an image forming unit, including: a latent image carrying member
on which a latent image is formed; and a developing apparatus developing the latent
image on the latent image carrying member with a magnetic brush made of developer
comprising toner and magnetic carrier, including: a developer carrying member being
rotated in a state where the magnetic brush is being formed thereon so as to develop
the latent image; a first permanent magnet being built in the developer carrying
member at a fixed position facing the latent image carrying member, the first permanent
magnet serving as a main pole and generating a magnetic field of the main pole
so as to form a first magnetic brush of the developer on the developer carrying
member; a developing unit casing covering the developer carrying member, the developing
unit casing having an aperture to expose the developer carrying member at the position
facing the latent image carrying member; a second permanent magnet being built
in the developer carrying member at a fixed pos
