Electrophotography – Control of electrophotography process – Control of developing
Reexamination Certificate
1999-07-23
2002-05-14
Grainger, Quana M. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of developing
C399S274000
Reexamination Certificate
active
06389245
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine, a printer, an apparatus for displaying recorded images, or a facsimile equipment, which forms visible images by developing electrostatic latent images formed on an image bearing member by an electrophotographic method, an electrostatic recording method, or the like. The invention also relates to a developing device used for the image forming apparatus.
2. Related Background Art
There has been known a developing device that bears a dry developer as a visualizing agent on a surface of a developer bearing member, and supplies this developer to the vicinity of a surface of an image bearing member that bears an electrostatic latent image so as to develop the electrostatic latent image into a visible image by applying an alternating electric field between the image bearing member and the developer bearing member.
In this respect, the developer bearing member described above is generally provided with a developing sleeve for use in many cases. The developer bearing member is, therefore, referred to as a “developing sleeve” in the following description. Also, since the image bearing member is generally provided with a photosensitive drum in many cases, the image bearing member is referred to as a “photosensitive drum” in the following description.
As the above-mentioned development method, there is known the so-called magnetic brush development method whereby to form a magnetic brush on a surface of a developing sleeve in which a magnet which serves as magnetic field generating means is disposed. The magnetic brush is made of a developer (two-component developer) comprising a two-component system composition (carrier particles and toner particles), for example. This method is arranged to enable the magnetic brush to slide on or approach the photosensitive drum that faces the magnetic brush with a fine development gap between them, and then, to apply continuously the alternating electric field between the developing sleeve and the photosensitive drum (between S-D), hence performing the development by the repeated transfer and counter-transfer of the toner particles from the developing sleeve to the photosensitive drum (as disclosed in the specifications of Japanese Patent Application Laid-Open No. 55-32060 and Japanese Patent Application Laid-Open No. 59-165082, for example).
As shown in
FIG. 5
, the developing device
18
for the two-component magnetic brush development is provided with a developing container
18
a
which is divided into a developing chamber R
1
and an agitating chamber R
2
by a partition wall
19
. In the developing chamber R
1
and the agitating chamber R
2
, the agitating and conveying screws
23
and
24
serving as the agitating and conveying members are rotatively contained, respectively. At an opening of the developing chamber R
1
, the developing sleeve
25
, which rotates in a direction indicated by an arrow “c” in
FIG. 5
is arranged to face the photosensitive drum
3
which rotates in a direction indicated by an arrow a with a fine gap therebetween. The magnet
29
is fixedly arranged in the interior of the developing sleeve.
Also, a regulating blade
28
is arranged to face the developing sleeve
25
with a predetermined gap in order to provide the developer on the surface of the developing sleeve
25
in a form of a thin film.
In the developing container
18
a
, there is contained the developer
22
having the toner particles and the magnetic particles mixed for it. The mixing ratio of the toner particles and the magnetic particles (hereinafter referred to as the “T/C ratio”) is kept constant by droppig and supplying a toner in an amount matching that of the toner that has been consumed for development, from a toner storage chamber
21
that contains the toner to be supplied.
The dropped and supplied toner is agitated by the screw
24
in the agitating chamber R
2
to be mixed with the developer
22
in the developing chamber
18
a
, and then carried. At this time, the developer
22
is conveyed along a longitudinal direction of the developing container in a direction opposite to a developer conveying direction in which the developer is conveyed by the conveying screw
23
in the developing chamber R
1
. The partition wall
19
is provided with openings on the front side and the back side respectively in FIG.
5
. Through these openings, the developer is delivered.
Now, it is extremely important to maintain the T/C ratio of the two-component developer in the developing container
18
a
for the stabilized image output. Various methods have been proposed for the detection and maintenance of this ratio.
For example, detecting means is arranged on the circumference of the photosensitive drum
3
to irradiate light on the toner transferred from the developing sleeve
25
to the photosensitive drum
3
. Thus, the toner supply amount is adjusted based on a transmitted light or a reflected light at that time. With the result thereof, the T/C ratio is detected. There is another method in which detecting means is arranged in the vicinity of the surface layer of the developing sleeve
25
, and then, the T/C ratio is detected based on a reflected light when light is irradiated on the developer coated on the developing sleeve
25
. Also, there is a method proposed and practiced, in which the T/C ratio is detected by the provision of a sensor in the developing container
18
a
to detect the change in the apparent magnetic permeability of the developer in a predetermined volume in the vicinity of the sensor by the utilization of the coil inductance.
However, the method of maintaining the T/C ratio at a constant value on the basis of an amount of the developing toner on the photosensitive drum
3
has a problem that the amount of toner on the photosensitive drum
3
is caused to change due to the factors other than the changes of the T/C ratio, such as the fluctuation of the gap between the photosensitive drum
3
and the developing sleeve
25
or the change in the electrical potential of a latent image, and as a result, the toner supply operation is made erroneous eventually. Also, the method of detecting the T/C ratio by the reflective light when the light is irradiated to the developer applied on the developing sleeve
25
has a problem that it becomes impossible to detect the exact T/C ratio if the detecting means is stained by the toner flown in all directions.
In contrast, the sensor that uses the method of detecting the T/C ratio by the detection of the change in the apparent magnetic permeability of the developer
22
within a predetermined volume in the vicinity of the sensor (hereinafter referred to the “toner concentration sensor”) is not affected by the problem of the contamination due to the toner flown in all directions, while the costs of the sensor per se are lower. Therefore, this T/C ratio detecting means is best suited for the low-cost and smaller-space copying machine or an image forming apparatus, such as a printer.
The toner concentration sensor that utilizes the change in magnetic permeability of the developer as described above is arranged to determine that a T/C ratio of the developer becomes lower when the magnetic permeability of the developer within a predetermined volume becomes large, for example, and then, it causes the initiation of the toner supply. If, on the contrary, the magnetic permeability becomes smaller, it is determined that the T/C ratio of the developer is made higher, thus ceasing the toner supply. This sensor controls the T/C ratio of the developer in accordance with such sequence.
Nevertheless, the toner concentration sensor in the method of detecting the change in the apparent magnetic permeability of the developer within a predetermined volume as described above has a problem that if the bulk density of the developer itself, that is, the weight of the developer per unit volume, may be affected to present some changes, the apparent magnetic permeability of the developer may also
Hibino Masaru
Kobayashi Yoshiaki
Ozawa Ichiro
Shida Masanori
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