Electrophotography – Diagnostics – Consumable
Reexamination Certificate
2002-07-24
2003-10-28
Pendegrass, Joan (Department: 2852)
Electrophotography
Diagnostics
Consumable
C399S030000
Reexamination Certificate
active
06640060
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image forming apparatus such as a copying machine or a printer of the electrophotographic type, the electrostatic recording type or like type in which a developer is made to adhere to a latent image formed on an image bearing member to thereby visualize the latent image, and particularly to an image forming apparatus using a two-component developer including a toner and a carrier as a developer, and provided with a toner replenishing device for replenishing with the toner.
2. Description of Related Art
FIG. 13
of the accompanying drawings schematically shows the cross-sectional construction of an example of a developing device using a two-component developer including a toner and a carrier as a developer.
FIG. 14
of the accompanying drawings shows the developing device of
FIG. 13
as it is seen from above it.
In this example, the developing device
2
is provided with a developing container
10
, and a developing sleeve
2
A as a developer carrying member is provided in the opening portion thereof opposed to an image bearing member
1
. A magnet roller
3
as magnetic field generating means is fixedly disposed in the developing sleeve
2
A.
A screw
5
and B screw
6
as carrying and agitating means for carrying the developer to the developing sleeve
2
A are disposed in the developing container
10
. The A screw
5
and the B screw
6
are disposed substantially parallel to each other, and an inner wall
7
for partitioning the space between the A screw
5
and the B screw
6
is provided so that the developer may not come and go therebetween.
As will be understood from
FIG. 14
, the inner wall
7
is absent at the lengthwisely opposite end portions so that the developer can come and go between the A and B screws
5
and
6
. The A screw
5
and the B screw
6
are adapted to carry the developer in opposite directions.
The developing sleeve
2
A and the A screw
5
and the B screw
6
are connected together by gears (not shown) or the like, and when the developing sleeve
2
A, the A screw
5
and the B screw
6
are rotated in the directions of arrows, the developer is uninterruptedly circulated therein as indicated by arrows in FIG.
14
.
An inductance sensor
12
which is toner density detecting means is installed in proximity to the B screws
6
. The two-component developer is basically comprised of a nonmagnetic toner and a carrier having magnetism, and the magnetic permeability of the developer is determined by the amount of carrier occupying a predetermined volume. Therefore, the inductance sensor
12
is installed to measure the magnetic permeability of the developer to thereby measure the ratio between the toner and the carrier (hereinafter referred to as the “toner density”).
Above the developing container
10
of the developing device
2
, there is installed a toner replenishing device
9
for replenishing with a necessary amount of toner. A toner replenishing port
8
is located a little downstream of the inductance sensor
12
, and when the toner is used for image formation and the toner density in the developer lowers, the amount of lowering of the toner density is measured when the developer passes the inductance sensor
12
, and the developing container
10
is replenished with the necessary amount of toner from the toner replenishing device
9
through the toner replenishing port
8
and thus, the toner density in the developer is always kept constant.
As the toner density detecting means
12
, use may be made of one of the optical density detection type, besides the inductance sensor described herein.
In a new developing device
2
, there is prepared a standard developer adjusted in advance to predetermined toner density. When the new developing device
2
is set in an image forming apparatus, the agitating means
5
and
6
are rotated for a predetermined time and the developer uniformly pervades over the A screw
5
and the B screw
6
and the circulation of the developer becomes steady and the charged amount of the toner becomes settled. In this state, the measurement of the toner density is effected by the toner density detecting means
12
. The value measured at this time is stored in a storing device (e.g. an EP-ROM free to write in or the like) mounted on the developing device, and is defined as a toner density reference value T inherent to this developing device.
During the control of the toner density during the printing operation, the difference between the measured value S and the aforementioned reference value T is compared, whereby it is possible to know How much the current toner density deviates as compared with the toner density of the standard developer and therefore, the amount of toner to replenish with can be calculated. By endowing the developing device with the toner density reference value T inherent to the developing device correspondingly to the developing device, toner density control optimum for each developing device
2
can be effected.
When the toner replenishment by the toner replenishing device
9
stagnates and the measured value S lowers and reaches a preset predetermined value (hereinafter referred to as the “limit value L”), it is judged that the developing device is not being replenished with the toner from the toner replenishing device
9
, and the image forming apparatus is stopped and the supply of the toner to the toner replenishing device
9
is demanded.
In the above-described construction, however, the following problem has sometimes arisen with respect to the setting of the limit value L.
FIG. 12
of the accompanying drawings is an illustration showing an example of the transition of the measured value S, and the axis of abscissas indicates the number of prints and the axis of ordinates indicates the measured value S of the toner density.
During ordinary use, toner density control is effected so that the measured value S may converge around the vicinity of the reference value T. However, if high coverage images such as solid images are continuously printed, the toner in the developing device
2
will be rapidly consumed and therefore, the measured value S temporarily sharply lowers (Smin). Accordingly, unless the limit value L is set to a low level with a certain degree of safety rate foreseen with respect to Smin, the limit value L will be unexpectedly exceeded during the continuation of high coverage images or the like, and in spite of the presence of the toner in the toner replenishing device
9
, the absence of the toner may be judged by mistake and the image forming apparatus may be stopped.
If in order to avoid such wrong detection, the limit value L is set to low developer density with the safety rate sufficiently given, the developer density will now become considerably low before the measured value S reaches the limit value L and therefore, the lowering of image density will occur and good images cannot be ensured. Also, image formation and agitation or the like are effected in a state in which the toner is little, namely, a carrier-rich state and therefore, the deterioration of the carrier progresses, and when the toner replenishing device
9
is replenished with the toner, if toner replenishment is effected at a stretch, fogged images may occur. If as described above, the limit value L is set too high, the possibility of effecting wrong detection will increase, and if the limit value L is set too low, the possibility of causing an inconvenience to images or the developing device will increase and therefore it has been very difficult to optimally set the limit value by the conventional construction.
Also, a single limit value L has always been used and therefore, it can be judged that the developing device is in a state in which it is not replenished with the toner from the toner replenishing device
9
, but is has been impossible to discriminate whether it is the absence of the toner in the developing container
10
, or the trouble of the toner replenishing device
9
(such as the badness of the toner discharging scr
Kinoshita Masahide
Uyama Masao
Yamaguchi Seiji
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Pendegrass Joan
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