Photocopying – Projection printing and copying cameras – With developing
Reexamination Certificate
1999-01-13
2001-08-28
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
With developing
C399S254000, C399S256000
Reexamination Certificate
active
06281961
ABSTRACT:
This application is based on applications Nos. 10-005504, 10-005511, 10-016755, 10-016579, 10-022455 and 10-029009 filed in Japan, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a developing device used for electrophotographic type copiers and printers. More particularly, it relates to a developing device of a vertical circulation type wherein each screw is arranged up and down or upper, middle, and lower so that developer should circulate smoothly and unevenness of toner-density problem should be solved quickly.
2. Description of the Related Art
As an example of a conventional developing device of vertical circulation type, Japanese Unexamined Patent Publication No. 5-333691 here will be referred to.
FIGS. 44 and 45
illustrate the structure of a conventional developing device disclosed in the publication. In a developing device
900
according to the publication, a developer reservoir
903
for supplying and a developer reservoir
906
for stirring are arranged up and down. A partition wall
904
is arranged between the developer reservoir
903
and the developer reservoir
906
whereby the partition wall
904
separates the developer reservoirs
903
and
906
.
An upper auger
902
is arranged in the developer reservoir
903
and transports developer from left to right in
FIG. 45. A
lower auger
905
is arranged in the developer reservoir
906
and transports developer from right to left in FIG.
45
. That is, transporting direction of the auger
902
and that of the auger
905
are opposite to each other.
The lower auger
905
delivers developer to the upper auger
902
at downstream end
911
for the developer reservoir
906
. The upper auger
902
delivers developer to the lower auger
905
at downstream end
912
for the developer reservoir
903
. Thereby, developer is circulated clockwise in FIG.
45
and stirred. As apparent from
FIG. 44
, the upper auger
902
supplies developer to a developer carrier
907
. Then, the lower auger
905
collects developer remaining on the developer carrier
907
after development.
However, the developing device
900
has the following problems.
Firstly, in the developing device
900
, the relation between developer-transporting capability of the upper auger
902
and that of the lower auger
905
is not considered at all. Therefore, there is a fear that the balance between developer-transporting capability of the upper auger
902
and that of the lower auger
905
may not be found. When developer-transporting capabilities of the augers
902
and
905
do not find a balance, developer does not circulate smoothly. Thereby, developer receives an excessive load and developer is likely to deteriorate soon. Also, thereby, distribution of developer within the developing device becomes imbalance and image-density may be uneven.
Secondly, in the developing device
900
, both the developer reservoirs
903
and
906
are separated by the partition wall
904
except the downstream ends
911
and
912
. Thereby, portions where the augers
902
and
905
can deliver developer to each other are limited to the downstream ends
911
and
912
. Therefore, developer circulates clockwise only, in actual. That is, developer can hardly move from one of the augers to other auger while being transported horizontally by the augers
902
and
905
.
Thus, in case that toner-density of developer becomes uneven at some parts, developer keeps circulating for some time with its toner-density uneven. In other words, it takes time for developer to recover from unevenness of toner-density in the clockwise circulation. This also causes unevenness of image-density.
Thirdly, as described, since portions where developer can be delivered up and down are limited to the downstream ends
911
and
912
, balance of developer to be delivered between the upper auger and the lower auger is lost in case that the developing device
900
is not installed horizontally. As a result, developer is likely to concentrate in either the developer reservoir
903
or the developer reservoir
906
. Thereby, a motor M for driving the augers
902
and
905
has a large load and problem such as step-out occurs to the motor M.
SUMMARY OF THE INVENTION
To overcome the above mentioned problems in the conventional developing device, the primary object of the present invention is to provide an improved developing device. Further object of the present invention is to provide a developing device capable of circulating developer smoothly. Still further object of the present invention is to provide a developing device which can quickly make toner density uniform when toner-density varies and becomes uneven at some parts.
To achieve at least one of the objects, a developing device according to one aspect of the present invention comprises: an accommodating unit which accommodates developer therein, the developer being a mixture of toner and carrier; a first transporter which is located in the accommodating unit, the first transporter being for transporting the developer, the first transporter having a first transporting capability; and a second transporter which is located in said accommodating unit and is located above of the first transporter, the second transporter being for transporting the developer, the second transporter having a second transporting capability higher than the first transporting capability.
In the above mentioned developing device, since the second transporter has higher transporting capability than the first transporter, the second transporter transports developer faster than the first transporter. Therefore, distribution balance of developer is kept in a state that amount of developer present within the second transporter is less than that of developer present within the first transporter. Accordingly, the second transporter located above of the first transporter does not have to be buried in developer completely. That is, since total amount of toner to be accommodated in the accommodating unit is made not much, torque for driving the first and second transporters is reduced. Moreover, since developer does not receive serious stress due to its own weight, a life of developer becomes long.
In the present specification, term “transporter” means any elements which transport developer in a certain direction. Terms “screw” and “auger” are lower conception of “transporter”. The terms “screw” and “auger” are synonyms and defined as an element which includes a long rod with at least one blade and transports developer in longitudinal direction of the rod along with its axial rotation, herein. A blade may be arranged on a rod in its longitudinal direction spirally.
As to the first and second transporters, first and second augers can be employed. In this case, making transporting capability of the second auger higher than that of the first auger can be achieved by employing any one of the followings: (1) the rotation speed of the second auger is made faster than that of the first auger; (2) the blade-diameter of the second auger is made larger than that of the first auger; (3) the pitch of the second auger is made larger than that of the first auger; (4) the number of threads of the second auger is made larger than that of the first auger; (5) a paddle is provided on the first auger; (6) the axial diameter of the first auger is made larger than that of the second auger; and so on. A paddle of an auger herein is defined as a member which is designed to apply pressure only in a direction vertical to a developer-transporting direction, i.e., a normal direction of the developer-transporting direction: the paddle is not designed to impart transporting force to developer (pressure in an axial direction).
The accommodating unit of the developing device may have a first end and a second end opposing the first end. The first transporter may transport the developer from the first end to the second end, and deliver the developer to the second transporter at the second end. Similarly, the second trans
Hamamichi Suguru
Okuno Yukihiko
Sako Mineyuki
Shojo Yoshihiro
Yoshimoto Shin-ichi
Adams Russell
Kim Peter B.
McDermott & Will & Emery
Minolta Co. , Ltd.
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