Electrophotography – Image formation – Photoconductive member
Reexamination Certificate
2001-10-17
2004-12-07
Brase, Sandra (Department: 2852)
Electrophotography
Image formation
Photoconductive member
Reexamination Certificate
active
06829455
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to an image forming apparatus equipped with a driving force transmission mechanism, and a process unit used by such an image forming apparatus.
Conventionally, a driving system for driving a photoconductive drum, as an image bearing member, of an image forming apparatus such as a copying machine, a printer, or the like comprises: a driving gear, which receives the driving force from the motor of the main assembly of the image forming apparatus, and transmits the driving force; and a gear shaft, which is coaxial with the driving gear, and rotates with the driving gear. There are two methods for driving a photoconductive drum with the use of such a driving system: a driving method which employs a driving shaft with a coupling, and a driving method which employs a driving shaft without a coupling.
FIG. 12
shows the rough concept of a driving method which employs a driving shaft without a coupling.
Referring to
FIG. 12
, a gear shaft
13
directly connected to a drive gear
12
is put through a photoconductive drum
80
, and is used as the drum shaft for the photoconductive drum
80
. In this case, the photoconductive drum
80
is supported so that it rotates with the gear shaft
13
. With this driving method, the rotation of the driving gear
12
for transmitting the driving force of a motor
11
is directly transmitted to the photoconductive drum
80
.
FIG. 13
shows the rough concept of the driving method which employs a driving shaft with a coupling. In this case, the gear shaft
13
is indirectly connected to the photoconductive drum
80
, with the interposition of a coupling
23
, and the driving force from the motor
11
is transmitted to the photoconductive drum
80
through the gear shaft
13
and coupling
23
.
Comparing the two driving methods, the method which employs a coupling is superior in terms of cost. Further, in the case of an image formation system constructed around a photoconductive drum, a photoconductive drum has come to be integrally disposed, along with a single or a plurality of processing apparatuses, such as a developing apparatus, in a cartridge (process cartridge). Consequently, it has become considered important how easy a process cartridge is to mount into, or dismount from, the image forming apparatus main assembly. This has called attention to various couplings, that is, devices for connecting two shafts to transmit a driving force from one shaft to the other. Among various couplings, couplings such as the one shown in
FIG. 14
which comprise a combination of a female type coupler and a male type coupler, and in which driving force is transmitted through the engagement between the two couplers, have begun to attract special attention because of their superiority in terms of driving force transmission performance. The couplings such as the one shown in
FIG. 14
have come to be widely used, because of their advantage in driving force transmission performance.
However, a coupling based driving method is inferior to a direct driving method in terms of driving force transmission accuracy; in other words, there is a concern that a coupling based driving method suffers from the problem regarding the angle at which two shafts are connected to each other by a coupling, the problem regarding how two shafts are aligned with each other by a coupling, or the like problems. When an image forming apparatus suffers from the problems described above, an image becomes misaligned relative to a recording medium, degrading image quality. This problem is particularly conspicuous in an image forming apparatus which forms a color image on recording medium by placing a plurality of images different in color, in layers.
As a coupling for solving the above described problems, there is a coupling comprising a combination of a female type coupler and a male type coupler, at least one of which is in the form of a polygonal piller.
FIG. 15
shows an example of such a coupling comprising a female type coupler with a hole in the form of a polygonal pillar, and a male type coupler with a projection in the form of a polygonal pillar.
Referring to
FIG. 15
, a gear shaft
13
, that is, one of the components of the driving system I of the apparatus main assembly, is provided with a female type coupler
14
, which is attached to one end of the gear shaft
13
, and is provided with a twisted hole
50
, the cross section of which is in the form of an equilateral triangle.
On the other hand, the photoconductive drum
80
, or a cylindrical member which constitutes one of the components of the system to be driven by the driving system I, is provided with a twisted projection
10
, which is the same in twist angle as the twisted hole of the female type coupler
50
, and the cross section of which is in the form of an equilateral triangle. A male type portion
53
with the projection
10
in the form of a twisted pillar with a cross section in the form of an equilateral triangle doubles as a drum flange
80
. Although the projection
10
is in the form of an equilateral triangular pillar, here, it may be in the form of a polygonal pillar, the cross section of which is not in the form of an equilateral triangle. When one of the lateral walls of the hole of the female type portion is in contact with one of the lateral walls of the male type portion, the interface between the two members forms a twisted line
60
. Therefore, as a rotational force is applied to the female type portion while the two members are in engagement with each other, the male type portion, that is, the member on the photoconductive drum
80
side is pulled into the female type portion, or the member on the apparatus main assembly side, being accurately positioned relative to the apparatus main assembly. As a result, the two shafts are precisely connected by this effect, that the male type portion is pulled into the female type portion, and the play between the photoconductive drum
80
and apparatus main assembly in terms of the thrust and radial directions of the photoconductive drum
80
is eliminated.
FIG. 16
shows the cross sections of the female and male type portions
14
and
53
in engagement with each other, at a plane perpendicular to the axial lines of the two members. In FIG.
16
(
a
), the solid line represents the cross section of the female type portion
71
, or the driving side, with the hole
50
, the cross section of which is in the form of an equilateral triangle, and the broken line represents the projection
10
, or the driven side, the cross section of which is in the form of an equilateral triangle. Under the condition depicted by FIG.
16
(
a
), although the projection
10
is in the hole
50
, the edges of the projection
10
are not in contact with the corresponding lateral walls of the hole
50
, and therefore, there is play between the two members, and the axial line C
1
of the female type portion does not coincide with the axial line C
2
of the male type portion. However, as rotational force is applied to the female type portion
71
, the three lateral walls of the hole
50
contact the three edges of the projection
10
, one for one, automatically causing the axial lines C
1
and C
2
to coincide with each other, as shown in FIG.
16
(
b
). Under the condition depicted by FIG.
16
(
b
), the driving force applied to the female type portion
71
is transmitted as forces F by the interfaces (contact points) between the female and male type portions.
As described above, a coupling which comprises a combination of a female type portion and a male type portion, and in which the male type portion is engaged into, and then is placed in contact with, the female type portion, makes it possible to connect two shafts while automatically aligning the two shafts, accurately positioning them, and eliminating the play. Therefore, such a coupling is considered effective as a member for the connection between the photoconductive drum of an image formation unit in the form of a cartridge, and the image forming apparatus main assem
Fujiwara Yukihiro
Hoashi Shigeru
Murayama Kazunari
Numagami Atsushi
Ono Akio
Brase Sandra
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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