Electrophotography – Image formation – Photoconductive member
Reexamination Certificate
2002-10-08
2003-12-09
Grimley, Arthur T. (Department: 2852)
Electrophotography
Image formation
Photoconductive member
C074S440000
Reexamination Certificate
active
06661986
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an image forming apparatus of the electrophotographic type such as a copying machine or a laser beam printer, or an image forming apparatus of the electrostatic recording type, and a driving apparatus for driving image forming means used in the image forming apparatus.
2. Related Background Art
As one of color image forming apparatuses, there is known a color laser beam printer of the tandem type, in which a plurality of photosensitive drums are juxtaposed, for effecting the formation of an image by superimposing toners of four colors, i.e., yellow, magenta, cyan and black, one upon another. Driving the photosensitive drums which are image bearing members highly accurately is an important matter to obtain an image of good quality suffering little from banding (an uneven tone of an image) and color misregister.
FIG. 8
of the accompanying drawings shows an example of a conventional driving construction for a photosensitive drum. The reference numerals
21
and
22
designate the front side plate and rear side plate (front and rear frame metal plates), respectively, of the main body of an image forming apparatus. A drum shaft
71
is rotatably bearing-supported between the front and rear side plates
21
and
22
through bearings
23
and
24
. The photosensitive drum
11
is fixedly supported on the drum shaft
71
.
The frame
32
of a drum driving unit is mounted on and fixed to the outside of the rear side plate
22
. The rear end portion of the drum shaft
71
is rearwardly extended and is bearing-supported on the frame
32
through a bearing
33
and extends through the frame
32
to thereby protrude outwardly of the frame.
The reference numeral
34
denotes a motor mounted on and fixed to the inner side of the frame
32
, and the reference numeral
35
designates a motor gear secured to the rotary shaft of this motor
34
. A drum shaft gear
51
integrally disposed on the rear end portion of the drum shaft
71
is in meshing engagement with the motor gear
35
. The motor gear
35
is a small-diametered gear and the drum shaft gear
51
is a large-diametered gear, and these gears together constitute a reduction gear train. The drum shaft gear
51
is fixed to the drum shaft
71
by the use of a spring pin
52
, a compression spring
53
and a locating snap ring
54
. The spring pin
52
is a circumferential coupling member for the drum shaft gear
51
and the drum shaft
71
, and effects the transmission of drive. The compression spring
53
which is a biasing member and the locating snap ring
54
effect the axial positioning of the drum shaft gear
51
relative to the drum shaft
71
. This construction is a construction in which the rotatively driving force of the motor
34
is transmitted to the drum shaft
71
through the motor gear
35
and the drum shaft gear
51
which are the reduction gear train to thereby rotatively drive the drum shaft
71
, i.e., the photosensitive drum
11
.
The uneven rotation of the photosensitive drums may be mentioned as one of the causes of the occurrence of banding and color mitsregister. The uneven rotation of the photosensitive drums is caused by the speed fluctuation of the meshing frequency of the gear train of the drum driving system and besides, may be caused by the transmission of the speed fluctuation of image forming process means acting on the photosensitive drums, particularly the speed fluctuation of recording material transporting means for transferring toner images to a recording material and transporting it or the speed fluctuation of an intermediate transfer member.
As an ordinary method of preventing banding, there is known a method of providing a flywheel
61
on the drum shaft
71
, as shown in FIG.
8
. This intends to contrive the suppression of the speed fluctuation of the photosensitive drums in an area of a relatively high frequency zone by an inertial effect. The flywheel
61
is fixed to the drum shaft
71
by the use of a screw
62
.
On the other hand, as a method of preventing color misregister in an apparatus having a plurality of photosensitive drums, there are known the following two ways of view:
(1) The speed fluctuation of one revolution period of the photosensitive drum is made small to thereby reduce the expansion and contraction of an image of each color, and as a result, color misregister is suppressed.
(2) The amplitudes and phases of the expansion and contraction of images of respective colors caused by the speed fluctuation of one revolution period of the photosensitive drum are tuned to thereby cancel color misregister.
When an attempt is made to achieve an improvement in the accuracy of rotation of the photosensitive drum
11
along the way of view mentioned under item (1) above by the driving construction of
FIG. 8
, it is most important to make the vibration of the drum shaft gear
51
which is a driven gear provided on the drum shaft
71
small.
This will now be described. When the meshing position of two gears fluctuates in the radial direction thereof, the fluctuation of the rotating speed of the driven side occurs in proportion to the amount thereof. This is because the radial fluctuation of one revolution period, i.e., the vibration, of the driven gear is directly geometrically converted into the speed fluctuation of the one revolution period.
Here, the vibration of the above-described gear refers not to the vibration of the gear singly, but to the vibration in a state in which it is coupled to the drum shaft. To make the vibration of the gear in its coupled state small, it is necessary to make the vibration of the gear singly (a whole pitch meshing error) small and also, to couple the gear to the drum shaft so that there may be no eccentricity or inclination.
In the aforedescribed example of the conventional art, however, there are the following problems. Description will first be made of the problem of the flywheel provided with a view to prevent banding. In an apparatus of the tandem type, the radius of the flywheel is restricted by the interval between adjacent drums. Therefore, in order to secure a necessary amount of inertia, such design as increasing the thickness of the flywheel or axially offsetting and disposing the flywheel is usually made, but this results in the bulkiness of the apparatus.
Also, strength and rigidity are required of a drum shaft, a bearing, a frame, etc. for supporting the flywheel, and this results in a disadvantage in costs. Also, the addition of the flywheel leads to a corresponding increase in the necessary starting torque of a motor and therefore, a larger motor becomes necessary, and this means disadvantages in space and costs.
Further, in the case of a specification wherein the process speed of image formation is slowed down in conformity with the kind of the transfer material such as thick paper or OHT, there is the disadvantage that the inertial effect of the flywheel is greatly decreased. This is due to the fact that the inertial effect is proportional to the square of the speed, and when for example, the process speed is a half speed, the inertial effect becomes ¼, and when the process speed is a quarter speed, the inertial effect becomes {fraction (1/16)}. As a result, the flywheel is effective at {fraction (1/1)} speed (standard speed), but in a low speed mode, there is a case where the effect of the prevention of banding is not obtained. If the amount of inertial is determined in accordance with a low speed, the above-described various disadvantages will greatly increase.
Also, a scissors gear often used in the driving system of an automobile can effect smooth driving because a main gear and a sub-gear are mutually rotatably biased and backlash is eliminated, and can be expected to be effective to prevent banding, but is difficult to assemble and is not popular in business machines including image forming apparatuses.
Description will now be made of a problem peculiar to a method of coupling the drum shaft and the gear together in the aforedescribed example of
Gleitz Ryan
Grimley Arthur T.
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