Electrophotography – Machine operation
Reexamination Certificate
2000-03-21
2001-07-31
Chen, Sophia S. (Department: 2852)
Electrophotography
Machine operation
C399S167000, C399S299000
Reexamination Certificate
active
06269229
ABSTRACT:
RELATED APPLICATION
This application is based on application Ser. No. 11-088237 filed in Japan, the entire content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus applying color electrophotographic technology such as a color copier and a color printer.
2. Description of the Related Art
An electrophotographic process is used for image forming apparatuses such as digital copiers and laser printers. The electrophotographic process is to form an electrostatic latent image on the surface of a photoconductor drum by use of a photoconduction phenomenon and cause particles (toner) charged to the opposite polarity to adhere to the electrostatic latent image by electrostatic force to thereby form a visible image (development). Conventionally, dominating image forming apparatuses have been ones using only black toner and forming images (monochrome images) with the toner and the color of the paper. In recent years, however, image forming apparatuses forming color images with four colors, i.e. the three primary colors (yellow, magenta and cyan) and black have been becoming dominant.
Normally, in a tandem image forming apparatus, to form a color image, four photoconductor drums corresponding to the four colors are used and the four colors are superimposed one on another on the sheet of paper. Since colors are formed by superimposing the four colors, a color shift results in a color different from the intended one. Moreover, human eyes are sensitive even to a slight color shift. For this reason, in order that no color shift occurs, it is necessary to precisely convey paper and rotate the four photoconductor drums so as to be in synchronism with one another with high precision. Moreover, inconstant rotation speeds of the photoconductor drums significantly affect the color development.
Conventional image forming apparatuses include a type using one motor for one photoconductor drum, that is, using four drive motors for driving the four photoconductor drums, and a type in which the power of one drive motor is transmitted to the four photoconductor drums by a transmitting mechanism. The former type is inevitably high in cost because as many motors as the photoconductor drums are necessary and it is difficult to drive the photoconductor drums so as to be in synchronism with one another. In the latter type, the rotation speeds of the photoconductor drums tend to be inconstant because of vibrations generated by the gears and timing belts of the power transmitting system.
FIG. 6
shows an outline of an image forming apparatus of the latter type and photoconductor drum driving systems.
A charging unit
50
, an exposure unit
51
, a developer unit
52
and a transfer unit
53
are disposed around each of the photoconductor drums
1
K,
1
Y,
1
M,
1
C corresponding to the colors. One transfer belt
14
is disposed along all the photoconductor drums
1
K,
1
Y,
1
M,
1
C. Toner images developed on the photoconductor drums are transferred to the transfer belt
14
. The power of a drive motor
52
is transmitted to each pulley
55
by timing belts and gears. The power is further transmitted from the pulleys
55
to the photoconductor drums
1
K,
1
Y,
1
M,
1
C by gears and timing belts
56
. Further descriptions of the operations, functions and more detailed structures of these elements are omitted because they are similar to those of a conventional tandem color image forming apparatus.
In such conventional driving of the photoconductor drums
1
K,
1
Y,
1
M,
1
C, vibrations are generated due to the mesh between gears and between the timing belts
56
and pulleys
55
. Moreover, resonance occurs when the frequency of the vibrations coincides with the characteristic frequency of the power transmitting systems. The vibrations lead to inconstant rotation speeds of the photoconductor drums. This results in slight disaccord in rotation timings of the four rotary drums. Such inconstant rotation speeds of the photoconductor drums and disaccord in rotation timings of the photoconductor drums adversely affect images.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above-mentioned problems.
Another object of the present invention is to provide an image forming apparatus preventing the rotation timings of photoconductor drums from disaccording with one another.
Yet another object of the present invention is to provide an image forming apparatus forming images without any color shifts or color nonuniformness.
Still another object of the present invention is to provide an image forming apparatus preventing the rotation timings of photoconductor drums from disaccording from one another, and forming images without any color shifts or color nonuniformness.
These and other objects are attained by an image forming apparatus having first and second photoconductor drums, a driving member for rotating the first and second photoconductor drums, and a restricting member coupled to the first and second photoconductor drums to restrict rotations of the first and second photoconductor drums by associating the rotations apart from the driving member.
The invention itself, together with further objects and attendant advantages, will best be understood by reference to the following detailed description taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5016062 (1991-05-01), Rapkin
patent: 5216475 (1993-06-01), Ohno
patent: 6142690 (2000-11-01), Yoshimura et al.
patent: 9-114171 (1997-05-01), None
Chen Sophia S.
McDermott & Will & Emery
Minolta Co. , Ltd.
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