Electrophotography – Control of electrophotography process – Control of exposure
Reexamination Certificate
2002-12-11
2004-12-14
Chen, Sophia S. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of exposure
C399S055000, C399S129000
Reexamination Certificate
active
06832058
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an image forming apparatus utilizing an electrophotographic method such as, for example, a copying machine, a printer, and a facsimile machine.
At present, as regards an image forming apparatus of a certain kind utilizing an electrophotographic method, it is widely utilized an image forming apparatus of a reverse development type in which the surface of a drum-shaped photoreceptor which is an image forming member and is driven to rotate is charged to the specified polarity (negative, for example) by a charging means consisting of a charging device using, for example, corona discharge, an electrostatic latent image is formed by exposing the surface of this photoreceptor image-wise to an image exposure means using, for example, a laser optical system, and the electrostatic latent image is visualized through the toner deposition on the image-wise exposed area of the photoreceptor by a developing means using a two-component developer composed of toner particles which have been triboelectrically charged to the same polarity as the surface potential of the photoreceptor (negative, for example) and carrier particles (positively charged). In this case, in making toner particles adhere to the image-wise exposed area of the photoreceptor, a development bias voltage of the same polarity as the surface potential of the photoreceptor (negative polarity, for example) is applied to a developing roller (developer carrying member) which makes up a developing means and is arranged opposite to the photoreceptor with the developing region positioned in between.
When an image formation sequence is started by means of such an image forming apparatus, problems of various kinds are produced in some cases, depending on the relationship between the start timing of the application of the charging voltage and the start timing of the application of the development bias voltage. In the following, such problems will be explained with reference to FIG.
5
and FIG.
6
.
For example, as shown in
FIG. 5
, for the non-print area of the photoreceptor from which no toner image is to be transferred to an image recording medium such as a transfer paper sheet (hereinafter referred to as a recording medium simply) which is positioned, with respect to the rotating direction of the photoreceptor, at the downstream side of the print area of the photoreceptor from which a toner image is to be transferred to the recording medium, in the case where a condition is set in such a way that the development bias application region (Ra) to which a development bias voltage is to be applied substantially coincides with the region where the surface potential of the charged photoreceptor is raised to a specified potential value (Rb), to state it concretely, in the case where a condition is set so as to make the start point on the photoreceptor of the application of the charging voltage (Pb
1
) come to a more downstream position than the start point on the photoreceptor of the application of the developing bias voltage (Pa
1
), a “carrier adhering” phenomenon, in which carrier particles in the developer carried on the developing sleeve adheres on the surface of the photoreceptor, is produced in the region between a place located in the charging voltage application region facing the charging means at the starting time of the application of the charging voltage (Pb
1
) (for example, the place which is located at the downmost stream position with respect to the rotating direction of the photoreceptor in the charging voltage application region (i), refer to FIG.
1
), and the place where the surface potential has the same potential value as the development bias voltage (Vd) at the rising time of the surface potential (the place which is located in the developing region P at the starting time of the application of the development bias voltage (Pa
1
) (ii)). In this case, compared to the rise characteristic at the time of application of the development bias voltage shown by the wave form (A) in
FIG. 5
being sharp, the rise characteristic of the charge potential of the photoreceptor at the time of the application of the charging voltage is more gentle; therefore, by the setting of a condition to make the start point of the application of the charging voltage (Pb
1
) more downstream than the start point of the application of the development bias voltage (Pa
1
), it is obtained a state in which the development bias application region (Ra), which means the region being subjected to the application of the development bias voltage, comes to substantially coincide with the region where the charge potential has the specified potential value (Rb).
Further, also at the ending time of an image formation sequence, in the case where the stop point on the photoreceptor of the application of the charging voltage (Pb
2
) is determined to be more upstream than the stop point on the photoreceptor of the application of the development bias voltage (Pa
2
), a “carrier adhering” phenomenon, in which carrier particles in the developer carried on the developing sleeve adhere on the photoreceptor surface, is produced in the region between the place where the surface potential of the charged photoreceptor has the same potential value as the development bias voltage (Vd), which is lower than the specified surface potential (Vh) at the falling time of the surface potential (the place which is located at the developing region P at the stopping time of the development bias voltage (Pa
2
)), and the place which is located at the developing region P at the stopping time of the application of the charging voltage (Pb
2
).
On the other hand, for example, as shown in
FIG. 6
, in the case where, in order that the development bias voltage may be applied even to the region where the surface potential of the charged photoreceptor has not been raised to the specified potential value, when an image formation sequence is started, the application region of the development bias voltage (Ra) is determined to be larger than the region (Rb) where the surface potential of the charged photoreceptor is kept at the specified potential state, to state it concretely, in the case where the start point on the photoreceptor of the application of the charging voltage (Pb
1
) is determined to substantially coincide with the start point on the photoreceptor of the application of the development bias voltage (Pa
1
), toner particles in the developer carried on the developing sleeve adhere on the surface of the photoreceptor to form, for example, an unnecessary stripe-shaped toner image on the photoreceptor, in the region where the potential difference between the surface potential and the development bias voltage is large between a place which is located in the charging voltage application region at the starting time of the application of the charging voltage (Pb
1
) (for example, the place which is located at the downmost stream position with respect to the rotating direction of the photoreceptor in the charging voltage application region (i)), and the place where the surface potential of the charged photoreceptor has been raised to the same value as the development bias voltage (Vd) at its rising time (ii).
Further, also at the ending time of an image formation sequence, in the case where the stop point on the photoreceptor of the application of the charging voltage (Pa
2
) is determined to substantially coincide with the stop point on the photoreceptor of the development bias voltage (Pb
2
), toner particles in the developer carried on the developing sleeve adhere on the surface of the photoreceptor to form, for example, an unnecessary stripe-shaped toner image on the photoreceptor in the region where the difference between the surface potential and the development bias voltage is large between the place where the surface potential of the charged photoreceptor has the same potential value as the development bias voltage (Vd), which is lower than the specified potential value (Vh), at its falling time, and the place which is located at th
Akita Hiroshi
Kimura Takenobu
Sato Yotaro
Shigeta Kunio
Chen Sophia S.
Frishauf Holtz Goodman & Chick P.C.
Konica Corporation
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