Electrophotography – Control of electrophotography process – Control of transfer
Reexamination Certificate
2000-12-29
2002-09-24
Chen, Sophia S. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of transfer
Reexamination Certificate
active
06456804
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus for transferring, to a transferring material such as paper or a plastic sheet, a transferable image formed on a first image bearing body such as an electrophotographic photosensitive body, an electrostatic recording dielectric body or a magnetic recording magnetic body by a known image forming process means such as electrophotography, an electrostatic recording method or a magnetic recording method.
2. Related Background Art
FIG. 7
is a schematic diagram showing an example of transferring apparatus in a conventional image forming apparatus. This transferring apparatus is of a roller transferring type.
Reference numeral
1
denotes a rotating drum type electrophotographic photosensitive body (hereinafter referred to as a photosensitive drum) which is used as a first image bearing body. This photosensitive drum
1
is rotatingly driven in a clockwise direction indicated by an arrow at a predetermined peripheral speed (process speed) and a toner image corresponding to a target image information is formed on an outer circumferential surface of the photosensitive drum
1
as a transferable image (visualized image) by an operation of an electrophotography process appliance (not shown).
Reference numeral
5
denotes an electrically conductive elastic roller (herein after referred to as a transferring roller) which is used as transferring means (contact transferring member). This transferring roller
5
is disposed in parallel with the photosensitive drum
1
, pressed to the photosensitive drum
1
at a transferring location under a predetermined pressure so as to form a transferring nip portion N and rotatingly driven in a counterclockwise direction indicated by an arrow which is a forward direction of the photosensitive drum
1
at a predetermined peripheral speed nearly corresponding to the rotating peripheral speed of the photosensitive drum
1
.
Reference character P denotes a transferring material which functions as an image bearing body. This transferring body P is fed from a sheet feeding portion (not shown) and conveyed at a predetermined controlled timing to the transferring nip portion N which is a pressure contact portion between the photosensitive drum
1
and the transferring roller
5
. In other words, a top of the transferring material P is detected with a sensor
8
and a timing is adjusted so that a toner image forming position on the photosensitive drum
1
is matched with a writing start position on the top of the transferring material P.
The transferring material P which is conveyed at the predetermined timing to the transferring nip portion N is inserted under a predetermined pressure and conveyed in the transferring nip portion N, electric charges having a polarity reverse to that of a toner are imparted to a rear surface of the transferring material P by a function of a bias voltage applied to the transferring roller
5
from a power source
9
by way of a roller core metal and a toner image on the photosensitive drum
1
is transferred to the transferring material P with these electric charges.
After transferring the toner image, excessive electric charges are removed from the rear surface of the transferring material P using an antistatic wire or the like, the transferring material P is sent into a fixing apparatus (not shown) while bearing the transferred toner image and the toner image is fixed permanently on the transferring material P.
After the transferring material P has passed through the transferring nip, a surface of the photosensitive drum
1
is cleaned by wiping off the toner remaining after transferring the toner image using a cleaning apparatus (not shown) and used once again for forming an image.
The applicant of the present invention has already proposed an active transfer voltage control system (hereinafter referred to as ATVC system) which is capable of controlling the bias voltage to the above described transferring roller
5
so that favorable transferring performance can be always obtained regardless of changes in environmental conditions (Japanese Patent Application Laid-Open No. 2-123385).
Specifically, this ATVC system rotates the photosensitive drum
1
prior to an image forming step (preliminary rotation), applies the bias voltage to the transferring roller
5
during the preliminary rotation, measures an output current value at this time with an ammeter
10
and feeds back a measured value to a controller
11
. The ATVC system adjusts the bias voltage from the power source
9
with the controller
11
so that the above described output current value is a predetermined value and applies an adjusted voltage or a constant voltage having a value corrected with a coefficient or the like to the transferring roller
5
at a transferring time, thereby making it possible to always obtain a transferring bias voltage having an appropriate constant voltage characteristic regardless of remarkable variations of impedance of the transferring roller
5
independently of the environment.
Since the above described conventional system adjusts a constant bias voltage to be applied to the transferring roller
5
so that the current has the predetermined value in a condition where the photosensitive drum
1
is in direct contact with the transferring roller
5
, however, the conventional system has a defect that is causes improper transferring in cases where:
1) The transferring material P has high impedance (for example, in a case where a thick sheet is used or a print is made on a rear surface of the transferring material P which is used once for printing); and
2) The transferring roller
5
has low impedance.
This defect will be described using a figure of voltage-current characteristic curve of the power source for applying the bias voltage to the transferring roller
5
shown in FIG.
8
.
In
FIG. 8
, a curve A represents relationship between a bias voltage V to the transferring roller
5
and an output current I when the photosensitive drum
1
and the transferring roller
5
are rotated in a direct contact condition, and a voltage Va is determined in this case so as to obtain an output current Ia during the preliminary rotation and used as a constant bias voltage to the transferring roller
5
at a transferring step during image formation.
When paper (a transferring material-
1
) is used as the transferring material P, a V-I characteristic curve is a curve P
1
in a condition where the above described transferring material P
1
is inserted in a transferring nip portion N between the photosensitive drum
1
and the transferring roller
5
, whereby application of the constant bias voltage Va produces a transferring current I
1
. It may be questioned whether the transferring current I
1
is sufficient, but the toner image is transferred favorably in this case since the transferring current I
1
is higher than a critical transferring current value It as shown in FIG.
8
.
When a transferring material having high impedance, for example, thick paper (a transferring material-
2
) is used, however, the V-I characteristics is as represented by a curve P
2
which is nearer a V axis and the bias voltage Va produces only a transferring current I
2
which is lower than It, thereby causing improper transferring.
Furthermore, a curve A′ in
FIG. 8
represents a V-I characteristic in a case where impedance of the transferring roller
5
is lower than that represented by a curve A, and in this case, a voltage corresponding to the predetermined current value Ia during the preliminary rotation is Va′ and a constant bias voltage which is to be applied at the transferring time is Va. In this case, a transferring current for the transferring material-
1
is also lower than the critical transferring current value It, thereby causing improper transferring.
When the transferring roller
5
has rather low impedance, the curves P
1
and P
2
corresponding to the curve A′ are actually represented as curves which are slightly farther from the V
Izawa Satoru
Naito Norihito
Tanaka Yuko
Canon Kabushiki Kaisha
Chen Sophia S.
Fitzpatrick ,Cella, Harper & Scinto
LandOfFree
Image forming apparatus for enabling to selectively apply a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image forming apparatus for enabling to selectively apply a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image forming apparatus for enabling to selectively apply a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2867964