Electrophotography – Image formation – Combined or plural functions by single component
Reexamination Certificate
2002-08-09
2004-10-05
Ngo, Hoang (Department: 2852)
Electrophotography
Image formation
Combined or plural functions by single component
C399S149000, C399S354000
Reexamination Certificate
active
06801735
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus which uses an electrophotography method or an electrostatic method, such as a copying machine or a printer.
2. Related Background Art
In recent years, image forming apparatuses, such as copying machines and printers, of a cleanerless type have been put into practical use. This type of apparatus eliminates or significantly reduces waste toner by recycling residual toner using a developing apparatus after large transfer.
FIG. 1
is a schematic view of an example of a cleanerless image forming apparatus.
A reference numeral
104
denotes a rotating drum type electrophotography photosensitive body (photosensitive drum), serving as an image bearing body. The photosensitive body
101
is turned counterclockwise as indicated by an arrow at a predetermined circumferential speed. A reference numeral
102
indicates a magnetic brush member (magnetic brush charger), serving as a contact charging member, which brush member is disposed, a charging location a being formed with a magnetic brush in contact with the photosensitive drum
101
. A charging bias is applied to the magnetic brush member
102
by a bias power supply S
1
to uniformly charge the rotating photosensitive drum
101
by contact so that predetermined polarity and a predetermined potential are provided.
The uniformly charged surface of the rotating photosensitive drum
101
is subjected to image exposure L by image exposing means, not shown, as electrostatic latent image forming means, thus reducing the charging potential of the exposed bright part of the photosensitive drum surface, so that an electrostatic latent image corresponding to an image exposing pattern is formed on the photosensitive drum surface.
A reference numeral
103
indicates a developing apparatus, which develops the electrostatic latent image on the surface of the rotating photosensitive drum
1
to form a toner image ta. A reference numeral
103
a
indicates a developing member, such as a developing sleeve roller or a developing roller, to which a predetermined bias is applied. The developing member
103
a
and the photosensitive drum
101
are opposite to each other to provide a developing location b.
A reference numeral
104
indicates a transferring roller (conductive roller) serving as transferring means, which is pressed against the photosensitive drum
101
in a predetermined way to form a transferring location (transferring nip) c. A transferring sheet P is fed to the transferring location c from a sheet feeding mechanism, not shown, at predetermined control times, clamped at the transferring location c, and conveyed. While the transferring sheet P passes the transferring location c, a predetermined transferring bias, which is opposite in polarity to charged toner, is applied to the transferring roller
104
by a bias power supply S
3
to electrostatically transfer the toner image ta on the photosensitive drum
101
onto the transferring sheet P. A combination of reference characters, tb, indicates the toner image transferred onto the transferring sheet P.
After it passes the transferring location c, the transferring sheet P is separated from the photosensitive drum
101
, conveyed to fixing means, not shown, subjected to toner image fixing therein, and ejected as a print.
As the photosensitive drum
101
rotates, residual toner tc deposited on the drum due to toner image transfer onto the transferring sheet P goes through the charging location a to the developing location b, where the residual toner is cleaned (recovered) from the drum by the developing apparatus
102
simultaneously with developing.
Cleaning residual toner from the drum simultaneously with development is to recover the residual toner tc left on the photosensitive drum
101
due to image transfer, using fog removal bias (DC voltage applied to the developing means and fog removal potential difference V back, or difference between photosensitive drum surface potentials) at the developing apparatus
103
during development in the following steps. The treatment is performed in parallel with image forming steps, such as charging, exposure, development, and transfer, if the image area is longer in the direction of rotation of the photosensitive drum
1
than the circumference of the photosensitive drum
1
. This allows the residual toner tc to be recovered at the developing apparatus
103
and used in the following steps, thus eliminating waste toner. In addition, because no cleaning apparatus is necessary, space is significantly saved and the apparatus can markedly be reduced in size.
Contact charging apparatuses, that is, apparatuses which bring a contact charging member to which a voltage is applied into contact with a body to be charged to charge the body, have advantages over corona chargers of non-contact type because of a small amount of ozone produced, low electric power consumption, and so on. Thus charging apparatuses of such a type have been put into practice as charging means for a body to be charged, such as a photosensitive drum, in an image forming apparatus.
A magnetic brush member is preferably used as a contact charging member.
A magnetic brush member is electrically conductive magnetic particles which are magnetically bound on a sleeve, containing a magnet, to provide a magnetic brush. When it is stationary or rotates, the magnetic brush member is brought into contact with a charged body, and a voltage is applied to the member to start charging.
Alternatively, a fur brush member, a brush into which electrically conductive fibers are formed, or an electrically conductive roller (charging roller), a roll into which electrically conductive rubber is formed, is preferably used as a contact charging member.
Using an organic photosensitive body having a surface layer over which electrically conductive particles are spread as an image bearing body or an amorphous silicon photosensitive body in addition to a contact charging member as described above allows a charging potential almost equal to the DC component of a bias applied to the contact charging member to be provided on the surface of the image bearing body. Such a charging method is called “injection charging”. Using a small amount of electric power, injection charging can be performed without producing ozone because discharging is not done, using, for example, a corona charger to charge a body to be charged. This charging method has been a focus of attention.
However, when image forming is repeated, using a cleanerless image forming apparatus as described above, the preceding image is slightly left, that is, a “positive ghost” occurs because residual toner is not recovered by developing means. A positive ghost is caused by the part of the photosensitive drum surface which is not charged under the residual toner tc on the photosensitive drum
101
when the toner passes the charging location a. This phenomenon is distinctive if the contact charging member
102
is contaminated.
In charging the part of the photosensitive drum surface under the residual toner tc using the contact charging member
102
, it is essential to remove the residual toner tc from the photosensitive drum
101
during charging and return the toner to the photosensitive drum surface after charging to recover it using the developing apparatus
103
.
To solve this problem, means for preventing a positive ghost is available which makes it easy to take the residual toner tc in the magnetic brush member
102
by applying a bias opposite in polarity to a charging bias by a bias power supply to an electrically conductive brush
105
, auxiliary means for erasing the traces of the preceding image, which is disposed in contact with the photosensitive drum
101
upstream of the transferring location c in the direction of photosensitive drum rotation and downstream of the charging location a in the direction of photosensitive drum rotation.
The residual toner tc, which is conveyed from the transferring location c to a contact d between the surface
Gomi Fumiteru
Hashimoto Koichi
Komiya Yoshiyuki
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