Electrophotography – Having particular structure – Modular or displaceable
Reexamination Certificate
2000-06-08
2002-04-23
Grimley, Arthur T. (Department: 2852)
Electrophotography
Having particular structure
Modular or displaceable
C222SDIG001, C399S111000, C399S358000, C399S359000
Reexamination Certificate
active
06377765
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming unit, a latent image carrier unit, a developing unit and an image forming apparatus. In particular, the present invention relates to an image forming unit, a latent image carrier unit, a developing unit and an image forming apparatus which are characterized by a mechanism for enabling the user to replace the latent image carrier unit (or photosensitive drum unit) and the developing unit independently of each other and a mechanism for pressing a developing roller of the developing unit onto a photosensitive drum of the photosensitive drum unit, operable following at least one of a mounting movement when the photosensitive drum unit is mounted to the developing unit and a driving movement in the image forming unit.
2. Description of the Related Art
The image forming apparatus of an electronic photographic recording system, such as a copier or a printer, has widely prevailed in office use due to its high operation speed, high resolution and low noise, and the market thereof has recently been widened even to a personal use in which a lower machine cost, a smaller machine size and/or a higher resolution image are required.
In the prior art printer of an electronic photographic recording system using a static latent and image forming process, a static latent image is formed on a uniformly charged surface of a photosensitive drum by exposing it to a laser optical system or an LED array system in accordance with image information.
Then, in a developing process, a visible toner image is developed by sticking charged toner onto the static latent image on the photosensitive drum by using a developing roller, and the toner image is then statically transferred to a recording medium by using a transfer device. Thereafter, the transferred visible image is fixed on the recording medium by heat, pressure or light, and the recording medium is discharged to a stacker.
In such a printer of an electronic photographic recording system, the toner not transferred but left on the surface of the photosensitive drum is removed therefrom by a cleaning blade, and returned to a toner box of the developing unit through a toner returning mechanism for repeated use. The printer of an electronic photographic recording system provided with such a toner returning mechanism will be described below with reference to
FIGS. 20 and 21
.
In
FIG. 20
, a structure of one example of the printer of an electronic photographic recording system with the prior art toner returning mechanism is conceptually illustrated, wherein a photosensitive drum unit
60
includes a photosensitive drum
61
and a cleaning unit
62
having a cleaning blade
63
arranged with the drum in a unit, and a developing unit
70
is detachably mounted to the photosensitive drum unit
60
to form an image forming unit which in turn is detachably mounted to a printer device
100
.
The developing unit
70
is provided with a doctor blade
71
, a developing roller
72
comprising a magnetic roller and a sleeve, agitators
73
and
74
and a toner chamber
75
. A toner cartridge
83
is detachably mounted to the developing unit
70
, for dispensing toner into the developing unit
70
through an opening provided in a cartridge support member
81
.
In the image forming unit of such a structure, a toner returning mechanism
90
is provided to couple the cleaning unit
62
of the photosensitive drum unit
60
to the toner chamber
75
of the developing unit
70
for recycling the toner which is not transferred but is removed from the photosensitive drum
61
by the cleaning unit
62
.
A corona charger
86
is arranged at the opening in the housing of the image forming unit, and a transfer device
87
is disposed beneath the photosensitive drum unit
60
. An optical unit
88
such as an LED array is disposed downstream from the corona charger
86
in the sense of the rotational direction of the photosensitive drum.
In the above-mentioned printer of an electronic photographic recording system, after the photosensitive drum
61
is uniformly charged by the corona charger
86
, a static latent image is formed on the surface thereof by a light from the optical unit
88
in accordance with image information or printing information, and conveyed to a developing zone as the photosensitive drum
61
rotates. In the developing zone, a toner layer on the developing roller
72
is attracted to the static latent image on the photosensitive drum
61
by static attraction to form a visible toner image which in turn is transferred to the recording medium by the transfer device
87
and then fixed by the fixing device
88
. Finally, the recording medium
110
on which the visible image has been fixed is discharged to a stacker
101
.
In this connection, the surface of the photosensitive drum
61
is cleaned by the cleaning blade
63
after the transfer, and the removed toner is received by a waste toner tank
64
of the cleaner unit
62
. Thereafter, the surface of the photosensitive drum
61
is decharged by a decharging means (not shown) to resume the initial state.
The non-transferred waste toner is made to return from the cleaner unit
62
to the toner chamber
75
of the developing unit
70
through the toner returning mechanism
90
.
FIG. 21
is a plan view of the above-mentioned toner returning mechanism
90
including a flexible tube
91
and a rotatable coil member
92
accommodated in the flexible tube
91
. One end of the coil member
92
is connected to a helical gear
94
intermeshed with a helical gear
93
rotating in association with a coil member
76
provided in the waste toner tank
64
to return the waste toner in the waste toner tank
64
to the toner chamber
75
via the flexible tube
91
.
In the printer of an electronic photographic recording system with the prior art toner returning mechanism
90
, it is substantially impossible for the user to replace the photosensitive drum unit
60
and the developing unit
70
separately from each other although the developing unit is apparently detachable from the photosensitive drum unit
60
, since the toner returning mechanism
90
is firmly connected to the photosensitive drum unit
60
and the developing unit
70
.
In an example of a specification, for example, the developing unit is guaranteed to perform the printing of approximately ten thousand sheets, while the photosensitive drum unit is guaranteed to perform the printing of approximately fifty thousand sheets. In the printer of an electronic photographic recording system with the prior art toner returning mechanism, however, the image forming unit consisting of the photosensitive drum unit and the developing unit as described above must be replaced as a one-piece part, which means that the duration of replacement life of the image forming unit is necessarily matched with the developing unit having a shorter duration of replacement life, whereby it is impossible to effectively use the photosensitive drum.
In this regard, the duration of life of the developing unit is decided by that of the developing roller and/or an amount of toner contained therein, while the duration of life of the photosensitive drum unit is decided by that of the photosensitive drum.
A single component developing method using a non-magnetic developing agent, particularly in such a method of a contact developing system wherein the development is carried out by the contact of the photosensitive drum with the developing roller is believed advantageous for realizing the above-mentioned requirement for low cost, size reduction or high resolution image quality. However, printing defects, such as blur, are liable to occur in the above method if the photosensitive drum and the developing unit are detachably connected to each other so that the user is capable of replacing one of them with a fresh one, unless the photosensitive drum is assuredly in tight contact with the developing roller.
SUMMARY OF THE INVENTION
To solve such a problem, an object of the present invention is to provide
Hikita Tomohiro
Kuwabara Nobuo
Shishido Hisao
Armstrong Westerman & Hattori, LLP
Fujitsu Limited
Grimley Arthur T.
Ngo Hoang
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