Electrophotography – Image formation – Development
Reexamination Certificate
1998-07-24
2001-09-18
Grainger, Quana M. (Department: 2852)
Electrophotography
Image formation
Development
C399S302000, C399S223000
Reexamination Certificate
active
06292641
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an image forming apparatus and, more particularly, to an image forming apparatus having a plurality of developing units selectively operated to develop, for example, different color component images.
2. Description of the Related Art
Japanese Laid-Open Patent Application No. 64-971 discloses a technique for selectively driving a plurality of developing units by using a single drive power source. A power generated by the drive power source is transmitted to each of the developing units via a train of gears and a clutch provided to each of the developing units. Accordingly, one of the developing units can be selectively operated by operating the clutch.
According to this technique, since a power of the drive power source is transmitted to each clutch, a complex train of gears is needed and a space for accommodating the gears is needed. Accordingly, this technique is not appropriate for reducing size of an image forming apparatus using this technique.
Japanese Laid-Open Patent Application No. 4-280273 discloses a mechanism for selectively operating one of a plurality of developing units. This mechanism includes a drive gear which is driven by a single drive power source and four shift gears connected to respective developing units. Each of the shift gears is disengageably engaged with the drive gear by means of a pressing cam so that the shift gears are selectively engaged with the drive gear.
According to the above-mentioned mechanism, since the four shift gears are selectively engaged with the drive gear, a complex mechanism is needed for operating the pressing cam.
Additionally, Japanese Laid-Open Patent Applications No. 5-249833, No. 5-216337. No. 8-179621 and No. 5-333701 disclose developing apparatuses having a plurality of developing rollers such as a first developing roller for developing a latent image on a photosensitive drum by a first component color and a second developing roller for developing a latent image by a second component color. In these apparatuses, when a developing operation is switched from one of the developing rollers to another one of the developing rollers, a bristle cutting operation is performed by reversing the developing roller after the developing operation by the one of the developing units is completed.
However, the above-mentioned patent documents do not refer to a mechanism for driving each of the developing rollers. If each of the developing rollers has an individual drive power source, the size of the developing apparatuses is increased which results in an increase in the size of an image forming apparatus using such a developing apparatus. Accordingly, it has been suggested to use a common drive power source for the developing rollers.
When such a mechanism in which a power is selectively transmitted from a single common drive power source to a plurality of developing rollers is used, an engagement of a power transmitting gear is switched from one of the developing rollers to another one of the developing rollers. When a gear is engaged with another gear, the engagement can be smoothly performed when a top of a tooth of one of the gears faces a bottom of a tooth of the other one of the gears. On the other hand, if a top of a tooth of one of the gears faces a top of a tooth of the other one of the gears, it may be difficult to make a smooth engagement since the tops of the teeth run against each other. Accordingly, if such a condition occurs in the above-mentioned developing apparatus, a smooth switching operation of the driving mechanism of the developing rollers cannot be performed.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide an improved and useful image forming apparatus in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide an image forming apparatus which can selectively drive a plurality of developing units by a simple structure accommodated in a small space.
Another object of the present invention is to provide an image forming apparatus in which a switching operation of a driving mechanism of developing rollers can be smoothly performed.
A further object of the present invention is to provide an image forming apparatus which can provide an increased time for switching operations of developing rollers without increasing a total image processing time.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention an image forming apparatus provided with an intermediate transfer member and a plurality of image stations arranged along a direction of movement of the intermediate transfer member, each of the image stations comprising an image carrying member and a plurality of developing units so that latent images sequentially formed on the image carrying member are developed by one of the developing units and developed images are transferred onto the intermediate transfer member so as to be superimposed thereon, each of the image stations of the image forming apparatus comprising:
a developing unit driving system driving the plurality of developing units; and
a switching mechanism switching a transmission path of a power generated by the developing unit driving system so that the power is selectively transmitted to one of the plurality of developing units.
According to the above-mentioned invention, a plurality of developing units can be driven by the single common driving system with a simple structure occupying a small space.
In one embodiment of the present invention, a plurality of developing units are provided in each of the image stations, and the switching mechanism of each of the image stations includes:
a rotational member supporting a plurality of driving-side power transmission mechanisms each of which is a final stage of the developing unit driving system; and
a rotational driving mechanism rotating the rotational member, and
each of the plurality of developing units is connected to a driven-side power transmission mechanism selectively connectable to one of the driving-side power transmission mechanisms in accordance with a rotational position of the rotational member.
Accordingly, a rapid switching of the power transmission path can be reliably performed.
Additionally, the developing unit driving system, the rotational member and the rotational driving mechanism constituting the switching mechanism may be incorporated into a single unit so that an efficient assembly operation can be achieve.
Additionally, the developing unit driving system may include a power transmission shaft used as a center of rotation of the rotational member so as to simplify a structure of the developing unit driving system.
In one embodiment of present invention, the rotational driving mechanism may include a worm gear and a motor for driving the worm gear, the worm gear being engaged with a sector gear provided to the rotational member so as to rotate the rotational member. The motor may be a reversible motor.
Alternatively, the rotational driving mechanism may include a cam engaged with a cam follower provided to the rotational member so that a reverse operation of the rotational driving mechanism is not needed. The cam may include an annular groove, and the cam follower may movably fit in the annular groove so that there is no need to apply a force to the cam follower.
Further, the rotational driving mechanism may include a solenoid actuator for swinging the rotational member so that the rotational driving mechanism has a simple structure.
In one embodiment of the present invention, the developing unit driving system may comprise a motor and a train of gears connected to the motor.
Additionally, each of the driving-side power transmission mechanisms may comprise a gear, and each of the driven-side power transmission mechanisms may comprise a gear.
Additionally, there is provided according to another aspect of the present invention a developing apparatus for developing a latent image formed on an i
Kibune Hideaki
Saitoh Masanori
Takeyama Yoshinobu
Yanagawa Nobuyuki
Grainger Quana M.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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