Image forming apparatus having a developing-device assembly comprising developing devices

An image forming apparatus includes a developing-device assembly, developing rollers, roller drive gears, a transmission gear, a roller drive motor, a take-in gear, and a generator. The developing-device assembly rotates and stops at a development position where a developing device faces a photosensitive member, thereby switching a developing device to the next one. At the development position, the developing roller provided on each of the developing devices supplies toner to the photosensitive member, and the roller drive gear attached to each developing roller meshes with the transmission gear. The roller drive motor transmits mechanical power to the transmission gear via a power transmission path. The take-in gear disposed coaxial with a rotational center of the developing-device assembly is meshed with the transmission gear. The generator is housed in the developing-device assembly and has a gear meshing with the take-in gear.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an image forming apparatus, and more particularly to an image forming apparatus that has a developing-device assembly, which is rotated to switch a plurality of developing devices, and forms an image based on electrophotography.

2. Description of the Related Art

An image forming apparatus that forms an image based on electrophotography includes a photosensitive member, a charging device, an exposing device, a developing device, a transfer device and a fixing device. An image forming apparatus for monochromatic printing has one developing device, whereas an image forming apparatus for multi-color printing includes a plurality of developing devices and may additionally include an intermediate transfer member.

The image forming apparatus for multi-color printing includes a developing-device assembly comprising a plurality of developing devices. The developing-device assembly is rotated like a cylinder of a revolver-pistol, whereby each developing device is switched. Each developing device includes a developing roller and a toner container. The toner container contains toner to be supplied to the developing roller.

In general, the multi-color printing image forming apparatus forms a multi-color image using three colors, yellow, magenta and cyan, or four colors, i.e. these colors plus black. If the toner of any one of these colors runs short, a multi-color image of a desired color tone cannot be obtained. It is thus necessary to understand the residual amount of toner in each developing device.

The residual toner amount in the toner container cannot be confirmed from the outside of the image forming apparatus, so a sensor for detecting the residual toner amount is provided for each toner container. In this case, since the toner container rotates along with the developing-device assembly, such a sensor cannot be attached by wiring. To cope with the problem, a transparent window is provided at a part of the toner container, and the residual toner amount is optically detected through the window.

In a case where toner adheres to the inside of the window, however, the residual toner amount may not correctly be detected. In order to enhance the reliability in detection of the residual toner amount, it is desired to directly provide the sensor on the toner container. However, since the developing-device assembly rotates, electric power cannot be supplied to the sensor.

Jpn. Pat. Appln. KOKAI Publication No. 5-66681 discloses an image forming apparatus that uses a method of supplying power to a rotary member. According to this publication, a generator is provided between a rotary photosensitive drum and a shaft that supports the photosensitive drum, and the generator supplies electric power to a heater built in the photosensitive drum. In this case, the generator generates power when the photosensitive drum rotates. In addition, a battery is provided to enable power supply even when the photosensitive drum is at rest.

In the case where this method is applied to supply electric power to devices mounted in the developing-device assembly, the following problem arises. Since the developing-device assembly rotates only intermittently, power is supplied only when the developing-device assembly rotates. Further, the number of revolutions of the developing-device assembly, compared to that of the photosensitive drum, is not sufficient for power generation or power accumulation.

BRIEF SUMMARY OF THE INVENTION

The present invention may provide an image forming apparatus capable of supplying electric power to devices carried in a rotary developing-device assembly.

According to an embodiment of the invention, an image forming apparatus includes a developing-device assembly, a developing roller, a roller drive gear, a transmission gear, a roller drive motor, a take-in gear, and a generator. The developing-device assembly switches a plurality of developing devices, which are carried on the assembly, by rotating to a development position where one of the developing devices face a photosensitive member. The developing roller is provided on each of the plurality of developing devices and supplies toner to the photosensitive member at the development position. The roller drive gear is attached to each of the developing rollers. The transmission gear meshes with the roller drive gear attached to the developing roller of one of the developing devices that is located at the development position. The roller drive motor transmits mechanical power to the transmission gear via a power transmission path. The take-in gear is disposed coaxial with a rotational center of the developing-device assembly and is meshed with the transmission gear. The generator is housed in the developing-device assembly and has a gear meshing with the take-in gear.

Objects and advantages of the invention will become apparent from the description which follows, or may be learned by practice of the invention.

DETAILED DESCRIPTION OF THE INVENTION

An image forming apparatus according to an embodiment of the present invention will now be described with reference toFIGS. 1to6. The structure of the image forming apparatus is already described in senior U.S. patent application Ser. No. 10/254,784, so a description thereof is omitted here by reference, except for portions that require a particular description.

The image forming apparatus, as shown inFIG. 1, includes a developing-device assembly1, a transmission gear2, a roller drive motor3, a belt4, a take-in gear5, a generator6, and a photosensitive drum7.

The developing-device assembly1comprises a plurality of developing devices, for example, four developing devices8a,8b,8cand8din the present embodiment, and a core unit9for supporting the developing devices8a,8b,8cand8d. The developing devices8a,8b,8cand8dhave developing rollers10a,10b,10cand10dand toner containers11a,11b,11cand11d, respectively. The developing rollers10a,10b,10cand10dare provided at one end with roller drive gears12a,12b,12cand12d. The toner containers10a,11b,11cand11dcontain toners of different colors associated with the developing devices8a,8b,8cand8d. In the present embodiment, they contain toners of four colors, yellow, magenta, cyan and black, respectively. The developing devices8a,8b,8cand8dare attached to an outer peripheral surface of the core unit9.

As is shown inFIG. 2, the core unit9comprises a shaft13and a cylindrical support member14. The shaft13passes through a central part of the support member14and is supported in the inside of the image forming apparatus (not shown). The shaft13rotatably supports the developing-device assembly1within the image forming apparatus. Developing device-fixing members (not shown) are provided on an outer peripheral surface of the support member14. The developing device-fixing members are configured to permit easy removal of the developing devices8a,8b,8cand8d.

The developing-device assembly1is rotated by a drive mechanism that is disposed on a side (not shown) opposed to the side shown in FIG.1. The developing-device assembly1switches the developing devices8a,8b,8cand8dsuch that one of them is set in a development position facing the photosensitive drum7by rotating.

The transmission gear2is supported on the same inside of the image forming apparatus, where the roller drive gears12a,12b,12cand12dare disposed. As is shown inFIG. 1, the transmission gear2is engaged with the roller drive gear12aof the developing device8aset in the development operation state. A driven pulley15is attached to the transmission gear2.

As is shown inFIG. 1, a driving pulley16is attached to a rotational shaft of the roller drive motor3. The belt4is passed over the driving pulley16and driven pulley15.

The take-in gear5is fitted on the shaft13on the same side where the roller drive gears12a,12b,12cand12dare disposed. The take-in gear5meshes with the transmission gear2. The take-in gear5is freely rotatable relative to the shaft13, regardless of the rotation of the developing-device assembly1.

As is shown inFIG. 2, the generator6is disposed in a notch14aformed in a part of the support member14on that side where the take-in gear5is attached. It should suffice if the notch14acan receive the generator6inside the support member14. The generator6is of a rotary type, and the rotational shaft of the generator6is furnished with a gear6a. The gear6aof generator6meshes with the take-in gear5.

When the developing-device assembly1is in the rotational position for the development operation state, as shown inFIG. 1, the cylindrical photo-sensitive drum7provided as the photosensitive member is positioned near, and in parallel with, the developing roller10aof the developing device8athat is set in the development operation position. As is shown inFIG. 3, when the developing-device assembly1, transmission gear2, photosensitive drum7, etc., are viewed from their sides, the centers of the take-in gear5, the transmission gear2, the roller drive gear12aof developing device8aset in the development operation position and the photosensitive drum7are aligned in the radial direction of the take-in gear5that centers on the shaft13.

The transmission gear2and the gear6aof generator6are meshed with the take-in gear5such that the transmission gear2and the gear6aare displaced from each other in the axial direction of the shaft13. Therefore, even when the developing-device assembly1rotates, the gear6aof generator6does not collide with the transmission gear2. The take-in gear5has a portion meshing with the transmission gear2and a portion meshing with the gear6aof generator6, and these portions may be configured to have different diameters and different numbers of teeth so that mechanical powers corresponding to suitable numbers of revolutions may be transmitted to the transmission gear2and the gear6aof generator6, respectively.

In the present embodiment, mechanical power is transmitted from the roller drive motor3to the transmission gear2via a power transmission path that includes the driving pulley16, driven pulley15and belt4. Additionally, a tensioner may be provided at a position along the belt4so as to keep the tension of the belt4constant. The belt4, driving pulley16and driven pulley15may be a toothed belt and toothed pulleys, or a chain and sprockets.

As is shown inFIG. 4, mechanical power may be transmitted from the roller drive motor3to the transmission gear2via a power transmission path comprising a plurality of gears17combined as a gear train. Alternatively, as shown inFIG. 5, the power transmission path may comprise a driving bevel gear18aprovided on the roller drive motor3, a driven bevel gear18bprovided on the transmission gear2, and a drive shaft18chaving bevel gears at both ends thereof meshing with the bevel gears18aand18bto transmit mechanical power. Alternatively, the power transmission path may use such gears as a worm gear, a hypoid gear and a helical gear.

In the image forming apparatus with the above-described structure, when the developing-device assembly1is in the standby state, the developing rollers10a,10b,10cand10dare at rest in such a position that none of them faces the photosensitive drum7, as shown in FIG.6. When a developing process is started, the developing-device assembly1rotates and brings one of the developing rollers of the developing devices8a,8b,8cand8d, for example, the developing roller10aof the developing device8aas shown inFIG. 1, to a position facing the photosensitive drum7. With the rotation of the developing-device assembly1, the developing device Ba is brought to the development position near the photosensitive drum7, and the roller drive gear12ais engaged with the transmission gear2.

With the engagement between the roller drive gear12aand transmission gear2, mechanical power is transmitted from the roller drive motor3to the developing roller10avia the power transmission path, which comprises the driving pulley16, belt4and driven pulley15, the transmission gear2and the roller drive gear12a. The developing roller10ais rotated by the transmitted mechanical power. If the developing roller10aof the selected developing device8arotates, toner is supplied to the photosensitive drum7from the toner container11aof developing device8avia the developing roller10a.

Upon completion of development by the developing device8a, the developing-device assembly1rotates once again and brings the next developing device to the development position. Then, the roller drive gear attached to the developing roller of the developing device set at the development position meshes with the transmission gear2.

In addition, since the transmission gear2also meshes with the take-in gear5, the power transmitted from the roller drive motor3via the power transmission path is also transmitted from the transmission gear2to the take-in gear5. Then, the mechanical power from the roller drive motor3is transmitted to the generator6via the take-in gear5and the gear6aof generator6. Thus, the generator6generates electric power. Thereby, electric power can be supplied to devices mounted in the developing-device assembly1. The transmission gear2always meshes with the take-in gear5even when the developing-device assembly1rotates. Therefore, electric power can always be supplied to the devices mounted in the developing-device assembly1.

Possible devices to be mounted in the developing-device assembly1are, for instance, residual toner amount sensors attached to the toner containers11a,11b,11cand11d, rotational speed sensors for the developing rollers10a,10b,10cand10d, and a rotational position sensor for the developing-device assembly1.

Even when the developing-device assembly is at rest in the standby state, as shown inFIG. 6, the take-in gear5meshes with both the transmission gear2and the gear6aof generator6. Thus, the generator6can gain mechanical power from the roller drive motor3via the power transmission path, and can supply electric power to the devices mounted in the developing-device assembly1. In other words; even in the case where there is no need to rotate the developing roller10a,10b,10c,10d, mechanical power may be supplied from the roller drive motor3, whereby electric power can be supplied to the devices mounted in the developing-device assembly. Furthermore, the transmission of mechanical power to the generator6is effected by making use of the roller drive motor3, transmission gear2, driving pulley16, driven pulley15and belt4, which are provided to rotate the developing rollers10a,10b,10cand10d. Therefore, the structure of the image forming apparatus is not made complex.

In order to efficiently use electric power generated by the generator6, the core unit9may be provided with an electric power accumulation device.