Abstract:
A cleaning device for a dry electrophotographic device includes a cleaning brush brought into resilient contact with an object to be cleaned such as a photosensitive drum. A cleaning roll rotates while constantly being brought into contact with the cleaning brush and a cleaning blade is pressed against the cleaning roll to clean the cleaning roll. A rotation direction switching mechanism switches the rotation direction of the cleaning brush such that the rotation direction of the cleaning brush when cleaning the object, for example, during the formation of an image, is different from that when the brush is not cleaning the object.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a cleaning device for cleaning a photosensitive member, a transfer portion, or the like, in a dry electrophotographic device. 
     FIG. 6 shows a cleaning device in a conventional dry electrophotographic device in which toner 2, remaining on the surface of a photosensitive drum 1 after the respective processes of charging, exposure, development and transfer have been performed, is mechanically removed by a cleaning brush 3, or electrostatically removed when a brush bias-voltage applying mechanism 7 is employed. The toner 2 magnetically or electrostatically adhering to the cleaning roll 4 is scraped off mechanically by a cleaning blade 5 and is discharged from the device by a toner recovery screw 6. 
     Cleaning brush 3 has fine metallic bristles or the like, and cleaning roll 4 is brought into contact with cleaning brush 3 with a prescribed pressure so that toner 2 adhering to cleaning brush 3 can be transferred reliably to the cleaning roll 4. 
     Since the cleaning brush 3 and the cleaning roll 4 of the conventional cleaning device constantly and resiliently contact each other, the fine metallic bristles of the cleaning brush 3 are flattened over time. Therefore, the outer diameter of the cleaning brush 3 decreases gradually, so that the conventional cleaning device has a short service life in that the contact area between the cleaning brush 3 and the photosensitive drum gradually decreases, thereby deteriorating the cleaning capability of the cleaning device. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to overcome such disadvantages of the conventional systems and to provide a dry electrophotographic device having a cleaning device in which the service life of the cleaning brush is extended and a reliable cleaning capability of the cleaning device is maintained. 
     To attain the above-mentioned and other objects, a cleaning device for a dry electrophotographic device according to the present invention includes: a cleaning brush brought into resilient contact with an object to be cleaned such as a photosensitive drum, a photosensitive belt, or a transfer belt; a cleaning roll rotating while being brought into constant contact with the cleaning brush; a cleaning blade pressed against the cleaning roll, and a rotation direction switching device for switching the rotation direction of the cleaning brush such that the rotation direction of the cleaning brush when cleaning an object, for example, during the formation of an image, is different from that when the brush is not cleaning the object, for example, during a stand-by period for image formation. 
     As mentioned above, according to the present invention, the periodic or non-periodic change in the rotation direction of the cleaning brush prevents the collapse of the metallic bristles of the cleaning brush over time even when the cleaning roll constantly contacts the cleaning brush. Therefore, a dry electrophotographic device can be provided in which the contact area of the cleaning brush and the object to be cleaned is maintained and a high cleaning capability and high image quality are achieved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the present invention will be apparent from the following description when taken in connection with the accompanying drawings, in which: 
     FIG. 1 is a sectional view of a cleaning device in a cleaning mode according to a first embodiment of the present invention; 
     FIG. 2 is a view of a drive system for the cleaning device in the cleaning mode according to the first embodiment of the present invention; 
     FIG. 3 is a sectional view of the cleaning device in a stand-by mode according to the first embodiment of the present invention; 
     FIG. 4 is a view of a drive system for the cleaning device in a stand-by mode according to the first embodiment of the present invention; 
     FIG. 5 is a sectional view of a cleaning device in a stand-by mode according to a second embodiment of the present invention; and 
     FIG. 6 is a sectional view of a conventional cleaning device in a cleaning mode. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1-4, a first embodiment according to the invention is illustrated in which residual toner 2 remaining on the surface of a photosensitive drum 1 after the respective processes of charging, exposure, development and transfer have been performed is electrostatically removed by a cleaning brush 3 which has a bias voltage applied thereto by a brush bias-voltage applying mechanism 7 and which rotates in the direction of an arrow A. The toner 2 adhering to the cleaning brush 3 is transferred to a cleaning roll 4, to which a bias voltage higher than that applied to the cleaning brush 3 is applied by a roll bias-voltage applying mechanism 8. Cleaning roll 4 rotates in the direction of arrow B, and the toner 2 is conveyed to and scraped off by a cleaning blade 5, and discharged out of the device by a toner recovery screw 6. 
     As shown in FIG. 2, a case 9 is rotatably supported by a screw shaft 23 and contacts an eccentric cam 20. A retract spring 21 is connected to the case 9 which houses cleaning brush 3, the cleaning roll 4, the cleaning blade and the toner recovery screw 6 or the like, as shown in FIG. 1. Supported on the outside of the case 9 are a screw gear 15 connected to the toner recovery screw 6, a roll gear 16 connected to the cleaning roll 4 and a first brush gear 18 connected to the cleaning brush 3, as shown in FIG. 2. A cleaner drive gear 10, a brush drive gear 11, a cleaner gear 14, an idler gear 17 and a second brush gear 19 are provided in a main body of the device. 
     During a cleaning operation, the eccentric cam 20 is rotated against the tension of the retract spring 21, thereby to press the case 9 downwardly, as illustrated in FIG. 2. As a result, part of the cleaning brush 3 is brought into resilient contact with a prescribed area of the photosensitive drum 1, as shown in FIG. 1. The torque of the cleaner drive gear 10 provided coaxially with the rotational axis of the photosensitive drum 1, is transmitted to the cleaner gear 14 through a belt 12 to rotate the gear 14. The torque is transmitted in turn to the screw gear 15, the roll gear 16, the idler gear 17 and the first brush gear 18, thereby to rotate the cleaning brush 3 in the direction of arrow A such that the photosensitive drum 1 is cleaned, as mentioned above. 
     The torque of the brush drive gear 11, provided coaxially with the rotational axis of the photosensitive drum 1, is transmitted to the second brush gear 19 through a drive belt 13. However, the second brush gear 19 is provided separately from the first brush gear 18, so that it idly rotates. 
     On the other hand, when the cleaning device is in a stand-by mode or the like (e.g., when the cleaning device is not cleaning drum 1) immediately after the power is turned on, the second brush gear 19 is moved into the state shown in FIGS. 3 and 4. Specifically, when the eccentric cam 20 is rotated counterclockwise, as shown in FIG. 4, the case 9 is retracted to a stand-by position due to the tension of the retract spring 21 connected to the case 9. The movement of the case 9 disengages the first brush gear 18 from the idler gear 17 and engages the first brush gear 18 with the second brush gear 19, thereby separating the cleaning brush 3 from the photosensitive drum 1, as shown in FIG. 3. 
     When the first brush gear 18 thus engages the second brush gear 19, the cleaning brush 3 rotates in the direction of arrow C opposite to that during a cleaning operation (e.g., the direction of arrow A), as shown in FIG. 3. The brush bias-voltage applying mechanism 7 is switched to a ground position substantially simultaneously with changing the rotation direction (e.g., from the direction of arrow A to that of arrow C) of the cleaning brush 3 such that bias voltage is not applied to the cleaning brush 3. As a result, toner is easily removed from the cleaning brush 3 by the cleaning roll 4. The rotation of the eccentric cam 20 is synchronous with the actuation of a member when an image is formed, such as a print switch. 
     Referring to FIG. 5, a cleaning device according to a second embodiment of the present invention includes a flicker bar 22 rotatably provided at an upstream side from a contact portion of a cleaning brush 3 and a cleaning roll 4 in the rotation direction (e.g., in the direction of arrow B) of the cleaning roll 4. 
     Flicker bar 22 is out of contact with the cleaning brush 3 during a cleaning operation (e.g., when brush 3 is rotating in the direction of arrow A), as shown by the dotted lines in FIG. 5. Substantially simultaneously with the cleaning brush 3 being brought into a stand-by position and rotating in direction C opposite to that during a cleaning operation, the flicker bar 22 is rotated to a position shown by the solid lines and comes into contact with the cleaning brush 3 with a prescribed contact depth. The contact between the flicker bar 22 and the cleaning brush 3 separates toner from the cleaning brush 3. Since the drive system in the second embodiment is similar to that of the first embodiment, the explanation thereof will be omitted. 
     The flicker bar 22 may be made of conductive material and a bias voltage may be applied or grounded when the flicker bar 22 is brought into contact with the cleaning brush 3 to assist in removing toner from the cleaning brush 3. The flicker bar 22 also may be brought into constant contact with the cleaning brush 3. 
     In the first and second embodiments, although the brush bias-voltage applying mechanism 7 is switched to ground under a stand-by state, a reverse bias voltage may be applied to the cleaning brush 3 instead. 
     Further, although separate mechanisms are employed to change the rotation direction of the cleaning brush 3, the present invention is not restricted thereto. For example, a drive device such as a motor may be directly connected to the cleaning brush 3, thereby to change the rotation direction thereof. 
     Although the aforementioned embodiments are directed to cleaning a photosensitive drum, the present invention is not restricted thereto. Thus, it will be readily appreciated that the invention may be applied to, for example, a photosensitive belt, a transfer belt or a transfer roller. 
     As described above, according to the present invention, the periodic or non-periodic change in the rotation direction of the cleaning brush prevents the fine metallic bristles of the cleaning brush from collapsing over time even when the cleaning brush is brought into constant contact with the cleaning roll. Therefore, a dry electophotographic device can be provided, in which the contact area of the cleaning brush and an object to be cleaned is reliably maintained so that a high cleaning capability and high image quality are achieved. 
     While certain preferred embodiments have been shown and described, many changes and modifications within the spirit of the invention will be apparent to those of working skill in this technical field. Thus, the scope of the invention should be considered as limited only by the appended claims.