Abstract:
A cleaning device incorporated in an image forming apparatus for removing a toner remaining on a photoconductive drum by a fur brush and collecting the removed toner by a collecting roller. The cleaning device selectively moves the fur brush into and out of contact with both of the photoconductive drum and collecting roller.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a cleaning unit incorporated in a copier, printer, facsimile apparatus or similar image forming apparatus for removing a toner deposited from a photoconductive element. 
     It is a common practice with a copier, for example, to electrostatically form a latent image on a photoconductive drum and cause a toner to deposite on the latent image to produce a toner image matching a document image. After the toner image has been transferred to a recording medium, e.g., paper sheet, part of the toner usually remains on the photoconductive drum and has to be removed before the next copying cycle begins. A cleaning device for removing the toner remaining on the drum may be implemented by a fur brush, as well known in the art. In this type of cleaning device, the fur brush is made of a conductive material and held in pressing contact with the photoconductive element to scrape off the toner remaining on the drum. The toner deposited on the fur brush is electrostatically transferred to a collecting roller, and then a collecting blade removes the toner from the collecting roller. The removed toner is conveyed to the outside of the cleaning device by a coil. The fur brush is provided with some elasticity since it has to rotate while thrusting into the drum and the collecting roller to a predetermined extent. However, when left stationary over a long period of time, the fur of the fur brush remains in the collapsed position and cannot return to the original position. In such a condition, the cleaning device fails to fully remove the toner or to collect it in an expected manner, resulting in the degradation of image quality. In light of this, the fur brush may be spaced apart from the drum or from the collecting roller while an image forming operation is not under way, as proposed in the past. With such a conventional implementation, however, it is impossible to completely free the fur brush from collapse since the fur brush remains in pressing contact with one of the drum and collecting roller, although it may be spaced apart from the other. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a cleaning unit for an image forming apparatus which allows the fur of a fur brush to undergo a minimum of collapse to thereby eliminate the incomplete removal or collection of a toner. 
     A cleaning unit incorporated in an image forming apparatus for removing a toner remaining on a photoconductive element of the present invention comprises a conductive fur brush for scraping off the toner remaining on the photoconductive element, a collecting roller applied with a bias voltage for collecting the toner deposited on the fur brush, and a brush moving mechanism for moving the fur brush selectively into and out of contact with the photoconductive element and collecting roller. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawings in which: 
     FIG. 1 is a sectional side elevation showing a cleaning unit embodying the present invention; 
     FIG. 2 is a plan view of the embodiment; 
     FIG. 3 is a view as seen in a direction A--A of FIG. 2; 
     FIG. 4 is a view as seen in a direction B--B of FIG. 2; and 
     FIGS. 5 and 6 are views similar to FIG. 3, each showing the embodiment in a particular condition. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1 of the drawings, a cleaning unit embodying the present invention is shown and includes a fur brush 2. The fur brush 2 has conductive filaments and is rotatably held in contact with a photoconductive element 1. The fur brush 2 catches a toner remaining on the drum 1 with the free end thereof. A collecting roller 3 is applied with a bias voltage opposite in polarity to the toner and scrapes off the toner from the fur brush 2 due to the potential difference between it and the fur brush 2. Further, a collecting blade 4 scapes off the toner from the collecting roller 3. The toner so removed from the collecting roller 3 is conveyed to the outside of the cleaning unit by a screw 5. FIG. 2 shows a brush moving mechanism 6 for moving the fur brush 6 to any one of three different positions, i.e., a first scraping position, a second scraping position, and a retracted position respectively indicated by a solid line, a dash-and-dots line, and a dash-and-dot line in FIG. 1. The first scraping position is a usual position for scraping off the remaining toner from the drum 1. In the second scraping position, the fur brush 2 thrusts deeper into the drum 1 than in the first scraping position. In the retracted position, the fur brush 2 is spaced apart from both of the drum 1 and collecting roller 3. If desired, the toner removed from the collecting roller 3 by the collecting blade 4 may be accumulated within the cleaning device. In FIG. 1, there are also shown a precleaning charger 7, a power source 8 for driving the collecting roller 3, an upper casing 9a, a lower casing 9b, and a lower seal 10. 
     As shown in FIGS. 2 and 3, the shaft 2a of the fur brush 2 and the shaft 3a of the collecting roller 3 are journalled to opposite side plates 11 and 12. The brush moving mechanism 6 is arranged at the outside of both side plates 11 and 12 in a symmetrical configuration. Specifically, the side plates 11 and 12 (only 11 is shown in FIG. 3) are each formed with an elongate slot 13. The shaft 2a of the fur brush 2 is received in the slot 13 of each side plate through a ball bearing 20, so that the brush 2 may be movable between the second scraping position and the retracted position. A stub or cam lever shaft 19 is studded on an intermediate portion of each side plate 11 or 12. A cam lever 15 is rotatably supported by the cam lever shaft 19 at an intermediate portion thereof. The cam lever 15 abuts against the upper periphery of the shaft 2a via the ball bearing 22 at one end thereof. A spring 14 is anchored at one end thereof to the other end of the cam lever 15 to constantly bias the cam lever 15 upward. In this configuration, the shaft 2a of the fur brush 2 is constantly biased toward the second scraping position. A coil spring 16 is retained by the lower periphery of the shaft 2a via the ball bearing 22 at one end thereof and anchored to a suitable portion of associated one of the side plates 11 and 12 at the other end. The coiled portion of the coil spring 16 is coupled over the cam lever 19. The coil spring 16, therefore, biases the shaft 2a of the fur brush 2 upward toward the retracted position. A cam 17 is disposed above the upper edge of the end portion of the cam lever 15 remote from the shaft 2a and is so configured as to move the cam lever 15 in three different angular positions stepwise. The cam 17 is affixed to a cam shaft 18 which is journalled to the side plates 11 and 12 by slide bearings 21. As the cam shaft 18 is rotated, the cam 17 is brought to any one of three different angular positions stepwise. The cam spring 14 exerts a greater force than the coil spring 16. 
     The fur brush 2 is selectively rotated to any one of the three angular positions as stated above by a drive mechanism shown in FIGS. 2 and 4. As shown, the drive mechanism includes an input gear 25 mounted on an input shaft 24 which is in turn supported by a side plate 23 forming part of the cleaning unit. A gear 26 is mounted on the shaft 3a of the collecting roller 3 and held in mesh with the input gear 25. A bracket 28 is rotatably mounted on the shaft 2a of the fur brush 2 by a ball bearing 27. An idle gear 29 is supported by the bracket 28 via an idler shaft 30 and held in mesh with the gear 26. Further, the idle gear 29 is held in mesh with a gear 31 mounted on the shaft 2a. In FIG. 2, the reference numerals 34 and 32 designate a cam gear and a ball bearing, respectively. In FIG. 4, the reference numeral 33 designates an idler spring exerting an downward force. 
     To remove the toner remaining on the drum 1, the fur brush 2 is brought to the first scraping position indicated by a solid line in FIG. 1. In this position, the fur brush 2 is rotatable while thrusting into both of the drum 1 and collecting roller 3 by a predetermined amount (about 1.5 millimeters). Should the fur brush 2 be left stationary over a long period of time, it would lose elasticity to give rise to the previously discussed problem. In the illustrative embodiment, the cam 17 and, therefore, the cam lever 15 is moved from the position of FIG. 3 to the position of FIG. 5 upon the elapse of a predetermined period of time (several seconds) after the fur brush 2 has been positioned in the first scraping position or when the machine is brought to an OFF state. In the position of FIG. 5, i.e., the retracted position, the fur brush 2 is spaced apart from both of the drum 1 and collecting roller 3. As the fur of the fur brush 2 sequentially lies down due to aging, it also degrades the image quality. In such a condition, the cam 17 is rotated to move the cam lever 15 to the position shown in FIG. 6, i.e., the second scraping position. In the second scraping position, the fur brush 2 thrusts deeper into the drum 1 than in the first scraping position by an amount corresponding to the collapse of the fur (possibly about 0.5 millimeter) and, therefore, uniformly contacts the drum 1 to insure desirable images. Such a collapse of the fur of the fur brush 2 may be detected in terms of the count of a counter or similar detecting means responsive to the number of copies produced (e.g. about 200K in the case of a copy counter). 
     While an image forming operation is not under way, the cam 17 remains in the position of FIG. 5 which is angularly spaced apart from the position of FIG. 3 by 270 degrees in the clockwise direction, by a drive (e.g. spring clutch) from the body, not shown. When the machine is held in an OFF state, a home position sensing means, not shown, causes the fur brush 2 to remain in the position of FIG. 5. To move the fur brush 2 to the second scraping position, the cam 17 is rotated 90 degrees clockwise from the reference position of FIG. 3 to the position of FIG. 6. The displacement of the fur brush 2 has to be accompanied by the displacement of the idle gear 29. At this instant, the idle gear 9 and the gear 26 mounted on the roller shaft 3a are surely held in mesh since the bracket 28 supporting the idle gear 29 is constantly biased downward by the idler spring 33. 
     In summary, it will be seen that the present invention provides a cleaning unit which allows a fur brush to undergo a minimum of collapse by spacing it apart from a photoconductive element and a collecting roller by a brush moving mechanism. The fur brush is capable of thrusting into the drum in a plurality of amounts stepwise. Hence, after an image forming cycle has been repeated a predetermined number of times, the fur brush can thrust into the drum in a greater amount to eliminate incomplete removal or collection of a toner due to the collapse of the fur brush. 
     Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof.