Abstract:
A method for cleaning a charging brush which charges a drum including an electroconductive substrate and an insulating surface layer over the electroconductive substrate, including the steps of grounding the electroconductive substrate of the drum contacting a brush portion of the charging brush with the insulating surface of the drum while the charging brush and the drum are rotated and applying an alternating electric field to the brush portion of the charging brush to vibrate to brush portion to remove fouling adhered to the brush portion.

Description:
BACKGROUND 
     1. Field 
     This patent specification relates to a method and a device for cleaning a charging brush which charges a surface of a photoconductive element to be used in an electrophotographic process of an image forming apparatus, such as a copying machine, a facsimile, and a printer, etc., and more particularly to a method and a device that can effectively clean a charging brush at a reduced cost. 
     2. Discussion 
     A roll-shaped brush structure, having a large number of elastic, electrically conductive threads at its outer periphery to charge a surface of a photoconductive element used in an electrophotographic printing process, is commonly known. The charging brush contacts the surface of the photoconductive element and applies a high voltage to the surface thereof so as to cause corona discharge, thereby electrostatically charging the surface of the photoconductive element. 
     The useful life of the charging brush ends when it becomes unable to cause effective corona discharge due to fouling, such as toner or an additive to toner adhered to the conductive threads of the brush. As described in Japanese Patent Laid-Open Publications Nos. 6-289755 and 7-89627, it may be comparatively easy to remove fouling from a charging roller that does not have a brush structure, by washing the charging roller. However, it is difficult to recycle a charging brush which is at the end of its useful life. 
     The reason why it is difficult to recycle a charging brush which is at the end of its life due to the above-described fouling by material adhering to conductive threads of the brush, is believed to be as follows. 
     It is believed that the fouling material needs to be removed before a used charging brush could be reused. A charging brush is generally constructed of a pile fabric of conductive threads, which is secured to a metal sheet or is wound around a shaft in a shape of a roller. An attempt can be made to remove fouling adhered to a charging brush by using an air blow or by scraping off with a scraper. However, when the fouling is removed by the above-mentioned methods, it is likely that at least some of the conductive threads will come out as well, thereby causing abnormal discharge or cutting off an exposure optical path in an electrophotographic printing process. When the fouling is swept by the scraper, tips of the conductive threads might be scraped which may damage the conductive threads and cause abnormal discharge. In addition, because the conductive thread is deformed due to an excessive force exerted thereon, an outside shape or dimensions set for the charging brush may not be maintained. 
     Various proposals have been made to address the above-mentioned problems. When a recycling process to reuse a charging brush is performed, it is important that costs involved are kept to a minimum by decreasing the work needed for the process. It is believed that costs cannot be satisfactory decreased with the known prior art technology in which a specific jig is used or the amount of work is not sufficiently decreased. 
     A method for reducing total costs involved in recycling work has been proposed. According to this method, a current leak caused when a photoconductive drum is damaged is checked at the time when a changing brush is cleaned. Specifically, a current leak check is carried out by running a current. When a photoconductive element is damaged such that a portion of a photoconductive layer thereof has come off and the ground (GND) layer is exposed, an excessive current is fed to an exposed portion of a ground (GND) layer from a charging brush. At least a portion of the charging brush can burn or otherwise be damaged due to the passage of the excessive current, and thereby the charging brush may become unsuitable for further use. Also, the photoconductive element may become unsuitable for further use because burnt out conductive threads may stick at the place where the portion of the ground (GND) layer of the photoconductive element is exposed. 
     As described above, the prior proposal may lead to making unusable both the photoconductive element and the charging brush by performing a cleaning of the charging brush and a current leak check of the photoconductive element at the same time. 
     SUMMARY 
     An object of the disclosure herein is to overcome the above-mentioned and other problems. 
     The system and method disclosed herein advantageously provide a novel charging brush cleaning device wherein a charging brush used in an electrophotographic printing process can be cleaned effectively by reducing the total costs involved without decreasing the performance of the charging brush. 
     According to preferred embodiments, fouling adhered to a charging brush is removed by vibrations caused in a portion of the charging brush by an alternating electric field applied thereto. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the system and method disclosed herein and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
     FIG. 1 is a schematic drawing illustrating an exemplary construction of a cleaning device according to a first embodiment; 
     FIG. 2 is a schematic drawing illustrating an exemplary construction of a cleaning device according to a second embodiment; and 
     FIG. 3 is a schematic drawing illustrating an exemplary construction of a cleaning device according to a third embodiment. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, FIG. 1 is a schematic drawing illustrating an exemplary construction of a cleaning device according to a first preferred embodiment. A cylindrical drum  1  includes an inner wall which is grounded (GND), and an outer surface which is overlaid by an insulator  2 . A charging brush roller  3  includes a brush  6  having a large number of elastic, electrically conductive threads  5  arranged on an outer periphery of a core shaft  4 . A drum rotation drive section  7  rotatably drives the drum  1 . A brush rotation drive section  8  rotatably drives the charging brush roller  3 . 
     An alternating electric field supply section  9  applies an alternating electric field to the charging brush roller  3 . One side of the alternating electric field supply section  9  is connected to the drum  1  and another to the charging brush roller  3 , to thereby apply AC voltage therebetween. A current control section  10 , which is disposed in the alternating. electric field supply section  9 , prevents a passage of a current when it detects a flow of the current which is equal to or greater than a predetermined value. An alarm section  11  includes a lamp and/or a buzzer for giving an indication to an operator when passage of excessive current is detected by the current control section  10 . A cleaning blade  12  removes fouling on a surface of the drum  1 . 
     A cleaning method using a cleaning device having the above-mentioned configuration will now be described below. 
     The charging brush roller  3  is set such that a surface of the drum  1  extends into the brush  6  of the charging brush roller  3  by approximately 0.5 mm (i.e., the surface of the drum  1  digs into the brush  6  by approximately 0.5 mm). Then, the drum rotation drive section  7  rotatably drives the drum  1  at a circumferential velocity of about 40 mm/sec. At the same time, the brush rotation drive section  8  rotatably drives the charging brush roller  3  at about 1.5 times the circumferential velocity of the drum  1  in the reverse direction of the rotation of the drum  1 . In addition, an alternating electric field of 1500 volts and 2000 Hz frequency is applied to the charging brush roller  3  by the alternating electric field supply section  9  while the charging brush roller  3  and the drum  1  are rotated. 
     By applying the alternating electric field to the charging brush roller  3 , minute vibrations are generated in the brush  6  by an electromagnetic force produced in or at the conductive threads  5 . Fouling “a”, such as toner or an additive which has adhered to the conductive threads  5 , is sifted or shed by the vibrations. Thus, the charging brush roller  3  is cleaned. 
     According to this cleaning method, an effective cleaning of the charging brush roller  3  is performed without imposing an excessive load on the conductive threads  5 . 
     If the drum  1  becomes damaged, excessive current may be fed to the charging brush roller  3  from the alternating electric field supply section  9 . In such a case, a current control section  10  detects the passage of excessive current. Then, a current limiter in the current control section  10  functions to end the feeding of the excessive current to the brush  6 , thus keeping the conductive threads  5  from being burnt or otherwise damaged, and keeping the drum  1  from damage such as by burnt or melted threads  5 . When the drum  1  is damaged, a passage of an excessive current is detected by the current control section  10 . Then, a lamp or a buzzer in the alarm section  11  is activated based on a detection signal from the current control section  10  to report the possible damage caused to the drum  1  to an operator. 
     FIG. 2 is a schematic drawing illustrating an exemplary construction of a cleaning device according to a second embodiment. A difference in the construction of the device between the first embodiment and the second embodiment is that a photoconductive drum  15  used in an electrophotographic printing process employed in the second embodiment instead of the drum  1  employed in the first embodiment. The construction of the drum  1  and that of the photoconductive drum  15  are identical with each other. The photoconductive drum  15  is cylindrical in shape. An inner wall of the photoconductive drum  15  is grounded (GND), and an outer surface of it is overlaid with an electrical insulator  16 . The same reference numerals that designate corresponding members in the first embodiment are used in the second embodiment and a description of the identical members will be omitted. 
     Because a cleaning method according to the second embodiment is identical to that in the first embodiment, a description of the cleaning method also will be omitted. According to the second embodiment, whether or not the photoconductive drum  15  becomes damaged is detected at the same time the charging brush roller  3  is cleaned, which can be an advantage over the first embodiment. 
     When the photoconductive drum  15  is damaged, a passage of an excessive current can be detected by an operation of the current limiter of the current control section  10 . Based on a detection signal from the current control section  10 , a lamp and/or a buzzer is activated in the alarm section  11  to inform an operator of the damage caused to the photoconductive drum  15 . Because the current limiter of the current control section  10  is not activated when the photoconductive drum  15  is not damaged, the photoconductive drum  15  is deemed to be suitable for recycling, and the absence of an activation of the alarm section  11  can be used to identify a drum  15  that need not be replaced because it still has useful life left. 
     FIG. 3 is a schematic drawing illustrating an exemplary construction of a cleaning device according to a third embodiment. According to the third embodiment, the charging brush roller  3  and the photoconductive drum  15  are installed in a process cartridge  20  used in an electrophotographic printing process. The charging brush roller  3  is cleaned and damage of the photoconductive drum  15  is detected while they are installed in the process cartridge  20  without dismantling the process cartridge  20 . The same reference numerals designate corresponding members in FIGS. 1 and 2 are used in the third embodiment and a description of the identical members will be omitted. 
     The process cartridge  20  in FIG. 3 has been used and reclaimed to be recycled. The process cartridge  20  includes a new toner containing section  21  filled with fresh toner, a used toner containing section  22  where used toner is contained, and an image forming section  23 . The image forming section  23  includes members used in an electrophotographic printing process, such as the photoconductive drum  15 , which is cylindrical-shaped and an inner wall of it is grounded while a surface of it is overlaid with the insulator  16 , and the brush  6  having a large number of conductive threads  5  arranged on an outer periphery of the core shaft  4 . 
     The image forming section  23  also includes the charging brush roller  3 , a developing roller  24  to develop a latent image formed on the photoconductive drum  15 , a toner supply roller  25  to supply the developing roller  24  with toner, a rotation drive section  26  including a plurality of gears which rotatably drive the photoconductive drum  15  and the charging brush roller  3 . 
     A cleaning device includes the alternating electric field supply section  9  which applies an alternating electric field to the charging brush roller  3  and has a grounded pole connected to the photoconductive drum  15 . The cleaning device also includes the charging brush roller  3 , the current control section  10 , which is disposed in the alternating electric field supply section  9  and which prevents a passage of a current when it detects a current which is equal to or greater than a predetermined value, and the alarm section  11  including a lamp and/or a buzzer for giving an indication to an operator when passage of excessive current is detected by the current control section  10 . 
     According to the third embodiment, the charging brush roller  3  is cleaned in the same manner as described in the first embodiment, and whether or not the photoconductive drum  15  becomes damaged is detected in the same manner as described in the second embodiment while the charging brush roller  3  and the photoconductive drum  15  are installed in the process cartridge  20  without dismantling the process cartridge  20 . The above-described cleaning of the charging brush roller  3  and the detection of damage caused to the photoconductive drum  15  can be performed when the process cartridge  20  is set to a predetermined position in the cleaning device. 
     In addition, according to the third embodiment, the photoconductive drum  15  and the charging brush roller  3  can be rotatably driven by the rotation drive section  26  which is included in the process cartridge  20 . Therefore, it may eliminate necessity of including the rotation drive section  26 , which rotates the photoconductive drum  15  and the charging brush roller  3 , in the cleaning device. 
     In the above-described embodiments, the charging brush roller  3  and the drum  1  (or the photoconductive drum  15 ) can be configured to rotate relatively such that they may slide in contact with each other. The method of cleaning according to the present invention can be applied not only to the charging brush roller  3  but also to other brush-shaped members that have conductive threads and are used in an electrophotographic printing process. A photoconductive belt or other structure can be used in place of the drums  1  and  15 . 
     Numerous additional modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein. 
     This document claims priority and contains subject matter related to Japanese Patent Application No. 2000-040698, filed on Feb. 18, 2000, and the entire contents thereof are herein incorporated by reference.