Patent Publication Number: US-6219523-B1

Title: Image forming apparatus and developing agent recovery method in image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus that recovers residual toner left on an image carrier after transferring a developer image on an image receiving medium and a developer recovery method in an image forming apparatus. 
     2. Description of the Related Art 
     A device using a magnetic roller as a cleaning means to remove and recover residual toner left on a photosensitive drum after transferring an image at an image forming apparatus of an electro-photographic system has been disclosed in Japanese Laid Open Patent No. 5-289594. However, for this cleaning means according to a magnetic brush roller, it is required to supply proper bias voltage between a photosensitive drum and the magnetic brush roller in order to get the good cleaning property. 
     On the other hand, there is an image forming apparatus using such a cleaning unit  1  as shown in FIG.  1  as a cleaning means to scrape off residual toner from the surface of a photosensitive drum with a cleaning blade. 
     The cleaning unit  1  has a carry-out paddle  6  made of a magnetic material for feeding waste toner scraped with a cleaning blade  3  to a recovery auger  4  that conveys waste toner toward a recovery box. 
     The cleaning unit  1  using this type of carry-out paddle  6 , that is made of a magnetic material, has a film-shaped peeling member  7  that contacts a blade portion of the carry-out paddle  6  and peels off waste toner adhered to the carry-out paddle  6  to the recovery auger  4  side, and whenever the blade portion  6   a  of the carry-out paddle  6  is rotated, the peeling member  7  is brought in contact with tile blade portion  6   a  and peels waste toner therefrom. 
     Therefore, during the cleaning, the peeling member  7  is brought in contact with the blade portion  6   a  whenever the carry-out paddle  6  is rotated and the contacting sound and vibration tend to be produced and furthermore, the peeling member  7  is subject to the abrasion by the contact with the carry-out paddle  6   
     Therefore, for an image forming apparatus that is installed in an office and demanded to be kept in a calm and satisfactory environment, it is demanded to reduce noise and vibration of its cleaning unit as could as possible, and a cleaning unit capable of certainly feeding waste toner that is scraped with a cleaning blade to a recovery unit is demanded so that more higher cleaning effect can be obtained. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a calm and good environment without causing noises and vibrations around an image forming apparatus installed in an office, etc. without generating noises and vibrations. 
     Another object of the present invention is to maintain the high cleaning property by feeding waste toner scraped by a cleaning blade certainly to the recovery auger side up to the life end of the cleaning unit. 
     According to the present invention, an image forming apparatus comprising: image forming means for forming a developer image on an image carrier using magnetic developer; transferring means for transferring the developer image formed on the image carrier onto an image receiving medium; and cleaning means for scraping residual toner left on the image carrier into a container by a developer removing means after passing the transferring means, for conveying the scraped residual toner to the residual toner recovery position from the position facing the image carrier in the container by a developer carry-out means comprising a roller shaped magnetic member, and for peeling off the residual toner from the surface of the image carry-out means by a peeling means opposing to the developer carry-out means at the recovery position through a gap leaving a thin layer of the magnetic developer is provided. 
     Further, according to the present invention, a developer recovery method of an image forming apparatus comprising the steps of: a charging step for charging the surface of the image carrier to a prescribed potential; an exposing step for exposing and scanning the charged surface of the image carrier and forming an electrostatic latent image; a developing step for forming a developer image by feeding a magnetic developer to the electrostatic latent image formed on the surface of the image carrier; a transferring step for transferring the developer image formed on the image carrier on an image receiving medium; a scraping step for scraping residual developer left on the image carrier in a container after the transferring step is completed; a conveying step for conveying the residual developer scraped in the container to the residual developer recovery position from the position facing the image carrier by the magnetic developer carry-out roller in the container; and a peeling step for peeling the residual developer from the surface of the developer carry-out roller by a peeling means facing the developer carry-out roller through a gap at the recovery position leaving the thin layer of the magnetic developer is provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and benefits of the present invention will become clear by the following explanation referring to the attached drawings. 
     FIG. 1 is a schematic diagram showing a cleaning unit described in the Description of Related Art; 
     FIG. 2 is a schematic diagram showing an image forming unit of the image forming apparatus of the present invention; 
     FIG. 3 is a schematic diagram showing the cleaning unit shown in FIG. 2; and 
     FIG. 4 is a diagram showing the relation between a ratio of “Distance A” that is a gap between separated waste toner and a developer carry-out roller against “Distance C” between the cleaning blade and the photosensitive drum shown in FIG.  3  and amount of separated waste toner. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be explained below in detail with reference to attached drawings. 
     FIG. 2 is a schematic diagram showing an image forming unit  10  of the electro-photographic image forming apparatus such as printers, copying machines, etc. relative to the present invention. A photosensitive drum  11  that is an image carrier is rotated in the arrow direction “s”. Around the photosensitive drum  11 , there are arranged an electrifying charger  12  that is a charging device, an exposing unit  13  of an exposure device, a developing device  14 , a transferring charger  16   a  that is a transferring device, a peeling charger  16   c , a paper peeling claw  16   c , a cleaning unit  17  that is a cleaner, and a discharging lamp  18  along the rotating direction of the arrow “s”. 
     Then, the developing device  14  will be described in detail. A developer containing unit  20  of the developing device  14  contains a developer  23  comprising magnetic toner  21  and carrier  22 . At the position  20  facing the photosensitive drum  11  in the developer container unit  20 , a developing roller  24  is provided. 
     The developing roller  24  has a magnet roller  27  having a number of magnetic poles and extending in the axial direction in a hollow cylindrical shaped developing sleeve  26  that is made of non-magnetic material. The developing sleeve  26  and the magnet roller  27  are provided coaxial and relatively rotatably. The developing sleeve  26  rotates in the arrow direction “t” and the magnet roller  27  rotated in the arrow direction “U”. 
     As a result, the rotation of the developer  23  becomes the same as the conveying direction of the developer  23  and it becomes possible to increase conveying amount of developer and therefore, the developing can be made at a more high speed. Further, a non-magnetic developer control blade  28  is formed in the developer containing unit  20  and a stirrer  30  is provided almost at the center of the developer containing unit  20  to stir the developer  23  so as to prevent cohesion and supply the developer  23  to the developing roller  24 . 
     In this developing unit  14 , the developer  23  is stirred by the stirrer  30  and supplied to a developer magnetic absorbing area [E] around the developing roller  24 . 
     The developer  23  supplied to the developer magnetic absorbing area [E] and magnetically absorbed is adsorbed on the developing sleeve  26  and stirred with the magnetic toner  21  by the rotation of the carrier  22  that rotates the magnet roller  27  that rotates relatively with the developer sleeve  26  and thus, the magnetic toner  21  is charged. 
     A ratio of weight of toner to weight of carrier  22  on the developing sleeve  26 ; that is, a specific density is maintained at, for instance, about 50%. 
     Next, the cleaning unit  17  will be described in detail. As shown in FIG. 3, at the positions of a container  31  of the cleaning unit  17  facing the photosensitive drum  11 , a cleaning blade  32  is provided as a developer removing means to scrape off magnetic residual toner left on the photosensitive drum  11  after passing the transfer charger  16   a  and further, a recovery blade  33  is provided. 
     Further, in the container  31 , a recovery auger  34  is provided to convey waste toner that is residual toner scraped off from the photosensitive drum  11  with the cleaning blade  32  to a recovery box which is not shown. 
     Further, there is provided a magnetic developer carry-out roller  36  in 12 mm diameter that is a developer carry-out means for conveying the waste toner scraped by the cleaning blade  32  and accumulated at a position facing the photosensitive drum  11  between the cleaning blade  32  and the recovery blade  33  to the recovery position facing the recovery auger  34 , in enclosed space from the cleaning blade  32  in the container  31  to the recovery auger  34 . 
     The developer carry-out roller  36  comprises a shaft  36   a  attached with magnets  36   b  in the feather shape covered by a non-magnetic material made hollow cylinder  36   c.    
     At the recovery position around the developer carry-out roller  36 , there is arranged a film shaped waste toner peeling member  37  that is made of mylar and to be attached to the bottom of an exhaust path  35  of the recovery auger  34 . The waste toner peeling member  37  peels off waste toner attached to the surface of the developer carry-out roller and supplies to the recovery auger  34 . 
     Next, the arrangement of the developer carry-out roller  36  and the waste toner peeling member  37  in the cleaning unit  17  will be described in detail. The waste toner peeling member  37  and the developer carry-out roller  36  are kept separated with a gap and not in contact with each other in the container  31 . 
     When the gap between the waste toner peeling member  37  and the developer carry-out roller  36  is taken as “Distance A”, in order to peel off waste toner from the developer carry-out roller  36 , this “Distance A” must be less than the thickness of a waste toner layer formed on the developer carry-out roller  36 . Accordingly, “Distance A” should be less than the minimum layer thickness of waste toner on the surface of the developer carry-out roller  36  that is controlled until it is conveyed to the position of the waste toner peeling member  37  after scraped off by the cleaning blade  32 . That is, when the minimum layer thickness of waste toner to be controlled on the surface of the developer carry-out roller  36  is assumed to be “Distance B”, “Distance A” must always be less than “Distance B” (Distance A&lt;Distance B). 
     In FIG. 3, the thickness of the waste toner layer on the surface of the developer carry-out roller  36  is controlled by “Distance C”, that is a gap between the photosensitive drum  11  and the developer carry-out roller  36  and “Distance D”, that is a gap between the inner wall of the container  31  and the developer carry-out roller  36  at the scraping position of the cleaning blade  32 . Therefore, in FIG. 3, “Distance B” is equivalent to a smaller distance of either “Distance C” or “Distance D”. 
     Further, when the relation between the ratio of “Distance A” to “Distance C” and the waste toner peeling amount by the waste toner peeling member  37  was investigated and the results shown in FIG. 4 were obtained. 
     Normally, amount of waster toner peeled by the waste toner peeling member  37  from the surface of the developer carry-out roller  36  increases with the decrease in “Distance A”. Actually, however, when “Distance A” exceeds a certain degree and becomes too narrow, amount of peeled waste toner will decrease conversely. 
     This is attributable to a phenomenon that the waste toner scraped off from the photosensitive drum  11  by the cleaning blade  32  and accumulated in the region of “Distance C” between the cleaning blade  32  and the photosensitive drum  11  is pulled by the thin layer of waste toner in a certain thickness left on the surface of the developer carry-out roller  36  and therefore, the waste toner is conveyed more efficiently than a case wherein no waste toner is left on the developer carry-out roller  36 . 
     In other words, when “Distance A” is narrowed, amount of waste toner peeled off from the developer carry-out roller  36  by the waste toner peeling member  37  can be increased but amount of waste toner conveyed by the developer carry-out roller  36 ; that is, amount of waste toner recovered from “Distance C” decreases and a whole amount of toner decreases. On the contrary, when a certain degree of “Distance A” is maintained, amount of waste toner peeled off from the developer carry-out roller  36  by the waste toner peeling member  37  decreases but amount of waste toner conveyed by the developer carry-out roller  36  increases and a whole amount of waste toner conveyed increases. 
     From the above-mentioned relation, in order to get the good cleaning property by increasing a total amount of toner peeled off by increasing a conveying amount of waste toner, the range of “Distance A” shown in FIG. 4 is regarded to be proper as shown below: 
     
       
         [(Distance  A )/(Distance  C )]%=20-30%  
       
     
     Further, in FIG. 3, actual “Distance A” is 1.25 mm, “Distance C” is 5 mm, and “Distance D” is 5 mm. 
     When the image formation is started, in the image forming unit  10 , a toner image is formed by a magnetic toner on the photosensitive drum  11  through the electrifying charger  12 , the exposing unit  13  and the developing device  14  according to the rotation of the photosensitive drum  11  in the arrow direction “s”. 
     On the other hand, when an image receiving medium fed from the paper feeding unit is supplied to the position of the transfer charger  16   a  in synchronism with a toner image on the photosensitive drum  11 , a toner image on the photosensitive drum  11  is transferred onto the image receiving medium by the transfer charger  16   a . Then, the image receiving medium is peeled off from the photosensitive drum  11  by the peeling charger  16   b  and thereafter, the image is fixed through the fixing processing. 
     Further, after completing the transfer of the image, the photosensitive drum  11  reaches the cleaning unit  17 , where residual toner is removed, the charge is eliminated by the charge eliminating lamp  18 , and next image forming is enabled. 
     When removing residual toner on the photosensitive drum  11 , the cleaning unit  17  scrapes off residual toner left on the photosensitive drum  11  with the cleaning blade  32  after completing the image transfer. Further, the cleaning unit  17  carries out waste toner scraped with the cleaning blade  32  and accumulated between the recovery blade by adsorbing it magnetically on the surface of the developer carry-out roller  36  that rotates in the arrow direction “v” toward the recovery auger  34 . 
     Thereafter, waste toner is peeled off from the surface of the developer carry-out roller  36  with the waste toner peeling member  37  and fed to the recovery auger  34 . After peeling waste toner by the waste toner peeling member  37 , a thin layer of waste toner in the thickness of “Distance A” is formed on the surface of the developer carry-out roller  36 . When the developer carry-out roller  36  holding the thin layer of waste toner in the thickness of “Distance A” on its surface reaches the position of the cleaning blade  32 , the conveying amount of waste toner in the direction of the recovery auger  34  is increased by efficiently adsorbing accumulated water toner by the magnetic force of the waster toner thin layer in the thickness of “Distance A”. 
     Thus, when waste toner adsorbed on the surface of the developer carry-out roller  36  and conveyed is peeled off with the waste toner peeling member  37  through the gap of “Distance A”, the conveying amount of waste toner by the developer carry-out roller  36  can be increased. Accordingly, the peeling amount of waste toner by the waste toner peeling member  37  can be increased, the more satisfactory cleaning property is obtained and an image of good quality is obtained. 
     Further, because the waste toner peeling member  37  is not in contact with the surface of the developer carry-out roller  36 , neither sliding contact sound nor vibration is produced between the developer carry-out roller  36  and the waste toner peeling member  37  during the cleaning and therefore, it is possible to maintain the surrounding environment of a place wherein the image forming apparatus is installed in the calm and good state. 
     Further, because the waste toner peeling member  37  is not in contact with the surface of the developer carry-out roller  36 , the wear of the waste toner peeling member  37  is prevented, waste toner can be certainly fed up to the life end of the recovery auger  34  and a high cleaning performance can be maintained for an extended period. 
     The present invention is not restricted to the above-mentioned embodiment but can be variously modified within the scope of the present invention. For instance, in the above-mentioned embodiment, “Distance A”, that is a gap between the developer carry-out means and the peeling means can be within a range wherein peeling amount of waste toner can be increased with the peeling means and to increase peeling amount of waste toner more effectively, “Distance A” can be within the range of 20-30% of “Distance C”, that is a gap between the developer carry-out means and the image carrier. Further, for instance, the peeling means can be made by resin, etc. 
     As described above in detail, according to the present invention, waste toner is peeled off with the peeling means provided through a gap in the state leaving a thin layer of waste toner in the thickness equivalent to the gap. Therefore, according to the present invention, as a result of effects of increased conveying amount of waste toner with the developer carry-out means and increased peeling amount of waste toner with the peeling means, more good cleaning property and an image of good quality are obtained. Further, according to the present invention, as the peeling means and the developer carry-out means are not in contact with each other, noise and vibration during the cleaning can be prevented and the surrounding environment wherein the image forming apparatus is installed can be held in the calm and good state. Further, the abrasion of the peeling means can be prevented, waste toner can be peeled and recovered certainly at the recovery position up to the life end of the cleaner and the satisfactory cleaning proper can be obtained for an extended period