Patent Publication Number: US-7596337-B2

Title: Cleaner unit and image forming apparatus including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Japanese Patent Application No. 2006-95015 filed Mar. 30, 2006 in the Japan Patent Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     This invention relates to an electrophotographic image forming apparatus. 
     Electrophotographic image forming apparatus are known to transfer toner (developer) onto a recording medium such as a recording sheet and an OHP sheet to form an image onto the recording medium. During the transfer, however, part of the supplied toner is likely to adhere to a photosensitive drum and a conveyor mechanism belt to form waste toner. 
     If printing (image formation) is performed with the photosensitive drum and the conveyor mechanism belt to which the waste toner adhered, the waste toner is retransferred onto the reverse side of the recording medium. An undesirable image may be formed onto the recording medium. 
     A conventional electrophotographic image forming apparatus is therefore provided with a waste toner container that collects the waste toner so as to avoid forming an undesirable image onto the recording medium. 
     SUMMARY 
     The larger the capacity of the waste toner container, the more of the waste toner can be collected in the container. As a result, exchange frequency of the container can be reduced. Utility for a user is improved. However, in order to include a large container in an image forming apparatus, the image forming apparatus has to be undesirably increased in size. The size of the image forming apparatus may be larger than preferred. 
     In the aforementioned image forming apparatus, the waste toner container may be formed to be flat so that the height of the container remains short but the capacity of the container can be expanded in a horizontal direction. A conveying roller may be also provided at the entrance of the container for the purpose of conveying the collected toner to the waste toner container. However, it is difficult to convey the waste toner to the inner part of the container even in use of the conveying roller. A dead space is created in the container in which the waste toner can never be stored. 
     In the aforementioned image forming apparatus, volumetric efficiency is small between the waste toner container and the waste toner actually stored. Thus, the waste toner container has to be elongated in a vertical direction so as to store a sufficient amount of waste toner. 
     Accordingly, in the aforementioned image forming apparatus, there is a problem that the waste toner container, and consequently, the image forming apparatus, may be increased in size. 
     It would be desirable to reduce an image forming apparatus in size, in a vertical direction, while allowing the image forming apparatus to store a sufficient amount of waste toner. 
     A cleaner unit may be detachable from an electrophotographic image forming apparatus provided with a belt. It would be desirable that the cleaner unit includes a cleaner roller, a cleaner shaft, a blade, a toner container, and a toner squeeze pump. The cleaner roller is brought into contact with the belt. The cleaner shaft is brought into contact with the cleaner roller. The blade is brought into contact with the cleaner shaft. The toner container includes a storage space storing toner and an opening allowing toner to be delivered to the storage space. The toner squeeze pump is provided outside the storage space. The cleaner roller collects toner adhered to a surface of the belt to a surface of the cleaner roller. The cleaner shaft collects the toner adhered to the surface of the cleaner roller to a surface of the cleaner shaft. The blade scrapes off the toner adhered to the surface of the cleaner shaft. The toner squeeze pump delivers the toner scraped off by the blade toward an opening of the storage space and compresses the toner stored in the storage space. A part of a bottom wall of the toner container which continues from the opening extends in a substantially horizontal direction, when the cleaner unit is attached to the image forming apparatus. 
     The cleaner roller may be made of polyurethane foam or silicone rubber foam. The cleaner shaft may be made of metal. The blade may be made of polyurethane. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described below, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a sectional side view showing main parts of a laser printer according to an embodiment; 
         FIG. 2  is an enlarged view of a belt cleaner according to the embodiment; 
         FIG. 3  is an enlarged view of a portion A in  FIG. 2 ; 
         FIG. 4  is a table showing test results of conveying state of waste toner when minimum gap sizes between an elliptic rotor and a rotor housing and an angle between a first wall and a second wall are used as testing parameters; 
         FIG. 5  is a table showing test results of conveying state of waste toner when the angle between the first wall and the second wall is used as a testing parameter; and 
         FIG. 6  is a table showing test results of conveying state of waste toner when a width size of an apex of the second wall and a distance from the apex of the second wall to a peripheral surface of a cleaning shaft are used as testing parameters. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the present embodiment, an electrophotographic image forming apparatus according to the invention is applied to a laser printer which is used connected to a computer. 
     1. External Structure of Laser Printer 
       FIG. 1  shows main parts of a laser printer  1  of the present embodiment. In  FIG. 1 , the upper side in  FIG. 1  is regarded as upward in the direction of gravity. The right side in  FIG. 1  is normally regarded as the front side. 
     A housing  3  of the laser printer  1  is formed into a substantially box-like (e.g., square) shape. A discharge tray  5  is provided on the top of the housing  3  so as to receive a printed sheet or an OHP sheet (hereinafter, simply referred to as “paper”) discharged from the housing  3 . 
     In the present embodiment, the housing  3  is provided with a not shown frame member made of metal or resin therein. Component members such as a developer toner cartridge  70  and a fixing unit  80  are detachably attached to the frame member. 
     2. Internal Structure of Laser Printer 
     The laser printer  1  includes an image forming portion  10 , a feeder portion  20 , and a conveyer  30 . The image forming portion  10  forms an image on paper. The feeder portion  20  feeds the paper to the image forming portion  10 . The conveyer  30  conveys the paper to four developing toner cartridges  70 K,  70 Y,  70 M, and  70 C composing the image forming portion  10 . 
     The paper to which image formation is completed at the image forming portion  10  is turned around so that a conveying direction of the paper is rotated upward by approximately 180° at an intermediate conveying roller  90  and a not shown discharge chute. Then, the paper is discharged from a discharge portion  7  onto the discharge tray  5  by a discharge roller  91 . 
     2.1. Feeder Portion 
     The feeder portion  20  includes a feed tray  21 , a feed roller  22 , and a separation pad  23 . The feed tray  21  is provided at the bottom of the housing  3 . The feed roller  22  is provided at the upper front of the feed tray  21 . The feed roller  22  feeds (conveys) paper placed on the feed tray  21  to the image forming portion  10 . The separation pad  23  applies a predetermined conveying resistance to the paper fed by the feed roller  22  so as to separate the paper one by one. 
     The paper on the feed tray  21  is conveyed to the image forming portion  10  disposed in a substantially middle part of the housing  3  as if to make a U-turn at the front side of the housing  3 . For this purpose, a conveying roller  24  that applies a conveying force to the paper is provided at a region making a U-turn in a paper conveying path between the feed tray  21  and the image forming portion  10 . 
     A pressure roller  25  is disposed to face the conveying roller  24  across the paper conveying path to press paper onto the conveying roller  24 . The pressure roller  25  is pressed against the conveying roller  24  by a not shown resilient member such as a coil spring. 
     Registration rollers  26  and  27  are provided downstream of the conveying roller  24  in the paper conveying direction. The registration roller  26  abuts the front end of the paper conveyed by the conveying roller  24  so as to correct orientation of the paper. The registration roller  26  then conveys the paper toward the image forming portion  10 . The registration roller  27  is provided to face the registration roller  26 . The registration roller  27  is pressed against the registration roller  26  by a not shown resilient member such as a coil spring. 
     2.2. Conveyer 
     The conveyer  30  includes a drive roller  31 , a driven roller  32 , and a conveyor belt  33 . The drive roller  31  rotates in conjunction with the operation of the image forming portion  10 . The driven roller  32  is rotatably disposed at a distance from the drive roller  31 . The conveyor belt  33  runs between the drive roller  31  and the driven roller  32 . 
     Paper conveyed from the feed tray  21  is sequentially conveyed toward the vicinity of the four developer toner cartridges  70 K,  70 Y,  70 M, and  70 C, as the conveyor belt  33  rotates with the paper positioned thereon. 
     A belt cleaner  100  removes toner adhered to the surface of the conveyor belt  33 . From now on, details of the belt cleaner  100  will be described. 
     2.2.1. Details of Belt Cleaner  100   
       FIG. 2  is an enlarged view of the belt cleaner  100 .  FIG. 3  is an enlarged view of a portion A of  FIG. 2 . For example, the belt cleaner  100  is detachably installed inside the housing  3  on the lower side of the conveyor belt  33 . Particularly, the belt cleaner  100  may be designed to be capable of being attached to and detached from the frame member provided in the housing  3 . 
     In  FIG. 3 , a cleaning roller  101  removes toner adhered to the surface of the conveyor belt  33 . A cleaning shaft  102  conveys the toner adhered to the cleaning roller  101  toward a waste toner container  105 . 
     The cleaning roller  101  may be, for example, made of polyurethane foam or silicone rubber foam. The cleaning shaft  102  may be, for example, made of metal. 
     In the present embodiment, the cleaning roller  101  is brought into contact with the conveyor belt  33  while rotating in reverse of a rotation direction D 1  of the conveyor belt  33 . In this manner, the toner adhered to the conveyor belt  33  is scraped off to be removed. 
     An electric charge (negative charge in the present embodiment) opposite to an electric charge of the toner is applied to the cleaning shaft  102 . The cleaning shaft  102  is then brought into contact with the external surface of the cleaning roller  101  while being rotated. In this manner, the toner adhered to the surface of the cleaning roller  101  is transferred to the cleaning shaft  102  and removed from the cleaning roller  101 . 
     The waste toner adhered to the surface of the cleaning shaft  102  is scraped off by a release blade  103 . The release blade  103  is formed into a thin plate. The waste toner is then conveyed to the waste toner container  105  by the waste toner squeeze pump mechanism  110 . 
     The blade  103  may be, for example, made of polyurethane. 
     An antiscattering blade  104  prevents scattering of waste toner scraped off from the cleaning shaft  102  to the side of the cleaning roller  101 . One end of the antiscattering blade  104  is secured to the inner wall of a casing  108 . The other end of the antiscattering blade  104  is formed into a flexible film which slidably abuts on the outer surface of the cleaning shaft  102 . 
     The waste toner container  105  includes a storage space  106  in which the waste toner is collected. The waste toner squeeze pump mechanism  110  is provided on the outer side of the storage space  106  across an entrance  107  of the storage space  106  (waste toner container  105 ). The waste toner squeeze pump mechanism  110  is capable of compressing the waste toner collected in the storage space  106 . 
     The waste toner squeeze pump mechanism  110  includes an elliptic rotor  111 , a rotor housing  114 , and a toner retaining member, which may be a reed valve  115 . The elliptic rotor  111  pushes the waste toner scraped off from the cleaning shaft  102  toward the entrance  107  by rotating. The rotor housing  114  is provided to enclose the elliptic rotor  111 . The reed valve  115  prohibits the waste toner delivered into the storage space  106  from flowing backward to the outside of the storage space  106 . 
     The elliptic rotor  111  has a substantially elliptic cross section. The elliptic rotor  111  rotates around a rotation axis orthogonal to the cross section. The rotor housing  114  is composed of a first wall  112  and a second wall  113 . The first wall  112  extends in a horizontal direction continuing from the entrance  107  of the toner container  105 . The second wall  113  extends substantially orthogonal to the first wall  112 . 
     The reed valve  115  may be in the form of an elastic thin plate which slidably abuts on the peripheral surface of the elliptic rotor  111  from the side of the entrance  107  toward a rotation center O 1  of the elliptic rotor  111 . 
     Due to the above structure, when a force from the inside toward the outside of the storage space  106  acts on the reed valve  115  in the waste toner squeeze pump mechanism  110  of the present embodiment, contact surface pressure between the reed valve  115  and the elliptic rotor  111  is increased. 
     Accordingly, even if a force large enough to open the reed valve  115  acts on the reed valve  115 , by increased pressure inside the storage space  106  due to the pressure of the compressed waste toner, the reed valve  115  is reliably prohibited from being open. Thus, the waste toner would not leak out of the storage space  106 . 
     As shown in  FIG. 2 , a waste toner measurement sensor  120  is provided on the back side (left side in  FIG. 2 ) in a horizontal direction of the waste toner container  105 . The waste toner measurement sensor  120  determines whether the waste toner stored in the storage space  106  has reached a predetermined amount. The waste toner measurement sensor  120  generates a signal when a switch (not shown) is depressed by the pressure of the compressed waste toner provided inside the storage space  106 . 
     An elastic film door  121  is provided on the side of the entrance  107  of the waste toner measurement sensor  120  in such a manner as to partition the storage space  106  into the entrance  107  side and the waste toner measurement sensor  120  side. The film door  121  is designed to be opened by pressure of the waste toner stored on the entrance  107  side when the pressure has reached to a predetermined level. 
     Accordingly, in the present embodiment, the waste toner measurement sensor  120  does not operate simply by filling the storage space  106  with waste toner. The waste toner measurement sensor  120  operates when the inner pressure inside the storage space  106  has exceeded the predetermined level. 
     2.3. Image Forming Portion 
     Referring to  FIG. 1 , the image forming portion  10  includes a scanner portion  60 , a developer toner cartridge  70 , and a fixing unit  80 . 
     The image forming portion  10  of the present embodiment is of a so-called direct tandem type which allows color printing. In the present embodiment, four toner cartridges  70 K,  70 Y,  70 M, and  70 C corresponding to four colors of toner (developer), that is black, yellow, magenta, and cyan, are arranged in series from the upstream side along the paper conveying direction. 
     The four developer toner cartridges  70 K,  70 Y,  70 M, and  70 C are only different in color of ink stored therein, and identical in structure. Accordingly, the four developer toner cartridges  70 K,  70 Y,  70 M, and  70 C are collectively called developer toner cartridges  70 . 
     2.3.1. Scanner Portion 
     The scanner portion  60  forms an electrostatic latent image on the surface of a photosensitive drum  71 . The photosensitive drum  71  is provided in the upper portion in the housing  3 . The photosensitive drum  71  is respectively provided for each of the four developer toner cartridges  70 K,  70 Y,  70 M, and  70 C. Particularly, the scanner portion  60  includes a laser source, a polygon mirror, fθ lens and a reflector. 
     A laser beam emitted from the laser source based on image data is biased by the polygon mirror. After passing the fθ lens, the beam is reflected and bent downward by the reflector. As a result, the beam is radiated on the surface of the photosensitive drum  71  to form an electrostatic latent image. 
     2.3.2. Developer Toner Cartridge 
     Hereinafter, the structure of the developer toner cartridge  70 C is explained as an example by way of  FIG. 1 . 
     The developer toner cartridge  70  is detachably arranged inside the housing  3  on the down side of the scanner portion  60 . The developer toner cartridge  70  is provided with a casing  75  which accommodates the photosensitive drum  71 , a charger  72 , and a toner container  74 . 
     A transfer roller  73  is rotatably supported to the frame member on the side opposite to the photosensitive drum  71  across the conveyer belt  33 . 
     The photosensitive drum  71  carries an image to be transferred onto paper. The photosensitive drum  71  has a cylindrical shape, the outmost surface of which is formed by a positively charged photosensitive layer, for example, made of polycarbonate. 
     The charger  72  charges the surface of the photosensitive drum  71 . The charger  72  is disposed obliquely upward at the back of the photosensitive drum  71 . The charger  72  is disposed at a predetermined distance from the photosensitive drum  71  so as not to contact the photosensitive drum  71 . 
     The charger  72  according to the present embodiment employs a scorotron charger which positively charges the surface of the photosensitive drum  71  substantially evenly by using corona discharge from charging wire, for example, made of tungsten. 
     The transfer roller  73  is disposed to face with the photosensitive drum  71  and rotates in conjunction with rotation of the transfer belt  33 . When the paper passes near the photosensitive drum  71 , the transfer roller  73  applies an electric charge (negative charge in the present embodiment) opposite to the electric charge of the photosensitive drum  71  to the paper from the surface side opposite to a print surface of the paper, so as to transfer the toner adhered to the surface of the photosensitive drum  71  onto the print surface. 
     The toner container  74  includes a toner chamber  74 A, a toner supply roller  74 B and a developer roller  74 C. The toner chamber  74 A stores toner. The toner supply roller  74 B and the developer roller  74 C supply toner to the photosensitive drum  71 . 
     The toner stored in the toner chamber  74 A is supplied to the developer roller  74 C by the rotation of the toner supply roller  74 B. The toner supplied to the developer roller  74 C is carried onto the surface of the developer roller  74 C. The carried toner is adjusted to have a predetermined thickness (to be even) on the surface of the developer roller  74 C by a layer thickness control blade  74 D. The toner is then supplied to the surface of the photosensitive drum  71  exposed by the scanner portion  60 . 
     2.3.3. Fixing Unit 
     The fixing unit  80  is disposed downstream of the photosensitive drum  71  in the paper conveying direction. The fixing unit  80  heats and melts the toner transferred onto the paper to be fixed. The fixing unit  80  is detachably attached to the aforementioned frame member. 
     Particularly, the fixing unit  80  includes a beating roller  81 , and a pressure roller  82 . The heating roller  81  is disposed on the side of the print surface of the paper. The heating roller  81  applies a conveying force to the paper while heating the toner. The pressure roller  82  is disposed to face the heating roller  81  across the paper. The pressure roller  82  presses the paper toward the side of the heating roller  81 . 
     The heating roller  81  is rotationally driven in synchronization with the developer roller  74 C and the conveyer belt  33 . The pressure roller  82  is rotated by a rotational force of the heating roller  81  via the paper contacting the heating roller  81 . 
     2.3.4. Outline of Image Forming Operation 
     In the image forming portion  10 , an image is formed onto the paper as follows. 
     That is, the surface of the photosensitive drum  71 , along with the rotation thereof, is positively and uniformly charged by the charger  72 . Then, the surface of the photosensitive drum  71  is exposed by rapid scanning of a laser beam emitted from the scanner portion  60 . Thereby, an electrostatic latent image corresponding to an image to be formed on the paper is formed on the surface of the photosensitive drum  71 . 
     Next, the positively charged toner carried onto the developer roller  74 C by the rotation thereof is supplied to the electrostatic latent image formed on the surface of the photosensitive drum  71 , that is, a part of the surface of the uniformly and positively charged photosensitive drum  71  which is exposed by a laser beam and where the electric potential is lowered, when brought into contact with the photosensitive drum  71 . Thereby, the electrostatic latent image on the photosensitive drum  71  is visualized. A toner image by reversal development is carried on the surface of the photosensitive drum  71 . 
     Thereafter, the toner image on the photosensitive drum  71  is transferred onto the paper by a transfer bias applied to the transfer roller  73 . The paper to which the toner image is transferred is conveyed to the fixing unit  80  and heated. The toner transferred as the toner image is fixed on the paper to complete image formation. 
     3. Characteristics of Laser Printer According to Present Embodiment 
     In the belt cleaner  100  according to the present embodiment, the waste toner inside the storage space  106  can be compressed by the waste toner squeeze pump mechanism  110 . Therefore, the waste toner can be accumulated in the waste toner container  105  while being compressed inside the storage space  106 . 
     Accordingly, as shown in  FIGS. 2 and 3 , even though the portion of a bottom wall  109  (see  FIG. 3 ) of the waste toner container  105  continuing from the entrance  107  of the waste toner container  105  extends in a substantially horizontal direction to form the storage space  106  extending in the horizontal direction, sufficient amount of waste toner can be stored in the waste toner container  105 . Therefore, in the present embodiment, miniaturization of the laser printer  1  in a vertical direction can be achieved while a sufficient amount of waste toner can be stored. 
     In the belt cleaner  100  of the present embodiment, even if the pressure inside the storage space  106  is increased by the compressed waste toner, the reed valve  115  remains closed as mentioned above. Therefore, it is difficult for the waste toner to leak out of the storage space  106 . Accordingly, even if the capacity and the vertical size of the storage space  106  are reduced, much waste toner can be stored. 
     In the elliptic rotor  111  of the waste toner squeeze pump mechanism  110  of the present embodiment, the waste toner is pumped when the reed valve  115  is pushed by each of the two edges of a major axial portion of the elliptic rotor  111 , which compresses the waste toner in the storage space  106 . Thus, when the elliptic rotor  111  is rotated once, the waste toner is pumped twice. 
     On the other hand, for example, a rolling piston pump which rotates an eccentric round rotor may be adopted instead of the elliptic rotor  111 . In this case, however, when the round rotor rotates once, the waste toner is pumped once. Therefore, the rolling piston pump has lower efficiency than the waste toner squeeze pump mechanism  110  of the present embodiment. 
     Accordingly, the belt cleaner  100  of the present embodiment allows efficient collection of the waste toner. 
     As shown in  FIG. 3 , the waste toner scraped off from the cleaning shaft  102  by the release blade  103  falls into a gap between the elliptic rotor  111  and the second wall  113  to be conveyed toward the entrance  107  along with rotation of the elliptic rotor  111 . Therefore, if minimum gap sizes L 1  and L 2  between the rotor housing  114  and the elliptic rotor  111 , that is, the minimum gap size L 1  between the first wall  112  and the elliptic rotor  111 , and the minimum gap size L 2  between the second wall  113  and the elliptic rotor  111 , become too large, the amount of waste toner capable of being conveyed is decreased. The amount of waste toner remaining in the gap between the rotor housing  114  and the elliptic rotor  111  is increased. As a result, pumping efficiency of the waste toner squeeze pump mechanism  110  becomes low. 
     On the other hand, if the minimum gap sizes L 1  and L 2  between the rotor housing  114  and the elliptic rotor  111  become too small, solidified waste toner or foreign bodies may be easily stuck in the gap between the elliptic rotor  111  and the rotor housing  114 . There is high risk of stopping the rotation of the elliptic rotor  111 . 
     Thus, in the present embodiment, the minimum gap L 1  between the first wall  112  and the elliptic rotor  111  is set to be 0.3 mm to 2 mm, as later explained. In this manner, occurrence of deficiency is avoided to the waste toner squeeze pump mechanism  110  while decrease in the pumping efficiency is restricted. 
     Similarly, the minimum gap L 2  between the second wall  113  and the elliptic rotor  111  is set to be 0.3 mm or above and below 1.4 mm, as later explained. In this manner, occurrence of deficiency is avoided to the waste toner squeeze pump mechanism  110  while decrease in the pumping efficiency is restricted. 
     The conveyor belt  33  and the cleaning shaft  102  are disposed above the second wall  113 . Thus, there is a fear that the waste toner may be heaped up at the apex of the second wall  113 . 
     The heaped waste toner may fall on the side facing away from the elliptic rotor  111  over the second wall  113 . The fallen waste toner may not be conveyed into the storage space  106 . 
     In the present embodiment, a width size L 3  at the apex of the second wall  113  is set to be below 1 mm, as later explained. Thereby, the waste toner is prohibited from falling on the side facing away from the elliptic rotor  111  over the second wall  113 . The waste toner can be conveyed into the storage space  106 . Efficient collection of the waste toner can be achieved. 
     The narrower the width size L 3  of the apex of the second wall  113 , the better the waste toner is prevented from being heaped up at the apex of the second wall  113 . 
     However, in the present embodiment, the first and the second walls  112  and  113  are integrally formed by die molding such as injection resin molding. Thus, it is difficult to form the overall second wall  113  from the apex to the base to be thin due to manufacturing constraints. 
     To overcome the above constraints, the apex of the second wall  113  may be separately manufactured. Thereby, the separately manufactured apex may be attached to an apex portion of the second wall  113  so as to reduce the width size L 3  of the apex of the second wall  113 . However, this would increase the number of parts and assembling steps of the belt cleaner  100 , resulting in increase in manufacturing costs of the laser printer  1 . 
     In the present embodiment, a taper portion  116  where the width size L 3  is tapered toward the apex is provided at least on the apex portion of the second wall  113 , as shown in  FIG. 3 . Therefore, the first and the second walls  112  and  113  can be integrally molded by die molding while reducing the width size L 3  of the apex of the second wall  113 . 
     Accordingly, in the present embodiment, efficient collection of the waste toner can be achieved without increasing the manufacturing costs of the belt cleaner  100  (rotor housing  114 ). 
     If the second wall  113  is bent away from the elliptic rotor  111  so that an angle θ (see  FIG. 3 ) between the first and the second walls  112  and  113  is more than 90°, a lump of waste toner heaped as if leaning on the second wall  113  does not fall apart even if the elliptic rotor  111  is rotated, as later explained. Thus, the waste toner cannot be efficiently collected. 
     In order to efficiently collect the waste toner, the second wall  113  may be bent toward the elliptic rotor  111  so that the angle θ is less than 90°. However, in the case of integral die molding of the first and the second walls  112  and  113 , the second wall  113  cannot be simply cut out in a vertical direction if the second wall  113  is bent toward the elliptic rotor  111 . Thus, a die structure may become complicated. The manufacturing costs of the rotor housing  114  may be increased. 
     In the present embodiment, the second wall  113  is orthogonal to the first wall  112 . Thus, the second wall  113  is substantially parallel to a perpendicular direction. Accordingly, collection efficiency of the waste toner is not deteriorated. The second wall  113  can be easily cut out in a vertical direction. 
     Accordingly, the waste toner can be efficiently collected without increasing the manufacturing costs of the rotor housing  114 . 
     In the present embodiment, the waste toner adhered to the surface of the cleaning shaft  102  is scraped off by the release blade  103 . The scraped waste toner may be scattered to the side facing away from the elliptic rotor  111  over the second wall  113 . The waste toner may be unable to be conveyed into the storage space  106 . 
     In order to solve the above problem, a distance L 4  (see  FIG. 3 ) between the apex of the second wall  113  and the peripheral surface of the cleaning shaft  102  may be reduced. However, if the distance L 4  is extremely reduced, the waste toner heaped at the apex of the second wall  113  may expand to the extent to abut the peripheral surface of the cleaning shaft  102 . 
     Then, the expanded waste toner may fall on the side facing away from the elliptic rotor  111  over the second wall  113 . The waste toner may be unable to be conveyed into the storage space  106 . 
     In the present embodiment, the distance L 4  between the apex of the second wall  113  and the peripheral surface of the cleaning shaft  102  is set to 1.5 mm and above, as later explained. Then, the scraped waste toner is prohibited from being scattered to the side facing away from the elliptic rotor  111  over the second wall  113 . The waste toner heaped at the apex of the second wall  113  is prohibited from becoming huge. 
     The distance L 4  may be any distance as far as equal to 1.5 mm and above. However, the extended distance L 4  causes the vertical size of the belt cleaner  100  to be large. Thus, in the present embodiment, the distance L 4  is set between 1.5 mm to 2.5 mm, in consideration of the vertical size of the belt cleaner  100  and the variations in size. 
       FIG. 4  shows a table of test results of conveying state of waste toner when the minimum gap sizes L 1  and L 2  between the elliptic rotor  111  and the rotor housing  114  and the angle θ between the first wall  112  and the second wall  113  are used as testing parameters. Whether or not the waste toner has been favorably conveyed was determined by visual observation. 
       FIG. 5  shows a table of test results of conveying state of waste toner when the angle θ between the first wall  112  and the second wall  113  is used as a testing parameter.  FIG. 6  shows a table of test results of conveying state of waste toner when the width size L 3  of the front end of the second wall  113  and the distance L 4  from the front end of the second wall  113  to the peripheral surface of a cleaning shaft  102  are used as testing parameters. 
       FIGS. 4 to 6 , the elliptic rotor  111  having a diameter of 8 mm is a prototype, and the elliptic rotor  111  having a diameter of 10 mm is a mass production prototype. The diameter of the elliptic rotor  111  is not a parameter that affects the sizes L 1  to L 3  and the distance L 4 . 
     The elliptic rotor  111  according to the present embodiment is made of resin. There is no problem in strength (bending rigidity) of the elliptic rotor  111  if the diameter is 8 mm and above. The diameter of the mass production prototype is 10 mm in consideration of safety margin. 
     As shown in  FIG. 4 , when the minimum gap size L 1  between the first wall  112  and the elliptic rotor  111  is set to be 0.3 mm to 2 mm as mentioned above, the waste toner can be favorably conveyed. Also as shown in  FIG. 6 , when the minimum gap size L 2  between the second wall  113  and the elliptic rotor  111  is set to be 0.3 mm or above and below 1.4 mm, the waste toner can be favorably conveyed. 
     As shown in  FIGS. 4 and 5 , if the angle θ between the first wall  112  and the second wall  113  is set larger than 90°, a lump of waste toner heaped as if leaning on the second wall  113  does not fall apart, as mentioned above. Regardless of the minimum gap sizes L 1  and L 2  between the elliptic rotor  111  and the rotor housing  114 , the waste toner cannot be smoothly conveyed. Accordingly, it is preferable that the angle θ between the first wall  112  and the second wall  113  is set to be 90° to favorably convey the waste toner. 
     Also as shown in  FIG. 6 , when the width size L 3  of the apex of the second wall  113  is set to be below 1 mm as mentioned above, accumulation of waste toner can be avoided at the apex of the second wall  113 . The waste toner can be favorably conveyed. 
     Also as shown in  FIG. 6 , when the distance L 4  between the apex of the second wall  113  and the peripheral surface of the cleaning shaft  102  is set to be 1.5 mm and above as aforementioned, the waste toner can be favorably conveyed. 
     OTHER EMBODIMENTS 
     In the above embodiment, the elliptic rotor  111  is used in the waste toner squeeze pump mechanism  110 . However, for example, a rolling piston pump may be used instead. 
     Also in the above embodiment, the first wall  112  and the second wall  113  are connected orthogonal to each other. However, for example, the first wall  112  and the second wall  113  may be connected to form a smooth curve which is substantially parallel to a locus drawn by the top of the major axis of the elliptic rotor  111 . 
     An embodiment of the present invention is described in the above. However, it should be noted that the present invention can be practiced in various manners without departing from the scope of the present invention.