Abstract:
An image-forming device includes an electrophotographic image-forming section, a receptacle, a detecting unit, a shielding member, a drive mechanism. The electrophotographic image-forming section transfers developer onto a recording sheet to form developer image thereon. The receptacle collects developer not transferred onto the recording sheet. The receptacle includes a detection portion. The detecting unit detects light passing through the detection portion. The shielding member is movably disposed in the detection portion to move between a first position blocking the light to be detected by the detecting unit and a second position allowing the light to pass through the detection portion. The drive mechanism moves the shielding member between the first position and the second position in a direction different from a vertical direction.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese patent application No. 2007-289827 filed Nov. 7, 2007. The entire contents of the priority application are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to an electrophotographic image-forming device. 
     BACKGROUND 
     For example, the image-forming device disclosed in Japanese Patent Application Publication No. 2005-257813 is provided with a receptacle for collecting developer not transferred onto the recording sheet (waste toner). Specifically, this image-forming device supplies a motive force to a screw shaft used to convey waste toner via a slipper clutch, whereby the slipper clutch interrupts the transfer of the motive force to the screw shaft when torque greater than a prescribed amount is applied to the screw shaft. An encoder that rotates together with the screw shaft detects the rotating speed of the screw shaft. 
     As the amount of waste toner accumulated in the receptacle increases, the rotational force for rotating the screw shaft is increased. When the slipper clutch interrupts the transfer of the motive force, reducing the rotating speed of the screw shaft, it is determined that the amount of toner accumulated in the receptacle has exceeded a prescribed amount, indicating chat the receptacle should be replaced. 
     SUMMARY 
     However, since the image-forming device described above employs a disk encoder, the maximum height of the receptacle cannot be made smaller than the diameter of the encoder, making it difficult to reduce the height of the overall image-forming device. 
     In view of the foregoing, it is an object of the present invention to reduce the maximum height of the receptacle mounted on the image-forming device. 
     To achieve the above and other objects, one aspect of the invention provides an image-forming device including an electrophotographic image-forming section, a receptacle, a detecting unit, a shielding member, a drive mechanism. The electrophotographic image-forming section transfers developer onto a recording sheet to form developer image thereon. The receptacle collects developer not transferred onto the recording sheet. The receptacle includes a detection portion. The detecting unit detects light passing through the detection portion. The shielding member is movably disposed in the detection portion to move between a first position blocking the light to be detected by the detecting unit and a second position allowing the light to pass through the detection portion. The drive mechanism moves the shielding member between the first position and the second position in a direction different from a vertical direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a side cross-sectional view showing the principle structure of an image-forming device according to a first embodiment of the present invention; 
         FIG. 2  is a perspective view showing the top of a belt cleaner according to the first embodiment; 
         FIG. 3  is a perspective view showing the bottom of the belt cleaner; 
         FIG. 4  is a perspective view showing the top of the belt cleaner when a cover has been removed; 
         FIG. 5  is an enlarged view of a region A in  FIG. 4 ; 
         FIG. 6  is a rear view or the belt cleaner from the side indicated by an arrow B in  FIG. 4 ; 
         FIG. 7  is a cross-sectional view of the belt cleaner along the plane VII-VII in  FIG. 6 ; 
         FIG. 8  is an enlarged cross-sectional view of a region B in  FIG. 6 ; 
         FIG. 9  is a side view of a mechanism for driving a shielding member according to the first embodiment; 
         FIG. 10  is a block diagram showing a control system in the image-forming device of the first embodiment; 
         FIG. 11  is a block diagram showing the principle components of a sensor controller according to the first embodiment; 
         FIG. 12  is a flowchart illustrating steps in a process for controlling the shielding member according to the first embodiment; 
         FIG. 13  is a graph showing the signal outputted from the sensor controller over time when toner has not accumulated in a detection space; 
         FIG. 14  is a graph showing the signal outputted from the sensor controller over time when toner has accumulated in the detection space; 
         FIG. 15  is a graph showing the signal outputted from the sensor controller over time when the belt cleaner is not mounted in the image-forming device; and 
         FIG. 16  is a side view of a mechanism for driving the shielding member according to a second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The preferred embodiment applies the electrophotographic image-forming device according to the present invention to a laser printer employing toner powder as the developer. The laser printer according to the preferred embodiment will be described next while referring to the accompanying drawings. 
     First Embodiment 
     1. Structure of the Image-Forming Device 
     In  FIG. 1 , an image-forming device  1  is oriented such that the top is the direction from which the force of gravity is applied, while the right side of the image-forming device  1  will be referred to as the “front.” The image-forming device  1  has a substantially box-shaped (solid rectangular shaped) casing  3 . A discharge tray  5  is provided on the top surface of the casing  3  for receiving and holding sheets of paper, transparencies, or the like (hereinafter simply referred to as paper) discharged from the casing  3  after printing. 
     In this embodiment, frame members (not shown) formed of metal, synthetic resin, or the like are provided on the inside of the casing  3 . Toner cartridges  70 , a fixing unit  80 , and the like described later are detachably mounted on the frame members. 
     The image-forming device  1  also includes an image-forming unit (electrophotographic image-forming section)  10  for forming images on the paper, a feeding unit  20  for supplying paper to the image-forming unit  10 , and a conveying mechanism  30  for conveying paper to four toner cartridges  70 K,  70 Y,  70 M, and  70 C constituting the image-forming unit  10 . 
     The image-forming device  1  further includes an intermediate conveying roller  90  disposed downstream of the fixing unit  80 , a discharge chute (not shown) for guiding the paper upward and back coward the front, so that the paper is inverted substantially 180 degrees, and a discharge roller  91  for discharging the paper from the casing  3  via a discharge opening  7  After images have been formed on a sheet of paper in the image-forming unit  10 , the intermediate conveying roller  90  receives and conveys the sheet along the discharge chute to the discharge roller  91 , and the discharge roller  91  discharges the paper through the discharge opening  7  onto the discharge tray  5 . 
     1.1. Feeding Unit 
     The feeding unit  20  includes a paper tray  21  accommodated in the bottommost section of the casing  3 , a feeding roller  22  disposed above the front end of the paper tray  21  for feeding (conveying) sheets of paper from the paper tray  21  to the image-forming unit  10 , and a separating pad  23  for separating the sheets of paper supplied by the  20  feeding roller  22  by applying a prescribed resistance to the paper so that one sheet is fed at a time. 
     A U-shaped conveying path is provided in the front end of the casing  3  for guiding sheets of paper fed by the feeding roller  22  from the paper tray  21  toward the image-forming unit  10  provided substantially in the center of the casing  3 . A conveying roller  24  is disposed along this substantially U-shaped conveying path leading from the paper tray  21  to the image-forming unit  10  for applying a force to the sheet to convey the sheet to the image-forming unit  10  as the sheet follows the U-shaped path. 
     A pinch roller  25  is disposed at a position opposing the conveying roller  24  along the conveying path for pressing the sheet or paper against the conveying roller  24 . Coil springs (not shown) or other urging means urge the pinch roller  25  toward the conveying roller  24 . 
     A registration roller  26  and a pinch roller  27  disposed in opposition to the registration roller  26  are provided downstream of the conveying roller  24  in the paper-conveying direction for conveying the sheet of paper toward the image-forming unit  10  after first correcting skew in the paper as the leading edge of the paper conveyed by the conveying roller  24  contacts the rollers. Coil springs (not shown) or other urging means urge the pinch roller  27  toward the registration roller  26 . 
     1.2. Conveying Mechanism 
     The conveying mechanism  30  includes a drive roller  31  that is rotated in association with the operations of the image-forming unit  10 , a follow roller  32  rotatably disposed at a position separated from the drive roller  31 , and a conveying belt  33  wound around the drive roller  31  and follow roller  32 . 
     When a sheet of paper is conveyed from the paper tray  21  onto the conveying belt  33 , the circulating conveying belt  33  sequentially conveys the sheet to each of the four toner cartridges  70 K,  70 Y,  70 M, and  70 C. 
     A belt cleaner  100  is disposed beneath the conveying belt  33  for removing toner deposited on the surface thereof. The belt cleaner  100  will be described in greater detail below. 
     1.3. Image-Forming Unit 
     The image-forming unit  10  includes a scanning unit  60 , the toner cartridges  70 , and the fixing unit  80 . The image-forming unit  10  according to this embodiment is a direct tandem-type unit capable of printing color images. 
     In this embodiment, the four toner cartridges  70 K,  70 Y,  70 M, and  70 C are arranged in a series along the paper-conveying direction and correspond to the four toner colors black, yellow, magenta, and cyan in order from the upstream side of the paper-conveying direction. 
     1.3.1. Scanning Unit 
     The scanning unit  60  is an exposure device disposed in the upper section of the casing  3  for forming electrostatic latent images on the surfaces of photosensitive drums  71  provided in each of the toner cartridges  70 K,  70 Y,  70 M, and  70 C. Specifically, the scanning unit  60  includes laser light sources, a polygon mirror, fθ lenses, and reflecting mirrors. 
     Each laser light source emits a laser beam based on image data. The laser beam is deflected off the polygon mirror through an fθ lens. Subsequently, a reflecting mirror bends the optical path of the laser beam, and another reflecting mirror bends the optical path again to a downward direction so that the bean is irradiated on the surface of the corresponding photosensitive drum  71 , forming an electrostatic latent image thereon. 
     1.3.2. Toner Cartridges 
     Since the toner cartridges  70 K,  70 Y,  70 M, and  70 C all have the same structure, differing only in the color of toner accommodated therein, only the structure of the cyan toner cartridge  70 C will be described below. Further, in the following description, the toner cartridges  70 K,  70 Y,  70 M, and  70 C will be referred to collectively as the toner cartridges  70 . 
     The toner cartridges  70  are detachably mounted in the casing  3  below the scanning unit  60 . Each toner cartridge  70  includes the photosensitive drum  71 , a charger  72 , and a toner-accomodating unit  74 . 
     Each photosensitive drum  71  functions to carry an image to be transferred onto the paper. The photosensitive drum  71  is a cylindrical member, the outer surface of which is coated with a positive-charging photosensitive layer formed of polycarbonate or the like. 
     Each charger  72  functions to charge the surface of the corresponding photosensitive drum  71 . The charger  72  is disposed diagonally above and rearward of the corresponding photosensitive drum  71 , opposing the photosensitive drum  71 , but is separated a prescribed distance therefrom. 
     The charger  72  according to this embodiment is a Scorotron charger having a charging wire formed of tungsten or the like for producing a corona discharge and functions to charge the surface of the photosensitive drum  71  with a uniform positive polarity. 
     Transfer rollers  73  are disposed on the opposite side of the conveying belt  33  from the photosensitive drums  71  and are rotatably supported in frame members (not shown) of the conveying mechanism  30 . The transfer rollers  73  rotate along with the circular movement of the conveying belt  33 . 
     The transfer rollers  73  function to transfer toner images carried on the photosensitive drums  71  onto a sheet of paper as the paper passes each of the photosensitive drums  71 . The transfer rollers  73  apply a charge of opposite polarity to the charge of the photosensitive drums  71  to the side of the paper opposite the printing surface, causing the toner deposited on the surfaces of the photosensitive drums  71  to be transferred onto the printing surface. 
     The toner-accommodating unit  74  has a toner-accommodating chamber  74 A for accommodating toner, a supply roller  74 B and a developing roller  74 C for supplying toner to the corresponding photosensitive drum  71 , and a thickness-regulating blade  74 D for regulating the thickness of toner carried on the surface of the photosensitive drum  71 . 
     With this construction, the supply roller  74 B rotates to supply toner accommodated in the toner-accommodating chamber  74 A onto the developing roller  74 C. The toner carried on the surface of the developing roller  74 C is regulated to a prescribed uniform thickness by the thickness-regulating blade  74 D. Subsequently, the layer of toner carried by the developing roller  74 C is supplied to areas on the surface of the photosensitive drum  71  that were exposed by the scanning unit  60 . 
     1.3.3. Fixing Unit 
     The fixing unit  80  is detachably mounted in the frame members of the casing  3  described earlier at a position downstream of the photosensitive drums  71  with respect to the paper-conveying direction. The fixing unit  80  functions to fix the toner transferred onto the paper with heat. 
     The fixing unit  80  includes a heating roller  81  disposed on the printing surface side of the paper that applies a conveying force to the paper while heating the toner, and a pressure roller  82  disposed on the opposite side of the paper in opposition to the heating roller  81  for pressing the paper against the heating roller  81 . 
     2. Detailed Description of the Belt Cleaner 
     As shown in  FIGS. 2 and 3 , the belt cleaner  100  is detachably mounted as a modular unit in the frame members constituting the body of the image-forming device  1 . 
     The belt cleaner  100  includes a receptacle  101  for collecting toner not transferred onto the paper. The receptacle  101  includes a receptacle body  102  and a top cover  103  covering the top of the receptacle body  102 . The top cover  103  is detachably attached to the receptacle body  102  by screws or another fastening means. 
     An intake opening  104  is provided in the top surface of the receptacle  101  (top cover  103 ) at the front end thereof for introducing toner removed from the conveying belt  33  into the receptacle  101 . 
     A cleaning roller  105  is disposed in the intake opening  104  for removing toner deposited on the surface of the conveying belt  33 . A cleaning shaft  106  conveys toner deposited on the surface of the cleaning roller  105  to a waste-toner-accumulating section (toner accumulating portion)  107  (see  FIG. 1 ). 
     In this embodiment, the cleaning roller  105  contacts the conveying belt  33  while rotating in a direction (counterclockwise direction) opposite the circulating direction of the conveying belt  33  (indicated by D 1  in  FIG. 1 ). In this way, the cleaning roller  105  can scrape off toner deposited on the conveying belt  33 . 
     The cleaning shaft  106  rotates in contact with the outer surface of the cleaning roller  105 . Further, since the cleaning shaft  106  is charged with a polarity (negative charge) opposite the polarity carried by the toner, the toner carried on the surface of the cleaning roller  105  is transferred to the cleaning shaft  106 , thereby removing waste toner from the cleaning roller  105 . 
     As shown in  FIG. 1 , a thin plate-shaped blade  108  contacts the surface of the cleaning shaft  106  for scraping off the waste toner transferred to this surface, allowing the toner to fall into the waste-toner-accumulating section  107 . 
     The waste-toner-accumulating section  107  is configured of a space for accommodating waste toner and is formed the receptacle body  102  and the top cover  103 . First and second toner-conveying pump mechanisms (toner conveying mechanisms)  109  and  110  are disposed in the waste-toner-accumulating section  107  for conveying the waste toner toward the back (rear side) of the waste-toner-accumulating section  107 , while compacting the waste toner accommodated therein. 
     The first and second toner-conveying pump mechanisms  109  and  110  have respective elliptical rotors  109 A and  110 A that are elliptically shaped in a cross section taken orthogonal to their rotational axes. The elliptical rotors  109 A and  110 A extend in a direction parallel to the axial direction of the cleaning roller  105  (hereinafter referred to as the widthwise direction) and convey waste toner toward the rear of the waste-toner-accumulating section  107 . 
     As shown in  FIG. 4 , a wall  111  extends across substantially the entire width of the waste-toner-accumulating section  107  near the rear side of the receptacle  101 , which is the downstream end in the direction that the first and second toner-conveying pump mechanisms  109  and  110  convey waste toner. The wall  111  functions as a dam for blocking waste toner conveyed by the first and second toner-conveying pump mechanisms  109  and  110  from moving further rearward. 
     As shown in  FIG. 1 , the wall  111  has a height H 1  set lower than a height H 2  of the waste-toner-accumulating section  107 . The height H 2  is a distance between the bottom wall of the receptacle body  102  and the top cover  103 . Hence, when the waste toner accumulated in the waste-toner-accumulating section  107  increases, the waste toner flows over the wall  111 , as indicated in  FIG. 7 , and flows into a waste-toner-detecting section  112  provided on the other side of the wall  111  from the waste-toner-accumulating section  107 . 
     As shown in  FIG. 4 , a detection portion  113  is provided on one end of the waste-toner-detecting section  112  in the widthwise direction. The detection portion  113  forms a detection space  113   a . Waste toner that flows over the wall  111  into the waste-toner-detecting section  112  accumulates in the detection space  113   a . As shown in  FIG. 3 , a recessed part  102 A is provided in the receptacle body  102 , and the detection portion  113  protrudes downward from the recessed part  102 A. 
     As shown in  FIG. 4 , a photosensor (detecting unit)  114  is fixedly attached to the casing  3  of the image-forming device  1  at a position opposing the detection space  113   a  formed by the detection portion. The photosensor  114  emits a beam of light into the detection space  113   a  and receives the light exiting from the detection space  113   a.    
     More specifically, the photosensor  114  has a light-emitting unit  114 A positioned on one side of the detection space  113   a  in the widthwise direction, and a light-receiving unit  114 B positioned on the other side when the belt cleaner  100  is mounted in the casing  3  (frame members), as shown in  FIG. 8 . Therefore, the detection space  113   a  (detection portion  113 ) is interposed between the light-emitting unit  114 A and the light-receiving unit  114 B while the belt cleaner  100  is mounted in the casing  3 . 
     Normally, it would be necessary to provide light-transmissible windows in the detection portion  113  constituting the detection space  113   a  at regions corresponding no a light path L of the light emitted from, the light-emitting unit  114 A. However, the detection portion  113  in this embodiment is constructed entirely of transparent members formed of an acrylic or the like, allowing the transmission of light. 
     In addition, a shielding member  115  is provided in the detection space  113   a  and is capable of being displaced between a first position blocking the light path L and a second position not blocking the light path L. The shielding member  114  is moved in a direction different from the vertical direction. In this embodiment, as shown in  FIG. 7 , the shielding member  115  is periodically pivoted in a substantially horizontal direction (front-to-rear direction in this embodiment) about a pivoting shaft  115 A disposed on the upper end of the shielding member  115 . The upper end of the shielding member  115  is fixed to the pivoting shaft  115 A. 
     An auger  116  is provided in the waste-toner-detecting section  112  near the wall  111  for conveying waste toner flowing into the waste-toner-detecting section  112  toward the detection space  113   a . Specifically, the auger  116  conveys waste toner flowing from regions other than the end in which the detection space  113   a  is provided into the waste-toner-detecting section  112  toward the detection space  113   a.    
     The auger  116  is a screw-type powder-conveying pump configured of a screw. As shown in  FIG. 5 , the screw portion of the auger  116  is configured of a spiral-shaped blade  116 A provided around a rotational shaft  116 B, and a discharge opening  116 C through which toner conveyed by the blade  116 A is discharged. 
     As shown in  FIG. 7 , the detection portion  113  includes a sloped guiding surface  113 A for guiding waste toner conveyed by the auger  116  toward the light path L, i e., toward the region in the detection space  113   a  between the light-emitting unit  114 A and light-receiving unit  114 B. The sloped guiding surface  113 A is sloped relative to the vertical and positioned on the bottom of the detection space  113   a  in an area opposing the discharge opening  116 C of the auger  116 . 
     As shown in  FIG. 9 , a pivoting center  115 B of the pivoting shaft  115 A is offset horizontally from a rotational center  116 D of the auger  116  (rotational shaft  116 B). The pivoting shaft  115 A is also coupled to the rotational shaft  116 B (auger  116 ) via a linkage  117  for converting the rotational motion of the rotational shaft  116 B to a pivoting motion. Hence, when the auger  116  (rotational shaft  116 B) rotates, the shielding member  115  is moved pivotably displaced horizontally at periods proportionate to the rotational speed. 
     The linkage  117  is a drive mechanism including a crank pin  117 A disposed at an eccentric position to the rotational center  116 D of the rotational shaft  116 B, and a linking lever  117 B with one end fixed to the pivoting shaft  115 A. A U-shaped cam groove  117 C is formed in the other end of the linking lever  117 B for slidably contacting the outer peripheral surface of the crank pin  117 A. 
     Since the belt cleaner  100  has no electric motor or other driving means in this embodiment, a drive force must be obtained from the main structure of the image-forming device  1  to rotate the auger  116 , cleaning roller  105 , and first and second toner-conveying pump mechanisms  109  and  110 . In this embodiment, these components are rotated mechanically in association with the rotation of the conveying belt  33 . 
     3. Electrical Structure of the Image-Forming Device 
     As shown in  FIG. 10 , the control system of the image-forming device  1  includes an exposure controller  201  for controlling operations of the scanning unit  60 ; a high-voltage controller  202  for controlling high voltages used in operations of the toner cartridges  70 , e g., high voltages used in operations for developing toner on the photosensitive drum  71  and for transferring toner onto the paper; a panel controller  203  for controlling a control panel (not shown) by which the user inputs settings and operations; a sensor controller  204  fox controlling the light-emitting unit  114 A and light-receiving unit  114 B of the photosensor  114  and the like; and a motor controller  205  for controlling an electric motor provided in the image-forming device  1  as the drive source. 
     The control system is also provided with a ROM  206  and a RAM  207  for storing data. More specifically, the RON  206  is a read-only storage device capable of preserving stored data, even when the power supply is interrupted. The RAM  207  is a read/write storage device capable of storing data only when receiving a power supply. 
     The control system also includes a CPU (determining unit)  208  that performs computations based on programs stored on the ROM  206  for controlling the exposure controller  201  and other controllers; and a timer  209  for keeping track of time and outputting signals indicating this time. 
     As shown in  FIG. 11 , the sensor controller  204  includes a light emission control circuit  210  for controlling operations of the light-emitting unit  114 A, and a comparator  211  for determining whether the signal level outputted by the light-receiving unit  114 B exceeds a reference level when the light-receiving unit  114 B receives light and for outputting a LOW signal to the CPU  208  when the signal level exceeds this reference level and a HIGH signal when the signal level does not exceed this reference level. 
     4. Control Operations Related to the Photosensor 
     4.1. Steps in the Control Process 
     When the power switch (not shown) of the image-forming device  1  is turned on, the image-forming device  1  begins a warm-up operation. During this operation, the image-forming device  1  begins to rotate the conveying belt  33  and the auger  116 , at which time the CPU  208  executes the control process shown in  FIG. 12 . This control process is referred to in the following description as a toner detection process. 
     At the beginning of the toner detection process in S 100 , the CPU  208  activates the sensor controller  204 . In S 110  the CPU  208  determines based on output from the sensor controller  204  whether the belt cleaner  100  is mounted in the casing  3 . The method of determining whether the belt cleaner  100  is mounted in the casing  3  will be described later in greater detail. 
     If the CPU  208  determines at this time that the belt cleaner  100  is mounted in the casing  3  (S 110 : YES), then in S 120  the CPU  208  determines based on output from the sensor controller  204  whether the waste-toner-accumulating section  107  can still accumulate toner. In other words, the CPU  208  determines whether the amount of waste toner accumulated in the waste-toner-accumulating section  107  has exceeded a predetermined amount. The method of determining whether the waste-toner-accumulating section  107  can still accumulate toner will be described later in greater detail. 
     If the CPU  208  determines that the waste-toner-accumulating section  107  can still accumulate toner (S 120 : YES), then the CPU  208  ends the current control process. However, if the CPU  208  determines that the waste-toner-accumulating section  107  can no longer accumulate toner (S 120 : YES), then in S 130  the CPU  208  issues a warning indicating this situation, and subsequently ends the current control process. In this embodiment, the CPU  208  displays a warning (error) message on a display section of the control panel (not shown) in the process of S 130 . 
     Further, if the CPU  208  determines in S 110  that the belt cleaner  100  is not mounted in the casing  3  (S 110 : NO), then in S 140  the CPU  208  issues a warning indicating that the belt cleaner  100  is not mounted in the casing  3 , and subsequently ends the control process. In this embodiment, the CPU  208  displays a warning (error) message on the display section of the control panel (not shown) in the process of S 140 . 
     4.2. Determining When the Belt Cleaner is Mounted and Determining the Toner Level 
     Since the shielding member  115  periodically pivots about the pivoting shaft  115 A, the light path L is periodically blocked by the shielding member  115  when the belt cleaner  100  is mounted in the casing  3  and toner has not accumulated in the detection space  113   a.    
     Hence, when the belt cleaner  100  is mounted in the casing  3  and toner has not accumulated in the detection space  113   a , the comparator  211  outputs a signal that periodically alternates between a HIGH signal and a LOW signal, as indicated in  FIG. 13 . 
     If the belt cleaner  100  is mounted in the casing  3  but toner has accumulated in the detection space  113   a , then the light path L is continuously blocked by the Loner. Therefore, the comparator  211  continuously outputs a HIGH signal, as indicated in  FIG. 14 . 
     Further, since the photosensor  114  is mounted in the casing  3 , if the belt cleaner  100  is not mounted in the casing  3 , the light path L is continuously not blocked. Therefore, the comparator  211  continuously outputs a LOW signal, as indicated in  FIG. 15 . 
     Accordingly, in this embodiment, the CPU  208  determines that the belt cleaner  100  is mounted in the casing  3  and that the waste-toner-accumulating section  107  is capable of further accumulating toner when light is periodically detected ( FIG. 13 ), determines that the waste-toner-accumulating section  107  can no longer accumulate toner (S 120 : NO of  FIG. 12 ) when the light is not periodically detected ( FIG. 14 ), and determines that the belt cleaner  100  is not mounted in the casing  3  when the light is continuously detected ( FIG. 15 ). 
     However, if the shielding member  115  cannot pivot due to a failure of the auger  116 , pivoting shaft  115 A, or shielding member  115 , the comparator  211  continuously outputs either a high signal or a low signal. Accordingly, the image-forming device  1  of this embodiment cannot distinguish between a case in which one of the above components has failed and a case in which either the waste-toner-accumulating section  107  can no longer accumulate toner or the belt cleaner  100  is not mounted in the casing  3 . 
     However, it is necessary to issue some kind of warning in either case since the image-forming device  1  cannot continue to operate. Therefore, the image-forming device  1  of this embodiment alerts the user by issuing a warning message, as described above, whenever the light is not periodically detected. 
     5. Features of the Image-Forming Device According to this Embodiment 
     In this embodiment, the shielding member  115  is periodically reciprocated in a horizontal direction between a position blocking the light path L of light detected by the light-receiving unit  114 B and a position not blocking the light path L. Therefore, it is not necessary to allocate space in the vertical direction, i.e., the height direction for moving the shielding member  115 . 
     Thus, the maximum height dimension of the belt cleaner  100  can be reduced, thereby reducing the height dimension of the image-forming device  1 . 
     Further, in this embodiment described above, the detection space  113   a  is formed by the sloped guiding surface  113 A for guiding toner conveyed into the detection space  113   a  toward the light path L, thereby ensuring that toner conveyed into the detection space  113   a  is reliably detected. 
     Second Embodiment 
     In the first embodiment described above, the shielding member  115  is pivoted. However, in a second embodiment, a shielding member  215  is reciprocated in a direction parallel to the horizontal, as shown in  FIG. 16 . 
     More specifically, as shown in  FIG. 16 , a lever  117 D fixed to the pivoting shaft  115 A pivots together with the linking lever  117 B. A restricting pin  117 E, which is provided on a side wall of the detection part  113 , is slidably inserted into an elongated hole  215 C formed in the shielding member  115  for restricting displacement of the shielding member  215 . A coupling pin  215 D is fixed to the shielding member  215 . The coupling pin  215 D is slidably inserted into an elongated hole  117 F of the linkage  117 . 
     Therefore, when the linking lever  117 B pivots, the shielding member  215  reciprocates in the front-to-rear direction (left-to-right direction in  FIG. 16 ), while the vertical displacement of the shielding member  215  is restricted by the restricting pin  117 E and the elongated hole  215 C. 
     Variations of the Embodiments 
     In these embodiments described above, the shielding members  115  and  215  is reciprocated in the front-to-rear direction of the image-forming device  1 , but the present invention is not limited to this configuration. For example, the shielding members  115  and  215  may be reciprocated in the widthwise direction. 
     Further, while the “direction different from the vertical direction” is a horizontal direction in these embodiments described above, the present invention is not limited to this direction. 
     Further, while the shielding members  115  and  215  are reciprocated by a drive force obtained from the auger  116  in these embodiments described above, the present invention is not limited to this configuration. 
     Further, while the present invention is applied to a direct tandem laser printer in these embodiments described above, the present invention is not limited to this application. For example, the present invention may be applied to a monochrome electrophotographic image-forming device. 
     Further, while an exposure device is employed for scanning laser beams over the photosensitive drums  71  in these embodiments described above, the present invention is not limited to this configuration. For example, a plurality of LEDs may be arranged along the axial direction of the photosensitive drums  71 , and the photosensitive drums  71  may be exposed by flashing the LEDs. 
     While the invention has been described in detail with reference to specific embodiments thereof, it would be apparent to those skilled in the art that many modifications and variations may be made therein without departing from the spirit of the invention, the scope of which is defined by the attached claims.