Patent Publication Number: US-8977161-B2

Title: Image forming apparatus and light scanning device

Description:
INCORPORATION BY REFERENCE 
     This application is based upon, and claims the benefit of priority from the corresponding Japanese Patent Application No. 2012-029333, filed in the Japan Patent Office on Feb. 14, 2012, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     This disclosure relates to an image forming apparatus that forms an image on a sheet and to a light scanning device that scans an object to be scanned with light. 
     Image forming apparatuses, such as printers and copiers, often have an image bearing member that has an image to be transferred to a sheet, and an exposure unit that irradiates the image bearing member with light to form an electrostatic latent image thereon. High-speed image forming is achieved by making the exposure unit form an electrostatic latent image on the image bearing member at high speeds. 
     A typical exposure unit includes a housing and various optical elements accommodated in the housing. Such optical elements include, for example, a light-emitting element that emits light to form an electrostatic latent image and a rotating mirror that scans the image bearing member with light. Due to the emission of light from the light-emitting element and rotation of the rotating mirror, heat is generated and stays in the housing. 
     Because, as mentioned above, the exposure unit includes various optical elements, the housing of the exposure unit needs to be highly dustproof. Thus, the housing has a sealed structure. However, such a sealed structure encourages the heat to stay in the housing. Deformation of the housing due to the heat may change the optical settings of optical elements in the housing. Hence, it is preferable to use a resin having high heat resistance as the resin constituting the housing. In this case, the housing of the exposure unit may be relatively expensive. In particular, when the rotating mirror in the exposure unit is operated at high speed to increase the image-forming speed, the amount of heat accumulated in the housing may increase. Thus, the housing may be made from a resin having greater heat resistance. Consequently, an increase in the maximum image-forming speed achieved by an image forming apparatus (hereinbelow, “maximum image-forming speed”) may cause an increase in cost of the housing. 
     A reduction in size of the housing of the exposure unit may reduce the cost of the materials of the housing. However, such a reduction in size of the housing can further encourage the heat to stay in the housing. 
     Most optical elements in the exposure unit are made from an optical resin. Hence, the optical elements in the exposure unit may be made from a highly heat resistant optical resin, taking into consideration the heat accumulated in the housing. Therefore, an increase in image-forming speed may cause an increase in cost of the optical elements, as therefore the housing. 
     The relationship between the image-forming speed and the cost of material of the exposure unit, as described above, may be an obstacle to increasing the maximum image-forming speed. 
     SUMMARY 
     An image forming apparatus according to an embodiment of this disclosure includes an image bearing member, an exposure unit, and a main housing. An electrostatic latent image is formed on the image bearing member. The exposure unit includes an optical device that irradiates the image bearing member with light to form the electrostatic latent image, and a housing that defines a storage space in which the optical device is located. The main housing includes a partition wall that divides an inner space of the main housing into a first space, in which the image bearing member is located, and a second space in which the exposure unit is located. The housing includes a first opening wall having a first opening through which the storage space communicates with the second space. The optical device irradiates the image bearing member with light through the first opening. 
     A light scanning device according to another embodiment of this disclosure includes an optical device, a housing, and a main housing. The optical device scans an object to be scanned with light. The housing defines a storage space in which the optical device is located. The main housing includes a partition wall that creates an inner space in which the optical device and the housing are located and an another space. The housing includes an opening wall having an opening through which the storage space communicates with the space in which the optical device is located. The optical device irradiates the object to be scanned with light through the opening. 
     Additional features and advantages are described herein, and will be apparent from the following Detailed Description and the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a schematic cross-sectional view of a printer, which is an example of an image forming apparatus. 
         FIG. 2  is a schematic perspective view of an embodiment of a printer. 
         FIG. 3  is a schematic perspective view of an upper part of the printer. 
         FIG. 4  is a schematic perspective view of the upper part of the printer without a front cover, a sheet-output portion, a left rib wall, and a right rib wall. 
         FIG. 5  is a schematic perspective view of the upper part of the printer without the front cover, the sheet-output portion, the left rib wall, the right rib wall, and an upper plate. 
         FIG. 6  is a schematic perspective view of the upper part of the printer without the front cover, the sheet-output portion, the left rib wall, the right rib wall, the upper plate, and an exposure unit. 
         FIG. 7  is a schematic perspective view of the exposure unit. 
         FIG. 8  is a schematic plan view of the exposure unit. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the attached drawings, an example image forming apparatus will be described below. Note that terms representing directions, such as upper, lower, left, and right, are intended to help clarify the descriptions. The drawings and the details of the description given below are not limiting the configuration of the image forming apparatus and light scanning device. 
       FIG. 1  is a schematic cross-sectional view of a printer  100 , which is an example of an image forming apparatus.  FIG. 2  is a schematic perspective view of the printer  100 . The printer  100  will be described with reference to  FIGS. 1 and 2 . 
     The printer  100  includes a rectangular box-shaped main housing  200 . The main housing  200  accommodates various units for forming an image (described below). 
     The main housing  200  includes a front wall  210  that stands upright, a back wall  220  opposite the front wall  210 , a left wall  230  that stands upright between the front wall  210  and the back wall  220 , and a right wall  240  opposite the left wall  230 . The main housing  200  further includes an upper wall  250  that closes an area enclosed by the upper edges of the front wall  210 , back wall  220 , left wall  230 , and right wall  240 , and a lower wall  260  opposite the upper wall  250 . 
     The front wall  210  includes a front cover  211  provided adjacent to the front edge of the upper wall  250 , and upright plates  212  provided on the left and right sides of the front cover  211 . The front cover  211  horizontally extends along the front edge of the upper wall  250 . The upright plates  212  vertically extend downwardly from the front edge of the upper wall  250 . Hence, the front wall  210  has a gate shape, defining an opening  213  at a lower part of the main housing  200 . 
     The printer  100  includes a cassette  300  that stores sheets. The cassette  300  is inserted into the main housing  200  from the opening  213  defined by the front wall  210 . 
     The cassette  300  includes a lift plate  310  that supports the sheets. The lift plate  310  raises the leading edges of the sheets. 
     The printer  100  includes a sheet-feed roller  320  that is in contact with the leading edge of the sheets raised by the lift plate  310 , and a separation plate  321  located adjacent to the sheet-feed roller  320 . The sheet-feed roller  320  is rotated such that it picks up a sheet from the cassette  300 . The separation plate  321  applies friction to a lower surface of the sheet. When the sheet-feed roller  320  picks up several sheets from the cassette  300 , the sheets are separated by the friction applied by the separation plate  321 . When the sheet-feed roller  320  picks up a sheet from the cassette  300 , the sheet-feed roller  320  feeds the sheet downstream in a sheet feeding direction by overcoming the friction applied by the separation plate  321 . Thus, the sheets are fed downstream in the sheet feeding direction one at a time. The sheets are then transported upward along a transport path formed along the back wall  220  of the main housing  200 . 
     The printer  100  further includes a registration roller pair  330  that receives the sheet fed from the sheet-feed roller  320 , and an image forming section  400  that forms an image on the sheet. The registration roller pair  330  feeds the sheet to the image forming section  400 , in synchronization with an image forming process (described below) that is performed by the image forming section  400 . 
     The image forming section  400  includes a photoconductive drum  410  on which an electrostatic latent image and a toner image are formed, a charger  420  that uniformly charges the circumferential surface of the photoconductive drum  410 , and an exposure unit  500  that irradiates the charged circumferential surface of the photoconductive drum  410  with a laser beam. As the photoconductive drum  410  rotates, an electrostatic latent image is formed on the photoconductive drum  410 , and subsequently, a toner image is formed on the photoconductive drum  410 . The toner image is eventually transferred to the sheet fed by the registration roller pair  330 . 
     The printer  100  receives image data from an external device (for example, a personal computer (not shown)). The exposure unit  500  scans the circumferential surface of the photoconductive drum  410  with a laser beam, based on the image data. As a result, an electrostatic latent image, corresponding to the image data, is formed on the circumferential surface of the photoconductive drum  410 . The photoconductive drum  410  is an example of an image bearing member. The image bearing member is an example of an object to be scanned. 
     The image forming section  400  also includes a developing unit  430  that supplies toner to the circumferential surface of the photoconductive drum  410  on which the electrostatic latent image is formed, and a toner container  440  that supplies toner to the developing unit  430 . Due to the supply of the toner from the developing unit  430 , the toner image corresponding to the electrostatic latent image is formed on the circumferential surface of the photoconductive drum  410 . The toner is supplied from the toner container  440  to the developing unit  430  as necessary, so that there is enough toner in the developing unit  430 . 
     The image forming section  400  also includes a transfer roller  450  that receives the sheet fed from the registration roller pair  330 , in cooperation with the photoconductive drum  410 . While the sheet passes between the photoconductive drum  410  and the transfer roller  450 , the transfer roller  450  attracts the toner image on the circumferential surface of the photoconductive drum  410  to the sheet. Thus, the toner image is transferred to the sheet. The photoconductive drum  410  and the transfer roller  450  feed the sheet upward. 
     The printer  100  further includes a fixing unit  600  that fixes the toner image to the sheet. The fixing unit  600  includes a heating roller  610  that generates heat to fuse the toner on the sheet, and a pressure roller  620  that presses the surface of the sheet provided with the toner image onto the heating roller  610 . The sheet leaving the photoconductive drum  410  and the transfer roller  450  passes between the heating roller  610  and the pressure roller  620 , during which the toner fused by the heating roller  610  permeates into the sheet, and the toner image is fixed to the sheet. Then, the fixing unit  600  sends the sheet upwardly. 
     The printer  100  includes a sheet-output roller  340 . The fixing unit  600  sends the sheet to the sheet-output roller  340 . The sheet-output roller  340  outputs the sheet outside from the inside of the main housing  200 . 
     The upper wall  250  of the main housing  200  includes a sheet-output portion  251  that receives the sheet output from the main housing  200  by the sheet-output roller  340 . The sheet-output portion  251  includes an inclined surface extending downward from the upper edge of the front wall  210 . 
     The upper wall  250  also includes a left rib wall  252  protruding upwardly on the left side of the sheet-output portion  251 , a right rib wall  253  protruding upwardly on the right side of the sheet-output portion  251 , and a top plate  254  extending between the left rib wall  252  and the right rib wall  253  along the upper edge of the back wall  220 . An output port  255 , through which the sheet is outputted, is located between the top plate  254  and the sheet-output portion  251 . The sheet-output portion  251 , the top plate  254 , the left rib wall  252 , and the right rib wall  253  define a concave portion in which sheets fed from the output port  255  are stacked. In this embodiment, the sheet-output portion  251 , the left rib wall  252 , and the right rib wall  253  are integrally formed. 
       FIGS. 3 and 4  are schematic perspective views of the printer  100 . Referring to  FIGS. 1 ,  3 , and  4 , the main housing  200  will be described.  FIG. 3  mainly shows the upper wall  250  of the main housing  200 .  FIG. 4  shows the printer  100  without the front cover  211 , the sheet-output portion  251 , the left rib wall  252 , and the right rib wall  253 . 
     As illustrated in  FIG. 1 , the main housing  200  includes an inner wall  270  that divides the inner space into a space where the exposure unit  500  is located (hereinbelow, “second space  120 ”) and a space in which the other devices for forming an image are located (hereinbelow, “first space  110 ”). For example, the other devices located in the first space  110  are the cassette  300 , the image forming section  400 , and the fixing unit  600 . The inner wall  270  is an example of a partition wall. 
     When the cassette  300  is inserted into the main housing  200 , dust may enter the first space  110 . Because the inner wall  270  separates the second space  120  and the first space  110 , the exposure unit  500  in the second space  120  is appropriately protected from the dust floating in the first space  110 . In other words, the inner wall  270  blocks the dust. 
     The inner wall  270  includes a support plate  271  that supports the exposure unit  500 , an open plate  273  having an opening  272  through which a laser beam emitted from the exposure unit  500  passes, a standing plate  274  that stands upright between the exposure unit  500  and the front cover  211 , and an upper plate  275  that covers the opening between the upper edges of the open plate  273  and the standing plate  274 . The laser beam emitted from the exposure unit  500  passes through the opening  272  and travels to the photoconductive drum  410 . The opening  272  is an example of a second opening. The open plate  273  is an example of a second opening wall. 
     As illustrated in  FIGS. 3 and 4 , the front cover  211 , the sheet-output portion  251 , the left rib wall  252 , and the right rib wall  253  are removable from the printer  100 . When the front cover  211 , the sheet-output portion  251 , the left rib wall  252 , and the right rib wall  253  are removed from the printer  100 , the upper plate  275  of the inner wall  270  is exposed. 
       FIGS. 5 and 6  are schematic perspective views of the upper part of the printer  100 . Referring to  FIGS. 1 and 4  to  6 , the main housing  200  will be described in more detail.  FIG. 5  shows the printer  100  without the front cover  211 , the sheet-output portion  251 , the left rib wall  252 , the right rib wall  253 , and the upper plate  275 .  FIG. 6  shows the printer  100  without the front cover  211 , the sheet-output portion  251 , the left rib wall  252 , the right rib wall  253 , the upper plate  275 , and the exposure unit  500 . 
     As illustrated in  FIGS. 5 and 6 , the inner wall  270  includes a left plate  276  that stands upright from the support plate  271  on the left side of the exposure unit  500 , and a right plate  277  that stands upright from the support plate  271  on the right side of the exposure unit  500 . Unlike the open plate  273 , no opening is formed in the support plate  271 , the standing plate  274 , the upper plate  275 , the left plate  276 , or the right plate  277 . Therefore, the support plate  271 , the standing plate  274 , the upper plate  275 , the left plate  276 , and the right plate  277  completely separate the first space  110  from the second space  120 . The support plate  271 , the standing plate  274 , the upper plate  275 , the left plate  276 , and the right plate  277  are an example of a second closing wall. 
     As illustrated in  FIG. 1 , the main housing  200  further includes a dustproof glass member  278  that closes the opening  272 . Thus, the second space  120  is completely separated from the first space  110 . Instead of the dustproof glass member  278 , another closing member that prevents dust floating in the first space  110  from entering the second space  120  may be attached to the open plate  273  so as to close the opening  272 . 
       FIG. 7  is a schematic perspective view of the exposure unit  500 . Referring to  FIGS. 1 and 7 , the exposure unit  500  will be described. 
     As illustrated in  FIG. 1 , the exposure unit  500  includes a housing  510 . The housing  510  defines a storage space  501  in which the optical device  520  is located. In other words, the housing  510  has a storage space  501  therein. The optical device  520  irradiates the photoconductive drum  410  with a laser beam to form an electrostatic latent image. 
     As illustrated in  FIG. 7 , the housing  510  includes an open-top box member  511  and a lid member  512  to close the opening in the box member  511 . 
       FIG. 8  is a schematic plan view of the exposure unit  500 . Referring to  FIGS. 1 and 8 , the exposure unit  500  will be described in more detail.  FIG. 8  shows the exposure unit  500  without the lid member  512 . 
     As illustrated in  FIG. 8 , the optical device  520  includes a laser light source  521  that emits a laser beam, an optical element group  522  that adjusts the properties of the laser beam (for example, the beam diameter), and a polygon mirror  523  that receives the laser beam passing through the optical element group  522 . The laser light source  521  emits a laser beam toward the polygon mirror  523 . The laser light source  521  is an example of the light source. 
     As illustrated in  FIG. 1 , the optical device  520  also includes a motor  524  that rotates the polygon mirror  523 . Due to rotation of the polygon mirror  523 , the laser beam is deflected toward the photoconductive drum  410 . Due to rotation of the polygon mirror  523 , the photoconductive drum  410  is scanned with a laser beam moved in the left-right direction in  FIG. 8 . The motor  524  causes the polygon mirror  523  to rotate at a high speed. This causes the motor  524  to generate heat. Thus, the motor  524  serves as a heat source. As will be described below, in this embodiment, accumulation of heat generated by the heat source (for example, the motor  524 ) in the storage space  501  is appropriately suppressed. The polygon mirror  523  and the motor  524  are an example of a deflection element. 
     As illustrated in  FIG. 8 , the optical device  520  includes an fθ lens  529  extending in the left-right direction. The fθ lens  529  receives the laser beam deflected by the polygon mirror  523  and forms an image on the circumferential surface of the photoconductive drum  410 . The fθ lens  529  is an example of an imaging lens. 
     The box member  511  includes a first support plate  513 , which supports the optical element group  522 , the polygon mirror  523 , the motor  524 , and the fθ lens  529 , and a second support plate  514 , which supports the laser light source  521 . The box member  511  also includes an open plate  515  facing the fθ lens  529 . The open plate  515  has an opening  516  through which a laser beam moved in the left-right direction in  FIG. 8  can pass. The laser beam emitted toward the second space  120  through the opening  516  passes through the transparent dustproof glass member  278  attached so as to close the opening  272  and travels to the circumferential surface of the photoconductive drum  410 . 
     The storage space  501  communicates with the second space  120  through the opening  516 . Thus, air in the storage space  501  can flow into the second space  120 , and air in the second space  120  can flow into the storage space  501 ; that is, air may be exchanged between the storage space  501  and the second space  120 . Opening  516  is an example of a first opening. Open plate  515  is an example of a first opening wall. 
     The box member  511  further includes a first facing plate  519  facing the open plate  515 , and a second facing plate  517  facing the second support plate  514 . Unlike the open plate  515 , no opening is formed in the first facing plate  519 , the second facing plate  517 , the first support plate  513 , the second support plate  514 , or the lid member  512 . Therefore, the first facing plate  519 , the second facing plate  517 , the first support plate  513 , the second support plate  514 , and the lid member  512  completely separate the storage space  501  from the second space  120 . The first facing plate  519 , the second facing plate  517 , the first support plate  513 , the second support plate  514 , and the lid member  512  are an example of a first closing wall. 
     As described above, air is exchanged between the storage space  501  and the second space  120  through the opening  516 . Thus, heat generated by the motor  524  may be released from the storage space  501  to the second space  120 . Therefore, the accumulation of heat in the storage space  501  is prevented. 
     As described above, the polygon mirror  523  is rotated in the storage space  501 . The rotation of the polygon mirror  523  may facilitate exchange of air between the storage space  501  and the second space  120 . Therefore, accumulation of heat in the storage space  501  is further relieved. 
     As described above, dust may enter the first space  110  of the main housing  200 . However, because the inner wall  270  separates between the second space  120  and the first space  110 , the exposure unit  500  in the second space  120  is protected from the dust floating in the first space  110 . 
     Accordingly, the printer  100  can protect the optical device  520  of the exposure unit  500  from dust. Furthermore, the printer  100  can increase the maximum image-forming speed achieved by the printer  100 , without requiring the housing  510  of the exposure unit  500  and the optical device  520  in the housing  510  to have excessively high heat resistance. Furthermore, using the printer  100 , the housing  510  of the exposure unit  500  may be reduced in size. 
     It is desirable that the second space  120  have a capacity that is at least 1.5 times as large as that of the storage space  501 . The inventor observed no marked increase in temperature inside the storage space  501  while the polygon mirror  523  was rotated by the motor  524  and the motor  524  was generating heat, when the second space  120  has a capacity at least 1.5 times as large as that of the storage space  501 . 
     The provision of the dustproof glass member  278  is optional. As long as the distance between the opening  516  provided in the open plate  515  of the exposure unit  500  and the opening  272  provided in the open plate  273  of the inner wall  270  is large enough, the air existing between the open plates  515  and  273  prevents the air inside the first space  110  from flowing into the storage space  501 . The inventor found that, even if the opening  272  is not covered by a closing member, such as the dustproof glass member  278 , entrance of dust into the storage space  501  is almost completely prevented using a distance of at least 1 cm between the open plates  515  and  273 . 
     Although the printer has been described as an example of an image forming apparatus in the embodiment of this disclosure, the spirit of this disclosure may also be applied to other image forming apparatuses, such as copiers and multifunction peripherals, and light scanning devices, such as projectors, which scan an object to be scanned (e.g., a screen) with light. 
     It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.