Abstract:
An image forming apparatus with a plate having holes is described. An image forming apparatus includes image carriers, side walls, and a plate disposed below the image carriers. The plate includes a plurality of holes along the sides of the plate near the side walls. The image carriers, the side walls, and the plate form one or more passages for air to flow during operation of a cooling fan.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from Japanese Patent Application No. 2008-083986, filed on Mar. 27, 2008, the entire subject matter of which is incorporated herein by reference. 
       FIELD 
       [0002]    Aspects of the invention relate to an image forming apparatus configured to electrophotographically form an image on a recording medium. More specifically, aspects of the invention relate to an image forming apparatus including a sheet supply unit that is configured to hold recording media in stack, and a plurality of image formation units that are arranged in line along an upper surface of the sheet supply unit. 
       BACKGROUND 
       [0003]    A known image forming apparatus may include some units that produce heat, such as an image formation unit having an image carrier, e.g. a photosensitive drum, and a scanner unit that is configured to expose the photosensitive drum to light. To prevent overheating in such units of the image forming apparatus, a variety of cooling methods by channeling air inside the apparatus have been proposed. For example, such a structure has been proposed that includes a passage that is configured to channel air between the image formation unit and the scanner unit, a duct that is configured to convey air to a lower part of the image formation unit, and a fan that is configured to produce air. 
       SUMMARY 
       [0004]    Aspects of the invention provide an image forming apparatus configured to effectively discharge air inside. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    Illustrative aspects will be described in detail with reference to the following figures in which like elements are labeled with like numbers and in which: 
           [0006]      FIG. 1  is a side sectional view schematically illustrating an internal structure of an illustrative example of an image forming apparatus using features described herein; 
           [0007]      FIG. 2  is a perspective view of an engine frame of the image forming apparatus; and 
           [0008]      FIG. 3  is a cross sectional view taken along the line X-X of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    An illustrative embodiment will be described in detail with reference to the accompanying drawings. An image forming apparatus according to aspects of the invention applies is shown in  FIG. 1 . 
         [0010]    It is noted that various connections are set forth between elements in the following description. It is noted that these connections in general and, unless specified otherwise, may be direct or indirect and that this specification is not intended to be limiting in this respect. 
         [0011]    For ease of discussion, in the following description, the top or upper side, the bottom or lower side, the left or left side, the right or right side, the front or front side, and the rear or rear side are used to define the various parts when an image forming apparatus  1  is disposed in an orientation in which it is intended to be used. In  FIG. 1 , the left side is referred to as the front or front side, the right side is referred to as the rear or the rear side, the up side is referred to as the top or upper side, and the down side is referred to as the bottom or lower side. 
         [0012]    A general structure of the image forming apparatus  1  will be described. 
         [0013]    As shown in  FIG. 1 , the image forming apparatus  1  is a color printer of direct transfer tandem type, and may include a generally box-shaped housing  2 . A top surface of the housing  2  contains an output tray  5  on which a recording medium, e.g. a recording sheet  4  having an image thereon can be placed. It is appreciated that indirect configurations of the printer may also be used (in which the printer includes a transfer belt that conveys an image to a recording medium). 
         [0014]    A sheet supply tray  7  may be disposed in a lower portion of the housing  2  and configured to load a stack of sheets  4  therein. The sheet supply tray  7  may be configured to be pulled out toward the front. The sheet supply tray  7  is provided with a sheet pressing plate (not shown) inclinable to raise the front end of the stack of sheets  4 . A pickup roller  11  to pick up sheets  4  is disposed in a front upper portion of the sheet supply tray  7 . A separation roller  12  and a separation pad  13  are disposed on a downstream side of the pickup roller  11  in a direction where a sheet  4  is conveyed (hereinafter referred to as a sheet conveying direction). The separation roller  12  and the separation pad  13  are configured to separate the sheets  4  picked up by the pickup roller  11  one by one. 
         [0015]    The uppermost recording sheet  4  in the sheet supply tray  7  is pressed against the pickup roller  11 , fed and caught between the sheet supply roller  12  and the separation pad  13 , and singly separated from a stack of recording sheets  4 . The recording sheet  4  is then fed by a pair of feed rollers  14  toward registration rollers  15 . The registration rollers  15  feed the recording sheet  4  at a predetermined timing onto a belt unit  20 . 
         [0016]    The belt unit  20  is configured to be attached to and removed from the housing  2  and includes a drive roller  21 , a tension roller  22 , and a conveyor belt  23 . The drive roller  21  and the tension roller  22  are spaced apart in the front-rear direction in parallel to each other at their rotation shafts. The tension roller  22  is urged toward the front by a spring (not shown) to apply an appropriate tension to the conveyor belt  23 . Thus, the conveyor belt  23  is horizontally extended between and looped around the drive roller  21  and the tension roller  22 . The conveyor belt  23  is an endless semiconducting belt (transfer belt) made of a resin such as polycarbonate. When the drive roller  21  disposed at the rear is driven and rotated by a main motor (not shown), the conveyor belt  23  rotates counterclockwise in  FIG. 1  to convey the sheet  4  thereon rearward. 
         [0017]    Inside the conveyor belt  23 , four transfer rollers  24  are spaced apart at regular intervals in the front-rear direction. The transfer rollers  24  are disposed facing respective photosensitive drums  31  of process units, e.g., image formation units  30  via the conveyor belt  23 . In other words, the conveyor belt  23  is sandwiched between the transfer rollers  24  and the corresponding photosensitive drums  31 . During image transfer, a bias is applied between the transfer rollers  24  and the corresponding photosensitive drums  31 , and a specified amount of current is passed therebetween. 
         [0018]    A belt cleaner unit  40  is disposed below the belt unit  20 . The belt cleaner unit  40  includes a cleaning roller  41  and is configured to remove waste, such as toner and dust adhering to the conveyor belt  23 . 
         [0019]    The image forming apparatus  1  includes four image formation units  30  paired with LED units  50 . The image formation units  30  are disposed at front of the corresponding LED units  50 . The image formation units  30  are provided for four colors of black, cyan, magenta, and yellow and arranged in this color order from an upstream side with respect to the sheet conveying direction or from the front side of the image forming apparatus  1 . The image formation units  30  and the LED units  50  are arranged in line along the sheet conveying direction. The image formation units  30 , the LED units  50 , and the belt unit  20  function as an image formation device. 
         [0020]    Each image formation unit  30  is of known construction and includes an electrostatic latent image carrier, e.g. the photosensitive drum  31 , a toner chamber  32 , and a developing roller  33 . The toner chamber  32  accommodates a developer, e.g. one-component toner, which is to be positively charged, of black, cyan, magenta, or yellow. The developing roller  33  is disposed opposite to the photosensitive drum  31  and configured to positively charge toner and supply it to the photosensitive drum  31 . In the image formation unit  30 , upon rotation of the photosensitive drum  31 , the surface of the photosensitive drum  31  is uniformly and positively charged by a scorotron charger (not shown), and exposed to light emitted from an array of light emitting diodes (LEDs, not shown) arranged in a line at a lower end of the LED unit  50  across the width of a sheet or in the left-right direction of the image forming apparatus  1 , and an electrostatic latent image is formed, on the surface of the photosensitive drum  31 , based on the image to be formed on the sheet  4 . 
         [0021]    When the developing roller  33  rotates, positively charged toner carried on the developing roller  33  is supplied to the electrostatic latent image formed on the surface of the photosensitive drum  31 . Thus, the latent image on the photosensitive drum  31  becomes visible, and a toner image, in which toner is adhered to an exposed area only, is carried on the surface of the photosensitive drum  31 . 
         [0022]    While the sheet  4  is conveyed by the conveyor belt  23  and passes between each photosensitive drum  31  and its corresponding transfer roller  24 , the toner image carried on the surface of each photosensitive drum  31  is successively transferred onto the sheet  4  by the current. The sheet  4  to which the toner image of each color has been transferred in this manner is conveyed to a fixing unit  60 . 
         [0023]    The fixing unit  60  is disposed at the rear of the conveyor belt  23  in the housing  2 . The fixing unit  60  includes a heat roller  61  and a pressure roller  62 . The heat roller  61  has a heat source such as a halogen lamp and is configured to be driven and rotated. The pressure roller  62  is disposed facing the heat roller  61  so as to press the heat roller  61  from below and configured to be rotated along with the rotation of the heat roller  61 . In the fixing unit  60 , the sheet  4  having the toner image of each color thereon is heated while it is conveyed between the heat roller  61  and the pressure roller  62 , and the toner image of each color is thermally fixed onto the sheet  4 . The sheet  4  on which the toner image of each color has been thermally fixed is conveyed between ejection rollers  63 , which are disposed diagonally above the fixing unit  60 . The sheet  4  is further conveyed between ejection rollers  64  disposed in the upper portion of the housing  2 , and is finally ejected to the output tray  5 . 
         [0024]    A fan  67  is disposed above the fixing unit  60 . The fan  67  and a circuit board  69  are disposed on the right side of the image forming apparatus  1 . The fan  67  is configured to circulate air, e.g. suck air through a duct  66  that is disposed above the fixing unit  60  and behind the image formation units  30 . The circuit bard  69  is configured to supply power to the individual parts. A pair of engine frames  70  is disposed on the right and left sides of the belt unit  20 , the image formation units  30 , the belt cleaner unit  40 , and the LED units  50  to support them. 
         [0025]    The engine frames  70  that support the above units will be described with reference to  FIG. 2 .  FIG. 2  is a perspective, partially cutaway view of the engine frames  70 . As shown in  FIG. 2 , the engine frames  70  are formed of sheet metal by stamping to have left-right symmetry, and disposed inside the housing  2 . The engine frames  70  are connected by tubular reinforcing members  80  disposed horizontally at four places of a front upper portion, a front lower portion, a rear upper portion, and a rear lower portion. A flat partition plate  71  is fixed at the lower ends of the engine frames  70  and configured to horizontally partition between the belt cleaner unit  40  and the sheet supply tray  7 . 
         [0026]    Each engine frame  70  is provided with a belt unit mounting portion  72  in which the belt unit  20  is mounted via a resin member (not shown), four image forming unit mounting portions  73  in which the image formation units  30  are mounted, a belt cleaner mounting portion  74  in which the belt cleaner unit  40  is mounted via a resin member (not shown), and four LED unit mounting portion  75  to which the LED units  50  are mounted. The partition plate  71  is formed with a number of holes  77 . The holes  77  are disposed in two rows along and on each side of the partition plate  71  with respect to the sheet conveying direction. 
         [0027]      FIG. 3  is a cross sectional view taken along the line X-X of  FIG. 1  in which the LED units  50  are not shown. As shown in  FIG. 3 , the engine frames  70  are supported between a pair of resin frames  2 L,  2 R that make up a part of the housing  2 , such that the partition plate  71  is disposed a predetermine distance apart above the sheet supply tray  7 . The resin frames  2 L,  2 R are made of a synthetic resin and shaped in hollow rectangular solids. The right resin frame  2 R accommodates the fan  67  and the circuit board  69 , and the left resin frame  2 L accommodates a drive system  88  configured to drive each unit. The belt cleaner unit  40 , the belt unit  20 , the four image formation units  30 , and the four LED units  50  are disposed above the partition plate  71  in this order from the bottom between the pair of the engine frames  70 . 
         [0028]    As shown in  FIGS. 1 and 3 , the duct  66  is disposed behind the rearmost image formation unit  30  and an intake  66 A of the duct  66  is oriented toward an upper portion of the image formation unit  30 . When the fan  67  is driven, a current of air is produced as shown by arrows A (broken and unbroken) of  FIG. 3 . That is, air passes through the holes  77  of the partition plate  71  from a space above the sheet supply tray  7 , and clearances between the left and right sides of the belt cleaner unit  40  and the belt unit  20  and the corresponding engine frames  70 . Then, air diffuses around each image formation unit  30 , passes around each LED unit  50 , moves upward through the intake  66 A, and is discharged outside from the fan  67 . This passage of air allows each image formation unit  30  and neighboring components to be cooled favorably. 
         [0029]    In this embodiment, air is taken through the holes  77  that are formed on the partition plate  71  from the space above the sheet supply tray  7  which is freely ventilated with outside. This eliminates the need for a duct or intake for feeding air downward. Thus, the image forming apparatus  1  of the embodiment can provide an increased flexibility in designing, and a simple structure, which can reduce manufacturing costs. As shown in the embodiment, when the left and right resin frames  2 L,  2 R are provided with the drive system  88  and the circuit board  69  respectively, a space for providing an intake may be reduced, however, there is no need to dispose such an intake. In addition, when air passes between the driving system  88  and the image formation units  30 , air warmed by a motor (not shown) disposed in the driving system  88  can be favorably discharged. 
         [0030]    This illustrative embodiment shows, but is not limited to, that electrostatic latent images are formed on the photosensitive drums  31  by LEDs. The electrostatic latent images may be formed on the photosensitive drums  31  by laser light. 
         [0031]    This illustrative embodiment shows, but is not limited to, that air inside is discharged from the right side of the image forming apparatus  1  by the fan  67 . Air inside may be discharged from the rear side, top side, front side, left side, bottom side and any combinations of sides of the image forming apparatus  1 . 
         [0032]    It will be appreciated that this embodiment also applies to other types of image forming apparatuses, such as a facsimile machine having an image reading device, e.g. a scanner, and a copier, as well. 
         [0033]    While the features herein have been described in connection with various example structures and illustrative aspects, it will be understood by those skilled in the art that other variations and modifications of the structures and aspects described above may be made without departing from the scope of the inventions described herein. Other structures and aspects will be apparent to those skilled in the art from a consideration of the specification or practice of the features disclosed herein. It is intended that the specification and the described examples only are illustrative with the true scope of the inventions being defined by the following claims.