Patent Publication Number: US-9411309-B1

Title: Image forming apparatus

Description:
FIELD 
     Embodiments described herein relate generally to an image forming apparatus. 
     BACKGROUND 
     There is known an image forming apparatus including a fan in a housing. In the image forming apparatus, when a fan is driven, the air on the outside flows into the housing. 
     The image forming apparatus is sometimes used in an environment with a lot of dust or dirt (hereinafter collectively referred to as “dust”). In this case, a lot of dust intrudes into the image forming apparatus together with the air. 
     In general, as measures against dust, it is known to provide a filter for dust collection. However, if the image forming apparatus is used in the environment with a lot of dust, an amount of dust accumulating in the filter increases. Therefore, it is likely that a frequency of replacement of the filter increases. Further, clogging sometimes occurs in the filter. If the clogging occurs in the filter, it is likely that a flow of the air in the housing is deteriorated. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view showing an image forming apparatus in a first embodiment; 
         FIG. 2  is a diagram schematically showing a configuration example of the image forming apparatus in the first embodiment; 
         FIG. 3  is a front view showing an intermediate transfer unit, a fan, and a duct in the first embodiment; 
         FIG. 4  is a perspective view showing a developing unit, the fan, and the dust in the first embodiment; 
         FIG. 5  is a perspective view showing the fan and the duct in the first embodiment; 
         FIG. 6  is a front view showing a bent section in the first embodiment; 
         FIG. 7  is a perspective view showing the bent section in the first embodiment; 
         FIG. 8  is a sectional view of the bent section shown in  FIG. 7  taken along line F 8 -F 8 ; 
         FIG. 9  is a sectional view showing a first modification of the bent section in the first embodiment; 
         FIG. 10  is a sectional view showing a second modification of the bent section of the first embodiment; and 
         FIG. 11  is a front view showing an image forming apparatus in a second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, there is provided an image forming apparatus including a fan and a duct. The fan and the duct are provided in a housing. If the fan is driven, the duct guides the air flowing into the housing from an intake port of the housing toward components in the housing. The duct includes a bent section that changes a flowing direction of the air. The bent section includes holes. 
     Exemplary embodiments are explained below with reference to the drawings. Note that, in the following explanation, the same reference numerals and signs are attached to components having the same or similar functions. Explanation of the components is sometimes omitted. 
     Note that “above” in this application includes not only “right above” but also “obliquely above”. That is, “the air flowing upward” includes not only “the air flowing directly upward” but also “the air flowing obliquely upward”. Similarly, “below” includes not only “right below” but also “obliquely below”. That is, “the air flowing downward” includes not only “the air flowing directly downward” but also “the air flowing obliquely downward”. 
     First Embodiment 
       FIG. 1  shows an image forming apparatus  1  in a first embodiment. As shown in  FIG. 1 , the image forming apparatus is a multi function peripheral (MFP) of an electrophotographic system. 
     First, the overall configuration of the image forming apparatus  1  is explained. 
       FIG. 2  schematically shows a configuration example of the image forming apparatus  1 . As shown in  FIG. 2 , the image forming apparatus  1  includes a housing  2 , a scanner unit  3 , and a printer unit  4 . 
     The housing (a machine body or a case)  2  forms an outer hull of the image forming apparatus  1 . The housing  2  is formed in, for example, a box shape. The housing  2  houses the scanner unit  3  and the printer unit  4 . 
     The scanner unit  3  reads image information of an original document as digital data. 
     The printer unit  4  forms an image on a sheet on the basis of image data. The image forming apparatus  1  forms an image using recording agents. The recording agents are, for example, toners. 
     The printer unit  4  is explained in detail. 
     As shown in  FIG. 2 , the printer unit  4  includes an intermediate transfer unit  11 , a paper feeding unit  12 , a conveying path  13 , a secondary transfer unit  14 , a fixing unit  15 , and a paper discharge unit  16 . 
     The intermediate transfer unit (a primary transfer unit)  11  includes an intermediate transfer belt  21 , a plurality of rollers  22   a ,  22   b ,  22   c , and  22   d , and a plurality of image forming units  23 Y,  23 M,  23 C, and  23 K. 
     The intermediate transfer belt  21  is endlessly formed. The plurality of rollers  22   a ,  22   b ,  22   c , and  22   d  support the intermediate transfer belt  21 . Consequently, the intermediate transfer belt  21  is capable of endlessly traveling in a direction indicated by an arrow A in  FIG. 2 . 
     The plurality of image forming units (process units)  23 Y,  23 M,  23 C, and  23 K include a yellow image forming unit  23 Y, a magenta image forming unit  23 M, a cyan image forming unit  23 C, and a black image forming unit  23 K. The image forming units  23 Y,  23 M,  23 C, and  23 K respectively include photoconductive drums  25 , charging units  26 , exposing units  27 , developing units  28 , and transfer rollers  29 . The configurations of the image forming units  23 Y,  23 M,  23 C, and  23 K are the same one another except that colors of recording agents are different. Therefore, in the figure, characters Y, M, C, and K respectively meaning yellow, magenta, cyan, and black are attached to signs of the components. 
     The charging units (electrifying chargers)  26  charge the surfaces of the photoconductive drums  25 . The charging units  26  include discharge needles  26   a  and grids  26   b  (see  FIG. 6 ). For example, the charging units  26  are charging units of a scorotron type. When charging the photoconductive drums  25 , the charging units  26  emit ozone. Therefore, the air containing the ozone tends to be held up in the vicinities of the charging units  26 . 
     The exposing units (exposing scanning heads)  27  expose the surfaces of the photoconductive drums  25  to light. Consequently, electrostatic latent images based on image data are formed on the surfaces of the photoconductive drums  25 . 
     The developing units  28  are capable of storing the recording agents corresponding to the colors. The developing units  28  supply the recording agents to the surfaces of the photoconductive drums  25 . Consequently, the recording agents adhere to latent image portions of the photoconductive drums  25 . 
     A deficiency tends to occur if the temperature of the recording agents rises. Therefore, the developing units  28  are one of components that should be cooled among the components of the image forming apparatus  1 . 
     The transfer rollers  29  face the intermediate transfer belt  21  from the opposite side of the photoconductive drums  25 . Consequently, the recording agents are transferred (primarily transferred) from the surfaces of the photoconductive drums  25  to the intermediate transfer belt  21 . 
       FIG. 3  shows the intermediate transfer unit  11  of the image forming apparatus  1 . As shown in  FIG. 3 , the four image forming units  23 Y,  23 M,  23 C, and  23 K are disposed side by side in the horizontal direction. In the image forming units  23 Y,  23 M,  23 C, and  23 K, the charging units  26  and the developing units  28  are disposed below the photoconductive drums  25 . 
     The paper feeding unit  12 , the conveying path  13 , the secondary transfer unit  14 , the fixing unit  15 , and the paper discharge unit  16  are explained. 
     As shown in  FIG. 2 , the paper feeding unit  12  includes a paper feeding cassette  31  and a pickup roller  32 . 
     The paper feeding cassette  31  includes a storing unit  31   a . The storing unit  31   a  is formed in a bowl shape opened at the top. The storing unit  31   a  is capable of storing a plurality of sheets P on which images are printed. For example, the storing unit  31   a  is capable of storing a large number of (e.g., approximately several hundred) sheets P. 
     As shown in  FIG. 3 , the housing  2  includes an opening  2   a . The paper feeding cassette  31  is inserted into the inside of the opening  2   a  of the housing  2 . Consequently, the paper feeding cassette  31  is mounted on the housing  2 . In a state in which the paper feeding cassette  31  is mounted on the housing  2 , the storing unit  31   a  is located on the inside of the housing  2 . The storing unit  31   a  is disposed below the intermediate transfer unit  11 . Note that the paper feeding cassette  31  can be drawn out from the housing  2 . 
     As shown in  FIG. 2 , the pickup roller  32  is provided in the paper feeding cassette  31 . The pickup roller  32  sends the sheet P stored in the paper feeding cassette  31  to the conveying path  13 . 
     The conveying path  13  leads from the paper feeding unit  12  to the paper discharge unit  16  through the secondary transfer unit  14  and the fixing unit  15 . The sheet P is conveyed on the conveying path  13 . 
     The secondary transfer unit  14  includes a transfer roller  14   a . The transfer roller  14   a  is in contact with the outer surface of the intermediate transfer belt  21 . One belt roller  22   d  supporting the intermediate transfer belt  21  is included in components of the secondary transfer unit  14 . The belt roller  22   d  is opposed to the transfer roller  14   a  across the intermediate transfer belt  21 . The sheet P is held between the transfer roller  14   a  and the belt roller  22   d  together with the intermediate transfer belt  21 . Consequently the recording agents on the intermediate transfer belt  21  are transferred (secondarily transferred) onto the surface of the sheet P. The sheet P passed through the secondary transfer unit  14  is sent toward the fixing unit  15 . 
     The fixing unit  15  includes a heat roller  15   a  and a press roller  15   b . The heat roller  15   a  is controlled to a fixing temperature (a printing temperature) suitable for fixing of the recording agents. The press roller  15   b  faces the sheet P from the opposite side of the heat roller  15   a . The sheet P having the recording agents transferred thereon is held between the heat roller  15   a  and the press roller  15   b . Consequently, the sheet P is heated and pressed between the heat roller  15   a  and the press roller  15   b . Consequently, the recording agents transferred onto the sheet P are fixed on the sheet P. 
     The sheet P passed through the fixing unit  15  is discharged to the paper discharge unit  16 . 
     An air blowing structure of the image forming apparatus  1  is explained with reference to  FIGS. 3 to 5 . Note that, in the figures referred to below, a flow of the air is represented by an arrow F. 
     The air blowing structure in this embodiment is a structure for blowing the air on the outside of the housing  2  toward the charging units  26  and the developing units  28  of the image forming units  23 Y,  23 M,  23 C, and  23 K. The charging units  26  and the developing units  28  are respectively examples of “components (components in the housing)”. 
     More specifically, the image forming apparatus includes a fan  35  and a duct  36 . 
     As shown in  FIG. 3 , the fan  35  is provided in the housing  2 . The fan  35  faces a sidewall  2   b  of the housing  2 . The sidewall  2   b  of the housing  2  includes an intake port  37 . The intake port  37  is provided in a position corresponding to the fan  35 . The intake port  37  opens to the outside of the housing  2 . Therefore, if the fan  35  is driven, the air on the outside of the housing  2  flows into the housing  2  through the intake port  37 . 
     The duct  36  guides the air flowing into the housing  2  toward a predetermined region in the housing  2 . In this embodiment, the duct  36  guides the air flowing into the housing  2  toward the charging units  26  and the developing units  28 . Specifically, the duct  36  includes a branching section  40 , a first channel  41 , and a second channel  42 . 
     As shown in  FIGS. 3 and 4 , the branching section  40  is located in the vicinity of the fan  35 . The air flowing into the housing  2  from the intake port  37  flows into the branching section  40  first. In this embodiment, the branching section  40  is located above the charging units  26  and the developing units  28 . 
     The first channel  41  and the second channel  42  are respectively channels for sending the air to different regions in the housing  2 . The first channel  41  and the second channel  42  branch from the branching section  40 . The first channel  41  and the second channel  42  extend in opposite directions each other. For example, the first channel  41  extends upward from the branching section  40 . The second channel  42  extends downward from the branching section  40 . The air in the branching section  40  flows separately into the first channel  41  and the second channel  42 . 
     The second channel  42  is explained in detail below. 
     The second channel  42  includes a first guide section  51 , a bent section  52 , and a second guide section  53 . 
     The first guide section  51  connects the branching section  40  and the bent section  52 . The first guide section  51  guides the air in the branching section  40  toward the bent section. Specifically, the first guide section  51  extends downward from the branching section  40 . For example, the first guide section  51  extends further downward than the charging units  26  and the developing units  28 . The first guide section  51  guides the air in the branching section  40  downward. 
     The bent section  52  is located between the first guide section  51  and the second guide section  53 . The bent section  52  connects the first guide section  51  and the second guide section  53 . 
       FIGS. 6 to 8  show details of the bent section  52 . As shown in  FIGS. 6 to 8 , the bent section  52  is bent with respect to the first guide section  51 . The bent section  52  changes a flowing direction of the air flowing in from the first guide section  51 . Note that the bent section  52  may be bent in an arcuate shape with respect to the first guide section  51 . Instead, the bent section  52  may be bent in a right-angled shape with respect to the first guide section  51 . 
     For example, the bent section  52  is bent at an angle equal to or larger than 90 degrees. In this embodiment, the bent section  52  is bent at approximately 180 degrees. Note that the bending angle of the bent section  52  is not particularly limited. The bent section  52  only has to be bent even a little with respect to the first guide section  51 . 
     As shown in  FIG. 3 , in this embodiment, the bent section  52  is located in the bottom of the duct  36 . The bent section  52  is located below the charging units  26  and the developing units  28 . The bent section  52  changes a flow of the air flowing from the intake port  37  toward a direction different from the direction to the charging units  26  and the developing units to be directed toward the charging units  26  and the developing units  28 . In this embodiment, the bent section  52  changes a flow of the air flowing downward to be directed upward. 
     More specifically, as shown in  FIG. 8 , the bent section  52  in this embodiment includes a first surface section  52   a  and a second surface section  52   b . The first surface section  52   a  is a wall surface section located on the inner side in the bending direction of the bent section  52  in the bent section  52 . On the other hand, the second surface section  52   b  is a wall surface section located on the outer side in the bending direction of the bent section  52  in the bent section  52 . 
     From another viewpoint, as shown in  FIG. 6 , the first surface section  52   a  is located on the same side as the charging units  26  and the developing units  28  with respect to an internal space S of the bent section  52 . On the other hand, the second surface section  52   b  is located on the opposite side of the charging units  26  and the developing units  28  with respect to the internal space S of the bent section  52 . In this embodiment, the first surface section  52   a  is an upper surface section of the bent section  52 . The second surface section  52   b  is a lower surface section of the bent section  52 . 
     As shown in  FIG. 8 , the air flowing into the bent section  52  from the first guide section  51  hits the second surface section  52   b  in the bent section  52 . Thereafter, the air hit the second surface section  52   b  flows along the second surface section  52   b . A flowing direction of the air flowing into the bent section  52  changes along the second surface section  52   b.    
     More specifically, the second surface section  52   b  includes a first plane  60 , a first corner  61 , a second plane  62 , a second corner  63 , and a third plane  64 . 
     The first plane  60  is located between the first guide section  51  and the first corner  61 . The first plane  60  extends substantially in parallel to the first guide section  51 . For example, the first plane  60  extends substantially in the vertical direction. 
     The first corner  61  is located between the first plane  60  and the second plane  62 . The first corner  61  is formed in an arcuate shape. The first corner  61  smoothly connects the first plane  60  and the second plane  62 . For example, the first corner  61  is bent approximately 90 degrees. The first corner  61  changes a flow of the air flowing downward to be directed substantially to the horizontal direction. 
     The second plane  62  extends in a direction crossing the first plane  60 . For example, the second plane  62  extends in a direction substantially orthogonal to the first plane  60 . The second plane  62  extends substantially in the horizontal direction. The second plane  62  is located in the bottom of the bent section  52 . The second plane  62  forms the bottom surface of the bent section  52 . The air, the flowing direction of which is changed by the first corner  61 , flows substantially in the horizontal direction along the second plane  62 . The second plane  62  guides the air flowing substantially in the horizontal direction to the second corner  63 . Note that the bent section  52  does not have to include the second plane  62 . That is, the first corner  61  and the second corner  63  may be directly connected. 
     Note that the “bottom surface” in this application means one plane. In this embodiment, the second plane  62  forms an example of the “bottom surface”. The “bottom surface” in this application also means “a bottom surface in the gravity direction”. On the other hand, the “bottom surface section” may include, in addition to one plane, a corner adjacent to the plane. In this embodiment, the first corner  61 , the second plane  62 , and the second corner  63  are collectively referred to as “bottom surface section”. The “bottom surface section” in this application also means “a bottom surface section in the gravity direction”. 
     The second corner  63  is located between the second plane  62  and the third plane  64 . The second corner  63  is formed in an arcuate shape. The second corner  63  smoothly connects the second plane  62  and the third plane  64 . For example, the second corner  63  is bent approximately 90 degrees. The second corner  63  changes a flow of the air flowing substantially in the horizontal direction to be directed upward. 
     The third plane  64  is located between the second corner  63  and the second guide section  53 . The third plane  64  extends substantially in parallel to the second guide section  53 . For example, the third plane  64  extends substantially in the vertical direction. 
     The second guide section  53  is explained. 
     As shown in  FIGS. 3 and 4 , the second guide section  53  is located between the bent section  52  and the charging units  26  and the developing units  28 . The second guide section  53  guides the air passed through the bent section  52  toward the charging units  26  and the developing units  28 . An internal space of the second guide section  53  extends across the bottoms of the charging units  26  and the developing units  28 . 
     As shown in  FIG. 5 , the second guide section  53  includes a plurality of discharge ports  53   a . The discharge ports  53   a  open toward the respective charging units  26  and the respective developing units  28 . The air flowing into the second guide section  53  spreads in the second guide section  53  and is discharged from the discharge ports  53   a  toward the charging units  26  and the developing units  28 . 
     As explained above, the charging units  26  emit ozone when the charging units  26  charge the surfaces of the photoconductive drums  25 . Therefore, the ozone tends to be held up around the charging units  26  and the photoconductive drums  25 . For example, properties of the surfaces of the photoconductive drums  25  sometimes change if the surfaces are in contact with the ozone for a long time. If the properties of the surfaces of the photoconductive drums  25  change, a failure sometimes occurs in an image printed on the sheet P. 
     Therefore, in this embodiment, the air is discharged from the duct  36  toward the charging units  26 . If the air is discharged from the duct  36  toward the charging units  26 , the air around the charging units  26  and the photoconductive drums  25  is ventilated. Consequently, the ozone is eliminated from around the charting units  26  and the photoconductive drums  25 . This makes it possible to reduce the likelihood of occurrence of a deficiency in the photoconductive drums  25 . The ozone eliminated from around the photoconductive drums  25  is removed by an ozone filter provided in the housing  2 . 
     As explained above, the recording agents stored in the developing units  28  sometimes cause a deficiency when the temperature of the recording agents rises. 
     Therefore, in this embodiment, the air is discharged from the duct  36  toward the developing units  28 . If the air is discharged from the duct  36  toward the developing units  28 , the developing units  28  are cooled. Consequently, the recording agents stored in the developing units  28  are cooled. This makes it possible to reduce the likelihood of occurrence of a deficiency in the recording agents. 
     Holes  71  provided in the duct  36  are explained. 
     As shown in  FIGS. 6 and 7 , the bent section  52  in this embodiment includes a plurality of holes  71 . The holes  71  are provided in the second surface section  52   b  of the bent section  52 . For example, the holes  71  are arranged in a row. For example, the holes  71  are arranged in a direction crossing a flowing direction of the air in the bent section  52 . Instead, a part or all of the holes  71  may be arranged along the flowing direction of the air in the bent section  52 . Note that the bent section  52  may include only one hole  71 . 
     The holes  71  cause the inside and the outside of the duct  36  to communicate with each other. The holes  71  cause a part of the air flowing in the duct  36  to flow out to the outside of the duct  36  halfway in the duct  36 . 
     In this embodiment, the holes  71  open in a direction different from the direction toward the charging units  26  and the developing units  28 . The holes  71  cause a part of the air flowing in the duct  36  to flow out toward a direction different from the direction toward the charging units  26  and the developing units  28 . 
     At least a part of the holes  71  are provided in the bottom surface section of the bent section  52 . That is, at least a part of the holes  71  are provided in any one of the first corner  61 , the second plane  62 , and the second corner  63 . 
     As shown in  FIG. 8 , in this embodiment, the hole  71  is provided in the second corner  63  of the bent section  52 . More specifically, the hole  71  includes a first portion  71   a  and a second portion  71   b . The first portion  71   a  is located at substantially the same height as the second plane  62  or below the second plane  62 . On the other hand, the second portion  71   b  is located above the second plane  62 . That is, at least a part of the holes  71  are located above the bottom surface (the second plane  62 ) of the duct  36 . 
     Note that, instead, at least a part of the holes  71  may be formed in the second plane  62  of the bent section  52 . At least a part of the holes  71  may be formed in the third plane  64  of the bent section  52 . 
     From another viewpoint, at least a part of the holes  71  are located on the opposite side of the charging units  26  and the developing units  28  with respect to the internal space S of the bent section  52 . In this embodiment, at least the first portion  71   a  is located on the opposite side of the charging units  26  and the developing units  28  with respect to the internal space S of the bent section  52 . 
     In this embodiment, the holes  71  have a polygonal shape. For example, the holes  71  have a square shape. Note that the shape of the holes  71  is not particularly limited. The holes  71  may have another polygonal shape (e.g., a triangular shape or a hexagonal shape) and may have a circular shape. 
     The number and the size of the holes  71  are not particularly limited. For example, the holes  71  may cause 10 percent or more of the air passing in the duct  36  to flow out. The holes  71  in this embodiment cause approximately 20 percent of the air passing in the duct  36  to flow out. Note that a flow rate of the air flowing out from the holes  71  is not limited to the example explained above. 
     As shown in  FIG. 6 , the bent section  52  is located above the storing unit  31   a  of the paper feeding cassette  31 . The holes  71  open from the bent section  52  toward the inside of the storing unit  31   a  of the paper feeding cassette  31 . The holes  71  cause a part of the air flowing in the duct  36  to flow out toward the inside of the storing unit  31   a  of the paper feeding cassette  31 . 
     Note that, instead, the holes  71  may open toward the outside of the housing  2 . That is, the holes  71  may cause a part of the air flowing in the duct  36  to flow out to the outside of the housing  2 . 
     The action of the holes  71  is explained. 
     The air flowing into the bent section  52  from the first guide section  51  hits the second surface section  52   b  in the bent section  52 . The air flows along the second surface section  52   b  of the bent section  52 . Consequently, the bent section  52  changes a flowing direction of the air. 
     Dust included in the air is heavy in terms of mass compared with the air. Therefore, the dust has a large inertial force compared with the air. Therefore, if a bending direction of the air changes, the dust included in the air tends to gather on the outer side in the bending direction compared with the air. That is, the dust included in the air tends to flow along the second surface section  52   b  in the bent section  52 . 
     In this embodiment, the holes  71  are provided in the second surface section  52   b  of the bent section  52 . Therefore, at least a part of the dust flowing along the second surface section  52   b  is drawn into the holes  71  in a process of passing the bent section  52 . That is, at least a part of the dust flowing along the second surface section  52   b  is discharged to the outside of the duct  36  together with the air flowing out from the holes  71 . Consequently, an amount of the dust included in the air after passing the bent section  52  can be reduced. That is, an amount of the dust flowing toward the charging units  26  and the developing units  28  can be reduced. 
     In this embodiment, the second surface section  52   b  of the bent section  52  is provided in the bottom in the gravity direction of the bent section  52 . Therefore, the dust having relatively high density included in the air tends to drop onto the second surface section  52   b  of the bent section  52  with the gravity. Therefore, the dust having the relatively large density tends to gather on the second surface section  52   b . The dust having the relatively large density is discharged from the holes  71  together with the air flowing out from the holes  71 . Therefore, the amount of the dust included in the air after passing the bent section  52  can be further reduced. That is, the amount of the dust flowing toward the charging units  26  and the developing units  28  can be further reduced. 
     As shown in  FIG. 6 , the storing unit  31   a  of the paper feeding cassette  31  is disposed below the holes  71 . The storing unit  31   a  of the paper feeding cassette  31  is less easily affected by the dust compared with the charging units  26  or the developing units  28 . That is, the storing unit  31   a  of the paper feeding cassette  31  less easily causes a problem in the function of the image forming apparatus  1  even if the dust flows into the storing unit  31   a.    
     In this embodiment, the dust discharged from the holes  17  is discharged to the inside of the storing unit  31   a  provided below the holes  71 . The dust discharged to the storing unit  31   a  is dispersed to adhere to the sheets P stored in the storing unit  31   a  together with other dust present in the air. Consequently, the dust discharged to the storing unit  31   a  is sent to the conveying path  13  in a state in which the dust is dispersed on the sheets P. The conveying path  13  has fixed resistance to the dust. Therefore, the dust discharged to the storing unit  31   a  less easily causes a deficiency of the image forming apparatus  1 . 
     With such a configuration, it is possible to provide the image forming apparatus  1  that less easily causes a deficiency even if the image forming apparatus  1  is used in an environment with a lot of dust. 
     That is, the image forming apparatus  1  is sometimes used in the environment with a lot of dust. In this case, a lot of dust intrudes into the inside of the image forming apparatus  1  together with the air. For example, if the dust deposits on the charging units  26 , it is likely that a charging failure occurs. As a result, it is likely that a failure occurs in an image formed on the print sheet P. 
     Therefore, the image forming apparatus  1  in this embodiment includes the fan  35  and the duct  36 . If the fan  35  is driven, the duct  36  guides the air flowing into the housing  2  from the intake port  37  of the housing  2  toward the charging units  26  and the developing units  28 . The duct  36  includes the bent section  52  that changes a flowing direction of the air. The bent section  52  includes the holes  71 . 
     With such a configuration, at least a part of the dust flowing in the duct  36  can be discharged to the outside of the duct  36  halfway in the duct  36 . Consequently, an amount of the dust flowing in the duct  36  can be reduced. This makes it possible to reduce the likelihood of adhesion of the dust to the components such as the charging units  26  or the developing units  28 . 
     In this embodiment, the holes  71  open in a direction different from the direction from the bent section  52  toward the charging units  26  and the developing units  28 . With such a configuration, the dust discharged from the holes  71  flows in the direction different from the direction toward the charging units  26  and the developing units  28 . This makes it possible to reduce the likelihood of adhesion of the dust, which is discharged from the holes  71 , to the charging units  26  or the developing units  28 . 
     In this embodiment, the bent section  52  includes the second surface section  52   b  located on the outer side in the bending direction of the bent section  52 . At least a part of the holes  71  are provided in the second surface section  52   b  of the bent section  52 . With such a configuration, further efficiency of removal of dust can be attained. That is, the dust flowing into the bent section  52  tends to flow along the second surface section  52   b  located on the outer side in the bending direction. Therefore, the dust tends to be caught by the holes  71  in a process of flowing along the second surface section  52   b . Therefore, the dust can be more efficiently discharged. 
     In this embodiment, at least a part of the holes  71  are provided in the bottom surface section in the gravity direction of the bent section  52 . The dust having relatively high density tends to gather on the bottom surface section of the bent section  52  with the gravity. Therefore, if at least a part of the holes  71  are provided in the bottom surface section of the bent section  52 , the dust can be more efficiently discharged. 
     In this embodiment, the bent section  52  is located in the bottom of the duct  36 . The bent section  52  changes a flow of the air flowing downward to be directed upward. In this embodiment, in such a bent section  52 , at least a part of the holes  71  are provided in the bottom surface section in the gravity direction of the bent section  52 . With such a configuration, the dust having relatively high density has difficulty in flowing upward from the bottom surface section of the bent section  52 . Therefore, the amount of the dust flowing in the duct  36  can be further reduced. The dust having difficulty in flowing upward in the bent section  52  is held up on the bottom surface section of the bent section  52 . The dust held up on the bottom surface section of the bent section  52  is discharged to the outside of the duct  36  together with the air flowing out from the holes  71 . Therefore, if at least apart of the holes  71  are provided in the bottom surface section of the bent section  52 , the dust can be more efficiently discharged. 
     In this embodiment, the bent section  52  includes the first corner  61  and the second corner  63 . The first corner  61  changes a flow of the air flowing downward to be directed to substantially the horizontal direction. The second corner  63  changes a flow of the air flowing substantially in the horizontal direction to be directed upward. At least a part of the holes  71  are provided in the second corner  63  of the bent section  52 . With such a configuration, a flowing direction of the air is changed a plurality of times by the first corner  61  and the second corner  63 . The dust tends to move to the outer side in the bending direction according to the plurality of times of the change in the flowing direction. Therefore, the dust tends to gather near the second corner  63 . Therefore, if at least a part of the holes  71  are provided in the second corner  63 , the dust can be more efficiently discharged. 
     Further, in this embodiment, the second corner  63  is a corner for directing the flow of the air flowing substantially in the horizontal direction upward. Therefore, the dust having relatively high density tends to be held up near the second corner  63  with the gravity. Therefore, if at least a part of the holes  71  are provided in the second corner  63 , the dust can be more efficiently discharged. 
     In this embodiment, the second portion  71   b  of the hole  71  is located above the bottom surface (the second plane  62 ) of the bent section  52 . With such a configuration, a part of the dust about to move upward in the second corner  63  tends to be caught by the holes  71 . Therefore, with the configuration, the dust can be more efficiently discharged. 
     In this embodiment, the image forming apparatus  1  further includes the paper feeding cassette  31  disposed below the bent section  52 . The holes  71  open from the bent section  52  toward the paper feeding cassette  31 . Compared with the charging units  26  or the developing units  28 , the paper feeding cassette  31  has less likelihood of occurrence of a deficiency even if dust flows into the paper feeding cassette  31 . That is, with the configuration, compared with when the dust adheres to the charging units  26  or the developing units  28 , reliability of the image forming apparatus  1  can be improved. 
     The image forming apparatus  1  in first and second modifications is explained. The modifications are different from the first embodiment in the position of the holes  71 . Note that the other components in the modifications are the same as the components in the first embodiment. Therefore, explanation of the components same as the components in the first embodiment is omitted. 
     First Modification 
       FIG. 9  shows the bent section  52  of the image forming apparatus  1  in the first modification. As shown in  FIG. 9 , the holes  71  in this modification are located above the bottom surface (the second plane  62 ) of the bent section  52 . The holes  71  are provided, for example, in the third plane  64 . With such a configuration, even dust flowing apart from the bottom surface of the bent section  52  tends to be caught by the holes  71 . 
     Second Modification 
       FIG. 10  shows the bent section  52  of the image forming apparatus  1  in the second modification. As shown in  FIG. 10 , the holes  71  in this modification are provided in the bottom surface (the second plane  62 ) of the bent section  52 . For example, the holes  71  are disposed in a position not overlapping the first guide section  51  in a flowing direction of the air in the first guide section  51 . 
     As explained above, the dust having relatively high density tends to gather on the second surface section  52   b  with the gravity. Therefore, with the configuration of this modification, the dust having relatively high density can be efficiently discharged. 
     Note that, as indicated by a long and short two dashes line in  FIG. 10 , the holes  71  may be disposed in a position overlapping the first guide section  51  in the flowing direction of the air in the first guide section  51 . However, in this case, a part of the air flowing into the bent section  52  from the first guide section  51  is likely to directly flow out from the holes  71 . 
     Therefore, in this modification, the holes  71  are disposed in the position not overlapping the first guide section  51  in the flowing direction of the air in the first guide section  51 . With such a configuration, the dust included in the air can be collected near the second surface section  52   b  by changing the flow of the air in the bent section  52 . Consequently, the dust can be efficiently discharged. 
     Second Embodiment 
     The image forming apparatus  1  in a second embodiment is explained. This embodiment is different from the first embodiment in that the image forming apparatus  1  includes a filter  81 . Note that the other components in this embodiment are the same as the components in the first embodiment. Therefore, explanation of the components same as the components in the first embodiment is omitted. 
       FIG. 11  shows the image forming apparatus  1  in the second embodiment. As shown in  FIG. 11 , the image forming apparatus  1  includes the filter  81 . The filter  81  is provided on the outside of the bent section  52 . The filter  81  faces the holes  71 . For example, the filter  81  is formed of nonwoven fabric or urethane. Note that the material of the filter  81  is not particularly limited. 
     The air flowing out from the holes  71  passes through the filter  81 . In this process, dust discharged from the holes  71  is collected by the filter  81 . The filter  81  is located on the outside of the duct  36 . Therefore, even if clogging occurs in the filter  81  because of the dust, a flow of the air in the duct  36  is not deteriorated. That is, even if clogging occurs in the filter  81 , a pressure loss less easily occurs in the duct  36 . Therefore, the flow of the air in the duct  36  is less easily deteriorated. Therefore, a frequency of replacement of the filter  81  can be reduced. Since a pressure loss less easily occurs in the duct  36 , a reduction in the size of the fan  35  can be attained. 
     The filter  81  is detachably attached to the duct  36 . For example, if the paper feeding cassette  31  is drawn out from the housing  2 , the filter  81  is exposed to the outside. That is, the filter  81  can be replaced through the opening  2   a  of the housing  2  on which the paper feeding cassette  31  is mounted. 
     With such a configuration, the dust discharged to the outside of the duct  36  from the holes  71  can be collected by the filter  81 . This makes it possible to further reduce the likelihood of adhesion of the dust to the charging units  26  or the developing units  28 . This also makes it possible to reduce the likelihood of adhesion of the dust to the other portions of the image forming apparatus  1 . 
     In this embodiment, the filter  81  is detachably attached to the duct  36 . With such a configuration, cleaning of the image forming apparatus  1  can be facilitated. 
     The image forming apparatus  1  in the first and second embodiments is explained above. However, embodiments are not limited to the first and second embodiments. For example, the bent section  52  is not limited to the bent section bent upward. The bent section  52  may be a bent section bent horizontally or may be a bent section bent downward. The fan  35  is not limited to the fan disposed on the upstream side of the duct  36 . The fan  35  may be a fan disposed on the downstream side of the components (e.g., the charging units  26  or the developing units  28 ) in the housing  2 . 
     For example, the duct  36  does not need to be provided across the entire space between the intake port  37  of the housing  2  and the components in the housing  2 . The duct  36  may be partially provided in the housing  2 . The duct  36  is not limited to the duct integrally provided with the housing  2 . A part of the duct  36  may be formed by the surfaces or the like of the components housed in the housing  2 . 
     For example, a general filter  85  for dust collection may be provided in the duct  36  together with the holes  71  (see an alternate long and two short dashes line in  FIG. 8 ). The filter  85  is provided halfway in the intake port  37  or the duct  36 . Note that if the filter  85  is disposed on the downstream side of the holes  71  in the flowing direction of the air, the dust adhering to the filter  85  can be reduced. Therefore, a frequency of replacement of the filter  85  can be reduced. If the filter  85  is disposed on the downstream side of the holes  71 , clogging less easily occurs in the filter  85 . Therefore, the flow of the air is less easily deteriorated in the housing  2 . Therefore, a reduction in the size of the fan  35  can be attained. 
     According to at least one embodiment explained above, an image forming apparatus includes a fan and a duct. The fan is provided in a housing. The duct is provided in the housing. If the fan is driven, the duct guides the air flowing into the housing from an intake port of the housing toward components in the housing. The duct includes a bent section that changes a flowing direction of the air. The bent section includes holes. Consequently, it is possible to provide the image forming apparatus  1  that less easily causes a deficiency even if the image forming apparatus  1  is used in an environment with a lot of dust. 
     While certain embodiments have been described these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms: furthermore various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.