Abstract:
A duct for an image forming apparatus for forming an image on a recording material, the duct includes a discharge opening for discharging air; a fan, mounted to a neighborhood of the discharge opening, for discharging the air; first and second openings for suction of air; a first guiding portion, having first and second openings, for guiding the sucked air; a separation member, provided in the first guiding portion, for separating a flow of the air sucked by the first opening and a flow of the air sucked by the second opening; a second guiding member, disposed overlapped with the first guiding portion, for guiding the air guided by the first guiding portion; a first interconnection opening for feeding the air from the first opening to the second guiding portion; a second interconnection opening for feeding the air from the second opening to the second guiding portion, wherein the first interconnection opening is disposed closer to the discharge opening than the second interconnection opening, and wherein the first interconnection opening has a size smaller than the second interconnection opening.

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to a duct mounted in an image forming apparatus, such as a printer, a facsimile machine, a multifunction image forming apparatus and so on. 
     An image forming apparatus, that is, an apparatus for forming an image on recording medium, is made up of a photosensitive drum (photosensitive drums), a developing apparatus (developing apparatuses), a charging apparatus (charging apparatuses), a fixing apparatus, etc. Some image forming apparatuses are provided with an air exhausting apparatus, which has an air duct (which hereafter may be referred to simply as duct). The duct is disposed close to one of the abovementioned components. For example, in order to prevent the toner which scattered from the development sleeve, which rotates at a high speed, from adhering to the photosensitive drum(s), an air exhausting apparatus having a duct is placed in the adjacencies of the photosensitive drum and/or developing apparatus (Japanese Laid-open Patent Applications 2005-215232). There is also an image forming apparatus in which an air exhausting apparatus having a duct is disposed next to its corona discharging apparatus, in order to prevent the photosensitive drum(s) and the mechanism therefor, from being affected by the by products of coronal discharge. Further, there is an image forming apparatus in which an exhausting apparatus having a duct is disposed next to its fixing apparatus, in order to prevent the adjacencies of the fixing apparatus from overheating. 
     Japanese Laid open Patent Application 2005-140971 discloses an air exhausting apparatus for an image forming apparatus. This air exhausting apparatus is made up of an air duct and an air drawing fan. The duct is disposed directly below where the distance between the development sleeve and photosensitive drum is smallest, and the fan is located at the rear end of the duct (part of air passage). The air duct shown in  FIG. 8  is provided with multiple air intake openings, which are aligned in the front-to-rear direction (relative to where fan is present), that is, the direction parallel to the axial line of the photosensitive drum. The duct is in the form of a parallelepiped. Its top wall has three air intake openings, which are arranged with equal intervals. The exhausting apparatus is provided with an unshown forced air flow generating apparatus, which is in connect with one of the lengthwise ends of the duct  10 . The forced air flow generating apparatus generates an air flow in such a direction that air flows out of the common air outlet opening  144  which leads to the forced air flow generating apparatus, in the direction indicated by arrow marks in  FIGS. 8(   a ) and  8 ( b ). The air drawing duct  327  is provided with partitioning walls  121  and  122 , which are positioned to provide three air passages  131 ,  132 , and  133  which extend from the air intake openings  111 ,  112 , and  113  to the common air outlet opening  144  (forced air flow generating apparatus) without intersecting with each other. Arranging the air passages and air intake openings  111 ,  112 , and  113  as described above equalizes the multiple air intake openings in the amount by which air is taken into the duct  327  through them. 
     However, the above described duct structure suffers from the following problem. That is, it makes an air intake closer to the common openings  114  higher in air speed, making the multiple air intake openings different in the amount by which air is taken into the duct  327  through them. Further, air is drawn into the duct  327  through the air intake openings  111 ,  112 , and  113  in the direction indicated by the arrow marks in  FIG. 8(   b ). That is, the air flows which generate as air is drawn into the duct  327  are inclined relative to the direction perpendicular to the lengthwise direction of the duct  327  (direction parallel to axial line of photosensitive drum); the downstream ends of the air flows are closer to the common air outlet opening  144 . In addition, the farther from the common opening  144  the air intake opening, the smaller the intake opening in the amount of force by which air is drawing into the duct  327  through it. Thus, in terms of the amount by which air is drawing into the duct  327 , the duct  327  is not uniform across the entirety of its lengthwise range; its air intake openings are different in the amount of force by which air is drawn into the duct  327 . Therefore, in order to minimize the effect of the above-described phenomenon, it is necessary to provide a substantial amount of distance between each air intake opening and the common air outlet opening, making it necessary to increase the duct in size. 
     SUMMARY OF THE INVENTION 
     Thus, the primary object of the present invention is to provide an air duct for an air exhausting apparatus, which is no larger in size than a conventional air duct for an air exhausting apparatus, and yet, is uniform in the amount of force by which air is drawing into the duct, across its entire range in its lengthwise direction. 
     According to an aspect of the present invention, there is provided a duct for an image forming apparatus for forming an image on a recording material, said duct comprising a discharge opening for discharging air; a fan, mounted to a neighborhood of said discharge opening, for discharging the air; first and second openings for suction of air; a first guiding portion, having first and second openings, for guiding the sucked air; a separation member, provided in said first guiding portion, for separating a flow of the air sucked by said first opening and a flow of the air sucked by said second opening; a second guiding member, disposed overlapped with said first guiding portion, for guiding the air guided by said first guiding portion; a first interconnection opening for feeding the air from said first opening to said second guiding portion; a second interconnection opening for feeding the air from said second opening to said second guiding portion, wherein said first interconnection opening is disposed closer to said discharge opening than said second interconnection opening, and wherein said first interconnection opening has a size smaller than said second interconnection opening. 
     These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic sectional view of the image forming apparatus in one of the preferred embodiments of the present invention, showing the general structure of the apparatus. 
         FIG. 2  is a schematic drawing which shows the external appearance of the air duct (which is an air drawing duct in this case), and the positioning of the air duct. 
         FIG. 3  is a longitudinal sectional view of the air drawing duct. 
         FIG. 4  is schematic drawing which shows the relationship between the distance between the upstream wall and downstream walls of each of the subsections of the second section of the air duct, and the length of the air flow in the subsection. 
         FIG. 5  is a schematic drawing which shows the direction and strength of the air flow in the air duct, which were obtained by the calculation based on the results of the simulation. 
         FIG. 6  is a schematic phantom perspective view of the modified version of the duct in the first embodiment. 
         FIG. 7  is a schematic drawing which shows, in concept, the air flow resistance in the modified version of the air drawing duct in the first embodiment. 
         FIG. 8  is a schematic drawing which shows the second comparative air drawing duct. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, the image forming apparatus in the first embodiment of the present invention will be described in detail with reference to the appended drawings. However, the application of the present invention is not limited to the air exhausting apparatuses in the following embodiments of the present invention. That is, the present invention is applicable to a part, parts, or the entirety, of any air duct which extends from one end of an apparatus in which the air duct is placed, to the other, and which has multiple air intake openings (or air outlet openings), which are arranged in the lengthwise direction of the duct, across the entire lengthwise range of the duct, to draw air into the duct (or to blow air out of duct), and a common air passage through which air is drawn out of (or into) the apparatus. 
     This embodiment will be described with reference to an image forming apparatus which employs an intermediary transfer belt, and which forms a full-color image by layering multiple toner images of the primary colors (into which an optical image of an intended image was separated), on the intermediary transfer belt. However, the present invention is also applicable to an image forming apparatus which directly layers two or more toner images, different in color, onto recording medium. It can also be embodied in the form of an air duct usable with an image forming apparatus having an intermediary transfer drum or recording medium transferring drum, instead of the intermediary transfer belt or recording medium conveying drum, respectively. In other words, the present invention is applicable to various types of air duct usable with various image forming apparatuses, which are different in usage, for example, printers, various printing machines, copying machines, multifunction image forming apparatuses, etc. 
     &lt;Image Forming Apparatus&gt; 
       FIG. 1  is a schematic sectional view of the image forming apparatus in one of the preferred embodiments of the present invention, and shows the general structure of the apparatus. The image forming apparatus  30  shown in  FIG. 1  is a full-color laser printer, that is, an electrophotographic image forming apparatus. It employs an intermediary transferring member. The image forming apparatus  30  is provided with a photosensitive drum  1 , as an image bearing member, which is disposed in the main assembly of the image forming apparatus  30 . It is also provided with a charging device  2 , an exposing apparatus  8 , a developing apparatus  3 , a primary transfer roller  4 , and a cleaning apparatus  6 , which are arranged in the adjacencies of the peripheral surface of the photosensitive drum  1 , in the listed order, in terms of the rotational direction of the photosensitive drum  1 . 
     The charging device  2  uniformly charges the peripheral surface of the photosensitive drum  1 . The exposing apparatus  8  forms an electrostatic latent image on the peripheral surface of the photosensitive drum  1  by scanning (exposing) the uniformly charged peripheral surface of the photosensitive drum  1  with the beam of laser light LB which its emits while modulating the beam of laser light LB with the pictorial signals inputted into the exposing apparatus  8 . More specifically, as the beam of laser light LB is emitted from a semiconductor laser (light source) while being modulated with the pictorial signals, it is deflected by a polygon mirror, which is being rotated at a preset high speed, in a manner to oscillate, and then, is projected onto the peripheral surface of the photosensitive drum  1  by way of a focusing lens (lenses), mirrors, etc. 
     The developing apparatus  3  deposits toner to the electrostatic latent image formed on the peripheral surface of the photosensitive drum  1 , forming thereby a toner image on the peripheral surface of the photosensitive drum  1 . The developing apparatus  3  is made up of a development rotary  3 A, and four development units, that is, a yellow development unit  3 Y, a magenta development unit  3 M, a cyan development unit  3 C, and a black development unit  3 K, which are held in the rotary  3 A. The yellow development unit  3 Y, magenta development unit  3 M, cyan development unit  3 C, and black development unit  3 K contain yellow, magenta, cyan, and black toners, respectively. The development rotary  3 A is rotatable by an unshown driving apparatus in the direction indicated by an arrow mark so that any of the development units ( 3 Y,  3 M,  3 C, and  3 K) held in the rotary  3 A can be moved into the development position in which the development unit opposes the photosensitive drum  1 . 
     The primary transfer roller  4  is pressed against the peripheral surface of the photosensitive drum  1 , with the presence of the intermediary transfer belt  5  (intermediary transferring member) between the primary transfer roller  4  and photosensitive drum  1 . It is used to transfer (primary transfer) the toner image formed on the photosensitive drum  1 , onto the intermediary transfer belt  5 . The intermediary transfer belt  5  is supported and kept tensioned by a driver roller  10  and three follower rollers  11 ,  12 , and  13 , and is circularly driven by the driver roller  10  in the direction indicated by an another arrow mark while remaining in contact with the peripheral surface of the photosensitive drum  1 . The cleaning apparatus  6  removes and recovers the toner remaining on the photosensitive drum  1  after the transfer (primary transfer). 
     As an image forming operation start signal is issued, the photosensitive drum  1  is rotationally driven in the direction indicated by the arrow mark, at a preset process speed, while its peripheral surface is uniformly charged to a preset potential level (which is negative in this embodiment) by the charging apparatus  2 . Then, the uniformly charged peripheral surface of the photosensitive drum  1  is scanned by the beam of laser light LB emitted by the exposing apparatus  8 ; it is exposed by the exposing apparatus  8 . As a result, an electrostatic latent image, which corresponds to the first primary color (yellow component) of an intended full-color image, is effected on the peripheral surface of the photosensitive drum  1 . 
     While the latent image for yellow color is being formed, the development unit  3 Y of the developing apparatus  3  is moved into the development position by the rotation of the development rotary  3 A. In the development position, the electrostatic latent image on the photosensitive drum  1  is reversely developed into a visible image by the application of development bias; yellow toner is adhered to the numerous exposed points of the uniformly charged portion of the peripheral surface of the photosensitive drum  1 . Then, the yellow toner image formed on the photosensitive drum  1  is transferred (primary transfer) onto the intermediary transfer belt  5  by the application of the primary transfer bias to the primary transfer roller  4 . After the transfer (primary transfer) of the yellow toner image onto the intermediary transfer belt  5 , the toner remaining on the photosensitive drum  1 , that is, the toner which was not transferred onto the photosensitive drum  1 , is removed by the cleaning apparatus  6 . Also after the primary transfer of the yellow toner image, the development rotary  3 A is rotationally driven to sequentially move the magenta, cyan, and black development units  3 M,  3 C, and  3 B, respectively, into the development position. 
     Then, the process (which includes formation of electrostatic latent image, development of latent image, primary transfer, and cleaning) similar to the one carried out to form the yellow toner image, that is, the toner image of the first primary color, is repeated three times to sequentially form the magenta (second color), cyan (third color), and black (fourth color) toner images. As the magenta, cyan, and black toner images are sequentially formed on the photosensitive drum  1 , they are sequentially transferred in layers onto the intermediary transfer belt  5  so that they align with the yellow toner image on the intermediary transfer belt  5 . As a result, a single full-color toner image, which matches in color to the intended full-color image, is effected on the intermediary transfer belt  5 . 
     Meanwhile, the recording mediums P in a cassette  16   a  ( 16   b ) are fed into the main assembly of the image forming apparatus  30  while being separated one by one by a pickup roller  17   a  ( 17   b ) and a pair of separation rollers  18   a  ( 18   b ), and then, are conveyed to a pair of registration rollers  21  through a recording medium conveyance path  20 . 
     The image forming apparatus  30  is also provided with a secondary transfer roller  14 , which is disposed in a manner to oppose the roller  13 . The secondary transfer roller  14  can be placed in contact with, or separated from, the intermediary transfer belt  5 . As the secondary transfer roller  14  is pressed against the roller  13 , it is pressed upon the intermediary transfer belt  5 , forming thereby the second transferring portion. The recording medium P is conveyed to the second transferring portion by the registration rollers so that it arrives at the second transferring portion at the same time as the full-color image on the intermediary transfer belt  5  reaches the secondary transfer portion. In the secondary transferring portion, the four toner images, different in color, (which make up a full-color image), on the intermediary transfer belt  5  are transferred together (secondary transfer) onto the recording medium P by the secondary transfer roller  14  to which the secondary transfer bias is being applied. The secondary transfer residual toner, that is, the toner on the intermediary transfer belt  5 , which was not transferred onto the recording medium P, is removed by the cleaning apparatus  15 . 
     After the transfer of the full-color toner image onto the recording medium P, the recording medium P is conveyed to the fixing apparatus  23 , which is made up of a fixation roller  23   b  and a pressure roller  23   a . The fixation roller  23   b  has an internal heater, and forms a fixation nip between itself and the pressure roller  23   a . Then, the recording medium P is conveyed through the fixation nip N of the fixing apparatus. While the recording medium P is conveyed through the fixation nip N while remaining pinched between the two rollers  23   b  and  23   a , the full-color toner image is fixed to the recording medium P by being subjected to heat and pressure. Thereafter, the recording medium P is discharged into a tray  26  by way of two pairs of discharge rollers  24  and  25 . 
     &lt;Duct&gt; 
       FIG. 2  is a schematic drawing which depicts the external appearance of the air suctioning duct in the first embodiment (which hereafter may be referred to simply as duct) and the positioning of the duct.  FIG. 3  is a longitudinal schematic sectional view of the air suctioning duct.  FIG. 4  is a schematic drawing which described the relationship between the distance between the upstream wall and downstream walls of each of the subsections of the second section of the air duct, and the length of the air flow in the subsection.  FIG. 5  is a schematic drawing which shows the direction and strength of the air flow in the air duct, which were obtained by the calculated based on the results of the simulation. More specifically,  FIG. 2(   a ) is an external perspective view of the entirety of the duct, and  FIG. 2(   b ) is a schematic sectional view of the duct, at Plane A in  FIG. 2(   a ).  FIG. 3(   a ) is a longitudinal and horizontal schematic sectional view of the second section of the duct, and  FIG. 3(   b ) is a longitudinal and horizontal schematic sectional view of the first section of the duct.  FIGS. 5(   a ) and  5 ( b ) correspond to the duct in the first embodiment and Comparative Example 1 of duct, respectively. 
     Referring to  FIG. 1 , the image forming apparatus  30  is provided with an air duct  27 , which is disposed, as an air drawing duct, on the downstream side of the developing apparatus  3 , in order to recover toner particles as they scatter from the developing apparatus  3 . The air drawing duct  27  is roughly the same in length as the photosensitive drum  1 , and is disposed in the narrow space surrounded by the photosensitive drum  1 , development rotary  3 A, and intermediary transfer belt  5 . 
     Next, referring to  FIG. 2 , the air drawing duct  27  has an air outlet opening  44  (which hereafter will be referred to as outlet opening  44 ) through which air is drawn out from the duct  27  by a fan  50 . The air drawing duct  27  also has a first section and a second section  41 . The first and second sections  40  and  41  are the two types of air passages in the duct  27 . The first section has multiple subsections  40 , which hereafter will be referred to as the first ducts  40 , whereas the second section  41  will be referred to as the second duct  41 . Each first duct  40  has an air intake opening (which hereafter will be referred to as intake opening), and a connective opening  45  as the air passage between the first and second ducts  40  and  41 . After air is taken into the first duct  40 , it is sent into the second duct  41  through the connective opening  45 . The second duct  41  is the second air guiding passage, in which air is flowed toward the air outlet opening  44 . 
     The outlet opening  44  is open at one of the lengthwise ends of the duct  27 ; it is located at one of the lengthwise ends of the lateral wall of the duct  27 , which has the intake openings  42 . The intake openings  42  are the opening through which the internal air of the image forming apparatus  30  (which is example of image forming apparatus which forms image on recording medium P) is drawn into the duct  27 . The multiple first ducts  40  and multiple connective openings  45  are arranged in the direction parallel to the lengthwise direction of the air drawing duct  27 , making up the first air guiding section. 
     Referring to  FIG. 3 , the multiple first ducts  40  are different in the size of the connective opening  45 . For example, the connective opening  45  of the first duct  40  is different in size from that of the second first duct  40 . 
     Further, the multiple first ducts  40  are different in their distance from the outlet opening  44 . For example, the distance of the first duct  40  from the outlet opening  44  is greater than the distance of the second first duct  40  from the outlet opening  44 . Further, the size of the connective opening  45  of the first duct  40  is greater in the size of the connective opening  45  of the second first duct  40 . 
     The distance between the intake opening of each of the multiple first ducts  40 , and the connective opening  45 , is greater than the distance between the adjacent two partitioning walls  43 . 
     The air drawing duct  27  has a double-deck structure. That is, the first section of the duct  27  (made up of multiple first ducts  40 ), that is, the first air guiding section, constitutes the top tier, whereas the second duct  41 , that is, the second air guiding section, constitutes the bottom tier. 
     The image forming apparatus  30  has the photosensitive drum  1 , which is an example of image bearing member which bears a toner image. Each air intake opening  42  is located so that it opposes the peripheral surface of the photosensitive drum  1 . 
     Referring to  FIG. 2(   a ), the air drawing fan  50  is located at the rear end of the second duct  41 . The multiple intake openings  42 , which are for drawing air from the adjacencies of the photosensitive drum  1  into the air drawing duct  27 , are arranged in a straight line parallel to the axial line of the photosensitive drum  1 , along the peripheral surface of the photosensitive drum  1  which is the object to be protected from the above mentioned stray toner particles, that is, the toner particles scattered from the developing apparatus. 
     The air drawing duct  27  is double-decked as described above. More specifically, the second ducts  41 , which extends in the lengthwise direction of the air drawing duct  27 , and the nine first ducts  40 , which extend in the widthwise direction the second duct  41 , are arranged side by side in the lengthwise direction of the air drawing duct  27  (direction in which second duct  41  extends). The second duct  41  is the air passage through which air flows toward the outlet opening  44 , whereas each first duct  40  is the connective passage, between the intake opening  42  and connective opening  44 , through which air is drawn into the second duct  41 . 
     The nine intake openings  42 , which the nine first ducts  40  have one for one, are the same in size (cross section). Each first duct  40  is in connection to the second duct  41  on the opposite side from the corresponding intake opening  42 . The air drawing duct  27  is provided with the air outlet opening  44 , which is open at the rear end of the second duct  41 . The air outlet opening  44  is fitted with the air drawing fan  50  and a toner recovery filter  51 . Incidentally, the air drawing fan  50  may be attached to the air drawing duct  27 , or disposed away from the air drawing duct  27 . 
     Referring to  FIG. 2(   b ), the adjacent two first ducts  40  are separated from each other by the partitioning wall  43 , which is an example of partitioning plate. The second duct  41  and first ducts  40  are partitioned from each other by the floor wall (bottom wall)  46 . The floor wall  46  is provided with the connective openings  45 , each of which is an example of connective hole, through which each first duct  40  is in connection with the second duct  41 . 
     As the air drawing fan  50 , with which the air outlet opening  44  is fitted, is started, an air flow is generated, which flows into the air drawing duct  27  from outside the air drawing duct  27  through the intake openings  42 . After advancing into the first ducts  40  through their air intake openings  42 , the air flows downward through the connective opening  45 , and joins (combines) with the air flow in the second duct  41  as it flows downward through the connective opening  45 . Then, after the air flow from the first duct  40  joins the air flow in the second duct  41 , the combination of the two bodies of air flows toward the outlet opening  44 , and then, is exhausted through the outlet opening  44 . Thus, the stray toner particles, more specifically, the toner particles having scattered from the developing apparatus  3 , are picked up by this air flow, enter the first ducts  40  with the air flow, descend with the air flow through the connective openings  45 , join the air flow in the second duct  41  at the connective opening  45 . Then, they are exhausted through the outlet opening  44 . The air drawing duct  27  is placed below the contact area between the developing apparatus  3  and photosensitive drum  1 , and is set in such an attitude so that the connective openings  45  are positioned higher than the corresponding intake openings  42 . Therefore, even after the air drawing fan  50  stopped, it does not occur that the toner particles in the air drawing duct  27  come out through the intake openings  42 . 
     Referring to  FIG. 3(   a ), in terms of the lengthwise direction of the air drawing duct  27 , the dimension of each intake opening  42  is roughly the same as the interval between the adjacent two partitioning walls  43 . Therefore, as the air drawing fan  50  is activated, the presence of the partitioning walls  43  allows virtually no area in the adjacencies of the peripheral surface of the photosensitive drum  1 , to be free from the air flow which occurs in the area in which the intake openings  42  of the air drawing duct  27  face the peripheral surface of the photosensitive drum  1 . Further, the air drawing duct  27  in the first embodiment is provided with the nine small air intake openings  42 , instead of a single large air intake opening. Therefore, the difference in the amount of air flow between the lateral edge portions and center portion of each first duct  40  is smaller. Further, as air is drawn into the second duct  41  of the air drawing duct  27  through the first ducts  40 , the air is made to flow in parallel to the partitioning walls  43 . Therefore, the angle at which air is drawn into the air drawing duct  27  through the first ducts  40 , across the entire lengthwise range of the air drawing duct  27  (entire range of photosensitive drum), is roughly 90° relative to the lengthwise direction of the lengthwise direction of the air drawing duct  27 . The outlet opening  44  is open at one of the lengthwise ends of the air drawing duct  27 . Therefore, if the first ducts  40  is not provided with a substantial number of partitioning walls such as the partitioning walls  43 , the air flows which air generates as it is drawn into the air drawing duct  27  through the first ducts  40  are likely to deviate in such a direction that its downstream end is closer to the outlet opening  44  than its upstream end. However, with the employment of the above described structural arrangement in accordance with the present invention, the direction of the air flow entering the air drawing duct  27  is roughly 90° relative to the lengthwise direction of the duct  27 . Therefore, each first duct  40  is minimized in the nonuniformity in the amount of force by which air is drawn into the first duct  40 , in terms of the lengthwise direction of the duct  27 . Also in terms of the lengthwise direction of the duct  27 , each of the connective openings  45  with which the floor wall  46  is provided is the same in dimension as the interval between the adjacent two partitioning walls  43 . Therefore, the air passage which the adjacent two partitioning walls  43  provide between the first duct  42  and connective opening  45  is uniform in cross section. Therefore, the partitioning walls  43  contribute to the straightening of air flow, across their entire length. Therefore, the air drawing duct  27  is even in the amount of force by which air is drawing into the duct  27 , across its entire lengthwise range, more specifically, at least between the adjacent two intake openings  42 . 
     Further, as described above, each of the multiple first ducts  40  separated from the next first ducts  40  by the partitioning walls  43  is provided with the connective opening  45 . The multiple connective openings  45  are adjusted (made different) in size using the following method. That is, in terms of the lengthwise direction of the air drawing duct  27 , the multiple connective openings  45  are the same in dimension, whereas in terms of the direction perpendicular to the lengthwise direction of the air drawing duct  27 , they are different in dimension. More specifically, the connective openings  45  are adjusted (made different) in size so that the farther they are from the outlet opening  44 , the greater in size they are. Therefore, the first ducts  40  are roughly the same in the amount of air flow. Thus, the air pressure loss attributable to the second duct  41  is compensated for by this arrangement. That is, of any two first ducts  40 , the one which is farther from the outlet opening  44 , being therefore less in the amount of the difference between its internal and external pressures, than the other, is provided with the necessary amount of air flow. Since the first ducts  40  are individually adjusted in the amount of air flow as described above to make the air drawing duct  27  uniform across its entire lengthwise range, in the amount and direction of air flow. Therefore, the air drawing duct  27  can highly efficiently and evenly draw air across the entire range of an object (photosensitive drum  1  in the first embodiment), along which it is placed. 
     Further, the relationship between the interval D between the adjacent two partitioning walls  43  and the distance L from the intake opening  42  to the connective opening  45  is: D&lt;L. Incidentally, the distance D is the distance from the intake opening  42  to the edge of the connective opening  45 . Referring to  FIG. 4 , if the relationship between the interval D and distance L is changed to D&gt;L, the force which generates an air flow in the air drawing duct  27  increases in its component which pulls the air in the air drawing duct  27  toward the outlet opening  44 , making the partitioning walls  43  less effective in their function to rectifying (straightening) the air movement. With the partitioning walls  43  being less effective in their air flow rectifying function, the air flow between the intake  42  and connective opening  45 , that is, the air flow in each first duct  40 , is likely to deviate in angle. With the air flow in the first duct  40  being deviated in angle, the first ducts  40  are unequal in the amount of force by which the external air is drawn into the air drawing duct  27  through their intake openings  42 . In this embodiment, therefore, the air drawing duct  27  is structured so that the relationship between the interval D and distance L is: D&lt;L. Therefore, the partitioning walls  43  are more effective in their function of rectifying air movement. Therefore, the air flow between the intake  42  and connective opening  45  is less likely to deviate in angle. Therefore, the air drawing duct  27  in this embodiment is uniform across its entire lengthwise range in the amount of force by which air is suctioned into the duct  27 . 
     Further, all the first ducts  40  share the floor wall  46 , and the adjacent two first ducts  40  share the partitioning wall  43  which separates them. In other words, the air drawing duct  27  is structured as if the second duct  41  and corresponding first duct  40  were formed by folding a single duct. Therefore, the second and first ducts  41  and  40  can be placed in a tiny space, such as the one shown in  FIG. 1 . Further, each partitioning wall  43  is shared by the adjacent two ducts which are separated by the wall. Therefore, the air drawing duct  27  is significantly smaller in the amount of material necessary to produce it, greater (as large as possible) in the size of the cross section of the air passage, and less in weight than an air drawing duct  27  in accordance with the prior art. 
     Next, referring to  FIG. 3(   b ), the second duct  41  is shaped so that its cross section is in the form of a long and narrow regular parallelepiped. In terms of the lengthwise direction of the air drawing duct  27 , its dimension is the same as that of the first duct  40 . In other words, it is shaped so that it is as large as possible in terms of the cross section of the air flow therein while being limited in its external size. On the downstream side of the outlet opening  44 , the air drawing fan  50  and toner recovery filter  51  are disposed ( FIG. 2(   a )). As the air drawing fan  50  is started to extract air from within the main assembly of the image forming apparatus  30 , the second duct  41  is reduced in internal pressure, causing the air to flow into the second duct  41 . As the air enters the second duct  41  through each intake opening  42 , it descents into the second duct  41  through the connective opening  45 , and joins the air flow in the second duct  41 . Then, it ascends at a gentle angle through the second duct  41 , and is exhausted through the outlet opening  44 . 
     The second duct  41  is provided with the outlet opening  44 , the plane of which is perpendicular to the lateral wall of the air drawing duct  27 , which is provided with the intake openings  42 . In terms of the direction perpendicular to the lengthwise direction of the air drawing duct  27 , the outlet opening  44  is on the same side of the air drawing duct  27  as the intake opening  42 , that is, on the opposite side of the air drawing duct  27  from the connective opening  45 . Therefore, the line of air flow, which connects a given connective opening  45  and the outlet opening  44  does not intersect or overlap with the line of air flow, which connect another connective opening  45  and the outlet opening  44 . Therefore, the body of air having entered the second duct  41  through one of the connective openings  45 , and the body of air having entered the second duct  41  through another connective opening  45  are virtually undisturbedly guided to the outlet opening  44 ; they are guided while remaining in the same state as the state in which they were after they are rectified, being therefore remaining roughly in parallel to each other. Further, of any two first ducts  40 , the one closer to the outlet opening  44  is greater, in the angle of the line of air flow which connects this first duct  40  to the outlet opening  44 , than the other first duct  40 . Therefore, of any two connective openings  45 , the difference between the one closer to the outlet opening  45  and the other, in the length of the virtual air passage in the second duct  42 , through which a body of air has to travel to reach the outlet opening  44  after it enters the second duct  42  through the connective openings  45 , is significantly smaller than it is in the case of an air drawing duct in accordance with the prior art. Therefore, the connective openings  45  of the air drawing duct  27  in the first embodiment are significantly less different in the amount of air pressure, being therefore more uniform in the amount by which air flows into the second duct  41  through them than those of an air drawing duct in accordance with the prior art. Therefore, the connective openings  45  of the air drawing duct  27  in the first embodiment are more uniform in the amount by which air flows through them than those of an air drawing duct  27  in accordance with the prior art. 
     The air drawing duct  27  is structured so that air is drawn through the first and second sections. The first section is made up of the multiple first subsections (first ducts  40 ) which are high in flow resistance. The second section (second duct  41 ), that is, the common duct, which is not partitioned, being therefore low in flow resistance. Therefore, even thought the air drawing duct  27  is in the form of a long and narrow regular parallelepiped, being therefore small in cross section, its intake openings  42 , which are arranged across the entire lengthwise range of the duct  27 , are uniform in the amount of force by which air is drawn into the duct  27  through the intake openings  42 . Therefore, the air drawing duct  27  is uniform in the amount of air drawing force, across its entire lengthwise range, that is, the range from the outlet opening  44  to the farthest intake opening  42 , and can draw air with the minimum amount of pressure loss. 
     Further, the pressure loss which is caused by the first ducts  40  closer to the outlet opening  44 , is utilized to provide a sufficient amount of difference in air pressure between the connective opening  45  and intake opening  42  of each of the first ducts  40  farther from the outlet opening  44 , in order to secure a necessary amount of air flow. 
     With the employment of the above described structural arrangement, it is possible to make all the first ducts  40  of the air drawing duct  27  between one lengthwise end of the air drawing duct  27  to the other, significantly less different in the amount of air flow. In other words, an air exhausting duct, such as the air drawing duct  27  in this embodiment, which is more desirable in the characteristic of the air flow therein, higher in efficiency, and smaller in size, can be realized by structuring the air drawing duct  27  as if its second section (second ducts  41 ) and first section (made up of first ducts  40 ), were created by folding a single air duct into the top and bottom sections. 
     In the case of the air drawing duct  27 , air flow is uniform in each of its intake openings  42 , and also, the intake openings  42  are small in the difference in the direction of air flow. An air drawing duct which is desirable in the characteristic of the air flow therein and high in efficiency can be made more compact by structuring it so that the top section (first section made up of first ducts  40 ) and bottom section (second duct  41 ) share a partitioning wall (flow wall  46  of first section), and also, so that the adjacent two first ducts  40  share a partitioning wall (partitioning wall  43 ). With the employment of this structural arrangement, an air drawing duct  27  can be reduced in cross section without sacrificing the second duct  41  in cross section. 
       FIG. 5(   a ) shows the direction and strength of the air flow in the air duct, which were obtained by the calculation based on the results of the simulation carried out with the use of an air drawing duct which is the same in measurements as the air drawing duct  27  to study the internal air flow of the air drawing duct  27 . The arrows in the drawing are vectorial; they show the direction and velocity of the air flow in each first duct  40 . Since the air drawing duct  27  is structured so that air flows from the intake opening  42  to the corresponding connective opening  45 , not only is the air flow in each first duct  40  perpendicular to the lateral wall of the air drawing duct  27 , which has the first ducts  42 , but also, all the first ducts  40  are virtually uniform in internal air velocity. In order to equalize all the first ducts  40  in the velocity with which air is drawn through them, the balance among each intake opening  42 , corresponding connective opening  45 , and corresponding outlet opening  44  has to be optimized. 
     In this embodiment, all the intake opening  42  are made the same in dimension, being 28 mm in width and 3 mm in length. However, the connective openings  45  are made the same in the dimension in terms of the lengthwise direction of the air drawing duct  27 , being 28 mm in width, but, different in the dimension in terms of the direction perpendicular to lengthwise direction of the air drawing duct  27 , being 1 mm, 1 mm, 1 mm, 2.5 mm, 5 mm, 10 mm, 20 mm, and 20 mm, respectively, listing in the order of the closest one to the outlet opening  44 . The outlet opening  44  is 18 mm×13 mm in size. The amount of air flow which the exhaust fan  50  needs to generates is 486,400 mm 3 /sec. 
     The numerical values given above are the referential values set based on the assumption that the size of the outlet opening  44  is as described above. In other words, the amount of air flow which the air drawing fan  50  is required to generate can be reduced by enlarging the outlet opening  44 . 
     Incidentally, in this embodiment, the air drawing duct  27  is roughly 280 mm in overall length. However, the overall length of the air drawing duct  27  is determined by the length of the photosensitive drum  1 , in other words, the dimension of the recording medium P, which is needless to say. Further, each intake opening  42  may be reduced in width from 28 mm so that the air drawing duct  27  can be provided a larger number of intake openings  42  (which will be arranged in higher density) than the number of intake openings  42  in this embodiment. In such a case, the number of first ducts  40  will be greater than 9, which is obvious. 
       FIG. 5(   b ) shows the direction and strength of the air flow in the air duct, which were obtained by the calculation based on the results of the simulation carried out with the use of an air drawing duct  127 , that is, the first comparative air drawing duct, which is the same in external appearance and the structure of the second duct  41  (second section) as the air drawing duct  27 , but, is different in the first section (it does not have partitioning wall; there is no first duct  40 ). However, in order to balance the nine intake openings  142  in terms of the amount of air flow, the air drawing duct  127  is structured so that the greater the distance from the outlet opening  44 , the greater in size the intake openings  142 . 
     In this case, the farther from the outlet opening  44 , the smaller the amount of air drawing force, as described above, and also, the difference in the amount of air drawing force is substantial. Therefore, even if the intake openings  142  farther from the outlet opening  44  are substantially increased in size compared to those closer to the outlet opening  44 , those farther from the outlet opening  44  do not increase much in air flow. Moreover, the direction in which air is drawn into the air drawing duct  127  is not perpendicular to the wall of the air drawing duct  127 , which has the intake openings  142 ; air is drawn into the air drawing duct  127  at a certain angle. 
     &lt;Modified Version&gt; 
       FIG. 6  is a schematic perspective view of the modified version of the air drawing duct in the first embodiment, and  FIG. 7  is a schematic drawing which shows the concept of the air flow resistance of the air drawing duct. The air drawing duct  227 , that is, the modified version of the air drawing duct  27  shown in  FIG. 1 , is mostly the same in structure as the air drawing duct  27 ; the air drawing duct  227  is different from the air drawing duct  27  only in that the intake openings  242  of the air drawing duct  227  are different from the intake openings  42  of the air drawing duct  27 . Therefore, the structural components of the air drawing duct  227  shown in  FIGS. 6 and 7 , which are similar in structure to their counterparts of the air drawing duct  27 , are given the same referential symbols as those given to the counterparts, and will not be described in detail. The intake opening  242  and connective opening  245  are different from the intake opening  42  and connective opening  45  of the air drawing duct  27  only in the dimension (in terms of direction in which they are aligned. 
     Referring to  FIG. 6 , the air drawing duct  227  is provided with multiple first ducts  40  and a single second duct  41 . The connective opening  245  of each of the first ducts  40  of the air drawing duct  227  is the same in size as the connective opening  245  of the other first duct  40  of the air drawing duct  227 . However, the intake opening  242  of each of the first ducts  40  of the air drawing duct  227  is different in size from the other first duct  40  of the air drawing duct  227 . 
     In other words, the air drawing duct  227  is structured so that all of its connective openings  245  are equal in size, and also, so that the farther from the outlet opening  44 , the greater in size the intake openings  242 . This setup was devised to equalize all the intake openings  242  in air flow velocity (which is comparable to relationship between connective opening  45  in  FIG. 3(   a ), and connective openings  42  in  FIG. 2(   a )). 
     Referring to  FIG. 7 , it may be reasonable to think that the air drawing duct  227  is structured so that the first ducts  40 , which branch from the second duct  41  and are higher in flow resistance than the second duct  41 , align side by side in parallel in the direction parallel to the axial line of the photosensitive drum. Strictly speaking, the outlet opening  44  is placed on the opposite side from the connective opening  45  in terms of the direction perpendicular to the axial line of the photosensitive drum  1 , to prevent the lines of air flow which connect the multiple first ducts  40  to the outlet opening  44 , from overlapping or intersecting. Therefore, in a strict sense, it cannot be said that the flow resistance of the second duct  41 , and the flow resistances of the first ducts  40 , which combine to make up the overall air flow resistance of the air drawing duct  27 , are connected in series. However, for convenience, they may be thought to be connected in series. 
     In this case, the air drawing fan  50  and toner recovery filter  51  are connected in series. As a body of air flows into a given first duct  40  through the intake opening  242 , it flows into the second duct  41  through the connective opening  245 , and joins the air flow in the second duct  42 . 
     Therefore, the air drawing duct  227  is desired to be structured so that the closer to the outlet opening  44 , the greater in the air flow resistance the first ducts  40  (inclusive of those of corresponding connective opening and intake opening). This is for compensating the connective openings  245  for their loss in air pressure (negative pressure), the amount of which corresponds to their distance from the outlet opening  44 . 
     As for a method for increasing the air flow resistance of the first duct  40  (inclusive of those of corresponding connective opening  245  and intake opening  242 ), in the case of the air drawing duct  27 , shown in  FIG. 2 , it is structured so that the closer to the outlet opening  44 , the smaller in size the connective opening  45  of the first duct  40 . In the case of the air drawing duct  227 , it is structured so that the closer to the outlet opening  44 , the smaller the intake openings  242 . 
     Incidentally, the effects similar to the above described effects can be achieved using methods other than the above described ones. For example, the first ducts  40  may be reduced in cross section, or an object capable of increasing the air flow resistance of the first duct  40  itself may be placed in the first duct  40 . These methods may be individually employed or in combination. 
     In the above, the first embodiment and its modified version were described with reference to the cases in which the air drawing ducts  27  and  227  recover the toner particles having scattered from the developing apparatus  3  shown in  FIG. 1 . However, their application is not limited to a developing apparatus. For example, they may be placed in the adjacencies of the charging device  2  to recover ozone, or in the adjacencies of the cleaning apparatus  6  to recover the scattered recovered toner. Further, instead of being placed in the adjacencies of the peripheral surface of the photosensitive drum  1 , they may be placed in the adjacencies of the fixing apparatus  23  to prevent the increase in humidity. 
     Further, not only are the air drawing ducts  27  and  227  effective to draw the internal air of an apparatus (image forming apparatus  30 ), but also, to blow external air into an apparatus, uniformly across the entire range of the apparatus, to air cool the interior of the apparatus. In this case, the intake openings  42  is to be read as “outlet openings  42 ”, and the outlet opening  44  is to be read “intake opening  44 ”. The air drawing duct  27 , which is an example of air duct, is to be read as “air supply duct  27 ”. The air drawing fan  50 , which is an example of fan, is to be read as “air supply fan  50 ”. The second duct  41 , which is an example of air passage creates an air flow directed toward the first duct  40 . 
     The intake opening  42 , which is an example of opening through which air is drawn, is to be read as “voutlet opening  42 ”. Thus, the first duct  40  sends the air supplied from the second duct  41  through the connective opening  45 , which is an example of passage between the second duct  41  and first duct  40 , to the “voutlet opening  42 ”. 
     Comparative Example 2 
       FIG. 8  is a schematic drawing of Comparative Example 2 of air drawing duct.  FIG. 8(   a ) is a plan view of the air drawing duct, as seen from the intake opening side, and  FIG. 8(   b ) is a side view of air drawing duct, the wall of which having the intake openings is facing upward. 
     As an image forming apparatus which uses toner is operated, toner articles sometimes leak from its developing apparatus, cleaning apparatus, etc. Thus, as the image forming apparatus is used for an extended length of time, toner particles scatter in the image forming apparatus. Further, a corona discharging device or the like generates ozone while it discharges corona to charge a photosensitive member. Thus, in the case of an image forming apparatus which uses toner and a corona discharging device (as charging apparatus), not only do toner sometimes scatter in the image forming apparatus, but also, ozone is released into the interior of the image forming apparatus. If toner scatters in an image forming apparatus and/or ozone is released within the image forming apparatus, the photosensitive drum, charging apparatus, etc., are contaminated by the toner and/or ozone, which may results in the nonuniform charging of the photosensitive drum. Further, there is a possibility that the scattered toner particles and/or ozone may adhere to the surface of the gears and shafts which are involved in the driving of the photosensitive drum and the like. The adhesion of the toner and/or ozone increases the amount of frictional load to which the driving mechanism is subjected, or may reduce the image forming apparatus in operational accuracy. 
     Therefore, it was proposed to provide an image forming apparatus with an air drawing duct  327 , which is for drawing air to capture the scattered toner particles and/or ozone in the image forming apparatus with a filter, in order to remove them, and which is uniform in the amount of air drawing force, across roughly its entire range in terms of the lengthwise direction of the photosensitive drum (Patent Document 1). 
     Referring to  FIG. 8(   a ), the air drawing duct  327  is in the form of a parallelepiped. Its top wall has three air intake openings  111 ,  112 , and  113 , which are aligned with equal intervals. There are unshown air drawing fan and a toner recovery filter, which are connected in series, and are located next to the outlet opening, that is, the opening with which one of the lengthwise ends of the air drawing duct  327  is provided. 
     Referring to  FIG. 8(   b ), there are two partitioning walls  121  and  122  in the air drawing duct  327 . The partitioning wall  121  separates an air flow passage  131  from an air flow passage  132 . The air flow passage  131  is dedicated to the intake opening  111 , and extends from the intake opening  111  to the outlet opening  144 . The air flow passage  132  is dedicated to intake opening  112 , and extends from the intake opening  112  to the outlet opening  144 . The partitioning wall  122  separates the air flow passage  132  from an air flow passage  133 , which is dedicated to the intake opening  113  and extends from the intake opening  113  to the outlet opening  144 . Therefore, the air passages  131 ,  132 , and  133  which are dedicated to the intakes  111 ,  112 , and  113 , respectively, and extend therefrom to the outlet opening  144  where the unshown air drawing fan is located, do not intersect. 
     Further, the air drawing duct  327  is structured so that the air flow passage  131  corresponding to the intake opening  111 , that is, the intake opening closest to the outlet opening  144  is smaller in cross section than the air flow passage  132  corresponding to the intake opening  112 , and also, so that the air flow passage  133  corresponding to the intake opening  113 , that is, the intake opening farthest from the outlet opening  144  is larger in cross section than the air flow passage  132  corresponding to the intake opening  112 . That is, the air flow passages  131 ,  132 , and  133  are made different in cross section to roughly equalize them in the amount of air flow. Incidentally, the air flow passages  131 ,  132 , and  133  may be adjusted in the amount of air flow by making the intake openings  111 ,  112 , and  113  different in the size of cross section. 
     Also in the case of the air drawing duct  327 , that is, second comparative example of air drawing duct, the farther from the outlet opening  144 , the smaller the amount of air drawing force. That is, in terms of the air drawing force, the intake opening  111  is stronger than the intake opening  112 , which is stronger than the intake opening  113 . Structuring the air drawing duct  327  to provide the intake  113 , that is, the farthest intake opening from the outlet opening  144 , with a sufficient amount of air drawing force, makes the intake opening  111 , that is, the closest intake opening to the outlet opening  144 , excessively high in the amount of air drawing force, making it possible for a toner image formed on the photosensitive drum to be disturbed. Further, it makes the direction in which air is drawn into the air drawing duct  327  through the intake openings  111 ,  112 , and  113 , incline as shown in  FIG. 8(   b ), in a manner to place the downstream end of the air flow closer to the outlet opening  144  than the upstream end, instead of making the air flow perpendicular to the photosensitive drum. This was the cause of the reduction in the efficiency with which the scattered toner particles and ozone are recovered. In order to prevent the occurrence of this phenomenon, the intervals among the intake openings  111 ,  112 , and  113  must be substantially increased, making it necessary to increase in size the air drawing duct  327 . Increasing in size the air drawing duct  327  makes it impossible for the duct  327  to be placed in a tiny space, such as the internal space of an image forming apparatus. 
     On the other hand, the air drawing duct  27  shown in  FIG. 2 , which is the air drawing duct in the first embodiment, is provided with a substantially larger number of intake openings  42  which are substantially smaller in the measurement in terms of the direction parallel to the axial line of the photosensitive drum than the air drawing duct  327 . Further, the intake openings  42  are arrange side by side in parallel in a single straight line from one lengthwise end of the air drawing duct  27  to the other. Therefore, the second duct  41  of the air drawing duct  27  in the first embodiment is smaller in the difference in the amount of air drawing force, between the outlet opening  44  and the opposite end from the outlet opening  44 . In other words, the amount of force with which air is drawing into the air drawing duct  27  across its range closer to the opposite lengthwise end of the air drawing duct  27  from the outlet opening  44  was increased by providing a large number of narrower (in terms of direction parallel to axial line of photosensitive drum) intake openings, which are arranged side by side in parallel in a straight line from lengthwise end of the air drawing duct  27  to the other. Not only can this structural arrangement minimize each intake opening  42  in terms of the nonuniformity in the amount of internal air flow, but also, it minimizes the difference, in the direction in which air is drawn into the air drawing duct  27 , among the intake openings  42 . 
     As described above, according to the present invention, an air duct can be made uniform in the amount by which air is drawn into the duct, across its entire range in terms of its lengthwise direction, without increasing the duct in size. 
     Incidentally, in the preceding embodiments of the present invention, the air drawing ducts were disposed next to the photosensitive drum. However, the preceding embodiments are not intended to limit the location of the placement of an air drawing duct in accordance with the present invention, to the adjacencies of a photosensitive drum. For example, an air drawing duct in accordance with the present invention may be placed next to an intermediary transferring member, that is, a member on which a toner image is borne. In other words, it may be placed in the adjacencies of any object, from which air needs to be evenly drawn away, across its entire lengthwise range. 
     While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims. 
     This application claims priority from Japanese Patent Application No. 046088/2007 filed Feb. 26, 2007, which is hereby incorporated by reference.