Patent Publication Number: US-6708009-B2

Title: Image forming device having paper dust removing units

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a Continuation-in-Part of application Ser. No. 09/852,746 filed May 11, 2001, now U.S. Pat. No. 6,505,019, which in turn is a Continuation-in-Part of application Ser. No. 09/817,170 filed Mar. 27, 2001, now U.S. Pat. No. 6,415,119, and a Continuation-in Part of application Ser. No. 09/824,054 filed Apr. 3, 2001 now abandoned, which in turn is a Divisional application of Ser. No. 09/409,386 filed Sep. 30, 1999, now patented as U.S. Pat. No. 6,219,505 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an image forming device such as a laser printer. 
     An image forming device such as a laser printer generally includes a sheet supply section for supplying sheets and an image forming section for forming an image on a sheet supplied from the sheet supply section. The sheet supply section generally includes a sheet supply tray on which a stack of sheets is mounted, a sheet supply roller positioned near one end and above the sheet supply tray, and a separation pad positioned in confrontation therewith. Upon rotation of the sheet supply roller, an uppermost sheet on the sheet supply tray is nipped between the sheet supply roller and the separation pad and is delivered to the image forming section. 
     The image forming section includes a photosensitive drum, a charger, a scanner device, a developing roller and an image transfer roller those positioned around the photosensitive drum and in order in a rotating direction thereof. In accordance with the rotation of the photosensitive drum, a surface of the photosensitive drum is uniformly charged by the charger, and then, the surface is exposed to laser beam emitted from the scanner device and scanned at high speed in accordance with image data to form an electrostatic latent image on the surface. Then, toners carried on the developing roller are supplied to the surface of the photosensitive drum by the rotation of the developing roller to form a visible toner image on the surface of the photosensitive drum corresponding to the electrostatic latent image. The toner image carried on the surface of the photosensitive drum is then transferred onto the sheet supplied from the sheet supply section when the sheet passes between the photosensitive drum and the image transfer roller. Thus, a toner image can be formed on the sheet. 
     In the image forming device, paper dusts may be inevitably generated on the sheet due to the friction against the separation pad because each sheet is supplied while being nipped between the sheet supply roller and the separation pad. Thus, image quality may be lowered, if such paper dusts are mixed with the toners at the image forming section. 
     To avoid this problem, known is a paper dust removing roller disposed upstream of the sheet supply roller. The paper dust removing roller has a width approximately the same as that of the separation pad in order to remove the paper dust on the sheet before the sheet reaches the image forming section. However, paper dusts have already inherently existed over the entire surface of the sheet due to sheet cutting. Therefore, it would be difficult to remove the inherent paper dusts only by such paper dust removing roller having the width the same as that of the separation pad. 
     Both inherently generated paper dusts as well as the paper dusts generated due to the friction with the separation pad may be removed by a paper dust removing roller as far as the paper dust removing roller has a width the same as the sheet width. However, amount of the paper dust generated by the friction against the separation pad is greater than the inherently generated amount. Therefore, even if the removal of the paper dust is intended by such paper dust removing roller having the paper width, paper dust cannot be removed uniformly, but removal unevenness occurs between an area where paper dusts were generated due to the friction against the separation pad and an area where the paper dusts have been inherently generated. Thus, uniform removal of the paper dusts cannot be achieved. 
     Further, a plurality of paper dust removing rollers can be provided along a sheet supply path in order to remove the paper dust on the sheet supplied from the sheet supply section. However, a paper dust transport mechanism and a paper dust accumulator are provided for every paper dust removing roller for transporting and accumulating paper dusts removed by each paper dust removing roller. Therefore, an entire structure becomes complicated, and mechanical components and parts are increased, which renders a resultant image forming device bulky and costly. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the present invention to overcome the above-described drawbacks, and to provide an image forming device capable of efficiently removing paper dust from the sheet and providing high quality image. 
     Another object of invention is to provide such image forming device with a simplified arrangement and capable of reducing numbers of mechanical parts, yet performing a sufficient paper dust removal by a plurality of paper dust removing units. 
     Still another object of the present invention is to provide such image forming device capable of stably transporting, by way of the paper dust transport means, the paper dusts removed by the paper dust removing unit to assure a sufficient falling distance between the paper dust removing unit and the paper dust transport means in order to unit and the paper dust transport means in order to provide a sufficient paper dust accumulation space below the paper dust removing unit. 
     Still another object of the present invention is to provide such image forming device capable of preventing paper dusts absorbed by the paper dust removing unit from again returning back to a sheet transport path in order to avoid mixture of the paper dusts with developing agent such as toners in a image forming operation performed at downstream of the paper dust removing unit. 
     These and other objects of the present invention will be attained by providing an image forming device for forming an image on an image recording medium, the device including a sheet supply section, an image forming section, a sheet transport path, and an improved at least two paper dust removing units. The sheet supply section includes a sheet supply roller and a separation pad for nippingly supplying each image recording medium therebetween. The image forming section is adapted for forming an image on the image recording medium supplied from the sheet supply section. The sheet transport path extends from the sheet supply section to the image forming section and defines a sheet feeding direction. The at least two paper dust removing units include a first paper dust removing unit and a second paper dust removing unit. The first paper dust removing unit is disposed at a position beside the sheet transport path and is contactable with the image recording medium for removing paper dusts from the image recording medium running in the sheet transport path toward the image forming section. The second paper dust removing unit is disposed at a position beside the sheet transport path and different from the position of the first paper dust removing unit with respect to the sheet feeding direction and also is contactable with the image recording medium for also removing paper dusts from the image recording medium running in the sheet transport path toward the image forming section. 
     In one preferred embodiment, the first paper dust removing unit includes a first paper dust removing member in contact with the image recording medium during its travel in the sheet transport path, and the second paper dust removing unit includes a second paper dust removing member in contact with the image recording medium during its travel in the sheet transport path. The first paper dust removing member has a width perpendicular to the sheet feeding direction greater than the width of the separation pad, and the second paper dust removing unit has a width perpendicular to the sheet feeding direction greater than the width of the image recording medium. The width of the first paper dust removing member is smaller than the width of the image recording medium. As such, the first paper dust removing member can remove paper dusts from the image recording medium at least in an area corresponding to the width of the separation pad. Also, the second paper dust removing unit can remove paper dusts in overall surface of the image recording medium. 
     The image forming device further provides a paper dust accumulating section for congregately accumulating therein paper dusts removed by at least two paper dust removing units from the image recording mediums and then released from the respective paper dust removing units. 
     In other aspect of the invention, there is provided an image forming device including the image forming section, a sheet transport path extending to the image forming section, a paper dust removing member, a scraping member, and a reverse transport preventive member. The paper dust removing member is positioned in confrontation with the sheet transport path and contactable with the image recording medium passing therethrough for removing paper dusts from the image recording medium. The scraping member is in contact with the paper dust removing member for scraping off the paper dusts from the paper dust removing member. The paper dust removing member is supported rotatably in a normal direction equivalent to the sheet feeding direction and a reverse direction opposite to the normal direction. The reverse transport preventive member is disposed between a first contact position defined between the paper dust removing member and the image recording medium and a second contact position defined between the paper dust removing member and the scraping member for preventing the paper dusts released from the scraping member from being transported back toward the sheet transport path during the reverse rotation of the paper dust removing member. 
     In still another aspect of the invention, there is provided an image forming device including the image forming section, a paper dust removing unit for removing paper dusts from the image recording medium to be supplied to the image forming section, a paper dust transport unit, and a regulation wall. The paper dust transport unit is disposed lower than the first paper dust removing unit for transporting in a paper dust transporting direction the paper dusts falling down from the paper dust removing unit. The regulation wall is disposed at a part of the paper dust transport unit for regulating a flow of the paper dusts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a side cross-sectional view showing an essential portion of a laser printer according to one embodiment of the present invention; 
     FIG. 2 is an enlarged cross-sectional view particularly showing a sheet transport path in the laser printer of FIG. 1; 
     FIG.  3 ( a ) is a plan view of a sheet; 
     FIG.  3 ( b ) is a front view showing a second paper dust removing roller in a second transport portion as viewed from an arrow A of FIG. 2; 
     FIG.  3 ( c ) is a cross-sectional view showing a first paper dust removing roller according to the first embodiment of the present invention; 
     FIG.  3 ( d ) is a plan view showing a pad member according to the first embodiment; 
     FIG. 4 is an enlarged cross-sectional view showing a first transport portion of the laser printer of FIG. 1; 
     FIG. 5 is an enlarged cross-sectional view showing a modification to the first transport portion of FIG.  4 . 
     FIG. 6 is a front view partially in cross-section showing a first paper dust removing roller, a regulation wall and an auger member in the laser printer of FIG. 1; 
     FIG. 7 is a plan view showing an essential portion around the auger member in the laser printer of FIG. 1; 
     FIG. 8 is a cross-sectional view showing gear transmission mechanism disposed adjacent to a sheet transportation path of the laser printer shown in FIG. 1; 
     FIG. 9 is an enlarged cross-sectional view showing sheet transport path of a laser printer according to a second embodiment of the present invention; 
     FIG. 10 is a cross-sectional view showing a second paper dust removing roller in the laser printer according to the second embodiment; 
     FIG. 11 is a cross-sectional view showing an essential portion of a paper dust transport portion and a transport drive portion in the laser printer according to the second embodiment; 
     FIG. 12 is a front view showing the paper dust transport portion of the laser printer according to the second embodiment; 
     FIG.  13 ( a ) is a cross-sectional view showing a power transmission mechanism of the laser printer according to the second embodiment; 
     FIG.  13 ( b ) is a front view showing the power transmission mechanism of FIG.  13 ( a ), and 
     FIG. 14 is a schematic view showing a relationship between a pair of second paper dust removing rollers and the image recording medium according to a modified embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An image forming device according to a first embodiment of the present invention will be described with reference to FIGS. 1 through 8 in which an electro-photographic type laser printer  1  is shown. 
     (1) General Arrangement and Image Forming Operation 
     As shown in FIG. 1, the printer  1  includes a main casing  2 , a feeder portion  4  for feeding a sheet  3  as an image recording medium, and an image forming section  5  for forming an image on the fed sheet  3 . The feeder portion  4  and the image forming section  5  are installed in the casing  2 . 
     The feeder portion  4  includes a sheet supply tray  6  positioned on a bottom of the main casing  2  and detachable therefrom, a sheet supply section  7  disposed at one side of the sheet supply tray  6 , a sheet mount plate  8  disposed in the sheet supply tray  6 , a first transport portion  9  (a first paper dust removing unit), a second transport portions  10  (a second paper dust removing unit), and a register roller  11 . The first and second transport portions  9  and  10  are positioned at a downstream side of the sheet supply section  7  in a sheet feeding direction. The register roller  11  is positioned downstream of the first and second transport portions  9 , 10 . 
     The sheet supply tray  6  is of a box shape with an upper open construction so as to accommodate therein a stack of sheets  3 . The sheet supply tray  6  is slidable with respect to the bottom of the main casing  2 , so that the tray  6  is detachable from the casing  2 . 
     The sheet supply section  7  includes a sheet supply roller  12  and a separation pad  13  in confrontation therewith. As shown in FIG. 2, the separation pad  13  includes a support frame  13   a,  a pad member  13   b,  and a spring  13   c.    
     The support frame  13   a  has generally L-shape in cross-section including a flat member positioned immediately below the sheet supply roller  12  and a support member extending downwardly from one side edge of the flat member and bent at a right angle with respect to the flat member. A lower end portion of the support member is pivotally connected to the main casing  2 . The pad member  13   b  is embedded in one surface of the flat member to confront with the sheet supply roller  12 . The flat member has an opposite surface to which the spring  13   c  is seated for urging the pad member  13   b  toward the sheet supply roller  12 . 
     The pad member  13   b  has a generally rectangular shape and is formed of an elastic material such as a polyurethane rubber. As shown in FIGS.  3 ( a ) and  3 ( d ), the pad member  13   b  has a width B in a direction perpendicular to the sheet feed direction smaller than a width W of the sheet, the width W being a maximum width of the sheet undergoing printing by the laser printer  1 . The pad member  13   b  is in contact with at least a widthwise center portion of the sheet  3  for the sheet supply. 
     A sheet mount plate  8  is adapted for mounting thereon the sheet stack. The sheet mount plate  8  has a rear end pivotally connected to the sheet supply tray  6  and a front free end movable in a vertical direction. A compression spring (not shown) is provided below the sheet mount plate  8  for normally urging the sheet mount plate  8  upwardly. Therefore, if sheet stack amount on the sheet mount plate  8  is increased, the free end of the sheet mount plate  8  is pivotally moved downwardly about the rear pivot axis against the biasing force of the compression spring (not shown). An uppermost sheet  3  on the sheet stack on the sheet mount plate  8  is urged toward the sheet supply roller  12  because of the biasing force of the compression spring associated with the sheet mount plate  8 . Upon rotation of the sheet supply roller  12 , a leading end portion of the uppermost sheet is nipped between the sheet supply roller  12  and the pad member  13   b . In this manner each uppermost sheet is separated from the sheet stack and is delivered. 
     Incidentally, the sheet supply section  7  employs the friction/separation system and provides the following relationship in the friction force at the sheet supply timing. That is, frictional force between the sheet supply roller  12  and the sheet  3  is greater than the frictional force between the pad member  13   b  and the sheet  3 , and the latter frictional force is greater than the frictional force between overlapping sheets. 
     The sheet is delivered to the register roller  11  through a sheet transport path  38  between the sheet supply section  7  and the image forming section  5  by way of first and second transport portions  9  and  10  described later. The register roller  11  includes a pair of rollers for correcting diagonal feeding of the sheet  3  so as to feed the sheet  3  in a correct orientation to the image forming section  5 . 
     The image forming section  5  includes a scanner portion  17 , a process unit  18 , and a fixing portion  19 . The scanner portion  17  is disposed at an upper interior portion of the main casing  2 , and includes a laser emitting portion (not shown), a rotatably driven polygon mirror  20 , lenses  21   a,    21   b,  and a reflection mirror  22 . The laser beam according to image data is emitted from the laser emitting portion and is scanningly irradiated at high speed onto a surface of the photosensitive drum  23  of the process unit  18  through an optical path as shown by a dotted chain line in FIG. 1 defined by the polygon mirror  20 , the lenses  21   a,  the reflection mirror  22  and the lens  21   b.    
     The process unit  18  is disposed below the scanner portion  17  and is provided detachable from the main casing  2 . The process unit  18  includes a drum cartridge and a developing cartridge  24 . The drum cartridge houses therein the photosensitive drum  23  serving as a photosensitive member, an image transfer roller  25 , and a scorotoron charger  37 . The developing cartridge  24  is detachable from the drum cartridge and houses therein a toner hopper  26 . the developing roller  27 , a toner layer thickness regulation blade  28 , and a toner supply roller  29 . 
     In the toner hopper  26 , positively chargeable non-magnetic single component type polymerized toners are filled as the developing agents. Such toners are supplied to the developing roller  27  by the toner supply roller  29 , and are carried on the developing roller  27  as a constant thin thickness toner layer because of frictional sliding relation with the toner layer thickness regulation blade  28 . On the other hand, the photosensitive drum  23  is rotatably disposed in confronting relation to the developing roller  27 . The photosensitive drum  23  includes a drum body which is grounded, and a positively chargeable photosensitive layer made from polycarbonate formed over the drum body. 
     In accordance with the rotation of the photosensitive drum  23  in a direction indicated by an arrow, the surface of the drum  23  is uniformly charged with positive polarity by means of the scorotoron charger  37 , and is subjected to exposure to laser beam scanningly emitted from the scanner portion  17  at high speed according to the print data, whereupon electrostatic latent image is formed on the photosensitive surface. Then, in accordance with the rotation of the developing roller  27 , the toner carried on the developing roller  27  and charged with positive polarity is supplied to the exposed part of the photosensitive drum  23 , the potential level of the exposed part being lower than that of the remaining part of the photosensitive drum surface uniformly positively charged. Thus, a visible toner image is formed on the photosensitive drum  23  to complete a reverse image developing. 
     The transfer roller  25  is positioned inmediately below the photosensitive drum  23 . The transfer roller  25  includes a rotation shaft made of a metal and connected to an electrical power source, and an electrically conductive rubber layer formed over the rotation shaft. A predetermined transfer bias voltage is applied to the rotation shaft for the toner transfer from the photosensitive drum  23  to the sheet  3 . When the sheet  3  passes between the photosensitive drum  23  and the transfer roller  25 , the visible toner image is transferred onto the sheet  3 , which is then delivered to the fixing portion  19  through a transport belt  30 . 
     The fixing unit  19  is positioned beside the process unit  18  and downstream side of the process unit  18 . The fixing unit  19  includes a heat roller  31 , a pressure roller  32  in pressure contact with the heat roller  31 , and a feed roller  33  positioned downstream of the heat roller  31  and the pressure roller  32 . The heat roller  31  is made from a metal and is provided with a halogen lamp as a heat source. The toner image transferred onto the sheet  3  at the process unit  18  is thermally fixed to the sheet  3  when the image carrying sheet passes through the heat roller  31  and the pressure roller  32 . The sheet  3  is then delivered to a downstream side feed roller  34 , a discharge roller  35  disposed in the main casing  2  by way of the feed roller  33 . The sheet  3  fed by the downstream side feed roller  34  is discharged onto a discharge tray  36  by way of the discharge roller  35 . 
     In the laser printer  1 , residual toners remaining on the surface of the photosensitive drum after the toner transfer to the sheet  3  by the transfer drum  25  are collected by the developing roller  27 . This toner collection manner is so called a cleaner-less system in which a blade for wiping out the residual toner and a residual toner container can be dispensed with, to simplify an overall arrangement of the image forming device. 
     A sheet re-circulation unit  41  is provided for forming images on both surfaces of the sheet  3 . The re-circulation unit  41  includes a sheet reverse section  42  and a re-circulation tray  43  integrally therewith. The re-circulation unit  41  is positioned at a rear wall of the main casing  2  in such a manner that the sheet reverse section  42  is attached beside the rear wall, and the re-circulation tray  43  is detachably insertedly assembled into the rear wall at a position above the feeder section  4 . 
     The sheet reverse section  42  has a casing  44  having a rectangular cross-section and attached to the rear wall of the main casing  2 . In the casing  44 , a flapper  45 , reverse rollers  46  and re-circulation rollers  47  are provided. Further, a reverse guide plate  48  extends upwardly from an upper end portion of the casing  44 . The flapper  45  is pivotably provided at the rear portion of the main casing  2  and is positioned at a downstream side of the feed roller  33 . The flapper  45  is pivotally moved upon energization or de-energization of a solenoid (not shown) for switching a feeding direction of the one-sided image carrying sheet  3  fed by the feed roller  33  either to the downstream feed roller  34  as shown by a solid line or to the reverse rollers  46  as shown by a broken line. 
     The reverse rollers  46  include a pair of rollers and are positioned downstream of the flapper  45  and at an upper portion of the casing  44 . Rotational direction of the reverse rollers is changeable in both normal and reverse directions. The reverse rollers  46  are first rotated in the normal direction to direct the sheet  3  toward the reverse guide plate  48 , and then rotated in the reverse direction to transport the sheet  3  in the reverse direction. 
     The re-circulation rollers  47  are positioned downstream of the reverse rollers  46  and are positioned immediately therebelow in the casing  44 . The re-circulation rollers  47  include a pair of rollers to direct the sheet  3  reversely driven by the reverse rollers  46  toward the re-circulation tray  43 . The reverse guide plate  48  is constituted by a plate like member extending upwardly from the upper end of the casing  44  for guiding travel of the sheet  3  fed by the reverse rollers  46 . 
     For printing an image on a back surface of the sheet  3  whose front surface has been formed with an image, in the sheet reverse section  42 , the flapper  45  is switched to a position allowing the sheet  3  to be fed toward the reverse roller pair  46 . Thus, the sheet  3  whose front surface has been formed with an image is received in the sheet reverse section  42 . After the sheet  3  reaches the reverse roller  46 , the reverse roller  46  is rotated in a normal direction for temporarily discharging the paper upwardly along the reverse guide plate  48 . When a major part of the sheet  3  is fed out of the casing  44  and a trailing end portion of the sheet  3  is nipped between the reverse roller pair  46 , the normal rotation of the reverse roller pair  46  is stopped. Then, the reverse roller pair  46  are reversely rotated to feed the sheet  3  downwardly toward the re-circulation roller pair  47 . A sheet sensor  56  is provided downstream of the fixing portion  19  for detecting the sheet  3 . A reverse timing for changing the rotating direction of the reverse roller  46  from the normal rotation to the reverse rotation is controlled such that the reverse timing occurs after elapse of a predetermined period starting from a detection timing at which the sheet sensor  56  detects a trailing edge of the sheet  3 . Further, the flapper  45  is switched to its original posture, i.e., a posture allowing the sheet to be fed to the downstream feed roller  34  from the feed roller  33  upon completion of feeding of the sheet to the reverse roller  46 . Then, the sheet  3  reversely fed by the re-circulation roller pair  47  is delivered to the re-circulation tray  43  by the re-circulation roller pair  47 . 
     The re-circulation tray  43  has a sheet receiving portion  49 , a tray  50  and diagonal feed rollers  51 . The sheet receiving portion  49  is externally attached to the main casing  2  at a position below the sheet reverse section  42 , and has an arcuate sheet guide member  52 . The sheet  2  substantially vertically downwardly oriented from the re-circulation roller pair  47  can be oriented in a substantially horizontal direction along the curvature of the sheet guide member  52  toward the tray  50 . 
     The tray  50  has a rectangular plate-like shape, and is oriented in a horizontal direction above the sheet tray  6 . An upstream end of the tray  50  is connected to the sheet guide member  52 , and a downstream end of the tray  50  is connected to a re-circulation path guide  53  provided along the sheet transport path  38  in order to guide the sheet  3  from the tray  50  to the second transport portion  10 . 
     At a sheet path on the tray  50 , two diagonally feed rollers  51 ,  51  are positioned spaced away from each other in the sheet feeding direction. These diagonally feed rollers  51 ,  51  are adapted to feed the sheet in a direction for permitting the sheet to be in abutment with a reference plate (not shown). The reference plate is positioned at one widthwise edge area of the tray  50 . Each diagonally feed roller  51  includes a diagonal feed drive roller  54  whose rotation axis extends substantially perpendicular to the sheet feeding direction, and a diagonal feed driven roller  55  in nipping relation to the drive roller  54 . A rotation axis of the driven roller  55  extends in a direction displacing from the direction perpendicular to the sheet feeding direction, but extends in a slanting direction for allowing the sheet to be brought into abutment with the reference plate. 
     The sheet  3  delivered from the sheet receiving portion  49  to the tray  50  moves toward the image forming section  5 , with the sheet having been turned upside down, through the re-circulation path guide  53  while one widthwise edge of the sheet is in slidingly abutting relation to the reference plate by the driving of the diagonally feed rollers  51 . At the image forming section  5 , the back surface of the sheet  3  is in confrontation with the photosensitive drum  23  for transferring a toner image to the back surface from the photosensitive drum  23 . The toner image is then fixed at the fixing portion  19 , and is then discharged onto the discharge tray  36 . 
     (2) Paper Dust Removal at Sheet Path 
     In the laser printer  1 , as shown in FIG. 2, the first and second transport portions  9  and  10  are disposed at the sheet transport path  38  for efficiently removing paper dusts spreading over the entire surface of the sheet  3  accompanied by sheet cutting for providing cut sheets or generated due to friction force occurring between the pad member  13   b  and the sheet supply roller  12  at the paper supply section  7 . 
     The first transport portion  9  is positioned at a frontal side of the sheet transport path  38  and downstream of the sheet supply roller  12  of the sheet supply section  7  with a predetermined space therefrom. Further, the first transport portion  9  is positioned upstream of a joining portion between the sheet transport path  38  and a downstream end of the re-circulation path guide  53 . The first transport portion  9  includes a first transport roller  9   a  for transporting the sheet  3 , a first paper dust removing roller  9   b  and positioned in opposition to the first transport roller  9   a  with respect to the sheet transport path  38 , a first sponge member  9   c  serving as a first scraper disposed immediately below the first paper dust removing roller  9   b,  and first reverse transport preventive member  9   m  for preventing the paper dust from being transported from the first sponge member  9   c  to the sheet transport path  38 . 
     The first transport roller  9   a  is positioned inwardly of a curvature of the sheet transport path  38 , and includes a metallic roller shaft  9   d  and a rubber layer  9   e  formed thereover. The roller shaft  9   d  is rotatably supported by the main casing  2 . The first transport roller  9   a  is drivingly rotatable in a direction indicated by an arrow, (clockwise direction in FIG. 1) through a power transmission from a motor (not shown). That is, a region of the first transport roller  9   a  confronting the sheet transport path  38  is rotated in the normal direction, i.e., in the sheet feeding direction. 
     The first paper dust removing roller  9   b  is disposed outwardly of the curvature of the sheet transport path  38 , and includes a metallic roller shaft  9   f  and a rubber layer  9   g  having easily chargeable surface. The rubber layer is made from a fluororesin, or rubber whose outer surface is formed with fluorine coating. The first paper dust removing roller  9   b  is shown in FIG.  3 ( c ). The first paper dust removing roller  9   b  is so positioned as to brought into contact with the sheet surface (to be in contact with the photosensitive drum) which has been contacted with the pad member  13   b,  and to align with a longitudinally center portion of the first transport roller  9   a,  the center portion being in confrontation with the separation pad  13 . The width (axial length) of the rubber layer roller  9   g  is smaller than a width of a roller  10   g  of a second paper dust removing roller  10   b  described later, and slightly greater than the width B of the pad member  13   b  as shown in FIGS.  3 ( c ) and  3 ( d ). 
     The main casing  2  has a support member  100   a,  and the first paper dust removing roller  9   b  has a roller shaft  9   f  roatably supported by the support member  100   a  as shown in FIG.  2 . The first paper dust removing roller  9   b  is driven by the first transport roller  9   a  and rotated in a direction indicated by an arrow (counterclockwise direction in FIG.  1 ). That is, a region of the first paper dust removing roller  9   b  confronting the sheet transport path  38  is rotated in the normal direction, i.e., in the sheet feeding direction. The first transport roller  9   a  and the first paper dust removing roller  9   b  nip the sheet  3  therebetween for transporting the sheet  3  while removing the paper dusts from the sheet  3 . Incidentally, the first transport roller  9   a  and the first paper dust removing roller  9   b  can be reversely rotated for removing a jamming sheet. 
     The first sponge member  9   c  is formed from a material which can easily charge the first paper dust removing roller  9   b.  Typical material is urethane foam. The first sponge member  9   c  is positioned immediately below the first paper dust removing roller  9   b  and in pressure contact therewith at a position opposite to the sheet transport path  38  with respect to the paper dust removing roller  9   b  so as to scrape off the paper dust from the paper dust removing roller  9   b.  The first sponge member  9   c  is in sliding contact with the first paper dust removing roller  9   b  to frictionally charge the surface of the first paper dust removing roller  9   b.  A width of the first sponge member  9   c  is slightly greater than the width of the roller  9   g  of the first paper dust removing roller  9   b  as shown in FIG.  3 ( c ). 
     As shown in FIG. 2, the first reverse transportation preventive member  9   m  is disposed downstream of a contacting position between the first paper dust removing roller  9   b  and the sheet  3  in the normal rotating direction of the roller  9   b,  and upstream of a contacting position between the first paper dust removing roller  9   b  and the first sponge member  9   c  in the normal rotating direction of the roller  9   b.  The first reverse transportation preventive member  9   m  extends in parallel with the axial direction of the first paper dust removing roller  9   b  and confronts the roller  9   b  with a predetermined space. As best shown in FIG. 4, the first reverse transportation preventive member  9   m  is L-shape in cross-section having a base portion  9   n  and a tip portion  9   p  bent from the base portion  9   n.  The first reverse transportation preventive member  9   m  is provided integrally with the support member  10   a  of the main casing  2  as a part of the support member. As shown in FIG. 6, a width of the first reverse transportation preventive member  9   m  is greater than the widths of the first paper dust removing roller  9   b  and the first sponge member  9   c.    
     As shown in FIGS. 2 and 4, the base portion  9   n  is positioned opposite to the sheet transport path  38  with respect to the first paper dust removing roller  9   b  and slantingly extends in generally vertical direction and spaced away from the first paper dust removing roller  9   b.  The tip portion  9   p  is bent from an upper end of the base portion  9   n  at an acute angle toward the first paper dust removing roller  9   b.  A gap L between a tip end  9   t  of the tip portion  9   p  and the outer peripheral surface of the first paper dust removing roller  9   b  is in a range of from 0.2 to 2.0 mm, preferably, 0.5 to 2.0 mm. That is, this gap L permits the paper dusts (about several μmm in size) adhered onto the first paper dust removing roller  9   b  during its normal rotation to pass through the gap toward the first sponge member  9   c,  but prevents a lump of paper dusts (about several mm in size) scrapped off by the first sponge member  9   c  and then released therefrom from passing through the gap toward the sheet transport path  38  during reverse rotation of the first paper dust removing roller  9   b.    
     As shown in FIG. 4, the first reverse transportation preventive member  9   m  is designed to provide an angle θ at an intersection between lines Y and Z not more than 90 degrees, in which the line Y is a tangential line with respect to a line X connecting between the tip end  9   t  of the tip end portion  9   p  and a rotational center of the first paper dust removing roller  9   b,  and the line Z is the extending direction of the tip end portion  9   p.  Further, the tip end portion  9   p  is positioned upstream of the line x in the normal rotating direction of the first paper dust removing roller  9   b.  With this arrangement, the tip end  9   t  can confront with and contact with the paper dusts adhered onto the first paper dust removing roller  9   b  from the first sponge member  9   c  during reverse rotation (clockwise rotation in FIG. 4) of the first paper dust removing roller  9   b.    
     As shown in FIG. 2, the second transport portion  10  is positioned above and downstream of the first transport portion  9 . Further, the second transport portion  10  is positioned downstream of the joining portion between the sheet transport path  38  and the downstream end of the re-circulation path guide  53 . The second transport portion  10  includes a second transport roller  10   a  for transporting the sheet  3 , a second paper dust removing roller  10   b  positioned in opposition to the second transport roller  10   a  with respect to the sheet transport path  38 , a second sponge member  10   c  serving as a scraper disposed immediately below the second paper dust removing roller  10   b,  and a second reverse transportation preventive member  10   m  for preventing the paper dust from being transported from the second sponge member  10   c  to the sheet transport path  38 . 
     The second transfer roller  10   a  is positioned inwardly of the curvature of the sheet transport path  38 , and includes a metallic roller shaft  10   d  and a rubber layer  10   e  formed thereover. The roller shaft  10   d  is rotatably supported by the main casing  2 . The second transport roller  10   a  is drivingly rotatable in a direction indicated by an arrow, (clockwise direction in FIG. 1) through a power transmission from the motor (not shown). That is, a region of the second transport roller  10   a  confronting the sheet transport path  38  is rotated in the normal direction, i.e., in the sheet feeding direction. 
     The second paper dust removing roller  10   b  is disposed outwardly of the curvature of the sheet transport path  38 , and includes a metallic roller shaft  10   f  and a rubber layer  10   g  having easily chargeable surface. The rubber layer is made from a fluororesin, or rubber whose outer surface is formed with fluorine coating. The second paper dust removing roller  10   b  is so positioned as to brought into contact with an entire sheet surface (to be in contact with the photosensitive drum  23 ) which has been contacted with the pad member  13   b.  To this effect, a width (axial length) of the rubber layer roller  10   g  is slightly greater than the sheet width A as shown in FIG.  3 ( b ). 
     The main casing  2  has a second support member  100   b,  and the roller shaft  10   f  of the second paper dust removing roller  10   b  is rotatably supported by the support member  100   b.  The second paper dust removing roller  10   b  is positively driven upon power input from a motor (not shown), so that the second paper dust removing roller  10   b  is rotatable in a normal direction indicated by an arrow in FIG. 2, that is, in the sheet feeding direction (counter clockwise direction in FIG.  1 ) at a region facing with the sheet transport path  38 . The sheet  3  is nipped between the second transport roller  10   a  and the second paper dust removing roller  10   b  for feeding, while the paper dust is removed by the second paper dust removing roller  10   b.  The second transport roller  10   a  and second paper dust removing roller  10   b  are reversely rotatable for removing jamming sheet described later. 
     The second sponge member  10   c  is formed from a material which can easily charge the second paper dust removing roller  10   b.  Typical material is urethane foam. The second sponge member  10   c  is positioned immediately below the second paper dust removing roller  10   b  and in pressure contact therewith at a position opposite to the sheet transport path  38  with respect to the paper dust removing roller  10   b  so as to scrape off the paper dust from the paper dust removing roller  10   b.  The second sponge member  10   c  is in sliding contact with the second paper dust removing roller  10   b  to frictionally charge the surface of the roller  10   g  of the second paper dust removing roller  10   b.  A width of the second sponge member  10   c  is slightly greater than the width (axial length) of the second paper dust removing roller  10   b  as shown in FIG.  3 ( b ). 
     As shown in FIG. 2, the second reverse transportation preventive member  10   m  is disposed downstream of a contacting position between the second paper dust removing roller  10   b  and the sheet  3  in the normal rotating direction of the roller  10   b,  and upstream of a contacting position between the second paper dust removing roller  10   b  and the second sponge member  10   c  in the normal rotating direction of the roller  10   b.  The second reverse transportation preventive member  10   m  extends in parallel with the axial direction of the second paper dust removing roller  10   b  and confronts the roller  10   b  with a predetermined space. The second reverse transportation preventive member  10   m  is L-shape in cross-section having a base portion  10   n  and a tip portion  10   p  bent from the base portion  10   n.  The second reverse transportation preventive member  10   m  is provided integrally with the support member  100   b  as a part of the support member  100   b.  As shown in FIG.  3 ( b ), a width of the second reverse transportation preventive member  10   m  is greater than the widths of the second paper dust removing roller  10   b  and the second sponge member  10   c.    
     The base portion  10   n  is positioned opposite to the sheet transport path  38  with respect to the second paper dust removing roller  10   b  and slantingly extends in generally vertical direction and spaced away from the second paper dust removing roller  10   b.  The tip portion  10   p  is bent from a lower end of the base portion  10   n  at an acute angle toward the second paper dust removing roller  10   b.  A gap between a tip end of the tip portion  10   p  and an outer peripheral surface of the second paper dust removing roller  10   b  is in a range of from 0.2 to 2.0 mm, preferably, 0.5 to 2.0 mm. That is, this gap permits the paper dusts (about several μmm in size) adhered onto the second paper dust removing roller  10   b  during its normal rotation to pass through the gap toward the second sponge member  10   c,  but prevents a lump of paper dusts (about several mm in size) scrapped off by the second sponge member  10   c  from passing through the gap toward the sheet transport path  38  during reverse rotation of the second paper dust removing roller  10   b.    
     Similar to the first reverse transportation preventive member  9   m,  the second reverse transportation preventive member  10   m  is designed to provide an angle at an intersection between a tangential line with respect to a line connecting between the tip end of the tip end portion  10   p  and a rotational center of the second paper dust removing roller  10   b  and an extension line of the tip end portion  10   p  as being not more than 90 degrees. Further, the tip end portion  10   p  is positioned upstream of the line connecting between the tip end of the tip end portion  10   p  and the rotational center of the second paper dust removing roller  10   b  in the normal rotating direction of the second paper dust removing roller  10   b.  With this arrangement, the tip end of the second reverse transportation preventive member  10   m  can confront with and contact with the paper dusts adhered onto the second paper dust removing roller  10   b  from the second sponge member  10   c  during reverse rotation of the second paper dust removing roller  10   b.    
     In the laser printer  1 , the sheet  3  stacked on the sheet supply tray  6  is separated from the sheet stack and supplied in cooperation with the sheet supply roller  12  and the separation pad  13 . During this sheet supply, a large amount of paper dusts are generated at the image forming surface of the sheet due to the friction against the separation pad  13 . However, when the sheet  3  is transported to the first transport portion  9  and the sheet  3  is nipped between the first transport roller  9   a  and the first paper dust removing roller  9   b,  the image forming surface is in brought into contact with the roller  9   g  of the first paper dust removing roller  9   b.  Because the width of the first paper dust removing roller  9   b  is greater than that of the separation pad  13 , the paper dusts spreading in a width substantially equal to the width of the pad member  13   b  is scraped off by the roller  9   g  of the first paper dust removing roller  9   b  and are electrostatically absorbed thereon. The paper dusts transferred onto the roller  9   g  of the first paper dust removing roller  9   b  is then scraped off therefrom by the first sponge member  9   c  by the normal rotation of the first paper dust removing roller  9   b,  after the paper dusts passes through the gap L between the first reverse transportation preventive member  9   m  and the first paper dust removing roller  9   b.    
     Then, when the sheet  3  is transferred to the second transport portion  10  and the sheet  3  is nipped between the second transport roller  10   a  and the second paper dust removing roller  10   b,  the image forming surface is in brought into contact with the roller  10   g  of the second paper dust removing roller  10   b.  Because the width of the second paper dust removing roller  10   b  is greater than the sheet width, the paper dusts having been generated at the sheet cutting and spreading over entire width of the sheet as well as residual paper dusts which have not been completely removed by the first paper dust removing roller  9   b  can be scraped off by the roller  10   g  of the second paper dust removing roller  10   b  and are electrostatically absorbed thereon. The paper dusts transferred onto the roller  10   g  of the second paper dust removing roller  10   b  is then scraped off therefrom by the second sponge member  10   c  through the normal rotation of the second paper dust removing roller  10   b,  after the paper dusts passes through the gap between the second reverse transportation preventive member  10   m  and the second paper dust removing roller  10   b.    
     Accordingly, greater amount of paper dusts generated by the friction of the sheet against the pad member  13   b  can be removed from the sheet by the first and second paper dust removing rollers  9   b  and  10   b,  and a lesser amount of paper dusts inherently generated upon sheet cutting can be removed by the second paper dust removing roller  10   b.  As a results, the above described paper dusts can be removed efficiently and uniformly over the surface of the sheet by the first and second transport portions  9  and  10 . Consequently, entry of the paper dusts into the image forming section  5  can be prevented effectively to provide high quality image. 
     The paper dusts removed by the first and second transport portions  9 ,  10  are scraped by the first and second sponge members  9   c,    10   c,  and accumulated thereon to become paper dust lumps, which are then fallen down onto a receiving surface  65  described later. 
     Because the second paper dust removing roller  10   b  is disposed downstream of the first paper dust removing roller  9   b  in the sheet feeding direction, the sheet  3  supplied by the sheet supply section  7  is first subjected to paper dust removal by the first paper dust removing roller  9   b,  the dust being generated in greater amount due to the friction against the pad member  13   b,  and then, subjected to paper dust removal by the second paper dust removing roller  10   b,  the dust having being inherently spreading in a lesser amount over the entire surface of the sheet due to paper cutting. Accordingly, efficient paper dust removal in accordance with the amount of paper dust can be performed, thereby achieving uniform paper dust removal. 
     Further, since the width of the second paper dust removing roller  10   b  is greater than the sheet width whereas the width of the first paper dust removing roller  9   b  is greater than that of the separation pad  13  and smaller than the width of the second paper dust removing roller  10   b,  the first paper dust removing roller  9   b  does not necessarily has a longer width but has an optimum width yet performing sufficient paper dust removal. Thus, production cost can be lowered. 
     Further, as described above, in the laser printer  1 , the first paper dust removing roller  9   b  is spaced away from and downstream of the sheet supply roller  12  by a predetermined space to avoid direct contact therewith. Assuming that the first paper dust removing roller  9   b  is in direct contact with the sheet supply roller  12 . If a subsequent sheet  3  is slightly pulled out and follows a precedent sheet  3  in partly overlapping relation with the precedent sheet due to the frictionally sliding relationship between the sheet supply roller  12  and the separation pad  13 , operation of the laser printer  1  may be stopped while the leading end portion of the subsequent sheet is nipped between the sheet supply roller  12  and the first paper dust removing roller  9   b.  Therefore, the nipped leading end portion of the subsequent sheet may be shaped into a curl. Therefore, sheet jamming may occur due to the subsequent feeding of the curly sheet, or image distortion may occur at the curled portion. 
     However, because the first paper dust removing roller  9  is positioned out of contact from the sheet supply roller  12 , no nipping occurs at the leading end portion of the subsequent sheet even if the subsequent sheet is slightly pulled out and follows the precedent sheet. This prevents the leading end portion from being curled. Consequently, sufficient sheet supply is achievable while sufficiently removing the paper dust removal. 
     Further, in the first and second sheet transport portions  9  and  10 , the first sponge member  9   c  is provided in confrontation with the first paper dust removing roller  9   b  to scrape off the paper dust adhered to the first paper dust removing roller  9   b,  and the second sponge member  10   c  is provided in confrontation with the second paper dust removing roller  10   b  to scrape off the paper dust adhered to the second paper dust removing roller  10   b.  Thus, paper dust scraping is performed at each sponge member for each paper dust removing roller. As a result, paper dust removing efficiency of each paper dust removing roller can be maintained enabling paper dust removing for a long duration. 
     Incidentally, because the width of the first and second sponge members  9   c  and  10   c  is slightly greater than the width of the associating first and second paper dust removing rollers  9   b  and  10   b,  respectively, paper dust can be desirably scraped off even if a paper dust area slightly exceeds from the width of the paper dust removing rollers due to the pressure contact between the sheet and the paper dust removing rollers. 
     Further, in the laser printer  1 , the sheet  3  supplied by the sheet supply section  7  is first delivered by the first transport roller  9   a  and the first paper dust removing rollers  9   b  while the paper dusts are removed, and is then delivered by the second transport roller  10   a  and the second paper dust removing rollers  10   b  while the paper dusts are again removed. Therefore, desirable sheet transportation to the image forming section  5  results while performing efficient paper dust removal. 
     Further, the second paper dust removing roller  10   b  is not slave-driven by the second transport roller  10   a  but the second paper dust removing roller  10   b  is a self-driving component, because it is supplied with driving power from the motor (not shown). Therefore, constant rotation of the second paper dust removing roller  10   b  can result to perform effective paper dust removal and effective sheet feeding, even if a resistive load is applied to the entirety of the roller portion  10   g  of the second paper dust removing roller  10   b  due to the contact with the sheet  3  and the second sponge member  10   c.    
     Further, in the laser printer  1 , the re-circulation unit  41  is provided, and the first transport portion  9  is disposed upstream of the joint portion between the sheet transport path  38  and the re-circulation path guide  53 , whereas the second transport portion  10  is disposed downstream of the joint portion. With such a construction, since the first paper dust removing roller  9   b  is disposed upstream of the joint portion, the first paper dust removing roller  9   b  is exclusively in contact with the sheet  3  supplied from the sheet supply section  7 . Further, since the second paper dust removing roller  10   b  is disposed downstream of the joint portion, the second paper dust removing roller  10   b  is in contact with the sheet supplied from the sheet supply section  7  and the sheet supplied from the re-circulation path guide  53 . 
     Therefore, the first paper dust removing roller  9   b  removes the greater amount of paper dusts generated due to the friction against the pad member  13   b  with respect to the sheet supplied from the sheet supply section  7 , whereas the second paper dust removing roller  10   b  removes the paper dust on the sheet which has been subjected to paper dust removal by the first paper dust removing roller  9   b  and which has been fed from the sheet supply section  7 , and also removes the paper dust on the sheet fed from the re-circulation path guide  53 . Regarding the sheet fed from the re-circulation path guide  53 , one image forming surface which has been in contact with the roller portion  9   g  of the first paper dust removing roller  9   b  is not in confrontation with the second paper dust removing roller  10   b,  but an opposite surface of the sheet is in contact therewith. Because the opposite surface of the sheet does not carry the paper dusts caused by the friction against the pad member  13   b.  Accordingly, the second paper dust removing roller  10   b  can only remove the lesser amount of paper dusts caused by paper cutting over the entire surface of the sheet. 
     As shown in FIG. 1, the feeder portion  4  of the laser printer  1  also includes a multiple purpose tray  14  for stacking thereon a stack of a random size sheets  3 , a multiple purpose sheet supply mechanism  15  for supplying the sheet on the multiple purpose tray  14 , and a multiple purpose sheet transport portion  16 . 
     As shown in FIG. 2, the multiple purpose sheet supply mechanism  15  includes a multiple purpose sheet supply roller  15   a  and a multiple purpose separation pad  15   b  positioned in direct confrontation with the multiple purpose sheet supply roller  15   a.  The multiple purpose separation pad  15   b  includes a support frame  15   c,  a multiple purpose pad member  15   d  and a spring  15   e.    
     The support frame  15   c  has a base end portion pivotally supported to the main casing  2  and having an L-shape cross-section, and a free end portion integral with the base end portion and in confrontation with and below the multiple purpose sheet supply roller  15   a.  The free end portion is embedded with the multiple purpose pad member  15   d,  and the spring  15   e  is seated on the other side of the pad member  15   d  for normally urging the multiple purpose pad member  15   d  toward the sheet supply roller  15   a.    
     The multiple purpose pad member  15   d  has a generally rectangular plate shape and is made from an elastic material such as polyurethane rubber. A width of the multiple purpose separation pad  15   b  has such width as to contact with a widthwise center portion of the sheet for the sheet feeding. 
     Upon rotation of the multiple purpose sheet supply roller  15   a,  an uppermost sheet on the sheet stack on the multiple purpose tray  14  is nipped between the multiple purpose sheet supply roller  15   a  and the multiple purpose separation pad  15   b.  In this manner each uppermost sheet is separated from the sheet stack and is delivered. 
     The multiple purpose transport portion  16  is positioned above the second transport portion  10 , downstream of the multiple purpose sheet supply mechanism  15  and upstream of the register roller  11  disposed at a sheet transport path  38   a  between the multiple purpose sheet supply mechanism  15  and the image forming section  5 . The multiple purpose transport portion  16  includes a multiple purpose transport roller  16   a  for transporting the sheet  3 , a multiple purpose paper dust removing roller  16   b  in confrontation therewith, a multiple purpose sponge member  16   c  as a scraping member immediately below the multiple purpose paper dust removing roller  16   b,  and a multiple purpose reverse transportation preventive member  16   m  for preventing the paper dusts released from the multiple purpose sponge member  16   c  from being transported into the sheet transport path  38   a.    
     The multiple purpose transport roller  16   a  includes a metallic roller shaft  16   d  and a rubber layer  16   e  formed thereover. The roller shaft  16   d  is rotatably supported by the main casing  2 , and is drivingly rotatable in a direction indicated by an arrow in FIG. 2 (counterclockwise direction in FIG. 1) through a power transmission from a motor (not shown). That is, the region of the roller  16   a  in confrontation with the sheet transport path  38   a  is drivingly rotated in the normal direction the same as the sheet feeding direction. 
     The multiple purpose paper dust removing roller  16   b  includes a metallic roller shaft  16   f  and a rubber layer  16   g  having easily chargeable surface. The rubber layer is made from a fluororesin, or rubber whose outer surface is formed with fluorine coating. The multiple paper dust removing roller  16   b  is so positioned as to brought into contact with the sheet surface which has been contacted with the multiple purpose pad member  15   d , and to align with a center portion of the multiple purpose transport roller  16   a , the center portion being in confrontation with the multiple purpose separation pad  15   b . The width (axial length) of the multiple purpose rubber layer roller  16   g  is slightly greater than a width of the multiple purpose pad member  15   d.    
     The main casing  2  has a support member  100   c,  and the roller shaft  16   f  of the multiple purpose paper dust removing roller  16   b  is rotatably supported by the support member  100   c.  The multiple purpose paper dust removing roller  16   b  is driven by the multiple purpose transport roller  16   a,  and is rotated in a direction indicated by an arrow (clockwise direction) in FIG. 2, that is, in the sheet feeding direction at a region facing with the sheet transport path  38   a.  The sheet  3  is nipped between the multiple purpose transport roller  16   a  and the multiple purpose paper dust removing roller  16   b  for feeding, while the paper dust is removed by the multiple purpose paper dust removing roller  16   b.  The multiple purpose transport roller  16   a  and the multiple purpose paper dust removing roller  16   b  are reversely rotatable for removing jamming sheet. 
     The multiple purpose sponge member  16   c  is formed from a material which can easily charge the multiple purpose paper dust removing roller  16   b.  Typical material is urethane foam. The multiple purpose sponge member  16   c  is positioned immediately below the multiple purpose paper dust removing roller  16   b  and in pressure contact therewith at a position opposite to the sheet transport path  38   a  extending from the multiple purpose sheet supply mechanism  15  with respect to the paper dust removing roller  16   b  so as to scrape off the paper dust from the paper dust removing roller  16   b.  A width of the multiple purpose sponge member  16   c  is slightly greater than the width of the roller  16   g  of the multiple purpose paper dust removing roller  16   b.  The multiple purpose sponge member  16   c  is in sliding contact with the multiple purpose paper dust removing roller  16   b  to frictionally charge the surface of the roller portion  16   g  of the multiple purpose paper dust removing roller  16   b.    
     As shown in FIG. 2, the multiple purpose reverse transportation preventive member  16   m  is disposed downstream of a contacting position between the multiple purpose paper dust removing roller  16   b  and the sheet  3  in the normal rotating direction of the roller  16   b,  and upstream of a contacting position between the multiple purpose paper dust removing roller  16   b  and the multiple purpose sponge member  16   c  in the normal rotating direction of the roller  16   b.  The multiple purpose reverse transportation preventive member  16   m  extends in parallel with the axial direction of the multiple purpose paper dust removing roller  16   b  and confronts the roller  16   b  with a predetermined space. The multiple purpose reverse transportation preventive member  16   m  is L-shape in cross-section having a base portion  16   n  and a tip portion  16   p  bent from the base portion  16   n.  The multiple purpose reverse transportation preventive member  16   m  is provided integrally with the support member  100   c  of the main casing  2  as a part of the support member  100   c.  A width of the multiple purpose reverse transportation preventive member  16   m  is greater than the widths of the multiple purpose paper dust removing roller  16   b  and the multiple purpose sponge member  16   c.    
     As shown in FIG. 2 the base portion  16   n  is positioned opposite to the sheet transport path  38   a  with respect to the multiple purpose paper dust removing roller  16   b  and therebelow, and slantingly extends in generally vertical direction and spaced away from the multiple purpose paper dust removing roller  16   b.  The tip portion  16   p  is bent from an upper end of the base portion  16   n  at an acute angle toward the multiple purpose paper dust removing roller  16   b.  A gap between a tip end of the tip portion  16   p  and the multiple purpose paper dust removing roller  16   b  is in a range of from 0.2 to 2.0 mm, preferably, 0.5 to 2.0 mm. That is, this gap permits the paper dusts (about several μmm in size) adhered onto the multiple purpose paper dust removing roller  16   b  during its normal rotation to pass through the gap toward the multiple purpose sponge member  16   c,  but prevents a lump of paper dusts (about several mm in size) scrapped off by the multiple purpose sponge member  16   c  and released therefrom from passing through the gap toward the sheet transport path  38   a  during reverse rotation of the multiple purpose paper dust removing roller  16   b.    
     Similar to the first reverse transportation preventive member  9   m,  the multiple purpose reverse transportation preventive member  16   m  is designed to provide an angle at an intersection between a tangential line with respect to a line connecting between the tip end of the tip end portion  16   p  and a rotational center of the multiple purpose paper dust removing roller  16   b  and an extension line of the tip end portion  16   p  as being not more than 90 degrees. Further, the tip end portion  16   p  is positioned upstream of the line connecting between the tip end of the tip end portion  16   p  and the rotational center of the multiple purpose paper dust removing roller  16   b  in the normal rotating direction of the multiple purpose paper dust removing roller  16   b.  With this arrangement, the tip end of the multiple purpose reverse transportation preventive member  16   m  can confront with and contact with the paper dusts adhered onto the multiple purpose paper dust removing roller  16   b  from the multiple purpose sponge member  16   c  during reverse rotation of the multiple purpose paper dust removing roller  16   b.    
     The sheet  3  stacked on the multiple purpose sheet supply tray  14  in the multiple purpose sheet supply mechanism  15  is separated from the sheet stack and supplied in cooperation with the multiple purpose sheet supply roller  15   a  and the multiple purpose separation pad  15   b.  During this sheet supply, a large amount of paper dusts are generated at the surface of the sheet due to the friction against the multiple purpose separation pad  15   b.  However, when the sheet  3  is transported to the multiple purpose transport portion  16  and the sheet  3  is nipped between the multiple purpose transport roller  16   a  and the multiple purpose paper dust removing roller  16   b,  the paper dusts generated upon friction against the multiple purpose separation pad  15   b  and spreading in a width substantially equal to the width of the multiple purpose pad member  15   d  is scraped off by the roller  16   g  of the multiple purpose paper dust removing roller  16   b  and are electrostatically absorbed thereon, because the width of the multiple purpose paper dust removing roller  16   b  is slightly greater than that of the multiple purpose separation pad  15   b.  The paper dusts transferred onto the roller  16   g  of the multiple purpose paper dust removing roller  16   b  is then scraped off therefrom by the multiple purpose sponge member  16   c  by the rotation of the multiple purpose paper dust removing roller  16   b  in the direction of arrow (clockwise direction in FIG. 2) after the paper dusts pass through the gap between the multiple purpose reverse transportation preventive member  16   m  and the multiple purpose paper dust removing roller  16   b.    
     In this way, paper dust generated upon friction against the multiple purpose separation pad  15   b  and spreading over the width of the multiple purpose separation pad  15   b  can be desirably removed off from the surface of the sheet  3 . The paper dusts will become a paper dust lump after scraped off from multiple purpose paper dust removing roller  16   b  by the multiple purpose sponge member  16   c  and being deposited thereon, and then the paper dust lump will be falling down onto the receiving surface  65  as described later. 
     In the laser printer  1 , when sheet jamming occurs at a sheet nipping state between the first transport roller  9   a  and the first paper dust removing roller  9   b,  or between the second transport roller  10   a  and the second paper dust removing roller  10   b  during sheet feeding to the image forming section  5  through the sheet transport path  38 , the jammed sheet can be pulled out from the sheet supply section  7 , i.e., from the lower side of the first transport portion  9  after pulling out the sheet supply tray  6 . In such a case, the first paper dust removing roller  9   b  and the second paper dust removing roller  10   b  those in contact with the sheet  3  are reversely rotated, which causes the paper dust lumps scraped by and accumulated on the first and second sponge members  9   c  and  10   c  to be transported back toward the first paper dust removing roller  9   b  and the second paper dust removing roller  10   b.    
     However, during the reversal rotation of the first paper dust removing roller  9   b  and the second paper dust removing roller  10   b,  the paper dust lumps cannot pass through the gap L between the tip end  9   t  of the first reverse transportation preventive member  9   m  and the first paper dust removing roller  9   b  nor through the gap between the second reverse transportation preventive member  10   m  and the second paper dust removing roller  10   b  when the lumps are brought into confrontation with the tip end portions of the first and second reverse transportation preventive members  9   m,    10   m,  respectively. Thus, the lumps are dammed at the tip end portions  9   p,    10   p  of the first and second reverse transportation preventive member  9   m,    10   m,  respectively. Therefore, these lumps cannot be introduced into the sheet transport path  38 . 
     Accordingly, even by the reversal rotations of the first and second paper dust removing rollers  9   b,    10   b  during removal of the jamming sheet, the paper dusts collected by the first and second sponge members  9   c,    10   c  will not be discharged into the sheet transport path  38 . Consequently, a subsequent sheet can be protected against such paper dusts. Thus, adhesion of paper dusts onto the photosensitive drum  23  can be obviated, and a desirable image formation can result. 
     Similarly, when sheet jamming occurs at a sheet nipping state between the multiple purpose transport roller  16   a  and the multiple purpose paper dust removing roller  16   b  during sheet feeding to the image forming section  5  through the sheet transport path  38   a,  the jammed sheet can be pulled out from the sheet supply section, i.e., from the multiple purpose supply tray  14 . In such a case, the multiple purpose paper dust removing roller  16   b  in contact with the sheet  3  is reversely rotated, which causes the paper dust lumps scraped by and accumulated on the multiple purpose sponge member  16   c  to be transported back in accordance with the reverse rotation of the multiple purpose paper dust removing roller  16   b.    
     However, during the reversal rotation of the multiple purpose paper dust removing roller  16   b,  the paper dust lump cannot pass through the gap between the multiple purpose reverse transportation preventive member  16   m  and the multiple purpose paper dust removing roller  16   b  when the lump is brought into confrontation with the tip end portion  16   p  of the multiple purpose reverse transportation preventive member  16   m.  Thus, the lump is dammed at the tip end portion  16   p  of the multiple purpose reverse transportation preventive member  16   m.  Therefore, the lump cannot be introduced into the sheet transport path  38   a.    
     Accordingly, even by the reversal rotation of the multiple purpose paper dust removing roller  16   b  during removal of the jamming sheet, the paper dusts collected by the multiple purpose sponge member  16   c  will not be discharged into the sheet transport path  38   a.  Consequently, a subsequent sheet can be protected against the paper dusts. Thus, adhesion of paper dusts onto the photosensitive drum  23  can be obviated, and a desirable image formation can result. 
     Further, in the laser printer  1 , because of the above described gap distance ranging from 0.2 to 2.0 mm, the respective gaps allow the paper dusts to pass therethrough toward the first sponge member  9   c,  the second sponge member  10   c  and the multiple purpose sponge member  16   c,  respectively, during normal rotations of the first paper dust removing roller  9   b,  the second paper dust removing roller  10   b  and the multiple purpose paper dust removing roller  16   b,  but the gaps prevent the paper dusts from passing therethrough in the reverse direction during reverse rotations of the first paper dust removing roller  9   b,  the second paper dust removing roller  10   b  and the multiple purpose paper dust removing roller  16   b.  Thus, with such a simple arrangement, paper dusts adhered onto the rollers  9   b,    10   b,    16   b  can surely be transported to the sponge members  9   c,    10   c,    16   c,  and reversal transportation of the paper dusts from the sponge members  9   c,    10   c,    16   c  to the transport paths  38 ,  38   a  can be prevented. 
     Further, because of the above described orientations of the tip end portions  9   p,    10   p  and  16   p  of the first reverse transportation preventive member  9   m,  second reverse transportation preventive member  10   m  and multiple purpose reverse transportation preventive member  16   m,  the tip end portions  9   p,    10   p,    16   p  can confront and contact with the paper dust lumps transported back in accordance with the reverse rotations of these rollers  9   b,    10   b,    16   b.  Therefore, the paper dust lumps cannot be transported back any more. Thus, the first reverse transportation preventive member  9   m,  second reverse transportation preventive member  10   m  and multiple purpose reverse transportation preventive member  16   m  can prevent reversal transportation of the paper dust lumps. 
     Further, because of the above described relationship between widths of the reverse transportation preventive members  9   m,    10   m  and  16   m  and widths of the associated rollers  9   b,    10   b,    16   b  and the sponge members  9   c,    10   c,    16   c,  respectively, in the reverse rotations of the first paper dust removing roller  9   b,  second paper dust removing roller  10   b,  and multiple purpose paper dust removing roller  16   b,  the paper dust lumps can surely be blocked by the first reverse transportation preventive member  9   m,  second reverse transportation preventive member  10   m  and multiple purpose reverse transportation preventive member  16   m,  even if the paper dust lumps are spreading over the entire width of the sponge members  9   c,    10   c,    16   c,  and these paper dust lumps are transferred toward the rollers  9   b,    10   b,    16   b  over their entire widths. 
     Further, the first reverse transportation preventive member  9   m,  second reverse transportation preventive member  10   m,  and multiple purpose reverse transportation preventive member  16   m  are not separate members but provided integrally with the support members  100   a,    100   b,    100   c  of the main casing  2 , respectively. Therefore, the first reverse transportation preventive member  9   m,  second reverse transportation preventive member  10   m,  and multiple purpose reverse transportation preventive member  16   m  can be easily formed to reduce the number of mechanical components, to thus lower the production cost. 
     Further, in the above described embodiment, taking the first reverse transportation preventive member  9   m  for instance, the base portion  9   n  and the tip end portion  9   p  are flat plate shapes, and the base end portion  9   n  and the tip end portion  9   p  are formed by bending at an acute angle at a proper portion. Instead of this arrangement, as shown in FIG. 5, another arrangement of the first reverse transportation preventive member  9   m ′ is conceivable such that a tip end portion  9   p ′ is an extension of a curved portion instead of the acute angled bent portion. In the modification, a tip end face  9   t ′ is directed to confront against the reversal rotation of the first paper dust removing roller  9   b,  and the tip end portion  9   p ′ is intersected with the tangential line at an angle not more than 90 degrees, and further, the tip end portion  9   b  is disposed upstream of the line X connecting between the tip end face  9   t ′ and the rotational center of the first paper dust removing roller  9   b  in the normal rotating direction thereof. 
     (3) Paper Dust Chute 
     The paper dusts scraped by the first sponge member  9   c,  the second sponge member  10   c,  and the multiple purpose sponge member  15   c  are dropped down from each sponge due to gravity when the scraped paper dust has become a mass or lump of a predetermined size. In the laser printer  1 , there is provided a paper dust chute  39  for guiding downward travel of the paper dust mass. The paper dust chute  39  vertically extends in front of the sheet transport path  38  and is constituted by a guide plate section  61 , an extension section  62  and a partition plate  63 . 
     The guide plate  61  is a thin plate like member constituting a front side of the sheet transport path  38  so as to guide the sheet  3  from the sheet supply section  7  to the image forming section  5 . Thus, the guide plate  61  has one side serving as the sheet transport path  38 , and another side serving as the paper dust chute. More specifically, the guide plate  61  includes a first guide plate  61   a  for directing the sheet  3  from the second transport portion  10  to the register roller  11 , and a second guide plate  61   b  for directing the sheet  3  from the first transport portion  9  to the second transport portion  10 . 
     The first guide plate  61   a  is a thin plate member slantingly extending from an upper space of the second transport portion  10  to the front of the register roller  11 . The first guide plate  61   a  has one side face guiding the travel of the sheet  3  from the second transport portion  10  to the register roller  11 . Another side face of the first guide plate  61   a  allows the paper dust falling from the multiple purpose transport portion  16  positioned above the first guide plate  61   a  to direct downwardly. The first guide plate  61   a  has a lower end integrally provided with an extension portion  62   a  slantingly extending downwardly for covering an upper portion of the second transport portion  10 . 
     The second guide plate  61   b  is a thin plate member and is moderately curved in S-shape from the lower space of the second transport portion  10  to the lower space of the first transport portion  9 . The second guide plate  61   b  has one side face guiding the travel of the sheet  3  from the first transport portion  9  to the second transport portion  10 . Another side face of the second guide plate  61   b  allows the paper dust falling from the second transport portion  10  positioned above the second guide plate  61   b  to direct downwardly as well as the paper dust falling from the multiple purpose transport portion  16 . The second guide plate  61   b  has an intermediate portion provided with a thin plate-like extension portion  62   b  slantingly extending downwardly for covering an upper portion of the first transport portion  9 . 
     Further, the base end portions  9   n,    10   n  of the first and second reverse transportation preventive member  9   m,    10   m  also serve as guide members for guiding downward travel of the falling paper dusts. 
     Incidentally, a third guide plate  61   c  is formed continuously from the second guide plate  61   b  at a position lower than the confronting position between the first paper dust removing roller  9   b  and the first sponge member  9   c.  The third guide plate  61   c  has a lower end portion bent horizontally at a position above the attachment/detachment path of the sheet supply tray  6 . 
     The partition plate  63  is positioned in front of the second guide plate  61   b  with a predetermined space therefrom. The partition plate  63  includes a side plate  63   c  extending in a vertical direction and a bottom plate  63   d  bent at substantially right angle from a lower end of the side plate  63   c  toward frontward. 
     Further, a front side bottom wall  64  is provided in front of and below the first paper dust removing roller  9   b  and first sponge member  9   c.  The front side bottom wall  64  positioned above and extends in parallel with the attachment/detachment path of the sheet supply tray  6 , and has a front end portion contiguous with a front wall of the main casing  2 , and a rear end portion serving as the receiving surface  65  for receiving thereon the paper dusts falling down from the multiple purpose transport portion  16 , the second transport portion  10 , and the first transport portion  9 . 
     The receiving surface  65  includes a recessed portion  66 , a slant wall portion  67  and a ridge portion  68 . The recessed portion  66  has a semi-circular cross-section and is positioned opposite to the sheet transport path  38  with respect to the first paper dust removing roller  9   b  and the first sponge member  9   c,  and extends in the axial direction of the first paper dust removing roller  9   b.  The slant wall portion  67  is positioned closer to the sheet transport path  38  than the recessed portion  66  to the sheet transport path  38 , and is slanted upwardly toward the sheet transport path  38 . The ridge portion  68  is positioned opposite to the first paper dust removing roller  9   b  and first sponge member  9   c  with respect to the recessed portion  66 , and has a height lower than the upper end portion of the slant wall portion  67 . Incidentally, an auger member (spiral feed member)  71  as paper dust transport unit described later is provided at a space of the recessed portion  66 . 
     With this arrangement, the paper dust scraped by the multiple purpose sponge member  16   c  in the multiple purpose transport portion  16  and becoming paper dust lumps are guided along the first guide plate  61   a  and dropped onto the extension portion  62   a,  and also guided along the base end portion  10   n  of the second reverse transportation preventive member  10   m.  Then, the paper dusts are further guided along the second guide plate  61   b  and dropped onto the extension portion  62   b,  and then guided along the base end portion  9   n  of the first reverse transportation preventive member  9   m,  and then dropped onto the receiving surface  65 . 
     Further, the paper dusts scraped by the second sponge member  10   c  in the second transport portion  10  and becoming the lumps are guided along the second guide plate  61   b  and dropped onto the extension portion  62   b,  and then guided along the base end portion  9   n  of the first reverse transportation preventive member  9   m.  Then, the paper dusts are dropped onto the receiving surface  65 . The paper dusts scraped by the first sponge member  9   c  and becoming the lumps are dropped onto the receiving surface  65 . 
     Incidentally, in the laser printer  1 , the base end portions  9   n,    10   n  of the first and second reverse transportation preventive members  9   m,    10   m  also serve as guide members for guiding downward travel of the paper dusts. Therefore, additional guide members are not required at side areas of the first and second paper dust removing rollers  9   b,    10   b.  Accordingly, simple construction results with reducing mechanical components, to thus lower the production cost. 
     (4) Transportation and Collection of Paper Dust 
     The laser printer  1  provides, as shown in FIGS. 6 and 7, the auger member  71  for transporting the paper dusts falling on the receiving surface  65  from a paper dust falling down area  83  to paper dust accumulating portions  84  those described later. 
     The auger member  71  is disposed along the recessed portion  66  of the receiving surface  65 . As shown in FIGS. 6 and 7, the auger member  71  includes a shaft member  72 , a first spiral portion  73  and a second spiral portion  74  integrally mounted over the shaft member  72 . Spiral direction of the second spiral portion  74  is opposite to that of the first spiral portion  73 . An auger drive gear  75  is mounted on one end of the shaft member  72  and beside the second spiral portion  74  for drivingly rotating the auger member  71  through a gear train  90  described later connected to a motor (not shown). 
     More specifically, as shown in FIG. 8, the gear train  90  includes a motor coupling gear  91 , an upper gear train  92  for transmitting power from the motor coupling gear  91  to the multiple purpose sheet supply mechanism  15  for driving the same, and a lower gear train  93  for transmitting power from the motor coupling gear  91  to the auger member  71  for drivingly rotating the same. The motor coupling gear  91  is a two sage gear including a large diameter gear in meshing engagement with the upper gear train  92  and a small diameter gear in meshing engagement with the lower gear train  93 . 
     The upper gear train  92  includes three transmission gears  94 ,  95 ,  96  arrayed in a vertical direction. A multiple purpose sheet supply roller drive gear  97  is fixedly mounted on one end of the roller shaft of the multiple purpose sheet supply roller  15   a.  The transmission gear  96  is meshedly engaged with the multiple purpose sheet supply roller drive gear  97 , so that the latter is rotatable in the counterclockwise direction by the rotation of the large diameter gear of the motor coupling gear  91  through the transmission gears  94 ,  95 ,  96 . 
     The lower gear train  93  includes two transmission gears  98 , 99  arrayed in the vertical direction. The transmission gear  99  is meshedly engaged with the auger drive gear  75 , so that the shaft member  72  of the auger member  71  is rotatable in a clockwise direction by the rotation of the small diameter gear of the motor coupling gear  91  through the transmission gears  98 ,  99 . 
     Thus, as shown in FIG. 2, the auger member  71  is rotated such that the its surface moves downwardly at a side in confrontation with the slant wall portion  67  on the receiving surface  65  and moves upwardly at a side in confrontation with the ridge portion  68 . 
     As show in FIGS. 6 and 7, the first spiral portion  73  is disposed at axially half length of the shaft member  72  and is adapted for transporting the paper dusts toward one axial end of first paper dust removing roller  9   b  (C direction in FIG. 6) upon rotation of the shaft member  72 . The second spiral portion  74  is disposed at axially remaining half length of the shaft member  72  and is adapted for transporting the paper dusts toward other axial end of the first paper dust removing roller  9   b  (D direction in FIG. 6) upon rotation of the shaft member  72 . Thus, by the rotation of the shaft member  72  the auger member  72  can transport the paper dusts in opposite directions simultaneously toward both axial ends. 
     The paper dusts falling from the first transport portion  9 , the second transport portion  10  and multiple purpose transport portion  16  can be transported toward both ends of the auger member  71  by the rotation thereof. The thus distributed paper dusts into two directions can be accumulated in the paper dust accumulators  84  described later. 
     Incidentally, in the laser printer  1 , rotation speed of the first paper dust removing roller  9   b  is set to about 180 r.p.m. However, rotation speed of the auger member  71  is lower than that of the first paper dust removing roller  9   b  such as about 60 r.p.m. By setting the rotation sped of the auger member  71  lower than that of the first paper dust removing roller  9   b,  scattering of the paper dusts during their transportation by the auger member  71  can be prevented, and driving noise can be lowered. Further, frictional wearing of the auger member  71  due to the friction against the paper dusts can also be lowered. 
     The laser printer  1  is provided with a regulation wall  76  at a part of and along the auger member  71 . As shown in FIGS. 2,  6  and  7 , the regulation wall  76  includes a first partition wall and a second partition wall. The first partition wall includes one side first partition wall  77  disposed across the first spiral portion  73  in a direction perpendicular to the axial direction of the auger member  71 , and another side first partition wall  78  disposed across the second spiral portion  74  in a direction perpendicular to the axial direction of the auger member  71 . The second partition wall  79  extends in parallel with the auger member  71  with a predetermined space therefrom. One end of the second partition wall  79  is joined to the front end of the one side partition wall  77  and another end of the second partition wall  79  is joined to the front end of the other side partition wall  78 , so that the regulation wall  76  is in a U-shape in a plan view. 
     More specifically, the first partition walls  77 ,  78  have generally rectangular shape, and have widths in a direction perpendicular to the axial direction of the auger member  71  approximately the same as the width of the receiving surface  65 . Lower ends of the first partition walls  77 , 78  are positioned lower than the contacting region between the first paper dust removing roller  9   b  and the first sponge member  9   c,  and are spaced away from an upper portion of the auger member  71  by a predetermined space. Upper ends of the first partition walls  77 , 78  are positioned upper than the contact region between the first paper dust removing roller  9   b  and the first sponge member  9   c,  and extend to a lid member  85  described later. The first partition walls  77 ,  78  are disposed in confronting relation and outwardly of the axial ends of the first paper dust removing roller  9   b  and the first sponge member  9   c.    
     The second partition wall  79  includes a central wall  80  extending in parallel with the auger member  71  with a predetermined space therefrom, a one side slant wall  81  extending from and bent at one end of the central wall  80  toward the auger member  71 , and another side slant wall  82  extending from and bent at another end of the central wall  80  toward the auger member  71 . The central wall  80  and the slant walls  81 ,  82  are provided integrally with each other. 
     The one side slant wall  81  extends between the one end of the central wall  80  and the front end of the one side first partition wall  77 , and is continuous with the central wall  80 . Thus, the one side slant wall  81  provides a gradually narrowing space between the one side slant wall  81  and the auger member  71  toward one end of the auger member  71 , i.e., in one paper dust transporting direction C. 
     The other side slant wall  82  extends between the other end of the central wall  80  and the front end of the other side first partition wall  78 , and is continuous with the central wall  80 . Thus, the other side slant wall  82  provides a gradually narrowing space between the other side slant wall  82  and the auger member  71  toward the other end of the auger member  71 , i.e., in the other paper dust transporting direction D. 
     The lower end of the second partition wall  79  including the central wall  80  and slant walls  81 ,  82  is joined with an upper surface of the front side bottom wall  64 , whereas the upper end of the second partition wall  79  extends to the lid member  85  described later. 
     The front side bottom wall  64  including the receiving surface  65  is divided into the paper dust falling portion  83  and the paper dust accumulators  84  by the regulation wall  76  provided by the first partition walls  77 ,  78  and the second partition wall  79 . 
     That is, the paper dust falling portion  83  is a region on the front side bottom wall  64  and at the axially center portion of the auger member  71  and below the first paper dust removing roller  9   b  and the first sponge member  9   c,  so that the paper dusts scraped off from the first paper dust removing roller  9   b  are falling on the region. This region is an interior of the first partition walls  77 ,  78  and the second partition wall  79 . On the other hand, the paper dust accumulators  84  are regions on the front side bottom wall  64  and adjacent to each end of the auger member  71  where the paper dusts transported by the auger member  71  are accumulated. The latter regions are an exterior of the first partition walls  77 ,  78  and the second partition wall  79 . 
     Paper dusts scraped off at the multiple purpose transport portion  16 , second transport portion  10  and first transport portion  9  and falling onto the paper dust falling portion  83  are transported toward the paper dust accumulators  84  at both ends of the auger member  71  according to the rotation of the auger member  71 . During the transportation, since the one slant wall  81  and the other slant wall  82  of the second partition wall  79  are directed to gradually reduce the width of the transportation passage between the wall and the auger member  71  toward the transporting direction, paper dusts transported by the auger member  71  can be guided toward one side partition wall  77  and the other side partition wall  78  by the slant walls  81 ,  82 . Accordingly, the paper dusts transported by the auger member  71  can be smoothly and desirably moved past through the lower edge of the one and the other side partition walls  77 ,  78 , and can reach the paper dust accumulators  84  each disposed downstream of the first partition walls. Further, the one side and other side partition walls  77 ,  78  can prevent paper dusts already accumulated in the paper dust accumulator  84  from being reversely moved, i.e., from being returned back to the paper dust falling portion  83  disposed upstream of the partition walls  77 ,  78  in the paper dust transporting direction. Consequently, sufficient falling length from the first transport portion  9  to the auger member  71  can be obtained at the paper dust falling portion  83 . As a result, sufficient amount of paper dusts can be deposited on the paper dust falling portion  83 , and can be removed therefrom. 
     Incidentally, in the laser printer  1 , since the first transport portion  9  is first brought into contact with the sheet  3  supplied from the sheet supply section  7 , greater amount of paper dusts may be released from the first transport portion  9 . However, since the paper dust falling portion  83  is isolated from the first transport portion  9  by the regulation wall  76  as a region surrounding the lower front side of the first transport portion  9 , the paper dusts can be fallen into the paper dust falling portion  83  and thereafter transported by the auger member  71 . Accordingly, sufficient amount of paper dust removal can be attained with ensuring sufficient falling stroke from the first transport portion  9  to the auger member  71 , while removing a greater amount of paper dusts at the first transport portion  9 . 
     Further, since the regulation wall  76  is higher than the contacting region between the first paper dust removing roller  9   b  and the first sponge member  9   c,  the regulation wall  76  can prevent the paper dusts fallen from the first transport portion  9  from being scattered toward the external side of the regulation wall  76 , i.e., toward the paper dust accumulators  84  and remaining area of the front side bottom wall  64 . Incidentally, the first transport portion  9  is in confrontation with the internal side of the regulation wall  76  defining the paper dust falling portion  83 . 
     The paper dusts released from the first transport portion  9  are fallen onto the receiving surface  65  at a position below the auger member  71 . In this case, the slant surface  67  guides the paper dusts toward the auger member  71 , and the paper dusts can be involved into the auger member  71  rotating downwardly at a side confronting to the slant surface  67 . Accordingly, the paper dusts can be smoothly directed toward the paper dust accumulators  84 . After the paper dusts are transported to the paper dust accumulators  84 , the paper dusts can be smoothly discharged from the auger member  71  into the paper dust accumulators  84  at the ridge portion  68  whose upper end is lower than the slant surface  67  and where the surface of the auger member  71  confronting the ridge portion  68  is moved upwardly. 
     As shown in FIG. 2, the lid member  85  is provided above the front side bottom wall  64  for covering the regulation wall  76 . The lid member  85  is in a plate like shape and positioned below the bottom wall  63   d  of the partition plate  63 . The lid member  85  extends between the front wall of the main casing  2  and a position adjacent to the extension portion  62   b  positioned above the first paper dust removing roller  9   b  and first sponge member  9   c.  A support portion  86  upstands from the front side bottom wall  64  for fixing the lid member  85  by a screw  87 . 
     An opening  88  is provided between a rear side (a side of the sheet transport path  38 ) of the lid member  85  and the extension portion  62   b.  The opening extends in the axial direction of the first paper dust removing roller  9   b.  By covering the upper side of the regulation wall  76  with the lid member  85 , scattering of the paper dusts fallen from the first transport portion  9  can be effectively eliminated. 
     Further, since the opening  88  is provided between the lid member  85  and the extension portion  62 , the paper dusts released from the second transport portion  10  and the multiple purpose transport portion  16  those positioned above the lid member  85  can be introduced into the paper dust falling portion  83  and the paper dust accumulators  84  through the opening  88 . After the paper dusts released from the second transport portion  10  and multiple purpose transport portion  16  are introduced into the paper dust falling portion  83 , these paper dusts can be transported to the paper dust accumulators  84  by the auger member  71 . Thus, effective paper dust removal can be provided. 
     Further, since the lid member  85  is positioned higher than the contact region between the first paper dust removing roller  9   b  and the first sponge member  9   c,  the paper dusts released from the first transport portion  9  cannot be easily scattered outwardly through the opening  88 . Thus, more effective paper dust removal can be attained. 
     Further, in the laser printer  1 , the paper dust accumulators  84  can be disposed on the front side bottom wall  64  since the paper dusts removed by the multiple purpose transport portion  16 , second transport portion  10  and first transport portion  9  are transported toward axial ends of the auger member  71  through rotation thereof. Therefore, it is unnecessary to provide a paper dust accumulation space at a position lower than the front side bottom wall  64 . To this effect, the auger member  71  is disposed above the attachment/detachment space of the sheet supply tray  6 . As a result, attachment/detachment work of the sheet supply tray  6  can be performed easily while ensuring smooth removal of the paper dusts from the sheet  3  supplied from the sheet supply tray  6 . 
     The laser printer  1  is of an electro-photographic type laser printer in which an electrostatic latent image is developed into a visible image which in turn transferred onto the sheet  3 . Therefore, it is absolutely necessary to remove the paper dusts from the paper otherwise the paper dusts may be mingled into the image forming section  5  at the time of image transfer. In the present embodiment however, paper dusts can be efficiently removed from the sheet  3  by the first and second transport portions  9 ,  10  and the multiple purpose transport portion  16 . Further, even if the first paper dust removing roller  9   b,  the second paper dust removing roller  10   b  and the multiple purpose paper dust removing roller  16   b  are rotated in the reverse direction for removing a jamming sheet, the paper dusts scraped by the first sponge member  9   c,  the second sponge member  10   c  and the multiple purpose sponge member  16   c  cannot be discharged into the sheet transport paths  38 , 38   a.  Therefore, adhesion of the paper dusts onto the subsequent sheet can be prevented. Thus, a desirable image can be formed on the subsequent sheet  3 . 
     Further, in the laser printer  1 , residual toner remaining on the surface of the photosensitive drum  23  after the image transferring operation is collected by the developing roller  27  with a cleaner-less system of the electro-photographic printing system using the non-magnetic single component type toners. If the paper dusts from the sheet  3  is adhered onto the surface of the photosensitive drum  23  at the time of image transfer operation, the paper dust may be collected together with the residual toner by the developing roller  27  and may be mixed with the toner in the developing cartridge  24 , to thus degrade the output image. However, in the present embodiment, the paper dusts on the sheet  3  can be efficiently removed by the first and second transport portion  9 ,  10  and the multiple purpose transfer portion  16  in the image forming operation, and further, can be prevented the reversal transportation of the paper dusts into the sheet transport paths  38 ,  38   a,  the paper dusts having been scraped by the first sponge member  9   c,  second sponge member  10   c  and the multiple purpose sponge member  16   c  in spite of the reversal rotation of the first paper dust removing roller  9   b,  second paper dust removing roller  10   b  and multiple purpose paper dust removing roller  16   b  for removing the jamming sheet. Therefore, the subsequent sheet is not subjected to the adhesion of the paper dusts, and a desirable image can be formed while easily collecting the residual toner with the cleanerless system. 
     As described above, in the laser printer  1 , the multiple purpose transport portion  16 , the second transport portion  10 , and the first transport portion  9  are arrayed substantially in the vertical direction and in front of the sheet transport path  38 , and paper dusts removed by these portions  16 ,  10 ,  9  are respectively dropped because of their gravity through the chute  39  and are fallen onto the receiving portion  65 . Thereafter, these paper dusts are congregately accumulated into the receiving portion  65 . Accordingly, paper dusts removed at every multiple purpose transport portion  16 , the second transport portion  10  and the first transport portion  9  can be guided with the simple arrangement and can be accumulated congregately. Thus, it is not necessary to provide each paper dust accumulator for each transport portion, which in turn simplifies the overall device, and can reduce numbers of mechanical components to provide a compact device. 
     Further, in the laser printer  1 , since one side face of the guide plate  61  constituting the sheet transport path  38  can be utilized as the paper dust chute  39 , which can also simplify the overall device, and can reduce numbers of mechanical components to provide a compact device. 
     Further, in the laser printer  1 , since the first guide plate  61   a  is provided with the extension portion  62   a  covering the upper side of the second transport portion  10 , and the second guide plate  61   b  is provided with the extension portion  62   b  covering the upper side of the first transport portion  9 , the extension portion  62   a  prevents the paper dusts from falling onto the second transport portion  10 , the paper dust being released from the multiple purpose transport portion  16  positioned above the second transport portion  10 , and further, the extension portion  62   b  prevents the paper dusts from falling onto the first transport portion  9 , the paper dust being released from the multiple purpose transport portion  16  as well as from the second transport portion  10  positioned above the first transport portion  9 . Consequently, desirable paper dust removing operations in the first and second transport portions  9  and  10  can be attained for a long period. 
     Further, in the laser printer  1 , the first paper dust removing roller  9   b  in the first transport portion  9  removes the paper dusts on the sheet  3  in rotational contact therewith, and then the paper dusts adhered onto the first paper dust removing roller  9   b  is scrapped off by the first sponge member  9   c  disposed opposite to the sheet transport path  38  with respect to the first paper dust removing roller  9   b.  Further, the second paper dust removing roller  10   b  in the second transport portion  10  removes the paper dusts on the sheet  3  in rotational contact therewith, and then the paper dusts adhered onto the second paper dust removing roller  10   b  is scrapped off by the second sponge member  10   c  disposed opposite to the sheet transport path  38  with respect to the second paper dust removing roller  10   b.  The paper dusts scraped by the first and second sponge members  9   c  and  10   c  are stayed thereon in confrontation with the sheet transport path  38  and are grown into paper dust masses, whereupon each paper dust mass is dropped because of its gravity along the paper dust chute  39 . In this way, entry of the scrapped paper dusts into the sheet transport path  38  can be prevented, while the paper dusts removed by the first and second transport portions  9  and  10  can be congregately accumulated in the paper dust accumulators  84 . 
     Further, the multiple purpose paper dust removing roller  16   b  in the multiple purpose transport portion  16  removes the paper dusts on the sheet  3  in rotational contact therewith, and then the paper dusts adhered onto the multiple purpose paper dust removing roller  16   b  is scrapped off by the multiple purpose sponge member  16   c  disposed opposite to the sheet transport path  38   a  with respect to the multiple purpose paper dust removing roller  16   b.  The paper dusts scraped by the multiple purpose sponge members  16   c  are dropped because of its gravity along the paper dust chute  39 . In this way, entry of the scrapped paper dusts into the sheet transport path  38   a  can be prevented, while the paper dusts removed by the multiple purpose transport portions  16  can be congregately accumulated in the paper dust accumulator. 
     (5) Second Embodiment 
     An image forming device according to a second embodiment of the present invention will be described with reference to FIGS.  9  through  13 ( b ) wherein like parts and components are designated by the same reference numerals and characters as those shown in the first embodiment shown in FIGS. 1 through 8. A laser printer  101  according to the second embodiment is different from the first embodiment in terms of the arrangement of collection of paper dusts. 
     In a second transport portion  110 , a second paper dust removing roller  110   b  is driven upon power input from a motor (not shown) into an input gear  110   h  as shown in FIG. 10, serving as power input means mounted on one end portion of the roller shaft  110   f,  so that the second paper dust removing roller  110   b  is rotatable in a direction indicated by an arrow in FIG. 9, that is, in the sheet feeding direction (counter clockwise direction in FIG. 9) at a region facing with the sheet transport path  38 . The sheet  3  is nipped between the second transport roller  10   a  and the second paper dust removing roller  110   b  for feeding, while the paper dust is removed by the second paper dust removing roller  110   b.    
     Regarding paper dust collecting arrangement, a lower end of a second guide plate  161   b  is integrally provided with a receiving plate  161   c  bent at substantially right angle from the second guide plate  161   b  toward frontward. The receiving plate  161   c  is positioned above an attachment/detachment path of the sheet supply tray  6  and extends in parallel therewith. An upper surface of the receiving plate  161   c  surves as a receiving surface  165  adapted for receiving paper dusts removed by and falling from the multiple purpose transport portion  16 , the second transport portion  10  and the first transport portion  9 . 
     A partition plate  163  is positioned in front of the second guide plate  161   b  with a predetermined space therefrom. The partition plate  163  includes a side plate  163   c  extending in a vertical direction and a bottom plate  163   d  bent at substantially right angle from a lower end of the side plate  163   c  toward frontward. Further, a plate-like fixing portion  163   a  bendingly extends upwardly from a front end of the bottom plate  163   d  for fixing a paper dust transport plate  166  and a transport drive portion  167  described later. 
     The laser printer  101  further provides a paper dust accumulators  168  for accumulating therein paper dusts falling onto the receiving surface  165  due to their gravity from the multiple purpose transport portion  16 , the second transport portion  10  and the first transport portion  9 . The printer  101  also provides the paper dust transport plate  166  for transporting paper dusts on the receiving surface  165  toward the paper dust accumulators  168 , and the transport drive portion  167  for driving the paper dust transport plate  166 . 
     As shown in FIG. 12, the paper dust accumulators  168  are positioned below the multiple purpose transfer portion  16 , the second transfer portion  10  and the first transfer portion  9 . The paper dust accumulator  168  is provided at spaces located outward of the widthwise ends of the receiving surface  165 , so that all paper dusts falling on the receiving surface  165  can be ultimately accumulated in the accumulators  168 . 
     The paper dust transport plate  166  is positioned above the sheet supply tray attachment/detachment path and above the receiving surface  165 . The plate  166  includes a T-shaped plate like base portion  169  as viewed from the front as shown in FIG. 12 and a generally L-shaped thin plate-like wiper plate  170  as shown in FIG. 9 protruding rearwardly from and integrally with a widthwise center portion of the lower portion of the base portion  169  and extending downwardly to a position below the first transport portion  9 . As shown in FIG. 11, the paper dust transport plate  166  has a T-shape in plan view in which the wiper plate  170  protrudes perpendicularly from the widthwise center portion of the base portion  169 . The base portion  169  is fixed to a rack  174  of the transport drive portion  167  through screws  171  interposing the fixing portion  163   a  of the partition plate  163  between the paper dust transport plate  166  and the rack  174 . The fixing portion  163   a  is formed with an elongated horizontally extending slot  163   b  through which the screws  171  extend. The paper dust transport plate  166  is reciprocally and horizontally movable along the horizontally extending slot  163   b  in accordance with the horizontal movement of the rack  174 . A lower end of the wiper plate  170  is spaced away from the receiving surface  165  by a predetermined distance (about 2 mm) as shown in FIG. 9, so that the lower end is out of sliding contact from the receiving surface  165  during reciprocating movement of the wiper plate  170 . 
     The transport drive portion  167  is disposed above the paper dust transport plate  166  and the paper dust accumulator  168  as shown in FIG. 9, and is separated from the first and second transport portions  9 ,  10  and the multiple purpose transport portion  16  by the partition plate  163 . The transport drive portion  167  includes a power transmission mechanism  194  (see FIGS.  13 ( a ) and  13 ( b )), a first bevel gear  172 , a composite gear  173  and the rack  174 . 
     The power transmission mechanism  194  is disposed along a side wall of the main casing  2 , and includes an input gear  177 , a conversion gear portion  178  and an output gear  179 . 
     The input gear  177  is fixedly mounted on one end of an input shaft  180  drivingly rotated in one direction by a motor (not shown). The input gear  177  is meshedly engaged with a first conversion gear  181  of the conversion gear portion  178  described later. 
     The conversion gear portion  178  includes the first conversion gear  181 , a second conversion gear  182 , a pendulum member  183 , and a third conversion gear  184 . The first conversion gear  181  has a large diameter first outer gear  185  meshedly engaged with the input gear  177 , and a small diameter first inner gear  186  concentrically integral with the first outer gear  185  and meshedly engaged with the second conversion gear  182 . 
     The second conversion gear  182  has a gear teeth meshedly engaged with the first inner gear  186  of the first conversion gear  181 . A cylindrical sleeve  187  extends from a wheel body of the second conversion gear  182  in an axial direction thereof at a position offset from the rotational center of the second conversion gear  182 . The sleeve  187  is loosely engaged with a slot  188  formed in the pendulum member  183 . 
     The pendulum member  183  is a plate member in a form of an elongated sector shape. The pendulum member  183  has a lower end formed with an arcuate teeth portion  189  meshedly engaged with a third inner gear  192  of the third conversion gear  184  described later. The slot  188  is formed in a longitudinal direction of the pendulum member  183  and at a width-wise center thereof. A pivot support  190  is provided between one end of the slot  188  and the arcuate teeth portion  189 . Thus, the pendulum member  183  is pivotally movably supported by the pivot support  190 , while the sleeve  187  of the second conversion gear  182  is loosely engaged with the slot  188 . 
     The third conversion gear  184  has a large diameter third outer gear  191  meshedly engaged with the output gear  179 , and a small diameter third inner gear  192  provided integrally and concentrically with the third outer gear  191  and meshedly engaged with the arcuate teeth portion  189  of the pendulum member  183 . 
     The output gear  179  is fixedly mounted on one end portion of an output shaft  193  which transmits power to the first bevel gear  172 . The output gear  179  is adapted for transmitting power from the third outer gear  191  of the third conversions gear  184  to the first bevel gear  172 . 
     As shown in FIG. 11, the first bevel gear  172  is mounted on another end portion of the output shaft  193  which transmits power from the output gear  179 . The first bevel gear  172  is meshedly engaged with a second bevel gear  176  of the composite gear  173  directing perpendicular to the first bevel gear  172 . 
     As shown in FIG. 9, the composite gear  173  has a pinion gear  175  meshedly engaged with the rack  174  and the second bevel gear  176  provided integrally with the pinion gear  175  and positioned in radially inner side thereof. The pinion gear  175  is rotatable about a horizontal axis. 
     The rack  174  has a rack teeth  174   a  meshedly engaged with the pinion gear  175  of the composite gear  173 . The rack  174  has an elongated rectangular shape whose longitudinal length is slightly greater than the width of the first paper dust removing roller  9   b . The rack  174  extends in parallel with the axial direction of the first paper dust removing roller  9   b  in a state where the rack teeth  174   a  is meshedly engaged with the pinion gear  175 . Upon rotation of the pinion gear  175 , the rack  174  is linearly reciprocatingly moved in the axial direction of the first paper dust removing roller  9   b  while a rear surface of the rack  174  is in sliding contact with the fixing portion  163   a  of the partition plate  163  (FIG.  11 ). 
     In the transport drive portion  167  as shown in FIGS.  13 ( a ) and  13 ( b ), when the rotation of the motor (not shown) in one direction is transmitted to the input gear  177 , the first outer gear  185  of the first conversion gear  181  meshedly engaged with the input gear  177  is rotated. Therefore, the second conversion gear  182  is rotated through the rotation of the first inner gear  186  of the first conversion gear  181 , so that the sleeve  187  is circularly moved. Thus, the pendulum member  183  is laterally pivotally moved about the pivot support  190  because of the engagement between the sleeve  187  of the second conversion gear  182  and the slot  88  of the pendulum member  183 , so as to reciprocally move the arcuate teeth portion  189 . Accordingly, the rotating direction of the third inner gear  192  meshedly engaged with the arcuate teeth portion  189  is cyclically altered in both directions. Consequently, rotating direction of the output gear  179  is cyclically altered through the third outer gear  191 . 
     As shown in FIG. 11, when this reciprocal rotation of the output shaft  193  is transmitted to the rack  174  through the first bevel gear  172 , the second bevel gear  176  and the pinion gear  175 , the rack  174  is reciprocally moved in the horizontal direction at a predetermined cycle. Therefore, as shown in FIG. 11, the paper dust transport plate  166  fixed to the rack  174  by the screws  171  can be horizontally displaced over the receiving surface  165  in the axial direction of the first paper dust removing roller  9   b  between stroke ends indicated by two dotted chain lines in FIG.  12 . Each stroke end is positioned outwardly of each axial end of the first paper dust removing roller  9   b.  As a result, the wiper plate  170  can be driven to linearly reciprocatingly wipe the paper dusts dropped onto the receiving surface  165  and even at the position outwardly of the axial ends of the first paper dust removing roller  9   b.    
     The transport drive portion  167  including the gear transmission from the input gear  177  to the output gear  179  provides speed deceleration in such a manner that the reciprocal moving speed of the paper dust transport plate  166  is not more than 100 mm/sec. 
     In the laser printer  101 , the transport drive portion  167  is disposed above the paper dust transport plate  166  and the paper dust accumulator  168 , and is isolated by the partition plate  163 . Therefore, the partition plate  163  can effectively prevent paper dust from entering into the transport drive portion  167 , the paper dust being released from the multiple purpose transport portion  16 , the second transport portion  10  and the first transport portion  9  due to gravity, or transported by the paper dust transport plate  166 , or the accumulated in the accumulator  168 . As a result, operational malfunction of the transport drive portion  167  due to entry of the paper dust can be eliminated, to provide a stabilized operation thereof, thereby providing sufficient paper dust removing operation for a long duration of time. 
     Further, in the laser printer  101 , the paper dust is wiped by the wiper  170  of the paper dust transport plate  166 , the wiper being reciprocatingly moved in the horizontal direction, and is transported to the paper dust accumulators  168 . Therefore, stabilized transportion of the paper dusts is achievable with a simple arrangement without any complicated transportation mechanism. 
     Further, the wiper  170  is linearly reciprocatingly moved along the axial direction of the first paper dust removing roller  9   b.  Therefore, desirable transportation of the paper dusts toward the accumulator  168  can be attained without any residual paper dusts on the receiving surface  165  with a minimized space and simplified arrangement. 
     Assuming that the wiper  170  is not a linear reciprocation type but a pivotally moving reciprocation type. In the latter case, in order to reduce a non-wiped out area, large pivotally moving locus is required, which in turn makes the entire device bulky. In order to avoid bulky arrangement without enlargement of the pivotal moving region, a flexible blade member may be used which may be deformed or flexed in contacting with an opponent component. However, a complicated arrangement is required for assembling the flexible blade and number of mechanical components may be increased. 
     In contrast, if the wiper  170  is provided linearly reciprocatingly movable in the axial direction of the first paper dust removing roller  9   b  as in the second embodiment, simple arrangement results with a minimized space capable of providing a desirable transportation of the paper dusts into the accumulator  168  without non-wiped out area. 
     Further, since the paper dust transport plate  166  is moved at a low speed such as not more than 100 mm/sec., the paper dusts on the receiving surface  165  can be transported to the accumulator  168  without any scattering of the paper dust. Accordingly, entry of the paper dust into the transport drive portion  167  can further be avoided, to attain desirable paper dust removing operation for a long duration of time. 
     Further, since the wiper  170  is spaced away from the receiving surface  165  by the predetermined gap (about 2 mm) while the wiper is reciprocatingly moved in the horizontal direction, frictional contact of the wiper  170  agaist the receiving surface  165  can be eliminated, to avoid damage to the wiper. Thus, enhanced durability of the paper dust transport plate  166  results for providing efficient transportation of the paper dust. Incidentally, since the paper dusts falling onto the receiving surface  165  is not a fine particle but in the form of a mass, the paper dusts can still be wiped by the wiper  170  regardless of the predetermined gap. The gap does not affect the transportation of the paper dusts mass. 
     Further, in the laser printer  101 , since paper dusts removed by the multiple purpose transport portion  16 , the second transport portion  10  and the first transport portion  9  are accumulated, by the transportation of the paper dust transport plate  166 , into the paper dust accumulators  168  positioned at the widthwise ends of the receiving surface  165 , it is not necessary to provide an accumulation space at a position immediately below the receiving surface  65 . Consequently, the paper dust transport plate  166  can be positioned above the attachment/detachment path of the sheet supply tray  6 , yet performing efficient paper dust removal from the sheet supplied from the sheet supply tray  6 , while ensuring smooth attachment/detachment of the sheet supply tray  6 . 
     Further, in the laser printer  101 , driving force in one direction input into the input gear  177  can be converted into the driving force in reciprocating direction through the conversion gear portion  178  in the power transmission mechanism  194 , and thereafter, the reciprocally driving force is output to the paper dust transport plate  166  through the output gear  179 . In this way, one directional driving force can be converted into reciprocating directional driving force with the simple arrangement, to provide reciprocal motion of the paper dust transport plate  166 . 
     While the invention has been described in detail and with reference to the specific embodiments thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention. 
     For example, in the above-described embodiments, only one first transport portion  9  and only one second transport portion  10  are provided. However, a plurality of first transport portions and a plurality of second transport portions can be provided. Alternatively, a plurality of transport portions can be provided for one of the first and second transport portions. 
     Further, in the depicted embodiments, the first transport portion  9  provided with the first paper dust removing roller  9   b  is provided upstream of the second transport portion  10  provided with the second paper dust removing roller  10   b.  However, the second transport portion  10  provided with the second paper dust removing portion  10   b  can be disposed upstream of the first transport portion  9  provided with the first paper dust removing roller  9   b.  In the latter case, since the area of the paper dusts generated by the friction against the pad member  13  will slightly expand in the widthwise direction of the sheet  3  due to the contact with the second paper dust removing roller  10   b,  the width of the first paper dust removing roller  9   a  and the width of the first sponge member  9   c  should desirably be greater than the widths thereof in case of the arrangement where the first transport portion  9  is provided upstream of the second transport portion  10 . 
     Further, in the above described embodiment, a center register type is applied for the sheet feeding from the sheet supply section  7  to the first transport portion  9 , and the auger member  71  is adapted to transport paper dusts toward both axial ends thereof. Instead of this arrangement, a side register type can be applied and the auger member  71  can be adapted for transporting the paper dusts to one side only, the one side being opposite to the sheet register portion. 
     Further, in the first embodiment, the rotating direction of the auger  71  is such that the surface of the auger member  71  is moved downwardly at a side facing the first transport portion  9 . However, if the distance between the auger receiving portion of the receiving surface  65  and the first transport portion  9  is sufficiently long in the horizontal direction, the rotating direction of the shaft member  72  of the auger member  71  is not restrictive, but the surface of the auger member can be moved upwardly at a side facing the first transport portion  9 . 
     Further, in the first embodiment, the second partition wall  79  of the regulation wall  76  includes the center wall  80  extending in parallel with the auger member  71  with a predetermined space therefrom, the one side slant wall  81  and the other side slant wall  82  extending from the ends of the center wall  80  toward the auger member  71  by bending at the ends of the center wall. These walls are integrally with each other. However, the second partition wall is not limited to the above-described configuration. For example, a plurality of walls can be used to make a center wall with a slit between the neighboring walls. Alternatively, an opening or a notch can be formed at a longitudinally intermediate portion of the second partition wall  79 . 
     Further, in the above-described embodiments, the first reverse transportation preventive member  9   m,  the second reverse transportation preventive member  10   m,  and the multiple purpose reverse transportation preventive member  16   m  are positioned spaced away from the corresponding first paper dust removing roller  9   b,  second paper dust removing roller  10   b,  and multiple purpose paper dust removing roller  16   b,  respectively. However, these preventive members  9   m,    10   m,    16   m  can be contacted with the corresponding rollers by constituting these preventive members by brushes, films and unwoven fabrics those allowing the paper dusts to be transported during the normal rotation of the paper dust removing rollers  9   b,    10   b,    16   b,  but preventing the paper dusts from passing therethrough during reversal rotation of these rollers. 
     Further, in the above described embodiments, the second paper dust removing roller  10   b,    110   b  has a width perpendicular to the sheet feeding direction greater than the width of the sheet  3  for removing the paper dusts from overall surface of the sheet  3 . However, paper dusts generated upon sheet cutting is particularly located adjacent to the cutting edge, i.e., widthwise edge potions of the sheet  3 . Therefore, as shown in FIG. 14, two second paper dust removing roller  10   b ′ are provided on a roller shaft  10   f ′ at positions corresponding to the widthwise edge portions of the sheet  3  for removing the paper dust from the sheet  3  at least in areas corresponding to the widthwise edge portions of the sheet  3 . 
     Further, the present invention is particularly available for the sheet supply section  7  in which sheet separation is achieved by making use of a friction, which easily provides paper dusts. However, the present invention is also available for another sheet separation systems other than frictional separation, such as a system using pawls or a system using a bank.