Patent Publication Number: US-7715766-B2

Title: Developing unit and image forming apparatus using the same

Description:
This Nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2006-328474 filed in Japan on 5 Dec. 2006, the entire contents of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   (1) Field of the Invention 
   The present invention relates to a developing unit and an image forming apparatus using this. The present invention is, in particular, directed to a developing unit for visualizing an electrostatic latent image formed on a photoreceptor drum with a developer that has been electrified by blending two components, i.e., an electrostatically chargeable toner and a magnetic carrier, wherein toner which falls from the developing roller&#39;s developing area for supplying toner to the photoreceptor drum is collected, as well as to an image forming apparatus using this. 
   (2) Description of the Prior Art 
   In a conventional image forming apparatus such as a printer etc. using the electrophotography, a printout of an image is formed by electrifying a photoreceptor drum that is driven rotationally by a charger, forming an electrostatic latent image by illuminating the photoreceptor drum with light in accordance with image information, forming a toner image by applying toner to the electrostatic latent image by a developing unit and transferring the toner image to a sheet material or other recording media. 
   As a developer used for the developing unit of the image forming apparatus, use has been made of, for example a dual-component developer which is prepared by mixing two components, or an electrostatically chargeable toner and a magnetic carrier. 
   The thus constructed image forming apparatus entails the problem that the toner scattering from the developing roller of the developing unit adheres onto the photoreceptor drum surface and the thus adhering toner transfers to the recording medium, the transfer belt or the like, degrading image quality. 
   Further, with increase in the processing speed and with downsizing of the carrier particles (e.g., the carrier&#39;s particle size has reduced from 80 μm to 50 μm in diameter) to support high-speed configurations of recent image forming apparatus, another problem has emerged that the carrier drops from the developing roller surface, dirtying the apparatus interior and also producing scratches on the photoreceptor drum with the dropping carrier. 
   To deal with these conventional problems, there has been a proposal in that a toner collecting roller with a scraper is provided for the developing unit so as to collect scattered toner and the collected developer having adhered on the toner collecting roller is removed by the scraper (see patent document 1: Japanese Patent Application Laid-open Hei 7-319279). 
   When in the above-described prior art the scraper is mounted to the developing unit, it is a common practice that in order to make the scraper uniformly abut the toner collecting roller, the scraper is backed with a reinforcement arranged on the scraper supporting side and fixed to the scraper fixture etc., using screws at plural places (some or several places). 
   However, since the scraper becomes worn out at its front contact part which is put in sliding contact with the toner collecting roller, the scraper needs to be replaced periodically upon maintenance. For this reason, the scraper attachment structure with screw fastening as stated above entails the problem that the work in assembling the scraper and its replacement for maintenance are complicated. 
   Further, the attachment structure of the scraper with screw fastening gives rise to a fear that the scraper might be deformed by stress concentration at the screw-fastened positions and also makes the developing unit bulky. 
   SUMMARY OF THE INVENTION 
   The present invention has been devised in view of the above problems, it is therefore an object of the present invention to provide a developing unit which permits its scraper to be assembled and disassembled with one-touch handling and can realize uniform abutment of the scraper against its toner collecting roller without deforming the scraper, hence can prevent the photoreceptor drum from being damaged with the falling developer and can prevent degradation of image quality, as well as providing an image forming apparatus using the developing unit. 
   In order to solve the above problem, the developing unit and image forming apparatus using the developing unit according to the present invention are configured as follows. 
   A developing unit according to the first aspect of the present invention is one that visualizes an electrostatic latent image formed on, for example a photoreceptor drum as an electrostatic latent image bearer with a developer that is prepared and electrified by mixing two components, an electrostatically chargeable toner and magnetic carrier, comprising: a collecting roller for collecting the developer falling from the developing area of a developing roller that supplies the toner to the photoreceptor drum; and a developer remover for removing the developer collected by the collecting roller from the collecting roller, and is characterized in that the developer remover comprises: a casing for supporting the collecting roller; a scraper disposed elongated along the axial direction of the collecting roller and abutted against the outer periphery of the collecting roller so as to scrape off the developer adhering to the outer periphery of the collecting roller; and, a supporter for supporting the scraper, and the supporter presses the scraper against the casing to hold the scraper. 
   A developing unit according to the second aspect of the present invention is characterized in that, in addition to the above first configuration, the casing comprises: a collecting roller supporter for rotatably supporting the collecting roller; a first scraper supporting part for supporting the scraper; and, a first attachment part to which the supporter is attached, the casing is mounted to the developing unit body which has the developing roller disposed therein and stores the developer, and the supporter comprises: a second attachment part attached to the first attachment part; and a second scraper supporting part for supporting the scraper against the first scraper supporting part along the axial direction of the collecting roller. 
   A developing unit according to the third aspect of the present invention is characterized in that, in addition to the above second configuration, the first scraper supporting part or the second scraper supporting part includes a scraper positioning portion for positioning the scraper, and the scraper has a scraper-side engaging portion corresponding to the scraper positioning portion. 
   It is preferable in the present invention to provide projections as the scraper positioning portion in the casing by so-called half-punching while forming fitting holes as the scraper-side engaging portions that correspond to the scraper positioning portion. 
   A developing unit according to the fourth aspect of the present invention is characterized in that, in addition to the above third configuration, the scraper positioning portion has first and second scraper positioning projections that are formed at both longitudinal ends of the first scraper supporting part or the second scraper supporting part and are projected towards the side to which the scraper is attached, and the scraper-side engaging portion has first and second scraper-side engaging portions, the first scraper-side engaging portion having a configuration for fitting the first scraper positioning projection therein, and the second scraper-side engaging portion having a configuration that allows for movable engagement of the second scraper positioning projection with respect to the longitudinal direction of the first scraper supporting part or the second scraper supporting part. 
   It is preferable in the present invention to provide a pair of circular projections as the scraper positioning portion in the casing by so-called half-punching while forming a circular fitting hole (first scraper-side engaging portion) and an elongated (elliptic) fitting hole (second scraper-side engaging portion) as the scraper-side engaging portions that correspond to the scraper positioning portion. 
   A developing unit according to the fifth aspect of the present invention is characterized in that, in addition to any one of the above second to fourth configurations, the first attachment part has a supporter positioning portion for positioning the supporter, and the second attachment part has a supporter-side engaging portion corresponding to the supporter positioning portion. 
   It is preferable in the present invention to provide projections as the supporter-positioning portion in the casing by so-called half-punching while forming fitting holes as the supporter-side engaging portions that correspond to the supporter positioning portion. 
   A developing unit according to the sixth aspect of the present invention is characterized in that, in addition to the above fifth configuration, the supporter positioning portion has first and second supporter positioning projections that are formed at both longitudinal ends of the first attachment part and are projected towards the side to which the supporter is attached, and the supporter-side engaging portion has first and second supporter-side engaging portions, the first supporter-side engaging portion having a configuration for fitting the first supporter positioning projection therein, and the second supporter-side engaging portion having a configuration that allows for movable engagement of the second supporter positioning projection with respect to the longitudinal direction of the first attachment part. 
   It is preferable in the present invention to provide a pair of circular projections as the supporter positioning portion in the casing by so-called half-punching while forming a circular fitting hole (first supporter-side engaging portion) and an elongated (elliptic) fitting hole (second supporter-side engaging portion) as the supporter-side engaging portions that correspond to the supporter positioning portion. 
   A developing unit according to the seventh aspect of the present invention is characterized in that, in addition to any one of the above first to sixth configurations, the scraper includes a plate-like blade and a holder for holding the blade, and the holder is laid over the blade along the longitudinal direction of the blade. 
   A developing unit according to the eighth aspect of the present invention is characterized in that, in addition to any one of the above first to seventh configurations, the supporter is formed of a leaf-spring material, abuts the scraper uniformly with respect to the axial direction of the collecting roller and presses the scraper toward the casing. 
   A developing unit according to the ninth aspect of the present invention is characterized in that, in addition to any one of the above first to eighth configurations, the supporter is formed so that the distal end of the abutment portion that abuts the scraper against the casing is bent or curved in a direction opposite to the scraper. 
   A developing unit according to the tenth aspect of the present invention is characterized in that, in addition to any one of the above second to ninth configurations, the collecting roller supporter axially and rotatably supports the collecting roller at both ends thereof by means of resinous bearings. 
   An image forming apparatus according to the eleventh aspect of the present invention is one which includes a developing unit for visualizing an electrostatic latent image formed on, for example, a photoreceptor drum as an electrostatic latent image bearer with a developer that is prepared and electrified by mixing two components, an electrostatically chargeable toner and magnetic carrier, comprising: a collecting roller for collecting the developer falling from the developing area of a developing roller that supplies the toner to the photoreceptor drum; and a developer remover for removing the developer collected by the collecting roller from the collecting roller, and which produces a printed output of an image by transferring a developer image formed on the surface of the photoreceptor drum to a transfer medium, by an electrophotographic process, and is characterized in that a developing unit defined in any one of the above first to tenth aspects is used as the developing unit. 
   According to the first aspect of the invention, since the scraper can be mounted to the casing easily without the need of fastening the scraper with screws, it is possible to replace the scraper with one-touch handling and it is also possible to realize uniform abutment of the scraper against the collecting roller without causing any scraper deformation. As a result, it is possible to remove the developer from the collecting roller in a reliable manner, hence realize a developing unit that can prevent the photoreceptor drum from being damaged with falling developer and can inhibit degradation of image quality. 
   Further, since the collecting roller and scraper are assembled to the casing that is prepared separately from the developing unit, it is possible to position and fix the scraper with high precision based on the collecting roller by use of the casing in a simple manner, compared to the conventional practice in which the scraper has to be positioned with precision relative to the collecting roller that is positioned and held on the developing unit side. 
   According to the second aspect of the invention, in addition to the effect obtained from the first aspect, it is possible to insert and mount the scraper easily by virtue of the second scraper supporting part without the need to assemble or disassemble the supporter and/or the scraper with screw-fastening or the like. 
   According to the third aspect of the invention, in addition to the effect obtained from the second aspect, the scraper can be easily positioned relative to the casing with improved positioning accuracy. 
   According to the fourth aspect of the invention, in addition to the effect obtained from the third aspect, the scraper can be easily positioned relative to the casing with precision along its longitudinal direction or the axial direction of the collecting roller. 
   According to the fifth aspect of the invention, in addition to the effects obtained from the second to fourth aspects, the scraper supporter can be easily positioned relative to the casing with improved positioning accuracy. 
   According to the sixth aspect of the invention, in addition to the effect obtained from the fifth aspect, the supporter can be easily positioned with precision relative to the casing along its longitudinal direction or the axial direction of the collecting roller. 
   According to the seventh aspect of the invention, in addition to the effects obtained from the first to sixth aspects, the rigidity of the blade can be uniformly enhanced. 
   According to the eighth aspect of the invention, in addition to the effects obtained from the first to seventh aspects, since the scraper can be pressed uniformly across its whole surface by the elastic force of the supporter, the scraper can be stably pressed against the casing. 
   According to the ninth aspect of the invention, in addition to the effects obtained from the first to eighth aspects, it is possible to enhance the strength of the second scraper supporting part, and also perform easy scraper insertion. 
   According to the tenth aspect of the invention, in addition to the effects obtained from the second to ninth aspects, it is possible to keep the relative position of the collecting roller and the scraper with precision. 
   According to the eleventh aspect of the invention, since the scraper can be replaced by one-touch handling without the need of fastening the scraper with screws, it is possible to improve the assembly and maintenance performance of the scraper. Further, since the scraper can be abutted uniformly against the toner collecting roller without causing any scraper deformation, it is possible to scrape the collected developer in a reliable manner. As a result, it is possible to collect the falling developer efficiently, hence it is possible to realize a developing unit which prevents the photoreceptor drum from being damaged by the developer and realizes prevention against degradation of image quality. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an illustrative view showing an overall configuration of an image forming apparatus according to the embodiment of the present invention; 
       FIG. 2  is a partial detailed view showing the configuration of the apparatus body of the image forming apparatus; 
       FIG. 3  is an overall side sectional view showing a developing unit and toner feed device that constitute the image forming apparatus; 
       FIG. 4  is a sectional view showing the configuration of the developing unit; 
       FIG. 5A  is a side sectional view showing a configuration of a mixing roller that constitutes the developing unit of the same embodiment; 
       FIG. 5B  is a sectional view cut along a plane B 1 -B 1 ′ in  FIG. 5A ; 
       FIG. 5C  is a sectional view cut along a plane B 2 -B 2 ′ in  FIG. 5A ; 
       FIG. 5D  is a sectional view cut along a plane B 3 -B 3 ′ in  FIG. 5A ; 
       FIG. 5E  is a sectional view cut along a plane B 4 -B 4 ′ in  FIG. 5A ; 
       FIG. 6A  is a sectional view showing a configuration of a developer removing device that constitutes the developing unit; 
       FIG. 6B  is an illustrative view for illustrating the operation of a scraper and scraper supporter that constitute the developer removing device; 
       FIG. 7A  is a plan view, viewed in the direction of arrow C, showing a casing that constitutes the developer removing device shown in  FIG. 6A ; 
       FIG. 7B  is a plan view showing the casing, viewed in the direction of arrow D in  FIG. 7A ; 
       FIG. 8  is a plan view showing the configuration of the scraper; 
       FIG. 9  is a perspective view showing the configuration of the scraper supporter; 
       FIG. 10A  is an illustrative view showing a mounting operation of the casing and scraper; 
       FIG. 10B  is a sectional view showing a state where the casing and scraper are fit in place; 
       FIG. 11  is an illustrative view showing a variational example of a scraper supporter configuration according to the present embodiment; and 
       FIG. 12  is an illustrative view showing a variational example of a scraper positioning structure according to the present embodiment. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The best mode for carrying out the present invention will hereinafter be described with reference to the accompanying drawings. 
     FIG. 1  shows one embodiment of the present invention and is an illustrative view showing an overall configuration of an image forming apparatus according to the embodiment of the present invention.  FIG. 2  is a partial detailed view showing the configuration of an apparatus body of the same image forming apparatus. 
   As shown in  FIGS. 1 and 2  an image forming apparatus  1 A according to the present embodiment processes image data captured by a scanner etc., or image data transmitted from without to output a monochrome (single color) image, based on the electrophotography, by forming an electrostatic latent image on a rotationally driven, cylindrical photoreceptor drum (electrostatic latent image bearer)  3 , visualizing the electrostatic latent image with an electrified developer prepared by mixing two components, or an electrostatically chargeable toner and magnetic carrier, and transferring the developed image to a predetermined sheet of recording paper (to be referred to as paper hereinbelow) as a recording medium. A developing unit for visualizing the electrostatic latent image on photoreceptor drum  3  includes, as shown in  FIG. 2 , a collecting roller  220  for collecting the developer falling from the developing area of a developing roller  202  for supplying toner to photoreceptor drum  3  and a developer removing device (developer remover)  230  for removing the developer collected by collecting roller  220  therefrom. 
   As shown in  FIG. 1 , this image forming apparatus  1 A includes a paper feed tray  8  which can stack multiple sheets of paper P thereon; a paper conveying portion  59  for conveying paper P fed from this paper feed tray  8  to an image forming portion  14 ; and a paper conveyor system  7  for conveying the paper P with an unfixed toner image printed thereon by image forming portion  14  to a fixing unit  6  where the unfixed toner is fused and fixed on to the paper. The image forming apparatus, based on the conveying speeds of paper P corresponding to a multiple number of preset printout processing modes, can select and control the conveying speed of paper P in accordance with a print request and automatically feed paper P from paper feed tray  8  to a paper output tray  9 . 
   To begin with, the overall configuration of image forming apparatus  1 A will be described. 
   Image forming apparatus  1 A is essentially composed of, as shown in  FIG. 1 , an apparatus body  1 A 1  including a light exposure unit  1 , a developing unit  2 , a toner feed device  30 , a photoreceptor drum  3 , a charger  4 , a charge erasing device  41 , a cleaner unit  5 , a fixing unit  6 , paper conveyor system  7 , a paper feed path  7   a , paper feed tray  8 , paper output tray  9 , a transfer device  10  and the like, and an automatic document processor  1 A 2 . 
   Formed on the top surface of apparatus body  1 A 1  is an original placement table  21  made of transparent glass on which a document is placed. Automatic document processor  1 A 2  is arranged on the top of this original placement table  21  so that it can pivotally open upwards, while a scanner portion  22  as a document reader for reading image information of originals is arranged under this original placement table  21 . 
   Arranged below scanner portion  22  are light exposure unit  1 , developing unit  2 , photoreceptor drum  3 , charger  4 , charge erasing device  41 , cleaner unit  5 , fixing unit  6 , paper conveyor system  7 , paper feed path  7   a , paper output tray  9  and transfer device  10 . Further, paper feed tray  8  that accommodates paper P therein is arranged under these. 
   Light exposure unit  1  provides a function of emitting laser beam in accordance with the image data output from an unillustrated image processor to irradiate the photoreceptor drum  3  surface that has been uniformly electrified by charger  4  so as to write and form an electrostatic latent image corresponding to the image data on the photoreceptor drum  3  surface. This light exposure unit  1  is arranged directly under scanner portion  22  and above photoreceptor drum  3 , and includes laser scanning units (LSUs)  13   a  and  13   b  including laser emitters  11 ,  11  and a reflection mirror  12 . 
   In the present embodiment, in order to achieve high-speed printing operation, multiple laser beams from multiple laser emitters  11  are used to reduce the irradiation frequency of each laser beam (the processing load of each laser beam per unit time is reduced). More specifically, a two-beam technique using a pair of laser emitters  11  to emit two laser beams is adopted. 
   Here, in the present embodiment laser scanning units (LSUs)  13   a  and  13   b  are used for light exposure unit  1 , but an array of light emitting elements, e.g., an EL (electroluminescence) or LED (light-emitting diode) writing head may also be used. 
   Photoreceptor drum  3  has an approximately cylindrical shape, is arranged under light exposure unit  1  and is controlled so as to rotate in a predetermined direction (in the direction of arrow A in the drawing) by an unillustrated drive means and control means. Arranged along the peripheral surface of this photoreceptor drum  3 , starting from the position at which image transfer ends downstream in the rotational direction of the photoreceptor drum are, as shown in  FIG. 2 , a paper separation claw  31 , cleaner unit  5 , charger  4  as an electric field generator, developing unit  2  and charge erasing device  41  in the order mentioned. 
   Paper separation claw  31  is disposed so as to be moved into and out of contact with the outer peripheral surface of photoreceptor drum  3  by means of a solenoid  32 . When this paper separation claw  31  is put in abutment with the outer peripheral surface of photoreceptor drum  3 , it functions to peel off the paper P that has adhered to the photoreceptor drum  3  surface during the unfixed toner image on photoreceptor drum  3  being transferred to the paper P. 
   Here, as a drive means for paper separation claw  31 , a drive motor or the like may be used instead of solenoid  32 , or any other drive means may also be selected. 
   Developing unit  2  visualizes the electrostatic latent image formed on photoreceptor drum  3  with black toner, and is arranged at approximately the same level at the side (on the right side in the drawing) of photoreceptor drum  3  downstream of charger  4  with respect to the rotational direction of the photoreceptor drum (in the direction of arrow A in the drawing). A registration roller  15  is disposed under this developing unit  2  on the upstream side with respect to the recording medium feed direction. This developing unit  2  will be detailed later. 
   Toner feed device  30  temporarily holds the toner discharged from a toner container  300  filled with toner, in an intermediate hopper  33  and then supplies it to developing unit  2 . This toner feed device is arranged adjacent to developing unit  2 . 
   Registration roller  15  is operated and controlled by an unillustrated drive means and control means so as to convey the paper P delivered from paper feed tray  8  into and between photoreceptor drum  3  and a transfer belt  103  whilst making the leading end of the paper P register with the toner image on the photoreceptor drum  3 . 
   Charger  4  is a charging means for uniformly charging the photoreceptor drum  3  surface at a predetermined potential, and is arranged over photoreceptor drum  3  and close to the outer peripheral surface thereof. 
   Here, a discharge type charger  4  is used in the present embodiment, but a contact roller type or a brush type may be used instead. 
   Charge erasing device  41  is a pre-transfer erasing means for lowering the surface potential of the photoreceptor drum  3  in order to facilitate the toner image formed on the photoreceptor drum  3  surface to transfer to paper P, and is laid out on the downstream side of developing unit  2  with respect to the photoreceptor drum&#39;s direction of rotation and under photoreceptor drum  3  and close to the outer peripheral surface of the same. 
   Though in the present embodiment, charge erasing device  41  is configured using a charge erasing electrode, a charge erasing lamp or any other method can be used instead of the charge erasing electrode. 
   Cleaner unit  5  removes and collects the toner left on the surface of photoreceptor drum  3  after development and image transfer, and is disposed at approximately the same level at the side of photoreceptor drum  3  (on the left side in the drawing), on the approximately opposite side across photoreceptor drum  3  from developing unit  2 . 
   As described above, the visualized electrostatic image on photoreceptor drum  3  is transferred to the paper P being conveyed as transfer device  10  applies an electric field having an opposite polarity to that of the electric charge of the electrostatic image. For example, when the electrostatic image bears negative (−) charge, the applied polarity of transfer device  10  should be positive (+). 
   Transfer device  10  is provided as a transfer belt unit in which a transfer belt  103  having a predetermined resistivity (ranging from 1×10 9  to 1×10 13 Ω·cm in the embodiment) is wound and tensioned on a drive roller  101 , a driven roller  102  and other rollers, and is disposed under photoreceptor drum  3  with the transfer belt  103  surface put in contact with part of the outer peripheral surface of photoreceptor drum  3 . This transfer belt  103  conveys paper P while pressing the paper against photoreceptor drum  3 . 
   An elastic conductive roller  105  ( FIG. 2 ) having a conductivity different from that of drive roller  101  and driven roller  102  and capable of applying a transfer electric field is laid out at a contact point  104  ( FIG. 2 ) where transfer belt  103  comes into contact with photoreceptor drum  3 . 
   Elastic conductive roller  105  is composed of a soft material such as elastic rubber, foamed resin etc. Since this elasticity of elastic conductive roller  105  permits photoreceptor drum  3  and transfer belt  103  to come into, not line contact, but area contact of a predetermined width (called a transfer nip) with each other, it is possible to improve the efficiency of transfer to the paper P being conveyed. 
   Further, a charge erasing roller  106  for erasing the electric field that has been applied to the paper P being conveyed through the transfer area so as to achieve smooth conveyance of the paper to the subsequent stage is disposed on the interior side of transfer belt  103 , on the downstream side, with respect to the direction of paper conveyance, of the transfer area of transfer belt  103 . 
   As shown in  FIG. 2 , transfer device  10  also includes a cleaning unit  107  for removing dirt due to leftover toner on transfer belt  103  and a plurality of charge erasing devices  108  for erasing electricity on transfer belt  103 . Erasure of charge by erasing devices  108  may be performed by grounding via the apparatus or by positively applying charge of a polarity opposite to that of the transfer field. 
   The paper P with the static image (unfixed toner) transferred thereon by transfer device  10  is conveyed to fixing unit  6 , where it is pressed and heated so as to fuse the unfixed toner and fix it to the paper P. 
   Fixing unit  6  includes a heat roller  6   a  and a pressing roller  6   b  as shown in  FIG. 2  and fuses and fixes the toner image transferred on paper P by rotating heat roller  6   a  so as to convey the paper P held between heat roller  6   a  and pressing roller  6   b  through the nip therebetween. Arranged on the downstream side of fixing unit  6  with respect to the direction of paper feed is a conveyance roller  16  for conveying paper P. 
   Arranged on the downstream side of this conveyance roller  16  with respect to the direction of paper feed is a paper discharge roller  17  for discharging paper P to paper output tray  9 . 
   Heat roller  6   a  has a sheet separation claw  611 , a thermistor  612  as a roller surface temperature detector and a roller surface cleaning member  613 , all arranged on the outer periphery thereof and also includes a heat source  614  for heating the heat roller surface at a predetermined temperature (set fixing temperature: approximately 160 to 200 deg. C.) in the interior part thereof. 
   Pressing roller  6   b  is provided at its each end with a pressing element  621  capable of abutting the pressing roller  6   b  with a predetermined pressure against heat roller  6   a . In addition a sheet separation claw  622  and a roller surface cleaning element  623  are provided on the outer periphery of pressing roller  6   b , similarly to the outer periphery of heat roller  6   a.    
   In this fixing unit  6 , as shown in  FIG. 2  the unfixed toner on the paper P being conveyed is heated and fused by heat roller  6   a , at the pressed contact (so-called fixing nip portion)  600  between heat roller  6   a  and pressing roller  6   b , so that the unfixed toner is fixed to the paper P by the anchoring effect to the paper P by the pressing force from heat roller  6   a  and pressing roller  6   b.    
   As shown in  FIG. 1 , paper feed tray  8  stacks a plurality of sheets (paper) to which image information will be output (printed), and is arranged under image forming portion  14  made up of light exposure unit  1 , developing unit  2 , photoreceptor drum  3 , charger  4 , charge erasing device  41 , cleaner unit  5 , fixing unit  6  etc. A paper pickup roller  8   a  is disposed at an upper part on the paper output side of this paper feed tray  8 . 
   This paper pickup roller  8   a  picks up paper P, sheet by sheet, from the topmost of a stack of paper stored in paper feed tray  8 , and conveys the paper downstream (for convenience&#39; sake, the supply side of paper P (the cassette side) is referred to as upstream and the paper output side is referred to as downstream) to the registration roller (also called “idle roller”)  15  side in paper feed path  7   a.    
   Since the image forming apparatus  1 A according to the present embodiment is aimed at performing high-speed printing operations, a multiple number of paper feed trays  8  each capable of stacking 500 to 1500 sheets of standard-sized paper P are arranged under image forming portion  14 . Further, a large-capacity paper feed cassette  81  capable of storing multiple kinds of paper in large volumes is arranged at the side of the apparatus while a manual feed tray  82  for essentially supporting printing etc. for irregular sized paper is arranged over the large-capacity paper feed cassette  81 . 
   Paper output tray  9  is arranged on the opposite side across the apparatus from that of manual feed tray  82 . It is also possible to configure such a system that instead of paper output tray  9 , a post-processing machine for stapling, punching of output paper and the like and/or a multi-bin paper output tray etc., may be arranged as an option. 
   Paper conveyor system  7  is laid out between the aforementioned photoreceptor drum  3  and paper feed tray  8 , and conveys paper P supplied from paper feed tray  8 , sheet by sheet, by way of paper feed path  7   a  provided for paper conveyor system  7 , to transfer device  10 , where a toner image is transferred from photo receptor drum  3  to the paper, further conveying it to fixing unit  6  where the unfixed toner image is fixed to the paper, then conveys the sheet as it is being guided by paper feed paths and branch guides, in accordance with the designated paper output processing mode. 
   In the image forming apparatus  1 A according to the present embodiment, two predetermined output processing modes, namely, one-sided printing mode and two-sided printing mode are prepared. In one-sided printing mode, there are two ways of paper output, i.e., the faceup output by which the paper is discharged with its printed surface faceup and the facedown output by which the paper is discharged with its printed surface facedown. 
   Next, developing unit  2  and its peripheral components that constitute image forming apparatus  1 A according to the present embodiment will be described with reference to the drawings. 
     FIG. 3  is an overall side sectional view showing a developing unit and toner feed device that constitute the image forming apparatus according to the present embodiment. 
   In this embodiment, as shown in  FIG. 3 , toner feed device  30  is arranged adjacent to developing unit  2 . A duct  50  for sending air to a hopper  200  that forms the exterior of developing unit  2  is provided under this toner feed device  30  in order to forcibly remove heat arising during the operation of developing unit  2 . 
   Toner feed device  30  is arranged adjacent to developing unit  2 , and temporarily reserves the toner discharged from toner container  300  filled with toner, in intermediate hopper  33  and then feeds the toner to developing unit  2 . In the present embodiment, toner container  300  is configured so that a container body  310  charged with toner is rotatably supported by a supporting structure  350 . 
   The toner thus sent out to intermediate hopper  33  is agitated therein by an agitator  34  first. Agitator  34  is composed of an agitator shaft  34   a  and agitating vanes  34   b  attached thereto. As agitator shaft  34   a  turns, agitating vanes  34   b  rotate about agitator shaft  34   a  to thereby agitate the toner in intermediate hopper  33  that has been fed from toner container  300 . 
   The toner thus agitated by agitator  34  is sent by the agitating action of agitator  34  and conveyed to the feed roller  36  side via a conveying roller  35 . Feed roller  36  sends out the toner that has been conveyed from agitator  34  via conveying roller  35 , to an opening  30   a  that is formed at the position where intermediate hopper  33  abuts developing unit  2 , to thereby supply the toner to developing unit  2 . 
   Provided on the bottom side (the underside when toner container  300  is mounted on image forming apparatus  1 A) of supporting structure  350  of toner container  300  is a shutter opening and closing mechanism  400  for opening and closing a toner feed aperture  300   a  through which toner supplied from toner container  300  is discharged out of supporting structure  350 , as shown in  FIG. 3 . Specifically, as toner feed aperture  300   a  of supporting structure  350  is released by shutter opening and closing mechanism  400 , communication between toner feed aperture  300   a  and opening  33   a  provided for intermediate hopper  33  is established, so that the toner discharged from toner container  300  is supplied to intermediate hopper  33 . 
   Next, the characteristic configuration of developing unit  2  according to the present embodiment will be described in detail with reference to the drawings. 
     FIG. 4  is a sectional view showing the configuration of the developing unit according to the present embodiment;  FIG. 5A  is a side sectional view showing a configuration of a mixing roller that constitutes the developing unit;  FIG. 5B  is a sectional view cut along a plane B 1 -B 1 ′ in  FIG. 5A ;  FIG. 5C  is a sectional view cut along a plane B 2 -B 2 ′ in  FIG. 5A ;  FIG. 5D  is a sectional view cut along a plane B 3 -B 3 ′ in  FIG. 5A ; and  FIG. 5E  is a sectional view cut along a plane B 4 -B 4 ′ in  FIG. 5A . 
   As shown in  FIG. 4 , developing unit  2  includes hopper  200  forming its exterior, and a toner input port  201  for leading toner is formed in this hopper  200  at a position where opening  30   a  ( FIG. 3 ) provided for toner feed device  30  to deliver toner abuts the hopper  200 . This hopper  200  reserves the developer therein and incorporates developer roller  202 , a paddle roller  203 , a mixing roller  204 , a conveying roller  205 , a regulating member  207  and collecting roller  220 . 
   Developing unit  2  is mounted inside image forming apparatus  1 A in such a manner that the peripheral surface (the developer adhering on the peripheral area) of developing roller  202  that is partly exposed from hopper  200  opposes in proximity to the peripheral surface of photoreceptor drum  3 . That is, the peripheral surface area of developing roller  202  opposing photoreceptor drum  3  forms the developing position (developing area). 
   In hopper  200 , the toner that was fed from toner feed device  30  ( FIG. 3 ) and input through toner input port  201  is conveyed by conveying roller  205  to mixing roller  204 , where the toner is mixed with a magnetic carrier to thereby prepare a dual-component developer. Mixing roller  204  mixes the aforementioned newly formed dual-component developer with the existing developer inside hopper  200 . The developer obtained by mixing with mixing roller  204  is tribo-electrified as it is agitated by paddle roller  203 , then supplied to developing roller  202  for developing electrostatic latent images, and conveyed by developing roller  202  to the electrostatic latent image formed on photoreceptor drum  3 . The developer supplied to developing roller  202  and conveyed thereby is controlled as to its layer thickness by regulating member  207  that is supported by a supporting member  212  as a part of hopper  200 . In this way, the supplied amount of developer to be supplied to photoreceptor drum  3  is regulated. 
   Hopper  200  is made of a metallic material having a high thermal conductivity such as aluminum as a countermeasure against increase in temperature inside developing unit  2 , and has an approximately prism-shaped configuration having an opening  200   a  ( FIG. 3 ) facing (opposing) the peripheral surface of photoreceptor drum  3  and also having toner input port  201  for leading toner, formed at a position in abutment with opening  30   a  provided for toner feed device  30  to deliver toner. 
   Provided on the upper outside part of supporting member  212  that forms the top of hopper  200  is a pressure relief mechanism  217  for reducing the pressure inside hopper  200 . This pressure relief mechanism  217  is periodically operated to release the pressure inside developing unit  2  so that toner scattering inside the apparatus can be prevented. 
   Developing roller  202  is arranged at the position inside hopper  200  where opening  200   a  is formed while conveying roller  205  that conveys the developer (toner) supplied from toner input port  201  into hopper  200  to mixing roller  204  is disposed rotatably at a position that opposes toner input port  201 . 
   A toner concentration sensor  213  for detecting the toner concentration inside hopper  200  is provided at the bottom opposing the lower side of mixing roller  204  in hopper  200  and somewhat closer to the photoreceptor drum  3  side. Image forming apparatus  1 A is configured so as to supply toner from toner input port  201  based on the measurement of toner concentration sensor  213  when the amount of toner being mixed and agitated by mixing roller  204  becomes lower than the proper amount. 
   Arranged adjacent to and below developing roller  202  is collecting roller  220  for collecting the developer leaving developing roller  202 . 
   Developing roller  202  is arranged a development gap (about 0.5 to 1.5 mm) apart from photoreceptor drum  3  as shown in  FIG. 4 . Developing roller  202  is formed of a magnet roller  214  with multiple magnetic poles and a non-magnetic sleeve  215  that is approximately cylindrically formed of an aluminum alloy, brass or the like and is arranged rotatably over, and relative to the magnet roller  214 . In this magnetic roller  214 , a plurality of bar magnets having rectangular sections, specifically magnetic pole elements N 1  and N 2  providing N-pole magnetic fields and magnetic pole elements S 1 , S 2  and S 3  providing S-pole magnetic fields, are radially arranged apart one from another in the order shown in  FIG. 4 . 
   Magnet roller  214  is unrotatably supported and fixed at its both ends by the side walls of hopper  200 . Magnetic pole element N 1  is disposed at a position opposing the peripheral surface of photoreceptor drum  3 . 
   The chained line designated at P 1  of magnetic pole element N 1  represents the center of the width of the magnetic pole element N 1  or the central axis of the magnetic pole, with respect to the circumferential direction of developing roller  202 . Similarly, the chained line P 2  of magnetic pole element N 2  represents the center of the width of the magnetic pole element N 2  or the central axis of the magnetic pole. These magnetic pole&#39;s center axes P 1  and P 2  are radially extended from the developing roller&#39;s central axis O 2  and formed across the full length of the magnet elements (across the length of sleeve  215 ). The magnetic pole element N 1  that opposes the peripheral surface of photoreceptor drum  3  is positioned so that the magnetic pole&#39;s center axis P 1  substantially coincides with the line (plane) that passes through both the center axis of photoreceptor drum  3  and the center axis of developing roller  202 . 
   The above magnetic pole elements are laid out in the order of N 1 , S 3 , S 2 , N 2  and S 1  in the rotational direction of developing roller  202 . The magnetic field created by the thus arranged magnetic pole elements N 1 , N 2 , S 1 , S 2  and S 3 , attracts the dual-component developer particles made of toner and carrier to rotating sleeve  215  so as to form brush-like spikes (to be referred as magnetic brush) extending in the circumferential direction of the sleeve. As the photoreceptor drum  3  rotates, the photoreceptor drum  3  surface is rubbed in the above-mentioned development gap area by the magnetic brush created on rotating developing roller  202  to thereby achieve development. 
   Regulating member  207  controls the amount of the developer conveyed between itself and developing roller  202  while performing principal electrification of the developer, and is formed of a non-magnetic metal plate having an approximately rectangular section. One end of regulating member  207  opposes the outer peripheral surface of developing roller  202  (sleeve  215 ) with a gap G 1  in between. 
   Regulating member  207  is disposed inside opening  200   a  of hopper  200  and between magnetic pole elements S 1  and N 2  and fixed to opening  200   a  by a cover element  216  that is attached to regulating member  207 . This regulating member  207  is formed of a non-magnetic metal plate such as aluminum, stainless steel or the like. 
   Mixing roller  204  agitates and conveys the toner supplied from toner feed device  30  ( FIG. 3 ) as shown in  FIG. 5A  and is comprised of a rotary shaft  204   a  arranged substantially parallel to developing roller  202  ( FIG. 4 ) and a plurality of separate plate-like agitating elements  204   b  ( 204   b   1  to  204   b   4 ). 
   Agitating elements  204   b  are arranged inclined at an angle of approximately 45 degrees with the direction in which the axis of rotary shaft  204   a  extends (to be referred to as the axial direction). Agitating elements  204   b  include agitating element  204   b   3  disposed at the approximate center, with respect to the axial direction, of rotary shaft  204   a , a group  204 B 1  of an agitating element  204   b   1  and multiple agitating elements  204   b   2  arranged on the right side in the drawing and a group  204 B 2  of an agitating element  204   b   4  and multiple agitating elements  204   b   2  arranged on the left side in the drawing. Here, agitating elements  204   b   1  and  204   b   4  are disposed at both ends with respect to the axial direction of rotary shaft  204   a.    
   In the present embodiment, group  204 B 1  includes as many agitating elements  204   b   2  as group  204 B 2  does. That is, mixing roller  204  has an odd number of agitating elements  204   b . Thus, provision of an odd number of agitating elements  204   b  enables the developer to be conveyed and agitated in one specified direction by making the developer flow off-balance as a whole. 
   As shown in  FIGS. 5B and 5E , agitating elements  204   b   1  and  204   b   4  arranged at both ends of rotary shaft  204   a  have approximately semicircular shapes which are point symmetrical with respect to rotary axis  204   a . Detailedly, agitating elements  204   b   1  and  204   b   4  each have a hemi-elliptic shape by cutting an elliptic shape having a major axis L 1  passing through rotary axis  204   a  in half along the line that is substantially perpendicular to the major axis L 1 . 
   A plurality of agitating elements  204   b   2  are provided between agitating element  204   b   3  and agitating element  204   b   1  and between agitating element  204   b   3  and agitating element  204   b   4 , each being inclined with the axial direction of rotary shaft  204   a  and having a substantially elliptic shape, as shown in  FIG. 5C . With this configuration, it is possible to make each agitating element produce a stronger conveying force in the direction of the rotary axis. 
   Agitating element  204   b   3  arranged at the substantially center of rotary shaft  204   a  has a substantially elliptic shape having a cutout portion  204   c  at the position opposing the aforementioned toner concentration sensor  213  as shown in  FIG. 5D , so that light for detection from toner concentration sensor  213  is permitted to pass through. Another cutout portion  204   c  is formed in the agitating element at a position point symmetrical, with respect to the center of rotary axis  204   a , to the position of the aforementioned cutout. That is, a pair of cutout portions  204   c  are formed at positions point symmetrical to each other with respect to the center of rotary axis  204   a . Thus, this configuration of agitating element  204   b   3  makes it possible to prevent output ripples from occurring at toner concentration sensor  213  due to developer&#39;s volume density change which would occur as agitating element  204   b  of mixing roller  204  rotates. 
   Arranged between developing roller  202  and mixing roller  204 , as shown in  FIG. 4  is paddle roller  203 , which agitates and electrifies the developer that was prepared by mixing of mixing roller  204  to supply the developer to developing roller  202 . 
   Paddle roller  203  is formed with a supporting shaft extending longitudinally and a plurality of flat plate-like blades radially extending from the supporting shaft so that the blades can rotate about the supporting shaft. As paddle roller  203  rotates about the supporting shaft, the developer can be agitated. 
   As the characteristic configuration in the developing unit  2 , collecting roller  220  for collecting the developer falling from the developing area of developing roller  202  and developer removing device (developer remover)  230  for removing the developer collected by collecting roller  220  from collecting roller  220  are arranged under the developer roller  202 . 
   Collecting roller  220  has a plurality of magnetic poles fixedly arranged with a predetermined gap relative to developing roller  202 . The collecting roller is arranged downstream of the developing area of the developing roller  202  with respect to the rotational direction of photoreceptor drum  3 , and is rotationally driven against the rotational direction of photoreceptor drum  3 . 
   Next, developer removing device  230  which is the characteristic component of developing unit  2  of the present embodiment will be described in detail with reference to the drawings. 
     FIG. 6A  is a sectional view showing a configuration of a developer removing device that constitutes the developing unit of the present embodiment;  FIG. 6B  is an illustrative view for illustrating the operation of a scraper and scraper supporter that constitute the developer removing device;  FIG. 7A  is a plan view, viewed in the direction of arrow C, showing a casing that constitutes the developer removing device shown in  FIG. 6A ;  FIG. 7B  is a plan view showing the casing, viewed in the direction of arrow D in  FIG. 7A ;  FIG. 8  is a plan view showing the configuration of the scraper;  FIG. 9  is a perspective view showing the configuration of the scraper supporter;  FIG. 10A  is an illustrative view showing amounting operation of the casing and scraper; and  FIG. 10B  is a sectional view showing a state where the casing and scraper are mounted in place. 
   (Developer Removing Device  230 ) 
   As shown in  FIG. 6A , developer removing device  230  is comprised of a casing  240  for holding collecting roller  220 , a scraper  250  for removing the developer adhering on the outer periphery of collecting roller  220  and a scraper supporter  260  for supporting scraper  250 , and is constructed so that scraper supporter  260  holds scraper  250  by pressing the scraper against casing  240 . 
   (Casing  240 ) 
   Casing  240  has an approximately U-shaped section as shown in  FIG. 6A , and is essentially contracted of, as shown in  FIGS. 7A and 7B , a pair of collecting roller supporters  241  for rotatably holding collecting roller  220 , a scraper supporting part (first scraper supporting part)  242  for supporting scraper  250 , a scraper supporter attachment (first attachment part)  243  to which scraper supporter  260  is attached and a bottom part  244 . 
   (Collecting Roller Supporter  241 ) 
   Collecting roller supporters  241  are formed by bending both ends of casing  240  at right angles with the direction in which the axis of collecting roller  220  extends (to be referred to as the axial direction) ( FIG. 7A ). Collecting roller supporters  241  are integrally formed with casing  240 . Collecting roller supporters  241  position collecting roller  220  relative to hopper  200  of developing unit  2 . 
   Collecting roller supporters  241  are provided with resinous bearings  270  which provide self-lubricating properties, so as to axially support both ends of the shaft, designated at  221 , of collecting roller  220  in a rotatable manner by means of these bearings  270 . 
   Collecting roller supporter  241  is formed with an attachment hole  241   a  and an attachment access  241   b.    
   Bearing  270  ( FIGS. 6A and 6B ) has a roughly, cylindrical shape and holds shaft  221  of collecting roller  220  by its hollow part. Bearing  270  is positioned to collecting roller supporter  241  by inserting its outer periphery  271  through attachment access  241   b  of collecting roller supporter  241  into attachment hole  241   a  and fitting therein. Illustratively, this periphery  271  is defined with a pair of semi-cylindrical surfaces and a pair of attachment facets  272  and  272  formed parallel to each other along the bearing  270 &#39;s axis (the same axis as that of collecting roller  220 ). 
   Attachment hole  241   a  is a through hole having substantially the same diameter as the diameter (major axis) of circumferential periphery  271  of bearing  270 . However, the attachment hole is not limited to this. That is, it may be a blind hole that is closed on the collecting roller supporter  241 &#39;s end side. 
   Attachment access  241   b  is a cutout portion for allowing bearing  270  to be inserted from the circumferentially outside of attachment hole  241   a  into attachment  241   a . This attachment access  241   b  may also be a blind cutout that is closed on the collecting roller supporter  241 &#39;s end side. 
   The open width W 2  of attachment access  241   b  and the distance W 1  (minor axis) between flat attachment facets  272  and  272  of bearing  270  are specified so that “open width W 2 ≧distance W 1 ” holds. 
   (Scraper Supporting Part  242 ) 
   As shown in  FIGS. 7A and 7B , scraper supporting part (first scraper supporting part)  242  is formed with a pair of scraper positioning portions (first and second scraper positioning projections)  242   a  and  242   b  that are circularly projected inwards of casing  240  by so-called half-punching and position scraper  250  at both the longitudinal ends of scraper supporting part  242 . 
   (Scraper Supporter Attachment  243 ) 
   Scraper supporter attachment  243  is affixed with its outside surface positioned and fixed to the hopper  200  side (developer unit body side) as shown in  FIGS. 7A and 7B . 
   Scraper supporter attachment (first attachment part)  243  is formed with a pair of scraper supporter positioning portions (first and second scraper supporter positioning projections)  243   a  and  243   b  that are circularly projected inwards of casing  240  by so-called half-punching and position the scraper supporter at both the longitudinal ends of scraper supporter attachment  243 . 
   (Scraper  250 ) 
   As shown in  FIGS. 6A and 8 , scraper  250  is arranged elongated along the axial direction of collecting roller  220  with its distal end abutted against the outer peripheral surface of collecting roller  220  in a counter manner by its elastic deformation (flexible deformation) so as to scrape down the carrier particles that dropped from the developing area and have been captured by the collecting roller  220  surface by the magnetic attraction of collecting roller  220  and return the collected carrier to hopper  200 . 
   In the present embodiment, scraper  250  is comprised of a plate-like blade  251  and a holder  252  that supports the blade  251  and also functions as a reinforce. The blade  251  and holder  252  are integrally laminated in their longitudinal direction with blade  251  exposed on its one side edge (the side edge to be abutted against collecting roller  220 ). 
   (Blade  251 ) 
   Blade  251  is formed of a stainless sheet of 0.1 mm thick, and has a pair of holes, i.e., a circular fitting hole (the first scraper-side engaging portion)  251   a  ( FIG. 8 ) and an elongated (elliptic shaped) fitting hole (the second scraper-side engaging portion)  251   b  ( FIG. 8 ) extended in the longitudinal direction of blade  251  as the engaging portions (scraper-side engaging portions) corresponding to scraper positioning portions  242   a  and  242   b , respectively. Fitting hole  251   b  is formed in such a shape as to allow scraper positioning portion  242   b  to be moved (adjusted in position) with respect to the longitudinal direction of scraper supporting part  242  or blade  251 . 
   That is, blade  251  is exactly positioned by fitting circular fitting hole  251   a  to one of scraper positioning portions,  242   a  while elongated fitting hole  251   b  is fitted to the other scraper positioning portion  242   b . Formation of fitting hole  251   b  as an elongated hole makes it possible to make an adjustment in position in the longitudinal direction when fitting hole  251   b  is engaged with scraper positioning portion  242   b  even if the attachment position gets out of place due to shaping accuracy, shape errors and the like. As a result, it is possible to ensure the mounting of blade  251  to scraper positioning portions  242   a  and  242   b.    
   (Holder  252 ) 
   Holder  252  is formed of a stainless sheet of 1 mm thick, and has through holes  252   a  and  252   b  formed at the positions opposing fitting holes  251   a  and  251   b  of blade  251  as shown in  FIG. 8 . Through holes  252   a  and  252   b  are formed to be greater in diameter than fitting holes  251   a  and  251   b  so as not to interfere with scraper positioning portions  242   a  and  242   b  to be fitted to the fitting holes  251   a  and  251   b . Further, as shown in  FIGS. 6A ,  10 A and  10 B, the edges, of holder  252 , extending along the longitudinal direction (the axial direction of collecting roller  220 ), located on the opposite side (the surface side) from the holder  252 &#39;s attachment surface to which blade  251  is attached are beveled at approximately 45 degrees by forming edge portions  252   c . Though edge portion  252   c  has the effect as describe below when scraper  250  is attached to casing  240 , it is not necessarily formed. If edge portions  252   c  are formed, it is good enough if at least the edge that is located on the front side of the holder with respect to the direction in which scraper  250  is attached to casing  240 , or on the side that will touch scraper supporter  260  when scraper  250  is mounted to casing  240  ( FIGS. 10A and 10B ) is beveled. 
   (Scraper Supporter  260 ) 
   Scraper supporter (supporter)  260  has an approximately J-shaped section as shown in  FIG. 6A . Further, as shown in  FIG. 9 , the scraper supporter is formed elongated along scraper  250  and is formed along its longitudinal direction with an attachment surface (second attachment part)  261  and a supporting surface (second scraper supporting part)  262 . 
   Attachment surface  261  is attached to scraper supporter attachment  243  in casing  240 . 
   Supporting surface  262  positions and holds scraper  250  with casing  240  by pressing scraper  250  against scraper supporting part  242  along the axial direction of the collecting roller  220  (the longitudinal direction of scraper). 
   In the present embodiment, scraper supporter  260  is formed of a material for leaf spring in such a shape that when attachment surface  261  is affixed to casing  240 , the supporting surface  262  uniformly presses scraper  250  across the axial length of collecting roller  220 . Accordingly, scraper  250  is urged toward scraper supporting part  242  by scraper supporter  260 . 
   (Supporting Surface  262 ) 
   As shown in  FIG. 6B , supporting surface  262  is set at a position designated at Q in the drawing when scraper  250  is not mounted. That is, it is located closer to scraper supporting part  242  than it is located at the position designated at P in the drawing when scraper  250  is mounted properly. In other words, scraper  250  is mounted between supporting surface  262  and scraper supporting part  242 , opposing the elastic force of supporting surface  262  so that scraper  250  is supported by scraper supporter  260  by the elastic force that is generated by the displacement of supporting surface  262  (the displacement from position Q to position P). 
   Further, supporting surface  262  is bent (curved) on the free end side across its full length so that its distal end  262   a  ( FIG. 9 ) extends in the opposite direction of scraper  250 . Since this configuration enhances the rigidity of the distal end  262   a  (free end), supporting surface  262  is able to press scraper  250  uniformly with respect to the axial direction of collecting roller  220 . As a result, it is possible to uniformly abut scraper  250  against collecting roller  220  across the full length thereof without causing any deformation in scraper  250  with respect to the axial direction of collecting roller  220 . This configuration of distal end  262   a  also contributes to facilitating insertion of scraper  250 . 
   (Attachment Surface  261 ) 
   On the other hand, formed on attachment surface  261  (second attachment part) of scraper supporter  260  as the engaging portions (supporter side engaging portions) corresponding to scraper supporter positioning portions  243   a  and  243   b  are a pair of holes, i.e., a circular fitting hole (the first supporter-side engaging portion)  261   a  and an elongated (elliptic shaped) fitting hole (the second supporter-side engaging portion)  261   b  extended in the longitudinal direction of the scraper supporter  260 . Fitting hole  261   b  is formed in such a shape as to allow scraper supporter positioning portion  243   b  to be moved (adjusted in position) with respect to the longitudinal direction of scraper supporter attachment  243  or blade  251 . 
   That is, attachment surface  261  is exactly positioned by fitting circular fitting hole  261   a  to one of scraper supporter positioning portions,  243   a  while elongated fitting hole  261   b  is fitted to the other scraper supporter positioning portion  243   b . Formation of fitting hole  261   b  as an elongated hole makes it possible to make an adjustment in position in the longitudinal direction when fitting hole  261   b  is engaged with scraper supporter positioning portion  243   b  even if the attachment position gets out of place due to shaping accuracy, shape errors and the like. As a result, it is possible to ensure the attachment of attachment surface  261  of scraper supporter  260  to scraper supporter positioning portions  243   a  and  243   b.    
   Further, attachment surface  261  is fixed to scraper supporter attachment  243  along its length by spot-welding at five spots SP. In the present embodiment, since scraper supporter  260  is bent forming an L-shaped curved portion across its full length between attachment surface  261  and supporting surface  262  while front end  262   a  of supporting surface  262  is flexed so as to enhance rigidity, the influence from the stress concentration generated by spot welding at five spots SP can be eliminated. As a result, it is possible to uniformly press and support scraper  250  by making supporting surface  262  uniformly flex and deform. 
   Next, the mounting of developer removing device  230  ( FIGS. 6A and 6B ) according to the present embodiment will be described. 
   First, when scraper supporter  260  is attached to casing  240 , attachment surface  261  of scraper supporter  260  is placed along scraper supporter attachment  243  ( 243   a ,  243   b ) of casing  240 , as shown in  FIGS. 7B and 9 . 
   Then, the circular fitting hole  261   a  of attachment surface  261  is fitted on scraper supporter positioning portion  243   a  of scraper supporter attachment  243 , to thereby position one end side. Thereafter, elongated fitting hole  261   b  is fitted onto scraper supporter positioning portion  243   b  to thereby position scraper supporter  260  to casing  240 . Then, scraper supporter  260  is fixed to casing  240  by spot welding SP. 
   Next, to mount scraper  250  to casing  240 , front end  262   a  of supporting surface  262  of scraper supporter  260  is brought away from casing  240  by opposing the elastic force so that scraper  250  is interposed between casing  240  and supporting surface  262  of scraper supporter  260 . 
   At this time, scraper  250  is set with its blade  251  side opposing scraper supporting part  242  of casing  240 , as shown in  FIGS. 6A and 6B . Then, as shown in  FIGS. 10A and 10B , circular fitting hole  251   a  formed in blade  251  is fitted onto scraper positioning portion  242   a  of scraper supporting part  242  to thereby position one end side. Thereafter, elongated fitting hole  251   b  is fitted onto scraper positioning portion  242   b  to thereby position scraper  250  to casing  240 . Thus, scraper  250  is held and positioned by the elastic force of supporting surface  262  of scraper supporter  260 . 
   Next, when collecting roller  220  is mounted to casing  240 , each bearing  270  is fitted into corresponding attachment hole  241   a  with its attachment facets  272  (having a shorter size W 1 ) in alignment with opening W 2  of attachment access  241   b  ( FIG. 7A ) of collecting roller supporter  241  of casing  240 . Then, the bearing  270  is rotated so as to shift the short-sized portion W 1  away from the opening W 2  to thereby match the semi-cylindrical surfaces of periphery  271  of bearing  270  with the circular part of attachment hole  241   a.    
   As described above, it is possible to construct developer removing device  230  as an integrated structure by assembling collecting roller  220  and scraper  250 , which are prepared separately, into casing  240 . 
   Since, as constructed above it is not only possible to assemble collecting roller  220  and scraper  250  simply and exactly with a simple structure, but also make scraper  250  abut uniformly and stably against collecting roller  220 , the developer that drops from the developing area can be reliably collected by collecting roller  220  and the developer collected by collected roller  200  can be efficiently removed by developer removing device  230 . 
   Further, according to the present embodiment, casing  240 , scraper  250  and scraper supporter  260  are constructed so that they can be assembled without using any screw fastening or the like as described above, collecting roller  220  and scraper  250  can be fixed simply and exactly and can be assembled and disassembled by one-touch handling. As a result, it is possible to markedly improve workability and maintenance performance. 
   Further, according to the present embodiment, since a beveled surface is formed as edge portion  252   c  at the front end of holder  252  that is inserted first, and since the distal end  262   a  of scraper supporter  260  is bent at a predetermined angle so that the front end  262   a  of scraper supporter  260  always spreads open and outwards (is set floated), upon insertion of scraper  250  into and between casing  240  the other side surface  262  of scraper supporter  260  can be spread open easily when edge portion  252   c  of holder  252  abuts front end  262   a  of scraper supporter  260 , it hence is possible to insert scraper  250  easily. 
   Also, according to the present embodiment, since use of a leaf-spring material for scraper supporter  260  provides a clipping function to nip holder  252 , it is possible to press and fix scraper  250  to casing  240  in a simple manner. 
   Further, according to the present embodiment, since the supporting surface  262  of scraper supporter  260  is adapted to come into area contact with holder  252  of scraper  250 , the scraper  250  can be uniformly pressed against casing  240  by scraper supporter  260 . 
   Though in the present embodiment the bent portion formed between attachment surface  261  and supporting surface  262  of scraper supporter  260  is approximately J-shaped so that the flat portion of supporting surface  262  abuts the top surface of holder  252 , the bent shape of scraper supporter  260  of the present invention is not limited to this. 
   As a variational example of the present embodiment, the bent portion between an attachment surface  361  and supporting surface  362  of a scraper supporter  330  may be formed in an approximately L-shape, as shown in  FIG. 11 . Here, in  FIG. 11 , description of the other components having the same configurations as those in developer removing device  230  of the above-described embodiment is omitted by allotting the same reference numerals. 
   Further, though, in the present embodiment, the positioning of scraper  250  is done by forming projections as scraper positioning portions  242   a  and  242   b  by half-punching the scraper supporting part  242  of casing  240 , the present invention should no be limited to this. That is, projections may be formed on the scraper supporter side to position scraper  250 . A variational example of the present embodiment will be described below. 
     FIG. 12  shows a variational example of the present embodiment. Though not illustrated, a scraper supporter  460  is positioned and fixed to a casing  440 . In this case, a scraper  450  may be positioned to scraper supporter  460  as follows. That is, in scraper supporter  460 , a pair of fitting portions  460   a  (scraper positioning portions: first and second scraper positioning projections) are formed in the area where the scraper supporter abut a holder  452  of a blade  451  of scraper  450 , at both ends in its length. In holder  452 , a pair of fitting holes  452   a  (scraper side engaging portions) are formed at the positions corresponding to the above two fitting portions  460   a . In this arrangement, one fitting portion  460   a  is fitted to corresponding fitting hole  452   a  (first scraper side engaging portion), then the other fitting portion  460   a  is engaged with its corresponding fitting hole  452   a  (second scraper side engaging portion) in a position-adjustable manner as in the above embodiment. Since it is possible with this configuration to integrally position scraper  450  with scraper supporter  460  with a simple manner, mounting of scraper  450  into casing  440  can be made easy. Here, it should be noted that the positioning accuracy between scraper  450  and casing  440  becomes prone to be affected by the bending accuracy of scraper supporter  460  and the shaping accuracy of fitting portions  460   a.    
   Having described preferred embodiments of the present invention, it goes without saying that the present invention should not be limited to the above-described examples, and it is obvious that various changes and modifications will occur to those skilled in the art within the scope of the appended claims. Such variations are therefore understood to be within the technical scope of the present invention. 
   For example, in the above-described embodiment, the present invention is applied to an image forming apparatus including a monochrome developing unit, but the present invention can be also be applied to a color image forming apparatus including a plurality of developing units.