Patent Publication Number: US-7720430-B2

Title: Image forming apparatus

Description:
BACKGROUND 
   1. Field 
   The present invention relates to an image forming apparatus. 
   2. Related Art 
   Heretofore, in a laser printer, there has been provided a configuration wherein an electrically conductive member is disposed on the side of the non-image-forming surface of paper (a recording medium) in the conveyance path between transfer member and fixation member. A patent document JP-A-2002-328552, for example, discloses a configuration wherein the electrically conductive member (conveyance metal plate) which is earthed (grounded) to a conveyance guide (guide member) arranged on the side of the non-image-forming surface is disposed. According to the configuration, an appropriate potential difference can be established between the paper (recording medium) charged during transfer and the conveyance guide (guide member) arranged on the side of the non-image-forming surface of the paper, so that the paper can be stably conveyed. 
   Meanwhile, in the field of image forming apparatuses, a request for the reduction of a size has been more eagerly made at present. When the reduction of the size of the whole apparatus is to be realized for the purpose of meeting the request, various components need to be arranged more densely, and various members concentrate also in the vicinity of a conveyance path which is constructed between transfer member and fixation member. In such a situation, when the various members are charged, there is the problem that the behavior of the recording medium being conveyed cannot be stably controlled by the prior-art configuration wherein only the members on the side of the non-image-forming side of the recording medium are merely grounded. More specifically, in the case where the reduction of the size is intended, not only the members on the side of the non-image-forming surface of the recording medium, but also the members on the side of the image forming surface thereof need to be arranged nearer to the recording medium being conveyed, and hence, the problem occurs anew that the charging of the members on the side of the image forming surface become liable to exert influence on the behavior of the recording medium. 
   SUMMARY 
   The present invention provides an image forming apparatus having a configuration in which the charging of members disposed on the side of the image forming surface of a recording medium, between transfer member and fixation member, can be restrained from acting on the recording medium, so as to stably control the behavior of the recording medium. 
   An image forming apparatus includes: an image carrier that carries a developer image; a transfer member that transfers the developer image carried on the image carrier onto an image forming surface of a recording medium being conveyed; a fixation member that is disposed downstream of the transfer member in a conveyance direction of the recording medium, and fixes the developer image transferred on the recording medium; a first member that is disposed between the transfer member and the fixation member to face the image forming surface of the recording medium; and a second member that is disposed between the transfer member and the fixation member to face a non-image forming surface that is opposite the image forming surface, wherein the first member is provided with a first electrically-conductive member having an electric conductivity and being grounded. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
       FIG. 1  is a side sectional view of essential portions showing one configuration of a laser printer according to a first embodiment of the image forming apparatus; 
       FIG. 2  is a plan view showing the part of a process cartridge except a development cartridge; 
       FIG. 3  is a side view of the part shown in  FIG. 2 ; 
       FIG. 4  is a perspective view showing the arrangement of the process cartridge, a duct and a guide member in the laser printer; 
       FIG. 5  is a perspective view showing a configuration in the vicinity of a duct portion; 
       FIG. 6  is a perspective view showing a state where a first electrically-conductive member has been detached from the duct portion; 
       FIG. 7  is a perspective view showing the arrangement of the process cartridge, the duct, the guide member and one frame of an apparatus body in the laser printer; 
       FIG. 8  is a plan view showing the arrangement of the process cartridge, the duct and the guide member; 
       FIG. 9  is a sectional view showing sectional plane IX-IX shown in  FIG. 8 ; 
       FIG. 10  is a sectional view showing sectional plane X-X shown in  FIG. 8 ; 
       FIG. 11  is a view of the process cartridge as seen from the back surface side thereof; 
       FIG. 12A  is a view of the process cartridge as seen from the side of a fixation portion, while  FIG. 12B  is an explanatory diagram for conceptually explaining the behavior of the rear end part of a conveyance sheet of paper at the end part of the process cartridge; 
       FIG. 13  is an explanatory view for explaining the positional relationship of various members by using an enlarged view in which part of  FIG. 10  is enlarged; 
       FIG. 14  is a model view showing part of  FIG. 9  on enlarged scale and in rough-overview manner; 
       FIG. 15  is a plan view showing the guide member; 
       FIG. 16  is a perspective view showing the guide member; 
       FIG. 17  is a perspective view showing a state where a second electrically-conductive member has been detached from the guide member; 
       FIG. 18  is a side sectional view of essential portions exemplifying a laser printer according to a second embodiment; 
       FIG. 19  is a perspective view showing the vicinity of a guide member which is employed in the laser printer in  FIG. 18 ; 
       FIG. 20  is a perspective view showing a state where a second electrically-conductive member and a charge removal brush have been detached from the configuration in  FIG. 19 ; 
       FIG. 21  shows a configuration obtained by modifying the configuration in  FIG. 13 , and is an enlarged view showing the sections of the essential portions of the laser printer in  FIG. 18 , on enlarged scale; and 
       FIG. 22  shows a modification to the configuration in  FIG. 14 , and is an explanatory view for explaining the position of the charge removal brush in the laser printer in  FIG. 18 . 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   Embodiment will be described below with reference to the drawings. 
   First Embodiment 
   A first embodiment of the present invention will be described. 
   First, the general configuration of a laser printer according to the first embodiment will be described with reference to  FIGS. 1 through 4 .  FIG. 1  is the side sectional view of essential portions showing one embodiment of a laser printer which is the image forming apparatus of the invention.  FIG. 2  is a plan view showing the part of a process cartridge except a development cartridge, and  FIG. 3  is the side view of the part. Besides,  FIG. 4  is a perspective view showing the arrangement of the process cartridge, a duct and a guide member in the laser printer. 
   The laser printer  1  includes a body casing  2 , and a feeder section  4  for feeding paper  3  as a recording medium, an image formation section  5  for forming an image on the fed paper  3 , which are accommodated in the body casing  2 . 
   An attachment/detachment opening  6  for attaching and detaching the process cartridge  20  to be stated below is formed in the sidewall of one side of the body casing  2 , and a front cover  7  for opening and closing the attachment/detachment opening  6  is provided. The front cover  7  is turnably supported on a cover shaft (not shown) which is inserted through the lower end part thereof. Thus, when the front cover  7  is closed about the cover shaft, the attachment/detachment opening  6  is closed by the front cover  7  as shown in  FIG. 1 , and when the front cover  7  is opened (inclined down) with the cover shaft as a fulcrum, the attachment/detachment opening  6  is opened, and the process cartridge  20  can be attached to or detached from the body casing  2  through the attachment/detachment opening  6 . By the way, in the laser printer  1 , a body part except the process cartridge  20  is an apparatus body  1   a . In this embodiment, the process cartridge  20  including various components such as a photosensitive member  29  is configured so as to be attachable to and detachable from the apparatus body  1   a , and the practicable configuration of the process cartridge  20  will be stated later. 
   In the first embodiment, a side on which the front cover  7  is disposed as viewed in  FIG. 1  shall be termed “front side”, and the opposite side “rear side”. In the ensuing description, the front and rear direction of the laser printer  1  shall be taken as an “X-axial direction”, the height direction of the laser printer  1  as a “Y-axial direction”, and the widthwise direction of the paper being conveyed as a “Z-axial direction”. 
   The feeder section  4  includes at a bottom part in the body casing  2 , a paper feed tray  9  which is dismountably mounted, a feed roller  10  and a separation pad  10  which are disposed above the front end part of the paper feed tray  9 , a pickup roller  12  which is disposed on the rear side of the feed roller  10 , a pinch roller  13  which is arranged below the front side of the feed roller  10  in opposition to this feed roller, a paper-powder removal roller  8  which is arranged above the front side of the feed roller  10  in opposition to this feed roller, and registration rollers  14  which are disposed above the rear side of the feed roller  10 . 
   Included inside the paper feed tray  9  is a paper presser plate  15  on which the sheets of paper  3  can be placed in stacked fashion. The paper presser plate  15  is swingably supported at its rear end part, thereby to be swingable between a placement position where the front end part of this paper presser plate lies below and extends along the bottom plate  16  of the paper feed tray  9 , and a conveyance position where the front end part thereof lies above and inclines. 
   A lever  17  for lifting up the front end part of the paper presser plate  15  is disposed at the front end part of the paper feed tray  9 . The lever  17  is formed substantially in the shape of letter L as viewed in section, so as to turn under the paper presser plate  15  from the front side of this paper presser plate. The upper end part of the lever  17  is mounted on a lever shaft  18  which is disposed at the front end part of the paper feed tray  9 , while the rear end part thereof abuts on the lower surface of the front end part of the paper presser plate  15 . Thus, when a turning drive force which is clockwise as viewed in  FIG. 1  is input to the lever shaft  18 , the lever  17  turns with a fulcrum at the lever shaft  18 , and the rear end part of the lever  17  lifts up the front end part of the paper presser plate  15 , so as to locate this paper presser plate  15  at the conveyance position. Incidentally, reference sign  15 ′ indicates a state where the paper presser plate has been lifted up. 
   When the paper presser plate  15  is located at the conveyance position, the sheets of paper  3  on the paper presser plate  15  are pressed against the pickup roller  12  and begin to be conveyed toward the interspace between the feed roller  10  and the separation pad  11  by the rotation of the pickup roller  12 . 
   On the other hand, when the paper feed tray  9  is dismounted from the body casing  2 , the paper presser plate  15  has its front end part moved downwards by its own weight, and it is located at the placement position. When the paper presser plate  15  is located at the placement position, the sheets of paper  3  can be placed on the paper presser plate  15  in the stacked fashion. 
   The sheets of paper  3  delivered toward the interspace between the feed roller  10  and the separation pad  11  by the pickup roller  12  are reliably separated one by one and then fed when they are interposed between the feed roller  10  and the separation pad  11  by the rotation of the feed roller  10 . The fed sheet of paper  3  passes between the feed roller  10  and the pinch roller  13 , and it has paper powder removed by the paper-powder removal roller  8 , whereupon it is conveyed to the registration rollers  14 . 
   The registration rollers  14  consists of a pair of rollers, and after registration, they convey the sheet of paper  3  to a transfer position which lies between the photosensitive member  29  and a transfer roller  32  as stated later, and at which a toner image (corresponding to a developer image) on the photosensitive member  29  is transferred onto the sheet of paper  3 . The photosensitive member  29  serves as “an image carrier”. 
   The image formation section  5  includes a scanner portion  19 , the process cartridge  20 , and a fixation portion  21 . 
   The scanner portion  19  is disposed at an upper part within the body casing  2 , and the scanner portion  19  includes a laser light source which is not shown, a polygonal mirror  22  which is driven to rotate, an fθ lens  23 , a reflector  24 , a lens  25 , and a reflector  26 . A laser beam which is emitted from the laser light source and which is based on image data, is deflected by the polygonal mirror  22  and is passed through the fθ lens  23  as indicated by a chain line. Thereafter, the optical path of the laser beam is turned by the reflector  24  and is passed through the lens  25 . Further, the optical path is crooked downwards by the reflector  26 . Thus, the laser beam is projected onto the surface of the drum body  34  or the photosensitive member  29  of the process cartridge  20  as stated later. 
   The process cartridge  20  is detachably attached to the body casing  2  under the scanner portion  19 . The process cartridge  20  includes as a housing, an upper frame  27 , and a lower frame  28  which is formed as a member separate from the upper frame  27  and which is combined with the upper frame  27 . The process cartridge  20  includes within the housing, the photosensitive member  29 , a scorotron charger  30  (hereinbelow, also simply termed “charger  30 ”) being a charging unit, the development cartridge  31 , the transfer roller  32 , and a cleaning brush  33 . 
   The photosensitive member  29  includes the drum body  34  which is in the shape of a cylinder and whose outermost surface layer is formed of a positively-charged photosensitive layer made of polycarbonate, etc., and a metal-made drum shaft  35  which extends in the lengthwise direction of the drum body  34  along the axis of this drum body  34 . As shown in  FIGS. 2 through 4 , the drum shaft  35  is supported by the upper frame  27 , and the drum body  34  is supported so as to be rotatable relative to the drum shaft  35 , whereby the photosensitive member  29  is disposed so as to be rotatable about the drum shaft  35  in the upper frame  27 . 
   As shown in  FIG. 1 , the scorotron charger  30  is supported by the upper frame  27 , and it is arranged in opposition to the photosensitive member  29  with a predetermined spacing so as not to touch this photosensitive member  29 , obliquely above the rear side of this photosensitive member  29 . The scorotron charger  30  includes a discharging wire  37 , counter electrodes  38   a ,  38   a  which are arranged in opposition to each other and with a predetermined spacing in the axial direction of the photosensitive member  29 , and a grid electrode  38   b  which is disposed between the discharging wire  37  and the photosensitive member  29  and which controls the quantity of electric discharge from the discharging wire  37  to the photosensitive member  29 . In the scorotron charger  30 , a bias voltage is applied to the counter electrodes  38   a ,  38   a  and the grid electrode  38   b , while at the same time, a high voltage is applied to the discharging wire  37 , and the discharging wire  37  is caused to generate corona discharge, whereby the surface of the photosensitive member  29  is uniformly charged to the positive polarity. 
   In the scorotron charger  30 , a wiper  36  for cleaning the discharging wire  37  is disposed in a manner to embrace the discharging wire  37 . 
   As shown in  FIGS. 1 and 4 , the development cartridge  31  is formed in the shape of a box whose rear side is open, and it is detachably attached to the lower frame  28 . As shown in  FIG. 1 , a toner accommodation chamber  39 , a supply roller  40 , a development roller  41  and a layer-thickness regulation blade  42  are disposed in the development cartridge  31 . 
   The toner accommodation chamber  39  is formed as the front internal space of the development cartridge  31  which is partitioned by a partition plate  43 . In the toner accommodation chamber  39 , a nonmagnetic single-component toner of positively-charging property is packed as a developing agent. Used as the toner is a polymerized toner which is obtained in such a way that polymerizable monomers, for example, a styrenic monomer such as styrene and an acrylic monomer such as acrylic acid, alkyl (C1-C4) acrylate or alkyl (C1-C4) methacrylate are copolymerized by suspension polymerization or the like. Such a polymerized toner is substantially globular and exhibits a very good fluidity, and it can achieve image formation of high image quality. 
   Incidentally, a coloring agent such as carbon black, a wax, etc. are compounded in such a toner, and an additive such as silica is added in order to enhance the fluidity. The mean grain diameter of the toner is about 6-10 μm. 
   An agitator  44  is disposed within the toner accommodation chamber  39 . The toner in the toner accommodation chamber  39  is stirred by the agitator  44  and is emitted toward the supply roller  40  from a port  45  communicating in the front and rear direction under the partition plate  43 . 
   The supply roller  40  is arranged on the rear side of the port  45 , and is rotatably supported by the development cartridge  31 . This supply roller  40  is configured in such a way that a metal-made roller shaft is covered with a roller which is made of an electrically-conductive foamed material. The supply roller  40  is driven to rotate by the input of power from a motor not shown. 
   The development roller  41  is rotatably supported by the development cartridge  31  on the rear side of the supply roller  40 , in a state where this development roller  41  touches the supply roller  40  so as to be compressed each other. The development roller  41  opposes to and touches the photosensitive member  29  in a state where the development cartridge  31  is attached to the lower frame  28 . The development roller  41  is configured in such a way that a metal-made roller shaft  96  (not shown in  FIG. 1 , refer to  FIG. 4 ) is covered with a roller which is made of an electrically-conductive rubber material. As shown in  FIG. 4 , the roller shaft  96  has both its end parts protruded from the side surfaces of the development cartridge  31  outwards in a widthwise direction orthogonal to the front and rear direction, at the rear end part of this development cartridge  31 . The constituent roller of the development roller  41  is such that the surface of a roller body which is made of electrically-conductive urethane rubber or silicone rubber containing carbon particles or the likes is covered with a coat layer of fluorinated urethane rubber or silicone rubber. A development bias is applied to the development roller  41  during development. The development roller  41  is driven to rotate in the same direction as that of the supply roller  40  by the input of power from a motor not shown. 
   As shown in  FIG. 1 , the layer-thickness regulation blade  42  includes a blade body  46  which is made of a metallic leaf spring member, and it is provided at its distal end part of the blade body  46  with a pressing portion  47  of semicircular section which is made of insulating silicone rubber. The layer-thickness regulation blade  42  is supported by the development cartridge  31  above the development roller  41 , and has the pressing portion  47  brought into pressed touch onto the development roller  41  by the elastic force of the blade body  46 . 
   The toner emitted from the port  45  is supplied onto the development roller  41  by the rotation of the supply roller  40 . On this occasion, the toner is frictionally charged into the positive polarity between the supply roller  40  and the development roller  41 . The toner supplied onto the development roller  41  advances into the interspace between the development roller  41  and the pressing portion  47  of the layer-thickness regulation blade  42  with the rotation of the development roller  41 , and it is further charged here, so as to be carried on the development roller  41  as a thin layer of predetermined thickness. 
   The transfer roller  32  serves as “transfer member”, and is configured so as to transfer the toner image carried on the photosensitive member  29 , onto the sheet of paper  3 . The transfer roller  32  is rotatably supported by the lower frame  28 , and it is arranged so as to oppose to and touch the photosensitive member  29  in the up and down direction and to form a nip between it and the photosensitive member  29 , in the state where the upper frame  27  and the lower frame  28  are combined. Here, the transfer roller  32  is configured in such a way that a metal-made shaft member  32   a  is covered with a roller  32   b  made of an electrically-conductive rubber material. A transfer bias of negative polarity is applied to the transfer roller  32  during transfer. Besides, the transfer roller  32  is driven to rotate in the direction opposite to that of the photosensitive member  29  by the input of power from a motor not shown. Incidentally, a bias which is opposite in polarity to the bias applied to the charger  30  is applied as the transfer bias. 
   The cleaning brush  33  is mounted on the lower frame  28 , and it is arranged so as to oppose to and touch the photosensitive member  29  on the rear side of this photosensitive member  29 , in the state where the upper frame  27  and the lower frame  28  are combined. 
   The surface of the photosensitive member  29  is positively charged uniformly by the scorotron charger  30  by the rotation of this photosensitive member  29 , and it is thereafter exposed to light by the high-speed scanning with the laser beam from the scanner portion  19 , thereby to be formed with an electrostatic latent image corresponding to the image which is to be formed on the sheet of paper  3 . 
   Subsequently, when the toner which is carried on the development roller  41  and which is positively charged is brought into opposition to and touch with the photosensitive member  29  by the rotation of the development roller  41 , it is supplied to the electrostatic latent image which is formed on the surface of the photosensitive member  29 , that is, the exposed part which has been exposed to the light by the laser beam and whose electric potential is lower, in the surface of the photosensitive member  29  positively charged uniformly. Thus, the electrostatic latent image of the photosensitive member  29  is visualized, and the toner image based on reversal development is carried on the surface of the photosensitive member  29 . 
   Thereafter, the toner image carried on the surface of the photosensitive member  29  is transferred onto the sheet of paper  3  by the transfer bias applied to the transfer roller  32 , while as shown in  FIG. 1 , the sheet of paper  3  being conveyed by the registration rollers  14  passes through the transfer position P 1  between the photosensitive member  29  and the transfer roller  32 . The sheet of paper  3  on which the toner image has been transferred, is conveyed to the fixation portion  21 . 
   Incidentally, residual toner which remains on the photosensitive member  29  after the transfer is recovered by the development roller  41 . Paper powder from the sheet of paper  3  as is adherent on the photosensitive member  29  after the transfer is recovered by the cleaning brush  33 . 
   The fixation portion  21  serves as “fixation member”, and fixes the toner image (developer image) transferred by the transfer roller  32 , onto the sheet of paper (recording medium)  3 . The fixation portion  21  is disposed on the rear side of the process cartridge  20 , and it includes a fixation frame  48 , and a heating roller  49  and a pressing roller  50  which are disposed within the fixation frame  48 . 
   The heating roller  49  includes a metal pipe whose surface is coated with a fluorine resin, and a heating halogen lamp disposed in the metal pipe. The heating roller  49  is driven to rotate by the input of power from a motor not shown. 
   The pressing roller  50  is arranged under the heating roller  49  and in opposition thereto so as to press this heating roller  49 . This pressing roller  50  is configured by covering a metal-made roller shaft with a roller made of a rubber material, and it is driven in accordance with the rotating drive of the heating roller  49 . 
   In the fixation portion  21 , the toner transferred onto the sheet of paper  3  at the transfer position P 1  is thermally fixed while this sheet of paper  3  passes between the heating roller  49  and the pressing roller  50 . The sheet of paper  3  on which the toner has been fixed, is conveyed to a paper-ejection path  51  which extends in the up and down direction toward the upper surface of the body casing  2 . The sheet of paper  3  conveyed to the paper-ejection path  51  is ejected onto a paper-ejection tray  53  formed on the upper surface of the body casing  2 , by paper-ejection rollers  52  disposed on the upper side of the paper-ejection path  51 . 
   As shown in  FIG. 2 , the upper frame  27  disposed in the process cartridge  20  includes a left sidewall  54 , a right sidewall  55  and an upper wall  56  integrally. 
   As shown in  FIGS. 2 and 3 , the left sidewall  54  includes a left lower plate portion  57  which opposes to the drum body  34  from one side in the widthwise direction (the axial direction of the photosensitive member  29 ) (hereinbelow, one side in the widthwise direction shall be termed the “left side”, and the other side in the widthwise direction the “right side”), an extension plate portion  58  which extends from the upper end edge of the left lower plate portion  57  toward the right side, and a left upper plate portion  59  which extends upwards from the right end edge of the extension plate portion  58 . 
   A bearing member  66  that supports the drum shaft  35  is fitted into the left lower plate portion  57 , and the drum shaft  35  is inserted through a hole, not shown, which is formed in the bearing member  66 . 
   As shown in  FIG. 3 , the left upper plate portion  59  is provided on its front side with a first terminal  61  for electric is supply to the discharging wire  37  of the scorotron charger  30 , and it is provided on its rear side with a second terminal  62  for electric supply to the counter electrodes  38   a ,  38   a  and grid electrode  38   b  of the scorotron charger  30 . The upper end edge of the left upper plate portion  59  is formed by a horizontal part which extends substantially horizontally in the front and rear direction, and an inclined part which extends obliquely downwards from the rear end of the horizontal part. 
   As shown in  FIG. 2 , the right sidewall  55  is formed in the shape of a flat plate, and it opposes to the drum body  34  from the right side. The upper end edge of the right sidewall  55  is formed in correspondence with the upper end edge of the left upper plate portion  59 , by a horizontal part which extends substantially horizontally in the front and rear direction and which opposes to the horizontal part of the upper end edge of the left upper plate portion  59 , and an inclined part which extends obliquely downwards from the rear end of the horizontal part and which opposes to the inclined part of the upper end edge of the left upper plate portion  59 . Besides, a bearing member  67  is fitted into the right sidewall  55 , and the drum shaft  35  is inserted through a hole, not shown, which is formed in the bearing member  67 . 
   As stated above, the drum shaft  35  of the photosensitive member  29  is supported through the bearing members  66  and  67  which are respectively arranged at the left and right. Both the end parts of the drum shaft  35  protrude from the respective bearing members  66  and  67  outwards in the left and right directions, and stopper members  78  are respectively fitted outside both the end parts. Thus, the drum shaft  35  is prevented from coming off, by the stopper members  78 . Connected to the end part of the drum shaft  35  protruding from the left bearing member  66  is earth member, not shown, which is disposed on the body casing  2  in order to ground the drum shaft  35  in the state where the process cartridge  20  is attached to the body casing  2 . 
   The drum shaft  35  supports the drum body  34  so as to be relatively rotatable, between the bearing members  66  and  67 . A gear member (not shown) is mounted on the left end part of the drum body  34  in the axial direction thereof, and power is transmitted from a main motor, not shown, to the gear member, whereby the drum body  34  (refer to  FIG. 1 ) is rotated. 
   The upper wall  56  includes an upper horizontal portion  64  and an upper inclined portion  65  as shown in  FIG. 2 . The upper horizontal portion  64  is spanned between the horizontal part of the upper end edge of the left upper plate portion  59  and the horizontal part of the upper end edge of the right sidewall  55 . 
   The upper horizontal portion  64  is arranged over the photosensitive member  29 . Besides, the upper horizontal portion  64  is provided with a laser entrance window  164  for entering the high-speed-scanning laser beam LB (refer to  FIG. 1 ) from the scanner portion  19 , substantially in a rectangular shape as is viewed in plan. Further, a plurality of air passages  162  to be stated later are provided in adjacency to the laser entrance window  164 . 
   The upper inclined portion  65  is spanned between the inclined part of the upper end edge of the left upper plate portion  59  and the inclined part of the upper end edge of the right sidewall  55 . This upper inclined portion  65  is arranged obliquely above the rear side of the photosensitive member  29  with a predetermined spacing from the upper horizontal portion  64  in the front and rear direction. The scorotron charger  30  stated before is disposed on the upper inclined portion  65 . The discharging wire  37  is extended between the left upper plate portion  59  and the right sidewall  55  in the upper inclined portion  65 , and the counter electrodes  38   a ,  38   a  and the grid electrode  38   b  are spanned between the left upper plate portion  59  and the right sidewall  55  in the upper inclined portion  65 . 
   The lower frame  28  is provided with a pair of sidewalls  92  as shown in  FIG. 2 , and the left sidewall  92  is formed with an opening  111  for exposing a transfer electrode  113 , as shown in  FIG. 3 . The left sidewall  92  is provided with a cleaning electrode  104  for applying a cleaning bias to the cleaning brush  33  ( FIG. 1 ). 
   Next, the configuration of the conveyance path will be described. 
   First, a member on the side of the image forming surface of the sheet of paper  3  will be described.  FIG. 5  shows the perspective view of a duct portion  100  which corresponds to the member on the image forming surface side, and  FIG. 6  shows a state where a first electrically-conductive member has been detached from a duct body  101 .  FIG. 7  is a perspective view showing the arrangement of the process cartridge, the duct, the guide member and one frame of the apparatus body in the laser printer, and  FIG. 8  is a plan view showing the arrangement of the process cartridge, the duct and the guide member.  FIG. 9  is a sectional view showing section IX-IX (center section) shown in  FIG. 8 , and  FIG. 10  is a sectional view showing section X-X shown in FIG.  8 . 
   The laser printer  1  according to the first embodiment is configured so as to form an image on the sheet of paper while this sheet of paper is being conveyed between the transfer roller  32  and the fixation portion  21  shown in  FIG. 1 . In the sheet of paper  3  which is conveyed between the transfer roller  32  and the fixation portion  21  (hereinbelow, the sheet of paper which lies in a conveyance state between the transfer roller  32  and the fixation portion  21  shall be termed the “conveyance sheet of paper  3 ′”), the surface on the side of the photosensitive member  29  corresponds to the image forming surface, the duct portion  100  is arranged on the image forming surface side of the conveyance sheet of paper  3 ′ in opposition to the image forming surface. The duct portion  100  corresponds to the “first member”, and is disposed so as to confront the image forming surface of the conveyance sheet of paper  3 ′. 
   On the other hand, the guide member  110  which corresponds to a member on a non-image-forming surface side is arranged between the transfer roller  32  and the fixation portion  21  and on the side of the surface of the conveyance sheet of paper  3 ′ opposite to the image forming surface thereof (that is, on the side of the non-image-forming surface of the conveyance sheet of paper  3 ′). Here, in the conveyance sheet of paper  3 ′, the surface on the side of the transfer roller  32  corresponds to the opposite surface (the non-image-forming surface). The guide member  110  is arranged in opposition so as to confront the non-image-forming surface of the conveyance sheet of paper  3 ′. The duct portion  100  and the guide member  110  are configured so as to oppose to each other, and in forming the image, the sheet of paper  3  pass between the duct portion  100  and the guide member  110 . 
   As shown in  FIG. 5 , the duct portion  100  includes the first electrically-conductive member  102  which is made of a flat metal member (for example, a zinc-coated member prepared by zincking a stainless steel plate or an iron plate), and which exhibits an electric conductivity. The first electrically-conductive member  102  is disposed so as to cover the outer surface of the duct body  101  made of a non-electrically-conductive material (here, a resin material) in the duct portion  100 , and it is grounded. Concretely, the first electrically-conductive member  102  is connected with an electrically-conductive frame  120  disposed for the scanner portion  19 , by screw members  106  as shown in  FIGS. 5 and 6 , and both the first electrically-conductive member  102  and the frame  120  are connected to the earth member, not shown, in the laser printer  1 . The frame  120  overlies the process cartridge  20  as shown in  FIGS. 7 and 8 , and the scanner unit  19  (refer to  FIG. 1 ) is arranged between the frame  120  and the process cartridge  20  so as to be mounted on this frame  120 . 
   As shown in  FIGS. 5 and 6 , the first electrically-conductive member  102  is arranged so as to directly oppose to the image forming surface of the conveyance sheet of paper  3 ′ (refer to  FIG. 1 ) in the duct portion  100 . Besides, the first electrically-conductive member  102  includes parts which cover the outer surface of the duct portion  100  being the member on the side of the image forming surface, that is, a flat coverage portion  102   a  which covers one wall surface of the duct body  101 , and a flat coverage portion  102   b  which covers the other wall surface. Further, the first electrically-conductive member  102  includes coverage portions  102   c  and  102   d  which cover sidewalls. These coverage portions  102   a ,  102   b ,  102   c  and  102   d  are arranged so as to annularly cover the wall surfaces of the duct body  101  around this duct body  101 . Besides, the first electrically-conductive member  102  is mounted on the duct body  101  by screw members  105 . Extension portions  102   e  and  102   f  are respectively extended from the coverage portions  102   a  and  102   b  onto a side opposite to the side of the conveyance sheet of paper  3 ′ ( FIG. 1 ), and these extension portions  102   e  and  102   f  are connected with the frame  120  by the screw members  106  in the vicinity of the upper end part of the duct portion  101 . 
   In the configuration of the first embodiment, the first electrically-conductive member  102  which exhibits the electric conductivity and which is grounded is disposed in the duct portion  100  which is interposed between the transfer roller  32  and the fixation portion  21 , so that the potential of the entirety of the first electrically-conductive member  102  and the duct portion  100  as combined approaches to zero. Therefore, even when the duct portion  100  is arranged nearer to the conveyance sheet of paper  3 ′ ( FIG. 1 ) due to the reduction of the size of the laser printer  1 , the potential of the image forming surface side is controlled to be constant, and the behavior of the conveyance sheet of paper  3 ′ can be stabilized. Particularly in the laser printer  1  of this embodiment, the charger  30  is arranged on the image forming surface side of the conveyance sheet of paper  3 ′, while the transfer roller  32  is arranged on the non-image-forming surface side, and the bias which is opposite in polarity to the bias applied to the transfer roller  32  is applied to the charger  30 , so that the conveyance sheet of paper  3 ′ becomes liable to be attracted to the duct portion  100 . In contrast, in the configuration according to this embodiment, the first electrically-conductive member  102  is grounded to zeroize its potential, whereby the potential difference between the conveyance sheet of paper  3 ′ and the duct portion  100  including the first electrically-conductive member  102  is made small, so that the attraction of the conveyance sheet of paper  3 ′ is effectively preventable. Besides, the duct portion  100  does not exert influence on the sheet of paper, so that the distance between the duct portion  100  and the conveyance sheet of paper  3 ′ can be set small, and the reduction of the size of the whole apparatus (especially, the reduction of the size in the height direction) is realized. 
   As shown in  FIG. 5 , the duct portion  100  is provided with suction ports  103 ,  107  and  108 , through which air in the interior of the laser printer  1  is drawn by suction so as to be exhausted to the exterior. Concretely, as shown in  FIG. 7 , a fan  170  and an exhaust port  171  communicating with the internal space of the duct portion  100  are provided in a frame  172  which forms one sidewall of the laser printer  1 , and the internal air of the laser printer  1  is drawn through the suction ports  103 ,  107  and  108  by the suction based on the fan  170 , so as to be exhausted out of the laser printer  1  through the interior of the duct portion  100 . 
   As shown in  FIG. 9 , the duct portion  100  according to this embodiment is configured so that air within the charger  30  can is be drawn through the suction port  108  by suction, so as to be exhausted out of the apparatus through the exhaust port  171 . Incidentally, with the configuration in which the air within the charger  30  is exhausted by the duct portion  100  in this manner, the interior of the charger  30  can be advantageously held clean, but there is disadvantageously posed the problem that the duct portion  100  becomes liable to be charged under the influence of the air from the charger  30 . Since the bias opposite in polarity to the transfer bias is applied to the charger  30 , the conveyance sheet of paper  3 ′ ( FIG. 1 ) charged in the same polarity as that of the transfer bias is attracted toward the duct portion  100 . In the configuration of the first embodiment, however, the first electrically-conductive member  102  is disposed in the grounded state within such a duct portion  100 , so that the interior of the charger  30  is held clean, and the attraction of the conveyance sheet of paper  3 ′ to the duct portion  100  is effectively suppressed. In  FIG. 9 , the stream of the air from the charger  30  toward the duct portion  100  is indicated by an arrow F 1 . 
   As shown in  FIG. 9 , the duct portion  100  is configured so that, not only the air within the charger  30 , but also the air of a space  140  on the side of the fixation portion  21  can be exhausted to the exterior. In  FIG. 9 , the streams of the air from the space  140  on the fixation portion side, toward the duct portion  100  are indicated by arrows F 2  and F 3 . As shown in  FIGS. 5 and 7 , the large number of suction ports  103  (only three of which have the reference numeral assigned thereto in  FIG. 5 ) are provided in that wall part of the duct body  101  of the duct portion  100  which lies on a downstream side in the conveyance direction of the sheet of paper, and the plurality of suction ports  107  (only three of which have the reference numeral assigned thereto in  FIG. 5 ) are provided in that end part of the duct body  101  which lies on a side opposing to the conveyance sheet of paper  3 ′ ( FIG. 1 ). The air from the space  140  on the charger side flows into the duct portion  100  through the suction ports  103  and  107  as shown in  FIG. 9 , and it is exhausted from the exhaust port  171  shown in  FIG. 7 . Incidentally, although not shown in FIG.  9 , a plurality of vent holes  142  (refer to  FIG. 16 ) are provided in the guide member  110 , and air outside the laser printer  1  enters the interior thereof through the vent holes  142 . In  FIG. 9 , the stream of the air is indicated by an arrow F 4 . 
     FIG. 11  is the view of the process cartridge as seen from the back surface side thereof. 
   In the first embodiment, the housing (concretely, the lower frame  28 ) of the process cartridge  20  forms part of the member on the image forming surface side, together with the duct portion  100 . 
   As shown in  FIGS. 10 and 11 , that lower frame  28  of the housing of the process cartridge  20  which forms part of the member on the image forming surface side is provided with an attraction suppression portion  130  at a position which lies downstream of the transfer position P 1  based on the transfer roller  32 , in the paper conveyance direction. The attraction suppression portion  130  is configured so that the rear end part of the sheet of paper having passed through the transfer position P 1  may be restrained from being attracted onto the side of the process cartridge  20 , by the abutment of the portion  130  on the rear end part. More specifically, when the sheet of paper has passed through the transfer position P 1 , the rear end part thereof is released from the support of the photosensitive member  29 , and the image forming surface side thereof becomes free from restraint. In this state, the rear end part of the sheet of paper is apprehended to be attracted to that part of the housing (specifically, the lower frame  28 ) of the process cartridge  20  which lies on the image forming surface side (that is, to the end part of the process cartridge  20 ). In the configuration shown in  FIGS. 10 and 11 , however, the attraction suppression portion  130  is disposed at the fixation-portion side end part of the lower frame  28  in the process cartridge  20 , so that even after the sheet of paper has passed through the transfer position P 1 , the rear end part of the sheet of paper is less liable to be attracted to the end part of the lower frame  28 , owing to the abutment of the attraction suppression portion  130 , and the behavior of the sheet of paper is stabilized still more. 
     FIG. 12A  shows the view of the process cartridge  20  as seen from the side of the fixation portion, while  FIG. 12B  conceptually illustrates the behavior of the rear end part of the conveyance sheet of paper  3 ′ at the end part of the process cartridge  20 . Incidentally, the conveyance sheet of paper  3 ′ exemplified in  FIG. 12B  is a sheet of paper of maximum size for use in the laser printer  1 . As shown in  FIG. 11  and  FIGS. 12A and 12B , the attraction suppression portion  130  is configured of first protrusive portions  135  which protrude in directions opposing to the sheet of paper, at positions opposing to both the end parts of the conveyance sheet of paper  3 ′ (refer to  FIGS. 1 and 12B ) in the widthwise direction thereof (that is, in the Z-axial direction), and rib-like second protrusive portions  133  which are disposed so as to extend in the paper conveyance direction, at positions nearer to the middle of the conveyance sheet of paper  3 ′ than the positions of the first protrusive portions  135  in the widthwise direction (Z-axial direction) of this conveyance sheet of paper  3 ′. 
   In the configuration, as shown in  FIG. 12B , both the widthwise end portions of the conveyance sheet of paper  3 ′ are supported by the first protrusive portions  135 , and the support by the first protrusive portions  135  is difficult to influence that widthwise middle part of the conveyance sheet of paper  3 ′ on which the image is formed. The rib-like second protrusive portions  133  extending in the paper conveyance direction are disposed in addition to the first protrusive portions  135 , and the prevention of the attraction of the rear end part of the sheet of paper is attained also at the middle side parts without considerably influencing the image formation. In  FIG. 12B , the behavior of the rear end part of the conveyance sheet of paper  3 ′ in an ordinary mode is conceptually illustrated by a dot-and-dash line N, while the behavior of the rear end part of the conveyance sheet of paper  3 ′ in the case where a very strong attraction has occurred (that is, in the worst case) is indicated by a two-dot chain line M. As seen from the figure, in the case of using the sheet of paper of the maximum size, the second protrusive portions  133  support the conveyance sheet of paper  3 ′ only in the case where the very strong attraction has occurred. 
   As shown in  FIG. 12A , the first protrusive portions  135  protrude in such a manner that their protrusion amounts gradually become smaller from both the end sides of the sheet of paper in the widthwise direction thereof (in the Z-axial direction), toward the middle side of this sheet of paper. In this manner, the first protrusive portions  135  are constructed having the protrusion amounts which gradually become smaller from both the end sides toward the middle side, so that even in the case where the attraction of the conveyance sheet of paper  3 ′ has occurred as in  FIG. 12B , the influence on the part of the widthwise middle side on which the image is formed in the conveyance sheet of paper  3 ′ is relieved still further, and an image formation quality is enhanced still more. 
   As shown in  FIG. 11 , the first protrusive portions  135  include slant surfaces  135   a  each of which is constructed so as to confront the conveyance sheet of paper  3 ′ ( FIGS. 1 and 12B ) and to incline relative to the image forming surface of the sheet of paper. Each of the slant surfaces  135   a  is formed substantially in the shape of a triangle as viewed from the rear surface side thereof. In more detail, as shown in  FIG. 11  and  FIGS. 12A and 12B , the triangular shape has a small protrusion amount on the side of an end part  135   b , and a large protrusion amount on the side of an end part P 3 . Thus, the slant surfaces  135   a  gradually come nearer to the conveyance sheet of paper  3 ′ toward the downstream side in the conveyance direction and both the end sides in the widthwise direction. In this manner, in the first protrusive portions  135  disposed at both the widthwise end portions, the slant surfaces  135   a  are constructed so as to gradually come nearer to the conveyance sheet of paper  3 ′ toward the downstream side in the conveyance direction and both the end sides in the widthwise direction (Z-axial direction), so that while both the end parts of the conveyance sheet of paper  3 ′ are supportable, the protrusion of the first protrusive portions  135  is less liable to hamper the conveyance of the sheet of paper. 
   As shown in  FIG. 13 , the distance L 2  between each second protrusive portion  133  and the sheet of paper being conveyed is set larger than the distance L 1  between each first protrusive portion  135  and the recording medium being conveyed. With the setting, the sheet of paper is chiefly supported by the first protrusive portions  135  of the large protrusion amount, and the support by the second protrusive portions  133  is moderated as compared with the support by the first protrusive portions  135 . Accordingly, the influence of the second protrusive portions  133  on the image formation on the sheet of paper can be restrained to the utmost. That is, even in the case of the occurrence of the very strong attraction as indicated by the two-dot chain line M in  FIG. 12B , the support by the first protrusive portions  135  is chief, and abutment forces do not become very large as to the support by the second protrusive portions  133 . Besides, regarding the weak attraction as in the conveyance sheet of paper  3 ′ in the ordinary mode indicated by the dot-and-dash line N, the support by the first protrusive portions  135  suffices, and the sheet of paper is not supported by the second protrusive portions  133 , so that the middle side of the sheet of paper in the widthwise direction thereof can be protected still more. Incidentally, the conveyance sheet of paper  3 ′ of the maximum size (for example, A4-format) for use in the laser printer  1  is exemplified in  FIGS. 12A and 12B , but sheets of paper having smaller sizes are also usable. In a case where such a smaller size is employed and where the size of the sheet of paper in the widthwise direction thereof is smaller than the interval between the end parts  135   b  and  135   b , the occurrence of attraction is coped with in such a way that the sheet of paper is supported by only the second protrusive portions  133 , without being supported by the first protrusive portions  135 . 
   As shown in  FIG. 11  and  FIGS. 12A and 12B , the plurality of second protrusive portions  133  are disposed at a mutual interval in the widthwise direction of the sheet of paper being conveyed (in the Z-axial direction). According to the configuration, a plurality of support positions are established, so that the attraction of the sheet of paper can be suppressed more stably, and the second protrusive portions  133  are spaced in the widthwise direction, so that the influence on the image is suppressed more than in a case where the second protrusive portions  133  are continuously disposed. Since the second protrusive portions  133  are rectilinearly constructed along the paper conveyance direction, the influence on the image is reduced still further. 
   As shown in  FIG. 13 , the attraction suppression portion  130  is disposed upstream of the first electrically-conductive member  102  in the paper conveyance direction, so that the sheet of paper is smoothly conveyed, not only at the part where the first electrically-conductive member  102  is disposed, but also on the upstream side thereof (that is, in the region between the parts where the transfer roller  32  and the first electrically-conductive member  102  are disposed). 
   In the first embodiment, the attraction suppression portion  130  as described above is provided in the housing of the process cartridge  20 , so that the attraction is effectively preventable in that housing (specifically, lower frame  28 ) of the process cartridge  20  which is near to the nip position (transfer position P 1 ) between the photosensitive member  29  and the transfer roller  32  and which is more liable to cause the attraction phenomenon. 
   The cleaning brush  33  is disposed in the process cartridge  20  as shown in  FIGS. 1 and 9 , and the paper powder having adhered to the photosensitive member  29  can be removed by the cleaning brush  33 . In the first embodiment, in the process cartridge  20 , the cleaning brush  33  and a housing part surrounding the cleaning brush  33  (the part of the lower frame  28  as surrounds the cleaning brush  33 ) are configured as a paper-powder removal device  160 . As described above, the housing of the process cartridge  20  is constructed as part of the member on the image forming surface side. In this regard, as shown in  FIG. 11  and the explanatory view of  FIG. 14  (explanatory view for explaining part of  FIG. 9  on enlarged scale and in rough-overview manner), a resin film  131  for receiving the paper powder is mounted on that part of the housing of the process cartridge  20  which corresponds to the feed roller  10  in the widthwise direction (Z-axial direction) of the conveyance sheet of paper  3 ′ (FIG.  12 (B)), in a state where the resin film  131  is partly protruded. By the way, in  FIG. 11 , the resin film  131  is indicated by hatching. As shown in  FIGS. 15 and 16 , the feed roller  10  is arranged over the predetermined range of the widthwise (Z-axial) middle part of the conveyance sheet of paper  3 ′ ( FIG. 12B ), and the resin film  131  shown in  FIG. 11  is arranged in substantially the same range as the range where the feed roller  10  is disposed (feed roller arrangement region C 1 ), in the Z-axial direction. Incidentally, although the resin film  131  is arranged in substantially the same range as the feed roller arrangement region C 1  in the Z-axial direction here, it may well be arranged over a region which includes the feed roller arrangement region C 1  and which is somewhat larger than this region C 1 . Besides, as described above, the resin film  131  is arranged over the predetermined range of the widthwise (Z-axial) middle part of the conveyance sheet of paper  3 ′ (FIG.  12 B), but parts on both the sides of the resin film  131  as oppose to the conveyance sheet of paper  3 ′ (parts of regions C 2  and C 3  in  FIG. 11 ) are formed as non-arrangement regions in which the resin film is not arranged. 
   More specifically, when the resin film for preventing the paper powder from dropping is arranged at part of the paper-powder removal device  160  (concretely, at part of the lower frame  28 ), the paper powder can be effectively removed, but on the other hand, the charging of the resin film becomes a problem. However, when the resin film is arranged only at the part corresponding to the feed roller  10  liable to generate the paper powder, as in the above configuration, the paper powder can be effectively removed with the charging suppressed. 
   As shown in  FIG. 14 , the resin film  131  includes a film body  131   a  made of, for example, PET, and an adhesive layer  131   b . In that protrusive portion  131   c  of the resin film  131  which protrudes from the housing (namely, the lower frame  28 ) of the paper-powder removal device  160 , the adhesive layer  131   b  is exposed onto the side of the photosensitive member  29 . According to this configuration, the effect of removing the paper powder can be more enhanced by the simple arrangement. More specifically, a sheet member (such as dual-side tape) both the surfaces of which are provided with an adhesive medium is disposed so as to cover the film body  131   a  as the adhesive layer  131   b . One surface of the adhesive layer  131   b  is bonded with the film body  131   a , while part of the other surface is bonded with the outer surface of the housing (namely, the lower frame  28 ). Besides, that part of the adhesive layer  131   b  which is not bonded with the housing (namely, that part of the adhesive layer  131   b  which lies at the protrusive portion  131   c  of the resin film  131 ) is exposed onto the side of the photosensitive member  29 . 
   Next, the member provided on the side of the non-image-forming surface will be described. 
     FIG. 15  is a plan view exemplifying the guide member  110 , and  FIG. 16  is a perspective view corresponding to  FIG. 15 .  FIG. 17  is a perspective view exemplifying a state where the second electrically-conductive member  112  has been detached from the guide member  110 . 
   As stated before, in the laser printer  1  according to the first embodiment, the guide member  110  which corresponds to the member on the non-image-forming surface side is arranged in opposition so as to confront the non-image-forming surface of the conveyance sheet of paper  3 ′ ( FIG. 13 ). Further, the guide member  110  is provided with the second electrically-conductive member  112  exhibiting the electric conductivity and being grounded, as shown in  FIGS. 15 through 17 . The second electrically-conductive member  112  is made of a flat metal member (for example, a zinc-coated member prepared by zincking a stainless steel plate or an iron plate). This electrically-conductive member  112  is disposed so as to cover part of the outer surface of the guide member  110  (more concretely, so as to cover the outer surface of that member body portion  111  of the guide member  110  which is made of a non-electrically-conductive material). Besides, the second electrically-conductive member  112  is arranged so as to directly oppose to the non-image-forming surface (opposite to the image forming surface) of the conveyance sheet of paper  3 ′ being conveyed ( FIG. 13 ). 
   In the configuration of the first embodiment, the second electrically-conductive member  112  which is grounded is provided in the guide member  110  which is disposed on the side of the opposite surface to the image forming surface defined between the transfer roller  32  and the fixation portion  21 . As regards the members constituting the conveyance path, therefore, the electric potential of the entirety of the second electrically-conductive member  112  and the guide member  100 , being the member on the non-image-forming surface side, as combined can be approached to zero, not only on the image forming surface side, but also on the non-image-forming surface side. In the laser printer  1  of this embodiment, the transfer roller  32  is disposed on the side of the non-image-forming surface of the conveyance sheet of paper  3 ′ ( FIG. 13 ), so that the guide member  110  is easily charged in the same polarity as that of the transfer bias, and the behavior of the conveyance sheet of paper  3 ′ ( FIG. 13 ) is liable to become unstable. However, when the second electrically-conductive member  112  is grounded to zeroize the potential thereof, a potential difference is established between the conveyance sheet of paper  3 ′ ( FIG. 13 ) and the guide member  110  including the second electrically-conductive member  112 , and the conveyance sheet of paper  3 ′ is attracted, whereby the behavior of this conveyance sheet of paper can be stabilized. On this occasion, the non-image-forming surface side of the conveyance sheet of paper  3 ′, is attracted, so that no influence is exerted on an image quality. 
   The guide member  110  extends from the transfer roller  32  toward the fixation portion  21 , and it includes a plurality of guide ribs  114  extending along the conveyance direction. In the example of  FIG. 15 , the second electrically-conductive member  112  is disposed so that the upstream-side end portions  114   a  of the guide ribs and the upstream-side end part  112   a  of the second electrically-conductive member  112  may become substantially the same positions in the conveyance direction of the recording medium. The second electrically-conductive member  112 , however, may well be disposed on a further upstream side relative to the upstream-side end portions of the guide ribs  114 . 
   As shown in  FIG. 13 , part of the second electrically-conductive member  112  is arranged at a position opposing to the process cartridge  20 . Thus, the sheet of paper  3  is located so as to smoothly pass between the process cartridge  20  and the guide member  110 . Besides, the process cartridge  20  is provided with a transfer member accommodation portion  150  which surrounds the periphery of the transfer roller  32  so as to accommodate this transfer roller  32 , and the second electrically-conductive member  112  is arranged in adjacency to the transfer member accommodation portion  150 . In case of a configuration in which the transfer roller  32  is exposed onto the downstream side thereof, the second electrically-conductive member may well be disposed so as to adjoin the transfer roller  32 . In the first embodiment, the second electrically-conductive member  112  is disposed at the position adjoining the transfer member accommodation portion  150 , so that the stabilization of the behavior of the sheet of paper  3  is attained in the vicinity of the transfer roller  32 , and the sheet of paper  3  is smoothly shifted from the transfer roller  32  to the guide member  110 . 
   In the first embodiment, as shown in  FIG. 13 , the distance L 3  between the first electrically-conductive member  102  and the sheet of paper  3  being conveyed (that is, the shortest distance from the first electrically-conductive member  102  to the conveyance sheet of paper  3 ′) is set larger than the distance L 4  between the second electrically-conductive member  112  and the sheet of paper  3  being conveyed (that is, the shortest distance from the second electrically-conductive member  112  to the conveyance sheet of paper  3 ′). With the setting, the second electrically-conductive member  112  is nearer to the conveyance sheet of paper  3 ′ than the first electrically-conductive member  102 , so that the sheet of paper  3  is more liable to be attracted on the side of the second electrically-conductive member  112  than on the side of the first electrically-conductive member  102 . Accordingly, the image forming surface of the sheet of paper  3  is effectively protected, and the image quality can be held at a high precision. More specifically, the potential difference is established also between the conveyance sheet of paper  3 ′ and the duct portion  100  including the first electrically-conductive member  102 , by grounding this first electrically-conductive member  102 . Therefore, when the distance L 3  is set to be smaller than the distance L 4 , a force by which the first electrically-conductive member  102  attracts the conveyance sheet of paper  3 ′ exceeds a force by which the second electrically-conductive member  112  attracts the conveyance sheet of paper  3 ′, contrariwise to the above, and there occurs the drawback that the conveyance sheet of paper  3 ′ is attracted to the duct portion  100 . In contrast, in the configuration according to the first embodiment, such a drawback does not occur, and the behavior of the conveyance sheet of paper  3 ′ becomes very stable. 
   Second Embodiment 
   Next, a laser printer according to a second embodiment will be described. 
     FIG. 18  is a side sectional view of essential portions exemplifying a laser printer according to second embodiment, and  FIG. 19  is a perspective view showing the vicinity of a guide member which is employed in the laser printer in  FIG. 18 .  FIG. 20  is a perspective view showing a state where a second electrically-conductive member  112  and a charge removal brush  200  have been detached from the configuration in  FIG. 19 .  FIG. 21  shows a configuration into which the configuration in  FIG. 13  as shown in first embodiment has been modified (that is, a configuration in which the charge removal brush  200  is attached to the configuration in  FIG. 13 , so as to correspond to the laser printer according to this embodiment), and it is an enlarged view showing the sections of the essential portions of the laser printer in  FIG. 18 , on enlarged scale.  FIG. 22  shows a configuration into which the configuration in  FIG. 14  as shown in first embodiment has been modified (that is, a configuration in which the charge removal brush  200  is attached to the configuration in  FIG. 14 , so as to correspond to the laser printer according to the second embodiment).  FIG. 14  is an explanatory view for explaining the position of the charge removal brush  200  in the laser printer in  FIG. 18 . 
   The laser printer  1  in  FIG. 18  as exemplified in the description of the second embodiment differs from the first embodiment in the point that the charge removal brush  200  being charge reduction member is connected to the second electrically-conductive member  112  by connection member having an electric conductivity (concretely, an electrically-conductive adhesive to be stated later), and the configuration of this laser printer except the charge removal brush  200  and the connection member is the same as in first embodiment. Accordingly, the same numerals and signs as in first embodiment are assigned to parts except the charge removal brush  200 , and the parts shall be omitted from detailed description. 
   In the configuration according to the second embodiment, the charge removal brush  200  for reducing electric charges borne on a sheet of paper (a recording medium) is disposed between a transfer position P 1  based on a transfer roller  32  being transfer member and a fixation portion  21  being fixation member, and at a position nearer to the transfer position P 1  with respect to a first electrically-conductive member  102 . 
   Also in the configuration according to the second embodiment, as in the first embodiment, a duct portion  100  (namely, a member on the side of the image forming surface of the sheet of paper) configured between the transfer roller  32  and the fixation portion  21  is provided with the first electrically-conductive member  102  which exhibits an electric conductivity and which is grounded, so that the potential of the duct portion  100  including the first electrically-conductive member  102  approaches to zero. Therefore, even when the duct portion  100  is arranged nearer to the sheet of paper being conveyed, due to the reduction of the size of the laser printer  1  (that is, even in a case where a small-sized configuration is formed as in the configuration according to this embodiment, or in a case where further reduction in size is achieved), the electric potential of the image forming surface side is controlled to be constant, and the behavior of the sheet of paper can be stabilized. 
   Especially in the image forming apparatus which employs an electrophotographic scheme as in the configuration according to this embodiment, a charger  30  is arranged on the image forming surface side of the sheet of paper being conveyed, and the transfer roller  32  is arranged on the non-image-forming surface side thereof. A bias which is opposite in polarity to a bias applied to the transfer roller  32  is usually applied to the charger  30  as in the configuration according to the second embodiment, so that the sheet of paper after the transfer of an image is liable to be attracted to the duct portion  100  being the member on the image forming surface side. In the configuration according to this embodiment, however, the first electrically-conductive member  102  is grounded to zeroize its potential, so that the potential difference between the sheet of paper being conveyed and the duct portion  100  including the first electrically-conductive member  102  is made small, and the attraction of the sheet of paper to the duct portion  100  is preventable. 
   In addition to such a configuration, the second embodiment is configured so that the potential difference between the sheet of paper being conveyed and the whole duct portion  100  including the first electrically-conductive member  102  can be made still smaller. More specifically, even when the potential in the vicinity of the duct portion  100  is substantially zeroized by disposing the first electrically-conductive member  102  as described above, a certain degree of potential difference is yet apprehended to occur between the sheet of paper and the duct portion  100  being the member on the image forming surface side, in a case where the sheet of paper bears a large quantity of charges. In contrast, in the configuration according to the second embodiment, the charges borne on the sheet of paper can be reduced by the charge removal brush  200  before the sheet of paper being conveyed reaches the vicinity of the duct portion  100 , so that the potential difference between the sheet of paper and the duct portion  100  can be made still smaller, and the behavior of the recording medium being conveyed can be stabilized still more. 
   In the second embodiment, as in the first embodiment, in addition to the first electrically-conductive member  102 , the second electrically-conductive member  112  which is grounded is disposed in a guide member  110  which is configured between the transfer roller  32  and the fixation portion  21  and which is a member on the non-image-forming surface side. Accordingly, not only on the image forming surface side, but also on the non-image-forming surface side, the potential of the entirety of the second electrically-conductive member  112  and the guide member  110  as combined can be approached to zero. Usually, in the image forming apparatus which employs the electrophotographic scheme as in the configuration according to the second embodiment, the transfer roller  32  is disposed on the side of the non-image-forming surface of the sheet of paper being conveyed, the guide member  110  being the member on the non-image-forming surface side is easily charged in the same polarity as that of the transfer bias, and the behavior of the sheet of paper being conveyed is liable to become unstable. In the second embodiment, however, a potential difference is generated between the sheet of paper being conveyed and the guide member  110  including the second electrically-conductive member  112 , by grounding the second electrically-conductive member  112  and zeroizing the potential thereof, whereby the sheet of paper is attracted, and its behavior can be stabilized. As described above, the guide member  110  which extends from the transfer roller  32  toward the fixation portion  21  is disposed as the member on the non-image-forming surface side. In this regard, as shown in  FIGS. 19 and 21 , the guide member  110  is provided with a plurality of guide ribs  114  which extend along the conveyance direction of the sheet of paper, in the same manner as in the first embodiment. 
   On the other hand, with such a configuration, it is apprehended that the sheet of paper will come into strong touch with the guide ribs  114  of the guide member  110  when the second electrically-conductive member  112  attracts the sheet of paper to bring this sheet of paper into touch with the guide ribs  114 . With the configuration in which the sheet of paper being conveyed come into strong touch with the guide ribs  114  in this manner, large vibrations are bestowed on the sheet of paper at the time of the touch, and hence, the developer image transferred on the sheet of paper is liable to be disordered. When the sheet of paper being conveyed comes into strong touch with the guide ribs  114 , charges are removed from the sheet of paper at a stroke at the time of the touch, so that the developer image transferred on the sheet of paper is liable to be disordered. In the configuration according to the second embodiment, however, the arrangement capable of stabilizing the behavior of the sheet of paper is realized by the second electrically-conductive member  112 , while at the same time, the charge removal brush  200  is disposed at the position which is further upstream of the upstream-side end portions  114   a  of the guide ribs  114  in the conveyance direction of the sheet of paper, so that the charges borne on the sheet of paper can be reduced to some degree by the charge removal brush  200  before the sheet of paper comes into touch with the guide ribs  114 . Accordingly, the extent of the touch between the sheet of paper and the guide ribs  114  becomes very light, the shock (vibrations) and the sudden charge removal at the touch with the guide ribs  114  do not concur, and the disorder of the image at the touch with the guide ribs  114  is effectively preventable. 
   In the configuration according to the second embodiment, the charges are reduced to some degree by the charge removal brush  200  before the sheet of paper reaches the vicinity of the second electrically-conductive member  112 , but the charges are not completely removed by the charge removal brush  200 . Therefore, even after the sheet of paper has passed through the vicinity of the charge removal brush  200 , a certain amount of charges remain on the sheet of paper. Accordingly, a certain potential difference is established by the remaining charges and the guide member  110  including the second electrically-conductive member  112 , which is kept at the zero level, and the function of attracting the sheet of paper is fulfilled by the guide member  110  including the second electrically-conductive member  112 . 
   Next, the charge removal brush  200  will be described in detail. 
   As shown in  FIG. 19 , the charge removal brush  200  includes a flat holder plate  204  which is made of a resin material (for example, PET material), and a plurality of filamentous portions  202  which are made of an electrically-conductive fibrous material (for example, an organic electrically-conductive fiber in which copper sulfide or the like is chemically bonded with a acrylic fiber, a Nylon fiber or the like) and which are mounted on the holder plate  204 . The filamentous portions  202  are respectively bonded to the holder plate  204  so that their lower ends may lie below the center of the holder plate  204 . The arrangement region of the filamentous portions  202  is defined over a predetermined region in the widthwise direction of the sheet of paper, and a recording medium opposition portion opposing to the sheet of paper is formed by the plurality of filamentous portions  202 . In the second embodiment, the recording medium opposition portion is formed over the whole width of an image-formable region in the sheet of paper. 
   As shown in  FIGS. 19 and 20 , the plurality of filamentous portions  202  in the above charge removal brush  200  are connected to the second electrically-conductive member  112  by an electrically-conductive adhesive, on their sides opposite to is their sides on which they are bonded to the holder plate  204 . That is, in this configuration, the plurality of portions  202  of the electrically-conductive fibrous material as constitute the recording medium opposition portion are connected to the second electrically-conductive member  112  by the electrically-conductive adhesive, so that the charges of the sheet of paper are efficiently reduced. Incidentally, the “electrically-conductive adhesive” corresponds to “connection member having an electric conductivity”. Also, the “second electrically-conductive member” corresponds to “ground member”. The electrically-conductive adhesive usable is, for example, an adhesive made of a pasty electrically-conductive resin in which the electrically-conductive particles of gold, silver, nickel, carbon or the like are compounded with an epoxy resin or the like resin as a base, but any other adhesive may well be employed as long as it has an electric conductivity and functions as a bonding medium. 
   As shown in  FIG. 21 , the charge removal brush  200  is disposed at a position at which it is capable of touching the sheet of paper being conveyed (conveyance sheet of paper  3 ′) (in other words, at a position at which part of the brush  200  is located on the traveling path of the conveyance sheet of paper  3 ′). Concretely, as shown in  FIG. 22 , the distal end  202   a  of the charge removal brush  200  is located at a position which coincides with an orthogonal plane D 2  that is orthogonal to a plane D 1  connecting the transfer position P 1  and the rotating axis J 1  of the photosensitive member  29 , and that passes through the transfer position P 1 . In this configuration, the charge removal brush  200  is arranged so as not to widely intersect an extension direction in which the sheet of paper extends from the transfer position P 1 , so that the sheet of paper is less liable to undergo a shock in the charge reduction mode. Incidentally, the distal end  202   a  of the charge removal brush  200  may well be located at a position which is slightly downwardly spaced from the orthogonal plane D 2  which is orthogonal to the plane D 1  connecting the transfer position P 1  and the rotating axis J 1  of the photosensitive member  29 . 
   As shown in  FIG. 21 , the charge removal brush  200  is disposed so as to protrude in a direction intersecting the conveyance path of the sheet of paper (the path of the conveyance sheet of paper  3 ′). When, in this manner, the charge removal brush  200  is disposed so as to protrude in the direction intersecting the conveyance path, a time period for which the charge removal brush  200  opposes to the sheet of paper becomes shorter per unit area thereof, than in a configuration in which the charge removal brush  200  is arranged so as to extend along the conveyance path. Accordingly, while the charges can be reduced to some degree, they are difficult to be removed very suddenly. 
   As shown in  FIG. 19 , the guide member  110  includes positioning portions  115  which position the charge removal brush  200 . The positioning portions  115  are constructed as projections which project in the bottom surface  110   a  of the guide member  110 . As shown in  FIGS. 19 and 20 , the positioning portions  115  support the lower end part of the holder plate  204  in the charge removal brush  200 , thereby to repress the downward movement of the holder plate  204  relative to the guide member  110 . As a result, the charge removal brush  200  is stably positioned to the guide member  110 . Accordingly, the charge removal brush  200  and the sheet of paper which is conveyed while being guided by the guide member  110  can be prevented from becoming excessively distant or coming into excessive touch, and the charges can be stably reduced from the sheet of paper. Moreover, a mounting error in the case of mounting the charge removal brush  200  on the apparatus can be mitigated. 
   Other Embodiments 
   The present invention is not limited to the embodiments described above with reference to the drawings, but embodiments to be stated below by way of example shall also be covered within the technical scope of the invention, and the invention can further be variously altered and carried out within a scope not departing from the purport thereof, otherwise than the ensuing description. 
   (1) In each of the embodiments, the first electrically-conductive member  102  has been disposed in the duct portion  100 , but it may well be disposed in any member other than the duct portion  100 . 
   (2) In each of the embodiments, the first electrically-conductive member  102  has been constructed of the flat metal member, but it may well have any other configuration. The first electrically-conductive member may well be constructed of, for example, a resin member having an electric conductivity. Likewise, the second electrically-conductive member may well be constructed of any member other than the flat metal member (of, for example, a resin member having an electric conductivity.) 
   (3) In each of the embodiments, the first electrically-conductive member  102  is formed so as to extend orthogonally to the plane of the conveyance sheet of paper  3 ′, by covering the duct body  101  of the duct portion  100  with this first electrically-conductive member  102 , but any other configuration may well be employed. By way of example, the first electrically-conductive member  102  may well be disposed so as to become parallel to the plane of the conveyance sheet of paper  3 ′, and it may well be arranged so as to incline relative to the plane of the conveyance sheet of paper  3 ′. 
   (4) Incidentally, regarding the configuration of the first protrusive portions  135  and the second protrusive portions  133  which constitute the attraction suppression portion  130 , the peculiar effect of suppressing the attraction of the sheet of paper is achieved even by a configuration in which the first electrically-conductive member  102  is not disposed (that is, a configuration in which the member  100  on the image forming surface side is not grounded), and a synergetic effect can be expected owing to the coexistence of the attraction suppression portion  130  and the first electrically-conductive member  102 . 
   (5) In second embodiment, the charge removal brush which includes the plurality of filamentous portions constructed in the shape of the brush has been exemplified as the charge reduction member, but the charge reduction member may well be constructed of a charge removal plate of metal material or the like in which a plurality of tip portions are arrayed in the widthwise direction of the plate. 
   (6) In each of the first and the second embodiments, the image forming apparatus in which the first electrically-conductive member and the second electrically-conductive member are both disposed has been exemplified, but it is also allowed to employ a different configuration in which only the first electrically-conductive member is disposed without disposing the second electrically-conductive member. Besides, second embodiment has exemplified the configuration in which the charge reduction member is further disposed in the image forming apparatus provided with both the first electrically-conductive member and the second electrically-conductive member, but the charge reduction member may well be disposed in a configuration in which only the first electrically-conductive member is disposed without disposing the second electrically-conductive member.