Patent Publication Number: US-7216864-B2

Title: Paper supply cassette for an image forming device

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a paper supply cassette and an image forming device equipped with the paper supply cassette. 
   2. Description of the Related Art 
   Image forming devices, such as laser printers and copy machines, that are provided with a detachably mounted paper supply cassette are well known in the art. The paper supply cassette includes an integrally formed case and a handle part. The case can holds a stack of recording sheets. The handle part is formed as a decorative plate on the front surface of the paper supply cassette and is used by a user to grip the handle part when inserting or removing the paper supply cassette. A supporting part is provided between the integrally formed case and the handle part. The supporting part supports a separating unit, which functions to separate and convey the sheets from the stack in the paper supply cassette one sheet at time. 
   SUMMARY OF THE INVENTION 
   However, the separating unit must be precisely mounted in the paper supply cassette so that sheets can be precisely separated from the stack. To meet this requirement, the separating unit must be redesigned each time there is a change in the design of the paper supply cassette, and the separating performance of this separating unit must be demonstrated. Thus, a great amount of time and effort is required to manufacture a paper supply cassette having a separating unit with sufficient separating ability. 
   A sheet supply cassette according to the present invention holds recording sheets and that is used detachably mounted in an image forming device. The sheet supply cassette includes a case that holds a stack of recording sheets. The case has a separation portion that separates recording sheets from the stack of recording sheets, and a receiving portion that receives the separation portion. The sheet supply cassette also includes a handle part provided as a separate member from the case. The handle part is fixed to the case and has a handle for pulling the case. The case has a handle-part-side end that is adjacent to the handle part and the receiving portion is located at the handle-part-side end. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
       FIG. 1  is a central cross-sectional view showing a laser printer according to an embodiment of the present invention; 
       FIG. 2  is an exploded perspective view showing a paper supply cassette according to the embodiment; 
       FIG. 3  is a perspective view showing details of a guide ribs for guiding sheets conveyed from a lower paper supply cassette to an image forming section; 
       FIG. 4  is a view taken along line IV-IV of  FIG. 3 ; 
       FIG. 5  is a view taken along line V-V of  FIG. 3 ; 
       FIG. 6  is a perspective view showing a handle part on which guiding ribs are provided; 
       FIG. 7  is a cross-sectional view showing essential components of the paper supply cassette; 
       FIG. 8  is a perspective view showing the area of the paper supply cassette around a sheet separating portion; 
       FIG. 9  is a side view in partial phantom showing the positional relationship between the paper supply cassette and a right frame of the laser printer when the paper supply cassette is mounted in the laser printer; 
       FIG. 10  is a perspective view showing the laser printer of  FIG. 1 ; 
       FIG. 11  is a perspective view showing a handle part according to a variation of the embodiment; 
       FIG. 12  is a cross-sectional view showing a modification of the guide ribs of  FIG. 3 ; 
       FIG. 13  is a cross-sectional view showing another modification of the guide ribs of  FIG. 3 ; and 
       FIG. 14  is a cross-sectional view showing still another modification of the guide ribs of  FIG. 3 . 
   

   DETAILED DESCRIPTION OF THE EMBODIMENT 
   A laser printer  1  according to an embodiment of the present invention will be described with reference to the accompanying drawings. First, overall structure of the laser printer  1  will be described with reference to  FIG. 1 .  FIG. 1  is a central sectional view of the laser printer  1 . 
   As shown in cross-section in  FIG. 1 , the laser printer  1  includes a feeder section  4 , and an image forming section, all accommodated in a main body case  2 . The feeder section  4  is for feeding sheets  3 . The image forming section is for forming imaged on each fed sheet  3 , and includes a scanner unit  16 , a process cartridge  17 , and a fixing unit  18 . Note that the right side of  FIG. 1  is the front surface of the laser printer  1 . 
   A sheet delivery tray  46  is formed as an upwardly slanting recess located at the upper center surface of the main case body  2 . Printed sheets  3  are discharged from the laser printer  1  into a stack on the tray  46 . A space that holds a process cartridge  17  is provided in a portion close to the front upper surface of the main body case  2 . The space is open to the front side so the process cartridge  17  can be inserted. A cover  54  that pivots downward is provided on a right end side (front side) of the main body case  2 . The cover  54  is for covering the space. A process cartridge  17  is inserted and removed where the cover  54  is opened widely. 
   A sheet delivery path  44  is provided at the rear part in the main body case  2  (left side in  FIG. 1 ). The sheet delivery path  44  is formed in a semi-arc shape that extends vertically along the back of the main body case  2 . The sheet delivery path  44  delivers the sheet  3  from a fixing device  18 , which is provided on a rear end side in a lower part of the main body case  2 , to the sheet delivery tray  46 , which is provided on an upper part of the main body case  2 . A sheet delivery roller  45  for conveying the sheet  3  is provided along the sheet delivery path  44 . 
   The feeder unit  4  includes a paper supply cassette  6 , a feed roller  8 , a conveying roller  11 , a paper dust removing roller  10 , and register rollers  12 . The paper supply cassette  6  is for holding stacked sheets  3  and is detachably mounted in the bottom section of the main casing  2 . The paper supply cassette  6  can be inserted through the front face of the laser printer  1  by moving in a front-to-back direction and removed from the laser printer  1  by moving in a back-to-front direction. The feed roller  8  is disposed in the lower section of the main casing  2  for picking up and feeding a sheet of the sheet  3  from the paper supply cassette  6 . The conveying roller  11  is disposed downstream from the feed roller  8  in the direction for conveying the sheet  3 . The paper dust removing roller  10  presses against the conveying roller  11  with the sheet  3  interposed therebetween and removes paper dust from the sheet  3  while conveying the sheet  3  in cooperation with the conveying roller  11 . The register rollers  12  are provided downstream from the conveying roller  11  in the conveying direction of the sheet  3  for regulating the timing at which the sheet  3  is fed for printing. 
   Next, the duplex printing unit  26  will be described. The duplex printing unit  26  is disposed above the paper supply cassette  6  and includes reverse conveying rollers  50   a ,  50   b , and  50   c  arranged in a substantially horizontal orientation. A reverse conveying path  47   a  is provided on the rear side of the reverse conveying roller  50   a  and a reverse conveying path  47   b  is provided on the front side of the reverse conveying roller  50   c . The reverse conveying path  47   a  extends from the discharge roller  45  to the reverse conveying rollers  50   a  and branches from the discharge path  44  near the end of the discharge path  44  with respect to the sheet feed direction of the sheet  3 . The reverse conveying path  47   b , on the other hand, extends from the reverse conveying roller  50   c  to the register rollers  12 . 
   When performing duplex printing, first an image is formed on one side of the sheet  3 . Then a portion of the sheet  3  is discharged onto the discharge tray  46 . When the trailing edge of the sheet  3  becomes interposed between the discharge rollers  45 , the discharge rollers  45  stop rotating forward and begin rotating in reverse. At this time, the trailing edge of the sheet  3  contacts the arched surface of the discharge path  44  and is guided along the arched surface to the reverse conveying path  47   a , without returning to the discharge path  44 . The sheet  3  is conveyed from the reverse conveying path  47   a  to the reverse conveying rollers  50   a ,  50   b , and  50   c  and is subsequently guided to the register rollers  12  along the reverse conveying path  47   b . According to this operation, the sheet  3  is conveyed to the image forming unit with its front and back surfaces switched in order to form an image on the other side of the sheet  3 . 
   A low-voltage power source circuit board  90 , the high-voltage power source circuit board  95 , and an engine circuit board  98  are provided between the duplex printing unit  26  and the image forming unit. A chute  80  is disposed between these circuit boards  90 ,  95 , and  98  and the image forming unit for separating these circuit boards  90 ,  95 ,  98  from the fixing unit  18 , the processing cartridge  17 , and other devices. The chute  80  is formed of a synthetic resin and spans between left and right frames  100  and  110  that are provided in the laser printer  1  to support such devices as the scanning unit  16  and fixing unit  18 . A guiding plate  81  is provided on the top of the chute  80  for guiding the sheet  3 . The guiding plate  81  forms a portion of the conveying path for the sheet  3 . In addition to the chute  80 , a steel tray  120  on which the scanning unit  16  is fixed spans between the frames  100  and  110  above the chute  80  and two underbars  130  span between the frames  100  and  110  below the chute  80 . The underbars  130  are reinforced by folding back both lengthwise steel edges of the elongated steel plate toward the center of the plate surface. 
   The low-voltage power source circuit board  90  functions to drop the voltage supplied from a source external to the laser printer  1 , such as a single-phase 100V source, to a voltage of 24V, for example, to be supplied to components in the laser printer  1 . The high-voltage power source circuit board  95  generates a high-voltage bias that is applied to components in the processing cartridge  17 . The engine circuit board  98  drives a DC motor (not shown), a solenoid (not shown), a laser emitting section (not shown), and the like. The DC motor is the source for driving parts involved in mechanical operations, such as the rollers in the laser printer  1 . The solenoid (not shown) is for switching the operating direction of this drive system. 
   The scanner unit  16  of the image forming section includes a laser beam emitting section (not shown), a polygon mirror  19 , a fθ lens  20 , reflecting mirrors  21   a ,  21   b , and a relay lens  22 . The laser beam emitting section is located right below the sheet delivery tray  46  of the main body case  2  and irradiates a laser beam. The polygon mirror  19  rotates to scan the laser beam from the laser beam emitting section in a main scanning direction across the surface of a photosensitive drum  27 . The fθ lens  20  is for stabilizing scanning speed of the laser beam reflected from the polygon mirror  19 . The reflecting mirrors  21   a ,  21   b  are for reflecting the laser beam. The relay lens  22  is for adjusting the focal position in order to focus the laser beam from the reflecting mirror  21  onto the photosensitive drum  27 . With this configuration, the laser beam is irradiated from the laser beam emitting section based upon predetermined image data and passes through or is reflected by the polygon mirror  19 , the fθ lens  20   a , the reflecting mirror  21 , the relay lens  22  and the fθ lens  20   b  in this order as indicated by an alternate long and dash lines A in  FIG. 1  to expose and scan the surface of the photosensitive drum  27  of the process cartridge  17 . 
   The fixing device  18  in the image forming section is disposed downstream from the process cartridge  17  with respect to the direction of sheet transport. The fixing device  18  in the image forming section includes a heating roller  41 , a pressing roller  42  for pressing the heating roller  41 , and a pair of conveying rollers  43 . The conveying rollers  43  are provided downstream from the heating roller  41  and the pressing roller  42 . The heating roller  41  is formed by coating a hollow aluminum roller with a fluorocarbon resin and sintering the assembly. The heating roller  41  includes a metal tube and a halogen lamp for heating inside the metal tube. The pressing roller  42  includes a silicon rubber shaft having low hardness that is covered by a tube formed of a fluorocarbon resin. The silicon rubber shaft is urged upward by a spring (not shown), pressing the pressing roller  42  against the heating roller  41 . While the sheet  3  from the process cartridge  17  passes between the heating roller  41  and the pressing roller  42 , the heating roller  41  pressurizes and heats toner that was transferred onto the sheet  3  in the process cartridge  17 , thereby fixing the toner onto the sheet  3 . Afterward, the sheet  3  is transported to the sheet delivery path  44  by the conveying rollers  43 . 
   The process cartridge  17  includes a drum cartridge  23  and a developing cartridge  24  that is detachably mounted on the drum cartridge  23 . The drum cartridge  23  includes the photosensitive drum  27 , a Scorotron charger  29 , and a transfer roller  30 . The developing cartridge  24  includes a developing roller  31 , a supply roller  33 , and a toner hopper  34 . 
   The photosensitive drum  27  is arranged in the drum cartridge  23  so as to contact the developing roller  31 . The photosensitive drum  27  is rotatable clockwise as indicated by the arrow in  FIG. 1 . The photosensitive drum  27  includes positively charging organic photo conductor coated on a conductive base material. The positively charging organic photo conductor is made from a charge transfer layer dispersed with a charge generation material. When the photosensitive drum  27  is exposed by a laser beam, the charge generation material absorbs the light and generates a charge. The charge is transferred onto the surface of the photosensitive drum  27  and the conductive base material through the charge transfer layer and counteracts the surface potential charged by the Scorotron charger  29 . As a result, a potential difference is generated between regions of the photosensitive drum  27  that were exposed and regions that were not exposed by the laser light. By selectively exposing and scanning the surface of the photosensitive drum  27  with a laser beam based upon image data, an electrostatic latent image is formed on the photosensitive drum  27 . 
   The Scorotron charger  29  is disposed above the photosensitive drum  27 . The Scorotron charger  29  is separated from and out of contact with the photosensitive drum  27  by a predetermined distance. The Scorotron charger  29  generates a corona discharge from a wire made from tungsten, for example, and is turned ON by a charging bias circuit unit (not shown) of the high-voltage power source  95  to positively charging the surface of the photosensitive drum  27  to a uniform charge of positive polarity. 
   The developing roller  31  is disposed further downstream than the Scorotron charger  29  with respect to the rotation direction of the photosensitive drum  27 , that is the clockwise direction as viewed in  FIG. 1 . The developing roller  31  is rotatable counterclockwise as indicated by an arrow in  FIG. 1 . The developing roller  31  includes a roller shaft made from metal covered with a roller made from a conductive rubber material. A development bias is applied to the developing roller  31  from a development bias circuit unit (not shown) of the high-voltage power source  95 . 
   The supply roller  33  is rotatably disposed beside the developing roller  31  on the opposite side from the photosensitive drum  27  across the developing roller  31 . The supply roller  33  is in pressed contact with the developing roller  31 . The supply roller  33  includes a roller shaft made of metal coated with a roller made of a conductive foam material and is adapted to triboelectrify toner supplied to the developing roller  31 . Furthermore, the supply roller  33  is rotatable counterclockwise as indicated by an arrow in  FIG. 1 . This is the same rotation direction as developing roller  31 . 
   The toner hopper  34  is provided beside the supply roller  33 . The inside of the toner hopper  39  is filled with developer to be supplied to the developing roller  31  by the supply roller  33 . In this embodiment, non-magnetic, single-component toner with a positive charging nature is used as a developer. The toner is a polymeric toner obtained by copolymerizing polymeric monomers using a well-known polymerization method such as suspension polymerization. 
   Examples of polymeric monomers include styrene monomers and acrylic monomers. Styrene is an example of a styrene monomer. 
   Examples of acrylic monomers include acrylic acid, alkyl (C1 to C4) acrylate, and alkyl (C1 to C4) methacrylate. A coloring agent, such as carbon black, and wax are mixed in the polymeric toner. An externally added agent such as silica is also added in order to improve fluidity. Particle diameter of the polymeric toner is approximately 6 to 10 μm. 
   An agitator  36  is provided for agitating toner accommodated in the toner hopper  34  and supplying the toner into a developing chamber  37 . The agitator  36  has a coarse mesh-like plate shape extending in the axial direction (near-to-far direction in  FIG. 1 ) and has a bend in the middle when viewed as a cross-section. A rotating shaft  35  is disposed on one end of the agitator  36 . Film members  36   a  for scraping the inner wall of the toner hopper  34  are provided on the other end of the agitator  36  and in the bend in the middle of the agitator  36 . The rotating shaft  35  is rotatably supported in the center of both lengthwise ends of the toner hopper  34  and, hence, supports the agitator  36 . When the agitator  36  is rotated in the direction indicated by the arrow, toner accommodated in the toner hopper  34  is agitated and supplied into the developing chamber  37 . 
   The transfer roller  30  is disposed below the photosensitive drum  27  and downstream from the developing roller  31  with respect to the rotating direction of the photosensitive drum  27 . The transfer roller  30  is rotatable counterclockwise as indicated by an arrow in  FIG. 1 . The transfer roller  30  includes a metal roller shaft coated with a roller made from an ion-conductive rubber material. During the transfer process, a transfer bias circuit unit (not shown) of the high-voltage power source  95  applies a transfer forward bias to the transfer roller  30 . The transfer forward bias generates a potential difference between the surfaces of the photosensitive drum  27  and the transfer roller  30 . The potential difference electrically attracts toner that electrostatically clings to the surface of the photosensitive drum  27  toward the surface of the transfer roller  30 . 
   It should be noted that the laser printer  1  employs what is known as a cleanerless developing system, wherein the developing roller  31  recovers toner remaining on a surface of the photosensitive drum  27  after the transfer roller  30  transfers toner from the photosensitive drum  27  to the sheet  3 . 
   Next, the structure of the paper supply cassette  6  will be described in detail with reference to  FIGS. 2 through 9 .  FIGS. 2 ,  6 ,  7 ,  8 , and  9  include direction arrows to indicate the orientation of the laser printer  1 , wherein −Z direction, −X direction, +X direction, +Z direction, +Y direction, and −Y direction correspond to forward, leftward, rightward, backward, up, and down, respectively. As shown in  FIG. 2 , the paper supply cassette  6  includes a case unit  160 , an accommodating section cover  170 , and the handle part  180 . 
   The case unit  160  has an open-top box shape to hold stacked sheets  3 . The case unit  160  includes a bottom plate  160   a  and side walls  160   b ,  160   c ,  160   d , and  160   e . The bottom plate  160   a  have a substantially rectangular shape and a surface area slightly larger than that of the sheet  3 . The side walls  160   b ,  160   c ,  160   d , and  160   e  extend from the four edges of the bottom plate  160   a  in the +Y direction, which is a direction perpendicular to the surface of the bottom plate  160   a . Each of these side walls  160   b ,  160   c ,  160   d , and  160   e  are connected with adjacent side walls at the corners of the bottom plate  160   a , forming the open-top box shape. The case unit  160  is formed of a synthetic resin material. A guide plate  161  and a pair of guide plates  162  are provided on the bottom plate  160   a  for maintaining the alignment of the stacked sheets  3 . The surfaces of the guide plates  162  are flush with the surfaces of the side walls  160   d  and  160   c . The guide plate  161  can move in the Z directions (front and rear directions of the case unit  160 ) and the guide plates  162  can move in the X directions (left and right directions). Hence, different sizes of the sheet  3  can be maintained in alignment depending on the intended usage. 
   A paper pressing plate  167  is disposed in the bottom plate  160   a  for pressing the stacked sheets  3  toward the feed roller  8  when the paper supply cassette  6  is mounted in the laser printer  1 . As shown in  FIG. 8 , the paper pressing plate  167  is a flat steel plate shaped substantially like an H as can be seen in  FIG. 2 . As shown in  FIG. 7 , a support shaft  167   a  provided on the end of the paper pressing plate  167  farthest from the feed roller  8  supports the paper pressing plate  167  near the center of the bottom plate  160   a . The end of the paper pressing plate  167  nearest to the feed roller  8  is capable of moving in a vertical direction as the paper pressing plate  167  rotates about the support shaft  167   a . A spring  167   b  is disposed on the underside of the paper pressing plate  167  for urging the paper pressing plate  167  toward the feed roller  8 . As the number of sheets of the sheet  3  stacked on the paper pressing plate  167  increases, the paper pressing plate  167  pivots about the support shaft  167   a  downward against the urging force of the spring  167   b  by an amount that corresponds to the amount of sheets. 
   As shown in  FIG. 2 , an opening  160   m  is formed through the side wall  160   b  of the case unit  160  at a location substantially center in the widthwise direction (X directions). The opening  160   m  is defined by a side-wall-opening edge  160   n . When the accommodating section cover  170  is fitted to the side wall  160   b , a central part of the accommodating section cover  170  covers the opening  160   m.    
   Protruding ends  160   f  and  160   g  are provided on the front side wall  160   b  of the case unit  160 . The protruding ends  160   f  and  160   g  are fixing members that extend following the plane of the front side wall  160   b  from either end in the X directions (left and right directions). Two screw holes  163  are formed in the outer edge of each of the protruding ends  160   f  and  160   g . The handle part  180  is fixed onto the protruding ends  160   f  and  160   g  by inserting screws  164  into the screw holes  163 . Vibration absorbing members  165  are fixed on the side wall  160   b  so as to face outward from the case unit  160 , that is, in the −Z direction. The vibration absorbing members  165  absorb vibrations generated by driving in the laser printer  1  that are transferred to the paper supply cassette  6 , thereby reducing vibration and noise generated by resonance in the paper supply cassette  6 . A separation portion  166  is also disposed on the side wall  160   b  at a position above the opening  160   m . The separation portion  166  is for separating and conveying the sheet  3  accommodated in the case unit  160  to be printed one sheet at a time. The separation portion  166  will be described in more detail later. 
   The accommodating section cover  170  is formed from a synthetic resin and is fixed to the side wall  160   b  by snapping the accommodating section cover  170  in place between the protruding ends  160   f  and  160   g . Hence, the accommodating section cover  170  covers the surface on which the vibration absorbing members  165  are provided, but does not cover the protruding ends  160   f  and  160   g , and forms an enclosed space therein. Slanted surfaces  171   a  and  171   b  are formed on the inner surface of the accommodating section cover  170 . The slanted surfaces  171   a  and  171   b  slant, from approximately the center toward both ends of the accommodating section cover  170 , downward in the −Y direction and outward in the X directions (left and right directions of the paper supply cassette  6 ). The enclosed space between the side wall  160   b  and the accommodating section cover  170  serves as a paper dust accommodating unit for collecting paper dust from the sheets of the sheet  3  that is generated by friction between the sheet  3  and a rubber pad  201   a  of the separation portion  166  (see  FIG. 7 ). 
   As shown in  FIG. 2 , a plurality of guiding ribs  172  extend in the Y direction along the outer surface of the accommodating section cover  170 , that is, along the surface that is substantially parallel to the side wall  160   b  and that faces in a paper guiding side (−Z direction). Each guiding rib  172  arches, with respect to the Y directions, in the −Z direction as shown in  FIGS. 4 and 7  and also in the −X direction as shown in  FIG. 3 . Each guiding rib  172  includes ridges  172 A that extend in the direction in which sheets  3  are conveyed. As shown in  FIG. 5 , each ridge  172 A is curved with respect to the direction perpendicular to the conveying direction so that the end of each guiding rib  172  has a substantial C-shape. In other words, each ridge  172 A is formed with a curving surface that extends along the ridge  172 A. 
   The handle part  180  is a decorative plate formed from a synthetic resin and covers the side wall  160   b  on which the accommodating section cover  170  is provided. The handle part  180  includes a plate surface  180   a  and a handle section  180   b . The plate surface  180   a  is substantially flat and extends in the X and Y directions (left, right, up, down directions). The handle section  108   b  extends substantially parallel to the plate surface  180   a , but as can be seen in  FIG. 1  is positioned further outward in the Z direction than the plate surface  180   a . The distance between the plate surface  180   a  and handle section  180   b  is set to about the thickness of a user&#39;s fingers, for example. As can be seen in  FIG. 2 , the handle section  180   b  is formed with an arched shape at its lower edge. The arched shape enables a user to more easily insert his or her fingers in between the plate surface  180   a  and the handle section  180   b.    
   As shown in  FIG. 6 , the plate surface  180   a  is formed with screw receivers  181  for receiving the screws  164 . Two screw receivers  181  are formed one each lengthwise end on the back surface of the plate surface  180   a , that is, the surface facing in the +Z direction. The handle part  180  is fixed to the case unit  160  by inserting the screws  164  into the screw receivers  181  through the screw holes  163  formed in the protruding ends  160   f  and  160   g  shown in  FIG. 2 . 
   Guiding ribs  182  are provided on the back surface of the plate surface  180   a . The guiding ribs  182  extend in the Y directions following the shorter dimension of the plate surface  180   a . The guiding ribs  182  have a concave arched shape that corresponds to outward-protruding arched shape of the guiding ribs  172 . The ridge portions of the guiding ribs  182  are formed with a curved surface similar to ridges portions of the guiding ribs  172 . The guiding ribs  182  are disposed in confrontation with the guiding ribs  172  provided on the accommodating section cover  170  with a prescribed distance maintained between corresponding ones of the guiding ribs  182  and the guiding ribs  172 . Therefore, as shown in  FIG. 7 , a paper conveying path  183  is formed between the guiding ribs  172  and the guiding ribs  182 . When the laser printer  1  includes two or more paper supply cassettes,  6 , the paper conveying path  183  serves as a path for guiding paper conveyed from the lower paper supply cassette, positioned below the upper paper supply cassette in  FIG. 10 , toward the image forming unit. In this case, another feeder unit  4  is provided for the lower paper supply cassette. The other feeder unit  4  serves as a sheet conveyor unit for conveying sheets from the lower paper supply cassette, through the paper conveying path  183  (shown in  FIG. 7 ), toward the image forming unit. Paper can be conveyed smoothly through the paper conveying path  183  because the guiding ribs  172  and the guiding ribs  182  contact the leading edge of the paper with only a small surface area, which offers little frictional resistance to the paper. 
   As shown in  FIG. 2 , the case unit  160 , the accommodating section cover  170 , and the handle part  180  of the paper supply cassette  6  are all formed as separate members from each other. Each is formed by an injection molding process. The bottom plate  160   a  and the side walls  160   b ,  160   c ,  160   d , and  160   e  are formed in a single injection molding process to form the case unit  160 . Accordingly, the molds for forming each part can be manufactured separately. Therefore, the parting lines where the molds divide can be designed separately for the case unit  160 , the accommodating section cover  170 , and the handle part  180 . Accordingly, the molds can be produced with a larger draft angle, thus allowing the product to be released from the mold during production without deforming. Further, the ridges of the guiding ribs  172  and guiding ribs  182  can be easily formed in the curved shape. 
   Next, the separation portion  166  and a receiving portion  160   i  for receiving the separation portion  166  will be described with reference to  FIGS. 8 and 9 .  FIG. 8  is an enlarged perspective view showing the area of the paper supply cassette  6  around the separation portion  166 . The separation portion  166  includes the separating pad  201  and a spring  201   d . The separating pad  201  is for separating the sheet  3  one sheet at a time in cooperation with the feed roller  8 , which is for feeding out the sheet  3 . The spring  201   d  is for pressing the separating pad  201  toward the feed roller  8  when the paper supply cassette  6  is mounted in the laser printer  1 . 
   The separating pad  201  is formed from a synthetic resin and, as shown in  FIG. 8 , includes a support plate  201   b  and two guide members  201   c . The support plate  201   b  is substantially rectangular in shape as shown in  FIG. 8  and curved to follow the outer surface of the feed roller  8  as shown in  FIG. 7 . The two guide members  201   c  are shaped like poles protruding from the support plate  201   b  near the lengthwise ends of the support plate  201   b  and extend in a direction substantially orthogonal to the surface of the support plate  201   b . A rubber pad  201   a  is fixed to the top of the support plate  201   b.    
   The receiving portion  160   i  is located at the end of the case unit  160  that is adjacent to the handle part  180 . 
   More specifically, the receiving portion  160   i  is provided in approximately the widthwise (X directions) center. The receiving portion  160   i  includes guide wall portions  160   j , support wall portions  160   k , and the opening  160   m.    
   The guide wall portions  160   j  and the support wall portions  160   k  are located near the side-wall-opening edge  160   n . The guide wall portions  160   j  and the support wall portions  160   k  are formed integrally with the side wall  160   b  of the case unit  160 . The guide wall portions  160   j  are provided at two locations corresponding to the guide members  201   c . The opening  160   m  includes holding sections (openings)  160   h  for holding the guide members  201   c . More specifically, the holding sections  160   h  are defined by the guide wall portions  160   j . The support wall portions  160   k  are provided integrally with the guide wall portions  160   j  and face upward (+Y direction). The guide members  201   c  can be inserted into or withdrawn from the holding sections  160   h  following the direction in which the guide members  201   c  protrude. The spring  201   d  is disposed between the holding sections  160   h  and presses the rubber pad  201   a  on the surface of the separating pad  201  toward the feed roller  8 . 
   As shown in  FIG. 7 , the guide wall portions  160   j  restrict the direction in which the guide members  201   c  can be inserted or withdrawn to a single direction. As a result, play of the guide members  201   c  is reduced and the surface of the rubber pad  201   a  always contacts the peripheral surface of the feed roller  8  at the same prescribed angle. When the guide members  201   c  moves downward and contact the support wall portions  160   k , the support wall portions  160   k  prohibit further movement of the guide members  201   c , thereby preventing the separating pad  201  from dropping through the opening  160   m  With this construction, the guide wall portions  160   j  and the support wall portions  160   k  support the separation portion  166  with restricted movement so that the separation portion  166  separates sheets from the stacked sheet  3  one sheet at a time with great precision. 
   As shown in  FIGS. 7 and 8 , a paper dust removing roller  202  and a sponge  203  are provided downstream in the paper conveying direction from the separating pad  201 . The paper dust removing roller  202  and the sponge  203  are located between the separating pad  201  and the accommodating section cover  170  that covers the opening  160   m . The peripheral surface of the paper dust removing roller  202  electrostatically attracts paper dust that is generated by friction between sheet  3  and the separating pad  201  as the sheet  3  is conveyed. The sponge  203  rubs against the outer surface of the paper dust removing roller  202  to tribocharge the paper dust removing roller  202  and scrapes off paper dust that has been deposited on the peripheral surface thereof. The paper dust removing roller  202  is formed from fluoroplastic, for example. A metal plate  204  includes an elongated plate surface and two lengthwise ends. The lengthwise ends are folded to extend in a direction orthogonal to the plate surface. The sponge  203  is fixed on the plate surface of the metal plate  204 . A shaft  202   a  of the paper dust removing roller  202  is rotatably supported on the folded lengthwise ends of the metal plate  204 , such that the peripheral surface of the paper dust removing roller  202  is maintained in contact with the sponge  203 . 
   The metal plate  204  is supported in the side wall  160   b  at a position in the −Z direction from the separating pad  201 , that is, downstream in the conveying direction of the sheet  3 . The metal plate  204  is supported also by other support wall portion (not shown) provided to the side wall  160   b . A spring (not shown) is disposed beneath the metal plate  204  to urge the paper dust removing roller  202  to press against the feed roller  8  as shown in  FIG. 7 . As mentioned previously, a paper dust accommodating unit is constructed by the space between the side wall  160   b  and the accommodating section cover  170 . The paper dust accommodating unit is open only where the separation portion  166  and the paper dust removing roller  202  and sponge  203  are fixed to the side wall  160   b.    
   Next, a mechanism for positioning the paper supply cassette  6  in the left and right frames  100  and  110  will be described with reference to  FIGS. 1 ,  8 , and  9 .  FIG. 9  shows the positional relationship of the paper supply cassette  6  and the right frame  110  when the paper supply cassette  6  is mounted in the laser printer  1 . Because both the left frame  100  and the right frame  110  have the same positioning construction, description of the left frame  100  has been omitted. 
   As shown in  FIG. 8 , a guide member  192  and a positioning piece  191  are provided on the side wall  160   c  on the right of the paper supply cassette  6 . The guide member  192  protrudes from the side wall  160   c  at a position near the handle part  180  in the lengthwise direction and near the bottom plate  160   a  in the height direction. The guide member  192  extends exactly a prescribed distance in the Z direction, which is parallel to the mounting direction of the paper supply cassette  6 . Both lengthwise ends of the guide member  192  slant downward toward the bottom plate  160   a . Although not shown in the drawings, another guide member  192  is provided on the opposite lengthwise end of the side wall  160   c.    
   The positioning piece  191  protrudes from the side wall  160   c  and is located nearer to the handle part  180 , and farther from the bottom plate  160   a , than is the guide member  192 . As with the guide member  192 , the positioning piece  191  extends exactly a prescribed distance in the direction parallel to the mounting direction of the paper supply cassette  6 . The guide member  192  has a lock part  191   a  that is slightly thicker than the other portions of the positioning piece  191 . Two ribs are provided near the center of the positioning piece  191 . The ribs serve as reinforcement for preventing the positioning piece  191  from collapsing. A positioning piece and guide members are also provided on the side wall  160   d  on the left side of the paper supply cassette  6 . 
   As shown in  FIG. 1 , the paper supply cassette  6  is detachably mounted between the chute  80  and the underbars  130 , which span between the left frame  100  and right frame  110 . As shown in  FIG. 9 , a guide rail  196  and a positioning member  195  are provided on the inner surface of the right frame  110 , that is, the surface that confronts the left frame  100 . 
   The guide rail  196  is a rail-shaped protrusion that extends nearly the entire length of the right frame  110  in the Z directions (forward and rear directions). The two guide members  192  slidingly contact the guide rail  196 , thus guiding the paper supply cassette  6 , while the paper supply cassette  6  is mounted or removed. 
   The positioning member  195  includes upper and lower rail pieces for guiding the positioning piece  191  while the positioning piece  191  is interposed therebetween. Lock parts  195   a  protrude within the guiding groove between the two rails of the positioning member  195 . The lock parts  195   a  apply resistance to movement of the lock part  191   a  in the Z directions and so engage the positioning piece  191  at a prescribed position. Although not shown in the drawings, a guide rail and positioning member are also provided on the left frame  100 . Therefore, because the positioning member  195  maintains the paper supply cassette  6  at a prescribed position in the laser printer  1 , the positional relationship between the feed roller  8  and the separating pad  201  remains uniform even after repeated mounting and removing of the paper supply cassette  6 . This ensures that the stacked sheet  3  can be reliably separated one sheet at a time. 
   Next, the operations of the laser printer  1  during a printing process will be described with reference to  FIGS. 1 and 7 . The topmost sheet  3  of the stack on the pressing plate  167  is pressed against the feed roller  8  by the urging force of the spring  167   b . A printing process begins when print data is received from a host computer (not shown). At the beginning of the printing process, the topmost sheet of the sheet  3  is conveyed between the feed roller  8  and rubber pad  201   a  by frictional force generated between the rotating feed roller  8  and the sheet  3 . Because the rubber pad  201   a  always contacts the feed roller  8  at the same angle and with the same urging force from the spring  201   d , the rubber pad  201   a  separates the sheets  3  with uniform precision, so that separated sheets  3  can be conveyed to the register rollers  12  one sheet at a time. That is, the separating pad  201  contacts the leading edge of the stacked sheets  3  (with respect to the direction of conveyance) at a prescribed angle of inclination and applies frictional force to the sheets  3 . Those sheets  3  that do not receive conveying force from the feed roller  8  are held in place by the frictional force from the separating pad  201 . Only the uppermost sheet  3  is transported because it is applied with the feed roller&#39;s conveyance force, which overcomes the friction is force of the rubber pad  201   a.    
   As shown in  FIG. 4 , the underside surface of the sheet  3  rubs over the rubber pad  201   a  while the feed roller  8  is conveying the sheet  3 . This generates paper dust. However, the paper dust removing roller  202  is charged by rubbing against the sponge  203  while the paper dust removing roller  202  rotates following rotation of the feed roller  8 . 
   Therefore, the generated paper dust is electrostatically attracted to the paper dust removing roller  202 . In addition, the sponge  203  scrapes the paper dust that was attracted to the paper dust removing roller  202  off from the paper dust removing roller  202 . The paper dust enters the paper dust accommodating unit formed by the accommodating section cover  170  and the side wall  160   b  and is spread to the left and right sections of the paper dust accommodating unit by the slanted surface  711   a  and slanted surface  171   b  (see  FIG. 2 ). Because paper dust is removed with this construction, it is possible to prevent disorders from occurring during an image forming process by the laser printer  1  caused by paper dust remaining on the sheet  3 . Although a portion of the paper dust that is not completely removed by the paper dust removing roller  202  may be conveyed toward the image forming unit on the sheet  3 , this paper dust is removed by the paper dust removing roller  10  disposed further downstream in the conveying direction. 
   The laser beam emitting section (not shown) of the scanner unit  16  generates a laser beam based upon a laser drive signal generated by an engine base plate  98 . The laser beam falls incident on the polygon mirror  19 . The polygon mirror  19  affords the laser beam with a scan movement in a main scanning direction (the direction perpendicular to the conveying direction of the sheet  3 ) while reflecting the laser beam toward the fθ lens  20 . The fθ lens  20  converts the constant angular speed of the laser light from the polygon mirror  19  to a constant velocity scan. Then, the reflecting mirror  21   a  reflects the laser beam toward the lens  22 , which converges the laser beam. The reflecting mirror  21   b  reflects the converged laser beam to focus on the surface of the photosensitive drum  27 . 
   The Scorotron charger  29  charges the surface of the photosensitive drum  27  to a surface potential of, for example, approximately 1000 V. The laser beam from the scanner unit  16  scans across the surface of the photosensitive drum  27  in the main scan direction. The laser beam selectively exposes and does not expose the surface of the photosensitive drum  27  based on the laser drive signal described above. That is, portions of the surface of the photosensitive drum  27  that are to be developed are exposed by the laser light and portions that are not to be developed are not exposed. The surface potential of the photosensitive drum  27  decreases to, for example, approximately 100V at exposed portions, also referred to as bright parts. Because the photosensitive drum  27  rotates clockwise as indicated by an arrow in  FIG. 1  at this time, the laser beam also exposes the photosensitive drum  27  in an auxiliary scanning direction, which is also the conveying direction of the sheet  3 . As a result of the two scanning actions, an electrical invisible image, that is, an electrostatic latent image is formed on the surface of the photosensitive drum  27  from exposed areas and unexposed areas, which are also referred to as dark parts. 
   The agitator  36  supplies the toner in the toner hopper  34  to the development chamber  37  by rotation of the agitator  36 . Then the supply roller  33  supplies the toner in the development chamber  37  to the developing roller  31  by rotation of the supply roller  33 . At this time, the toner is triboelectrically charged to a positive charge between the supply roller  33  and the developing roller  31  and is regulated to a layer with constant thickness by a layer thickness control blade  32 . A positive bias of, for example, approximately 300 to 400 V is applied to the developing roller  31 . The toner, which is borne on the developing roller  31  and charged positively, is transferred to the electrostatic latent image formed on the surface of the photosensitive drum  27  when the toner comes into contact with the photosensitive drum  27 . That is, because the potential of the developing roller  31  is lower than the potential of the dark parts (which are at a voltage of +1000 V) and higher than the potential of the bright parts (which are at a voltage of +100V), the positively-charged toner moves selectively to the bright parts where the potential is lower. In this way, a visible image of toner is formed on the surface of the photosensitive drum  27  and development is performed. 
   The registration rollers  12  perform a registration operation on the sheet  3  to deliver the sheet  3  so that the front edge of the visible image formed on the surface of the rotating photosensitive drum  27  and the leading edge of the sheet  3  coincide with each other. A negative constant voltage is applied to the transfer roller  30  while the sheet  3  passes between the photosensitive drum  27  and the transfer roller  30 . The negative constant voltage that is applied to the transfer roller  30  is lower than the potential of the bright part (+100 V), so the toner electrostatically clinging to the surface of the photosensitive drum  27  moves toward the transfer roller  30 . However, the toner is blocked by the sheet  3  and cannot transfer to the transfer roller  30 . As a result, the toner is transferred onto the sheet  3 . That is, the visible image formed on the surface of the photosensitive drum  27  is transferred onto the sheet  3 . 
   Then, the sheet  3  having the toner transferred thereon is conveyed to the fixing device  18 . The heating roller  41  of the fixing device  18  applies heat of approximately 200 degrees, and the pressing roller  42  applies a pressure, to the sheet  3  with the toner image to fix the toner image permanently on the sheet  3 . Note that the heating roller  41  and the pressing roller  42  are each grounded through diodes so that the surface potential of the pressing roller  42  is lower than the surface potential of the heating roller  41 . Accordingly, the positively charged toner that clings to the heating roller  41  side of the sheet  3  is electrically attracted to the lower surface potential of the pressing roller  42 . Therefore, the potential problem of the toner image being distorted because the toner is attracted to the heating roller  41  at the time of fixing is prevented. 
   The sheet delivery roller  43  delivers the sheet  3  with the fixed toner image from the fixing device  18  and conveys the sheet  3  on the sheet delivery path  44 . The sheet delivery roller  45  delivers the sheet  3  to the sheet delivery tray  46  with a toner image side facing downward. Similarly, the sheet  3  to be printed next is stacked over the earlier delivered sheet  3  with a printed surface facing downward in the delivery tray  46 . In this way, a user can obtain the sheets  3  aligned in the order they were printed. 
   To remove the paper supply cassette  6 , the user can grip the handle part  180  with the user&#39;s fingers or the like between the plate surface  180   a  and the handle section  180   b  shown in  FIG. 4  and pull the paper supply cassette  6  outward to replace the sheet  3  or the like. At this time, the user may accidentally grip the paper conveying path  183  formed vertically in the paper supply cassette  6  (Y direction). However, since the ridges of the guiding ribs  172  and guiding ribs  182  are rounded to form curved surfaces, there will be only a small line load if the user accidentally touches the ridges. Therefore, there is no risk of the user harming his or her fingers. 
   As shown in  FIG. 2 , the four screws  164  fixing the handle part  180  to the case unit  160  are all screwed into the screw receivers  181  following the same direction (−Z direction). Hence, all the screws can be screwed in from the same direction when assembling the paper supply cassette  6 . The positions where the screws fix the handle part  180  to the case  160  incur a load when the user pulls on the handle part  180  to remove the paper supply cassette  6 . However, these fixed areas are strong enough to withstand such a load because the handle part  180  is fixed by screws rather than hooks. Further, the handle part  180  is securely fixed because a plurality of screws are used. The screw holes  163  formed near the ends of both protruding ends  160   f  and  160   g  on the side wall  160   b  are separated a sufficient distance from the side wall  160   c  and side wall  160   d . Hence, assembly of the paper supply cassette  6  can be performed smoothly without interference between the screwdriver or other tool and the side wall  160   c  and side wall  160   d.    
   Generally, the separation portion  166  must be mounted into the paper supply cassette  6  with high precision. Also, the separation portion  166  must be demonstrated to have sufficient separating performance prior to shipping the product. Because the paper supply cassette  6  includes the separately-formed case unit  160 , accommodating section cover  170 , and handle part  180 , time and effort required to redesign the separation portion  166  and once again demonstrate its separating performance can be spared. Hence, when modifications are made to the design of the laser printer  1 , the case unit  160  can be used without change, since its separating performance for conveying the sheet  3  has already been demonstrated. Further, a newly designed handle part can be fixed to this case unit  160  to form the paper supply cassette. In this way, it is possible to eliminate the time and effort required to redesign the separation portion  166  and to demonstrate its separating performance. 
   Further, because the case unit  160  and handle part  180  are fixed by inserting screws all in a single direction, the manufacturing process can be simplified. The use of a plurality of screws to fix these components also improves the fixing strength. 
   Further, because components of the paper supply cassette  6  on one side of the receiving portion  160   i  are molded separately from those on the other side, the receiving portion  160   i  can be said to serve as one edge of the case unit  160 . Accordingly, the mold used to form the receiving portion  160   i  can be designed with a greater degree of freedom that takes heat dissipated during the molding process into consideration. This enables forming the receiving portion  160   i  with high precision. 
   Since the handle part  180 , case unit  160 , and accommodating section cover  170  are each formed separately through injection molding, manufacturing process of these components is simplified. Also, when modifications are made to the design of the laser printer  1 , only molds for the modified components need to be remanufactured. Further, since the parting lines can be set separately for each component, it is possible to set a larger draft angle to facilitate the rounding of edges and the like. Hence, production costs for the paper supply cassette  6  are less than production costs for a conventional paper supply cassette, thereby enabling a reduction in the overall production cost of the laser printer  1 . 
   As shown in  FIG. 10 , the handle part  180  has a width in X directions that is equal to or less than the width of the main casing  2 . Note that the X directions are orthogonal to the mounting direction of the paper supply cassette  6 . Therefore, the handle part  180  does not stick out on the left and right sides of the main casing  2 . This provides a sense of unity with the design of the main casing  2 . 
   Further, paper dust that the paper dust removing roller  202  removes from the sheet  3  accumulates in the paper dust accommodating unit formed by the accommodating section cover  170  and the side wall  160   b . Accordingly, the limited space within the paper supply cassette  6  can be used effectively without needing to provide a separate paper dust accommodating unit. In addition, the ridges of the guiding ribs  172  and guiding ribs  182  are formed with curved surfaces and no sharp edges. Therefore, if the user accidentally grips the guiding ribs  172  or guiding ribs  182  with his or her fingers when reloading the sheet  3  in the paper supply cassette  6 , for example, the guiding ribs  172  and guiding ribs  182  will not hurt the user&#39;s fingers because the design is safe. 
   While the invention has been described in detail with reference to specific embodiments thereof, it would be apparent to those skilled in the art that many modifications and variations may be made therein without departing from the spirit of the invention, the scope of which is defined by the attached claims. 
   For example, a handle unit  185  shown in  FIG. 11  can be fixed to the case unit  160  instead of the accommodating section cover  170  and the handle part  180 . The handle unit  185  has no guide ribs. In this modification, the handle unit  185  is formed with a surface facing the −Z direction that is identical to that of the handle part  180 . However, the handle unit  185  has a surface facing the +Z direction that is formed with inner wall surfaces  185   a . The inner wall surfaces  185   a  encompass the area of the side wall  160   b  where the vibration absorbing members  165  are provided, but do not cover the protruding ends  160   f  and  160   g . As with the handle part  180 , when the handle unit  185  is fixed to the case unit  160 , an enclosed space is formed by the inner wall surfaces  185   a  and the side wall  160   b . This enclosed space functions as a paper dust accommodating unit for accumulating paper dust from the sheet  3  that is generated by friction between the sheet  3  and the rubber pad  201   a -shown in  FIG. 7 . 
   The embodiment describes the paper supply cassette as being used in a laser printer with only a single paper supply cassette. However, the paper supply cassette according to the present invention can be used as the lower paper supply cassette in a laser printer that has two paper supply cassettes. In this way, it is possible to simplify the production process by reducing the number of parts used in assembly. In other words, because the paper conveying path  183  is formed by the handle part  180  and accommodating section cover  170 , the handle part  180  and accommodating section cover  170  can be used when the paper conveying path  183  is necessary and can be easily replaced by the handle unit  185  when the paper conveying path  183  is not necessary. 
   The embodiment describes the accommodating section cover  170  formed with guiding ribs  172  that have curved ridges  172 A. However, an accommodating section cover  270  shown in  FIG. 12  can be provided instead. The accommodating section cover  270  is formed with guiding ribs  272  having ridges  272 A that slant with respect to the direction perpendicular to the conveying direction. In other words, each ridge  272 A is formed with a slanting surface that extends along the ridge  272 A. 
   Also, the embodiment describes the accommodating section cover  170  formed with guiding ribs  172  that in the Z direction arch from the Y directions. However, the arch shape can be formed using flat surfaces arranged at slanting angles with respect to the Y directions. For example, as shown in  FIG. 13 , an accommodating section cover  370  is formed with guiding ribs  372  that include two slanting surfaces  372 A and  372 B instead of the smooth arc shape of the guiding ribs  172 . As shown in  FIG. 14 , an accommodating section cover  470  is formed with guiding ribs  472  that include a flat surface  472 B in its Y-direction center and two slanting surfaces  472 A and  472 C at either side of the flat surface  472 B.