Patent Publication Number: US-8977185-B2

Title: Configuration for an image forming apparatus having an upright recording medium storage unit

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the foreign priority benefit under Title 35, United States Code, §119(a)-(d) of Japanese Patent Application No. 2007-092115 filed on Mar. 30, 2007 in the Japan Patent Office, the disclosure of which is herein incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an image forming apparatus such as a laser printer. 
     As an image forming apparatus such a laser printer, an upright-type image forming apparatus is generally known. For example, Japanese Laid-open Patent Application No. 2003-302889 discloses such an upright-type image forming apparatus, in which a paper feed tray (recording sheet storage unit) for storing papers as recording sheets and a paper output tray (recording sheet receiving unit) are arranged back and forth with these trays positioned upright. 
     In this image forming apparatus, the paper feed tray is arranged higher than the paper output tray, so that a paper conveyance passage extending from a lower part of the paper feed tray to a lower part of the paper output tray for conveying a paper is bent to form an L-shaped configuration. An image forming unit which forms an image on a paper is positioned intermediate of this paper conveyance passage at an extension extending downward from the lower part of the paper feed tray. 
     More specifically, the image forming unit includes a developer unit equipped with a toner cartridge and a developing roller, and a fixing device for thermally fixing developer that is transferred on a paper. The image forming unit is arranged such that the fixing device is positioned below the developer unit on the paper conveyance passage. Further, in this image forming apparatus, the toner cartridge is arranged between the paper output tray and the paper feed tray. 
     However, in this image forming apparatus, because the fixing device is positioned below the developer unit, heat generated at the fixing device rises to the developer unit. This may cause the developer unit to be heated disadvantageously, and as a result heat deterioration of the developer may occur. Further, because this image forming apparatus is configured such that the toner cartridge is arranged between the paper output tray and the paper feed tray, the size of the whole apparatus becomes disadvantageously large in a horizontal direction. 
     In view of the foregoing drawbacks of the prior art, the present invention seeks to provide an upright-type image forming apparatus which can restrict an increase in the size of the apparatus in the horizontal direction as well as heat deterioration of the developer. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided an image forming apparatus comprising a recording sheet storage unit for storing recording sheets substantially in an upright position, an image forming unit which forms an image on a recording sheet conveyed from the recording sheet storage unit, and a recording sheet receiving unit for storing the recording sheet conveyed from the image forming unit substantially in an upright position. In the image forming apparatus, a paper conveyance passage for conveying the recording sheet extends upward from a lower portion of the recording sheet storage unit toward the recording sheet receiving unit. The image forming unit positioned on the paper conveyance passage comprises a fixing device and a developer unit at least including a developer carrier, and the fixing device is arranged above the developer unit. Further, a developer receptacle for storing developer that is supplied to the image forming unit is arranged adjacent to one longitudinal end of the developer carrier. 
     With this configuration of the image forming apparatus, the developer receptacle is arranged adjacent to one longitudinal end of the developer carrier. Because the developer receptacle is not positioned between the recording sheet storage unit and the recording sheet receiving unit, it is possible to reduce the distance between the recording sheet storage unit and the recording sheet receiving unit to the extent corresponding to the size of the developer receptacle, thereby reducing the size of the image forming apparatus in the horizontal direction. Further, because the fixing device is arranged above the developer unit at least including the developer carrier, the developer carrier, etc. of the developer unit are not heated by the heat generated and rising from the fixing device. This can prevent heat deterioration of the developer. 
     According to the present invention, it is possible to reduce the size of the image forming apparatus in the horizontal direction. It is also possible to prevent heat deterioration of the developer due to heat generated and rising from the fixing device. 
     Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and aspects of the present invention will become more apparent by describing in detail illustrative, non-limiting embodiments thereof with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a laser printer as an image forming apparatus according to one embodiment of the present invention; 
         FIG. 2  is a perspective view showing the laser printer of  FIG. 1  with a top cover, a front cover, and a front side cover opened; 
         FIGS. 3A and 3B  are vertical sections of the laser printer, in which  FIG. 3A  shows a state where a process cartridge is attached to the laser printer, and  FIG. 3B  shows a state where the process cartridge is detached from the laser printer; 
         FIG. 4  is a vertical section of the laser printer showing a state where a paper feed tray is pulled out from the laser printer in an upward direction; 
         FIG. 5  is a top view showing the configuration of a toner feed auger, a toner collect auger, and a feed roller; 
         FIGS. 6A and 6B  are front views of a toner cartridge to be detachably mounted in a toner cartridge storage section, in which  FIG. 6A  shows a state where an operating handle is in an engaged position, and  FIG. 6B  shows a state where the operating handle is in a disengaged position; 
         FIG. 7  is a right side view of the toner cartridge; 
         FIGS. 8A and 8B  are vertical sections of the toner cartridge as seen from the front side, in which  FIG. 8A  shows a state where the operating handle is in the engaged position, and  FIG. 8B  shows a state where the operating handle is in the disengaged position; 
         FIG. 9A  is a vertical section of the toner cartridge as seen from the left side, and  FIG. 9B  is a left side view of the toner cartridge; 
         FIGS. 10A and 10B  are rear views of the toner cartridge, in which  FIG. 10A  shows a state where the operating handle is in the engaged position, and  FIG. 10B  shows a state where the operating handle is in the disengaged position; 
         FIGS. 11A and 11B  are front views of the toner cartridge storage section, in which  FIG. 11A  shows a state where a shutter member is released, and  FIG. 11B  shows a state where the shutter member is closed; 
         FIGS. 12A and 12B  show the toner cartridge received in the toner cartridge storage section, in which  FIG. 12A  shows a state where the operating handle is in the engaged position, and  FIG. 12B  shows a state where the operating handle is in the disengaged position; 
         FIGS. 13A and 13B  are perspective views partly showing the inner lower structure of the toner cartridge storage section as shown in  FIGS. 11A and 11B , in which  FIG. 11A  shows a state where the shutter member is released, and  FIG. 11B  shows a state where the shutter member is closed; and 
         FIG. 14  is a vertical section showing a modification of the laser printer. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     One preferred embodiment of the present invention will be described in detail with reference to the attached drawings. 
     Exterior of Laser Printer 
     As seen in  FIGS. 1 and 2 , an image forming apparatus according to one embodiment of the present invention is provided as an upright-type laser printer  1 , which has a relatively short length in the front-back direction compared to the right-and-left direction and the height of which is tall. 
     The laser printer  1  has a main body casing  2 . A top cover  3  is provided at an upper part of the main body casing  2 , and a paper output tray  4  is positioned at a front upper part of the main body casing  2 . Provided at a front lower part of the main body casing  2  is a front lower cover  5  which is pivotally supported in the main body casing  2  to open and close a space for attaching a process cartridge  11  to be described later. A toner cartridge storage section  6  in the form of a longitudinal box is positioned at the left side of the main body casing  2  as seen from the front side of the laser printer  1 , and a front side cover  7  is pivotally supported to open and close a front opening of the toner cartridge storage section  6 . 
     As seen in  FIG. 2 , the rear end portion of the top cover  3  is pivotally connected to the upper end portion of a paper feed tray  8  that is arranged in an upright position. When lifting the front end portion of the top cover  3  in the upward direction, a paper loading opening  8 A is released at the upper end of the paper feed tray  8 . 
     The paper output tray  4  is substantially parallel to the paper feed tray  8  and arranged in an upright position. The paper output tray  4  is positioned ahead of the paper feed tray  8  so that the paper feed tray  8  and the paper output tray  4  are arranged back and forth. A paper output opening  4 A opens at the upper end of the paper output tray  4 . 
     The front lower cover  5  is pivotally connected at its lower end portion to the lower part of the main body casing  2 , so that when pivotally rotating the upper end portion of the front lower cover  5  in the downward direction, an attachment opening  9  for the process cartridge  11  is released. 
     The front side cover  7  is pivotally supported at its lower end portion to the lower part of the toner cartridge storage section  6 . When pivotally rotating the upper end portion of the front side cover  7  in the downward direction, atoner cartridge  40  to be described later can be removed from the main body casing  2  by sliding it in the forward direction. 
     Internal Structure of Laser Printer 
     As seen in  FIGS. 3A and 3B , a feeder unit  10 , the process cartridge  11  as an example of the image forming unit, a scanner unit  12 , and a fixing device  13  are arranged in the main body casing  2 . The feeder unit  10  pulls out a paper (not shown) downward from the paper feed tray  8  and feeds the paper to the process cartridge  11 . The process cartridge  11  forms an image on the paper to be fed from the feeder unit  10 . The paper output tray  4  is also arranged in the main body casing  2  so as to receive and store papers on which images are formed by the image forming unit. 
     Structure of Paper Feed Tray 
     The paper feed tray  8  as a recording sheet storage unit stores a stack of papers in a state where the papers are placed substantially in an upright position. A paper pressure plate  14  is provided in the paper feed tray  8  so as to press the lower end of the stack of papers toward a paper feed opening  8 B provided at the lower part of the paper feed tray  8 . The paper feed tray  8  can be pulled out upward from the main body casing  2  (See  FIG. 4 ). 
     Structure of Paper Output Tray 
     The paper output tray  4  as a recording sheet receiving unit stores printed papers that are sequentially fed from the fixing device  13  in a sate where the papers are placed substantially in an upright position. The paper output tray  4  forms an installation space for the scanner unit  12  with the paper feed tray  8 . The lower end of the paper output tray  4  is positioned higher than the lower end of the paper feed tray  8 . Provided downward of the paper output tray  4  are the feeder unit  10 , the process cartridge  11 , and the fixing device  13 , which are arranged in this order along a paper conveyance passage and from the bottom of the laser printer  1 . 
     The paper output opening  4 A at the upper end of the paper output tray  4  is positioned substantially at the same height as the upper end of the paper feed tray  8 , and papers are stored in the paper output tray  4  with the upper ends thereof protruding from the paper output opening  4 A. For this reason, a paper support  15  is provided just behind the paper output opening  4 A of the paper output tray  4 . The paper support  15  is slidably mounted so that when in use it is pulled upward from the main body casing  2  to thereby prevent printed papers from falling over. Provided at the front lower side of the paper output tray  4  are a pair of paper output rollers  16 ,  16  for feeding a paper to the paper output tray  4  (see  FIG. 4 ). The lower end (bottom portion) of the paper output tray  4  is positioned higher than the lower end (bottom portion) of the paper feed tray  8 . 
     Structure of Feeder Unit 
     The feeder unit  10  is positioned adjacent to the paper feed opening  8 B at the lower part of the paper feed tray  8 . As best seen in  FIG. 4 , the feeder unit  10  includes a feed roller  17  which pulls out a paper downward from the paper feed tray  8  and feeds the same to the subsequent process, a separation pad  18  and a separation roller  19  between which the lower end of the paper (i.e., leading end of the paper along the conveyance direction) is fed so that the paper is separated and fed on one-by-one basis, a registration roller  20  with which a leading end of the paper that is fed from the separation roller  19  is brought into contact so that the paper is temporarily constrained and thereafter conveyed upward to the process cartridge  11 . The registration roller  20  is positioned ahead of the separation roller  19  closer to the front side of the main body casing  2 , and conveys the paper upward to the process cartridge  11 . 
     Structure of Process Cartridge 
     A toner cartridge  40  to be described later as an embodiment of a developer receptacle is separable from the process cartridge  11 . The process cartridge  11  includes a toner feed auger  21  and a toner collect auger  22  as an example of a developer carrying member, a feed roller  23 , a developing roller  24  as an example of a developer carrier, a photosensitive drum  25 , a charger  26 , and a transfer roller  27 . 
     The toner feed auger  21 , the toner collect auger  22 , and the feed roller  23  supply the developing roller  24  with toner (developer) stored in the toner cartridge  40  to be described later as well as collect remaining toner and return it into the toner cartridge  40 . As best seen in  FIG. 5 , the toner feed auger  21 , the toner collect auger  22 , and the feed roller  23  are accommodated in a development chamber  29  that is defined in a cartridge body  28 . The development chamber  29  is arranged just below the developing roller  24  as shown in  FIG. 4 . 
     As seen in  FIG. 5 , the toner feed auger  21  is adjacent to and parallel with the feed roller  23 . When the toner feed auger  21  is actuated, for example, by rotating the rotational shaft  21 A in the clockwise direction of  FIG. 4 , toner is carried in the horizontal direction from one end of the toner feed auger  21  to the other. In other words, toner is carried axially along the toner feed auger  21  from one lower end of  FIG. 4  to the other upper end, so that toner is uniformly axially supplied over the surface of the feed roller  23 . 
     The toner collect auger  22  is adjacent to and parallel with the toner feed auger  21 . However, a separation wall  28 A formed in the cartridge body  28  is interposed and separates the toner collect auger  22  from the toner feed auger  21 . The separation wall  28 A divides the development chamber  29  into two half chambers (reference numerical omitted). The toner collect auger  22  rotates in the reverse direction of the toner feed auger  21 . When the toner collect auger  22  is actuated by rotating the rotational shaft  22 A in the anticlockwise direction of  FIG. 4 , that is in the reverse rotational direction of the rotational shaft  2 A of the toner feed auger  21 , toner is carried axially along the toner collect auger  22  from the upper end of  FIG. 5  to the other lower end. 
     As seen in  FIG. 5 , the two half chambers are communicated to each other at one end (i.e., upper end of  FIG. 5 ) of the development chamber  29 , so that remaining toner carried by the toner feed auger  21  axially toward this one end is collected and carried back toward the other end of the development chamber  29 . 
     Detachable Structure of Process Cartridge 
     The process cartridge  11  is attached to and detachable from the main body casing  2  through the attachment opening  9  when the front lower cover  5  is opened as shown in  FIG. 2 . As seen in  FIGS. 2 to 4 , guide grooves  30 ,  30  are formed in the right and left inner side walls of the main body casing  2  around the attachment opening  9 . The guide grooves  30 ,  30  extend in the forward and backward direction of the main body casing  2 . As seen in  FIG. 3A , the rotational shaft  25 A of the photosensitive drum  25  extends outward from both side surfaces of the cartridge body  28  of the process cartridge  11  so that the both ends of the rotational shaft  25 A are slidably guided along the guide grooves  30 ,  30  of the main body casing  2 , thereby allowing sliding engagement and disengagement of the process cartridge  11  relative to the main body casing  2 . 
     According to this detachable structure, the process cartridge  11  is inserted from the attachment opening  9  provided at the front side of the laser printer  1 , and it is attached to a predetermined position of the main body casing  2  below the fixing device  13 . See  FIG. 3A . Meanwhile, the process cartridge  11  is easily removed from the predetermined position of the main body casing  2  by pulling out the process cartridge  11  through the attachment opening  9  of the laser printer  1 . See  FIG. 3B . 
     Operation of Process Cartridge 
     In the process cartridge  11 , the toner feed auger  21  as shown in  FIG. 5  supplies toner to the surface of the feed roller  23 . As seen in  FIG. 4 , toner that is supplied to the surface of the feed roller  23  makes a frictional contact with the developing roller  24  and is charged positively. Therefore, the toner adheres and is deposited on the surface of the developing roller  24 . A doctor blade  60  wipes off the deposited toner and restricts the thickness of the toner so that a thin toner layer having a constant thickness is formed on the developing roller  24 . 
     The photosensitive drum  25  includes a photosensitive layer having positive charge characteristics. When the charger  26  generates and applies a corona discharge from a charge wire made of tungsten, etc., the photosensitive layer formed on the surface of the photosensitive drum  25  is uniformly charged in the plus polarity. The positively charged photosensitive layer on the photosensitive drum  25  is then exposed to a laser beam irradiated from the scanner unit  12  based on image data. This exposure process lowers the potential of an exposed area on the photosensitive layer, so that a latent image associated with the image data is formed on the photosensitive drum  25 . 
     Plus charged toner carried on the developing roller  24  adheres to the latent image that is formed on the photosensitive layer of the photosensitive drum  25 . By this reversal process, a toner image is formed on the photosensitive layer of the photosensitive drum  25 . A paper is conveyed along the paper conveyance passage and passes between the photosensitive drum  25  which carries the toner image on the photosensitive layer and the transfer roller  27 , during which the toner image is transferred on the paper. The transfer roller  27  includes a roller shaft, which is made of metal and covered with a rubber material. When a transfer bias is applied to the transfer roller  27 , the toner image formed on the photosensitive drum  25  is transferred to the paper. 
     Structure of Scanner Unit 
     As best seen in  FIG. 4 , the scanner unit  12  is arranged between the paper output tray  4  and the paper feed tray  8 . The scanner unit  12  is installed in an upright position using a dead space formed between the paper output tray  4  and the paper feed tray  8 . The scanner unit  12  includes a polygon mirror  31  which is rotatively driven to perform high speed scanning, a lens  32 , a reflecting mirror  33 , etc. The photosensitive layer of the photosensitive drum  25  is exposed when a laser beam is emitted and reflected at the reflecting mirror to irradiate the photosensitive layer based on the image data. 
     The polygon mirror  31  is arranged such that the rotation shaft of the polygon mirror  31  extends in the horizontal direction. 
     Structure of Fixing Device 
     The fixing device  13  is arranged above the process cartridge  11 . The fixing device  13  includes a heating roller  34  and a pressure roller  35  which are positioned oppositely and rotate to pinch and convey a paper toward the paper output tray  4 , and a pair of conveyance rollers  36 ,  36 . The pair of conveyance rollers  36 ,  36  are positioned downstream of the paper conveyance passage so as to receive the paper from the heating roller  34  and the pressure roller  35  and to convey the same to the pair of paper output rollers  16 ,  16 . 
     Operation of Fixing Device 
     A paper on which a toner image has been transferred between the photosensitive drum  25  and the transfer roller  27  in the process cartridge  11  is conveyed and passes between the heating roller  34  and the pressure roller  35  provided in the fixing device  13 . During this time the toner image formed on the paper is thermally fixed by the heating roller  34 . 
     Paper Conveyance Passage 
     The paper conveyance passage along which a paper is conveyed extends from the paper feed tray  8  toward the paper output tray  4 . The paper conveyance passage has a substantially U-shaped configuration and protrudes downward from the paper feed tray  8  and the paper output tray  4 . The paper conveyance passage is defined by the feed roller  17 , the separation roller  19 , guide rollers  19 A, a paper guide  38 , the registration roller  20 , the photosensitive drum  25  and the transfer roller  27 , the heating roller  34  and the pressure roller  35 , the conveyance rollers  36 ,  36 , and the paper output rollers  16 ,  16 , etc. Of this conveyance passage, the passage from the registration roller  20  to the paper output rollers  16 ,  16  is directed to the upward direction as shown in  FIG. 3 . 
     According to this embodiment, the guide rollers  19 A,  19 A are positioned oppositely to the separation roller  19 . The feed roller  17  is a roller by which a paper stored in the paper feed tray  8  is conveyed downward through the paper feed opening  8 B provided at the lower part of the paper feed tray  8 . When a paper is conveyed along the paper conveyance passage and passes between the separation roller  19  and the guide roller  19 A and also through the paper guide  38 , the paper is curved into a U-shape with the front side and the reverse side thereof being turned over at the leading end. 
     The paper conveyance passage having a substantially U-shaped configuration and protruding downward indicates that the paper conveyed from the paper feed tray  8  is guided downward and then the paper is reversed while the leading end of the paper is curved into a U-shape, and thereafter the paper is guided and conveyed upward. The outlet of the paper conveyance passage is formed between the paper output rollers  16 ,  16 . Further, the paper feed opening  8 B is provided at the lower part of the paper feed tray  8 , and the paper discharge opening (reference numeral omitted) of the paper output tray  4  is positioned higher than the paper feed opening  8 B of the paper feed tray  8 . 
     In other words, the substantially U-shaped paper conveyance passage directly connects between the paper feed opening  8 B of the paper feed tray  8  and the paper discharge opening of the paper output tray  4 . 
     Further, in this U-shaped paper conveyance passage, the vertical distance from the paper feed opening  8 B of the paper feed tray  8  to the bottom portion of the conveyance passage (also referred to as a “downward conveyance passage”) is smaller than the vertical distance from the bottom portion of the conveyance passage to the paper discharge opening of the paper output tray  4  (also referred to as an “upward conveyance passage”). Therefore, the registration roller  20 , the process cartridge  11 , and the fixing device  13  can be arranged in this order along the upward conveyance passage. 
     To be more specific, the U-shaped paper conveyance passage is configured such that the upward conveyance passage is longer in the vertical distance than the downward conveyance passage. This makes it possible to reduce the vertical size of the laser printer  1  around the paper feed tray  8  when compared with the configuration in which the upward conveyance passage is shorter in the vertical distance than the downward conveyance passage. Therefore, it is possible to arrange the paper feed tray  8  in a lower position of the main body casing  2 , which facilitates a paper loading operation into the paper feed tray  8  and thereby improves the operationality of the laser printer  1 . 
     Especially, according to this embodiment, the paper feed tray  8  is pulled out upward from the main body casing  2  upon loading papers into the paper feed tray  8 . In this instance, the paper feed tray  8  is readily pulled out upward and the paper loading operation is easily performed if the paper feed tray  8  is arranged in a lower position of the main body casing  2  as described above. 
     Structure of Manual Paper Feed Unit 
     As seen in  FIG. 4 , a lower cover  37  is pivotally connected to the lower part of the main body casing  2 . The lower cover  37  is positioned below the front lower cover  5  and covers the region around the registration roller  20 . The lower cover  37  has an arcuately curved section, the lower end of which is pivotally supported in the main body casing  2 . In order to form a continuous surface with the lower end portion of the lower cover  37  opened, in the main body casing  2  the paper guide  38  has a guide surface  38 A which curves upward toward the registration roller  20 . 
     When the lower cover  37  is pivotally rotated downward to the position of  FIG. 4 , the arcuately curved inner surface of the lower cover  37  comes in contact with the guide surface  38 A of the paper guide  38  to form a continuous surface so that a paper is guided along this continuous surface and supplied toward the registration roller  20 . Therefore, a manual paper feed unit  39  is formed at the front side of the laser printer  1  by the lower cover  37  and the paper guide  38 . 
     Structure of Toner Cartridge 
     The toner cartridge  40  has a front shape as shown in  FIGS. 6A and 6B  and a right side elevation as shown in  FIG. 7 . The toner cartridge  40  is received in the toner cartridge storage section  6  as shown in  FIG. 1  in a such a position to be adjacent to one longitudinal end of the developing roller  24  (see  FIG. 3 ). To be more specific, the toner cartridge  40  is positioned on the lower end side of  FIG. 5  adjacent to the toner feed auger  21  and the toner collect auger  22 , and is received in the toner cartridge storage section  6  as shown in  FIG. 1 . 
     As seen in  FIGS. 6A ,  6 B and  FIG. 7 , the toner cartridge  40  includes a toner receptacle unit  41  in the form of a longitudinal box, and a toner feed unit  42  provided below and in communication with the toner receptacle unit  41 . The toner feed unit  42  is in the form of a hollow cylinder. The toner receptacle unit  41  is a receptacle for storing toner as developer. The toner feed unit  42  receives toner from the toner receptacle unit  41 , and supplies the toner feed auger  21  with toner as well as collects remaining toner from the toner collect auger  22 . 
     As best seen in the front-side vertical sections of  FIGS. 8A and 8B , the toner receptacle unit  41  and the toner feed unit  42  are in communication with each other through a slit-shaped communication hole  43 , so that toner stored in the toner receptacle unit  41  is filled into the toner feed unit  42  through the communication hole  43 . An upper agitator  44  is provided in the toner receptacle unit  41  so as to force toner out from the toner receptacle unit  41  though the communication hole  43 . Similarly, a lower agitator  45  is provided in the toner feed unit  42  so as to agitate the toner that is supplied from the toner receptacle unit  41  through the communication hole  43 . 
     As seen in the vertical section of  FIG. 9A  and the rear views of  FIGS. 10A and 10B , the rotational shaft  44 A of the upper agitator  44  is driven by a driving gear  46  provided at the rear side surface of the toner receptacle unit  41 , and the rotational shaft  45 A of the lower agitator  45  is driven by a driving gear  47  also provided at the rear side surface of the toner receptacle unit  41 . The driving gear  46  and the driving gear  47  are meshed with an interlocking gear  48  so that the upper agitator  44  and the lower agitator  45  are synchronously rotated. The driving gear  46  is driven when a driving force is supplied from a motor provided in the printer main body (not shown). 
     As seen in  FIGS. 8A ,  8 B and  FIG. 9A , an inner cylinder  49  is provided in the toner feed unit  42 . The inner cylinder  49  is rotatable along the inner periphery of the toner feed unit  42 . The inner cylinder  49  is provided with an operating handle  49 A at the front end thereof. The operating handle  49 A protrudes from the front end of the inner cylinder  49  for manipulating the inner cylinder  49 . Provided at the rear end of the inner cylinder  49  is an operating protrusion  49 B for restricting the rotational position of the inner cylinder  49 . The operating protrusion  49 B is fitted into a fitting hole  50 B of a shutter member  50  (see  FIGS. 13A and 13B ) provided in the toner cartridge storage section  6 . 
     An operating protrusion  49 C for rotatively manipulating the shutter member  50  to be described later is formed on the front end portion of the outer peripheral surface of the inner cylinder  49 . Further, a slit-like toner introducing hole  49 D is formed in the peripheral wall of the inner cylinder  49  and extends along the axial direction of the inner cylinder  49 . 
     As best seen in  FIGS. 9A and 9B , the operating handle  49 A has a substantially lying U-shaped side section. As shown in  FIGS. 6A and 6B , both ends of the operating handle  49 A extend through arcuate openings  42 A,  42 A formed in the front side surface of the toner feed unit  42  so that the operating handle  49 A becomes rotatable in a predetermined angle range as seen from the front side of the toner feed unit  42 . 
     Similarly, as shown in  FIGS. 10A and 10B , the operating protrusion  49 B extends through an arcuate opening  42 B formed in the rear side surface of the toner feed unit  42  so that the rotating movement of the operating protrusion  49 B is restricted at both end portions of the arcuate opening  42 B. 
     When the operating handle  49 A is in an engaged position shown in  FIG. 6A , as seen in  FIG. 8A , the toner introducing hole  49 D of the inner cylinder  49  is in conformity with the communication hole  43  so that the tone receptacle unit  41  comes into direct communication with the toner feed unit  42  to thereby allow toner in the toner receptacle unit  41  to be introduced into and filled in the toner feed unit  42 . On the contrary, when the operating handle  49 A is in a disengaged position shown in  FIG. 6B , as seen in  FIG. 8B , the toner introducing hole  49 D of the inner cylinder  49  is not in communication with the communication hole  43  so that toner is not introduced into the toner feed unit  42 . 
     As best seen in  FIGS. 11A and 11B , the toner cartridge storage section  6  shown in  FIG. 2  includes an upper storage room  6 A whose shape corresponds with the front shape of the toner receptacle unit  41 , and a lower storage room  6 B whose shape corresponds with the front shape of the toner feed unit  42 . The upper storage room  6 A and the lower storage room  6 B are continuously formed to receive therein the toner cartridge  40  as shown in  FIGS. 12A and 12B . 
     Toner Feed/Collect Mechanism 
     A right side wall lower portion  6 C, which constitutes the lower storage room  6 B of the toner cartridge storage section  6  as shown in  FIGS. 11A and 11B , abuts on one side end of the cartridge body  28  (i.e., lower end of  FIG. 5 ). Further, as a mechanism for supplying the development chamber  29  (see  FIG. 5 ) with toner stored in the toner feed unit  42  of the toner cartridge  40  and for collecting remaining toner from the development chamber  29  and introducing it into the toner feed unit  42 , as seen in  FIGS. 13A and 13B , a toner feed opening  6 D and a toner collect opening  6 E are formed in the side wall lower portion  6 C of the toner cartridge storage section  6 . 
     As seen in  FIG. 7 , a toner feed opening  42 C and a toner collect opening  42 D are formed in the peripheral wall of the toner feed unit  42  at right side of the toner feed unit  42  in a manner corresponding to the toner feed opening  6 D and the toner collect opening  6 E, respectively. Further, a toner feed opening  49 E and a toner collect opening  49 F are also formed in the peripheral wall of the inner cylinder  49  as shown in  FIG. 9A . 
     As seen in  FIGS. 13A and 13B , the shutter member  50  having an arcuate cross-section is provided at the inner side of the side wall lower portion  6 C of the toner cartridge storage section  6 . The shutter member  50  is slidable along the inner peripheral surface of the lower storage room  6 B (see  FIGS. 11A and 11B ). The shutter member  50  has a cutout  50 A for the engagement with the operating protrusion  49 C of  FIGS. 12A and 12B  and a fitting hole  50 B for the fitting engagement with the operating protrusion  49 B. 
     Operation of Toner Feed/Collect Mechanism 
     When the operating handle  49 A is in the engaged position as shown in  FIG. 6A , the toner feed opening  49 E and the toner collect opening  49 F of the inner cylinder  49  as shown in  FIG. 9A  are respectively in direct communication with the toner feed opening  42 C and the toner collect opening  42 D of the toner feed unit  42  as shown in  FIG. 7 . In this engaged position of the operating handle  49 A, the shutter member  50  is engaged with the operating protrusions  49 B,  49 C and has been rotated to a released position as shown in  FIG. 13A  to thereby release the toner feed opening  6 D and the toner collect opening  6 E. As a result, the toner feed opening  49 E of the inner cylinder  49 , the toner feed opening  42 C of the toner feed unit  42 , and the toner feed opening  6 D of the toner cartridge storage section  6  come into direct communication. Also, the toner collect opening  49 F of the inner cylinder  49 , the toner collect opening  42 D of the toner feed unit  42 , and the toner collect opening  6 E of the toner cartridge storage section  6  come into direct communication. 
     Therefore, when the operating handle  49 A is in the engaged position as shown in  FIG. 6A , toner stored in the toner feed unit  42  of the toner cartridge  40  is supplied to the toner feed auger  21  shown in  FIG. 5  through the toner feed openings  49 E,  42 C, and  6 D. At the same time, remaining toner carried by the toner collect auger  22  is collected and carried back toward the toner feed unit  42  through the toner collect openings  6 E,  42 D, and  49 F. 
     Meanwhile, when the operating handle  49 A is in the disengaged position as shown in  FIG. 6B , the toner feed opening  49 E and the toner collect opening  49 F of the inner cylinder  49  as shown in  FIG. 9A  are not in communication with the toner supply opening  42 C and the toner collect opening  42 D of the toner feed unit  42  as shown in  FIG. 7 . In this disengaged position of the operating handle  49 A, the shutter member  50  has been rotated to a closed position as shown in  FIG. 13B  to thereby close the toner feed opening  6 D and the toner collect opening  6 E. 
     Therefore, when the opening handle  49 A is in the disengaged position as shown in  FIG. 6B , supply of toner to the toner feed auger  21  (see  FIG. 5 ) is stopped. Also, collection of toner from the toner collect auger  22  is stopped. 
     Detachable Mechanism for Toner Cartridge 
     As seen in  FIG. 13 , as a detachable mechanism for the toner cartridge  40 , an engagement groove  6 F is formed in the peripheral wall of the lower storage room  6 B to which the shutter member  50  is slidably mounted. The engagement groove  6 F is engageable with the operating protrusion  49 C (see  FIGS. 9A and 9B ) that is rotatable with the operating handle  49 A of the inner cylinder  49 . 
     The engagement groove  6 F has an L-shaped configuration consisting of a straight portion which extends in the front and back direction of the inner peripheral wall of the lower storage room  6 B, and an arcuate portion which extends from the back end of the straight portion along the inner peripheral surface of the lower storage room  6 B. The straight portion of the engagement groove  6 F is formed in such a position that when the operating handle  49 A is in the disengaged position as shown in  FIG. 6B , the operating protrusion  49 C corresponds to the straight portion. The cutout  50 A of the shutter member  50  also conforms to the straight portion of the engagement groove  6 F. 
     Meanwhile, the arcuate portion of the engagement grove  6 F is formed to allow the movement of the operating protrusion  49 C when the operating handle  49 A is manipulated to rotate from the disengaged position to the engaged position as shown in  FIG. 6A . 
     Therefore, a user inserts the toner cartridge  40  into the toner cartridge storage section  6  from the front side of the laser printer  1  and slides it in the backward direction while the operating handle  49 A is in the disengaged position of  FIG. 6B . Thereafter, the user manipulates to rotate the operating handle  49 A into the engaged position of  FIG. 6A . Accordingly, it is possible to readily attach the toner cartridge  40 . It is also possible to readily disengage and pull out the toner cartridge  40  from the toner cartridge storage section  6  by the reverse operation. 
     As described above, according to the laser printer  1  as one embodiment of the image forming apparatus, a paper stored in the paper feed tray  8  is conveyed to the paper output tray  4  through the separation roller  19 , the registration roller  20 , the photosensitive drum  25  and the transfer roller  27 , the heating roller  34  and the pressure roller  35 , the conveyance rollers  36 ,  36 , and the paper output rollers  16 ,  16 . During the conveyance of the paper, a toner image is formed on the paper by the process cartridge  11  and the scanner unit  12  which are positioned along the paper conveyance passage, and thereafter the toner image is thermally fixed on the paper by the fixing device  13 . 
     A paper can also be inserted into the main body casing  2  through the manual paper feed unit  39  that is formed at the front side of the laser printer  1  with the lower cover  37  being opened. When the paper is inserted from the lower cover  37 , the paper is guided along the guide surface  38 A of the paper guide  38  and supplied to the registration roller  20 , by which the paper is carried toward the process cartridge  11 . After a toner image is formed and fixed on the paper, the paper is discharged and stored in the paper output tray  4 . 
     According to the laser printer  1 , because the fixing device  13  is arranged above the process cartridge  11  as the developer unit which comprises the developing roller  24 , etc., the process cartridge  11  is not heated by the heat generated and rising from the heating roller  34  of the fixing device  13 . The heat rising from the heating roller  34  of the fixing device  13  passes between the paper output rollers  16 ,  16  and goes through the paper output tray  4  and is smoothly discharged into the air. A heat release opening may be formed in the upper part of the main body casing  2 . 
     Namely, according to the laser printer  1 , heat deterioration of toner can be prevented in the process cartridge  11 . As a result, a high-quality toner image can be formed on a paper. 
     Further, in the laser printer  1  as one embodiment of the present invention, the toner cartridge  40  is arranged adjacent to one longitudinal end of the process cartridge  11  which includes the tone feed auger  21 , the toner collect auger  22 , the feed roller  23 , the developing roller  24 , etc. This can prevent the size of the laser printer  1  from increasing in the height as well as in the depth (width in the front-back direction). 
     Providing the toner feed auger  21  for carrying toner in the axial direction thereof enables toner to be carried smoothly from the toner cartridge  40  arranged adjacent to one longitudinal end of the process cartridge  11 . Further, because the development chamber  29  is arranged below the developing roller  24 , it is possible to reliably prevent toner in the development chamber  29  from leaking into the photosensitive drum  25 . 
     Further, the process cartridge  11 , the fixing device  13 , and the manual paper feed unit  39  are arranged below the paper output tray  4  by effectively utilizing a dead space. This can advantageously prevent an increase in the depth (width in the front-back direction) of the laser printer  1 . Further, because the toner cartridge  40  is separately detachable from the laser printer  1 , attachment and detachment of the toner cartridge  40  can be readily performed. Furthermore, because the toner cartridge  40  is pulled out from the front side of the laser printer  1 , even if the size of the toner cartridge  40  is large, it is possible to readily pull out the toner cartridge  40  from the laser printer  1 . 
     According to the laser printer  1 , the toner feed unit  42  is positioned substantially at the same height as the development chamber  29  in the horizontal direction. Therefore, toner is supplied and collected between the toner feed unit  42  and the development chamber  29  to thereby reliably and smoothly circulate the toner. 
     Further, the paper output opening  4 A is formed at the upper end of the paper output tray  4  so that discharged papers can be stored in the paper output tray  4  with the upper ends thereof protruding from the opening  4 A. This is advantageous because the height of the paper output tray  4  is restricted as low as possible, and papers protruding from the paper output opening  4 A of the paper output tray  4  can be readily removed by directly pulling them in the upward direction. Therefore, it is possible to improve the operationality of the laser printer  1 . 
     Especially, the upper end of the paper output tray  4  and the upper end of the paper feed tray  8  are substantially at the same height in the vertical direction, so that the paper feed tray  8  is readily pulled out from the main body casing  2  when compared with the configuration in which the paper output tray  4  protrudes upward to a greater extent from the paper feed tray  8 . 
     Papers stored in the paper feed tray  8  may not be conveyed reliably if the papers are bent or wrinkles are formed on the papers due to absorption of moisture. For this reason, in order to prevent papers from being bent, it is preferable that the paper feed tray  8  has a height longer than the height (length in the conveyance direction) of the papers to be stored therein. It is also preferable that the main body casing  2  surrounds all-around surfaces of the papers in order to shut out moisture. 
     On the contrary, the above drawbacks do not occur in the paper output tray  4 . Therefore, it is possible to form the paper output opening  4 A at the upper end of the paper output tray  4  so that papers protrude from the paper output opening  4 A. 
     Further, the bottom portion of the paper output tray  4  is positioned lower than the paper discharge opening, so that a sufficient height of the paper output tray  4  is ensured for supporting discharged papers in the tray  4  without protruding the paper output tray  4  upward to a greater extent from the main body casing  2 . 
     According to the laser printer  1 , the manual paper feed operation, the attachment and detachment of the process cartridge, the attachment and detachment of the toner cartridge, and the removal of papers from the paper output tray  4  are all performed from the front side of the laser printer  1 , thereby leading to improved operationality. Further the paper feed tray  8  can be pulled out upward from the main body casing  2 . Therefore, papers can be supplied from above the main body casing  2  as well as from the front side, leading to improved operationality. 
     Although the present invention has been described in detail with reference to the above preferred embodiment, the present invention is not limited to this specific embodiment and various changes and modifications may be made without departing from the scope of the appended claims. 
     In the above preferred embodiment, the present invention has been applied to the laser printer  1 . However, the present invention may be applicable to other image forming apparatus such as a copying machine and a multifunction device. 
     In the above preferred embodiment, the developing roller  24  is employed as the developer carrier. However, the present invention is not limited to this specific embodiment and, for example, a belt for carrying toner may be employed. 
     Further, in the above preferred embodiment, as an example of the developer unit, the process cartridge  11  includes the photosensitive drum  25 , etc. in addition to the developing roller  24 . However, the present invention is not limited to this specific embodiment. For example, in the case where the cartridge body  28  is separable between the photosensitive drum  25  and the developing roller  24 , a unit including the developing roller  24 , i.e., a developer cartridge, may be defined as the developer unit. 
     According to the above preferred embodiment, the laser printer  1  is configured as an upright-type printer in which the paper output tray  4  is installed in an upright position as shown in  FIGS. 3A and 3B . However, the present invention is not limited to this specific embodiment, and the paper output tray  4  may be tilted backward. One example of this configuration is shown in  FIG. 14 . As seen in  FIG. 14 , a supporting member  2 A is provided at a lower part of the main body casing  2 . The supporting member  2 A extends backward and supports the paper output tray  4  such that the whole laser printer  1  tilts backward to retain the paper output tray  4  in the backward tilting position. 
     Further, according to the above preferred embodiment, the toner feed auger  21  is positioned closer to the feed roller  23  and the toner collect auger  22  is positioned remote from the feed roller  23 . However, the present invention is not limited to this specific configuration, and they can be arranged reversely.