Patent Publication Number: US-7711311-B2

Title: Image forming apparatus with transparent window in sheet receiving surface

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an image forming apparatus such as a printer, a copier, a facsimile machine or a complex machine having functions of these apparatuses. 
   2. Description of the Related Art 
   An image forming apparatus such as a printer includes a developing mechanism for supplying toner particles to an image bearing member and a toner container for replenishing the developing mechanism with the toner particles. This toner container has a container main body for storing the toner particles and is normally detachably mounted in a main body of the image forming apparatus so as to be replaceable as the toner is used up. This holds true for an ink cartridge of the ink-jet type in a printer or the like. 
   Generally, an image forming apparatus has a casing structure, and component members such as the above image bearing member, developing mechanism and toner container are accommodated in the casing so as not to be visible from the outside (see, for example, Japanese Unexamined Patent Publication NO. 2006-23347). Upon replacing the toner container, a user opens an opening cover of the casing, takes the used toner container out from the inside of the casing, mounts a new toner container and closes the opening cover. The user can see the toner container only when the opening cover is open. 
   A printer or the like includes a sheet receiving surface for receiving a sheet discharged after an image forming process. For example, in a small-size printer generally used in an office or the like, an auxiliary tray is attached to this sheet receiving surface in many cases. This auxiliary tray is used to auxiliary support sheets upon discharging large-size sheets to the sheet receiving surface or for an improvement in the alignment of sheets. 
   In a conventional image forming apparatus, a user cannot know which toner container is actually mounted with the opening cover closed. In other words, the manufacturer and model number of the toner container mounted in the main body of the image forming apparatus cannot be known, and the opening cover had to be opened in order to know these. Accordingly, the user had to confirm the model number and the like by opening the opening cover every time despite its cumbersomeness, for example, in the case of ordering a new toner container or in the case of being required to notify the model number of the toner container at the time of requesting maintenance. 
   Accordingly, it is normally thought to provide a window on a sheet receiving surface of a printer located at a position easy to see by a user so that the user can see a part of a mounted toner container from the outside. However, the auxiliary tray is attached to the sheet receiving surface in many cases as described above and, if the window is additionally provided, it is not preferable in terms of design since the sheet receiving surface becomes unnecessarily complicated to impair an aesthetic impression. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide an image forming apparatus capable of avoiding making a sheet receiving surface look complicated while enabling a user to see a consumable supplying member such as a toner container or an ink cartridge mounted in an image forming apparatus main body to be seen from the outside. 
   In order to accomplish this object, one aspect of the present invention is directed to an image forming apparatus, comprising an apparatus main body having a casing structure and adapted to perform an image forming operation; a sheet receiving surface constituting a part of the casing structure and adapted to receive a sheet discharged after an image forming process is performed in the apparatus main body; a window provided on the sheet receiving surface for enabling a part of the interior of the apparatus main body to be seen; and an auxiliary tray attached to the sheet receiving surface and displaceable between an unfolded position to auxiliary support a discharged sheet and an accommodated position to be accommodated in the sheet receiving surface, wherein the window is provided at a bottom surface of a recess formed by recessing a part of the sheet receiving surface, and the auxiliary tray is accommodated in the recess when being located at the accommodated position and includes a transparent portion for ensuring the visibility of the window. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view showing the external appearance of a printer according to a first embodiment of the invention. 
       FIG. 2  is a schematic lateral section of the printer of  FIG. 1  along forward and backward directions. 
       FIG. 3  is a perspective view showing a state where a toner container is mounted in an apparatus main body. 
       FIG. 4  is a perspective view showing a state where the toner container is detached from the apparatus main body. 
       FIG. 5  is a top view of an opening cover and the toner container. 
       FIGS. 6A to 6E  are schematic top views showing variations of the shape of a window. 
       FIG. 7  is a section along VII-VII of  FIG. 5 . 
       FIG. 8  is a section along VII-VII of  FIG. 5  showing a modification. 
       FIG. 9A  is a top view of an auxiliary tray at an accommodated position and  FIG. 9B  is a top view of the auxiliary tray at an unfolded position. 
       FIG. 10  is a section along X-X of  FIG. 9A . 
       FIG. 11  is a perspective view showing a used state of the auxiliary tray. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, embodiments of the present invention are described with reference to the accompanying drawings. 
     FIG. 1  is a perspective view showing the external appearance of a printer  1  according to one embodiment of an image forming apparatus (apparatus for receiving a consumable supplying member) of the present invention. In  FIG. 1 , X-X directions are forward and backward directions, Y-Y directions are transverse directions, and Z-Z directions are vertical directions, wherein +X direction is forward direction; −X direction backward direction; +Y direction rightward direction; −Y direction leftward direction; +Z direction upward direction; and −Z direction downward direction. This holds true for other figures affixed with direction indicators. 
   The printer  1  (image forming apparatus) performs an image forming operation and an image transferring operation based on image information inputted from an external apparatus such as a personal computer. The printer  1  is constructed such that various devices for image formation are mounted in an apparatus main body  10  having a casing structure in the form of a quadrangular prism. 
   A sheet cassette  11  is mounted at the bottom of the front surface of the apparatus main body  10 . The sheet cassette  11  is a drawer container for storing a sheet stack P 1  (see  FIG. 2 ) as a collection of sheets P to which images are transferred, and is detachably mounted in the apparatus main body  10 . 
   A manual sheet feeder  12  is provided above the sheet cassette  11 . The manual sheet feeder  12  includes a rectangular plate-like member and has the bottom end thereof mounted in such a manner as to be rotatable relative to the front part of the apparatus main body  10 , thereby being able to be opened and closed relative to the apparatus main body  10  (see  FIG. 2 ). A user can feed a sheet by setting this manual sheet feeder  12  in an open state in the case of wishing manual sheet feed instead of automatic sheet feed from the sheet cassette  11 . The outer surface of the manual sheet feeder  12  serves as a decorative plate for the front part of the apparatus main body  10 . 
   A discharge unit  13  is provided on the upper surface of the apparatus main body  10 . The discharge unit  13  is formed by partly recessing the upper surface of the apparatus main body  10  and receives a printed sheet on the recessed bottom surface (sheet receiving surface  130 ). The sheet receiving surface  130  is formed by a curved plate  131  located at the back side of the upper surface of the apparatus main body  10  and an opening cover  132  located at the front side. 
   The curved plate  131  has such a moderately curved surface that the downward inclination thereof gradually increases from the front side toward the back side and a part adjacent to a sheet discharge port  133  is at the lowest position. The opening cover  132  is a flat member and assembled in a state moderately inclined down so as to be connected with the front end edge of the curved plate  131 . With such a discharge unit  13 , a plurality of sheets discharged from the sheet discharge port  133  have the trailing ends thereof in a conveying direction aligned near the sheet discharge port  133  by the inclination of the sheet receiving surface  130 . 
   The opening cover  132  is opened upward with the rear end edge thereof as an axis of rotation (see  FIGS. 3 and 4 ). The opening cover  132  is opened and closed upon replacing a toner container  30 . Further, a confirmation portion  15  including a window  152  (see  FIG. 5 ) enabling a part of the toner container  30  to be seen is provided in the transverse center of the opening cover  132 . A triangular auxiliary tray  16  is mounted on the confirmation portion  15 . These are described in detail later. 
   The sheet receiving surface  130  is formed with a recessed surface  134  extending in forward and backward directions from the curved plate  131  to the opening cover  132 . This recessed surface  134  is for reducing the contact resistance of a sheet with the sheet receiving surface  130  and ensuring smooth sheet discharge. The recessed surface  134  has left and right lateral steps  135  widened from the back side toward the front side. Similarly, the sheet receiving surface  130  is widened from the back side toward the front side, and upper walls  136  located at the left and right sides of the sheet receiving surface  130  are narrowed from the back side toward the front side. Accordingly, the depth and aerodynamic surface shape created by the presence of the above lateral steps  135  and upper walls  136  give a stylish and speedy aesthetic impression to the user operating (seeing) from the front side of the apparatus main body  10 . 
   An operation panel unit  14  is provided on the right upper wall  136 . The operation panel unit  14  is for receiving the operation of the user to the printer  1  and displaying information on the operation of the printer  1 . Here is illustrated the operation panel unit  14  provided with a display  141  including an indicator for displaying stored states of sheets and toner particles and an occurrence of a jam, a cancel key  142  for interrupting a printing operation and a start key  143  for instructing a printing operation. Besides the above, a manufacturer emblem  17  is provided on the outer front surface of the apparatus main body  10 , and a vent  18  and a power switch  19  are respectively provided on the left surface. 
   As described above, an outer casing (casing) of the apparatus main body  10  is partly constructed by decorative surfaces (front surfaces) of the sheet cassette  11  and the manual sheet feeder  12  and the sheet receiving surface  130  (upper surface) of the discharge unit  13 . The color of the outer casing may be a monochromatic color such as an ivory color, but it is preferable to let, for example, the sheet receiving surface  130  or the decorative surface of the manual sheet feeder  12  and the sheet receiving surface  130  have a deeper (darker) color as compared to other parts. By doing so, it is possible not only to improve the design by two-tone colors, but also to make the sheet discharged onto the sheet receiving surface  130  easily recognizable by the user. In this case, the color of the sheet receiving surface  130  and the like may be, for example, 2 or smaller in lightness represented by Munsell values of the Munsell chart (JIS) and a difference in lightness between the color of the sheet receiving surface  130  and the like and that of the other parts may be 3 or greater in the Munsell value of the Munsell chart (JIS). 
   Next, the internal construction of the printer  1  is described.  FIG. 2  is a schematic lateral section of the printer of  FIG. 1  along forward and backward directions. The printer  1  includes the aforementioned sheet cassette  11 , an image forming assembly  20  and a fixing device  27  in the apparatus main body  10 . The sheet cassette  11  stores the stack P 1  of sheets used for printing. The image forming assembly  20  performs an image transfer process to sheets P fed one by one from the sheet stack P 1  stored in the sheet cassette  11  or fed from the aforementioned manual sheet feeder  12 . The fixing device  27  applies a fixing process to the sheet P having the image transfer process applied thereto. 
   A lifter  111  is provided in the sheet cassette  11  to lift up a dispensing end (downstream end) of the sheet stack P 1 . A pickup roller  112  for dispensing the sheets P one by one from the sheet stack P is provided at the downstream end of the sheet cassette  11 , and the end of the sheet stack P 1  lifted up by the lifter  111  is held in contact with the pickup roller  112 . The sheet P dispensed by the driving of this pickup roller  112  is fed to the image forming assembly  20  via a sheet conveyance path  113  and a pair of registration rollers  114  disposed at the downstream end of the sheet conveyance path  113 . The sheet P fed from the manual sheet feeder  12  is conveyed to the pair of registration rollers  114  via an unillustrated feed roller. 
   The image forming assembly  20  transfers a toner image to the sheet P based on an image data given from an external apparatus. The image forming assembly  20  includes a photoconductive drum  21  rotatably provided about a drum center axis extending in transverse direction, and a charger  22 , an exposing device  23 , a developing device  24  (developing mechanism), a transfer roller  25  and a cleaning device  26  arranged along the circumferential surface of the photoconductive drum  21 . 
   The photoconductive drum  21  is for forming an electrostatic latent image and a toner image in conformity with this electrostatic latent image on the circumferential surface thereof. An amorphous silicon photoconductive drum having an amorphous silicon layer formed on the circumferential surface thereof is suitably used as the photoconductive drum  21 . 
   The charger  22  is for uniformly charging the circumferential surface of the photoconductive drum  21  rotating clockwise about the drum center axis. Here, a charger of the type to impart electric charges to the circumferential surface of the photoconductive drum  21  by corona discharge is illustrated as the charger  22 . Instead of such a charger  22 , a charging roller for imparting electric charges to the photoconductive drum  21  while being rotated by the photoconductive drum  21  with the circumferential surface thereof held in contact with the circumferential surface of the photoconductive drum  21  may be used. 
   The exposing device  23  irradiates the circumferential surface of the rotating photoconductive drum  21  with a laser beam modulated based on the image data. Electric charges are removed from parts of the circumferential surface of the photoconductive drum  21  irradiated with the laser beam, whereby an electrostatic latent image in conformity with a laser beam irradiation pattern is formed on the circumferential surface of the photoconductive drum  21 . 
   The developing device  24  supplies toner particles to the circumferential surface of the photoconductive drum  21  via a developing roller  241  built therein. When the toner particles are supplied to the photoconductive drum  21 , it is attached to a part where the electrostatic latent image is formed, whereby a toner image is formed on the circumferential surface of the photoconductive drum  21 . The toner container is detachably attached to the developing device  24 , and toner particles are replenished from this toner container when the toner particles in the developing device  24  are used up. 
   The transfer roller  25  forms a nip portion together with the photoconductive drum  21  and transfers the toner image formed on the circumferential surface of the photoconductive drum  21  to a sheet P fed to the nip portion. The toner image on the circumferential surface of the photoconductive drum  21  is positively charged. On the other hand, the transfer roller  25  imparts negative electric charges having a polarity opposite to the electric charges of the toner image to the sheet P. The positively charged toner image on the circumferential surface of the photoconductive drum  21  is peeled off toward the front side of the negatively charged sheet P to be transferred to the sheet P. 
   The cleaning device  26  cleans the circumferential surface of the photoconductive drum  21  by removing the toner residual thereon after the transfer process. The circumferential surface of the photoconductive drum  21  cleaned by this cleaning device  26  moves toward the charger  22  again for a next image forming process. 
   The fixing device  27  is for fixing the toner image transferred to the sheet P in the image forming assembly  20  to the sheet P by heating. The fixing device  27  includes a heat roller  271  having an electric heating element mounted therein and a pressure roller  272  whose circumferential surface is opposed to that of the heat roller  271 . The sheet P after the transfer process passes through a nip portion between the heat roller  271  driven to rotate and the pressure roller  272  rotated by the heat roller  271  in an opposite direction to have the fixing process applied thereto by obtaining heat from the heat roller  271 . The sheet P having the fixing process applied thereto is discharged to the discharge unit  13  via a sheet discharge path  28 . The sheet discharge path  28  is a conveyance path along which sheets P of the respective sizes are discharged with reference to a center line of a width direction (direction normal to a sheet conveying direction) of the sheet receiving surface  130 . 
     FIGS. 3 and 4  are perspective views showing a mounted state of the toner container (consumable supplying member) in the apparatus main body  10 , wherein  FIG. 3  shows a state where the toner container  30  is mounted in the apparatus main body  10  (developing device  24 ) and  FIG. 4  shows a state where the toner container  30  is detached from the apparatus main body  10 . 
   In the case of replacing the toner container  30 , the user grips the front end of the opening cover  132  and lifts it upward to turn the opening cover  132  by about 90° about a rotary shaft  132   a , whereby the opening cover  132  is set in an open state. By this operation, the toner container  30  mounted in an accommodation space V in the apparatus main body  10  is exposed as shown in  FIG. 3 . 
   Subsequently, the toner container  30  is taken out of the accommodation space V by lifting the left and right surfaces of the toner container  30  with both hands (see  FIG. 4 ). Then, a new toner container  30  filled with toner particles is mounted in the accommodation space V. At this time, the toner container  30  needs to be mounted while being exactly positioned with an installation portion  301  provided on the upper surface of the developing device  24 . In other words, the user needs to mount the toner container  30  in a correct installation direction, so that a toner outlet, a drive gear of an agitator and the like of the toner container  30  are positioned with a toner reception port, a driver of the agitator and the like of the installation portion  301 . After the new toner container  30  is mounted, the opening cover  132  is closed. 
   In the printer  1  constructed as described above, the confirmation portion  15  is provided on the opening cover  132  in this embodiment to know the toner container  30  actually mounted in the apparatus main body  10  even when the opening cover  132  is closed and further to show a transverse center position of the discharge unit  13  (sheet receiving surface  130 ). Further, an indicator  32  (visual confirmation portion) arranged at a position facing the confirmation portion  15  with the toner container  30  mounted in the apparatus main body  10  is provided on the upper surface of a container main body  31  of the toner container  30 . These constructions are described in detailed below. 
     FIG. 5  is a top view of the opening cover  132  and the toner container  30 . The confirmation portion  15  is provided at the center position of the opening cover  132  with respect to both transverse direction and forward and backward directions. In this embodiment, the confirmation portion  15  includes a window recess  151  formed by recessing the opening cover  132  at the above center position (recess formed by recessing a part of the casing) and a window  152  provided at the bottom surface of the window recess  151 . 
   By providing the window  152  at the bottom surface of the window recess  151  instead of providing it in flush with the opening cover  132 , the interference of the window  152  with sheets discharged to the discharge unit  13  and other objects can be suppressed and the window  152  can be prevented from being scratched and smeared. On the other hand, since the recess is present at the front side of the discharge unit  13  with respect to the sheet conveying direction, i.e. at a position where the user holds the sheet discharged to the discharge unit  13  for removal, there is an advantage that the user can easily hold a sheet end. Further, the user can grasp the widthwise center position of the sheet by recognizing the window recess  151  by touch. 
   For example, a transparent plastic plate can be used as the window  152 . The window recess  151  is a recess substantially triangular when viewed from above and the window  152  has a triangular shape one size smaller than the window recess  151 . Both shapes have directivities. 
   The window  152  has an isosceles triangular shape having a bottom side parallel to the front edge of the apparatus main body  10  and an apex  152 T faced backward. The window recess  151  has an analogous isosceles triangular shape and includes a parallel section  1511  before the above bottom side and an inclined surface  1512  at the front side of the parallel section  1511 . The parallel section  1511  is where a rotary shaft enable the upward rotation of the auxiliary tray  16  is formed. The inclined surface  1512  supports the auxiliary tray  16  rotated upward by a specified angle. 
   In a positional relationship with the discharge unit  13 , the apex  152 T of the window  152  and an apex  151 T of the window recess  151  are located at the front side with respect to the sheet conveying direction and at the transverse center position of the sheet receiving surface  130 . Further, the apices  151 T,  152 T are faced toward the rear side with respect to the sheet conveying direction. By having such a positional relationship, the user can know the widthwise center position of the sheet discharged to the discharge unit  13 . 
   Accordingly, even if a multitude of sheets are stacked up on the sheet receiving surface  130  to form a thick sheet stack, the user can recognize the center of the sheet stack and grab the sheet stack at this center position in a well-balanced manner. Thus, even users having weak hands or users sitting on wheelchairs can stably remove the sheet stack from the sheet receiving surface  130  without disrupting a stacked state of the sheets. 
   In a relationship with the toner container  30 , the apex  152 T of the window  152  and the apex  151 T of the window recess  151  are faced in the installation direction of the toner container  30  into the apparatus main body  10 . In the printer  1  of this embodiment, the toner container  30  is installed from the front side of the apparatus main body  10  as shown in  FIGS. 4 and 5 . In order to simply show this installation direction of the toner container  30  to the user, the window  152  and the window recess  151  have transversely symmetric triangular shapes with the apices  152 T,  151 T thereof faced backward from the front side of the apparatus main body  10 . Thus, the user can install the toner container  30  into the apparatus main body  10  by being navigated by the facing direction of the apices  152 T,  151 T and, therefore, it can be prevented to install the toner container  30  in a wrong mounting direction. Further, since the window  152  and the window recess  151  have symmetric shapes having the apices faced in the installation direction, design can be improved. 
   Variations of the shape of the window  152  (window recess  151 ) are shown in  FIGS. 6A to 6E . A window  152   a  shown in  FIG. 6A  has an isosceles triangular shape similar to the window  152  shown in  FIG. 5 . A window  152   b  shown in  FIG. 6B  has a substantially triangular shape (or pentagonal shape) with a parallel extended section attached at the bottom side. A window  152   c  shown in  FIG. 6C  is shaped such that two sides extending to an apex are transversely symmetrical curves. A window  152   d  shown in  FIG. 6D  has a substantially triangular shape whose apex is a curve instead of an acute angle and which has a parallel extended section attached at the bottom side. A window  152   e  shown in  FIG. 6E  has a substantially triangular shape (or hexagonal shape) with an apex section parallel to the bottom side and a parallel extended section attached at the bottom side. In this way, the shape of the window  152  (window recess  151 ) preferably has a transversely symmetrical shape whose apex is formed by straight lines or curves to face in the installation direction of the toner container  30 . However, the window  152  may also be shaped to have no directivity and may, for example, have a circular or rectangular shape. 
   The toner container  30  includes the container main body  31  and the indicator  32  provided on the upper surface of the container main body  31 . The container main body  31  has a casing structure, and toner particles are stored inside. The agitator for agitating the toner particles, a conveyance screw for guiding the toner particles to the toner discharge port (not shown) formed in the bottom wall of the container main body  31  and the like are also provided in the container main body  31 . 
   The indicator  32  is provided on the upper surface of the container main body  31  for displaying specified indication information. The indicator  32  is arranged at a position to face the confirmation portion  15  with the toner container  30  mounted in the apparatus main body  10 . Further, the indicator  32  has an isosceles triangular shape having substantially the same size as the window  152  and is positioned in alignment with the correct mounting direction of the toner container  30  into the apparatus main body  10 . 
   As shown in  FIG. 5 , the indicator  32  is provided on the upper surface of the container main body  31  so as to face and conform in shape to the window  152 , i.e. so as to conform the apex  152 T of the window  152  and an apex  32 T of the indicator  32  when the toner container  30  is mounted into the apparatus main body  10  in the correct direction. In other words, the indicator  32  has a transversely symmetrical triangular shape having the apex  32 T faced in the installation direction of the toner container  30  similar to the window  152 . By letting the window  152  and the indicator  32  have directivities in this way, the user can easily notice an erroneous mounting based on a difference between the directivities of the window  152  and the indicator  32  in the case of attempting to mount the toner container  30  into the apparatus main body  10  in a wrong direction. The shapes illustrated in  FIGS. 6A to 6E  may also be adopted as variations of the shape of the indicator  32 . 
   The indicator  32  may be a seal having an adhesive surface capable of adhering to the container main body  31  on the underside thereof or the like. In this embodiment is shown an example in which an indicator recess  33  substantially triangular when viewed from above is provided in the center of the upper surface of the container main body  31 , and a seal for the indicator  32  is attached to a bottom surface  331  thereof. The indicator  32  includes a dingbat indicator  321  for displaying a dingbat indicating toner particles and a character indicator  322  indicating the manufacturer name (“ABCDE” in  FIG. 5 ) as indication information. Besides, symbols other than characters may be displayed in the indicator  32 . Instead of forming the indicator  32  of the seal or the like, a triangular indicator including the above dingbat and characters may be directly formed on the upper surface of the container main body  31  by die machining. 
   If the front side of the apparatus main body  10  where the user is standing face to face with the printer  1  upon replacing the toner container  30  is set to be a reference side, the indication information such as characters, symbols or dingbats displayed on the indicator  32  is oriented in a correct direction when viewed from front when the toner container  30  is properly mounted in the apparatus main body  10 . In other words, the characters “ABCDE” are so printed as to be normally made out by the user reading from the front side of the apparatus main body  10 . Thus, if the toner container  30  is properly mounted in the apparatus main body  10 , the user can read the indication information of the indicator  32  in a correct direction from front. Therefore, the user can easily see or read the indication information and, if the toner container  30  is mounted in a wrong direction, such an error can be quickly noticed since the character information or the like is inverted. 
   In the printer  1  according to this embodiment, the window  152  is provided on the opening cover  132  constituting a part of the outer casing of the apparatus main body  10 . Thus, external light can enter the apparatus main body  10  through the window  152 . Since members susceptible to external light such as the photoconductive drum  21  are present in the apparatus main body  10 , a light shielding structure (light shielding portion) for preventing the diffusion of incident light through the window  152  into the interior of the apparatus main body  10  is provided in the vicinity of the window  152 . This light shielding structure is described with reference to  FIG. 7 . 
     FIG. 7  is a section along VII-VII of  FIG. 5 . It should be noted that the auxiliary tray  16  is not shown in  FIG. 7  to simplify the drawing. As described above, the window  152  is provided at the bottom surface of the window recess  151  formed by recessing the part of the opening cover  132 . The window recess  151  includes a side wall  153  extending in a recessing direction and a bottom wall  154  continuous with the side wall  153 , and a transparent plate constituting the window  152  is fitted on an end edge  155  of the bottom wall  154 . 
   The indicator recess  33  of the toner container  30  is provided on an upper surface  31 F of the toner container  30  and includes a bottom surface  331  to which the seal constituting the indicator  32  is attached and a side wall  332  (light-blocking wall) continuous with the peripheral edge of the bottom surface  331 . The indicator recess  33  has a triangular shape larger than the window recess  151  when viewed from above so as to be able to accommodate the window recess  151  and has such a depth as not to interfere with the window  152  with the opening cover  132  closed at a correct position. 
   The window  152  enters the indicator recess  33  beyond the upper surface  31 F of the toner container  30  to come close to the bottom surface  331  (indicator  32 ) when the opening cover  132  is closed. The side wall  153  of the window recess  151  is opposed close to the side wall  332  of the indicator recess  33 . Further, the underside of the opening cover  132  and the upper surface  31 F of the toner container  30  are opposed close to each other. In other words, the indicator recess  33  and the window recess  151  projecting from the underside of the opening cover  132  are so shaped as to have directivities and the window recess  151  is accommodated inside the side wall  332  defining the indicator recess  33  when the toner container  30  is mounted in a correct installation direction. 
   Accordingly, external light incident through the window  152  is prevented from diffusing into the interior of the apparatus main body  10  by the bottom surface  331  of the indicator recess  33  close to the bottom wall  154 , the side wall  332  close to the side wall  153  and the upper surface  31 F close to the underside of the opening cover  132 . On the other hand, toner particles may fly in the interior of the apparatus main body  10 , but are unlikely to reach the lower surface of the window  152  due to the presence of the bottom surface  331 , the side wall  332  and the upper surface  31 F, whereby the smearing of the window  152  is suppressed. 
     FIG. 8  is a section along VII-VII of  FIG. 5  showing another embodiment of the light-shielding structure. Here is shown an example in which a rib  333  (light shielding wall) stands on an upper surface  31 F of a toner container  30 A to surround the window recess  151  projecting from the underside of the opening cover  132 . In other words, the rib  333  has a substantially triangular shape slightly larger than the window recess  151  when viewed from above. The rib  333  is opposed close to the side wall  153  of the window recess  151  when the opening cover  132  is closed. The toner container  30 A provided with such a rib  333  has the aforementioned effects of shielding light and hindering flying toner particles. 
   Next, the auxiliary tray  16  is described with reference to  FIGS. 9A to 11 .  FIG. 9A  is a top view showing an accommodated position where the auxiliary tray  16  is accommodated in a recess of the confirmation portion  15  (window recess  151 ), and  FIG. 9B  is a top view showing an unfolded position where the auxiliary tray  16  is lifted up and turned to support the leading end of a sheet discharged to the discharge unit  13  with respect to the sheet conveying direction.  FIG. 10  is a section along X-X of  FIG. 9A . 
   The auxiliary tray  16  is used to auxiliary support sheets upon discharging large-size sheets to the discharge unit  13  or upon better aligning sheets, in the form of a triangular frame and rotatably mounted on the confirmation portion  15  of the opening cover  132 . As a result of disposing the auxiliary tray  16  on the confirmation portion  15 , the auxiliary tray  16  is arranged at a position at a front side of a sheet in the conveying direction and in the widthwise center of the sheet receiving surface, i.e. at a position suited to auxiliary supporting the sheets. The auxiliary tray  16  includes a frame portion  161 , an opening surrounding wall  162 , slants  163 , a rotary portion  164  and a sheet supporting surface  165 . 
   The frame portion  161  is a triangular frame member engageable with the window recess  151  and having an opening inside. As shown in  FIG. 10 , the frame portion  161  has a thickness substantially equal to the depth of the window recess  151  and an upper surface  161 T thereof is substantially flush with the upper surface of the opening cover  132  at the accommodated position. Accordingly, the leading end of the sheet discharged onto to the sheet receiving surface  130  will, in no likelihood, get caught by the auxiliary tray  16 . Such a small clearance as not to impair the rotatability of the auxiliary tray  16  is defined between the outer surrounding wall of the frame portion  161  and the side wall  153  of the window recess  151 . 
   The opening surrounding wall  162  is a triangular wall surface defining the above opening when viewed from above. This opening ensures the visibility of the window  152  upon mounting the auxiliary tray  16  utilizing the recess of the confirmation portion  15 . 
   The slants  163  are inclined surfaces inclined down from the upper surface  161 T of the frame portion  161  toward the opening surrounding wall  162 . The slants  163  have a function of making the window  152  easier to see even in directions other than the one from right above. The window recess  151  tends to collect dust because of its concave surface. By providing the slants  163 , the user can easily clean off not only dust remaining in the middle part of the window  152 , but also dust remaining near the opening surrounding wall  162  of the window  152 . 
   The rotary portion  164  is provided near the bottom side of the frame portion  161  and shaft-coupled to the parallel section  1511  of the window recess  151  to realize a lift-up and turning movement of the auxiliary tray  16 . The auxiliary tray  16  is displaceable between the accommodated position where it is accommodated in the window recess  151  and the unfolded position where it auxiliary support sheets by being turned about the rotary portion  164 . 
   The sheet supporting surface  165  is a triangular supporting surface located on the underside of the frame portion  161  for supporting sheets. As shown in  FIG. 9B , the sheet supporting surface  165  appears on the upper surface of the discharge unit  13  while being at a specified angle to the sheet receiving surface  130  when the auxiliary tray  16  is at the unfolded position. At this time, the upper surface  161 T of the frame portion  161  is in contact with the inclined surface  1512  of the window recess  151  and the auxiliary tray  16  is in a stable state. Then, the sheet supporting surface  165  supports sheets P discharged to the discharge unit  13  as shown in  FIG. 11 . On the other hand, when the auxiliary tray  16  is at the accommodated position, the sheet supporting surface  165  is in contact with the bottom wall  154  of the window recess  151 . 
   The user can normally accommodate the auxiliary tray  16  constructed as above in the window recess  151  and lift up and turn it to the unfolded position if necessary to support sheets discharged to the discharge unit  13 . Since the auxiliary tray  16  is accommodated utilizing the confirmation portion  15 , it is not necessary to separately ensure an accommodation space for the auxiliary tray  16 . In addition, since the auxiliary tray  16  is formed with the opening, the visibility of the window  152  is not impaired. This auxiliary tray  16  can also be used as a grip upon opening the opening cover  132 . 
   According to the printer  1  of this embodiment constructed as above, the user can confirm the indication information displayed on the indicator  32  of the toner container  30  through the window  152  from the outside of the printer  1 . Thus, the user can know which toner container  30  is actually mounted in the apparatus main body  10  without opening the opening cover  132  extra. Hence, the user can quickly understand the model number of the toner container  30  and other necessary information, for example, at the time of ordering a new toner container  30  or requesting maintenance, wherefore user convenience can be improved. 
   Here, the image forming assembly including the photoconductive drum  21  might be influenced by external light because the outer casing of the apparatus main body  10  is provided with the window  152 . However, the light shielding structure of fitting the projecting part of the window recess  151  into the indicator recess  33  of the toner container  30  when the opening cover  132  is closed is adopted in this embodiment. Accordingly, the side wall  332  mainly functions as a light shielding wall and the diffusion of external light into the interior of the apparatus main body  10  can be suppressed. Such a light shielding structure can also suppress the adhesion of toner particles, which might be flying in the apparatus main body  10 , to the window  152 . 
   Further, the window  152  is provided at the bottom surface of the window recess  151  and arranged at a position slightly lower than the sheet receiving surface  130 . Thus, external forces are unlikely to act on the window  152  and scratches and smearing can be suppressed, wherefore the visibility of the window  152  can be ensured in a satisfactory manner over a long term. 
   Further, the window  152  is provided in the widthwise middle part of the opening cover  132  arranged at the leading end side in the sheet conveying direction and the apex  152 T of the window recess  152  (apex  151 T of the window recess  151 ) is located in the widthwise center of the sheet receiving surface  130 . Thus, the user can utilize the window  152  (apex  152 T) as a center indicator and can know the widthwise center position of a sheet discharged to the discharge unit  13 . 
   Further, the auxiliary tray  16  can be assembled utilizing the confirmation portion  15  (window recess  151 ), can be normally accommodated in the window recess  151  and can auxiliary support sheets by being turned according to needs. Further, the auxiliary tray  16  is formed with the opening to ensure the visibility of the window  152 . Since the recess of the sheet receiving surface  130  provided for the window  152  is effectively utilized in this way, it is not necessary to ensure a separate accommodation space for the auxiliary tray  16 . Further, the design of the sheet receiving surface  130  does not look complicated. 
   The printer  1  according to the embodiments of the present invention is described above, but the present invention is not limited thereto. For example, the present invention may be embodied as follows. 
   [1] The printer is illustrated as an example of the image forming apparatus in the above embodiment. It goes without saying that the present invention is also applicable to copiers, facsimile machines, complex machines of these and other image forming apparatuses. 
   [2] Although the window  152  is provided in the widthwise center of the opening cover  132  in the above embodiment, it may not necessarily be provided in the widthwise center. Further, another window may be provided in addition to the window  152  having the auxiliary tray  16  assembled therewith. For example, a window may be provided on the front surface of the apparatus main body (outer surface of the manual sheet feeder  12  in the above embodiment). It is preferable to arrange an illumination device in the vicinity of the window  152  so as to improve the visibility of the window  152  even in a dark place. 
   [3] In the above embodiment, the auxiliary tray  16  is provided with the opening as the transparent portion for ensuring the visibility of the window  152 . A transparent plate, a transparent film, a slit plate or the like may be mounted at this opening. Instead of providing the auxiliary tray  16  with the opening, a transparent triangular plate may be used as the auxiliary tray  16 . 
   [4] In the above embodiments, the indicator  32  of the toner container  30  is triangular and printed with characters and dingbats as indication information. The shape of the indicator  32  is arbitrary and may be one of various shapes having directivities other than triangular shapes or one of various shapes having no directivity. Further, the shape of the window  152  and that of the indicator  32  of the toner container  30  may not necessarily conform to each other. 
   The indication information preferably includes at least one of characters, a symbol and a dingbat, but may be mere color information or the like. In order to improve the visibility of the indicator  32  in a dark plate, the indicator  32  may be made of a fluorescent or light storing material or may be formed by a luminescent or thermosensitive panel or the like. 
   A part of the toner container  30  (consumable supplying member) having no particular indication information may serve as a visual confirmation portion. In other words, a part of the outer surface of the toner container  30  (container main body  31 ) may be made visible through the window  152  without particularly providing the toner container  30  with the indicator  32  as shown in the above embodiment. Alternatively, the window  152  may be provided at a position where a part other than the toner container  30  is visible. 
   [5] In the above embodiments, the engaging structure of the indicator recess  33  and the window recess  151  is illustrated as the light shielding structure. Instead, the light shielding structure may, for example, be such that the window recess  151  is surrounded by a spongy lightproof sealing member having a light shielding property on the underside of the opening cover  132  and the projecting end of the lightproof sealing member is held in contact with or in proximity to the upper surface of the toner container  30 . 
   [6] In the above embodiments, the electrophotographic printer  1  and the toner container  30  to be mounted therein are illustrated as examples of the image forming apparatus and the consumable supplying member. Besides, the present invention is also applicable, for example, to ink-jet printers and ink cartridges mounted therein. Further, the present invention is widely applicable to various household apparatuses, various industrial electric/mechanical apparatuses and the like and consumable supplying members mounted therein. 
   The specific embodiment described above mainly embraces inventions having the following constructions. 
   An image forming apparatus according to one aspect of the present invention comprises an apparatus main body having a casing structure and adapted to perform an image forming operation; a sheet receiving surface constituting a part of the casing structure and adapted to receive a sheet discharged after an image forming process is performed in the apparatus main body; a window provided on the sheet receiving surface for enabling a part of the interior of the apparatus main body to be seen; and an auxiliary tray attached to the sheet receiving surface and displaceable between an unfolded position to auxiliary support a discharged sheet and an accommodated position to be accommodated in the sheet receiving surface, wherein the window is provided at a bottom surface of a recess formed by recessing a part of the sheet receiving surface, and the auxiliary tray is accommodated in the recess when being located at the accommodated position and includes a transparent portion for ensuring the visibility of the window. 
   According to such an image forming apparatus, a user can see the part of the interior of the apparatus main body through the window provided on the apparatus main body. Thus, the user can know a state inside such as which members are actually mounted in the apparatus main body without opening an opening cover or the like. Since the auxiliary tray is to be accommodated in the recess including the window, it is not necessary to separately provide an accommodation space for the auxiliary tray and it can be avoided to make the sheet receiving surface look complicated even if the auxiliary tray and the window are provided on the sheet receiving surface. 
   In the above construction, it is preferable that the auxiliary tray includes a frame portion shaped to be engageable with the recess and an opening formed inside the frame portion; and that the frame portion has a thickness substantially equal to the depth of the recess. 
   According to this construction, the upper surface of the frame portion is substantially in flush with the sheet receiving surface without projecting therefrom when the auxiliary tray is at the accommodated position. Thus, there is no likelihood that the leading end of a sheet discharged onto the sheet receiving surface gets caught by the auxiliary tray. 
   In this case, a slant inclined downward toward the opening is preferably formed on a surface of the frame portion to become an outer surface when the frame portion is at the accommodated position. 
   According to this construction, since the above slant is formed, the widow can be seen in a direction other than the one from right above even if the auxiliary tray is to be accommodated in the recess where the window is provided. Further, dust and the like tend to be collected in the recess, but the user can easily clean the dust and the like remaining in the recess since the slant is provided. 
   In this construction, it is preferable that a consumable supplying member to be detachably mounted in the apparatus main body is further provided; and that the window enables a part of the consumable supplying member to be seen with the consumable supplying member mounted in the apparatus main body. 
   According to this construction, the user can see the part of the consumable supplying member through the window provided on the apparatus main body. Thus, the user can know which consumable supplying member is actually mounted in the apparatus main body without opening the opening cover or the like. 
   In this case, it is preferable that the apparatus main body includes a developing mechanism inside; and that the consumable supplying member is a toner container for supplying toner to the developing mechanism. 
   According to this construction, the user can know which toner container is actually mounted in the apparatus main body without opening the opening cover or the like. 
   Further, in this case, an indicator for displaying specified indication information is preferably provided in a part or the entirety of a visual confirmation portion of the toner container. 
   According to this construction, the user can confirm the indication information displayed on the toner container through the window. Thus, the user can easily identify the mounted toner container based on the indication information. 
   In the above construction, the recess is preferably provided at a front side of a sheet to be discharged onto the sheet receiving surface in a sheet conveying direction and near the widthwise center of the sheet receiving surface. 
   According to this construction, by arranging the recess as above, the auxiliary tray can also be arranged at the front side of the sheet to be discharged onto the sheet receiving surface in the sheet conveying direction and in the widthwise center of the sheet receiving surface. Thus, the auxiliary tray can be arranged at a position suited to auxiliary supporting the sheet. In addition, the user can recognize the widthwise center position of a sheet (sheet stack) using the recess as a marker. 
   In this case, the recess and/or the auxiliary tray preferably have a symmetric shape with an apex faced toward a back side of the sheet receiving surface in the sheet conveying direction. 
   According to this construction, the widthwise center position of a sheet stack can be displayed by a simple and comprehensive shape. Further, since the center indicator has the symmetric shape with the apex faced toward the back side of the sheet receiving surface in the sheet conveying direction, design can be improved. 
   In the above construction, the window preferably serves as a center indicator indicating the widthwise center position of a sheet discharged onto the sheet receiving surface. 
   According to this construction, the user can recognize the widthwise center position of a sheet (sheet stack) using the window as a marker. Thus, the user can remove the sheet in a well-balanced manner by grabbing the recognized widthwise center position of the sheet. 
   In this case, the window preferably has a symmetric shape with an apex faced toward the back side of the sheet receiving surface in the sheet conveying direction and arranged at the widthwise center position of a sheet to be discharged onto the sheet receiving surface. 
   According to this construction, the widthwise center position of a sheet stack can be displayed by a simple and comprehensive shape. Further, since the center indicator has the symmetric shape with the apex faced toward the back side of the sheet receiving surface in the sheet conveying direction, design can be improved. 
   As described above, according to the image forming apparatus of the present invention, the user can know which members are actually mounted in the apparatus main body from the outside of the image forming apparatus main body. Thus, for example, at the time of ordering a toner container or requesting maintenance, the necessary model number of the toner container or the like can be quickly grasped, whereby user convenience can be improved. Further, since the auxiliary tray is to be accommodated in the recess including the window, even if the auxiliary tray and the window are provided on the sheet receiving surface, it can be avoided to make the sheet receiving surface look complicated and design can be improved. 
   This application is based on patent application Nos. 2007-002460 and 2007-002461 filed in Japan, the contents of which are hereby incorporated by references. 
   As this invention may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds are therefore intended to embraced by the claims.