Abstract:
In an image forming apparatus for forming a color image by superimposing one toner on another of a plurality of colors, a positional relationship among the image forming parts for different colors is critical. It is difficult to have a positional relationship within a desired limit among image scanning units, if a plurality of image scanning units are mounted on separate mount plates as in the above-described image forming apparatus. This may cause a color aberration. In order to obtain an image forming apparatus to solve the issue, an apparatus having high mounting accuracy of scanning unit is provided.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an image forming apparatus, such as a color photocopier and a color printer, of electrophotographic type or electrostatic recording type.  
           [0003]    2. Related Background Art  
           [0004]    [0004]FIG. 5 is a schematic sectional view of an image forming apparatus for better understanding of the present invention.  
           [0005]    As shown in FIG. 5, an image scanning unit  101  emits light A such as laser light, so that a photosensitive drum of a process cartridge  102  is irradiated with the light A. The light A which irradiated the photosensitive drum forms a latent image on the photosensitive drum, thereby allowing a toner image formed by specified development means to be transferred onto an endless intermediate transferring unit one after another.  
           [0006]    The process cartridge unit  102  incorporates means for charging the photosensitive drum, or development means for forming the toner image. The toner-supplying container  104  is disposed for supplying the process cartridge  102  with toner.  
           [0007]    A toner-supplying container  104  of larger volume requires less frequent replacement of the container: however, it ends up to a larger image forming apparatus. In this reason, the toner-supplying container  104  is disposed between two adjacent image scanning units  101  so that space in the apparatus can be utilized effectively.  
           [0008]    The toner-supplying container  104  disposed between two adjacent image scanning units  101  is detachably mounted in the apparatus, since the container needs to be replaced with new one when toner in the cartridge is used up. The toner-supplying container  104  is inserted into the image forming apparatus along the mount plate  103  for mounting the image scanning unit  101 , and mounted in the apparatus by supporting means (not shown). As described above. the toner-supplying container  104  is mounted in the apparatus by using a guide plate, for example, the mount plate  103 , as a guide member, for mounting the image scanning unit  101 .  
           [0009]    In an apparatus for forming a color image by superimposing one toner on another of a plurality of colors, a positional relationship among the image forming stations for different colors is critical. It is, however, extremely difficult to have a positional relationship within a desired limit among image scanning units, if a plurality of image scanning units  101  are mounted on separate mount plates  103  as in the above-described image forming apparatus. Failure of having the positional relationship within a desired limit may cause a color aberration.  
           [0010]    Therefore, it is envisioned that positioning accuracy of the plurality of image scanning units is improved by mounting them on a single supporting member. However, a color image forming apparatus having a plurality of image forming stations in a tandem manner generally includes three to four image scanning units, thereby giving rise to such a problem that the supporting member becomes large accordingly, and thus it is difficult to keep enough stiffness of the supporting member.  
         SUMMARY OF THE INVENTION  
         [0011]    In view of the above-described problem, it is an object of the present invention to provide an image forming apparatus with high mounting accuracy of image scanning units.  
           [0012]    It is another object of the present invention to provide an image forming apparatus with high frame stiffness.  
           [0013]    It is a further object of the present invention to provide an image forming apparatus having: a plurality of image forming stations for forming an image, each of the image forming stations comprising an image scanning unit and toner cartridges, the toner cartridges being detachably mountable on a main assembly of the apparatus; a supporting member for supporting the image scanning units; and a plurality of guide members for guiding the toner cartridges, wherein the plurality of guide members are fixed to the supporting members.  
           [0014]    Further objects of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a schematic sectional view of an image forming apparatus according to the present invention;  
         [0016]    [0016]FIG. 2 is a sectional view illustrating a positional relationship among an image scanning unit, a toner-supplying container, and a guide member;  
         [0017]    [0017]FIG. 3 is a top view of the image forming apparatus, with the top cover thereof uncovered, illustrating a positional relationship among positioning holes on supporting means and the guide member;  
         [0018]    [0018]FIG. 4 is an illustration of shielding light with the guide member; and  
         [0019]    [0019]FIG. 5 is a schematic sectional view of a comparative example of the image forming apparatus according to the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    Referring to the attached drawings, an image forming apparatus according to an embodiment of the present invention will be described.  
         [0021]    [0021]FIG. 1 is a schematic sectional view of the image forming apparatus according to the embodiment. FIG. 2 is a sectional view of illustrating a positional relationship among image scanning units, toner-supplying containers, and guide members. FIG. 3 is a top view of the image forming apparatus illustrating a positional relationship among positioning holes on supporting means and the guide member. FIG. 4 is an illustration of shielding light with the guide member.  
         [0022]    As shown in FIG. 1, the image forming apparatus according to this embodiment has four process cartridges  1 Y,  1 M,  1 C, and  1 K for four colors, which are detachable to the main assembly of the apparatus. Each process cartridge is provided with a photoreceptor (a photosensitive drum)  2 , a charging device  3  for charging the photoreceptor  2 , a development device  5  for replenishing the photoreceptor  2  with toner, and a cleaner  4  for cleaning the photoreceptor  2 .  
         [0023]    Further, the image forming apparatus includes the following components: four image scanning units, as optical means,  6 Y,  6 M,  6 C, and  6 K, each of which forming a latent image on the corresponding photoreceptor  2  by irradiating laser light thereon; an intermediate transferring unit  8  having a transfer belt  9  for holding a toner image transferred from each of the photoreceptors  2 , and rollers  10 ,  11 ,  12  for driving the belt  9 ; first transferring chargers (first transferring rollers)  13 , each of which being mounted to the corresponding image forming station, for transferring the toner image from the corresponding photoreceptor  2  to the belt  9 ; a second transferring charger (a second transferring roller)  14  for transferring the toner image held on the belt  9  to a sheet of recording paper; a recording paper conveying unit  15 ; a fixing unit  22 ; and toner-supplying containers  32 , detachably mounted to the main assembly, for replenishing the corresponding development device  5  with toner (see FIG. 2).  
         [0024]    At each of the image forming stations for four colors, the image scanning unit  6  irradiates laser light A on the photosensitive drum  2  based on image information to form a latent image thereon, after the photosensitive drum  2  is uniformly charged by the charging device  3 . Then, the toner-supplying container  32  replenishes the development device  5  with toner for visualizing the latent image, and the development device  4  develops the latent image formed on the photosensitive drum  2  so as to form a toner image.  
         [0025]    The toner image formed on the photosensitive drum  2  is first transferred onto the transferring belt  9  by means of the first transferring roller  13 . Upon completing the first transferring, the photosensitive drum  2  is cleaned by the cleaner  4  for forming a new image.  
         [0026]    Through the above-described processes, the toner images of four colors are superimposed one after another on the intermediate transferring belt  9 , beginning with yellow to magenta, cyan, and black in this order, in the apparatus according to the present embodiment.  
         [0027]    Meantime, the recording paper conveying unit  15  conveys a sheet of recording paper P from a feeding cassette  16  or a feeding tray  17  to a second transferring area, and the toner image formed on the transferring belt  9  is transferred to the sheet P by means of the second transferring roller  14 .  
         [0028]    The sheet P having the toner image thereon is conveyed to the fixing unit  22 , and discharged onto a discharge tray  26  by means of discharge rollers  25  after the toner image is fixed at a nip between a fixing roller  23  and a pressure roller  24 .  
         [0029]    Now, a positional relationship between the image scanning unit  6  and the toner-supplying container  32  will be described. The following descriptions will be made for a set of the image scanning unit  6  and the toner-supplying container  32 , because the four image scanning units  6  and the four toner-supplying containers  32  are mounted in the apparatus in an alternate arrangement, corresponding to the process cartridges  1 Y,  1 M,  1 C, and  1 K. Besides, the image scanning units  6  have a same structure and the containers  32  have another same structure.  
         [0030]    Having an L-shape structure, the image scanning unit  6  is pivotably mounted to a supporting member  33  and a part of the unit  6  is inserted into the supporting member  33 . Laser light, emitted by a light emitting source  28 , is deflected at a polygon mirror (not shown), diffracted at a mirror  29 , passes through a lens  30 , and then irradiates on the photosensitive drum  2  of the process cartridge  1 . Because of the L-shape structure of the image scanning unit  6  as described above, the image scanning unit  6  is readily adjustable in position relative to the photosensitive drum  2 , thereby allowing an image to be formed with a small amount of deviation from perfect alignment.  
         [0031]    The supporting member  33 , which is a single sheet for supporting four image scanning units, is fixed to a front side plate  39  and a back side plate  40  by screws or the like, respectively. at the front and the back of the apparatus. Four guide members  37  forming four housing chambers for housing the toner-supplying containers  32  are fixed to the supporting member  33 . These guide members are also fixed to the side plates  39  and  40  by screws or the like.  
         [0032]    The guide member  37  with a U-shape structure formed by bending a single sheet metal is designed to form the housing chamber for housing the toner-supplying container  32  so that the toner supplying container  32  does not contact with the adjacent image scanning unit  6 . Since the guide member  37  has a U-shape structure made from a single sheet metal as described above, opposing ends of the U shape tend to move outward and inward. To prevent this movement, the front and back sides of the U shape, as viewed in the direction of mounting the toner supplying container, are screwed to the front side plate  39  and the back side plate  40 , respectively, and also the bottom of the U shape is fixed to the supporting member  33  by screws or the like, thereby allowing the opposing sides of the guide member  37  to keep a specified distance with each other. With this arrangement, the supporting member  33  is supported not only by the side plates  39  and  40 , but also by the four guide members  37  fixed to the side plates  39  and  40 , thus having high stiffness, even though the supporting member  33  is a large single sheet metal for supporting the four image scanning units  6 . A guide rail  38  for guiding the toner-supplying container  32  is disposed on the inner surface of the U-shape guide member  37 .  
         [0033]    The guide rail  38  is screwed onto the inner surface of the guide member  37 . A rail portion  32   a  of the toner-supplying container  32  is slidable on the guide rail  38  so that the toner-supplying container  32  can be attached and detached. The guide rail  38  may be Integrally built in the guide member  37  by bending a part of the guide member  37  made from a sheet metal and the like into a rail shape.  
         [0034]    Referring now to FIG. 3, a relationship between the guide member  37  and the supporting member  33  will be described in further detail.  
         [0035]    The guide member  37  is precisely positioned to the supporting member  33  with reference to a locating point  37   a , and is fastened to the supporting member  33  at a screw hole  34  with a screw. A light emitting side (a side opposing to the photosensitive drum) of each of the image scanning units  6 Y,  6 M,  6 C, and  6 K is inserted into a rectangular slot  36  provided at the supporting member  33 . Each of the image scanning units  6  is then mounted to the supporting member  33  with reference to a fit reference hole  35 . The unit  6  is also pivotably adjustable relative to the fit reference hole  35 .  
         [0036]    Since the guide  37  is precisely positioned with reference to the locating point  37   a , the guide member  37  is also precisely positioned with reference to the fit reference hole  35  formed in the same member as the locating point  37   a . Accordingly, the guide member  37  is precisely positioned relative to the rectangular slot  36 , and thus maintains its precise positional relationship with the image scanning unit  6 . The supporting member  33  for pivotably adjusting the image scanning unit  6  has an adjusting plate  43  moveable in the lateral direction of the rectangular slot  36 .  
         [0037]    The image scanning unit  6  is provided with a fit hole into which a fit shaft (not shown) of the adjusting plate  43  is fitted, and is pivotably adjusted relative to the fit reference hole  35 , when the adjusting plate  43  moves in the lateral direction of the rectangular slot  36 . A certain adjustable range is necessary in order to adjust the image scanning unit  6 . The maximum adjustable range is determined based on clearance between the image scanning unit  6  and the rectangular slot  36  when the image scanning unit  6  is inserted into the rectangular slot  36 . More particularly, viewed from the top, the guide member  37  indicated by a dashed line in FIG. 3 is configured not to lie inside the rectangular slot  36 .  
         [0038]    Referring now to FIG. 4, there will be described a relationship between the image scanning unit  6  and the toner-supplying container  32 , when the toner-supplying container  32  is inserted into a housing chamber formed from the guide member  37 .  
         [0039]    The guide member  37  is provided with the guide rail  38 , along which the toner-supplying container  32  is slidably inserted when the toner supplying container is inserted. While being inserted, the toner-supplying container  32  may contact with the guide member  37  since the toner supplying container  32  swings from side to side.  
         [0040]    The image scanning unit  6  is, however, supported not to contact with the guide member  37  as described above, and therefore the image scanning unit  6  is not influenced when the toner-supplying container  32  collides with the guide member  37  and press or vibrate it during insertion.  
         [0041]    The guide member  37  extends further by L in the light axis direction from a light opening  31  for emitting light of the image scanning unit  6 , thus reaching substantially close to the process cartridge  1 . The front side plate 3° covers the entire side, except the insertion openings  42  for inserting and taking out the toner supplying containers  32 . The back side plate  40  covers the entire side opposite to the insertion openings  42 . With this arrangement, after coming out from the light opening  31  of the image scanning unit  6 , light emitted from the image scanning unit  6  is shielded, by the guide member  37 . Accordingly, there is no light leakage in the process for irradiating the light onto the process cartridge  1 , and no risk that hazardous light enters eyes of an operator while replacing the toner-supplying container  32  with a new one.  
         [0042]    The supporting member  33  has higher stiffness because of reinforcement by the four guide members  37  as described above.  
         [0043]    In addition, the guide member  37  creates a partition between the image scanning unit  6  and the adjacent toner-supplying container  32 . This partition allows the toner-supplying container  32  to be inserted into the main assembly of an image forming apparatus without contact with the adjacent image scanning unit  6 , and thus the image scanning unit  6  to be supported accurately in a predetermined location at all times.  
         [0044]    Further, the plurality of guide members  37  serves to block a light path of the image scanning unit and to prevent leakage of laser light emitted by the light sources of the image scanning units  6 . Consequently, there is provided an image forming apparatus which offers a high level of safety such that hazardous light does not enter eyes of an operator while replacing the toner-supplying container  32  with a new one.  
         [0045]    The present invention is not limited to the above-described embodiment and various modifications can be made within the spirit and scope of the technical ideas defined in the appended claims.