Abstract:
An enclosure includes a first enclosure and a second enclosure. A deflector deflects a light emitted from a light source. A first optical system leads the light emitted from the light source to the deflector. A second optical system includes at least one optical element, and leads the light deflected by the deflector onto a surface to be scanned. The first enclosure holds the light source, the deflector, and the first optical system, and the second enclosure holds the at least one optical element included in the second optical system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present document incorporates by reference the entire contents of Japanese priority documents, 2006-144116 filed in Japan on May 24, 2006, and 2007-109171 filed in Japan on Apr. 18, 2007. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an optical scanning device and an image forming apparatus equipped with the optical scanning device, such as a digital copying machine and a laser printer. 
         [0004]    2. Description of the Related Art 
         [0005]    Various types of optical scanning devices for scanning a surface of an object to be scanned, such as a photoreceptor, have been developed and put into practical use. Of these optical scanning devices, those included in image forming apparatuses, such as a laser printer, have different configurations in most cases, even if the optical scanning devices are produced by the same manufacturer. This is because layouts of the image forming apparatuses equipped with the optical scanning devices are different from one another. 
         [0006]    For example, in a digital copying machine shown in  FIG. 16A , a paper feeding unit  201 , a scanner  202 , and an imaging engine unit  203  are respectively arranged at the bottom, the top, and the center of the digital copying machine, and a copy receiving tray  206  to which paper is discharged is located on one of the sides of the digital copying machine. In this layout, it is necessary to convey paper fed from the paper feeding unit  201  to a transfer unit that is located below a photosensitive drum  204 . Therefore, an optical scanning device  205  is inevitably arranged above the photosensitive drum  204  in terms of a process configuration and procedures of electrophotographic processing. The digital copying machine contains the optical scanning device  205 , so that an overall width of the digital copying machine needs to be larger than the same for the optical scanning device  205  (with minimizing the overall width of the digital copying machine as much as possible). Consequently, the optical scanning device  205  needs to include a reflection mirror for reflecting a scanning beam to shorten the overall width of the optical scanning device  205 . 
         [0007]    In a laser printer shown in  FIG. 16B , a paper feeding unit  301  is arranged at the bottom of the laser printer, and an imaging engine unit  303  is arranged on top of the paper feeding unit  301 . In this layout, a paper path is longitudinally arranged on one of the sides of the laser printer, and paper is conveyed through the paper path and discharged onto a copy receiving tray  306  that is located on the top of the laser printer. Therefore, an optical scanning device  305  is inevitably arranged on the (slightly downward) lateral side of a photosensitive drum  304  in terms of a process configuration and procedures of electrophotographic processing. Then, an interface device  307  is arranged adjacent to the optical scanning device  305 , so that the optical scanning device  305  needs to include a reflection mirror for reflecting a scanning beam to minimize a size of the optical scanning device  305 . 
         [0008]    In a full-color printer shown in  FIG. 16C , a paper feeding unit  401  is arranged at the bottom of the full-color printer, and an imaging engine unit  403  is arranged on top of the paper feeding unit  401 . The imaging engine unit  403  includes a plurality (in this case, four) of photosensitive drums  404  and a plurality (in this case, four) of optical scanning devices  405  corresponding to each of the photosensitive drums  404  respectively. In this layout, a paper path is longitudinally arranged on one of the sides of the full-color printer, and paper is conveyed through the paper path and discharged onto a copy receiving tray  406  that is located on the top of the full-color printer. Therefore, the optical scanning devices  405  are inevitably arranged lateral to the photosensitive drums  404 . In this case, the optical scanning devices  405  have no need to include a reflection mirror because there is no component adjacent to the optical scanning devices  405 . If the optical scanning devices  405  respectively include a reflection mirror, an overall height of the full-color printer becomes disadvantageously too high. Consequently, any reflection mirror is not used in the optical scanning devices  405  to keep the overall height of the full-color printer in a user-friendly manner. 
         [0009]    As described above, when different layouts of image forming apparatuses are produced, it is necessary to produce optical scanning devices having different configurations corresponding to each of the layouts of the image forming apparatuses. 
         [0010]    However, although optical scanning devices have different configurations from one another, if the optical scanning devices have the same size of a scanning field (for example, in a case of an A4 paper, 297 mm in a longitudinal direction), the same scanning lens can be used among the optical scanning devices. Therefore, in optical scanning devices produced by the same manufacturer, the same scanning lens is used in common even among different models of optical scanning devices. 
         [0011]    Incidentally, to achieve a desired imaging performance, relative positions (layouts) of a light source, a deflector, and a scanning lens in the different models of the optical scanning devices need to be identical with one another regardless of reflection angles of light beams. 
         [0012]    In this manner, although some elements can be used in common among different models of optical scanning devices, various types of optical scanning devices are produced in accordance with various layouts of image forming apparatuses as described above, and thus it causes an increase of production costs. Moreover, from a viewpoint of the promotion of recycling, it is not preferable to produce various types of optical scanning devices because it is difficult to reuse the optical scanning devices. 
       SUMMARY OF THE INVENTION 
       [0013]    It is an object of the present invention to at least partially solve the problems in the conventional technology. 
         [0014]    An optical scanning device according to one aspect of the present invention includes an enclosure that includes a first enclosure and a second enclosure; a light source that emits a light; a deflector that deflects the light emitted from the light source; a first optical system that leads the light emitted from the light source to the deflector; and a second optical system that includes at least one optical element, and that leads the light deflected by the deflector onto a surface to be scanned. The first enclosure holds the light source, the deflector, and the first optical system, and the second enclosure holds the at least one optical element included in the second optical system. 
         [0015]    An image forming apparatus according to another aspect of the present invention includes an optical scanning device that includes an enclosure that includes a first enclosure and a second enclosure, a light source that emits a light, a deflector that deflects the light emitted from the light source, a first optical system that leads the light emitted from the light source to the deflector, and a second optical system that includes at least one optical element, and that leads the light deflected by the deflector onto a surface to be scanned. The first enclosure holds the light source, the deflector, and the first optical system, and the second enclosure holds the at least one optical element included in the second optical system. 
         [0016]    A method according to still another aspect of the present invention is for configuring an optical scanning device that includes an enclosure that includes a first enclosure and a second enclosure, a light source that emits a light, a deflector that deflects the light emitted from the light source, a first optical system that leads the light emitted from the light source to the deflector, and a plurality of second optical systems each including at least one optical element, having a different optical path, and leading the light deflected by the deflector onto a surface to be scanned. The method includes causing the first enclosure to hold the light source, the deflector, and the first optical system; causing a second enclosure to hold optical elements for the optical scanning device other than those held by the first enclosure; and combining selectively the first enclosure with a second enclosure from among the second enclosures. 
         [0017]    The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a side view of a digital copying machine as an example of an image forming apparatus equipped with an optical scanning device according a first embodiment of the present invention; 
           [0019]      FIG. 2  is a side view of the optical scanning device shown in  FIG. 1 ; 
           [0020]      FIG. 3  is an overhead view of a first enclosure shown in  FIG. 2 ; 
           [0021]      FIG. 4  is a side view of a laser printer as an example of an image forming apparatus equipped with an optical scanning device according a second embodiment of the present invention; 
           [0022]      FIG. 5  is a side view of the optical scanning device shown in  FIG. 4 ; 
           [0023]      FIG. 6  is a side view of a color printer as an example of an image forming apparatus equipped with an optical scanning device according a third embodiment of the present invention; 
           [0024]      FIG. 7  is a side view of the optical scanning device shown in  FIG. 6 ; 
           [0025]      FIG. 8  is a schematic diagram for explaining a basic layout of an optical system in the optical scanning device; 
           [0026]      FIG. 9A  is a simplified schematic diagram for explaining an optical path of the optical scanning device according the first embodiment; 
           [0027]      FIG. 9B  is a simplified schematic diagram for explaining an optical path of the optical scanning device according the second embodiment; 
           [0028]      FIG. 9C  is a simplified schematic diagram for explaining an optical path of the optical scanning device according the third embodiment; 
           [0029]      FIG. 10  is a side view of a fixed portion in the optical scanning device for explaining a loose fitting; 
           [0030]      FIG. 11  is a side view of the fixed portion viewed in a direction perpendicular to an arrow A shown in  FIG. 10 ; 
           [0031]      FIG. 12  is a side view of an optical scanning device in which an fθ lens is fixed to a second enclosure; 
           [0032]      FIG. 13  is a simplified schematic diagram for explaining a layout of an optical system included in the optical scanning device shown in  FIG. 12 ; 
           [0033]      FIG. 14  is a schematic diagram for explaining an example of an optical scanning device included in a tandem type of a color-image forming apparatus according to a conventional technology; 
           [0034]      FIG. 15  is a schematic diagram for explaining another example of an optical scanning device included in a tandem type of a color-image forming apparatus according to a conventional technology; 
           [0035]      FIG. 16A  is a side view of,a digital copying machine as an example of an image forming apparatus equipped with an optical scanning device according a conventional technology; 
           [0036]      FIG. 16B  is a side view of a laser printer as an example of an image forming apparatus equipped with an optical scanning device according the conventional technology; and 
           [0037]      FIG. 16C  is a side view of a full-color printer as an example of an image forming apparatus equipped with an optical scanning device according the conventional technology. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0038]    Exemplary embodiments of the present invention are explained in detail below with reference to the accompanying drawings. 
         [0039]    As an example of an image forming apparatus equipped with an optical scanning device, a digital copying machine  10  according a first embodiment of the present invention is explained in detail below with reference to  FIG. 1 . The digital copying machine  10  includes a paper feeding unit  1 , a scanner  2 , and an imaging engine unit  3 . The paper feeding unit  1 , the scanner  2 , and the imaging engine unit  3  are respectively arranged at the bottom, the top, and the center of the digital copying machine  10 . 
         [0040]    The imaging engine unit  3  includes a photoconductive drum  4  as an image carrier, an optical scanning device  5 , a charger  6 , a developing device  7 , a transfer roller  8 , a cleaning device  9 , a pair of fixing rollers  11 , and a pair of paper stop rollers  12 . The charger  6 , the developing device  7 , the transfer roller  8 , and the cleaning device  9  are arranged around the photoconductive drum  4 . The optical scanning device  5  is arranged above the photoconductive drum  4 , the charger  6 , the developing device  7 , the transfer roller  8 , and the cleaning device  9 . The pair of fixing rollers  11  is arranged on the left side of the photoconductive drum  4 . 
         [0041]    The optical scanning device  5  includes a polygon scanner  51 , an fθ lens  52 , a reflection mirror  53 , and a toroidal lens  54 . In addition, the optical scanning device  5  further includes a light source unit  56  and a cylindrical lens  57  (see  FIG. 3 ). 
         [0042]    The paper feeding unit  1  includes paper feed trays  13   a  and  13   b , paper feed rollers  14   a  and  14   b , and two pairs of conveyance rollers  15 . The paper feed rollers  14   a  and  14   b  are respectively provided on top of the paper feed trays  13   a  and  13   b  to feed paper to a paper path. The two pairs of conveyance rollers  15  are arranged on the paper path. 
         [0043]    A surface of the photoconductive drum  4  is electrostatically charged at a predetermined electric potential uniformly by the charger  6 . In the optical scanning device  5 , a laser diode (LD) of the light source unit  56  is driven to emit a laser beam as a scanning light based on image data of a text that is scanned by the scanner  2 . The laser beam emitted from the LD is irradiated onto a rotational polygon mirror included in the polygon scanner  51 . Then, the laser beam is deflected by the rotational polygon mirror, and led to the photoconductive drum  4  via the fθ lens  52  and the like. As a result, an electrostatic latent image is formed on the photoconductive drum  4 . The developing device  7  deposits toner particles on the electrostatic latent image, and thereby developing the electrostatic latent image into a toner image. In other words, the electrostatic latent image is visualized by the developing device  7 . 
         [0044]    On the other hand, paper fed from the paper feeding unit  1  is conveyed from the pair of paper stop rollers  12  to a transfer position, which is just between the photoconductive drum  4  and the transfer roller  8 , to meet timing of the toner image. The toner image is transferred onto the paper at the transfer position, and the paper with the toner image is further conveyed towards the pair of fixing rollers  11 . The toner image is fixed on the paper while the paper passes between the pair of fixing rollers  11 . The paper with a copy image is discharged onto a copy receiving tray  16 . To stand by for next copying, after the toner image is transferred onto the paper, the surface of the photoconductive drum  4  is cleaned by the cleaning device  9 , and also a residual electric potential is removed from the surface of the photoconductive drum  4  by a neutralization device (not shown). 
         [0045]      FIG. 2  is a side view of the optical scanning device  5 . 
         [0046]    The optical scanning device  5  includes the polygon scanner  51  as a rotational deflector, the fθ lens  52 , the reflection mirror  53 , the toroidal lens  54 , a dust-proof glass  55 , a first enclosure  61 , a second enclosure  62 , a screw  63 , screws  64 , a cover  65 , and a leaf spring  66 . In addition, as shown in  FIG. 3 , the optical scanning device  5  further includes the light source unit  56  and the cylindrical lens  57 . The first enclosure  61  is combined with the second enclosure  62  by the screw  63 , and thereby forming a frame of the optical scanning device  5 . The first enclosure  61  is made of a steel sheet, and formed by press working. The second enclosure  62  is made of a resin material, and formed by injection molding. Alternatively, the first enclosure  61  and the second enclosure  62  can be formed by die-casting. An opening of the combined first and second enclosures  61  and  62  is covered with the cover  65  to protect against dust. The cover  65  is fixed to the first and second enclosures  61  and  62  by screws. 
         [0047]    The polygon scanner  51  includes a rotational polygon mirror  51   a  and a bearing member  51   b . The polygon scanner  51  is fixed to the first enclosure  61  by a plurality of the screws  64 . Furthermore, the bearing member  51   b  is inserted into a hole provided on the first enclosure  61  to fix the polygon scanner  51  thereto. 
         [0048]    The fθ lens  52  is fixed to the first enclosure  61  by adhesion, and mainly used to focus an image in a main scanning direction. Then, the light source unit  56  and the cylindrical lens  57  are also fixed to the first enclosure  61  (see  FIG. 3 ). 
         [0049]    The reflection mirror  53 , the toroidal lens  54 , and the dust-proof glass  55  are held by the second enclosure  62 . The toroidal lens  54  is mainly used to focus an image in a sub scanning direction. The toroidal lens  54  and the dust-proof glass  55  are fixed to the second enclosure  62  by adhesion. The reflection mirror  53  is held by a bias force of the leaf spring  66  included in the second enclosure  62 . 
         [0050]      FIG. 3  is an overhead view of the first enclosure  61 . The light source unit  56  includes the LD and a coupling lens, and fixed to the first enclosure  61  by screws. The cylindrical lens  57  is fixed to the first enclosure  61  by adhesion. Incidentally, it is assumed that optical elements located upstream of the polygon scanner  51  are referred to as a first optical system, and optical elements located downstream of the polygon scanner  51  are referred to as a second optical system. The light source unit  56  and the cylindrical lens  57  belong to the first optical system. 
         [0051]    A laser beam emitted from the light source unit  56  is irradiated onto the rotational polygon mirror  51   a  via the cylindrical lens  57 . The laser beam is deflected by the rotational polygon mirror  51   a , and irradiated onto the reflection mirror  53  via the fθ lens  52 . The laser beam is reflected by the reflection mirror  53 , and irradiated onto the photoconductive drum  4  via the toroidal lens  54 . As a result, print data is written on the surface of the photoconductive drum  4 . 
         [0052]    As another example of the image forming apparatus equipped with the optical scanning device, a laser printer  20  according a second embodiment of the present invention is explained in detail below with reference to  FIG. 4 . The laser printer  20  includes a paper feeding unit  21  and an imaging engine unit  23 . The paper feeding unit  21  is arranged at the bottom of the laser printer  20 , and the imaging engine unit  23  is arranged on top of the paper feeding unit  21 . 
         [0053]    The imaging engine unit  23  includes a photoconductive drum  24  as an image carrier, an optical scanning device  25 , a charger  26 , a developing device  27 , a transfer roller  28 , a cleaning device  29 , a pair of fixing rollers  31 , a pair of paper stop rollers  32 , and a pair of paper discharging rollers  37 . The charger  26 , the developing device  27 , the transfer roller  28 , and the cleaning device  29  are arranged around the photoconductive drum  24 . The optical scanning device  25  is arranged on the slightly downward lateral side of the photoconductive drum  24 . The pair of fixing rollers  31  is arranged above the photoconductive drum  24 . 
         [0054]    The paper feeding unit  21  includes a paper feed tray  33 , a paper feed roller  34 , and a pair of conveyance rollers  35 . The paper feed roller  34  is provided on top of the paper feed tray  33  to feed paper to a paper path. The pair of conveyance rollers  35  is arranged on the paper path. 
         [0055]    The laser printer  20  does not include a scanner, and thus image data is transmitted from an external device such as a personal computer to the laser printer  20 . An image forming process is basically identical to that is performed by the digital copying machine  10  according to the first embodiment, and thus the detailed description of the process is omitted, but briefly explained below. A toner image formed on the photoconductive drum  24  is transferred and fixed onto paper fed by the paper feeding unit  21 , and the paper with the image is discharged onto a copy receiving tray  36  that is located on the top of the laser printer  20 . 
         [0056]      FIG. 5  is a side view of the optical scanning device  25 . The portions identical to those in  FIG. 2  for the first embodiment are denoted with the same reference numerals. Then, the portions similar to those in  FIG. 2  for the first embodiment are denoted with the same reference numerals followed by “B”. 
         [0057]    For example, materials and layouts of the first enclosure  61 , the polygon scanner  51 , the fθ lens  52 , and the first optical system (the light source unit  56  and the cylindrical lens  57 ), which are included in the optical scanning device  25 , are the same as those in the optical scanning device  5 . Therefore, the above elements can be used in common between the optical scanning device  5  and the optical scanning device  25 . 
         [0058]    A second enclosure  62 B has a different shape from the second enclosure  62  because layouts of two numbers of the reflection mirrors  53  (hereinafter, referred to as the first and second reflection mirrors  53 ) and the toroidal lens  54  are different between the optical scanning device  5  and the optical scanning device  25 . The first and second reflection mirrors  53 , and the toroidal lens  54  are fixed to the second enclosure  62 B in the optical scanning device  25 . 
         [0059]    The first enclosure  61  is combined with the second enclosure  62 B by a screw and the like. An opening of the combined first and second enclosures  61  and  62 B is covered with a cover  65 B to protect against dust. The cover  65 B is fixed to the first and second enclosures  61  and  62 B by screws. The cover  65 B includes an opening for emitting a scanning light. A dust-proof glass  55 B is attached to the opening. 
         [0060]    A laser beam emitted from the light source unit  56  is irradiated onto the rotational polygon mirror  51   a  via the cylindrical lens  57 . The laser beam is deflected by the rotational polygon mirror  51   a , and further irradiated onto the first reflection mirror  53  via the fθ lens  52 . The laser beam is reflected by the first reflection mirror  53 , and further reflected by the second reflection mirror  53 , and then irradiated onto the photoconductive drum  4  via the toroidal lens  54 . As a result, print data is written on the surface of the photoconductive drum  4 . 
         [0061]    As still another example of the image forming apparatus equipped with the optical scanning device, a color printer  70  according a third embodiment of the present invention is explained in detail below with reference to  FIG. 6 . The color printer  70  includes a paper feeding unit  71  and an imaging engine unit  73 . The paper feeding unit  71  is arranged at the bottom and the top of the laser printer  20 , and the imaging engine unit  73  is arranged on top of the paper feeding unit  71 . 
         [0062]    The color printer  70  employs a four-drum tandem engine. The imaging engine unit  73  includes four imaging units  72 C,  72 M,  72 Y, and  72 Bk (for cyan (C), magenta (M), yellow (Y), and black (Bk) color respectively), a pair of fixing rollers  81 , a pair of paper stop rollers  82 , and a pair of paper discharging rollers  87 . 
         [0063]    The imaging units  72 C,  72 M,  72 Y, and  72 Bk are tandemly arranged in this order from the bottom. Each of the imaging units  72 C,  72 M,  72 Y, and  72 Bk has the same configuration except for a color of toner to be used therein. Reference numerals are not assigned to portions of the imaging units  72 M,  72 Y, and  72 Bk, which are identical to those in the imaging unit  72 C. The pair of fixing rollers  81  and the pair of paper discharging rollers  87  are arranged above the photoconductive drum included in the imaging unit  72 Bk. The pair of paper stop rollers  82  is arranged below a photoconductive drum  74  included in the imaging unit  72 C. 
         [0064]    Each of the imaging units  72 C,  72 M,  72 Y, and  72 Bk includes the photoconductive drum  74  as an image carrier, an optical scanning device  75 , a charger  76 , a developing device  77 , a transfer roller  78 , and a cleaning device  79 . The charger  76 , the developing device  77 , the transfer roller  78 , and the cleaning device  79  are arranged around the photoconductive drum  74 . The optical scanning device  75  is arranged on the lateral side of the photoconductive drum  74 . In this case, each of the imaging units  72 C,  72 M,  72 Y, and  72 Bk includes a writing device, so that the optical scanning device  75  is arranged on the lateral side of the photoconductive drum  74 . In the color printer  70 , image data is separated by colors, and the imaging units  72 C,  72 M,  72 Y, and  72 Bk respectively emit a scanning light with a color component corresponding to each of the separated colors. 
         [0065]    The paper feeding unit  71  includes a paper feed tray  83 , a paper feed roller  84 , and a pair of conveyance rollers  85 . The paper feed roller  84  is provided on top of the paper feed tray  83  to feed paper to a paper path. The pair of conveyance rollers  85  is arranged on the paper path. 
         [0066]    In the color printer  70 , an image is formed with toners in cyan, magenta, yellow, and black colors in each of the imaging units  72 C,  72 M,  72 Y, and  72 Bk. When paper is fed from the paper feeding unit  71  to the imaging engine unit  73 , the paper is conveyed from the pair of paper stop rollers  82  to each of the photoconductive drums  74  to meet timing of toner images to be formed thereon. The toner images are sequentially transferred onto the paper to be overlapped with one another by the transfer roller  78 . As a result, a full-color image is formed on the paper. Incidentally, in a case of a monochrome image, only the imaging unit  72 Bk is used to form a toner image in black, and the black toner image is transferred onto paper. The toner image is fixed onto the paper by the pair of fixing rollers  81 , and the paper is discharged to a copy receiving tray  86  that is located on the top of the color printer  70  through the pair of paper discharging rollers  87  and stacked thereon. 
         [0067]      FIG. 7  is a side view of the optical scanning device  75 . The portions identical to those in  FIGS. 2 and 5  for the first and second embodiments are denoted with the same reference numerals. Then, the portions similar to those in  FIGS. 2 and 5  for the first and second embodiments are denoted with the same reference numerals followed by “C”. 
         [0068]    For example, materials and layouts of the first enclosure  61 , the polygon scanner  51 , the fθ lens  52 , and the first optical system (the light source unit  56  and the cylindrical lens  57 ), which are included in the optical scanning device  75 , are the same as those in the optical scanning devices  5  and  25 . Therefore, the above elements can be used in common among the optical scanning device  5 , the optical scanning device  25 , and the optical scanning device  75 . 
         [0069]    A second enclosure  62 C, the second enclosure  62 , and the second enclosure  62 B respectively have a different shape because a layout of the toroidal lens  54  is different among the optical scanning device  5 , the optical scanning device  25 , and the optical scanning device  75 . In the optical scanning device  75 , the toroidal lens  54  is fixed to the second enclosure  62 C by adhesion. Then, the rotational polygon mirror  51   a , the fθ lens  52 , and the toroidal lens  54  are linearly arranged, and thus the optical scanning device  75  has no need to include the reflection mirror  53 . 
         [0070]    The first enclosure  61  is combined with the second enclosure  62 C by a screw and the like. An opening of the combined first and second enclosures  61  and  62 C is covered with a cover  65 C to protect against dust. The cover  65 C is fixed to the first and second enclosures  61  and  62 C by screws. The second enclosure  62 C includes an opening for emitting a scanning light. A dust-proof glass  55 C is attached to the opening. In this case, the second enclosure  62 C is made of a resin material, and formed by injection molding. Alternatively, the second enclosure  62 C can be made of a steel sheet, and formed by press working because the second enclosure  62 C has a simple shape. 
         [0071]    A laser beam emitted from the light source unit  56  is irradiated onto the rotational polygon mirror  51   a  via the cylindrical lens  57 . The laser beam is deflected by the rotational polygon mirror  51   a , and irradiated onto the photoconductive drum  4  via the fθ lens  52  and the toroidal lens  54 . As a result, print data is written on the surface of the photoconductive drum  4 . Incidentally, image data is separated by colors, and the imaging units  72 C,  72 M,  72 Y, and  72 Bk respectively emit a scanning light with a color component corresponding to each of the separated colors. 
         [0072]    Then, a basic layout of an optical system in an optical scanning device is explained below with reference to  FIG. 8 . 
         [0073]    A laser beam emitted from a light source (not shown) is irradiated onto a polygon mirror  101  via a first optical system such as a cylindrical lens (not shown), and deflected in a main scanning direction by the polygon mirror  101 . Then, the laser beam is irradiated onto a surface of an object to be scanned  104  via a first scanning lens  102  and a second scanning lens  103 . 
         [0074]    It is assumed that a distance between a reflection surface of the polygon mirror  101  and the first scanning lens  102  is referred to as a distance L 1 , and a distance between the reflection surface of the polygon mirror  101  and the second scanning lens  103  is referred to as a distance L 2 , and then a distance between the reflection surface of the polygon mirror  101  and the surface of the object  104  is referred to as a distance L 3 . In consideration for a focal length of each of the scanning lenses, each of the distances L 1 , L 2 , and L 3  needs to be kept constant to achieve a desired imaging performance. For example, when the optical scanning device is used in a different image forming apparatus having a different configuration, if the distance L 3  is changed due to the change of the configuration, it is not possible to achieve a desired imaging performance. 
         [0075]    In the same manner as the above example, the optical scanning devices  5 ,  25 , and  75  respectively have a different configuration (overall shape) from one another.  FIGS. 9A to 9C  are simplified schematic diagrams for explaining an optical path of the optical scanning devices  5 ,  25 , and  75  respectively. As shown in  FIGS. 9A ,  9 B, and  9 C, a shape of an optical path extending from the rotational polygon mirror  51   a  to the surface of the object to be scanned (the photoconductive drum)  4 ,  24 , or  74  is changed depending on the number of the reflection mirrors  53 , or with or without the reflection mirror  53 . 
         [0076]    It is assumed that a distance between the rotational polygon mirror  51   a  and the fθ lens  52  is referred to as a distance L 11 , and a distance between the rotational polygon mirror  51   a  and the toroidal lens  54  is referred to as a distance L 12 , and then a distance between the rotational polygon mirror  51   a  and the surface of the object to be scanned (the photoconductive drum)  4 ,  24 , or  74  is referred to as a distance L 13 . Each of the distances L 11 , L 12 , and L 13  are identical among the optical scanning devices  5 ,  25 , and  75 . 
         [0077]    Furthermore, as shown in  FIG. 3 , it is assumed that a distance between the light source unit  56  and the rotational polygon mirror  51   a  is referred to as a distance L 0 , and a distance between the cylindrical lens  57  and the rotational polygon mirror  51   a  is referred to as a distance L. The distances L 0  and L also need be kept constant. According to the first to third embodiments, the first enclosure  61  and optical elements held by the first enclosure  61  are used in common among the optical scanning devices  5 ,  25 , and  75  without any change or modification. Therefore, the distances L 0  and L can be kept constant among the optical scanning devices  5 ,  25 , and  75 . 
         [0078]    In other words, the common used optical elements such as the polygon scanner  51 , the fθ lens  52 , and the toroidal lens  54  are identical among the optical scanning devices  5 ,  25 , and  75 . In addition, both the distances L 1 , L 2 , and L 3  and the distances L 0  and L are identical among the optical scanning devices  5 ,  25 , and  75 . Therefore, although the optical scanning devices  5 ,  25 , and  75  respectively have a different configuration from one another, the optical scanning devices  5 ,  25 , and  75  have the same optical performance. Thus, the optical scanning devices  5 ,  25 , and  75  can achieve the desired imaging performance. 
         [0079]    Furthermore, the first enclosure  61  and the optical elements held by the first enclosure  61  can be used in common among the optical scanning devices  5 ,  25 , and  75  without any change or modification. Therefore, it is possible to reduce production costs of the optical scanning devices  5 ,  25 , and  75 . Moreover, parts of the optical scanning devices  5 ,  25 , and  75  or the optical scanning devices themselves can effectively be reused or recycled. 
         [0080]    Furthermore, in the optical scanning devices  5 ,  25 , and  75 , each of the second enclosures  62 ,  62 B, and  62 C is fixed to the first enclosure  61  in the same fixing position (position of a fixing member) by the same fixing method. Therefore, the first enclosure  61  can be selectively attached to any of the second enclosures  62 ,  62 B, and  62 C. Moreover, optical elements held by the second enclosure  62 ,  62 B, or  62 C, such as the toroidal lens  54  and the reflection mirror  53 , and optical elements held by the first enclosure  61 , such as the polygon scanner  51  and the fθ lens  52 , are arranged to be able to achieve the desired imaging performance (see  FIGS. 9A ,  9 B, and  9 C). Therefore, it is possible to provide various types of optical scanning devices applicable to various types of image forming apparatuses having a different configuration easily. 
         [0081]    Furthermore, in the optical scanning devices  5 ,  25 , and  75 , the covers  65 ,  65 B, and  65 C respectively have a different shape, and materials of the covers  65 ,  65 B, and  65 C are not defined to be identical to one another. Therefore, if fixing/coupling members has a different material and a different shape from one another, the rate of expansion or shrinkage of each of the members are also different. With temperature variation, it may cause a distortion in the shape of each of the members depending on how tight the member is fixed. Consequently, it is necessary to pay attention to the temperature variation of the periphery of the optical scanning device, and the temperature variation of the first enclosure  61 , which is caused by a rotation of the polygon scanner  51 . To avoid the above burden, a fixed portion is partially to be loosely fixed as shown in  FIG. 10 . 
         [0082]    As shown in  FIG. 10 , when the second enclosure  62  is fixed to the first enclosure  61 , the first enclosure  61  and the second enclosure  62  are overlapped with each other, and fixed by a shoulder screw  30 . In this time, a gap G between an undersurface of a head of the shoulder screw  30  and a member subjected to be fixed (the second enclosure  62 ) is minimized, and thereby absorbing a difference between expansion/shrinkage levels of the first enclosure  61  and the second enclosure  62 . A position of a hole  60  (a guide groove in which a body portion of the shoulder screw  30  is inserted) is appropriately set (in either direction indicated by an arrow A) based on the expansion/shrinkage levels of the first enclosure  61  and the second enclosure  62 .  FIG. 11  is a side view of the fixed portion viewed in a direction perpendicular to the arrow A shown in  FIG. 10 . In this direction, it is not necessary to consider the difference between the expansion/shrinkage levels of the first enclosure  61  and the second enclosure  62 , so that there is little gap between the hole  60  and the shoulder screw  30 . 
         [0083]    The loose fixing as shown in  FIG. 10  can be used not only to fix between the first and second enclosures, but also to fix the cover  65  to the first and second enclosures, and to fix the entire optical scanning device to a main frame of the image forming apparatus (not shown). The loose fixing can be selectively used depending on a difference between expansion/shrinkage levels of members to be fixed. 
         [0084]    For example, the cover  65  can be loosely fixed to either one of the first enclosure  61  or the second enclosure  62  (and firmly fixed to the other enclosure), or can be loosely fixed to both of the first enclosure  61  and the second enclosure  62 . 
         [0085]    Also, either one of the first enclosure  61  or the second enclosure  62  can be firmly fixed to the frame of the image forming apparatus, and the other enclosure can be loosely fixed to the frame of the image forming apparatus. In this case, the cover  65  can be firmly fixed to one of the enclosures that is firmly fixed to the frame of the image forming apparatus (and loosely fixed to the other enclosure). 
         [0086]    Incidentally, in the optical scanning devices  5 ,  25 , and  75 , the fθ lens  52 , which is included in (the optical elements located on the downstream side of the rotational polygon mirror  51   a  of) the second optical system, is located relatively close to the polygon scanner  51  (i.e., the distance L 11  is small), so that the fθ lens  52  is fixed to the first enclosure  61 . 
         [0087]    In a case of an optical system in which the fθ lens  52  is located far from the polygon scanner  51  (i.e., a difference between the distances L 11  and L 12  is small), the fθ lens  52  can be fixed to the second enclosure instead of the first enclosure. In this case, another enclosure capable of including the whole second optical system (an enclosure having an optical path corresponding to a layout of the image forming apparatus) is prepared as the second enclosure, and an appropriate one of the second enclosures is selectively used (by combining with the first enclosure). 
         [0088]      FIG. 12  is a side view of an optical scanning device  95  in which the fθ lens  52  is fixed to a second enclosure  62 D (i.e., the whole second optical system is included in the second enclosure  62 D). A configuration of the optical scanning device  95  is similar to that is in the optical scanning device  75  according to the third embodiment.  FIG. 12  depicts the optical scanning device  95  in a case in which the distance L 11  between the rotational polygon mirror  51   a  and the fθ lens  52  is relatively large.  FIG. 13  is a schematic diagram for explaining a layout of an optical system corresponding to the configuration shown in  FIG. 12 . In the same manner as the optical system shown in  FIG. 8 , it is assumed that the distance between the reflection surface of the polygon mirror  101  and the first scanning lens (an fθ lens)  102  is referred to as the distance L 1 , and the distance between the reflection surface of the polygon mirror  101  and the second scanning lens (a toroidal lens)  103  is referred to as the distance L 2 , and then the distance between the reflection surface of the polygon mirror  101  and the surface of the object  104  is referred to as the distance L 3 . Incidentally, in this case, the configuration of the optical scanning device is similar to that is in the third embodiment, but it is also applicable to a configuration of an optical scanning device similar to those in the first or second embodiment. 
         [0089]    On the contrary, in a case of an optical system in which a difference between the distances L 11  and L 12  is small and the distance L 12  is small, the fθ lens  52  and the toroidal lens  54  can be fixed to the first enclosure. Depending on degrees of the distances L 11  and L 12 , the fθ lens  52  and the toroidal lens  54  can be fixed to either the first enclosure or the second enclosure. Namely, although an example in which the toroidal lens  54  is fixed to the first enclosure is not shown in the drawings, both the fθ lens  52  and the toroidal lens  54  can be fixed to either one of the first enclosure or the second enclosure. 
         [0090]    Furthermore, in the above embodiments, the second optical system includes the fθ lens, the toroidal lens, and the reflection mirror only, but optical elements to be included in the second optical system are not limited to the above-mentioned lenses. Any other optical elements such as a curved mirror can be used as the optical elements included in the second optical system. Also, degrees of the distances L 11 , L 12 , and L 13  can be apparently changed (i.e., the optical path can be extended or shrunk) by adding a flat glass thereto or removing the flat glass therefrom. 
         [0091]    The first enclosure (the first enclosure  61  in the embodiments) and the second enclosure (the second enclosures  62 ,  62 B, and  62 C in the embodiments), which form the frame of the optical scanning device, can be processed by any processing method depending on shapes, the workability, and the number of the enclosures to be processed. In the embodiments, components to be held by the first enclosure  61  are defined, and also shapes of portions to which the components are fixed are simple. Therefore, as for the first enclosure, it is preferable to process by deformation processing such as press working to reduce the production cost of the first enclosure. 
         [0092]    On the other hand, a shape of the second enclosure needs to be changed in accordance with various layouts of optical elements corresponding to layouts of image forming apparatuses. Therefore, a shape of the second enclosure occasionally becomes complicated, such as in the cases of the second enclosures  62  and  62 B. In these cases, the second enclosure can easily be processed by a method of dissolving a material, such as by die-casting or by injection molding. 
         [0093]    In this manner, the enclosure of the optical scanning device according to the embodiments can be formed by a combination of the first enclosure (the first enclosure  61 ) that is used in common among various layouts of image forming apparatuses and the second enclosure (the second enclosure  62 ,  62 B, or  62 C) that is selectively changed depending on the layouts of the image forming apparatuses. Moreover, optical elements included in each of the first and second enclosures can also be used in common among the various layouts of the image forming apparatuses. Therefore, it is possible to provide the optical scanning device having an appropriate configuration corresponding to any layout of the image forming apparatus with low costs and a simple method. Furthermore, it is possible to achieve a desired imaging performance in any types of the optical scanning devices constant. 
         [0094]    In the embodiments, the fθ lens, which is included in the second optical system, is arranged on the first enclosure  61 . This is because, out of components to be precisely managed to keep a distance from the rotational deflector constant, components adjacent to the rotational deflector, i.e., components that need to keep not only the distance from the rotational deflector constant but also a relative position from the rotational deflector constant (not to be affected by a reflection and the like) are arranged on the first enclosure to avoid causing any effect on the optical performance as much as possible. As a result, the first enclosure can be used in common among optical scanning devices having different configurations, and it makes possible a simultaneous achievement of common use of elements included in the optical scanning device and the diversification of the optical scanning devices. Furthermore, a complicated shape of, for example, a turn-round portion of the optical path, which is caused by the action of the reflection mirror, can be separated (as the second enclosure) from the first enclosure. Therefore, components of the first enclosure can be processed by press working with low costs, and thus the production costs of the optical scanning device can be reduced. 
         [0095]    Furthermore, in a conventional manner, a specification of the optical scanning device can be easily changed by selecting (setting) the number of beams emitted from the light source, and a rotation speed and a rotation direction of the polygon scanner as the rotational deflector. Therefore, it is possible to provide more various types of optical scanning devices. 
         [0096]    The above configuration of the optical scanning device can be applied to an optical scanning device used in a tandem type of a color-image forming apparatus as disclosed in Japanese Patent No. 3862950 and Japanese Patent Application Laid-Open No. 2004-354848, which are applied separately by the present applicant. The optical scanning device used in the color-image forming apparatus disclosed in Japanese Patent No. 3862950 employs a configuration shown in  FIG. 14 , and the optical scanning device used in the color-image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 2004-354848 employs a configuration shown in  FIG. 15 . As shown in  FIGS. 14 and 15 , a first enclosure and components fixed to the first enclosure are used in common between the optical scanning devices. 
         [0097]    In the optical scanning devices shown in  FIGS. 14  and  15 , a polygon scanner  121  and two fθ lenses  122  are fixed to a first enclosure  110 . Lights emitted from four light source units (not shown) are deflected by a two-stage polygon mirror included in the polygon scanner  121 , and led to a reflection mirror  123   a  or  123   b , which is fixed to a second enclosure  111   a  or  111   b . Other optical elements and optical paths included in the optical scanning device are identical to those disclosed in Japanese Patent No. 3862950 and Japanese Patent Application Laid-Open No. 2004-354848, and the description of those portions, which are not shown in  FIGS. 14 and 15 , is omitted. 
         [0098]    The embodiments of the present invention are explained in detail above with reference to the accompanying drawings, but the present invention is not limited to the embodiments. For example, a setting of the optical path in the optical scanning device can be changed depending on a layout of an image forming apparatus equipped with the optical scanning device. Also, it is possible to change settings of layouts of optical elements, with or without the reflection mirror, the number of the reflection mirrors, and the like accordingly. Moreover, shapes of the first and second enclosures can be changed, and a setting of optical elements included in each of the first and second enclosures can be changed. Furthermore, settings of the distances L 1  to L 3 , L 11  to L 13 , L, and L 0  can be changed. 
         [0099]    Furthermore, settings of the number of beams emitted from the light source, and a rotation speed and a rotation direction of the polygon scanner as the rotational deflector can be changed. Therefore, it is possible to provide various types of the optical scanning devices. In addition, the optical scanning device according to the present invention can be applied to a multi-beam optical scanning device. 
         [0100]    A configuration of the image forming apparatus equipped with the optical scanning device can also be changed. The image forming apparatus can employ any other transfer method such as an intermediate transfer method. As for units included in the image forming apparatus, such as the developing device and the fixing device, any kinds of devices can be used. The image forming apparatus according to the present invention is not limited to just a copying machine and a printer, but includes a facsimile machine, a multifunction product, and the like. 
         [0101]    As described above, according to one aspect of the present invention, it makes possible to achieve both common use of elements of the optical scanning device and the diversification of the optical scanning devices. Moreover, it makes possible to provide the optical scanning device in accordance with various layouts of the image forming apparatuses with low costs and a simple method. Furthermore, any configuration of the optical scanning devices can achieve a desired imaging performance constant. 
         [0102]    In addition, a complicated shape of, for example, a turn-round portion of the optical path can be separated (as the second enclosure) from the first enclosure. Therefore, it is possible to reduce not only the production cost of the first enclosure but also the production costs of the entire optical scanning device and the image forming apparatus. 
         [0103]    Furthermore, according to another aspect of the present invention, optical elements to be precisely laid out are partially held by the enclosure to avoid causing any effect on the optical performance as much as possible. Thus, it is possible to achieve both the common use of elements included in the optical scanning device and the diversification of the optical scanning devices. 
         [0104]    Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.