Abstract:
An optical beam scanning apparatus and an image forming apparatus equipped with the optical beam scanning apparatus of the present invention include: an attaching plate attached to a main body housing of the optical beam scanning apparatus; a holder attached to the attaching plate; and a laser drive board screwed to the holder, wherein the holder is provided with plural pinching portions capable of pinching the holder by means of an outside apparatus, an attachment hole used to attach the attaching plate, and an attaching screw, being in a loose fit state, to be thread coupled to the attaching plate. According to the optical beam scanning apparatus and the image forming apparatus equipped with the optical beam scanning apparatus of the present invention, it is possible to perform rotary adjustment of the light source about the optical axis with ease and at high accuracy even in a small space.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field of the Invention 
         [0002]    The present invention relates to an optical beam scanning apparatus and an image forming apparatus equipped with the optical beam scanning apparatus, and more particularly, to an optical beam scanning apparatus configured to be capable of performing rotary adjustment of the light source about the optical axis and an image forming apparatus equipped with the optical beam scanning apparatus. 
         [0003]    2. Related Art 
         [0004]    An image forming apparatus of the electrophotgraphic method, such as a laser printer, a digital copying machine, and a laser facsimile machine, is equipped with an optical beam scanning apparatus that forms an electrostatic latent image on the photoconductive drum by irradiating a laser beam (optical beam) on the surface of the photoconductive drum and scanning the laser beam thereon. 
         [0005]    Recently, in order to increase the scanning rate on the surface of the photoconductive drum, there has been proposed a method (multi-beam method) for increasing the number of laser beams scanned at a time by providing plural light sources (laser diodes) to a single laser unit. According to the multi-beam method, plural beams for respective color components (for example, yellow, magenta, cyan, and black) emitted from the corresponding light sources undergo processing in the pre-deflection optical systems, while they are combined into a single beam to go incident on the polygon mirror. The beam deflected on the polygon mirror passes through the fθ lens forming the post-deflection optical system, after which it is separated into beams of the respective color components that are irradiated onto the photoconductive drums of the respective color components. 
         [0006]    Incidentally, it is necessary for an optical beam scanning apparatus and an image forming apparatus using plural light sources (laser diodes) to perform rotary adjustment of the light sources (laser diodes) about the optical axis to maintain a specific sub-scanning beam pitch on the photoconductive drums. To be more specific, for example, in the case of 600 dpi (Dot Per Inch), it is necessary to perform rotary adjustment of the light source (laser diode) about the optical axis to maintain 42 μm as the sub-scanning beam pitch, and for example, in the case of 1200 dpi, it is necessary to perform rotary adjustment of the light source (laser diode) about the optical axis to maintain 21 μm as the sub-scanning beam pitch. Further, it is also necessary for the light source (laser diode) to match the optical axes with the collimator lens. 
         [0007]    Such being the case, there have been proposed various techniques for the rotary adjustment about the optical axis and the optical axis matching with the collimator lens for an optical beam scanning apparatus and an image forming apparatus. 
         [0008]    According to the technique proposed in JP-A-2005-164997, a light source unit is formed by fixing a multi-beam light source, a collimator lens, and an aperture integrally to a base, and the light source unit thus formed is attached to the housing in an attachable/detachable manner. Also, the base is divided into a portion where the laser diode of the light source is fixed and a portion fixed to the housing, so that the position of the laser diode is fixed in a state where the rotary adjustment has been performed. This configuration enables attachment to/detachment from the housing while the light source is kept in a state where the angle of rotation has been adjusted. 
         [0009]    In addition, according to the technique proposed in JP-A-2003-43389, a laser unit is assembled with an inclination by being rotated about the fitting portion of an optical unit before the optical unit is attached to the image forming apparatus. This configuration makes it possible to achieve a specific sub-scanning beam pitch interval by extracting only sub-scanning components at the laser spot interval, which in turn enables a specific angle to be maintained using attachment means, such as an attaching screw, after rotary adjustment of the laser unit is performed. 
         [0010]    Further, according to the technique proposed in JP-A-2002-341272, because a BD slit and a BD sensor are formed of an integral unit, a BD detection unit is able to perform rotary adjustment of the optical unit about the center of the optical axis of the scanning lens. 
         [0011]    Generally, by taking a tolerance of components into account, it is preferable to perform rotary adjustment about the optical axis in the optical beam scanning apparatus and the image forming apparatus in a state where all the unit components of the optical beam scanning apparatus and the image forming apparatus have been assembled. 
         [0012]    However, when the rotary adjustment about the optical axis is performed in an assembled state, the rotary adjustment about the optical axis is normally performed by making access to the light source (laser diode) from behind because of supporting and screwing for the rotary adjustment. This requires a space to allow access to the light source (laser diode) from behind for performing adjustment, and therefore poses a problem that the units of the optical beam scanning apparatus and the image forming apparatus are increased in size. 
         [0013]    To be more concrete, as is shown in  FIG. 1 , roughly speaking, a pre-deflection optical system  1 - b  and a post-deflection optical system  1 - c  are provided within a unit  1 - a  of the optical beam scanning apparatus. Laser units  1 - d  through  1 - g , for example, of respective colors are disposed in the pre-deflection optical system  1 - b . However, when rotary adjustment about the optical axis is performed by making access to the light sources (laser diodes  1 - d  through  1 - g ) from behind, a space to allow access in the directions indicated by arrows is necessary. The unit  1 - a  of the optical beam scanning apparatus therefore has to be increased as large as the unit  1 - h.    
         [0014]    As a countermeasure, a hole may be provided in the unit of the optical beam scanning apparatus, so that access is made to the light sources (laser diodes) from the outside of the unit. This countermeasure, however, requires a die of the sliding structure for the unit, which deteriorates the accuracy or increases the cost. 
         [0015]    With the technique disclosed in JP-A-2005-164997, the light source unit can be attached to/detached from the housing while the light source is kept in a state where the angle of rotation has been adjusted. However, because attachment and detachment are performed by the positioning method, when attachment or detachment is performed, the optical axis is shifted from that of the collimator lens due to the influence of an error. This gives rise to a risk of deteriorating the performance of the optical scanning apparatus and the image forming apparatus. 
         [0016]    The optical housing can be adjusted from the outside with the techniques proposed in JP-A-2003-43389 and JP-A-2002-341272. However, because a die of the sliding structure is required for the unit housing, the accuracy is deteriorated or the cost is increased as a result. 
       SUMMARY OF THE INVENTION 
       [0017]    The present invention was devised in view of the foregoing, and therefore has an object to provide an optical beam scanning apparatus capable of performing rotary adjustment of the light source about the optical axis with ease and at high accuracy even in a small space and an image forming apparatus equipped with the optical beam scanning apparatus. 
         [0018]    In order to solve the problems discussed above, an optical beam scanning apparatus according to one aspect of the present invention includes: an attaching plate attached to a main body housing of the optical beam scanning apparatus; a holder attached to the attaching plate; and a laser drive board screwed to the holder, wherein the holder is provided with plural pinching portions capable of pinching the holder by means of an outside apparatus, an attachment hole used to attach the attaching plate, and an attaching screw, being in a loose fit state, to be thread coupled to the attaching plate. 
         [0019]    In order to solve the problems discussed above, an image forming apparatus according to another aspect of the present invention is an image forming apparatus equipped with an optical beam scanning apparatus using plural light sources, wherein the optical beam scanning apparatus includes: an attaching plate attached to a main body housing of the optical beam scanning apparatus; a holder attached to the attaching plate; and a laser drive board screwed to the holder, wherein the holder is provided with plural pinching portions capable of pinching the holder by means of an outside apparatus, an attachment hole used to attach the attaching plate, and an attaching screw, being in a loose fit state, to be thread coupled to the attaching plate. 
         [0020]    The optical beam scanning apparatus according to the firstly mentioned aspect of the present invention is provided with the attaching plate attached to the main body housing of the optical beam scanning apparatus, the holder attached to the attaching plate, and the laser drive board screwed to the holder, wherein the holder is provided with plural pinching portions capable of pinching the holder by means of an outside apparatus, the attachment hole used to attach the attaching plate, and the attaching screw, being in a loose fit state, to be thread coupled to the attaching plate. 
         [0021]    Regarding the image forming apparatus according to the secondly mentioned aspect of the present invention; in an image forming apparatus equipped with an optical beam scanning apparatus using plural light sources, the optical beam scanning apparatus is provided with the attaching plate attached to the main body housing of the optical beam scanning apparatus, the holder attached to the attaching plate, and the laser drive board screwed to the holder, wherein the holder is provided with plural pinching portions capable of pinching the holder by means of an outside apparatus, the attachment hole used to attach the attaching plate, and the attaching screw, being in a loose fit state, to be thread coupled to the attaching plate. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    In the drawings: 
           [0023]      FIG. 1  is an explanatory view used to describe a manner in which a unit in an optical beam scanning apparatus and an image forming apparatus in the related art is increased in size; 
           [0024]      FIG. 2  is a side view showing the configuration of an image forming apparatus incorporating an optical beam scanning apparatus to which the present invention is applied; 
           [0025]      FIG. 3  is a view showing the detailed configuration of the optical beam scanning apparatus of  FIG. 2 ; 
           [0026]      FIG. 4  is another view showing the detailed configuration of the optical beam scanning apparatus of  FIG. 2 ; 
           [0027]      FIG. 5  is an explanatory view used to describe a method for performing rotary adjustment of a light source by making a part of optical units into a separate piece; 
           [0028]      FIG. 6  is a view showing an example where a part of the optical units are made into a separate piece; 
           [0029]      FIG. 7  is a view showing the detailed configuration of a holding member of  FIG. 6 ; 
           [0030]      FIGS. 8A and 8B  are, respectively, a plan view and a front view showing the configuration when an outside apparatus is attached to the holding member; 
           [0031]      FIG. 9  is a view showing another example where a part of the optical units are made into a separate piece; 
           [0032]      FIG. 10  is a view showing still another example where a part of the optical units are made into a separate piece; and 
           [0033]      FIG. 11  is a view showing still another example where a part of the optical units are made into a separate piece. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0034]    Hereinafter, embodiments of the present invention will be described with reference to the drawings. 
         [0035]      FIG. 2  shows the configuration of an image forming apparatus  2  incorporating an optical beam scanning apparatus  11  to which the present invention is applied. Because the image forming apparatus  2  normally uses four kinds of image data separated in colors for respective color components including Y (yellow), M (magenta), C (cyan), and B (black) and four sets of various devices used to form images of the respective color components corresponding to Y, M, C, and B, the image data for the respective color components and the corresponding devices are identified by appending capitals Y, M, C, and B as a suffix. 
         [0036]    As is shown in  FIG. 2 , the image forming apparatus  2  includes first through fourth image forming portions  12 Y,  12 M,  12 C, and  12 B that form images of respective color components separated in colors. 
         [0037]    The image forming portions  12  ( 12 Y,  12 M,  12 C, and  12 B) are disposed below the optical beam scanning apparatus  11  at the corresponding positions to which laser beams L (LY, LM, LC, and LB) of the respective color components are irradiated by a first post-deflection bending mirror  39 B and third post-deflection bending mirrors  41 Y,  41 M, and  41 C in the optical beam scanning apparatus  11  in order of the image forming portions  12 Y,  12 M,  12 C, and  12 B. 
         [0038]    A carrying belt  13  that carries a recording sheet of paper P, onto which images formed individually by the image forming portions  12  ( 12 Y,  12 M,  12 C, and  12 B) are transferred, is disposed below the image forming portions  12  ( 12 Y,  12 M,  12 C, and  12 B). 
         [0039]    The carrying belt  13  is pulled across a belt driving roller  14  rotated in the direction indicated by an arrow by an unillustrated motor and a tension roller  15 , and is therefore rotated at a specific velocity in the direction in which the belt driving roller  14  is rotated. 
         [0040]    The image forming portions  12  ( 12 Y,  12 M,  12 C, and  12 B) are formed in a cylindrical shape to be able to rotate in the direction indicated by the arrow, and respectively include photoconductive drums  16 Y,  16 M,  16 C, and  16 B on which electrostatic latent images corresponding to images exposed by the optical beam scanning apparatus  11  are formed. 
         [0041]    On the periphery of the photoconductive drums  16  ( 16 Y,  16 M,  16 C, and  16 B), the following are disposed respectively in order in the direction in which the photoconductive drums  16  ( 16 Y,  16 M,  16 C, and  16 B) are rotated: charging devices  17  ( 17 Y,  17 M,  17 C, and  17 B) that confer specific potential to the surfaces of the photoconductive drums  16  ( 16 Y,  16 M,  16 C, and  16 B), developing devices  18  ( 18 Y,  18 M,  18 C, and  18 B) that develop the electrostatic latent images formed on the surfaces of the photoconductive drums  16  ( 16 Y,  16 M,  16 C, and  16 B) by supplying toners of the corresponding colors, transferring devices  19  ( 19 Y,  19 M,  19 C, and  19 B) that transfer toner images on the photoconductive drums  16  ( 16 Y,  16 M,  16 C, and  16 B) onto a recording medium, that is, a recording sheet of paper P, carried by the carrying belt  13 , cleaners  20  ( 20 Y,  20 M,  20 C, and  20 B) that remove residual toner on the photoconductive drums  16  ( 16 Y,  16 M,  16 C, and  16 B), and static erasers  21  ( 21 Y,  21 M,  21 C, and  21 B) that remove residual potential remaining on the photoconductive drums  16  ( 16 Y,  16 M,  16 C, and  16 B) after the toner images are transferred. 
         [0042]    The transferring devices  19  ( 19 Y,  19 M,  19 C, and  19 B) respectively oppose the photoconductive drums  16  ( 16 Y,  16 M,  16 C, and  16 B) from the back surface of the carrying belt  13  while the carrying belt  13  is present between the photoconductive drums  16  ( 16 Y,  16 M,  16 C, and  16 B) and the selves. 
         [0043]    A paper cassette  22  accommodating recording sheets of paper P, on which images formed by the image forming portions  12  ( 12 Y,  12 M,  12 C, and  12 B) are transferred, is disposed below the carrying belt  13 . Also, the cleaners  20  ( 20 Y,  20 M,  20 C, and  20 B) remove residual toner, respectively, on the photoconductive drums  16  ( 16 Y,  16 M,  16 C, and  16 B) that was not transferred when the toner images were transferred onto a recording sheet of paper P, respectively, by the transferring devices  19  ( 19 Y,  19 M,  19 C, and  19 B). 
         [0044]    A feeding roller  23  that is formed almost in a semicircular shape and feeds recording sheets of paper P accommodated in the paper cassette  22  one by one from the top, on the side in close proximity to the tension roller  15  is disposed at one end of cassette  22 . 
         [0045]    Between the feeding roller  23  and the tension roller  15 , a registration roller  24  that matches the top end of a single recording sheet of paper P taken out from the cassette  22  with the top end of the toner image formed on the photoconductive drum  16 B in the image forming portion  12 B (black) is disposed. 
         [0046]    At the position in close proximity to the tension roller  15  between the registration roller  24  and the first image forming portion  12 Y and substantially opposing the position on the outer periphery of the carrying belt  13  corresponding to the position at which the tension roller  15  and the carrying belt  13  come in contact with each other, an attraction roller  25  that confers a specific electrostatic attraction force to a single recording sheet of paper P carried at specific timing by the registration roller  24  is disposed. 
         [0047]    In close proximity to one end of the carrying belt  13  and the belt driving roller  14  and substantially on the outer periphery of the carrying belt  13  that comes into contact with the belt driving roller  14 , a first registration sensor  26   a  and a second registration sensor  26   b  that detect the position of an image formed on the carrying belt  13  or an image transferred onto a recording sheet of paper P are disposed spaced apart by a certain distance in the axial direction of the belt driving roller  14  (because  FIG. 2  is a sectional front view, the first registration sensor  26   a  positioned ahead of the sheet surface is not shown). 
         [0048]    At the position on the outer periphery of the carrying belt  13  that comes into contact with the belt driving roller  14  where a recording sheet of paper P carried by the carrying belt  13  will not come into contact, a carrying belt cleaner  27  that removes toner or paper dust from a recording sheet of paper P adhering on the carrying belt  13  is disposed. 
         [0049]    In a direction in which a recording sheet of paper P carried by the carrying belt  13  is separated from the belt driving roller  14  and carried further, a fixing device  28  that fixes the toner image, which has been transferred onto the recording sheet of paper P, on the recording sheet of paper P is disposed. 
         [0050]      FIG. 3  and  FIG. 4  show the configuration of the optical beam scanning apparatus  11  of  FIG. 2  in detail. 
         [0051]    The optical beam scanning apparatus  11  includes an optical deflector  29  comprising a polygonal mirror main body (so-called polygon mirror)  29   a  having, for example, eight plane reflecting surfaces (plane reflecting mirrors) disposed to form a regular polygon and a motor  29   b  that rotates the polygonal mirror main body  29   a  in the main scanning direction at a specific velocity, and light sources  30  ( 30 Y,  30 M,  30 C, and  30 B) that output optical beams, respectively, toward the first through fourth image forming portions  12 Y,  12 M,  12 C, and  12 B of  FIG. 2 . 
         [0052]    The optical deflector  29  is deflection means for deflecting optical beams (laser beams) emitted from the light sources  30  ( 30 Y,  30 M,  30 C, and  30 B) toward the image planes disposed at the specific positions, that is, toward the outer peripheral surfaces of the photoconductive drums  16 Y,  16 M,  16 C, and  16 B in the first through fourth image forming portions  12 Y,  12 M,  12 C, and  12 B, respectively, at a specific linear velocity. In addition, pre-deflection optical systems  31  ( 31 Y,  31 M,  31 C, and  31 B) are disposed between the optical deflector  29  and the light sources  30  ( 30 Y,  30 M,  30 C, and  30 B), and a post-deflection optical system  32  is disposed between the optical deflector  29  and the image planes. 
         [0053]    A direction in which the respective laser beams are deflected (scanned) by the optical deflector  29  is referred to as “main scanning direction”, and a direction orthogonal to both the main scanning direction and the axial line used as the reference of deflection operations provided to the laser beams by the optical deflector  29  for the laser beams scanned (deflected) by the optical deflector  29  to travel in the main scanning direction is referred to as “sub-scanning direction”. 
         [0054]    As is shown in  FIG. 4 , the pre-deflection optical systems  31  respectively include light sources  30  ( 30 Y,  30 M,  30 C, and  30 B) comprising laser diodes and provided for respective color components, finite focusing lenses  33  ( 33 Y,  33 M,  33 C, and  33 B) that confer a specific focusing property to laser beams emitted from the light sources  30  ( 30 Y,  30 M,  30 C, and  30 B), apertures  34  ( 34 Y,  34 M,  34 C, and  34 B) that confer an arbitrary sectional beam shape to laser beams L having passed through the finite focusing lenses  33  ( 33 Y,  33 M,  33 C, and  33 B), and cylinder lenses  35  ( 35 Y,  35 M,  35 C, and  35 B) that further confer a specific focusing property in the sub-scanning direction to the laser beams L having passed through the apertures  34  ( 34 Y,  34 M,  34 C, and  34 B). They trim the sectional beam shape of laser beams emitted from the respective light sources  30  ( 30 Y,  30 M,  30 C, and  30 B) into a specific shape and then guide the leaser beams to the reflection surface of the optical deflector  29 . 
         [0055]    For a laser beam LC for cyan exiting from the cylinder lens  35 C, the optical path is bent by a bending mirror  36 C, after which it is guided to the reflection surface of the optical deflector  29  by traveling straight through an optical path combining optical component  37 . For a laser beam LB for black exiting from the cylinder lens  35 B, the optical path is bent by a bending mirror  36 B, after which it is guided to the reflection surface of the optical deflector  29  by being reflected on the optical path combining optical component  37 . A laser beam LY for yellow exiting from the cylinder lens  35 Y passes by above the bending mirror  36 C, after which it is guided to the reflection surface of the optical deflector  29  by traveling straight through the optical path combining optical component  37 . For a laser beam LM for magenta exiting from the cylinder lens  35 M, the optical path is bent by a bending mirror  36 M for the laser beam LM to pass by above the bending mirror  36 B, after which it is guided to the reflection surface of the optical deflector  29  by being reflected on the optical path combining optical component  37 . 
         [0056]    The post-deflection optical system  32  includes an fθ lens  38  (fθ lenses  38   a  and  38   b ) comprising a set of two lenses and used to optimize the shapes and the positions on the image planes of the laser beams L (Y, M, C, and B) deflected (scanned) by the polygonal mirror main body  29   a , a horizontal synchronization detection photo-detector (not shown) that detects the respective laser beams L to match the horizontal synchronizations of the laser beams L (LY, LM, LC, and LB) having passed through the fθ lens  38  (fθ lenses  38   a  and  38   b ), a horizontal synchronization bending mirror (not shown) that bends the respective laser beams L toward the horizontal synchronization detection photo-detector, an optical path correction element (not shown) disposed between the horizontal synchronization bending mirror and the horizontal synchronization detection photo-detector to bring the laser beams L (LY, LM, LC, and LB) of the respective color components reflected on the horizontal synchronization bending mirror toward the horizontal synchronization detection photo-detector almost into agreement with the position of incidence on the detection surface of the horizontal synchronization detection photo-detector, and plural post-deflection bending mirrors  39 Y,  40 Y, and  41 Y (yellow);  39 M,  40 M, and  41 M (magenta);  39 C,  40 C, and  41 C (cyan); and  39 B (black) that guide the laser beams L (LY, LM, LC, and LB) of the respective color components exiting from the fθ lens  38  (fθ lenses  38   a  and  38   b ) to the corresponding photoconductive drums  16  ( 16 Y,  16 M,  16 C, and  16 B). 
         [0057]    Incidentally, when rotary adjustment about the optical axis is performed while the optical beam scanning apparatus  11  and the image forming apparatus  2  are assembled, rotary adjustment about the optical axis is performed normally by making access to the light source (laser diode) from behind. This requires a space to allow access to the light source (laser diode) from behind to perform adjustment, and the units of the optical beam scanning apparatus  11  and the image forming apparatus  2  are undesirably increased in size. 
         [0058]    Such being the case, in the present invention, as is shown in  FIG. 5A , a part of the optical units (the pre-deflection optical systems  31  or the post-deflection optical system  32 ) are made into a separate piece, and rotary adjustment of the light source is performed by an outside apparatus in the direction indicated by an arrow. Then, after the sub-scanning beam pitch on the photoconductive drum  16  is set to a specific value, as is shown in  FIG. 5B , it is incorporated into a main body housing H of the optical beam scanning apparatus  11 . 
         [0059]    In a case where a part of components forming the optical unit are made into a separate piece, for example, as is shown in  FIG. 6 , the pre-deflection optical systems  31  ( 31 Y,  31 M,  31 C, and  31 B), that is, the light sources  30  ( 30 Y,  30 M,  30 C, and  30 B), the finite focusing lenses (collimator lenses)  33  ( 33 Y,  33 M,  33 C, and  33 B), the cylinder lenses  35  ( 35 Y,  35 M,  35 C, and  35 B), and the optical path combining optical component  37  are made into a separate piece and mounted on the same attaching plate  42 . 
         [0060]    In the case of the example of  FIG. 6 , holding members  43  ( 43 Y,  43 M,  43 C, and  43 B) respectively holding the light sources  30  ( 30 Y,  30 M,  30 C, and  30 B) are provided. 
         [0061]      FIG. 7  shows the detailed configuration of the holding member  43  of  FIG. 6 .  FIG. 7A  is a plan view of the holding member  43  and  FIG. 7B  is a front view of the holding member  43 . 
         [0062]    The holding member  43  comprises a holder  44  that holds the corresponding light source  30 , and a laser drive board  45  screwed to the holder  44 . 
         [0063]    The holder  44  is provided with pinching portions  46 - 1  and  46 - 2  to pinch the holder  44  firmly when the outside apparatus (the outside apparatus  49  of  FIG. 8 ) adjusts rotations of each light source  30  about the optical axis. Each light source  30  is disposed on a line linking these two pinching portions  46 - 1  and  46 - 2 . It should be noted that each light source  30  is fixed by means of light source fixing screws  53 - 1  and  53 - 2 . 
         [0064]    Also, attachment holes  47 - 1  and  47 - 2  are made in the holder  44  at specific positions, and the holder  44  is fixed to the attaching plate  42  by inserting holder attaching screws (holder attaching screws  52 - 1  and  52 - 2  of  FIG. 8 ) into the attachment holes  47 - 1  and  47 - 2 . 
         [0065]    The laser drive board  45  is positioned by a positioning protrusion  54  and fixed to the holder  44  with a laser drive board fixing screw  48 . 
         [0066]    The attachment holes  47 - 1  and  47 - 2  are designed to be slightly larger than the diameter of the screw for the holder attaching screws (the holder attaching screws  52 - 1  and  52 - 2  of  FIG. 8 ). Accordingly, the rotary adjustment (angle θ) of each light source  30  about the optical axis and the optical axis adjustment (X direction and Y direction) with the collimator lens are enabled for a quantity comparable to the clearance thus secured. Furthermore, there is a clearance between the attachment holes (the attachment holes  47 - 1  and  47 - 2 ) and the holder attaching screws (the holder attaching screws  52 - 1  and  52 - 2 ), and a fixing position (X direction and Y direction) and a fixing angle (angle θ) of the holder are adjustable with respect to the holder attaching screws (the holder attaching screws  52 - 1  and  52 - 2 ). 
         [0067]      FIG. 8  shows the configuration when the outside apparatus  49  is attached to the holding member  43 . 
         [0068]      FIG. 8A  is a plan view when the outside apparatus  49  is attached to the holding member  43 , and  FIG. 8B  is a front view when the outside apparatus  49  is attached to the holding member  43 . 
         [0069]    As are shown in  FIGS. 8A and 8B , schematically, the outside apparatus  49  comprises an adjusting arm main body  50  that performs rotary adjustment of each light source  30  about the optical axis, and rods  51 - 1  and  51 - 2  attached to the holding member  43 . 
         [0070]    The rods  51 - 1  and  51 - 2  of the outside apparatus  49  are attached, respectively, to the pinching portions  46 - 1  and  46 - 2  of the holding member  43 . At least one of these two rods  51 - 1  and  51 - 2  is extendable in the X direction, and the length L between the two rods  51 - 1  and  51 - 2  is therefore adjustable. This configuration allows the two rods  51 - 1  and  51 - 2  to apply a constant load on the holder  44 . 
         [0071]    The holder attaching screws  52 - 1  and  52 - 2  are temporarily screwed, respectively, into the attachment holes  47 - 1  and  47 - 2  made in the holder  44  to the extent that the outside apparatus  49  is able to adjust the holding member  43 . In this instance, a required load is applied to the rods  51 - 1  and  51 - 2  in the optical axis direction of the light source  30 . 
         [0072]    The outside apparatus  49  has three degrees of freedom including the X direction, the Y direction, and the angle θ. By adjusting the holder  44  pinched between the rods  51 - 1  and  51 - 2  in the X direction and the Y direction and at the angle θ, not only is it possible to perform the optical axis matching with the collimator lens for the position of the laser beam to approximate to a specific pre-set value, but it is also possible to adjust rotations of each light source  30  about the optical axis. In addition, by making a part of components forming the optical system unit into a separate piece to perform rotary adjustment of each light source  30  about the optical axis by the outside apparatus  49 , errors caused when adjustment is performed can be suppressed to only the error caused when the separate piece is incorporated into the optical beam scanning apparatus  11  or the image forming apparatus  2 . It is thus possible to perform rotary adjustment of the light source about the optical axis with ease and at high accuracy to maintain a specific sub-scanning beam pitch on the photoconductive drum  16 , even in a small space. Consequently, it is possible to prevent the units of the optical beam scanning apparatus  11  and the image forming apparatus  2  from being increased in size. 
         [0073]    It should be noted that the center of rotation of the adjusting arm main body  50  of the outside apparatus  49  coincides with the center of the laser emission point of each light source  30 . Accordingly, not only can the optical axis matching with the collimator lens be performed at high accuracy, but also rotations of each light source  30  about the optical axis can be adjusted at high accuracy. 
         [0074]    When the optical axis matching with the collimator lens and the rotary adjustment of each light source  30  about the optical axis are completed by the outside apparatus  49 , the holder attaching screws  52 - 1  and  52 - 2  used to fix the holder  44  are tightened, and the holder  44  is completely fixed to the attaching plate  42 . 
         [0075]    As is shown in  FIG. 6 , in the embodiment of present invention, the pre-deflection optical systems  31  ( 31 Y,  31 M,  31 C, and  31 B), that is, the light sources  30  ( 30 Y,  30 M,  30 C, and  30 B), the finite focusing lenses (collimator lenses)  33  ( 33 Y,  33 M,  33 C, and  33 B), the cylinder lenses  35  ( 35 Y,  35 M,  35 C, and  35 B), and the optical path combining optical component  37  are made into a separate piece and mounted on the same attaching plate  42 . The present invention, however, is not limited to this case, and for example, as is shown in  FIG. 9 , besides the pre-deflection optical systems  31 , the optical deflector  29  (the polygonal mirror main body (so-called polygon mirror)  29   a  and the motor  29   b ) may be further added to the separate piece and mounted on the same attaching plate  42 . By adopting the arrangement shown in  FIG. 6 , it is possible to forestall an influence of heat generated while the polygonal mirror main body  29   a  is rotating during printing or the like. 
         [0076]    Alternatively, as is shown in  FIG. 10 , besides the pre-deflection system  31  and the optical deflector  29 , for example, the fθ lens  38   b  of the post-deflection optical system  32  may be further added to the separate piece and mounted on the same attaching plate  42 . It goes without saying that both the fθ lenses  38   a  and  38   b  of the post-deflection optical system  32  may be added to the separate piece and mounted on the same attaching plate  42 . 
         [0077]    By adopting the arrangement as shown in  FIG. 10 , it is possible to lessen errors caused when the separate piece is incorporated into the optical beam scanning apparatus  11  or the image forming apparatus  2 . 
         [0078]    Further, as is shown in  FIG. 11 , besides the pre-deflection optical system  31 , for example, the fθ lens  38   b  of the post-deflection optical system  32  may be further added to the separate piece and mounted on the same attaching plate  42 . It goes without saying that both the fθ lenses  38   a  and  38   b  of the post-deflection optical system  32  may be added to the separate piece and mounted on the same attaching plate  42 .