Abstract:
The invention concerns light-beam deflecting apparatus in which a polygon mirror is pushed against a flange to hold it stationary. The light-beam deflecting apparatus includes a base member; a polygon mirror being rotatable in respect to the base member; a flange contacting the polygon mirror to hold the polygon mirror; and pushing member to push the polygon mirror against the flange. One or both of contacting surfaces of the polygon mirror and the flange is/are finished to a surface roughness of Ry, which fulfills a first formula of Ry≧3 μm or a second formula of 3 μm≦Ry≦20 μm.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a light-beam deflecting apparatus, in which a polygon mirror is pushed against a flange to hold it stationary, a manufacturing method of the light-beam deflecting apparatus and an image-forming apparatus.  
           [0002]    Conventionally, electro-photographic image-forming apparatus, such as laser-beam printers, digital copiers, etc., have employed a light-beam deflecting apparatus for scanning a light-beam, in order to write images onto a photoreceptor drum. In the conventional light beam deflection apparatus, a polygon mirror combined with magnets is rotatably inserted into a central axis of the base body with a bearing between them, and driving coils are disposed opposite the magnets so that the rotational torque, caused by the relative magnetic forces generated between the permanent magnets and the driving coils when electronic currents flow into the driving coils, rotates the polygon mirror at a high rate, while forming an air gap between the base body and a rotating disk including the polygon mirror, etc.  
           [0003]    In the abovementioned light-beam deflecting apparatus, since the polygon mirror is pushed against the flange to hold it stationary relative to the flange, and contacting surfaces of both the polygon mirror and the flange should be finished as accurate surfaces to improve an inclined angle of a mirror surface of the polygon mirror, such the contacting surfaces are finished so that surface roughness Ry is not greater than 1 μm (Ry≦1 μm). In the conventional configuration, however, in which both the contacting surfaces push against relative to each other to fix the polygon mirror onto the flange, there has been a fear that the position of the polygon mirror possibly deviates from its original position due to a centrifugal force generated by its high-speed rotation, resulting in unbalance of the mass distribution of the rotating disk, and increase of the vibrations.  
         SUMMARY OF THE INVENTION  
         [0004]    To overcome the abovementioned drawbacks in conventional light-beam deflecting apparatus, it is an object of the present invention to provide a light-beam deflecting apparatus, which makes it possible to prevent the polygon mirror from deviating from the original position and to stably rotate the polygon mirror, even if the polygon mirror, pushed against the flange, rotates at a high rate during its operating time, and a method for manufacturing the light-beam deflecting apparatus, and further, an image-forming apparatus equipped with the light-beam deflecting apparatus.  
           [0005]    Accordingly, to overcome the cited shortcomings, the abovementioned object of the present invention can be attained by light-beam deflecting apparatus, methods for manufacturing the light-beam deflecting apparatus and image-forming apparatus described as follow.  
           [0006]    (1) A light-beam deflecting apparatus, comprising: a base member; a polygon mirror being rotatable in respect to the base member; a flange contacting the polygon mirror to hold the polygon mirror; and a pushing member to push the polygon mirror against the flange; wherein one or both of contacting surfaces of the polygon mirror and the flange is/are finished to a surface roughness of Ry, which fulfills a first formula of Ry≧3 μm.  
           [0007]    (2) The light-beam deflecting apparatus of item  1 , wherein surface roughness Ry fulfills a second formula of 3 μm≦Ry≦20 μm.  
           [0008]    (3) The light-beam deflecting apparatus of item  1 , wherein one or both of contacting surfaces of the polygon mirror and the flange is/are finished to surface roughness Ry, by employing one of an abrasive blasting, a cutting machining, a laser machining, a dry ice blasting, a chemical processing and a form rolling, or by employing a combination of a plurality of machining methods arbitrarily selected from them.  
           [0009]    (4) A method for manufacturing a light-beam deflecting apparatus, which incorporates a polygon mirror being rotatable in respect to a base member and a flange contacting the polygon mirror to hold the polygon mirror, comprising the steps of: finishing one or both of contacting surfaces of the polygon mirror and the flange to a surface roughness of Ry, which fulfills a first formula of Ry≧3 μm; and fixing the polygon mirror onto the flange by pushing the polygon mirror against the flange so that both of the contacting surfaces contact each other with a pushing force applied, in order to assemble the light-beam deflecting apparatus.  
           [0010]    (5) The method of item  4 , wherein surface roughness Ry fulfills a second formula of 3 μm≦Ry≦20 μm.  
           [0011]    (6) The method of item  4 , wherein one or both of the contacting surfaces is/are finished to surface roughness Ry, by employing one of an abrasive blasting, a cutting machining, a laser machining, a dry ice blasting, a chemical processing and a form rolling, or by employing a combination of a plurality of machining methods arbitrarily selected from them.  
           [0012]    (7) The method of item  4 , wherein one or both of the contacting surfaces is/are finished to surface roughness Ry, which fulfills a third formula of Ry&lt;3 μm, before performing the finishing step.  
           [0013]    (8) An image-forming apparatus, comprising: a photoreceptor; and the light-beam deflecting apparatus cited in item  1 ; wherein a light-beam, reflected from the polygon mirror, writes image information on the photoreceptor.  
           [0014]    (9) The image-forming apparatus of item  8 , wherein surface roughness Ry fulfills a second formula of 3 μm≦Ry≦20 μm.  
           [0015]    (10) The image-forming apparatus of item  8 , wherein one or both of contacting surfaces of the polygon mirror and the flange is/are finished to surface roughness Ry, by employing one of an abrasive blasting, a cutting machining, a laser machining, a dry ice blasting, a chemical processing and a form rolling, or by employing a combination of a plurality of machining methods arbitrarily selected from them.  
           [0016]    Further, to overcome the abovementioned problems, other light-beam deflecting apparatus and methods for manufacturing the light-beam deflecting apparatus, embodied in the present invention, will be described as follow:  
           [0017]    (11) A light-beam deflecting apparatus, characterized in that, a base member, a polygon mirror rotating in respect to the base member, a flange contacting the polygon mirror to hold the polygon mirror and a pushing member to push the polygon mirror against the flange are provided, and a surface roughness (Ry) of one or both of contacting surfaces of the polygon mirror and the flange fulfills Ry≧3 μm.  
           [0018]    According to the abovementioned light-beam deflecting apparatus, since a surface roughness (Ry) of at least one of contacting surfaces of the polygon mirror and the flange fulfills Ry≧3 μm, the frictional force between the contacting surfaces sufficiently increases when the polygon mirror is pushed against the flange to hold the polygon mirror, and thereby, the positional deviation of the polygon mirror, caused by the centrifugal force due to its high-speed rotating action during its operating time, hardly occurs, resulting in the stable rotation of the rotating disk without changing its vibration mode. Incidentally, in the present specification, the term of “surface roughness (Ry)” indicates the maximum height defined by JIS-B-0601.  
           [0019]    It is desirable that the surface roughness (Ry) of the contacting surface fulfills the formula of 3 μm≦Ry≦20 μm. When the surface roughness (Ry) fulfills Ry ≦20 μm, it is possible to maintain the unit characteristics of the light-beam deflecting apparatus, such as the inclination angle of the mirror surface of the polygon mirror, etc., in an appropriate state. Further, the contacting surface can be finished to the abovementioned surface roughness (Ry), by employing one of an abrasive blasting, a cutting machining, a laser machining, a dry ice blasting, a chemical processing and a form rolling.  
           [0020]    (12) A manufacturing method of a light-beam deflecting apparatus, characterized in that, the method include a process for finishing one or both of contacting surfaces of a polygon mirror, rotating in respect to a base member, and a flange, contacting the polygon mirror to hold the polygon mirror, to a surface roughness of Ry, which fulfills Ry≧3 μm or desirably 3 μm≦Ry≦20 μm, and an assembling process for fixing the polygon mirror onto the flange by contacting the contacting surfaces of them each other and by applying a pushing force to them.  
           [0021]    According to the manufacturing method mentioned above, since the polygon mirror is fixed onto the flange by contacting the contacting surfaces of them each other and by applying a pushing force to them in its assembling process, after at least one of the contacting surfaces is finished to a surface roughness of Ry≧3 μm, the frictional force between the contacting surfaces sufficiently increases, and thereby, the positional deviation of the polygon mirror, caused by the centrifugal force due to its high-speed rotating action during its operating time, hardly occurs. Therefore, it becomes possible to manufacture a light-beam deflecting apparatus, in which the polygon mirror can stably rotates without generating any vibrations.  
           [0022]    In this case, an abrasive blasting, a cutting machining, a laser machining, a dry ice blasting, a chemical processing or a form rolling can be employed for the surface-finish processing.  
           [0023]    Further, it is possible to finish the contacting surface so that its surface roughness (Ry) fulfills Ry&lt;3 μm, before performing the abovementioned surface-finish processing. Of cause, it is also applicable that the abovementioned surface-finish processing is performed without finishing the contacting surface to the surface roughness Ry &lt;3 μm in advance.  
           [0024]    Further, an image-forming apparatus, embodied in the present invention, characterized in that, the abovementioned light-beam deflecting apparatus is provided, and a light-beam, reflected from the polygon mirror, writes image information on the photoreceptor element. According to the image-forming apparatus, since the positional deviation of the polygon mirror, caused by the centrifugal force due to its high-speed rotating action during its operating time, hardly occurs, and the polygon mirror can stably rotates without generating any vibrations, it becomes possible to perform a stable image-forming operation for a long time. In addition, since the inclination angle of the mirror surface of the polygon mirror, as well as other characteristics, can be maintained in a desirable state, it becomes possible to contribute to a high-quality image-forming operation. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    Other objects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:  
         [0026]    [0026]FIG. 1 shows a cross-sectional side view of a light-beam deflecting apparatus structured as a first embodiment of the present invention;  
         [0027]    [0027]FIG. 2 shows a partial side view of a light-beam deflecting apparatus, for explaining an effect of the light-beam deflecting apparatus shown in FIG. 1;  
         [0028]    [0028]FIG. 3 shows a partial cross sectional view of a light-beam deflecting apparatus, illustrating a variation of it;  
         [0029]    [0029]FIG. 4( a ) shows changes of vibration amplitudes in a horizontal direction, and FIG. 4( b ) shows measuring results of inclination angles, each illustrating an effect of the first embodiment of the present invention;  
         [0030]    [0030]FIG. 5( a ) shows an explanatory illustration for explaining a surface-finish processing performed by an abrasive blasting, and FIG. 5( b ) shows an explanatory illustration for explaining a surface-finish processing performed by a cutting machining, each illustrating a manufacturing method in the second embodiment of the present invention;  
         [0031]    [0031]FIG. 6( a ) shows an explanatory illustration for explaining a surface-finish processing performed by a laser machining, and FIG. 6( b ) shows an explanatory illustration for explaining a surface-finish processing performed by a dry ice blasting, each illustrating a manufacturing method in the second embodiment of the present invention;  
         [0032]    [0032]FIG. 7( a ) shows an explanatory illustration for explaining a surface-finish processing performed by a chemical processing, and FIG. 7( b ) shows an explanatory illustration for explaining a surface-finish processing performed by a form rolling, each illustrating a manufacturing method in the second embodiment of the present invention; and  
         [0033]    [0033]FIG. 8 shows a perspective view of a simplified structure of a light-beam scanning optical unit. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0034]    Referring to the drawings, the first, the second and the third embodiment of the present invention will be detailed in the following.  
         [0035]    First Embodiment  
         [0036]    [0036]FIG. 1 shows a cross-sectional side view of a light-beam deflecting apparatus structured as a first embodiment of the present invention. As shown in FIG. 1, first light-beam deflecting apparatus  10  comprises base body  11  made of a metallic material such as aluminum, etc., printed circuit board  12  attached and fixed onto base body  11 , coils  13  formed and fixed onto printed circuit board  12 , fixed yoke  14  mounted into base body  11  so as to oppose to coils  13  and rotating disk  15 , which rotates relative to base body  11 .  
         [0037]    Rotating disk  15  comprises polygon mirror  17  having mirror surface  17   a  formed on it, flange  18  for holding polygon mirror  17  stationary relative to it, pushing plate  16  for pushing lower side surface  17  of polygon mirror  17  against upper end surface  18   c  of flange  18  by inserting leaf spring  24  between upper side surface  17   b  of polygon mirror  17  and pushing plate  16  to fix polygon mirror  17  onto flange  18 , bearing  20  fixed along inner circumferential surface  18   b  of flange  18  and magnets  22  inserted and fixed into concave holes  18   a  of flange  18 , and rotates in the integrated state. In addition, polygon mirror  17  and flange  18  are made of aluminum.  
         [0038]    At first, lower thrust-bearing  21   b  is inserted into the lowest position of central axis  11   a  of base body  11 , and then, radial-bearing  19  is fitted through central axis  11   a , and further, upper thrust-bearing  21   a  is inserted into the upper position of central axis  11   a . Screw  25   a  fastens fixing plate  25   a  to fix the abovementioned assembly. In the manner mentioned above, upper thrust-bearing  21   a , radial-bearing  19  and lower thrust-bearing  21   b  are fixed onto base body  11  and form concave section  26 . Upper thrust-bearing  21   a , radial-bearing  19  and lower thrust-bearing  21   b  are made of ceramic materials.  
         [0039]    Bearing  20  fixed to flange  18  is located in concave section  26  with gaps between them, so that the rotational torque, caused by the relative magnetic forces generated between magnets  22  and coils  13  when electronic currents flow into coils  13 , rotates rotating disk  15  at a high rate while forming an air gap between concave section  26  and rotating disk  15 .  
         [0040]    The contacting surface of polygon mirror  17  with flange  18 , mentioned above, will be detailed in the following. Since upper end surface  18   c  of flange  18  shown in FIG. 1 is finished so that its surface roughness (Ry) fulfills a condition of 3 μm≦Ry≦20 μm, the surface roughness is larger than that of conventional one. Further, since lower side surface  17   c  of polygon mirror  17  is finished so that its surface roughness (Ry) fulfills a condition of Ry≦1 μm, when upper end surface  18   c  and lower side surface  17   c  contact each other, a friction coefficient (μ) between them becomes large value. Referring to FIG. 2, this effect will be explained as follow.  
         [0041]    When lower side surface  17   c  of polygon mirror  17  is pushed against upper end surface  18   c  of flange  18  with pushing force T generated by leaf spring  24 , which is inserted into a gap between pushing plate  16  and upper side surface  17   b  of polygon mirror  17 , friction force F in a tangential direction between upper end surface  18   c  and lower side surface  17   c  can be expressed by the following equation. 
         
       F=μ×T 
     
         [0042]    As mentioned above, since friction coefficient μ between upper end surface  18   c  and lower side surface  17   c  is larger than that of conventional one, friction force F also becomes large value. Even when centrifugal force F′, caused by a high speed rotating operation of the polygon mirror when activating the light-beam deflecting apparatus, is applied to polygon mirror  17 , as shown in FIG. 2, positional deviations of polygon mirror  17  and unnecessary vibrations of rotating disk  15  hardly occur, compared to conventional light-beam deflecting apparatus, since abovementioned friction force F is larger than centrifugal force F′. Therefore, it becomes possible to stably rotate polygon mirror  17 . In addition, provided that the surface roughness (Ry) at upper end surface  18   c  of flange  18  fulfills a condition of Ry≦20 μm, it becomes possible to maintain the unit characteristics of the light-beam deflecting apparatus, such as an inclination angle of the polygon mirror, etc., in good conditions.  
         [0043]    Next, referring to FIG. 3, a variation of the first embodiment will be detailed in the following. In the example shown in FIG. 3, leaf spring  24  shown in FIG. 1 is omitted, and pushing plate  16   a  directly pushes polygon mirror  17  against flange  18 . Polygon mirror  17  is sandwiched by pushing plate  16   a  and upper end surface  18   c  of flange  18  and is fixed between them by fastening screw  16   b  into flange  18  with a fastening gap between pushing plate  16   a  and upper end surface  18   c  of flange  18 . Accordingly, as well as the construction shown in FIG. 1, lower side surface  17   c  of polygon mirror  17  is pushed against upper end surface  18   c  of flange  18  with a constant pushing force, and upper end surface  18   c  is finished at surface roughness (Ry) in a range of 3 μm≦Ry≦20 μm.  
       Embodiment Examples  
       [0044]    The abovementioned effect of the first embodiment will be further detailed in the following, referring to embodiment examples. In the embodiment examples and the comparison examples, upper end surface  18   c  of flange  18  is finished by employing the abrasive blasting, so that its surface roughness (Ry) varies at various values within a range of 0.08-80 μm. The surface roughness (Ry) at lower side surface  17   c  of polygon mirror  17  is maintained at a constant value, namely, Ry=0.05 μm. Incidentally, the surface roughness tester is employed for measuring the surface roughness, and the measuring results are evaluated based on JIS-B-0601 (Japan Industrial Standard corresponding to ISO 4287).  
         [0045]    A plurality of light-beam deflecting apparatus, which are manufactured under the same conditions as those of the light-beam deflecting apparatus shown in FIG. 1, except that the surface roughness at upper end surface  18   c  of flange  18  is varied by the abovementioned method, are continuously operated for 24 hours at a rotating velocity of 50000 rpm, and the vibrations in a horizontal direction are measured before and after rotating the polygon mirror, in order to find changes of the vibration amplitudes in a horizontal direction before and after rotating the polygon mirror. FIG. 4( a ) shows the changes of the vibration amplitudes in a horizontal direction. Since the change of the vibration amplitude corresponds to the change of mass balance in rotating disk  15  (shown in FIG. 1), the vibration amplitude in the horizontal direction increases according with the increase of the mass unbalance, when the polygon mirror deviates from the original position. As shown in FIG. 4( a ), when the surface roughness (Ry) at upper end surface  18   c  of flange  18  is not lower than 3 μm, good results, in which the changes of the vibration amplitudes are small, are obtained in every cases. On the contrary, when the surface roughness (Ry) is not greater than 1 μm, the changes of the vibration amplitudes become considerably large.  
         [0046]    Further, the inclination angle of the mirror surface of the polygon mirror in each light-beam deflecting apparatus is measured by irradiating laser-beam onto the mirror surface. FIG. 4( b ) shows the measuring results of the inclination angles. As shown in FIG. 4( b ), when the surface roughness (Ry) at upper end surface  18   c  of flange  18  is not greater than 20 μm, good results, in which the inclination angles are not so large, are obtained, though the inclination angle should be zero in an ideal state. On the contrary, when the surface roughness (Ry) exceeds 20 μm, the inclination angle is getting considerably large.  
         [0047]    Second Embodiment  
         [0048]    Next, as the second embodiment of the present invention, a method for manufacturing the light-beam deflecting apparatus, shown in FIG. 1, will be detailed in the following. FIGS.  5 ( a )- 7 ( b ) show explanatory illustrations for explaining various methods of finishing upper end surface  18   c  of flange  18 , which is an objective surface for the surface processing, in a predetermined surface roughness.  
         [0049]    The method of the surface processing, shown in FIG. 5( a ), employs the abrasive blasting. High-pressure air fed from pipeline  32  and abrasive grains, such as alumina powders, etc., fed from pipeline  33  are simultaneously supplied to nozzle  31 , so that the abrasive grains are blasted onto upper end surface  18   c  of flange  18 , serving as an objective surface, at a high rate from nozzle  31 . Flange  18  is fixed onto work table  36  rotated by motor  35  to apply the abrasive blasting to upper end surface  18   c  while rotating flange  18  and protecting the non-objective surface of flange  18  with mask  37 . Although alumina powders, having an average particle size of 100 μm, can be employed for the above purpose, it is possible to adjust the surface roughness (Ry) by appropriately changing the average particle size. Incidentally, although the surface roughness (Ry) at upper end surface  18   c  of flange  18 , before the surface processing, can be set at Ry≦1 μm by the cutting machining, etc., it is also applicable to set it at Ry≧1 μm.  
         [0050]    The method of the surface processing, shown in FIG. 5( b ), employs the cutting machining. Flange  18  is fixed onto table  42  by inserting fixing tool  43  into inner circumferential surface  18   b  of flange  18 , and then, upper end surface  18   c  is cut and ground by pushing cutting tool  44 , made of a polycrystalline diamond, etc., onto it, while motor  41  is rotating flange  18  with table  42 . Since the surface roughness of the tip of cutting tool  44  is directly transferred onto upper end surface  18   c  of flange  18 , it is possible to adjust the surface roughness of upper end surface  18   c  by changing the surface roughness of the tip of cutting tool  44 . Incidentally, although the surface roughness (Ry) at upper end surface  18   c  of flange  18 , before the surface processing, can be set at Ry≦1 μm, it is also applicable to set it at Ry≧1 μm.  
         [0051]    The method of the surface processing, shown in FIG. 6( a ), employs the laser machining. The optical system, comprising Nd:YAG-laser  51 , collecting lens  52  and deflecting mirror  53 , revolves around flange  18  fixed stationary, to irradiate its laser-beam onto upper end surface  18   c , while randomly changing the intensity of the laser-beam and/or randomly vibrating deflecting mirror  53 . The surface roughness of upper end surface  18   c  can be adjusted by changing the output power and/or the irradiating time of Nd:YAG-laser  51 . Instead of rotating the optical system, it is also applicable to rotate flange  18 . Incidentally, although the surface roughness (Ry) at upper end surface  18   c  of flange  18 , before the surface processing, can be set at Ry≦1 μm, it is also applicable to set it at Ry≧1 μm.  
         [0052]    The method of the surface processing, shown in FIG. 6( b ), employs the dry ice blasting. This method is basically the same method as that shown in FIG. 5( a ), except that dry ice particles are employed as the abrasive grains. Concretely speaking, high-pressure air fed from pipeline  62  and dry ice particles fed from pipeline  63  are simultaneously supplied to nozzle  61 , so that the abrasive grains are blasted onto upper end surface  18   c  of flange  18 , serving as an objective surface, at a high rate from nozzle  61 , while flange  18  is rotated by means of the rotating device similar to that shown in FIG. 5( a ). Since the dry ice particles vaporize after blasting and remain no dust, it is possible to conduct a clean machining and to make the post-processing easy. Therefore, the dry ice particles are desirable for the abovementioned purpose. Further, the surface roughness can be adjusted by changing the particle size of the dry ice particles. Incidentally, although the surface roughness (Ry) at upper end surface  18   c  of flange  18 , before the surface processing, can be set at Ry≦1 μm, it is also applicable to set it at Ry≧1 μm.  
         [0053]    The method of the surface processing, shown in FIG. 7( a ), employs the chemical processing. In case that flange  18  is made of aluminum, flange  18 , non-objective surface of which is protected by mask  73 , is dipped into a solution of sodium hydroxide by hanging it with hanging tool  72  to corrode upper end surface  18   c . In this case, since upper end surface  18   c  is not corroded uniformly, an appropriate surface roughness can be obtained on upper end surface  18   c . Further, the surface roughness can be adjusted by changing the density of the solution and/or the dipping time. In addition, either other alkalic solutions or strong acid solutions, such as sulfuric acid, etc., can be employed as the corroding solution. Incidentally, although the surface roughness (Ry) at upper end surface  18   c  of flange  18 , before the surface processing, can be set at Ry≦1 μm, it is also applicable to set it at Ry≧1 μm.  
         [0054]    The method of the surface processing, shown in FIG. 7( a ), employs the form rolling. The surface roughness pattern formed on the press-surface of form-rolling tool  81  can be transferred onto upper end surface  18   c  of flange  18  by pushing form-rolling tool  81  against upper end surface  18   c , while flange  18  is rotated by means of the rotating device similar to that shown in FIG. 5( b ). Further, the surface roughness can be adjusted by changing the surface roughness pattern formed on the press-surface of form-rolling tool  81 . Incidentally, it is desirable that the surface roughness (Ry) at upper end surface  18   c  of flange  18 , before the surface processing, is set at Ry≦1 μm.  
         [0055]    After upper end surface  18   c  of flange  18  is finished, so that its surface roughness (Ry) fulfills a condition of 3 μm≦Ry≦20 μm, by employing one of the abovementioned methods, the light-beam deflecting apparatus can be assembled by contacting lower side surface  17   c  of polygon mirror  17  with upper end surface  18   c  of flange  18 , and pushing polygon mirror  17  against flange  18  with leaf spring  24  and pushing plate  16  to fix polygon mirror  17  onto flange  18  in a state of contacting both surfaces  17   c ,  18   c  each other with the pushing force of leaf spring  24 .  
         [0056]    Third Embodiment  
         [0057]    Next, as the third embodiment of the present invention, an example of the light-beam scanning optical unit, which is employed in the image-forming apparatus, and incorporates the light-beam deflecting apparatus shown in FIG. 1, will be detailed in the following, referring to FIG. 8. FIG. 8 shows a perspective view of the simplified structure of the light-beam scanning optical unit.  
         [0058]    As shown in FIG. 8, the light-beam scanning optical unit comprises: light-beam deflecting apparatus  72  having polygon mirror  73  and fixed on base plate  100 ; semiconductor laser  76 ; collimator lens  75  (the optical system for shaping the light-beam); first cylindrical lens  71 ; fθ lens  70 ; second cylindrical lens  80 ; reflecting mirror  90 ; timing detecting mirror  82 ; and synchronized detector  81 . The laser beam emitted from semiconductor laser  76  is collimated into a parallel light (a collimated beam) by collimator lens  75 , and the collimated beam enters into polygon mirror  73 , rotating in the arrow direction shown in the drawing, after passing through first cylindrical lens  71  in the first image optical system. The light-beam reflected from mirror surface  73   a  of polygon mirror  73  passes through fθ lens  70  and second cylindrical lens  80  in the second image optical system, and is further reflected by reflecting mirror  90 , so that the light-beam, having a predetermined spot-diameter, scans the circumferential surface of photoreceptor drum  91  incorporated in the image-forming apparatus. Synchronizing signals in a main-scanning direction are detected at every time before starting the scanning action of one scanning line by synchronized detector  81  into which the light-beam, reflected from timing detecting mirror  82 , enters. While, photoreceptor drum  101  rotates in a sub-scanning direction, synchronizing with the synchronizing signals detected by synchronized detector  81 .  
         [0059]    According to the abovementioned configuration, it is possible to write image information onto the circumferential surface of photoreceptor drum  91  with the laser-beam emitted from semiconductor laser  76 . Further, in light-beam deflecting apparatus  72  embodied in the present invention, since the positional deviation of polygon mirror  73 , caused by the centrifugal force due to its high-speed rotating action during its operating time, hardly occurs, and thereby, polygon mirror  73  can stably rotate without generating any vibrations, it becomes possible to perform a stable image-forming operation for a long time. In addition, since the inclination angle of mirror surface  73   a  of polygon mirror  73 , as well as other characteristics, can be maintained in a desirable state, it becomes possible to perform a high-quality image-forming operation.  
         [0060]    Although the present invention has been described referring to the abovementioned embodiments, the scope of the present invention is not limited to the abovementioned embodiments. Disclosed embodiments can be varied by a skilled person without departing from the spirit and scope of the present invention. For instance, other materials, such as resin materials, etc., can be employed for the polygon mirror and the flange. Further, although the contacting surface of the flange is finished as a coarse surface in the abovementioned embodiments, it is also applicable that only the contacting surface of the polygon mirror is finished as a coarse surface, or both contacting surfaces are finished as a coarse surface. Still further, it is also applicable that the surface processing is performed by employing a plurality of the methods mentioned above.  
         [0061]    According to the light-beam deflecting apparatus embodied in the present invention, it becomes possible to prevent the polygon mirror from deviating from the original position and to stably rotate the polygon mirror, even if the polygon mirror, pushed against the flange, rotates at a high rate during its operating time. Further, it is also possible to maintain the unit characteristics of the light-beam deflecting apparatus, such as the inclination angle of the mirror surface of the polygon mirror, etc., in an appropriate state.  
         [0062]    Further, according to the method of manufacturing the light-beam deflecting apparatus, embodied in the present invention, it becomes possible to manufacture the light-beam deflecting apparatus in which the positional deviation of the polygon mirror hardly occurs, even if the polygon mirror, pushed against the flange, rotates at a high rate during its operating time, and thereby, the polygon mirror can stably rotate, and the unit characteristics can be maintained in an appropriate state.  
         [0063]    Further, according to the image-forming apparatus equipped with the light-beam deflecting apparatus embodied in the present invention, it becomes possible to perform a stable image-forming operation for a long time, and to contribute to a high-quality image-forming operation.