Abstract:
An optical deflection device having: a rotor unit including a rotary polygon mirror having a plurality of mirror surfaces on the side surface portion and a holding member holding the polygon mirror; an air dynamic pressure bearing including a rotary bearing member to support the rotor unit and a fixed bearing member rotatably supporting the rotary member; and a stator unit which supports the fixed bearing member, including a winding coil oppositely arranged to the magnet, wherein prior to an assembly process, the adhesive agent layer is formed between the outer peripheral surface of the rotary bearing member and the inner peripheral surface of the holding member, the holding member and the rotary bearing member are set at the following condition, (the inner diameter of the holding member before the assembling)≧(the outer diameter of the rotary bearing member before the assembling).

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a producing method of an optical deflection device provided in an imagewise exposure device used for an image forming apparatus such as a laser beam printer, laser copier, and laser facsimile device.  
           [0002]    In the image forming apparatus such as the laser beam printer, the laser light is made incident on a rotary polygon mirror (polygon mirror) which is rotated at an equal speed, on the base of the read-out information as a writing means of the image, and the reflected light is made to scan and is projected on the photoreceptor surface and the image recording is conducted.  
           [0003]    When the polygon mirror is rotated at the low speed, although it is used by being directly fixed on a rotation axis of a drive motor, when it is rotated at the high speed, the rotary polygon mirror is fixed on the outer cylindrical member and is rotated by using an air dynamic pressure bearing (air bearing) which is rotated in the floating status without touching the fixedly arranged inner cylindrical member. Further, because the air dynamic pressure bearing is rotated in the non-contact status, there are features such as a long life and low noise.  
           [0004]    For the optical deflection device having the dynamic pressure bearing, the present applicant discloses the technology by each specification of Tokkaihei No. 7-243437, 7-259849, 8-114219 and 8-121471. The present applicant further discloses Tokkai 2001-221972 in which the inner peripheral surface of a polygon mirror and the outer peripheral surface of an outer cylindrical bearing are adhered together, and a flange member is adhered to either the outer peripheral surface of the outer cylindrical bearing or an end portion of the polygon mirror.  
           [0005]    In the optical deflection device having: a rotor unit including a rotary polygon mirror having a plurality of mirror surfaces on the side surface portion and a holding member holding the polygon mirror; an air dynamic pressure bearing including a rotary bearing member to rotatably support the rotor unit and a fixed bearing member; and a stator unit which supports the fixed bearing member, including a winding coil which is oppositely arranged to the magnet, in the conventional assembly process in which the outer peripheral surface of the rotary bearing member and the inner peripheral surface of the holding member are fixed by the shrink-fit, it is necessary to increase the fixing strength that the shrink-fit margin (that is, the difference between the outer diameter of the rotary bearing member and the inner diameter of the holding member) is increased.  
           [0006]    However, when the shrink-fit margin is increased, the inner diameter of the rotary bearing member changes. Particularly, when a portion of the outer peripheral surface of the rotary bearing member and the inner peripheral surface of the holding member are shrunk-fit and fixed, the inside stress of the rotary bearing member becomes non-uniform, and the inner peripheral surface of the rotary bearing member is inclined surface-like, and the rotation becomes unstable. Further, in the non-uniformity of the inside stress of the rotary bearing member, the inner peripheral surface of the rotary bearing member is deformed due to the change of the environmental temperature, and the unstable rotation is generated.  
         SUMMARY OF THE INVENTION  
         [0007]    The object of the present invention is to solve the above-described problem in an optical deflection device and to provide a producing method of the optical deflection device by which the stable rotating performance is obtained.  
           [0008]    The above object is attained by any one of the following structures (1)-(3).  
           [0009]    (1) An optical deflection device having: a rotor unit including a rotary polygon mirror having a plurality of mirror surfaces on the side surface portion and a holding member holding the polygon mirror; an air dynamic pressure bearing including a rotary bearing member for supporting the rotor unit and a fixed bearing member for rotatably supporting the rotary bearing member; and a stator unit which supports the fixed bearing member, including a winding coil which is oppositely arranged to the magnet, wherein the optical deflection device is characterized in that prior to an assembly process in which the adhesive agent layer is formed between the outer peripheral surface of the rotary bearing member and the inner peripheral surface of the holding member and they are fixed, the holding member and the rotary bearing member are set at the following condition, (the inner diameter of the holding member before the assembly process)≧(the outer diameter of the rotary bearing member before the assembly process).  
           [0010]    (2) An optical deflection device having: a rotor unit including a rotary polygon mirror having a plurality of mirror surfaces on the side surface portion and a holding member holding the polygon mirror; an air dynamic pressure bearing including a rotary bearing member for supporting the rotor unit and a fixed bearing member for rotatably supporting the rotary bearing member; and a stator unit which supports the fixed bearing member, including a winding coil oppositely arranged to the magnet, wherein the optical deflection device is characterized in that: prior to an assembly process, the adhesive agent layer is formed between the outer peripheral surface of the rotary bearing member and the inner peripheral surface of the holding member and they are fixed, the holding member and the rotary bearing member are set at the following conditions, (the inner diameter of the holding member before the assembly process)≧(the outer diameter of the rotary bearing member before the assembly process), and (the film thickness of the adhesive agent layer after the assembly process)&gt;{(the inner diameter of the holding member before the assembly process)−(the outer diameter of the rotary bearing member before the assembly process)}×½.  
           [0011]    (3) A producing method of the optical deflection device having: a rotor unit including a rotary polygon mirror having a plurality of mirror surfaces on the side surface portion and a holding member holding the polygon mirror; an air dynamic pressure bearing including a rotary bearing member to support the rotor unit and a fixed bearing member to rotatably support the rotary bearing member; and a stator unit which supports the fixed bearing member, including a winding coil oppositely arranged to the magnet, wherein the producing method of the optical deflection device is characterized in that: the inner diameter of the holding member and the outer diameter of the rotary bearing member are set at the following conditions, and the outer peripheral surface of the rotary bearing member on which the adhesive agent is coated, is inserted into the inner peripheral surface of the holding member which has been heated and they are fixed, (the inner diameter of the holding member before the assembly)≧(the outer diameter of the rotary bearing member before the assembly), and (the film thickness of the adhesive agent layer after the assembly)&gt;{(the inner diameter of the holding member before the assembly)−(the outer diameter of the rotary bearing member before the assembly)}×½. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a structural view of a color copier.  
         [0013]    [0013]FIG. 2 is a sectional view showing an embodiment of an imagewise exposure device.  
         [0014]    [0014]FIG. 3 is a perspective view of the imagewise exposure device.  
         [0015]    [0015]FIG. 4 is a plan view of the imagewise exposure device.  
         [0016]    FIGS.  5 ( a ) and  5 ( b ) are a plan view and sectional view of an optical deflection device.  
         [0017]    FIGS.  6 ( a ) and  6 ( b ) are exploded sectional views of the optical deflection device.  
         [0018]    [0018]FIG. 7 is an enlarged sectional view of a rotor unit.  
         [0019]    [0019]FIG. 8 is a characteristic view showing the correlation among the inner diameter of the holding member before the assembly, the difference of the outer diameter of an outer cylindrical member, and the changing amount of the inner diameter of the outer cylindrical member.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    (Image Forming Apparatus)  
         [0021]    Before the description of the embodiment of a producing method of an optical deflection device of the present invention, the structure of a color copier as an example of an image forming apparatus in which a plurality of sets of the optical deflection devices are mounted will be described below.  
         [0022]    (The Structure of the Image Forming Apparatus)  
         [0023]    [0023]FIG. 1 is a structural view of the color copier.  
         [0024]    This image forming apparatus is called a tandem type color image forming apparatus, and is composed of plural sets of image forming sections  9 Y,  9 M,  9 C, and  9 K, a belt-like intermediate transfer body  6 , a sheet feed conveying means and a fixing device  14 .  
         [0025]    The image forming section  9 Y which forms a yellow image, has a charging means  2 Y, imagewise exposure device  3 Y, developing device  4 Y, and cleaning means  8 Y, which are arranged on the periphery of the image carrier  1 Y. The image forming section  9 M forming a magenta image has the image carrier  1 M, charging means  2 M, imagewise exposure device  3 M, developing device  4 M, and cleaning means  8 M. The image forming section  9 C forming the cyan image has the image carrier  1 C, charging means  2 C imagewise exposure device  3 C, developing device  4 C, and cleaning means  8 C. The image forming section  9 K forming the black image has the image carrier  1 K, charging means  2 K, imagewise exposure device  3 K, developing device  4 K, and cleaning means  8 K.  
         [0026]    The intermediate transfer body  6  is wound around a plurality of rollers and rotatably supported. Each color of images formed by the image forming sections  9 Y,  9 M,  9 C, and  9 K is successively transferred onto the rotating intermediate transfer body  6  by the primary transfer means  7 Y,  7 M,  7 C and  7 K, and the synthesized color image is formed. A transfer sheet P accommodated in a sheet feed cassette  10  is fed by a sheet feed means  11 , and through the intermediate rollers  12 A,  12 B,  12 C,  12 D, and registration roller  13 , it is conveyed to the secondary transfer means  7 A, and a color image is transferred onto the transfer sheet P. The transfer sheet P on which the color image is transferred is fixing processed by a fixing device  14 , and nipped by a delivery sheet roller  15 , and placed on the delivery sheet tray  16  outside the image forming apparatus.  
         [0027]    On the one hand, after the color image is transferred onto the transfer sheet P by the secondary transfer means  7 A, the residual toner on the intermediate transfer body  6  from which the transfer sheet P is separated, is removed by the cleaning means  8 A.  
         [0028]    The  5 Y,  5 M,  5 C,  5 K are toner replenishing means by which the new toners are respectively replenished to the developing devices  4 Y,  4 M,  4 C and  4 K.  
         [0029]    (Imagewise Exposure Device)  
         [0030]    In the image forming apparatus such as the laser printer, as the writing means of the image, on the base of the read-out information, the laser beam is made incident on the rotary polygon mirror (polygon mirror) which is rotated at the equal speed, and the reflected light is made to scan and is projected onto the photoreceptor surface of the image carrier  1 , and the image recording is conducted.  
         [0031]    [0031]FIG. 2 is a sectional view showing an embodiment of the imagewise exposure device, and FIG. 3 is a perspective view of the imagewise exposure device  3 , and FIG. 4 is a plan view of the imagewise exposure device  3 .  
         [0032]    The imagewise exposure device  3  is composed of an optical deflection device  30  and scanning optical system  31 . Hereinafter, the image carriers  1 Y,  1 M,  1 C and  1 K in the color printer are called the image carrier  1 , and the imagewise exposure devices  3 Y,  3 M,  3 C and  3 K are called the imagewise exposure device (writing device)  3 , each optical deflection device of the imagewise exposure devices  3 Y,  3 M,  3 C and  3 K is called the optical deflection device  30 , and each scanning optical system of the imagewise exposure devices  3 Y,  3 M,  3 C and  3 K is called the scanning optical system  31 .  
         [0033]    The scanning optical system  31  is composed of an optical main body  31 A, cover body  31 B, fθ lens  32 , the second cylindrical lens  33 , cover glass  34 , semiconductor laser (light source section)  35 , collimator lens  36 , the first cylindrical lens  37 , index mirror  38  for the timing detection, and index sensor  39  for the synchronization detection.  
         [0034]    The optical deflection device  30  composed of the rotary polygon mirror (polygon mirror)  301 , and optical members  32 - 39  of the scanning optical system  31 , are arranged and fixed at a predetermined position in the optical main body  31 A.  
         [0035]    The laser beam (light flux) L emitted from the semiconductor laser  35 , becomes a parallel light by the collimator lens.  36 , and next, passes the first cylindrical lens  37  of the first image formation optical system, and is incident on the rotary polygon mirror (polygon mirror)  301  of the optical deflection device  30 . The reflected light of the rotary polygon mirror  301  passes the second image formation optical system composed of the fθ lens  32  and the second cylindrical lens  33 , and passes the cover glass  34 , and on the peripheral surface of the image carrier  1 , scans by a predetermined spot diameter in the condition that a predetermined pitches are shifted in the sub-scanning direction. In this condition, the main-scanning direction is finely adjusted already by an adjustment mechanism (not shown). The synchronization detection for each one line, is conducted in such a manner that the laser beam (light flux) L before the scanning start is made incident on the index sensor  39  through the index mirror  38 .  
         [0036]    (Optical Deflection Device)  
         [0037]    [0037]FIG. 5( a ) is a plan view of the optical deflection device  30 , and FIG. 5( b ) is a sectional view of the optical deflection device  30 . FIGS.  6 ( a ) and  6 ( b ) show exploded sectional views of the optical deflection device  30 , and FIG. 6( a ) is a sectional view of a rotor unit  300 , and FIG. 6( b ) is a sectional view of a stator unit  310 .  
         [0038]    In the optical deflection device  30  by which the rotary polygon mirror  301  is rotated as a rotation body at the high speed, an air dynamic pressure bearing is provided between the rotor unit (rotor)  300  which is a rotation body, and the stator unit (stator)  310  which is a no-rotation body, and the equal speed rotation is conducted (refer to FIGS.  6 ( a ) and  6 ( b )). Outside the column shaped radial shaft section  311 A which is erected on a support base member  311 , a cylindrical fixed bearing member (hereinafter, called also inner cylindrical member)  312  is fixedly provided, and the radial fixed section is structured by the radial shaft section  311 A and the inner cylindrical member  312 .  
         [0039]    On both-side end portions of the inner cylindrical member  312 , in almost vertical direction of the radial shaft section  311 A, the disk-shaped upper thrust fixed member (hereinafter, called upper thrust plate)  313  and the lower thrust fixed member (hereinafter, called lower thrust plate)  314  are fixedly provided, and the thrust fixed portion is structured. The inner cylindrical member  312 , upper thrust plate  313 , and lower thrust plate  314  are fixed by the screw  315  after they are mounted on the radial shaft section  311 A.  
         [0040]    On the flat surface portion of the support base member  311 , a printed board  317  on which a plurality of winding coils  316  are arranged on the same surface, is attached.  
         [0041]    The above-described support base member  311 , inner cylindrical member  312 , upper thrust plate  313 , lower thrust plate  314 , winding coil  316  and printed board  317  are integrated, and form the stator unit  310 .  
         [0042]    On the one hand, in the rotor unit  300  which is a unit to rotate the optical deflection device  30  at an equal speed, the cylindrical rotary bearing member (hereinafter, called also outer cylindrical member)  302  around the rotating axis is integrally provided. The inner diameter of the outer cylindrical member  302  is larger than the outer diameter of the inner cylindrical member  312  by an adjusted fine interval of several μms. By the inner peripheral surface of this outer cylindrical member  302  and the outer peripheral surface of the inner cylindrical member  312 , the radial dynamic pressure bearing section is structured.  
         [0043]    Further, the upper end surface of the outer cylindrical member  302  is opposite to the thrust surface of the upper thrust plate  313 , and structures the upper thrust dynamic pressure bearing section. In the same manner, the lower end surface of the outer cylindrical member  302  is opposite to the thrust surface of the lower thrust plate  314 , and structures the lower thrust dynamic pressure bearing section. The air dynamic pressure bearing is structured by the above-described radial dynamic pressure bearing section, upper thrust dynamic pressure bearing section, and the lower thrust dynamic pressure bearing section.  
         [0044]    The inner cylindrical member  312  structuring the air dynamic pressure bearing, outer cylindrical member  302 , upper thrust plate  313 , and lower thrust plate  314  are formed of ceramic such as alumina or silicon nitride, or metallic material such as stainless steel, aluminum or brass, or metallic material which is galvanizing processed or resin coated.  
         [0045]    In the optical deflection device  30 , the holding member (flange member)  303  is fixed on the outer peripheral surface of the outer cylindrical member  302  in such a manner that the inner diameter (diameter) D1 of the holding member  303  before the assembly, outer diameter (diameter) D2 of the outer cylindrical member  302  before the assembly, and the film thickness A of the adhesive agent layer satisfy D1≧D2, and A&gt;(D1−D2)×½, and the rotary polygon mirror  301  whose outside surface is a mirror surface is adjusted so that the center of the rotary polygon mirror  301  coincides with the rotation center of the rotor unit  300 , and attached onto the holding member  303 . The holding member  303  is formed of the metallic material such as the stainless steel, aluminum, or brass.  
         [0046]    On the lower end surface of the holding member  303 , a magnet  304  for the torque generation which is formed like a ring with the multi-pole pairs is fixed. (The producing method of the optical deflection device)  
         [0047]    [0047]FIG. 7 is an enlarged sectional view of the rotor unit  300 .  
         [0048]    An assembly process of the rotor unit  300  will be shown below.  
         [0049]    (1) The inner diameter D1 of the holding member  303  before the assembly and the outer diameter D2 of the outer cylindrical member  302  before the assembly are measured, and the inner diameter (diameter) D1 and the outer diameter (diameter) D2 and the film thickness A of the adhesive agent layer after the assembly are selected so that they satisfy the expressions of D1≧D2.  
         [0050]    (2) On the outer peripheral surface of the outer cylindrical member  302 , the adhesive agent is uniformly coated. As the adhesive agent, the anaerobic acrylic resin, for example, 648UV made by LOCTITE Co. is used.  
         [0051]    (3) The holding member  303  is heated at the high temperature (for example, about 180° C.), and the inner diameter D1 of the holding member  303  is increased, and inserted on the outer peripheral surface of the outer cylindrical member  302 .  
         [0052]    (4) After the assembly, the adhesive agent is hardened at soon, and the condition of A&gt;(D1−D2)×½ is achieved. Then, the temperature of the holding member  303  is lowered from the high temperature to the normal temperature, and the inner diameter D1 of the holding member  303  is reduced, and the outer peripheral surface of the outer cylindrical member  302  is tightened by the holding member  303 , and becomes the fixed condition.  
         [0053]    (5) The adhesive agent protruded up and down the adhesive section of the holding member  303  and outer cylindrical member  302  is hardened by the UV light irradiation.  
         [0054]    (6) The rotary polygon mirror  301  is fixed on the holding member  303 , and the assembly process of the rotor unit  300  is completed.  
         [0055]    (The Inner Diameter Change of the Outer Cylindrical Member  302  After the Assembly of the Rotor Unit  300 )  
         [0056]    [0056]FIG. 8 is a characteristic view showing the correlation among the inner diameter D1 of the holding member  303  before the assembly, the difference δ of the outer diameter D2 of the outer cylindrical member  302 , and the inner diameter changing amount of the outer cylindrical member  302 .  
         [0057]    In order to stably rotate the rotor unit  300 , it is necessary that the inner diameter changing amount of each portion of the outer cylindrical member  302  after the assembly is not larger than 1.0 μm, and in order to satisfy that, the difference δ between the inner diameter D1 of the holding member  303  before the assembly, and the outer diameter D2 of the outer cylindrical member  302 , is not smaller than 0 μm.  
         [0058]    When the difference δ between the inner diameter D1 of the holding member  303  and the outer diameter D2 of the outer cylindrical member  302 , is not smaller than 80 μm, the strength is insufficient at the time of high temperature, and when the external force of 10 kgf is added at 80° C., the shaft slippage is generated, and it is not practically durable.  
         [0059]    Accordingly, when the difference δ is set to 80 μm≧(D1−D2)≧0 μm, the rotor unit  300  can be stably rotated.  
         [0060]    In this connection, the present invention is not limited to the above-described embodiment. That is, within the scope without departing from the spirit of the present invention, the present invention is applied in the same manner by variously modifying also for the high speed rotation device, and optical deflection device.  
         [0061]    The producing method of the optical deflection device of the present invention has the effects which will be described below.  
         [0062]    (1) As compared to the conventional producing method by which the inner diameter of the holding member before the assembly is processed smaller than the outer diameter of the outer cylindrical member, and shrunk fit to it, or as compared to the conventional processing method in which this shrink-fit and adhesive agent are jointly used, according to the producing method of the present invention, the internal stress of the outer cylindrical member is small, the distortion of the inner diameter is very small, and the stable equal speed rotation is attained.  
         [0063]    (2) When the holding member is heated and expanded, the gap between the inner diameter of the holding member and the outer diameter of the outer cylindrical member is increased, and the operability is increased.  
         [0064]    (3) When it is in the interference-fit condition by the film thickness of the adhesive agent after the assembly, the enough strength is maintained also at the time of high temperature.  
         [0065]    (4) When it is set at (the inner diameter of the holding member before the assembly)≧(the outer diameter of the rotary bearing member before the assembly), and (the film thickness of the adhesive agent layer after the assembly)&gt;{(the inner diameter of the holding member before the assembly)−(the outer diameter of the rotary bearing member before the assembly)}×½, the enough strength is maintained also at the time of high temperature, and the gap between the inner diameter of the holding member and the outer diameter of the outer cylindrical member is increased, and the operability is increased. Further, the hardening of the adhesive agent is accelerated by the heat of the holding member, and the production efficiency is increased.  
         [0066]    (5) The inner diameter distortion of the outer cylindrical member is prevented, and the tightening strength of the outer cylindrical member and the holding member is secured.