Abstract:
The optical scanning apparatus includes a polygonal rotatable mirror which deflects a light beam emitted from a light source, a drive motor which rotates said polygonal rotatable mirror, and an optical box which holds said drive motor, wherein an fitting hole in which a bearing of said drive motor engages is provided in said optical box, and a wall surface of this fitting hole has notch portions partially arranged. Thereby, the heat release property of the bearing of the polygonal rotatable mirror drive motor becomes good.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an optical scanning apparatus which is used for image forming apparatuses such as a laser printer and a laser facsimile.  
         [0003]     2. Description of Related Art  
         [0004]     An optical scanning apparatus (scanner unit) used for an image forming apparatus such as a laser beam printer deflects and emits a light beam, which corresponds to image information and is emitted from a semiconductor laser, with a polygonal rotatable mirror which performs a high-speed rotation. An electrostatic latent image according to the image information is formed on a photosensitive member by scanning a photosensitive member by the light beam emitted from the optical scanning apparatus. Subsequently, the electrostatic latent image on the photosensitive member is visualized in a toner image by a developing apparatus, and this is transferred to a recording medium such as recording paper. The recording medium is sent to a fixing apparatus after that, and printing is completed by performing the heat fixing of the toner on the recording medium.  
         [0005]     In recent years, acceleration of the image forming apparatus progresses, and in order to correspond to this acceleration, also in an optical scanning apparatus, the rotating speed of a polygonal rotatable mirror arrives at several tens of thousands of rpm increasingly.  
         [0006]     By the way, a mounting structure to the scanner unit of a polygonal rotatable mirror drive motor which is provided in a scanner unit, is common as the structure disclosed in Japanese Patent Application Laid-Open No. 2003-295099. The structure is shown in  FIG. 9 .  
         [0007]     As shown in  FIG. 9 , a polygonal rotatable mirror  22  is put on a flange  23  installed on a rotary shaft  20 , and is fixed by a leaf spring  21 . The rotary shaft  20  is inserted rotatably into bearing sleeve  31 , and an end of the rotary shaft  20  contacts with a thrust plate  32  to constitute a rotor  24 . The rotor  24  is arranged so as to face a stator coil  26 . The motor in this embodiment has the dynamic pressure liquid bearing structure that the dynamic pressure generating groove  25  is formed in the rotary shaft  20  and oil is contained in the sleeve  31 . When a current flows into the stator coil  26 , the rotor  24  rotates, and thereby, the polygonal rotatable mirror  22  also rotates.  
         [0008]     A motor drive circuit is mounted on a printed board  27  which is made of metal. This printed board  27  is fixed to a printed board mounting surface  30  provided on the outer periphery of the bearing sleeve  31  by a joint method such as caulking. Hence, the printed board  27  and bearing sleeve  31  can be dealt as one piece. In addition, the printed board  27  is fixed to a mounting surface  28  of an optical box  29 , which contains a lens, not shown, the above-mentioned drive motor, and the like, with fixing means such as screws. At this time, the bearing sleeve  31  is engaged in a hole, provided in the optical box  29 , with almost no gap.  
         [0009]     This structure has a merit that the drive motor for the rotation of the polygonal rotatable mirror  22  is simply mounted in the optical box  29  of a scanner unit, and is effective for the cost reduction of the scanner unit.  
         [0010]     Nevertheless, when an optical scanning apparatus with such structure is mounted in a high-speed printer with a large number of output sheets per unit time, the following subjects should be taken into consideration. In order to make an optical scanning apparatus correspond to high-speed printing, there are a method of increasing the number of faces of a polygonal rotatable mirror, a method of increasing a number of light beams, a method of increasing the rotational speed of a polygonal rotatable mirror, and the like. Among these, when setting the rotational speed of a polygonal rotatable mirror highly, there arises a problem that the temperature of a bearing of the polygonal rotatable mirror drive motor rises and the durability of the motor falls. In particular, when the rotational speed of a polygonal rotatable mirror is high, the loss in a bearing also becomes large, and a calorific quantity is also large, and hence, this problem becomes still more remarkable.  
         [0011]     What is conceivable so as to solve the above-mentioned problems is means of mounting a metal heat release member in a bearing as described in, for example, Japanese Patent Application Laid-Open H5-303050 and Japanese Patent Application Laid-Open H6-59208. Nevertheless, this causes another problem that a part count increases and the component cost of an optical scanning apparatus increases.  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention is accomplished in view of the above-described subjects.  
         [0013]     An object of the present invention is to provide an optical scanning apparatus excellent in the heat release property of a bearing of a polygonal rotatable mirror drive motor.  
         [0014]     Another object of the present invention is to provide an optical scanning apparatus excellent in the heat release property of a bearing of a polygonal rotatable mirror drive motor with suppressing cost.  
         [0015]     A further object of the present invention is to provide an optical scanning apparatus comprising: a polygonal rotatable mirror which deflects a light beam emitted from a light source; a drive motor which rotates said polygonal rotatable mirror; and an optical box which holds said drive motor, wherein an fitting hole in which a bearing of said drive motor fits is provided in said optical box, and an inner surface of the fitting hole has a plurality of notch portions.  
         [0016]     A still further object of the present invention will become clear by reading the following detailed explanation with referring to accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a perspective view showing an optical scanning apparatus of a first embodiment;  
         [0018]      FIG. 2  is a perspective view showing a shape of a motor mounting part in the optical scanning apparatus of the first embodiment;  
         [0019]      FIG. 3  is a sectional view showing a mounting state of a motor in the optical scanning apparatus of the first embodiment;  
         [0020]      FIG. 4  is an enlarged view of  FIG. 3 , and is a conceptual drawing showing an aspect of heat release of a bearing;  
         [0021]      FIG. 5  is an explanatory diagram about an effect of a cooling fan;  
         [0022]      FIG. 6  is a perspective view showing a shape of a motor mounting part in an optical scanning apparatus of a second embodiment;  
         [0023]      FIG. 7  is a conceptual drawing explaining an action of a rib;  
         [0024]      FIG. 8  is a plan explaining an optimal shape of the rib; and  
         [0025]      FIG. 9  is a sectional view for explaining relation between a motor bearing and an optical box of a conventional optical scanning apparatus. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     Embodiment 1  
       [0026]     An optical scanning apparatus of a first embodiment according to the present invention will be described using FIGS.  1  to  4 .  
         [0027]      FIG. 1  is a perspective view showing the optical scanning apparatus of a first embodiment according to the present invention. On an optical path in front of a semiconductor laser  1 , a collimator lens  2 , a cylindrical lens  3 , a aperture  8 , and a polygonal rotatable mirror  4  are arranged one by one, and an imaging lens  5  is arranged on an optical path in a reflecting direction of the polygonal rotatable mirror  4 . Furthermore, an optical system  6  for horizontal synchronization detection and a sensor  7  for horizontal synchronization detection are provided in a predetermined portion of the reflecting direction of the polygonal rotatable mirror  4 . The polygonal rotatable mirror  4  is installed in a motor  4 M rotating this. These are held with an optical box  10  made of a resin, and are blocked up by a cover member  20  made of a resin or a metal. An fitting hole  11  for installing the motor  4 M is provided in a predetermined position of the optical box  10 . A shape of the vicinity of this fitting hole  11  will be described in detail using  FIG. 2  later.  
         [0028]     A light beam emitted from the semiconductor laser  1  is made to be approximately parallel light by the collimator lens  2 , and is shaped by the aperture  8  and is condensed linearly on the polygonal rotatable mirror  4  by the cylindrical lens  3 . The light beam which condensed to the polygonal rotatable mirror  4  is deflected by the polygonal rotatable mirror  4  in a predetermined direction vertical to a rotary shaft, and is imaged on a rotating drum-like photosensitive member through the imaging lens  5 . The light beam imaged on the photosensitive member forms an electrostatic latent image in connection with main scanning by the rotation of the polygonal rotatable mirror, and vertical scanning by the rotation of the rotating drum. In addition, after a part of the light beam deflected by the polygonal rotatable mirror  4  passes the optical system  6  for horizontal synchronization detection, it is introduced into the horizontal synchronizing signal detector  7 . The semiconductor laser  1  starts write modulation in the timing according to an output signal from the horizontal synchronizing signal detector  7 .  
         [0029]      FIG. 2  is an enlarged view showing a shape of a motor mounting portion of the optical box  10 . The fitting hole  11  having a shape into which a bearing of the motor  4 M fits is provided in a bottom face of the optical box  10 . The fitting hole  11  is constituted of fitting portions  11   a  and notch portions  11   b.  A diameter of the portion of the fitting portions  11   a  has a shape corresponding to an outer diameter of the bearing  4 M 2 . The notch portions  11   b  having a curvature with a diameter larger than the diameter of the portion of the fitting portions  11   a  is provided in an inner circumferential face of a cylindrical wall face of the fitting hole  11 . In addition, a seat surface  12  is provided near the fitting hole  11 .  
         [0030]      FIG. 3  is a sectional view showing a state that the motor is mounted on the optical box.  FIG. 4  is an enlarged view of  FIG. 3 . The motor  4 M is constituted of a motor board(printed board)  4 M 1  which is made of iron and is caulked to a metal bearing  4 M 2 , and a magnetic circuit composed of a stator implemented on the motor board  4 M 1 , a rotor facing this, and the like. A surface of the motor board  4 M 1  is coated in insulation, and a motor driver  4 M 7  and a circuit pattern are provided on this insulating coat. The stator has a stator core  4 M 3  provided on the motor board  4 M 1  through a stator supporting member  4 M 8  made of resin, and a stator coil  4 M 4  which is wrapped around this. In addition, a rotor  4 M 5  is fixed to a flange portion  4 M 6  mounted on the rotary shaft, and a magnet  4 M 9  is mounted on an inner circumferential surface of the rotor  4 M 5 . The polygonal rotatable mirror  4  is pressed to the flange portion  4 M 6  by a pressure bar spring, or the like. Hence, the polygonal rotatable mirror  4  is linked with the rotor  4 M 5  integrally through the above-mentioned flange portion. When the rotor  4 M 5  rotates by the above-mentioned stator being excited, the polygonal rotatable mirror also rotates. The rotation control of the motor  4 M is performed by the motor driver  4 M 7 . In addition, the cylindrical bearing  4 M 2  is projected from a backside of the motor board  4 M 1 . Furthermore, the bearing  4 M 2  is commonly made of a metal such as brass.  
         [0031]     In the mounting of the motor  4 M to the optical box  10 , positioning is performed using the fitting hole  11  and seat surface  12 . The positioning of the motor  4 M in a horizontal direction (scanning direction) is performed by the bearing  4 M 2  being engaged with the fitting hole  11 , and the bearing  4 M 2  being supported by the fitting portions  11   a.  In addition, the seat surface  12  is higher than the bottom face of the optical box  10 , and the positioning of the motor  4 M in a vertical direction is performed by the motor board  4 M 1  being placed on the seat surface  12 . Then, as shown in  FIG. 1 , the motor  4 M is firmly fixed to the optical box  10  with fixing screws  15 . Hence, the motor  4 M is fixed to the optical box  10  by the motor board  4 M 1  being fixed to the optical box  10 .  
         [0032]     As mentioned above, since the optical scanning apparatus of this embodiment has the structure that the fitting hole which is provided in the bottom face of the optical box, and to which the bearing of the motor is engaged is cut partially, it has a feature of excelling in the heat release property of heat occurring in the bearing.  
         [0033]      FIG. 4  is an enlarged view of the vicinity of the bearing of the motor in the optical scanning apparatus of this embodiment. Reference character G denotes a gap (air-gap) between the bottom face of the optical box  10 , and the motor board  4 M 1 . As mentioned above, in the fitting hole  11 , the notch portions  11   b  are arranged partially. Therefore, although the bearing  4 M 2  is supported by the fitting portions  11   a,  a region where the bearing  4 M 2  contacts with air outside the optical box can be enlarged in comparison with a conventional optical scanning apparatus.  
         [0034]     When the rotation of the polygonal rotatable mirror and rotor is continued at the time of a continuous print operation and the like, heat occurs from the bearing  4 M 2  and motor driver  4 M 7 . The bearing  4 M 2  of this embodiment is an oil dynamic pressure bearing where lubricating oil is poured into an interior space, and a calorific quantity becomes large when especially rotating speed is high. In addition, when rotating speed, is high, a current which flows into the stator coil  4 M 4  also becomes large, and hence, the calorific quantity from the vicinity of the bearing becomes large.  
         [0035]     Nevertheless, since the optical scanning apparatus of this embodiment has the above-mentioned structure, as shown by an arrow in the  FIG. 4 , it is possible to release heat occurring from not only a bottom end section of the bearing but also an outer peripheral portion of a cylindrical section of the bearing in the notch portion  11   b,  to the external of the optical box. As a result, when the polygonal rotatable mirror is continuously rotated at high speed at the time of continuous print operation and the like, it is possible to release the heat occurring from the bearing  4 M 2 , stator coil  4 M 4 , and the like efficiently, and to suppress the temperature rise of the bearing  4 M 2 . The lower the temperature of the bearing  4 M 2  is at the time of motor rotating, the longer the lifetime of the motor can be extended. Hence, it is possible to attain the long lifetime of an optical scanning apparatus by using the structure of this embodiment.  
         [0036]     In addition,  FIG. 5  is a schematic diagram showing an aspect of cooling of an optical scanning apparatus in an image forming apparatus using the optical scanning apparatus of this embodiment. As shown in the diagram, it is common to provide a cooling fan  50  in a main body of an image forming apparatus. In addition, in this embodiment, the optical scanning apparatus is fixed on the optical bench  30  which is made of sheet metal and becomes a part of a body frame of the image forming apparatus. Hence, as shown by a wavy line arrow in the diagram, airstreams are formed in a bottom of the optical box  10  and a top of the cover member  20 . As mentioned above, since the notch portions  11   b  are provided in the fitting hole where the bearing  4 M 2  of the motor is engaged, this is such structure that an area that the bearing  4 M 2  contacts the air outside the optical box becomes large. Hence, when the optical scanning apparatus of the present invention is used in an image forming apparatus with such structure, it is possible to attain increasingly the long lifetime of the bearing since it is possible to enhance a cooling effect of the bearing by the cooling fan.  
         [0037]     In addition, since it is common that the optical box  10  is produced by injection molding which uses a mold, cost increase by providing the notch portions  11   b  in the fitting hole  11  as mentioned above hardly occurs. Hence, it is possible to provide a low-price optical scanning apparatus in comparison with the case that a metal heat release member and the like are mounted as a separate part.  
         [0038]     As explained above, since the notch portions are arranged partially in the fitting hole of the optical box in the optical scanning apparatus of this embodiment, it is possible to provide the optical scanning apparatus in a low price which has long lifetime and is excellent in the heat release property of the motor bearing to correspond to the high-speed rotation of the polygonal rotatable mirror. Furthermore, it is possible to provide an image forming apparatus which corresponds to high-speed printing and has long lifetime in a low price, by applying the optical scanning apparatus of this embodiment to the image forming apparatus.  
         [0039]     In addition, in the description of this embodiment, an aspect that three notch portions of the fitting hole are provided in equal intervals of 120 degrees is illustrated and explained. Nevertheless, even if this has the structure different from this embodiment, for example, four places since it is not necessary to limit this to three places as the gist of the present invention, it is needless to say that the same effect is obtained. Nevertheless, it is preferable to provide three or more notch portions  11   b  (in other words, three or more fitting portions  11   a ) so as to secure the horizontal positioning accuracy of the motor.  
       Embodiment 2  
       [0040]      FIG. 6  is a perspective view showing the vicinity of a motor mounting part of an optical box in an optical scanning apparatus of a second embodiment according to the present invention. In addition, since it is the same as those explained in detail in the first embodiment about fundamental structure, its operation, and the like of the entire optical scanning apparatus, detailed explanation is omitted here.  
         [0041]     The fitting hole  11  composed of the fitting portions  11   a  and notch portions  11   b,  and the seat surface  12  on which the motor board  4 M 1  sits is provided in the bottom face of the optical box  10  similarly to the first embodiment. Furthermore, an annular rib  13  is provided in the periphery of the fitting hole  11 . As for the height of the rib  13 , the rib  13  is set so as to become lower slightly than the seat surface  12 . Hence, there never arise drawbacks such as tilt of a motor shaft by the contact of the motor board  4 M 1  and rib  13 .  
         [0042]      FIG. 7  is a sectional view showing an aspect of the motor being mounted to the optical box in the optical scanning apparatus of this embodiment. Similarly to the first embodiment, at the time of the mounting of the motor  4 M to the optical box  10 , the motor  4 M is positioned by the fitting portions  11   a  of the fitting hole  11  and the seat surface  12 , and the motor board  4 M 1  is firmly tightened together with screws. The effect of progress in the heat release property of the bearing  4 M 2  by the notch portions  11   b  provided in the fitting hole  11  is the same as that of the description in the first embodiment.  
         [0043]      FIG. 8  is a schematic diagram from the viewpoint of the above part of the motor  4 M for explaining the position of the above-mentioned rib  13 . As shown in  FIG. 7 , the circumferential rib  13  is produced in the size a little smaller than an external form of the motor board  4 M 1 , and has a shape of filling mostly a gap between the motor board  4 M and optical box  10 .  
         [0044]     In the optical scanning apparatus of this embodiment, as mentioned above, since the rib  13  is provided in the periphery of the fitting hole  11  of the optical box  10 , it is possible to enhance the sealability of the optical scanning apparatus and it has an advantage of excelling in dust resistance.  
         [0045]     When the rotational speed of the polygonal rotatable mirror  4  is high, it may arise that dust outside the optical box invades inside the optical box through the notch portions  11   b  as shown by a wavy line arrow in  FIG. 7 , by the occurrence of the convection current accompanying the rotation of the polygonal rotatable mirror  4 . However, since the circumferential rib  13  is provided in the periphery of the fitting hole  11  in the optical scanning apparatus of this embodiment, dust outside the optical box collides with an wall of the rib  13  even if the dust invades through the notch portions  11   b.  Hence, it is possible to suppress the diffusion of the dust inside the optical box. Hence, it is possible to suppress the image deterioration by the deposit of dust on the polygonal rotatable mirror, scanning lens, and the like.  
         [0046]     As explained above, the optical scanning apparatus of this embodiment has the structure that the notch portions are arranged partially in the fitting hole of the optical box, and the annular rib is provided in the periphery of the fitting hole. Hence, it is possible to provide an optical scanning apparatus which is excellent in the heat release property of the motor bearing to correspond to the high-speed rotation of the polygonal rotatable mirror, can suppress image deterioration by the invasion of dust, and has long lifetime in a low price.  
         [0047]     The present invention is not limited to the above-described examples, but includes modifications within technological idea.  
         [0048]     This application claims priority from Japanese Patent Application No. 2004-274959 filed Sep. 22, 2004, which is hereby incorporated by reference herein.