Abstract:
A rotary apparatus includes a stator portion, a rotor portion rotatably supported by the stator portion and including a permanent magnet, a ring-shaped stator core arranged opposingly to the permanent magnet and including a plurality of electromagnetic coils wound around a plurality of locations of the stator core discretely existing along its circumferential direction, and a ring member for supporting a free end of the stator core.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a rotary apparatus usable as a driver in a rotary mechanism used in a light deflector of an image forming apparatus in a digital copying machine, a laser beam printer, or the like, and a deflection-scanning apparatus using the rotary apparatus. 
     2. Related Background Art 
     FIG. 1 is a view illustrating the overall structure of a scanning optical system with a deflection-scanning apparatus. As illustrated in FIG. 1, a laser unit  2  is mounted in an optical box  1 , a rotary polygonal mirror  3  of the deflection-scanning apparatus and lenses  4  and  5  are arranged along an optical path L emerging from the laser unit  2  in the optical box  1 , and a photosensitive member  6  of a recording medium is disposed outside of the optical box  1 . 
     Laser light emerging from the laser unit  2  is deflected by the rotary polygonal mirror  3  rotatably supported by a bearing apparatus, transmitted through the lenses  4  and  5  and projected as a light spot on the photosensitive member  6  disposed outside of the optical box  1 . A main scan is thus performed. 
     In the vicinity of the photosensitive member  6 , there are arranged a corona discharger for uniformly electrifying a surface of the photosensitive member  6 , a developing unit for visualizing an electrostatic latent image formed on the surface of the photosensitive member  6  to obtain a toner image, a transferor for transferring the toner image to a recording paper, and the like. Recording information of the laser light generated by the laser unit  2  is thus printed on the recording paper or the like. 
     For example, in a deflection-scanning apparatus as illustrated in FIG. 2 which is disclosed in Japanese Patent Application Laid-Open No. 6-123850, a rotary polygonal mirror  3  is supported rotatably about a fixed shaft  31  through a flange  27  and is rotatable at a high speed by means of a magnetic action between a permanent magnet  30  on a rotor side and a yoke  32  with an electromagnetic coil  33  on a stator side opposed to the rotor side. 
     However, since the yoke  32  is supported in a cantilever manner, vibrations occur due to the rotation of the rotor caused by a change of poles. The vibration adversely influences a life of the rotary apparatus and a deflection precision of the beam deflected by the deflection-scanning apparatus. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a rotary apparatus in which a vibration due to its rotation is difficult to occur. 
     Another object of the present invention is to provide a deflection-scanning apparatus which uses the rotary apparatus to enhance a precision of a beam deflection. 
     A rotary apparatus of the present invention for achieving the above object includes a stator portion, a rotor portion which is rotatably supported by the stator portion and includes a permanent magnet, a ring-shaped stator core which is arranged opposingly to the permanent magnet and includes a plurality of electromagnetic coils wound around a plurality of locations of the stator core discretely existing along its circumferential direction, and a ring member which supports a free end of the stator core. 
     Further, in a deflection-scanning apparatus of the present invention for achieving the above object, a deflector, such as a rotary polygonal mirror, is rotated by a rotary apparatus, which includes a stator portion, a rotor portion which is rotatably supported by the stator portion and includes a permanent magnet, a ring-shaped stator core which is arranged opposingly to the permanent magnet and includes a plurality of electromagnetic coils wound around a plurality of locations of the stator core discretely existing along its circumferential direction, and a ring member which supports a free end of the stator core. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view illustrating the structure of a prior art scanning optical system. 
     FIG. 2 is a view illustrating the structure of a prior art deflection-scanning apparatus. 
     FIG. 3 is a view illustrating the structure of a first embodiment according to the present invention. 
     FIG. 4 is a view illustrating the structure of a second embodiment according to the present invention. 
     FIG. 5 is a view illustrating the structure of a third embodiment according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described with reference to FIGS. 3 to  5 . 
     FIG. 3 illustrates the structure of a first embodiment. FIG. 3 shows a deflection-scanning apparatus with a rotary apparatus to be used in an scanning optical system. A bearing portion  12  is fixed to a housing  11  of a stator portion, and a rotary shaft  13  is rotatably mounted to the bearing portion  12 . A washer member  14  of a rotor portion is fixed to the rotary shaft  13 , and a rotary polygonal mirror  15  is mounted on the washer member  14  and fixed thereto by a hold-down spring  16 . The periphery of the washer member  14  extends downward in a cylindrical form, and an annular permanent magnet  17  is mounted to the cylindrically-extending portion of the washer member  14 . A base plate  18  provided with an electric circuit is mounted on an upper portion of the housing  11 . A ring-shaped stator core  20  is mounted on the substrate  18  through a support member  19  so that the stator core  20  faces the permanent magnet  17 . Electromagnetic coils  21  are wound around circumferentially different portions of the stator core  20 , respectively. An inner circumferential face of a free end of the stator core  20  is supported by force-fitting of a non-magnetic, non-conductive and cylindrical ring member  22  provided on the base plate  18 . 
     According to the above structure, the rotation of the permanent magnet  17  causes the polarity to switch, and a force in the rotating direction is exerted on the stator core  20 . In this occasion, occurrence of vibrations is prevented because the stator core  20  is firmly fixed by the support member  19  and the ring member  22 . 
     A spacing in a radial direction between the permanent magnet  17  and the stator core  20  is ordinarily about 1 mm, so that the ring member  22  with a thickness of about 0.5 mm can be force-fitted into the spacing. Material of the ring member  22  is preferably a general resin. However, material with carbon or the like mixed therein is not preferable since such material causes eddy currents and increases a value of steady current. Therefore, resin material with dielectric material such as glass added thereto to improve its rigidity is preferable. 
     In a second embodiment illustrated in FIG. 4, a ring member  22  is bonded to a stator core  20  with an adhesive  23  and further bonded to a base plate  18  with an adhesive  24 . The stator core  20  is hence firmly bonded to the ring member  22  and the base plate  18 , so the vibration can be suppressed. 
     In the above embodiments, a so-called inner rotor type in which the rotor is arranged inside of a magnetic circuit is described, but the present invention can also be applied to an outer rotor type in which the rotor is arranged outside of the magnetic circuit. A third embodiment illustrated in FIG. 5 is directed to an outer rotor type wherein a ring member  22  is force-fitted into the periphery of a free end of a stator core  20  such that the above-discussed same technical advantage can be obtained. In FIG. 5, the same reference numerals as those in FIG. 3 designate the same members. An inner peripheral surface of the stator core  20  is directly fixed to a bearing portion  12 . 
     Although the ring member in the above embodiments is formed of non-magnetic and non-conductive material, materials other than such material can also be used. Metal can also be used, for example. Where the metal ring member is used, eddy current occurs and a value of steady current increases. Thus, a load is given to the motor. However, the metal is stronger than the resin material, so that the occurrence of vibration can be advantageously prevented. 
     Thus, the stator core  20  is firmly fixed by the ring member  22  along its circumference, so that the rigidity of the stator core  20  can be increased and the vibration due to the electromagnetic force acting when the magnetic pole of the rotor passes the front of the electromagnetic coil  21  as the rotor rotates can be suppressed. Hence, noises due to the vibration, such as noise whose frequency is a multiple, by the number of poles of the permanent magnet  17 , of a fundamental frequency determined by the rotation number of the motor apparatus, can be suppressed. 
     Further, since the stator core  20  is entirely fixed firmly, it is difficult to transfer the vibration due to imbalance of the rotor to the stator core  20 . As a result, the vibration with the fundamental frequency and the noise due to this vibration can be suppressed. 
     Furthermore, when that deflection-scanning apparatus is used in a scanning optical apparatus, such as the laser beam printer as illustrated in FIG. 1, the vibration with the fundamental frequency can be suppressed and a relative positional deviation between the scanning optical apparatus and the photosensitive member can be prevented. Thus, a so-called pitch variation on the image formed by the scanning can be prevented, and a preferable image can be formed. 
     As described in the foregoing, the stator core is held by the ring member in the rotary apparatus of the present invention, so that the occurrence of vibration due to the rotation can be prevented. 
     Further, in the deflection-scanning apparatus of the present invention, a beam can be deflected with a high precision by using that rotary apparatus.