JP2005352059A - Optical deflector, manufacturing method thereof, optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical deflector which maintains a highly accurate reflection surface even at a high temperature and at a high rotation speed, modifies the balance of a highly accurate rotating body, and of which the vibration is small with low noise, and to provide a optical scanner using the optical deflector and an image forming apparatus giving a high image quality. <P>SOLUTION: The optical deflector is characterized by that a plurality of stages of polygon mirrors are formed in a rotation axis direction, the rotating body supported with a bearing is rotationally driven by a motor, and the diameter of the center holes corresponding to the respective stages of the polygon mirrors are substantially the same. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical deflector used in an optical writing device of an electrophotographic copying machine, a printer, a facsimile machine, or a combination of these, an image forming apparatus such as the optical writing device using the optical deflector, and the copying machine. Relates to the device.

  In recent years, an electrophotographic recording apparatus using a laser writing apparatus such as a digital copying machine or a laser printer has been developed to have an optical deflector of 20000 revolutions / minute or more as the printing speed increases and the pixel density increases. Optical deflectors using dynamic pressure bearings have been put to practical use in order to satisfy the required quality of long life, high durability and low noise.

  As such an optical deflector, a high-speed rotating body that is outside a ceramic fixed shaft and constitutes a gas dynamic pressure bearing together with the fixed shaft is provided on a ceramic sleeve having a constant thickness in the radial direction and an outer periphery thereof. There is a configuration in which a metal outer cylindrical member having a larger thermal expansion coefficient than that of the ceramic sleeve fixed by shrink-fitting is used, and the outer peripheral cylindrical member is shrink-fitted to the ceramic sleeve (see, for example, Patent Document 1). ). In the high-speed rotating body, after the outer peripheral inner cylindrical member is fixed to the ceramic sleeve by shrink fitting, the inner diameter thereof is processed into a predetermined spelling shape. The inner diameter of the ceramic sleeve is predetermined so that the gap generated in the ceramic fixed shaft and the ceramic sleeve is uniform according to the shrinkage compression stress, which is relaxed by the radial centrifugal stress acting by the friction and the thermal expansion due to friction. The spelling shape is determined.

  However, as in the invention described in Patent Document 1, when a mirror-finished rotary polygon mirror is shrink-fitted, the reflecting surface is distorted due to compressive stress during shrink-fitting, resulting in deterioration of flatness and maintaining a highly accurate reflecting surface. Can not. As a result, there is a problem that a good image output cannot be obtained.

  Moreover, even when the reflecting surface of the rotary polygon mirror is processed after shrink fitting, when the temperature of the rotating body rises due to high-speed rotation, the linear expansion coefficient of the ceramic sleeve is smaller than the linear expansion coefficient of the metal outer cylindrical member, Compressive stress due to shrink fitting is removed, the reflective surface is distorted, flatness deteriorates, and a highly accurate reflective surface cannot be maintained. As a result, there is a problem that a good image output cannot be obtained.

The invention described in Patent Document 1 has further problems in addition to the problems described above. That is, since the high-speed rotating body is configured by superimposing two parts, the angle variation (surface tilt) of the reflecting surface of the polygon mirror increases, and further, the unbalance changes and the balance of the rotating body is lost, causing vibration. Tends to grow. Further, the vibration generated by the optical deflector vibrates around the optical deflector and causes noise and image degradation. The noise level tends to be particularly high at a high speed of 20000 rpm.

For the purpose of solving the above problems, the present applicant forms a cylindrical protrusion protruding in the axial direction on a metal outer peripheral member that is shrink-fitted or press-fitted into a ceramic sleeve supported by a hydrodynamic bearing, A boss-like protrusion protruding in the axial direction radially inward of the reflecting surface is formed on the polygon mirror whose thermal expansion coefficient substantially matches that of the metal outer peripheral member, and the outer peripheral surface of the boss-like protrusion is a cylindrical protrusion. A patent application was filed regarding a polygon scanner configured to be fixedly fitted to the inner peripheral surface of the portion (see, for example, Patent Document 2). According to the invention described in Patent Document 2, even if distortion occurs in the fitting portion between the sleeve having a different coefficient of thermal expansion and the metal outer peripheral member when the temperature rises, the influence of the distortion acting on the reflection surface of the polygon mirror is reduced. It can be made small enough to be ignored, and the beam deflection function can be maintained with high accuracy.

  However, the invention described in Patent Document 2 is provided with a boss-like protrusion that protrudes in the axial direction on the polygon mirror and is fixed to the cylindrical protrusion that protrudes in the axial direction of the metal outer peripheral member. Is biased toward the mirror. As a result, the unbalance of the rotating body due to the balance correction of the rotating body could not be sufficiently reduced, and the unbalanced vibration was large. Further, since the mirror surface processing reference surface provided on the mirror is fixed and the reflecting surface is mirror-finished, the angle variation of the reflecting surface with respect to the rotation center axis of the hydrodynamic bearing is large.

Further, when the rotation is performed at 30000 revolutions / minute or more, the deformation of the mirror due to the centrifugal force increases, and the flatness of the mirror reflecting surface may deteriorate.
Japanese Patent Laid-Open No. 7-190047 JP 2000-306439 A

  Therefore, the present invention has been made in view of the problems of the conventional description, and an object of the present invention is to maintain a highly accurate reflecting surface even at a high temperature and at a high speed, and to vary the angle of the reflecting surface (surface collapse). By providing a structure that can obtain a good image output and that the center of gravity of the rotating body can be arranged near the middle of the hydrodynamic bearing, it is possible to correct the balance of the rotating body with high accuracy and reduce vibration. The object is to provide a low-noise optical deflector. It is another object of the present invention to provide a high-precision, low-vibration and low-noise optical scanning device using the optical deflector of the present invention, and to provide an image forming apparatus with high image quality and low noise.

  In order to achieve the above object, an invention according to claim 1 is an optical deflector for rotating a rotating body formed by a plurality of stages of polygon mirrors in the direction of a rotation axis and supported by a bearing by a motor, wherein the polygon The diameter of the center hole corresponding to each stage of the mirror is made substantially the same.

The invention according to claim 2 is an optical deflector that rotationally drives a rotating body formed by a plurality of stages of polygon mirrors in the direction of the rotation axis and supported by a bearing by a motor,
The diameter (B) of the center hole corresponding to each step of the polygon mirror is in the range of 5 to 50% of the inscribed circle diameter (A) of the polygon mirror.

  The invention described in claim 3 is the invention described in claim 1 or 2, characterized in that the polygon mirror is fixed to the rotating body by providing a gap in the inner periphery of the center hole.

  According to a fourth aspect of the present invention, in the invention of the third aspect, the center hole of the polygon mirror is formed in a cylindrical shape, and the polygon mirror is a rotating body formed by a fixed portion formed at one end of the center hole of the rotating body. It is characterized by being fixed to.

  The invention according to claim 5 is the invention according to claim 1 or 2, wherein the polygon mirror has a center hole fixed to the bearing member of the rotating body by shrink fitting.

  According to a sixth aspect of the present invention, in the fifth aspect of the present invention, the polygon mirror includes a polygon mirror inscribed circle diameter (A), a diameter of a central hole corresponding to each polygon mirror (B), and the polygon mirror. The linear expansion coefficient (C) and the linear expansion coefficient (D) of the bearing member of the rotating body satisfy the condition of “| C−D | × B / A ≦ 5 × 10 −6”.

  A seventh aspect of the invention is characterized in that, in the invention of the first or second aspect, both ends of the rotating shaft member of the rotating body are rotatably supported by two fixed bearing members.

  The invention described in claim 8 is characterized in that, in the invention described in claim 2, the center hole diameters B corresponding to the respective stages of the polygon mirror are substantially equal in size.

  The invention according to claim 9 is the invention according to any one of claims 1 to 8, wherein the reflecting surface formed on the polygon mirror is integrated by fixing the polygon mirror to the rotating body, and then mirror-finished. It is formed.

  According to a tenth aspect of the present invention, there is provided an optical scanning apparatus for scanning a scanning line by guiding a beam from a semiconductor laser to a surface to be scanned through an optical system including an optical deflector to form a light spot. The optical deflector according to any one of claims 1 to 8 is used as the deflector.

  In the invention described in claim 11, there are a plurality of beams from the semiconductor laser, and a plurality of scanning lines are adjacently scanned by being guided to the scanning surface through an optical system including an optical deflector to form a plurality of light spots. In the optical scanning device, the optical deflector according to any one of claims 1 to 8 is used as the optical deflector.

  According to a twelfth aspect of the present invention, there is provided an image forming apparatus in which a latent image is formed on a photosensitive surface of a photosensitive medium by optical scanning with an optical scanning device, and the latent image is visualized to obtain an image. An optical scanning device according to claim 10 or 11 is used as an optical scanning device that performs optical scanning of a surface.

  According to the first aspect of the present invention, there is provided an optical deflector in which a plurality of mirror reflecting surfaces are formed in the axial direction, and optical scanning with a plurality of light beams from a plurality of light sources is possible. It is possible to provide an optical deflector for high-speed rotation that suppresses a deformation difference due to centrifugal force.

  According to the second aspect of the present invention, there is provided an optical deflector in which a plurality of stages of mirror reflecting surfaces are formed in the axial direction, and optical scanning with a plurality of light beams by a plurality of light sources is possible. It is possible to provide an optical deflector for high-speed rotation in which deformation due to centrifugal force is suppressed to a low level. Further, it is possible to provide an optical deflector for high-speed rotation that can commonly use an optical system for a low-speed machine. When the center hole diameter (B) of the polygon mirror is smaller than 5% of the inscribed circle diameter (A) of the polygon mirror, the bearing load resistance due to the bearing member arranged on the inner peripheral side of the center hole is reduced, When it is larger than 50%, the deformation of the mirror reflecting surface due to the centrifugal force becomes large.

  According to the invention described in claim 3, in addition to the effects of the invention described in claim 1 or 2, an optical deflector can be provided in which deformation of the mirror reflecting surface at each stage is suppressed to be small.

  According to the invention described in claim 4, in addition to the effect of the invention described in claim 3, an optical deflector characterized by suppressing a change in balance due to a deviation of the mirror reflecting surface and suppressing unbalance vibration. Can be provided.

  According to the fifth aspect of the present invention, in addition to the effect of the first or second aspect of the invention, an optical deflector in which deformation due to the centrifugal force of the mirror reflecting surface is suppressed to be small by using shrink fitting stress. Can provide.

  According to the sixth aspect of the invention, in addition to the effect of the fourth aspect of the invention, deformation due to the temperature of the mirror reflecting surface caused by shrink fitting of a material having a different linear expansion coefficient between the bearing member and the mirror is suppressed to be small. An optical deflector can be provided.

  According to the invention described in claim 7, in addition to the effect of the invention described in claim 1 or 2, an optical deflector suitable for high-speed rotation can be provided by arranging the center of gravity of the rotating body between the bearings. .

  According to the invention described in claim 8, in addition to the effect of the invention described in claim 2, it is possible to provide an optical deflector in which the difference in deformation due to the centrifugal force of the mirror reflecting surface at each stage is suppressed to a small value.

  According to the ninth aspect of the present invention, it is possible to provide a method of manufacturing an optical deflector capable of forming a highly accurate reflective surface with a constant angle with respect to the central axis (rotation central axis) of the hydrodynamic bearing surface of the sleeve. .

  According to the tenth aspect of the present invention, it is possible to provide an optical scanning device in which the reflecting surface of the optical deflector is maintained with high accuracy and the scanning beam shape is constant and stable.

  According to the eleventh aspect of the present invention, it is possible to provide a multi-beam optical scanning device in which the reflecting surface of the optical deflector is maintained with high accuracy and the scanning beam shape is constant and stable.

  According to the invention of the twelfth aspect, it is possible to provide an image forming apparatus having a high and high image quality, with the scanning beam of the optical scanning device being constant and stable.

  Embodiments of an optical deflector, an optical scanning device, and an image forming apparatus according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a plan view showing an example of a polygon mirror used in an optical deflector. In FIG. 1, the inscribed circle diameter of a polygon mirror having a regular hexagonal plane shape is A, and the center hole diameter is B. The six planes that form the outer peripheral surface of the polygon mirror are light reflecting surfaces that deflect the light flux from the plateau as it rotates. FIG. 2 shows a polygon mirror as shown in FIG. 1, which is made of a single material (for example, high-purity aluminum alloy), has an inscribed circle diameter A of 36 mm, and a center hole diameter B that is gradually changed from 3 mm to 30 mm. It is the figure showing the result of having calculated the deformation amount which arises by the influence of the centrifugal force by rotation of each polygon mirror. In FIG. 2, the horizontal axis represents the rotational speed of the polygon mirror, and the vertical axis represents the mirror flatness of the polygon mirror. As shown in FIG. 2, the largest change in mirror flatness (that is, the most deformed one) is the case where the center hole diameter B is 30 mm and the change in mirror flatness is the smallest (ie, The least deformed one) had a center hole diameter of 3 mm.

  The above deformation refers to a convex surface in which the center of each mirror surface of the polygon mirror, more specifically, the center portion in the rotation direction of each mirror surface forming a flat surface bulges outward from both ends in the rotation direction due to the centrifugal force generated by the rotation. It means to become. If such deformation is large, the accuracy in reflecting light will be reduced. Therefore, the smaller the amount of deformation, the higher the accuracy of the polygon mirror, and the ideal shape is a polygon mirror having a deformation amount of zero.

  As apparent from FIG. 2, the size of the center hole diameter B affects the deformation amount of the mirror flatness of the polygon mirror. That is, if the diameter of the center hole is increased, the change in flatness of the mirror is increased at high speed rotation, and if the diameter of the center hole is decreased, the change in flatness of the mirror is reduced at high speed rotation. It is presumed that the rigidity of the polygon mirror is lowered when the diameter of the center hole is increased. Conventionally, polygon mirrors formed in a plurality of stages in the direction of the rotation axis have different center hole diameters corresponding to the polygon mirrors at each stage. For this reason, the polygon mirrors at each stage have different flatness, and there is a problem that the optical characteristics of the polygon mirrors at each stage are different.

  Therefore, by making the central hole diameters of the polygon mirrors in a plurality of stages the same, it is possible to reduce the difference in mirror flatness of each stage, thereby reducing the difference in optical characteristics between the mirrors in each stage. it can.

  By the way, the flatness of the mirror used for the optical deflector usually needs to be 0.32 μm or less, and the flatness of 0.16 μm is required for a highly accurate one. On the other hand, when the optical deflector is rotated at a high speed, heat generation and power consumption increase, so that 50,000 to 60000 rpm is a practical limit. Here, as shown in FIG. 2, when the diameter of the center hole of the mirror is 50% of the inscribed circle diameter of the mirror (that is, 18 mm), the amount of deformation due to the centrifugal force of 50000 rpm can be approximately 0.32 μm or less. . This means that components such as lenses used for 20000 rpm to 30000 rpm can be used as they are, and environmental burden can be reduced by sharing components.

  Further, if the center hole diameter B of the mirror is made 40% or less of the inscribed circle diameter A of the mirror, the deformation due to the centrifugal force at 60000 rpm can be made approximately 0.32 μm or less. As a result, even in a member used for higher-speed rotation, it is possible to reduce the environmental load by sharing the parts.

  Furthermore, if the center hole diameter B of the mirror is 30% or less (that is, 12 mm) of the inscribed circle diameter A of the mirror, the deformation due to the centrifugal force at 60000 rpm can be made approximately 0.16 μm or less. As a result, it is possible to reduce the environmental load by sharing the components up to the components used at higher speed and with higher accuracy. As described above, the smaller the ratio of the center hole diameter B to the inscribed circle diameter A, the smaller the deformation of the reflecting surface of the polygon mirror due to centrifugal force. Since the bearing load resistance of the bearing member arranged on the inner peripheral side is reduced, the lower limit of the ratio is preferably 5%.

  The plan view of FIG. 3 shows a state where the sleeve 302 is shrink-fitted into the center hole of the polygon mirror 301. In FIG. 3, the diameter of the center hole of the polygon mirror 301 is 10 to several tens μm smaller than the outer diameter of the sleeve 302. The polygon mirror 301 is heated and expanded to enlarge the diameter of the center hole and shrink the sleeve 302.

  FIG. 4 is a diagram showing the deformation amount of mirror flatness generated by centrifugal force due to rotation in a polygon mirror in which sleeves of different materials are shrink-fitted. In any material, the inscribed circle diameter of each mirror surface is 36 mm, and the diameter of the shrink fit is 18 mm. In FIG. 4, the horizontal axis and the vertical axis are the same as those in FIG. In FIG. 4, it can be seen that the amount of deformation of the mirror flatness is smaller when a sleeve of a different material is inserted than when a gap is provided in the center hole of the polygon mirror (when no sleeve is inserted). Further, the amount of deformation of the mirror flatness is “aluminum alloy> stainless steel> alumina ceramics” depending on the material used for the sleeve.

  As described above, the amount of deformation generated varies depending on the material used for the sleeve, but the main factor is that the Young's modulus of each material used for the sleeve is different. The Young's modulus of each material shown in FIG. 4 has a relationship of “aluminum alloy <stainless steel <alumina ceramics”. That is, the amount of deformation of the mirror flatness due to centrifugal force is reduced by shrink fitting using a material having a high Young's modulus.

  However, a material with a large Young's modulus has another problem because it has a different coefficient of linear expansion from that of high-purity aluminum used for the polygon mirror. Since the polygon mirror is rotated at a high speed by the motor, the polygon mirror itself can be heated by the influence of heat generated by the motor. When a polygon mirror using a material having a high Young's modulus as a sleeve becomes high temperature due to heating of the motor, there is a concern that the flatness of the mirror may deteriorate due to a difference in linear expansion coefficient between the polygon mirror and the sleeve.

  Therefore, the influence on the change in the flatness of the polygon mirror when a sleeve made of a different material is used as the sleeve to be shrink fitted onto the polygon mirror will be described with reference to FIG. In FIG. 5A, the material of the polygon mirror is made of high-purity aluminum, and the sleeve is made of nonmagnetic stainless steel SUS304, ferromagnetic stainless steel SUS430, nonmagnetic stainless steel SUS304, and alumina ceramics, and the temperature of the polygon mirror is set. It is the result of having calculated mirror flatness when it heats from 20 degreeC to 60 degree | times.

  FIG. 5B is a graph showing the calculation result in FIG. When the inscribed circle diameter of the polygon mirror is A, the center hole diameter corresponding to the polygon mirror is B, the linear expansion coefficient of the polygon mirror is C, and the linear expansion coefficient of the member used for the sleeve is D, the flatness of the mirror and the graph The horizontal axis | C−D | × B / A is approximately linear.

  Here, the flatness of the mirror used for the optical deflector usually needs to be 0.32 μm or less, and the highly accurate one needs to have a flatness of 0.16 μm or less. According to the graph of FIG. 5B, the flatness of approximately 0.32 μm or less can be maintained if the horizontal axis | CD | × B / A satisfies the following conditions. That is, by satisfying | C−D | × B / A ≦ 5 × 10 −6, the mirror flatness can be made 0.16 μm or less.

  Further, if the condition of | C−D | × B / A ≦ 3 × 10 −6 is satisfied, the flatness of the mirror can be reduced to about 0.16 μm or less.

  FIG. 6 shows physical property values of each material used in the above calculation.

  Next, an embodiment of the optical deflector according to the present invention will be described with reference to FIGS. The hydrodynamic bearing used in the embodiment can use a fluid other than air as the lubricating fluid.

  In FIG. 7, an attachment reference surface 21 a to the optical housing 1 is formed on the lower surface of the cover case 21. The cover case 21 is fixed to the housing 1 on the reference surface 21a. A cylindrical bearing mounting portion 1b is formed on the upper surface of the central portion of the housing 1, and a fixed shaft 2 constituting a hydrodynamic bearing is fitted and fixed to the inner peripheral side of the bearing mounting portion 1b. On the cylindrical surface of the fixed shaft 2, dynamic pressure generating grooves 2a are formed at two axial positions. When the rotating body 3 starts to rotate, the air pressure in the bearing clearance formed between the sleeve 16 and the fixed shaft 2 is increased by the dynamic pressure generating groove 2a, and the rotating body 3 in the radial direction (radial direction) without contact. Can be supported.

  A fixed portion 5 of an attraction type magnetic bearing is formed inside the fixed shaft 2, and the fixed portion 5 includes a ring-shaped permanent magnet 8 magnetized in two poles in the rotation axis direction, and the ring-shaped permanent magnet. The first fixed yoke plate 9 made of a ferromagnetic material having a center circle smaller than the inner diameter of the magnet 8 and the ferromagnetic material having a center circle smaller than the inner diameter of the ring-shaped permanent magnet 8 similarly. And a second fixed yoke plate 10. The fixed portion 5 is fixed by being sandwiched in the axial direction by press-fitting and fixing the cap 6 and the stopper 7 to the inner cylinder portion of the fixed shaft 2. A fine hole having a diameter of about 0.2 to 0.5 is formed in the center of the cap 6 to attenuate the vertical vibration by using the viscous resistance when air passes. Both the cap 6 and the stopper 7 are made of a non-magnetic material such as a stainless steel plate.

  The first fixed yoke plate 9 and the second fixed yoke plate 10 sandwich the ring-shaped permanent magnet 8 in the axial direction, and the center circle of the first fixed yoke plate 9 and the center circle of the second fixed yoke plate 10 are Arranged and fixed so as to be coaxial with the rotation center axis. As a material of the ring-shaped permanent magnet 8, a rare earth permanent magnet is mainly used. Steel plates are used for the fixed yoke plates 9 and 10.

  On the upper surface of the housing 1, a printed circuit board 11 having a hole formed in the center is disposed. A stator 12 is fitted and fixed to the outer diameter of the bearing mounting portion 1 b of the housing 1. Since a conductive material such as an aluminum alloy is used for the housing 1, an eddy current flows through the housing 1 due to the influence of an alternating magnetic field due to the rotation of the rotor magnet 14. If this eddy current increases, the loss of the motor increases. Therefore, the printed circuit board 11 is preferably made of an iron substrate and magnetically shielded so that the loss does not increase.

  The printed circuit board 11 is mounted with a hall element 13 that is a position detection element for switching energization to the winding coil. The motor unit includes a rotor magnet 14 attached to the rotating body 3, a stator 12 around which a winding coil 12a is wound, a printed circuit board 11 to which the winding coil 12a is connected, a hall element 13 mounted on the printed circuit board 11, and the like (not shown). It is configured using members. The stator 12 is formed by stacking silicon steel plates so that an eddy current flows and iron loss does not increase.

  The rotating body 3 includes a sleeve 16, a flange 17 fixed to the outside of the sleeve 16, a polygon mirror 18 fixed to the flange 17, a rotating part 19 of a magnetic bearing fixed to the polygon mirror 18, and an inner part of the flange 17. It is comprised with the rotor magnet 14 fixed to the surrounding surface. The sleeve 16 is made of ceramics, and the flange 17 is made of an aluminum alloy. The sleeve 16 and the flange 17 are fixed by shrink fitting. The motor rotor magnet 14 fixed to the lower side of the flange 17 is fixed by adhesion or press fitting.

  The rotor magnet 14 may be a permanent magnet divided in the circumferential direction, but is formed in a ring shape so that adhesion or press-fitting can be easily performed. The rotor magnet 14 can be press-fitted and fixed using a plastic magnet having a linear expansion coefficient substantially the same as that of the flange 17, thereby reducing a change in unbalanced vibration of the rotating body due to a temperature change, and as a motor for higher speed rotation. Is preferred.

  A cylindrical press-fitting inner diameter portion 17a is formed at the upper end of the flange 17 so as to protrude from the upper end, and a flat cylindrical press-fitting outer diameter portion 18a is formed by punching the ceiling portion of the polygon mirror 18 downward. It is press-fitted and fixed to the inner peripheral surface of the press-fitted inner diameter portion 17a. The linear expansion coefficients of the flange 17 and the polygon mirror 18 are substantially equal, and the press-fit inner diameter portion 17a and the press-fit outer shape portion 18a are through holes having a diameter φD2 larger than the diameter φD1 of the hydrodynamic bearing. The flange 17 is formed with a mirror-finishing reference surface 17 b orthogonal to the hydrodynamic bearing surface 16 a of the sleeve 16. The reference surface for mirror surface processing is formed on the opposite side of the polygon mirror 18 with the mirror contact surface 17c as a boundary.

  The polygon mirror 18 is integrally formed with two stages of reflecting surfaces in the axial direction. The polygon mirror 18 is hollowed in a substantially cup shape, and the dynamic pressure bearing surface 16a formed on the sleeve 16 and the reflection surface 18c and a part of the reflection surface 18d formed on the polygon mirror 18 are arranged in the direction of the rotation axis. Overlap is fixed at the position. A rotating portion 19 of an attraction type magnetic bearing is fixed to the polygon mirror 18 by press fitting. An outer cylindrical surface that forms a magnetic gap is formed between the central circle of the first fixed yoke plate 9 and the central circle of the second fixed yoke plate 10 on the rotating portion 19 of the attractive magnetic bearing. It arrange | positions so that a cylinder surface may become coaxial with a rotation center axis | shaft. A permanent magnet or a steel-based ferromagnetic material is used for the rotating portion 19 of the attractive magnetic bearing. The attraction type magnetic bearing supports a rotating body including a polygon mirror 18 and a rotor of a motor described later in a non-contact manner in the thrust direction.

  In order to rotate the rotator 3 at a high speed, balance correction is performed at two locations of a correction surface 18 b provided on the polygon mirror 18 and an inner peripheral surface 14 a of the magnet rotor 14. Since the center of gravity 3a of the rotating body is arranged in the vicinity of the middle of the hydrodynamic bearing, the balance of the rotating body can be corrected with high accuracy, and unbalanced vibration can be reduced to a very small level.

  The printed circuit board 11 is patterned with the motor winding 12a and the hall element 13, and the drive circuit 20 sequentially switches the energization to the motor winding 12a in accordance with the position detection signal of the hall element 13 to rotate the rotating body 3. Control at a constant speed.

  The reflection surface 18c and the reflection surface 18d of the polygon mirror 18 are integrally formed by ultraprecision cutting by the following method. First, in the first step, the sleeve 16 and the flange 17 are fixed by shrinkage fitting. In the second step, the inner diameter of the sleeve 16 to be the dynamic pressure bearing surface 16a is finished with high accuracy. In the third step, a mirror-finished reference surface 17b used for forming the reflecting surfaces 18c and 18d of the polygon mirror 18 on the flange 17 is formed. As shown in FIG. 10, the sleeve 16 is fixed by passing a taper-shaped processing jig 22 through the inner diameter of the sleeve 16. The flange 17 is formed with a mirror-finishing reference surface 17b which is cut by the processing blade 23 and is orthogonal to the inner diameter central axis of the sleeve 16 (the central axis of the dynamic pressure bearing) with high accuracy. In the fourth step, the polygon mirror 18 is press-fitted into the flange 17. In the fifth step, the flange 17 is fixed by the mirror-finished reference surface 17b, and the highly accurate reflective surface 18c and reflective surface 18d are formed at a constant angle with respect to the central axis of the inner diameter of the sleeve 16 by ultra-precision cutting. Is done.

  As described above, in Example 1, the interior of the polygon mirror 18 is hollowed out in a substantially cup shape, and the diameters of the mirror center holes corresponding to the mirror reflecting surfaces 18c and 18d at each stage are the same. The difference in the deformation amount of the mirror surface due to is suppressed to a small level.

  Furthermore, since the inner circumference of the polygon mirror 18 is formed with a gap over the entire circumference and is not fastened with a material having a different linear expansion coefficient, deformation due to a temperature change of the mirror reflecting surfaces 18c and 18d can be suppressed to be small. Furthermore, since the center of gravity 3a of the rotating body is arranged at the approximate center of the hydrodynamic bearing, the balance of the rotating body can be corrected with high accuracy.

  Furthermore, since the polygon mirror 18 and the flange 17 are press-fitted and the flange and the sleeve are shrink-fitted, the unbalanced change of the rotating body due to temperature can be suppressed, and vibration generated during high-speed rotation can be reduced. It becomes. Further, since the mirror-finishing reference surface 17b orthogonal to the hydrodynamic bearing surface 16a of the sleeve 16 is formed on the flange 17, an optical deflector having a small angle variation of the reflecting surface and high scanning position accuracy of optical scanning is provided. Can be obtained.

  Since the mirror surface processing reference surface 17b is formed on the opposite side of the polygon mirror 18 with the mirror contact surface 17c as a boundary, the mirror surface processing reference surface of the mirror reflection surface has high squareness accuracy with respect to the rotation center axis of the hydrodynamic bearing. The surface 17b can be exposed to the outside of the rotating body 3 in a state where the sleeve 16, the flange 17, and the polygon mirror 18 are integrated, and can be used for mirror processing of the mirror reflecting surface. The press-fitting and fixing portion between the flange 17 and the polygon mirror 18 is formed by press-fitting and fixing the press-fitting inner diameter portion 17 a formed on the flange 17 and the press-fitting outer diameter portion 18 a formed on the polygon mirror 18. The stress due to the press-fitting is difficult to be transmitted to the mirror reflecting surfaces 18c and 18d, and the deformation of the reflecting surface is suppressed to a small level.

  Since the press-fitting fitting portion has a diameter larger than the diameter of the dynamic pressure bearing, it is possible to form a reference surface for mirror finishing with high squareness accuracy with respect to the rotation center axis of the dynamic pressure bearing. Since the rotor magnet 14, which is a driving permanent magnet, is fixed to the flange 17, the deformation of the mirror reflecting surfaces 18 c and 18 d due to the fixing of the rotor magnet 14 is suppressed to be small. Since the sleeve 16 is made of ceramics, the dynamic pressure bearing surface has high wear resistance and can have a long life.

  Since the sleeve 16 and the flange 17 are fixed by shrink fitting, the joining of the sleeve 16 and the flange 17 formed using materials having different linear expansion coefficients is firmly fixed without loosening due to a temperature change. Thereby, the vibration change is suppressed small. Further, since the rotating part 19 of the magnetic bearing is fixed to the polygon mirror 18, the variation in the height position of the reflecting surface is small, and the position accuracy of the reflecting surface is high.

  Further, since the polygon mirror 18 has a plurality of stages of reflecting surfaces (18c and 18d) formed in the axial direction, optical scanning from a plurality of light sources is possible. The reflecting surfaces 18c and 18d are formed by mirror processing after integrating the sleeve 16, the flange 17, and the polygon mirror 18, so that the angle of the sleeve 16 with respect to the center axis (rotation center axis) of the hydrodynamic bearing surface 16a is constant. A highly accurate reflective surface can be formed.

  Next, the configuration and operation of the optical deflector using the dynamic pressure air bearing of the second embodiment will be described with reference to FIG. In FIG. 11, an attachment reference surface 31 a to the optical housing is formed on the lower surface of the cover case 31. A housing 32 is fixed to the cover case 31, and a cylindrical bearing mounting portion 32a is formed to project from the center of the upper surface of the housing 32. A dynamic pressure bearing is configured on the inner peripheral side of the bearing mounting portion 32a. A first fixing sleeve 33 is fixed. A bearing mounting portion 31b is formed at the upper center of the cover case 31, and a second fixing sleeve 34 constituting a hydrodynamic bearing is fixed.

  Under the fixed sleeve 33, a suction type magnetic bearing fixing portion 35 is fixed to the housing 32. The attraction magnetic bearing fixing portion 35 is fixed by press-fitting and fixing the cap 36 to the center portion of the lower surface of the housing 32. A fine hole (about 0.2 mm to 0.5 mm) that attenuates vertical vibrations is formed in the center of the cap 36 using viscous resistance when air passes. The cap 36 is made of a non-magnetic material such as a stainless steel plate.

  The attraction type magnetic bearing fixing portion 35 includes a ring-shaped permanent magnet 37 magnetized in two poles in the rotation axis direction, and a ferromagnetic material in which a central circle having the same outer diameter as the ring-shaped permanent magnet 37 and a smaller inner diameter is formed. And a second fixed yoke plate 39 made of a ferromagnetic material in which a central circle smaller than the inner diameter of the ring-shaped permanent magnet 37 is formed. The first fixed yoke plate 38 and the second fixed yoke plate 39 sandwich the ring-shaped permanent magnet 37 in the axial direction, and a center hole that is the inner diameter of the first fixed yoke plate 38 and a center that is the inner diameter of the second fixed yoke plate 39. The hole is arranged and fixed so as to be coaxial with the rotation center axis. The ring-shaped permanent magnet 37 is mainly made of a rare earth material. The fixed yoke plates 38 and 39 are made of steel plate materials.

  On the upper surface of the housing 32, a printed circuit board 40 having a hole formed in the center is disposed. A stator 41 is fitted and fixed to the outer diameter of the bearing mounting portion 32a of the housing 32. The housing 32 is made of a conductive material such as an aluminum alloy. The printed circuit board is preferably made of an iron substrate so that an eddy current does not flow through the housing 32 due to the influence of an alternating magnetic field due to the rotation of the rotor magnet 42 and the loss of the motor does not increase. The printed circuit board 40 is mounted with a hall element 43 that is a position detection element for switching energization to the winding coil.

The motor unit includes a rotor magnet 42 attached to a rotating body 44, a stator 41 around which a winding coil 41a is wound, and a printed circuit board 40 to which the winding coil 41a is connected.
The Hall element 43 is mounted on the printed circuit board 40. As the stator 41, a laminate of silicon steel plates is used so that eddy current flows and iron loss does not increase.

  The rotating body 44 includes a rotating shaft 45, a polygon mirror 46 fixed to the outside of the rotating shaft 45, a rotating portion 45a of a magnetic bearing formed at one end of the rotating shaft 45, and a rotor magnet fixed to the lower side of the polygon mirror 46. 42. A groove for forming a dynamic pressure bearing (not shown) is formed on the cylindrical surface of the rotary shaft 45. When the rotating body 44 starts to rotate, the air pressure in the bearing clearance formed between the fixing sleeves 33 and 34 disposed at both ends of the rotating shaft 45 increases, and the rotating body 44 in the radial direction (radial direction) without contact. Support. The load in the thrust direction of the rotating body 44 is supported by the magnetic bearing.

  The material of the rotating shaft 45 is stainless steel (SUS430) made of a ferromagnetic material. The polygon mirror 46 is integrally formed with two stages of reflecting surfaces in the axial direction, and is fixed to the center of the rotating shaft 45 by shrink fitting. The diameter of the central hole of the polygon mirror 46 is 10 mm, which is 28% of the inscribed circle diameter of 36 mm.

  The inscribed circle diameter A of the polygon mirror 46 is 36 mm, the center hole diameter B of the polygon mirror 46 is 10 mm, the linear expansion coefficient C of the polygon mirror 46 is 24.6 × 10 −6 (/ ° C.), and the linear expansion coefficient D of the rotary bearing member Is 10.3 × 10 −6 (/ ° C.), | CD | × B / A is 4.0 × 10 −6 (/ ° C.), and the temperature of the polygon mirror 46 is 60 ° C. The flatness is a concave surface of 0.17 μm. The motor rotor magnet 42 fixed to the lower side of the polygon mirror 46 is fixed by adhesion or press fitting.

  The rotor magnet 42 may be a permanent magnet divided in the circumferential direction, but is formed in a ring shape so that adhesion or press-fitting can be easily performed. If a plastic magnet having a linear expansion coefficient substantially the same as that of the polygon mirror 46 is used for the rotor magnet 42 and fixed by press-fitting, the change in unbalanced vibration of the rotating body due to the temperature change can be reduced, and the motor can be rotated at a higher speed. Will be suitable. The rotating portion 45a of the attraction type magnetic bearing formed at one end of the rotating shaft 45 has an outer portion that forms a magnetic gap between the center circle of the first fixed yoke plate 38 and the center circle of the second fixed yoke plate 39. A cylindrical surface is formed, and the outer cylindrical surface is arranged so as to be coaxial with the rotation center axis.

  The rotating body 44 performs balance correction on the correction surfaces (46a, 42a) at two upper and lower positions in order to rotate at a high speed. Since the center of gravity 44a of the rotating body is disposed in the vicinity of the middle of the hydrodynamic bearings at both ends of the rotating shaft 45, the balance of the rotating body can be corrected with high accuracy, and unbalanced vibration can be reduced to a very small level. . On the printed board 40, motor windings 41a and hall elements 43 are wired in a circuit pattern. The drive circuit 47 sequentially switches the energization to the motor winding 41a in accordance with the position detection signal of the Hall element 43 to rotate the rotating body 44 and perform constant speed control. The reflecting surfaces (46b and 46c) of the polygon mirror 46 are integrally formed by performing ultraprecision cutting by the following method.

  That is, in the first step, the rotary shaft 45 and the polygon mirror 46 are fixed by shrinkage fitting. Next, in the second step, a mirror-finishing reference surface 46d used for forming the reflecting surfaces (46b and 46c) of the polygon mirror 46 is formed. A mirror-finishing reference surface 46 d that is fixed on the basis of the outer diameter of the rotary shaft 45 and is orthogonal to the central axis of the hydrodynamic bearing is formed on the polygon mirror 46. Next, in the third step, the polygon mirror 46 is fixed on the mirror-finishing reference surface 46d, and a highly accurate reflective surface 46b at a certain angle with respect to the central axis of the hydrodynamic bearing is obtained by ultraprecision cutting. 46c is formed.

  In the second embodiment, since the diameters of the mirror center holes corresponding to the mirror reflecting surface 46b and the mirror reflecting surface 46c of each stage are the same, the difference in the deformation amount of the mirror surface due to the centrifugal force can be suppressed small. Further, by setting the diameter of the central hole of the polygon mirror 46 to 30% or less of the diameter of the inscribed circle of the polygon mirror 46, the deformation of the polygon mirror 46 due to the centrifugal force when rotating at 60000 rpm can be made 0.16 μm or less. As a result, even in a high-speed and high-precision polygon mirror, it is possible to reduce the environmental load by sharing optical components. Furthermore, since the center hole of the polygon mirror 46 is shrink-fitted and fixed to the rotating shaft 45, the deformation due to the centrifugal force of the mirror reflecting surface can be suppressed to a small extent by using the shrink-fitting stress.

  Furthermore, the polygon mirror inscribed circle diameter A (mm), the center hole diameter B (mm) corresponding to the polygon mirror, the linear expansion coefficient C (/ ° C.) of the polygon mirror, and the linear expansion coefficient D of the bearing member of the rotating body (/ ° C.) satisfies the condition of | C−D | × B / A ≦ 5 × 10 −6 (/ ° C.), the rotary shaft 45 and the polygon mirror 46 which are bearing members of the rotating body are linear Even with materials having different expansion coefficients, deformation due to temperature of the mirror reflecting surface due to shrink fitting can be suppressed to a small level. Furthermore, both ends of the rotating shaft 45 that is a bearing member of the rotating body are rotatably supported by a fixed sleeve 33 that is two bearing members on the fixed side, and the center of gravity of the rotating body is arranged between the bearings to rotate at high speed. It can be set as the rotary body structure suitable for.

  Furthermore, by making the diameters of the center holes corresponding to the mirror reflectors 46b and 46c substantially the same, the difference in deformation due to the centrifugal force between the mirror reflectors 46b and 46c can be kept small. Further, the mirror reflecting surfaces 46b and 46c formed on the polygon mirror 46 are formed by integrating the rotating shaft 45 and the polygon mirror 46 and then performing mirror surface processing, so that the central axis ( The angle with respect to the rotation center axis) is constant, and a highly accurate reflecting surface can be formed.

  Next, an embodiment of the optical scanning device using the optical deflector described so far will be described as a third embodiment of the present invention with reference to FIG. FIG. 12 shows a configuration of a main part of an optical scanning device provided with the optical deflector according to the present invention. The optical scanning device shown in FIG. 12 is an example of a single beam system.

The optical scanning device according to the present embodiment includes a light source 101, a coupling lens 102, an aperture 103, a cylindrical lens 104, a polygon mirror 105, a lens 106, and a lens 107.
, A mirror 108, a photoconductor 109, a mirror 110, a lens 111, and a light receiving element 112. The light source 101 is a semiconductor laser element that emits light for optical scanning. The coupling lens 102 is a lens for adapting the light emitted from the light source 101 to the optical system. The aperture 103 makes the beam light for optical scanning a predetermined shape. The cylindrical lens 104 condenses incident beam light in the sub-scanning direction. The polygon mirror 105 is an optical deflector, and reflects incident light on the deflection reflection surface.

  The lenses 106 and 107 are lenses for forming an image of the beam light on the photoconductor 109. The mirror 108 bends the optical path of the beam light and guides it to the photoconductor 109. The photoconductor 109 forms an electrostatic latent image in accordance with the irradiated beam light. The mirror 110 and the lens 111 collect the beam light on the light receiving element 112. The light receiving element 112 is a light detection element such as a photodiode.

  A beam emitted from the light source 101 which is a semiconductor laser element is a divergent light beam, and is coupled to a subsequent optical system by a coupling lens 102. The coupled beam depends on the optical characteristics of the optical system, and may be a weak divergent light beam, a weak converging light beam, or a parallel light beam. When the beam that has passed through the coupling lens 102 passes through the aperture 2 of the aperture 103, the light-peripheral portion of the light beam is cut off at a portion where the light intensity is low, and is shaped into a beam, and enters the cylindrical lens 104 that is a linear imaging optical system To do.

  The cylindrical lens 104 has a substantially semi-cylindrical shape, has a power for converging light in the sub-scanning direction with a direction in which light is not refracted in the main scanning direction, and focuses an incident beam in the sub-scanning direction. The light is condensed near the deflection reflection surface of the polygon mirror 105 which is an optical deflector.

  The polygon mirror 105 rotates at a constant speed. The beam condensed by the polygon mirror with this rotation is deflected at a constant angular velocity by the deflecting reflection surface, and is transmitted through the two lenses 106 and 107 forming the “scanning optical system”, and the optical path is transmitted by the bending mirror 8. Are bent and condensed as a light spot on the photoconductive photosensitive member 109 forming the substance of the “scanned surface”.

  The surface to be scanned is scanned with the light condensed on the photoconductor 109. Prior to scanning, the beam enters the mirror 110 and is focused on the light receiving element 112 by the lens 111. The writing timing for the photoconductor 109 is determined by a control means (not shown) based on the output of the light receiving element 112.

  Thus, the optical deflector according to the present invention can be applied to a single beam type optical scanning device. In the single beam type optical scanning device to which the optical deflector according to the present invention is applied, the reflection surface of the polygon mirror 105 as the optical deflector is maintained with high accuracy, so that the shape of the scanning beam is constant and stable optical scanning is performed. It can be carried out.

  Next, another embodiment of the optical scanning device provided with the optical deflector according to the present invention will be described with reference to FIG. In addition, the same element as FIG. 12 is shown with the same code | symbol. The light source 101A is a semiconductor laser array in which four light emission sources ch1 to ch4 are arranged in a line at equal intervals.

In the present embodiment, the light emitting sources ch1 to ch4 are arranged in the sub-scanning direction, but the semiconductor laser array 101A may be tilted so that the arrangement direction of the light emitting sources is tilted with respect to the main scanning direction.
The four beams emitted from the four light emission sources ch1 to ch4 are divergent light beams in which the major axis direction of the elliptical far field pattern is directed to the main scanning direction as shown in FIG. Are coupled to a subsequent optical system by a coupling lens 102 common to both beams.

  The form of each coupled beam depends on the optical characteristics of the subsequent optical system, and may be a weak divergent light beam, a weak convergent light beam, or a parallel light beam. The four beams transmitted through the coupling lens are shaped by the aperture 3 and converged in the sub-scanning direction by the action of the cylindrical lens 104 that is a common line imaging optical system. The four beams that have converged in the sub-scanning direction are separated from each other in the sub-scanning direction in the vicinity of the deflection reflection surface of the polygon mirror 105, which is an optical deflector, as long line images in the main scanning direction.

  The four beams deflected at a constant angular velocity by the deflecting reflecting surface of the polygon mirror 105 are transmitted through the two lenses 106 and 107 constituting the scanning optical system, and the optical path is bent by the bending mirror 108. The four beams whose optical paths are bent are condensed as four light spots separated in the sub-scanning direction on the photoconductor 109 that is the substance of the surface to be scanned, and the four scanning lines on the surface to be scanned are simultaneously collected. Scan. Prior to optical scanning, one of the beams enters the mirror 110 and is focused on the light receiving element 112 by the lens 111. The timing of writing on the photoconductor 109 by the four beams is determined by a control means (not shown) based on the output of the light receiving element 112.

  The scanning optical system in the present embodiment is an optical system that condenses four beams simultaneously deflected by the optical deflector (polygon mirror 105) as four light spots on the surface to be scanned of the photoconductor 109. Thus, the present invention can also be applied to a multi-beam type optical scanning device constituted by two lenses 106 and 107. In the multi-beam type optical scanning device using the optical deflector according to the present invention, the reflection surface of the polygon mirror 105 as the optical deflector is maintained with high accuracy, so that the scanning beam shape is constant and stable optical scanning is performed. It can be carried out.

  Next, as an embodiment of an image forming apparatus provided with the optical deflector according to the present invention, an embodiment of a tandem type full color laser printer will be described with reference to FIG. In FIG. 14, a transport belt 202 for transporting transfer paper (not shown) fed from a paper feed cassette 201 disposed in the horizontal direction is provided on the lower side in the apparatus. On the conveying belt 202, a yellow (Y) photosensitive member 203Y, a magenta (M) photosensitive member 203M, a cyan (C) photosensitive member 203C, and a black (K) photosensitive member 203K convey the transfer paper. They are arranged at equal intervals in order from the upstream side in the direction. Hereinafter, subscripts Y, M, C, and K are appropriately added to the reference numerals to distinguish each color.

  These photoconductors 203Y, 203M, 203C, and 203K are all formed to have the same diameter, and process members that perform an image forming process according to an electrophotographic process are sequentially disposed around the photoconductors 203Y, 203M, 203C, and 203K. The photoconductor 203Y will be described as an example. A charging charger 204Y, an optical scanning device 205Y, a developing device 206Y, a transfer charger 207Y, a cleaning device 208Y, and the like are arranged around the photoreceptor 203Y in this order. The same applies to the other photoconductors 203M, 203C, and 203K. That is, in the present embodiment, the photoconductors 203Y, 203M, 203C, and 203K are irradiated surfaces set for each color, and a pair of optical scanning devices 205Y, 205M, 205C, and 205K is provided for each of them. 1 is associated.

In addition, a registration roller 209 and a belt charging charger 210 are provided around the conveyance belt 202 at the upstream side of the photoconductor 205Y, and a belt separation charger 211, at a downstream side of the photoconductor 205K. Static elimination charger 212, cleaning device 213
Etc. are provided in order. In addition, a fixing device 214 is provided downstream of the belt separation charger 211 in the transport direction, and is connected to a paper discharge tray 215 via a paper discharge roller 216.

  In the above configuration, for example, in the full color mode (multiple color mode), each of the photoconductors 203Y, 203M, 203C, and 203K is based on an image signal of each color for Y, M, C, and K. An electrostatic latent image is formed by optical scanning of a light beam by the optical scanning devices 205Y, 205M, 205C, and 205K. These electrostatic latent images are developed with the corresponding color toners to become toner images, and are superimposed on each other by being sequentially transferred onto transfer paper that is electrostatically attracted onto the transport belt 202 and transported. The transfer paper on which the toner images of the respective colors are superimposed is fixed on the transfer paper as a full color image by the fixing device 214, and the transfer paper on which the image is fixed is discharged to the paper discharge tray 215 by the paper discharge roller 216.

  In the black mode (monochrome mode), the photoconductors 203Y, 203M, and 203C and these process members are deactivated, and only the photoconductor 203K is lighted based on the black image signal. An electrostatic latent image is formed by optical scanning of a light beam by a scanning device (one optical scanning device) 205K. This electrostatic latent image is developed with black toner to become a toner image, and is electrostatically attracted onto the transport belt 2 and transferred onto the transfer paper transported. The toner image transferred onto the transfer paper is fixed on the transfer paper as a monochrome image by the fixing device 214, and the transfer paper on which the image has been fixed is discharged onto a paper discharge tray 215 by a paper discharge roller 216.

  As described above, the light deflection apparatus according to the present invention can also be applied to a color image forming apparatus such as a tandem type full color laser printer. The tandem type full color laser printer using the optical deflector according to the present invention is shared by the optical scanning devices 205Y, 205M, 205C and 205K, and is reflected by one optical deflector 300 in which two-stage mirrors are formed in the axial direction. Since the surface is maintained with high accuracy, the scanning beam shape is constant, and stable optical scanning can be performed. Each of the above embodiments is an example of a preferred embodiment of the present invention, and the present invention is not limited to this, and various modifications are possible.

The present invention can be applied to a digital facsimile, a digital printer, and a digital copying machine.
Further, the present invention can be applied not only to black and white images but also to image forming apparatuses that form color images.

It is a top view which shows the example of the polygon mirror used for the optical deflector concerning this invention. It is the graph which showed the correlation of the rotation speed of the polygon mirror used for the optical deflector concerning this invention, and flatness. It is a top view which shows the example which inserted the sleeve in the polygon mirror used for the optical deflector concerning this invention. It is a graph which shows the correlation of the mirror flatness for the sleeve diameter shrink-fitted to the polygon mirror used for the optical deflector according to the present invention. It is the table | surface and graph which showed the correlation with the material of the sleeve shrink-fitted on the polygon mirror used for the optical deflector concerning this invention, and a mirror plane. FIG. 6 is a table showing physical property values as a basis for calculating the correlation between the sleeve material and the mirror flatness shown in FIG. 5. It is sectional drawing which shows embodiment of the optical deflector concerning this invention. It is sectional drawing which shows the part of the rotary body of the said optical deflector. It is a disassembled perspective view which shows embodiment of the optical deflector concerning this invention. It is processing explanatory drawing of the reference surface for mirror surface processing of the flange used for the optical deflector concerning this invention. 1 is a perspective view showing an embodiment of an optical scanning device according to the present invention. 1 is a perspective view showing an embodiment of a multi-beam optical scanning device according to the present invention. 1 is a front view schematically showing an image forming apparatus according to the present invention.

Explanation of symbols

3 Rotating body 16 Sleeve 17 Flange 18 Polygon mirror 44 Rotating body 46 Polygon mirror 46b, 46c Mirror reflection surface 105 Polygon mirror 205 Optical scanning device

Claims (12)

An optical deflector that rotationally drives a rotating body formed by a plurality of stages of polygon mirrors in the rotation axis direction and supported by a bearing by a motor,
An optical deflector characterized in that the diameter of the central hole corresponding to each stage of the polygon mirror is substantially the same. An optical deflector that rotationally drives a rotating body formed of a plurality of polygon mirrors in the direction of the rotation axis and supported by a bearing by a motor,
An optical deflector characterized in that the diameter (B) of the center hole corresponding to each stage of the polygon mirror is in the range of 5 to 50% of the inscribed circle diameter (A) of the polygon mirror.   3. The optical deflector according to claim 1, wherein the polygon mirror is fixed to a rotating body with a gap provided in an inner periphery of a center hole. The center hole of the polygon mirror is formed in a cylindrical shape,
4. The optical deflector according to claim 3, wherein the polygon mirror is fixed to the rotating body by a fixing portion formed at one end of the central hole of the rotating body.   3. The optical deflector according to claim 1, wherein the polygon mirror has a center hole fixed to a bearing member of a rotating body by shrink fitting. The polygon mirror has a polygon mirror inscribed circle diameter (A),
The diameter (B) of the center hole corresponding to each polygon mirror,
A linear expansion coefficient (C) of the polygon mirror;
The optical deflector according to claim 5, wherein a linear expansion coefficient (D) of the bearing member of the rotating body satisfies the following condition.
| C-D | × B / A ≦ 5 × 10 ⁻⁶   3. The optical deflector according to claim 1, wherein both ends of the rotating shaft member of the rotating body are rotatably supported by two fixed bearing members.   3. The optical deflector according to claim 2, wherein the center hole diameters B corresponding to the respective stages of the polygon mirror are substantially equal in size.   9. The method of manufacturing an optical deflector according to claim 1, wherein the reflecting surface formed on the polygon mirror is mirror-finished after the polygon mirror is fixed to the rotating body and integrated. The manufacturing method of the optical deflector characterized by the above-mentioned.   9. An optical scanning device that scans a scanning line by guiding a beam from a semiconductor laser to a surface to be scanned through an optical system including an optical deflector to form a light spot, as the optical deflector. An optical scanning device using the optical deflector according to any one of the above.   In the optical scanning device that scans a plurality of scanning lines adjacently by forming a plurality of light spots by guiding a plurality of beams from the semiconductor laser to an scanned surface through an optical system including an optical deflector. An optical scanning apparatus using the optical deflector according to claim 1 as a deflector.   An image forming apparatus that forms a latent image on a photosensitive surface of a photosensitive medium by an optical scanning device and visualizes the latent image to obtain an image, and performs optical scanning on the photosensitive surface of the photosensitive medium. An image forming apparatus using the optical scanning device according to claim 10 or 11 as the device.

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