JP2008095713A - Dynamic pressure bearing device and deflection scanning device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid a trouble such as the uplift of a shaft member by flowdization of oil, leakage of oil, or scuffing between a sleeve and the shaft member. <P>SOLUTION: The dynamic pressure bearing device including upper and lower dynamic pressure generating grooves 7a and 7b formed in the sleeve 2 rotatably supporting a shaft member 1 is constituted so that clearance C<SB>2</SB>of bearing gap in a lower dynamic pressure generation part is larger than clearance C<SB>1</SB>in an upper dynamic pressure generation part. Necessary bearing rigidity is ensured by the upper clearance C<SB>1</SB>, and the influence by expansion of a bearing hole 5 of the sleeve 2 in a tapered shape at the time of fixing a thrust plate 4 to the lower end of the sleeve 2 by caulking is reduced by increasing only the lower clearance C<SB>2</SB>. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a hydrodynamic bearing device and a deflection scanning device used in a laser beam printer, an optical / magnetic disk device, and the like.

  2. Description of the Related Art A deflection scanning device used for a laser printer, a digital copying machine, or the like uses a dynamic pressure bearing device for obtaining a stable and smooth rotation at a bearing portion that supports a rotating polygon mirror that rotates at high speed. Also, in an information recording device such as an optical disk or a magnetic disk, a dynamic pressure bearing has been widely used to support a disk rotating at high speed.

  FIGS. 3A and 3B show a cross section of a hydrodynamic bearing device in a conventional example. FIG. 3A shows a state in which the shaft member 101 is attached, and FIG. 3B shows a state in which the shaft member 101 is not attached. ing. This hydrodynamic bearing device includes a shaft member 101, a sleeve 102 that rotatably supports the shaft member 101 in a bearing hole 105, a disk 103 that is fixed to the lower end of the sleeve 102 and seals the bearing hole 105, The thrust plate 104 is supported by the plate 103. Further, oil 106 that is a working fluid is filled between the inner surface of the bearing hole 105 of the sleeve 102 and the outer surface of the shaft member 101 and between the thrust plate 104 and the end surface of the shaft member 101.

  The bearing hole 105 of the sleeve 102 is provided with large-diameter portions 105a, 105b, and 105c at the upper end, the lower end, and the center, respectively. Further, between the large diameter portion 105a at the upper end and the large diameter portion 105c at the center, and between the large diameter portion 105c at the center and the large diameter portion 105b at the lower end, herringbone-like dynamic pressure generating grooves 107a and 107b, respectively. Is formed. A spiral groove is formed on the upper surface of the thrust plate 104. The upper end portion of the shaft member 101 protrudes upward from the bearing hole 105 of the sleeve 102, and the illustrated boss portion is fixed to the upper portion thereof.

  In the dynamic pressure bearing device configured as described above, when the shaft member 101 rotates, dynamic pressure is generated in the oil 106 in the bearing gap by the action of the dynamic pressure generating grooves 107a and 107b provided in the bearing hole 105 of the sleeve 102, The shaft member 101 rotates without contact with the bearing hole 105 of the sleeve 102. Further, in the thrust direction, dynamic pressure is generated by the action of the spiral groove provided in the thrust plate 104, and the shaft member 101 is supported in a floating state. When this hydrodynamic bearing device is used in a deflection scanning device, a rotary polygon mirror (not shown) is integrally coupled to a boss portion at the upper end of the shaft member 101, and a rotor of a motor is used to drive the rotation. Are also fixed to the shaft member 101.

  FIG. 4 shows the pressure balance of dynamic pressure. The dynamic pressures a1 and a2 toward the fold line A at the center of the dynamic pressure generation groove 107a are generated by the upper herringbone dynamic pressure generation groove 107a having the fold line A. As a result, the oil 106 flows toward the center folding line A. Further, the oil 106 flows toward the folding line B at the center of the dynamic pressure generating groove 107b by the lower herringbone dynamic pressure generating groove 107b. Normally, the shaft member 101 can be stably rotated by designing so that a1 = a2 and b1 = b2.

  However, the disk 103 that seals the lower end of the sleeve 102 is usually assembled by caulking. Therefore, as shown in FIG. 5A, the inner diameter of the lower end of the sleeve 102 is expanded, the cylindricality of the bearing hole 105 is deteriorated, and the pressure balance in the upper and lower dynamic pressure generating grooves 107a and 107b is a1>. a2, b1> b2. As a result, as shown in FIG. 5B, a transport force is generated that sends the oil 106 toward the lower end of the sleeve 102 in the direction indicated by the arrow R1. This transport force (pressure) is represented by (a1-a2) + (b1-b2). At this time, since the lower end of the sleeve 102 is sealed, the oil 106 having nowhere to flow flows so as to push up the shaft member 101 as indicated by an arrow R2. For this reason, the subject that the height of the rotor of a motor and the reflective surface of a rotary polygon mirror was not stabilized occurred.

In order to solve this problem, Patent Document 1 discloses that the position of the folding line of the herringbone-shaped dynamic pressure generating groove of the hydrodynamic bearing device is shifted upward to avoid the shaft member from floating and oil leaking out. The structure to perform is disclosed.
JP 2004-301325 A

  However, as the rotational speed becomes higher (25000 r / min or more), due to variations in the amount of spread when the disk is caulked, the shaft floating, oil leakage, shaft member can be achieved by simply shifting the folding line of the dynamic pressure generating groove. It has become difficult to solve problems such as sleeve galling.

  The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and is capable of avoiding troubles such as shaft member floating due to oil flow, oil leakage, and sleeve / shaft member galling. An object of the present invention is to provide a pressure bearing device and a deflection scanning device.

  In order to achieve the above object, a hydrodynamic bearing device according to the present invention includes a shaft member and a sleeve that are relatively rotatably fitted, and a working fluid that is interposed in a bearing gap between the shaft member and the sleeve. At least one of the member and the sleeve has a first dynamic pressure generating portion formed so as to be located above the bearing gap, and a second dynamic pressure formed so as to be located below the bearing gap. And a generating portion, and the clearance in the second dynamic pressure generating portion is larger than the clearance in the first dynamic pressure generating portion.

  By making the clearance of the dynamic pressure generating part wider so that the lower part is wider than the upper part, the influence of the expansion of the inner diameter of the sleeve when the disk is crimped to the lower end of the sleeve is suppressed. As a result, the shaft member can be prevented from floating with respect to the sleeve, and problems such as oil leakage and galling between the shaft member and the sleeve can be avoided to stabilize the bearing performance.

  If the clearance of the dynamic pressure generating portion is excessively widened, the bearing rigidity is lowered and the shaft member cannot be supported, causing problems such as the shaft member swinging around and the shaft member and the sleeve being galled. Therefore, the clearance of only the dynamic pressure generating portion below is widened so that the overall bearing rigidity does not decrease too much.

  The clearance of the lower dynamic pressure generating groove is preferably 0.5 to 1.0 μm wider than the clearance of the upper dynamic pressure generating groove.

  By using such a dynamic pressure bearing device for the bearing portion of the rotary polygon mirror, it is possible to greatly contribute to speeding up and performance improvement of the deflection scanning device.

  The best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1A is a cross-sectional view showing a main part of a deflection scanning apparatus according to an embodiment, and a rotary polygon mirror 11 having a reflection surface 11a for deflecting and scanning a light beam and for rotationally driving the mirror. It has a drive part. FIGS. 1B and 1C show cross sections of the hydrodynamic bearing device. FIG. 1B shows a state where the shaft member 1 is not attached, and FIG. 1C shows a state where the shaft member 1 is attached. Show.

  As shown in FIG. 1A, the shaft member 1 is integrated with a rotor 12 composed of a permanent magnet 12a and a yoke 12b, and a rotary polygon mirror 11. The sleeve 2 is integrated with the stator 13 and the circuit board 14 including the drive coil 13a and the stator core 13b, and the shaft member 1 and the sleeve 2 are fitted so as to be rotatable with respect to each other.

  The stator core 13b has multi-pole pole shoes, and a drive coil 13a is wound around each pole shoe. The energization is sequentially switched depending on the rotational position of the permanent magnet 12 a magnetized in multiple poles, and a rotational force is generated between the rotor 12 and the stator 13. The stator core 13b around which the drive coil 13a is wound is fixed to the circuit board 14 together with circuit components constituting the drive circuit, and the circuit board 14 is integrated with the sleeve 2. Such a rotor part and a stator part are produced individually and assembled as a motor. After a predetermined amount of oil 6 as the working fluid is injected into the sleeve 2 by the oil supply device, the shaft member 1 that is rotatably fitted to the inner diameter portion of the sleeve 2 is inserted to complete the motor.

  As shown in FIGS. 1B and 1C, a hydrodynamic bearing device that is a bearing portion that rotatably supports the rotary polygon mirror 11 has a sleeve 2 that rotatably supports the shaft member 1 in the bearing hole 5. Have. Furthermore, it has a disc 3 fixed to the lower end of the sleeve 2 and sealing the bearing hole 5 and a thrust plate 4 supported by the disc 3, and between the sleeve 2 and the shaft member 1 and between the thrust plate 4 and the shaft member 1. In between, oil 6 is filled.

  The upper end portion, the lower end portion, and the central portion of the bearing hole 5 of the sleeve 2 are large diameter portions 5a, 5b, and 5c, respectively. Between the large diameter portion 5a at the upper end and the central large diameter portion 5c, and between the central large diameter portion 5c and the large diameter portion 5b at the lower end, a herring that constitutes the first and second dynamic pressure generating portions Bone-like dynamic pressure generating grooves 7a and 7b are formed. A spiral groove is formed on the upper surface of the thrust plate 4.

  In the dynamic pressure bearing device configured as described above, when the shaft member 1 rotates, the dynamic pressure is generated in the oil 6 by the action of the dynamic pressure generating grooves 7a and 7b provided in the bearing hole 5 of the sleeve 2, and the shaft member 1 rotates without contact with the bearing hole 5 of the sleeve 2. Also in the thrust direction, dynamic pressure is generated by the action of the spiral groove provided in the thrust plate 4, and the shaft member 1 is supported in a floating state. The disk 3 is fixed by caulking in order to close the opening at the lower end of the sleeve 2, and as a result, the inner diameter of the lower end of the sleeve 2 is expanded, the cylindricity is deteriorated, and the bearing gap is expanded.

  In particular, the lower dynamic pressure generating portion is easily affected by the deterioration of the cylindricity by assembling the disk 3, and as the rotational speed becomes higher (25000 r / min or more), the amount of variation spreading in a tapered shape is generated. . As a result, problems such as floating of the shaft member 1, oil leakage, and galling of the shaft member 1 and the sleeve 2 occur.

Therefore, as shown in FIG. 1 (c), the clearance C ₂ in the lower dynamic pressure generating portion is configured to be larger than the clearance C ₁ in the upper dynamic pressure generating portion in advance. Makes it less susceptible to taper shape due to tightening.

  If the clearance of the dynamic pressure generating portion is excessively widened, there is a problem that the bearing rigidity is lowered and the shaft member 1 cannot be supported, the shaft member 1 is swung around, or the shaft member 1 and the sleeve 2 are galling. Arise.

Therefore, the clearance C ₁ of the upper dynamic pressure generating portion where the bearing rigidity is most required is set to, for example, about 5 μm so as to obtain an appropriate bearing rigidity, and the clearance C ₂ of the lower dynamic pressure generating portion is set to the upper portion. It is set wider by 0.5 to 1.0 μm than the dynamic pressure generating portion.

  For example, as shown in FIG. 2, the inner diameter of the portion having the dynamic pressure generating groove 7b below the bearing hole 5 is made larger than the portion having the upper dynamic pressure generating groove 7a. Α = 0.012L to 0.050L (α is the sum of shift amounts of the folding lines A and B in the dynamic pressure generating grooves 7a and 7b, and L is the width La and Lb of the dynamic pressure generating grooves 7a and 7b. (Sum) is preferably established.

  Instead of providing the dynamic pressure generating groove on the sleeve, the dynamic pressure generating groove may be provided on the shaft member, or the dynamic pressure generating groove may be provided on both the sleeve and the shaft member.

  According to the present embodiment, floating of the shaft member 1, oil leakage, galling of the shaft member 1 and the sleeve 2, and the like can be extremely effectively avoided.

1 shows a deflection scanning device according to an embodiment, in which (a) is a schematic sectional view thereof, (b) is a sectional view showing only a sleeve of (a), and (c) is a sectional view showing a sleeve and a shaft member. is there. It is a figure which shows the bearing hole of the sleeve of the apparatus of FIG. It is a figure explaining the hydrodynamic bearing apparatus by one prior art example. It is a figure which shows the pressure balance of the dynamic pressure in the prior art example of FIG. It is a figure which shows deterioration of the pressure balance of the dynamic pressure in the prior art example of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Shaft member 2 Sleeve 3 Disc 4 Thrust board 5 Bearing hole 6 Oil 7a, 7b Dynamic pressure generating groove 11 Rotating polygon mirror 12 Rotor 13 Stator 14 Circuit board

Claims (3)

  A shaft member and a sleeve, which are relatively rotatably fitted, and a working fluid interposed in a bearing gap between them, and at least one of the shaft member and the sleeve is provided above the bearing gap. A first dynamic pressure generating portion formed so as to be positioned; and a second dynamic pressure generating portion formed so as to be positioned below the bearing gap, wherein the first dynamic pressure generating portion is provided. A fluid dynamic bearing device, wherein the clearance in the second dynamic pressure generating part is larger than the clearance in the part.   2. The hydrodynamic bearing device according to claim 1, wherein a clearance in the second dynamic pressure generating portion is larger by 0.5 to 1.0 μm than a clearance in the first dynamic pressure generating portion.   3. A deflection scanning apparatus comprising: a bearing portion comprising the hydrodynamic bearing device according to claim 1; and a rotary polygon mirror rotatably supported by the bearing portion.

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