JP2003214428A - High-speed rotating body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small high-speed rotating body having vibration resistance, and excellent rotation accuracy stable in a wide range from slow rotation to fast rotation, in a high-speed rotating body having a predetermined load and rotating with high speed. <P>SOLUTION: This rotating body is miniaturized by combining a herringbone gas dynamic-pressure bearing with a magnetic bearing to enhance the rigidity of a radial bearing. Unstable vibration of the high-speed rotating body generated by the miniaturization is restrained, and an unstable dynamic pressure distribution produced at both ends of the bearing is absorbed by a circumferential groove formed at both ends of a herringbone gas dynamic-pressure slot formed on a fixed shaft, so that good and stable rotation is enabled. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed rotating body, such as a rotary supporting device for a polygon mirror, which has a strong demand for highly accurate and stable rotation.

[0002]

2. Description of the Related Art For example, polygon mirrors are used in laser printers, bar code readers, facsimiles and laser copying machines. Since the efficiency of such a polygon mirror increases as the rotation speed increases, a rotation speed of 20000 rpm or more has been required. Conventionally, for example, a precision ball bearing has been used as a bearing for such a high-speed rotating body. However, it is difficult to maintain stable rotation accuracy for a long period of time due to problems such as seizure and abrasion, and the limit of use is about 16000 rpm.

Therefore, a grooved gas dynamic pressure bearing is used to support such a rotating body rotating at a high speed. Since the grooved gas dynamic pressure bearing is a bearing mechanism that supports a rotating body in a non-contact manner via an air film, it has features of low noise and low friction loss, but has a low bearing load capacity. Therefore, it is weak against external vibration, and shake of the rotating body easily occurs, so that it is difficult to obtain stable rotation accuracy.

The above problem has been disclosed in, for example, Japanese Patent Laid-Open No. 60-98213, and as shown in the cross-sectional view of FIG. 5, the bearing length 51 is increased to increase the bearing rigidity. A high-speed rotating body 53 using a gas dynamic pressure bearing for suppressing the swing of the rotating body 52, and Japanese Patent Laid-Open No. 63-2664.
As shown in the sectional view of FIG. 6, which is disclosed in Japanese Unexamined Patent Publication No. 20, the thrust gas dynamic pressure bearings 62a and 62b are provided at both ends of the radial gas dynamic pressure bearing 61, and the rotor is driven by the gas dynamic pressure generated in the thrust direction. It suppresses the runout of 63 and the rotary shaft 6
A high-speed rotating body in which 1 has been downsized has been proposed.

[0005]

By the way, the conventional ball bearing is used in the high-speed rotating body disclosed in the above-mentioned prior art and using the long-axis gas dynamic pressure bearing having the increased radial rigidity for supporting the rotating body. The rotating body is larger than the high-speed rotating body, and the size of the apparatus is increased. Further, the gas dynamic pressure bearing generally requires precise processing for obtaining shape accuracy such as cylindricity, roundness, and surface roughness to about 1 μm in order to obtain good rotation accuracy. For this reason, if the rotation axis is a long axis, processing becomes difficult. Even if it can be processed, the manufacturing cost is high and it is not practical.

Further, in a high-speed rotating body in which thrust dynamic pressure bearings are provided at both ends of the radial gas dynamic pressure bearing of the rotating body, the contact area of the thrust bearing surface becomes large when the rotating body is started, and the initial contact period of the rotation becomes large. Requires large starting torque. Further, on the thrust bearing surface, a ringing phenomenon (adsorption phenomenon between smooth flat surfaces) is likely to occur, and the rotating body may not be activated.

Further, in general, when a cylindrical inner diameter is ground, the inner diameters of both ends thereof are likely to be larger or smaller than the central portion of the cylinder. That is, as shown in FIGS. 2A and 2B, the inner diameter of the end of the rotary shaft is machined into an arc shape. Therefore, at both ends of the radial bearing, an unstable dynamic pressure distribution is likely to occur due to a change in the bearing clearance and an increase in the number of revolutions, and an unpredictable vibration is generated in the rotating body and a synchronous vibration natural frequency. Vibration of the conical mode occurs due to amplification of vibration of the rotating body and resonance with magnetic force balance in the thrust direction. As a result, the bearing of the rotating body and the fixed shaft may come into contact with each other, or vibration due to impact may not be attenuated.

Therefore, the present invention has been made to solve the above-mentioned problems, and its purpose is to provide a small rotating body, a small starting torque, a stable rotation accuracy from the initial rotation to high-speed rotation, and a strong earthquake resistance. The object is to provide a high-speed rotating body that achieves the property.

[0009]

To achieve the above object, the high-speed rotating body of the present invention is characterized in that a housing and a fixed shaft are erected on the housing and rotatably supported outside the fixed shaft. A radial gas dynamic pressure bearing consisting of a rotating shaft and a rotating body having a ring-shaped magnet fixed to the outer periphery are fixed to the outer periphery of the rotating shaft, are on the same plane as the ring-shaped magnet, and are fixed in the radial direction. A high-speed rotating body including a radial direction and a magnetic bearing portion supporting a thrust direction, which is composed of a ring-shaped magnet fixed to the housing that holds a clearance, and has a load capacity and the magnetic force of the radial gas dynamic pressure bearing. Eccentricity ratio (eccentricity ratio = deviation of the center of the rotor from the radial bearing center / radial bearing clearance) 0.3 to 0.7 It was. Further, the load capacity of the dynamic pressure of the radial gas is larger than the radial load capacity of the magnetic bearing in the operating rotation range. And, on the bearing surface of the fixed shaft, a herringbone gas dynamic pressure generating groove and a circumferential groove which is located at both ends of the herringbone gas dynamic pressure generating groove and is continuous with the herringbone gas dynamic pressure generating groove is formed. . Furthermore, the circumferential groove is ⅓ to 2 of the groove width.
/ 3 is located so as to project outward with respect to the radial bearing surface of the rotary shaft.

[0010]

The rotating body is held by the magnetic bearing in a non-contact state with the fixed shaft even when the rotating body is stopped. Further, in the rotating body, a gas dynamic pressure is generated by the herringbone groove in the clearance between the fixed shaft and the rotating shaft as the number of rotations increases, and the gas is combined with the magnetic force by the magnetic bearing, so that it is outside in a wide range from the initial rotation to high-speed rotation. It has high bearing rigidity and high damping performance in both radial and thrust directions against a dynamic impact. Further, as the speed of the rotating body increases, the load capacity of gas dynamic pressure due to the herringbone groove becomes larger than the load capacity of the magnetic bearing, and whirl motion (revolution motion of the rotating body) generated in the rotating body is suppressed to reduce the high speed rotation. Enables higher rotation accuracy.

Further, the circumferential grooves, which are located at both ends of the herringbone groove provided on the bearing surface of the fixed shaft and are continuous with the herringbone groove and have a large depth, are unstable at both ends of the rotating body. Suppress dynamic pressure distribution.

[0012]

As described above, according to the present invention,
The bearing rigidity of the high-speed rotating body is increased, and at the same time, the occurrence of unstable vibration and whirl motion due to high-speed rotation is suppressed, so that the rotating body is small and has a strong earthquake resistance against external impact. At the same time, it becomes possible to maintain high rotation accuracy in a wide range from a low speed rotation range to a high speed rotation range, which has been difficult with conventional gas bearings.

[0013]

EXAMPLES Examples of the present invention will be described below, but before that, the principles of the gas dynamic pressure bearing and the whirl motion will be described. <Principle of Gas Dynamic Pressure Bearing> The basic principle of the gas dynamic pressure bearing utilizes the property of gas as a viscous fluid, and the load capacity is generated by the two effects shown in the conceptual diagram of FIG.
The first effect shown in FIG. 3 (a) is that two opposing surfaces 3
When the gas is dragged into the narrowing clearance 33 due to the sliding motion of 1, 32, pressure is generated, which exerts a pressing force of the surface, that is, a load, and a gas film is formed between the sliding surfaces. is there. The second effect shown in FIG. 3 (b) is that when the two surfaces 34, 35 are pressed against each other and approach each other at a speed, the gas 36 between the two surfaces 34, 35 is eliminated at a rate proportional to the approach speed. This must be done, and this displacement causes a pressure buildup, which opposes the pressing forces of the two surfaces. It is a so-called squeeze effect because it is an unsteady dynamic pressure effect of gas film formation.

<Principle of Generation of Whirl Motion> FIG. 4 is a schematic diagram for explaining the whirl motion of the radial bearing.
For simplicity, the vertical axis is assumed and the effect of gravity is not considered. Now, if the rotating shaft 41 rotating at the angular velocity ω is eccentric by e, pressure is generated in the gas lubrication film between the fixed bearing 42 and the rotating shaft 41 by the dynamic pressure effect, and the rotating shaft 41 is rotated. Force F to return to the original bearing center 43
In addition to e, a force Fω that attempts to swing it is generated. Then, when the rotating shaft 41 starts to whirling at an angular velocity Ω, a pressure due to the squeeze effect is generated, and a force FΩ for suppressing the whirling is generated.

Assuming that the mass of the rotating body 41 supported by the bearing is m, the centrifugal force acting on the rotating body 41 is meΩ ² , so that it tries to swing around at an angular velocity Ω such that meΩ ² = Fe. At that time, if Fω = FΩ, there is no decelerating force or accelerating force, and the steady whirling with a constant radius 44 continues. If Fω <FΩ, the whirling speed is reduced, the centrifugal force becomes smaller, and the whirlpool gradually subsides. Conversely, Fω
If> FΩ, whirling is accelerated, centrifugal force wins,
It gets more and more intense. Therefore, in order to suppress the occurrence of whirl motion, the centripetal component Fe of the gas film reaction force is increased. It is necessary to weaken the influence of the dynamic pressure effect on the fluctuation component of the gas film reaction force without reducing the squeeze effect. The present invention suppresses the whirl motion by increasing the centripetal component Fe of the gas film reaction force by the dynamic pressure of the herringbone-shaped groove and the magnetic force of the magnetic bearing.

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic sectional structure of a high-speed rotating polygon mirror according to the embodiment. A ceramic fixed shaft 12 is erected in the center of an aluminum housing 11. The ceramic fixed shaft 12 is a ceramic rotary shaft 13
The depth 6 to 8 angled in opposite directions to the axial direction so that the highest pressure portion is generated in the central portion 14 of the bearing surface of
Micron dynamic pressure generating grooves, that is, herringbone dynamic pressure generating grooves 15a and 15b were formed. Further, the herringbone gas dynamic pressure generating grooves 15a and 15b have a depth of 10 at both ends.
Micron circumferential grooves 16a, 16b were formed. The circumferential grooves 16a and 16b have a width of 2.0 mm, and 1/3 of the groove width is located outside the bearing surface of the rotary shaft 13.

On the inner circumference of the housing 11, a ring-shaped magnet 2 is provided at a position coaxial with the ceramic fixed shaft 12.
3 was adhesively fixed. An aluminum flange 17 is fixed to the outer circumference of the ceramic rotary shaft 13 by shrink fitting. This aluminum flange 17 has a lower surface and a concave portion on the outer periphery thereof, and ring-shaped magnets 18 and 19 are fixedly adhered thereto. Next, the polygonal mirror 20 made of aluminum was fixed onto the flange 18 made of aluminum with an adhesive or bolts to form the rotating body 21.

The rotating body 21 is inserted into the ceramic fixed shaft 12. At this time, the inner diameter of the rotating body 21 and the clearance 22 of the ceramic fixed shaft 12 were set to about 5 μm. Further, the clearance 24 between the ring-shaped magnet 19 on the outer periphery of the rotating body and the ring-shaped magnet 23 of the housing 11 is 1.
It was set to 5 mm. These two ring-shaped magnets 19 and 2
Due to the magnetic attraction force of 3, the rotating body 21 is fixed in its movement in the axial direction, and is rotatable in the radial direction even when the rotation is stopped. Also, two ring-shaped magnets 1
9 and 23 are fixed concentrically with respect to the bearing center, but the magnetic balance has a slight difference, and the rotor 21 is eccentric to the bearing center by 2.5 μm (eccentricity = 0.5). It was located. Therefore, a large dynamic pressure can be generated even at 10,000 rpm or less, and vibration resistance can be improved.

Next, the rotation body 21 is started by the housing 11
It is carried out by a motor composed of a coil 25 fixed to the above and a magnet 18 adhered and fixed to the aluminum flange 17 and a rotation control device (not shown). The rotating body 21 is started by the motor, and as the number of rotations increases, pressure is generated in the bearing clearance 22 by the herringbone gas dynamic pressure generating grooves 15a and 15b, and a load capacity in the radial direction is generated. The increased load capacity in the radial direction improves the vibration resistance of the bearing, suppresses the whirl of the rotating body, reduces the whirl radius, and improves the rotation accuracy.

The high-speed polygon mirror configured as described above is rotated at 30,000 rpm and the rotation accuracy is measured. The results are shown in Table 1 in comparison with those of the prior art. From the results shown in Table 1, it was confirmed that the high speed rotating body of the present invention has extremely excellent rotating performance.

[0021]

[Table 1]

[Brief description of drawings]

FIG. 1 is a sectional view of a high-speed rotating polygon mirror showing an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining the shape of a rotating shaft of the present invention.

FIG. 3 is a schematic diagram for explaining the principle of a gas dynamic pressure bearing.

FIG. 4 is a schematic diagram for explaining whirl motion that occurs in a rotating body that uses a gas dynamic pressure bearing.

FIG. 5 is a sectional view of a polygon mirror for explaining a conventional technique.

FIG. 6 is a cross-sectional view of a miniaturized polygon mirror for explaining a conventional technique.

[Explanation of symbols]

11 Aluminum Housing 12 Ceramic Fixed Shaft 13 Ceramic Rotation Shaft 14 Radial Bearing Centers 15a, 15b Herringbone Dynamic Pressure Generation Grooves 16a, 16b Circumferential Groove 17 Aluminum Flange 18 Link Magnet 19 Ring Magnet 20 Aluminum polygon mirror 21 High-speed rotating body 22 Clearance between ceramic rotary shaft and ceramic fixed shaft 23 Ring magnet 24 Magnetic bearing clearance 25 Coil 31, 32 Two opposing surfaces 33 Narrowing clearance 34, 35 Pressing Two planes 36 Gas 41 Rotating shaft 42 Fixed bearing 43 Bearing center 44 Track of whirl motion 51 Bearing 52 Rotating body 53 High speed rotating body 61 Radial gas dynamic pressure shafts 62a, 62b Thrust gas dynamic pressure bearing 63 Rotating body 64 High speed rotating body

Continued front page    (72) Inventor Hiroyuki Izume             1-1 Kitakita, Ibigawa-cho, Ibi-gun, Gifu Prefecture             Ibiden Co., Ltd. Ogaki Kita Factory (72) Inventor Naoyuki Jimbo             1-1 Kitakita, Ibigawa-cho, Ibi-gun, Gifu Prefecture             Ibiden Co., Ltd. Ogaki Kita Factory (72) Inventor Kazushige Ohno             1-1 Kitakita, Ibigawa-cho, Ibi-gun, Gifu Prefecture             Ibiden Co., Ltd. Ogaki Kita Factory F term (reference) 3J011 AA10 AA11 BA02 CA02 KA02                       MA03 SD10                 3J102 AA01 AA08 BA03 BA04 BA17                       BA18 CA02 CA03 CA11 CA22                       DA07 DA36 GA02

Claims (5)

[Claims] 1. A housing, a radial gas dynamic pressure bearing portion comprising a rotating shaft rotatably supported on the outside of the housing, a fixed shaft provided upright on the housing, and a ring-shaped magnet fixed to the outer circumference. A rotating body is fixed to the outer periphery of the rotating shaft, is on the same plane as the ring-shaped magnet, and supports the radial direction and the thrust direction, which is composed of a ring-shaped magnet fixed to the housing that maintains a constant clearance in the radial direction. A high-speed rotating body including a magnetic bearing portion for performing eccentricity (eccentricity ratio = radial bearing) by combining the load capacity of the radial gas dynamic pressure bearing and the load capacity of the magnetic bearing in the radial direction. High-speed rotating body, characterized in that the amount of displacement of the center of the rotating body from the center / radial bearing clearance) is 0.3 to 0.7. 2. The load capacity of the herringbone gas dynamic pressure bearing for supporting the rotating body is larger than the radial load capacity of the magnetic bearing in the operating speed range of the rotating body. The high-speed rotating body described in. 3. In the radial gas bearing, a herringbone gas dynamic pressure generating groove is formed on the bearing surface of the fixed shaft, and a circumferential groove is formed at both ends of the herringbone gas dynamic pressure generating groove. Claims 1 and 2 characterized
The high-speed rotating body described in. 4. The high-speed rotating body according to claim 1, wherein the circumferential groove formed on the bearing surface of the fixed shaft is deeper than the herringbone gas dynamic pressure generating groove. . 5. The circumferential groove is ⅓ of the groove width.
The high-speed rotating body according to claim 3 or 4, wherein 2/3 is positioned so as to project outward with respect to a radial bearing surface of the rotary shaft.