JP3176070B2 - Dynamic pressure air bearing type rotating device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic pressure air bearing type rotating device, for example, a dynamic pressure air bearing type rotating device for rotating a polygon mirror at high speed.

[0002]

2. Description of the Related Art Conventionally, a dynamic pressure air bearing type rotating device is used for a polygon scanner or the like which scans by rotating a polygon mirror at a high speed of 15,000 rpm or more. As such a dynamic pressure air bearing type rotating device, for example, an actual open flat 1-6
No. 9909 is known and is shown in FIG.

In FIG. 4, a polygon mirror 1 is supported by a rotating shaft 2, and the rotating shaft 2 is rotatably supported by a fixed shaft 3. The fixed shaft 3 is fixed to a base 4, and the rotating shaft 2 is radially supported by air dynamic pressure generated by a dynamic pressure generating groove 3 a formed on the fixed shaft 3. The rotating shaft 2 and the fixed shaft 3 are made of stainless steel such as SUS420, and the base 4 is made of an aluminum alloy or stainless steel.

[0004] On the other hand, there is another dynamic pressure air bearing type rotating device as shown in FIG. 5, for example. In FIG. 5, the fixed shaft 11 is shrink-fitted and fixed to a fixed shaft pedestal 12, and a herringbone groove 11a is formed on the outer periphery of the fixed shaft 11. The hollow rotating shaft 13 is rotatably supported by the fixed shaft 11, the thrust direction of the rotating shaft 13 is supported by a thrust bearing composed of magnets 14, 15, and 16 arranged in reciprocating polarities, and the radial direction is a herringbone groove 11a. Is supported by the air dynamic pressure generated by the

[0005] A polygon mirror 17 is fixed to the rotating shaft 13 and a rotor magnet 18 is fixed to the rotating shaft 13.
A stator 19 is fixed to 12 via a housing 20. Rotation axis by rotor magnet 18 and stator 19
A motor for rotating the motor 13 is configured, and the motor is driven by a driver unit (not shown).

The materials of the fixed shaft 11 and the rotating shaft 13 are as follows.
In consideration of corrosion resistance and wear resistance, stainless steel such as SUS420J2 is used. As a material of the fixed shaft pedestal 12,
SUS303 to reduce the difference in thermal expansion due to the temperature rise and to minimize the loosening of the shrink fit with the fixed shaft 11
Etc. are used. The thermal conductivity of any of these stainless materials is low as a metal.

[0007]

However, the dynamic pressure air bearing type rotary device made of these materials has a problem that the reliability of the device is reduced for the following reasons. .

That is, the polygon mirrors 1 and 17 are moved to tens of thousands of
In the case of rotating at a high speed of pm, heat is generated not only by the motor unit but also by a dynamic pressure radial bearing loss, a polygon mirror windage loss, and a windage loss of a rotating body including a rotating shaft and a rotor magnet. Tens of percent of these losses are converted to heat, and the rotating body and the fixed shaft also become heat sources. Therefore, in order to keep the temperature rise of the apparatus low, it is important how quickly the heat of the rotating body and the fixed shaft is released to the external surface via the fixed shaft. For this reason, it is necessary to make the fixed shaft made of a material having a high thermal conductivity so as to release the heat. This is important because the higher the rotation speed of the polygon mirrors 1 and 17, the more the various losses increase, the more important it is. become.

In the apparatus shown in FIGS. 4 and 5, the fixed shafts 3 and 11 are made of stainless steel having a low thermal conductivity as a metal so as to maintain the radial bearing characteristics. There is a problem that it is difficult to escape, the temperature of the polygon mirrors 1 and 17 tends to rise, and various problems such as deterioration of each part due to heat and deterioration of accuracy due to thermal expansion occur, thereby reducing the reliability of the apparatus. .

In view of the above, the present invention provides a fixed shaft made of a ceramic material and a rotating shaft made of a stainless steel material, thereby suppressing a rise in the temperature of the device and preventing corrosion (rust) from the groove for generating dynamic pressure of the fixed shaft. , Etc.) to improve the reliability of the device.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a housing, a fixed shaft fixed to the housing and having a groove on an outer periphery, and a fixed shaft arranged to surround the fixed shaft. A cylindrical rotating shaft rotatably supported on the
A thrust bearing that supports the rotating shaft in the thrust direction, a motor that drives the rotating shaft, and a rotating body that is supported by the rotating shaft, wherein the rotating shaft is supported in the radial direction by air dynamic pressure generated by the groove of the fixed shaft. The fixed shaft is made of a ceramic material made of SiC or alumina, the rotating shaft is made of a martensitic stainless steel material, and the linear expansion coefficient of the rotating shaft is the same as that of the fixed shaft. The bearing gap is set so as to be larger than the coefficient of linear expansion, so that the dynamic pressure bearing gap becomes wider as the temperature of the device increases, and a part of the fixed shaft is exposed to the outside of the housing.

[0012]

According to the present invention, when heat is generated by the rotation of the rotating shaft by the motor, the heat generated by the rotating shaft and the fixed shaft is released to the outside via the fixed shaft. At this time, the fixed shaft is made of a ceramic material with high thermal conductivity,
Heat is easily released to the outside.

Further, when the rotating shaft and the fixed shaft are generated, the gap between the fixed shaft and the rotating shaft tends to be somewhat larger because the stainless steel material has a higher linear expansion coefficient than the ceramic material. Therefore, the bearing friction torque between the fixed shaft and the rotating shaft is reduced, so that the radial bearing loss and the motor load are reduced, and the bearing load is reduced, thereby suppressing heat generation.

Further, since the ceramic material has extremely excellent corrosion resistance, even if a groove is formed in the fixed shaft made of the ceramic material, occurrence of corrosion from the groove is prevented.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIGS. 1 to 3 show an embodiment of a rotating device of the dynamic pressure air bearing type according to the present invention, which is applied to a polygon mirror scanner.

1 and 2, reference numeral 21 denotes a housing, and a fixed shaft base 22 is fixed to the housing 21.
A fixed shaft 23 is shrink-fitted and fixed to the fixed shaft pedestal 22,
The fixed shaft 23 has a herringbone groove 23a on the outer periphery.
Reference numeral 24 denotes a cylindrical rotating shaft, and the rotating shaft 24 is disposed so as to surround the fixed shaft 23. The rotation shaft 24 has an axis coinciding with the axis of the fixed shaft 23 and is rotatably supported by the fixed shaft 23.

The thrust direction of the rotating shaft 24 is supported by a thrust magnetic bearing 25, and the thrust magnetic bearing 25 is composed of magnets 25a, 25b and 25c arranged in reciprocal polarities. The rotating shaft 24 is driven by a motor 26, and the motor 26 includes a rotor magnet 27 fixed to the rotating shaft 24 and a stator 28 fixed to the housing 21.
26 is driven to rotate at a constant speed by a driver unit (not shown).

The rotating shaft 24 is a polygon mirror as a rotating body.
Specifically, the polygon mirror 29 is supported by the rotating shaft 24 by a mounting screw 31 which engages with a mirror retainer 30 and is screwed into a mirror receiver 24a of the rotating shaft 24. The above-described magnet 25b is fixed to the mirror retainer 30. The rotating shaft 24 is supported in the radial direction by the air dynamic pressure generated by the herringbone groove 23a, and the outer peripheral portion of the fixed shaft 23 and the inner peripheral portion of the rotating shaft 24 constitute a radial bearing.

Here, the fixed shaft 23 is made of a ceramic material such as SiC or alumina, and the rotating shaft 24 is made of a stainless material such as martensitic stainless steel SUS420J2. SUS4 as stainless steel material
The linear expansion coefficient of 20J2 is relatively close to the linear expansion coefficient of the ceramic material.

Reference numeral 32 denotes an optical housing for covering the polygon mirror 29; 33, an upper cover for supporting the magnet 25c; 34, a deflection window; and 35, a balance ring for balancing rotating members such as the rotating shaft 24. , 36 is an orifice for giving high damping performance in the axial direction, 37 is a Hall element for detecting the position of the rotor magnet 27 of the motor 26,
Reference numeral 38 denotes a wiring board for the motor 26. In addition, the fixed shaft pedestal 22
Alternatively, instead of forming the fixed shaft 23 separately as shown in FIG. 2 and then shrink-fitting and fixing as described above, the fixed shaft 23 may be integrally formed from the beginning as shown in FIG. Good.

According to the above configuration, since the fixed shaft 23 is made of a ceramic material, when heat is generated by driving the motor 26, the rotating members such as the rotating shaft 24, the mirror presser 30, and the rotor magnet 27 are used. The heat generated in the fixed shaft 23 and the like can be easily released to the outside through the fixed shaft 23. Therefore, an increase in the temperature of the device can be suppressed.

The linear expansion coefficient of the stainless material is larger than the linear expansion coefficient of the ceramic material, and the rotating shaft 24 is formed from the stainless material, and the rotating shaft 24 is formed from the ceramic material. Therefore, when the rotating shaft 24 and the fixed shaft 23 generate heat, the gap between the fixed shaft 23 and the rotating shaft 24 can be increased, and the bearing friction torque between the fixed shaft and the rotating shaft can be reduced. Therefore, the radial bearing loss and the load on the motor 26 are reduced, and the rise in the device temperature can be further suppressed.

Further, the ceramic material has extremely excellent corrosion resistance, and herringbone grooves 23a are formed on the outer periphery of the fixed shaft 23.
The fixed shaft made of stainless steel
Corrosion that occurs when a groove is formed in 23 can be prevented.

Since the above effects can be obtained, the corrosion of the fixed shaft can be prevented while suppressing the temperature rise of the device, and the reliability of the device can be improved.

On the other hand, ceramics is a material having excellent wear resistance and self-lubricating properties. Since the fixed shaft 23 is made of this ceramic material, seizure and the like can be prevented, and bearing characteristics are improved. be able to.

Further, since the rotating shaft 24 is made of a stainless steel material, deterioration of the rotating shaft 24 can be prevented, and the performance can be maintained for a long period of time.

Further, since SUS420J2 having a linear expansion coefficient close to that of the ceramic material is used as the material of the rotating shaft 24, it is possible to prevent the gap between the fixed shaft 23 and the rotating shaft 24 from becoming extremely large. A decrease in the performance of the radial bearing can be prevented.

Further, the fixed shaft pedestal 22 and the fixed shaft 23
3 is constituted by a pedestal-integrated fixed shaft 40 integrally formed as shown in FIG. 3, the structure can be simplified, the weight can be reduced, and the cost can be reduced.

For comparison with this embodiment, a description will be given of a problem when the fixed shaft and the rotating shaft are made of the following two materials.

As a first comparative example, when both the fixed shaft and the rotating shaft are made of a ceramic material, the hardness of the ceramic is very high, so that the precision machining of the inner diameter of the hollow rotating shaft becomes very difficult, and the cost is reduced. Increase. Also,
It is difficult to fix the polygon mirror to the rotating shaft made of ceramic material, and the difference between the coefficient of linear expansion of the material of the polygon mirror and the coefficient of linear expansion of the ceramic material is very large. It is.

As a second comparative example, when the fixed shaft is made of a metal material such as stainless steel and the rotating shaft is made of a ceramic material, in addition to the disadvantages of the first comparative example, heat escapes from the fixed shaft in the same manner as in the prior art. Becomes difficult, the equipment temperature rises,
Corrosion (rust, etc.) occurs from the dynamic pressure generating groove of the fixed shaft. Further, since the linear expansion coefficient of stainless steel is larger than the linear expansion coefficient of ceramics, a gap (about several μm) between the two becomes small due to the temperature rise of both. Therefore, the radial bearing loss is further increased, the gap is further reduced, and contact and seizure occur.

[0033]

According to the present invention, since the fixed shaft is made of a ceramic material, when heat is generated by driving the motor, the heat generated on the rotating shaft, the fixed shaft and the like is transmitted to the outside via the fixed shaft. It can be easily released, and the temperature rise of the device can be suppressed.

The linear expansion coefficient of the stainless material is larger than the linear expansion coefficient of the ceramic material, and the rotating shaft is composed of the stainless material and the fixed shaft is composed of the ceramic material. Thus, the gap between the fixed shaft and the rotating shaft can be made slightly larger, and the bearing friction torque between the fixed shaft and the rotating shaft can be reduced. As a result, the radial bearing loss and the load on the motor can be reduced, and the effect of suppressing the temperature rise of the device can be enhanced.

Furthermore, even if the ceramic material has extremely excellent corrosion resistance, even if a groove is formed on the outer periphery of the fixed shaft, the occurrence of corrosion from the groove can be prevented.

Therefore, corrosion of the fixed shaft can be prevented while suppressing a rise in the temperature of the device, and the reliability of the device can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing one embodiment of a dynamic pressure air bearing type rotating device according to the present invention.

FIG. 2 is an exploded perspective view showing a fixed shaft and a fixed shaft pedestal in FIG.

FIG. 3 is a perspective view showing another embodiment of the fixed shaft and the fixed shaft pedestal in FIG. 1;

FIG. 4 is a sectional view of a conventional dynamic pressure air bearing type rotating device.

FIG. 5 is a cross-sectional view of another conventional dynamic air bearing rotary device.

[Explanation of symbols]

 21 Housing 23 Fixed shaft 23a Herringbone groove (groove) 24 Rotary shaft 25 Thrust magnetic bearing (thrust bearing) 26 Motor 29 Polygon mirror (rotating body)

Continuation of the front page (56) References JP-A-1-275913 (JP, A) JP-A-4-54307 (JP, A) JP-A-1-69909 (JP, U) (58) Fields surveyed (Int) .Cl. ⁷ , DB name) F16C 17/02

Claims (1)

(57) [Claims] 1. A housing, a fixed shaft fixed to the housing and having a groove on an outer periphery, a cylindrical rotating shaft provided to surround the fixed shaft and rotatably supported by the fixed shaft;
A thrust bearing that supports the rotating shaft in the thrust direction, a motor that drives the rotating shaft, and a rotating body that is supported by the rotating shaft, wherein the rotating shaft is supported in the radial direction by air dynamic pressure generated by the groove of the fixed shaft. The fixed shaft is made of a ceramic material made of SiC or alumina, the rotating shaft is made of a martensitic stainless steel material, and the linear expansion coefficient of the rotating shaft is the same as that of the fixed shaft. A dynamic pressure air bearing, wherein a bearing gap is set so as to be larger than a linear expansion coefficient, and the dynamic pressure bearing gap is widened as the temperature of the device increases, and a part of the fixed shaft is exposed to the outside of the housing. Mold rotating device.