Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-01-04
2001-04-10
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S06700R, C384S107000, C384S112000, C384S113000
Reexamination Certificate
active
06215217
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to a high-speed motor such as a polygon mirror, a hard disc and, in particular, relates to a vibration attenuation technique for a motor in which a dynamic pressure bearing is used as a radial bearing.
2. Related Art
Of various kinds of motors, the motor disclosed in Japanese Patent Unexamined Publication No. Sho. 64-3318, for example, employs an air dynamic pressure bearing as a radial bearing so that a rotor is floated to the thrust direction by utilizing magnetic force generated between a magnet disposed on a rotor side and a magnet disposed on a stator side. Thus, since the rotor is in a completely non-contact state during the rotation thereof, the rotor can be rotated at a high speed. In such an arrangement, an annular air chamber for an air damper is formed between a fixed shaft and the rotor in a manner that the air chamber is communicated with the outside through a small hole (orifice). According to such an arrangement, the motor can be provided with an air damper by the small hole and the annular air chamber for an air damper, so that the vertical vibration of the rotor can be suppressed due to the resistance of the air when passing through the small hole.
Further, Japanese Patent Unexamined Publication No. Hei. A-8-196056 discloses a motor in which the effect similar to that of the aforesaid publication is obtained by forming grooves extending from an annular air chamber for an air damper to the outside with respect to a dynamic pressure portion in stead of a small hole forming the air damper.
In order to constitute such an air damper, a small hole or grooves serving as an orifice is required. However, in the case of forming such a hole by the drill processing like the prior art, the minimum diameter ø and length of the hole are limited to about 0.4 mm and 5 mm, respectively, even if it is desired to made them smaller. Further, in the case of combining a member having been subjected to such a hole making process with another member by means of a screw etc. thereby to form an annular air chamber for an air damper, there arises a case that the annular air chamber for an air damper communicates with the outside through the combined surface and the chamber does not serve as a damper. Furthermore, as the motor is further miniaturized, it is required to make the resistance of the flow path of the orifice of the air damper larger. Thus, although a narrow long hole is required as the orifice, it is difficult to form such a small and narrow hole by the normal boring process.
In the case of forming the groove at the dynamic pressure generating portion, there arises a problem that the rigidity of a dynamic pressure bearing is degraded.
SUMMARY OF INVENTION
In view of the aforesaid problem of the prior art, an object of the present invention is to provide a motor with a built-in air damper which can freely set a damping factor of vertical vibration of a rotor with a small number of parts and without performing a complicated and troublesome processing.
According to an aspect of the present invention, there is provided a dynamic pressure bearing motor comprising:
a stator having a stator core around which a driving coil is wound and a fixed shaft;
a rotor having a center hole in which said fixed shaft is inserted and a rotor magnet opposing to said stator core;
thrust bearing means, provided at each of said rotor and said stator, for supporting said rotor to thrust direction by magnetic force acting mutually therebetween;
radial bearing means for supporting said rotor to radial direction by dynamic pressure generated between outer peripheral surface of said fixed shaft and inner peripheral surface of said center hole;
a dynamic pressure generation portion defined by said radial bearing means and generates the dynamic pressure between said outer peripheral surface of said fixed shaft and said inner peripheral surface of said center hole;
an annular air chamber for an air damper communicating with said dynamic pressure generation portion; and
an annular clearance for communicating said annular air chamber for an air damper with external air, wherein said dynamic pressure generation portion, said annular air chamber for an air damper and said annular clearance for the air damper are disposed in this order along axial direction of said rotor.
As described above, according to the motor of the present invention, when the rotor rotates, the stator
40
and the rotor
20
are placed in the non-contact state to each other by the dynamic pressure generated at the dynamic pressure generation portion. Further, when the motor starts rotating, the rotor is held at the magnetically balanced position in the thrust bearing. In this state, since the stator and the rotor are placed in the completely non-contact state to each other, the rotor can be rotated at a high speed and the life time of the motor can be elongated. Since the rigidity of the thrust bearing utilizing the magnetic force is relatively small, the rotor vibrates vertically due to the external force etc. applied thereto. However, in the present invention, when the rotor vibrates vertically due to the disturbance along the axial direction of the motor shaft applied thereto, the exhausting and entering of the air through the narrow annular clearance for the air damper between the external and the annular chamber for the air damper generates the friction of the air. As a result, the vibration energy of the rotor along the vertical direction is absorbed by the friction, so that the vibration of the rotor can be suppressed. Further, according to the damper formed in the motor of this embodiment, the size of the space and the length along the axial direction of the motor shaft of the annular clearance for the air damper can be designed freely depending on how the outer peripheral surface of the fixed shaft and the inner peripheral surface of the center hole of the rotor are shaped. Accordingly, it is possible to constitute the motor having desired damping factor of the vibration of the rotor along the vertical direction.
REFERENCES:
patent: 4798476 (1989-01-01), Sakatani et al.
patent: 5018880 (1991-05-01), Nakasugi et al.
patent: 6064130 (2000-05-01), Konno et al.
patent: 64-3318 (1989-01-01), None
patent: 8-196056 (1996-07-01), None
Kabushiki Kaisha Sankyo Seiki Seisakusho
Nguyen Tran
Sughrue Mion Zinn Macpeak & Seas, PLLC
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