Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-04-27
2001-10-23
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
Reexamination Certificate
active
06307295
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a complex bearing apparatus that incorporates a radial hydrodynamic bearing and an axial magnetic bearing. Also, the present invention relates to a spindle motor that incorporates the complex bearing assembly or mechanism.
BACKGROUND OF THE INVENTION
A complex bearing assembly or mechanism, which includes a hydrodynamic bearing for the radial support and a magnetic bearing for the axial support, has widely been employed as one component of a spindle motor for use in a magnetic memory device such as hard disc drive and a laser scanner for attaining a high-speed and high-precision rotation of the motor.
In this conventional complex bearing assembly, in particular a frictional wear at the radial dynamic bearing has been considered as a problematic matter that should be solved. Specifically, at the very beginning of the rotation of the motor in which the rotational speed of the motor has not been increased enough, the hydrodynamic pressure generated in the radial bearing is still small. Disadvantageously, this results in a continuous and/or discontinuous frictional contact in between a support member and a rotatably member supported for rotation, e.g., a fixed sleeve and a shaft inserted in the sleeve. Then, when the rotational speed of the motor is increased to a certain extent and, thereby, a rotational axis of the rotating member is stabled, the frictional contact between the support and rotatable members will come to an end.
As is known in the art, the frictional contact results in a frictional wear that decreases a durability of the spindle motor. The frictional wear depends upon the transitional rotational speed at which the frictional contact between the shaft and the sleeve comes to an end. That is, the frictional wear increases in proportion to the transitional rotational speed. This in turn means that, in order to attain a highly reliable bearing assembly and spindle motor having such bearing assembly, the transitional rotational speed is required to be minimized.
In the meantime, in the complex bearing assembly in which the shaft is extended vertically, a load or gravity of a rotational portion or rotor of the bearing assembly acts on the axial bearing and a centrifugal force caused by an unbalanced force of the rotor acts on the radial bearing. Also, no static force acts in a certain direction on the radial bearing, which in turn means that a portion where the radial bearing receives the centrifugal force moves with the rotation of the rotor.
Therefore, when the rotor rotates at a relatively low speed, the centrifugal force due to the unbalanced force of the rotor is greater than the hydrodynamic force derived in the radial bearing, which allows the sleeve to contact with the shaft. The contact portion between the shaft and sleeve moves around the shaft continuously. If the contact could be retained until a relatively high rotational speed of rotor, an increased contact force or energy consumption between the contacting rotor and shaft will provide a significant wear or damage to both rotor and shaft.
A most effective way to solve those problems is to increase the hydrodynamic force at the lower rotational speed of the rotor. In general, the hydrodynamic force changes according to diameter, length, and eccentricity of the bearing members and clearance between opposing sleeve and shaft. Specifically, the hydrodynamic force increases with the increase of diameter and length and the with the decrease of the clearance. The increase of the diameter and length results in an increase of the size of the motor and a system incorporating the motor, which fails to meet the current tendency of a compactness of the device. Also, a reduction in clearance requires a significant precision for the manufacturing of the shaft and sleeve. Further, the eccentricity, which is determined by the unbalanced mass, can not be controlled in practice.
On the other hand, the increase of diameter, length, or the decrease of clearance may result in a great increase of the rotational friction or resistance, which gives rise to an increase of power consumption by the motor that incorporates such bearing. In addition, the conventional hydrodynamic bearing, which changes its performance with the temperature at use, decreases its threshold rotational number for an instability such as half frequency whirl.
SUMMARY OF THE INVENTION
Accordingly, a complex bearing assembly as well as a spindle motor incorporating the complex bearing assembly of the present invention includes a base member, a first cylindrical member having a cylindrical outer periphery defined therein, and a second cylindrical member having a cylindrical inner periphery defined therein. The inner periphery has a greater diameter than that of the outer periphery of the first member so that the outer periphery of the first member is positioned in the inner periphery of the second member. Also, one of the first and second cylindrical members is fixed to the base member so that the other of the first and second cylindrical members rotates relative to the fixed member.
The assembly includes a radial bearing formed by the inner and outer peripheries. The radial bearing allows the rotatable cylindrical member to be supported between inner and outer peripheries in a radial direction relative to the fixed cylindrical member by means of a hydrodynamic force generated in a rotational movement of the rotatable cylindrical member. The assembly further includes an axial bearing. The axial bearing has a first magnetic member secured on the rotatable cylindrical member and extended around a rotational axis of the bearing assembly, and a second magnetic member secured on the fixed cylindrical member and extended around the first magnetic members while leaving a space therebetween. This causes the first and second magnetic members to cooperate to generate a magnetic force therebetween for supporting the rotatable member in an axial direction relative to the fixed cylindrical member. In particular, one of the first and second magnetic member is positioned in a coaxial fashion with the rotational axis of the bearing assembly and the other of the first and second magnetic member is positioned in an eccentric fashion with the rotational axis of the bearing assembly.
Also, a process for manufacturing the complex bearing assembly has providing an assembled complex bearing assembly. The complex bearing assembly includes a first member and a second member supported for rotation relative to the first member by radial and axial bearings. In particular, the process further includes measuring a rotational number of the second member at which the second member, after it is started rotating, becomes to lose frictional contacts with the first member.
REFERENCES:
patent: 3746407 (1973-07-01), Stiles et al.
patent: 4523800 (1985-06-01), Yamashita et al.
patent: 4988906 (1991-01-01), Littlefield
patent: 5448121 (1995-09-01), Tada
patent: 5822846 (1998-10-01), Moritan et al.
patent: 6066903 (2000-05-01), Ichiyama
Komura Osamu
Murabe Kaoru
Otsuki Makoto
McDermott & Will & Emery
Nguyen Tran
Sumitomo Electric Industries Ltd.
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