Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-01-17
2002-11-12
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C369S256000, C360S099120, C417S423700
Reexamination Certificate
active
06479912
ABSTRACT:
RELATED PATENT APPLICATIONS
This application claims priority of Japanese Patent Application No. 2000-009409 filed on Jan. 18, 2000 and of Japanese Patent Application No. 2000-012256 filed on Jan. 20, 2000. The complete disclosures of both applications are hereby incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to an automatic balancing apparatus which reduces vibrations of a rotational shaft during the rotation of a rotor such as a motor.
BACKGROUND OF THE INVENTION
Many electric appliances, such as computers, are such that a rotor is rotated by a motor and the like. For example, a recording and regenerating apparatus placed in a computer and a CD player has a mechanism to rotate a disc as a recording medium. In recent years, such apparatus are required to accommodate super high speed rotations of 6,000 to 10,000 rpm. Therefore, vibrations of the rotor occur especially when it rotates at a high speed as the rotation exceeds the resonant frequency. The rotational vibration (end play) results in a variety of problems, such as tracking errors.
As a solution to the above issue, for example, a rotation control apparatus is suggested in Tokkai H10-257710.
FIG. 1
is a longitudinal section of a spindle motor to which the rotation control apparatus of Tokkai H10-257710 is attached.
FIG. 2
is a cross section of a main part of the rotation control apparatus.
As shown in
FIG. 1
, spindle motor
51
is comprised of: stator
53
which is fixed to hub
52
; rotor
54
which has permanent magnet
54
a
placed across from stator
53
; and spindle shaft
55
which is fixed to the center of rotation of rotor
54
. When stator
53
is magnetized as electricity flows therein, the magnetic field, which rotates rotor
54
, is generated between stator
53
and rotor
54
. As a result, rotor
54
rotates together with spindle shaft
55
.
Rotation control apparatus
56
, as shown in
FIGS. 1 and 2
, is comprised of case
57
, which is mounted to spindle shaft
55
such that spindle shaft
55
passes through the inside, and a turntable (not shown in the figures). Case
57
and the turntable rotate together with spindle shaft
55
.
A ring-shaped space is formed around the shaft inside case
57
, and magnet
58
is placed at the innermost portion of the space. Magnet
58
is bipolarly magnetized in the vertical direction (the axial direction of spindle shaft
55
). Additionally, a plurality of balancer balls
59
, made of a magnetic body, are placed on the outer circumference of magnet
58
in the space of case
57
. Balancer balls
59
are drawn up and fixed to the outer circumference of magnet
58
by the magnetic force.
With rotation control apparatus
56
as configured above, balancer balls
59
rotate together with spindle shaft
55
(or rotor
54
) while being fixed on the outer circumference of magnet
58
when spindle motor
51
is started. Once the rotational speed of spindle shaft
55
(or rotor
54
) gradually increases and exceeds the resonant frequency, balancer balls
59
are separated from magnet
58
and move towards the outer wall
57
a
of case
57
. As a result, the rotational vibrations of spindle shaft
55
(or rotor
54
) are reduced by the effect of balancer balls
59
.
As described above, the rotation control apparatus
56
of Tokkai H10-257710 reduces the rotational vibrations of spindle shaft
55
(or rotor
54
) when the rotational speed of spindle shaft
55
of spindle motor
51
increases and exceeds the resonant frequency. As a result, tracking errors and the like can be prevented.
However, such an apparatus has a configuration in which the outer circumference of magnet
58
is bipolarly magnetized in the axial direction such that balancer balls
59
are fixed to the outer circumference of magnet
58
when the rotation is less than the resonant frequency. Therefore, balancer balls
59
are not placed on the outer circumference of magnet
58
with equal distance from each other, for example bunching up together, when spindle motor
51
is suspended. As a result, the rotational center is deviated when the motor is resumed, causing a loss of balance in the rotation. Consequently, the rotational characteristics of the apparatus are lowered when the motor is in motion.
Moreover, balancer balls
59
are fixed on the spherical outer circumference of disc-shaped magnet
58
only by the magnetic force. This means that the force of magnet
58
to hold balancer balls
59
is weak in the tangential direction. Hence, fixation the fixing force (holding force) to balancer balls
59
is weak at the beginning of the rotation, and balancer balls
59
tend to shift in the circumferential direction with the centrifugal force at the beginning of the rotation. In addition to the deviation of the rotational center, bumping sounds are caused when balancer balls
59
collide with each other. Further, the shift of balancer balls
59
at the beginning of the rotation tends to amplify the vibration at the rotational center, causing a decrease in the rotational characteristics when the apparatus is started.
Rotation control apparatus
56
as described above reduces the rotational vibrations when the rotation of rotor
54
exceeds the resonant frequency. However, when the speed of rotor
54
continually increases and exceeds a given value, the apparatus can no longer control the vibration. In other words, a range of rotation in which balancer balls
59
shift in the circumferential direction but on the same radius line to reduce the rotational vibrations is limited to a given band of rotational frequencies. Therefore, once the rotation reaches the given speed, the effect of reducing the rotational vibrations cannot be performed.
One may reduce the rotational vibrations in a rotational range with higher speed by establishing the resonant frequency of rotor
54
higher than as described above. However, with such establishment, balancer balls
59
do not function to reduce the rotational vibrations until the speed reaches the resonant frequency, rather they increase the vibrations. Therefore, the rotational vibrations become at low rotation speed, less than the resonant frequency become an issue.
Hence, the present invention intends to provide an automatic balancing apparatus which prevents a decrease in the rotational characteristics when a motor is started by firmly fixing balancer balls on the outer circumference of a magnet with equal distance from each other when the motor is at rest.
Additionally, the present invention intends to provide an automatic balancing apparatus which reduce rotational vibrations corresponding to any rotational speed, such as in the case of the low speed rotation, when the rotation of the rotational body is less than the resonant frequency, and in the case of the super-high speed rotation, when the rotation exceeds a given value above the resonant frequency, as well as in any other cases.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, an automatic balancing apparatus is disclosed which comprises: a support shaft which is rotated by a drive; a case body which is fixed to the support shaft and which rotates together with the support shaft; a ring magnet which is placed at the inside corner, in the radial direction, of an inner space of the case body; and a balancing member, the balancing member further comprising a plurality of magnetic bodies which are movable in the inner space of the case body and which can be drawn up by the magnetic field of the ring magnet; wherein, when the rotational frequency of a rotor, which rotates together with the case body, exceeds the resonant frequency, the automatic balancing apparatus reduces vibrations of the rotor; and the outer circumference of the ring magnet has a flat portion.
In accordance with another aspect of the invention, an automatic balancing apparatus is disclosed which comprises: a support shaft which is rotated by a drive; a case body which is fixed to the support shaft and which rotates together with the support shaft; a ring magnet which is placed at the inside co
Higuchi Daisuke
Hock Yeoh Kian
Kikuchi Yoshimi
Dougherty Thomas M.
Mohandesi Iraj A
Reed Smith LLP
Sankyo Seiki Mfg. Co. Ltd.
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