Dynamic information storage or retrieval – Dynamic mechanism subsystem – Specific detail of storage medium support or motion production
Reexamination Certificate
2001-02-26
2003-04-22
Davis, David (Department: 2652)
Dynamic information storage or retrieval
Dynamic mechanism subsystem
Specific detail of storage medium support or motion production
C360S099080
Reexamination Certificate
active
06552992
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an automatic balancing mechanism and, more particularly, to an automatic balancing mechanism for a disk driver free from vibrations due to a characteristic angular velocity of a rotor.
DESCRIPTION OF THE RELATED ART
A driving mechanism is, by way of example, incorporated in an optical disk memory system, and an optical disk is driven for rotation by the driving mechanism.
A typical example of the disk driving mechanism is illustrated in
FIG. 1
of the drawings. An electric motor
1
has a rotor
2
, and the rotor
2
is rotated around an axis
3
of rotation. A turn table
4
is fixed to the rotor
2
, and is driven for rotation by the electric motor
1
. A pulley
5
is movable in the direction of axis
3
, and magnetic force or elastic force of a spring is exerted on the pulley
5
, and presses an optical disk
6
against the turn table
4
. While the rotor
2
is turning around the axis
3
, the turn table
4
, the pulley
5
and the optical disk
6
turn around the axis
3
together with the rotor
2
. Thus, the turn table
4
, the pulley
5
and the optical disk
6
turn together, and assume to have a center of gravity. If the center of gravity is aligned with the axis
3
, any unbalance does not take place, and the turn table
4
, the pulley
5
and the optical disk
6
are stable during the rotation. However, the turn table
4
, the pulley
5
and the optical disk
6
are assembled and disassembled at every usage, and it is impossible to make the center of gravity aligned with the axis
3
at all times. Thus, the unbalance is unavoidable, and is causative of vibrations during high-speed rotation. The magnitude of vibrations is dependent on the amount of unbalance and the rotating speed. The distance between the axis
3
and the center of gravity and the weight of the assembly
4
/
5
/
6
affect the amount of unbalance.
The disk driving mechanism has been designed to rotate the disk at relatively low speed, and the centrifugal force due to the unbalance is relatively small. Even though the optical disk
6
vibrates due to the unbalance of the assembly
4
/
5
/
6
, a data read-out head (not shown) exactly reads out data bits from the optical disk. For this reason, any anti-vibration means is not provided for the prior art disk driving mechanism.
Data access speed is getting faster and faster, and a constant linear velocity disk driving mechanism drives the optical disk at 6000 rpm during a data access to an inside area. When the optical disk is driven for rotation at more than 4000 rpm, the vibrations due to the unbalance becomes serious, and the read-out head falls into an error in the data read-out. Thus, a suitable anti-vibration means is required for the high-speed disk driving mechanism.
An automatic balancing mechanism is well known in the field of mechanical dynamics. For example, an automatic balancing mechanism is introduced in the book entitled as “Mechanical Dynamics”, and
FIG. 2
illustrates the automatic balancing mechanism. A circular groove
10
is formed in a disk
11
integral with a rotor, and two balls
12
/
13
are movable along the circular groove
10
. When the disk
11
is driven for rotation, the centrifugal force F is exerted on each ball
12
/
13
, and is given by equation 1.
F=m r &ohgr;
2
Equation 1
Where m is the mass of the ball
12
/
13
, r is the radius of curvature of the circular groove and &ohgr; is the angular velocity. The component force F
1
in X direction and the component force F
2
in Y direction are expressed by equations 2 and 3.
F
1
=m r &ohgr;
2
sin &agr; Equation 2
F
2
=m r &ohgr;
2
cos &agr; Equation 3
where &agr; is the angle between X-axis and the line drawn between the ball
12
/
13
and the center S of the disk
11
. If the center of gravity G of the rotor is deviated from the center S of the disk
11
by distance
e
, unbalance takes place, and the centrifugal force F
3
due to the unbalance is given by equation 4.
F
3
=Me&ohgr;
2
Equation 4
where M is the mass of the rotor. If the centrifugal forces F are balanced with the centrifugal force F
3
, the balance in Y-direction is expressed as
F
1
+(−
F
1
)=0 Equation 5
The component force F
1
exerted on the ball
12
cancels the component force F
1
exerted on the other ball
13
. On the other hand, the component forces F
2
exerted on the balls
12
/
13
are balanced with force F
3
, and the balance in X-direction is expressed as
m r &ohgr;
2
cos &agr;=Me&ohgr;
2
Equation 6
Therefore, the balls
12
/
12
are positioned at certain positions satisfying equation 6.
When the automatic balancing mechanism
11
/
12
/
13
is simply used for the prior art disk driving mechanism
1
/
4
/
5
/
6
incorporated in the optical data storage system, serious vibrations suddenly take place in the assembly
4
/
5
/
6
. The serious vibrations are derived from the characteristic angular velocity as follows.
FIGS. 3A and 3B
illustrate two kinds of relative relation between the center of gravity G and the balls
12
/
13
. Point “O” is indicative of the center of bearings supporting the rotor, and the component force N in the normal direction and the component force T of the tangential direction form the centrifugal force F.
If the angular velocity &ohgr; is less than the characteristic angular velocity &ohgr; 0, the center of gravity G is on the same side as the balls
12
/
13
with respect to the center S as shown in FIG.
3
A. In this situation, the component forces N are balanced with the reaction from the disk
11
, and the component forces T make the balls
12
/
13
closer to each other. Then, the unbalance takes place, and is increased together with the positions of the balls
12
/
13
.
On the other hand, if the angular velocity &ohgr; is greater than the characteristic angular velocity &ohgr;0, the center of gravity G is on the line between the center S and the center O as shown in FIG.
3
B. In this situation, the component forces N are also balanced with the reaction from the disk
11
, and the component forces T cause the balls
12
/
13
to place at the appropriate positions shown in FIG.
2
. Then, the center S is coincident with the center O, and the component forces T are decreased to zero.
When the electric motor
1
is energized, the electric motor
1
increases the angular velocity &ohgr;, and the angular velocity &ohgr; exceeds over the characteristic angular velocity &ohgr;0. While the electric motor
1
is increasing the angular velocity &ohgr; under the characteristic angular velocity &ohgr;0, the automatic balancing mechanism
11
/
12
/
13
and the prior art disk driving mechanism
1
/
4
/
5
/
6
/ are established in the relative relation shown in
FIG. 3A
, and the serious vibrations take place. Even after the angular velocity &ohgr; exceeds over the characteristic angular velocity &ohgr;0, there is a possibility to move the balls
12
/
13
from the positions shown in
FIG. 3B
to the positions shown in
FIG. 3A
, and the movement causes the serious vibrations to take place.
SUMMARY OF THE INVENTION
It is therefore an important object of the present invention to provide an automatic balancing mechanism which prevents a driving mechanism from vibrations due to the characteristic angular velocity.
To accomplish the object, the present invention proposes to forcibly locate the center of gravity at a certain point opposite to movable weight members.
In accordance with one aspect of the present invention, there is provided an automatic balancing mechanism associated with a rotor driven for rotation around a rotating axis comprising a first weight means associated with the rotor so as to make a center of gravity offset from the rotating axis of the rotor, a stopper means stationary with respect to the rotor and defining a first moving path on the opposite side to the first weight means and the center of gravity with respect to a virtual line perpendicular to the rotating axis, and a plurality
Kitamura Kazuhiko
Takeuchi Makoto
Davis David
Scully Scott Murphy & Presser
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