Disk drive motor

DETAILED DESCRIPTION Accordingly, it is an object of the present invention to provide a disk drive motor of which impairment of rotational performance, in particular run-out of the rotary part of the motor, is suppressed at high speed operation of the motor.
Another object of the present invention is to provide a disk drive motor that offers high rotational performance while accommodating dimensional errors of the motor and disk.
It is still another object of the present invention to provide a disk drive motor which can be fabricated at reduced costs but yet is capable of operating with high rotational performance.
To attain those objects, a disk drive motor according to the present invention comprises a rotor having an annular space formed therein coaxially with the axis of rotation, and balancing members accommodated in the annular space and capable of changing its mass distribution circumferentially along the circle of the annular space.
When the motor speed is low, the balancing members assume random positions within the annular space.
As the motor is driven at speed beyond a predetermined value, the balancing members distribute at equal spaces along the radially outer circumferential surface of the annular space, due to effect of centrifugal force.
In case of any imbalance occurring during the rotation, the balancing members temporarily gather to a portion of the annular space where the mass imbalance is taking place.
However, when the motor speed exceeds the value at which resonance takes place due to coincidence between the frequency of the vibration of the balancing members and the natural frequency of the motor, the balancing members move to a position symmetrical with the point of mass imbalance to eliminate the mass imbalance, thereby suppressing the run-out.
The drive motor may have means for urging the balancing members radially inward so as to prevent the random movement of the balancing members during low-speed operation of the motor.
Such urging means effectively urges the balancing members towards the radially inner end of the annular space, thereby reducing vibration and noise which otherwise may be produced due to random movement of the balancing members within the annular space during low-speed operation of the motor