The present invention relates to a disk drive device for rotating a disk-shaped replaceable storage medium at high speed for reproduction of or recording and reproduction of information, and more specifically to a disk drive device suitable for high speed rotation of disks including CD-ROM, DVD-ROM, DVD-RAM, MO, removable HDD and so on.
In conventional CD-ROM drive devices, causes for lowering positional accuracy are classified into two kinds: (1) vibrations caused by a spindle driving system and a pickup driving system, and (2) disturbing vibrations transmitted from the outside. Typical examples of the cause of the kind (1) includes vibrations due to unbalance of a rotating system, electromagnetic vibrations of a motor, and driving reaction force of the pickup driving system. One of the most important subjects in designing such devices is to ensure a required positioning accuracy despite of such causes for lowering positioning accuracy.
In particular, data transfer has recently been effected at high speed and so attended by high speed rotation of a disk, which involves vibrations due to unbalance of the above-mentioned rotating system.
Japanese Patent Unexamined Publication No. 3-86968 discloses, as a proposal for suppressing the vibrations due to unbalance, a magnetic disk device provided with an endless cylindrical balancing case, in which a fluid is filled to be movable, and which is mounted on an outer peripheral portion of a spindle part in such a manner as to be coaxial with a magnetic disk.
Data transfer speed has been increased in a disk drive device, which must deal with multi-media having a large volume of images and moving image information. High speed data transfer in a disk drive device can be achieved by (1) increasing the rotational speed of a disk and (2) increasing a signal detecting frequency of a servo system. In recent years, therefore, the above measure (1) has rapidly promoted high speed operation of spindle motors.
A problem associated with high speed rotation of a spindle motor is an increase in vibrations due to unbalance of a rotating system. In optical disk drive devices such as CD-ROM drive devices and the like, a disk serving as storage medium is characteristically replaceable. Disks are manufactured in large quantities by pressing, and so involve dispersion in thickness and concentricity between a clamp inside diameter and a disk outside diameter. Further, weight unbalance is caused due to printing of characters and patterns on a disk or to a label or the like applied on the disk for identification of the disk.
When a disk with such unbalance is rotated, unbalance vibration occurs due to inconsistency between a center of gravity of and an axis of rotation of a rotating system. A force F for generating such unbalance vibration is expressed by the following formula
F=mxc2x7xcex5xc2x7xcfx892xe2x80x83xe2x80x83(1)
where xcex5 is a distance between the center of gravity of and the axis of rotation of the rotating system, m is a mass of a rotating body, and xcfx89=a rotational frequency.
As seen from the formula (1), unbalance vibration is in proportion to the square of a rotational frequency, so that high speed rotation sharply increases the unbalance vibration. The unbalance vibration not only causes vibration of an optical pickup system to impede read/write of signals, but also causes generation of noises and vibration of a system itself, to which the device is mounted, thus remarkably lowering reliability of the system itself.
By the way, keeping step with the tendency of high speed data transfer, the disk rotation speed is becoming higher. In a 24xc3x97 speed or 32xc3x97 speed CD-ROM drive, for example, a disk is rotated at 5,000 to 7,000 rpm, which raises a problem of disk unbalance vibration as mentioned above.
To cope with this, there has been proposed an arrangement, in which a disk rotating mechanism is provided with an unbalance correcting mechanism comprising an annular-shaped groove and correcting bodies (correcting balls) adapted to roll within the groove. With this arrangement, a range of rotational frequency adequately exceeding the resonance point of elastic members supporting a driving system is used for operation, but forces acting on the correcting bodies become unstable around the resonance point such that, when the correcting bodies begin rolling within the groove, they will never stop rolling, and so vibrations caused due to rolling of the correcting bodies become problematic. Further, in the case where the disk rotation speed is low and the device is set vertical, dead loads on the respective correcting bodies are greater than centrifugal forces generated by rotation, resulting in a phenomenon that the correcting bodies fail to rise along the annular groove and behave violently in a lower part of the groove.
An object of the present invention is to provide a low vibration mechanism for rotation driving systems, which tend to be operated at high speed, and for suppressing vibrations produced at the time of low speed rotation and ensuring reliability in a disk drive device having a built-in unbalance correcting mechanism, such as CD-ROM drives of high data transfer.
In order to achieve the above object, the invention provides a disk drive device comprising a rotation driving mechanism for rotating a disk-shaped storage medium having an information recording surface, a head for at least reading an information on the storage medium, support members holding a base plate, on which the rotation driving mechanism and the head are mounted, correcting members for correcting unbalance of rotatingly movable parts including the storage medium, an unbalance correcting mechanism having a rolling groove in the rotation driving mechanism, and auxiliary member or members provided in the rolling groove for increasing or reducing rolling and sliding resistances of the correcting members on surfaces in the rolling groove, the auxiliary member or members making rolling and sliding resistances of the correcting members different between an outer side surface of the rolling groove, which serves as a track surface for the correcting members, and a bottom surface of the rolling groove. The rolling and sliding resistances of the correcting members on the bottom surface of the rolling groove are made larger than the rolling and sliding resistances of the correcting members on the outer side surface of the rolling groove.
Further, a rolling motion auxiliary member or members are provided in the rolling groove for assisting in rolling motion of the correcting members. The rolling motion auxiliary member or members comprise an annular-shaped elastic member or members provided at an outer side surface thereof with or without irregularities, and is provided on an inner peripheral side surface of the rolling groove.