Dynamic information storage or retrieval – Dynamic mechanism subsystem – Specified detail of transducer assembly support structure
Reexamination Certificate
1999-04-27
2001-07-10
Miller, Brian E. (Department: 2754)
Dynamic information storage or retrieval
Dynamic mechanism subsystem
Specified detail of transducer assembly support structure
C369S044140
Reexamination Certificate
active
06259671
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an object lens actuator for use in optical disk units, and in particular to an object lens actuator which is characterized by a vibration control arrangement for suppressing undesired resonant vibrations.
BACKGROUND OF THE INVENTION
In a conventionally known optical head for use in an optical disk unit or a magneto-optical disk unit, to the end of accurately converging a light beam upon each track on a disk, and collecting the light reflected therefrom with a light receiving element, a moveable member carrying an object lens is supported by a base member via four sheet springs at a neutral position so as to be moveable in both the focusing and tracking directions, and the moveable member is actuated in a controlled manner by using a magnetic actuator consisting of a focusing coil, tracking coils, and permanent magnet pieces.
In such an optical head, spurious vibration modes of the spring system supporting the moveable member and the angular error of the object lens with respect to the optical axis in a low frequency range tend to impair the accuracy in converging the light beam, and this could lead to read/write errors.
In particular, there has been a growing demand to increase the rotational speed of the disk in the optical disk unit or the magneto-optical disk unit, and the response speed of the head to achieve a higher access speed, and this makes the problems associated with the vibration of the moveable member in a floating support even more serious.
It is possible, as proposed in Japanese patent laid open publication No. 7-78437 for instance, to arrange the moveable member and the coils symmetrically with respect to the optical axis, and to make the point of application of the inertial force on the moveable member coincide with the point of application of the restoring force of the spring and the electronic drive force as accurately as possible so that such undesired vibrations may be minimized. However, in such an optical head which is not adapted to place the object lens at an extreme end of the moveable part, compact and light-weight design involves some difficulty. For this reason, a design which would allow the moveable member and the coils to be arranged in an asymmetric pattern is more desirable.
For instance, the arrangement proposed in Japanese patent laid open publication No. 6-325387 comprises a main body having a relatively large vertical through hole for receiving a core standing upright from a base member, and a support piece for the object lens which extends from the main body in a direction perpendicular to the focusing direction, the focusing coil and the tracking coils being retained inside the vertical through hole. However, the support piece for the object lens tends to have a reduced thickness, and the vibration of this part could lead to a problem.
For instance, Japanese patent laid open publication No. 5-197991 discloses an arrangement in which a so-called inertia damper using a spring and a mass is used for controlling the rotation in a direction perpendicular to the focusing direction. It may be conceivable to apply this arrangement to that including an object support piece extending from the main body, and use the inertia damper to directly control the vibration of the support piece. However, it is difficult to install the inertia damper without involving optical interferences. Also, the structure tends to be highly complex while the moveable part tends to be both bulky and heavy, and the freedom in design would also be restricted.
According to the object lens actuator employing a moveable member having an object lens support piece extending from the spring-supported main body in a direction perpendicular to the focusing direction which is disclosed in Japanese patent applications Nos. 8-250982 and 8-250983 (Japanese patent laid open publications Nos. 10-79128 and 10-79129) filed by the applicant of this application, an impact damper consisting solely of a spring or consisting of a spring and a mass extends from the main body so as to strike and move away from the support piece when the main body vibrates. The impact damper vibrates and strikes the support piece in an opposite phase from that of the support piece. This suppresses higher resonant frequency vibrations of the support piece, and controls the vibration of the moveable member supporting the object lens with the result that the rotational speed of the disk and the head speed may be increased. However, this arrangement requires a certain mounting space around the object lens because the impact damper is required to be adjacent to the object lens support piece, and the moveable part tends to be undesirably bulky and massive, although not so much as an inertia damper.
BRIEF SUMMARY OF THE INVENTION
The present invention was made in view of such problems of the prior art, and its primary object is to provide an object lens actuator which can reduce the peak value of the higher frequency resonant vibration of the moveable member supporting the object lens and to thereby control the vibration thereof without increasing the overall weight so that the rotational speed of the disk and the head speed may be increased, and the access speed and storage density of the optical disk unit or the magneto-optical disk unit may be increased.
The inventors of this application have noted that in the arrangement where the shape of the moveable member and the coil mounting positions are asymmetric, because the mass of the moveable part is offset toward the object lens, a mass is required to balance the mass of the moveable part.
According to the present invention, such an object can be accomplished by providing an object lens actuator including a moveable member, the moveable member comprising: a main body resiliently supported on a base member by a spring member at a neutral position so as to be moveable in both a focusing and tracking directions, and having a focusing coil and a tracking coil; an object lens support piece extending from the main body in a direction perpendicular to the focusing direction; and a mass balancer for placing a gravitational center at a prescribed position; characterized by that: the mass balancer is provided with a resonant vibration mode which substantially agrees with a higher resonant frequency of the moveable part but is opposite in phase.
Thus by utilizing the mass balancer for placing the gravitational center of the moveable part of the actuator at a desired location, and giving it a resonant mode having a same resonant frequency as a higher resonant frequency of the actuator and an opposite phase, the peak values of the higher resonant vibrations of the moveable part of the object lens actuator can be reduced without increasing the necessary mounting space, the number of component parts or the overall weight.
REFERENCES:
patent: 4568142 (1986-02-01), Iguma
patent: 5107409 (1992-04-01), Tadokoro
patent: 5446721 (1995-08-01), Sekimoto
patent: 5453881 (1995-09-01), Suzuki
patent: 5479386 (1995-12-01), Takeshita
patent: 5602808 (1997-02-01), Futugawa et al.
patent: 5719834 (1998-02-01), Futugawa et al.
patent: 5844881 (1998-12-01), Kasuga et al.
patent: 6069867 (2000-05-01), Ikegame
patent: 0426441 (1991-05-01), None
patent: 0553551 (1993-08-01), None
patent: 0594139 (1994-04-01), None
patent: 0311489 (1989-12-01), None
patent: 4-245033 (1992-09-01), None
patent: 5-197991 (1993-08-01), None
patent: 6-325387 (1994-11-01), None
patent: 7-78437 (1995-03-01), None
patent: 10-79129 (1998-03-01), None
patent: 10-79128 (1998-03-01), None
Altman, III Franklin D.
Miller Brian E.
NHK Spring Co. Ltd.
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