Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1998-05-27
2001-07-24
Klimowicz, William (Department: 2754)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
Reexamination Certificate
active
06266300
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an optical deflection device for deflecting a light beam, such as a laser beam, which is used, for example, as an element of an optical system for recording digital data on and reading the recorded digital data from an optical disk or optical-magnetic disk, and, in particular, to such an optical deflection device having an electromagnetic driver assembled therein for rotationally driving an optical deflection element, which deflects a light beam made incident thereon.
2. Description of the Related Art
As a representative optical deflection device, a galvano-mirror device is well known. The galvano-mirror device comprises a yoke member, a movable member rotatably supported by the yoke member through the intermediary of a pair of resilient elements, an optical deflection element, such as a prism, a mirror or the like, securely attached to the movable member, and an electromagnetic driver for rotationally driving the movable member with respect to the yoke member.
The electromagnetic driver includes a pair of permanent magnets provided on the yoke member, and an electromagnetic coil provided on the movable member and interposed between the permanent magnets. The electromagnetic coil is disposed in a magnetic field, generated by the pair of permanent magnets, and the movable member, carrying the optical deflection element, is rotated in accordance with Fleming's Rule, when the electromagnetic coil is electrically energized.
In general, there is a demand for the optical deflection device to have a constructional compactness and for the movable member, and therefore the optical deflection element, to exhibit a high-speed drive capability. The high-speed drive capability of the optical deflection element depends upon a product of the magnetic flux density (B) of a magnetic field, produced by the permanent magnets, and a wire length (L) of the electromagnetic coil, i.e. B×L. An increase in the magnetic flux density (B) results in a bulkiness of the optical deflection device. Accordingly, the wire length (L) of the electromagnetic coil should be increased in order for the high-speed drive capability of the optical deflection element to be improved.
Nevertheless, the longer the wire length (L) of the electromagnetic coil, the larger a resistance and a self-inductance of the electromagnetic coil. Thus, it is difficult to improve the high-speed drive capability of the optical deflection element by merely extending the wire length (L) of the electromagnetic coil.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide an optical deflection device, having an electromagnetic driver assembled therein for rotationally driving an optical deflection element, wherein a high-speed drive capability of the optical deflection element can be efficiently and effectively improved without substantially increasing a bulkiness of the optical deflection device.
In accordance with the present invention, there is provided an optical deflection device comprising a base member, a movable member having an optical deflection element, such as a prism element, a reflective mirror element, a light-beam-deflecting hologram element or the like, a set of resilient support elements at the sides of the movable member and interposed between the base member and the movable member, such that the movable member is resiliently and movably supported by the resilient elements with respect to the base member, and an electromagnetic driver that rotationally drives the movable member with respect to the base member. The electromagnetic driver includes a first set of permanent magnets provided on the base member to produce a first magnetic field, and a second set of permanent magnets provided on the base member to produce a second magnetic field, and the first set of permanent magnets and the second set of permanent magnets are reversed arrangements such that the first magnetic field and the second magnetic field are reversed with respect to each other. The electromagnetic driver further includes a first electromagnetic coil provided on the movable member and disposed in the first magnetic field, a second electromagnetic coil provided on the movable member and disposed in the second magnetic field, and the respective first and second electromagnetic coils are electrically energized in the first and second magnetic fields in such a manner that electric currents flow through the first and second electromagnetic coils in opposite directions, whereby the respective first and second electromagnetic coils are subjected to rotational forces in the same rotational direction.
Preferably, the movable member comprises a holder portion for receiving the optical deflection element, resulting in a simple and compact arrangement of the optical deflection device. In this case, the first and second electromagnetic coils may be symmetrically provided on the holder portion about a vertical plane that includes the center of mass of the holder portion. The holder portion of the movable member may be cylinder-shaped.
Preferably, the permanent magnets in the first set are sector-shaped, and are associated with each other to surround the first electromagnetic coil, and the permanent magnets in the second set are sector-shaped, and are associated with each other to surround the second electromagnetic coil. In this case, the sector-shaped permanent magnets in each set are arranged such that opposite magnetic poles are opposing each other.
So that stable and reliable resilient and movable support of the movable member can be obtained, each of the resilient support elements may comprise a leaf-spring assembly which is formed from a plurality of leaf-spring elements arranged at uniformly angular intervals around an elastic-main-axis of the movable member.
The elastic-main-axis of the movable member may coincide with an inertial-main-axis of the movable member, to thereby ensure a stable and reliable rotational movement of the movable member. Alternatively, the elastic-main-axis of the movable member may coincide with a thrust-main-axis of the movable member, to thereby ensure a stable and reliable rotation of the movable member. Preferably, the elastic-main-axis of the movable member coincides with both the inertial-main-axis and the thrust-main-axis of the movable member, to thereby obtain a greater stability e and reliability of the movable member's rotational movement. Also, the leaf-spring elements are preferably identical to each other.
The optical deflection device may further comprise a set of releasable couplings, provided at the sides of the movable member, releasably connecting an end of the corresponding leaf-spring assembly to the movable member, whereby simple and correct mounting of the leaf-spring between the base member and the movable member can be obtained.
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Nishiyama Masataka
Tanaka Akihiro
Asahi Kogaku Kogyo Kabushiki Kaisha
Chen Tianjie
Greenblum & Bernstein P.L.C.
Klimowicz William
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