Seiko Instruments & Electronics Ltd.

Atsunobu Nakajima

Hiroyoshi Yamamoto

Ikuo Nanno

Seiji Hoshi

Hideo Hoshi

Chikara Miyata

Shigeru Inagaki

An apparatus actuates an objective lens in axial and circumferential directions through annular magnetic gaps which are formed by yokes and a magnet. In order to retain the objective lens in the neutral position in the circumferential direction, two or four magnetic pieces are mounted on a lens mount and disposed near the circumferetial ends of the annular magnetic gaps in which the force caused by the magnetic potential energy in the magnetic gaps acts on the magnetic pieces to pull them back in the direction of the magnetic gaps so that a magnetic spring for retaining the objective lens at the neutral position is formed by the magnetic pieces.

Apparatus for actuating objective lens

An axially focusable objective lens is retained in a neutral position in the axial focusing direction by means of at leaast one magnetic member disposed inside or near the ends of magnetic gaps formed by yokes and magnets. The magnetic member is mounted on the periphery of a retaining tube which carries the objective lens and is positioned in the magnetic gaps which exhibit a non-uniform magnetic field distribution so that the magnetic member is subjected to a force acting in a direction in which the potential energy becomes stable. This force is utilized as a magnetic spring in the axial focusing direction. The magnetic spring requires no additional space thereby enabling a reduction in the size of the actuator and achieving excellent temperature characteristics.

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Tokyo, Japan

Atsunobu Nakajima