| 摘要 |
PURPOSE:To eliminate the precession motion of a condenser lens to obtain always stable phase characteristics and to improve tracking servo characteristics by constituting a magnetic circuit so that the center of thrust generated in a tracking coil coincides approximately with the position of the center of gravity of the whole of a moving part including the condenser lens and equalizing spring forces of two, upper and lower flat springs for focus driving and setting the position of the center of gravity of the whole of the moving part in the about middle between fixing positions of two falt springs. CONSTITUTION:The magnetic circuit consists of a magnet 18 and a yoke 19, and the magnet 18 is so constituted that the surface magnetic field acts always with a width wider than that of a tracking coil 11 even if a condenser lens 9 is moved vertically in the focus direction. Spring forces K of two, upper and lower flat springs 15 are equal to each other, and the position of a gravity center G of the whole of the moving part including the condenser lens 9 is set in the middle between fixing parts of two flat springs 15. Further, the magnetic circuit is so arranged that the center A of thrust acting upon the tracking coil coincides approximately with the position of the gravity center G.
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