| 摘要 |
PURPOSE:To drive an objective lens in the direction of optical axis by forming a magnetic field so that a part of the direction of magnetic flux line is made parallel with the optical axis of the objective lens and arranging a coil to cross the magnetic flux line not in paralllel with the optical axis of the objective lens in a magnetic field thereby utilizing a force component exerted on the coil. CONSTITUTION:Focus control coils 24, 25 are provided to a position biased to the outside of magnets 15, 16, then an outside part of both sides of the coil 24 placed in a direction vertical to the X axis crosses the magnetic flux line titled upward left to the X-Z axia plane, the inner side part crosses the upward magnetic flux line in parallel with the Z axis. Similarly, the outside of both sides of the coil 25 vertical to the X axis crosses the magnetic flux line at the down right direction of the X-Z plane and in parallel with the inner side and the Z axis downward. In flowing currents with equal amplitude in the direction as shown in the figure to coils 24, 25, forces F1, F2 along with the X axis are cancelled, and forces F'1, F'2 are generated to each side at the outside of both the coils 24, 25 crossing the magnetic flux line having a slope in the X-Z axis plane are generated, and objective lens 21 is driven in the Z axis with the forces of the F'1, F'2 and is moved downward in the focus direction to the disc. |
