JPH0212618A - Objective lens driving device - Google Patents

Abstract

PURPOSE:To strengthen tortional rigidity in a track direction and to obtain a stable servo characteristic by making concave a surface facing the magnet of a yoke. CONSTITUTION:The surface facing a magnet 7 of a yoke 10 is formed to be a concave surface 11 so that a magnetic gap 9 length may become shorter from the center of the yoke 10 to a side edge. Consequently, a magnetic flux density in the magnetic gap 9 always has a constant value in the track direction. An objective lens 1, a movable part 2, wires 3a to 3d, a fixed part 4, a focus coil 5, track coils 6a to 6d, the magnet 7 and a yoke 8b are in the same constitution as usual. Thus, the tortional rigidity in the track direction is strengthened, and the stable servo characteristic can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an objective lens driving device in an optical disk device, and more particularly to a magnetic circuit for driving the objective lens.

[Prior Art] Conventionally, in this type of objective lens driving device, as shown in FIG. A supporting stationary member 4 is provided, and a focus coil 5 for driving in the focus direction and a pair of track coils 8a, 6b, 6c, and 6d for driving in the track direction are formed in the movable portion 2.

In addition, at both ends of the movable part 2, the magnet 7 and the yoke 8a,
A magnetic circuit consisting of 8b is provided.

The movable section 2 is driven upward in the r direction by passing a drive current through the focus coil 5, and in the left and right directions by passing a drive current through the track coils 6a, 6b, 8c, and ad.

[Problems to be Solved] The conventional objective lens driving device described above has a magnetic gap 9 forming a magnetic circuit for driving the objective lens l.
Since the yoke 8a is formed of a flat surface, the magnetic flux density in the magnetic gap 9 decreases as it deviates from the center in the track direction compared to the center of the magnetic gap.

That is, as shown in FIG. 5, the magnetic flux density is.

In the magnetic gap 9, the central part in the track direction is high and the part around the circumference is low. This is thought to be due to the increase in leakage magnetic flux in the surrounding area, which increases magnetic resistance.

Therefore, when the objective lens l is in a stationary state, as shown in FIG. 6, a pair of track coils 6a.

6b is placed symmetrically with respect to the center line A of the magnetic circuit in the track direction, and the coverage generated in the track direction is balanced. However, as shown in FIG. 7, when the objective lens l moves in the track direction (rightward in the figure), the track coil 6b moves in the direction of high magnetic flux density,
The track coil 6a moves in a direction where the magnetic flux density becomes lower.

Therefore, if the same 'li flow is applied, the force generated in the tiger shift coil 6b will be greater than the force generated in the track coil 6a, and the coverage will be lost, so the torsional rigidity in the track direction will be weakened. In consideration of the above-mentioned problems, the moon was created by forming the surface of the yoke that faces the magnet into a concave shape, which keeps the magnetic flux density in the magnetic gap constant in the track direction. To provide an objective lens driving device in which the force generated in each track coil is always constant even if the objective lens moves in the track direction.

[Means for Solving the Problems] In order to achieve the above object, an objective lens driving device of the present invention includes an objective lens and a magnetic circuit for driving the objective lens, in which a magnetism of a yoke of the magnetic circuit and a magnetic circuit for driving the objective lens are provided. The opposing surfaces are formed into concave surfaces such that the magnetic gap becomes shorter from the center of the yoke toward the side edges.

[Embodiment] Next, an embodiment of the present invention will be described with reference to FIGS. 1 to 3.

FIG. 1 is a plan view of one embodiment of the present invention, FIG. 2 is a side view of the same, and FIG. 3 is a diagram showing the relationship between distance in the track direction and magnetic flux density.

In FIGS. 1 and 2, reference numeral 10 denotes a yoke, and the surface of this yoke 10 facing the magnet 7 is formed into a concave surface 11 such that the length of the magnetic gap 9 decreases from the center of the yoke 10 to the side edges. It is formed.

Therefore, the magnetic flux density in the magnetic gap 9 always has a constant value in the track direction, as shown in FIG.

Note that objective lens 1. Movable part 2. Wires 3a3b, 3c
, 3d, fixed part 4. The focus coil 5, track coils 6a, 6b, 6c, 6d, m-stone 7, and yoke 8b have the same configuration as the conventional one.

[Effects of the Invention] As explained above, in the present invention, by making the surface of the yoke that faces the magnet a concave surface, the magnetic flux density in the magnetic gap is always constant in the traverse and ν directions. Even if the same current is passed through a pair of track coils and the track coils move in the track direction, the forces generated in each of the track coils are always constant and the coverage is not disrupted. Therefore, the torsional rigidity in the track direction is increased, which has the effect of providing stable servo characteristics.

[Brief explanation of the drawing]

FIG. 1 is a plan view of an embodiment of the present invention, FIG. 2 is a side view of the same, FIG. 3 is a diagram showing the relationship between the distance in the track direction and magnetic flux density, and FIG. 4 is a plan view of the conventional example. FIG. 5 is a diagram showing the relationship between the distance in the track direction and the magnetic flux density in a conventional example, and FIGS. 6 and 7 are diagrams showing the relationship between the magnetic circuit and the objective lens. l2 objective lens 7, magnet 8b, yoke 9: magnetic gap 10: yoke agent patent attorney Yoshihira Watanabe Figure 10: U-7 Figure 7 Trick way of the leopard! ! 1!璽γ Figure d 3c, 3d Figure 9 Do m- Reading turtle in the track direction

Claims (1)

[Claims] In an objective lens driving device that has an objective lens and a magnetic circuit that drives the objective lens, the surface of the magnetic circuit that faces the magnetism of the yoke is arranged such that the magnetic gap becomes shorter from the center of the yoke toward the side edges. An objective lens driving device characterized in that it is formed into a concave surface.