JPH0690802B2 - Objective lens actuator - Google Patents

Description

TECHNICAL FIELD The present invention relates to an objective lens actuator used for an optical disc or the like.

[Conventional technology]

Conventionally, this type of objective lens actuator accurately focuses a light spot on the optical disk surface, and therefore performs focusing for adjusting focus and tracking for adjusting positional deviation. For this reason, the objective lens actuator includes a permanent magnet that generates a magnetic force line, two coils, a focusing coil that generates a driving force in the optical axis direction and a tracking coil that generates a driving force in a direction perpendicular to the optical axis, and the coils thereof. And a spring member that generates a reaction force with respect to the driving force.

FIG. 6 shows an external view of a conventional example.

The lens holder 20 is instructed by the rod-shaped spring material 10,
It holds the objective lens 1. In the opening provided in the lens holder 20, the yokes 2A, 2B are provided with the permanent magnets 13A, 13B at positions facing the yokes 2A, 2B, and the permanent magnets 13A, 13B of the lens holder are opposed to each other. And the tracking movement and the focusing movement of the lens are performed by the magnetic action of the track coils 4a, 4b, 5a, 5b and the focus coil 6 provided on the side portions.

FIG. 4 shows the relationship between the track coils 4a and 4b and the magnetic field generated by the permanent magnets.

[Problems to be Solved by the Invention]

The conventional objective lens actuator described above has the following problems.

The track coils 4a, 4b, 5a, 5b have a current component in two directions in the magnetic field generated by the permanent magnets 13a, 13b, that is, a component (Y direction) parallel to the optical axis which is a driving force for tracking. , And a component (X direction) in the direction perpendicular to the optical axis (see FIG. 4). In general, the current components flowing in the X direction (direction orthogonal to the optical axis) are opposite to each other on the sides of the coil, so the magnetic forces generated by the two currents must cancel each other. Therefore, the coils are arranged in the relationship as shown in FIG. 8A with respect to the distribution of the magnetic flux density of the permanent magnet shown in FIG. However, when the track coils 4a, 4b, 5a, 5b move in the optical axis direction due to an operation such as focusing,
When the coil center position deviates from the magnet center as shown in FIG. 8B or C, magnetic forces of different magnitudes are generated on the two sides of the track coils 4a, 4b, 5a, 5b, and the moment (M ₁ , M
₂ ) causes the objective lens actuator to shift.

[Means for Solving the Problems]

A lens holder to which an objective lens is attached, an optical axis direction moving means for moving the lens holder in the optical axis direction, a first rectangular coil attached to the lens holder, and the first rectangular coil attached to the lens holder. A second rectangular coil arranged adjacent to the rectangular coil; and a permanent magnet having a magnetic pole in a direction orthogonal to the optical axis direction and facing the first rectangular coil and the second rectangular coil. ,
The lens holder moves in the direction orthogonal to the optical axis by the interaction between the first rectangular coil and the second rectangular coil and the magnetic flux generated by the permanent magnet, and the optical axis direction is the vertical direction. At this time, when the lens holder is moved upward by the optical axis direction moving means, the magnetic flux received by the upper cross section of the first rectangular coil decreases and the magnetic flux received by the upper cross section of the second rectangular coil decreases. When the lens holder is moved downward by the optical axis direction moving means, the magnetic flux received by the lower cross section of the first rectangular coil decreases and the magnetic flux received by the lower cross section of the second rectangular coil decreases. When the lens holder is reduced and the lens holder is moved in the vertical direction, the first
The magnetic flux received by the upper cross section of the rectangular coil is substantially the same as the magnetic flux received by the lower cross section of the first rectangular coil, and the magnetic flux received by the upper cross section of the second rectangular coil and the second rectangle. A cutout or a hole is provided in a part of the permanent magnet so that the magnetic flux received by the lower cross section of the coil is substantially the same.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 shows a perspective view of an embodiment of the present invention. The objective lens 1 attached to the lens holder 20 is movable in the optical axis direction (focusing direction) and the direction orthogonal to the optical axis (tracking direction). It is held on the base 100 by 10 springs and 4 springs.

Permanent magnet having magnetic poles in the direction orthogonal to the optical axis of the objective lens
3A, 3B are arranged to hold the optical axis of the objective lens, between the permanent magnets 3A, 3B and the center yokes 2A, 2B, the track coils 4a, 4b and 5a, 5b wound in a rectangular shape are arranged, On the surface of the permanent magnets 3A, 3B facing the objective lens, the direction parallel to both side surfaces parallel to the optical axis of the permanent magnets 3A, 3B is deep at the center of the track coils 4a, 4b and 5a, 5b in the optical axis direction. One pair of permanent magnets 3A and 3B are formed symmetrically with the optical axis so that the flat surfaces of the permanent magnets 3A and 3B are shaped like the letter D at positions where both sides of the rectangular notch are formed in the vertical direction.

The magnetic flux density distribution between the permanent magnets 3A, 3B and the center yokes 2A, 2B is shown in Fig. 7 and the magnetic flux density distribution in the optical axis direction near the center point in the direction parallel to the optical axis is the same as the conventional example. The magnetic flux density distribution in the optical axis direction in the vicinity of the cutouts on both side surfaces parallel to the direction decreases from the measured value shown in FIG. 2 to a concave magnetic flux density distribution in the vicinity of the central portion of the optical axis length. As a result, as shown in FIG. 3A, the case where the track coil in the magnetic flux is located at the center of the magnetic flux density distribution, the case where it is located above FIG.
When located in the lower direction of FIG. C, the change in magnetic flux density in the upper cross section and the lower cross section of the track coil in the drawing is reduced in each case. Therefore, the moment generated by the current flowing through the track coil as shown in FIG. 4 is the moment M1 and the moment as shown in FIG.
It will be M2, but the difference will be small and they will cancel each other out.

As described above, according to the above configuration, the unnecessary rotation moment generated in the lens holder 20 is extremely reduced. Further, the force component orthogonal to the optical axis generated by the current flowing in parallel with the optical axis of the track coil is equivalent to the conventional example, and the effective force component generated does not change and only unnecessary turning moment is generated. There is an effect that a reduced and favorable objective lens actuator can be provided.

The effect of the present invention is that not only the actuator structure according to the embodiment but also the rectangular and ring-shaped track coils arranged parallel to the optical axis in the objective lens actuator having the magnetic poles orthogonal to the optical axis direction similarly to the present embodiment are used. The same effect can be obtained in all actuators configured to perform tracking operation by being arranged in the magnetic flux generated by the magnet.

Further, according to this example, the same effect can be obtained even if the notch is a circular hole or the like.

〔The invention's effect〕

As described above, the present invention has an effect that the operation of the objective lens actuator can be stabilized simply by changing the shape of the permanent magnet.

[Brief description of drawings]

FIG. 1 is an upper perspective view and a partial detailed view of the present invention, FIG. 2 is a magnetic flux density distribution diagram of the permanent magnet of the present invention, and FIG. 3 is an explanatory view showing a track coil arrangement in the magnetic flux density distribution of the present invention, FIG. 4 is an explanatory view showing the flow of current in the optical axis direction of the track coil, FIG. 5 is an explanatory view showing a turning moment generated in the track coil, and FIG. 6 is an upper perspective view of a conventional example.
FIG. 7 is a magnetic flux density distribution diagram of a conventional permanent magnet, and FIG. 8 is an explanatory diagram showing a track coil arrangement in the magnetic flux density distribution. 1 ... Objective lens, 2A, 2B ... Center yoke, 3A, 3B ...
Permanent magnet, 4a, 4b, 5a, 5b …… Track coil, 6 …… Focus coil, 10 …… Spring, 20 …… Lens holder, 10
0 …… Base.

Claims (4)

[Claims] 1. A lens holder to which an objective lens is attached, an optical axis direction moving means for moving the lens holder in the optical axis direction, a first rectangular coil attached to the lens holder, and an attachment to the lens holder. A second rectangular coil disposed adjacent to the first rectangular coil, and has a magnetic pole in a direction orthogonal to the optical axis direction and faces the first rectangular coil and the second rectangular coil. A permanent magnet, wherein the lens holder moves in a direction orthogonal to the optical axis by an interaction between the first rectangular coil and the second rectangular coil and a magnetic flux generated by the permanent magnet, When the direction is vertical, the magnetic flux received by the upper cross-section of the first rectangular coil is reduced when the lens holder is moved upward by the optical axis direction moving means. At the same time, the magnetic flux received by the upper cross section of the second rectangular coil decreases, and when the lens holder moves downward by the optical axis direction moving means, the magnetic flux received by the lower cross section of the first rectangular coil decreases. In the objective lens actuator in which the magnetic flux received by the lower cross section of the second rectangular coil is reduced, the magnetic flux received by the upper cross section of the first rectangular coil and the magnetic flux received by the upper cross section of the first rectangular coil when the lens holder moves in the vertical direction. The magnetic flux received by the lower cross section of the first rectangular coil is substantially the same, and the magnetic flux received by the upper cross section of the second rectangular coil is substantially the same as the magnetic flux received by the lower cross section of the second rectangular coil. The objective lens actuator is characterized in that a cutout or a hole is provided in a part of the permanent magnet so that 2. The amount of magnetic flux generated by the permanent magnet changes in the order of a first increase, a first decrease, a second increase, and a second decrease as it progresses upward. The objective lens actuator according to claim 1. 3. A first position is a vertical position where the amount of magnetic flux generated by the permanent magnet changes from the first increase to the first decrease, and the amount of magnetic flux generated by the permanent magnet is the first position. Is defined as the second position, and the vertical position at which the amount of magnetic flux generated by the permanent magnets shifts from the second increase to the second decrease is defined as the third position. When the lens holder is not moving in the vertical direction, the lower cross-section of the first rectangular coil and the lower cross-section of the second rectangular coil are located at the first position, and 3. The objective lens actuator according to claim 2, wherein the upper cross section of the first rectangular coil and the upper cross section of the second rectangular coil are located at the third position. 4. A magnetic flux at a position moved upward by x from the first position and a magnetic flux at a position moved downward by x from the first position within a predetermined range in the vertical direction about the first position. The magnetic flux becomes substantially the same, and within a predetermined range in the vertical direction centered on the third position, the magnetic flux at a position moved by x upward from the third position and the position moved by x downward from the third position. The objective lens actuator according to claim 3, wherein the magnetic fluxes at the above positions are substantially the same.