JP2697007B2 - Objective lens actuator - Google Patents

Description

Description of the Related Art [0002] Conventionally, an objective lens actuator of this type performs focusing for adjusting a focus and tracking for adjusting a position shift in order to accurately place a light spot on an optical disk surface. For this purpose, the objective lens actuator is composed of two coils: a permanent magnet that generates a line of magnetic force, 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 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 supported by the rod-shaped spring material 10 and holds the objective lens 1. In the opening hole provided in the lens holder 20, the yokes 2A and 2B
Permanent magnets 13A and 13B are disposed at positions facing A and 2B, respectively, and track coils 4a, 4b, 5a and 5b and focus coils provided at the facing and side portions of the permanent magnets 13A and 13B of the lens holder. The tracking and focusing movements of the lens are performed by the magnetic action with the lens 6. FIG. 4 shows the relationship between the track coils 4a and 4b and the magnetic field generated by the permanent magnet.

[Problems to be solved by the invention]

The above-mentioned conventional objective lens actuator has the following problems.

The track coils 4a, 4b, 5a, 5b generate current components in two directions in the magnetic field generated by the permanent magnets 13a, 13b, that is, a component parallel to the optical axis serving as a driving force for tracking (Y
Direction) and a component (X direction) perpendicular to the optical axis direction (see FIG. 4). Generally, in the X direction (perpendicular to the optical axis)
Current components flowing in opposite directions on the opposite sides of the coil, the magnetic forces generated by both currents must cancel each other. For this reason, the coils are arranged in the relationship 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 is shifted from the magnet center as shown in FIG. 8B or C, the track coils 4a, Magnetic forces of different magnitudes are generated on the two sides 4b, 5a, 5b, and the moment causes a displacement of the objective lens actuator.

[Means for solving the problem]

The objective lens actuator of the present invention has, in particular, a first coil for performing focusing, a second coil for performing tracking, and a permanent magnet for applying a magnetic field to these two coils. In the objective lens actuator having a rectangular shape in the magnetic field, a material having high magnetic permeability in which at least one concave portion is provided near a center of a driving force of the second coil along a line parallel to the first coil. A plate is bonded to a surface of the permanent magnet facing the coil.

〔Example〕

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

 FIG. 1 shows a perspective view of one embodiment of the present invention.

The objective lens 1 attached to the lens holder 20 has an optical axis direction and a direction orthogonal to the optical axis (tracking direction).
And is held on the base 100 by four springs 10 so as to be movable.

Tracks in which permanent magnets 3A and 3B having magnetic poles in the direction orthogonal to the optical axis of the objective lens are arranged so as to sandwich the optical axis of the objective lens, and are inserted in a rectangular shape between the permanent magnets 3A and 3B and the center yokes 2A and 2B. In the objective lens actuator having the coils 4a, 4b and 5a, 5b, the track coils 3A, 3B are disposed on the surfaces of the permanent magnets 3A, 3B in a direction perpendicular to the optical axis of the objective lens 1.
And iron plates 50 and 51 having rectangular grooves near the center of the optical axis direction.

The magnetic flux density distribution between the permanent magnets 3A, 3B and the center yokes 2A, 2B is shown in FIG.
The magnetic flux density distribution in the vicinity of the central portion is reduced in a concave shape by attaching 1. Thus, as shown in FIG. 3A, when the track coil in the magnetic flux density distribution is located at the center of the magnetic flux density distribution, in FIG. 3B, when it is located above, and in FIG. In each case, the change in magnetic flux density applied to the upper cross section and the lower cross section of the track coil in FIG. Therefore, a current flows through the tracking coils as shown in FIG. 4, the moment generated moments M ₁ and moment as shown in FIG. 5
The M ₂ becomes a that cancel each other becomes the difference is less.

As described above, according to the above configuration, unnecessary rotation moment generated in the lens holder 20 is extremely reduced, and only a component of a force orthogonal to the optical axis generated by current flowing in parallel with the optical axis of the track coil is generated. Is effective, and good tracking operation characteristics can be obtained.

〔The invention's effect〕

As described above, the present invention provides an objective lens actuator having a good tracking operation characteristic without greatly reducing the magnetic flux density with a simple configuration in which a grooved iron plate is attached to a permanent magnet holding a track coil. There are effects that can be provided.

The effect of the present invention is not only the actuator configuration according to the embodiment, but also a rectangular and ring-shaped track coil arranged in parallel with the optical axis by an objective lens actuator having a magnetic pole perpendicular to the optical axis direction as in the present embodiment. The same effect can be obtained for all actuators configured to perform the tracking operation by being arranged in the magnetic flux generated by the permanent magnet.

Furthermore, the shape of the groove formed on the iron plate that is in contact with the permanent magnet is not limited to this example.

[Brief description of the drawings]

1 is an upper perspective view of the present invention, FIG. 2 is a magnetic flux density distribution diagram of the permanent magnet of the present invention, FIG. 3 is an explanatory diagram showing the arrangement of track coils in the magnetic flux density distribution of the present invention, and FIG. FIG. 5 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 rotational moment generated in the track coil, FIG. 6 is an upper perspective view of the conventional example, and FIG. FIG. 8 is a diagram showing a magnetic flux density distribution of a 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, 5
1,52 ... iron plate, 100 ... base.

Claims (1)

(57) [Claims] 1. Fine adjustment of a light beam emitted from an optical head in a direction perpendicular to a disk surface via an objective lens driven by a permanent magnet and first and second coils fixed to the objective lens side. Focusing) and fine adjustment (tracking) in the radial direction of the disk in the objective lens actuator, wherein the second coil is rectangular in the magnetic field, and the second coil is located near the center of the driving force of the second coil. An objective lens actuator, wherein a plate made of a material having high magnetic permeability and having at least one concave portion provided along a line parallel to one coil is bonded to a surface of the permanent magnet facing the coil.