JPH02113445A - Object lens actuator - Google Patents

Abstract

PURPOSE:To reduce unnecessary angular moment produced in a lens holder and to obtain excellent tracking operation characteristics by adhering grooved iron plates on permanent magnets pinching a track coil. CONSTITUTION:Iron plates 50 and 51 provided with rectangular grooves are adhered on permanent magnets 3A and 3B of this object lens actuator. By the iron plates 50 and 51 provided with the rectangular groove, the magnetic flux density distribution between the magnets 3A, 3B and center yokes 2A, 2B is reduced in recessed state at the central part. Therefore, even when the center of track coils 4a, 4b and 5a, 5b existing in the magnetic field is deviated from the center of the magnets 3A and 3B, the change in magnetic flux density received at a cross-sectional section is reduced. Then, the moment produced by the electric currents flowing through the track coils is compensated with each other and only the component intersecting orthogonally with the optical axis becomes effective. Therefore, excellent tracking operation characteristics can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Prior Art] Conventionally, this type of objective lens actuator performs focusing to adjust focus and tracking to adjust positional deviation in order to accurately apply a light spot to the surface of an optical disk. For this reason, the objective lens actuator is
A permanent magnet that generates magnetic lines of force, a focusing coil that generates a driving force in the direction of the optical axis, and a tracking coil that generates a driving force perpendicular to the optical axis, and a reaction force to the driving force of the coil. It has a spring material that generates.

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

The lens holder 20 is supported by a rod-shaped spring member 10 and holds the objective lens 1. In the opening hole provided in the lens holder 20, there are yokes 2A and 2B, and in positions facing these yokes 2A and 2B, there are permanent magnets 13A and 13.
B is arranged, and the permanent magnet 13A of the lens holder,
Track coils 4a, 4b provided on the opposing and side parts of 13B.

5a, 5b and the focusing coil 6, tracking movement and focusing movement of the lens are performed. FIG. 4 shows the relationship between the track coils 4a, 4b and the magnetic fields generated by the permanent magnets.

[Problem to be solved by the invention]

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

Track coils 4a, 4b, 5a, 5b are permanent magnets 1
In the magnetic fields generated by 3a and 13b, there are two current components in two directions: a component parallel to the optical axis (Y direction) that serves as a driving force for tracking, and a component perpendicular to the optical axis direction (X direction). (See Figure 4). Generally, the X direction (
Since the current components flowing in directions perpendicular to the optical axis are in opposite directions on opposite sides of the coil, the magnetic forces generated by both types of flow must cancel each other out. For this reason, the coils are arranged in a relationship as shown in FIG. 8A with respect to the distribution of magnetic flux density of the permanent magnet shown in FIG. 7. However, due to operations such as focusing, the track coils 4a, 4b, 5a, 5b
If movement in the optical axis direction occurs, and the coil center position deviates from the magnet center as shown in FIG. 8B or C, the track fill 4a.

Different magnitudes of magnetic force are generated on the two sides 4b, 5a, and 5b, and the moment causes a shift in the objective lens actuator.

[Means to solve the problem]

In particular, the objective lens actuator of the present invention includes a first coil for focusing, a second coil for tracking, and a permanent magnet that applies a magnetic field to these two coils, and the second coil is the second coil for tracking. In an objective lens actuator having a rectangular shape in a magnetic field, a plate of high magnetic permeability material is provided with at least one recess along a line parallel to the first coil near the center of the driving force of the second coil. is adhered to the surface of the permanent magnet facing the coil.

〔Example〕

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

FIG. 1 shows a perspective view of an embodiment of the invention.

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

Permanent magnets 3A, 3B having magnetic poles perpendicular to the optical axis of the objective lens are arranged to sandwich the optical axis of the objective lens, and a track is inserted in a rectangular shape between the permanent magnets 3A, 3B and the center yokes 2A, 2B. The permanent magnet 3A in the objective lens actuator configured to include coils 4a, 4b and 5a, 5b.

It has a structure in which an iron plate 50, 51 having a rectangular groove is adhered to the surface of the lens 3B in a direction perpendicular to the optical axis of the objective lens l near the center of the optical axis of the track coils 3A and 3B.

The magnetic flux density distribution between the permanent magnets 3A, 3B and the center yokes 2A, 2B is determined from the actual measured values shown in Figure 2. By adhering the iron plates 50 and 51 having rectangular grooves, the magnetic flux density distribution near the center becomes concave. Decrease.

From this, as shown in Fig. 3A, the track coil in the magnetic flux density distribution is located at the center of the magnetic flux density distribution, Fig. 3B, the case where it is located upward, and Fig. 3C downward. In this case, the change in magnetic flux density experienced by the upper and lower cross-sectional parts of the track coil in the figure is reduced in each case. Therefore, as shown in FIG. 4, when a current flows through the track coil, the generated moments become a moment M and a moment M2 as shown in FIG. 5, but the difference between them becomes small and they cancel each other out.

In this way, according to the above configuration, the unnecessary rotational moment generated in the lens holder 20 is extremely reduced, and only the force component perpendicular to the optical axis generated by the current flowing parallel to the optical axis of the track coil is generated. is effective, and good tracking operation characteristics can be obtained.

[Effects of the Invention] As explained above, the present invention has a simple configuration in which an iron plate with grooves is attached to a permanent magnet that holds a track coil, and it is possible to achieve good tracking operation characteristics without greatly reducing the magnetic flux density. Furthermore, the effect of the present invention is that it can provide an objective lens actuator having a magnetic pole perpendicular to the optical axis direction, and the effect of the present invention is not limited to the actuator configuration according to the embodiment. Similar effects can be obtained in all actuators configured to perform a tracking operation by placing a rectangular or ring-shaped tracking coil in the magnetic flux generated by the permanent magnet.

Furthermore, the shape of the groove formed in the iron plate attached to the permanent magnet is not limited to this example.

FIG.

1... Objective lens, 2A, 2B... Center yoke, 3A, 3B... Permanent magnet, 4a, 4
b, 5a.

5b...Track coil, 6...Focus coil, 10...Spring, 20...
・Lens holder, 51゜52... Iron plate, 100
······base.

Agent: Patent Attorney Susumu Uchihara

[Brief explanation of drawings]

FIG. 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 track coil arrangement in the magnetic flux density distribution of the present invention, and FIG. An explanatory diagram showing the flow of current in the optical axis direction of the track coil, Fig. 5 is an explanatory diagram showing the rotational moment generated in the track coil, Fig. 6 is an upper perspective view of the conventional example, and Fig. 7 is an explanatory diagram of the conventional example. Magnetic flux density distribution diagram of a magnet, Figure 8 is a magnetic flux density distribution diagram Figure 2 Figure 3

Claims (1)

[Claims] The first and second magnets are fixed to the permanent magnet and the objective lens side.
In an objective lens actuator that performs fine adjustment (focusing) of a light beam emitted from an optical head in the vertical direction to the disk surface and fine adjustment (tracking) in the radial direction of the disk via an objective lens driven by a coil. , the second coil has a rectangular shape within the magnetic field and has at least one recess along a line parallel to the first coil near the center of the driving force of the second coil. An objective lens actuator characterized in that a plate made of this material is adhered to a surface of the permanent magnet facing the coil.