JPS6129429A - Objective lens driver for optical information recording device - Google Patents

Abstract

PURPOSE:To suppress the generation of a magnetic field leaked out of a magnetic circuit and to reduce a magnetic field source of a recording magnetic field, by providing an auxiliary yoke at a position opposite to an optical information recording medium in order to form an open magnetic path by the magnetic field. CONSTITUTION:Auxiliary yokes 111a and 111b are attached to the right and left magnetic circuits within a space, and the magnetic characteristics and forms (especially thickness) of those auxiliary yokes are selected properly to suppress a leakage magnetic field within the space. In this example, the magnetic circuit is closed toward an optical axis and especially at the medium side. Thus the leakage magnetic field is small at the medium side and can be ignored practically. Therefore it is not needed to increase a magnetic field source of a recording magnetic field as conventional.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical information recording device suitable for optical memory pickups, particularly magneto-optical memory pickups, and more particularly to an objective lens driving device thereof.

[Background of the invention]

FIG. 1 illustrates a conventional optical information recording device pickup (optical information recording device). The objective lens 1 is It is fixed to the support frame 2 around which the coil 6 is wound. This coil 6 is inserted into a magnetic circuit (composed of a yoke 8 and a magnet 7) that generates a magnetic field in a direction parallel to the plane of the paper and perpendicular to the optical axis (Z-axis). In addition, the support frame 2 has plate-shaped springs 3a+ 313+ 4
It is supported by a and 4b, and its movement is restricted. Then, by passing a current through the coil 6, the objective lens 1 moves to Z
They are driven in directions perpendicular to the axis (optical axis direction) and the Z axis and parallel to the paper surface. In addition, 9 is a fixed frame for the magnet 7, yoke 8, etc., and 10 is a mounting frame for all the above-mentioned members.

FIG. 2 shows a schematic diagram of the magnetic circuit in the case of FIG.

Conventionally, due to the configuration of the device, the magnetic circuit was open on the media side, that is, on the objective lens 1 side, and the wetting magnetic flux from here caused the
A wetting magnetic field is formed. still.

The arrows in the figure schematically represent the flow of magnetic flux.

This wetting magnetic flux forms a magnetic field on and around the optical axis, but since this acts as a bias magnetic field, it may interfere with recording and reproduction in optical information recording devices, especially in optical information recording devices.

Here, magneto-optical recording will be explained.

FIG. 3 is a schematic diagram of this, and the media are the substrate 11 and the protective film 1.
It is generally composed of three layers: a recording film 13 sandwiched between two layers.

A permanent magnet or coil for generating a recording magnetic field is placed on the opposite side of the pickup or on the side of the pickup across the medium. The figure exemplifies the case where the recording magnetic field generating permanent magnet 14 is arranged on the opposite side of the pickup across the medium. Light emitted from a light source passes through an objective lens 1 located at a position determined by a drive circuit and is focused on a recording film surface 13 of the medium.

FIG. 4 is an enlarged view of the media portion showing the state of recording. As the light is converged by the objective lens 1, the temperature of the recording film 13 that is hit by the light increases. Since the recording film 13 is made of a magnetic material, it rapidly loses its magnetization when the temperature rises above one Curie point.

When the recording film is cooled while applying an external magnetic field (dashed arrow), the film is magnetized in the direction of the external magnetic field (black arrow), thereby performing recording.

During reproduction, information is reproduced by applying light with a lower power to the media than during recording, and observing that the polarization state of the light returning from the media has changed6.In addition, in the case of magneto-optical recording, the external What is the strength of the applied magnetic field?

Generally, it is about 100 to 300 Gauss on the media surface.

Magneto-optical recording and reproduction are performed according to the principle explained based on Figures 3 and 4, but as mentioned above, in the conventional example, the magnetic circuit is open in the optical axis direction, especially on the media side. , the leakage magnetic field on the media side is large. For this reason, magnetic recording cannot be performed unless the recording magnetic field has a strength exceeding the leakage magnetic field, and therefore a strong magnetic field generation source (magnet or coil) must be prepared. Also,
Demagnetization occurs when the media passes through the leakage magnetic field, which also causes a deterioration of the S/N during reproduction.

[Purpose of the invention]

The object of the present invention is to eliminate the drawbacks of the above-mentioned prior art.

In a drive mechanism of an optical information recording device that is driven in multiple dimensions, the purpose is to suppress the generation of a magnetic field leaking from a magnetic circuit that is a drive source, particularly in the optical axis direction.

[Summary of the invention]

To achieve this object, the present invention is characterized in that an auxiliary yoke for forming a closed magnetic path is provided at a position facing the optical information recording medium so that the magnetic field circuit has a closed magnetic path.

[Embodiments of the invention]

Embodiments of the present invention will be described below based on the drawings.

FIG. 5 is a diagram showing a pickup for an optical information recording device according to an embodiment of the present invention.

In the figure, 101 is an objective lens, 102 is a support frame, and 10
3 a = 103 b p 104 a + 104
b is a spring, 105 is a moving frame, and 106 is a drive coil.

107a and 107b are magnets, 108a and 108b are yokes, 109 is a fixed frame, and 110 is a mounting frame, each of which corresponds to the conventional example shown in FIG.

The main change compared to FIG. 1 is that an auxiliary yoke 111 is fixed to the open side of the magnetic circuit to form a closed magnetic path within the plane of the paper in the figure. Thereby, generation of a leakage magnetic field on the objective lens 101 side in the Z-axis (optical axis) direction can be suppressed.

FIG. 6 shows a schematic diagram of the magnetic circuit in the case of FIG.
By attaching each of the auxiliary yokes and appropriately selecting the magnetic properties and shape (particularly the thickness) of the auxiliary yokes, leakage magnetic fields within the plane of the paper can be suppressed. The table below shows actual measurements of the effect.

Table (A silicon steel plate with a thickness of 1 mm is used as the auxiliary yoke) The measurement is the strength of the magnetic field in the direction along the optical axis at a point 5 mm away from the pickup. Figure 7 shows another embodiment of the present invention. This figure shows an example, and the difference from the embodiment shown in FIG. 5 is that the direction of the yoke 108 is reversed. That is, the yoke 108 opens in the opposite direction to the objective lens 101. Therefore, in the closed portion on the objective lens 101 side, leakage magnetic flux from the yoke 108 can be suppressed by appropriately selecting its material, thickness, etc.

If necessary, it is also possible to attach an auxiliary yoke 111 to the open side of the yoke 108 as in the embodiment shown in FIG. 5 and measure the leakage magnetic flux from this circuit.
It is also possible to form the 10 itself from a soft magnetic material and use it also as an auxiliary yoke.

[Function and Effect] As explained above, according to the present invention, since the magnetic circuit is closed in the optical axis direction, especially on the media side, the leakage magnetic field on the media side is small and can be practically ignored. Although it is possible to set up to a certain value, there is no need to increase the magnetic field generation source of the recording magnetic field as in the conventional example. In addition, in this case, the driving performance of the magnetic circuit does not change, and furthermore, the shape of the driving device does not need to be changed significantly. Therefore, an optical information recording device with excellent functions can be provided without the drawbacks of the above-mentioned conventional technology. You can.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway vertical sectional view of a conventional optical information recording device, FIG. 2 is a schematic diagram of the magnetic circuit of the device shown in FIG. 1, and FIG. 3 is a principle diagram of the optical information recording device. 4 is a schematic diagram showing an optical information recording state, FIG. 5 is a partially cutaway vertical sectional view of an optical information recording device according to an embodiment of the present invention, FIG. 6 is a schematic diagram of a magnetic circuit, and FIG. The figure is a partially cutaway vertical sectional view of an optical information recording device according to another embodiment of the present invention. 101... Objective lens, 102... Support frame, 105... Moving frame, 106...
Drive coil, 111... Auxiliary yoke. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 1/ Figure 6 1O Figure 7

Claims (1)

[Claims] an objective lens disposed facing an optical information recording medium and having an optical axis perpendicular to the surface of the recording medium; a support frame fixed to the center of the objective lens; In the objective lens driving device, which is composed of a coil wound around a support frame and capable of moving the objective lens in multiple dimensions according to the current flowing through the coil, optical information is transmitted so that the magnetic field forms an open magnetic path. An objective lens drive device for an optical information recording device, characterized in that an auxiliary yoke is arranged at a position facing a recording medium.