JP2762931B2 - Objective lens actuator with tracking error detection - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens actuator for a read-only or read / write erasable optical head mounted on an optical disk apparatus, to a high-speed access type using a high numerical aperture lens, and further to a tracking servo. The present invention relates to an optical head actuator that operates reliably and has tracking error detection that can be inexpensive.

[0002]

2. Description of the Related Art FIG. 6 shows an example of a configuration of a one-beam system in a magneto-optical head for high-speed access. Laser 6
The divergent light emitted from 1 is converted into parallel light by a collimator lens 62, travels straight through a beam splitter A63 and a beam splitter B64, and enters an optical path system corresponding to one whose optical length changes with the inner circumference and outer circumference of the optical disk. 4 at this tip
An objective lens actuator 66 to which a 5 ° mirror 65 is attached is attached, and causes the objective lens to follow the surface deflection and eccentricity of the optical disk. These tracking operations are driven by signals obtained by focus error detection and tracking error detection, which will be described later, based on the beam deflected by the beam splitter A63.

In this optical system, when the optical disk 67 is tilted in the radial direction with the rotation, it follows the optical path shown by the broken line in the figure. The reflected light from the optical disk 67 goes in the reverse order, and is deflected by the beam splitter A63 on an axis deviated from the optical axis of the original optical design as shown by the broken line, and
The tracking error detection is detected in a state where the tracking error is offset from the center axis 8.

FIGS. 7 and 8 show an optical system having this offset in more detail. The light emitted from the laser 71 becomes a parallel beam, and the beam splitter 72
The light is deflected by an angle and reaches the optical disk 74 through the objective lens 73, and the return light goes straight and reaches the two-divided sensor 75. Here, the tracking error detection is obtained from the differential output of the two from the differential amplifier 76. When tracking error detection is performed in this optical system in a state where the light beam is offset from the central axis of the two-divided sensor 75, as shown in FIG. 8, a state without offset (A), a state with offset (B), and (C) The tracking error signal having such an offset results in an unstable tracking operation.

[0005]

In the above-described magneto-optical head, it is necessary to increase the optical path length from the disk to the detection of the tracking error, so that the tracking offset is impossible. Further, in order to configure a polarization optical system for magneto-optical detection, it is necessary to control the transmittance and reflectance of P-waves and S-waves, which are polarized waves of a beam splitter, and there is a disadvantage that the optical configuration becomes complicated.

In particular, in the case of a magneto-optical head configuration, it is necessary to control the plane of polarization. Therefore, a configuration in which the optical configuration shown in FIG. 6 is directly disposed below the objective lens actuator can be considered. It is necessary to satisfy the polarization condition of the beam splitter that also serves as the raising mirror. That is, it is necessary to optimize the transmission efficiency of P-polarized light and the reflection efficiency of S-polarized light. When the beam is incident on the beam splitter as S-polarized light, it is important to increase the reflection efficiency of P-polarized light that is a magneto-optical signal. Further, it is difficult to design a beam splitter having a large transmission efficiency of S-polarized light for detecting a tracking error.

Therefore, an object of the present invention is to reduce the offset of tracking error detection corresponding to the above-mentioned optical head for high-speed access, and to satisfy the optical conditions of a polarization system for detecting a magneto-optical signal. is there.

[0008]

According to the present invention, in order to achieve the above-mentioned object, an aspherical plastic lens is disposed on a lens holder which is a movable body, and a pair of separated optical sensors are disposed immediately below. . The aspherical plastic lens generally has a fringe around the aspherical plastic lens portion, and focuses on detecting a diffracted beam for detecting a tracking error using the flat surface of this portion.

The lens holder is supported by adding a dummy wire to a total of seven wires, in which an optical sensor for tracking error detection and three outputs and a reverse bias are added to four wires for focus and tracking, and three wires for output and reverse bias. Configure. The actuator has a structure that translates not only in the focus direction but also in the tracking direction.

In the electromagnetic drive, the form of the magnetic circuit and the focus and tracking coils are devised. In the case of the tracking drive, a single rectangular coil is used to increase the drive sensitivity.
The two sides are configured to be electromagnetically driven, and the magnetic circuit has long and short magnets arranged at point symmetric positions.

According to the objective lens actuator with tracking error detection of the present invention, a substantially rectangular frame-shaped objective lens holder of an objective lens actuator of an optical disc apparatus and an actuator supported by a wire spring at this portion are wound around a rectangular frame. A focusing coil and a pair of rectangular tracking coils on the opposite side are disposed at diagonal positions of the rectangular frame, and the magnetic circuit for electromagnetically driving these coils has a substantially closed magnetic circuit configuration. The magnets are arranged so as to be point-symmetrical on the opposite sides of the rectangular frame, and the long and short magnets are arranged with the magnetic field application directions of the coils opposite to each other, and the lens holder is an aspheric plastic lens. Beam emitted from the objective lens through the main body is tracked from the pre-groove optical disc Characterized in that the diffracted reflected light which is the basis of the difference signal and a pair of disposed on the lens holder so as to receive an optical sensor arrangement disposed in the lower part of the lens through an edge portion of the aspherical plastic lens.

In the objective lens actuator with tracking error detection of the present invention, in addition to four wire springs for applying a drive current for focusing and tracking when supporting the lens holder of the actuator, a two-element optical sensor is provided. It is characterized in that three or more wires for detecting a signal are added and the wires are arranged symmetrically.

[0013]

According to the present invention, the following operation is performed in two orthogonal directions based on the focus and tracking error signals. Further, tracking error detection is performed by an optical sensor provided immediately below the aspherical plastic lens. As a result, in the conventional optical head, it is necessary to increase the optical length such as the inner peripheral position in the separated optical head in which the distance of the two-divided sensor for detecting the tracking error from the optical disk can be accessed on the inner and outer circumferences. Compared to,
Since the optical path length is reduced by about 1/50, the problem of offset can be solved. Further, good characteristics can be obtained even in a polarization optical system such as magneto-optics.

[0014]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an exploded perspective view showing an embodiment of the present invention. FIG. 2 shows an optical system for detecting a tracking error. FIG. 3 shows an optical path system for detecting a tracking error signal using an aspheric plastic lens. FIG. 4 is a diagram for explaining a functional configuration intended to serve also as a wire that can conduct a current or a detected current when a plurality of wires supporting the lens holder are arranged. FIG. 5 is an exploded perspective view of the actuator. This will be described below with reference to the drawings.

Referring to FIG. The long actuator base 11 forms a magnetic circuit. The actuator base 11 is provided with a circular slit through which a collimator beam passes, and a magnetic gap is formed along a line extending in a direction perpendicular to the tracking direction (disc contact direction) .
Gunnet 15 is attached. A metal spring 16A constituting a parallel leaf spring at an end of the actuator base 11 ,
A stand portion 17 for attaching B, C, D, E, F, G, H is provided. This stand part 17 has a printed base
Paste the board, for example, by soldering eight gold
The wire spring, which is a genus spring, is arranged vertically in the drawing.

Four metal springs 16A, 16B extending from one of the stand portions 17 constituting the actuator base .
Transfer C, D, E, F, G, H to square frame lens holder 18
Pudding pasted on the wound focus coil
Attached to the substrate 19. This bonding is performed at both ends of the wire spring by light beam heating using a cream solder, a halogen lamp or the like.

Focus winding is performed around the lens holder 18 for focusing and tracking drive, and a pair of lens holders and printed circuit boards 19A and B for supporting conductive wires are arranged in a rectangular lens frame in the figure. I do. Further, a tracking coil described later is attached to the lens holder 18.

Further, optical sensors 20 and 2 for detecting the tracking error signal of the objective lens are provided on the lens holder 18.
Attach 1. The connection of the wire is performed on the printed circuit board 1.
9A and 9B. The objective lens 22 is attached on this. Actuator frame of the frame-shaped lens holder 18
An electromagnetic drive type actuator is fitted in the magnetic gap of the base 11 . The detection of the tracking error signal from the reflected light from the optical disk can be obtained by subtracting the signal received by the optical sensor by the differential amplifier 23.

FIG. 2 shows a style in which the incident light of the objective lens actuator and the diffracted and reflected light by the pre-groove optical disk are transmitted by being turned back. The dispersion angle θ of the ± 1st-order diffracted light is represented by Expression (1).

Θ = sin ⁻¹ (λ / P) (1) where: λ; wavelength, P; pitch width of the optical disc For example, if λ = 0.68 μm and P = 1.2 μm, θ =
34.5 °. Numerical aperture (NA) of the objective lens = 0.
When it is set to 55, the half angle is 33.4 °, so that a light amount equal to or more than の of the reflected light is emitted as shown in the figure. As described above, since the diffractive optical axis extends over the edge of the aspherical plastic lens, by providing an optical sensor at this edge, the ± first-order light, which is the source of the tracking error signal, is detected.

FIG. 3 shows the incident light of the aspherical plastic lens and the reflected light from the optical disk. ± 1 order light is received by the optical sensors 20 and 21 disposed below the aspherical plastic lens, and is tracked by the differential amplifier 23. Obtain an error signal. The reflected light is indicated by oblique lines.

FIG. 4 shows the structure of a device that is supported by a wire spring and supplies power. 2 shows reverse bias and detection terminals of a focus drive coil, a tracking drive coil, and a PIN optical sensor. From now on, it is necessary to supply a minimum of seven wires to the portion mounted on the lens holder, and it is configured to be supported by eight wire springs for balancing.

FIG. 5 is an exploded view of the components described with reference to FIGS. Only the parts hidden in FIG. 1 will be described. After the focus coil is wound around the lens holder 18, the flat rectangular coils 28 and 29 are arranged at diagonal positions.

The magnetic circuit comprises a U-shaped yoke 24 (yoke) and the actuator base 11. Yoke 26 holes 26,27 collimated beam passes and Actuators
It is provided on the eta base 11 . On the actuator base 11, a long magnet and a short magnet are arranged at rotationally symmetric positions around a hole through which the collimated beam passes so that long and short magnets 14 and 15 have opposite polarities. I have.

These magnets are driven in a magnetic cap having a yoke structure corresponding to the above-mentioned focus coil and tracking coil. In particular, the drive sensitivity is more than doubled by arranging the reverse magnetic pole with respect to the current in the opposite direction on the opposite side of the tracking coils 28 and 29. However, for focus driving, a short magnet works in a direction to reduce the thrust. However, in an optical disk servo, in a system in which a point is set for high-speed random access, a still operation is used as a reference, and a high sensitivity that can cope with a small amount of current during tracking is required. For this purpose, although the focus drive sensitivity is slightly affected as described above, it is more advantageous that the tracking drive sensitivity can achieve twice or more the conventional value.

[0026]

As described above, the present invention has an advantage that a tracking error signal can be detected in an optical disk apparatus compatible with high-speed access with a small tracking offset. Moreover, it is not necessary to use a beam splitter or a prism mirror in consideration of a polarization system as in the case of a magneto-optical head, and it is possible to configure the apparatus at low cost.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of an objective lens actuator with tracking error signal detection of the present invention.

FIG. 2 is a drawing illustrating the principle of tracking error signal detection.

FIG. 3 is a diagram illustrating detection of a tracking error signal by an aspheric plastic lens.

FIG. 4 is supported by a wire spring of an objective lens actuator with tracking error signal detection.

FIG. 5 is an exploded perspective view of an objective lens actuator with tracking error signal detection.

FIG. 6 shows a configuration of a conventional magneto-optical head.

FIG. 7 shows tracking error signal detection of a conventional optical head.

FIG. 8 is a diagram for explaining occurrence of an offset of a tracking error signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Actuator base 14 Long magnet 15 Short magnet 16 Wire spring 18 Lens holder 20 Optical sensor 21 Optical sensor 22 Aspherical plastic objective lens 23 Differential amplifier 28, 29 Square flat coil 61 Laser 63, 64 Beam splitter 68 Two-split sensor

Claims (2)

(57) [Claims] An objective lens actuator having a substantially rectangular frame shape for an objective lens actuator of an optical disk device and an actuator supported by a wire spring at this portion, a focus coil wound around a rectangular frame shape and a square-shaped focus coil on the opposite side. A pair of tracking coils are arranged at diagonal positions of the rectangular frame, and a magnetic circuit for electromagnetically driving these coils has a substantially closed magnetic circuit configuration, and a pair of long and short magnets are pointed to opposite sides of the rectangular frame. Symmetrically arranged, long and short magnets are mounted with the magnetic field application direction of the coil reversed, and the lens holder passes through the lens body of the aspheric plastic lens and exits from the objective lens The diffracted reflected light whose beam forms a tracking error signal from the pre-groove optical disc is A pair of tracking error detection with the objective lens actuator that is arranged to configure the lens holder so as to receive an optical sensor, and wherein arranged in the lower part of the lens through the edge portions of the. 2. In supporting the lens holder of the actuator, in addition to four wire springs for applying a drive current for focusing and tracking, three or more wires for detecting a signal from a two-element optical sensor are provided. In addition, it is characterized by being arranged symmetrically.
An objective lens actuator with tracking error detection according to claim 1 .