JP2790920B2 - Tracking method for optical disk device and tracking device using this method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking method used for a magneto-optical disk or the like in which information can be freely written and read, and a tracking apparatus using the method.

[0002]

2. Description of the Related Art In writing data on a magneto-optical disk, a magnetic field is formed so as to be orthogonal to the magneto-optical disk, and a part of the magnetic field is irradiated with a laser beam. In other words, since the coercive force of the portion of the magneto-optical disk irradiated with the laser beam is reduced, only the portion is magnetized in the direction of the magnetic field, and data is recorded using this characteristic. 4A is a sectional view of the magneto-optical disk, FIG. 4B is a top view of the magneto-optical disk viewed from the recording surface side, and FIG. FIG. 4 is a schematic explanatory diagram of a photoelectric conversion element that measures the amount of return light of FIG. FIG. 4 (A),
As shown in (B), on the recording surface of the magneto-optical disk D,
A land (convex portion) 1 as a data recording portion and a groove-like groove 2 formed between the lands 1 are formed. The surface of the recording surface is covered with a translucent cover 4. The step between land 1 and groove 2 is from λ / 8 to λ
/ 4 (λ is the wavelength of the detection light to be used), and when the light beam is focused on the land 1,
The return light from the land 1 is received and detected.
Is modulated, and the amount of return light received is greatly reduced. In the conventional magneto-optical disk device, the data writing area is the surface of the land 1. Therefore, in the recording or reproducing operation, it is necessary to accurately perform tracking correction so that the beam spot A of the laser beam is always located in the land 1. The tracking error signal for performing the tracking correction is obtained by receiving the return light from the magneto-optical disk D by a photoelectric conversion element (pin photodiode) 3 including four divided light receiving sections 3a to 3d shown in FIG. Will be That is, the movement of the laser beam in the tracking direction is corrected based on the detection result of the light amount by the photoelectric conversion element 3.

In a conventional magneto-optical disk drive, a push-pull method is employed as tracking correction. Hereinafter, the tracking correction method will be described. First,
When the beam spot A is at the normal recording or reproducing position indicated by the symbol (a) in FIG. 4B, the spot of the return light formed on the photoelectric conversion element 3 because the spot A does not deviate from the land 1, Groove 2 as shown by the symbol (b)
No part is modulated by When the beam spot A is displaced in one of the tracking directions (indicated by the symbol C) as shown in the symbol (c) or (d) in FIG. Depart from 1 and hang on groove 2. As described above, the spot is modulated in the groove 2 and the amount of the returning light from this portion is greatly reduced. Therefore, the signs (e) and (f) of the returning light formed on the photoelectric conversion element 3 are shown. The amount of received light in any of the portions will decrease. Therefore, FIG.
As shown in the figure, the sum of the received light amounts of the light receiving units 3a and 3d and the sum of the received light amounts of the light receiving units 3b and 3c are obtained. The displacement direction and the displacement amount of the beam spot A can be calculated. The movement of the laser beam in the tracking direction is corrected based on the calculation result.

[0004]

However, in order to accurately obtain a tracking error signal by the above-described push-pull method, the position of the beam spot of the return light formed on the photoelectric conversion element 3 must be adjusted. Each light receiving section 3
Must be exactly centered between a to 3d. For this reason, the mounting error of the photoelectric conversion element 3 must ensure the accuracy within a range that does not affect the output of the tracking error signal, but it is very difficult to obtain such accuracy in practice. Have difficulty. Even if the return light is located at the center of each of the light receiving sections 3a to 3d at the time of assembly, there is a possibility that the position of the photoelectric conversion element 3 may be shifted after a certain period of use. When the movement control of the laser beam is performed in such a state, even if the beam spot A is accurately positioned on the land 1, the center of the return light is shifted with respect to the photoelectric conversion element 3. By having
An error signal in the same state as when the spot is shifted in any direction is output. Furthermore, recently, in order to reduce the weight of the optical head, a method of arranging an optical system on the fixed side and oscillating the light transmitted from the fixed side optical system by a galvanometer mirror to thereby perform tracking correction has been considered. . However, in this tracking correction method, the return light from the disk is also shaken by swinging the galvanomirror, and the position of the return light moves with respect to the center of the photoelectric conversion element 3 shown in FIG. A state occurs where an error signal cannot be obtained. As a result, the accuracy of the tracking control is reduced, and offset is likely to occur. Accordingly, an object of the present invention is to provide a tracking method of an optical disk device that can perform tracking correction normally even if a light receiving spot of return light is displaced from a photoelectric conversion element, and a tracking device using the method. .

[0005]

According to the tracking method of the present invention, a light beam spot is irradiated including a boundary portion between a land and a groove on a recording surface of a disk.
In stores the light quantity of return light from the spot as a reference value indicating a normal spot position, spot land side Oh
Or the amount of light detected when displaced to the groove side
Compared with the values, on the basis of the detected light amount difference of their, it is characterized in Rukoto moves correcting optical beam in the tracking direction. Furthermore tracking device according to the present invention, a light irradiating means for irradiating a spot of the light beam on the recording surface of the disk, and the photoelectric conversion means to obtain a photoelectric conversion output based on the intensity of the returning light from the disk, the light beam spot Day
Including the boundary between the land and groove on the disc recording surface.
The output of the amount of return light in the projected state is adjusted to the normal spot position.
Means for storing as a reference value indicating the position,
A beam moving means for moving the correction optical beam in the tracking direction by comparing the amount of light output from the serial photoelectric conversion means, is characterized in that is provided.

[0006]

According to the present invention, the light beam spot is irradiated between the land and the groove of the optical disk, and the light beam is moved in the tracking direction based on the change in the amount of return light. Thus, tracking can be performed normally regardless of the position of the photoelectric conversion element. According to the operation of the present invention having the structure described in the second aspect, when the light beam from the light irradiation means is irradiated on the magneto-optical disk, this return light is incident on the photoelectric conversion means. When the entire output of the received light amount from the photoelectric conversion unit changes, the beam moving unit corrects the movement of the light beam in the tracking direction based on the change in the output.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 2 is a perspective view showing an arrangement configuration of an optical system in the magneto-optical disk device. FIG. 1 is a block diagram showing details of the photoelectric conversion element and its signal processing system in FIG. FIG.
The optical system shown in FIG. 1 includes a semiconductor laser 11 for irradiating a laser beam B, and a collimating lens 12 for converting the laser beam B emitted from the semiconductor laser 11 into a parallel light beam.
A beam splitter 13 for reflecting the laser beam B converted into a parallel light beam;
A galvanomirror 14 that totally reflects the laser beam reflected in the right angle direction in a substantially right angle direction, a prism 15 that refracts the laser beam emitted from the galvanomirror 14 toward the objective lens 16, and a magneto-optical disk D. A Wollaston prism 18 that divides return light B ′ from the light into three light beams, a detection system lens 19, a photoelectric conversion element 20 that photoelectrically converts the incident return light B ′, and the like. Reference numeral 17 denotes a monitor light receiving element, which controls a current for driving the semiconductor laser 11 based on the amount of light detected by the monitor light receiving element 17 to prevent runaway of the semiconductor laser 11 itself.

In the above optical system, the prism 15
And an objective lens 16 and a focus correction mechanism (not shown) are mounted on an optical head, and the optical head is moved along the recording surface of the disk D by means of a linear motor or the like as shown by symbols (g) and (h). To move in the radial direction. In the present embodiment, the semiconductor laser 11, the collimating lens 12, the beam splitter 13, and the galvanomirror 14 constitute a light irradiating unit 27, which is arranged on a fixed portion such as a pickup chassis.

The photoelectric conversion element 20 is, for example, a six-division pin photodiode, and its light-receiving surface is divided into six light-receiving portions 20a to 20f as shown in FIG. In order to obtain a tracking error signal, the light receiving unit 20
An adder 21 for adding the outputs of the photodiodes 20a to 20d is connected to the output sides of the photodiodes 20a to 20d, and the output side includes a light amount detector 24 and a galvanomirror driver 25
Is connected. Reference numeral 14 denotes the galvanomirror. The galvanomirror 14 is driven to rotate by a small angle in the direction indicated by the symbol α in FIG. 2 by a drive unit 25 constituted by a magnetic drive mechanism (not shown), so that the light beam spot converged on the disk D from the objective lens 16 It is swung in the tracking correction direction.

As described above, in this tracking correction method, since the tracking error signal is obtained by summing the light receiving amounts of all the four light receiving sections 20a to 20d, the photoelectric conversion element does not need to be divided into four. The reason why four light receiving sections are provided in this embodiment is to obtain a focus error signal from the photoelectric conversion element 20. When the beam spot A is formed between the groove and the land, that is, when the spot is properly irradiated on the disk recording surface, the light amount detection unit 24 outputs the light.
A register (not shown) for storing a light amount detection output value output from the controller, a function of calculating a difference between a signal output from the adder 21 and a light amount stored in the register, and outputting the difference signal It has. The galvanomirror driving unit 25 rotates the galvanomirror 14 based on the difference signal output from the light amount detection unit 24 so as to cancel the difference. In this embodiment, the beam moving means 26 is constituted by the galvanomirror driving unit 25 and the galvanomirror 14.

The operation of the tracking device having the above configuration will be described with reference to FIG. In the tracking method of the present invention, a state in which a beam spot A by a laser beam B irradiated from the light irradiation means 27 is irradiated between the land 1 and the groove 2 as shown by a symbol (R) in FIG. That is, part of spot A is groove 2
Is a normal spot irradiation state. The light quantity at this irradiation position is stored as a reference value in a register (not shown) in the light quantity detection unit 24.
The recording method on the magneto-optical disk is performed by heating the land 1 with a laser and applying a magnetic field with a magnetic head. Even if the portion is on the groove 2, the recording / reproducing function is not affected.

FIG. 3 (L) shows a normal spot irradiation state, and the spot A is shifted from the position of FIG.
When it is displaced in the left direction in the figure, the photoelectric conversion element 20
The total amount of light applied to the light source increases. This means that, at the position indicated by the symbol (R), the right side of the beam spot A in the drawing is the groove 2.
In the position indicated by the reference numeral (nu), the entire beam spot A This is because the amount of return light from the entire spot increases. Therefore, the total value of the light amounts output from the light receiving units 20a to 20d of the photoelectric conversion elements that receive the return light increases as a whole. This change in the output signal from the adding unit 21 is detected by a light amount detecting unit 24 connected at a subsequent stage. The light amount detector 24 compares the reference value stored in the register with the light amount when the beam spot A moves to the position indicated by the reference numeral (nu). As a result of this comparison, if the total light amount increases, it is determined that the beam spot A has moved to the left, and further it has been displaced in that direction by the increased light amount. And sends a signal to move the laser beam so as to cancel the displacement corresponding to the increased light amount. The galvanomirror drive unit 25 that has received this signal rotates the galvanomirror 14 based on this signal.

On the other hand, when the beam spot A is displaced rightward in the figure as shown by the reference numeral (ル) in FIG. 3, the area of the spot which is in contact with the groove 2 increases.
The amount of return light decreases, and the light receiving output of the photoelectric conversion element 20 decreases accordingly. The output signal from the photoelectric conversion element 20 is compared with a reference value stored in a register by a light amount detection unit 24 connected at a subsequent stage. That is, the light amount detection unit 24 compares the reference value with the light amount when the beam spot A moves to the position indicated by the reference numeral (L) in the same manner as described above. As a result of this comparison, if the total light amount decreases, it is assumed that the beam spot A has moved to the right, and it is known that the beam spot A has been displaced in that direction by the reduced light amount.
A signal for moving the laser beam so as to offset the displacement corresponding to the reduced light amount in the left direction in the figure is transmitted. The galvanomirror drive unit 25 that has received this signal rotates the galvanomirror 14 based on this signal. As described above, a tracking error signal is obtained based on the amount of return light from the entire light receiving portion of the photoelectric conversion element 20, and tracking correction is performed according to the error signal. At this time, a normal spot position is set. For example, the output value of the received light amount stored in the register is used as a reference. Therefore, the value stored in this register, that is, the reference value, can be set arbitrarily, and the spot irradiation position in the normal state can be freely selected. For example, spot A shown in FIG.
The state where only a small part of the groove 2 is on the groove 2 can be regarded as a normal spot position.

According to the apparatus and the tracking method of the embodiment described in detail above, it is easy to determine in which tracking direction the beam spot A has moved simply by measuring the increase or decrease of the total amount of light applied to the photoelectric conversion element 20. Can be detected. That is, in this embodiment, since the beam spot A is formed between the land 1 and the groove 2, even if the photoelectric conversion element 20 and other optical system parts have mounting errors, the Even when the beam spot A is not formed at the center of the photoelectric conversion element 20 as described above, accurate movement control of the laser beam can be performed only by measuring the increase / decrease of the light amount based on the light amount at this position. it can. Further, even when the beam is swung in the tracking direction by the operation of the galvanometer mirror 14 and the return light at this time moves with respect to the photoelectric conversion element, no fluctuation occurs in the tracking error signal. Therefore, the conventional offset does not occur.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the invention. In the above-described embodiment, the photoelectric conversion element is shown as being divided into four parts. However, this is for the case where focusing control is performed. A two-part photoelectric conversion element may be used. Even in this case, the same effect as in the above embodiment can be obtained. Further, in the above-described embodiment, the case where the beam spot is formed on the right side of the groove in the drawing is illustrated, but it is needless to say that the beam spot may be formed on the left side of the groove. Even in this case, the same effects as in the above embodiments can be obtained.

[0016]

According to the present invention described in detail above, a tracking correction method for a magneto-optical disk capable of performing normal tracking even if the relative position between the photoelectric conversion element and the return light is displaced, and a tracking correction using this correction method Equipment can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a photoelectric conversion element and a signal processing system thereof.

FIG. 2 is a perspective view showing a schematic configuration of an optical system.

FIG. 3 is an explanatory diagram showing an operation state.

FIG. 4A is a cross-sectional view of the magneto-optical disk, and FIG. 4B is a top view of FIG.

FIG. 5 is a schematic explanatory view of a photoelectric conversion element for measuring the amount of return light from a magneto-optical disk.

[Explanation of symbols]

 Reference Signs List 1 groove 2 land 20 photoelectric conversion means 26 beam moving means 27 light irradiation means A beam spot D magneto-optical disk

(56) References JP-A-63-66734 (JP, A) JP-A-1-273230 (JP, A) JP-A-3-132925 (JP, A) (58) Fields investigated (Int) .Cl. ⁶ , DB name) G11B 7/09-7/095 G11B 11/10

Claims (2)

(57) [Claims] In a state where a spot of a light beam is irradiated including a boundary portion between a land and a groove on a recording surface of a disk, the light amount of return light from the spot is stored as a reference value indicating a normal spot position. And the spot is on the land side
Alternatively, the detected light amount when displaced to the groove side is
Compared with standard values, based on the detection light amount difference of its tracking method for an optical disc apparatus according to claim Rukoto moves correcting optical beam in the tracking direction. 2. The method according to claim 1, wherein the spot of the light beam is transferred to a recording surface of a disk.
Light irradiating means for irradiating the light beam, photoelectric conversion means for obtaining a photoelectric conversion output based on the amount of return light from the disk, and light beam
Between the land and groove on the disc recording surface
Return light intensity output in the state of irradiation including the boundary part
Means for storing as a reference value indicating a normal spot position
And this reference value is compared with the light output from the photoelectric conversion means.
Compare to tracking device of an optical disk apparatus that the beam moving means for moving the correction optical beam in the tracking direction, characterized in that is provided.