JP2910367B2 - Focusing pull-in method and device in optical pickup device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focusing pull-in method and apparatus in an optical pickup device for recording / reproducing information on / from an optical recording medium.

In the present invention, optical recording media include not only optical recording media such as optical disks and optical cards, but also magneto-optical recording media such as magneto-optical disks and magneto-optical cards.

In the present invention, recording / reproducing information includes recording information on an optical recording medium, reproducing information recorded on an optical recording medium, and recording and reproducing.

[0004]

2. Description of the Related Art In an optical pickup device, it is necessary to perform focusing control for adjusting a distance between an objective lens and an optical recording medium such that focused projection light is correctly focused on the surface of the optical recording medium. is there. Focusing control is basically performed based on a focusing error signal. Since the dynamic range of the focusing error signal is relatively narrow, it is necessary to forcibly move the objective lens so that the optical recording medium falls within this dynamic range before focusing control based on the focusing error signal. This is focusing focusing.

A specific description will be given with reference to the drawings.

FIG. 1 shows an example of a conventional optical pickup device.

The diffused laser light emitted from the semiconductor laser 11 is collimated by a collimating lens 12,
The light enters the objective lens 15 through the polarizing beam splitter 13 and the half-wave plate 14, and is condensed by the objective lens 15,
The light is projected on the magneto-optical disk 30. The reflected light from the magneto-optical disk 30 is collimated by the objective lens 15 and
The light beam passes through the two-wavelength plate 14 and is deflected at right angles by the polarization beam splitter 13. This light is further transmitted to lens 16
While being condensed by the beam splitter 17, a part of the light passes through the beam splitter 17 to the photodetector 21 and another part is reflected by the beam splitter 17 and reflected by the photodetector. It is incident on each of 22. The light spots formed on the photodetectors 21 and 22 are represented by SP ₁ and SP ₂ respectively.

These light detectors 21 and 22 are located before and after the focal position of the reflected light condensed by the lens 16 when the light projected onto the magneto-optical disk 30 is correctly focused. Are arranged at the respective positions. Also,
The photodetectors 21 and 22 are composed of three-division photodiodes. The photodetector 21 includes photodiodes 21a, 21b and 21c, and the photodetector 22 includes photodiodes 22a,
Consists of 22b and 22c. Central photodiode 21
The width of b, 22b is narrow.

To create a focusing error signal,
For example, a double beam size method is used, and an electric circuit for that is shown in FIG. The subtractors 41, 42, and 43 perform an operation according to the following equation to generate a focusing error signal FE. Here, the output signal of each photodiode is also represented using the code assigned to the photodiode.

FE = (21a + 21c−21b) − (22a + 22c−22b) (1)

The focusing error signal FE may be created by the following equation except for the central photodiode.

FE = (21a + 21c) − (22a + 22c) (2)

[0013] As shown in FIG. 4 (A), the objective lens 15 moves away from the magneto-optical disc 30 the light spot SP ₁ on the photodetector 21 is decreased, on the photodetector 22 the light spot SP
₂ will be larger. Conversely, the objective lens 15 is a magneto-optical disk
When approaching 30, as shown in FIG.
₁ increases and the light spot SP ₂ decreases.

As shown in FIG. 2, the focusing error signal FE represented by the equation (1) or (2) is a so-called S, where the horizontal axis is the distance between the objective lens and the magneto-optical disk, and the vertical axis is the signal level. Draw a curve. Focusing control based on this focusing error signal (moving the objective lens so that the position of the objective lens with respect to the magneto-optical disk is in focus) is possible only between the minimum peak and the maximum peak in the S-shaped curve. It is. Therefore, if the objective lens is too close to or far from the magneto-optical disk,
A focusing pull-in operation for forcibly moving the objective lens to a position where focusing control is possible is required.

A pull-in signal is required for this focusing pull-in operation. One idea is to use the central photodiode 21b or 22b of the photodetector 21 or 22 as the pull-in signal. Photodiode 21
The output signal of b is shown in FIG. 2 as the focusing pull-in signal FD. The pull-in operation is performed until the signal FD reaches the threshold level _Vth .

However, according to this method, the retraction can be performed only in a direction approaching the magneto-optical disk from a position where the objective lens is far from the magneto-optical disk. That is, there is a problem that the focusing pull-in is in one direction.

[0017]

DISCLOSURE OF THE INVENTION The present invention makes it possible to perform bidirectional retraction with a simple structure.

In the focusing pull-in method according to the present invention, the light receiving signal on the central light receiving surface of the two photodetectors having the light receiving surface divided into three is compared with each other to determine the smaller one of the light receiving signal levels, The determined light receiving signal is output as a pull-in signal.

The focusing retracting device according to the present invention compares the light receiving signals on the central light receiving surface of the two photodetectors having the light receiving surface divided into three parts, and determines the smaller one of the light receiving signal levels. , And switching means for selecting the signal determined by the comparing means and outputting the selected signal as a pull-in signal.

The focusing pull-in method and apparatus according to the present invention are not limited to the conventional optical pickup apparatus as shown in FIG. 1, but all optical pickup apparatuses having two photodetectors each having a light receiving surface divided into three. For example, the applicant has already
The present invention can also be applied to the optical pickup device proposed in, for example, Japanese Patent No. 78,3-210479.

According to the present invention, the smaller one of the light receiving signals on the central light receiving surface of the two photodetectors is selected and used as the pull-in signal. The level of the smaller light receiving signal decreases as the distance from the in-focus position in both directions with respect to the in-focus position, that is, the level increases in any direction toward the in-focus position, and peaks at the in-focus position. Therefore, focusing pull-in can be performed from both directions near and far from the optical recording medium.

[0022]

FIG. 6 shows an embodiment of the present invention.

The output signals fd ₁ and fd ₂ of the central photodiodes 21 b and 22 b of the two photodetectors 21 and 22, respectively.
Are compared by the comparator 51. These output signals fd ₁ and fd ₂ are used as switching switching circuits.
Enter in 52. The switching of the switching circuit 52 is controlled by the output of the comparator 51.

The output signal f of the photodiodes 21b and 22b
FIG. 5 shows d ₁ and fd ₂ as the focusing error signal F
It is drawn with E. The focusing error signal FE is the same as that produced by the circuit shown in FIG.

The comparator 51 outputs two signals fd
The levels of ₁ and fd ₂ are compared, and the circuit 52 is controlled such that the signal of the smaller level is selectively output by the switching circuit 52 in accordance with the comparison result. For example, switching the switching circuit 52 if the output of the comparator 51 is positive is connected to the input B signal fd ₂ is selected, the signal fd ₁ is selected the output of the comparator 51 is connected to the input A if it is negative You. The output signal fd ₁ or fd ₂ of the switching circuit 52 is amplified by the amplifier 53 and then output as the focusing pull-in signal FD.

The pull-in signal FD thus created
Are shown in FIG. 7 together with the focusing error signal FE. Since the signal level of the pull-in signal FD gradually increases from both sides toward the focus position, focusing pull-in can be performed in both directions. The distance at which this signal FD intersects with an appropriate threshold level _Vth is the point at which the focus shifts to focusing control using the focusing error signal FE.

[Brief description of the drawings]

FIG. 1 shows a configuration example of an optical system of an optical pickup device.

FIG. 2 is a graph showing a focusing pull-in signal created based on one concept.

FIG. 3 is a circuit diagram showing a circuit for creating a focusing error signal.

FIGS. 4A and 4B show light spots at two photodetectors.

FIG. 5 shows a light receiving signal of a photodiode at the center of two photodetectors.

FIG. 6 is a circuit diagram showing a circuit for creating a focusing pull-in signal according to an embodiment of the present invention.

FIG. 7 is a graph showing a created focusing pull-in signal.

[Explanation of symbols]

 21, 22 Photodetector 21b, 22b Central photodiode 51 Comparator 52 Switching circuit

Claims (6)

(57) [Claims] 1. A method according to claim 1, wherein the reflected light from the optical recording medium is divided into two parts and condensed, and the divided and condensed reflected lights are respectively disposed before and after a focal position in a focused state, and The reflected light is respectively received by two photodetectors each having a light receiving surface divided into three, and
By comparing the light receiving signals on the light receiving surface at the center of the two photodetectors with each other, the one having the smaller light receiving signal level is determined,
A focusing pull-in method in an optical pickup device, wherein the determined light receiving signal is output as a pull-in signal. 2. The difference between the sum of the light receiving signals of the light receiving surfaces on both sides of one photodetector and the light receiving signal of the central light receiving surface, and the sum and center of the light receiving signals of the light receiving surfaces on both sides of the other photodetector. 2. The method according to claim 1, wherein a focusing error signal is created by calculating a difference between the difference from the light receiving signal of the light receiving surface of the focusing error signal. 3. A focusing error signal is calculated by calculating a difference between a sum of light reception signals on both sides of the one photodetector and a sum of light reception signals on both sides of the other photodetector. The method of claim 1, wherein the method comprises creating. 4. A beam splitter means for splitting the reflected light from the optical recording medium into two, and before the focal position in a focused state of the condensed reflected light split by the light beam splitter means. Each later placed, and 3
Two photodetectors each having a divided light-receiving surface, comparing means for comparing light-receiving signals on the light-receiving surface at the center of the two light detectors with each other, and determining a smaller light-receiving signal level; Switching means for selecting a signal determined by the means and outputting the signal as a pull-in signal. 5. The difference between the sum of the light receiving signals on the light receiving surfaces on both sides of one photodetector and the light receiving signal on the central light receiving surface, and the sum and center of the light receiving signals on the light receiving surfaces on both sides of the other photodetector. 5. The apparatus according to claim 4, further comprising a focusing error signal generating means for calculating a difference between the light receiving signal of the light receiving surface and a difference of the light receiving signal. 6. A focusing error signal generating means for calculating a difference between a sum of light receiving signals on both light receiving surfaces of one photodetector and a sum of light receiving signals on both light receiving surfaces of the other photodetector. 5. The device according to claim 4, further comprising: