JP2695909B2 - Optical information recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to at least one of optical information recording on a recording medium and optical information reproduction from the medium as in an optical disk device. More particularly, the present invention relates to an optical information recording / reproducing apparatus provided with means for determining whether or not a focusing means for focusing a light beam on a medium is located near a focal point with respect to a recording medium.

(Prior Art) In an optical disk apparatus, an objective lens is focused on a disk perpendicular to the disk surface based on a focus error signal so that the focal position of the objective lens for focusing a light beam on the disk coincides with the recording surface of the disk. Control (focus servo) for moving in the direction is required. The focus error signal is obtained by calculation from the output of the photodetector that detects the reflected light from the optical disk.

Such a focus error signal generally has a zero level when the objective lens is at the focal point, and its polarity changes depending on the direction of defocus before and after the objective lens. However, the position of the objective lens far from the focal point, that is, the focus servo pull-in range , The focus error signal will be at zero level. For this reason, it is not possible to know whether the objective lens is at the in-focus position only from the focus error signal.

Therefore, in order to perform the initial pull-in of the focus servo or the pull-in operation when the focus servo is out of the pull-in range during the operation, it is determined whether or not the objective lens is located near the focal point. Must be used. In a conventional optical disk device, a determination signal corresponding to the sum of all light amounts incident on a photodetector is used to make this determination.

Specifically, for example, when the photodetectors are placed before and after the focal point of the condenser lens that condenses the reflected light, the objective lens is moved near the focal point by adding the output signals of these photodetectors. , A determination signal for determining whether or not the position is located is obtained. Since this determination signal is a signal whose level gradually decreases as it deviates from the vicinity of the focal point as shown in FIG. 6, the threshold level Vt shown by the broken line
The level was determined based on h, and it was determined that the lens was located near the focal point when Vth or more.

However, since the level of the determination signal gradually changes with respect to the defocus, it is difficult to accurately determine whether or not the signal is near the focal point. For example, if a signal obtained by level-determining the determination signal at the threshold level is used for focus servo abnormality detection, it is determined that there is no abnormality over a relatively wide range, and the detection sensitivity of abnormality detection is low. For this reason, even if the information on the optical disk cannot be read out of the focal point, there is a possibility that the focus servo operation will be continued without meaning.

(Problems to be Solved by the Invention) As described above, in the related art, since the level change of the determination signal for determining whether or not it is located near the focal point is gradual, the determination is accurately performed. There was a problem that it was difficult to do.

The present invention solves such a problem, and provides an optical information recording / reproducing apparatus capable of accurately determining whether or not a focusing means for focusing a light beam on a medium is located near a focal point. The purpose is to provide.

[Configuration of the Invention] (Means for Solving the Problems) In the present invention, after the reflected light from the recording medium is condensed by a condensing lens, the light is branched into first and second optical paths by a light branching unit. A light detection area is provided at a position closer to the light branching unit from the focal position of the condenser lens on the first optical path and at a position closer to the light branching unit from the focal position of the condenser lens on the second optical path. Are respectively provided with first and second photodetectors divided into at least a central portion and a peripheral portion.

The signal obtained by subtracting the output signal of the peripheral portion from the output signal of the central portion of the first photodetector, and the signal obtained by subtracting the output signal of the peripheral portion from the output signal of the central portion of the second photodetector. Using the added determination signal, it is determined whether the focusing unit is located near the focal point with respect to the recording medium.

(Operation) A signal obtained by subtracting the output signal of the peripheral portion from the output signal of the central portion of the first photodetector, and a signal obtained by subtracting the output signal of the peripheral portion from the output signal of the central portion of the second photodetector. Is high when the focusing means is located near the focal point, the level rapidly decreases when the focusing means is out of the vicinity of the focal point, and the polarity is inverted after the level is lowered.

Therefore, by comparing this determination signal with a certain threshold level to determine the level, or by detecting the zero-cross point and performing positive / negative polarity determination, it is highly accurate whether the focusing means is located near the focal point. Is determined.

The determination result obtained in this way may be used for abnormality detection during focus servo, or a focus servo loop for moving the focusing means in a direction perpendicular to the surface of the recording medium based on the focus error signal. It may be used for a focus servo pull-in operation that closes near a zero cross point of a signal.

(Example) Hereinafter, an example of the present invention is described with reference to drawings.

FIG. 1 shows a configuration of a main part of an optical disk device according to an embodiment of the present invention. In FIG. 1, a light source 1 is, for example, a semiconductor laser. A light beam emitted from the light source 1 is converted into a parallel light beam by a collimating lens 2, and then passes through a first beam splitter 3 and an objective lens 4 as a focusing unit. The light is focused on the recording surface of the optical disk 5. The optical disk 5 is a medium capable of recording and / or reproducing information by irradiating a light beam. For example, a writable disk such as a read-only disk such as a compact disk and a laser vision disk, a magneto-optical disk, and a write-once optical disk. Media and the like.

The light reflected from the recording surface of the optical disk 5 passes through the objective lens 4 in the direction opposite to the incident light, and is reflected by the first beam splitter 3 and separated from the incident light. The light reflected by the first beam splitter 3 is transmitted to a condenser lens 6
After being condensed by the light beam, the light beam is incident on a second beam splitter 7 as a light branching unit, and is branched into first and second optical paths 8 and 9.

On the first optical path 8, the first photodetector 10 is located at a position closer to the beam splitter 7 from the focal position P ₁ of the condenser lens 6.
Is disposed on the second optical path 9, and a second photodetector 11 is disposed at a position closer to the side opposite to the beam splitter 7 from the focal position P ₂ of the condenser lens 6. The distance between the photodetector 11 and the focal position P ₂ a distance and the second between the photodetector 10 and the focal position P ₁ is set equal. Photodetectors 10, 11
For example, as shown in FIGS. 2 (a) and 2 (b), the light detection area is divided into a rectangular shape into a central portion 21 and peripheral portions 22 on both sides thereof.

Output signals of the first and second photodetectors 10 and 11 are input to the arithmetic circuit 12. In the arithmetic circuit 12, the outputs of the central portion 21 and the peripheral portion 22 of the first photodetector 10 are A ₁ and B _1, and the outputs of the central portion 21 and the peripheral portion 22 of the second photodetector 11 are A ₂ , when the _{B 2, S 1 = (a} 1 -B 1) - (a 2 -B 2) S 2 = (a 1 -B 1) + (a 2 -B 2) consisting performs an operation. That is, the arithmetic circuit 12 performs the above-described arithmetic operation to determine whether the objective lens 4 is positioned near the focal point with respect to the optical disk 5 and determine the signal S ₁ for determining whether the objective lens 4 is focused on the optical disk 5. generating a focus error signal S ₂ indicating an error position.

Determination signal S ₁ output from the arithmetic circuit 12 is input to the focus servo circuit 14 through the level determination circuit 13, the focus error signal S ₂ is input directly to the focus servo circuit 14. The focus servo circuit 14 drives an actuator 15 for moving the objective lens 4 in a direction perpendicular to the optical disk 5.

3 (a), (b), (c), and (d) show photodetectors 10, 1 due to a change in the focus error of the objective lens 4 with respect to the optical disk 5.
1 shows changes in output signals A ₁ , B ₁ , A ₂ , and B ₂ . When the objective lens 4 is at the focal point (the position where the focal point of the objective lens 4 coincides with the recording surface of the optical disk 5), the light beams incident on the photodetectors 10 and 11 have the same size, but the objective lens 4 As 4 moves out of focus, the photodetectors 10, 11
The light beams incident on each of the light sources A ₁ , B ₁ ,
A ₂ and B ₂ show such a change.

FIGS. 3 (e) (f) are FIGS. 3 (a) (b) (c)
(D) A determination signal S corresponding to a change in the signals A ₁ , B ₁ , A ₂ , and B _2
1 and shows the change of the focus error signal S _2. Determination signals S ₁ is shown a high level in the vicinity of the focal point as shown in FIG. 3 (e), rapid level drops deviates from the focal point. The determination signals S ₁ is the level determined by the threshold level Vth indicated by a broken line in FIG. 3 (e) is guided to the level determination circuit 13 in FIG. 1, position the objective lens 4 in the vicinity of the focal point is greater than Vth If it is smaller, it is determined that it is out of the vicinity of the focal point.

Here, the determination signals S ₁ shown in FIG. 3 (e) determination signal according to the prior art shown in FIG. 6 _{(A 1 + B 1 + A} 2 + B 2)
As compared to the above, since the signal level greatly changes when the focus slightly deviates from the focal point, if the abnormality is detected based on the threshold level Vth, the normality is not determined over a wide range as in the related art, and a more strict Abnormality detection becomes possible.

Also, as Figure 3 by various causes in close proximity of the focal point (e) and sixth the level of the determination signal, as shown in FIG drops somewhat, determination signals S ₁ according to the present invention have been described above Since the signal level greatly changes when the object is out of the focal point, it is possible to determine whether the objective lens 4 is located near the focal point by the determination based on the threshold level Vth regardless of the drop. By the way, in the conventional technology, when the threshold level Vth is increased in order to narrow the range in which the focus servo is determined to be normal, a drop in the level of the determination signal very close to the focal point is detected, and the vicinity of the focal point is detected. However, there is a risk that it may be determined that this is not the case even though it is.

Furthermore, state determination signals S ₁ is equal to or higher than the threshold level Vth, i.e. in a state where the objective lens 4 is determined when located near the focal point, when the focus error signal S ₂ becomes zero since the position of exactly focus, close the focus servo loop in the focus error signal timing near the zero cross point S ₂ in the state in which determination signal S ₁ is determined to the threshold level Vth or more, pulling the focus servo By doing so, a very smooth retraction operation can be performed. The on / off of the focus servo loop is determined, for example, by a determination circuit in the focus servo circuit 14.
Can be based on the 13 determination result of and the focus error signal S _2.

In the above embodiment, the determination signal is set to the positive threshold level Vt.
Although the level is determined based on h, the threshold level of the level determination may be set to the zero level, and the determination as to whether the area is near the focal point may be performed based on the polarity determination of positive or negative.

In the above embodiment, the photodetector is divided into strips as shown in FIG. 2, but may be divided into a central portion 41 and a peripheral portion 42 as shown in FIG. As shown in FIG. 5, the central part 51 and the peripheral part 52 may be divided concentrically.

In addition, the present invention can be variously modified and implemented without departing from the gist.

[Effects of the Invention] According to the present invention, it is possible to determine with high accuracy whether or not a focusing unit for focusing a light beam on a medium is located near a focal point.

Therefore, it is possible to accurately detect an abnormality in which the objective lens largely deviates from the focal point during the focus servo, and it is determined that the objective lens is located near the focal point during the pull-in operation of the focus servo. Since the point at which the focus error signal crosses zero during the period becomes the focal point, by closing the focus servo loop at the timing of the zero cross, the focus servo pull-in operation can be performed smoothly.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an optical information recording / reproducing apparatus according to an embodiment of the present invention, FIG. 2 is a diagram showing a configuration of first and second photodetectors in FIG. 1, and FIG. FIG. 4 is a diagram showing an output signal of a photodetector, a signal for determining the signal, and a focus error signal.
FIG. 5 and FIG. 5 are diagrams showing another example of the configuration of the photodetector used in the present invention, and FIG. 6 is a diagram showing a signal for determination according to the prior art. DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Collimate lens 3 ... First beam splitter 4 ... Objective lens (focusing means) 5 ...
.., Optical disk, 6... Condenser lens, 7... Second beam splitter (light splitting means), 8, 9... 1st and 2nd optical paths, 10, 11. , An arithmetic circuit, a level determining circuit, a focus servo circuit, and an actuator.

Claims (2)

(57) [Claims] 1. An optical information recording / reproducing apparatus for irradiating a recording medium with a light beam focused by a focusing means and performing at least one of optical information recording and optical information reproduction, wherein reflection from the recording medium is performed. A condenser lens for condensing light; a light branching unit for branching light condensed by the condenser lens into first and second optical paths; and a focal position of the condenser lens on the first optical path. From the focal position of the condenser lens on the second optical path and from the focal position of the condensing lens on the second optical path to the position opposite to the light branching unit, and the light detection area is at least a central part. First and second photodetectors divided into a peripheral portion, a signal obtained by subtracting an output signal of a peripheral portion from an output signal of a central portion of the first photodetector, and a second photodetector. From the output signal at the center to the output signal at the periphery Arithmetic means for generating a signal for determination by adding a signal obtained by subtracting the signal, and determining means for determining whether the focusing means is located near the focal point with respect to the recording medium using the signal for determination. An optical information recording / reproducing device, comprising: 2. An optical information recording / reproducing apparatus for irradiating a recording medium with a light beam focused by a focusing means and performing at least one of optical information recording and optical information reproduction, wherein the reflection from the recording medium is performed. A condenser lens for condensing light; a light branching unit for branching light condensed by the condenser lens into first and second optical paths; and a focal position of the condenser lens on the first optical path. From the focal position of the condenser lens on the second optical path and from the focal position of the condensing lens on the second optical path to the position opposite to the light branching unit, and the light detection area is at least a central part. A first and a second photodetector divided into a peripheral portion, a first difference signal obtained by subtracting an output signal of a peripheral portion from an output signal of a central portion of the first photodetector, From the output signal at the center of the photodetector Calculating means for generating a determination signal by adding the second difference signal obtained by subtracting the output signal, and generating a focus error signal indicating an error of a focus position of the focusing means with respect to the recording medium; Determining means for determining whether the focusing means is located near the focal point with respect to the recording medium using a signal; and after determining that the focusing means is located near the focal point by the determining means. Means for closing a focus servo loop for moving the focusing means in a direction perpendicular to the surface of the recording medium based on the focus error signal near a zero cross point of the focus error signal. Optical information recording / reproducing device.