JPH1049880A - Circuit and method for focus search of optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly bring an objective lens to an optional focus position of disk in which a plurality of layers able to be focused are provided in the thickness direction. SOLUTION: The focus search circuit is provided with a driving means for moving an objective lens 2 to a disk D in which a plurality of layers able to be focused are provided in the thickness direction, a detecting circuit 3 for detecting based on a focus error signal that the objective lens 2 reaches the vicinity of a focused position, and a delaying means for delaying a movement speed of the objective lens 2 by an output of the detecting circuit 3. A pass- instructing circuit 4 is connected to the detecting circuit 3. At which time a position where a focus of the objective lens 2 is naturally met is detected by the detecting circuit 3 is input to the indicating circuit 4 beforehand. The pass- instruction circuit 4 generates a signal to neglect the focused position detected by the detecting circuit 3 until the objective lens 2 comes to the vicinity of the natural focus position, and drive the objective lens 2 at a high speed. When it is detected based on a count of focused positions neglected by the detecting circuit 3 that the objective lens 2 comes to the vicinity of the natural focus position, the pass-instruction circuit 4 drives the delaying means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus search circuit and a focus search method for moving an objective lens of an apparatus for recording and reproducing an optical disk toward and away from the disk.

[0002]

2. Description of the Related Art In an optical disk recording / reproducing apparatus, an objective lens of a pickup device is set at the start of recording / reproducing operation.
It is widely known that an operation of approaching and moving a disc to detect a focus position, that is, a so-called focus search operation is required. In such a focus search operation, the speed at which the objective lens is moved closer to the disk becomes a problem. That is, if the moving speed of the objective lens is too fast, it is difficult to accurately stop the objective lens when it reaches the focus position. On the other hand, if the moving speed of the objective lens is too slow, the focus search time becomes long. In view of such a problem, the applicant has previously proposed an apparatus shown in FIG. 10 (see Japanese Patent Publication No. 7-1549).

[0003] A square wave output from an oscillation circuit (7) is input to an integration circuit (5) comprising a resistor R and capacitors C1 and C2 connected in parallel, and a focus search shown by a solid line in FIG. A drive signal, and the focus search drive signal is provided to a pickup disposed below the disk D.
Supplied to (1). Based on the focus search drive signal, the objective lens (2) of the pickup (1) is moved closer to or away from the disk. As the inclination of the focus search drive signal shown by the line A in FIG. Is fast moving. The capacitor C2 is switchably grounded via a switch SW1, and when the switch SW1 is OFF, the moving speed of the objective lens (2) is high. On the optical path between the objective lens (2) and the pickup (1),
As is well known, a beam splitter (80) is provided, and light partially reflected by the beam splitter (80) is condensed by a cylindrical lens (81) and input to the optical sensor (8). The optical sensor (8) outputs a focus error signal indicating the defocus of the objective lens (2) by an electric signal. The focus error signal is supplied to a detection circuit (3) connected to the integration circuit (5).

The focus error signal is output from the objective lens (2).
Is at the 0 level from the position away from the disc to the vicinity of the focus position, and when the objective lens (2) reaches the vicinity of the focus position and then passes through the focus position, 3
An S-shaped waveform as shown in (a) is obtained (see the Nikkei Electronics July 1982 issue). The reason for the S-shaped waveform will be described later. Point b, which is the zero-cross point of the S-shaped waveform, indicates a position where the objective lens (2) has reached the focus point by the focus search operation. Point a indicates the rising position of the focus error signal when the objective lens (2) is driven near the focus in-focus position. The point c indicates the position where the focus error becomes maximum until the objective lens (2) reaches the point b after the objective lens (2) exceeds the point a and is further driven. The detection circuit (3) closes the switch SW1 when the focus error signal is at the point a or the point c. Capacitors C1 and C
2 are connected in parallel, and the time constant of the focus search drive signal generated from the integration circuit (5) increases. Accordingly, since the inclination of the focus search drive signal becomes gentle as shown by the line B in FIG. 4, the objective lens (2) moves slowly until reaching the point b, which is the in-focus position, and reliably moves to the point b. Can be reached. When the point b is reached, the mode shifts to a focus servo mode for finely adjusting the objective lens (2).

[0005]

In recent years, a so-called two-layer D in which two focusable layers are provided in the thickness direction of a disc.
VD (Digital video disc) has been proposed. this is,
As shown in FIG. 2, the number of focusable layers is two, thereby increasing the disk capacity and achieving high-density recording and reproduction. The first layer is sequentially arranged from the side closer to the objective lens (2).
(60), the second layer (61). In such a DVD, depending on the recorded contents of the disc, the reproduced signal is first transmitted to the second layer (61).
May be taken out of In this case, in the conventional focus search circuit, the objective lens (2) is gradually approached to the disk, and first, the objective lens (2) is focused on the first layer (60). Thereafter, the objective lens (2) is further moved to focus the objective lens (2) on the second layer (61). That is, since the focus is once focused on the unnecessary first layer (60) from which the reproduction signal is not taken out, and then focused on the second layer (61), it takes time to detect the focus position. It is also possible to form a disc having three or more layers of focus positions, and it is necessary to quickly perform a focusing operation on an arbitrary layer with respect to such a disc.
SUMMARY OF THE INVENTION It is an object of the present invention to quickly move an objective lens to an arbitrary focusing position on a disk having a plurality of focusable layers provided along a thickness direction.

[0006]

[Means for solving the problem] The focus search circuit comprises:
Drive means for moving the objective lens (2) with respect to the disc D, and a focus error signal indicating an amount of defocus from the in-focus position of the objective lens (2). Detecting means for detecting that the object has reached the vicinity, and delay means for reducing the moving speed of the objective lens (2) with respect to the disk D in response to the output of the detecting means are provided.
When the objective lens (2) moves up and down with respect to the disc D on which a plurality of focusable layers are provided in the thickness direction, the detection means detects a position where the objective lens (2) should originally focus. The apparatus is provided with counter means for counting the number of in-focus positions detected by the detecting means in advance by inputting the number of the position to be detected by the means, and from the counted number, the in-focus position to be detected next should be originally in focus Until the position is detected, the passage instructing means for ignoring the detected focus position and issuing a signal to quickly move the objective lens (2) up and down is connected. The passage instructing means detects, from the output of the counter means, that the next in-focus position to be detected is a position to be originally focused, and moves the detecting means to the vicinity of the in-focus position of the objective lens (2). Has a switching function of activating the delay means when the arrival of the signal is detected.

[0007]

In the focus search operation, the objective lens (2) moves quickly up and down with respect to the disk, and the detecting means detects the in-focus position. However, when the detected focus position is not the position to be focused, the passage instructing means ignores the focus position and moves the objective lens (2) at a high speed. The passage instructing means detects that the next in-focus position is a position to be originally focused, and if the detecting means detects that the objective lens (2) has reached the vicinity of the in-focus position, the objective The vertical movement speed of the lens (2) is reduced. Therefore, in the conventional configuration, during the movement of the objective lens (2), the moving speed of the objective lens (2) is slowed down each time it approaches the focus position.
In the present invention, since the objective lens (2) is moved by ignoring the position that should not be focused by the signal from the passage instruction means, the objective lens (2) is moved to the original focused position. You can move fast.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an example of the present invention will be described in detail with reference to the drawings. The same reference numerals are used for the same configurations as those in the related art. The disk mainly used in the present apparatus is provided with a plurality of focusable metal film layers (60) and (61) in the thickness direction of the disk as shown in FIG.
The distance between the layer (60) and the second layer (61) is provided at about 40 μm.
The objective lens (2) is controlled by a focus search mode in which the lens reaches a focus position from a position away from the disk, and after the focus search operation is completed, the objective lens (2) is fine-tuned in accordance with the rotational vibration of the disk. It is divided into a focus servo mode for accurate focusing. Among them, the device according to the present embodiment is characterized in the focus search mode, and the description of the focus servo mode is omitted.
FIG. 1 is an internal block diagram of the disk recording / reproducing apparatus. The objective lens (2) of the pickup (1) is provided so as to be able to move up and down. The focus search drive signal from the integration circuit (5) is input to the pickup (1), and the objective lens (2) is input by the focus search drive signal. ) Moves toward the disk.

The integrating circuit (5) comprises a resistor (R), capacitors (C1, C2) and a switch (SW1) connected in parallel, and a square wave from the oscillating circuit (7) is input as in the prior art. Also, a beam splitter (80) is provided on the optical path between the objective lens (2) and the disk, and the beam splitter (8) is provided.
(0) is partially reflected by the cylindrical lens (8
The light is condensed by 1), input to the translucent optical sensor (8), and a focus error signal is output from the optical sensor (8) as in the related art. A focus error signal is detected by a detection circuit (3) for detecting a rising position and a maximum value of the error signal.
The switch SW1 of the integration circuit (5) is switched by the detection circuit (3). The detection circuit (3) includes a counter that counts the in-focus position that has passed, as described later.
(45) is connected to the passage instruction circuit (4).

The method of generating a focus error signal by the beam splitter (80), the cylindrical lens (81), and the optical sensor (8) is called an astigmatism method. The cylindrical lens (81) functions as a lens only in the X direction of FIG. 5, and as a single vertical line at the point B in FIG.
At point A, the light is condensed as one line horizontally. A for the optical sensor (8)
The light receiving surface is arranged between the point B and the point B, and as shown in FIG. Such an area + ---
Calculate the output of Objective lens (2)
When the focusing distance is set, the irradiation area of each of the four divided surfaces of the optical sensor (8) is equal. Therefore, the operation result is 0.
Even when the objective lens (2) is extremely far away from the disk, no image is formed on the optical sensor (8).
Becomes

When the objective lens (2) is slightly away from the focus distance with respect to the disk, the point A is shifted from the focus position by B
As the point approaches, the coupling surface on the optical sensor (8) becomes a horizontally long circle as shown in FIG. 6 (b). Therefore, the operation result is positive. Conversely, when the objective lens (2) is closer to the disc than the focusing distance, the point A moves away from the normal position, and the coupling surface on the optical sensor (8) is as shown in FIG. As shown, it becomes a vertically long circle, and the calculation result is negative. For this reason, when the objective lens (2) is gradually approached from the position away from the disk, the calculation result gradually increases from 0 and once reaches the positive maximum value. Thereafter, since the objective lens (2) moves toward the in-focus position, the calculation result approaches 0, and when the objective lens (2) moves away from the in-focus position, a signal having characteristics opposite to those described above is obtained. That is, the focus error signal has an S-shape as shown in FIG. Fig. 3 (a), (b)
The right direction is the direction approaching the disk, and a
The point is the rising position, the point c is the maximum position of the focus error signal, and the point b is the focusing position.

A command signal for passing through the first layer (60) is input to the passage instruction circuit (4) in advance. In the focus search operation, when the passage instruction circuit (4) operates,
Even if the S-shaped waveform corresponding to the first layer (60) is detected, the detection circuit (3) ignores the S-shaped waveform and outputs a signal indicating that the focusing operation to the next second layer (61) is to be performed. ).

(Focusing operation) In order to focus on the second layer (61) through the first layer (60) from the state where the objective lens (2) is away from the disk, refer to the flowchart of FIG. Take the steps shown. Initially, no focus servo operation is performed, and a focus servo loop (not shown) is open. Oscillation circuit (7)
Is converted into a focus search drive signal by the integration circuit (5) and supplied to the pickup (1). The focus search drive signal at this time is indicated by A in FIG.
As shown by the line, the inclination is large, and the objective lens (2) approaches the disk quickly (S1). Objective lens (2) is the first layer (60)
, The focus error signal becomes S
A character waveform appears (S2). The detection circuit (3) detects the point a of the S-shaped waveform, but the counter (45) detects that the S-shaped waveform is the first time, that is, the S-shaped waveform corresponding to the first layer (60). This is output to the detection circuit (3) (S3). The passage instruction circuit (4) issues a signal to ignore the first appearing S-shaped waveform (S4). Therefore, there is no change in the focus search drive voltage, and the objective lens (2) passes through the focus position with the first layer (60) at a high speed and moves toward the second layer (61).

When the objective lens (2) is driven close to the second layer (61), an S-shaped waveform appears again in the focus error signal (S2). Since the first S-shaped waveform has already been detected by the counter (45), the passage instruction circuit (4) determines that the objective lens (2) will focus next on the second layer (61). No signal is sent to the detection circuit (3) (S3). When the detection circuit (3) detects the point a (S5), the switch SW1 of the integration circuit (5) is closed to make the gradient of the focus search drive voltage gentle. The objective lens (2) slowly approaches the disk (S6), and as a result, the focus error signal becomes as shown in FIG.
As shown in the figure, the period of the S-shaped waveform becomes longer.

When the detection circuit (3) detects the point b, the focus search operation ends (S7). Next, the focus servo loop is closed, and the objective lens (2) is controlled so as to accurately focus on the rotational vibration of the disk. Therefore,
In this apparatus, when recording / reproducing is started from the second layer (61), the first layer (60) is ignored and the second layer (61) is directly accessed. Focusing operation can be performed quickly. The detection circuit (3) may close the switch SW1 of the integration circuit (5) after detecting the point c. The focus error signal in this case is indicated by a broken line in FIG.

As a method for delaying the movement of the objective lens (2) after the detection circuit (3) detects the point a or the point c,
Instead of the capacitor C2 and the switch SW1, as shown in FIG. 8, a brake means (9) for applying a brake pulse having a voltage opposite to the focus search drive voltage may be provided. Due to the brake pulse from the brake means (9), the voltage value of the focus search drive voltage decreases, and the moving speed of the objective lens (2) decreases. The width of the brake pulse is determined by the weight of the objective lens 2, the viscosity of a damper mechanism (not shown) supporting the objective lens 2, and the like.

In the above embodiment, two focusable layers are provided along the thickness direction of the disk. However, three or more layers can be provided. In this case, the passage instruction circuit
(4) is one more than the layer to be focused at the time of focus search.
A signal is sent to the detection circuit (3) so as to pass through the layer immediately before at a high speed. The counter (45) and the passage instructing circuit (4) are usually constituted by a microcomputer, but the comparator (40) shown in FIG. 9 may be used as a means for counting the S-shaped waveform of the passing focus error signal. . This means that a negative voltage of −V _CC , which is a constant level, is applied to the negative terminal (42) of the comparator (40), and the positive terminal (41) is applied.
Is applied with a focus error signal. When the S-shaped waveform signal is a positive voltage, the comparator (40) keeps its state, and when the voltage is −V _CC or less, the comparator (40) is inverted. By counting the inverted number, the number of S-shaped waveforms of the passed focus error signal can be determined.

The description of the above embodiments is for the purpose of illustrating the present invention and should not be construed as limiting the invention described in the appended claims or reducing the scope thereof. Further, the configuration of each part of the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made within the technical scope described in the claims.

[Brief description of the drawings]

FIG. 1 is a block diagram of a focus search circuit.

FIG. 2 is a sectional view showing a first layer and a second layer of the disc.

3A is a focus error signal when the objective lens moves fast, and FIG. 3B is a focus error signal when the objective lens moves slowly.

FIG. 4 is a diagram showing a focus search drive signal.

FIG. 5 is a perspective view showing an arrangement relationship of a beam splitter, a cylindrical lens, and an optical sensor.

FIG. 6 is a diagram showing an image formed on an optical sensor.

FIG. 7 is a flowchart showing a focus search operation.

FIG. 8 is a block diagram of another focus search circuit.

FIG. 9 is a diagram illustrating a comparator of the detection circuit.

FIG. 10 is a block diagram of a conventional focus search circuit.

[Explanation of symbols]

 (2) Objective lens (3) Detection circuit D disk

Claims (3)

[Claims] A drive means for moving the objective lens (2) toward and away from the disk (D) and a focus error signal indicating a focus shift amount from a focus position of the objective lens (2). ) Reaches the vicinity of the in-focus position, and focuses on an optical disc provided with delay means for reducing the approach speed of the objective lens (2) to the disc D in response to the output of the detection means. In the search circuit, when the objective lens (2) moves up and down with respect to the disk D on which a plurality of focusable layers are provided along the thickness direction, the detection means includes the objective lens (2). It is provided in advance with the number of the in-focus position detected by the detecting means, and the counter means for counting the number of in-focus positions detected by the detecting means. The focus position should be the focus Until it is detected that the in-focus position has been detected, the passage instructing means for outputting a signal to quickly move the objective lens (2) up and down is connected. Next, it is detected that the focus position to be detected is a position to be originally focused,
A focus search circuit for an optical disc, characterized by having a switching function for activating a delay means when the detection means detects the arrival of the objective lens (2) near the in-focus position. 2. A focus search circuit for an optical disk according to claim 1, wherein said delay means is a brake means for issuing a brake pulse having a voltage opposite to a drive voltage to said drive means. 3. An object lens (2) is brought close to a disk D on which a plurality of focusable layers are provided along a thickness direction,
By the time the objective lens (2) reaches the vicinity of the original focus position, the focus position detected in the middle is ignored,
(2) is quickly moved up and down, and when the objective lens (2) reaches the vicinity of the position where the objective lens should be focused, the disk D of the objective lens (2) is moved.
Focus search method for an optical disc in which the approach speed to the object is reduced and the objective lens (2) is surely focused.