JP2726010B2 - Focus servo controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus servo control device used for a reproducing apparatus of an optical disk such as a compact disk (hereinafter, referred to as a disk), and more particularly to a focus servo control which can surely perform a focus servo operation of an optical system. It relates to a control device.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing a circuit configuration of a conventional focus servo control device. Hereinafter, description will be made with reference to the drawings. Reference numeral 1 denotes a photodiode (D1 to D1) divided into four parts for detecting a focus state of a light beam on a disk.
In 4), a signal corresponding to the amount of light applied to each photodiode is output according to the focus state. 11 to 14 are amplifiers for amplifying the signal from each photodiode, 2
a and 2b are two pairs of diagonal photodiodes (D1 and D3).
And an adder for adding the output signals from D2 and D4).
A diagonal sum signal A and a diagonal sum signal B are output. Reference numeral 3 denotes a subtracter for generating a focus error signal, which outputs a signal corresponding to the difference between the diagonal sum signal A and the diagonal sum signal B. Reference numeral 4 denotes a comparator for obtaining a focus detection signal indicating that the focus point has been reached, and outputs a focus detection signal when the focus error signal becomes smaller than the reference signal. 6 is a phase compensation circuit, 71 is a focus search signal generator for generating a triangular wave focus search signal, and is provided to a lens drive coil 81 for moving an objective lens back and forth in order to find a rough focus position when power is turned on. Send a signal. Reference numeral 72 denotes a switch for switching between a focus search signal and a focus error signal. Reference numeral 7 denotes a control unit for performing focus servo control. The signal for controlling the drive coil 81 is switched from the focus search signal to the focus error signal output from the subtractor 3. 8 is a lens drive coil 81
This is a power amplifier that amplifies the signal to be sent to.

FIGS. 5A and 5B are diagrams for explaining a conventional focus servo method. FIG. 5A shows a state of a light beam on a photodiode, FIG. 5B shows a focus error signal, and FIG. 5C shows a focus detection signal. FIG. Hereinafter, description will be made with reference to the drawings. In a CD player, in order to converge a light beam on a disk surface, a focus servo method is adopted so that an objective lens is moved by a focus error signal for detecting a focus state so that the disk surface is always focused. . The optical system is composed of a cylindrical lens and a spherical objective lens. When the objective lens is moved back and forth near the focal point, the photodiode (D1 to D
4) Above, due to the astigmatism caused by the cylindrical lens, FIG.
As shown in (a), when the objective lens is too close to the focal point, the light beam changes to a vertically elliptical shape, when it is at the focal point changes to a perfect circle, and when it is too far from the focal point, the light beam changes to a horizontal oval shape.

After the output signal of the photodiode 1 divided into four is amplified by the amplifiers 11 to 14, the output signal from the diagonally arranged diode (the set of D1 and D3) is input to the adder 2a. Generate a diagonal sum signal A. An output signal from a diode (a set of D2 and D4) arranged diagonally is input to an adder 2b to generate a diagonal sum signal B. At the focal point, the diagonal sum signal A and the diagonal sum signal B become equal, and when deviating from the focal point, a difference occurs between the two diagonal sum signals A and B. Therefore, the diagonal sum signal A and the diagonal sum signal B are input to the subtractor 3 to obtain a difference between the two outputs, and the difference is extracted as a focus error signal. This focus error signal is transmitted to the phase compensating circuit 6,
The focus servo control is performed via the power amplifier 8 to the lens drive coil 81 for moving the objective lens so that the focus error signal always becomes 0.

However, the depth of focus of the objective lens is very shallow, and the distance between the disk and the objective lens greatly deviates from the focal point when the disk is inserted or when the operation is started due to a difference in the thickness of the disk or warpage. Is always there. For this reason, the amount of light that is diffused and impinges on the surfaces of the respective diodes (D1 to D4) decreases, and both the diagonal sum signal A and the diagonal sum signal B decrease. As a result, a focus error signal is hardly output (or unstable), and focus servo control cannot be immediately performed using this signal.

Therefore, in order to first find the approximate focal point,
The focus search signal generator 71 generates a triangular focus search signal, and switches the switch 72 to send the focus search signal to the lens drive coil 81 that moves the objective lens, thereby moving the objective lens back and forth. As a result, a focus error signal as shown in FIG. 5B is obtained from the subtractor 3 as a difference signal between the diagonal sum signal A and the diagonal sum signal B (output signal of the subtractor 3). The focus error signal is input to the comparator 4, and a focus detection signal is output at a point near the focus where the output is inverted as compared with the reference signal (FIG. 5C). The control unit 7 determines that the objective lens has been moved close to the focal point based on the focus detection signal output when the output is inverted, and closes the focus servo loop.

That is, the control unit 7 instructs the switch 72 to
A signal sent to the lens drive coil 81 for moving the objective lens is switched from a focus search signal to a focus error signal. Thereafter, by performing focus servo control so that the focus servo signal output from the subtractor 3 becomes 0, it is possible to always focus on the disk surface.

[0008]

If the depth of focus of the objective lens is very shallow and the distance between the disk and the objective lens is far away from the focal point, light is diffused and each diode (D
1 to D4), and the diagonal sum signal A and the diagonal sum signal B also decrease. As shown in FIG. 5B, the focus error signal gradually approaches 0 not only at the point F (point near focus) of the S-shaped curve but also near both ends (point E).
By comparing the focus error signal with the reference signal, F
At this point, the output of the comparator 4 changes from H to L, but also at point E, the focus error signal is lower, so that it changes from H to L or from L to H due to noise or the like. as a result,
A focus detection signal is output despite the fact that the focus servo is substantially deviated from the correct focus vicinity point (point F in FIG. 5C), and focus servo is performed at an incorrect position (point E in FIG. 5C). There is a problem that the loop is closed. The position where focus servo control is possible is near point F, and focus servo control cannot be performed at the position of point E.

When the reference level is set low, the output from the vicinity becomes unstable (H or L) due to noise. Conversely, if the reference level is set high, the level of the focus error signal changes due to variations in the amount of reflected light from disk to disk, so that there is a problem that a focus detection signal cannot be obtained. Therefore, it was difficult to adjust the reference level.

According to the present invention, a focus servo which can reliably operate a focus servo control by closing a focus servo loop and switching from a focus search signal to a focus error signal after the objective lens is reliably brought close to the focal point. It is an object to provide a control device.

[0011]

In order to solve the above problems, a focus servo control device (1) according to the present invention irradiates a light beam to an optical disk and reads a signal recorded on the optical disk by the reflected light. A focus servo control device for performing focus control of an optical system in an optical pickup, wherein light having an irradiation shape that changes according to a focusing state of the optical system is received by four light receiving elements, and the light receiving device is located at a diagonal position. Two sets of first and second sets of sum signals of the outputs of the light receiving elements
In a focus servo control device that performs focus control of the optical system by a focus servo loop that drives the optical system in accordance with the difference signal of the diagonal sum signal of the above, the optical system is controlled irrespective of control by the focus servo loop. A focus search means for driving to find a focal point; an addition means for adding a bias signal to the first diagonal sum signal; an addition signal obtained by the addition means; A comparison means for comparing the angle sum signal with the signal, and a servo lock means for starting control by the focus servo loop when an output state from the comparison means changes.

Further, the focus servo control device (2) according to the present invention is the focus servo control device (1), wherein the diagonal sum signal that first reaches a maximum value when the objective lens approaches the focal point is used. When the diagonal sum signal A is the diagonal sum signal and the other diagonal sum signal is the diagonal sum signal B, when the objective lens is located sufficiently away from the focal point, A + bias signal C)>
The bias signals C and D are added to at least one of the diagonal sum signals A and B so that a relationship of (diagonal sum signal B + bias signal D) is obtained.

Further, the focus servo control device (3) according to the present invention, in the focus servo control device (1), converts the diagonal sum signal that first reaches a local maximum value when the objective lens approaches the focal point. When the diagonal sum signal A is the diagonal sum signal and the other diagonal sum signal is the diagonal sum signal B, when the objective lens is located sufficiently away from the focal point, A + bias signal C)>
The bias signals C and D are added to at least one of the diagonal sum signals A and B so that a relationship of (diagonal sum signal B + bias signal D) is obtained. When approaching the focal point, after the state of the output from the comparing means changes, when the state changes again,
The control by the focus servo loop is started.

[0014]

In the position where the objective lens is far away from the focal point, the added signal obtained by adding the bias signal to the first diagonal sum signal output from the four light receiving elements by the adding means asymptotically approaches the bias signal. , The second diagonal sum signal asymptotically approaches zero. That is, the two signals are substantially different from each other only by the bias signal.
If this bias signal is set to be larger than the noise of the diagonal sum signal, even if the objective lens moves in a range far away from the focal point, the two signals compared by the comparing means are binarized. The state of the output signal does not change. The state of the output signal from the comparing means changes when the second diagonal sum signal increases and exceeds the (first diagonal sum signal + bias signal). In such a state, it is determined that the objective lens has moved near the focal point, and the servo lock unit closes the focus servo loop,
Subsequent focus servo becomes possible.

Further, according to the focus search signal,
When the objective lens approaches the focal point, (the diagonal sum signal A + the bias signal C) first reaches a maximum value and then decreases. With a delay, the (diagonal sum signal B + bias signal D) reaches the maximum value. For the first time between them, when both are equal is the in-focus point. Therefore, the servo lock means closes the focus servo loop when the state of the output signal from the comparison means changes for the first time, so that subsequent focus servo becomes possible.

Further, according to the focus search signal,
When the objective lens approaches the focal point, (the diagonal sum signal A + the bias signal C) first reaches a maximum value and then decreases. With a delay, the (diagonal sum signal B + bias signal D) reaches the maximum value. In the meantime, there are two times when both become equal, and the latter is the near point of focus. Therefore, after the state of the output signal from the comparing means has changed, when the state changes again, the servo lock means closes the focus servo loop, thereby enabling the subsequent focus servo.

[0017]

FIG. 1 is a block diagram showing a circuit configuration of a focus servo control device according to an embodiment of the present invention. Hereinafter, description will be made with reference to the drawings. Reference numeral 1 denotes photodiodes (D1 to D4) divided into four for detecting the focus state of the light beam on the disk, and outputs a signal corresponding to the amount of light applied to each photodiode according to the focus state. 1
Reference numerals 1 to 14 denote amplifiers for amplifying a signal from each photodiode, and 2a and 2b denote two pairs of diagonal photodiodes (D
1 and D3, and D2 and D4), and outputs a diagonal sum signal A and a diagonal sum signal B. 3
Is a subtractor for generating a focus error signal, which outputs a signal corresponding to the difference between the diagonal sum signal A and the diagonal sum signal B.

Reference numeral 52 denotes a comparator for obtaining a focus detection signal indicating that the camera has reached the near-focus point. A bias signal is added to the diagonal sum signal A via the adder 51 (the diagonal sum signal). A + reference signal) and the diagonal sum signal B are compared. When the (diagonal sum signal A + reference signal) is greater than the diagonal sum signal B, a high-level signal (hereinafter abbreviated as H) is output, and when it is smaller, a low-level signal (hereinafter abbreviated as L). Is output. Reference numeral 6 denotes a phase compensation circuit, and reference numeral 71 denotes a focus search signal generator that generates a triangular focus search signal. The focus search signal generator sends a signal to a lens driving coil 81 that moves the objective lens back and forth in order to search for an approximate focus position. Reference numeral 72 denotes a switch for switching between a focus search signal and a focus error signal. Reference numeral 7 denotes a control unit for performing focus servo control. The control unit includes a microcomputer or the like. As a result of the focus search, it detects that the objective lens has entered a servo-enabled range. The switch 71 is controlled so as to switch the control of the lens drive coil 81 from the focus search signal to the focus error signal output from the subtractor 3 by the focus detection signal. Reference numeral 8 denotes a power amplifier that amplifies a signal sent to a lens driving coil 81 that moves the objective level before and after the focal point.

FIGS. 2A and 2B are diagrams for explaining a focus servo method according to an embodiment of the present invention. FIG. 2A shows a state of a light beam on a photodiode, FIG. 2B shows a signal waveform, and FIGS.
(E) is a diagram showing a focus detection signal. Hereinafter, the focus servo method will be described with reference to the drawings. The focusing system is composed of a cylindrical lens and a spherical objective lens. When the objective lens is moved back and forth near the focal point,
On the divided photodiodes (D1 to D4), the light beam when the objective lens is too close to the focal point due to the cylindrical lens as shown in FIG. Changes to a perfect circle, and if it is too far from the focal point, it changes to a horizontal ellipse.

Therefore, the photodiode 1 divided into four parts
Are amplified by the amplifiers 11 to 14, and the output signals from the diagonally arranged diodes (the set of D1 and D3) are input to the adder 2a to generate a diagonal sum signal A. The bias signal is added by the adder 51 to generate (diagonal sum signal A + bias signal). An output signal from one diagonally arranged diode (a set of D2 and D4) is added to an adder 2
b to generate a diagonal sum signal B. The state of both signals at this time is shown in FIG.

At the position (S1) where the objective lens is too close to the photodiode 1, (diagonal sum signal A + bias signal) is a bias signal, and diagonal sum signal B is zero. Then, as the objective moves in the direction to go away,
(Diagonal sum signal A + bias signal) increases and reaches a maximum value (position S2) and then decreases. One diagonal sum signal B reaches the local maximum (position S4) later than the former, and then decreases. Then, when the objective lens is positioned near the focusing point (S
At the position (S6) far from (3), the (diagonal sum signal A
(+ Bias signal) returns to the state where the bias signal and the diagonal sum signal B are 0. If the value of the bias signal to be added to the diagonal sum signal A is set to a value larger than the diagonal sum signal B, the focus detection signal cannot be obtained, so that the bias signal exceeds the noise of the diagonal sum signals (A and B). If the value is set to a low value, the output signal of the comparator 52 is stable, and the in-focus point can be clearly detected.

When these two signals are input to the comparator 52 and compared, as shown in FIG. 2C, assuming that the horizontal axis is the distance between the disk and the objective lens, the positions (S1 to S3) that are too close to the objective lens. ), (Diagonal sum signal A + bias signal)
The output of H is larger in the case of, and both signals are the same at the position of S3. Thereafter, the diagonal sum signal B increases (S3 to S3).
S5) L is output. Furthermore, the objective lens moves and S
At positions S5 to S6, (diagonal sum signal A + bias signal) becomes larger and H is output.

Considering the movement of the objective lens and the timing of the output signal, first, the objective lens moves at a constant speed in a direction away from a position too close by the focus search signal (a direction from position S1 to position S6). The timing of the output signal in this case is as shown in FIG.
Assuming that the horizontal axis is the time axis, the (diagonal sum signal A + bias signal) initially outputs a larger H, and then the diagonal sum signal B increases and outputs the L. When the objective lens further moves, (diagonal sum signal A + bias signal) becomes larger and H is output. During the movement of the objective lens (in the direction in which the objective lens moves away), this signal changes from H to L.
Is a point near the focus, and a focus detection signal is output.

Next, when the objective lens moves at a constant speed in a direction approaching from a position far away from the focus search signal (a direction from position S6 to position S1), the signals output corresponding to the positions are the same. However, since the moving direction of the objective lens is reversed, the output timing is reversed as shown in FIG. At first, the (diagonal sum signal A + bias signal) is larger and H is output, and thereafter, the diagonal sum signal B is increased and L is output. When the objective lens further moves, (diagonal sum signal A + bias signal) becomes larger and H is output. During the movement of the objective lens (in the direction in which the objective lens approaches)
Then, the point at which this signal changes from L to H becomes a near focus point, and a focus detection signal is output.

In any case, there are two points where the magnitudes of both signals match (timing corresponding to the positions of S3 and S5). However, the control unit 7 determines the direction of moving the objective lens. Therefore, whether the point near the focus changes from H to L or from L to H is uniquely determined from the direction of movement of the objective lens, and the opposite point is set as the point near the focus. There is no fear.

The in-focus point detection signal obtained by the comparator 52 is sent to the control unit 7, which determines that the objective lens can be moved close to the focal point based on the in-focus point detection signal, and closes the focus servo loop. . That is, the control unit 7 instructs the switch 72 to switch the signal sent to the lens drive coil 81 for moving the objective lens from the focus search signal to the focus error signal. Thereafter, by performing the focus servo control so that the focus servo signal output from the subtractor 3 becomes 0, it is possible to always focus on the disk surface.

According to the present embodiment, a bias signal larger than noise is added to one of the diagonal sum signals and compared with the other diagonal sum signal, so that the diagonal sum signal is located at a position away from the focal point. Even if the sum signal becomes small and the focus error signal, which is the difference signal, becomes small, the influence of noise on the comparison result is small and there is no possibility that the focus servo loop will be closed by erroneously recognizing the near-focus point position.

FIGS. 3A and 3B are diagrams for explaining a focus servo method according to a second embodiment of the present invention. FIG. 3A shows a state of a light beam on a photodiode, FIG. 3B shows a signal waveform, and FIG.
(E) is a diagram showing a focus detection signal. Hereinafter, the focus servo method will be described with reference to the drawings. In this embodiment, an example in which a bias signal is added to the diagonal sum signal B will be described. In this case, the adder 51 is put on the diagonal sum signal B side, or the adder 51 adds the negative bias signal as it is. The rest of the circuit configuration is the same as in the first embodiment, and a description thereof will be omitted.

FIG. 3A shows the shape of the light beam on the photodiode 1, which is the same as in the first embodiment. An output signal from a diagonally arranged diode (a set of D1 and D3) is input to an adder 2a to generate a diagonal sum signal A. An output signal from a diode (a set of D2 and D4) arranged on one diagonal is input to an adder 2b to generate a diagonal sum signal B. The adder (adder 51 of FIG. (To the sum signal B side) to add a bias signal to create a (diagonal sum signal B + bias signal). The state of both signals at this time is shown in FIG.

The position where the objective lens has come too close (S11).
In (2), (diagonal sum signal B + bias signal) is a bias signal, and diagonal sum signal A is 0. Thereafter, the diagonal sum signal A increases in accordance with the movement of the objective lens, and reaches a maximum value (S1).
3) and then decrease. (Diagonal sum signal B + bias signal) has a local maximum value (position of S15) later than the former.
Decreases after reaching. Then, at a position (S16) where the objective lens is too far from the near-focus point position (S14),
(Diagonal sum signal B + bias signal) returns to the state where the bias signal and diagonal sum signal A are 0. The bias signal to be added to the diagonal sum signal B is the same as that of the first embodiment.
And a lower value that exceeds the noise of B).

When these two signals are input to the comparator 52 and compared, as shown in FIG. 3C, assuming that the horizontal axis is the distance between the disk and the objective lens, the positions too close to the objective lens (S11 to S12) ), A larger L is output for the (diagonal sum signal B + bias signal), and both signals are the same at the position S12. Thereafter, the diagonal sum signal A increases (S
12 to S14) H is output. Further, at the positions S14 to S16 after the objective lens moves, (diagonal sum signal B + bias signal) becomes larger and L is output.

Considering the movement of the objective lens and the timing of the output signal as in the first embodiment, first,
The timing of the output signal when the objective lens moves at a constant speed in the direction away from the position too close to the focal point (the direction from position S11 to position S16) is shown in FIG.
As shown in (d), a point at which this signal changes from H to L during the movement of the objective lens becomes a near focus point, and a focus detection signal is output.

Next, when the objective lens moves at a constant speed in a direction approaching from a position too far from the in-focus position (direction from position S16 to position S11), the signals output corresponding to the positions are the same. However, since the moving direction of the objective lens is opposite, the output timing is reversed as shown in FIG. 3 (e) when the horizontal axis is the time axis, and this signal changes from L during the movement of the objective lens. The point that changes to H becomes a near focus point, and a focus detection signal is output.

The operation after the in-focus point detection signal is detected is the same as that of the first embodiment, and the description is omitted. In this way, the disk surface can always be focused. According to this embodiment, a bias signal larger than noise is added to one of the diagonal sum signals,
By comparing with the other diagonal sum signal, the diagonal sum signal becomes smaller at a position away from the focal point, and even if the focus error signal which is the difference signal becomes smaller, the influence of noise on the comparison result is reduced. There is no danger that the focus servo loop will be closed by mistakenly assuming that it is a small near-focus point position.

[0035]

As described above in detail, according to the present invention, it is possible to perform the focus servo reliably without fear that the position away from the focal point is mistaken for the focal point position and the focus servo loop is closed. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a circuit configuration of a focus servo control device according to an embodiment of the present invention.

2A and 2B are diagrams for explaining a focus servo method according to an embodiment of the present invention, wherein FIG. 2A shows a state of a light beam on a photodiode, FIG. 2B shows a diagonal sum signal waveform, and FIGS. e)
FIG. 4 is a diagram showing a focus detection signal.

3A and 3B are diagrams for explaining a focus servo method according to a second embodiment of the present invention, wherein FIG. 3A shows a state of a light beam on a photodiode, FIG. 3B shows a diagonal sum signal waveform, and FIG. ~
(E) is a diagram showing a focus detection signal.

FIG. 4 is a block diagram showing a circuit configuration of a conventional focus servo control device.

5A and 5B are diagrams for explaining a conventional focus servo method, wherein FIG. 5A shows a state of a light beam on a photodiode,
(B) is a diagram showing a focus error signal waveform, and (c) is a diagram showing a focus detection signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Photodiode 2a, 2b, 51 ... Adder 3 ... Subtractor 52 ... Comparator 7 ... Control part

Claims (3)

(57) [Claims] 1. A focus servo control device for irradiating an optical disk with a light beam and controlling a focus of an optical system in an optical pickup for reading a signal recorded on the optical disk by reflected light of the optical disk. Two sets of first and second diagonal sum signals are received by four light receiving elements, the light having an irradiation shape that changes according to the focus state, and the sum signals of the outputs of the light receiving elements at diagonal positions. A focus servo control device that controls the focus of the optical system by a focus servo loop that drives the optical system in accordance with the difference signal of: a general focus position of the optical system is searched regardless of control by the focus servo loop. Search means for driving, an addition means for adding a bias signal to the first diagonal sum signal, an addition signal obtained by the addition means, Comparing means for comparing the second diagonal sum signal with the servo signal, and a servo lock means for starting control by the focus servo loop when an output state from the comparing means changes. Focus servo controller. 2. When the objective lens approaches a focal point, the diagonal sum signal that first reaches a local maximum value is a diagonal sum signal A, and the other diagonal sum signal is a diagonal sum signal B. When the objective lens is at a position sufficiently distant from the focal point, the adding means is configured to satisfy a relationship of (diagonal sum signal A + bias signal C)> (diagonal sum signal B + bias signal D). A focus servo control device for adding the bias signals C and D to at least one of the diagonal sum signals A and B. 3. When the objective lens approaches the focal point, the diagonal sum signal that first reaches a local maximum value is a diagonal sum signal A, and the other diagonal sum signal is a diagonal sum signal B. When the objective lens is at a position sufficiently distant from the focal point, the adding means is configured to satisfy a relationship of (diagonal sum signal A + bias signal C)> (diagonal sum signal B + bias signal D). Adding the bias signals C and D to at least one of the diagonal sum signals A and B, wherein the servo lock means changes the state of the output from the comparison means when the objective lens approaches the focal point. A focus servo control device which starts control by the focus servo loop when the state changes again.