JP4200642B2 - Focus error signal calculation method and optical pickup device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a focus error signal calculation method and an optical pickup device.
[0002]
[Prior art]
Conventionally, an optical recording medium such as an optical disk has been proposed, and an optical pickup device that reads information signals from the optical recording medium has been proposed.
[0003]
As shown in FIG. 7, such an optical pickup device includes a light source 101 such as a laser diode, an objective lens 103 that focuses and irradiates a light beam emitted from the light source 101 on an optical recording medium 102, and An optical path branching element 104 that branches an optical path of a reflected light beam from the optical recording medium 102, an astigmatism generating element 105 that causes astigmatism in the reflected light beam, and a reflected light beam that has passed through the astigmatism generating element 105 And a photodetector 106 that is focused on the light receiving surface.
[0004]
In this optical pickup device, the focus error signal calculation circuit causes the light beam between the condensing point of the light beam by the objective lens 103 and the signal recording surface of the optical recording medium 102 based on the output of the photodetector 106. A focus error signal indicating the distance in the optical axis direction is calculated.
[0005]
As shown in FIG. 8, the photodetector has four light receiving surfaces arranged in a radial pattern, and the four light receiving surfaces receive the reflected light beam by dividing it into four around the optical axis. A first light receiving surface A that outputs a first light detection output a and a second light receiving surface B that outputs a second light detection output b around the optical axis of the reflected light beam. When the third light receiving surface C that outputs the third light detection output c and the fourth light receiving surface D that outputs the fourth light detection output d are used, the focus error signal calculation circuit converts the focus error signal Fe to
Fe = (a + c) − (b + d)
It is calculated by the operation.
The tracking error signal (push-pull signal) Tr is
Tr = (a + d) − (b + c)
It is calculated by the operation.
[0006]
In the optical pickup device, the objective lens 103 is supported by a biaxial actuator so as to be movable in the optical axis direction and the direction orthogonal to the recording track, and is moved in the optical axis direction based on a focus error signal. The moving operation is performed by a tracking servo operation that is moved in a direction orthogonal to the recording track based on the focus servo operation and the tracking error signal.
[0007]
[Problems to be solved by the invention]
By the way, in the optical pickup device as described above, the fluctuation of the tracking error signal (push-pull signal) Tr may affect the focus error signal Fe. That is,
Fe = (a + c)-(b + d) = (ab)-(dc)
Thus, the focus error signal is a difference signal between two push-pull signals. Then, as shown in FIG. 9, the tracking error signal (push-pull signal) is generated in a state where the position of the photodetector 106 is deviated from the optical axis of the reflected light beam and a and d and b and c are not equal. ) When Tr is no longer 0, the focus error signal is no longer 0 even if no focus error occurs as shown in FIG.
[0008]
As described above, when the focus error signal Fe is affected by the fluctuation of the tracking error signal (push-pull signal) Tr, the focus servo characteristic becomes unstable. In particular, a large-amplitude push-pull signal during a seek operation or the like. Is mixed with the focus error signal, and the focus servo characteristic is adversely affected. In addition, the push-pull signal unnecessarily vibrates the biaxial actuator, increasing the operating noise.
[0009]
Furthermore, in order to maintain the focus servo characteristic, it is necessary to maintain a high accuracy in the mounting position of the photodetector with a small tolerance for the positional deviation of the photodetector. That is, the balance of the S-shaped curve of the focus error signal is likely to deteriorate due to the positional deviation of the photodetector.
[0010]
Therefore, the present invention has been proposed in view of the above circumstances, and the focus error signal is prevented from being affected by fluctuations in the tracking error signal, so that stable focus servo operation can be performed, and light detection is performed. It is an object of the present invention to provide a focus error signal calculation method and an optical pickup device which are capable of increasing an allowable amount with respect to a position shift of a device.
[0011]
[Means for Solving the Problems]
In order to solve the above-described problems, a focus error signal calculation method according to the present invention is configured to irradiate a light beam emitted from a light source by condensing the light beam on an optical recording medium by an objective lens and reflecting the light beam from the optical recording medium. Astigmatism is generated in the light beam, and the reflected light beam is collected on the light receiving surface of the photodetector. Based on the output of the light detector, the light collecting point of the light beam by the objective lens and the signal recording surface of the optical recording medium A focus error signal calculation method for calculating a focus error signal indicating a distance in the optical axis direction of the luminous flux between the four light beams using a light detector having four light receiving surfaces arranged radially. The first light receiving surface, the second light receiving surface, which receives the divided light flux by dividing the reflected light beam around the optical axis by the four light receiving surfaces, and outputs the first light detection output a around the optical axis of the reflected light flux. The second receiver that outputs the light detection output b of Surface, the third and the third light receiving surface and a fourth fourth light receiving surfaces outputting light detection output d for outputting light detection output c, the first and second light receiving surface, the recording of the optical recording medium The third and fourth light receiving surfaces are arranged side by side in a direction perpendicular to the recording track of the optical recording medium , and gains for these light detection outputs a, b, c, and d are arranged. Is the first gain k ₁ or the second gain k _2, and the first and second gains k ₁ and k ₂ are k ₁ {the AC component of (ab)} + k ₂ {(c− d) AC component} = 0, or k ₁ {amplitude of (ab)} = k ₂ { amplitude of (cd)} , the focus error signal Fe is changed to Fe = _k 1 of _{(a-b) + k 2} (c-d) are those determined by calculation.
[0012]
Further, the optical pickup device according to the present invention has astigmatism in a light source, an objective lens that focuses and irradiates a light beam emitted from the light source, and a reflected light beam from the optical recording medium. An astigmatism generating element that causes aberration, a photodetector that collects a reflected light beam that has passed through the astigmatism generating element on a light receiving surface, and a light beam that is collected by an objective lens based on the output of the photodetector A focus error signal calculation circuit for calculating a focus error signal indicating a distance in the optical axis direction of the light beam between the point and the signal recording surface of the optical recording medium. The photodetector has four light receiving surfaces arranged in a radial pattern, and the four light receiving surfaces receive the reflected light beam divided into four around the optical axis.
[0013]
In this optical pickup device, the four light receiving surfaces are arranged around the optical axis of the reflected light beam, the first light receiving surface for outputting the first light detection output a, and the second light detection output b for outputting the second light detection output b. 2 light receiving surfaces, a third light receiving surface that outputs a third light detection output c, and a fourth light receiving surface that outputs a fourth light detection output d. The first and second light receiving surfaces are optical recordings. The third and fourth light receiving surfaces are arranged side by side in a direction perpendicular to the recording track of the optical recording medium, and these light detection outputs a, b, c, The gain for d is the first gain k ₁ or the second gain k _2, and the first and second gains k ₁ and k ₂ are k ₁ {AC component of (ab)} + k _2. = 0 {(c-d) AC components}, _{or, k 1 {(a-b} ) the amplitude _of} = k 2 {(c- When determined to be the amplitude}) of the focus error signal operation circuit the focus error signal _Fe, is shall determined by a calculation that Fe = k 1 (a-b ) + k 2 (c-d) .
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0015]
As shown in FIG. 1, an optical pickup device according to the present invention that performs a focus error signal calculation method according to the present invention includes a laser diode 1 serving as a light source, and a light beam emitted from the laser diode 1 as an optical recording medium. An objective lens 2 that is focused and irradiated on the optical disk 102, a beam splitter 3 that splits the optical path of the reflected light beam from the optical disk 102, and astigmatism in the reflected light beam that has passed through the beam splitter 3. An astigmatism generating element 4 and a photodetector 5 that collects a reflected light beam that has passed through the astigmatism generating element 4 on a light receiving surface are configured.
[0016]
In the optical pickup device, the objective lens 2 is supported by a biaxial actuator (not shown) so as to be movable in the optical axis direction of the objective lens 2 and the radial direction of the optical disk 102 (direction perpendicular to the recording track). It is moved by a focus servo operation that is moved in the optical axis direction based on the focus error signal and a tracking servo operation that is moved in the radial direction of the optical disk based on the tracking error signal.
[0017]
In this optical pickup device, the focus error signal and the tracking error signal are calculated based on the light detection output of the photodetector 5 by the calculation circuit 6 serving as a focus error signal calculation circuit. The focus error signal is a signal indicating the distance in the optical axis direction of the light beam between the condensing point of the light beam by the objective lens 2 and the signal recording surface of the optical disc 102. Based on the focus error signal, the biaxial actuator moves the objective lens 2 in the direction of the optical axis of the objective lens 2 to realize a focus servo operation. The tracking error signal is a signal indicating the radial distance of the optical disk 102 between the light beam condensing point by the objective lens 2 and the recording track of the optical disk 102. Based on the tracking error signal, the biaxial actuator moves the objective lens 2 in the radial direction of the optical disk perpendicular to the optical axis of the objective lens 2 to realize a tracking servo operation.
[0018]
As shown in FIG. 2, the photodetector 5 has four light receiving surfaces A, B, C, and D arranged in a radial pattern, and an optical disc is formed by these four light receiving surfaces A, B, C, and D. The reflected light beam from 102 is divided into four around the optical axis and received. The four light receiving surfaces A, B, C, and D output a first light receiving surface A that outputs a first light detection output a and a second light detection output b around the optical axis of the reflected light beam. A second light receiving surface B, a third light receiving surface C that outputs a third light detection output c, and a fourth light receiving surface D that outputs a fourth light detection output d.
[0019]
These light receiving surfaces A, B, C, and D are two pairs of light receiving surfaces that receive the returning light flux of the light beam irradiated on the area straddling the recording track on the optical disc 102. That is, the first and second light receiving surfaces A and B are light receiving surfaces that respectively receive the return light beams of the light beams irradiated on the two regions on the optical disk 102 with the recording track interposed therebetween, and The fourth light receiving surfaces C and D are light receiving surfaces that respectively receive the return light beams of the light beams irradiated on the two regions on the optical disk 102 across the recording track.
[0020]
The arithmetic circuit 6 calculates the tracking error signal Tr by the following calculation.
[0021]
Tr = (a + d) − (b + c)
This is a so-called “push-pull method” for detecting a tracking error signal.
[0022]
Further, the gain for each light detection output a, b, c, d from each light receiving surface A, B, C, D of the photodetector 5 is set to the first gain k ₁ or the second gain k ₂ . At this time, the arithmetic circuit 6 obtains the focus error signal Fe by the following calculation.
[0023]
Fe = (k ₁ · a + k ₂ · c) − (k ₁ · b + k ₂ · d)
= K ₁ · a + k ₂ · c-k ₁ · b-k ₂ · d
= K ₁ · a-k ₁ · b + k ₂ · c-k ₂ · d
= K ₁ (ab) + k ₂ (cd)
= K ₁ (ab) -k ₂ (dc)
This is a so-called “astigmatism method” for detecting a focus error signal. The astigmatism generated by the astigmatism generating element 4 with respect to the reflected light beam is the direction (A, C, and A) of the light receiving surfaces facing each other through the optical axis of the reflected light beam before and after the focal point of the reflected light beam. BD) is formed.
[0024]
By the way, in this optical pickup device, as shown in FIG. 3, the focus error signal is received for each of the two pairs of light receiving surfaces that receive the returning light flux of the light beam applied to the region straddling the recording track on the optical disk 102. Push-pull signals are obtained, and these push-pull signals are respectively multiplied by gains k ₁ and k ₂ .
[0025]
Accordingly, in this optical pickup device, the gain k ₁ , k ₂ is appropriately determined for each pair of light receiving parts A · B, D · C, thereby suppressing the influence of fluctuations in the tracking error signal on the focus error signal. be able to.
[0026]
The gains k ₁ and k ₂ are determined as follows prior to the reading of the information signal from the optical disc 102, thereby effectively suppressing the influence of the fluctuation of the tracking error signal on the focus error signal. be able to.
[0027]
k ₁ {AC (alternating current) component of (ab)} + k ₂ {AC (alternating current) component of (cd)} = 0
Or
k ₁ {amplitude of (a−b)} = k ₂ {amplitude of (cd)}
In this way, the influence of the tracking error signal fluctuation on the focus error signal is suppressed, so that the focus servo characteristics are stabilized.In particular, even during a seek operation, a large-amplitude push-pull signal becomes the focus error signal. Since they are not mixed, the focus servo characteristics do not deteriorate. Further, the push-pull signal does not unnecessarily vibrate the biaxial actuator, and the operation sound does not increase.
[0028]
Further, it is not necessary to maintain the accuracy of the mounting position of the photodetector in order to maintain the focus servo characteristic, and the tolerance for the positional deviation of the photodetector is large. That is, there is no deterioration in the balance of the S-curve of the focus error signal due to the positional deviation of the photodetector.
[0029]
As an example of the circuit configuration for determining the gains k ₁ and k ₂ in the arithmetic circuit of this optical pickup device, the light detection output from the first light receiving surface A is input via an amplifier 7 as shown in FIG. And a subtractor (push-pull calculator) 9 to which the light detection output from the second light receiving surface B is input via the amplifier 7. The output of the subtracter 9 is supplied to the buffer 10 and the integrator 11. A circuit that is sent to the hold circuit 12 via the circuit is conceivable. The integrator 11 performs integration based on the reference amplitude level. The hold circuit 12 holds the input / output value except during gain adjustment, and feeds back the held value to the amplifiers 7 and 8 as gain. The outputs of these amplifiers 7 and 8 are used for calculation of focus error signals as outputs from the respective light receiving surfaces A and B.
[0030]
Similarly, in this circuit, the light detection output from the fourth light receiving surface D is input through the amplifier 13 and the light detection output from the third light receiving surface C is input through the amplifier 14. Unit (push-pull computing unit) 15. The output of the subtracter 9 is sent to the hold circuit 18 via the buffer 16 and the integrator 17. The integrator 17 performs integration based on the reference amplitude level. The hold circuit 18 holds the input output value except during gain adjustment, and feeds back the held value to the amplifiers 13 and 14 as gain. The outputs of these amplifiers 13 and 14 are used for calculation of a focus error signal as outputs from the respective light receiving surfaces D and C.
[0031]
In this circuit, the integrators 11 and 17 may perform integration with reference to signals input to the other integrators 17 and 11 as shown in FIG.
[0032]
In this optical pickup device, the focus error signal obtained by executing the focus error signal calculation method according to the present invention, as shown in FIG. 6, even when there is an error in the mounting position of the photodetector, The influence of fluctuation of the tracking error signal is small. In FIG. 6, the “X direction” (horizontal axis) is the amount of positional deviation in the direction along the tangent line of the recording track on the optical disc, and the “Y direction” (the numerical value shown at each point) is on the optical disc. Is a positional deviation amount in a direction perpendicular to the recording track. The left vertical axis indicates the amount of influence of the tracking signal variation on the focus error signal, and the right vertical axis indicates the defocus amount.
[0033]
【The invention's effect】
As described above, in the focus error signal calculation method and the optical pickup device according to the present invention, the focus error signal can be obtained even when there is an error in the mounting position of the photodetector that detects the reflected light beam from the optical recording medium. Is prevented from being affected by fluctuations in the tracking error signal, so that the focus servo characteristics are not deteriorated even during high-speed seeking.
[0034]
That is, according to the present invention, the focus error signal is prevented from being affected by fluctuations in the tracking error signal, a stable focus servo operation can be performed, and the tolerance for the positional deviation of the photodetector can be increased. Thus, it is possible to provide a focus error signal calculation method and an optical pickup device that have been made in the above.
[Brief description of the drawings]
FIG. 1 is a side view showing a configuration of an optical pickup device according to the present invention that implements a focus error signal calculation method according to the present invention.
FIG. 2 is a plan view showing a configuration of a light receiving surface of a photodetector in the optical pickup device.
FIG. 3 is a plan view for explaining calculation of a focus error signal in the optical pickup device in association with a light receiving surface.
FIG. 4 is a circuit diagram showing a configuration of a circuit for determining a gain in an arithmetic circuit of the optical pickup device.
FIG. 5 is a circuit diagram showing another example of a circuit configuration for determining a gain in an arithmetic circuit of the optical pickup device.
FIG. 6 is a graph showing the influence of a change in tracking error on a focus error signal when the focus error signal calculation method is performed in the optical pickup device.
FIG. 7 is a side view showing a configuration of a conventional optical pickup device.
FIG. 8 is a plan view showing a configuration of a light receiving surface of a photodetector in the conventional optical pickup device.
FIG. 9 is a plan view showing a state in which the photodetector is displaced in the conventional optical pickup device.
FIG. 10 is a plan view for explaining that the focus error signal in the conventional optical pickup device is affected by the fluctuation of the tracking error signal, corresponding to the light receiving surface.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Laser diode, 2 Objective lens, 3 Beam splitter, 4 Astigmatism generating element, 5 Photo detector, 6 Arithmetic circuit, 102 Optical disk

Claims (2)

The light beam emitted from the light source is condensed and irradiated onto the optical recording medium by the objective lens, and astigmatism is generated in the reflected light beam from the optical recording medium. The reflected light beam is received by the photodetector. A focus error signal indicating the distance in the optical axis direction of the light beam between the condensing point of the light beam by the objective lens and the signal recording surface of the optical recording medium based on the output of the photodetector. A focus error signal calculation method for calculating,
Using the light detector having four light receiving surfaces arranged radially as the photodetector, the four light receiving surfaces receive the reflected light beam divided into four around the optical axis,
The four light receiving surfaces are a first light receiving surface that outputs a first light detection output a around the optical axis of the reflected light beam, a second light receiving surface that outputs a second light detection output b, and a third light receiving surface. The third light receiving surface for outputting the light detection output c and the fourth light receiving surface for outputting the fourth light detection output d, and the first and second light receiving surfaces serve as recording tracks of the optical recording medium. The third and fourth light receiving surfaces are arranged side by side in a direction perpendicular to the recording track of the optical recording medium , and gains for these light detection outputs a, b, c, and d are arranged. Is the first gain k ₁ or the second gain k ₂ ,
The first and second gains k ₁ and k ₂ are set to k ₁ {AC component of (ab)} + k ₂ { AC component of (cd)} = 0, or k ₁ {(a− b) amplitude} = k ₂ {( amplitude of (cd))} , the focus error signal Fe is
Fe = k ₁ (ab) + k ₂ (cd)
Focus error signal operation method Ru determined by calculation that. A light source;
An objective lens that focuses and irradiates a light beam emitted from the light source on an optical recording medium;
An astigmatism generating element for causing astigmatism in a reflected light beam from the optical recording medium of the light beam;
A photodetector that collects the reflected light beam that has passed through the astigmatism generating element on the light receiving surface;
Focus error signal calculation for calculating a focus error signal indicating the distance in the optical axis direction of the light beam between the condensing point of the light beam by the objective lens and the signal recording surface of the optical recording medium based on the output of the photodetector With circuit and
The photodetector has four light receiving surfaces arranged radially, and receives the reflected light flux divided into four around the optical axis by the four light receiving surfaces,
The four light receiving surfaces are a first light receiving surface that outputs a first light detection output a around the optical axis of the reflected light beam, a second light receiving surface that outputs a second light detection output b, and a third light receiving surface. The third light receiving surface for outputting the light detection output c and the fourth light receiving surface for outputting the fourth light detection output d, and the first and second light receiving surfaces serve as recording tracks of the optical recording medium. The third and fourth light receiving surfaces are arranged side by side in a direction perpendicular to the recording track of the optical recording medium , and gains for these light detection outputs a, b, c, and d are arranged. Is the first gain k ₁ or the second gain k ₂ ,
The first and second gains k ₁ and k ₂ are set to k ₁ {AC component of (ab)} + k ₂ { AC component of (cd)} = 0, or k ₁ {(a− b) amplitude} = k ₂ {( amplitude of (cd))} , the focus error signal calculation circuit calculates the focus error signal Fe as follows:
Fe = k ₁ (ab) + k ₂ (cd)
The optical pickup device Ru determined by calculation that.

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