JP3431595B2 - Disc tilt detecting device and disc tilt correcting device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses an optical disc drive for detecting an inclination between an optical disc medium and an optical axis of an objective lens of an optical pickup, and a detection signal from the disc tilt detecting device. The present invention relates to a disc tilt correction device that corrects a disc tilt.

[0002]

2. Description of the Related Art In recent years, the density of optical disk devices has been increasing, and there is a strong demand for improvement in the accuracy of the optical pickup system as the density increases. Above all, the perpendicularity of the optical axis of the objective lens of the optical pickup with respect to the optical disk medium is strictly required, and when a tilt error called tilt occurs between them, it is necessary to detect and correct it with high accuracy. . The conventional disc tilt detecting device is, for example, as shown in FIG. 7, an optical pickup 31 and an optical sensor 3.
2 and a differential amplifier 33, and an optical sensor 3
2 was equipped with the light emission source 34 and the light receiving elements 35a and 35b (for example, refer to Japanese Utility Model Laid-Open No. 60-127630). The optical pickup 31 irradiates the information track of the optical disc medium 30 with light. The optical sensor 32 is provided in the optical pickup 31, irradiates the optical disc medium 30 with light from a light emitting source 34, and receives reflected light from a light receiving element 35.
Light is received at a and 35b. The differential amplifier 33 includes the light receiving element 3
The difference between the outputs from 5a and 35b is calculated.

In this conventional disc tilt detecting device, light such as far infrared rays emitted from the light emitting source 34 is reflected by the optical disc medium 30 and reaches the light receiving elements 35a and 35b. Here, when the tilt is 0 °, that is, when the optical axis of the objective lens and the optical disk medium 30 are vertical, the reflected light reaches the boundary between the light receiving elements 35a and 35b, so that the tilt occurs. In this case, the reflected light is the light receiving element 3
It shifts to either 5a or 35b. Therefore, as the output of the differential amplifier 33 that calculates the difference between the outputs of the light receiving elements 35a and 35b, an electric signal according to the direction and amount of tilt can be obtained.

Further, the conventional disc tilt correction device has a structure in which the entire optical pickup is tilted by the tilt stage.

[0005]

However, in the above-mentioned conventional disc tilt detecting device, the detection accuracy is limited, and since the optical sensor 32 is separately provided on the optical pickup 31, the optical pickup 31 becomes large in size. Had. Further, in the above-described conventional disc tilt correction device, since the entire optical pickup is tilted by the tilt stage, the device becomes large in scale and there is a problem in responsiveness.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a disc tilt detecting device which has high detection accuracy and does not require a separate optical system as in the prior art. Another object of the present invention is to provide a disc tilt correction device having excellent responsiveness.

[0007]

According to a first aspect of the present invention, there is provided irradiation means for irradiating an information mark formed on a rotating optical disc medium with a laser beam focused by an objective lens, and a laser for irradiating the optical disc medium. beam
The difference in the amount of light received by the two light receiving elements that received the reflected light of
A differentiating means for outputting a differential value each, and the maximum value detecting means for detecting a maximum value of the output of said differentiating means, and the minimum value detecting means for detecting a minimum value of the output of said differentiating means, is detected
Differential means for calculating the difference between the maximum value and the minimum value, and the difference
Of the disc tilt based on the value output by the moving means.
It is characterized by comprising a detection means for detecting a direction and an amount . The invention according to claim 2 is the disk according to claim 1.
Including the tilt detection device, the disc tilt detection device
The disc tilt detected by the
A disc tilt correction device, characterized in that a first optical element and a second optical element having the same coma aberration are provided rotatably around the same optical axis from the light emitting means to the optical disc medium. There is.

[0008]

According to a third aspect of the present invention, there is provided first rotating means for rotating the first optical element about the optical axis, and second rotating means for rotating the second optical element about the optical axis. From the two components of the tilt detected by the disc tilt detector that are orthogonal to each other, a signal for appropriately rotating the first and second optical elements in the same direction and a signal for appropriately rotating the first and second optical elements in opposite directions are generated. It is characterized by further comprising a converting means for generating and supplying to the first rotating means and the second rotating means.

According to a fourth aspect of the invention, the disc tilt detection is performed.
The output device is a disc drive for tangential tilt detection.
A tilt detection device, the disc tilt correction device
Is a disc tilt detector for radial tilt detection.
Disc tilt detection for radial tilt detection.
The emitting device is a first light receiving means for detecting reflected light in a small area smaller than the interference area in the interference area between the reflected straight light of the reflected light of the laser beam in the far field and the first-order diffracted light by the information track. it comprises a differential means for calculating a difference between the amount of light received by the second light receiving means, the received light amount by the first light receiving means and the second light receiving means for detecting the reflected light of the interference region except the small areas Is characterized by.

[0011]

In the invention of claim 1, the irradiation means irradiates the information mark formed on the rotating optical disk medium with the laser beam focused by the objective lens. The differentiating means is composed of two light receiving elements placed in the scanning direction of the information mark.
A second difference for calculating the difference between the output of the light receiving element and these elements
The moving amount of the reflected light of the laser beam
Output the differential value. The maximum value detecting means samples and holds the maximum value of the output of the differentiating means. The minimum value detection means is
The minimum value of the output of the differentiating means is sampled and held. First
The differential means calculates the difference between the output of the maximum value detecting means and the output of the minimum value detecting means.

In the invention of claim 2 , the first optical element and the second optical element have equal coma and are rotatably installed around the same optical axis from the light emitting means to the optical disk medium. Has been done.

In the invention of claim 3 , the first rotating means rotates the first optical element about the optical axis. The second rotating means rotates the second optical element about the optical axis. The conversion means generates a signal for appropriately rotating the first and second optical elements in the same direction and a signal for appropriately rotating the first and second optical elements in opposite directions from the two components of the tilt detected by the disc tilt detection device which are orthogonal to each other. Then, it is supplied to the first rotating means and the second rotating means.

In the invention of claim 4 , the irradiation means irradiates the information track formed on the optical disk medium with the laser beam focused by the objective lens. The first light receiving means detects the reflected light in a small region smaller than the interference region in the interference region between the reflected straight light of the reflected light of the laser beam in the far field and the first-order diffracted light by the information track. The second light receiving means detects the reflected light in the interference area excluding the small area. The differential means calculates the difference between the amount of light received by the first light receiving means and the amount of light received by the second light receiving means. The differentiating means outputs a differential value of the change in the light amount of the reflected light of the laser beam. The maximum value detecting means samples and holds the maximum value of the output of the differentiating means. The minimum value detection means is
The minimum value of the output of the differentiating means is sampled and held. First
The differential means calculates the difference between the output of the maximum value detecting means and the output of the minimum value detecting means.

[0015]

Embodiments of the present invention will now be described in detail with reference to the drawings. (Embodiment 1) FIG. 1 is a block diagram of a disc tilt detecting device according to a first embodiment of the present invention. This disc tilt detecting device includes an objective lens 2, a light receiving lens 3, and a demultiplexing element 4.
, Light receiving elements 5a, 5b, 6a and 6b, summing amplifiers 7 and 8, and a differential amplifier 9. The irradiation means for irradiating the information track 1a formed on the optical disc medium 1 with the laser beam focused by the objective lens 2 has a well-known configuration and is not shown. An information track 1a is formed on the recording surface of the optical disc medium 1. The demultiplexing element 4 is a micro prism 4 on a flat plate base material.
a and 4b are formed on the optical axis of the reflected light of the laser beam in the far field, and the reflected straight light of the reflected light of the laser beam in the far field and the information track 1 are provided.
The reflected light that passes through a small area within the interference area with the first-order diffracted light by a and that is smaller than the interference area is received by the light receiving element 6a,
An optical element having a deflecting function of leading to 6b is configured.
The light receiving elements 5a and 5b are symmetrically provided along the radial direction of the optical disk medium 1 with the optical axis of the reflected light of the laser beam as the center, and detect the reflected light in the interference area excluding the small area. It constitutes the light receiving means of. Light receiving element 6
a and 6b are provided on both sides of the light receiving elements 5a and 5b at predetermined intervals in the radial direction of the optical disk medium 1.
It constitutes a first light receiving means for detecting the reflected light in the small area. The summing amplifiers 7 and 8 and the differential amplifier 9 constitute differential means for calculating the difference between the amount of light received by the light receiving elements 6a and 6b and the amount of light received by the light receiving elements 5a and 5b, and the light receiving elements 6a and 6b. Let each output of A1 and A2 be
The outputs of the light receiving elements 5a and 5b are B1 and B2, and the output A1 is the reflected light in the same interference region as the output B1, and the output A2 is the output B.
When the reflected light in the same interference area as 2 is detected, the following mathematical expression 1 is performed.

[0016]

[Equation 1]

Next, the operation will be described. Now the objective lens 2
It is assumed that a laser beam from a laser light emission source (not shown) is incident on and is focused on the information track 1a of the optical disc medium 1. The reflected light at this time passes through the objective lens 2 again, and passes through the light receiving lens 3 and the demultiplexing element 4 in the far field region where the laser beam is sufficiently diverged. Then, the demultiplexing element 4 includes the minute prisms 4a, 4
The light passing through the region where b is formed is received by the light receiving element 6a,
6b, the rest is moved straight and the light receiving elements 5a, 5b
Incident on.

Here, the optical disc medium 1 in the far field is used.
When the laser beam is reflected on the information track 1a as shown in FIG. 2A in the case where there is no disc tilt, the intensity distribution of the reflected light of the 0th order light, which is a straight light, is due to the scattering effect by the track edge. Occurs, and + 1st-order light and −1st-order light, which are first-order diffracted lights, are generated on both sides thereof. In the far field region, these interfere with each other to form a pattern as shown by hatching in FIG. That is, when the laser beam focused by the objective lens 2 irradiates almost the center line of the information track 1a, the 1st-order diffracted light has a property of having a constant phase difference with respect to the 0th-order light. Therefore, in the interference region in the far-field region, both of them are vector-added, and the intensity is reduced or increased almost uniformly in the non-interference region. On the other hand, when there is a disc tilt, wavefront aberration, that is, coma aberration occurs in the laser beam. Aberration means a non-uniform distribution of the phase difference in the same wave front, and if it exists, the phase differences of the 0th order light, the + 1st order light, and the −1st order light in the interference region also become nonuniform, and as a result, (B Or a non-uniform intensity distribution as shown in (C) occurs in the interference region. Figure 2
2B shows the case where the optical axis of the objective lens 2 is relatively inclined in the radial direction of the optical disc medium 1, that is, in the vertical (radial) direction with respect to the information track 1a, and FIG. 2C shows the radial direction. It shows a case of tilting by −θ. Therefore, if the difference between the small area in the interference area and the other part of the interference area is calculated, this aberration, that is, the amount and direction of tilt can be detected.

The reflected light passing through the small area portion is distributed to the light receiving elements 6a and 6b by the minute prisms 4a and 4b formed in the demultiplexing element 4, and the rest is distributed to the light receiving elements 5a and 5b. These minute prisms 4a and 4b may be glass processed or may be hologram elements. Therefore, the output signals of the light receiving elements 6a and 6b are A1 and A2,
If the output signals of the light receiving elements 5a and 5b are B1 and B2,
The addition amplifiers 7 and 8 and the differential amplifier 9 calculate the above-mentioned expression 1 and output the radial tilt detection signal Trad corresponding to the detected tilt amount. As described above, by obtaining the difference between the detection signals in the small area in the interference area of the 0th-order light and the 1st-order light or the -1st-order light and the other interference area, the disc tilt can be performed with high accuracy and on the optical pickup. Can be detected without providing a special sensor. That is, FIG.
In the conventional device shown in FIG. 1, the S / N ratio of the light receiving elements 35a and 35b is
It is difficult to accurately detect the tilt of 0.1 ° considering the offset and the offset. On the other hand, in this embodiment, even if the tilt is about 0.1 °, the above-mentioned wavefront aberration causes a phase difference of about several tens of degrees, which significantly changes the reflected light intensity distribution.

Further, in this embodiment, it is not necessary to provide the optical sensor 32 with the optical sensor 32 as in the conventional example,
It is possible to incorporate the elements shown in FIG. 1 into an optical pickup. At this time, by using the outputs of the light receiving element group consisting of the light receiving elements 5a and 5b and the light receiving elements 6a and 6b, the following equations 2 and 3 are calculated to obtain the reproduction signal RF
And the tracking error signal TE can be detected at the same time.

[0021]

[Equation 2]

[0022]

[Equation 3]

(Embodiment 2) Since the disk tilt detecting device of the above Embodiment 1 operates effectively in the radial tilt as described above, the tilt in the track tangential direction, that is, the tangential tilt is detected. It is necessary to use it together with the disc tilt detection device. Therefore, in a second embodiment, a disc tilt detecting device that detects the tangential tilt with high accuracy will be described. FIG. 3 is a block diagram of a disc tilt detecting device according to the second embodiment of the present invention.
The light receiving elements 13a and 13b, the differential amplifier 14, the maximum value detection circuit 15, the minimum value detection circuit 16, and the differential amplifier 17. The irradiation means for irradiating the information mark 11a formed on the rotating optical disk medium 11 with the laser beam focused by the objective lens 12 is well known and therefore not shown. Optical disc medium 1
On the recording surface of No. 1, the information mark 11a is recorded along the information track shown by the broken line. Light receiving element 13a, 1
3b are arranged adjacent to each other in the rotational tangent line of the optical disk medium 11, that is, in the tangential direction. The differential amplifier 14 constitutes second differential means for performing a differential operation on the outputs of the light receiving elements 13a and 13b. The light receiving elements 13a and 13b and the differential amplifier 14 constitute a differentiating unit that outputs a differential value of the change in the light amount of the reflected light of the laser beam. The maximum value detection circuit 15 constitutes a maximum value detection means for sampling and holding the maximum value of the output of the differentiating means, that is, the output of the differential amplifier 14. The minimum value detecting circuit 16 constitutes a minimum value detecting means for sampling and holding the minimum value of the output of the differentiating means, that is, the output of the differential amplifier 14. The differential amplifier 17 constitutes first differential means for calculating a difference between the output of the maximum value detecting means, that is, the maximum value detecting circuit 15 and the output of the minimum value detecting means, that is, the minimum value detecting circuit 16.

Next, the operation will be described. Light receiving element 13a, 1
The 3b and the differential amplifier 14 operate as a differentiator that performs differentiation of the reflected light detection signal obtained when the outgoing beam of the objective lens 12 scans the information mark 11a. That is, when there is no tilt, as shown in FIG.
The change in the amount of detected light when the information mark 11a is scanned, that is, the change in the sum output of the light receiving elements 13a and 13b has a symmetrical waveform that takes the maximum value when the emitted beam is located at the center of the information mark 11a. A waveform obtained by differentiating this is obtained from the differential amplifier 14. This is an S-order waveform with equal amplitudes of maximum and minimum values as shown in FIG. If tilt occurs in the positive or negative direction of the tangential direction, the coma aberration caused by the tilt causes the tilt in FIG.
As indicated by a solid line or a broken line in (B), the detected light amount is distorted forward and backward. The differential waveform at this time has an unbalanced maximum and minimum values as shown in FIG. 4B.

Therefore, the maximum value and the minimum value are sampled and held by the maximum value detection circuit 15 and the minimum value detection circuit 16, respectively, and the difference between them is calculated by the differential amplifier 17. Thus, at the output of the differential amplifier 17, a tangential tilt detection signal Ttan that becomes 0 at a tilt of 0 ° and changes an appropriate amount between positive and negative depending on the tilt direction and amount is obtained.

Thus, the tilt in the tangential direction can be detected by a simple optical system. In the second embodiment, the light receiving elements 13a and 13b and the differential amplifier 14 are used as the differentiating means, and the outputs of the light receiving elements 13a and 13b are differentially calculated by the differential amplifier 14. However, the differentiating means is used. Alternatively, the output of the single light receiving element may be electrically differentiated. However, in the case of such an electrically differentiating structure, the S / N may deteriorate. (Third Embodiment) In the first embodiment, the disc tilt detecting device for detecting the tilt of the radial component has been described, and in the second embodiment, the disc tilt detecting device for detecting the tilt of the tangential component has been described.
Of the light receiving elements 5a and 5b in the disc tilt detecting device
It is possible to realize a disc tilt detecting device capable of both tilt detection of a radial component and tilt detection of a tangential component by simply dividing each of the two. The disc tilt detecting device according to the third embodiment is a disc tilt detecting device that can perform both the tilt detection of the radial component and the tilt detection of the tangential component, and as shown in FIG. 5, the light receiving element 5a of FIG. Instead of the light receiving elements 5a1, 5
a2 is provided, instead of the light receiving element 5b, the light receiving element 5b1,
5b2 is provided. The other structure is the same as that of the disc tilt detecting device shown in FIG.
However, it is necessary to add the differential amplifier 14, the maximum value detection circuit 15, the minimum value detection circuit 16 and the differential amplifier 17 of the disc tilt detecting device shown in FIG. 3 to the disc tilt detecting device shown in FIG.

Next, the operation will be described. If the outputs of the light receiving element 5a1 and the light receiving element 5a2 are added, the light receiving element 5 of FIG.
It becomes equivalent to a, and if the outputs of the light receiving elements 5b1 and 5b2 are added, it becomes equivalent to the light receiving element 5b of FIG.
Further, if the outputs of the light receiving element 5a1 and the light receiving element 5b1 are added, it becomes equivalent to the light receiving element 13a of FIG. 3, and if the outputs of the light receiving element 5a2 and the light receiving element 5b2 are added, it becomes the light receiving element 13b of FIG. Will be equivalent. Therefore, by adding the addition amplifier necessary for these additions and the components of the electrical system of the disc tilt detection device of FIG. 3 to the disc tilt detection device of FIG. 1, tilt detection of the radial component and tangential component It is possible to realize a disc tilt detection device that can perform both tilt detection. (Embodiment 4) A disc tilt correction device is required in order to input a detection signal from the disc tilt detection device into a feedback system to correct tilt. Therefore, such a disc tilt correction device will be described.

FIG. 6 is a block diagram of a disc tilt correction device according to a fourth embodiment of the present invention. This disc tilt correction device includes an objective lens 21 and coma aberration lenses 22 and 23.
And rotating devices 24 and 25, and a conversion circuit 26. The laser light emitting source 20 and the objective lens 21 irradiate a focused laser beam onto an optical disk medium (not shown).
The coma aberration lenses 22 and 23 have coma aberrations equal to each other, and are installed on the optical axis of the focused laser beam. The rotation devices 24 and 25 include coma aberration lenses 22 and 2, respectively.
3 are rotated in the same direction and in opposite directions with respect to the optical axis of the focused laser beam. Conversion circuit 26
On the basis of the radial tilt detection signal Trad and the tangential tilt detection signal Ttan, generates the same-direction rotation signal φ and supplies it to the rotating device 24, and also generates the reverse direction rotation signal ψ and supplies it to the rotating device 25. .

Next, the operation will be described. Now, it is assumed that the coma aberration lenses 22 and 23 have coma aberration represented by the following Expression 4 with respect to a certain reference axis. This aberration function is displayed in polar coordinates, r is the radius from the optical axis of the lens, and θ is the azimuth angle. w is a coefficient. The coma aberration lenses 22 and 23 can be realized by a lens having an incident surface of such a shape, or can be realized by an ordinary concave or convex lens tilted along the optical axis. It may be like a hologram element. Here, assuming that the coma aberration lenses 22 and 23 are rotated by φ in the same direction and ψ in mutually opposite directions with respect to the reference axis, the combined aberration Ws of both is expressed by the following formula 5. As is clear from this, the reverse rotation angle ψ becomes a coefficient term, and the aberration coefficient is 0
It can be made variable up to 2 w. Further, the aberration can be rotated with respect to the reference axis by the rotation angle φ in the same direction.

[0030]

[Equation 4]

[0031]

[Equation 5]

Therefore, the conversion circuit 26 calculates the same direction rotation angle φ and the reverse direction rotation angle ψ based on the radial tilt detection signal Trad and the tangential tilt detection signal Ttan from the disc tilt detection device. That is, since both tilt components are orthogonal to each other, the direction of coma aberration is calculated from them as shown in the following formula 6, and this is defined as φ. Since the absolute value of the aberration is obtained by the following equation 7,
This is multiplied by an appropriate negative sign coefficient to obtain ψ. By rotating the coma aberration lenses 22 and 23 about the optical axis so as to obtain φ and ψ thus obtained, the coma aberration caused by the tilt can be canceled, and as a result, the tilt can be substantially corrected. .

[0033]

[Equation 6]

[0034]

[Equation 7]

In this way, tilts generated in the radial direction and the tangential direction can be substantially corrected. Further, since it is not a large-scale device such as tilting the entire optical pickup with a tilting stage as in the prior art, it has excellent responsiveness.

[0036]

As described above, according to the present invention, the irradiation means for irradiating the information beam formed on the optical disk medium with the laser beam focused by the objective lens and the reflection of the reflected light of the laser beam in the far field. A first light receiving means for detecting reflected light in a small area smaller than the interference area between the linearly traveling light and the first-order diffracted light by the information track, and a first light detecting means for detecting reflected light in the interference area excluding the small area. Since the second light receiving means and the differential means for calculating the difference between the light receiving quantity by the first light receiving means and the light receiving quantity by the second light receiving means are provided, the 0th order of the far field image of the information track,
Since the radial tilt is detected from the difference between the detection light in the small area in the primary light interference area and the detection light in the other interference area, the tilt in the radial direction can be made with high accuracy and on the optical pickup. It is possible to detect without providing a sensor.

Further, an irradiating means for irradiating the information mark formed on the rotating optical disk medium with the laser beam focused by the objective lens, a differentiating means for outputting a differential value of a light amount change of the reflected light of the laser beam, and a differentiating means. The maximum value detecting means for sampling and holding the maximum value of the output of the means, the minimum value detecting means for sampling and holding the minimum value of the output of the differentiating means, and the difference between the output of the maximum value detecting means and the output of the minimum value detecting means. If the first differential means for calculating is provided, the tangential tilt is detected from the difference between the maximum value and the minimum value of the information mark detection signal that has been differentiated. It can be detected in the system.

If the first optical element and the second optical element having the same coma aberration are rotatably provided around the same optical axis from the light emitting means to the optical disk medium, for example, the coma aberration characteristic is obtained. The radial tangential tilt can be corrected by rotating two lenses having the same direction in the same direction and in the opposite direction, so that a large-scale device such as tilting the entire optical pickup with a tilt stage as in the conventional case. It does not require and has excellent responsiveness.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a disc tilt detection device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of an intensity distribution of reflected light of an optical disc medium in a far field.

FIG. 3 is a configuration diagram of a disc tilt detection device according to a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of the amount of reflected light of an optical disc medium and its differential signal.

FIG. 5 is an arrangement explanatory diagram of a light receiving element included in a disc tilt detection device according to a third exemplary embodiment of the present invention.

FIG. 6 is a configuration diagram of a disc tilt correction device in Embodiment 4 of the present invention.

FIG. 7 is a configuration diagram of a conventional disc tilt detection device.

[Explanation of symbols]

1 Optical disc media 1a Information truck 2 Objective lens 3 Light receiving lens Quadrupling element 4a Micro prism 4b Micro prism 5a light receiving element 5b Light receiving element 5a1 light receiving element 5a2 light receiving element 5b1 light receiving element 5b2 light receiving element 6a Light receiving element 6b Light receiving element 7 addition amplifier 8 addition amplifier 9 differential amplifier 11 Optical disc media 11a Information mark 12 Objective lens 13a light receiving element 13b light receiving element 14 Differential amplifier 15 Maximum value detection circuit 16 Minimum value detection circuit 17 Differential amplifier 20 Laser emission source 21 Objective lens 22 Coma aberration lens 23 Coma aberration lens 24 rotator 25 rotator 26 Conversion circuit

Continuation of front page (56) Reference JP-A-5-81691 (JP, A) JP-A-60-35343 (JP, A) JP-A-4-76828 (JP, A) JP-A-2-247829 (JP , A) JP 3-273534 (JP, A) JP 61-187134 (JP, A) JP 6-251404 (JP, A) JP 4-92236 (JP, A) JP 6-295457 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G11B ^7/ 09-7/10

Claims (4)

(57) [Claims] 1. Information formed on a rotating optical disk medium
Laser bee focused on the information mark by the objective lens
Irradiation means for irradiating Two light receiving elements,Reflection of laser beam applied to the optical disk medium
Differentiate by detecting the difference in the amount of light received by two light receiving elements that receive light
Differentiating means to output as a value, Detects the maximum value of the output of the differentiating meansMaximum value detectionmeans
When, Detect the minimum value of the output of the differentiating meansMinimum value detectionmeans
When,Differential means for calculating the difference between the detected maximum value and minimum value
When,Disc discriminating based on the value output by the differential means.
Means for detecting the direction and amount of When, A disc tilt detecting device comprising: 2. The disc tilt detecting device according to claim 1.
Detected by the disc tilt detection device
Disc tilt compensation that optically corrects disc tilt
In the positive device, the first optical element and the second optical element having the same coma aberration are provided rotatably around the same optical axis from the light emitting means to the optical disc medium. Disc tilt correction device. To 3. A around the optical axis and the first rotating means for rotating the first optical element, a second rotating means for rotating the second optical element around the optical axis, said disk tilt detecting device The first rotation is generated from two components of the tilt detected by the above, which cause the first and second optical elements to rotate in the same direction by a proper amount and the signals in opposite directions to rotate an appropriate amount. 3. The disc tilt correction device according to claim 2, further comprising: a conversion unit that supplies the conversion unit and the second rotation unit. 4. The disc tilt detecting device comprises
It is a disc tilt detection device for the detection of the mechanical tilt.
Therefore, the disc tilt correction device further includes a radial
The disk tilt detecting device for tilt detection includes the disk tilt detecting device for radial tilt detection, and the disk tilt detecting device for radial tilt detection is in an interference region between the reflected straight light of the reflected light of the laser beam in the far field and the first-order diffracted light by the information track. A first light receiving means for detecting reflected light in a small area smaller than the interference area; and a second light detecting means for detecting reflected light in the interference area excluding the small area
A light receiving means, the disc tilt correction according to claim 3, characterized in that it comprises a differential means for calculating a difference between the amount of light received by said second light receiving means and the light receiving amount by the first light receiving means apparatus.