Focus jumping method

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a playback device for a plurality of types of optical discs having different substrate thicknesses.

【0002】

[Conventional technology]

An optical disc having a thickness of about 1.2 mm for reading information using a semiconductor laser such as a CD-ROM is provided. In this type of optical disc, the pickup objective lens is subjected to focus servo and tracking servo to irradiate the pit row on the signal recording surface with a laser beam to reproduce the signal. In addition, recently, the density for recording a long-time moving image is increasing.

【0003】

For example, a DVD standard has been proposed that records 4.7 Gbytes of information on one side of an optical disc with a diameter of 12 cm, which is the same as a CD-ROM. The DVD disc thickness is about 0.6 mm, and by pasting both sides together, one sheet can record 9.4 Gbytes of information. In order to reproduce an optical disc having these two signal recording surfaces, a method of reproducing two signal recording surfaces from one side of the disc and a method of reproducing one signal recording surface from both sides of the disc can be considered. However, the method of reproducing one signal recording surface from both sides is complicated because it is necessary to turn over the disc when trying to reproduce the other signal recording surface after the reproduction of one signal recording surface is completed. Is. Further, it is not possible to reproduce the other signal recording surface while reproducing one signal recording surface. For this reason, the method of reproducing two signal recording surfaces from one side has become the mainstream.

【0004】

[Problems to be Solved by the Invention]

In order to reproduce two signal recording surfaces from one side of an optical disc, it is necessary to refocus the objective lens in the optical pickup on the other signal recording surface during or after the reproduction of one signal recording surface. However, in the conventional method, when refocusing from one signal recording surface to another signal recording surface, the objective lens is braked when an S-shaped curve from the other signal recording surface begins to be observed. I was trying to stop the objective lens at the focal point, but the part where the S-shaped curve starts to be observed is usually the signal to be reproduced because there is about 10% noise with respect to the peak-to-peak value of the S-shaped curve. Since it is not possible to accurately determine whether or not the curve is an S-shaped curve from the recording surface, there is a problem that an accurate focus jump cannot be performed.

【0005】

Therefore, the present invention provides a method for solving such a problem and accurately performing a focus jump from an arbitrary signal recording surface to another signal recording surface.

【0006】

[Means for solving problems]

The present invention uses an optical pickup that reproduces an optical disk having two or more signal recording surfaces by using a laser beam, and applies a focus jump at a position in which an arbitrary signal recording surface during reproduction is in focus. When the objective lens in the optical pickup reaches a predetermined position of the S-shaped curve observed from the step and another signal recording surface different from the arbitrary signal recording surface, the objective lens is braked and the other signal recording surface is applied. It is characterized by consisting of a second step that focuses on.

【0007】

Further, the present invention uses an optical pickup that reproduces an optical disk having two or more signal recording surfaces by using a laser beam, and applies a focus jump at a position where an arbitrary signal recording surface during reproduction is in focus. It is characterized by comprising one step and a second step of applying a brake to the objective lens in the optical pickup after a predetermined time has elapsed after applying the focus jump to focus on another signal recording surface.

【0008】

Further, the present invention uses an optical pickup that reproduces an optical disk having two or more signal recording surfaces by using a laser beam, and applies a focus jump at a position in which an arbitrary signal recording surface during reproduction is in focus. Measure the time from step 1 and the focus jump until the objective lens in the optical pickup reaches a predetermined position on the S-shaped curve observed from another signal recording surface different from the arbitrary signal recording surface. However, the voltage for applying the brake to the objective lens is determined based on the measured time.

【0009】

Further, the present invention uses an optical pickup that reproduces an optical disk having two or more signal recording surfaces by using a laser beam, and applies a focus jump at a position in which an arbitrary signal recording surface during reproduction is in focus. Measure the time from step 1 and the focus jump until the objective lens in the optical pickup reaches a predetermined position on the S-shaped curve observed from another signal recording surface different from the arbitrary signal recording surface. It is characterized in that the time during which the objective lens is braked is determined based on the measured time.

【0010】

Further, the present invention is characterized in that the predetermined position is in the range of 0 to 100% of the peak-to-peak value of the S-shaped curve. Further, the present invention is characterized in that the optical pickup is an optical pickup capable of compatible reproduction of optical discs having different substrate thicknesses. Further, the present invention is characterized in that the optical disc is an optical disc having a first signal recording surface and a second signal recording surface.

【0011】

Further, the present invention is characterized in that the first signal recording surface of the optical disc is located at a position of 0.55 to 0.65 mm from the substrate surface, and the second signal recording surface is separated from the first signal recording surface by 40 to 70 μm.

【0012】

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described with reference to the drawings. The present invention mainly uses an optical pickup capable of compatible reproduction of optical discs having different substrate thicknesses to reproduce a dual-layer optical disc having two signal recording surfaces, and changes the focus state of the laser beam from the first signal recording surface. It discloses a method of switching to the second signal recording surface. With reference to FIG. 1, the two-layer optical disc 1 having two signal recording surfaces located at a position of 0.6 (margin of error ± 0.05) mm from the surface of the substrate has a pit on one of the substrates 2 made of translucent polycarbonate or the like. From an optical disc with a substrate thickness of 0.6 mm (margin of error ± 0.05 mm) on which a first signal recording surface 5 made of a metal reflective film 4 formed so as to cover the pit 3 is arranged, and a translucent polycarbonate or the like. An optical disc having a substrate thickness of 0.6 mm (margin of error ± 0.05 mm) having a pit 7 and a second signal recording surface 9 made of a metal reflective film 8 formed so as to cover the pit 7 is arranged on one of the substrates 10. , The first signal recording surface 5 and the second signal recording surface 9 are bonded together with an ultraviolet curable resin 6 so as to be inside. The thickness of the ultraviolet curable resin 6 is 40 to 70 μm, and the first signal recording surface 5 and the second signal recording surface 9 are separated by a distance of 40 to 70 μm. In the following, the dual-layer optical disc shown in FIG. 1 will be referred to as a dual-layer DVD.

【0013】

Further, referring to FIG. 2, the optical disk 20 having the signal recording surface at a position of 1.2 (margin of error ± 0.1) mm from the substrate surface has a pit 22 on one side of the substrate 21 made of translucent polycarbonate or the like. A signal recording surface 24 made of a metal reflective film 23 formed so as to cover the pit 22 is arranged, and a protective film 25 is formed on the signal recording surface 24. In the following, the optical disc shown in FIG. 2 is referred to as a CD.

【0014】

Figure 6 shows the rated values and playback conditions for CDs and dual-layer DVDs. The board thickness on the signal reading surface side of the CD is 1.2 (allowable range: 1.1 to 1.3) mm, the shortest pit length is 0.90 (allowable range: 0.80 to 1.0) μm, and the track pitch is 1.6 (allowable range: 1.5 to 1.5). 1.7) μm, and the reflectance is 70% or more. The substrate thickness on the signal reading surface side of the dual-layer DVD is 0.6 (allowable range: 0.55 to 0.65) mm, the shortest pit length is 0.40 (allowable range: 0.30 to 0.5) μm, and the track pitch is 0.74 (allowable range: 0.30 to 0.5) μm. Tolerance range: 0.73 to 0.75) μm, with a reflectance of 20 to 40%.

【0015】

The reproduction conditions are that the wavelength of the laser beam is 635 (allowable range: 620 to 650) nm, and in the case of CD, the spot diameter of the laser beam is 1.5 (allowable range: 1.4 to 1.6) μm, which is effective for the objective lens. The numerical aperture is 0.35 (allowable range: 0.30 to 0.40), and in the case of a dual-layer CD, the effective numerical aperture of the objective lens is 0.60 (allowable range: 0.55 to 0.65).

【0016】

Figure 3 shows an optical pickup 60 that can play CDs and dual-layer DVDs in a compatible manner. The optical pickup 60 selectively blocks a semiconductor laser 31 that emits a laser beam having a wavelength of 635 nm, a polarizing surface rotating means 32 that rotates the polarizing surface of the laser beam, a diffraction grating 35, a half mirror 36, a collimator lens 37, and a laser beam. It includes a polarization selecting means 38, an objective lens 42, and a light detector 43. The laser beam emitted from the semiconductor laser 31 reaches the half mirror 36 via the polarizing surface rotating means 32 and the diffraction grid 35, is half reflected by the half mirror 36, and is converted into parallel light by the collimator lens 37. The light passes through the polarization selection means 38, is focused by the objective lens 42, passes through the substrate of the optical disk, and irradiates the signal recording surface 5. The laser beam reflected by the signal recording surface 5 returns through the objective lens 42, the polarization selection means 38, and the collimator lens 37, is half transmitted by the half mirror 36, and is focused on the photodetector 43. And be detected.

【0017】

The objective lens 42 is designed so that light can be focused on the signal recording surface of an optical disc having a substrate thickness of 0.6 mm, and has a numerical aperture of 0.6 (allowable range: 0.55 to 0.65). The polarizing surface rotating means 32 has a structure in which a TN type liquid crystal 34 is sandwiched between two glasses 33 and 33 with transparent electrodes, and when a voltage is applied to the transparent electrodes, a voltage is applied to the TN type liquid crystal and a laser beam is applied. Passes through the TN type liquid crystal without being able to rotate its plane of polarization. When no voltage is applied to the transparent electrode, the laser beam is rotated 90 degrees on its plane of polarization and passes through the TN liquid crystal.

【0018】

Further, the polarization selecting means 38 has a structure in which a polarizing filter 40 provided on a portion corresponding to the outer peripheral portion of the laser beam is sandwiched between two pieces of glass 39, 39, and a polarization characteristic is provided in the central portion of the laser beam. A filter 41 that does not indicate is provided. The polarizing filter 40 has a characteristic of transmitting only a laser beam in a certain polarization direction, and in this embodiment, only a laser beam polarized in a direction parallel to the paper surface is transmitted. Therefore, the polarization selection means 38 exhibits the characteristics shown in FIG. That is, the outer peripheral portion 38a of the polarization selecting means 38 transmits only the laser beam polarized in the direction parallel to the paper surface by the polarizing filter 40, and the inner peripheral portion 38b transmits the laser beam regardless of the polarization direction of the laser beam. The polarizing filter 40 transmits a laser beam polarized in a direction parallel to the paper surface, but its transmittance is about 70 to 90%. Therefore, if no filter is provided on the inner peripheral portion 38b, the inside of the laser beam is transmitted. The transmittance differs between the peripheral portion and the outer peripheral portion, which causes a decrease in reproduction characteristics. Therefore, it is necessary to provide the filter 41 on the inner peripheral portion of the polarization selecting means 38.

【0019】

The playback operation of a dual-layer DVD having a substrate thickness of 0.6 mm on the signal reading surface side will be described. When the dual-layer DVD is played back, a voltage is applied to the polarizing surface rotating means 32 from the liquid crystal drive circuit 44. As a result, the laser beam having a wavelength of 635 nm emitted from the semiconductor laser 31 and polarized in a direction parallel to the paper surface is transmitted as it is without being rotated by the polarizing surface rotating means 32, and the diffraction grating 35 is transmitted. Through the half mirror 36, the light is half reflected, the collimator lens 37 makes the light parallel, the polarization selection means 38 transmits the entire outer peripheral portion without shading, and the light is condensed by the objective lens 42. The signal recording surface 5 is irradiated through the substrate 2 of the dual-layer DVD1. Subsequent operations are the same as those described in FIG. 3, and will be omitted. The spot diameter of the laser beam irradiated on the signal recording surface 5 is 0.9 (allowable range: 0.80 to 1.0) μm.

【0020】

Next, the playback operation of a CD having a substrate thickness of 1.2 mm on the signal reading surface side will be described. When the CD is played, no voltage is applied to the polarizing surface rotating means 32. As a result, the laser beam having a wavelength of 635 nm emitted from the semiconductor laser 31 and polarized in a direction parallel to the paper surface is rotated 90 degrees by the polarizing surface rotating means 32 and passes through the diffraction grating. Through the half mirror 36, the half is reflected by the collimator lens 37, the light is made parallel by the collimator lens 37, only the outer peripheral portion is shielded by the polarization selection means 38, and the light is collected by the objective lens 42 and passed through the substrate 21 of the CD20. The signal recording surface 24 is irradiated. Subsequent operations are the same as those described in FIG. 3, and will be omitted. The diameter of the inner peripheral portion 38b of the polarization selection means 38 has a numerical aperture of 0.6 (allowable range: 0.55 to 0.65), and in the case of an objective lens having an effective light beam diameter of 4 mm, the effective numerical aperture is 0.35 (allowable range: 0.30 to 0.40). Make a circle with a diameter of 2.3 (margin of error ± 0.2) mm so that it becomes. When the effective luminous flux diameter is other than 4 mm, the size of the through hole is proportionally set to a size such that the effective numerical aperture is 0.35. The spot diameter of the laser beam irradiated on the signal recording surface 24 is 1.5 (allowable range: 1.4 to 1.6) μm.

【0021】

A playback device for compatible playback of optical discs having different substrate thicknesses will be described with reference to FIG. The objective lens 42 in the optical pickup 60 is controlled by the servo mechanism 47 so that the signal to be reproduced is focused on the track formed as a pit train, and the laser beam is collected by the objective lens 42. It is illuminated and irradiates the signal recording surface 5 through the substrate 2 of the optical disk. The laser beam reflected by the signal recording surface 5 is detected by the photodetector 43 and detected as a reproduction signal. The reproduced signal detected by the photodetector 43 is sent to the preamplifier 45, and after performing predetermined amplification, it is sent to the discrimination circuit 48, the RF demodulation circuit 53, and the servo circuit 46. The servo circuit 46 controls the servo mechanism 19 based on the tracking error signal sent. Further, the discrimination circuit 48 identifies the type of optical disc mounted on the playback device based on the transmitted signal, and sends the discrimination result to the command circuit 49. The command circuit 49 issues a command to the NA switching circuit 50 based on the identification result sent in order to switch the numerical aperture of the objective lens 42 so as to match the identified optical disc. Further, the command circuit 49 also issues a command to the characteristic switching circuit 51 based on the sent identification result in order to switch to the demodulation circuit suitable for the reproduction of the identified optical disc. The NA switching circuit 50 switches the effective numerical aperture of the objective lens 42 via the liquid crystal drive circuit 44, and the characteristic switching circuit 51 switches the RF demodulation circuit 53.

【0022】

When the optical disc is mounted on the playback device, focus servo and tracking servo are performed, and then the optical disc rotates at a predetermined rotation speed to reproduce the signal. Further, the optical disc does not have to rotate at a predetermined rotation speed after the focus servo and the tracking servo have been performed, and the rotation of the optical disc may start after the focus servo has been performed. In the reproduction of the dual-layer DVD, the signal is reproduced by focusing on any one of the first signal recording surface 5 and the second signal recording surface 9, for example, the first signal recording surface 5. When the second signal recording surface is to be reproduced during the reproduction operation from the first signal recording surface, the focus jumps from the first signal recording surface 5 to the second signal recording surface 9 and becomes the second signal recording surface 9. You need to refocus. In this case, the focus jump is performed by controlling the servo mechanism 47 by the focus jump circuit 46a provided in the servo circuit 46. With reference to FIG. 7, normally, when the focus of the optical disk is pulled in, an S-shaped curve is generated while the objective lens 42 is controlled by the servo mechanism 47 and moves up and down in the vertical direction. Points A and B in Fig. 7 (a) are the focal points. Assuming that the S-shaped curve generated from the first signal recording surface 5 is S1 and the S-shaped curve generated from the second signal recording surface 9 is S2, the point A of the S-shaped curve S1 is described above during playback of the first signal recording surface. The objective lens 42 is located. When the focus jump is performed in this state, the focus jump moves to the position of the point C of the S-shaped curve S2 generated from the second signal recording surface 9, and the S-shaped curve S2 is observed in the direction of the arrow 14. Normally, when the objective lens 42 moves to the point C, the objective lens 42 is braked so that the objective lens 42 stops at the in-focus position B of the S-shaped curve S2 from the second signal recording surface 9. Although it is controlled, the region 13 shown in FIG. 7 (a) actually has a signal variation of about 10% when it is larger than the peak value of the S-shaped curve as shown in FIG. 7 (b). Therefore, the focuser is from the first signal recording surface 5 to the second signal recording surface 9. Even if the jump is performed, the timing at which the brake is applied to the objective lens 42 is not clear, and it is difficult to stop the objective lens 42 at the in-focus position B. Therefore, in the present invention, the brake is applied at the timing when the objective lens 42 is positioned between the points C and B of the S-shaped curve S2, and the focus is turned on. The brake may be applied from the point C until the peak value of the S-shaped curve S2 is reached, or the brake may be applied between the peak value and the point B. Therefore, the current value given to the objective lens 42 differs depending on which position of points C and B the brake is applied. That is, when the brake is applied at a point close to the focal position B, a larger current is applied.

【0023】

In the above, the case of focus jumping from the first signal recording surface 5 to the second signal recording surface 9 has been described, but conversely, the case of focus jumping from the second signal recording surface 9 to the first signal recording surface 5 is also performed. .. In order to clearly control the timing of applying the brake, a reference may be set to a predetermined level for the peak-to-peak value of the S-shaped curve, and the brake may be applied based on this reference. In the present invention, the criteria 11 and 12 are set in the range of 0 to 100% with respect to the peak-to-peak value of the S-shaped curve. When the focus jump is made from the first signal recording surface 5 to the second signal recording surface 9, the reference 11 is used, the movement is made from the point C in the direction of the arrow 14, and the brake is applied at the timing when the reference 11 is exceeded. Further, when the focus jump is performed from the second signal recording surface 9 to the first signal recording surface 5, the reference 12 is used. In this case, the focus jump is performed in the state of the point B, and the objective lens 42 moves to the point D of the S-shaped curve S1 generated from the first signal recording surface. After that, since it moves in the direction of arrow 15, the brake is applied at the timing when the reference 12 is exceeded. References 11 and 12 are the peaks of the s-shaped curve to It is set after measuring the peak value.

【0024】

When the focus jump is applied, the objective lens 42 is controlled by the circuit shown in FIG. This circuit consists of a terminal 60 to which a focus error signal is input, a terminal 61 to which a jump pulse 64 is applied, and an amplifier 62.Before the focus jump is performed, the switch 65 is connected to the terminal 66 side. The coil 63 of the actuator that moves the objective lens 42 via the amplifier 62 is controlled based on the focus error signal. When the focus jump is performed, the switch 65 is connected to the terminal 67 at the same time when the jump pulse 64 is applied from the terminal 61, and the coil 63 of the actuator that moves the objective lens 42 from the terminal 67 side via the amplifier 62. To control.

【0025】

Further, the voltage value at the time of applying the brake may be determined by the time after the start of the focus jump. For example, when the objective lens 42 moves from the point A to the point C and then moves in the direction of the arrow 14, the time to reach the reference 11 for the first time and the time for reaching the second time are measured in advance. Then, the value of the voltage to apply the brake is determined according to the measured time. In this case, when the brake is applied in the state where the reference 11 is reached for the second time, the voltage value becomes smaller than when the brake is applied in the state where the reference 11 is reached for the first time. In this case, the range of applied voltage is the range of 1 to 2V. This method can also be used when performing a focus jump from the second signal recording surface 9 to the first signal recording surface.

【0026】

Further, the time for applying the brake may be determined according to the measured time. In this case, if the focus jumps to point A or point C and the brake is applied when the reference 11 is reached for the first time, the braking time is set longer and the reference 11 is applied for the second time. If you want to apply the brakes when the brakes are reached, set the braking time short. In this case, the braking time is on the order of 1 msec. This method can also be used when performing a focus jump from the second signal recording surface 9 to the first signal recording surface.

【0027】

Further, according to the method of setting the reference points 11 and 12 and applying the brake as described above, it is possible to determine from which signal recording surface the focus jump was performed. That is, if the brake is applied at the timing exceeding the reference 11, it is a focus jump from the first signal recording surface to the second signal recording surface, and if the brake is applied at the timing exceeding the reference 12, the second signal recording surface 9 is applied. This is a focus jump from to the first signal recording surface 5.

【0028】

In the above, the case of a dual-layer DVD having two signal recording surfaces has been described, but the present invention is not limited to this, and it goes without saying that the case can be applied to a DVD having three or more signal recording surfaces.

【0029】

[Effect of the invention]

According to the present invention, a focus jump can be accurately performed in an optical playback device capable of compatible playback of a CD and a dual-layer DVD. Further, according to the present invention, in a multilayer DVD having two or more signal recording surfaces, it is possible to accurately perform a focus jump from an arbitrary signal recording surface to another signal recording surface.

[Simple explanation of drawings]

[Figure 1]

It is a figure which shows the cross-sectional structure of a two-layer DVD.

[Figure 2]

It is a figure which shows the cross-sectional structure of a CD.

[Fig. 3]

It is a figure which shows the structure of the optical pickup which enables the compatible reproduction of optical discs with different substrate thicknesses.

[Fig. 4]

It is a figure which shows the characteristic of the polarization selection means.

[Fig. 5]

It is a figure which shows the block diagram of the reproduction apparatus which performs compatible reproduction | reproduction of the optical disk which the substrate thickness is different.

[Fig. 6]

It is a chart which shows the rated value and a play condition of a CD and a double-layer DVD.

[Fig. 7]

This is the S-curve waveform observed when the focus is pulled in.

[Fig. 8]

It is a figure which shows the circuit structure at the time of applying a focus jump.

[Explanation of symbols]

1 Double layer DVD 2 ... Substrate 3 ... pit 4 Reflective film 5 1st signal recording surface 6 UV curable resin 7 Pit 8 Reflective film 9 2nd signal recording surface 10 Board 11 Standard 12 Standard 13 Area where S-shaped curve is not observed 31 Semiconductor laser 32 ... Polarized plane rotating means 33 Glass with transparent electrode 34 TN type liquid crystal 35 Diffraction grating 36 Half mirror 37 Collimator lens 38 Polarization selection means 39 Glass 40 Polarizing filter 41 Filter 42 Objective lens