JP3986521B2 - Optical disk device - Google Patents

Description

The present invention relates to an optical disc apparatus, in particular for example DVD or an optical disk tilt (inclination: tilt), such as a CD by detecting relates to an optical disk apparatus for mitigating the effects of the disc tilt.

  As the recording capacity of optical discs increases and the recording density thereof increases, the beam spot that irradiates the optical disc to reproduce or record signals has become minute. In particular, in an optical disc apparatus that performs recording (see, for example, Patent Document 1), in order to perform signal recording in a favorable state, a smaller beam spot is required than in an optical disc apparatus for reproduction. In order to obtain a minute spot, an objective lens having a large numerical aperture is adopted, and as a result, a side effect in which the deterioration of the spot quality due to the disc tilt becomes remarkable occurs.

  Degradation of spot quality due to disc tilt is mainly the occurrence of commatic aberration. The image is blurred and the spot diameter increases, and the central light intensity decreases. When the spot diameter increases, it becomes impossible to read a fine signal accurately. In the case of an optical disc based on the principle of recording by the heat of light, if the central intensity of light decreases, the temperature does not reach a predetermined value necessary for recording, so recording cannot be performed, and the total amount of light is required to obtain a predetermined temperature. In this case, since the region where the temperature is higher than the predetermined temperature is widened, fine recording cannot be performed.

  The disc tilt is a state that occurs when a disc with a large warp is used. The state in which the portion irradiated with the beam is tilted in the radial direction of the disk is called a radial tilt, and the state tilted in the tangential direction is called a tangential tilt.

  With reference to FIG. 1 and FIG. 2, the method of the prior art 1 for detecting and correcting such disc tilt will be described. In FIG. 1, a disk 1 which is a signal recording / reproducing body is held by a holding unit 2, rotated by a spindle motor 3a, and irradiated with light from an optical pickup 4, whereby a signal is recorded on the disk 1 or a disk. The signal from 1 is reproduced. The optical pickup 4 is held by a shaft 5a, and the shaft 5a is held by a shaft holder 5b. The shaft holder 5b is fixed on the shaft holder chassis 5c. The spindle motor 3a described above is fixed on the spindle motor chassis 3b, and the spindle motor chassis 3b and the shaft holder chassis 5c are connected by the support shaft 6. A cam 7 that swings the end of the shaft holder chassis 5c up and down is provided on the spindle motor chassis 3b.

  As shown in FIG. 2, a tilt sensor 8 that detects the tilt of the disk 1 is provided inside the optical pickup 4. The tilt sensor 8 is configured such that the light emitted from the internal LED is reflected by the reflective surface parallel to the sensor installation surface, and the reflective surface is tilted with reference to an electrical signal output according to the position where it falls on the internal light receiving sensor. In this case, the electronic component detects that the position where the reflected light falls on the internal light receiving sensor is shifted by the change of the output signal, thereby detecting the inclination of the reflecting surface.

  The light emitted from the optical pickup 4 is imaged on the disk 1 rotated by the spindle motor 3a to form a minute spot. The optical pickup 4 is moved along the shaft 5a by a drive unit (not shown). Therefore, the spot can be scanned two-dimensionally on the disk 1. As a result, the optical pickup 4 records the signal on the signal surface that is recessed from the surface of the disk 1 through the transparent cover glass layer, and reproduces the signal from the signal surface.

  The operation when the shape of the disk 1 has a constant inclination in the radial direction or the inclination gradually changes with the radius and the disk 1 is mounted on the apparatus will be described. .

  The tilt sensor 8 detects a radial tilt amount. The cam 7 is rotated by a drive source (not shown) and swings the end of the shaft holder chassis 5c up and down. As a result, the optical pickup 4 mounted on the chassis 5c changes its inclination around the support shaft 6. By detecting the relative angle of the optical pickup 4 with the tilt sensor 8 while changing the inclination of the optical pickup 4, the cam 7 is stopped in a state where the optical pickup 4 and the disk 1 are just in parallel with each other. can do. This eliminates coma from the spot on the disk 1. That is, in this prior art 1, the tilt of the optical pickup 4 is changed according to the disc tilt amount detected by the tilt sensor 8 to cancel the disc tilt.

  Unlike the prior art 1, there is a method in which coma generated by disc tilt is canceled by coma generated by tilting the objective lens. In this prior art 2, the tilt amount of the objective lens capable of canceling the coma caused by the disc tilt is checked in advance, and the objective lens tilt amount is controlled according to the detected disc tilt amount.

  There is also a method in which the tilt amount is not detected. In the prior art 3, the entire optical pickup is tilted so that the amplitude of the waveform from which the signal is reproduced, so-called RF amplitude is maximized, or the “jitter” indicating temporal fluctuation of the signal is minimized, or the objective lens Provide a means to tilt.

Using not only the main beam that reads the signal but also the sub beam used for tracking, the signal that correlates with the disc tilt is used from the detection signals of the reflected light from the pits and embossed structure formed in advance on the disc. There is a way to do it. In Prior Art 4, tilt servo is performed by adjusting the tilt of the entire optical disc and the tilt of the objective lens while detecting such a signal.
JP 2000-020992 A

  In the method of the prior art 1, the mechanism becomes large. Furthermore, it is difficult to respond to a radial tilt that changes during one round of the disk. For example, when the disc warpage fluctuates with one revolution of the disc 1 as a cycle, a dynamic response at a 45 msec cycle is required at 1 × speed of DVD, and at 6 msec cycle to support 8 × speed. This response is required, and high-speed response is required for the operation of tilting the optical pickup. However, such a high-speed response is difficult with the mechanism of the prior art 1.

  The method of Prior Art 2 is suitable for downsizing and high responsiveness compared to the method of tilting the whole pickup or the disc, but in order to realize it, both the disc tilt and the objective lens tilt are common and independent standards. Since it must be detected from the surface and it is necessary to use two tilt sensors, it is difficult to reduce the size by using the tilt sensor as in prior art 1.

  In the prior art 2, only the disc tilt is detected and the objective lens may be tilted according to the detected tilt amount. In this case, a physical quantity having a correlation with the tilt amount of the objective lens is manipulated. It will be. For example, if the actuator that holds the objective lens is operated by electromagnetic force, the current flowing through the coil is manipulated to generate a magnetic field imbalance and the actuator is tilted. In this case, the current value is a physical quantity. is there. Since this method uses open control instead of feedback control, it is unclear whether the actuator has actually tilted by the desired angle, and the correlation between the physical quantity to be operated and the tilt varies from pickup to pickup, so that the optimum state is achieved. There is no guarantee that it will be controlled.

  Prior art 3 is difficult to apply during recording.

  Furthermore, since the method of the prior art 4 depends on the physical format which is the shape of the disk, in a complex disk drive apparatus in which recording is performed on disks of various physical formats with one apparatus, the target of the drive apparatus Tilt servo cannot be applied to all discs.

  Therefore, a main object of the present invention is to provide a novel optical disc device and tilt detection method.

  Still another object of the present invention can be applied at the time of recording, can detect both radial tilt and tangential tilt, can be applied to a wide range of physical format discs, and does not use a separate extra light source, It is an object of the present invention to provide an optical disc apparatus and a tilt detection method and apparatus that can be realized with a small apparatus without increasing the laser output of the light source.

The present invention relates to a collimator lens that converts light from a light source into parallel light, an objective lens that forms an image of parallel light from the collimator lens on an optical disc, an objective lens holder that holds the objective lens, an objective lens holder, A light transmitting portion that is formed at a first position separated in the track tangential direction and through which transmitted parallel light is irradiated to the optical disk, a first condenser lens that receives the transmitted parallel light reflected from the optical disk, and a first collection An optical disc apparatus including a disc tilt sensor that receives incident light from an optical lens and includes a plurality of first light receiving sensors.

  In this case, the first condenser lens may be a collimator lens, and a first prism is provided at a position away from the optical axis between the collimator lens and the disc tilt sensor, and the disc tilt sensor is separated from the first prism. The incident light may be received.

  The optical disk apparatus further includes a reflecting unit that moves integrally with the objective lens and reflects parallel light at a second position opposite to the first position in the track tangential direction of the optical disk to output reflected parallel light. And a lens tilt sensor that receives incident light from the second condenser lens and has a plurality of second light receiving sensors.

  The reflecting portion includes a reflecting plate, and the reflecting plate includes a mirror provided integrally with the objective lens holder or a flat flange of the objective lens.

  The second condenser lens may be a collimator lens. In that case, a second prism is provided at a position away from the optical axis between the collimator lens and the lens tilt sensor, and the lens tilt sensor is separated from the second prism. Receiving incident light.

  The first prism and the second prism are provided at positions away from each other in the opposite direction from the optical axis, and change the direction of light in the opposite direction with respect to the optical axis.

  In order to detect the position of the beam falling on the first light receiving sensor or the second light receiving sensor, a difference between a pair of sensor outputs aligned in the moving direction of the beam, an output difference between a pair of sensors, or a moving direction of the beam A ratio obtained by dividing the difference between the paired sensor outputs by the sum, or a ratio obtained by dividing the output difference of the paired sensor group by the sum may be calculated.

  The tilt servo means tilts the objective lens by a predetermined amount using the objective lens tilt sensor in accordance with the disc tilt amount detected using the disc tilt sensor.

  Parallel light that has passed through, for example, a light transmission portion at a position away from the objective lens in the tangential direction, that is, in the track tangential direction of the disk is irradiated on the disk surface and collected by a collimator lens or a condenser lens for a light receiving sensor. For example, the light enters the plurality of first light receiving sensors of the disc tilt sensor.

  When the disc is tilted, the direction of the parallel light reflected by the disc changes according to the tilt of the disc, so that the direction of incidence on the collimator lens or the condensing lens for the light receiving sensor is tilted. As a result, the image height focused on the first light receiving sensor for disc tilt detection changes.

  From each of the first light receiving sensors, an electric signal of current or voltage is output according to the amount of incident light. The position of the reflected light falling on the first light receiving sensor for disc tilt detection moves from the position where there is no disc tilt, and therefore the output balance from each sensor also changes according to the location. The detection of the output balance uses a difference between a pair of sensor outputs arranged in the beam moving direction. Each sensor output balance of the divided sensor when there is no disc tilt is used as a reference value. A small reflector or objective lens that moves away from the objective lens in the tangential direction and in the opposite direction to the position of the parallel light used for disc tilting and moves in unison with the objective lens. The parallel light reflected by a part of the flat flange is condensed by a collimator lens or a condensing lens for a light receiving sensor, and then enters a second light receiving sensor divided into two or four divided toward a lens tilt sensor. .

  When the objective lens is tilted, the parallel light reflected by the reflecting portion such as a minute reflector that tilts together with the objective lens changes its direction according to the inclination of the objective lens, and thus enters the collimator lens or the condensing lens for the light receiving sensor. The direction is tilted. As a result, the image height focused on the objective lens tilt sensor changes. From each of the second light receiving sensors, an electric signal of current or voltage is output according to the amount of incident light. Due to the objective lens tilt, the position of the beam falling on the objective lens tilt sensor moves from the beam position in the state where there is no objective lens tilt, and the output balance from each sensor also changes according to the position. The detection of the output balance uses a difference between a pair of sensor outputs arranged in the beam moving direction or a ratio obtained by dividing the difference by the sum. Each sensor output balance of the divided sensor when there is no objective lens tilt is used as a reference value.

  In order to cancel the coma generated by the disc tilt, the objective lens is tilted by the tilt servo means to a state in which the objective lens is parallel to the disc and to a state before it is parallel. The disc tilt amount and the tilt amount of the objective lens that cancels coma aberration caused thereby are checked in advance, and after detecting the disc tilt amount, the lens is tilted according to the above-described relationship. When recording or reproducing a plurality of types of discs having different thicknesses and refractive indexes with a single optical pickup, the disc tilt amount and the tilt amount of the objective lens that cancels coma aberration caused thereby are examined for each type. In response to this, each tilt servo may be applied.

  When recording or playing back multiple types of discs with a single optical pickup using a dedicated laser, each sensor output balance of the split sensor when a disc without tilt is installed is when each laser is used. Since they are not the same, separate reference values are provided.

According to the present invention, since it can be applied also during recording, high-quality recording is possible. Further, since it can be applied to both radial tilt and tangential tilt, it is possible to sufficiently eliminate spot deterioration due to disc tilt. In particular, since the objective lens is tilted by a predetermined amount to cancel the coma aberration due to the disc tilt amount with respect to the disc tilt amount detected by the disc tilt sensor, the coma aberration due to the disc tilt can be easily and reliably detected. It can be canceled by tilting.

  In addition, it can be applied to various optical pickups because it can support a wide range of physical formats of discs.

  In addition, since no extra light source is used, the cost increase can be suppressed, and further, it is not necessary to increase the laser output of the pickup light source for tilt detection. Such a problem can be avoided.

  Further, since the entire pickup is not increased in size, tilt servo can be performed with a small pickup for a recording disk drive device installed in a notebook computer.

  The above object, other objects, features, and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

  Referring to FIG. 3, an optical disc apparatus 10 according to an embodiment of the present invention uses a disc 12 such as a DVD-R / RW as a medium for recording and reproducing signals. In FIG. 3, only the outer shape of the disk 12 is indicated by an imaginary line in order to clearly show the components below the disk 12. The disk 12 is held by a holding unit 14 and rotated by a spindle motor 16. An optical pickup 18 for recording a signal on the disk 12 and reproducing a signal from the disk 12 is provided below the disk 12. The optical pickup 18 can be moved in the axial direction of the shaft 20 by the shaft 20. Held. The shaft 20 is held by a shaft holder 22, and the shaft holder 22 is fixed on the chassis 24 together with the spindle motor 16.

  Although not shown, a transparent cover glass layer is formed on the surface of the disk 12, and a signal is recorded on the lower signal surface by a known method. Signal recording methods are well known, such as a method using pits with fine irregularities, a method of recording with a difference in refractive index and reflectance, or a method of recording with a difference in magnetic polarity, etc. However, the present invention can be applied to the physical format of such an arbitrary optical disc. However, various recording and reproduction principles are well known, and a description thereof is omitted here.

  The light emitted from the optical pickup 18 is imaged on the signal surface of the disk 12 to form a minute spot. The optical pickup 18 is moved along the shaft 20 by a drive unit (not shown). Therefore, the spot by the optical pickup 18 is scanned two-dimensionally on the disk 12. The signal is recorded on the signal surface of the disk 12 by the irradiation of the spot, and the signal is reproduced by the light irradiated on the signal surface.

  The configuration of the optical system to which the present invention is applied differs slightly depending on the above-described difference in the recording / reproducing system. In the embodiment of FIG. 3, the optical system in the case where the disk 12 is a DVD-R / RW is shown. However, the present invention is not limited to this.

  As shown in FIG. 4, a laser diode 26 as a light source for signal recording / reproduction is provided in the housing 62 of the optical pickup 18, and light from the laser diode 26 is incident on the diffraction grating 28. The diffraction grating 28 divides the incident light into three and enters the polarization beam splitter 30. The polarization beam splitter 30 reflects or transmits light according to the polarization. A front monitor 32 for detecting the amount of light is disposed on the front side surface of the polarizing beam splitter 30. Further, a collimator lens 34 for converting the radiated light into parallel light is provided in front of the polarization beam splitter 30, and the light that has passed through the collimator lens 34 is converted into linearly polarized light and circularly polarized light. 4 (1/4) wave plate 36 is provided.

  The light exiting the quarter-wave plate 36 is reflected by the reflection mirror 38 and forms an image on the disk 12 through the objective lens 40. The objective lens 40 is fixedly held by an objective lens holder 42. A through hole 44 that functions as a light transmitting portion is formed at a first position of the objective lens holder 42 in the vicinity of the objective lens 40 in the tangential direction of the track of the disk 12, that is, in the tangential direction. The objective lens holder 42 is held by a wire suspension 46, and this wire suspension 46 is held by a wire suspension plate 48.

  As shown in FIG. 6, below the objective lens 40, the tilt of the objective lens 40 is detected at a second position on the opposite side of the through-hole 44 with respect to the through hole 44 in the tangential direction. A lens tilt mirror 50 is provided integrally with the objective lens holder 42.

  As can be seen from FIG. 4, a tilt prism 52 for detecting tilt is disposed on the rear side surface of the polarizing beam splitter 30. As shown in FIG. A prism 54 provided at a distant position to refract the reflected light from the disk 12 and change the direction of the reflected light, and away from the optical axis in the opposite direction to the prism 54, and the reflected light from the lens tilt mirror 50 And a prism 56 for changing the direction of the reflected light in the direction opposite to that of the prism 54. A cylindrical lens 58 that generates astigmatism is provided behind the tilt prism 52. The light receiving sensor 60 receives light from the cylindrical lens 58 and converts the light into an electrical signal (current or voltage).

  Here, the flow of light used for normal signal reproduction will be described with reference to FIGS.

  Lights 64a, 64b and 64c emitted radially from the laser diode 26 are spherical waves, and pass through the diffraction grating 28, and are divided into three spherical waves each having a virtual light source. The light 64c is a chief ray of 0th-order light using the laser diode 26 on the optical axis of the collimator lens 34 as a light source, and the light 64a and the light 64b are symmetric with respect to the optical axis and have a virtual light source in the yz plane. The principal rays of the secondary light and the negative primary light. The zero-order light becomes a main beam with a large amount of light and is used for signal recording / reproduction, and the ± first-order light becomes two sub-beams with a small amount of light, and is used for a tracking servo called a differential push-pull method.

  First, the flow of 0th-order light will be described. The polarization beam splitter 30 splits the P wave component of the light into transmitted light and reflected light at a predetermined ratio, for example, 9: 1, and transmits the S wave component at a predetermined ratio, for example, 0:10, at the transmitted light and reflected light. Spectroscopy into light. In this optical system, since the polarization plane of the linearly polarized light of the laser diode 26 is arranged in parallel with the zx plane, all the light emitted from the laser diode 26 becomes a P wave. Therefore, one-tenth of the total amount of light is reflected, is incident on the front monitor 32 as light 66c, and the remaining light 68c is transmitted.

  The light 66c incident on the front monitor 32 is converted into an electric signal and used for auto power control. A control circuit, for example, a servo circuit (not shown) that applies an electric signal corresponding to the difference between the electric signal corresponding to the target light amount and the output of the front monitor 32 to the laser driver IC, thereby changing the current value supplied to the laser 26. ) Controls the current supplied to the laser diode 26 so that the electrical signal is maintained at a predetermined value, and as a result, the main beam 70c emitted from the objective lens 40 is maintained at a predetermined optical power. Be drunk.

  The light 68c transmitted through the polarizing beam splitter 30 is converted from a spherical wave to a plane wave, in other words, from radiated light to parallel light by the collimator lens 34. The direction is parallel to the optical axis.

  The parallel light converted by the collimator lens 34 enters the quarter-wave plate 36, and linearly polarized light is converted into circularly polarized light. Circularly polarized light refers to a state in which the phases of the P wave and S wave of light are shifted by ¼ wavelength. Then, the light 68c is changed in direction by the reflection mirror 38 and is incident on the objective lens 40 as light 70c. The light 70c forms an image on the signal surface of the disk 12 (light 72c) and is reflected (light 74c). At this time, since the phase of the light is inverted by reflection, in other words, the phase changes by ½ wavelength, so the relationship between the P wave and the S wave that are shifted by ¼ wavelength is reversed. That is, the direction of rotation of circularly polarized light is reversed.

  The reflected light travels in the reverse direction, and is first converted into parallel light 76c by the objective lens 40, and then passes through the quarter-wave plate 36 (light 78c). At this time, the circularly polarized light is converted into linearly polarized light. Unlike the forward path, however, the circularly polarized light is in the reverse direction, so that the polarization plane of the converted linearly polarized light is the S wave plane in the polarization beam splitter 30, that is, yz. Parallel to the plane.

  Next, the collimated light from the quarter-wave plate 36 is converted into focused light by the collimator lens 34, and enters the polarization beam splitter 30 as light 78c. Since the light 78c is linearly polarized into S waves, the polarization beam splitter 30 reflects 100% of the light, and the reflected light 80c changes the direction toward the light receiving sensor 60.

  When the light 78c reflected by the disk 12 returns to the laser diode 26, the noise on the reproduced signal becomes very large. This is so-called “return light noise”. By using the quarter wavelength plate 36 and the polarization beam splitter 30, the return light can be blocked or considerably reduced as described above.

  Of the light 80 c traveling toward the light receiving sensor 60, the effective light beam passes between the pair of tilt detection prisms 54 and 56 and enters the cylindrical lens 58. The ridgeline of the cylindrical lens 58 is inclined in the direction of 45 degrees with the xy plane with the optical axis as the x-axis direction. Therefore, the imaging position on the optical axis in this section does not coincide with the imaging position in a section perpendicular to this section. Such an astigmatic difference is generated because the astigmatism method is used for the focus servo. The astigmatism method is a well-known method and the principle is well known, and therefore the description thereof is omitted here.

  The light 80 c is collected on the optical axis near the light receiving sensor 60 by the collimator lens 34 and the cylindrical lens 58. The reason that the term “condensing” is used instead of imaging is that the light collected by the light receiving sensor 60 by the astigmatism method does not form an image because of the astigmatic difference. The light receiving sensor 60 is placed at an approximately middle position between the respective image forming points in the two cross sections defined by the cylindrical lens 58 described above.

  The light 80c is collected on the four-divided sensors 60a, 60b, 60c and 60d arranged at the optical axis position shown in FIG. The light receiving sensor 60 is divided into four parts for use in focusing and servoing at the same time as reproducing the recording signal. However, since this operation is well known, the description thereof is omitted here.

  Next, the flow of ± first-order light will be described with reference to FIGS. The principal rays 64a and 64b of the ± first-order light that are diffused light emitted from the virtual light source are incident on the collimator lens 34 with an inclination with respect to the optical axis, and after being converted into parallel light, the optical axis Proceed with the same inclination as. Then, the direction is changed by the reflection mirror 38, and an image is formed on the disk 12 as a sub beam by the objective lens 40. In the figure, light 68a and 68b represent ± first-order light passing through the center of the collimator, and light 72a and 72b represent ± first-order light passing through the center of the objective lens.

  The ± primary lights 72a and 72b are imaged on the signal surface of the disk 12 at positions separated from each other in the track longitudinal direction of the disk 12 from the optical axis. The reflected lights 76a and 76b are converted into parallel light by the objective lens 40, and the direction thereof is the same as when incident. Then, the light is condensed on the light receiving sensor 60 by the collimator lens 34 and the cylindrical lens 58 (80a, 80b). The reason for using the word “light collection” instead of imaging is the same as described above. Lights 80a and 80b represent the direction of light passing through the center of the cylindrical lens and are condensed on this extension.

  As shown in FIG. 8, the lights 80a and 80b are incident on the two-divided sensors 60e, 60f, 60g, and 60h that are spaced apart from each other in the y direction from the optical axis. These two-divided sensors are for detecting sub-beam detracking in the above-described differential push-pull method. As described above, this division direction is included in the principle and is well known, and thus the description thereof is omitted here.

  Subsequently, the tilt servo will be described. First, the deterioration of the spot on the disk signal surface in each of the case where the disk 12 is tilted and the case where the objective lens 40 is tilted will be described, and the influence of the disk tilt will be described. A method of canceling with lens tilt will be described. Next, a light path in this embodiment will be described, and a tilt detection method will be described. Further, the operation of the tilt servo will be described.

  First, consider a spot when only the disk 12 is tilted. FIG. 9 shows the state of the light beam when there is no tilt. Since the objective lens 40 is designed to have spherical aberration so as to cancel the spherical aberration caused by the disc thickness, no spherical aberration occurs in the spot on the signal surface of the disc 12. FIG. 10 is a schematic diagram showing an imaging spot on the disk signal surface observed from the side opposite to the objective lens in this case, and the light collection center away from the optical axis is an image of a paraxial ray. It coincides with the center.

  The state of the light beam when the disk 12 is tilted is shown in FIG. In this case, the imaging spot on the disc signal surface observed from the side opposite to the objective lens is shown in FIG. As can be seen from FIG. 12, due to the inclination of the disk 12, the light collection center away from the optical axis moves from the paraxial light beam imaging center to the side where the distance between the disk 12 and the objective lens 40 becomes narrower. is seperated. This state is a state where coma is generated.

  Next, consider a spot when only the objective lens 40 is tilted. FIG. 13 shows the state of light rays when the objective lens 40 is not tilted. In FIG. 13, since only the influence of the objective lens tilt is considered, the disk thickness is not used. On the other hand, since the lens is simply a spherical lens, spherical aberration occurs. FIG. 14 is a schematic diagram showing an imaging spot on the disk signal surface observed from the side opposite to the objective lens 40 in this case, and the light collection center away from the optical axis is the imaging center of the paraxial light beam. Is consistent with

  On the other hand, FIG. 15 shows the state of light rays when the objective lens 40 is tilted. FIG. 16 shows an imaging spot on the disc signal surface observed from the side opposite to the objective lens 40 in this case. In this case, as in the case of the previous disc tilt (FIG. 12), the light collection center away from the optical axis is changed from the imaging center of the paraxial light beam to the disc 12 by the tilt of the objective lens 40. Light is focused away from the side where the distance between the objective lenses is narrow. This state is a state where coma is generated.

  Further, consider a spot when a light beam incident on the objective lens 40 is tilted. In this case, both lens tilt and disk tilt are affected. The state of the light beam when there is no light beam tilt is the same as in FIG. 13, but the objective lens 40 is assumed to be a spherical lens that can easily track the light beam, and the disk 12 has a thickness. As shown in FIG. 17, spherical aberration occurs in the spot on the disk signal surface. In this case, the imaging spot on the disc signal surface observed from the side opposite to the objective lens 40 is the same as that in FIG. 14 described above, and the condensing center of the light beam away from the optical axis is the image of the paraxial light beam. It coincides with the center.

  On the other hand, FIG. 18 shows the state of the light beam when the incident light is tilted. In this case, coma occurs in image formation on the signal surface, and when the image formation spot on the disk signal surface is observed from the side opposite to the objective lens 40, the spot shown in FIG. In other words, due to the inclination of the incident light, the condensing center of the light beam away from the optical axis is separated from the imaging center of the paraxial light beam toward the incident light traveling direction side, thereby generating coma aberration.

  In order to cancel the coma generated by the disc tilt as shown in FIG. 11, the objective lens 40 may be tilted in the opposite direction to that shown in FIG. The objective lens 40 tilts the objective lens 40 in a direction parallel to the disk 12. However, if the objective lens 40 is completely parallel, the situation is the same as the light beam tilt shown in FIG. 18, and the coma aberration is not canceled out. The tilt state before reaching is good.

  In the optical pickup, in order to narrow the beam spot as much as possible, parallel light is incident on the objective lens with the light quantity distribution as uniform as possible. That is, only a relatively flat portion near the central portion of the intensity distribution of parallel light having a Gaussian distribution is incident. Therefore, the remaining part is eclipseed by the objective lens pupil. In the present invention, since the obtained light is effectively used for tilt detection, a separate light source is not necessary, and it is not necessary to increase the output of the semiconductor laser for generating the original beam.

  The tilt detection will be described with reference to FIGS. 19 to 22. In these drawings, the same or similar reference numerals as those in FIGS. 5 to 7 showing the normal operation are used as the reference numerals indicating the respective lights. It is pointed out beforehand.

  Lights 64a and 64b, which are part of the diffused light emitted from the laser 26, pass through the polarization beam splitter 30 to become light 67a and 67b, and become collimated light 68a and 68b by the collimator 34. Next, the lights 70a and 70b reflected by the reflecting mirror 38 do not enter the objective lens 40, and the light 70a passes through the through-hole 44 shown in FIG. 4 and is irradiated onto the surface of the disk 12 as light 76a. Reflected. The other light 70b is reflected by the mirror 50 attached to a part of the lens holder 42 that fixes and holds the objective lens 40, and becomes the light 76b.

  However, the mirror 50 may be omitted, and reflected light from a flat portion without the lens effect of the objective lens 40 may be used as the light 76b. In other words, the mirror 50 may be provided as the reflecting portion, or the flat flange portion of the objective lens 40 may be used.

  The objective lens 40 moves in the radial direction, i.e., the x direction in the figure for tracking, and thus it is difficult to use light emitted in the radial direction for tilt detection. On the other hand, since there is no lens shift in the tangential direction, i.e., the z direction in the figure, it is easy to use light produced near the lens. In this case, a through hole 44 is formed in the vicinity of the lens of the objective lens holder 42 in the tangential direction to form a light transmission portion, or a part of the objective lens holder 42 is deleted (notched). ) A light transmission part is formed.

  An aperture may be used on the reflecting surface for detecting the tilt of the objective lens 40 in order to limit the luminous flux of the reflected light so as not to adversely affect the detection of the recording signal as stray light.

  The reflected light beams 76 a and 76 b are changed in direction by the reflecting mirror 38 to become light beams 77 a and 77 b, further converted into focused light beams 78 a and 78 b by the collimator lens 34, then reflected by the polarization beam splitter 30, and transmitted to the tilt detection prism 52. Incident (lights 79a and 79b).

  The reflected light 79a from the disk 12 is changed in the radial direction, that is, in the z direction in the figure by the tilt detection prism 54, and is converted into light 80a as a four-divided sensor 60i for disc tilt detection shown in FIG. Incident on 60j, 60k and 60l.

  The reflected light 79b from the lens chilled mirror is changed by the tilt detection prism 56 in the radial direction and in the opposite direction to the light 79a, and the light 80b is used as the lens 80 for detecting the lens tilt shown in FIG. The light enters the divided sensors 60m, 60n, 60o and 60p.

  Since the light 80a and 80b fall off the optical axis in the radial direction, the sensors 60i, 60j, 60k, 60l, 60m, 60n, 60o, and 60p are located in the radial direction away from the optical axis. This is to avoid the ± first-order beam that falls off in the tangential direction when the differential push-pull method is used for tracking.

  In addition, since the light 80a and the light 80b have opposite angles, it is possible to separate and detect each other's light by separately arranging the sensors with the optical axis in between.

  Here, a quadrant sensor is used in order to cope with both radial and tangential tilts. However, when a single detection of radial or tangential is sufficient, a dual sensor may be used. FIG. 23 shows the state of the split sensor when only the radial tilt is detected.

  The light 67a and 78a, the light 68a and 77a, and the light 70a and 76a are shown to be in the opposite direction at the same angle, but this is when the light 70a is irradiated perpendicularly to the disk 12 Only. If the light is not irradiated vertically, the angles of these lights deviate and the directions are approximately reversed. In addition, the light 67b and 78b, the light 68b and 77b, and the light 70b and 76b are shown to be in the opposite direction at the same angle, but this is because the light 70b is perpendicular to the lens chilled mirror 50. Only when irradiated. If not illuminated vertically, the angle will be off and the orientation will be roughly reversed.

  The light on the sensor is defocused due to the astigmatism method, but may be imaged if the astigmatism method is not used.

  Since the disk is irradiated with parallel light, there is no concentration of optical power, and even if it is irradiated with the recording power, the recorded portion is not erased or overwritten to be deteriorated. Moreover, since it is parallel light, even if the reflected light from the disk is collected, it will not be diffracted by pits or grooves on the disk.

  First, the principle of tilt detection will be described with reference to FIG. FIG. 24 shows a general convex lens and parallel light incident on a light beam inclined by an angle θ with respect to the optical axis. The light beam forms an image at a position separated from the optical axis by an image height y. If the focal length of the lens is f, there is a relationship of y = f * sin θ. When θ is small, it can be approximated as sin θ≈θ, so y≈f * θ, and y is proportional to θ. Therefore, if the image height can be detected, the inclination of the incident light can be detected.

  Let us apply this principle to the light path of this embodiment. When the disc 12 having a warp is loaded, a radial tilt and a tangential tilt are entered. The reflected light 76 a of the parallel light 70 a irradiated on the disk 12 changes its direction according to the inclination of the disk 12. Since the direction of incidence on the collimator lens 34 is also inclined, the image height changes accordingly.

  Further, when the tilt of the actuator 22 (FIG. 3) on which the objective lens 40 is mounted is changed by some means, the reflected light 76b of the parallel light 70b irradiated on the lens chilled mirror 50 formed in a part thereof is The direction is changed according to the inclination of 22. Then, the direction of incidence on the collimator lens 34 is also inclined, and the image height changes accordingly.

  Next, a method for detecting the image height will be described in the case where the light receiving sensor is a quadrant sensor. For simplicity, it is assumed that the reflected light 80a falls on the center of the four-divided sensors 60i, 60j, 60k, and 60l in a state where there is no disc tilt.

  Let Ii, Ij, Ik, and Il be the current that flows according to the amount of light. If the beam falls to the center of the entire quadrant sensor, Ii = Ij = Ik = Il. If they deviate from the center, they become unbalanced.

  When the disk 12 is tilted in the radial direction, the position where the reflected light 80a is reflected moves in the direction in which the sensors 60i and 60j are aligned or in the direction in which the sensors 60l and 60k are aligned. When tilted in the tangential direction, the position where the reflected light 80a falls is moved in the direction in which the sensors 60i and 60l are aligned or in the direction in which the sensors 60j and 60k are aligned.

  For the radial direction, (Ii + Il)-(Ij + Ik) is used as the characteristic value representing the image height, that is, the current imbalance. For the tangential direction, (Ii + Ij) − (Ii + Ik) is used.

  Similarly, a case where the objective lens is tilted will be described. For simplicity, it is assumed that the reflected light 80b is incident on the center of the four-divided sensors 60m, 60n, 60o, and 60p when there is no lens tilt. The currents that flow according to the amount of light are Im, In, Io, and Ip. Im = In = Io = Ip when falling to the center of the entire beam split sensor. If they deviate from the center, they become unbalanced.

  When the objective lens 40, that is, the lens chilled mirror 50 is tilted in the radial direction, the position where the reflected light 80b is reflected moves in the direction in which the sensors 60m and 60n are aligned or the direction in which the sensors 60p and 60o are aligned. When tilted in the tangential direction, the position where the reflected light 80b falls is moved in the direction in which the sensors 60m and 60p are arranged or in the direction in which the sensors 60n and 60o are arranged.

  For the radial direction, (Im + Ip) − (In + Io) is used as the characteristic value representing the image height, that is, the current imbalance. For the tangential direction, (Im + In)-(Ip + Io) is used.

  The sign of these characteristic values can detect the tilt direction, that is, the sign of the angle. Although neither is shown, these calculations may be realized by a dedicated hardware circuit, or after AD conversion of the current value, the calculation may be performed by the computer. That is, the optical disc apparatus 10 of the embodiment has a control circuit (not shown), but the control circuit includes a calculation circuit and a computer.

  Although the above has been described for the case of a four-divided sensor, in the case of detecting either radial tilt or tangential tilt, a two-divided sensor may be used. Taking the case of detecting a radial tilt as an example, only the difference from the case of the quadrant sensor will be described with reference to FIG.

  The reflected light 80a falls on the two-divided sensors 60i and 60j. Let Ii and Ij be currents that flow according to the amount of light. When the disk 12 is tilted in the radial direction, the position where the reflected light 80a is reflected moves in the direction in which the sensors 60i and 60j are aligned. (Ii-Ij) is used in the radial direction as a characteristic value representing the image height, that is, the current imbalance.

  Similarly, the reflected light 80b falls on the sensors 60k and 60l. The currents that flow according to the amount of light are Ik and Il. When the lens 40, that is, the lens chilled mirror 50 is tilted in the radial direction, the position where the reflected light 80b is reflected moves in the direction in which the sensors 60k and 601 are aligned. (Ik-Il) is used in the radial direction as a characteristic value representing the image height, that is, the current imbalance.

  In order to cancel the coma generated by the disc tilt by the coma generated by the objective lens tilt, the objective lens may be tilted in the same direction as the disc tilt. Although the lens is tilted in the direction in which the lens is parallel to the disk, when the lens is completely parallel, the situation is the same as that of the light beam tilt, and coma is not canceled out.

  Therefore, the disc tilt amount and the tilt amount of the objective lens that cancels the coma caused thereby may be examined in advance, and after detecting the disc tilt amount, the lens may be tilted according to the above-described relationship. Since this is determined by the lens design, it is not necessary to set for each pickup.

  The actual operation is to multiply the characteristic value of either the disc tilt characteristic value or the lens tilt characteristic value by a coefficient, then adjust the tilt of the objective lens so that the difference between the two becomes zero, and perform servo control. Call. That is, the direction in which the objective lens is tilted is determined by the sign of the calculation result, the amount of tilt is determined by the absolute value of the calculation result, and the detection, calculation, and adjustment loops are repeated continuously.

  When there is no tilt, each of the lights 80a and 80b is incident on the approximate center of the entire four-divided sensor, but it is not necessarily required to be exactly the center. If the value deviates from the center, the characteristic value does not become zero, but the value may be recognized as an offset value and subtracted from the characteristic value, or the target value for tilt servo may be increased by that amount. That's fine. Even if it is located at the exact center, an offset occurs in the characteristic value due to the offset of the quadrant sensor output and other circuit outputs. This offset value can be measured in advance during the manufacturing process. Each characteristic value may be measured in a state where the objective lens is tilted so that the pick-up is in a normal posture with respect to the disc without warpage and the coma aberration does not occur on the disc.

  When recording or reproducing both DVD and CD discs with a single optical pickup, it is necessary to cope with two types of disc thickness tilts with the same objective lens. In such a case, the disc tilt amount and the tilt amount of the objective lens that cancels coma aberration caused by the disc tilt can be checked separately when using a CD and when using a DVD, and tilt servo can be applied accordingly. That's fine.

  Also, when both DVD and CD discs are recorded or reproduced with a single optical pickup and separate light sources are used inside the optical pickup, the tilt detection signal when a horizontal disc with no warpage is mounted is both. It does not necessarily match in the case of the light source. This is because if there is an error in the positions of both light sources, the directions of parallel light passing through the collimator lens and heading to the disk do not match. In such a case, the offset value may be measured separately. Here, CD and DVD are taken as an example, but the type of disk is not limited.

  Various methods for actually adjusting the tilt of the objective lens upon detection of the disc tilt have already been reported, and the present invention does not stick to a specific method.

  With reference to FIGS. 25 to 31, a case where only the disc tilt detection method described in the first embodiment is applied to the related art 1 will be described as a second embodiment.

  In the optical disc apparatus 10 shown in FIG. 25, a disc 12 as a signal recording / reproducing body is held by a holding unit 14 and rotated by a spindle motor 16 to receive light from an optical pickup 18, thereby causing a signal to be sent to the disc 12. Is recorded or the signal from the disk 12 is reproduced. The optical pickup 18 is held by a shaft 20 a so as to be movable in the axial direction of the shaft 20, and the shaft 20 is held by a shaft holder 22. The shaft holder 22 is fixed on the shaft holder chassis 24.

  The spindle motor 16 described above is fixed on a spindle motor chassis 84, and the spindle motor chassis 84 and the shaft holder chassis 24 are connected by a support shaft 86. A cam 88 that swings the end of the shaft holder chassis 24 up and down is provided on the spindle motor chassis 84.

  The optical pickup 18 shown in FIG. 26 is the same as the optical pickup 18 shown in FIG. 4 except for the following points. Here, the same or similar reference numerals are used, and redundant description is omitted. That is, in the second embodiment, only one prism 54 is provided between the polarization beam splitter 30 and the cylindrical lens 58 in order to detect only the disc tilt.

  27 to 30 showing the state of the light beam of the second embodiment, the light for detecting the objective lens tilt, that is, “b” is added in FIGS. 19 to 22 showing the first embodiment. Light is omitted. Accordingly, the same or similar reference numerals as in FIGS. 19 to 22 are used in FIGS.

  As shown in FIGS. 27 to 30, the disc tilt detection light 79a is changed to the light 80a by changing the direction of the light in the radial direction, that is, the z direction in the drawing, as shown in FIG. The light enters the two-divided sensors 60i and 60j for disc tilt detection.

  Since the light 80a falls off the optical axis in the radial direction, the sensors 60i and 60j are arranged in the radial direction away from the optical axis. This is to avoid the ± first-order beam that falls off in the tangential direction when the differential push-pull method is used for tracking. Here, in order to deal with only the radial tilt, a two-divided sensor is used.

  Since the principle of tilt detection has been described in the first embodiment, it will be omitted.

  The reflected light 76a of the parallel light 70a irradiated on the disk 12 having a warp that causes a radial tilt changes its direction according to the inclination of the disk 12. Accordingly, the direction of incidence on the collimator lens 34 is also inclined, and the image height changes accordingly.

  The method for detecting the image height is the same as in the first embodiment, and will be described briefly. Since only the radial tilt is detected, the case where the light receiving sensor is a two-divided sensor will be described. For simplicity, it is assumed that the reflected light 80a is incident on the center of the two-divided sensors 60i and 60j when there is no disc tilt. Let Ii and Ij be currents that flow according to the amount of light.

  If the beam falls to the center of the entire two-divided sensor, Ii = Ij. If they are off center, they will be unbalanced.

  When the disk 12 is tilted in the radial direction, the position where the reflected light 80a is reflected moves in the direction in which the sensors 60i and 60j are arranged. (Ii−Ij) is used for the radial direction as a characteristic value representing the image height, that is, the current imbalance.

  The sign of these characteristic values can detect the tilt direction, that is, the sign of the angle. In addition, by using a ratio obtained by dividing the difference in sensor output by the total sum, the incident position can be detected as a relative value based on the size of the two-divided sensor, so the size and shape of the two-divided sensor As long as the arrangement is the same, these characteristic values can be handled in the same manner even in various disks having different reflectivities.

  As in the previous embodiment, these calculations may be realized by a hardware circuit, or may be obtained by calculating with a computer after AD conversion of the current value.

  First, the radial tilt amount of the disc is detected by the method described above. Then, the cam 88 shown in FIG. 25 is rotated by a drive source (not shown) to swing the end of the shaft holder chassis 84 up and down. As a result, the optical pickup 18 mounted on the chassis 84 around the support shaft 86 changes its inclination. If the relative angle between the disk 12 and the pickup is detected by the aforementioned method while changing the tilt of the optical pickup 18, and the cam 88 is stopped in a state where the spot on the disk will be good, Coma is eliminated from spots on the disc.

  When there is no tilt, the light 80a is incident on the approximate center of the entire two-divided sensor, but it is not always necessary to be at the center. If the value deviates from the center, the characteristic value does not become zero, but the value may be recognized as an offset value and subtracted from the characteristic value, or the target value for tilt servo may be increased by that amount. That's fine. Even if it is positioned exactly in the center, an offset occurs in the characteristic value due to the offset of the two-divided sensor output and other circuit outputs. This offset value can be measured in advance during the manufacturing process. Each characteristic value may be measured in a state where the objective lens is tilted so that the pick-up is in a normal posture with respect to the disc without warpage and the coma aberration does not occur on the disc.

  When both DVD and CD discs are recorded or reproduced with a single optical pickup and separate light sources are used inside the optical pickup, the tilt detection signal when a horizontal disc with no warpage is mounted is It does not necessarily match in the case of the light source. This is because if there is an error in the positions of both light sources, the directions of parallel light passing through the collimator lens and heading to the disk do not match. In such a case, the offset value may be measured separately. Here, CD and DVD are taken as an example, but the type of disk is not limited.

  In the first embodiment, as a method of detecting the image height proportional to the tilt amount, that is, the position of the light incident on the divided sensor, the sensor output is divided into two by a symmetrical axis orthogonal to the direction of the tilt to be detected. Is a characteristic value. Here, a method will be described in which a ratio obtained by dividing the output difference by the total sum is used as the characteristic value. This third embodiment can also be applied to the second embodiment.

  The optical disk device 10 and its optical system, the light path, and the tilt detection method are exactly the same as those in the first embodiment, and a description thereof will be omitted.

  Next, a method for detecting the image height will be described in the case where the light receiving sensor is a quadrant sensor. For simplicity, it is assumed that the reflected light 80a (FIGS. 22 and 30) is incident on the center of the four-divided sensors 60i, 60j, 60 and 60l shown in FIG.

  Let Ii, Ij, Ik, and Il be the current that flows according to the amount of light. If the beam falls to the center of the entire quadrant sensor, Ii = Ij = Ik = Il. If they deviate from the center, they become unbalanced.

  When the disk 12 is tilted in the radial direction, the position where the reflected light 80a is reflected moves in the direction in which the sensors 60i and 60j are aligned or in the direction in which the sensors 60l and 60k are aligned. When tilted in the tangential direction, the position where the reflected light 80a falls is moved in the direction in which the sensors 60i and 60l are aligned or in the direction in which the sensors 60j and 60k are aligned.

  For the radial direction, ((Ii + Il) − (Ij + Ik)) / (Ii + Il + Ij + Ik) is used as the characteristic value representing the image height, that is, the current imbalance. For the tangential direction, ((Ii + Ij) − (Il + Ik)) / (Ii + Il + Ij + Ik) is used.

  Similarly, a case where the objective lens is tilted will be described. For simplicity, it is assumed that the reflected light 80 (FIGS. 22 and 30) is incident on the center of the four-divided sensors 60m, 60n, 60o, and 60p in a state where there is no lens tilt. The currents that flow according to the amount of light are Im, In, Io, and Ip. Im = In = Io = Ip when falling to the center of the entire beam split sensor. If they deviate from the center, they become unbalanced.

  When the objective lens 40, that is, the lens chilled mirror 50 is tilted in the radial direction, the position where the reflected light 80b is reflected moves in the direction in which the sensors 60m and 60n are aligned or the direction in which the sensors 60p and 60o are aligned. When tilted in the tangential direction, the position where the reflected light 80b falls is moved in the direction in which the sensors 60m and 60p are arranged or in the direction in which the sensors 60m and 60o are arranged.

  For the radial direction, ((Im + Ip)-(In + Io)) / (Im + Ip + Io + Ip) is used as the characteristic value representing the image height, that is, the current imbalance. For the tangential direction, ((In + Im) − (Ip + Io)) / (Im + In + Io + Ip) is used.

  The sign of these characteristic values can detect the tilt direction, that is, the sign of the angle. In addition, by using a ratio obtained by dividing the difference in sensor output by dividing the sum by the symmetric axis perpendicular to the tilt direction to be detected and dividing the sum by the sum, the incident position is relative to the size of the quadrant sensor. If the size, shape, and arrangement of the four-divided sensor are the same, the characteristic values of the reflected light of the disk and the lens chilled mirror that have different reflectivities are as follows. It can be handled in the same way. Of course, for the same reason, it can be applied to various disks having different reflectivities.

  Similar to the first and second embodiments, these calculations may be realized by a circuit, or may be obtained by calculating after AD conversion of the current value.

  Although the above has been described for the case of a four-divided sensor, in the case of detecting either radial or tangential tilt, a two-divided sensor may be used. Taking the case of detecting a radial tilt as an example, only the phase connection point with the case of the quadrant sensor will be described with reference to FIG.

  The reflected light 80a falls on the two-divided sensors 60i and 60j shown in FIG. Let Ii and Ij be currents that flow according to the amount of light. When the disk 12 is tilted in the radial direction, the position where the reflected light 80a is reflected moves in the direction in which the sensors 60i and 60j are aligned. (Ii−Ij) / (Ii + Ij) is used in the radial direction as the characteristic value representing the image height, that is, the current imbalance.

  Similarly, the reflected light 80b falls on the sensors 60k and 60l. The currents that flow according to the amount of light are Ik and Il. When the objective lens 40, that is, the lens chilled mirror 50 is inclined in the radial direction, the position where the reflected light 80b is reflected moves in the direction in which the sensor 60k and the sensor 601 are aligned. ((Ik−Il) / (Ik + Il)) is used for the radial direction as a characteristic value representing the image height, that is, the current imbalance.

  Since the operation of the tilt servo is the same as that of the first embodiment, description thereof is omitted.

FIG. 1 is an illustrative view showing a conventional optical disc apparatus except for a control circuit portion. 2 is an illustrative view showing a configuration of the optical pickup of the conventional apparatus shown in FIG. FIG. 3 is an illustrative view showing an embodiment of the present invention excluding a control circuit portion. FIG. 4 is an illustrative view showing a configuration of the optical pickup of FIG. 3 embodiment. FIG. 5 is an illustrative view showing sub-beams in the optical system of FIG. FIG. 6 is an illustrative view showing sub-beams in the yz plane of the optical system of FIG. FIG. 7 is an illustrative view showing sub-beams in the xy plane of the optical system of FIG. FIG. 8 is an illustrative view showing a divided arrangement of the light receiving sensors when the tilt detecting sensor is divided into four in the embodiment of FIG. FIG. 9 is an illustrative view showing a state of a light beam from the objective lens to the disc when there is no disc tilt. FIG. 10 is an illustrative view showing an imaging spot on the disc signal surface observed from the side opposite to the objective lens in FIG. FIG. 11 is an illustrative view showing a state of a light beam from the objective lens to the disk when there is a disk tilt. FIG. 12 is an illustrative view showing an imaging spot on the disc signal surface observed from the side opposite to the objective lens in FIG. FIG. 13 is an illustrative view showing a state of a light beam from the objective lens to the disk when there is no objective lens tilt. FIG. 149 is an illustrative view showing an imaging spot on the disc signal surface observed from the side opposite to the objective lens in FIG. FIG. 15 is an illustrative view showing a state of a light beam from the objective lens to the disk when there is an objective lens tilt. FIG. 16 is an illustrative view showing an imaging spot on the disc signal surface observed from the side opposite to the objective lens in FIG. FIG. 17 is an illustrative view showing a state of a light beam from the objective lens to the disk when there is no light beam tilt. FIG. 18 is an illustrative view showing a state of a light beam from the objective lens to the disk when there is a light beam tilt. FIG. 19 is an illustrative view showing light rays in the optical system of the optical pickup shown in FIG. FIG. 20 is a front view showing light rays in the yz plane of the optical system of FIG. FIG. 21 is a top view showing light rays in the zx plane of the optical system of FIG. FIG. 22 is a side view showing light rays in the xy plane of the optical system of FIG. FIG. 23 is an illustrative view showing a divided arrangement of the light receiving sensors when the tilt detection sensor is divided into two in the embodiment of FIG. FIG. 24 is an illustrative view showing an image height at which parallel light on which light beams inclined with respect to the optical axis are incident is formed. FIG. 25 is an illustrative view showing another embodiment of the present invention except for a control circuit portion. FIG. 26 is an illustrative view showing a configuration of the optical pickup of FIG. 25 embodiment. FIG. 27 is an illustrative view showing an optical system of the optical pickup of FIG. FIG. 28 is a front view showing a yz plane in the optical system of FIG. FIG. 29 is a top view showing a zx plane in the optical system of FIG. FIG. 30 is a side view showing the xy plane in the optical system of FIG. FIG. 31 is an illustrative view showing a divided arrangement of the light receiving sensors when the tilt detection sensor is divided into two in the embodiment of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Optical disk apparatus 12 ... Disk 18 ... Optical pick-up 26 ... Laser diode 30 ... Deflection beam splitter 34 ... Collimator lens 38 ... Reflection mirror 40 ... Objective lens 42 ... Objective lens holder 44 ... Through-hole 50 ... Lens tilt detection mirror 60 ... Light receiving sensor 60i-60p ... split sensor

Claims (1)

A collimator lens that converts light from the light source into parallel light,
An objective lens for imaging parallel light from the collimator lens on an optical disk;
An objective lens holder for holding the objective lens;
A light transmissive portion formed on the objective lens holder at a first position away from the objective lens in a track tangential direction of the optical disc, and through which the transmitted parallel light is irradiated to the optical disc;
A first condenser lens that receives the transmitted parallel light reflected from the optical disk, and a disk tilt sensor that receives incident light from the first condenser lens and includes a plurality of first light-receiving sensors;
A reflecting unit that moves integrally with the objective lens and that reflects the parallel light at a second position opposite to the first position in the track tangential direction of the optical disc and outputs reflected parallel light;
In an optical disc apparatus comprising: a second condenser lens that receives the reflected parallel light; and a lens tilt sensor that receives incident light from the second condenser lens and includes a plurality of second light receiving sensors.
A tilt servo means for tilting the objective lens by a predetermined amount using the objective lens tilt sensor according to the disc tilt amount detected using the disc tilt sensor,
An optical disc apparatus in which a tilt amount of an objective lens for canceling coma aberration due to a disc tilt, which is checked in advance for each disc having a different thickness and / or refractive index, is set in advance as the predetermined amount.