JP2007234158A - Optical disk drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk drive having a simple configuration capable of stably correcting wavefront aberration irrespective of deviation in characteristics of a liquid crystal element, for the optical disk drive with the liquid crystal element for the purpose of correcting the wavefront aberration. <P>SOLUTION: The optical disk drive includes the liquid crystal element for correcting the wavefront aberration. A driving voltage checking means 33, a driving voltage resetting means 34, and a liquid crystal element driving means 35 relate to the driving of the liquid crystal element. The liquid crystal element driving means 35 applies a driving voltage to the liquid crystal element. The driving voltage checking means 33 determines whether the driving voltage applied to the liquid crystal element 23 by the liquid crystal element driving means 35 or the driving voltage scheduled to be applied is appropriate at that point of time. When it is determined inadequate by the driving voltage checking means 33, the driving voltage resetting means 34 resets the value of the driving voltage set by the liquid crystal element driving means 35. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical disc apparatus used for recording / reproducing information on an optical recording medium, and more particularly to a technique for maintaining good recording / reproducing quality in an optical disc apparatus equipped with a liquid crystal element for correction of wavefront aberration.

  Optical recording media such as compact discs (hereinafter referred to as CDs) and digital versatile discs (hereinafter referred to as DVDs) are widely used. Furthermore, in recent years, in order to increase the amount of information in the optical recording medium, research on increasing the density of the optical recording medium has been advanced. For example, a high-density optical recording medium such as a Blu-ray disc (hereinafter referred to as BD) is also practical. It is becoming. Such recording / reproduction of the optical recording medium is performed by an optical disc apparatus including an optical pickup that reads and records information by irradiating the optical recording medium with a light beam from a light source.

  By the way, when the type of the optical recording medium is different, the thickness of the protective layer for protecting the recording surface of the optical recording medium may be different. For example, the thicknesses of the protective layers of CD, DVD, and BD are sequentially different from 1.2 mm, 0.6 mm, and 0.1 mm. For this reason, in an optical disc apparatus that supports a plurality of types of optical recording media, there may be a problem that the quality of information recording / reproduction deteriorates due to spherical aberration caused by the difference in the thickness of the protective layer depending on the optical recording medium. Also, in an optical pickup device corresponding to a high-density optical recording medium such as BD, an objective lens having a large numerical aperture (NA) is generally used, but spherical aberration is proportional to the fourth power of NA. Therefore, the influence of spherical aberration caused by variations in the protective layer cannot be ignored.

  Furthermore, in order to cope with a high-density optical recording medium, when the numerical aperture of the objective lens is increased and a short-wavelength light beam is used, the optical recording medium is inclined during information recording / reproduction, and the optical recording medium method is used. When the incident angle of the light beam with respect to the linear direction is tilted, the influence of coma aberration cannot be ignored.

  For this reason, for the purpose of correcting wavefront aberrations such as spherical aberration and coma aberration, a liquid crystal element is disposed in the optical system of the optical pickup provided in the optical disc apparatus, and the voltage applied to the liquid crystal element is controlled to pass through the liquid crystal element. 2. Description of the Related Art Conventionally, an optical disc apparatus that controls the phase of a light beam and corrects wavefront aberration is known as disclosed in Patent Document 1 and Patent Document 2, for example.

  However, the characteristics of a liquid crystal element used in an optical disk device for the purpose of correcting wavefront aberration vary with temperature. For this reason, when the driving voltage applied to the liquid crystal element is not controlled in consideration of the characteristic variation with respect to the temperature change of the liquid crystal element, the wavefront aberration such as spherical aberration and coma aberration is not sufficiently corrected by the liquid crystal element, and the information by the optical disk device Deterioration of recording / reproduction quality may become a problem.

  FIG. 8 schematically shows the relationship between the voltage applied to the liquid crystal element and the phase generated according to the applied voltage. FIG. 9 schematically shows how the relationship between the applied voltage and the generated phase varies depending on the temperature around the liquid crystal element. As shown in FIG. 8, the liquid crystal element has a region (a portion indicated by a broken circle in the figure) where the generated phase does not change even when the applied voltage changes.

  When correcting wavefront aberration using a liquid crystal element, the liquid crystal element generally has a plurality of regions with different voltages to be applied. When the ambient temperature of the liquid crystal element changes, FIG. As shown in FIG. 9, the case where three different applied voltages are applied to the liquid crystal element is shown, so that part or all of the voltages applied to the liquid crystal element can be changed even if the applied voltage is changed. There is a case where it enters an area where no phase difference occurs. In this case, in particular, correction of wavefront aberration by the liquid crystal element is insufficient, and there is a tendency that the quality of information recording / reproduction by the optical disk device is seriously deteriorated.

  In this regard, in Patent Document 2, a temperature sensor such as a thermistor is disposed in an optical disk device so as not to be affected by fluctuations in the characteristics of the liquid crystal element with respect to temperature changes in the optical disk device including the liquid crystal element. The voltage for driving the liquid crystal element is controlled using the ambient temperature of the liquid crystal element obtained by the above and data with respect to temperature fluctuations such as phase characteristics and response characteristics of the liquid crystal previously stored in a memory or the like provided in the optical disc apparatus. Technology is introduced.

However, as introduced in Patent Document 2, assuming that the optical disk device stores data for temperature fluctuations such as liquid crystal phase characteristics and response characteristics in advance, an optical disk device corresponding to a plurality of types of optical recording media is assumed. In this case, it is necessary to collect a large amount of data in advance, and this becomes a work burden during manufacturing. In addition, liquid crystal characteristics of liquid crystal elements have individual differences, and even if data stored in advance as liquid crystal characteristics with respect to temperature fluctuations is used, wavefront aberration may not be sufficiently corrected, which is a problem. .
JP 2005-259180 A JP 2000-298862 A

  In view of the above points, an object of the present invention is to provide an optical disc apparatus having a liquid crystal element for the purpose of correcting wavefront aberration, having a simple configuration capable of stably correcting wavefront aberration regardless of characteristic fluctuation of the liquid crystal element. An optical disk device is provided.

  In order to achieve the above object, the present invention condenses a light source and a light beam emitted from the light source on a recording surface of an optical recording medium, and guides reflected light reflected by the recording surface to a predetermined light receiving position. A liquid crystal element that includes an optical system, a liquid crystal, and two transparent electrodes that sandwich the liquid crystal, and is disposed in the optical system and corrects wavefront aberration; and a light that the reflected light is disposed at the light receiving position. An optical disc apparatus comprising: a light detection unit that converts information into an electric signal; and a liquid crystal element driving unit that is electrically connected to the transparent electrode and applies a driving voltage to the liquid crystal element. , Instructing to sequentially apply three kinds of driving voltages having a certain relationship, and in each case, relating to the characteristics of the reproduction signal obtained by processing the electrical signal converted by the light detection means, And the liquid crystal element An actual measurement value of a predetermined parameter that fluctuates with the characteristic variation is acquired, and the obtained three actual measurement values are compared with a predetermined reference stored in advance, and the liquid crystal element driving is performed before the actual measurement value is acquired. Drive voltage confirmation means for confirming whether the drive voltage applied by the means or the drive voltage to be applied is appropriate, and when the drive voltage is determined to be inappropriate by the drive voltage confirmation means And a drive voltage resetting means for resetting the drive voltage based on the relationship between the acquired three actually measured values and the predetermined reference.

  In the optical disk device having the above-described configuration, at least one of the transparent electrodes is divided into a plurality of regions, and the liquid crystal element driving unit sets a voltage to be applied to each of the plurality of regions, and A drive voltage is applied, and the three types of drive voltages are drive voltages that the liquid crystal element driving means has applied to or intended to apply to the liquid crystal element immediately before the actual measurement value is obtained. 1 driving voltage, a second driving voltage obtained by uniformly adding a predetermined value to the first driving voltage, and a third driving voltage obtained by subtracting a predetermined value from the first driving voltage. It is characterized by that.

  According to the present invention, in the optical disk apparatus having the above-described configuration, the drive voltage check means is inappropriate if any one of the acquired measured values does not satisfy the predetermined standard. It is characterized by judging that.

  According to the present invention, in the optical disc apparatus having the above-described configuration, when the driving voltage confirmation unit determines that the driving voltage is appropriate, the driving voltage applied by the liquid crystal element driving unit is the first driving voltage. The driving voltage is used.

  Further, the present invention is characterized in that, in the optical disc apparatus configured as described above, the predetermined parameter is an amplitude of an RF signal or a track error signal obtained by processing the electrical signal.

  According to the first configuration of the present invention, it is possible to detect a characteristic fluctuation of the liquid crystal element such as a characteristic variation with respect to the ambient temperature of the liquid crystal element and an individual variation of the liquid crystal, and set an appropriate value. Further, when resetting the drive voltage, the reset value is determined because of the configuration in which the reset value is determined based on three actually measured values obtained when three drive voltages having a certain relationship are applied to the liquid crystal element. It is easy to determine how much should be done, and it becomes possible to set an appropriate drive voltage stably in a short time. Also, the amount of data to be input in advance is not large, and the burden at the time of manufacturing is small.

  Further, according to the second configuration of the present invention, in the optical disc apparatus having the first configuration described above, when confirming the characteristic fluctuation of the liquid crystal element, the optimum drive voltage value applied to the liquid crystal element is not subjected to complicated processing. Therefore, the driving voltage applied by the liquid crystal element driving means can be controlled efficiently.

  Further, according to the third configuration of the present invention, in the optical disc apparatus having the first or second configuration, it is more appropriate to perform control so that all three acquired values are within a predetermined range. Therefore, even if the characteristics of the liquid crystal element slightly change, the possibility that the correction of wavefront aberration by the liquid crystal element is insufficient becomes low immediately.

  Also, according to the fourth configuration of the present invention, an appropriate drive voltage value can be quickly obtained in the optical disc device having the third configuration.

  Further, according to the fifth configuration of the present invention, in the optical disc apparatus having any one of the first to fourth configurations, the characteristic fluctuation of the liquid crystal element can be controlled using a signal included in the conventional optical disc apparatus. The configuration of the optical disk apparatus does not become particularly complicated.

  The content of the present invention will be described in detail below, but the embodiment shown here is an example, and the present invention is not limited to the embodiment shown here.

  FIG. 1 is a block diagram showing the configuration of the optical disc apparatus of the present embodiment. The optical disc apparatus 1 can reproduce information from the optical recording medium 16 and record information on the optical recording medium 16. Reference numeral 2 denotes a spindle motor, and the optical recording medium 16 is detachably held on a chuck portion (not shown) provided on the upper portion of the spindle motor 2. Then, when recording / reproducing information on the optical recording medium 16, the spindle motor 2 continuously rotates the optical recording medium 16. The rotation control of the spindle motor 2 is performed by the spindle motor control unit 3.

  Reference numeral 4 denotes an optical pickup that irradiates the optical recording medium 16 with a light beam emitted from a light source, and can write information on the optical recording medium 16 and read information recorded on the optical recording medium 16. To do. FIG. 2 is a schematic diagram showing an optical system of the optical pickup 4. As shown in FIG. 2, in the optical pickup 4, the light beams emitted from the light sources 17 and 18 have the same optical axis by the color synthesis prism 19, become parallel light by the collimator lens 20, pass through the beam splitter 21, Reflected by the rising mirror 22 and its optical axis is made substantially perpendicular to the recording surface 16a of the optical recording medium 16, passes through the liquid crystal element 23, and is recorded on the recording surface 16a on which information of the optical recording medium is recorded by the objective lens 24. Focused.

  The reflected light reflected by the optical recording medium 16 passes through the objective lens 24 and the liquid crystal element 23 in this order, is reflected by the rising mirror 22, is further reflected by the beam splitter 21, and is detected by the condenser lens 25. The light is collected on 26 light receiving portions (not shown). The photodetector 26 converts optical information contained in the received light beam into an electrical signal. In this embodiment, the light source 17 is a two-wavelength integrated laser diode that emits a light beam for CD and DVD, and the light source 18 is a laser diode that emits a light beam for BD. For this reason, the optical disc apparatus 1 can record and reproduce CDs, DVDs, and BDs.

  The optical pickup 4 is compatible with three different types of optical recording media 16, but as described above, these different types of optical recording media 16 have different protective layer thicknesses. In the optical pickup 4 having only one objective lens 24, spherical aberration becomes a problem. For this reason, the liquid crystal element 23 is arranged to correct the spherical aberration.

  3A and 3B are diagrams for explaining the configuration of the liquid crystal element 23 included in the optical pickup 4. FIG. 3A is a schematic cross-sectional view showing the configuration of the liquid crystal element 23, and FIG. It is a top view at the time of seeing the liquid crystal element 23 of 3 (a) from the upper surface. As shown in FIG. 3, the liquid crystal element 23 includes a liquid crystal 27, two transparent electrodes 28 a and 28 b that sandwich the liquid crystal 27, and two glasses that sandwich a portion 29 formed by the liquid crystal 27 and the transparent electrodes 28 a and 28 b. And a plate 30.

  As shown in FIG. 3B, the transparent electrode 28a constituting the liquid crystal element 23 is divided into a plurality of concentric regions 32a to 32f. On the other hand, the transparent electrode 28b facing the transparent electrode 28a is not divided and is a common electrode as a whole. The transparent electrode 28b may also be a plurality of concentric regions that are the same as the transparent electrode 28a. By configuring the transparent electrodes 28a and 28b in this way, it becomes possible to generate a desired phase difference with respect to the light beam passing through the liquid crystal element 23, and reproduction of information on various optical recording media 16 can be performed. It is possible to appropriately correct the spherical aberration that occurs when performing. The transparent electrodes 28a and 28b are electrically connected to the liquid crystal element driving means (liquid crystal element driving circuit) provided in the liquid crystal element control unit 6 (see FIG. 1), which will be described later, by the wiring 31, and this liquid crystal element control. The drive voltage applied to the transparent electrodes 28a and 28b is controlled by the unit 6.

  The operation of the liquid crystal element 23 configured as described above will be described. FIG. 4 shows the spherical aberration (solid line in the figure) that occurs when reproducing an optical recording medium 16 and the pattern of the phase difference (dashed line in the figure) that is generated in the liquid crystal element 23 to correct it. It is a graph. As for the phase difference pattern generated in the liquid crystal element 23, it is necessary to cancel the spherical aberration. Therefore, it is necessary to generate a pattern having an opposite phase to the phase difference pattern shown in FIG. However, it is not an antiphase pattern. In FIG. 4, the horizontal axis is the distance from the center O of the transparent electrode 28a concentrically divided, and the numbers below the horizontal axis are the region numbers of the transparent electrode 28a (see FIG. 3B). ) Corresponds.

  A predetermined voltage is applied to each of the regions 32a to 32f of the transparent electrodes 28a and 28b, and a phase difference pattern having a phase opposite to the phase difference (broken line) pattern shown in FIG. 4 is generated in each of the regions 32a to 32f. Then, the aberration is corrected to a level that does not cause a problem for reproduction of the optical recording medium 16, and an appropriate reproduction signal is obtained. Since the amount of spherical aberration generated varies depending on the type of the optical recording medium 16, the phase difference generated in the liquid crystal element 23 varies depending on the type of the optical recording medium 16, and the value of the drive voltage applied to the transparent electrodes 28a and 28b also varies. Come.

  Returning to FIG. 1, the optical disk apparatus 1 is provided with a signal processing unit 8. The signal processing unit 8 includes at least an RF signal processing unit 9, a track error signal processing unit 10, and a focus error signal processing unit 11. Contains. Then, an RF signal, a track error signal (TE signal), and a focus error signal (FE signal) are generated based on the electrical signal converted by the photodetector 26 (see FIG. 2). The RF signal is demodulated into data by the data demodulator 12 and output to an external device such as a personal computer via the interface 13.

  The TE signal and the FE signal are output to the actuator control unit 7. Based on these signals, the actuator controller 7 supplies a drive signal to an actuator (not shown) on which the liquid crystal element 23 and the objective lens 24 (both see FIG. 2) included in the optical pickup 4 are mounted. The actuator to which the drive signal is supplied operates each part based on the signal to move the objective lens 24 in the direction parallel to the optical axis to adjust the focus and the objective lens 24 in the radial direction of the optical recording medium 16. And tracking control for adjusting the spot position of the light beam to the track position formed on the optical recording medium 16 is performed.

  In addition, the laser control unit 5 controls the laser output of the light sources 17 and 18 (see FIG. 2) made of a semiconductor laser provided in the optical pickup device 4. The overall control unit 14 also includes a spindle motor control unit 3, a laser control unit 5, a liquid crystal element control unit 6, an actuator control unit 7, a signal processing unit 8, a data demodulation unit 12, an interface 13, and information necessary for control. The storage unit 15 and the like to be stored are controlled to control the entire apparatus.

  As described above, the optical disc device 1 of the present embodiment includes the liquid crystal element 23. However, the liquid crystal element 23 has characteristic fluctuations such as characteristic fluctuations due to changes in the surrounding environment and variations in individual liquid crystal characteristics. For this reason, the present embodiment is configured to correct the characteristic fluctuation of the liquid crystal element 23. Hereinafter, this point will be described in detail.

  FIG. 5 is a block diagram showing the configuration of the liquid crystal element control unit 9. The liquid crystal element control unit 9 includes drive voltage confirmation means 33, drive voltage resetting means 34, and liquid crystal element drive means 35. Hereinafter, each means will be described.

  The drive voltage confirmation unit 33 determines whether or not the drive voltage applied to the liquid crystal element 23 by the liquid crystal element drive unit 35 described later or the drive voltage to be applied is appropriate at that time. In this embodiment, whether the drive voltage is appropriate is determined based on the magnitude of the amplitude of the RF signal obtained from the signal processing unit 8. The amplitude of the RF signal fluctuates with the characteristic fluctuation of the liquid crystal element 23 for correcting the spherical aberration, and is a value related to the characteristic of the reproduction signal when the optical disc apparatus 1 performs reproduction. This is because the recording / reproduction quality of the optical disc apparatus 1 can be stabilized regardless of the characteristic variation of the liquid crystal element 23 if judged to be the reference. Note that the larger the amplitude of the RF signal, the better the characteristics of the reproduction signal.

  In this embodiment, the propriety of the drive voltage is determined based on the amplitude of the RF signal. However, the present invention is not limited to this, and various modifications can be made without departing from the object of the present invention. . That is, the parameter for determining the appropriateness of the drive voltage may be any parameter as long as it is related to the characteristics of the reproduction signal and varies with the characteristics variation of the liquid crystal element. For example, the amplitude or jitter of the TE signal The minimum value or the like may be used as a parameter.

  The timing at which the drive voltage confirmation unit 33 confirms whether or not the drive voltage is appropriate is not particularly limited, and is appropriately performed. For example, it is performed at the time of activation, when the optical recording medium 16 is replaced, when the temperature of the optical pickup 4 changes, or at a predetermined time interval. The drive voltage confirmation unit 33 outputs an instruction related to the application of the drive voltage to the liquid crystal element drive unit 35, and outputs information on the result confirmed here to the drive voltage resetting unit 34.

  The drive voltage resetting means 34 is applied to the liquid crystal element drive means 35 or the liquid crystal element 23 at the time of confirmation by the drive voltage confirmation means 33, or when the drive voltage to be applied is determined to be inappropriate. The liquid crystal element driving means 35 plays a role of resetting the value of the driving voltage set. The drive voltage resetting unit 34 outputs information on the reset drive voltage to the liquid crystal element driving unit 35.

  The liquid crystal element driving means 35 is electrically connected to the transparent electrodes 28a and 28b (see FIG. 3) constituting the liquid crystal element 23, and the initial set value and drive stored in the storage unit 15 (see FIG. 1). A voltage is applied to the transparent electrodes 28a and 28b in accordance with the indicated value of the voltage confirmation means 33 or the set value reset by the drive voltage resetting means 34. The transparent electrode 28a is divided into a plurality of regions 32a to 32f, and an applied voltage is set for each region.

  The presence of the drive voltage confirmation unit 33 and the drive voltage resetting unit 34 makes it possible to appropriately correct spherical aberration using the liquid crystal element 23 regardless of the characteristic fluctuation of the liquid crystal element 23. This will be described in detail with reference to the flowcharts shown in FIGS. 6 is a flowchart showing the operation of the drive voltage confirmation unit 33, and FIG. 7 is a flowchart showing the operation of the drive voltage resetting unit 34.

  At a predetermined timing, the driving voltage confirmation unit 33 applies the driving voltage (first driving voltage) that is applied by the liquid crystal element driving unit 35 or is scheduled to be applied to the liquid crystal element driving unit 35 at that time. An instruction is given (step S1). Note that this instruction is not necessarily required when the first voltage has already been applied. After the first driving voltage is applied by the liquid crystal element driving unit 35, the driving voltage confirmation unit 33 acquires the amplitude A1 of the RF signal obtained from the signal processing unit 8, and stores it in the storage unit 15 (step S2). ).

  Subsequently, the drive voltage confirmation unit 33 instructs the liquid crystal element drive unit 35 to apply a second drive voltage obtained by adding a predetermined value to the first drive voltage (step S3). To be precise, the second drive voltage here is uniform with respect to the voltage value applied to each of the plurality of regions 32a to 32f formed by dividing the transparent electrode 28a as the first drive voltage. Corresponds to a voltage applied by adding a predetermined value. In addition, as shown in FIG. 9, each region is uniformly changed because, in a region where the phase generated with respect to the change of the applied voltage changes at a substantially constant rate, the phase generated with the temperature fluctuation is changed. It takes into account that it fluctuates almost uniformly. After the second driving voltage is applied by the liquid crystal element driving unit 35, the driving voltage confirmation unit 33 acquires the amplitude A2 of the RF signal obtained from the signal processing unit 8, and stores it in the storage unit 15 (step S4). ).

  Subsequently, the drive voltage confirmation unit 33 instructs the liquid crystal element drive unit 35 to apply a third drive voltage obtained by subtracting a predetermined value from the first drive voltage (step S5). To be precise, the third drive voltage here is uniformly determined from the voltage value applied to each of the plurality of regions 32a to 32f formed by dividing the transparent electrode 28a as the first drive voltage. The voltage to be applied by subtracting the value of corresponds. In addition, the reason for the uniform change is the same reason as in the case of the second drive voltage. After the third driving voltage is applied by the liquid crystal element driving unit 35, the driving voltage confirmation unit 33 acquires the amplitude A3 of the RF signal obtained from the signal processing unit 8, and stores this in the storage unit 15 (step S6). ).

  In the second driving voltage, the predetermined value added to the first driving voltage and the predetermined value subtracted from the first driving voltage in the third driving voltage are the same or different values. It doesn't matter. However, the same value is preferable because it facilitates the process of determining the reset value of the drive voltage.

  Next, the drive voltage confirmation unit 33 compares all the amplitudes A1 to A3 of each RF signal stored in the storage unit 15 with a predetermined reference stored in the storage unit 15 in advance. It is confirmed whether or not the standard is satisfied (step S7). The predetermined standard has various values depending on the type of the optical recording medium targeted by the optical disc apparatus, the setting of the optical system of the optical pickup, etc., but at least the level of the reproduction signal obtained by processing the RF signal However, it can be determined based on the results of previous investigations so as to exceed a certain quality level.

  When all of the amplitudes A1 to A3 of the RF signal satisfy a predetermined criterion, the drive voltage confirmation unit 33 instructs the liquid crystal element drive unit 35 to set the first drive voltage as a set value (step). S8). In this embodiment, the first drive voltage is instructed to be a set value. However, the present invention is not limited to this, and the difference between A1 and A2 and A1 and A3 is referred to. Thus, a configuration that calculates a more optimal driving voltage may be used.

  On the other hand, when any one of A1 to A3 does not satisfy the predetermined standard, the drive voltage resetting unit 34 determines the reset value of the drive voltage. Hereinafter, description will be given mainly with reference to FIG. The drive voltage resetting unit 34 determines whether any two of A1 to A3 satisfy a predetermined standard (step S9). In the following, first, a case where any two satisfy a predetermined standard (steps S10 to S19) will be described, and then a case where any two do not satisfy a predetermined standard (steps S20 to S22) will be described.

  When any two of A1 to A3 satisfy a predetermined standard, the maximum value is found from A1 to A3 (step S10). Next, it is determined whether or not the maximum value is A1 (step S11). When the maximum value is A1, a difference between A1 and A2 (corresponding to B1) and a difference between A1 and A3 (corresponding to B2) are sequentially obtained (steps S12 and S13). When B1 and B2 are compared in magnitude, and B1 is larger, the characteristic of the liquid crystal element 23 is the same as that when the set value of the liquid crystal element driving means 35 is determined in advance. The first amplitude at which the maximum amplitude A1 among the first to third drive voltages is obtained is considered to change in a direction in which a large phase difference is generated (for example, the situation of FIG. 9 corresponds). The driving voltage resetting means 34 instructs the liquid crystal element driving means 35 to reset the driving voltage in the direction of reducing the driving voltage (step S15).

  On the other hand, when B2 is larger, the situation is the reverse of step S15, so the drive voltage resetting means 34 instructs the liquid crystal element drive means 35 to increase the first drive voltage. (Step S16). In steps S15 and S16, the value for increasing or decreasing the first drive voltage may be a small value. In this regard, it is preferable that the reset value can be determined from the magnitudes of B1 and B2.

  Next, the case where it is determined in step S10 that A1 is not the maximum value will be described. In this case, it is first determined whether or not the maximum value is A2 (step S17). When A2 is the maximum value, it is determined that the amplitude of the RF signal is maximized when a voltage in the vicinity of the second drive voltage is applied. Therefore, the drive voltage is regenerated based on the second drive voltage. The setting unit 34 determines the reset value and instructs the liquid crystal element driving unit 35 (step S18). On the other hand, when A3 is the maximum value, similarly to the case where A2 is the maximum value, the drive voltage resetting means 34 determines the reset value based on the third drive voltage, and the liquid crystal element driving means. 35 is instructed (step S19). Even when the reset value of the drive voltage is determined in steps S17 and S18, the reset value is reset based on the difference between A1 and A2 which is an intermediate value between A2 and A3, as in the case where A1 is the maximum value. It is preferable to determine the value because the drive voltage can be reset quickly.

  Next, a case will be described in which it is determined in step S9 that two of A1 to A3 do not satisfy a predetermined standard. The situation in this case is when either one of A2 or A3 meets the predetermined standard and the other two do not meet the predetermined standard, or when all of A1 to A3 do not meet the predetermined standard. is there. In any case, the order of the size from A1 to A3 is only A2, A1, A3, or A3, A1, A2. Therefore, it is determined which one of A2 and A3 is the maximum value (step S20), the drive voltage is reset based on the drive voltage when the maximum value is reached, and the drive voltage resetting means 34 drives the liquid crystal element. The means 35 is instructed (steps S21 and S22).

  That is, if A2 is the maximum value, it is reset to a drive voltage that is higher than the second drive voltage, and if A3 is the maximum value, it is reset to a drive voltage that is lower than the third drive voltage. However, the magnitude of the increase / decrease value of the second or third drive voltage is different from the case where any one of A2 or A3 satisfies a predetermined standard and the other two do not satisfy the predetermined standard, and from A1 to A3 Is set differently from the case where all of the above do not satisfy the predetermined criteria.

  As described above, when the driving voltage resetting unit 34 instructs the liquid crystal element driving unit 35 to reset the driving voltage, the driving voltage confirmation unit 33 determines again whether or not the reset driving voltage is appropriate. Then, resetting of the drive voltage is repeated until the amplitudes (A1 to A3) of all the RF signals of the first to third drive voltages satisfy a predetermined standard.

  In this way, by controlling the drive voltage applied by the liquid crystal element drive means 35 by the drive voltage confirmation means 33 and the drive voltage resetting means 34, the drive voltage can be corrected even when the liquid crystal element 23 has a characteristic fluctuation. Since an approximate examination can be made regarding the direction and the magnitude of the value, an appropriate drive voltage can be set stably and quickly.

  The method for controlling the driving voltage applied by the liquid crystal element driving means 35 described above is merely an example and is not intended to be limited to this, and can be changed without departing from the object of the present invention. In particular, in the present embodiment, the configuration requires that the amplitudes of all RF signals satisfy a predetermined standard. However, the present invention is not necessarily limited to this configuration, and if any one of the RF signals satisfies the predetermined standard. Even in this case, it is possible to prevent the recording / reproduction quality of the optical disc apparatus 1 from deteriorating due to the characteristic fluctuation of the liquid crystal element 23.

  However, it is possible to set the drive voltage applied by the liquid crystal element driving means 35 to a set value that makes the recording / reproduction quality of the optical disc apparatus 1 better by requesting that all satisfy a predetermined standard. Therefore, it is preferable because a margin can be obtained until the characteristic variation of the liquid crystal element 23 occurs due to an environmental change such as a temperature change and the recording / reproduction quality of the optical disc apparatus 1 falls outside the allowable range.

  In the optical disc apparatus 1 of the present embodiment described above, the liquid crystal element 23 is of a type that corrects spherical aberration, but the present invention is an optical disc apparatus that includes a liquid crystal element other than the type that corrects spherical aberration. For example, the present invention can also be applied to an optical disc apparatus that includes a liquid crystal element that corrects aberrations such as coma and astigmatism.

  In addition, the type and number of optical recording media that can be recorded / reproduced by the optical disc apparatus 1 are not limited to the configuration of this embodiment, and various changes can be made. Furthermore, in the present embodiment, the optical disk device 1 is a device capable of recording / reproducing. However, the present invention is not limited to this. For example, an optical disk device that only performs reproduction may be used.

  The optical disk apparatus of the present invention can be applied to an optical disk apparatus having a liquid crystal element for correcting wavefront aberration. According to the present invention, good recording / reproducing quality can be maintained even if characteristic fluctuation of the liquid crystal element occurs. It is possible to realize an optical disc device that can be used with a simple configuration.

These are block diagrams which show the structure of the optical disk apparatus of this embodiment. These are the schematic diagrams of the optical system of the optical pick-up with which the optical disk device of this embodiment is provided. These are explanatory drawings for explaining a configuration of a liquid crystal element included in the optical disc apparatus of the present embodiment. These are graphs showing spherical aberration and a phase difference pattern generated in the liquid crystal element to correct it. These are the block diagrams which showed the structure of the liquid crystal element control part of the optical disk apparatus of this embodiment. These are the flowcharts which show the operation | movement of the drive voltage confirmation means with which the optical disk apparatus of this embodiment is provided. These are the flowcharts which show the operation | movement of the drive voltage resetting means with which the optical disk apparatus of this embodiment is provided. These are the graphs which showed typically the relationship between the applied voltage applied to a liquid crystal element, and the phase to generate | occur | produce. These are graphs schematically showing how the relationship between the applied voltage and the generated phase varies depending on the temperature around the liquid crystal element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk apparatus 16 Optical recording medium 16a Recording surface 17, 18 Light source 23 Liquid crystal element 26 Photodetector (light detection means)
27 Liquid crystal 28a, 28b Transparent electrode 33 Drive voltage confirmation means 34 Drive voltage resetting means 35 Liquid crystal element drive means

Claims (5)

A light source;
An optical system for condensing the light beam emitted from the light source on the recording surface of the optical recording medium and guiding the reflected light reflected by the recording surface to a predetermined light receiving position;
A liquid crystal element having a liquid crystal and two transparent electrodes sandwiching the liquid crystal, and disposed in the optical system for correcting wavefront aberration;
A light detecting means that is arranged at the light receiving position and converts optical information of the reflected light into an electrical signal;
In an optical disc apparatus comprising: a liquid crystal element driving unit that is electrically connected to the transparent electrode and applies a driving voltage to the liquid crystal element.
A reproduction signal obtained by instructing the liquid crystal element driving means to sequentially apply three kinds of driving voltages having a certain relationship, and processing the electric signal converted by the light detecting means in each case The measured values of the predetermined parameters related to the characteristics of the liquid crystal element and fluctuating with the characteristics fluctuation of the liquid crystal element are obtained, and the three measured values thus obtained are compared with a predetermined reference stored in advance. Driving voltage confirmation means for confirming whether or not the liquid crystal element driving means was applied before acquisition of the actual measurement value or the driving voltage that was to be applied was appropriate;
When the drive voltage confirmation means determines that the drive voltage is inappropriate, the drive voltage is reset based on the relationship between the acquired three actually measured values and the predetermined reference. And an optical disc apparatus. At least one of the transparent electrodes is divided into a plurality of regions,
The liquid crystal element driving means sets the voltage to be applied to each of the plurality of regions and gives the driving voltage,
The three types of drive voltages are the first drive voltage that is the drive voltage that the liquid crystal element drive means has applied to the liquid crystal element or is scheduled to apply immediately before the actual measurement value is obtained. A second drive voltage obtained by uniformly adding a predetermined value to the first drive voltage, and a third drive voltage obtained by subtracting a predetermined value from the first drive voltage. The optical disc apparatus according to claim 1.   2. The drive voltage confirmation unit determines that the drive voltage is inappropriate when any one of the acquired actual measurement values does not satisfy the predetermined criterion. Alternatively, an optical disc apparatus according to claim 2.   4. The drive voltage confirmation unit according to claim 3, wherein when the drive voltage is determined to be appropriate, the drive voltage applied by the liquid crystal element drive unit is set as the first drive voltage. The optical disk device described.   5. The optical disc according to claim 1, wherein the predetermined parameter is an amplitude of an RF signal obtained by processing the electric signal or an amplitude of a track error signal. 6. apparatus.

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