JP4518138B2 - Optical disk playback device - Google Patents

Description

  The present invention relates to an optical disc reproducing apparatus for reproducing information from an optical disc such as a CD or a DVD.

  2. Description of the Related Art Conventionally, an optical disk reproducing apparatus irradiates a light beam from a semiconductor laser through an objective lens while rotating the optical disk, receives light reflected from the optical disk by a photodiode, and outputs the light from the photodiode. An RF signal that changes in accordance with the presence or absence of pits formed on the optical disk is generated from the received light signal, and information expressed by the pits formed on the optical disk is reproduced based on the RF signal. ing.

  By the way, if there is jitter in the RF signal, the signal waveform due to the pits may not be distinguished from noise, and the performance of reproducing information from the optical disk deteriorates. In addition, the reproduction performance deteriorates as the jitter value of the RF signal increases. Jitter is a position error (advance and delay) on the time axis of a signal pulse. The jitter value of the RF signal is one of the signal characteristic values of the received light signal output from the photodiode. The jitter value of the RF signal changes due to the influence of the aberration (ray aberration, wavefront aberration) of the light applied to the optical disc.

  Therefore, there is an optical disk reproducing apparatus in which the jitter value of the RF signal is improved by changing the tilt angle of the objective lens to change the influence of the aberration of the light applied to the optical disk. In other words, this optical disk reproducing apparatus performs a tilt angle optimizing operation for optimizing the tilt angle of the objective lens so that the jitter value of the RF signal is minimized (optimum).

  As shown in FIG. 6, the jitter value of the RF signal changes depending on the tilt angle of the objective lens, and becomes the minimum value (minimum value) when the tilt angle of the objective lens is a specific tilt angle. It changes like a quadratic curve in the vicinity of a specific tilt angle.

  Therefore, in the tilt angle optimization operation, the tilt angle of the objective lens is changed to several different tilt angles, the jitter value of the RF signal is measured at the several different tilt angles, and the jitter of the measured RF signal is measured. The tilt angle when the jitter value of the RF signal is minimized is obtained based on the value and the tilt angle of the objective lens at that time, and the tilt angle when the jitter value of the RF signal is optimum is determined as the optimum tilt angle. The tilt angle of the objective lens is optimized. Thus, by optimizing the tilt angle of the objective lens, the jitter value of the RF signal is improved to be minimized, and the performance of reproducing information from the optical disk is improved.

In the conventional tilt angle optimizing operation, the optimum tilt angle is obtained as shown in FIG. That is, first, the jitter value P ₀ of the RF signal at the initial arbitrary tilt angle θ ₀ of the objective lens is measured. Subsequently, in a predetermined first direction (for example, a radially outward direction of the optical disc), the tilt angle of the objective lens is changed from the initial tilt angle θ ₀ by a constant angle Δθ, so that each tilt angle θ ₊₁ , θ ₊₂ , The jitter values P ₊₁ , P ₊₂ ,... Of the RF signal at. This is repeated until a jitter value exceeding the threshold value is measured (in the illustrated example, the jitter value P ₊₈ is measured at the tilt angle θ ₊₈ ).

Similarly, in the second direction opposite to the first direction (for example, the radially inward direction of the optical disk), the tilt angle of the objective lens is changed from the initial tilt angle θ ₀ by a fixed angle Δθ, respectively. The jitter values P ₋₁ , P ₋₂ ,... Of the RF signal at the tilt angles θ ₋₁ , θ ₋₂ ,. This is repeated until a jitter value exceeding the threshold is measured (in the example shown, until the jitter value P- ₁₁ is measured at the tilt angle θ- ₁₁ ).

Then, based on the jitter value of the RF signal measured in the first direction and the second direction and the tilt angle of the objective lens at that time, the tilt angle θc of the objective lens when the jitter value of the RF signal is minimized. (For example, a tilt angle θc intermediate between two tilt angles (in the example shown, θ ₊₈ and θ ₋₁₁ ) when the measured jitter value exceeds a threshold value), and the obtained tilt angle θc The optimum tilt angle of the objective lens.

  Note that the jitter value of the RF signal does not change the tilt angle of the objective lens even if the tilt angle of the entire optical system from the semiconductor laser to the photodiode or the tilt angle of optical components other than the objective lens constituting the optical system is changed. It changes in the same way as when changing.

  Therefore, the tilt angle optimizing operation replaces the tilt angle of the objective lens with the tilt angle of the entire optical system from the semiconductor laser to the photodiode, or tilts of optical components other than the objective lens constituting the optical system. You may change the angle. Even in this case, as in the case of changing the tilt angle of the objective lens, the jitter value of the RF signal can be minimized (optimum), and the reproduction performance of information from the optical disk is improved. The tilt angle of the objective lens, the tilt angle of the entire optical system, and the tilt angle of optical components other than the objective lens are collectively referred to as the tilt angle of the optical system.

  In addition to the jitter value of the RF signal, the signal characteristic value of the light reception signal output from the photodiode includes the amplitude value of the RF signal and the amplitude value of the TE signal. The TE signal is a signal corresponding to the amount of deviation in the radial direction from the recording track of the optical disc of the condensing point of the light emitted from the semiconductor laser and collected by the objective lens.

  Even when the amplitude value of the RF signal is small, the signal waveform due to the pits may not be distinguished from noise, and the reproduction performance of information from the optical disk deteriorates. Also, the reproduction performance deteriorates as the amplitude value of the RF signal decreases. The amplitude value of the RF signal changes depending on the tilt angle of the objective lens, and becomes the maximum value (maximum value) when the tilt angle of the objective lens is a specific tilt angle, and in the vicinity of the specific tilt angle. It changes like a quadratic curve. Further, there is a correlation between the amplitude value of the RF signal and the amplitude value of the TE signal, and the amplitude value of the TE signal is a specific tilt angle having a tilt angle of the optical system, similar to the amplitude value of the RF signal. It becomes the maximum value (maximum value) when it is (tilt angle when the amplitude value of the RF signal becomes the maximum value), and changes in a quadratic curve in the vicinity of the specific tilt angle.

  Therefore, the tilt angle optimization operation is performed so that the amplitude value of the RF signal or the amplitude value of the TE signal is maximized instead of optimizing the tilt angle of the optical system so that the jitter value of the RF signal is minimized. In addition, the tilt angle of the optical system may be optimized. In this way, the amplitude value of the RF signal can be maximized, and the reproduction performance of information from the optical disk is improved.

  That is, in the conventional tilt angle optimizing operation, the tilt angle of the optical system is changed by a certain angle, and the signal characteristic value (RF signal jitter value, RF signal amplitude value, or TE signal) of each received light signal at each tilt angle. When the signal characteristic value of the received light signal is optimized based on the measured signal characteristic value and the tilt angle of the optical system at that time (the signal characteristic value is the value of the jitter value of the RF signal) In this case, when the signal characteristic value is the minimum value when the signal characteristic value is the RF signal amplitude value or the TE signal amplitude value, the maximum tilt angle is set as the optimum tilt angle. It is like that. By optimizing the tilt angle of the optical system in this way, the signal characteristic value of the received light signal is improved so as to be optimized, and the reproduction performance of information from the optical disc is improved.

  Such a tilt angle optimizing operation is performed when an optical disc is inserted or when reproduction of information from the optical disc is started. This is because, even if the tilt angle of the optical system is the same, the type of optical disk, the mounting state of the optical disk, the variation in the solid state of the optical disk, the temperature change and aging of the optical components that make up the optical system, This is because the signal characteristic value of the received light signal changes due to a temperature change or a change with time of the component.

On the other hand, the tilt angle control value is output to change the tilt angle, and the actual tilt angle change amount at that time is measured, and the tilt angle is determined based on the correlation between the tilt angle control value and the measured actual tilt angle change amount. There is known an optical disk reproducing apparatus in which an angle conversion coefficient indicating a correspondence between an angle control value and a voltage value or a current value supplied to an actuator that changes a tilt angle is set (see, for example, Patent Document 1). Also, the OPC operation for obtaining the optimum power of the laser beam at a plurality of different tilt angles is performed to obtain the provisional optimum laser power that is the optimum power of the laser beam at each tilt angle, and the tilt angle at which the provisional optimum laser power is the minimum is obtained. As an optimal tilt angle, an optical disc reproducing apparatus that optimizes the tilt angle is known (for example, see Patent Document 2). Also, an optical disk reproducing apparatus that measures a TE signal by changing the tilt angle by a fixed angle at the innermost and outermost positions of the optical disk, and optimizes the tilt angle based on the measured TE signal. Is known (see, for example, Patent Document 3). Further, the TE signal level and the RF signal level are measured by changing the tilt angle, and the tilt angle is intermediate between the tilt angle at which the TE signal level is maximum and the tilt angle at which the RF signal level is maximum. There is known an optical disk reproducing apparatus in which the tilt angle is optimized with the optimal tilt angle (see, for example, Patent Document 4). Further, the optimum tilt angle for recording on the inner circumference side of the optical disc and the optimum tilt angle for recording on the outer circumference side of the optical disc are obtained, and the recording speed is changed based on the difference between the two tilt angles. There is known an optical disk reproducing apparatus that determines the possible speed (see, for example, Patent Document 5).
JP 2006-59478 A Japanese Patent No. 3946714 JP 2006-236457 A JP 2006-114130 A JP-A-2005-243137

  By the way, in the conventional tilt angle optimizing operation described above, in order to accurately obtain the optimum tilt angle of the optical system, the signal characteristic value of the received light signal (the jitter value of the RF signal, the amplitude value of the RF signal, or the amplitude of the TE signal). When the difference between the threshold value and the threshold value is small, it is necessary to measure the signal characteristic value of the received light signal by changing the tilt angle of the optical system to a small value, but when the difference between the received signal characteristic value and the threshold value is large. It is not necessary to measure the signal characteristic value of the received light signal by changing the tilt angle of the optical system small, and it is sufficient to measure the signal characteristic value of the received light signal by changing the tilt angle of the optical system greatly.

  However, in the conventional tilt angle optimization operation, the signal characteristic value of the received light signal is measured by changing the tilt angle of the optical system by a constant angle Δθ regardless of the difference between the signal characteristic value of the received light signal and the threshold value. is doing. That is, when the difference between the signal characteristic value of the received light signal and the threshold value is large, the signal characteristic value is measured unnecessarily many times, and as a result, the time required to optimize the tilt angle of the optical system Becomes longer, and the time until the reproduction of information from the optical disk starts is delayed. Even if the contents disclosed in Patent Document 1 to Patent Document 5 described above are applied, the above problem cannot be solved.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an optical disk reproducing apparatus that can shorten the time required to optimize the tilt angle of an optical system.

  In order to achieve the above object, the invention of claim 1 is directed to a light emitting means for emitting light, a light collecting means for condensing and irradiating light emitted from the light emitting means onto the optical disk, and reflected light from the optical disk. A light receiving means for receiving a light and outputting a light receiving signal having a voltage level corresponding to the light receiving intensity, and irradiating the optical disk with the light emitted from the light emitting means through the light collecting means while rotating the optical disk, In an optical disk reproducing apparatus for reproducing information expressed by pits formed on an optical disk based on a light receiving signal output from the means, the entire optical system from the light emitting means to the light receiving means or the optical components constituting the optical system A tilt angle adjusting means for changing at least one tilt angle (hereinafter referred to as an optical system tilt angle) and a signal for measuring a signal characteristic value of a light receiving signal output from the light receiving means The tilt angle is optimized by changing the optical system tilt angle by the tilt angle adjusting means so that the signal characteristic value is optimized based on the characteristic value measuring means and the signal characteristic value measured by the signal characteristic value measuring means. The tilt angle optimizing means includes a first signal characteristic value measuring step in which the signal characteristic value is measured by the signal characteristic value measuring means, and the signal characteristic value measured in the first signal characteristic value measuring step. Based on the first tilt angle change amount determining step for determining the tilt angle change amount for changing the optical system tilt angle in a predetermined first direction, and the tilt determined by the first tilt angle change amount determining step. The signal characteristic value measured in the first tilt angle changing step for changing the optical system tilt angle in the first direction by the tilt angle adjusting means and the first signal characteristic value measuring step by the angle change amount has a predetermined threshold value. Super Until the first signal characteristic value measuring step, the first tilt angle change amount determining step, the first iteration step for repeating the first tilt angle change step, and the signal characteristic value is measured by the signal characteristic value measuring means. Based on the second signal characteristic value measurement step and the signal characteristic value measured in the second signal characteristic value measurement step, the optical system tilt angle is changed in a second direction opposite to the first direction. Tilt angle adjustment in the second direction by the second tilt angle change amount determination step for determining the tilt angle change amount and the tilt angle change amount determined in the second tilt angle change amount determination step. The second tilt angle changing step to be changed by the means, and the second signal characteristic value measuring step until the signal characteristic value measured in the second signal characteristic value measuring step exceeds the threshold value, the second tilt angle change amount determination The Signal characteristic values measured in the first signal characteristic value measurement step so far after the second repetition step of repeating the step and the second tilt angle changing step, and the first repetition step and the second repetition step. And the optical system tilt angle, and the optical system when the signal characteristic value is optimized based on the signal characteristic value measured in the second signal characteristic value measurement step and the optical system tilt angle at that time. The tilt angle adjustment means changes the optical system tilt angle so that the optical system tilt angle becomes the optimal tilt angle calculated in the optimal tilt angle calculation step. A tilt angle optimizing step that is optimized, and in the first tilt angle change amount determining step, a first signal characteristic value measuring step immediately before that time The larger the difference between the measured signal characteristic value and the threshold value, the larger the tilt angle change amount is determined, and the smaller the difference between the signal characteristic value measured in the immediately preceding first signal characteristic value measurement step and the threshold value is. The tilt angle change amount is determined to be small, and in the second tilt angle change amount determination step, the tilt angle change is increased as the difference between the signal characteristic value measured in the immediately preceding second signal characteristic value measurement step and the threshold value is larger. The amount is determined to be large, and the tilt angle change amount is determined to be smaller as the difference between the signal characteristic value measured in the immediately preceding second signal characteristic value measurement step and the threshold value is smaller.

  According to a second aspect of the present invention, in the optical disk reproducing apparatus according to the first aspect, the tilt angle optimizing unit is configured to measure the signal characteristic value while the optical system tilt angle is at an initial arbitrary tilt angle. The initial signal characteristic value measuring step measured by the above and the threshold setting step for setting the threshold based on the signal characteristic value measured in the initial signal characteristic value measuring step are executed.

  According to a third aspect of the present invention, in the optical disk reproducing apparatus according to the second aspect, the tilt angle optimizing means is configured such that the signal characteristic value measured in the first signal characteristic value measuring step exceeds the threshold value in the optimum tilt angle calculating step. Is calculated as an optimum tilt angle between the optical system tilt angle at the time when the signal characteristic value measured in the second signal characteristic value measurement step exceeds the threshold value. is there.

  According to a fourth aspect of the present invention, in the optical disc reproducing apparatus according to the third aspect, the tilt angle optimizing unit is configured to determine the signal characteristic value in the first tilt angle change amount determining step and the second tilt angle change amount determining step. Ri (i = 1, 2, 3,...), A plurality of characteristic value ranges divided according to the difference from the threshold, Ni is the coefficient value associated with each characteristic value range Ri, and the minimum Assuming that the tilt angle change amount is α, the tilt angle change amount Δθ is a tilt angle change amount Δθ = coefficient value Ni × minimum tilt angle depending on which of the characteristic value ranges Ri the measured signal characteristic value is. It is calculated and determined by the change amount α.

  According to a fifth aspect of the present invention, in the optical disk reproducing apparatus according to the fourth aspect, the signal characteristic value measuring means uses the jitter value of the RF signal detected corresponding to the pit formed on the optical disk as the signal characteristic value. Measure.

  According to the first aspect of the invention, the operation of measuring the signal characteristic value of the received light signal by changing the optical system tilt angle in the first direction is repeated until the signal characteristic value exceeding the threshold is measured, and the optical characteristic is measured. The operation of measuring the signal characteristic value of the received light signal by changing the system tilt angle in the second direction is repeated until the signal characteristic value exceeding the threshold value is measured, and then the measured signal characteristic value and at that time Based on the optical system tilt angle, the optimal tilt angle, which is the optical system tilt angle when the signal characteristic value of the received light signal is optimal, is calculated, and the optical system tilt angle is set to the calculated optimal tilt angle. Is adjusted. Thereby, the signal characteristic value of the received light signal is improved so as to be optimized, and the reproduction performance of information from the optical disk is improved.

  In addition, when the operation of measuring the signal characteristic value of the received light signal by changing the optical system tilt angle in order to calculate the optimum tilt angle, the larger the difference between the signal characteristic value and the threshold value, the larger the optical system tilt angle. As the difference between the signal characteristic value and the threshold value is smaller, the signal characteristic value is measured by changing the optical system tilt angle smaller. Therefore, where the difference between the signal characteristic value of the received light signal and the threshold value is large, the optimum tilt angle can be calculated without unnecessarily many measurements, and the optical system tilt angle is optimized as a result. The time required to do so can be shortened.

  According to the second aspect of the present invention, the threshold value is appropriately set, so that the optimum tilt angle can be calculated with higher accuracy.

  According to the invention of claim 3, the optimum tilt angle can be easily calculated from the optical system tilt angle when the signal characteristic value exceeding the threshold is measured.

  According to the invention of claim 4, the tilt angle change amount can be easily determined.

  According to the fifth aspect of the present invention, the jitter value of the RF signal is improved so as to be optimum, and the reproduction performance of information from the optical disk is improved.

  Hereinafter, an optical disk reproducing apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration of an optical disk reproducing apparatus according to the present embodiment. The optical disk reproducing device 1 is a device for reproducing information from an optical disk 2 such as a CD or a DVD. The optical disc reproducing apparatus 1 reproduces information from the optical disc 2 by irradiating the optical disc 2 with light and receiving reflected light from the optical disc 2. The optical disc reproducing apparatus 1 has a function of improving the reproduction performance of information from the optical disc 2 by changing the influence of the aberration (ray aberration, wavefront aberration) of the light applied to the optical disc 2.

  The optical disk reproducing apparatus 1 includes a disk sensor 11, a spindle motor 12, an optical pickup 13, a seek motor 14, a laser driving unit 15, a signal processing unit 16, a servo control unit 17, a reproduction processing unit 18, And an image / audio decoder 19. In addition, the optical disc playback apparatus 1 includes a jitter value measurement unit 20, a tilt adjustment unit 21, a memory 22, a remote controller 23, a remote control reception unit 24, and a CPU, ROM, and RAM for controlling the optical disc playback apparatus 1. The control part 25 grade | etc., Including these are provided. The ROM of the control unit 25 stores a program for controlling the operation of the optical disc playback apparatus 1 and various data.

  The disc sensor 11 detects that the optical disc 2 has been inserted from a disc insertion portion (not shown), and outputs a disc detection signal indicating that the optical disc 2 has been inserted. The optical disk 2 inserted into the disk insertion unit is mounted on the spindle motor 12 by a disk mounting mechanism (not shown) under the control of the control unit 25. The spindle motor 12 is rotationally driven under the control of the control unit 25 to rotate the mounted optical disk 2.

  The optical pickup 13 is a unit in which an optical system that irradiates light to the optical disc 2 and receives reflected light from the optical disc 2 is unitized. The optical pickup 13 has optical components such as a semiconductor laser 31, a collimating lens 32, a beam splitter 33, an objective lens 34, a light receiving lens 35, and a photodiode 36, and the optical disc 2 is irradiated with light by these optical components. At the same time, an optical system for receiving reflected light from the optical disk 2 is constructed. Further, the optical pickup 13 includes a focusing actuator 37, a tracking actuator 38, a tilt actuator 39, and the like.

  The semiconductor laser 31 is driven by the laser driving unit 15 to emit laser light. Light emitted from the semiconductor laser 31 is collimated by the collimator lens 32, passes through the beam splitter 33, is collected by the objective lens 34, and is irradiated onto the optical disc 2. The light irradiated on the optical disc 2 is reflected by the optical disc 2. The light reflected by the optical disk 2 is collimated by the objective lens 34, reflected by the beam splitter 33, and condensed on the photodiode 36 by the light receiving lens 35.

  The photodiode 36 receives the reflected light from the optical disc 2 through the objective lens 34, the beam splitter 33, and the light receiving lens 35, and outputs a light reception signal having a voltage level corresponding to the light reception intensity. The semiconductor laser 31 and the like constitute a light emitting means, the collimating lens 32 and the objective lens 34 and the like constitute a condensing means, and the photodiode 36 and the like constitute a light receiving means.

  The objective lens 34 is positioned by a lens support mechanism (not shown) in a direction perpendicular to the information recording surface of the optical disk 2 mounted on the spindle motor 12, the radial position of the optical disk 2 mounted on the spindle motor 12, and The tilt angle which is the tilt angle in the radial direction of the optical disc 2 with respect to the direction perpendicular to the information recording surface of the optical disc 2 mounted on the spindle motor 12 is supported so that it can change.

  The focusing actuator 37 is driven under the control of the servo control unit 17 to change the position of the objective lens 34 in a direction perpendicular to the information recording surface of the optical disc 2 mounted on the spindle motor 12. Due to the change in the position of the objective lens 34, the position of the condensing point of the light emitted from the semiconductor laser 31 and collected by the objective lens 34 is perpendicular to the information recording surface of the optical disc 2 mounted on the spindle motor 12. Change direction.

  The tracking actuator 38 is driven under the control of the servo control unit 17 to change the position of the objective lens 34 in the radial direction of the optical disc 2 mounted on the spindle motor 12. Due to the change in the position of the objective lens 34, the position of the condensing point of the light emitted from the semiconductor laser 31 and condensed by the objective lens 34 changes in the radial direction of the optical disc 2 mounted on the spindle motor 12.

  The tilt actuator 39 is driven under the control of the tilt adjusting unit 21, and the tilt angle of the objective lens 34 (inclination in the radial direction of the optical disc 2 with respect to the direction perpendicular to the information recording surface of the optical disc 2 mounted on the spindle motor 12). Change the angle. Due to the change in the tilt angle of the objective lens 34, the aberration (ray aberration and wavefront aberration) of the light emitted from the semiconductor laser 31 and collected by the objective lens 34 changes. The tilt adjustment unit 21 and the tilt actuator 39 constitute a tilt angle adjusting means.

  The seek motor 14 moves the optical pickup 13 in the radial direction of the optical disc 2 (seek operation) under the control of the control unit 25. The laser driving unit 15 causes the semiconductor laser 31 to emit light under the control of the control unit 25.

  The signal processing unit 16 generates an RF signal, an FE signal, and a TE signal from the light reception signal output from the photodiode 36. The FE signal is a signal corresponding to the amount of deviation of the condensing point of the light emitted from the semiconductor laser 31 and collected by the objective lens 34 from the information recording surface of the optical disc 2 in the direction perpendicular to the information recording surface. It is. The TE signal is a signal corresponding to the amount of deviation in the radial direction from the recording track of the optical disc 2 of the condensing point of the light emitted from the semiconductor laser 31 and condensed by the objective lens 34. The RF signal is a signal that changes in accordance with the presence or absence of pits formed on the recording track of the optical disc 2.

  Based on the FE signal generated by the signal processing unit 16, the servo control unit 17 determines the position of the condensing point of the light emitted from the semiconductor laser 31 and collected by the objective lens 34 on the information recording surface of the optical disc 2. The driving of the focusing actuator 37 (that is, the position of the objective lens 34 in the direction perpendicular to the information recording surface of the optical disc 2) is controlled so as to keep the state of Further, the servo control unit 17 determines the position of the condensing point of the light emitted from the semiconductor laser 31 and collected by the objective lens 34 based on the TE signal generated by the signal processing unit 16 as a recording track of the optical disc 2. The driving of the tracking actuator 38 (that is, the position of the objective lens 34 in the radial direction of the optical disc 2) is controlled so as to keep the upper position.

  The reproduction processing unit 18 detects pits formed on the optical disc 2 based on the RF signal generated by the signal processing unit 16, and information expressed by the pit arrangement based on the detected pit arrangement. (Binarized data binarized by “0” and “1”) is reproduced. The image / audio decoder 19 generates image data and audio data based on information (binary data) reproduced by the reproduction processing unit 18 under the control of the control unit 5. The image data and audio data generated by the image / audio decoder 19 are output to the external device 90 under the control of the control unit 25, and an image based on information reproduced from the optical disc 2 is displayed on the display 91 of the external device 90. At the same time, sound based on information reproduced from the optical disc 2 is output from the speaker 92 of the external device 90.

  The jitter value measuring unit 20 measures the jitter value of the RF signal output from the signal processing unit 16. Jitter is a position error (advance and delay) on the time axis of a signal pulse. That is, the jitter value of the RF signal is a position error on the time axis of the RF signal. The jitter value of the RF signal is one of the signal characteristic values of the received light signal output from the photodiode 36. The jitter value measuring unit 20 constitutes signal characteristic value measuring means.

  The tilt adjustment unit 21 is controlled by the control unit 25 so that the tilt angle of the objective lens 34 becomes a tilt angle indicated by the tilt control signal based on the tilt control signal output from the control unit 25. 39 (that is, the tilt angle of the objective lens 34) is controlled. The memory 22 is controlled by the control unit 25 to tilt the data indicating the jitter value of the RF signal measured by the jitter value measuring unit 20 and the tilt angle of the objective lens 34 when the jitter value of the RF signal is measured. Various data such as corner data are stored.

  The remote controller 23 is provided with various operation keys operated by the user to instruct various operations of the optical disc playback apparatus 1, and when the various operation keys are operated, an infrared signal associated with the operation is transmitted. To do. The remote control receiving unit 24 receives the infrared signal transmitted from the remote control 23 and converts it into an electrical signal, and outputs a remote control reception signal corresponding to the operation of the remote control 23.

  The control unit 25 determines the instruction content by operating the remote control 23 based on the remote control reception signal output from the remote control reception unit 24 and determines whether or not the optical disk 2 is inserted based on the disk detection signal output from the disk sensor 11. Based on the operation of the remote controller 23 and the insertion state of the optical disc 2, the information reproducing operation for reproducing information from the optical disc 2, the tilt angle optimizing operation for optimizing the tilt angle of the objective lens 34, etc. Control various operations. The control unit 25 constitutes a tilt angle optimization unit.

  FIG. 2 shows the configuration of the photodiode 36 and the signal processing unit 16 of the optical pickup 13. The photodiode 36 is divided into four light receiving areas D1, D2, D3, and D4. The light receiving signal E1 has a voltage level corresponding to the light receiving intensity of the light receiving area D1, and has a voltage level corresponding to the light receiving intensity of the light receiving area D2. The light receiving signal E2, the light receiving signal E3 having a voltage level corresponding to the light receiving intensity of the light receiving region D3, and the light receiving signal E4 having a voltage level corresponding to the light receiving intensity of the light receiving region D4 are output. The light reflected by the optical disc 2 is condensed and irradiated by the light receiving lens 35 so as to straddle the four light receiving regions D1, D2, D3, and D4 of the photodiode 36 with astigmatism (F in the figure). , The light focused and irradiated on the photodiode 36 is shown).

  The signal processing unit 16 adds an addition circuit 61 that adds the light reception signals E1 and E2 of the photodiode 36, an addition circuit 62 that adds the light reception signals E3 and E4 of the photodiode 36, and adds the light reception signals E1 and E3 of the photodiode 36. An adder circuit 63 and an adder circuit 64 for adding the light reception signals E2 and E4 of the photodiode 36 are provided. The signal processing unit 16 includes an addition circuit 65 that adds the addition output of the addition circuit 61 and the addition output of the addition circuit 62, a subtraction circuit 66 that obtains a difference between the addition output of the addition circuit 61 and the addition output of the addition circuit 62, And a subtraction circuit 67 for obtaining a difference between the addition output of the addition circuit 63 and the addition output of the addition circuit 64.

  The signal processing unit 16 generates an RF signal by the adder circuit 61, the adder circuit 62, and the adder circuit 65. That is, the signal processing unit 16 generates an RF signal by E1 + E2 + E3 + E4. In addition, the signal processing unit 16 generates a TE signal by the addition circuit 61, the addition circuit 62, and the subtraction circuit 66. That is, the signal processing unit 16 generates a TE signal by (E1 + E2) − (E3 + E4) by a so-called push-pull method. In addition, the signal processing unit 16 generates an FE signal by the addition circuit 63, the addition circuit 64, and the subtraction circuit 67. That is, the signal processing unit 16 generates an FE signal by (E1 + E3) − (E2 + E4) by a so-called astigmatism method.

  An information reproducing operation for reproducing information from the optical disc 2 is performed as follows under the control of the control unit 25. In the information reproducing operation, first, while rotating the optical disc 2 by the spindle motor 12, the optical pickup 13 irradiates the optical disc 2 with light and receives the reflected light from the optical disc 2. Then, based on the RF signal generated by the signal processing unit 16 at that time (that is, based on the light reception signal output from the photodiode 36 of the optical pickup 13), the reproduction processing unit 18 represents the pits of the optical disc 2. Play information. The information reproduction operation is performed in this way.

  The tilt angle optimizing operation for optimizing the tilt angle of the objective lens 34 is performed so that the jitter value of the RF signal is optimized (the position error of the RF signal on the time axis is minimized). This is an operation for adjusting the tilt angle. This tilt angle optimizing operation is performed as follows under the control of the control unit 25.

  In the tilt angle optimizing operation, first, similarly to the information reproducing operation, while the optical disk 2 is rotated by the spindle motor 12, the optical pickup 2 is irradiated with light and the reflected light from the optical disk 2 is received. Subsequently, in this state, the tilt angle of the objective lens 34 is changed to several different tilt angles by the tilt adjusting unit 21, and the jitter of the RF signal generated by the signal processing unit 16 at the several different tilt angles. The value is measured by the jitter value measuring unit 20, and the tilt of the objective lens 34 when the jitter value of the RF signal is minimized (optimum) based on the tilt angle when the jitter value is measured and the measured jitter value. An angle is obtained, and the obtained tilt angle is set as the optimum tilt angle. Then, the tilt angle of the objective lens 34 is adjusted and optimized by the tilt adjusting unit 21 so as to be the optimum tilt angle. The tilt angle optimization operation is performed in this way.

  By performing the tilt angle optimizing operation in this way, the jitter value of the RF signal is improved so as to be minimized, and the reproduction performance of information from the optical disc is improved. The tilt angle optimizing operation is performed when the optical disc 2 is inserted or when information reproduction from the optical disc 2 is started, and information is reproduced at the tilt angle of the objective lens 34 optimized by the tilt angle optimizing operation. Operation is performed.

  FIG. 3 shows a flowchart of the tilt angle optimizing operation. In the tilt angle optimizing operation, first, the control unit 25 rotates the optical disc 2 with the spindle motor 12 and irradiates the optical disc 2 with the optical pickup 13 and receives the reflected light from the optical disc 2. .

  Then, the control unit 25 uses the jitter value measurement unit 20 to measure the jitter value of the RF signal at the tilt angle of the objective lens 34 at that time (that is, the state where the objective lens 34 is at an initial arbitrary tilt angle) ( # 1) A threshold value is set based on the measured jitter value (# 2). At this time, the control unit 25 sets a value larger than the measured jitter value by a predetermined value as a threshold value.

  Subsequently, the control unit 25 determines a tilt angle change amount for changing the tilt angle of the objective lens 34 in the first direction (radially outward direction of the optical disc 2) (# 3). Then, the tilt angle of the objective lens 34 is changed in the first direction by the determined tilt angle change amount (# 4), and the jitter value of the RF signal is measured by the jitter value measuring unit 20 (# 5). . Details of the method of determining the tilt angle change amount in # 3 will be described later.

  If the jitter value of the RF signal does not exceed the threshold value (NO in # 6), the control unit 25 repeats the processes of # 3 to # 5. That is, the control unit 25 repeats the operation of measuring the jitter value of the RF signal by changing the tilt angle of the objective lens 34 in the first direction until the jitter value of the RF signal exceeding the threshold is measured. By repeating the processes of # 3 to # 5, the jitter value of the RF signal at a plurality of different tilt angles of the objective lens 34 is measured in the first direction.

  On the other hand, when the measured jitter value of the RF signal exceeds the threshold value (YES in # 6), that is, when the jitter value of the RF signal exceeding the threshold value is measured, the control unit 25 performs the second direction (optical disc). 2), the tilt angle change amount for changing the tilt angle of the objective lens 34 is determined (# 7), and the tilt adjustment unit 21 sets the second direction by the determined tilt angle change amount. The tilt angle of the objective lens 34 is changed to (# 8), and the jitter value measurement unit 20 measures the jitter value of the RF signal (# 9). Note that the method of determining the tilt angle change amount in # 7 is the same as the method of determining the tilt angle change amount in # 3, and details thereof will be described later.

  If the jitter value of the RF signal does not exceed the threshold value (NO in # 10), the control unit 25 repeats the processes of # 7 to # 9. That is, the control unit 25 repeats the operation of measuring the jitter value of the RF signal by changing the tilt angle of the objective lens 34 in the second direction until the jitter value of the RF signal exceeding the threshold is measured. By repeating the processes of # 7 to # 9, the jitter value of the RF signal at a plurality of different tilt angles of the objective lens 34 is measured in the second direction, as in the first direction.

  When the measured jitter value of the RF signal exceeds the threshold value, that is, when the jitter value of the RF signal exceeding the threshold value is measured (YES in # 10), the control unit 25 displays the measurement result up to that point. Based on (based on the jitter value of one or a plurality of RF signals measured in the processes of # 5 and # 9 and the optical system tilt angle at that time), the jitter value of the RF signal is minimized (optimum) The optimum tilt angle, which is the tilt angle of, is calculated (# 11). Details of the method for calculating the optimum tilt angle will be described later. Finally, the control unit 25 causes the tilt adjustment unit 21 to change the tilt angle of the objective lens 34 so that the calculated optimum tilt angle is obtained (# 12). Thereby, the tilt angle of the objective lens 34 is optimized so that the jitter value of the RF signal is minimized.

  FIG. 4 shows the relationship between the tilt angle of the objective lens 34 and the measured jitter value when measuring the jitter value of the RF signal in the tilt angle optimizing operation. In the tilt angle optimizing operation, as described above, the tilt angle of the objective lens 34 is changed until the jitter value of the RF signal exceeding the threshold value is measured in the first direction by the processes of # 3 to # 6. The operation of measuring the jitter value of the RF signal is repeated, and the tilt of the objective lens 34 is continued until the jitter value of the RF signal exceeding the threshold value is measured in the second direction by the processes of # 7 to # 10. The operation of changing the angle and measuring the jitter value of the RF signal is repeated.

  At this time, the determination of the tilt angle change amount for changing the tilt angle of the objective lens 34 in # 3 and # 7 is performed by the control unit 25 as follows. That is, the control unit 25 determines the tilt angle change amount according to the difference between the jitter value of the RF signal measured immediately before and the threshold value, and the larger the difference between the jitter value of the RF signal measured immediately before and the threshold value, the larger the difference. The tilt angle change amount is increased. The smaller the difference between the jitter value of the RF signal measured immediately before and the threshold value, the smaller the tilt angle change amount is.

By determining the tilt angle change amount in this way, in the tilt angle optimizing operation, the jitter value of the RF signal is measured, for example, as shown in FIG. That is, first, the jitter value P ₀ of the RF signal is measured at an initial arbitrary tilt angle θ ₀ of the objective lens 34, and a threshold is set based on the jitter value P ₀ .

Subsequently, the tilt angle change amount Δθ is determined according to the difference between the jitter value P ₀ and the threshold value, and the tilt angle of the objective lens 34 is changed from θ ₀ to the first direction by the tilt angle change amount Δθ. Then, the jitter value P _{+ 1} of the RF signal is measured at the tilt angle θ _{+ 1} . Further, the tilt angle change amount Δθ is determined according to the difference between the jitter value P _{+ 1} and the threshold value, and the tilt angle of the objective lens 34 is changed from θ _{+ 1} to the first direction by the tilt angle change amount Δθ. jitter value _{P +2} of the RF signal is measured by the tilt angle theta _+2.

Similarly, until the jitter value of the RF signal exceeding the threshold value is measured, the tilt angle change amount Δθ is determined according to the difference between the jitter value of the RF signal measured immediately before and the threshold value, and the determination is made. The operation of measuring the jitter value of the RF signal by changing the tilt angle of the objective lens 34 in the first direction by the tilt angle change amount Δθ is repeated. In the illustrated example, the process is repeated until the jitter value P ₊₄ of the RF signal is measured at the tilt angle θ ₊₄ .

  At this time, the larger the difference between the jitter value of the RF signal measured immediately before and the threshold value, the larger the tilt angle change amount Δθ is determined, and the difference between the jitter value of the RF signal measured immediately before and the threshold value is larger. Since the tilt angle change amount Δθ is determined to be smaller as the value is smaller, the jitter value of the RF signal is measured by greatly changing the tilt angle of the objective lens 34 where the difference between the jitter value of the RF signal and the threshold value is large. At the same time, as the difference between the jitter value of the RF signal and the threshold value becomes smaller, the tilt angle of the objective lens 34 is changed to be smaller and the jitter value of the RF signal is measured.

Further, in the second direction, the jitter value of the RF signal is measured as in the first direction. That is, the tilt angle change amount Δθ is determined according to the difference between the jitter value P ₀ and the threshold value, and the tilt angle of the objective lens 34 is changed from θ ₀ to the second direction by the tilt angle change amount Δθ. jitter value _{P -1} of the RF signal is measured by the tilt angle theta _-1. Further, the tilt angle change amount Δθ is determined according to the difference between the jitter value P ₋₁ and the threshold value, and the tilt angle of the objective lens 34 is changed from θ ₋₁ to the second direction by the tilt angle change amount Δθ. Thus, the jitter value P _{- 2} of the RF signal is measured at the tilt angle θ- ₂ .

Similarly, until the jitter value of the RF signal exceeding the threshold value is measured, the tilt angle change amount Δθ is determined according to the difference between the jitter value of the RF signal measured immediately before and the threshold value, and the determination is made. The operation of measuring the jitter value of the RF signal by changing the tilt angle of the objective lens 34 in the second direction by the tilt angle change amount Δθ is repeated. In the illustrated example, the process is repeated until the jitter value P- ₅ of the RF signal is measured at the tilt angle θ- ₅ .

  At this time, similarly to the first direction, as the difference between the jitter value of the RF signal measured immediately before and the threshold value is larger, the tilt angle change amount Δθ is determined to be larger, and the RF signal measured immediately before is increased. Since the tilt angle change amount Δθ is determined to be smaller as the difference between the jitter value and the threshold value is smaller, when the difference between the jitter value of the RF signal and the threshold value is larger, the tilt angle of the objective lens 34 is changed to be larger. As the jitter value of the signal is measured, and the difference between the jitter value of the RF signal and the threshold value becomes smaller, the tilt angle of the objective lens 34 is changed to be smaller and the jitter value of the RF signal is measured.

  FIG. 5 shows an example of a method of determining the tilt angle change amount in # 3 and # 7 of the tilt angle optimization operation. More specifically, the determination of the tilt angle change amount in # 3 and # 7 of the tilt angle optimization operation is performed by the control unit 25 as shown in FIG. 5, for example.

That is, the control unit 25 divides the section up to the threshold value of the jitter value of the RF signal to be measured into a plurality of characteristic value ranges corresponding to the magnitude of the difference between the jitter value of the RF signal and the threshold value. The plurality of characteristic value ranges thus set is Ri (i = 1, 2, 3,...). Further, coefficient values are associated with the characteristic value ranges Ri, and the coefficient values associated with the characteristic value ranges Ri are Ni. The minimum tilt angle change amount is α. As described above, the threshold is set based on the jitter value P ₀ of the RF signal measured at the initial arbitrary tilt angle θ ₀ of the objective lens 34. Therefore, the characteristic value range Ri is classified based on the jitter value P ₀ of the RF signal measured at an initial arbitrary tilt angle θ ₀ . The coefficient value Ni and the minimum tilt angle α are determined in advance.

Then, the control unit 25 determines that the jitter value P _k of the RF signal measured at an arbitrary previous tilt angle θ _k (k = 0, +1, +2,..., −1, −2,...) Is a characteristic. The tilt angle change amount Δθ is set to the tilt angle change amount Δθ depending on which range of the value range Ri is present (thus, depending on the magnitude of the difference between the jitter value of the RF signal measured immediately before and the threshold value). = Coefficient value Ni × Minimum tilt angle change amount α is calculated and determined.

In the example shown in FIG. 5, the characteristic value range Ri is divided into four ranges R ₁ , R ₂ , R ₃ , and R ₄ , and the coefficient values Ni are N ₁ = 10 and N ₂ = 4. , N ₃ = 2 and N ₄ = 1. Thus, in the example shown in FIG. 5, when the jitter value P _k of the RF signal measured at an arbitrary tilt angle theta _k immediately before is in the range of characteristic value range R _1, the tilt angle variation [Delta] [theta] is [Delta] [theta] = N ₁ × α = 10α is determined. When the jitter value P _k of the RF signal is within the characteristic value range R ₂ , the tilt angle change amount Δθ is determined as Δθ = N ₂ × α = 4α, and the jitter value P _{k of the} RF signal is When the characteristic value range R _{3 is in} the range, the tilt angle change amount Δθ is determined as Δθ = N ₃ × α = 2α, and the RF signal jitter value P _k is in the characteristic value range R _4. The tilt angle change amount Δθ is determined as Δθ = N ₄ × α = α.

  The determination of the tilt angle change amount in # 3 and # 7 of the tilt angle optimization operation is performed in this way. According to such a determination method of the tilt angle change amount, the tilt angle change amount Δθ increases as the difference between the jitter value of the RF signal measured immediately before and the threshold value increases, and the jitter of the RF signal measured immediately before increases. The tilt angle change amount Δθ can be easily determined such that the smaller the difference between the value and the threshold value, the smaller the tilt angle change amount Δθ.

  Note that the method of determining the tilt angle change amount is not limited to this, and the tilt angle change amount Δθ increases as the difference between the jitter value of the RF signal measured immediately before and the threshold value increases, and the RF signal measured immediately before is determined. Any determination method may be used as long as the difference between the jitter value and the threshold value decreases as the tilt angle change amount Δθ decreases.

The calculation of the optimum tilt angle in # 11 of the tilt angle optimizing operation is performed by the control unit 25 as follows, for example. That is, the control unit 25 determines the tilt angle (θ _{+4 in the} example shown in FIG. 4) when the jitter value measured in the first direction (jitter value measured in # 5) exceeds the threshold, and the second The tilt angle θc intermediate between the tilt angle (θ _{−5 in the} example shown in FIG. 4) when the jitter value measured in the direction (jitter value measured in # 9) exceeds the threshold is calculated, and the tilt is calculated. The angle θc is the optimum tilt angle. According to such a method for calculating the optimum tilt angle, the optimum tilt angle can be easily calculated.

The method for calculating the optimum tilt angle is not limited to this. For example, the tilt angle immediately before the jitter value measured in the first direction exceeds the threshold value (θ _{+3 in the} example shown in FIG. 4) and the second tilt angle are calculated. The tilt angle intermediate between the tilt angle immediately before the jitter value measured in the direction exceeds the threshold value (θ _{−4 in the} example shown in FIG. ₄ ) may be calculated as the optimum tilt angle. Further, a plurality of jitter values measured until the threshold value is exceeded in the first direction and the tilt angle of the objective lens at that time, and a plurality of jitter values measured until the threshold value is exceeded in the second direction and the objective at that time Based on the tilt angle of the lens, the tilt angle when the jitter value of the RF signal is minimized may be calculated by approximation calculation such as the least square method or interpolation calculation, and the tilt angle may be set as the optimum tilt angle.

  As described above, according to the optical disc reproducing apparatus 1 configured as described above, the operation of measuring the jitter value of the RF signal by changing the tilt angle of the objective lens 34 in the first direction measures the jitter value exceeding the threshold value. The operation of measuring the jitter value of the RF signal by changing the tilt angle of the objective lens 34 in the second direction is repeated until the jitter value exceeding the threshold value is measured, and the measurement is performed. Based on the jitter value and the tilt angle of the objective lens 34 at that time, an optimum tilt angle, which is a tilt angle when the jitter value of the RF signal is optimized, is calculated, and the calculated optimum tilt angle is obtained. The tilt angle of the objective lens 34 is adjusted. Thereby, the jitter value of the RF signal is improved so as to be optimized, and the reproduction performance of information from the optical disc 2 is improved.

  Moreover, when the operation of measuring the jitter value of the RF signal by changing the tilt angle of the objective lens 34 in order to calculate the optimum tilt angle is repeated, the larger the difference between the jitter value and the threshold value, the greater the difference of the objective lens 34. The jitter value is measured by changing the tilt angle greatly. The smaller the difference between the jitter value and the threshold value, the smaller the tilt angle of the objective lens 34 is measured and the jitter value is measured. Therefore, when the difference between the jitter value of the RF signal and the threshold value is large, the optimum tilt angle can be calculated without unnecessarily many measurements, and as a result, the tilt angle of the objective lens 34 is optimized. It is possible to reduce the time required for conversion. In addition, by setting the threshold value based on the measured jitter value of the RF signal, the threshold value can be set appropriately, whereby the optimum tilt angle can be calculated with higher accuracy.

  In addition, this invention is not restricted to the structure of the said embodiment, A various deformation | transformation is possible. For example, in the tilt angle optimizing operation, instead of changing the tilt angle of the objective lens, the tilt angle of the entire optical system from the semiconductor laser to the photodiode, or an optical component other than the objective lens constituting the optical system (semiconductor The tilt angle of the laser, collimating lens, etc.) may be changed. Even in this case, as in the case where the tilt angle of the objective lens is changed, the jitter value of the RF signal is improved to be minimum (optimum), and the reproduction performance of information from the optical disk is improved.

  Further, the tilt angle optimization operation is performed so that the amplitude value of the RF signal or the TE signal is maximized instead of optimizing the tilt angle of the objective lens so that the jitter value of the RF signal is minimized. In addition, the tilt angle of the optical system may be optimized. In this way, the amplitude value of the RF signal is improved so as to be maximized (optimum), and the reproduction performance of information from the optical disc is improved.

  Further, the tilt angle optimizing operation may be performed when information is reproduced from the inner peripheral area of the optical disc and when information is reproduced from the outer peripheral area. In addition, the direction in which the tilt angle is changed in the tilt angle optimizing operation is not limited to the radial direction of the optical disk playback device, and may be a tangential direction of the optical disk or a direction intermediate between the radial direction and the tangential direction.

1 is an electrical block configuration diagram showing a schematic configuration of an optical disc reproducing apparatus according to an embodiment of the present invention. The figure which shows the structure of the photodiode of the optical disk reproducing | regenerating apparatus, and a signal processing part. 6 is a flowchart showing a tilt angle optimizing operation of the optical disc reproducing apparatus. The figure which shows the relationship between the tilt angle of an objective lens, and the measured jitter value when measuring the jitter value of RF signal in the tilt angle optimization operation | movement of the same optical disk reproducing device. The figure which shows the example of the determination method of the tilt angle variation | change_quantity in the tilt angle optimization operation | movement of the optical disk reproducing device. The figure which shows the relationship between the tilt angle of an objective lens, and the measured jitter value when measuring the jitter value of RF signal in the tilt angle optimization operation | movement of the conventional optical disk reproducing device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk reproducing | regenerating apparatus 2 Optical disk 11 Disk sensor 12 Spindle motor 13 Optical pick-up 14 Seek motor 15 Laser drive part 16 Signal processing part 17 Servo control part 18 Playback processing part 19 Image / audio decoder 20 Jitter value measurement part 21 Tilt adjustment part 22 Memory 23 Remote Control 24 Remote Control Receiver 25 Control Unit 31 Semiconductor Laser 32 Collimating Lens 33 Beam Splitter 34 Objective Lens 35 Light Receiving Lens 36 Photodiode 37 Focusing Actuator 38 Tracking Actuator 39 Tilt Actuator 90 External Equipment 91 Display 92 Speaker

Claims (5)

A light emitting means for emitting light, a light collecting means for condensing and irradiating the light emitted from the light emitting means on the optical disc, and a voltage level corresponding to the intensity of the received light received from the reflected light from the optical disc Light receiving means for outputting the light receiving signal of
While rotating the optical disk, the light emitted from the light emitting means is irradiated onto the optical disk via the light collecting means, and pits formed on the optical disk based on a light reception signal output from the light receiving means In an optical disk playback device that plays back information expressed by
A tilt angle adjusting means for changing at least one tilt angle (hereinafter referred to as an optical system tilt angle) of the entire optical system from the light emitting means to the light receiving means or an optical component constituting the optical system;
Signal characteristic value measuring means for measuring the signal characteristic value of the received light signal output from the light receiving means;
Tilt angle optimization that optimizes the optical system tilt angle by changing the tilt angle adjusting means so that the signal characteristic value is optimized based on the signal characteristic value measured by the signal characteristic value measuring means Means and
The tilt angle optimization means includes:
A first signal characteristic value measuring step of measuring the signal characteristic value by the signal characteristic value measuring means;
First tilt angle change determining step for determining a tilt angle change amount for changing the optical system tilt angle in a predetermined first direction based on the signal characteristic value measured in the first signal characteristic value measuring step. When,
A first tilt angle changing step in which the tilt angle adjusting means changes the optical system tilt angle in the first direction by the tilt angle change amount determined in the first tilt angle change amount determining step;
The first signal characteristic value measurement step, the first tilt angle change amount determination step, and the first tilt until the signal characteristic value measured in the first signal characteristic value measurement step exceeds a predetermined threshold value. A first iteration step for repeating the angle change step;
A second signal characteristic value measuring step of measuring the signal characteristic value by the signal characteristic value measuring means;
Based on the signal characteristic value measured in the second signal characteristic value measurement step, a tilt angle change amount for changing the optical system tilt angle in a second direction opposite to the first direction is determined. 2 tilt angle change amount determination step;
A second tilt angle changing step in which the tilt angle adjusting means changes the optical system tilt angle in the second direction by the tilt angle change amount determined in the second tilt angle change amount determining step;
Until the signal characteristic value measured in the second signal characteristic value measurement step exceeds the threshold, the second signal characteristic value measurement step, the second tilt angle change amount determination step, and the second tilt angle A second iteration step that repeats the change step;
After the first repetition step and the second repetition step, the signal characteristic value measured in the first signal characteristic value measurement step and the optical system tilt angle at that time, and the second Based on the signal characteristic value measured in the signal characteristic value measuring step and the optical system tilt angle at that time, the optimum tilt angle calculating step for calculating the optimum tilt angle that is the optical system tilt angle when the signal characteristic value is optimal When,
A tilt angle optimizing step that optimizes the optical system tilt angle by changing the tilt angle adjusting means so that the optical system tilt angle becomes the optimal tilt angle calculated in the optimal tilt angle calculating step; And
In the first tilt angle change amount determination step, the tilt angle change amount is determined to be larger as the difference between the signal characteristic value measured in the first signal characteristic value measurement step immediately before and the threshold value is larger. The tilt angle change amount is determined to be smaller as the difference between the signal characteristic value measured in the first signal characteristic value measurement step immediately before that point and the threshold value is smaller.
In the second tilt angle change determining step, the tilt angle change is determined to be larger as the difference between the signal characteristic value measured in the immediately preceding second signal characteristic value measuring step and the threshold value is larger. The tilt angle change amount is determined to be smaller as the difference between the signal characteristic value measured in the immediately preceding second signal characteristic value measurement step and the threshold value is smaller.
An optical disk reproducing apparatus characterized by the above. The tilt angle optimization means includes:
An initial signal characteristic value measuring step of measuring the signal characteristic value by the signal characteristic value measuring means in a state where the optical system tilt angle is at an initial arbitrary tilt angle;
Executing a threshold setting step for setting the threshold based on the signal characteristic value measured in the initial signal characteristic value measuring step;
The optical disk reproducing apparatus according to claim 1, wherein: In the optimum tilt angle calculating step, the tilt angle optimizing means includes:
The optical system tilt angle when the signal characteristic value measured in the first signal characteristic value measurement step exceeds the threshold value, and the signal characteristic value measured in the second signal characteristic value measurement step exceeds the threshold value. An intermediate tilt angle between the optical system tilt angle and the optimal tilt angle is calculated.
The optical disk reproducing apparatus according to claim 2, wherein In the first tilt angle change amount determining step and the second tilt angle change amount determining step, the tilt angle optimizing means includes:
A plurality of characteristic value ranges divided according to the difference between the signal characteristic value and the threshold value are associated with Ri (i = 1, 2, 3,...) And the characteristic value ranges Ri. The coefficient value is Ni and the minimum tilt angle change is α,
The tilt angle change amount Δθ is calculated as follows: tilt angle change amount Δθ = coefficient value Ni × minimum tilt angle change amount α, depending on which of the characteristic value ranges Ri the measured signal characteristic value is. To decide,
The optical disk reproducing apparatus according to claim 3, wherein The signal characteristic value measuring unit measures a jitter value of an RF signal detected corresponding to a pit formed on the optical disc as the signal characteristic value.
The optical disk reproducing apparatus according to claim 4, wherein

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