JP2006155891A - Unit and method for tracking control - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a unit and a method for tracking control by a one-beam method while optimum servo coefficients can be adaptively set by optical disks. <P>SOLUTION: The difference (E-F) between and the sum (E+F) of E and F signals from terminals 11 and 12 are found by a subtracting amplifier 13 and a summing amplifier 14 and a dividing circuit 20 finds a standardized push-pull signal NPP=(E-F)/(E+F). Its amplitude is detected by a signal amplitude detecting circuit 30 and sent to a coefficient calculating circuit 50 through an A/D converting circuit 40 to set a tracking servo coefficient K corresponding to the amplitude of the NPP signal. A multiplying amplifier 80 multiplies the movement quantity signal CSL of the objective generated by the top holding circuits 65 and 66 and subtraction amplifier 70 by a coefficient K to generate a cancel signal and a subtracting amplifier 90 subtracts it from the push-pull signal PP. Consequently, the offset of the subtracting amplifier 90 is eliminated and the offset state for the PP signal is canceled, and an optimum tracking error signal is obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to tracking control of a light beam applied to an optical disc, and more particularly to a tracking control apparatus and tracking control method for canceling an offset generated in a tracking error signal generated by using a push-pull method in a one-beam method.

  An optical pickup that reproduces a signal recorded on an optical disc is an optical pickup that focuses a light beam, irradiates the signal surface of the optical disc, receives the return light, and outputs a reproduction signal and an error signal for servo. It has.

  Optical discs that are mounted on the spindle of an optical disc device and are driven to rotate are always subject to radial deflection due to eccentricity of the center hole or chucking, or optical axis deflection due to warpage or uneven thickness. . For this reason, the optical pickup follows the shake of the optical disk accompanying the rotational drive, and performs control so that the converging point of the light beam is always irradiated onto the track on the signal surface.

  For example, a compact disk (CD) has a track pitch of 1.6 μm, and on the other hand, tracking control is performed so that the condensing point of the light beam is in a range of about ± 0.1 μm from the track. Further, the fluctuation width in the optical axis direction of the signal surface is allowed to about ± 0.5 mm, and focus control is performed so that the focal point is in a range of about ± 1 μm from the signal surface.

  Such control of the irradiation position of the light beam is performed by finely moving a part of the optical system of the optical pickup by an actuator in accordance with a control signal. This control signal is a tracking error signal or a focus error signal obtained from the return light from the optical disc, and the above control is performed by supplying these signals to the servo system.

  As a typical method for obtaining the tracking error signal described above, a three-beam method and a one-beam method are used.

  In the three-beam method, a diffraction grating (grating) is arranged in the forward path of a light beam irradiated on an optical disc, and three light beams composed of a main beam (zero order light) and two sub beams (± first order light) are provided. And two sub beams are used for tracking error detection. In this method, light receiving elements for detecting two sub beams are arranged on both sides of the light receiving element for detecting the main beam, and the track position of the condensing point of the main beam irradiated to the track of the optical disk is arranged. A tracking error signal is obtained from a change in the return light of the sub-beam, which is generated according to the deviation amount from.

  On the other hand, the one-beam method is a method in which a single beam is irradiated onto the optical disc and a tracking error signal is obtained from the return light. In the optical system using the one-beam method, an optical element such as a grating required when the three-beam method is used can be omitted.

  FIG. 15 shows an example of an optical system of an optical pickup configured to obtain a tracking error signal by the one-beam method.

  The light from the laser diode 211 that is the light emitting element portion of the light emitting / receiving element 210 configured on the substrate 217 is reflected by the inclined surface 212a of the prism 212, condensed by the beam splitter 222 and the objective lens 223, and irradiated onto the optical disc 200. Is done. The focused light spot 224 is controlled to be positioned on the signal surface 200 a of the optical disc 200.

  The return light from the optical disc 200 passes through the objective lens 223 again and is separated by the beam splitter 222 into an optical path toward the photodetector 225 and an optical path toward the prism 212 of the light emitting / receiving element 210.

  The light receiving element portion of the light receiving and emitting element 210 includes photodetectors 213 and 215 each having a light receiving surface divided into four, and the return light incident from the inclined surface 212a of the prism 212 is detected by the photodetector. In addition to being incident on 213, the light is further reflected to form a focal point 214 at the upper surface 212 b of the prism 212, and also enters the photodetector 215.

  In this optical system, a focus error signal FE is obtained by the light receiving element portion of the light emitting / receiving element 210. Here, the focus error signal FE is obtained by the calculation of the following equation (1). However, in the equation (1), the signals a to d are the light detection signals from the light receiving areas a to d of the light receiving surface divided into four parts of the photodetector 213, and the signals e to g are similarly detected. It is assumed that the light detection signals are from the light receiving regions e to g of the light receiving surface divided into four parts of the device 215.

FE = {(a + d)-(b + c)}-{(e + h)-(f + g)} (1)
On the other hand, in this optical system, the tracking error signal TE can be obtained by any of the photodetectors 213 and 215 and the photodetector 225 described above.

For example, when the tracking error signal TE is obtained from the photodetector 225, it is the difference between the light detection signal (i + j) from the left light receiving region of the light receiving surface and the light detection signal (k + l) from the right light receiving region { (i + j) − (k + 1)} is taken out as the push-pull signal PP. In the following, a case where the tracking error signal TE is obtained from the photodetector 225 will be described as an example.
FIG. 16 illustrates the configuration of the light receiving surfaces of the optical detectors 213, 215, and 225 of the optical pickup using the one-beam method illustrated in FIG.

  The light receiving surface of each of these photodetectors is generally divided into two or more with respect to the track direction of the optical disc 200, and here, an example in which it is divided into four is shown. For example, in the photo detector 225, the light receiving surface is a light receiving region i, a light receiving region j, a light receiving region k, and a light receiving region 1 in order from one end.

  The E signal used for tracking control is obtained as the sum (i + j) of the signals from the two light receiving areas i on the left side of the light receiving surface divided into four and the signal from the light receiving area j. Similarly, the F signal used for tracking control is obtained as the sum (k + 1) of the signal from the light receiving region k, which is the two light receiving regions on the right side of the light receiving surface divided into four, and the signal from the light receiving region l. . Normally, the differential signal (E-F) between the E signal and the F signal is used for tracking control as the push-pull signal PP.

  By the way, when tracking control is performed by the one-beam method using the optical system as described above, if only the objective lens 223 is moved, the center of the photodetector with the light receiving surface divided coincides with the center of the return light. Therefore, as shown by the dotted line in FIG. 16, the incident position of the spot on the light receiving surface of the photodetector moves, and an offset occurs in the tracking error signal TE. For this reason, the positional relationship between the track and the light beam cannot be controlled correctly, and the RF reproduced from the optical disk may deteriorate.

  Therefore, this offset is canceled by using a movement amount signal corresponding to the movement amount of the objective lens 223 or the movement amount of the light spot 224 on the optical disc 200.

  For example, if the movement amount signal is CSL and the tracking control servo system coefficient is K by the one-beam method, the photodetector 225 obtains a tracking error signal TE by the following equation (2).

TE = {(i + j) − (k + 1)} − K × CSL (2)
Patent documents 1 and 2 are known as prior art.

Japanese Patent Laid-Open No. 08-124187 Japanese Patent Laid-Open No. 06-044587

  However, in the conventional tracking servo system, the servo coefficient K is a fixed value. However, since the characteristics of optical disks and optical pickups vary, the value of K cannot be optimized for all optical disks.

  For this reason, the optical pickup using the one-beam method has a problem that it is difficult to improve the accuracy and reliability of the tracking servo.

  The present invention has been made to solve such a problem, and can set a servo coefficient for each optical disc having different characteristics, thereby improving the accuracy and reliability of the servo system. It is an object of the present invention to provide a tracking control apparatus and a tracking control method using a beam method.

  The tracking control device of the present invention proposed to solve the above-described problem is obtained by subtracting a cancel signal multiplied by a correction coefficient from a push-pull signal obtained from a return beam of a light beam irradiated on an optical disc, thereby obtaining an objective. In a tracking control device that cancels an offset of a tracking error signal caused by movement of a lens or movement of a light beam irradiation position on an optical disk, the movement amount of the objective lens or movement of the light beam irradiation position on the optical disk is canceled. A movement amount signal detection means for detecting a movement amount signal generated according to the amount, a correction coefficient setting means for setting a correction coefficient to be multiplied by the movement amount signal according to the amplitude of the push-pull signal, and the offset component Cancel signal generation that generates a cancel signal by multiplying the set correction coefficient And means, the cancel signal is characterized in further comprising a tracking error signal generating means for generating a tracking error signal is subtracted from the push-pull signal.

  In addition, the tracking control device of the present invention proposed to solve the above-described problem is obtained by subtracting a cancel signal multiplied by a correction coefficient from a push-pull signal obtained from the return light of a light beam irradiated on an optical disc. In a tracking control device that cancels an offset of a tracking error signal generated in accordance with the movement of the objective lens or the irradiation position of the light beam on the optical disk, the movement amount of the objective lens or the irradiation position of the light beam on the optical disk A movement amount signal detection means for detecting a movement amount signal generated according to the movement amount of the signal, a correction coefficient setting means for setting a correction coefficient to be multiplied by the offset component according to the amplitude of the track wobble signal, and the movement amount signal Cancel by generating the cancel signal by multiplying by the correction factor set above And No. generation means, is characterized in that and a tracking error signal generating means for generating a tracking error signal by subtracting the canceling signal from the push-pull signal.

  In addition, the tracking control method of the present invention proposed to solve the above-described problem is obtained by subtracting a cancel signal multiplied by a correction coefficient from a push-pull signal obtained from the return light of a light beam irradiated on an optical disc. In the tracking control method for canceling the offset of the tracking error signal generated in accordance with the movement of the objective lens or the irradiation position of the light beam on the optical disk, the movement amount of the objective lens or the irradiation position of the light beam on the optical disk A movement amount signal detecting step for detecting a movement amount signal generated in accordance with the movement amount of the input signal, a correction coefficient setting step for setting a correction coefficient to be multiplied by the offset component according to the amplitude of the push-pull signal, and the offset component Is multiplied by the correction factor set above to generate a cancel signal. And Le signal generating step, characterized in that it has a tracking error signal generating step of generating a tracking error signal by subtracting said cancellation signal from said normalized push-pull signal.

  In addition, the tracking control method of the present invention proposed to solve the above-described problem is obtained by subtracting a cancel signal multiplied by a correction coefficient from a push-pull signal obtained from the return light of a light beam irradiated on an optical disc. In the tracking control method for canceling the offset of the tracking error signal generated in accordance with the movement of the objective lens or the irradiation position of the light beam on the optical disk, the movement amount of the objective lens or the irradiation position of the light beam on the optical disk A movement amount signal detecting step for detecting a movement amount signal generated according to the movement amount of the signal, a correction coefficient setting step for setting a correction coefficient to be multiplied by the movement amount signal according to the amplitude of the track wobble signal, and the offset component Cancel by generating the cancel signal by multiplying by the correction factor set above And No. generation step, is characterized in that it has a tracking error signal generating step of generating a tracking error signal by subtracting the canceling signal from the push-pull signal.

  According to the present invention as described above, it is possible to provide a tracking control device and a tracking control method capable of improving the reliability of the tracking servo with respect to the characteristic variation of the optical disk.

  According to the present invention, the value of the servo coefficient multiplied as the correction coefficient to the cancel signal for canceling the offset component of the push-pull signal is set according to the normalized amplitude of the push-pull signal NPP or the amplitude of the wobble track signal. Since the adaptive setting is made, it is possible to improve the accuracy and reliability of the servo with respect to the characteristic variation for each optical disk in the one-beam method, and to simplify the setting of the coefficient of the tracking servo, and A tracking control method can be provided.

  Hereinafter, preferred embodiments of a tracking control device and a tracking control method of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram illustrating a configuration example of a main part of a tracking control apparatus according to an embodiment of the present invention.

  This tracking control apparatus performs tracking control by extracting a push-pull signal from return light from an optical disk.

  The input terminals 11 and 12 receive the E signal and F signal from the optical pickup. The subtraction amplifier 13 generates these difference signals (E−F), and the addition amplifier 14 generates these sum signals (E + F).

  The division circuit 20 divides the signal (EF) by the signal (E + F) and sends the resulting signal (EF) / (E + F) to the signal amplitude detection circuit 30.

  Here, the signal (EF) is a signal corresponding to the push-pull signal PP obtained by differentially detecting the return light from the optical disk with a light receiving element having a divided light receiving surface. The signal (EF) / (E + F) divided by the sum signal (E + F) corresponds to the standardized push-pull signal NPP.

  The signal amplitude detection circuit 30 detects the amplitude of the standardized push-pull signal NPP from the division circuit 20. A specific circuit example for this will be described later. The amplitude detection signal (amplitude value) from the signal amplitude detection circuit 30 is converted into a digital signal by the A / D conversion circuit 40 and sent to the coefficient calculation circuit 50.

  The coefficient calculation circuit 50 is for setting a coefficient (gain) K of the tracking servo system in accordance with the amplitude of the standardized push-pull signal NPP. The coefficient calculation circuit 50 supplies coefficient (gain) control information to a later-described multiplication amplifier 80. send. The coefficient calculation circuit 50 is configured by a microcomputer or the like.

  On the other hand, as described above, in tracking control using the push-pull signal PP, an offset component generated in the push-pull signal PP must be canceled according to the movement amount of the objective lens of the optical pickup or the movement amount of the light spot on the optical disk. There was a problem that tracking control could not be performed correctly.

  For this reason, a signal for canceling the offset by multiplying an appropriate correction coefficient by the movement amount signal corresponding to the movement amount of the objective lens or the movement amount of the light spot on the optical disk (hereinafter simply referred to as a cancellation signal). Must be generated.

  The top hold circuits 65 and 66 and the subtracting amplifier 70 are parts that generate the movement amount signal.

The peak level of the E signal input from the input terminal 11 is held by the top hold circuit 65. Similarly, the peak level of the F signal input from the input terminal 12 is held by the top hold circuit 66. Then, the top hold value of the E signal and the top hold value of the F signal are subtracted by the subtracting amplifier 70 to obtain a movement amount signal CSL for generating a cancel signal. The movement amount signal CSL does not represent the amount of deviation between the track and the light spot on the optical disc.
The multiplication amplifier 80 multiplies the movement amount signal CSL by the servo coefficient K set by the coefficient value calculation circuit 50 and sends the result to the subtraction amplifier 90.

  On the other hand, the subtracting amplifier 71 subtracts the E signal and the F signal to generate a signal (EF) corresponding to the push-pull signal PP.

  Then, the subtracting amplifier 90 subtracts the movement amount signal CSL signal multiplied by the servo coefficient K from the push-pull signal PP and outputs it as a so-called top hold push-pull (TPP) signal.

  FIG. 2 schematically shows the top hold push-pull signal TPP. That is, the E signal and the F signal are signals whose peak levels are held constant. When the optical disk is, for example, a compact disk (CD), the intensity of the return light from the mirror surface on which no recording pit is formed is maximized, giving a top level.

  FIG. 3 shows an example of the signal amplitude detection circuit 30 for detecting the amplitude of the standardized push-pull signal NPP.

  The push-pull signal PP = {(i + j) − (k + l)} from the optical pickup and the sum signal (i + j + k + l) are input to this signal amplitude detection circuit. As described above, this push-pull signal PP corresponds to the signal (EF), and the sum signal corresponds to the signal (E + F).

  In the division circuit 20, the signal {(i + j)-(k + l)} from the subtraction amplifier 13 is divided by the signal (i + j + k + l) from the addition amplifier 14, and the resulting push-pull signal NPP = {(i + j) ) − (K + l)} / (i + j + k + l) is sent to the top hold circuit 32 and the bottom hold circuit 33.

  The top value held by the top hold circuit 32 and the bottom value held by the bottom hold circuit 33 are subtracted by the subtraction amplifier 34 and sent to the DC level detection circuit 35.

  The DC level detection circuit 35 detects a DC level corresponding to the amplitude of the standardized push-pull signal NPP from the difference signal between the top hold value and the bottom hold value of the NPP signal from the subtraction amplifier 34. The DC level detection circuit is composed of an analog / digital conversion circuit or the like, and the measured value is temporarily stored in a semiconductor memory or the like.

  In addition to the signal amplitude detection circuit 30 as described above, the standardized push-pull signal NPP may be analog / digital converted to measure the difference between the average value of the peak value and the bottom value of the signal. .

FIG. 4 shows a configuration example of the top hold circuit 32 and the bottom hold circuit 33 in the signal amplitude detection circuit of FIG.
FIG. 4A shows an example of the top hold circuit. The standardized push-pull signal NPP is input from the terminal 38 and charges the capacitor C1 through the resistor R1 and the diode D1 arranged in the forward direction. At this time, the capacitor C1 is charged to the maximum (peak) voltage of the NPP signal PP, and the voltage at both ends thereof is held at the peak value of the amplitude of the NPP signal.

  By inputting the voltage across the capacitor C1 to the operational amplifier 45, an output corresponding to the maximum amplitude of the NPP signal input from the terminal 38 is obtained from the terminal 39.

  Here, since the reverse resistance of the diode D1 viewed from the capacitor C1 and the input impedance of the operational amplifier 45 are both sufficiently large, the charge held in the capacitor C1 is a resistor connected in parallel with the capacitor C1. Discharge via R2. Therefore, the time constant given as the resistor R1 and the product C1 · R2 of the capacitor C1 and the resistor R2 is determined so as to be appropriate for the frequency of the input NPP signal.

  FIG. 4B shows an example of the bottom hold circuit. This configuration is the same as the configuration of the top hold circuit described above, but the direction of the diode D2 is opposite to that of the top hold circuit.

  That is, the terminal 38 to which the NPP signal is input is connected to the capacitor C2 via the resistor R3 and the diode D2 arranged in the reverse direction, and the voltage of the push-pull signal PP input to the terminal 38 is the capacitor C2. When the voltage is lower than both ends of the capacitor C2, the capacitor C2 is discharged through the diode D2 and the resistor R3. Therefore, the voltage across the capacitor C2 is held at the bottom value of the amplitude of the NPP signal. By inputting the voltage across the capacitor C2 to the operational amplifier 46, an output corresponding to the minimum amplitude of the push-pull signal PP input from the terminal 38 is obtained from the terminal 41.

  The top hold characteristic and the bottom hold characteristic of the above circuit are selected so as to be optimal for detecting the amplitude of the push-pull signal or track wobble signal obtained from each optical disk and each optical pickup.

  Next, another configuration example of the signal amplitude detection circuit 30 for detecting the amplitude of the standardized push-pull signal NPP will be described.

  FIG. 5 shows another configuration example of the signal amplitude detection circuit 30 for detecting the amplitude of the standardized push-pull signal NPP.

  In this circuit, the DC component of the push-pull signal NPP normalized by the division circuit 20 is removed by the DC removal circuit 36. Then, the value held top by the top hold circuit 33 is doubled by the operational amplifier 37 to obtain an amplitude value by the DC level detection circuit 35.

  In this way, the amplitude of the NPP signal may be obtained by doubling the top hold value without using the top hold circuit and the bottom hold circuit.

  FIG. 6 shows a configuration example of the DC removal circuit 36 used in the signal amplitude detection circuit described above.

  The standardized push-pull signal NPP is input from the terminal 42, and its DC component is blocked by the capacitor C3. The voltage at one end is input to the operational amplifier 47 via the resistor R5. As a result, a standardized push-pull signal NPP from which the direct current component has been removed and multiplied by a predetermined gain is output from the terminal 43.

  The characteristics of the DC component removal circuit are selected so as to be optimal for detecting the amplitude of the push-pull signal or track wobble signal obtained from each optical disk and each optical pickup.

  In addition, although a DC removal circuit constituting a high-pass filter is illustrated here, a band-pass filter having a characteristic of passing a push-pull signal PP or a track wobble signal component TW described later is used. You can also.

  Next, another embodiment of the tracking device of the present invention will be described.

  FIG. 7 is a block diagram showing another configuration example of the main part of the tracking control device as one embodiment of the present invention.

  The tracking control device detects the push-pull signal PP from the return light from the optical disk having a guide groove formed in a meandering manner on the optical disk, and removes the offset of the push-pull signal PP to obtain a tracking error signal. It has been done.

  The input terminals 111 and 112 receive the E signal and the F signal from the optical pickup. The subtraction amplifier 113 generates these difference signals (E−F), and the addition amplifier 114 generates these sum signals (E + F).

  The division circuit 120 divides the signal (E−F) by the signal (E + F), and a standardized push-pull signal (E−F) / (E + F), which is a result of the division, is a signal amplitude detection circuit. 130. Here, the differential detection of the track wobble signal TW corresponds to the push-pull signal.

  The signal amplitude detection circuit 130 detects the amplitude of the track wobble signal TW from the division circuit 120. As the signal amplitude detection circuit 130, a circuit similar to that shown as a specific example of the signal amplitude circuit 30 described above can be used. The amplitude value from the signal amplitude detection circuit 130 is converted into a digital signal by the A / D conversion circuit 140 and sent to the coefficient calculation circuit 150.

  The coefficient calculation circuit 150 is for controlling the tracking servo coefficient Kw according to the amplitude of the track wobble signal TW, and sends coefficient (gain) control information to a gain control amplifier 180 described later. The coefficient calculation circuit 150 is configured by a microcomputer or the like.

  On the other hand, as described above, in the tracking control by the push-pull method in the one-beam method, the push-pull signal is generated using the movement amount signal corresponding to the movement amount of the objective lens 123 or the movement amount of the light spot 224 on the optical disc 200. It is necessary to cancel the offset.

  The band-pass filters 163 and 164, the top hold circuits 165 and 166, and the subtraction amplifier 170 are parts that generate the movement amount signal.

  The a signal input from the input terminal 161 is sent to the top hold circuit 165 via the band pass filter 163, and the peak level is held. Similarly, the d signal input from the input terminal 162 is sent to the top hold circuit 166 via the band pass filter 164, and the peak level is held at the peak level. Then, the top hold values from the top hold circuits 165 and 166 are subtracted by the subtraction amplifier 170 to obtain a movement amount signal CSL for generating a cancel signal. The a signal and the d signal are track wobble signals from the light receiving area a and the light receiving area d at both ends of the photodetector whose light receiving surface is divided into four, and are from the optical disk on which the wobble track of the optical disk is formed. This is a signal obtained by differentially detecting the return light.

  The center frequency of the pass band of the bandpass filters 163 and 164 is set to about 22 kHz which is the wobbling frequency of the track of the optical disk.

  The subtracting amplifier 170 subtracts the top-held a signal from the top hold circuit 165 and the top-held d signal from the top hold circuit 166 to generate a movement amount signal CSL. As described above, the movement amount signal CSL does not represent the amount of deviation between the track and the light spot on the optical disc.

  Then, the gain control amplifier 180 multiplies this movement amount signal CSL by the servo coefficient Kw set by the coefficient value calculation circuit 150 and sends the result to the subtraction amplifier 190.

  Then, the subtraction amplifier 190 subtracts the movement amount signal CSL signal multiplied by the servo coefficient Kw from the push-pull signal, and outputs it as a push-pull signal WPP corresponding to the wobble amplitude of the track.

  FIG. 8 schematically shows the shape of the wobble track formed on the optical disc.

  The intensity of the return light of the light spot 224 irradiated to the track (wobble track) 301 of the optical disc 300 formed by meandering (wobble) the guide groove is modulated according to this wobble, so that the push-pull signal PP is Obtainable.

  Such a wobble track is used, for example, in a recordable magneto-optical disk. As a specific example, there is a magneto-optical disk with a diameter of 64 mm in which the wobble frequency is 22 kHz, the track pitch is 1.6 μm, and the wobble amplitude is 0.03 μm as described above. By forming this wobble track, the address of the signal to be recorded / reproduced can be formed on the optical disc.

  FIG. 9 shows an example of the amplitude detection circuit 130 for detecting the amplitude of the track wobble signal TW.

  The amplitude detection circuit 130 is the same as the amplitude detection circuit 30 described above, except that a push-pull signal is obtained as a track wobble signal TW obtained by differentially detecting return light from the wobble track. Is different.

  The signal amplitude detection circuit 130 receives the push-pull signal {(i + j) − (k + 1)} from the optical pickup and the sum signal (i + j + k + 1). This push-pull signal corresponds to the signal (E−F), and the sum signal corresponds to the signal (E + F).

  In the division circuit 120, the signal {(i + j) − (k + l)} from the subtraction amplifier 113 is divided by the signal (i + j + k + l) from the addition amplifier 114, and the result {(i + j) − (k + l)} / (i + j + k + l). ) Is sent to the top hold circuit 132 and the bottom hold circuit 133.

  Then, the top value held by the top hold circuit 132 and the bottom value held by the bottom hold circuit 133 are subtracted by the subtraction amplifier 134.

  The track wobble signal TW is sent to the DC level detection circuit 135, and the DC level corresponding to the amplitude is detected.

  FIG. 10 shows another example of the signal amplitude detection circuit 130 for detecting the amplitude of the track wobble signal TW.

  In this circuit, the DC component of the push-pull signal from the wobble track standardized by the division circuit 120 is removed by the DC removal circuit 136. Then, the value held top by the top hold circuit 133 is doubled by the operational amplifier 137, and the amplitude value is obtained by the DC level detection circuit 135. In this way, the amplitude of the track wobble signal TW may be obtained by doubling the top hold value without using the top hold circuit and the bottom hold circuit.

  Next, an embodiment of the tracking control method of the present invention will be described.

  In the above-described tracking control device according to the present invention, the servo coefficient K set to be optimal for each optical disc is, for example, the amplitude value of the push-pull signal NPP normalized by the total amount of light incident on the photodetector 225. Is a function of

  The standardized push-pull signal NPP is given by the following equation (3).

NPP = {(i + j) + (k + l)} / (i + j + k + l) (3)
The optimum tracking error signal TE is given by the following equation (4) or (5).

TE = (i + j) + (k + 1)} − K (NPP) × CSL (4)
TE = (i + j) + (k + l)} / (i + j + k + l) −K (NPP) × CSL (5)
That is, in order to obtain the best tracking error signal TE for each optical disk, the NPP value may be obtained for each optical disk.

  As described above, the amplitude value of the standardized push-pull signal NPP is detected by holding the top level and the bottom level of the standardized push-pull signal NPP without applying the tracking servo. Or a value obtained by holding the top level of the signal after removing the DC component from the standardized push-pull signal NPP.

  On the other hand, in the optical disk on which the wobble track is formed, the tracking servo coefficient Kw can be obtained with the tracking servo applied.

  The wobble track signal TW is given by the following equation (6).

Tw = {(i + j) + (k + l)} / (i + j + k + l) (6)
Further, since the best tracking servo coefficient Kw for each optical disk is a function value of the wobble track signal TW, the best tracking error signal TE for the optical disk is calculated by the following equation (7) or (8). Desired.

TE = {(i + j) + (k + 1)}-TW (Tw) × CSL (7)
TE = {(i + j) + (k + l)} / (i + j + k + l) −TW (Tw) × CSL (8)
FIG. 11 is a functional block diagram showing a main signal flow when tracking control is performed by the tracking control method according to the present invention described above.

  First, the amplitude of the push-pull signal PP obtained from the optical disk or the amplitude of the wobble track signal TW is obtained by the signal amplitude detection means 230.

  These amplitude values are converted into digital signals by an analog / digital (A / D) conversion means 240 and taken into the microcomputer 250.

  The microcomputer 250 is a means for calculating a tracking servo coefficient K or Kw, and converts the amplitude value of the push-pull signal PP or the amplitude value of the wobble track signal TW input via the A / D conversion means 240. In response, a multiplier 280 described later is controlled by the gain control signal. The amplitude value and the tracking servo coefficient value K (Kw) calculated by the microcomputer 250 are values obtained for each optical disk, and are stored in the memory 255 until at least the optical disk is switched. Retained. Note that the servo coefficient obtained here may be held in a level hold circuit and given to the servo circuit. The value of the servo coefficient that is held is not changed or updated unless there is an instruction from a microcomputer or the like.

  Note that K (NPP) or Kw (Tw), which is a function for calculating the best servo coefficient K for tracking by the one-beam method, exists for each type of optical disc and for each reproduction / recording time. Therefore, a plurality of functions are configured by an electric circuit or software.

  The multiplier 280 multiplies the CSL signal by the servo coefficient value K (NPP) or Kw (TW) in accordance with the gain control signal from the microcomputer 250. As described above, the CSL signal is a signal corresponding to the amount of movement of the objective lens of the optical pickup or the amount of movement of the light spot on the optical disk.

  The subtractor 290 subtracts the CSL signal multiplied by the servo coefficient value from the push-pull signal PP and outputs the result as a tracking error signal 290.

  FIG. 12 is an example of a function representing a change in Kw value with respect to the amplitude value of the standardized push-pull signal NPP.

  Thus, the value of the servo coefficient K changes according to the normalized amplitude value of the push-pull signal NPP.

  FIG. 13 is a flowchart showing a basic processing procedure for controlling the servo coefficient K using the standardized push-pull signal NPP by the tracking control method according to the present invention.

  First, in step S1, the focus servo is turned on so that the light beam applied to the optical disc is focused on the signal surface of the optical disc. At this time, the tracking servo is not turned on, and the light spot whose focus is controlled on the optical disc still does not follow the track.

  Next, in step S2, the amplitude of the standardized push-pull signal NPP is detected. Here, as described above, the level hold signal is A / D converted using a level hold circuit such as a top hold circuit or a bottom hold circuit, and then binarized, or the standardized push-pull signal NPP is converted to A A method of detecting from a signal value binarized after / D conversion is used.

  Next, in step S3, a servo coefficient K for obtaining an optimum tracking signal TE is calculated from the detected amplitude value of the standardized push-pull signal NPP. Here, the optimal tracking signal TE is the smallest in track deviation with respect to the difference in optical pickup, optical disc, tracking control method, etc., and in an environment where recording / reproducing signals on other optical discs is considered. This is a tracking error signal. The servo coefficient K is obtained by performing an operation using a microcomputer, an arithmetic processor, or the like using a function obtained in advance as described above. The above function can be obtained in advance by measuring the optimum coefficient value for the amplitude value of the standardized push-pull signal NPP, or by simulating an optical system.

  Next, in step S4, the calculated servo coefficient value K is multiplied by the CSL signal. As described above, the CSL signal is a signal corresponding to the amount of movement of the objective lens of the optical pickup or the amount of movement of the light spot on the optical disk. This multiplication is performed by passing the CSL signal through an operational amplifier and controlling the amplifier gain corresponding to the servo coefficient value from a microcomputer or the like.

  In step S5, the CSL signal multiplied by the servo coefficient value K (multiplied by K) is subtracted from the push-pull signal PP to obtain a standardized push-pull signal for obtaining an optimum tracking error signal TE. An NPP is generated. Here, the polarity of the CSL signal multiplied by K is the same as the offset polarity of the push-pull signal PP when the objective lens is moved, and the offset of the push-pull signal PP when the objective lens is moved is canceled. The

  With the above procedure, the processing for setting the coefficient of the tracking servo using the amplitude level of the push-pull signal NPP standardized with the total amount of return light from the optical disc is completed.

  Next, a basic processing procedure for controlling the servo coefficient Kw using the amplitude of the wobble track signal by the tracking control method according to the present invention will be described.

  FIG. 14 is a flowchart showing a basic processing procedure for controlling the servo coefficient Kw using the wobble track signal TW by the tracking control method according to the present invention.

  First, in step S11, the focus servo is turned on so that the light beam applied to the optical disc is focused on the signal surface of the optical disc. At this time, the tracking servo is not turned on, and the light spot whose focus is controlled on the optical disc still does not follow the track.

  Next, in step S12, the tracking servo is turned on, and the light spot that is focused on the optical disc is controlled to follow the track. At this time, tracking servo is applied using a push-pull signal PP or a WPP signal or TPP signal in which a temporary servo coefficient value is set.

  Next, in step S13, the amplitude of the wobble track signal WT is detected by push-pull signal calculation in a tracking-controlled state. Here, as described above, the level hold signal is A / D converted using a level hold circuit such as a top hold circuit or a bottom hold circuit, and then binarized, or the standardized push-pull signal NPP is converted to A A method of detecting from a signal value binarized after / D conversion is used.

  Next, in step S14, a servo coefficient Kw for obtaining an optimum tracking signal TE is calculated from the detected amplitude value of the wobble track signal TW. Here, the optimal tracking signal TE is the smallest in track deviation with respect to the difference in optical pickup, optical disc, tracking control method, etc., and in an environment where recording / reproducing signals on other optical discs is considered. This is a tracking error signal. The servo coefficient Kw is obtained by performing an operation using a microcomputer, an arithmetic processor, or the like using a function obtained in advance. The above function can be obtained by measuring in advance an optimum coefficient value for the amplitude value of the wobble track signal TW, or by simulating an optical system.

  In step S15, the CSL signal is multiplied by the calculated servo coefficient value Kw. As described above, the CSL signal is a signal corresponding to the amount of movement of the objective lens of the optical pickup or the amount of movement of the light spot on the optical disk. This multiplication is performed by passing the CSL signal through an operational amplifier and controlling the amplifier gain corresponding to the servo coefficient value from a microcomputer or the like.

  In step S16, the CSL signal multiplied by the servo coefficient value Kw (multiplied by Kw) is subtracted from the push-pull signal PP to generate a push-pull signal WPP for obtaining an optimum tracking error signal TE. The Here, the polarity of the CSL signal multiplied by Kw is the same as the polarity of the offset of the push-pull signal when the objective lens is moved, and the offset of the push-pull signal when the objective lens is moved is canceled.

  With the above procedure, the process of setting the tracking servo coefficient using the amplitude level of the wobble track signal is completed.

  In the above-described embodiment of the present invention, the case where tracking control is performed using the photodetector 225 in the optical system illustrated in FIG. 16 has been described. For example, the photodetector of FIG. Similar effects can be obtained by using a light receiving means in which a photodetector is arranged so that the one-time diffracted light distribution of the light spot reflected by the optical disk is divided into two as in 213 and 215. Note that the angle formed by the division direction of the light receiving surface of these photodetectors and the track on the optical disc is not necessarily parallel, and operates sufficiently from parallel to an angle of about 45 degrees.

  According to the embodiment of the present invention, the value of the servo coefficient multiplied as the correction coefficient to the cancel signal for canceling the offset component of the push-pull signal is set to the amplitude of the standardized push-pull signal NPP or the wobble track signal. Since the adaptive setting is made according to the amplitude, it is possible to improve the accuracy and reliability of the servo with respect to the characteristic variation for each optical disk in the one-beam method, and to simplify the setting of the coefficient of the tracking servo. A tracking control device and a tracking control method can be provided.

  It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

It is a figure which shows the structural example of the tracking control apparatus which concerns on this invention. It is a figure for demonstrating a TPP signal. It is a figure which shows an example of the signal amplitude detection circuit for detecting the amplitude of the standardized push pull signal NPP. It is a figure which shows an example of the top hold circuit and bottom hold circuit used for said signal amplitude detection circuit. It is a figure which shows another structural example of the signal amplitude detection circuit for detecting the amplitude of the standardized push pull signal NPP. It is a figure which shows an example of DC removal circuit of said signal detection circuit. It is a block diagram which shows another structural example of the tracking control apparatus which concerns on this invention. It is a figure for demonstrating a wobble track. It is a figure which shows an example of the amplitude detection circuit for detecting the amplitude of a wobble track signal. It is a figure which shows another example of the signal amplitude detection circuit for detecting the amplitude of the wobble track signal TW. It is a functional block diagram of a tracking control device to which a tracking control method according to the present invention is applied. It is a figure which shows an example of the function showing the change of the value of the servo coefficient K with respect to the amplitude value of the standardized push pull signal NPP. It is a flowchart which shows the basic process sequence which controls the value of the servo coefficient K using the standardized push pull signal NPP by the tracking control method which concerns on this invention. 4 is a flowchart showing a basic processing procedure for controlling the value of a servo coefficient K using a wobble track signal TW by the tracking control method according to the present invention. It is a figure which shows an example of the optical system of the optical pick-up made to obtain a tracking error signal by the 1 beam method. It is a figure for demonstrating the structure of the light-receiving surface of the photodetector used for said optical system.

Explanation of symbols

  11, 12 input terminals, 13 subtraction amplifier, 14 addition amplifier, 20 division circuit, 30 signal amplitude detection circuit, 40 A / D conversion circuit, 50 count value calculation circuit, 65, 66 top hold circuit, 70, 71 subtraction amplifier, 80 multiplication amplifier, 90 subtraction amplifier, 99 output terminals

Claims (17)

By subtracting the cancel signal multiplied by the correction coefficient from the push-pull signal obtained from the return light of the light beam irradiated on the optical disc, the object lens moves or the light beam irradiation position moves on the optical disc. In the tracking control device that cancels the offset of the generated tracking error signal,
A movement amount signal detecting means for detecting a movement amount signal generated according to the movement amount of the objective lens or the movement amount of the irradiation position of the light beam on the optical disc;
Correction coefficient setting means for setting a correction coefficient to be multiplied by the movement amount signal according to the amplitude of the push-pull signal;
Cancel signal generating means for generating a cancel signal by multiplying the offset component by the set correction coefficient,
Tracking error signal generating means for subtracting the cancel signal from the push-pull signal to generate a tracking error signal.   Push-pull signal normalization means for normalizing the push-pull signal by dividing the push-pull signal by a sum signal corresponding to the total amount of light incident on the photodetector that detects the return light, and the correction coefficient setting means is the normalization 2. The tracking control device according to claim 1, wherein the correction coefficient is set according to the amplitude of the push-pull signal.   3. The tracking control apparatus according to claim 2, wherein the correction coefficient setting means sets the correction coefficient as a function value having the amplitude of the standardized push-pull signal as a variable.   The push-pull signal normalization means is a photodetector having a light receiving surface in which a change in the amount of return light generated when the irradiated light beam crosses a track on the optical disc is divided into two or more with respect to the track direction. 3. The tracking control device according to claim 2, wherein the normalized push-pull signal is obtained by dividing the push-pull signal obtained by detecting by the sum signal from the photodetector.   The push-pull signal normalization means is a photodetector having a light receiving surface in which a change in the amount of return light generated when the irradiated light beam crosses a track on the optical disc is divided into two or more with respect to the track direction. The standardized push-pull signal is obtained by dividing the push-pull signal obtained by differential detection by the total signal of the return light from the mirror surface of the optical disk held in advance from the detector to normalize the push-pull signal. 3. The tracking control apparatus according to claim 2, wherein a signal is obtained.   2. The tracking control apparatus according to claim 1, wherein the correction coefficient setting means includes signal amplitude detection means for detecting the amplitude of the push-pull signal by top-holding and bottom-holding.   The correction coefficient setting means detects the amplitude of the push-pull signal from the average value of the peak value and the average value of the bottom value of the signal after analog / digital conversion of the push-pull signal. The tracking control device according to 1. By subtracting the cancel signal multiplied by the correction coefficient from the push-pull signal obtained from the return light of the light beam irradiated on the optical disc, the object lens moves or the light beam irradiation position moves on the optical disc. In the tracking control device that cancels the offset of the generated tracking error signal,
A movement amount signal detecting means for detecting a movement amount signal generated according to the movement amount of the objective lens or the movement amount of the irradiation position of the light beam on the optical disc;
Correction coefficient setting means for setting a correction coefficient to be multiplied by the offset component according to the amplitude of the track wobble signal;
Cancellation signal generating means for generating a cancellation signal by multiplying the movement amount signal by the set correction coefficient;
And a tracking error signal generating means for generating a tracking error signal by subtracting the cancel signal from the push-pull signal.   9. The tracking control apparatus according to claim 8, wherein the correction coefficient setting means sets the correction coefficient as a function value having an amplitude of the track wobble signal as a variable.   9. The tracking control apparatus according to claim 8, wherein the track wobble signal is detected in a state in which focus control is performed so that the irradiated light beam is focused on the optical disc and tracking control is performed. .   9. The tracking control apparatus according to claim 8, wherein the correction coefficient setting means includes signal amplitude detection means for detecting the amplitude of the track wobble signal by top-holding and bottom-holding the track wobble signal.   The correction coefficient setting means detects the amplitude of the track wobble signal from the average value of the peak value and the average value of the bottom value of the signal after analog / digital conversion of the track wobble signal. 9. The tracking control device according to 8. By subtracting the cancel signal multiplied by the correction coefficient from the push-pull signal obtained from the return light of the light beam irradiated on the optical disc, the object lens moves or the light beam irradiation position moves on the optical disc. In the tracking control method for canceling the offset of the generated tracking error signal,
A movement amount signal detection step of detecting a movement amount signal generated according to the movement amount of the objective lens or the movement amount of the irradiation position of the light beam on the optical disc;
A correction coefficient setting step of setting a correction coefficient to be multiplied by the offset component according to the amplitude of the push-pull signal;
A cancel signal generating step of generating a cancel signal by multiplying the offset component by the set correction coefficient;
A tracking error signal generating step of subtracting the cancel signal from the standardized push-pull signal to generate a tracking error signal.   A push-pull signal normalization step of normalizing the push-pull signal by dividing the push-pull signal by a sum signal corresponding to the total amount of incident light to the photodetector that detects the return light, and the correction coefficient setting step includes the standard 14. The tracking control method according to claim 13, wherein the correction coefficient is set according to the amplitude of the converted push-pull signal.   14. The tracking control method according to claim 13, wherein the correction coefficient is set as a function value having the amplitude of the standardized push-pull signal as a variable. By subtracting the cancel signal multiplied by the correction coefficient from the push-pull signal obtained from the return light of the light beam irradiated on the optical disc, the object lens moves or the light beam irradiation position moves on the optical disc. In the tracking control method for canceling the offset of the generated tracking error signal,
A movement amount signal detection step of detecting a movement amount signal generated according to the movement amount of the objective lens or the movement amount of the irradiation position of the light beam on the optical disc;
A correction coefficient setting step for setting a correction coefficient to be multiplied by the movement amount signal according to the amplitude of the track wobble signal;
A cancel signal generating step of generating a cancel signal by multiplying the offset component by the set correction coefficient;
A tracking error signal generating step of generating a tracking error signal by subtracting the cancel signal from the push-pull signal.   17. The tracking control method according to claim 16, wherein the correction coefficient is set as a function value having the amplitude of the track wobble signal as a variable.

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