JP4521541B2 - Tracking control device - Google Patents

Description

  The present invention relates to a tracking control apparatus used for recording / reproducing of an optical disc.

[Summary of Invention]
The present invention relates to a tracking control apparatus used for recording / reproducing of an optical disc. According to the present invention, a signal obtained by delaying a tracking error signal in a feedback control system constituting a tracking control device for a time corresponding to a period corresponding to one round of an optical disc is an inverse number of a closed loop transfer function of an output with respect to an input of the feedback control system. It is added to the tracking error signal in the feedback control system via a precompensation means having a transfer function.

  Alternatively, the present invention provides a closed loop of an output with respect to an input of the feedback control system, wherein a signal obtained by performing arithmetic processing on the tracking error signal stored for a time corresponding to a plurality of rotation cycles of the optical disc is recorded. It is added to the tracking error signal in the feedback control system via a precompensation means having a transfer function that is the reciprocal of the transfer function.

  As a result, the tracking error due to eccentricity caused by the optical disk and the optical disk rotation mechanism and the like is reduced without reducing the stability of the tracking control device, and the followable optical disk rotation speed is improved.

A tracking control device used for recording / reproducing of an optical disc is configured by a feedback control system. FIG. 17 is a configuration block diagram of a conventional tracking control device. As shown in FIG. 17, the feedback control system of the tracking control system, a tracking error detecting means 1, the transfer function G ₁ Stabilizing means 2 with, constituted by a tracking actuator 3 having a transfer function G _2.

In the feedback control system of this tracking control device, the tracking error detection means 1 detects the difference between the track position t ₁ on the optical disc and the light spot position s ₁ controlled by the tracking actuator 3, and the tracking error signal e _1. Is input to the stabilization compensator 2.

The stabilization compensator 2 compensates and outputs the frequency characteristics of the amplitude and phase of the tracking error signal e ₁ so that the tracking control device has a desired response characteristic and performs a stable operation. The output signal of the stability compensation means 2 drives the tracking actuator evening 3 controls the light spot position s _1.

  As a technique for improving the follow-up performance of such a feedback control system, for example, as described in Reference 1 “Section 4.10 of“ Dynamics and Control of Information Equipment ”published by Yokendo, edited by the Japan Society of Mechanical Engineers”. A method of repeated tracking control is known.

FIG. 18 is a block diagram showing the configuration of a tracking control apparatus using this repetitive tracking control method. As shown in FIG. 18, in the feedback control system of this tracking control device, in the configuration shown in FIG. 17, an addition means 7 is provided between the tracking error detection means 1 and the stabilization compensation means 2, and the addition means 7 A delay means 72 is provided for feeding back the output to the input of the adding means 7 with a transfer function e- ^Ls .

In this repetitive tracking control method, the tracking error signal e ₁ is added to the output of the delay means 72 by the adding means 7 to output a control signal f ₁ .

The control signal f ₁ is input to the delay unit 72 and the stabilization compensation unit 2.

The delay means 72 delays the control signal f ₁ by a time corresponding to the rotation period L of the optical disc, causes the adding means 7 to add the tracking error signal e _1, and outputs the control signal f ₁ .

The stabilization compensation means 2 compensates and outputs the frequency characteristics of the amplitude and phase of the control signal f ₁ so that the tracking control device has a desired response characteristic and performs a stable operation. The output signal of the stability compensation means 2 drives the tracking actuator 3 for controlling the light spot position s _1.

  As a result, the tracking error that could not be corrected before one rotation of the optical disk is corrected in advance, so that the follow-up performance is improved.

  Incidentally, in order to record high-quality image data on an optical disk medium for a long time, it is required to increase the recording density of the optical disk and increase the data transfer rate.

  In order to increase the recording density, it is necessary to use a short wavelength light source and to reduce the light spot diameter by increasing the numerical aperture of the objective lens. This reduces the mark length recorded on the optical disc and uses a narrow track pitch to reduce the area occupied by data per bit.

  In order to cope with this narrow track pitch, the tracking control device is required to have a sufficiently small tracking error compared to the track pitch. For example, in the case of a CD-ROM, the allowable value of the tracking error is ± 0.1 μm or less for a track pitch of 1.6 μm, and in the case of a DVD-ROM, it is ± 0.02 μm or less for a track pitch of 0.74 μm. The following error must be

  In order to increase the data transfer rate in the optical disk recording apparatus, it is required to reduce the bit length recorded on the optical disk and simultaneously increase the rotation speed of the optical disk.

  By the way, the tracks on the optical disk are concentric or spiral. Further, the optical disc has an eccentricity that occurs in the manufacturing process. Further, the spindle motor for rotating the optical disc and the mounting portion for attaching the optical disc to the spindle motor are also eccentric. Since the worst value of the eccentricity is the sum of these, when the track on the optical disk is viewed from the light spot of the optical head, the eccentricity is about ± 100 μm. Due to this eccentricity, the track position, which is the target value of the tracking control device, becomes a periodic function that changes as the optical disk rotates.

  Therefore, in order to cope with the high-speed rotation of the optical disk, the light spot position must follow the track position on the eccentric optical disk as described above at a high speed. For this purpose, it is necessary to increase the mechanical resonance frequency of the tracking actuator used in the optical head and simultaneously increase the bandwidth of the tracking control device.

  There are methods to increase the mechanical resonance frequency of the tracking actuator, such as reducing the mass of the moving part and increasing the elastic modulus. However, both methods have limitations, and the upper limit of the mechanical resonance frequency of the tracking actuator that is currently realized. Is about 100 Hz.

  On the other hand, widening the bandwidth of the tracking control device improves the follow-up performance with respect to high-speed rotation of the optical disc, but reduces the suppression characteristics against disturbances such as noise and vibration.

  For the above reason, in the tracking control apparatus using only the feedback control system as shown in FIG. 17, the light spot is high-speed with respect to the track on the optical disk rotating at high speed while satisfying the required tolerance of the tracking error. It was difficult to follow the position.

  On the other hand, the tracking control apparatus using the repetitive control method shown in FIG. 18 as described in Document 1 shows excellent tracking performance for periodically changing inputs. However, if it is a periodic component, it has the property of trying to suppress the error to an infinitely high frequency, which may cause problems in the stability of the tracking control device and may be vulnerable to non-periodic disturbances. Widely known.

  Further, in a method in which an optical disk rotates at a constant angular velocity (CAV method: Constant Angular Velocity or ZCAV method: Zoned Constant Angular Velocity), repetitive control using delay means 72 having a constant delay amount as shown in FIG. Good. However, a method of rotating at a constant linear velocity as in a CD (CLV method: Constant Linear Velocity), or a radius of an optical disk as in a DVD-RAM is divided into several regions, and a substantially constant line in the region. In the method of rotating at a speed (ZCLV method: Zoned Constant Linear Velocity), the cycle of one rotation changes depending on the radius of the optical disk, and therefore it is not possible to perform repetitive control by the method shown in FIG.

  The present invention has been created to solve such problems. The stability of the tracking control device is ensured, and the follow-up performance with respect to the track on the optical disk rotating at high speed is improved. The CLV method and the ZCLV method are provided. Thus, it is an object of the present invention to provide a tracking control device that is stable and has high tracking performance even when the period of one rotation changes depending on the radius of the optical disk.

In order to achieve the above object, a tracking control apparatus according to claim 1 generates a tracking error signal corresponding to a difference between a track position on an optical disc and a light spot position emitted from an optical head. Correction of the virtual track position by inputting the error signal generation means, the tracking error signal and the pre-compensation signal, performing the calculation using the first pulse transfer function and the second pulse, respectively, and adding them. A correction signal generating means for generating and storing a signal, and a signal obtained by delaying the output of the correction signal generating means from a signal obtained by compensating the amplitude and phase of the output of the correction signal generating means with a third pulse transfer function to generate a precompensation signal by the pre-compensation means for outputting the feedback and adding means to said correction signal generating means inputs, Serial includes a tracking error signal and the pre-distortion signal adding means for generating a drive signal obtained by adding, and control means for scanning the target track on the optical disk to the light spot based on the generated drive signals, When the pulse transfer function of the control means is G ₁ (z ⁻¹ ) G ₂ (z ⁻¹ ) , the correction signal generation means has the first pulse transfer function of 1 + G ₁ (z ⁻¹ ) G _2. (Z ⁻¹ ) and the second pulse transfer function is G ₁ (z ⁻¹ ) G ₂ (z ⁻¹ ), and the precompensation means includes the tracking error signal generation means and the correction signal. Precompensation to the adding means when the connection between the precompensating means and the adding means of the feedback control system constituting a closed loop by the generating means, the precompensating means, the adding means, and the control means is cut off Means side When the transfer function of the output of the light spot position with respect to the input from is Gcl (z ⁻¹ ), the third pulse transfer function is P ₁ (z ⁻¹ ) represented by the following equation (18). There,
P ₁ (z ⁻¹ ) = Ac (z ⁻¹ ) / {Bc ⁺ (z ⁻¹ ) Bc ⁻ (1)} (18)
Here, Gcl (z ⁻¹ ) = z ^−d Bc ⁺ (z ⁻¹ ) Bc ⁻ (z ⁻¹ ) / Ac (z ⁻¹ )
Ac (z ⁻¹ ): term of the pole of Gcl (z ⁻¹ )
Bc ⁺ (z ⁻¹ ): A stable zero term of Gcl (z ⁻¹ )
Bc ⁻ (z ⁻¹ ): term of unstable zero of Gcl (z ⁻¹ )
Bc ⁻ (1): The unstable zero of Gcl (z ⁻¹ ) is made constant as z ⁻¹ = 1.
thing,
d: Equivalent lead sampling number
The calculation result of the third pulse transfer function is calculated by a delay unit and a subtraction unit for converting the compensation amount for the light spot position into the compensation amount for the tracking error signal using the correction signal which is the virtual track position. Thus, the pulse transfer function of P ₁ (z ⁻¹ ) −z ^−d is obtained, and the response of the light spot position is obtained from the correction signal as Gcl (z ⁻¹ ) · P ₁ (z ⁻¹ ) When obtaining by multiplication, the pulse transfer function P ₁ (z ⁻¹ ) cancels the pole and stable zero point of Gcl (z ⁻¹ ), and the DC gain of the pre-compensation means is the direct current of Gcl (z ⁻¹ ). It is characterized by matching the reciprocal of the gain .

According to a second aspect of the present invention, there is provided a tracking control device for generating a tracking error signal corresponding to a difference between a track position on an optical disc and a light spot position emitted from an optical head, and the tracking error signal generating means. An error signal and a pre-compensation signal are input, and calculation is performed using the first pulse transfer function and the second pulse transfer function, respectively, and then added to generate and store a correction signal that is a virtual track position. Correction signal generating means and precompensation by subtracting a signal obtained by delaying the output of the correction signal generating means from a signal obtained by compensating the amplitude and phase of the output of the correction signal generating means with a third pulse transfer function A pre-compensation unit that generates a signal and outputs feedback to the correction signal generation unit input and output to the addition unit; and the tracking error An addition means for generating a drive signal obtained by adding a signal and the pre-compensation signal; and a control means for causing the light spot to scan a target track on the optical disk based on the generated drive signal, and the correction signal. When the pulse transfer function of the control means is G ₁ (z ⁻¹ ) G ₂ (z ⁻¹ ) , the generating means has the first pulse transfer function of 1 + G ₁ (z ⁻¹ ) G ₂ (z ^{− 1} ), and the second pulse transfer function is G ₁ (z ⁻¹ ) G ₂ (z ⁻¹ ),
The pre-compensation unit includes the tracking error signal generation unit, the correction signal generation unit, the pre-compensation unit, the addition unit, and the control unit. When the transfer function of the output of the light spot position with respect to the input from the pre-compensation means side to the adding means when the connection between them is disconnected is Gcl (z ⁻¹ ), the third pulse transfer function is P ₁ (z ⁻¹ ) represented by the following formula (21) ,
P ₁ (z ⁻¹ ) = Ac (z ⁻¹ ) Bc ⁻ (z) / [Bc ⁺ (z ⁻¹ ) {Bc ⁻ (1)} ² ]
... (21)
Here, Gcl (z ⁻¹ ) = z ^−d Bc ⁺ (z ⁻¹ ) Bc ⁻ (z ⁻¹ ) / Ac (z ⁻¹ )
Ac (z ⁻¹ ): term of the pole of Gcl (z ⁻¹ )
Bc ⁺ (z ⁻¹ ): A stable zero term of Gcl (z ⁻¹ )
Bc ⁻ (1): The unstable zero of Gcl (z ⁻¹ ) is made constant as z ⁻¹ = 1.
thing,
d: Equivalent lead sampling number
The calculation result of the third pulse transfer function is calculated by a delay unit and a subtraction unit for converting the compensation amount for the light spot position into the compensation amount for the tracking error signal using the correction signal which is the virtual track position. By doing so, it has a pulse transfer function of P ₁ (z ⁻¹ ) −z ^−d , and the response of the light spot position is multiplied by Gcl (z ⁻¹ ) · P ₁ (z ⁻¹ ) to the correction signal. when seeking to, the pulse transfer function _{P 1} ^{(z -1)} is offset poles and stable zeros of Gcl ^{(z -1),} further the pulse transfer function Gcl ^{(z -1)} and the product all frequencies , The phase difference is set to zero, and the DC gain of the pre-compensation means is made to coincide with the reciprocal of the DC gain of Gcl (z ⁻¹ ) .

According to a third aspect of the present invention, there is provided a tracking control apparatus for generating a tracking error signal corresponding to a difference between a track position on an optical disk and a light spot position emitted from an optical head, and the tracking error signal generating means. An error signal is stored in the storage means for a time corresponding to a rotation period of at least one rotation of the optical disc, and a correction signal is output by calculating a tracking error signal one rotation period before from the stored signal. A signal generating unit; a pre-compensating unit that generates a pre-compensation signal in which the amplitude and phase of the generated correction signal are compensated by a predetermined pulse transfer function; and the tracking error signal and the pre-compensation signal. An adding means for generating an added drive signal; and on the optical spot on the optical spot based on the generated drive signal Control means for scanning a target track, and the pre-compensation means uses the tracking error signal generation means, correction signal generation means, pre-compensation means, addition means, and control means as the predetermined pulse transfer function. The output of the light spot position with respect to the input from the pre-compensation means side to the addition means when the connection between the pre-compensation means and the addition means in the feedback control system constituting a closed loop is disconnected. When the transfer function is Gcl (z ⁻¹ ), it has a pulse transfer function P ₁ (z ⁻¹ ) expressed by the following equation (18) ,
P ₁ (z ⁻¹ ) = Ac (z ⁻¹ ) / {Bc ⁺ (z ⁻¹ ) Bc ⁻ (1)} (18)
^{Here, Gcl (z -1) = z} -d Bc + (z -1) Bc - (z -1) / Ac (z -1)
Ac (z ⁻¹ ): term of the pole of Gcl (z ⁻¹ )
Bc ⁺ (z ⁻¹ ): A stable zero term of Gcl (z ⁻¹ )
Bc ⁻ (z ⁻¹ ): term of unstable zero of Gcl (z ⁻¹ )
Bc ⁻ (1): Constant where the unstable zero of Gcl (z ⁻¹ ) is z ⁻¹ = 1
,
d: Equivalent lead sampling number
The pulse transfer function determines the pole and stable zero of Gcl (z ⁻¹ ) when the response of the light spot position is obtained by multiplying the correction signal by Gcl (z ⁻¹ ) · P ₁ (z ⁻¹ ). It is characterized by canceling and making the DC gain of the pre-compensation means coincide with the inverse of the DC gain of Gcl (z ⁻¹ ) .

According to a fourth aspect of the present invention, there is provided a tracking control device for generating a tracking error signal corresponding to a difference between a track position on an optical disc and a light spot position emitted from an optical head, and the tracking error signal generating means. An error signal is stored in the storage means for a time corresponding to a rotation period of at least one rotation of the optical disc, and a correction signal is output by calculating a tracking error signal one rotation period before from the stored signal. A signal generating unit; a pre-compensating unit that generates a pre-compensation signal in which the amplitude and phase of the generated correction signal are compensated by a predetermined pulse transfer function; and the tracking error signal and the pre-compensation signal. adding means for generating an addition drive signal, on the optical disk to the light spot based on the generated drive signals Control means for scanning a target track, and the pre-compensation means uses the tracking error signal generation means, correction signal generation means, pre-compensation means, addition means, and control means as the predetermined pulse transfer function. The output of the light spot position with respect to the input from the pre-compensation means side to the addition means when the connection between the pre-compensation means and the addition means in the feedback control system constituting a closed loop is disconnected. When the transfer function is Gcl (z ⁻¹ ), it has a pulse transfer function P ₁ (z ⁻¹ ) represented by the following equation (21) ,
_{^{P 1 (z -1) = Ac}} (z -1) Bc - (z) / [Bc + (z -1) {Bc - (1)} 2] ... (21)
^{Here, Gcl (z -1) = z} -d Bc + (z -1) Bc - (z -1) / Ac (z -1)
Ac (z ⁻¹ ): term of the pole of Gcl (z ⁻¹ )
Bc ⁺ (z ⁻¹ ): A stable zero term of Gcl (z ⁻¹ )
Bc ⁻ (z ⁻¹ ): term of unstable zero of Gcl (z ⁻¹ )
Bc ⁻ (1): Constant where the unstable zero of Gcl (z ⁻¹ ) is z ⁻¹ = 1
,
d: Equivalent lead sampling number
The pulse transfer function determines the pole and stable zero of Gcl (z ⁻¹ ) when the response of the light spot position is obtained by multiplying the correction signal by Gcl (z ⁻¹ ) · P ₁ (z ⁻¹ ). Furthermore , the product with the pulse transfer function Gcl (z ⁻¹ ) is zero in phase difference at all frequencies, and the DC gain of the pre-compensation means matches the reciprocal of the DC gain of Gcl (z ⁻¹ ). It is characterized by letting .

According to the present invention , it is possible to control the light spot position by generating a signal obtained by compensating the amplitude and phase of the tracking error signal at least one round before the optical disc and adding the tracking error signal. Accordingly, it is possible to reduce the tracking error over the entire number of rotations of the optical disk while ensuring the stability of the apparatus. In addition, the storage means can have a learning function. Therefore, the tracking error can be further reduced. Furthermore, even if there is a period in which a tracking error signal cannot be obtained due to scratches or dust on the optical disk, the possibility of causing tracking loss can be reduced. Furthermore, it is possible to reduce the tracking error in recording / reproducing of an optical disc using the CLV method, the ZCLV method, or the like.

As described above, according to the present invention , a signal obtained by compensating the amplitude and phase of the tracking error signal at least one round before the optical disc is generated, and the signal obtained by adding the tracking error signal is used to determine the position of the light spot. Since the control is performed, it is possible to reduce the tracking error over the entire number of rotations of the optical disk while ensuring the stability of the apparatus. Further, since the storage unit can have a learning function, the tracking error can be further reduced. further,
Even if there is a period in which a tracking error signal cannot be obtained due to scratches or dust on the optical disk, the possibility of occurrence of off-tracking can be reduced. Furthermore, it is possible to reduce the tracking error in recording / reproducing of an optical disc using the CLV method, the ZCLV method, or the like.

  Therefore, according to the tracking control device of the present invention, stable recording / reproduction can be performed on a large-capacity optical disk having a narrow track pitch. Also, tracking control can be performed on an optical disk rotating at high speed, and the data transfer rate can be improved.

[First Embodiment]
FIG. 1 is a block diagram showing the configuration of a tracking control apparatus according to the first embodiment of the present invention. 1st Embodiment shows the principle structure of the tracking control apparatus which concerns on this invention , and 2nd Embodiment-9th Embodiment shown below is based on 1st Embodiment.

  As shown in FIG. 1, the tracking control apparatus of the first embodiment is provided with an adding means 7 between the tracking error detecting means 1 and the stabilization compensating means 2 in the configuration shown in FIG. The correction signal generating means 5 and the precompensation means 6 having the transfer function P1 are arranged in this order on the path for introducing one input (the output of the tracking error detecting means 1) to the other input of the adding means 7. It is.

The correction signal generation means 5 takes in the tracking error signal e ₁ detected by the tracking error detection means ₁ and generates a correction signal c ₁ based on the tracking error signal e ₁ detected at least before one rotation of the optical disc.

The pre-compensation unit 6 generates a pre-compensation signal h ₁ based on the correction signal c ₁ and outputs it to the other input of the addition unit 7.

  Also in the first embodiment, the stabilization compensator 2 has the amplitude and phase of the feedback control system that is formed by the tracking error detector 1, the adder 7, the stabilization compensator 2 and the tracking actuator 3. Frequency characteristics are compensated for, and stable feedback control is realized. This also applies to the following second to ninth embodiments.

  The correspondence between the above configuration and claim 1 is as follows. The tracking error detection means 1 corresponds to the tracking error detection means. The stabilization means 2 and the tracking actuator 3 correspond to the control means. The adding means 7 corresponds to the adding means. The correction signal generation means 5 corresponds to the correction signal generation means. The pre-compensation means 6 corresponds to the pre-compensation means.

  Next, the basic operation of the tracking control apparatus of the first embodiment will be described with reference to FIG.

In Figure 1, it detects the difference between the track positions t ₁ and the light spot position s ₁ by the tracking error detection means 1, to obtain a tracking error signal e _1. The tracking error signal e ₁ is branched into two, one being input to the adding means 7 and the other being input to the correction signal generating means 5.

The correction signal generation means 5 outputs a correction signal c ₁ using the tracking error signal e ₁ detected at least before one rotation of the optical disk. The pre-compensation means 6 compensates the frequency characteristics of the amplitude and phase of the correction signal c ₁ with the transfer function P ₁ and outputs the pre-compensation signal h ₁ .

This pre-compensation signal h ₁ is added to the tracking error signal e ₁ by the adding means 7, and the resulting signal (driving signal) is compensated for frequency characteristics of amplitude and phase by the stabilizing compensation means 2, and tracking is input to the actuator 3, to drive it, to control the light spot position s _1.

  As described above, in the first embodiment, in addition to the tracking error signal for the track on which the optical head is scanning, the pre-compensation signal is generated using the tracking error signal detected at least one rotation before the optical disk. In addition, since tracking control is performed using a signal obtained as a result of calculation using the pre-compensation signal and the tracking error signal, the tracking error can be reduced. This will be specifically described below.

First, the transfer functions of the stabilization compensator 2 and the tracking actuator 3 are determined as G ₁ and G ₂ , respectively. From FIG. 1, the input / output relationship of the tracking error detecting means 1 is
t ₁ −s ₁ = e ₁ (1)
It is. The spot position s ₁ controlled by the tracking actuator 3 is:
(E ₁ + h ₁ ) G ₁ G ₂ = s ₁ (2)
It is.

  As described above, since the optical disk, the spindle motor, and the optical disk mounting portion are decentered, the track position on the rotating optical disk with respect to the light spot of the optical head is a function that changes periodically. Furthermore, adjacent tracks have a large positional correlation.

Therefore, to produce a pre-compensation signal h ₁ based on the tracking error which could not suppressed at least before one rotation. Further, it can be understood that the follow-up error can be reduced by performing correction in the next rotation using this signal.

Here, the track position at the m-th rotation of the optical disk is described as t _{1, m} , the light spot position as s _{1, m} , the tracking error signal as e _{1, m} , and the pre-compensation signal as h _{1, m} . When the pre-compensation signals h _{1 and m−1} obtained by using the tracking error signals e _{1 and m−1} before the (m−1) th rotation of the optical disk are used, the light spot position s ₁ at the mth rotation. _{, M} is
s _{1, m} = (e _{1, m} + h _{1, m-1} ) G ₁ G ₂ (3)
It becomes. By repeating this operation, t _{1, m} = s _{1, m} can be realized. In the following second to ninth embodiments, specific means and configurations for realizing this at high speed and stably are described. According to these embodiments, a tracking error characteristic as shown in FIG. 2 is obtained.

  FIG. 2 is a comparison diagram of the tracking error characteristics of the tracking control apparatus with respect to the rotational speed of the optical disk obtained by the present invention. In FIG. 2, (a) is a tracking error characteristic obtained by the tracking control apparatus of the present invention, and (b) is a tracking error characteristic obtained by a conventional tracking control apparatus.

As shown in FIG. 2, the rotation speed at which the tracking error is less than or equal to the allowable value e _{0 is} less than the rotation speed N _{1 in} the conventional tracking control apparatus as shown in FIG. in the tracking control apparatus of the embodiment of, as shown in FIG. (b), is expanded to the rotational speed N _2. That is, according to each embodiment of the present invention, it can be understood that the tracking error can be reduced over the entire rotation speed of the optical disc.

[Second Embodiment]
FIG. 3 is a block diagram showing the configuration of the tracking control device by analog control according to the second embodiment of the present invention .

  As shown in FIG. 3, the second embodiment includes a delay unit 10 as the correction signal generation unit 5 and a compensation unit 11 as the pre-compensation unit 6. Others are the same as in the first embodiment.

The delay means 10 outputs a correction signal c ₁ obtained by delaying the tracking error signal e ₁ by a time corresponding to one rotation period of the optical disc. The compensating means 11 outputs a pre-compensation signal h ₁ obtained by performing amplitude and phase compensation on the correction signal c ₁ .

  Next, the operation of the second embodiment will be described with reference to FIGS. FIG. 4 is a flowchart of the basic operation of the tracking control device of the second embodiment.

First, the operation principle of the tracking control device of the second embodiment will be described with reference to FIG. The transfer function of the compensation means 11 is represented by P ₁ (s), and the transfer functions of the stabilization compensation means 2 and the tracking actuator 3 are represented by G ₁ (s) and G ₂ (s), respectively.

When the connection between the compensation unit 11 and the addition unit 7 is disconnected with respect to the feedback control system formed by the tracking error detection unit 1, the addition unit 7, the stabilization compensation unit 2 and the tracking actuator 3, the input to the addition unit 7 is performed. signal transmission light spot position _{s 1} function for _{h 1 G cl} (s) is found by the following equation (4).
[Equation 1]
G _cl (s) = G ₁ (s) G ₂ (s) / {1 + G ₁ (s) G ₂ (s)} (4)
Therefore, the precompensation means 6 has a transfer function P ₁ (s) of the compensation means 11 of [Equation 2].
P ₁ (s) = {1 + G ₁ (s) G ₂ (s)} / G ₁ (s) G ₂ (s) (5)
It is realized to satisfy. That is, the precompensation means 6 has a transfer function that is the inverse of the closed-loop transfer function of the output with respect to the input of the feedback control system.

Then, the compensation means 11 of the pre-compensation means 6 corrects the frequency characteristics of the amplitude and phase with respect to the correction signal c ₁ by the transfer function P ₁ (s) shown in Expression (5), Output and perform tracking control.

At this time, the light spot position _{s 1} with respect to the correction signal _{c 1} is the formula (4), the formula the following formula (5) (6).

In other words, the correction signal c ₁ can be corrected by directly controlling the light spot position s ₁ without causing an amplitude difference and a time delay.

Next, the basic operation of the tracking control apparatus of the second embodiment will be described along FIG. 4 with reference to FIG. 3 as appropriate. In the figure, the tracking error detection means 1 detects a tracking error signal e ₁ for the track on which the optical head is scanning, and then inputs this tracking error signal e ₁ to the delay means 10 in the correction signal generation means 5. (Step S1). The delay means 10 delays the tracking error signal e ₁ for a time corresponding to one rotation period of the optical disc, and outputs it as a correction signal c ₁ (step S2).

Then, the compensation means 11 in the pre-compensation means 6 generates a pre-compensation signal h ₁ from the correction signal c ₁ (step S3), and the adding means 7 scans this pre-compensation signal h ₁ with the optical head. is added to the tracking error signal e ₁ for the track is performed (step S4).

  Next, the stabilization compensator 2 drives the tracking actuator 3 with the added signal to perform tracking control (step S5). In order to continuously perform tracking control on the rotating optical disk, the process returns to step S1 again, and the above-described operation is repeated.

  As a result, it is possible to reduce the tracking error over the entire number of rotations of the optical disk.

[Third Embodiment]
FIG. 5 is a block diagram showing the configuration of a tracking control device by digital control according to the third embodiment of the present invention .

In FIG. 5, in the third embodiment, the adder 18 and the stabilization compensator 19 are each constituted by a digital signal processing circuit, and the tracking error signal e ₁ is converted into a digital signal e ₁ by an A / D converter (ADC) 15. (k) is converted and applied to one input of the adding means 18, and the output digital signal of the stabilization compensating means 19 is converted into an analog signal by the D / A converter (DAC) 20 and supplied to the tracking actuator 3. It is configured.

That is, in this tracking control device by digital control, the tracking error signal e ₁ is converted into the digital signal e ₁ (k), and then the processing as the tracking control device is executed.

As shown in FIG. 5, the tracking error signal e ₁ detected by the tracking error detecting means 1 is converted into a digital signal e ₁ (k) by an A / D converter (ADC) 15, and the correction signal generating means 5 And input to the adding means 18.

Here, the correction signal generation means 5 includes a storage means 16. The storage means 16 stores digital data e ₁ (k) of the tracking error signal e ₁ for a time corresponding to at least one rotation period of the optical disc. Then, the storage means 16 uses the tracking error signal e ₁ (k) one round before the optical disk, and corrects the tracking error signal at the time advanced by the time corresponding to the d sampling period at the sampling time k as the correction signal c _1. Output to the precompensation means 6 as (k + d).

The pre-compensation unit 6 includes a compensation unit 17 having a pulse transfer function P ₁ (z ⁻¹ ). The compensation unit 17 digitally processes the correction signal c ₁ (k + d) input from the storage unit 16 and outputs a pre-compensation signal h ₁ (k).

The adding means 18 adds the digitized tracking error signal e ₁ (k) and the pre-compensation signal h ₁ (k), and inputs the addition result to the stabilization compensating means 19. The output of the stability compensation means 19 is converted into an analog signal by a D / A converter (DAC) 20, and drives the tracking actuator 3 performs tracking control by changing the optical spot position s _1.

The stabilization compensator 19 compensates the frequency characteristics of the amplitude and phase so that the feedback control system of the tracking controller operates stably, and at the same time, a pulse transfer function G ₁ for realizing a desired response characteristic. It has (z ⁻¹ ). A system in which the D / A converter (DAC) 20 and the tracking actuator 3 are connected in cascade has a pulse transfer function G ₂ (z ⁻¹ ).

  Next, the basic operation of the third embodiment will be described with reference to FIGS. FIG. 6 is a circuit / motion model diagram of the moving coil type tracking actuator having the first resonance mode. FIG. 7 is a schematic view of the relationship between the correction signal data stored in the storage means and the sampling clock. FIG. 8 is a flowchart of the basic operation of the tracking control device of the third embodiment.

First, the operation principle of the tracking control apparatus according to the third embodiment will be described with reference to FIGS. In this digital control system, the pulse transfer function P ₁ (z ⁻¹ ) of the compensating means 17 is determined depending on whether the pulse transfer function of the tracking actuator 3 has an unstable zero point or not.

In any case, after obtaining the transfer function of the tracking actuator 3 in a continuous system, it is converted into a discrete system to obtain a closed-loop pulse transfer function in the digital control system. Further, the pulse transfer function P ₁ (z ⁻¹ ) of the compensation means 17 is determined based on the closed-loop pulse transfer function.

となる。また、推力定数をＫ_ｉとおけば、駆動力ｆ(ｔ)は、
ｆ(t)＝Ｋ_ｉi(t) ・・・ （９）
となる。 A general moving coil type tracking actuator used for an optical head has a first resonance mode as described in, for example, Reference 2 “Radio Technology, Radio Technology Selection“ Optical Disc Technology ”, page 134”. It is represented by the model shown in FIG. FIG. 6A shows a circuit model of the tracking actuator, where v is a drive voltage, i is a drive current, R is a resistance component, and L is a reactance component. FIG. 6B is a motion model, and K _T , D _T , m _T , f (t), and x (t) represent an elastic coefficient, a viscosity coefficient, a mass of the movable part 70, a driving force, and a position, respectively. . 6 (a) and 6 (b), the drive voltage v (t) and the drive force f (t) are

It becomes. If the thrust constant is K _i , the driving force f (t) is
f (t) = K _i i (t) (9)
It becomes.

となる。また、トラッキングアクチュエータ３を電圧で駆動した場合の伝達関数Ｇ_２ｖ(ｓ)は、式（７）、式（８）、式（９）を用いて

となる。即ち、連続系におけるトラッキングアクチュエータ３のモデルは、電流駆動では２次、電圧駆動では３次の低域フィルタ型になる。 The transfer function G _2i (s) when the tracking actuator 3 is driven with current by performing Laplace transform with the initial value set to 0 using the equations (8) and (9) is:

It becomes. Further, the transfer function G _2v (s) when the tracking actuator 3 is driven with a voltage is obtained by using the equations (7), (8), and (9).

It becomes. That is, the model of the tracking actuator 3 in the continuous system is a secondary low-pass filter type for current driving and a tertiary for voltage driving.

Next, considering that the D / A converter (DAC) 20 that outputs a signal for driving the tracking actuator 3 functions as a zero-order holder, the transfer function in the continuous system is changed to the pulse transfer function of the digital control system. When converted to G ₂ (z ⁻¹ ), for example, as shown in Reference 3 “Corona“ Basic Digital Control ”, page 59, Table 3.5”, an unstable zero occurs depending on the difference between the denominator and the numerator. It is known. Here, z = exp (jωT _s ). However, _{T s} is the sampling period.

Table 1 shows Table 3.5 of Document 3. In Table 3.5 of Document 3, k = 2 when the tracking actuator 3 is driven with current. When driven by voltage, the value of k increases by one and becomes k = 3 due to an excessive phenomenon that changes from voltage to current. In either case, one or more unstable zeros are generated. On the other hand, the pulse transfer function G ₁ (z ⁻¹ ) of the stabilization compensator 19 of FIG. 5 is designed so as not to have an unstable zero point or an unstable pole. Here, k in Table 1 is a numerical value obtained by subtracting the order of the numerator from the order of the denominator of the transfer function of the continuous system, and is different from k representing the sampling time.

によって表される。なお、式（１２）において、Ａ_ｃ(ｚ^−１)、Ｂ_ｃ(ｚ^−１)は、いずれもｚ^−１の多項式である。また、ｚ^−ｄは、ｄ・Ｔ_ｓ、即ちｄサンプリング周期分の時刻の遅れに相当する。 The closed-loop pulse transfer function G _cl (z ⁻¹ ) of the light spot position s _{1 with} respect to the precompensation signal h ₁ (k) is

Represented by In Expression (12), A _c (z ⁻¹ ) and B _c (z ⁻¹ ) are both polynomials of z ⁻¹ . Z− ^d corresponds to d · T _s , that is, a time delay of d sampling periods.

Therefore, the pulse transfer function P ₁ (z ⁻¹ ) of the compensation means 17 is determined by the following procedure based on the equation (12). First, using a closed-loop pulse transfer function G _cl (z ⁻¹ ), P ₁ ′ (z ⁻¹ ) and P ₁ (z ⁻¹ ) are respectively defined as Equation (13) and Equation (14).

Here, in the equation (13), numerator z ^d indicates that the output is advanced by d sampling periods with respect to the input. Therefore, the input of P ₁ (z ⁻¹ ) uses the correction signal c ₁ (k + d) at the time advanced by d sampling periods. This will be described with reference to FIG. In FIG. 7, for example, it is assumed that sampling is controlled n times for one round of the optical disk. The signal stored at the time corresponding to the sampling clock (k + d) of the (m−1) th cycle is used at the time corresponding to the sampling clock k of the mth cycle. Similar processing is performed at other times.

となり、補正信号ｃ_１（ｋ）に対して光スポット位置ｓ_１は、振幅差及び時間遅れを生じることなく追従する。 Since adjacent tracks have a large positional correlation, a correction signal c ₁ (k + d) at a time equivalently advanced by d sampling periods can be obtained by this method. According to Expression (12) and Expression (14), the light spot position s _{1 with} respect to the correction signal c ₁ (k + d) is

Thus, the light spot position s ₁ follows the correction signal c ₁ (k) without causing an amplitude difference and a time delay.

(A) As described above, when the tracking actuator does not have an unstable zero point in the digital control system, a stable control system is realized by determining the pulse transfer function P ₁ (z ⁻¹ ) according to the equation (14). it can. That is, as the pulse transfer function P ₁ (z ⁻¹ ), a pulse transfer function derived from the inverse of the closed-loop pulse transfer function G _cl (z ⁻¹ ) of the output with respect to the input of the feedback control system is employed.

However, in the tracking control device using the moving coil type tracking actuator as described above, the closed-loop pulse transfer function G _cl (z ⁻¹ ) has an unstable zero point, and therefore the direct expression (14) from the expression (12). ) Is used to determine the pulse transfer function P ₁ (z ⁻¹ ), the pulse transfer function P ₁ (z ⁻¹ ) has an unstable pole and cannot constitute a stable control system.

(B) Therefore, when the pulse transfer function of the tracking actuator 3 has an unstable zero, the pulse transfer function P ₁ (z ⁻¹ ) in the digital control system is determined as follows.

In the pulse transfer function G _cl (z ⁻¹ ) of the equation (12), the zero point is divided into a stable zero point and an unstable zero point and is described as the following equation (16). In Equation (16), B _c ⁺ (Z ⁻¹ ) is a stable zero, and B _c ⁻ (Z ⁻¹ ) is a z ⁻¹ polynomial including an unstable zero.

Then, using this equation (16), the pulse transfer function P ₁ (z ⁻¹ ) is determined by the first and second methods described below to constitute a stable control system.

と定める。 In the first method, only the stable zero of the pulse transfer function Gcl (z ⁻¹ ) is canceled by the pole of the pulse transfer function P1 (z ⁻¹ ). In addition, z ⁻¹ = 1 is substituted into Bc ⁻ (z ⁻¹ ) including an unstable zero point to obtain a constant. That is, P1 ′ (z ⁻¹ ) and P1 (z ⁻¹ ) are respectively

It is determined.

By making the pulse transfer function P ₁ (z ⁻¹ ) of the compensating means 17 into the form of the equation (18), only the stable zero of the pulse transfer function G _cl (z ⁻¹ ) is _converted to the pulse transfer function P ₁ (z ^{− 1} ), and a stable control system is configured in response to the light spot position s _{1 with} respect to the correction signal c ₁ (k + d).

となり、低周波領域において光スポット位置ｓ_１は補正信号ｃ_１(ｋ)に時間遅れを生じることなく追従する。また、トラッキング制御装置の安定性も保たれる。 That is, in the first method, the response of the light spot position s ₁ to the correction signal c ₁ (k + d) is expressed by the following equations (12), (16), and (18):

Thus, the light spot position s ₁ follows the correction signal c ₁ (k) without causing a time delay in the low frequency region. In addition, the stability of the tracking control device is maintained.

Next, in the second method, the pulse transfer functions P ₁ ′ (z ⁻¹ ) and P ₁ (z ⁻¹ ) are determined as shown in the following equations (20) and (21), respectively. In Expressions (20) and (21), B _c ⁻ (Z) is obtained by replacing z ⁻¹ with z in the polynomial B _c ⁻ (Z ⁻¹ ).

となる。 In the second method, the response of the light spot position s _{1 to} the correction signal c ₁ (k + d) according to the equations (12), (16), and (21) is

It becomes.

Here, since B _c ⁻ (Z) and B _c ⁻ (Z ⁻¹ ) are complex conjugates, the light spot position s ₁ is time-delayed at all frequencies with respect to the correction signal c ₁ (k). Follow up without producing. In addition, the stability of the tracking control device is maintained.

Next, the operation will be described in detail with reference to FIG. In the figure, a tracking error detection means 1 detects a tracking error signal e ₁ for a track on which an optical head is scanning. The tracking error signal e ₁ is converted into a digital signal e ₁ (k) by an A / D converter (ADC) 15 and then input to the correction signal generating unit 5 and the adding unit 18.

Correction signal generating means 5, for example, used in a predetermined store area of the memory means 16 using the memory stores the tracking error signal e ₁ (k) of one by one, before one rotation of the optical disc tracking error signal e ₁ (k) of Then, a tracking error signal at a time advanced by a time corresponding to d · Ts at time k is calculated (step S11) and stored as a correction signal c ₁ (k + d) in another storage area of the storage means 16. (Step S12).

Then, the correction signal generation means 5 determines whether or not there is a correction signal c ₁ (k + d) stored before one rotation of the optical disc (step S13), and if not, sets the correction signal = 0 (step S14) and stores it. If there is the corrected signal c ₁ (k + d), it is read (step S15) and given to the pre-compensation means 6 to output the pre-compensation signal h ₁ (k) (step 16).

Here, the compensation means 17 constituting the pre-compensation means 6 is configured to have the pulse transfer function P ₁ (z ⁻¹ ) determined by the first and second methods. That is, when the pulse transfer function G ₂ (z ⁻¹ ) obtained by the zero-order hold function of the D / A converter (DAC) 20 and the transfer function of the tracking actuator 3 does not have an unstable zero point, the compensation means 17 The pulse transfer function P ₁ (z ⁻¹ ) is configured as shown in Equation (14). Further, when the pulse transfer function G ₂ (z ⁻¹ ) has an unstable zero, the compensation means 17 causes the pulse transfer function P ₁ (z ⁻¹ ) to be expressed by the equation (18) or the equation (21). Configured.

Next, the adding means 18 adds the pre-compensation signal h ₁ (k) obtained from the output of the compensating means 17 and the tracking error signal e ₁ (k), and outputs the result to the stabilization compensating means 19 (step 17). .

The stabilization compensation means 19 has a pulse transfer function G ₁ (z ⁻¹ ) for stabilizing the feedback control system and realizing a desired response characteristic. The output of the stability compensation means 19 controls the light spot position s ₁ by driving the tracking actuator is converted into an analog signal by a D / A converter (DAC) 20 (step 18).

  In order to continuously perform the tracking control on the rotating optical disk, the process returns to step S11 and the above operation is repeated. As a result, it is possible to reduce the tracking error over the entire number of rotations of the optical disk.

[Fourth Embodiment]
FIG. 9 is a block diagram showing the configuration of a tracking control apparatus based on digital control according to the fourth embodiment of the present invention .

In the tracking control apparatus by digital control of the fourth embodiment, in the third embodiment, the correction signal generation means 5 is ^replaced with the first calculation means 25 having the pulse transfer function Q ₁ (z ⁻¹ ), the pulse transfer function. The second calculating means 26 having Q ₂ (z ⁻¹ ), the adding means 27 and the storage means 16 are configured, and the precompensation means 6 is a compensating means 29 having a pulse transfer function P ₁ (z ⁻¹ ), a delay. The delay means 30 and the subtraction means 31 having the quantity z- ^d are used.

In the correction signal generation means 5, the first calculation means 25 receives the tracking error signal e ₁ (k) output from the A / D converter (ADC) 15, and the second calculation means 26 receives the previous calculation signal 26. The position compensation signal h ₁ (k) is input. The adding means 27 receives the outputs of the two calculating means 25 and 26 and outputs the virtual track position to the storage means 16. The storage unit 16 outputs the correction signal c ₁ (k + d) to the pre-compensation unit 6.

In the precompensation means 6, the correction signal c ₁ (k + d) is input to the compensation means 29 and the delay means 30, and the outputs of the compensation means 29 and delay means 30 are input to the subtraction means 31, A compensation signal h ₁ (k) is output.

In short, in the fourth embodiment, the tracking error signal e ₁ (k) after A / D conversion and the output h ₁ (k) of the pre-compensation unit 6 are input to the correction signal generation unit 5 to input the correction signal c _1. (k + d) is generated and input to the pre-compensation means 6 to obtain a pre-compensation signal h ₁ (k). The adding means 18 adds the pre-compensation signal h ₁ (k) to the tracking error signal e ₁ (k) and inputs it to the stabilization compensating means 19. The D / A converter (DAC) 20 converts the output of the stabilization compensator 19 into an analog signal and drives the tracking actuator 3.

Next, the basic operation of the fourth embodiment will be described with reference to FIG. In the fourth embodiment, the pulse transfer function P ₁ (z ⁻¹ ) in the digital control system in the case where the pulse transfer function of the tracking actuator 3 described in the third embodiment has an unstable zero point or not. Another example (third method) for realizing the above is realized.

The tracking error signal e ₁ (k) digitized by the A / D converter (ADC) 15 is input to the first calculating means 25 and the adding means 18. Further, the pre-compensation signal h ₁ (k) is input to the second calculating means 26.

The first computing means 25 obtains the output of the pulse transfer function Q ₁ (z ⁻¹ ) expressed by the following equation (23) with respect to the input tracking error signal e ₁ (k), and obtains this result. This is given to one input of the adding means 27.
[Equation 18]
Q ₁ (z ⁻¹ ) = 1 + G ₁ (z ⁻¹ ) G ₂ (z ⁻¹ ) (23)
The second computing means 26 obtains the output of the pulse transfer function Q ₂ (z ⁻¹ ) represented by the following equation (24) with respect to the input precompensation signal h ₁ (k), This result is given to the other input of the adding means 27.
[Equation 19]
Q ₂ (z ⁻¹ ) = G ₁ (z ⁻¹ ) G ₂ (z ⁻¹ ) (24)
The adding means 27 adds the outputs of the first and second calculating means 25 and 26, and

記憶し、光ディスクの1周前に記憶された信号を用いて、時刻ｋにおいてｄ・Ｔ_ｓ進んだ時刻に相当する信号を補正信号ｃ_１(ｋ＋ｄ)として補償手段２９及び遅延手段３０に出力する。

The signal corresponding to the time advanced by d · T _s at time k is output to the compensation means 29 and the delay means 30 as the correction signal c ₁ (k + d) using the signal stored and stored one round before the optical disk. .

Specifically, as shown in FIG. 7, the storage means 16 is stored at the time corresponding to the sampling clock k + d in the (m−1) th cycle at the time corresponding to the sampling clock k in the mth cycle. The corrected signal is output as the correction signal c ₁ (k + d).

For this correction signal c ₁ (k + d), the compensation means 29 calculates the pulse transfer function P ₁ (z ⁻¹ ) expressed by any one of the equations (14), (18), or (21). On the other hand, the delay means 30 performs a time delay for d sampling periods corresponding to d · T _s . The subtracting means 31 subtracts the output of the delay means 30 from the output of the compensating means 29 to generate a precompensation signal h ₁ (k) represented by the following equation (26). It outputs to the calculating means 26.
[Formula 21]
h ₁ (k) = P ₁ (z ⁻¹ ) c ₁ (k + d) −z ^−d c ₁ (k + d) (26)
The adding means 18 adds the pre-compensation signal h ₁ (k) and the tracking error signal e ₁ (k) and outputs the result to the stabilization compensating means 19. The output of the stability compensation means 19 drives the tracking actuator evening 3 via the D / A converter (DAC) 20, and controls the light spot position s _1.

  As a result, the tracking error can be reduced over the entire number of rotations of the optical disk, as in the above embodiments.

[Fifth Embodiment]
FIG. 10 is a block diagram of the storage means used in the tracking control device by digital control according to the fifth embodiment of the present invention .

  In FIG. 10, only parts related to the storage means 16 in the tracking control apparatus shown in FIG. 5 or 9 are taken out for easy explanation. Other parts are the same as those in FIG. 5 or FIG.

As shown in FIG. 10, in the fifth embodiment, the storage means 16 in the second to fourth embodiments is constituted by n memory elements 40, an adding means 41, and a multiplying means 39. The memory element 40 is composed of, for example, a plurality of D-flip flops corresponding to the number of bits of data to be operated. The memory element 40 takes in the output data of the preceding memory element connected in cascade for each sampling clock and one clock before The value stored in is output to the subsequent memory element connected in cascade. The output of the nth memory element 40 is input to the multiplication means 39. Multiplication means 39 multiplies the input data by an appropriate coefficient that satisfies | w | <1 and includes w = 0. The output of the multiplication means 39 is connected to the addition means 41, and the signal added with the input signal is input to the first memory element. The correction signal c ₁ (k + d) is extracted from the output of the (n−d) th memory element 40.

  According to the fifth embodiment, since the storage unit 16 can have a learning effect, the tracking error can be further reduced.

[Sixth Embodiment]
FIG. 11 is a block diagram of the storage means used in the tracking control apparatus by digital control according to the sixth embodiment of the present invention .

  In FIG. 11, only parts related to the storage means 16 in the tracking control apparatus shown in FIG. 5 or 9 are taken out for easy explanation. Other parts are the same as those in FIG. 5 or FIG.

  As shown in FIG. 11, in the sixth embodiment, the storage means 16 in the second to fourth embodiments is replaced with an arithmetic element 43 such as a high-speed CPU or a digital signal processor (DSP) and the arithmetic element 43. And a memory 46 connected via a data bus 44 and an address bus 45.

The arithmetic element 43 takes the input signal in time series in synchronization with the clock of the tracking control device and stores it in the memory 46, and after correcting the stored input signal for one rotation of the optical disk, the correction is performed. The signal c ₁ (k + d) is output.

Alternatively, the arithmetic element 43 takes in the input signal in time series in synchronization with the clock of the tracking control device and stores it in the memory 46. For the stored input signal, for example, moving average processing, least square method, etc. After the statistical signal processing is performed, the correction signal c ₁ (k + d) is output.

  According to the sixth embodiment, even when there is a period in which a tracking error signal cannot be obtained due to scratches or dust on the optical disk, the possibility of occurrence of tracking failure can be reduced.

  The data stored in the memory 46 may be an input signal corresponding to one rotation of the optical disc or an input signal obtained by a plurality of rotations of the optical disc.

[Seventh Embodiment]
FIG. 12 is a block diagram of the storage means used in the tracking control device by digital control according to the seventh embodiment of the present invention . Note that the seventh embodiment, CLV method, ZCLV scheme, CAV method, shows the principle configuration of the tracking controller corresponding to the ZCAV system, specifically, for example 8, as in each of Embodiments 9 Composed.

  In FIG. 12, only parts related to the storage means 16 in the tracking control apparatus shown in FIG. 5 or 9 are taken out for easy explanation. Other parts are the same as those in FIG. 5 or FIG.

  As shown in FIG. 12, in the storage means 16 of the seventh embodiment, optical head position information and optical disk rotation angle information in the radial direction of the optical disk are input in addition to the input signal and the tracking control device clock.

  Next, the basic operation of the tracking control device of the seventh embodiment will be described. First, the correction signal calculated using the tracking error signal for the track being scanned is stored as an input signal in the storage unit 16 together with the optical head position information and the optical disk rotation angle information in synchronization with the clock of the tracking control device. The optical head position information is used to know the radial position of the track on which the optical head is scanning on the optical disk.

  Next, the correction signal corresponding to the current optical head position and the rotation angle of the optical disk among the correction signals stored in the storage means 16 at the time before at least one rotation of the optical disk is read as an output signal.

  This correction signal is input to the pre-compensation means 6 to output a pre-compensation signal, the pre-compensation signal is added to the tracking error signal for the track being scanned, and tracking control is performed using the signal after the addition.

[Eighth Embodiment]
FIG. 13 is a block diagram of the storage means used in the tracking control device by digital control according to the eighth embodiment of the present invention . Note that the eighth embodiment, shown CLV method, ZCLV scheme, CAV method, a specific configuration of the corresponding tracking control apparatus ZCAV system.

  In FIG. 13, only parts related to the storage means 16 in the tracking control apparatus shown in FIG. Other parts are the same as those in FIG. 5 or FIG.

  As shown in FIG. 13, in the eighth embodiment, the storage means 16 in the second to fourth embodiments is replaced with an arithmetic element 47 such as a high-speed CPU or a digital signal processor (DSP) and the arithmetic element 47. And a memory 48 connected via a data bus 44 and an address bus 45.

  As shown in FIG. 13, the arithmetic element 47 in the storage means 16 of the eighth embodiment inputs optical head position information and optical disk rotation angle information in the radial direction of the optical disk in addition to the input signal and the tracking control device clock. Is done.

  Next, the operation of the tracking control apparatus of the eighth embodiment will be described with reference to FIGS. FIG. 14 is a flowchart of the basic operation of the tracking control apparatus of the eighth embodiment.

  In the figure, the tracking error signal for the track on which the optical head is scanning is input as an input signal to the arithmetic element 47, and optical head position information and optical disk rotation angle information in the radial direction of the optical disk are input.

  The arithmetic element 47 detects a tracking error signal for the track on which the optical head is scanning, calculates a correction signal using this signal (step S31), and uses the correction signal as optical head position information and optical disk rotation angle information. At the same time, it is stored in the memory 48 (step S32). The optical head position information is used to know which position on the radius of the track on which the optical head is scanning is on the optical disk.

  Specifically, the arithmetic element 47 uniquely determines the memory address using the optical head position information and the optical disk rotation angle information, and takes the input signal in time series in synchronization with the clock of the tracking control device. Is stored in the memory 48, and the stored input signal is delayed by one rotation of the optical disk and stored in the memory 48 together with the optical head position information and the optical disk rotation information.

  Alternatively, the arithmetic element 47 uniquely determines a memory address using the optical head position information and the optical disk rotation angle information, and takes in the input signal in time series in synchronization with the clock of the tracking control device to the memory 48. The stored input signal is subjected to statistical signal processing such as moving average processing and least square method, and stored in the memory 48 together with optical head position information and optical disk rotation information.

Next, the computing element 47 determines whether or not a correction signal corresponding to the current optical head position information and optical disk rotation angle information is stored in the memory 48 (step S33), and if not stored, the correction signal = 0. (Step S34) If it is stored, the correction signal c ₁ (k + d) corresponding to the current optical head position and the optical disk rotation angle is read from the memory 48 (Step S35).

At this time, in step 35, when the optical head position information and optical disk rotation angle information of the correction signal to be read does not match the optical head position information and optical disk rotation angle information of the stored correction signal, the closest optical head position is determined. After performing an interpolation process using a correction signal having information and optical disk rotation angle information, it is output as a correction signal c ₁ (k + d).

Then, the correction signal c ₁ (k + d) is input to the pre-compensation unit and the pre-compensation signal is output to the addition unit (step S36), and the pre-compensation signal is tracked for the track on which the optical head is scanning. The error signal is added (step S37).

  Next, tracking control is performed using the added signal (step S38). In order to perform tracking control continuously on the rotating optical disk, the process returns to step S31 again, and the above-described operation is repeated.

  The data stored in the memory 48 may be an input signal corresponding to one rotation of the optical disc or an input signal obtained by a plurality of rotations of the optical disc.

  Next, FIG. 15 is a diagram for explaining a method for detecting optical head position information and optical disk rotation angle information. In FIG. 15, a light spot 54 emitted from an optical head 53 scans an optical disk 50 attached to a spindle motor 51 and rotating. The optical head 53 is attached to an optical head moving mechanism 55 such as a linear motor, and moves in the radial direction of the optical disc 50.

  For example, in an optical disk recording apparatus using a DVD-RAM, a header recorded in advance on the optical disk 50 is optically read and an address signal is generated by the address decoding means 57. The clock reproducing means 58 optically reads the meandering signal of the groove formed on the optical disc 50 and reproduces the clock signal using, for example, a PLL circuit.

  By using the address signal obtained in this way, the position of the track scanned by the optical head 53 on the optical disk 50 can be known, and this is converted into optical head position information using the optical head position information detecting means 59. Output. Further, the optical disk rotation angle detection means 60 measures the clock signal using the address signal as the rotation angle origin signal and outputs optical disk rotation angle information.

  In addition to these means, the optical head position information can also be obtained by position detecting means 56 such as a linear encoder attached to the optical head moving mechanism 55, for example.

The optical disk rotation angle information can also be obtained by a rotation angle detection means 52 such as a rotary encoder attached to the spindle motor 51, for example. The optical head position information and the optical disc rotation angle information used in the seventh and eighth embodiments may be obtained using any of the above-described means.

  According to the eighth embodiment, since the optical head position information and the optical head rotational speed information are used, the tracking is performed in a recording / reproducing apparatus using the CLV method in which the period of one rotation changes according to the radius of the optical disk or the ZCLV method. Error can be reduced.

[Ninth Embodiment ]
FIG. 16 is a conceptual diagram of an optical disk used in a tracking control apparatus by digital control according to the ninth embodiment of the present invention . Incidentally, the ninth embodiment, shown CLV method, ZCLV scheme, CAV method, a specific configuration of the corresponding tracking control apparatus ZCAV system.

  In the ninth embodiment, the optical head position information is classified into a plurality of ranges according to the numerical values in the eighth embodiment, and one type of correction signal c1 (k + d) is used within the same range.

As shown in FIG. 16, the optical disk 50 of the ninth embodiment is divided into n regions by a radius from the center. The radius r from the center is
[Equation 22]
r _j ≦ r ≦ r _{j + 1} (j = 1, 2,..., n) (27)
Represented by

In the optical disc 50, the adjacent tracks are similar in the tendency of eccentricity and track meandering. Therefore, in each region represented by this equation by dividing the area (27), by using only the optical disc 1 round of the correction signal c _{1 (k} + d), data of the correction signal c _{1 (k} + d) The memory capacity for storing the evening can be reduced.

  In each of the eighth and ninth embodiments, the method for uniquely determining the memory address using the optical head position information and the optical disk rotation angle information is the same as the method for determining the address using these two pieces of information. A conversion table for assigning a corresponding memory address using two pieces of information is stored in the memory 48 in advance, and the same operation can be obtained by using this conversion table.

  In each of the first to ninth embodiments, a method for detecting a tracking error may be a generally used three-beam method, push-pull method, heterodyne method, or phase difference detection method. Furthermore, a detection method using reflected light of a pit formed in advance on an optical disc, a detection method using diffracted light from a groove, and a detection method using a tracking error detection signal recorded in advance. Either may be used.

  Further, in the third embodiment (FIG. 5) and the fourth embodiment (FIG. 9), the correction signal generation means 5, the pre-compensation means 6, the addition means 18 and the stabilization compensation means 19 are each made into individual blocks. Although shown, it goes without saying that these can be realized by a combination of an arithmetic unit such as a high-speed CPU or a digital signal processor and a memory.

  Further, the output of the stabilization compensator 19 is converted into an analog signal by the D / A converter (DAC) 20 and the tracking actuator 3 is driven. The output of the stabilization compensator 19 is converted to a pulse width modulation means (PWM). ), And the tracking actuator 3 is driven by the output pulse, the same operation can be realized.

  In addition, the stabilization compensator 2 or the stabilization compensator 19 used in each of the first to ninth embodiments can use a robust stabilization compensator as well as a generally used phase lead / lag compensation. Of course, a type compensator, a PI type compensator, or a PID type compensator may be used.

  Furthermore, the tracking actuator 3 used in each of the first to ninth embodiments is, for example, a second order, a third order, etc. in addition to the moving coil type actuator having the first order resonance mode shown in FIG. Of course, a moving coil type actuator having a higher-order resonance mode can also be used. In addition to the moving coil type, for example, a piezoelectric type, a linear motor type, a swing arm type, or a composite type that combines a plurality of these may be used. It goes without saying that the present invention can be similarly applied to a tracking control apparatus using any of these types of tracking actuators.

  The above embodiments can be applied not only to the optical disk recording apparatus but also to the tracking control system of the optical disk reproducing apparatus, the optical disk recording / reproducing apparatus, and the optical tape recording apparatus. Further, the present invention can be applied to the focus control device with the same configuration.

In that case, instead of the tracking error detection means and the tracking actuator, a focus error detection means and a focus actuator are used, respectively.

1 is a block diagram of the principle configuration of a tracking control device as a feedback control device according to a first embodiment of the present invention. It is a comparison figure of the tracking error characteristic of a tracking control device to the number of rotations of an optical disc. It is a block diagram of the configuration of the tracking control device by analog control according to the second embodiment of the present invention. It is a flowchart of the basic operation | movement of the tracking control apparatus of the 2nd Embodiment of this invention. It is a block diagram of the configuration of a tracking control device based on digital control according to a third embodiment of the present invention. It is a figure which shows the circuit model / motion model of the moving coil type tracking actuator which has a 1st resonance mode. It is a schematic diagram of the relationship between the correction signal data stored in the storage means and the sampling clock. It is a basic operation | movement flowchart of the tracking control apparatus of the 3rd Embodiment of this invention. It is a block diagram of the configuration of a tracking control device by digital control according to a fourth embodiment of the present invention. It is a block diagram of the memory | storage means used with the tracking control apparatus by the digital control which concerns on the 5th Embodiment of this invention. It is a block diagram of the memory | storage means used with the tracking control apparatus by the digital control which concerns on the 6th Embodiment of this invention. It is a block diagram of the memory | storage means used with the tracking control apparatus by the digital control which concerns on the 7th Embodiment of this invention. It is a block diagram of the memory | storage means used with the tracking control apparatus by the digital control which concerns on the 8th Embodiment of this invention. It is a basic operation flowchart of a tracking control device of an 8th embodiment of the present invention. It is a figure explaining the method to detect optical head position information and optical disk rotation angle information. It is a conceptual diagram of the optical disk used with the tracking control apparatus by the digital control which concerns on the 9th Embodiment of this invention. It is a configuration block diagram of a conventional tracking control device that is generally used. It is a block diagram of the configuration of a conventional tracking control device that improves tracking performance by repeated tracking control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tracking error detection means 2 Stabilization compensation means 3 Tracking actuator construction 5 Correction signal generation means 6 Precompensation means 7 Addition means 10 Delay means 11 Compensation means 15 A / D converter (ADC)
16 Storage means 17 Compensation means 18 Addition means 19 Stabilization compensation means 20 D / A converter (DAC)
25 first computing means 26 second computing means 27 adding means 29 compensating means 30 delay means 31 subtracting means 39 multiplying means 40 memory element 41 adding means 43 computing element 44 data bus 45 address bus 46 memory 47 computing element 48 memory 50 Optical disk 51 Spindle motor 52 Rotation angle detection means 53 Optical head 54 Light spot 55 Optical head moving mechanism 56 Position detection means 57 Address decoding means 58 Clock reproduction means 59 Optical head position information detection means 60 Optical disk rotation angle detection means 70 Movable part 72 Delay means

Claims (4)

Tracking error signal generating means for generating a tracking error signal corresponding to the difference between the track position on the optical disc and the position of the light spot emitted from the optical head;
The tracking error signal and the pre-compensation signal are input, and calculation is performed using the first pulse transfer function and the second pulse transfer function, respectively, and then added to generate a correction signal that is a virtual track position. Correction signal generation means for storing ;
A precompensation signal is generated by subtracting a signal obtained by delaying the output of the correction signal generation means from a signal obtained by compensating the amplitude and phase of the output of the correction signal generation means with a third pulse transfer function; Feedback to the correction signal generating means input and precompensation means for outputting to the adding means ;
Adding means for generating a drive signal obtained by adding the tracking error signal and the pre-compensation signal;
Control means for causing the light spot to scan a target track on the optical disk based on the generated drive signal, and
When the pulse transfer function of the control means is G ₁ (z ⁻¹ ) G ₂ (z ⁻¹ ) , the correction signal generation means has the first pulse transfer function of 1 + G ₁ (z ⁻¹ ) G _2. (Z ⁻¹ ), and the second pulse transfer function is G ₁ (z ⁻¹ ) G ₂ (z ⁻¹ ),
The pre-compensation unit includes the tracking error signal generation unit, the correction signal generation unit, the pre-compensation unit, the addition unit, and the control unit. When the transfer function of the output of the light spot position with respect to the input from the pre-compensation means side to the adding means when the connection between them is disconnected is Gcl (z ⁻¹ ), the third pulse transfer function is P ₁ (z ⁻¹ ) represented by the following formula (18) ,
P ₁ (z ⁻¹ ) = Ac (z ⁻¹ ) / {Bc ⁺ (z ⁻¹ ) Bc ⁻ (1)} (18)
Here, Gcl (z ⁻¹ ) = z ^−d Bc ⁺ (z ⁻¹ ) Bc ⁻ (z ⁻¹ ) / Ac (z ⁻¹ )
Ac (z ⁻¹ ): term of the pole of Gcl (z ⁻¹ )
Bc ⁺ (z ⁻¹ ): A stable zero term of Gcl (z ⁻¹ )
Bc ⁻ (z ⁻¹ ): term of unstable zero of Gcl (z ⁻¹ )
Bc ⁻ (1): The unstable zero of Gcl (z ⁻¹ ) is made constant as z ⁻¹ = 1.
thing,
d: Equivalent lead sampling number
The calculation result of the third pulse transfer function is calculated by a delay unit and a subtraction unit for converting the compensation amount for the light spot position into the compensation amount for the tracking error signal using the correction signal which is the virtual track position. To have a pulse transfer function of P ₁ (z ⁻¹ ) −z ^−d ,
When the response of the light spot position is obtained from the correction signal by multiplication of Gcl (z ⁻¹ ) · P ₁ (z ⁻¹ ), the pulse transfer function P ₁ (z ⁻¹ ) becomes Gcl (z ⁻¹ ). And the DC gain of the pre-compensation means are made to match the reciprocal of the DC gain of Gcl (z ⁻¹ ).
A tracking control device characterized by that. Tracking error signal generating means for generating a tracking error signal corresponding to the difference between the track position on the optical disc and the position of the light spot emitted from the optical head;
The tracking error signal and the pre-compensation signal are input, and calculation is performed using the first pulse transfer function and the second pulse transfer function, respectively, and then added to generate a correction signal that is a virtual track position. Correction signal generation means for storing;
A precompensation signal is generated by subtracting a signal obtained by delaying the output of the correction signal generation means from a signal obtained by compensating the amplitude and phase of the output of the correction signal generation means with a third pulse transfer function; Feedback to the correction signal generating means input and precompensation means for outputting to the adding means;
Adding means for generating a drive signal obtained by adding the tracking error signal and the pre-compensation signal;
Control means for causing the light spot to scan a target track on the optical disk based on the generated drive signal, and
When the pulse transfer function of the control means is G ₁ (z ⁻¹ ) G ₂ (z ⁻¹ ) , the correction signal generation means has the first pulse transfer function of 1 + G ₁ (z ⁻¹ ) G _2. (Z ^-1 ), and the second pulse transfer function is G ₁ (z ^-1 ) G ₂ (z ^-1 ),
The pre-compensation unit includes the tracking error signal generation unit, the correction signal generation unit, the pre-compensation unit, the addition unit, and the control unit. When the transfer function of the output of the light spot position with respect to the input from the pre-compensation means side to the adding means when the connection between them is disconnected is Gcl (z ⁻¹ ), the third pulse transfer function is P ₁ (z ⁻¹ ) represented by the following formula (21) ,
^{_{P 1 (z -1) = Ac}} (z -1) Bc - (z) / [Bc + (z -1) {Bc - (1)} 2] ... (21)
Here, Gcl (z ⁻¹ ) = z ^−d Bc ⁺ (z ⁻¹ ) Bc ⁻ (z ⁻¹ ) / Ac (z ⁻¹ )
Ac (z ⁻¹ ): term of the pole of Gcl (z ⁻¹ )
Bc ⁺ (z ⁻¹ ): A stable zero term of Gcl (z ⁻¹ )
Bc ⁻ (z ⁻¹ ): term of unstable zero of Gcl (z ⁻¹ )
Bc ⁻ (1): The unstable zero of Gcl (z ⁻¹ ) is made constant as z ⁻¹ = 1.
thing,
d: Equivalent lead sampling number
The calculation result of the third pulse transfer function is calculated by a delay unit and a subtraction unit for converting the compensation amount for the light spot position into the compensation amount for the tracking error signal using the correction signal which is the virtual track position. To have a pulse transfer function of P ₁ (z ⁻¹ ) −z ^−d ,
When the response of the light spot position is obtained by multiplying the correction signal by Gcl (z ⁻¹ ) · P ₁ (z ⁻¹ ), the pulse transfer function P ₁ (z ⁻¹ ) is Gcl (z ⁻¹ ) The pole and the stable zero are canceled out, and the product of the pulse transfer function Gcl (z ⁻¹ ) makes the phase difference zero at all frequencies, and the DC gain of the pre-compensation means is Gcl (z ⁻¹ ) Match the reciprocal of the DC gain,
A tracking control device characterized by that. Tracking error signal generating means for generating a tracking error signal corresponding to the difference between the track position on the optical disc and the position of the light spot emitted from the optical head;
The tracking error signal is stored in the storage means for a time corresponding to at least one rotation period of the optical disk, and a correction signal is output by calculating the tracking error signal one rotation period before from the stored signal. Correction signal generating means for performing,
Pre-compensation means for generating a pre-compensation signal in which the amplitude and phase of the generated correction signal are compensated with a predetermined pulse transfer function;
Adding means for generating a drive signal obtained by adding the tracking error signal and the pre-compensation signal;
Control means for causing the light spot to scan a target track on the optical disk based on the generated drive signal, and
The pre-compensation means uses the tracking error signal generation means, correction signal generation means, pre-compensation means, addition means, and control means as the predetermined pulse transfer function as a feedback control system that forms a closed loop. When the transfer function of the output of the light spot position with respect to the input from the pre-compensation means side to the adding means when the connection between the pre-compensation means and the adding means is disconnected is Gcl (z ⁻¹ ) , Having a pulse transfer function P ₁ (z ⁻¹ ) represented by the following equation (18) ,
P ₁ (z ⁻¹ ) = Ac (z ⁻¹ ) / {Bc ⁺ (z ⁻¹ ) Bc ⁻ (1)} (18)
^{Here, Gcl (z -1) = z} -d Bc + (z -1) Bc - (z -1) / Ac (z -1)
Ac (z ⁻¹ ): term of the pole of Gcl (z ⁻¹ )
Bc ⁺ (z ⁻¹ ): A stable zero term of Gcl (z ⁻¹ )
Bc ⁻ (z ⁻¹ ): term of unstable zero of Gcl (z ⁻¹ )
Bc ⁻ (1): Constant where the unstable zero of Gcl (z ⁻¹ ) is z ⁻¹ = 1
,
d: Equivalent lead sampling number
The pulse transfer function determines the poles and stable zeros of Gcl (z ⁻¹ ) when the response of the light spot position is obtained by multiplying the correction signal by Gcl (z ⁻¹ ) · P ₁ (z ⁻¹ ). Cancel, and make the DC gain of the pre-compensation means coincide with the inverse of the DC gain of Gcl (z ⁻¹ ),
A tracking control device characterized by that. Tracking error signal generating means for generating a tracking error signal corresponding to the difference between the track position on the optical disc and the position of the light spot emitted from the optical head;
The tracking error signal is stored in the storage means for a time corresponding to at least one rotation period of the optical disk, and a correction signal is output by calculating the tracking error signal one rotation period before from the stored signal. Correction signal generating means for performing,
Pre-compensation means for generating a pre-compensation signal in which the amplitude and phase of the generated correction signal are compensated with a predetermined pulse transfer function;
Adding means for generating a drive signal obtained by adding the tracking error signal and the pre-compensation signal;
Control means for causing the light spot to scan a target track on the optical disk based on the generated drive signal, and
The pre-compensation means uses the tracking error signal generation means, correction signal generation means, pre-compensation means, addition means, and control means as the predetermined pulse transfer function as a feedback control system that forms a closed loop. When the transfer function of the output of the light spot position with respect to the input from the pre-compensation means side to the adding means when the connection between the pre-compensation means and the adding means is disconnected is Gcl (z ⁻¹ ) And a pulse transfer function P ₁ (z ⁻¹ ) represented by the following equation (21) ,
^{_{P 1 (z -1) = Ac}} (z -1) Bc - (z) / [Bc + (z -1) {Bc - (1)} 2] ... (21)
^{Here, Gcl (z -1) = z} -d Bc + (z -1) Bc - (z -1) / Ac (z -1)
Ac (z ⁻¹ ): term of the pole of Gcl (z ⁻¹ )
Bc ⁺ (z ⁻¹ ): A stable zero term of Gcl (z ⁻¹ )
Bc ⁻ (z ⁻¹ ): term of unstable zero of Gcl (z ⁻¹ )
Bc ⁻ (1): Constant where the unstable zero of Gcl (z ⁻¹ ) is z ⁻¹ = 1
,
d: Equivalent lead sampling number
The pulse transfer function determines the poles and stable zeros of Gcl (z ⁻¹ ) when the response of the light spot position is obtained by multiplying the correction signal by Gcl (z ⁻¹ ) · P ₁ (z ⁻¹ ). Furthermore , the product with the pulse transfer function Gcl (z ⁻¹ ) is zero in phase difference at all frequencies, and the DC gain of the pre-compensation means matches the reciprocal of the DC gain of Gcl (z ⁻¹ ). Let
A tracking control device characterized by that.

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