JP2009099237A - Disk device and tracking servo device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To constitute a control system more robust to disturbance or the like by increasing low-frequency gain without increasing a gain cross frequency. <P>SOLUTION: The device includes: a first low frequency enhanced filter 111 and a second low frequency enhanced filter 112 connected in series to a controller 13 generating a drive signal for driving an actuator ; and one phase lead/lag compensation filter 121 connected in parallel to the low frequency enhanced filters 111 and 112. Since a synthetic transfer function of the controller 13 is obtained by adding the transfer function synthesized by the low frequency enhanced filters 111 and 112 and the transfer function of the phase lead/lag compensation filter 121 connected in parallel. The controller 13 has three or more poles. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a disk device and a tracking servo circuit applicable to a next-generation high-density optical disk such as a Blu-ray disk.

  In a disk device, for example, an optical disk recording / reproducing apparatus, laser light is used for signal recording and reproduction, and this laser light needs to be condensed at a predetermined position on the disk. For this reason, a mechanism for adjusting the position of the laser beam is provided. In general, a tracking mechanism for adjusting the radial position of the disk, a focus mechanism for controlling the vertical position of the disk, and the like are used. The light is condensed at a predetermined position above. For example, the laser beam position adjustment mechanism of the optical head is configured as a biaxial device including a tracking mechanism and a focus mechanism.

  In order to drive these mechanisms appropriately, a servo control system is configured. This servo control system includes a comparator that detects a deviation between the position of the laser beam and a predetermined position, and a laser from the output of the comparator. It comprises a controller that generates a signal for driving a mechanism for adjusting the position of light (referred to as an actuator as appropriate) and an actuator for adjusting the position of laser light.

  For example, in tracking servo control, a wide range of frequencies from low-frequency, large-amplitude position shifts, such as condensing position shifts synchronized with disk rotation caused by eccentricity during disk mounting, to high-frequency position shifts based on optical disc track formation accuracy. It is necessary to cope with the positional deviation. Similarly, focus servo control also needs to handle a wide range of frequency misalignment, from low-frequency, large-amplitude condensing position deviation synchronized with disk rotation due to disk warpage to high-frequency position deviation due to disk film thickness fluctuation. .

  The controller in the conventional servo circuit copes with such a wide frequency misalignment by emphasizing the low frequency band and compensating for the phase lead / lag in the high frequency band. Specifically, the low frequency component is emphasized in response to the error signal of the low frequency and large amplitude to suppress the position error of the low frequency, and the phase lead / lag compensation is performed at the high frequency and I try to suppress oscillation. In any case, it is desirable that the servo control calculation means suppresses the positional deviation of the low frequency as much as possible by enhancing the low frequency component of the error signal as much as possible. It is also desirable to improve the phase lag in the high frequency band by phase lead / lag compensation so that the system does not oscillate.

  However, if an attempt is made to cope with an error signal having a very high frequency in the servo circuit, there is a problem that the servo control system causes an oscillation phenomenon. Specifically, the phase delay at a high frequency is increased by emphasizing the low frequency band in the controller, causing an oscillation phenomenon. Therefore, it is necessary to stabilize the control system by appropriately compensating the phase in the high frequency band.

  In recent years, portable optical disk recording / reproducing apparatuses and high-speed rotation type optical disk recording / reproducing apparatuses have appeared. In these optical disk recording / reproducing apparatuses, since the rotational speed of the optical disk is faster than the conventional one, it is necessary to emphasize the low frequency band more than before. However, in the conventional controller, the enhancement of the low frequency band affects the high frequency band, thereby affecting the phase lead / lag compensation in the high frequency band, and as a result, the operation of the laser beam position adjusting mechanism is unstable. There was a problem of becoming.

  Japanese Patent Application Laid-Open No. 2004-228561 describes that the deviation from the rotation of the disk is suppressed by storing, in a memory, the deviation of the condensing position of the laser beam from the predetermined position due to the rotation of the disk.

JP 2004-95124 A

  However, depending on the method described in Patent Document 1, although the disturbance suppression effect at a specific frequency resulting from the rotation of the disk is enhanced, the performance at other frequencies is equivalent to that of the conventional one. The influence of unpredictable disturbances such as vibrations assumed in an optical disk recording / reproducing apparatus or the like cannot be sufficiently eliminated. Further, depending on the method described in Patent Document 1, it is necessary to newly provide an external storage device in order to store the deviation of the condensing position of the laser beam from the predetermined position due to the rotation of the disk, which increases the cost. There was a problem that.

  Accordingly, an object of the present invention is to provide a control system that can withstand disturbances not caused by the rotation of the disk, can perform good servo control during high-speed rotation, and can be configured at low cost. The object is to provide a tracking servo circuit.

In order to solve the above-described problem, the present invention includes a head unit that performs at least one of recording and reproduction of an information signal with respect to a disk-shaped recording medium;
An actuator for transferring the head part to a target position;
Error signal detection means for detecting an error signal proportional to the error between the target position and the actual position;
A controller that is supplied with the error signal detected by the error signal detection means and generates a control signal for driving the actuator;
An actuator drive circuit to which an output signal of the controller is supplied,
The controller includes first and second low-frequency emphasis filters and one phase lead / lag compensation filter,
The disk device is characterized in that the controller has three or more poles and three or more zeros.
Preferably, in the controller, the first and second low-frequency emphasis filters are connected in series, and the phase lead / lag compensation filter is connected in parallel to the series connection of the first and second low-frequency emphasis filters.
Preferably, the parameters of the controller are calculated by equations (4) to (8) described later when the poles of the control system are arranged on the real axis.

The present invention relates to an actuator for transferring a head portion that performs at least one of recording and reproduction of an information signal to / from a disk-shaped recording medium to a target position on the disk-shaped recording medium;
Error signal detection means for detecting an error signal proportional to the error between the target position and the actual position on the disk-shaped recording medium;
A controller that is supplied with the error signal detected by the error signal detection means and generates a control signal for driving the actuator;
An output signal of a controller is provided, and an actuator drive circuit for positioning the actuator at a target position,
The controller includes first and second low-frequency emphasis filters and one phase lead / lag compensation filter,
The tracking servo circuit is characterized in that the controller has three or more poles and three or more zeros.

According to the present invention, since the low-frequency emphasis filter has a two-stage configuration, the low-frequency gain can be enhanced without increasing the gain crossover frequency, so that a strong control system can be configured due to disturbance or the like. As a result, it is possible to realize an optical disk recording / reproducing apparatus that can be used in an environment where there is a disturbance or the like.
In addition, it is possible to realize an optical disk recording / reproducing apparatus that is driven at a high speed rotation accompanied by occurrence of a larger disturbance or the like.
Since the present invention can increase the low frequency gain without increasing the gain crossing frequency, it is not necessary to design a high resonance frequency for the mechanism (actuator) for adjusting the position of the laser beam. Thereby, an inexpensive optical disk recording / reproducing apparatus can be realized. In addition, since it does not require a large circuit scale, such as having an external memory, it is possible to realize an optical disk recording / reproducing apparatus that can rotate at high speed at low cost.

Matters corresponding to the claims of the present invention will be described. An optical disk 1 is used as a disk-shaped recording medium, and an optical head 2 is provided as a head unit that performs at least one of recording and reproduction of information signals with respect to the optical disk 1. An actuator for transferring the laser beam of the optical head 2 to the target position is provided. An error signal detection circuit 11 for detecting an error signal for servo control from the output signal of the light receiving unit in the optical head 2 is provided as an error signal detection means for detecting an error signal proportional to the error between the target position and the actual position. . The controller 13 generates a control signal for driving the actuator. The controller 13 includes first and second low-frequency emphasis filters (111 and 112) and one phase advance / lag compensation filter (121), and the controller 13 includes three or more poles and three or more Has zeros.
An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 relates to an optical disk recording / reproducing apparatus to which the present invention can be applied, and particularly shows the configuration of a servo circuit. Information signals are recorded on the optical disk 1 by the optical head 2, and information signals are reproduced from the optical disk 1 by the optical head 2.

  The optical disc 1 is a recordable optical disc such as a Blu-ray disc, DVD-RW, or DVD-R. The optical disk 1 is rotated at a predetermined rotational speed by the spindle motor 3. The disk-shaped recording medium is not limited to an optical disk, and a magnetic disk or the like may be used.

  The optical head 2 condenses the laser light source for recording / reproduction and the laser light emitted from the laser light source onto the recording surface of the optical disk 1 through the objective lens, and captures the reflected light from the optical disk 1. The optical system includes a light receiving unit that detects reflected light captured by the optical system.

  Further, a laser beam position adjusting mechanism realized by an electromagnetic actuator is mounted in the optical head 2, and the objective lens is controlled to move in the focus direction and the tracking direction by the actuator.

  An error signal detection circuit 11 for detecting an error signal for servo control from the output signal of the light receiving unit in the optical head 2 is provided, and the error signal detected by the error signal detection circuit 11 is supplied to the A / D converter 12. Are converted into digital signals. A digital error signal from the A / D converter 12 is supplied to the controller 13.

  The controller 13 generates a control signal for driving the actuator. The control signal is converted into an analog control signal by the D / A converter 14. An analog control signal is supplied to the actuator drive circuit 15. The actuator drive circuit 15 outputs a signal for driving the actuator in the optical head 2. The actuator displaces the objective lens so that the error signal becomes small.

  In the optical disk recording / reproducing apparatus, tracking control for positioning with respect to tracking by an actuator in the optical head 2 and focus control for positioning with respect to focus are performed. Although the present invention can be applied to any control, the following description will mainly describe tracking control.

  The operation of the above-described optical disk recording / reproducing apparatus will be schematically described. The optical disk 1 rotates at a predetermined rotational speed by the rotation of the spindle motor 3. The optical head 2 irradiates the optical disk 1 with laser light for recording / reproduction to perform signal recording / reproduction, and the position of the laser light is adjusted so that the laser light is irradiated to a predetermined position of the optical disk 1 by an actuator. adjust.

  The error detection circuit 11 connected to the optical head 2 generates an error signal indicating a deviation between a position where the laser beam is focused and a predetermined position from a signal obtained by the light receiving unit of the optical head 2. The A / D converter 12 connected to the error detection circuit 11 converts the error signal generated by the error detection circuit 11 into a digital signal. The controller 13 controlled by the A / D converter 12 generates a drive signal for driving the actuator from the digitized error signal from the A / D converter 12.

  The D / A converter 14 connected to the controller 13 converts the drive circuit control signal calculated by the controller 13 into an analog signal. The actuator drive circuit 15 connected to the D / A converter 14 generates a drive signal for driving the actuator based on the analog signal generated by the D / A converter 14. The drive signal generated in this manner appropriately drives an actuator (laser beam position adjusting mechanism) mounted on the optical head 2 so that the laser beam is condensed at a predetermined position. Recording and playback are possible.

  In the embodiment of the present invention, the controller 13 in the servo circuit described above includes a first low-frequency emphasis filter, a second low-frequency emphasis filter, and one phase lead / lag compensation filter. 13 has three or more poles and three or more zeros.

  In one embodiment of the present invention, as shown in FIG. 2, a first low-frequency emphasis filter 111 and a second low-frequency emphasis filter 112, and low-frequency emphasis filters 111 and 112, to which a controller 13 is connected in series. And a phase lead / lag compensation filter 121 connected in parallel. Each transfer function is described in each filter block. The controller 13 has a third-order filter configuration. Since the overall transfer function of the controller 13 is connected in parallel, it is obtained as the sum of the transfer function synthesized by the low-frequency emphasis filters 111 and 112 and the transfer function of the phase advance / lag compensation filter 121.

  In order to facilitate understanding of the present invention, an operation in which the controller 130 having the conventional configuration generates a control signal for controlling the drive circuit from the error signal will be described below.

  The deviation from the predetermined position where the laser beam should be collected, which is detected as an error signal, is mainly caused by external vibration, impact, disk eccentricity, and the like. In order to reduce the deviation caused by these, the controller 130 provided in the conventional servo circuit has one phase advance / lag compensation filter 132 connected in series to one low-frequency emphasis filter 131 as shown in FIG. It has a connected configuration. Each transfer function is described in each filter block.

  The low-frequency emphasis filter 131 is for emphasizing the low-frequency band, and is used for correcting the position shift in the low-frequency band by emphasizing the low-frequency band that is the main frequency component of the error signal. The phase lead / lag compensator 132 compensates for the phase in the high frequency band, and is used to stabilize the control system by compensating for the phase in the high frequency band and securing the phase margin.

  The controller 130 having such a configuration outputs a control signal corresponding to the frequency component of the error signal. The performance of the controller 130 can be known as a frequency response characteristic as shown in FIG. 4A shows an amplitude frequency response characteristic (hereinafter simply referred to as an amplitude characteristic), and FIG. 4B shows a phase frequency response characteristic (hereinafter simply referred to as a phase characteristic). In the amplitude characteristic and the phase characteristic, the horizontal axis is the frequency [Hz]. The vertical axis in the amplitude characteristic is an input / output amplitude ratio (hereinafter referred to as gain [dB]), and the vertical axis in the phase characteristic is an input / output phase difference (hereinafter referred to as phase [deg]).

In each characteristic, the center line indicates the position where gain = 0 [dB] and the position where phase = 0 [deg]. Gain indicates the ratio of output signal to input signal. If the phase is positive, the phase of the output signal is advanced, and if the phase is negative, the phase of the output signal is delayed.

  As shown in FIG. 4A, the controller 130 has a low-pass filter characteristic in which the gain decreases as the frequency increases in the servo frequency band. The higher the gain, the stronger the effect of suppressing disturbance. Further, as shown in FIG. 4B, the phase is delayed or slightly advanced in the servo frequency band. If the phase is excessively delayed or advanced, the risk of oscillation increases.

  Similarly, the behavior of the actuator (laser beam position adjusting mechanism) according to the frequency can also be seen from the frequency response characteristic, and the characteristic is shown in FIG. In general, an actuator has a resonance characteristic, but is approximated by a quadratic integral here.

  The overall frequency response characteristics of the servo circuit that controls the actuator having the frequency response characteristics shown in FIG. 5 by the controller 130 having the frequency response characteristics shown in FIG. 4 are shown in FIG. 6A (amplitude characteristics) and FIG. 6B (phase characteristics). It will be represented by What shows the frequency dependence when the actuator is controlled by the controller 130 is called an open loop frequency response characteristic. The gain characteristic indicates the error signal suppression capability in the frequency component indicated on the horizontal axis, and indicates that the error at the frequency can be reduced as the gain increases.

  In this open-loop frequency response characteristic, the frequency at which the gain characteristic is 0 [dB] is called a gain crossing frequency, and the difference between the phase characteristic at that time and −180 ° is called a phase margin (see FIG. 6B). . The phase margin represents the stability of the control system, and is desirably a large value. That is, in the optical disk recording / reproducing apparatus, the role of the controller is to ensure a sufficient gain in the main frequency component of the error signal and to maintain the stability of the system by ensuring the phase margin.

  In a portable optical disk recording / reproducing apparatus or the like, it is assumed that it can be operated while being carried. Assuming such an application, it is expected that disturbances at a low frequency such as vibration will be larger than those of a stationary optical disk recording / reproducing apparatus. In order to reduce the influence of this vibration, as shown in FIG. 7, it is necessary to increase the gain in the low frequency band of the control system, for example, 100 Hz, as compared with the conventional one.

  Also, in the optical disk recording / reproducing apparatus, the rotational speed of the disk may be increased for the purpose of increasing the data transmission rate. Increasing the rotational speed of the disk causes an increase in the frequency of disturbances originating from the eccentricity of the disk. In order to reduce this influence, as shown in FIG. 8, it is necessary to increase the gain of the control system at a higher frequency than the conventional one.

  In order to satisfy these performances, the controller 130 according to the conventional configuration is configured as follows. In order to increase the gain in the low frequency band, the low frequency emphasis frequency of the low frequency emphasis filter 131 is set high. This corresponds to reducing the coefficient c in the transfer function of the low-frequency emphasis filter 131.

  However, the gain improvement in the low frequency band by this method affects the phase lead / lag compensation in the high frequency band, resulting in a problem that the phase margin is deteriorated and the operation of the actuator becomes unstable.

  The optical disk recording / reproducing apparatus according to the present invention is characterized by using a controller capable of increasing the gain in the low frequency band without deteriorating the phase margin. This controller is characterized by using two or more low-frequency emphasis filters. The present invention makes it possible to increase the gain in the low frequency band by making the attenuation above the cutoff frequency of the low frequency emphasis filter steep. Furthermore, by using a parameter design method in which poles that determine the characteristics of the control system are arranged at optimal positions, a controller that further enhances the gain in the low frequency band can be realized.

  What shows the frequency dependence when the actuator is controlled by this controller is called an open loop frequency response characteristic. The gain characteristic indicates the error signal suppression capability in the frequency component indicated on the horizontal axis, and indicates that the error at the frequency can be reduced as the gain increases.

  In this open-loop frequency response characteristic, the frequency at which the gain characteristic is 0 [dB] is called a gain crossing frequency, and the difference between the phase characteristic at that time and −180 ° is called a phase margin (see FIG. 6B). . The phase margin represents the stability of the control system, and is desirably a large value. That is, in the optical disk recording / reproducing apparatus, the role of the controller is to ensure a sufficient gain in the main frequency component of the error signal and to maintain the stability of the system by ensuring the phase margin.

  Hereinafter, the controller parameter design method will be described. FIG. 9 shows a block diagram in a discrete system notation of the control system (see FIG. 1) of the optical disk recording / reproducing apparatus described above. The control system includes a controller block 141 corresponding to the controller 13 and a time delay element 143 connected between an actuator element 143 corresponding to the actuator and representing a delay time by the calculation of the controller. The actuator element represents both the 0th-order hold and the actuator. The controller 13 arranges two low-frequency emphasis filters 111 and 112 and one phase advance / lag compensation filter 121 as one element, and the coefficient c and coefficient d can also take complex values. It is said. As can be seen from the transfer function of the controller block 141, the controller 13 has three or more poles (the value of z having a denominator of 0 and three of the roots a and b) and three. It has the above zero point (the value of z where the numerator is 0, which is c, d, and e). Here, the coefficients a1 and a2 in FIG. 2 are set to the same value (a).

  The closed loop transfer function of the control system shown in FIG. 9 is expressed by Expression (1) obtained by multiplying the transfer function of each element, and can be modified as Expression (2). Here, a parameter for realizing a desired pole can be calculated by solving the coefficient comparison expression so that the poles of the expressions (1) and (2) match.

However, the coefficients C _{1 to} C ₅ are expressed by the following formula (9).

Here, the transfer function of the controller block 141 shown in FIG. 9 can be transformed into that shown in Equation (10). Accordingly, in realizing the controller, the coefficients a, Kp, b, cde, cd + de + ce, and c + d + e may be obtained. The value of a may be set to an arbitrary value from a frequency that requires low-frequency emphasis. In the case of such a discrete system, the position of the pole is represented by a position on the z plane. Here, the z plane refers to a plane composed of a horizontal axis (real axis) representing a real number and a vertical axis (imaginary axis) representing an imaginary number. At this time, if there is a pole on the real axis, the system is not oscillating and it is easy to realize a stable system. Therefore, in this z plane, when the poles p ₁ , p ₂ , p ₃ , p ₄ , and p ₅ are determined at predetermined positions on the real axis, the values of the coefficients a, Kp, b, cde, cd + de + ce, and c + d + e Can be obtained from the above-described equations (4) to (8), respectively.

  An example of the frequency response characteristic of the control system by the controller 130 having the conventional configuration is shown by a broken line in FIG. This frequency response characteristic is a coefficient set as follows.

Actuator gain (Gp = 4.7 × 10 ⁸ )
Sampling cycle = 2.0 × 10 ⁻⁶
Value corresponding to the low frequency cut-off frequency a = 0.999874
Value corresponding to low frequency emphasis frequency c = 0.996237
Value corresponding to phase advance frequency d = 0.81326
Value corresponding to phase lag frequency b = 0.833963
Coefficient α in the dead time element that represents the delay time by calculation = 0.65

  As described above, when an application such as a portable optical disk recording / reproducing apparatus is assumed, disturbances at low frequencies such as vibration are expected to increase. In order to reduce the influence of this vibration, the control system must be low. It is necessary to increase the gain in a frequency band, for example, 100 Hz, as compared with the conventional one. For example, the gain at 100 Hz is increased by 20 [dB].

  At this time, in the controller 130 according to this conventional configuration (FIG. 3), the low frequency emphasis frequency is increased by decreasing the value of the coefficient c. By setting the amplitude characteristics as indicated by the solid line in FIG. 10A, the low-frequency gain can be enhanced. However, as can be seen from the phase characteristic (solid line) shown in FIG. 10B, in this method, the phase margin is reduced. In order to satisfy the above-mentioned conditions in the low frequency band, there is no phase margin, and there is a problem that a stable system cannot be realized.

  FIG. 11 shows amplitude characteristics (FIG. 11A) and phase characteristics (FIG. 11B) when the low-frequency gain is increased to about 10 [dB] in the controller 130 having the conventional configuration. In this case, an adequate phase margin is ensured. That is, in the case of the controller 130 having the conventional configuration, in reality, the enhancement of about 10 [dB] is the limit.

  An example of the amplitude characteristic of the controller 13 (FIG. 2) according to the embodiment of the present invention is shown in FIG. 12, and an example of the phase characteristic is shown in FIG. FIG. 14A (amplitude characteristics) and FIG. 14B (phase characteristics) show frequency response characteristics of a control system (similar to FIG. 9) including the controller 13. In each of FIG. 14A and FIG. 14B, a broken line represents a frequency response characteristic before the low-frequency enhancement is performed when the controller 130 having the conventional configuration is used.

These specific characteristics are as follows: the coefficients a, Kp, b, cde, cd + de + ce, c + d + e when the poles p ₁ , p ₂ , p ₃ , p ₄ , and p ₅ of the control system are determined at predetermined positions on the real axis. Each value can be obtained from the above-described equations (4) to (8). p ₁ , p ₂ , p ₃ , p ₄ , p ₅
Is a value corresponding to 2.5 kHz in the continuous system, and the coefficient a is 0.998774. At this time, the following values are obtained from the equations (4) to (8).

Kp = 5.22672
b = 0.832957
cde = 0.969873
cd + de + ce = 2.93928
c + d + e = 2.96940

  As can be seen from FIG. 14A, in the embodiment of the present invention, the gain in the low frequency band, for example, 100 Hz, can be increased as compared with the conventional control system as compared with the conventional control system. For example, the gain at 100 Hz can be increased by 20 [dB]. Furthermore, as can be seen from the phase characteristics of FIG. 14B, the phase margin does not decrease and the stability of the control system is not lost.

  According to the embodiment of the present invention described above, it is possible to realize a control system in which the gain is 60 [dB] or more in a frequency band of 1/20 or less of the gain crossover frequency. As shown in FIG. 15, when the gain crossover frequency is 4.5 kHz, for example, 1/20 of the frequency is 225 Hz, and the gain can be 69 [dB] when the frequency is 225 Hz.

  On the other hand, in a servo control system using a conventional controller, as shown in FIG. 16, the gain is 55 [dB] at 1/20 of the crossing frequency, and cannot be 60 [dB] or more. Also from this point, it can be seen that the low-frequency enhancement effect of the present invention is large.

  Parameters calculated from the above-described equations (4) to (8) may be pre-calculated parameters, but the parameters can be calculated by the control parameter calculation circuit 16 as shown in FIG. The parameters may be changed according to the situation.

  As can be seen from the description of one embodiment of the present invention, in the present invention, the low-frequency emphasis filter has a two-stage configuration, so that the low-frequency gain can be increased without increasing the gain crossover frequency, and disturbance. A stronger servo control system can be configured. Thereby, it is possible to realize an optical disk recording / reproducing apparatus that can be used in an environment where disturbances and the like exist. Further, it is possible to realize an optical disk recording / reproducing apparatus that is driven at high speed rotation accompanied by occurrence of a larger disturbance or the like.

  Since the low-frequency gain can be enhanced without increasing the gain crossover frequency, it is not necessary to design the resonance frequency of the actuator for adjusting the position of the laser light to a high value, and an inexpensive optical disk recording / reproducing apparatus can be realized. . Furthermore, it is not necessary to store data such as correction values in the memory, so that an increase in circuit scale can be prevented and an inexpensive optical disk recording / reproducing apparatus can be realized.

  Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications and applications can be made without departing from the gist of the present invention. For example, in the above-described embodiment, a digital filter having three poles and three zeros is used. However, the present invention is not limited to this, and any digital filter having three or more poles may be used. Further, the controller may connect two low-frequency emphasis filters connected in series and one phase advance / lag compensation filter in series. Further, the controller may be constituted by a third-order filter. For example, two primary low-frequency emphasis filters and one phase advance / lag compensation filter may be connected in parallel.

It is a block diagram of a servo control system in a disk device to which the present invention can be applied. It is a block diagram which shows the structure of the controller used for the servo control system in one embodiment of this invention. It is a block diagram of the conventional controller. It is a graph which shows each the amplitude characteristic and phase characteristic of the conventional controller. It is a graph which shows the amplitude characteristic and phase characteristic of an actuator, respectively. It is a graph which each shows the amplitude characteristic and phase characteristic of the conventional servo control system. It is a graph used for description of the low region reinforcement operation of the conventional servo control system. It is a graph used for description of the low region reinforcement operation of the conventional servo control system. It is a block diagram of the discrete system description of a servo control system. It is a graph used for description of the problem of the low-frequency enhancement operation of the conventional servo control system. It is a graph used for description of the problem of the low-frequency enhancement operation of the conventional servo control system. It is a graph which shows the amplitude characteristic of the controller in one embodiment of this invention. It is a graph which shows the phase characteristic of the controller in one embodiment of this invention. It is a graph used for description of the low-frequency enhancement operation of the servo control system in one embodiment of the present invention. It is a graph used for description of the low-frequency enhancement operation of the servo control system in one embodiment of the present invention. It is a graph used for description of the low-frequency enhancement operation of the servo control system in one embodiment of the present invention. It is a block diagram of the modification of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk 2 Optical head 11 Error signal detection circuit 13 Controller 15 Actuator drive circuit

Claims (5)

A head unit that performs at least one of recording and reproduction of an information signal on a disk-shaped recording medium;
An actuator for transferring the head part to a target position;
Error signal detection means for detecting an error signal proportional to an error between the target position and the actual position;
A controller that is supplied with an error signal detected by the error signal detection means and generates a control signal for driving the actuator;
An actuator drive circuit to which the output signal of the controller is supplied,
The controller is composed of first and second low-frequency emphasis filters and one phase lead / lag compensation filter,
A disk device characterized in that the controller has three or more poles and three or more zeros.   In the controller, the first and second low-frequency emphasis filters are connected in series, and the phase lead / lag compensation filter is connected in parallel to the series connection of the first and second low-frequency emphasis filters. 2. The disk device according to claim 1, wherein: 2. The disk device according to claim 1, wherein the parameters of the controller are calculated by the following equations (4) to (8) when the poles of the control system are arranged on the real axis.

  2. The disk device according to claim 1, further comprising a circuit for calculating and setting parameters of the controller by the equations (4) to (8). An actuator for transferring a head part for recording and reproducing information signals to and from a disk-shaped recording medium to a target position on the disk-shaped recording medium;
Error signal detection means for detecting an error signal proportional to an error between the target position and the actual position on the disc-shaped recording medium;
A controller that is supplied with an error signal detected by the error signal detection means and generates a control signal for driving the actuator;
An output signal of the controller is provided, and an actuator drive circuit for positioning the actuator at the target position,
The controller is composed of first and second low-frequency emphasis filters and one phase lead / lag compensation filter,
A tracking servo circuit, wherein the controller has three or more poles and three or more zeros.

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