JP3699606B2 - Rotation servo control device and rotation servo control method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention belongs to a technical field of a rotation servo control device and a rotation servo control method for servo-controlling rotation of a rotating body such as a motor, and more specifically, a rotation servo control device for servo-controlling rotation of a rotating body by feedback control And belongs to the technical field of rotational servo control methods.
[0002]
[Prior art]
For example, so-called feedback control is generally used conventionally in a rotation servo control device that controls the rotation of a rotating body such as a spindle motor that rotates an optical disc in an information reproducing device that reproduces information from the optical disc.
[0003]
That is, more specifically, the rotation speed is detected based on the rotation signal provided from the signal generation device that is attached to the rotation body and generates a rotation signal indicating the rotation speed of the rotation body. Then, the detected rotational speed is subtracted from the target rotational speed, which is the target value for setting the rotational speed of the rotating body, to detect a control deviation, and further, a phase compensation process is performed on the control deviation. Feedback control is performed so as to amplify the control deviation after phase compensation by a so-called driver or the like and to control the rotation of the rotating body so as to cancel the control deviation.
[0004]
Here, among the methods for generating the rotation signal described above, as a simple method that can be used for a so-called consumer device, for example, a large number of slits are provided in the circumferential direction on a disk that rotates as the rotating body rotates. The disk (ie, the rotating body) is provided by irradiating a light beam such as a laser beam at a position through which the slit passes when the disk is rotating, and detecting that the light beam has passed through the slit. The number of rotations is detected, or four so-called hall elements are provided in a cross shape with a right angle of attachment in a plane parallel to the plane of rotation of the disk, and the disk rotates in the vicinity of the hall element. A method is used in which a change in the magnetic field generated during the detection is detected by each Hall element, and the number of rotations of the disk is detected from the detection result.
[0005]
[Problems to be solved by the invention]
However, in the rotational speed detection method using the plurality of slits, if the interval between the slits fluctuates, the pulse interval detected as a rotational signal is not sufficient even if the rotating body itself rotates at a constant rotational speed. There arises a problem that fluctuations occur, and therefore an accurate rotational speed may not be detected.
[0006]
Furthermore, also in the rotational speed detection method using the plurality of Hall elements, when the mounting angle of each Hall element varies (attachment position error), the rotating body itself similarly rotates at a constant rotational speed. Even in this case, the pulse interval detected as the rotation signal fluctuates. Therefore, in this case as well, there is a problem that the accurate rotation speed may not be detected.
[0007]
Therefore, the present invention has been made in view of the above problems, and the problem is that the rotation signal indicating the number of rotations of the rotating body generated along with the rotation of the rotating body includes fluctuations. Rotation servo control device and rotation servo control capable of accurately detecting the number of rotations and accurately controlling the rotation of the rotating body while minimizing the phase lag while minimizing the phase delay It is to provide a method.
[0008]
[Means for Solving the Problems]
  In order to solve the above problems, the invention described in claim 1 is a rotary servo control device that controls the rotation of a rotating means such as a spindle motor by feedback control, and generates a rotation signal synchronized with the rotation of the rotating means. A control deviation indicating a difference between a generation means such as a pulse generator and the current rotation speed of the rotation means indicated by the generated rotation signal and a target rotation speed that is the rotation speed at which the rotation means is to be rotated. Control deviation generating means such as a subtractor for generating a signal, and fluctuations in the period of the rotation signal that are included in the rotation signal when the rotation signal is generated based on the generated control deviation signal Compensation means such as a compensator that compensates the signal by proportional integral control and generates a compensation signal, and drive of a drive circuit that rotationally drives the rotation means based on the generated compensation signal And the compensation means multiplies the control deviation signal by a proportional term in the proportional-plus-integral control to generate a proportional deviation signal, and a proportional multiplication means such as a multiplier, and the control deviation signal. Multiplying an integral term in the proportional integral control, and the control deviation signal corresponding to one or a plurality of rotations of the rotating meansOnly the integral term ofAccumulation process, to accumulateIntegral termAveraging processing of accumulated results,And the integral termonlyIntegral averaging means such as a multiplier, a moving average filter and an integral arithmetic unit that perform corresponding integral calculation processing and generate an integrated average deviation signal, and add the proportional deviation signal and the integral average deviation signal. And an adding means such as an adder for generating the compensation signal.
[0009]
Therefore, when compensating for fluctuations in the period of the rotation signal by proportional integral control, a proportional deviation signal obtained by multiplying the control deviation signal by a proportional term, and multiplication processing, accumulation processing, averaging processing, and the control deviation signal are performed. The integral average signal obtained as a result of each integral calculation process is added to generate the compensation signal, so that the phase margin in the feedback control theory is reduced even if the rotation signal contains periodic fluctuations. Therefore, the period fluctuation can be removed without any problem, and the rotation means can be accurately feedback controlled.
[0010]
In order to solve the above-mentioned problem, the invention according to claim 2 is the rotary servo control device according to claim 1, wherein the generation means generates the rotation signal which is a pulse signal and the integral average. And an integrating multiplication means such as a multiplier that performs the multiplication process on the control deviation signal, and a number that is at least one less than the number of pulses of the rotation signal generated per one rotation of the rotation means. A plurality of delay means such as delay units connected in series and sequentially delaying the integral deviation signal by one sample timing, and the integral deviation signal delayed by each of the delay means are extracted every time one sample timing is delayed. And adding the extracted integral deviation signal to the original integral deviation signal before the delay to perform the accumulation process, The averaging process is performed by dividing the added addition means and the generated addition signal by the number of pulses of the rotation signal generated per rotation of the rotation means to generate the average deviation signal Dividing means such as a divider, and integrating means for performing the integration calculation process on the generated average deviation signal and generating the integrated average signal.
[0011]
Therefore, the integrated deviation signal delayed for each sample timing is extracted each time it is delayed, and after adding these and the integrated deviation signal of the current sample timing, at least the number of pulses of the rotation signal generated per rotation Therefore, the fluctuation of the period of the rotation signal can be effectively removed.
[0012]
In order to solve the above-mentioned problem, the invention according to claim 3 is the rotation servo control device according to claim 1 or 2, wherein the rotation signal is a frequency signal having a frequency corresponding to the number of rotations of the rotation means. The control deviation generating means further generates a difference between the frequency of the frequency signal and the target frequency corresponding to the target rotational speed as the control deviation signal. In addition, the compensation means is configured to generate the compensation signal based on the frequency indicated by the control deviation signal.
[0013]
Therefore, in a rotary servo control device that feedback controls the rotation of the rotating means by frequency control, fluctuations in the period of the rotation signal can be eliminated without reducing the phase margin in the feedback control theory, and the rotating means can be accurately feedback controlled. it can.
[0014]
In order to solve the above-mentioned problem, the invention according to claim 4 is the rotation servo control device according to claim 1 or 2, wherein the rotation signal is a frequency signal having a frequency corresponding to the number of rotations of the rotation means. A frequency conversion means such as a T-f converter for converting the rotation signal, a phase conversion means such as a T-θ converter for converting the rotation signal into a phase signal having a phase corresponding to a rotation angle of the rotation means, and the frequency Differential multiplication means such as a multiplier that multiplies a signal by a preset differential term to generate a differential signal, and the control deviation generation means includes a target corresponding to the phase of the phase signal and the target rotational speed. A difference from a target phase corresponding to a rotation angle is generated as the control deviation signal, the compensation means generates the compensation signal based on the phase indicated by the control deviation signal, and the driving means Configured for rotationally driving the rotation means on the basis of the compensated signal and the differential signal and the sum signal generated by adding.
[0015]
Therefore, in a rotary servo controller that feedback controls the rotation of the rotating means by phase control, fluctuations in the period of the rotation signal can be removed without reducing the phase margin in the feedback control theory, and the rotating means can be accurately feedback controlled. it can.
[0016]
Further, even when the rotation of the rotating means is controlled by so-called proportional-integral-derivative control, the rotation can be accurately feedback-controlled.
[0017]
In order to solve the above-mentioned problem, the invention according to claim 5 is the rotary servo control device according to any one of claims 1 to 4, wherein the rotating means optically records and reproduces information. The spindle motor rotates a disk-shaped recording medium such as an optical disk.
[0018]
Therefore, the rotation of the disk-shaped recording medium can be accurately feedback controlled by removing the fluctuation of the rotation signal period without reducing the phase margin in the feedback control theory.
[0019]
  In order to solve the above-mentioned problem, the invention according to claim 6 generates a rotation signal synchronized with the rotation of the rotation means in a rotation servo control method for controlling the rotation of the rotation means such as a spindle motor by feedback control. And a control step of generating a control deviation signal indicating a difference between a current rotation speed of the rotation means indicated by the generated rotation signal and a target rotation speed that is the rotation speed to rotate the rotation means. Based on the deviation generation step and the generated control deviation signal, a compensation signal is obtained by compensating for fluctuations in the period of the rotation signal included in the rotation signal at the time of generation of the rotation signal by proportional integral control. And a driving step of rotating the rotating means based on the generated compensation signal, and the compensation step includes adding the control deviation signal to the control deviation signal. A proportional multiplication step of multiplying the proportional term in the proportional integral control to generate a proportional deviation signal, a multiplication process for multiplying the control deviation signal by an integral term in the proportional integral control, and one of the rotating means. Or equivalent to multiple rotationsAccumulate only the integral term of the control deviation signalAccumulation processing, concernedIntegral termAveraging process of accumulated results and integration termonlyAn integration averaging step of performing a corresponding integral calculation process to generate an integral averaged deviation signal, and an adding step of adding the proportional deviation signal and the integral averaged deviation signal to generate the compensation signal. included.
[0020]
Therefore, when compensating for fluctuations in the period of the rotation signal by proportional integral control, a proportional deviation signal obtained by multiplying the control deviation signal by a proportional term, and multiplication processing, accumulation processing, averaging processing, and the control deviation signal are performed. The integral average signal obtained as a result of each integral calculation process is added to generate the compensation signal, so that the phase margin in the feedback control theory is reduced even if the rotation signal contains periodic fluctuations. Therefore, the period fluctuation can be removed without any problem, and the rotation means can be accurately feedback controlled.
[0021]
In order to solve the above-described problem, according to a seventh aspect of the present invention, in the rotational servo control method according to the sixth aspect, in the generation step, the rotation signal that is a pulse signal is generated, and The integral averaging step is executed by an integral multiplication step of performing the multiplication process on the control deviation signal, and at least one less than the number of pulses of the rotation signal generated per one rotation of the rotating means, A plurality of delay steps for sequentially delaying the integral deviation signal by one sample timing, and extracting the integral deviation signal delayed in each of the delay steps each time one sample timing is delayed. A delay addition step of generating an addition signal by performing the accumulation process by adding a signal to the original integral deviation signal before delay, and the generated A division step of performing the averaging process by dividing the added signal by the number of pulses of the rotation signal generated per one rotation of the rotation means, and generating the average deviation signal; An integration step of performing the integration calculation process on the averaged deviation signal and generating the integrated averaged signal.
[0022]
Therefore, the integrated deviation signal delayed for each sample timing is extracted each time it is delayed, and after adding these and the integrated deviation signal of the current sample timing, at least the number of pulses of the rotation signal generated per rotation Therefore, the fluctuation of the period of the rotation signal can be effectively removed.
[0023]
In order to solve the above problems, the invention according to claim 8 is the rotational servo control method according to claim 6 or 7, wherein the rotating means is a disc-shaped recording medium on which information is optically recorded and reproduced. It is comprised so that it may be a spindle motor which rotates.
[0024]
Therefore, the rotation of the disk-shaped recording medium can be accurately feedback controlled by removing the fluctuation of the rotation signal period without reducing the phase margin in the feedback control theory.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Next, preferred embodiments of the present invention will be described with reference to the drawings.
[0026]
Each embodiment described below applies the present invention to an information reproducing apparatus that reproduces information recorded on an optical disk while performing rotational servo control of the optical disk as a disk-shaped recording medium by a feedback control system. This is an embodiment when applied.
(I)First embodiment
First, a first embodiment according to the present invention will be described with reference to FIGS.
[0027]
1 is a block diagram showing a schematic configuration of the information reproducing apparatus according to the first embodiment, FIG. 2 is a block diagram showing a detailed configuration of the information reproducing apparatus, and FIG. 3 is a moving average according to the present invention. FIG. 4 and FIG. 5 are diagrams showing frequency-phase characteristics and frequency-gain characteristics in the information reproducing apparatus.
[0028]
First, the configuration of the information reproducing apparatus according to the first embodiment will be described with reference to FIG.
[0029]
As shown in FIG. 1, the information reproducing apparatus S of the first embodiment includes a pickup 1, a pickup control unit PC, a spindle motor 10 as a rotating means, and a spindle control unit SC.
[0030]
At this time, the spindle motor 10 serves as a generation unit that generates and outputs a pulse signal Srp including a pulse synchronized with the rotation (specifically, for example, a pulse signal Srp including four pulses per one rotation of the optical disk DK). A pulse generator 10a is included.
[0031]
The spindle controller SC includes a period detector 11, a Tf (period-frequency) converter 12 as a frequency conversion unit, a target frequency generator 13, and a subtractor 14 as a control deviation generation unit. It comprises a compensator 15 as compensation means, a D / A converter 16, and a drive circuit 17 as drive means.
[0032]
FIG. 1 shows only the part related to the servo control according to the present invention in the information reproducing apparatus S. In the actual information reproducing apparatus S, in addition to each member shown in FIG. An operation for inputting a reproduction processing unit that reproduces information recorded on the optical disc DK based on a detection signal from 1, a display unit that displays an operation state of the information reproduction device S, or a process that is executed by the information reproduction device S Department etc. are included.
[0033]
Next, an outline operation will be described.
[0034]
First, the pickup 1 irradiates the information recording surface of the optical disc DK with the light beam B, and outputs the detection signal based on the reflected light.
[0035]
At this time, the pickup control unit PC places an objective lens (an objective lens for condensing the light beam B on the information recording surface) in the pickup 1 in a direction perpendicular to or parallel to the information recording surface. Drive control is performed, and the focus position of the light beam B is changed to perform focus servo control or tracking servo control.
[0036]
On the other hand, the spindle motor 10 rotationally drives the optical disk DK based on a drive signal Si, which will be described later, and the pulse generator 10a includes the pulse signal Srp including a pulse synchronized with the rotation of the spindle motor 10 in parallel with this operation. Is output to the period detector 11.
[0037]
Next, the period detector 11 constituted by a counter or the like detects the rotation period of the spindle motor 10 based on the pulse signal Srp, generates a period signal St, and outputs it to the Tf converter 12.
[0038]
The T-f converter 12 converts the rotation cycle of the spindle motor 10 indicated by the cycle signal St into a rotation frequency, generates a frequency signal Sf, and outputs the frequency signal Sf to one input terminal of the subtractor 14.
[0039]
In parallel with this, the target frequency generator 13 generates a target frequency signal Sref indicating the rotation frequency at which the spindle motor 10 should be rotated, and outputs it to the other input terminal of the subtractor 14.
[0040]
Thus, the subtracter 14 subtracts the current rotational frequency of the spindle motor 10 indicated by the frequency signal Sf from the target frequency indicated by the target frequency signal Sref, and generates a control deviation signal Ser indicating the difference therebetween to compensate. Output to the device 15.
[0041]
Then, the compensator 15 digitizes the control deviation signal Ser and then performs phase compensation processing on the control deviation signal Ser by proportional integration control including periodic fluctuation removal processing by a moving average filter described later to generate a compensation operation signal Su. And output to the D / A converter 16.
[0042]
As a result, the D / A converter 16 converts the compensation operation signal Su from a digital signal to an analog signal, generates an analog operation signal Sau, and outputs the analog operation signal Sau to the drive circuit 17.
[0043]
The drive circuit 17 amplifies the analog operation signal Sau, which is a voltage signal, generates the drive signal Si having a current value corresponding to the voltage value, and outputs the drive signal Si to the spindle motor 10 to rotationally drive it.
[0044]
Next, the configuration and operation of the compensator 15 according to the present invention will be described with reference to FIGS.
[0045]
First, the overall configuration and operation of the compensator 15 will be described with reference to FIG.
[0046]
As shown in FIG. 2A, the compensator 15 includes an A / D converter 19, a multiplier 20 as a proportional multiplication unit, a multiplier 21 as an integral multiplication unit, and a moving average as an average filter unit. It comprises a filter 22, an integration calculator 23 as an integration means, and an adder 24 as an addition means.
[0047]
Next, the operation will be described.
[0048]
First, the A / D converter 19 converts the control deviation signal Ser output from the subtractor 14 from an analog signal to a digital signal, generates a digital control deviation signal Sda, and outputs the digital control deviation signal Sda to the multipliers 20 and 21, respectively. .
[0049]
Next, the multiplier 20 multiplies the digital control deviation signal Sda by a proportional term Kp set in advance in the proportional integration processing of the compensator 15 to generate a proportional control deviation signal Spd and the adder 24. Output to one input terminal.
[0050]
In parallel with this, the multiplier 21 multiplies the digital control deviation signal Sda by an integral term Ki set in advance in the proportional integration processing to generate an integral control deviation signal Sid and supplies it to the moving average filter 22. Output.
[0051]
Next, the moving average filter 22 having a configuration to be described later integrates the pulse period in the integral control deviation signal Sid sequentially input with the rotation of the spindle motor 10 by one rotation of the spindle motor 10 as will be described in detail later. Then, the operation of dividing by the number of pulses included in the one rotation is sequentially performed for each pulse in the integral control deviation signal Sid, the fluctuation of the pulse period in the integral control deviation signal Sid is removed, and the filter signal Sff is generated. To the integration calculator 23.
[0052]
By the averaging process in the moving average filter 22, the periodic fluctuation of the pulse in the integral control deviation signal Sid generated due to the position error of the rotation detection sensor in the pulse generator 10a is removed.
[0053]
Next, the integration calculator 23 performs a predetermined integration calculation in the proportional integration process on the filter signal Sff from which the periodic fluctuation has been removed to generate an integration signal Sif, and the other input of the adder 24 Output to the terminal.
[0054]
The adder 24 adds the proportional control deviation signal Spd from the multiplier 20 and the integration signal Sif from the integration calculator 23, and the compensation operation in which the fluctuation of the pulse period is removed and the phase is compensated. A signal Su is generated and output to the D / A converter 16.
[0055]
Here, the configuration and operation of the moving average filter 22 will be described.
[0056]
In the following description of the moving average filter 22, four Hall elements are arranged in a cross shape in a plane parallel to the rotating surface of the disk rotating with the rotation of the spindle motor 10 in the pulse generator 10 a, and these Hall elements The change in the magnetic field generated by the rotation of the disk is detected by each Hall element, and the pulse signal Srp synchronized with the rotation of the spindle motor 10 (that is, four equal intervals per one rotation of the spindle motor 10). A case where the pulse signal Srp) including a pulse is generated will be described.
[0057]
First, the configuration of the moving average filter 22 will be described.
[0058]
As shown in FIG. 2B, the moving average filter 22 of the first embodiment is one more than the number of pulses of the pulse signal Srp generated per rotation of the spindle motor 10 (“4” in the case of the first embodiment). A delay unit 25a, 25b and 25c as delay means connected in series with a smaller number, an adder 26 as delay addition means, and a divider 27 as division means.
[0059]
Here, the moving average filter 22 is a linear equation referred to as a so-called moving average model (when applied to the first embodiment, the linear equation H (z) is
[0060]
[Expression 1]
H (z) = {1 + z^-1+ Z^-2+ …… + z^-(N-1)} / N; (N is the number of pulses per rotation of the spindle motor 10)
It becomes. ) To perform an averaging process.
[0061]
The moving average model is detailed in, for example, “Automatic Control Handbook / Basics, Society of Instrument and Control Engineers, Ohmsha, 1983, pp216-217”.
[0062]
Next, the operation will be described.
[0063]
Each delay unit 25a, 25b, and 25c included in the moving average filter 22 sequentially delays the integral control deviation signal Sid by the interval between two adjacent pulses in the pulse signal Srp, and respectively delays the delay signals Sza, Szb, and Szc. And output to the adder 26.
[0064]
The adder 26 adds the original integral control deviation signal Sid before the delay and the delay signals Sza, Szb and Szc to each other, generates an addition signal Sa, and outputs it to the divider 27.
[0065]
Thereby, the divider 27 divides the addition signal Sa by the number of pulses of the pulse signal Srp generated per rotation of the spindle motor 10 (“4” in the case of the first embodiment), and generates the filter signal Sff. To the integration calculator 23.
[0066]
Next, the principle by which the fluctuation of the pulse period included in the pulse signal Srp is removed by the moving average filter 22 having the above-described configuration and operation will be described with reference to FIG.
[0067]
First, as a premise, in the pulse generator 10a of the first embodiment, as shown in FIG. 3A, a pulse signal Srp synchronized with the rotation of the spindle motor 10 by Hall elements 30a to 30d arranged in a cross shape. Furthermore, of the four Hall elements 30a to 30d, only the Hall element 30c is mounted with a deviation of d (rad) from the normal mounting position. It is assumed that a fluctuation t as shown in the uppermost part of FIG. 3B occurs in the pulse period of the pulse signal Srp. In the uppermost part of FIG. 3 (b), for each pulse of the pulse signal Srp, a code indicating the Hall element that generated each pulse is shown in correspondence with each pulse.
[0068]
Here, if the period of one rotation of the spindle motor 10 is T, as shown in FIG. 3B, the pulse period in the pulse signal Srp should be originally T / 4, but in the first embodiment, In this case, the pulse fluctuation t occurs due to the mounting position error of the Hall element 30c described above. Here, the pulse fluctuation t is a value equal to the product of the coefficient K (K = T / 2π (sec / rad)) and the position error d (rad).
[0069]
On the other hand, in FIG.₀Thru T_ThreeAs shown, the pulse period of the pulse signal Srp when viewed at one rotation of the spindle motor 10 is always a constant value T even if any Hall element has an error in its mounting position.
[0070]
Therefore, in the moving average filter 22, any one pulse of the pulse signal Srp is set as the head, and thereafter, an interval for each pulse until four pulses are detected (reference t in FIG. 3B).₀To t₆It shows with. ) And the interval T₀Thru T_ThreeAnd dividing these by the number of pulses generated during one rotation of the spindle motor 10 (“4” in FIG. 3), the exact value of the interval between two pulses in the pulse signal Srp ( In the case of FIG. 3, T / 4) is generated and output as the filter signal Sff.₀To P_ThreeAre sequentially executed for each pulse).
[0071]
Thereby, in the filter signal Sff, the fluctuation of the pulse period is removed, and further, the filter signal Sff indicating the regular pulse interval is generated for each regular pulse interval (T / 4).
[0072]
Next, transfer characteristics of the moving average filter 22 will be described with reference to FIG.
[0073]
4A shows the frequency-gain characteristic of the transfer characteristics, and FIG. 4B shows the frequency-phase characteristic of the transfer characteristics.
[0074]
As shown in FIG. 4, the moving average filter 22 has a characteristic that the gain is attenuated and the phase is rotated especially in the high frequency band in the operation described above.
[0075]
Therefore, in the present invention, the pulse fluctuation removal process by the moving average filter 22 is performed only on the integral control deviation signal Sid multiplied by the integral term, and specifically, the integral control deviation signal Sid is applied to the moving average filter. 22, after removing the pulse period variation, the signal is input to the adder 24 (by this process, the pulse period variation in the low frequency band is completely removed), while the proportional term is multiplied and the entire compensator 15 is multiplied. The proportional control deviation signal Spd that is dominant in the high frequency band when viewed in terms of transfer characteristics is input to the adder 24 without passing through the moving average filter 22.
[0076]
As a result, the transfer characteristics of the entire compensator 15 are shown in FIG. 5A (showing the frequency-gain characteristics of the transfer characteristics of the compensator 15) and FIG. 5B (of the transfer characteristics of the compensator 15). As shown in the frequency-phase characteristics, a decrease in gain and a phase delay in a high frequency band are suppressed to a minimum, and as a result, a decrease in gain and a phase delay are suppressed to a minimum. Pulse fluctuations in the pulse signal Srp can be removed.
[0077]
As described above, according to the operation of the spindle controller SC of the first embodiment, when the fluctuation of the cycle of the pulse signal Srp is compensated by the proportional integral control, the integral control deviation signal Sid multiplied by the integral term is added. On the other hand, after the averaging process is performed by the moving average filter 22 only, the integration operation is performed, and further, the compensation operation signal Su is generated by being added to the proportional control deviation signal Spd. Therefore, the pulse signal Srp includes a period variation. Even in such a case, the period fluctuation can be removed without reducing the phase margin, and the spindle motor 10 can be accurately feedback-controlled.
[0078]
In addition, the moving average filter 22 extracts the integrated control deviation signal Sid delayed by one sample timing every time it is delayed, and adds these to the integral control deviation signal Sid before the delay, and then generates it per revolution. Since the filter signal Sff is generated by dividing by the number of pulses of the pulse signal Srp to be generated, fluctuations in the cycle of the pulse signal Srp can be effectively removed.
[0079]
Further, when the rotation of the spindle motor 10 (that is, the optical disc DK) is feedback-controlled by frequency control, fluctuations in the cycle of the pulse signal Srp can be eliminated without reducing the phase margin, and accurate feedback control can be performed.
(II)Second embodiment
Next, 2nd Embodiment which is other embodiment which concerns on this invention is described based on FIG.
[0080]
FIG. 6 is a block diagram showing the configuration of the compensator according to the second embodiment. Further, in the configuration of the compensator, the same components as those of the compensator 15 of the first embodiment are denoted by the same member numbers. A detailed description will be omitted.
[0081]
In the first embodiment described above, the operation of the compensator 15 is performed digitally. However, in the second embodiment, a part of the compensator is configured using an analog circuit.
[0082]
In the information reproducing apparatus of the second embodiment, the configuration and operation other than the compensator included in the information reproducing apparatus are compensated without using the D / A converter 16 in the information reproducing apparatus S of the first embodiment. The information reproducing apparatus S is the same as the information reproducing apparatus S except that the analog operation signal Sau is directly output from the device, and detailed description thereof is omitted.
[0083]
First, the configuration and operation of the compensator 15 'according to the second embodiment will be described with reference to FIG.
[0084]
As shown in FIG. 6A, the compensator 15 ′ includes an analog inverting amplifier 42, an A / D converter 40, a moving average filter 22 ′, a D / A converter 41, a resistor 43a, and a capacitor 43b. An analog integrator 43 comprising an operational amplifier 43c, and R₁A resistor 44 having a resistance value of R₂A resistor 45 having a resistance value of R_ThreeAnd an analog adder 46 including an operational amplifier 46a.
[0085]
Further, as shown in FIG. 6B, the moving average filter 22 ′ has a configuration in which the divider 27 is removed from the moving average filter 22 of the first embodiment. The number of pulses of the pulse signal Srp generated per rotation (“4” in the case of the second embodiment) is one less than the number of serially connected delay devices 25 a to 25 c and the adder 26. .
[0086]
Next, the operation will be described.
[0087]
First, the analog inverting amplifier 42 inverts the polarity of the control deviation signal Ser output from the subtractor 14, generates the inverted deviation signal Srv, and outputs the inverted deviation signal Srv to the analog adder 46 via the resistor 44.
[0088]
On the other hand, the A / D converter 40 converts the control deviation signal Ser from an analog signal to a digital signal, generates a digital control deviation signal Sda, and outputs it to the moving average filter 22 '.
[0089]
The moving average filter 22 ′ performs an operation in the digital control deviation signal Sda for accumulating the pulse period in the digital control deviation signal Sda that is sequentially input with the rotation of the spindle motor 10 by one rotation of the spindle motor 10. This is performed sequentially for each pulse, and an addition signal Sa is generated and output to the D / A converter 41.
[0090]
At this time, in the moving average filter 22 ′, as in the case of the first embodiment, when a pulse signal Srp including four pulses per one rotation of the spindle motor 10 is generated, a linear equation is used.
[0091]
[Expression 2]
H ′ (z) = 1 + z^-1+ Z^-2+ Z^-3
The delay integration process indicated by is performed.
[0092]
More specifically, the delay devices 25a, 25b, and 25c sequentially delay the digital control deviation signal Sda by an interval between two adjacent pulses in the pulse signal Srp, thereby generating delayed signals Sza, Szb, and Szc, respectively. Are output to the adder 26, and the adder 26 adds the original digital control deviation signal Sda before the delay and the delayed signals Sza, Szb and Szc to each other, and the D / A converter as the added signal Sa. 41 is output.
[0093]
Next, the D / A converter 41 converts the addition signal Sa into an analog signal, generates an analog addition signal Saa, and outputs the analog addition signal Saa to the analog integrator 43.
[0094]
Thereby, the analog integrator 43 having the configuration shown in FIG. 6A performs the same integration process as the integration calculator 23 in the compensator 15 of the first embodiment on the analog addition signal Saa, and the analog integration signal Sia is generated and output to the analog adder 46 via the resistor 45.
[0095]
Then, the analog adder 46 adds the inverted deviation signal Srv and the analog integration signal Sia by the addition ratio determined by the resistance values of the resistors 44, 45 and 46, and the analog operation signal Sau similar to the first embodiment. Is output to the drive circuit 17.
[0096]
At this time, the resistance value R of the resistor 44₁, Resistance value R of resistor 45₂And the resistance value R of the resistor 46_ThreeRespectively, between the proportional term Kp and the integral term Ki in the compensator 15 of the first embodiment,
[0097]
[Equation 3]
R_Three/ (R₂× N) = Ki (N is the number of pulses per rotation of the spindle motor 10)
R_Three/ R₁= Kp
Is set to hold.
[0098]
Since there is the above-described relationship between the respective resistance values of the resistors 44, 45 and 46b and the proportional term Kp and the integral term Ki, compensation by proportional integral control similar to that of the compensator 15 of the first embodiment is compensated. It can also be implemented in the device 15 ', and further, the averaging process as the moving average filter 22' can be performed as in the case of the first embodiment.
[0099]
As described above, the analog operation signal Sau similar to that of the compensator 15 of the first embodiment can be generated also by the compensator 15 ′ of the second embodiment. As a result, the information reproducing apparatus of the second embodiment can also generate the analog operation signal Sau. The same effect as the information reproducing apparatus S of the first embodiment can be obtained.
(III)Third embodiment
Next, a third embodiment, which is another embodiment according to the present invention, will be described with reference to FIG.
[0100]
FIG. 7 is a block diagram showing a schematic configuration of the information reproducing apparatus according to the third embodiment. Here, in FIG. 7, about the same component as the information reproducing | regenerating apparatus S of 1st Embodiment shown in FIG. 1, the same member number is attached | subjected and detailed description is abbreviate | omitted.
[0101]
In the first embodiment described above, the case where the rotation of the spindle motor 10 is feedback controlled by the proportional-integral control based on the frequency has been described. However, in the third embodiment, the rotation of the spindle motor 10 is proportional-differential-integrated based on the phase. Feedback control is performed by the control.
[0102]
First, the configuration of the information reproducing apparatus according to the third embodiment will be described with reference to FIG.
[0103]
As shown in FIG. 7, the information reproducing apparatus S ′ according to the third embodiment includes a spindle controller SC ′ instead of the spindle controller SC in the information reproducing apparatus S according to the first embodiment.
[0104]
The spindle controller SC ′ includes the same period detector 11 as in the first embodiment, a Tf converter 12 as a frequency converter, a target frequency generator 13, a subtractor 14, and a D / A converter. 16 and the drive circuit 17, a T-θ converter 31 as a phase conversion means, a phase comparator 32, a target phase generator 33, a compensator 15 ″, and a multiplier 34 as a differential multiplication means , And an adder 35.
[0105]
Next, an outline operation will be described.
[0106]
First, the pickup 1 irradiates the information recording surface of the optical disc DK with the light beam B as in the first embodiment, and outputs a detection signal corresponding to the information on the optical disc DK based on the reflected light.
[0107]
At this time, the pickup control unit PC changes the focal position of the light beam B and performs focus servo control or tracking servo control.
[0108]
On the other hand, as in the case of the first embodiment, the spindle motor 10 rotates the optical disk DK based on the drive signal Si, and in parallel with this operation, the pulse generator 10a generates the pulse signal Srp to generate a cycle. Output to the detector 11.
[0109]
Next, the period detector 11 detects the rotation period of the spindle motor 10 based on the pulse signal Srp as in the case of the first embodiment, generates the period signal St, and generates the Tf converter 12 and T Output to -θ converter 31.
[0110]
The T-f converter 12 converts the rotation period of the spindle motor 10 indicated by the period signal St into a rotation frequency as in the case of the first embodiment, generates a frequency signal Sf, and generates a frequency signal Sf. Output to one input terminal.
[0111]
In parallel with this, the target frequency generator 13 generates the target frequency signal Sref and outputs it to the other input terminal of the subtractor 14 as in the case of the first embodiment.
[0112]
Thus, the subtractor 14 subtracts the current rotational frequency of the spindle motor 10 indicated by the frequency signal Sf from the target frequency indicated by the target frequency signal Sref, and generates and multiplies the frequency deviation signal Sef indicating the difference therebetween. Output to the unit 34.
[0113]
Thereby, the multiplier 34 multiplies the frequency deviation signal Sef by a preset differential term Kd in the proportional differential integral control of the second embodiment, generates a differential frequency signal Sfd, and supplies it to one terminal of the adder 35. Output.
[0114]
On the other hand, the T-θ converter 31 converts the rotation cycle of the spindle motor 10 indicated by the cycle signal St into a rotation phase, generates a phase signal Sp, and outputs it to one input terminal of the phase comparator 32.
[0115]
In parallel with this, the target phase generator 33 generates a target phase signal Srefp indicating the rotational phase at which the spindle motor 10 should be rotated, and outputs it to the other input terminal of the phase comparator 32.
[0116]
Thus, the phase comparator 32 subtracts the current rotational phase of the spindle motor 10 indicated by the phase signal Sp from the target phase indicated by the target phase signal Srefp, and generates a control deviation signal Sdp indicating the difference therebetween. Output to the compensator 15 ".
[0117]
The compensator 15 ″ having the same configuration and operation as the compensator 15 of the first embodiment performs the control deviation by proportional-integral control including period fluctuation removal processing by a moving average filter after digitizing the control deviation signal Sdp. A phase compensation process is performed on the signal Sdp to generate a compensation operation signal Sh and output it to the other input terminal of the adder 35.
[0118]
Thus, the adder 35 adds the compensation operation signal Sh and the differential frequency signal Sfd, generates an addition operation signal Spu, and outputs it to the D / A converter 16.
[0119]
Then, as in the case of the first embodiment, the D / A converter 16 converts the addition operation signal Spu from a digital signal to an analog signal, generates an analog operation signal Sau, and outputs the analog operation signal Sau to the drive circuit 17.
[0120]
As a result, the drive circuit 17 generates the drive signal Si as in the case of the first embodiment, and outputs the drive signal Si to the spindle motor 10 for rotational driving.
[0121]
At this time, in the compensator 15 ″, similar to the operation of the compensator 15 described above, only the control deviation signal Sdp multiplied by the integral term is subjected to the averaging process by the above-described moving average filter, and then the integration operation is further performed. The compensation operation signal Sh is generated by adding the control deviation signal Sdp multiplied by the proportional term to the output signal after the integration operation.
[0122]
In addition, since the detailed operation and the like of the compensator 15 ″ and the transfer characteristics thereof are the same as those of the compensator 15, detailed description thereof is omitted.
[0123]
As described above, according to the operation of the spindle control unit SC ′ of the third embodiment, the control deviation signal Sdp multiplied by the integral term is used when the fluctuation of the cycle of the pulse signal Srp is compensated by the proportional differential integral control. Since the compensation operation signal Sh is generated by adding the control deviation signal Sdp obtained by performing an integration operation after being subjected to the averaging process to the moving average filter and further multiplied by the proportional term, the pulse signal Srp is added to the pulse signal Srp. Even when periodic fluctuations are included, the periodic fluctuations can be removed without reducing the phase margin, and the spindle motor 10 can be accurately feedback controlled.
[0124]
Furthermore, when the rotation of the spindle motor 10 is feedback controlled by phase control, fluctuations in the cycle of the pulse signal Srp can be removed without reducing the phase margin, and accurate feedback control can be performed.
[0125]
In each of the embodiments described above, the case of removing the pulse period variation included in the pulse signal Srp generated using the Hall element has been described, but in addition to this, there are a large number of slits in the circumferential direction. In an information reproducing apparatus including a pulse generator of a type that generates a pulse signal Srp by irradiating a light beam such as a laser beam onto a disk that rotates as the spindle motor 10 rotates, the information reproduction apparatus is caused by a position error of the slit. It can also be applied when removing pulse fluctuations.
[0126]
Further, in each of the above-described embodiments, the moving average filter 22 has been described with respect to the configuration in which the pulses generated in one rotation of the spindle motor 10 are accumulated and averaged. Pulses generated over two revolutions or more may be accumulated and averaged.
[0127]
Further, in each of the above-described embodiments, the case where the present invention is applied to the spindle motor 10 in the information reproducing apparatus S or S ′ has been described. However, other than this, an information recording apparatus that records information on an optical disk It is also possible to apply the present invention to the rotation control of the spindle motor in the same way.
[0128]
Furthermore, the present invention is a rotation servo that controls rotation of a motor other than a spindle motor that rotates an optical disk and that should be rotated at a preset rotation speed by rotation servo control including feedback control. The present invention can be similarly applied to a control device or a rotation servo control method.
[0129]
【The invention's effect】
As described above, according to the first aspect of the present invention, when the fluctuation of the rotation signal cycle is compensated by proportional integral control, the proportional deviation signal obtained by multiplying the control deviation signal by the proportional term, and the control Since the compensation signal is generated by adding the integral average signal obtained as a result of performing multiplication processing, accumulation processing, averaging processing, and integration calculation processing on the deviation signal, the rotation signal includes periodic fluctuations. Even in such a case, the period fluctuation can be removed without reducing the phase margin in the feedback control theory, and the rotation means can be accurately feedback controlled.
[0130]
Therefore, by using an inexpensive configuration with low accuracy in generating the rotation signal, even if the rotation signal includes a periodic variation, the rotation unit can be effectively servo-controlled by effectively removing the variation.
[0131]
According to the invention described in claim 2, in addition to the effect of the invention described in claim 1, the integrated deviation signal delayed by one sample timing is extracted every time it is delayed, and these and the current sample timing are extracted. Since the average deviation signal is generated by adding the integral deviation signal and dividing by at least the number of pulses of the rotation signal generated per rotation, fluctuations in the period of the rotation signal can be effectively removed.
[0132]
According to the invention described in claim 3, in addition to the effect of the invention described in claim 1 or 2, in the rotary servo control device that feedback controls the rotation of the rotating means by frequency control, the phase margin in the feedback control theory is increased. Variations in the period of the rotation signal can be eliminated without reducing it, and the rotation means can be accurately feedback controlled.
[0133]
According to the invention described in claim 4, in addition to the effect of the invention described in claim 1 or 2, in the rotary servo control device that feedback controls the rotation of the rotating means by phase control, the phase margin in the feedback control theory is increased. Variations in the period of the rotation signal can be eliminated without reducing it, and the rotation means can be accurately feedback controlled.
[0134]
Furthermore, even when the rotation of the rotating means is so-called proportional integral derivative control, the rotation can be accurately feedback controlled.
[0135]
According to the invention described in claim 5, in addition to the effect of the invention described in any one of claims 1 to 4, the rotation of the disk-shaped recording medium can be performed without reducing the phase margin in the feedback control theory. It is possible to accurately perform feedback control by removing fluctuations in the period of the rotation signal.
[0136]
According to the sixth aspect of the present invention, when the fluctuation of the rotation signal cycle is compensated by proportional integral control, a proportional deviation signal obtained by multiplying the control deviation signal by the proportional term is multiplied by the control deviation signal. Since the integral average signal obtained as a result of performing the processing, the accumulation process, the averaging process, and the integral calculation process is added to generate the compensation signal, even when the rotation signal includes a periodic variation, The period fluctuation can be removed without reducing the phase margin in the feedback control theory, and the rotation means can be accurately feedback controlled.
[0137]
Therefore, by using an inexpensive configuration with low accuracy in generating the rotation signal, even if the rotation signal includes a periodic variation, the rotation unit can be effectively servo-controlled by effectively removing the variation.
[0138]
According to the invention described in claim 7, in addition to the effect of the invention described in claim 6, the integrated deviation signal delayed by one sample timing is extracted every time it is delayed, and these and the current sample timing are extracted. Since the average deviation signal is generated by adding the integral deviation signal and dividing by at least the number of pulses of the rotation signal generated per rotation, fluctuations in the period of the rotation signal can be effectively removed.
[0139]
According to the invention described in claim 8, in addition to the effect of the invention described in claim 6 or 7, the rotation of the disk-shaped recording medium can be performed with the period of the rotation signal without reducing the phase margin in the feedback control theory. The feedback can be accurately controlled by removing the fluctuation.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of an information reproducing apparatus according to a first embodiment.
FIG. 2 is a block diagram showing the configuration of the compensator of the first embodiment, (a) is a block diagram showing the overall configuration of the compensator, and (b) is a block showing the detailed configuration of the moving average filter. FIG.
3A and 3B are diagrams showing the operation of the moving average filter, wherein FIG. 3A is a schematic diagram showing the arrangement of Hall elements, and FIG. 3B is a timing chart showing the operation.
4A and 4B are diagrams illustrating transfer characteristics of a moving average filter, in which FIG. 4A is a diagram illustrating frequency-gain characteristics thereof, and FIG. 4B is a diagram illustrating frequency-phase characteristics thereof;
FIGS. 5A and 5B are diagrams illustrating transfer characteristics of the entire compensator, wherein FIG. 5A is a diagram illustrating frequency-gain characteristics thereof, and FIG. 5B is a diagram illustrating frequency-phase characteristics thereof;
6 is a block diagram showing a configuration of a compensator according to a second embodiment, FIG. 6A is a block diagram showing an overall configuration of the compensator, and FIG. 6B is a block showing a detailed configuration of a moving average filter. FIG.
FIG. 7 is a block diagram showing a schematic configuration of an information reproducing apparatus according to a third embodiment.
[Explanation of symbols]
1 ... Pickup
10 ... Spindle motor
10a ... Pulse generator
11. Period detector
12 ... Tf converter
13 ... Target frequency generator
14 ... Subtractor
15, 15 ', 15 "... compensator
16, 41 ... D / A converter
17 ... Drive circuit
19, 40 ... A / D converter
20, 21, 34 ... multiplier
22, 22 '... Moving average filter
23 ... Integral calculator
24, 26, 35 ... adder
25a, 25b, 25c ... delay devices
27: Divider
30a, 30b, 30c, 30d ... Hall element
31 ... T-θ converter
32 ... Phase comparator
33 ... Target phase generator
42. Analog inverting amplifier
43. Analog integrator
43a, 44, 45, 46b ... resistance
43b ... Capacitor
43c, 46a ... operational amplifier
46: Analog adder
S: Information reproducing device
B ... Light beam
SC ... Spindle control unit
PC ... Pickup controller
DK ... Optical disc
Srp ... pulse signal
St: Periodic signal
Sf: Frequency signal
Sref: Target frequency signal
Ser, Sdp: Control deviation signal
Su, Sh ... Compensation operation signal
Sau… Analog operation signal
Si: Drive signal
Sda: Digital control deviation signal Sda
Spd ... Proportional control deviation signal
Sid ... Integral control deviation signal
Sff: Filter signal
Sif ... Integral signal
Sza, Szb, Szc ... Delay signal
Sa: Addition signal
Sp: Phase signal
Srefp: Target phase signal
Sfd: Differential frequency signal
Spu: Addition operation signal
Srv: Inversion deviation signal
Saa: Analog addition signal
Sia: Analog integration signal

Claims (8)

In the rotary servo control device that controls the rotation of the rotating means by feedback control,
Generating means for generating a rotation signal synchronized with the rotation of the rotating means;
Control deviation generation means for generating a control deviation signal indicating a difference between the current rotation speed of the rotation means indicated by the generated rotation signal and a target rotation speed that is the rotation speed to rotate the rotation means;
Compensation means for generating a compensation signal based on the generated control deviation signal by compensating for a variation in the period of the rotation signal included in the rotation signal when the rotation signal is generated by proportional-integral control. When,
Drive means for rotating the rotation means based on the generated compensation signal,
The compensation means includes
A proportional multiplication means for multiplying the control deviation signal by a proportional term in the proportional integral control to generate a proportional deviation signal;
Multiplication processing for multiplying the control deviation signal by an integral term in the proportional integral control, accumulation processing for accumulating only the integral term of the control deviation signal corresponding to one or a plurality of rotations of the rotating means, the integration and integrating averaging means for averaging the accumulated result of the term, and the integral calculation processing each subjected to corresponding only to said integral term, to produce an integrated and averaged error signal,
Adding means for adding the proportional deviation signal and the integral average deviation signal to generate the compensation signal;
It is comprised by these. The rotation servo control apparatus characterized by the above-mentioned. The rotary servo control device according to claim 1,
The generating means generates the rotation signal that is a pulse signal,
The integral averaging means includes
Integral multiplication means for performing the multiplication processing on the control deviation signal;
A plurality of delay means connected in series to each other by at least one less than the number of pulses of the rotation signal generated per rotation of the rotation means, and sequentially delaying the integral deviation signal by one sample timing;
The integral deviation signal delayed by each of the delay means is extracted every time one sample timing is delayed, and the extracted integral deviation signal is added to the original integral deviation signal before the delay, respectively. A delay addition means for performing accumulation processing and generating an addition signal;
Dividing means for performing the averaging process by dividing the generated addition signal by the number of pulses of the rotation signal generated per rotation of the rotation means, and generating the average deviation signal;
An integration means for performing the integration calculation processing on the generated average deviation signal and generating the integral average signal;
A rotary servo control device comprising: In the rotary servo control device according to claim 1 or 2,
Frequency conversion means for converting the rotation signal into a frequency signal having a frequency corresponding to the rotation speed of the rotation means;
The control deviation generating means generates a difference between the frequency of the frequency signal and a target frequency corresponding to the target rotational speed as the control deviation signal,
The rotational servo control device, wherein the compensation means generates the compensation signal based on a frequency indicated by the control deviation signal. In the rotary servo control device according to claim 1 or 2,
Frequency conversion means for converting the rotation signal into a frequency signal having a frequency corresponding to the number of rotations of the rotation means;
Phase conversion means for converting the rotation signal into a phase signal having a phase corresponding to a rotation angle of the rotation means;
Differential multiplication means for generating a differential signal by multiplying the frequency signal by a preset differential term;
Further comprising
The control deviation generating means generates, as the control deviation signal, a difference between the phase of the phase signal and a target phase corresponding to a target rotation angle corresponding to the target rotation speed,
The compensation means generates the compensation signal based on the phase indicated by the control deviation signal,
The rotation servo control device characterized in that the drive means rotates the rotation means based on an addition signal generated by adding the generated compensation signal and the differential signal. In the rotation servo control device according to any one of claims 1 to 4,
The rotary servo control device, wherein the rotating means is a spindle motor that rotates a disk-shaped recording medium on which information is optically recorded and reproduced. In the rotation servo control method for controlling the rotation of the rotating means by feedback control,
A generation step of generating a rotation signal synchronized with the rotation of the rotation means;
A control deviation generating step for generating a control deviation signal indicating a difference between a current rotation speed of the rotation means indicated by the generated rotation signal and a target rotation speed that is a rotation speed to rotate the rotation means;
A compensation step for generating a compensation signal by compensating for a variation in the period of the rotation signal included in the rotation signal when the rotation signal is generated based on the generated control deviation signal by proportional-integral control. When,
A driving step of rotating the rotating means based on the generated compensation signal,
The compensation step includes
A proportional multiplication step of multiplying the control deviation signal by a proportional term in the proportional integral control to generate a proportional deviation signal;
Multiplication processing for multiplying the control deviation signal by an integral term in the proportional integral control, accumulation processing for accumulating only the integral term of the control deviation signal corresponding to one or a plurality of rotations of the rotating means, the integration averaging process of the accumulation result of the term, and the integral calculation processing each subjected to corresponding only to said integral term, the integral averaging step of generating an integrated average deviation signal,
Adding the proportional deviation signal and the integral average deviation signal to generate the compensation signal;
A rotation servo control method comprising: In the rotation servo control method according to claim 6,
In the generation step, the rotation signal which is a pulse signal is generated,
The integral averaging step includes
An integral multiplication step of performing the multiplication process on the control deviation signal;
A plurality of delay steps executed at least one less than the number of pulses of the rotation signal generated per one rotation of the rotation means, and sequentially delaying the integral deviation signal by one sample timing;
The integral deviation signal delayed in each delay step is extracted every time one sample timing is delayed, and the extracted integral deviation signal is added to the original integral deviation signal before the delay, respectively. A delay addition step of performing an accumulation process and generating an addition signal;
A division step of performing the averaging process by dividing the generated addition signal by the number of pulses of the rotation signal generated per one rotation of the rotation means, and generating the average deviation signal;
An integration step of performing the integration calculation process on the generated average deviation signal and generating the integrated average signal;
A rotation servo control method comprising: In the rotation servo control method according to claim 6 or 7,
The rotation servo control method, wherein the rotation means is a spindle motor that rotates a disk-shaped recording medium on which information is optically recorded and reproduced.

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