JPH10208369A - Disk reproducing device, and head position calculating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly read out TOC(table of contents) information at the time of loading a disk without using a limit switch. SOLUTION: A recorded EFM (8-14 modulation) signal is read out by an optical pickup head 12 from an optical disk 10 driven by a motor 11 to rotate at a constant linear velocity in a TOC position of the optical disk 10, and is amplified by an amplifier 13 and is then sent to a signal processing circuit 20, where an inverted frequency value is detected. The detected inverted frequency value is sent to a calculating function part 41 of a control circuit 40, where a comparison is made with an inverted frequency value of a reference EFM signal to obtain the present position of the optical pickup head 12 in the radial direction of the disk. A head transfer amt. is obtained from the evaluated head position in the radial direction of the disk and the TOC position, and hence the optical pickup head 12 is transferred in the radial direction of the disk by this amt. to access the TOC.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disk reproducing apparatus which detects a disk radial position of a reproducing head and transfers the disk to a target disk radial position, and a head position calculation for obtaining the position of the reproducing head on the disk. About the method.

[0002]

2. Description of the Related Art Conventionally, various types of disk-shaped recording media are known. Among them, a read-only optical disk such as a so-called compact disk,
2. Description of the Related Art Recordable optical disks capable of recording and erasing information signals as well as reproduction are widely known.

[0003] A read-only optical disk has a concavo-convex pattern, that is, a track in which phase pits are formed concentrically or spirally, on one surface based on a recorded information signal.

On the other hand, as the recordable optical disks, optical disks using a phase change type optical recording material and magneto-optical disks using a perpendicular magnetic recording material are known.

In the magneto-optical disk, a guide groove for guiding a light beam is formed on one surface, and a disk substrate made of a synthetic resin material such as polycarbonate or PMMA having a light transmitting property and covering the guide groove. Formed of a perpendicular magnetic recording material such as Te, Fe, Co, etc. formed as described above, and a protective layer formed so as to cover the recording layer for the purpose of protecting this recording layer. I have.

[0006] In the method of reproducing these optical disks, in the case of the former read-only optical disk, a light beam from a laser light source is irradiated from a disk substrate side in a state of being focused by an objective lens, and a reflection film of the optical disk is formed. A reproduction signal of an information signal recorded on a read-only optical disk can be obtained by utilizing the diffraction of the light flux reflected by the phase pits of the optical disk.

In the case of the latter recordable optical disk (in particular, a magneto-optical disk), the light beam from the laser light source is transmitted from the disk substrate side to the objective lens in the same manner as the above-mentioned read-only optical disk. By irradiating in a focused state and detecting the Kerr rotation angle in the light beam reflected by the recording layer of the optical disk, a reproduction signal of the information signal recorded on the magneto-optical disk can be obtained.

[0008]

By the way, at a predetermined position on the optical disk, for example, at the innermost position, a so-called TO
Disk management information such as C (Table Of Contents) is recorded. Immediately after the disk is mounted, it is usually necessary to read the disk management information in a normal case.

The following two methods are known as methods for reading the disk management information.

That is, in the first method, first, a reproducing head such as an optical pickup is forcibly moved to the inner peripheral side.
The position of the head at the innermost circumference is detected by a limit switch provided on the inner circumference, and based on this position, the head is sent to a recording area (a so-called TOC area) of the disc management information, and the disc management information is focused on. It is a method of reading.

The second method is to extract an absolute address previously recorded on a disk from a reproduction signal as an address in a disk radial direction where an optical pickup is located at the start of reproduction, and to extract the extracted address and a TOC area. A method of obtaining the head movement amount based on the address difference can be considered.

The first method has the disadvantage that a limit switch is required, the number of parts and the number of assembling steps are increased, the switch mounting accuracy is required, and a switch mounting space is required.

In the second method, the following procedure must be performed before reading a reproduction signal from the disk.

First, at the start of reproduction, a focus servo is applied at a position where the optical pickup is located, and a kick voltage for starting the diode is also applied to the spindle motor to rotate the disk. Speed control in which the tracking is turned on with the focus servo applied and the disk is accelerated / decelerated so that the probability of occurrence of a synchronization signal (for example, a pattern including 11T) extracted from a reproduction signal reproduced from the disk is increased. I do. The control speed is determined by comparing the length of a predetermined pattern of a synchronization signal extracted from a reproduction signal reproduced from a disc with the same length of a reference synchronization signal (for example, 11T).
Acceleration / deceleration control is performed so that the occurrence probability of coincidence between the two becomes high. A state in which only the acceleration / deceleration control is performed is hereinafter referred to as a rough servo state. By performing the rough servo, it is possible to substantially approach a rotation speed corresponding to a position where the optical pickup is located at the time of starting reproduction. In this state, by operating both the speed control and the phase control, it is possible to pull in the desired rotational speed. In this state, the PLL (Phase Locked Loo
p) The circuit is locked.

The above address can be read only when the PLL circuit is locked. In particular, the position where the optical pickup is located at the start of reproduction is located near the outermost periphery, and the TOC on the innermost periphery after the address reading is performed.
In order to access the area, it takes at least about 3 to 4 seconds.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and can detect the current position of an optical pickup head on a disk and access a TOC area without using a limit switch. A disk reproducing apparatus and a head position calculating method capable of determining the position of a focus-on portion before performing a pull-in operation (speed control and phase control) of a spindle motor and enabling quick access to TOC information. It is intended to provide.

[0017]

In order to solve the above-mentioned problem, a disk reproducing apparatus according to the present invention provides a run-length limited code in which a modulation pattern changes within an interval determined by a maximum inversion interval and a minimum inversion interval. A disk reproducing apparatus for reproducing a disk on which a digital signal modulated by the above is recorded; a rotation driving unit for driving the disk to rotate; a reproduction unit for reading a digital signal recorded on the disk; and the rotation driving unit. Control means for rotating at a constant speed, and under the condition of the constant speed rotation,
A first calculating means for calculating an average inversion frequency at a position where the reproducing means is currently located from the digital signal read by the reproducing means, and a calculation based on a possible generation pattern among the modulation patterns. Storage means for storing an average inversion frequency to be a reference; average inversion frequency at a position where the current reproducing means is calculated by the first arithmetic means; and average inversion frequency to be a reference stored in the storage means And a second calculating means for calculating the position of the disc radius method in which the reproducing means is currently located based on the above.

Here, by calculating the transfer amount of the reproducing means to the target disk diameter position based on the detected disk diameter position, the reproducing means can be sent to the target position. In this case, the disk is rotationally driven at a rotation speed at which the average reversal value of the run-length limited code of the signal reproduced at the target disk radial position becomes the reference average reversal value. Can be detected.

When a modulation signal modulated at a constant frequency is recorded on the disk, the modulation frequency component is extracted and compared with a reference modulation frequency to determine the current disk diameter position. The reproducing means can be transferred to a target disk diameter position according to the obtained disk diameter position.

Further, in order to solve the above-mentioned problem, the head position calculating method according to the present invention modulates a head by a run length limited code in which a modulation pattern changes within an interval determined by a maximum inversion interval and a minimum inversion interval. A head position calculating method for calculating a disk radial position of a reproducing head on a disk on which a digital signal is recorded,
Rotating the disc at a constant speed at a predetermined speed;
Turning on the focus servo and tracking servo by the reproducing head under the condition of the constant speed rotation, and calculating an average inversion frequency at a position where the reproducing head is currently located from the digital signal read by the reproducing head. Reading the average inversion frequency, which is a reference calculated based on a possible generation pattern among the modulation patterns stored in advance in the memory; and Calculating the position of the disc radius method where the reproducing head is currently located, based on the average inversion frequency and the reference average inversion frequency read from the memory.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a disk reproducing apparatus and a head position calculating apparatus according to the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of a disk reproducing apparatus according to an embodiment of the present invention. In FIG. 1, for example, a reproduction only optical disk 10 is rotated by a disk rotation driving motor (so-called spindle motor) 11. After rotation, the signal recorded on the optical disk 10 is read from an optical pickup head 12 as a reproducing head via an amplifier 13, and the read signal is processed by a signal processing circuit 16 to obtain a reproduced signal. The data is
The signal is converted into an analog signal by the A conversion unit 16, amplified, and sent to the speaker 18.

The optical pickup head 12 of the disc reproducing apparatus shown in FIG. 1 receives reflected light from the music reproducing optical disc 10 by a light receiving element divided into a plurality of light receiving sections.
An amplifier (a so-called RF amplifier) 1
The RF amplifier 13 extracts a so-called RF signal, focus error signal, tracking error signal, and the like, and sends the signal to the signal processing circuit 20. The signal processing circuit 20 has a reproduction signal processing unit 21 for reproducing digital signals and a servo signal processing unit 22 for processing servo signals. The reproduction signal processing unit 21 of the signal processing circuit 20 reads data from the RF signal, separates subcode data, and
0, or decodes the main data using a memory 25 such as a DRAM.
The servo signal processing unit 22 of the signal processing circuit 20
A focus control signal, a tracking control signal, and the like are output based on the signal, the focus error signal, the tracking error signal, and the like, and are sent to the drive circuit 30.

The drive circuit 30 moves the objective lens of the optical pickup head 12 in the optical axis direction to control the focus, and moves the objective lens of the optical pickup head 12 in the tracking direction to perform tracking. Tracking drive unit 3 for taking
2, a head transfer unit 33 for moving the optical pickup head 12 in the disk radial direction (so-called sled movement) to access the disk, and a rotation for rotationally driving the disk rotation drive motor (so-called spindle motor) 11. And a drive unit 34. Each of these drive units supplies a drive current to each unit according to each servo control signal from the servo signal processing unit 22 of the signal processing circuit 20, a disk access control signal from the control circuit 40, and the like.

The control circuit 40 includes sub-code data separated by the reproduction signal processing unit 21 of the signal processing circuit 20, partial data from the servo signal processing unit 22, and the key input unit 4.
Key input data and the like from 6 are supplied, and various control signals and data are sent to the amplifier 13, the D / A conversion unit 16, the signal processing circuit 20, the drive circuit 30, and the display unit 48.

The memory 49 stores a reference average inversion frequency F ₀ as a known value required in a disk diameter position calculation described later and a disk diameter R _{0 serving as} a target TOC position.

Here, as an example of the recording format of the optical disk 10 used in the disk reproducing apparatus of FIG. 1,
For data such as audio data, EFM (8-14 modulation: Eigh) which is a kind of run-length limited code
FIG. 2 shows a specific example in the case where recording is performed by performing (t-Fourteen Modulation).

FIG. 2 shows a recording format of one frame of a signal modulated by the EFM modulation method.
In FIG. 2, at the beginning of one frame, a sync pattern deviating from the EFM modulation rule (so-called out-of-rule) is used as a sync pattern of a reference channel bit clock inversion interval T (T = 1 / 4.3218 MHz) after modulation. A pattern having a portion where two 11-time inversion intervals 11T are continuous is arranged. Subsequent to such a sync pattern, subcode data, main data (for example, audio data, etc.), and parity data are arranged. In each data, one symbol (8 bits) of data before modulation corresponds to 14 channel bits after modulation, and a margin bit (connection bit) of 3 channel bits is arranged between each data of 14 channel bits. Have been.

Since the frequency of the EFM frame is 7.35 kHz and one EFM frame is 588 channel bits, the frequency of the channel bits is 4.3218 MHz (= 5
88 x 7.35 kHz).

The recording format shown in FIG. 2 is a so-called CD (compact disk) format.
It is also used as a format of a system for recording and / or reproducing a CD-ROM or a compressed audio signal on a small disk having a diameter of 64 mm. In this case, 2352 bytes of main data include synchronization data and header data. I have.

In the modulation rule of the EFM modulation method, the minimum inversion interval is 3T and the maximum inversion interval is 11T.
A conversion table for converting the 8-bit input data into 256 14-channel bit EFM words is predetermined. When the number of reversals in one word is totaled for these 256 EFM words, as disclosed by the present applicant in Japanese Patent Application No. Hei 6-330382 and the drawings, the EFM word with one reversal number is: Word EFM word with 2 inversion times: 56 words EFM word with 3 inversion times: 120 words EFM word with 4 inversion times: 70 words EFM word with 5 inversion times: 6 words.

From the above, 1 of 256 EFM words is obtained.
The average number of inversions in a word is (1 × 4 + 2 × 56 + 3 × 120 + 4 × 70 + 5 × 6)
/ 256 = 786/256, which is almost three times on average.

Next, the average number of inversions within one EFM frame is determined. As shown in FIG. 2, one EFM frame is composed of a subcode of 1 EFM word, main data of 24 EFM words, and parity of 8 EFM words, 11T + 11T + 2T, that is, a sync pattern of three inversions, and 34 EFM words. And a margin bit of the same location. Therefore, if the data to be EFM encoded is a random number and the inversion occurrence probability at each margin bit is １ ／, the average number of inversions in one EFM frame is (786/256) × 33 + ( From (）) × 34 + 3, it is about 121.32 times. "33" in this equation
Is the total number of words of the subcode, main data, and parity, "34" is the number of margin bits, and "3" is the number of inversions of the sync pattern.

Since the frequency of the EFM frame is 7.35 kHz as described above, the average inversion frequency of the EFM signal is about 445.85 × 10 ³ from (121.32 × 7.35 × 10 ³ ) / 2. Ie about 445.8
It can be considered as 5 kHz. The average inversion frequency of the EFM signal is a value that is almost reliable when the main data is data close to a random number such as compressed data.

In the embodiment of the present invention, the focus servo is turned on at the current radial position of the disk, the spindle motor is rotated at a constant speed, and the run length code is extracted from the reproduced signal reproduced from the disk. Then, the average inversion frequency at the current disk radial position is calculated from the extracted run-length code.

The calculated average reversal frequency at the radial position of the disk where the optical pickup is currently located,
The radial position of the disk where the optical pickup is currently located is determined from the average inversion frequency based on a possible generation pattern in the EFM modulation method stored in the memory in advance.

The above calculation is performed by the calculation function section 41 for the disk diameter position and the like of the control circuit 40 in FIG. 1, for example. Further, a head transfer amount is obtained based on the current position and the access destination address obtained by the arithmetic function unit 41, and the optical pickup head 12 in FIG. 1 is transferred in the disk radial direction by the obtained head transfer amount. like,
The control circuit 40 controls the head transfer section 33 of the drive circuit 30 so that the head can be accessed to the target position.

When the average inversion frequency is actually obtained, for example, as shown in FIG. 3, the reproduced RF signal supplied from the optical pickup head 12 shown in FIG. The signal is amplified by 53 (corresponding to the amplifier 13 in FIG. 1), divided by the frequency divider 54 to 1 / n, and the obtained signal is sent to a frequency-voltage conversion (fV conversion) circuit 55 to represent the frequency. The signal is converted into a voltage signal and is taken out via an output terminal 56. This voltage signal is sent to, for example, an A / D conversion terminal of a microcomputer used in the control circuit 40 shown in FIG. In addition, the average inversion frequency can also be obtained by detecting the edge of the reproduction RF signal or its divided output and counting the number of inversions per fixed time by a counter.

Next, the target position is set to the TOC of the optical disk.
A specific example when the position is set will be described with reference to FIGS.

FIG. 4 is a diagram showing the relationship between the disk diameter position of the optical disk 10 and the inverted frequency value of the EFM signal obtained as the above-mentioned reproduced RF signal.

In FIG. 4, the inversion frequency value (the value of the frequency divided by 1 / n) at the position of the disk diameter R ₀ that is the target TOC position on the optical disk 10 is F _0, and in the initial state. Optical pickup head 12
There has inverted frequency value at the position of the disc diameter R _x may focus has been turned to the position in the F _x. Optical disk 10
Is rotationally controlled at a rotational speed such that a constant linear velocity (for example, 1.2 m / s) becomes a predetermined reference at the target TOC position, and the inversion frequency value F at the TOC position is controlled.
₀ is 1 / n which is the inversion frequency that is the reference of the EFM signal.
Is obtained by dividing the frequency. For example, the dividing ratio 1 / n = 1/40
Assuming that the average inversion frequency of the EFM signal is about 4
Since the frequency is 45.85 kHz, the reference inversion frequency value F ₀ is about 108.85 Hz from (445.85 × 10 ³ ) / 4096.

Accordingly, since the relation of F ₀ : F _x = R ₀ : R _x is established, the current head position (the position of the disk diameter R _x ) is R _x = R ₀ × F _x / F _0.・ ・ It can be obtained by the formula of (1). In the above equation (1),
Since the R ₀ audio band F ₀ is a known value, the measured F _x
Is substituted to obtain _Rx . If the disk radial position (R _x ) where the current reproducing head (optical pickup head 12) is located is obtained in this way, the head transfer amount, that is, the distance L for moving the head in the disk radial direction, is L = R _x −R ₀ (2), and the control circuit 40 of FIG. 1 controls the head transfer section 33 of the drive circuit 30 so as to transfer the head by the distance L in the disk radial direction.

As a result, the target T
The TOC information can be obtained by being sent to the OC position and reading the record on the disk.

FIG. 5 is a flowchart for explaining the head access operation as described above.

In the first step S61 of FIG. 5, various initial settings of each circuit section according to the mounting of the optical disk are performed.
In the next step S62, the rotation drive of the disk is started. The rotation speed at this time is, as described above, the target TO
A constant linear velocity v ₀ (for example, 1.2 m /
s), for example, a diameter of 6.4 cm
In the case of the optical disk system described above, the TOC position is defined as a position where the disk diameter _R0 is 14.5 mm to 16.1 mm. The rotation frequency N at this time is: R ₀ = 16.1 (mm) = 16.1 × 10 ⁻³ (m) from N = v ₀ / (2πR ₀ ).
Then, it can be seen that N = about 11.86 Hz. Therefore, in step S62, rotation drive control is performed so that the rotation speed (rotation frequency) becomes approximately 11.68 Hz, and the process waits until the rotation is stabilized.

In the next step S62, a focus search is performed, and in the next step S64, the focus servo and the tracking servo are turned on.

Next, the process proceeds to step S65, where the reproduction RF
Read the inverted frequency value of the signal. This inversion frequency value is
As described above, the frequency divided by 1 / n is used. In the next step S66, the arithmetic function unit 4 of the control circuit 40 in FIG.
1 to calculate the above formulas (1) and (2) to determine the moving amount (head moving amount, moving distance) L, and step S67.
Then, the reproducing head (optical pickup head 12) is moved in the disk radial direction by the obtained distance L.

In the next step S68, the PLL is turned on by operating the speed servo and the phase servo for synchronizing with the clock of the reproduction RF signal, and the clock from the PLL is used for rotation control at a constant linear velocity. Also used as a data read clock. In the next step S69, reading of the TOC data of the sent head position is started.

According to such a method, the head can be quickly moved to the TOC position without using the limit switch and without reading the address at the current head position, and the TOC information can be read in a short time.

The target disk diameter position for transferring the head is not limited to the TOC position, but may be a desired disk diameter position. Also, the initial disk rotation speed may not be a constant linear speed at the TOC position, but may be a constant linear speed at another target disk diameter position.

Further, in the above-described embodiment, the EFM
Focusing on the average inversion frequency of the signal, the disc diameter position is obtained by comparing the inversion frequency of the reproduction RF signal. In addition, the reproduction of the recording signal including a predetermined reference frequency component is performed. The current disk radial position can also be obtained by detecting the frequency in the signal and comparing it with the above-mentioned reference frequency.

For example, in the case of a recordable optical disk such as a magneto-optical disk, a technique is known in which a guide groove (pre-groove) formed in advance is wobbled in accordance with address data. The groove wobbling signal is obtained by modulating address data at a fixed carrier frequency, and this modulation frequency can be used as the reference frequency.

That is, when reproducing a disk on which a signal modulated at a constant modulation frequency is recorded to form a pre-groove as a wobbling signal, for example,
Extracting the modulation frequency component from the wobbling signal obtained by detecting the pre-groove of the disk, and comparing the reproduced modulation frequency component with a modulation frequency serving as a reference of the modulation signal recorded on the original disk. As a result, the current disk diameter position of the reproducing head can be calculated. The extraction of the modulation frequency component is performed by, for example, B
The calculation formula used for obtaining the disk radial position by using a PF (band pass filter) is the same as the above formula (1). Similarly, the reproducing head is moved in the radial direction of the disk by calculating the head moving amount by the above equation (2).

In addition, it goes without saying that various modifications can be made without departing from the spirit of the present invention.

[0055]

As is apparent from the above description, according to the disk reproducing apparatus of the present invention, data is extracted from the signal read by the reproducing head from the optical disk which is driven to rotate at a predetermined rotation speed. Since the current disk diameter position of the reproducing head is calculated based on the average inversion value serving as the data reference and the inversion value of the reproduced data,
The current disk diameter position can be quickly obtained without reading the address information of the data content.

Also, based on the determined disk diameter position, the head transfer amount to the target disk diameter position is calculated, and the reproducing head is transferred by that amount.
Head access to the target position can be performed quickly.

Therefore, for example, the target position is set to T
By setting to the OC position, reading of the TOC information when the disc is mounted can be performed quickly without using a limit switch.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of a configuration of an embodiment of a disc reproducing apparatus according to the present invention.

FIG. 2 is a diagram showing an EFM frame of an EFM signal recorded on a disc.

FIG. 3 is a block diagram illustrating a configuration example for detecting an inverted frequency of a reproduction RF signal.

FIG. 4 is a diagram for explaining a relationship between a disc diameter position of an optical disc and an inversion frequency value.

FIG. 5 is a flowchart for explaining the operation of the disc reproducing apparatus of FIG. 1;

[Explanation of symbols]

Reference Signs List 10 optical disc, 11 motor, 12 optical pickup head, 13 amplifier, 20 signal processing circuit, 21 reproduction signal processing section, 22 servo signal processing section, 30 drive circuit, 31 focus drive section,
32 tracking drive unit, 33 head transfer unit,
34 rotation drive unit, 40 control circuit, 41 arithmetic function unit

Claims (8)

[Claims] 1. A disk reproducing apparatus for reproducing a disk on which a digital signal modulated by a run-length limited code whose modulation pattern changes within an interval determined by a maximum inversion interval and a minimum inversion interval. Rotation driving means for rotationally driving; reproducing means for reading a digital signal recorded on the disk; control means for rotating the rotary driving means at a constant speed; reading by the reproducing means under the condition of the constant speed rotation First calculating means for calculating the average inversion frequency at the position where the reproducing means is currently located from the obtained digital signal; and average inversion serving as a reference calculated based on a possible generation pattern among the modulation patterns. Storage means for storing the frequency; and a section in which the present reproduction means calculated by the first calculation means is located. Second calculating means for calculating the position of the disc radius method in which the reproducing means is currently located, based on the average inversion frequency at the location and the reference average inversion frequency stored in the storage means. Disk playback device. 2. A deciding means for deciding a transfer amount of said reproducing means on the basis of a position of a disc radius method where said reproducing means is currently located and a target position in a radial direction of said disc calculated by said second calculating means. 2. The disk reproducing apparatus according to claim 1, further comprising: 3. The disk reproducing apparatus according to claim 2, further comprising a transfer means for transferring said reproducing means based on the transfer amount determined by said determining means. 4. A disk reproducing apparatus according to claim 1, wherein a position in a disk radial direction at which a reference average inversion frequency is obtained is stored in said storage means in advance. 5. A disk radius position of a reproducing head on a disk on which a digital signal modulated by a run-length limited code whose modulation pattern changes within an interval determined by a maximum inversion interval and a minimum inversion interval is calculated. A step of rotating the disk at a constant speed at a predetermined speed; a step of turning on a focus servo and a tracking servo by a reproducing head under the state of the constant speed rotation; Calculating the average reversal frequency at the position where the reproducing head is currently located from the digital signal obtained from the digital signal, and a reference average calculated based on a possible generation pattern among the modulation patterns stored in the memory in advance. Reading the inversion frequency; and determining whether the current read head calculated above is located. Calculating the position of the disc radius method where the reproducing head is currently located based on the average inversion frequency at the location and the reference average inversion frequency read from the memory. . 6. The method according to claim 1, further comprising the step of determining a transfer amount of the reproducing head based on the calculated position of the reproducing head in the radius direction of the disk and a position in the radial direction of the disk to be accessed. The head position calculating method according to claim 5, wherein 7. The head position calculating method according to claim 6, further comprising the step of transferring the reproducing head based on the determined transfer amount. 8. The head position calculating method according to claim 5, wherein a position in the disk radial direction at which a reference average inversion frequency is obtained is stored in the memory in advance.