JPH08106742A - Magnetic disk device - Google Patents

Abstract

PURPOSE: To prevent the generation of errors due to an impulse from the outside, a head change and the instability of a control system in a data-surface servo type magnetic disk device. CONSTITUTION: A means 5 detecting the place of a head 2 at every sampling, a means 6, in which the place of the detected head 2 is stored, and a means 11, in which the position of the next head is predicted by using the current place of the head and the place of the head detected at the time of sampling before the current place by one are mounted on a control circuit 4 for a data- surface servo type magnetic disk device. When the place of the head predicted by the means 11 predicting the position of the head at the time of sampling exceeds an off-track slice value, a means 9 interrupting the measuring operation of a control-system correction value and a means 12 interrupting the write operation of the head are worked.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk device, and more particularly to a closed-loop servo type magnetic disk device for positioning a magnetic head by using preset servo information and preventing head off-track. The present invention relates to a magnetic disk device that can perform accurate positioning.

In recent years, in response to the demand for smaller size and larger capacity of magnetic disk devices, as a magnetic head positioning control method, a servo surface using a dedicated servo disk in which only head positioning information is recorded on the disk surface. In place of the servo system, each track on the disk is divided into multiple sectors, the head positioning information is written at a predetermined position in each sector, and the data is written in the remaining part (also called the data surface servo system) Are being adopted more often.

However, compared to the servo surface servo method, the data surface servo method can read the servo information only when the head passes through the servo information area. Therefore, the positioning characteristic (track tracking) is better than that of the servo surface servo method. It is said that the performance is inferior, and appropriate measures when the head deviates from the target track due to external impact,
Alternatively, when the heads are switched in a magnetic disk device having a plurality of heads, it is desired that the heads move quickly to a target track when the switched heads are not located on the same cylinder as the previous head. ing.

[0004]

2. Description of the Related Art In the conventional data surface servo system, a magnetic disk surface for recording data is divided into a plurality of sectors in the circumferential direction, and a servo for positioning a head is provided in a part of these sectors separately from a data area. An information area is provided. This servo information area is typically 10-20
Account for about%.

Usually, a servo controller, which is composed of a microprocessor, positions the head on a track by using the head position information obtained by the servo demodulator based on the signal recorded in the servo information area. To do. In such a data surface servo type magnetic disk device,
If the head moves from the target track to another track due to an external shock while the disk device is performing a read / write operation, the information on the other track may be erroneously read or written to another track. Error occurs. Therefore, in the conventional magnetic disk device, the position of the head is always confirmed by the read signal from the head, and when the position of the head exceeds the write-off track slice value, reading and writing to another track is prevented. It has a function of interrupting the read / write operation of the head at the time of detection, waiting for one rotation of the disk to correct the position of the head, and then rewriting from the interrupted sector.

On the other hand, in the conventional magnetic disk device of the data surface servo system having a plurality of heads, when the head for reading / writing is switched to another head (head change), the switched head is moved to the front. In consideration of the case where the head is not located on the same cylinder as the head, the head is made to reach the target cylinder by servo-compensating for the position error amount from the target cylinder regardless of the position of the switched head.

Further, in the conventional sector servo type magnetic disk device, in order to compensate for mechanical fluctuations due to temperature changes and the like of the disk device, the head position is measured at regular intervals. For example, the calibration is performed once every 5 minutes.

[0008]

However, in the conventional data surface servo type magnetic disk device which performs the above operation, since the servo information can be obtained only intermittently, the deviation of the head from the target track ( Off track)
Even if the read / write operation of the head is interrupted at the time of sampling when the detection is performed, there is a risk that the read / write operation is already performed on a track other than the target track.

Further, in a conventional data surface servo type magnetic disk apparatus having a plurality of heads, if the heads are attached to respective arms largely displaced, the heads may be pulled into a target cylinder by position control. It takes a long time to complete the operation, and the retractable distance for returning the misaligned head to the target track is also limited to the maximum computable value of the position error control. As a result, in the magnetic disk device in which the mounting error between the plurality of heads is large,
There is a problem that the performance of the magnetic disk device deteriorates because it takes time to change the head. Further, when the mounting error between the plurality of heads exceeds the maximum value that can be calculated by the position error control, there is a problem that the magnetic disk device causes a seek error.

Further, in the magnetic disk device which performs the measurement operation at a constant time interval, the measurement is started regardless of the state of the machine. Therefore, the measurement is performed even if the control system is not unstable, and the magnetic disk The performance of the device is degraded. That is, even if the control system becomes unstable, the measurement for compensation is not performed until a certain period of time elapses. Therefore, in the worst case, an error may occur in the time between the measurements.

Therefore, according to the present invention, in the conventional data surface servo type magnetic disk apparatus, even when there is an external impact, a head change is executed, or the control system becomes unstable, An object is to provide a magnetic disk device that does not cause an error.

[0012]

FIG. 1 shows a principle configuration of a first embodiment of the present invention for achieving the above object. This first
In the magnetic disk device 10 of the above-mentioned form, the magnetic recording medium 1 in which head positioning information is intermittently set in advance, the head 2 for reading and writing data from the magnetic recording medium 1, and the purpose of the head 2 are The head positioning mechanism 3 for moving the head 2 to the position of 1 and the control circuit 4 for moving the head 2 or following the data track by the digital servo system using the positioning information read by the head 2 are provided. In such a magnetic disk device 10, the control circuit 4 stores the head position detecting means 5 that detects the position of the head 2 by using the head positioning information for each sampling cycle, and the detected position of the head 2. Using the head position information storage means 6 to be stored, the current head position, and the head position detected at the time of the previous sampling,
Head 2 expected to be detected at the next sampling
Head position predicting means 11 which calculates and calculates the position of
The predicted head position is compared with a preset off-track slice value, and if the predicted position of the head 2 exceeds this off-track slice value, the measuring operation of the control system correction value is interrupted. Means 9 are provided.

The magnetic disk drive 1 shown in FIG.
At 0, when the predicted position of the head 2 exceeds the off-track slice value, the write operation interruption means 12 for immediately interrupting the write operation by the head 2 may be further provided. Next, the principle configuration of the second embodiment of the present invention that achieves the above-mentioned object is shown together with FIG. The magnetic disk device 10 of the second mode is different from that of the first mode in that the control circuit 4 uses a head position detecting means 5 for detecting the position of the head 2 by using the head positioning information for each sampling cycle. Using the head position information storage means 6 that stores the detected position of the head 2, the current head position, and the head position detected at the time of the previous sampling, it is predicted that the position will be detected at the next sampling. Head position predicting means 11 for calculating the position of the head 2 to be calculated, servo burst signal detecting means 13 for detecting a servo burst signal from the magnetic recording medium 1, and the predicted head position being preset to OFF. In comparison with the track slice value, if the predicted position of the head 2 exceeds this off-track slice value, the servo immediately before the detected servo burst is detected. In that the data rewrite unit 14 to rewrite data from there is Bobasuto sectors is provided.

Further, the principle configuration of the third embodiment of the present invention for achieving the object is shown in FIG. The magnetic disk device 20 according to the third embodiment has a magnetic recording medium 1 on which head positioning information is intermittently set in advance, a head 2 for reading and writing data from and on the magnetic recording medium 1, and this head. Head positioning mechanism 3 for moving 2 to a desired position
And movement of the head 2 or tracking of the data track,
A control circuit 4 for performing a digital servo method using the positioning information read by the head 2 is provided. In such a magnetic disk device 20, the control circuit 4 uses the head position detection means 5 for detecting the position of the head 2 by using the head positioning information for each sampling cycle.
A head position information storage means 6 for storing the detected position of the head 2, a head change detection means 15 for detecting a change of the head 2 which performs reading and writing among a plurality of heads, and first after the head change. Head position deviation detecting means 16 for detecting the deviation of the head 2 from the target cylinder after head change using the detected head position and the head position detected last before head change, and the read / write head after head change. When 2 is located in a cylinder outside the target cylinder, there is provided a speed control means 17 of the head positioning mechanism that controls the speed of the head positioning mechanism 3 until the head 2 is pulled into the target cylinder.

Also in the magnetic disk device 20 of the embodiment shown in FIG. 3, the control state monitoring means 18 of the head positioning mechanism for monitoring the control state of the head positioning mechanism 3 and the control state of the head positioning mechanism 3 are further checked. A control correction value measuring means 19 of the head positioning mechanism may be provided which starts measurement of the correction value when it is determined that the control state is unstable by comparing with a predetermined reference value.

[0016]

According to the magnetic disk device of the first aspect of the present invention, the head position is detected and stored using the head positioning information for each sampling period, and the current head position and the stored 1 The position of the head predicted to be detected at the next sampling is obtained from the head position detected at the previous sampling, and this value is compared with a preset off-track slice value. When the predicted position of the head exceeds the off-track slice value, the measurement operation of the control system correction value is interrupted and the write operation by the head is immediately interrupted.

According to the magnetic disk device of the second aspect of the present invention, the head position is detected and stored using the head positioning information for each sampling cycle, and the current head position and the stored 1 are stored. The position of the head predicted to be detected at the next sampling is obtained from the head position detected at the previous sampling, and the servo burst signal is detected from the magnetic recording medium. Then, the predicted head position is compared with a preset off-track slice value, and when the predicted position of the head exceeds this off-track slice value, the servo burst immediately before the detected servo burst is detected. Data is rewritten from a certain sector.

In the magnetic disk drive according to the third aspect of the present invention, a plurality of heads for reading and writing data from and to the magnetic recording medium are provided, and the head positioning information is used for each sampling cycle. When the position is detected and stored and a head change is detected, the head position detected first after the head change and the head position detected last before the head change are used to determine the target cylinder of the head after the head change. Deviation from is detected. When the read / write head after the head change is located in the cylinder outside the target cylinder, the speed control of the head positioning mechanism 3 is performed until the head is pulled up to the target cylinder.

In the modified example of the magnetic disk device of FIG. 3, the control state of the head positioning mechanism is monitored and the control state of the head positioning mechanism is compared with a predetermined reference value. Then, when it is determined that the control state is unstable, measurement of the correction value is started.

[0020]

Embodiments of the magnetic disk drive of the present invention will be described in detail below with reference to the drawings. FIG. 3 shows the basic configuration of the magnetic disk device of the present invention. In FIG. 3, a disk enclosure 30 includes a plurality of magnetic disks 31, a magnetic head 32 for reading and writing from the magnetic disk 31, a head actuator 33, a voice coil motor (VCM) 34, and a magnetic disk 3.
A disk drive motor 35 that rotates 1 is provided.

The signal read from the head 32 is input to the servo signal detecting section 41 to detect the servo signal. The detected servo signal is converted into a digital signal by the A / D converter 42 and input to the input / output interface 51 in the microprocessor 50. Further, the drive signal from the microprocessor 50 is converted into an analog signal by the D / A converter 43, amplified by the power amplifier 44, and input to the VCM 34 of the disk enclosure 30. Is controlled by.

In the microprocessor 50, in addition to the input / output interface 51 described above, a CPU 52 that executes various calculations and controls, and an RO that stores programs are stored.
There is an M53 and a RAM 54 for storing data, which are mutually connected by a bus 55. Next, one embodiment of the operation of the microprocessor 50 of the magnetic disk device configured as described above will be described with reference to FIG.

First, in step 401, the position signal XP obtained from the servo information at the current sampling point is detected. This position signal XP is used to obtain an error from the target position of the head 32, and the microprocessor 50 performs servo compensation for the error. The position signal XP is stored in the RAM 54. In this embodiment, in step 402, this position signal XP
And the difference ΔX (= XP−XO) from the position signal XO at the previous sampling point stored in the RAM 54 is calculated. After this calculation is completed, in step 403 the current position signal XP is set as the previous position signal XO in the RAM 5
Store in 4.

In the following step 404, the next predicted position XN of the head 32 is calculated by the formula XN = XP + | ΔX |. Then, in the following step 405, it is determined whether or not the predicted position XN at the next sampling point of the head 32 that has been predicted and calculated is larger than the off-track slice value. In this case, if XN <slice value, it is determined to be within the allowable range, the process proceeds to step 408, and the normal read / write operation is executed. On the other hand, when it is determined in step 405 that XN ≧ slice value, the process proceeds to step 406,
When performing the measurement operation, the measurement operation is interrupted,
In the following step 407, the write operation is interrupted without waiting for the next sampling.

FIG. 5 is an explanatory diagram for explaining the control procedure shown in the flowchart of FIG. 4 with time. In FIG. 5, TP indicates the current sampling point, TO indicates the previous sampling point, and TN indicates the next sampling point.
When the head 32 performs a normal operation without impact on the disk enclosure 30, the sampling point TO,
The position of the head 32 in TP and TN changes as shown by x in FIG. 5, and there is no great difference in the head position. on the other hand,
When a shock is applied to the disk enclosure 30 after the previous sampling point TO, the position of the head 32 at the current sampling point TP becomes XP.

Assuming that the head 32 moves linearly, the predicted position of the head 32 at the next sampling point TN is the head 32 at the current sampling point TP.
And the position of the head 32 at the immediately preceding sampling point TO. Then, when the predicted position of the head 32 exceeds the off-track slice value, the write operation is interrupted.

As described above, the magnetic disk device of the above-described embodiment predicts the next position by using the position signal detected at the current sampling and the position signal detected at the immediately previous sampling. With function. By predicting the next position, the write operation (or read operation) can be interrupted before the head exceeds the off-track slice value, so data is erroneously written in the sector between servo bursts, or between servo bursts. There is no risk of accidentally reading data from the sector. Furthermore, in this embodiment, since the measurement operation is interrupted during the measurement operation, it is possible to prevent the abnormal correction value from being captured even during the measurement operation.

Next, another embodiment of the operation of the microprocessor 50 of the magnetic disk device will be described with reference to FIG.
At step 601, the current position signal XP and the servo burst signal are detected, and these values are stored in the RAM 54. In the following step 602, this position signal XP
And the position signal XO at the previous sampling point stored in the RAM 54, the difference in head position ΔX (= XP).
-XO). After this calculation is completed, in step 603, the current position signal XP is stored in the RAM 54 as the previous position signal XO.

In the following step 604, the predicted position XN of the head at the next sampling point is calculated by the formula XN = XP + |
Calculate with ΔX |. Then, the following step 605.
Then, it is determined whether or not the predicted position XN at the next sampling point of the head 32 that has been predicted and calculated is larger than the off-track slice value. In this case, if XN <slice value, it is determined to be within the allowable range, the process proceeds to step 607, and the normal read / write operation is executed. On the other hand, if it is determined in step 605 that XN ≧ slice value, step 60
In step 6, the write operation is redone.

FIG. 7 illustrates the redo of the write operation in comparison with the redo of the write operation in the conventional device. FIG. 7A shows a sector of a certain track, a writing area of data and a servo signal.
7B shows the first write signal, FIG. 7C shows the second write signal in the conventional device, and FIG. 7D shows the second write signal in the device of the present invention.

For example, in sector n shown in FIG.
Consider the case where the off-track (off-track write) of the write operation shown in (b) is detected. In this case, the writing is interrupted thereafter. When such an off-track write is detected, in the conventional magnetic disk device, after waiting for one rotation of the disk, rewriting is performed from the sector in which the previous writing failed in the second writing. In the magnetic disk device of
After waiting for the rotation, at the time of the second writing, not the rewriting from the sector in which the previous writing has failed but the rewriting from the sector having the preceding servo burst is performed. Here, x is the number of sectors existing between servo bursts, which is predetermined.

As described above, the magnetic disk device of this embodiment has the function of holding the data of the sectors corresponding to the servo bursts and the sector having the preceding servo burst when the off-track write is detected. It has a function to rewrite from. Therefore, in the conventional magnetic disk device, there is a possibility of off-track writing even in the sector before the sector in which off-track writing is detected, but the present invention rewrites between servo bursts that are off-track written. As a result, it is possible to eliminate the read error due to the lack of the offset margin.

Next, still another embodiment of the operation of the microprocessor 50 of the magnetic disk device will be described with reference to FIG. This embodiment shows a control procedure for performing a head change in a magnetic disk device having a plurality of heads. First, in step 801, it is determined whether a head change command is input. If no head change command is input, this routine ends.

When the head change command is input, the process proceeds to step 802, and the head select signal is switched by the head change command, and then step 80
In 3, the head position error signal is detected. Then, based on the detected head position error signal, it is determined whether or not the head-changed head is on the target cylinder (step 804).
If the head-changed head is on the target cylinder, the process proceeds to step 806 to operate the position control system. If it is not on the target cylinder, step 80
Proceed to step 5 to operate the speed control system.

That is, in this embodiment, when the head position is not on the target cylinder immediately after the head change,
Performs speed control equivalent to coarse control during seek operation by the head. As a result, even if the mechanical head misalignment becomes large when the head is changed, the operation of controlling the head on the target cylinder can be completed in a shorter time than before, so that the performance of the magnetic disk device is improved. improves. In addition to this, since there is virtually no limit on the amount of deviation between the heads, a seek error due to an increase in the amount of deviation does not occur.

Further, according to the present invention, the measurement operation is not executed at a constant time interval in the conventional magnetic disk device. Therefore, in the present invention, the control states (seek core time, following time, integrator value) of the head actuator 33 and the VCM 34, which are the head positioning mechanism, are constantly monitored by the microprocessor,
The control state of the head actuator 33 and the VCM 34 is compared with a predetermined reference value, and the measurement of the correction value is started only when it is determined that the control state is unstable.

FIG. 9 is a block diagram showing the functions of this embodiment inside the CPU 52 shown in FIG. The CPU 52 includes a position signal detection unit 521, a control switching unit 522, a speed control unit 523, a position control unit 524 including an integrator, a servo compensation unit 525, and a control state monitoring unit 526. In this embodiment, the speed control time T from the speed control unit 523, the settling time Ts from the position control unit 524, and the value I of the integrator are the control state monitoring unit 526.
Is input to the head actuator 33 and the VCM 34 shown in FIG. 3 can be constantly monitored. This monitoring is performed by the head actuator 33 and the VCM.
This is done by comparing the control state of 34 with a predetermined reference value. As a result of this monitoring, when it is determined that the control of the actuator 33 and the VCM 34 is unstable, the measurement operation necessary signal RQ from the control state monitoring unit 526 is input to the measurement operation execution unit 527, and the measurement operation execution unit 527 The measurement operation is executed by using the measurement operation required signal RQ as a trigger.

As described above, in this embodiment, by providing the mechanical control state monitoring function, it is constantly monitored whether or not the control is stably performed. As a result, the actuator 33
Since the control state of the VCM 34 and the VCM 34 can be constantly monitored, the measurement operation can be performed only when necessary, and the waste of the operation of the apparatus can be minimized. Further, in this embodiment, since the actuator 33 and the VCM 34 do not continue control while being unstable, an error is unlikely to occur.

As described above, according to the present invention, since the off-track writing can be prevented by providing the function of predicting the off-track writing, the data is written beyond the slice value. Since the read error is prevented and the adjacent track is not written, the reliability of the device is improved. Further, even if it does not have the shock detection function, it is possible to prevent the off-track write from being left by having the function of returning the number of sectors for the servo burst from the off-track detection sector and rewriting the data.

Further, even when the head is changed, a seek error does not occur even if the head after the head change has a large deviation from the head before the head change. realizable. Furthermore, by performing the measurement operation only when necessary, it is possible to minimize the influence on the performance, and by performing the measurement operation immediately when an unstable element appears, the seek error is reduced. can do.

[0041]

As described above, according to the present invention, in the magnetic disk device of the data surface servo system, when there is an external impact, when a head change is executed, or when the control system becomes unstable. However, there is an effect that the error and the reliability and performance are improved.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of a magnetic disk device according to first and second embodiments of the present invention.

FIG. 2 is a principle configuration diagram of a magnetic disk device according to the embodiment of FIG. 3 of the present invention.

FIG. 3 is a block diagram showing an overall configuration of a magnetic disk device of the present invention.

FIG. 4 is a flowchart showing an embodiment of a procedure for detecting an abnormal state in the magnetic disk device of the present invention.

FIG. 5 is a diagram for explaining the operation of the head in the control procedure of FIG.

FIG. 6 is a flowchart showing another embodiment of the procedure for detecting an abnormal state in the magnetic disk device of the present invention.

FIG. 7 shows a rewriting operation at the time of off-track write detection in the control procedure of FIG. 6 in comparison with a conventional device, FIG. 7 (a) is a diagram showing adjacent sectors in which off-track is detected, ) Is a diagram showing the first write signal when the off-track is detected, (c) is a diagram for explaining rewriting of the conventional device when the off-track is detected, and (d) is when the off-track is detected. It is a figure explaining rewriting of the apparatus of this invention of this. It is a figure explaining operation.

FIG. 8 is a flowchart showing an example of a control procedure at the time of head change in the magnetic disk device of the present invention.

FIG. 9 is a block diagram showing a configuration for monitoring a control state of a head drive mechanism according to the present invention.

[Explanation of symbols]

 10, 20 ... Magnetic disk device of the present invention 30 ... Disk enclosure 31 ... Magnetic disk 32 ... Head 33 ... Head actuator 34 ... VCM 41 ... Servo signal detection unit 50 ... Microprocessor 522 ... Control switching unit 523 ... Speed control unit 524 ... Position control unit 526 ... Control state monitoring unit 527 ... Measurement operation execution unit

Claims (5)

[Claims] 1. A magnetic recording medium (1) in which head positioning information is intermittently set in advance, and the magnetic recording medium (1).
Head (2) for reading and writing data to and from the head positioning mechanism that moves this head (2) to the desired position
A magnetic disk comprising (3) and a control circuit (4) for moving the head (2) or following a data track by a digital servo method using the positioning information read by the head (2). Device (10), said control circuit (4)
However, the head position detection means (5) that detects the position of the head (2) by using the head positioning information for each sampling cycle.
And the head position information storage means (6) for storing the detected position of the head (2), the current head position, and the head position detected at the immediately previous sampling, and at the time of the next sampling The position of the head (2) predicted to be detected is calculated by calculating the head position prediction means (11) and the predicted head position is compared with a preset off-track slice value, and the head (2) is compared. A magnetic disk device comprising: a measurement operation interrupting means (9) for interrupting the measurement operation of the control system correction value when the predicted position of is above the off-track slice value. 2. The magnetic disk device according to claim 1, wherein the predicted head position is compared with a preset off-track slice value, and the predicted position of the head (2) determines the off-track slice value. If it exceeds, head immediately
(2) Writing operation interruption means for interrupting the writing operation by (1
A magnetic disk drive further comprising 2). 3. A magnetic recording medium (1) in which head positioning information is intermittently set in advance, and the magnetic recording medium (1).
Head (2) for reading and writing data to and from the head positioning mechanism that moves this head (2) to the desired position
A magnetic disk comprising (3) and a control circuit (4) for moving the head (2) or following a data track by a digital servo method using the positioning information read by the head (2). Device (10), said control circuit (4)
However, the head position detection means (5) that detects the position of the head (2) by using the head positioning information for each sampling cycle.
And the head position information storage means (6) for storing the detected position of the head (2), the current head position, and the head position detected at the immediately previous sampling, and at the time of the next sampling Head position prediction means (11) for calculating the position of the head (2) predicted to be detected, and servo burst signal detection means (13) for detecting a servo burst signal from the magnetic recording medium (1) Then, the predicted head position is compared with a preset off-track slice value. If the predicted position of the head (2) exceeds this off-track slice value, the position immediately before the detected servo burst is detected. A magnetic disk device comprising: a data rewriting means (14) for rewriting data from a sector having a servo burst. 4. A magnetic recording medium (1) in which head positioning information is intermittently set in advance, and the magnetic recording medium (1).
A plurality of heads (2) for reading and writing data to and from the head, a head positioning mechanism (3) for simultaneously moving these heads (2) to a desired position, and movement of the heads (2) or tracking of data tracks. A magnetic disk device (10) comprising a control circuit (4) for performing a digital servo method using the positioning information read by the head (2), wherein the control circuit (4) Head position detection means (5) that detects the position of the head (2) using the head positioning information for each
A head position information storage means (6) for storing the detected position of the head (2), and a head (2) for reading and writing from among the plurality of heads.
Using the head change detection means (15) for detecting the change of the head position, the head position detected first after the head change, and the head position detected last before the head change,
If the head position deviation detection means (16) that detects the deviation of the head (2) after the head change from the target cylinder and the read / write head (2) after the head change are located in the cylinder outside the target cylinder, Head positioning mechanism until (2) is pulled to the target cylinder
A magnetic disk device comprising: a speed control means (17) for a head positioning mechanism that controls the speed of (3). 5. The magnetic disk drive according to claim 4, wherein a head positioning mechanism control state monitoring means (18) for monitoring a control state of the head positioning mechanism (3), and the head positioning mechanism (3). The control correction value measuring means (19) of the head positioning mechanism for starting measurement of the correction value when the control state is compared with a predetermined reference value and it is determined that the control state is unstable is provided. A magnetic disk device characterized by the above.