JP2003007017A - Magnetic disk drive and flying height measurement circuit applied thereto - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic disk device having effective means for easily measuring a flying height and a floating fluctuation amount of a magnetic head slider within a magnetic disk with high resolution and a flying height measuring circuit applied to the magnetic disk device. provide. Kind Code: A1 A magnetic disk drive having a magnetic disk driven in rotation and a magnetic head slider floating on the magnetic disk, wherein a differentiated reproduction signal waveform read by the magnetic head slider is subjected to differentiation processing. A flying height measuring circuit for measuring the flying height of the magnetic head slider based on the amplitude value of the reproduced signal waveform. In the flying height measuring circuit, the flying height or the flying fluctuation amount of the magnetic head slider is measured for each arbitrary sector, the measurement data is accumulated, and the measured data is compared with a reference value prepared in advance, and the magnetic head slider is measured. If it is determined that the flying height or the floating fluctuation amount is abnormal, a predetermined processing operation is started.

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 having a function of measuring the flying height of a magnetic head slider for recording / reproducing data on / from a magnetic disk and a flying height measuring circuit mounted on the magnetic disk device.

[0002]

2. Description of the Related Art In recent years, the era of full-scale multimedia has arrived, and it is more important than ever to improve the performance of a magnetic recording / reproducing apparatus for recording a huge amount of data. In particular, in a computer represented by a hard disk (HDD) and a magnetic recording / reproducing apparatus for recording digital information, in order to increase the recording density, the recording format on the magnetic recording medium has a shorter wavelength and a narrower track pitch. As such, research and development and its practical application are being actively conducted.

In achieving such high-density recording, a giant magnetoresistive effect is used in place of an anisotropic magnetoresistive element (AMR) which has been conventionally used in a magnetic head, particularly a reproducing head. The use of devices (GMR) has been shifting. On the other hand, in the magnetic head mounted with the magnetoresistive element, as the recording density is improved,
The gap between the magnetic head and the magnetic disk (so-called flying height) is less than 30 nm and approaches 0 (zero) without limit. Therefore, the flying height margin within the allowable range is also small, and even if the flying height fluctuates very slightly, it is more likely that a crash will occur due to the collision between the magnetic head and the magnetic disk surface. This is the current situation.

In view of such a background, recently, the flying height (flying height) of the magnetic head is constantly monitored at the time of driving, and the risk of a crash is predicted by detecting a large change in the flying height. The demand for a function that dynamically controls the flying height is increasing.
Above all, there is a demand for the development of a highly accurate flying height measurement function (evaluation function) for dynamically monitoring the fluctuation of the flying height.

From such a demand, as a method for measuring the flying height of the magnetic head after the magnetic head (head slider assembly including the head actuator) is incorporated in the magnetic disk device, for example, Japanese Patent Laid-Open No. 2000-242242 is used. As disclosed in Japanese Patent Laid-Open No. 2000-195211, there has been proposed a method of measuring using a reproduced signal waveform read by a magnetic head.

[0006]

As described above, the distance between the magnetic head and the magnetic disk is 3 to improve the recording density.
It is below 0 nm and approaches 0 (zero) infinitely.
Therefore, the flying height margin within the allowable range is also small, and even if there is a very slight fluctuation in the flying height, there is a high possibility that a crash will occur due to the collision between the head and the magnetic disk surface. There is. Therefore,
It is important to be able to detect even small fluctuations in the flying height (flying height).

However, in the conventional method, the amplitude, half-value width, jitter, etc. of the reproduced signal are measured and the flying height is estimated comprehensively. However, the amplitude value and the half-value width of the reproduced signal waveform are measured. However, there is a problem that it is difficult to measure the flying height or the flying fluctuation amount with high resolution because the variation amount of each measured value with respect to the fluctuation of the flying amount, so-called detection sensitivity is low.

In addition, when measuring the jitter of the reproduced signal waveform, there is a problem that it is difficult to perform highly accurate measurement because it is affected by the rotation jitter of the magnetic disk drive system. Further, in the method disclosed in Japanese Patent Laid-Open No. 2000-195211, it is necessary to simultaneously measure three types of parameters, which causes a problem that the circuit configuration itself becomes complicated.

For this reason, there is no effective means for easily measuring the flying height or floating fluctuation of the magnetic head inside the magnetic disk drive with high resolution, and it is expected that the density will increase further in the future. It was a big problem in response to the request for conversion.

In order to solve the above problems, the present invention provides
It is an object of the present invention to provide a magnetic disk device and a flying height measuring circuit used for the same which are capable of easily measuring and evaluating the flying height or floating fluctuation amount of a magnetic head with higher resolution than ever before.

[0011]

In order to achieve the above object, a magnetic disk device according to the present invention is a magnetic disk device having a magnetic disk driven to rotate and a magnetic head slider floating above the magnetic disk. Therefore, the reproduction signal waveform read by the magnetic head slider is differentiated, and based on the amplitude value of the differentiated reproduction signal waveform,
A flying height measuring circuit for measuring a flying height or a floating fluctuation amount of the magnetic head slider is provided.

With such a structure, it becomes possible to detect the flying height or the floating fluctuation amount of the magnetic head slider in the magnetic disk device with high accuracy and by a simple method.

Further, in the magnetic disk device according to the present invention, in the flying height measuring circuit, the signal used for measuring the flying height is recorded in the track servo data area in advance, and the phase between adjacent tracks is changed. It is preferable that they are recorded in parallel. Since the signal used for measuring the flying height is recorded inline in the radial direction of the magnetic medium and the phases are aligned, the flying height is constant regardless of the position of the magnetic head slider in the radial direction of the magnetic medium. If so, the level of the measurement signal will be the same, and the flying height can be measured with high accuracy without being affected by the off-track of the magnetic head.

Further, in the magnetic disk device according to the present invention, the flying height measuring circuit measures the flying height or the flying fluctuation amount of the magnetic head slider for each arbitrary sector,
While accumulating the measurement data, compare the measurement data with the reference value prepared in advance, and if the threshold value is exceeded, it is determined that the flying height or flying fluctuation amount of the magnetic head slider is abnormal. It is preferable to start a predetermined processing operation. This is because it is possible to measure the flying height or the flying fluctuation amount of the magnetic head slider for each sector with high resolution, and therefore it is possible to predict the danger such as head crash from the very minute behavior fluctuation of the magnetic head slider.

The flying height measuring circuit according to the present invention is
The signal used for measuring the flying height recorded in the track servo data area in advance is reproduced by the magnetic head slider, the means for differentiating the reproduced signal waveform, and the amplitude of the differentiated reproduced signal waveform. A means for acquiring a value and a means for acquiring the flying height or the flying fluctuation amount of the magnetic head slider by comparing the amplitude value of the differentiated reproduction signal waveform with a reference amplitude value prepared in advance. Characterize.

With such a configuration, it becomes possible to detect the flying height or the floating fluctuation amount of the magnetic head slider with high accuracy and in a simple method inside the magnetic disk device.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a magnetic disk device and a flying height measuring circuit applied to the same will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a block diagram showing a main part of a magnetic disk device according to a first embodiment of the present invention. In FIG. 1, a head disk assembly includes a magnetic disk 1, a magnetic head 2, and a spindle motor (SPM) for rotating the magnetic disk 1.
3 and an actuator 5 on which the magnetic head slider 2 is mounted.

The magnetic head slider 2 has a structure in which a thin film head as a recording head and an MR element as a reproducing head are separated and formed on the same slider. However, the first embodiment of the present invention means that the magnetic head slider 2 is a reproducing head because it relates to the data reproducing operation.

The actuator 5 includes a voice coil motor (VCM) as a drive source, and the magnetic head 2 is positioned in the radial direction of the magnetic disk 1 by the current supplied from the VCM driver 6. The VCM driver 6 changes the current to VC based on the control signal from the servo controller 13.
Supply to M. Further, the spindle motor 3 is supplied with a drive current from the spindle motor driver 4.

Next, the preamplifier 11 is used for the magnetic disk 1.
The signal (data) recorded in is amplified. Further, the switch circuit 9 selects the servo data and the user data in the first stage, and selects the flying height measurement data and the servo data included in the servo data area in the second stage. Is connected to the processing circuit arranged in.

The user data processing circuit 7 performs reproduction processing for generating digital reproduction data. Then, the reproduction data is sent to the hard disk controller (HDC) 12. The user data processing circuit 7 executes the decoding process of the reproduced data at the timing of the read gate sent from the HDC 12.

The servo data processing circuit 8 executes the reproduction processing of the servo data at the timing of the servo gate output from the servo controller 13, and outputs the servo data including the seek data and the position error data to the servo controller 1.
3, the servo controller 13 controls the positioning of the magnetic head slider 2.

The HDC 12 has a function of performing data transfer control and processing for a flying height measurement result, which will be described later, while configuring an interface with a host system. In addition, inside the magnetic disk, the magnetic head slider 2
The flying height measuring circuit 10 for measuring the dynamic flying height or the floating fluctuation amount is constructed.

Further, the magnetic disk device according to the first embodiment of the present invention also includes a circuit (not shown) for accumulating data such as a reference amplitude value described later and a flag indicating the flying state of the magnetic head slider for each sector. Have together. A circuit for accumulating the reference amplitude value, data such as a flag indicating the flying state of the magnetic head slider for each sector, and the like is composed of a memory circuit inside or outside the hard disk controller.

Next, the flying height measuring circuit according to the first embodiment of the present invention will be described in detail. FIG. 2 is a block diagram showing a main part of the flying height measuring circuit according to the first embodiment of the present invention. In FIG. 2, the flying height measurement signal (hereinafter referred to as “measurement signal”) reproduced by the magnetic head slider 2 is input to a preamplifier 11 and a fixed gain amplifier 21 for amplification via a switch circuit 9. It Then, the A / D conversion circuit 22 for discretizing the measurement signal
In the measurement signal, a filter operation circuit 23 used to reduce noise outside the band used for the measurement (mainly in the high frequency region), a differentiation circuit 24 for differentiating the measurement signal, and a differentiated measurement An amplitude value calculation circuit 25 for detecting the amplitude value of the signal, a calculated amplitude value of the differential signal, and a reference amplitude value 27 prepared in advance to convert to a flying height or a floating fluctuation amount. Quantity calculation circuit 26
It consists of and.

In the first embodiment of the present invention, the reference amplitude value 26 is stored inside the external memory circuit or the hard disk controller (HDC). It is sufficient for practical use if the reference amplitude value 26 is at least 5 points or more.

Further, in the first embodiment, the flying height is measured by means of discretization in all steps using the A / D conversion circuit, but each process is configured by an analog circuit. You can go.

Next, the data structure of the servo area including the flying height measurement signal will be described. FIG. 3 is a diagram showing an outline of the data structure of the servo area. In FIG. 3, the servo area 30 includes a flying height measurement signal 31, AGC (Au
Signal 3 for "Tomatic Gain Control"
3, Gap signal 32 (for recognizing the boundary between AGC signal 33 and flying height measurement signal 41), erase signal 34, address code 35, burst signal 36, Gap
A signal 37 (for recognizing the boundary between the servo area and the user data area) is sequentially recorded. at least,
The flying height measurement signal 31 and the AGC signal 33 are continuously recorded on the adjacent tracks and have the same phase.

The operation of monitoring the flying height or fluctuation of the flying height for each arbitrary sector will be described with reference to z5. FIG. 5 is a flowchart showing an outline of the monitoring operation according to the first embodiment.

In FIG. 5, in the flying height measuring circuit, a flying height measuring signal (hereinafter referred to as a measuring signal) first selected and output by a preamplifier and a switch circuit section (not shown) is set to an amplitude level that is easy to handle. Therefore, it is amplified by a fixed gain amplifier (step S1). Next, after passing through the LPF circuit in order to reduce noise outside the band used for the measurement in the measurement signal, particularly high-frequency components, it is passed through a differentiating circuit to perform differentiation processing (step S2). Further, the amplitude value of the differentiated measurement signal is detected (step S3),
The detected amplitude value is compared with the reference amplitude value for flying height conversion stored in the hard disk controller or an external memory circuit (not shown) (step S4), and the flying height of the magnetic head slider or It is converted into a floating fluctuation amount (step S5).

Next, regarding the operation inside the hard disk controller, the flying height in the memory circuit inside or outside the hard disk controller is based on the flying height or flying fluctuation amount of the magnetic head slider obtained through steps S1 to S5. The amount data is updated (step S6), and the operation of determining whether the measured flying height data is normal or abnormal is performed (step S7). For such a determination operation, the upper and lower thresholds of the flying height or the floating fluctuation amount, which are stored in advance in the hard disk controller unit or an external memory circuit, are used.

Next, it is judged whether or not the measured flying height data is smaller than the lower limit value (step S8), and if it is smaller than the lower limit value (step S8: YES), the flying of the magnetic head slider for each sector is performed. The data of the status flag portion of the data indicating the state is updated (step S
9). On the contrary, if the lower limit value is abnormal (step S
8: NO), it is determined whether or not the measured flying height data is larger than the upper limit value (step S10).

If it is larger than the upper limit value (step S1)
0: YES), the data of the status flag portion of the data indicating the flying state of the magnetic head slider for each sector is updated (step S11). On the contrary, when it is equal to or less than the upper limit value (step S10: NO), the current flying height is within the normal range and the status flag is not updated.
(The initial value remains unchanged.) Then, the magnetic head slider is moved (positioned) to an arbitrary sector, and a series of flying height monitoring operations are performed.

As described above, since it is possible to measure the flying height or the flying fluctuation amount of the magnetic head slider for each sector with high resolution, it is possible to predict the danger such as a head crash due to a very small fluctuation in the behavior of the magnetic head slider. It is possible. Further, since the flying height measurement signal is also only slightly added to the servo data area, it has almost no effect on the format capacity of the entire magnetic disk.

Next, a magnetic disk device equipped with a flying height measuring circuit according to the first embodiment of the present invention, and a magnetic disk device equipped with a circuit that uses a reproduction amplitude value or a half width as a conventional flying height estimation means. The result of comparing the flying height monitoring performances of the devices will be described. The experiment was conducted by forcibly changing the flying height of the magnetic head slider.

FIG. 5 is a diagram comparing the amount of change (ratio) of each characteristic value (amplitude, half width, differential amplitude value), that is, the detection sensitivity, with respect to the change in the flying height of the magnetic head slider. Figure 5
As is clear from the above, when the magnetic disk device of the present invention is used, it is clear that the detection sensitivity is much higher than that of the conventional magnetic disk device. It can also be detected sensitively. Therefore, it becomes possible to sufficiently predict the danger such as head crash. As a result, it is possible to provide a magnetic disk device and a flying height measuring circuit applied to the magnetic disk device, which has an effective means for easily measuring the flying height and variation of the magnetic head slider in the magnetic disk device with high resolution.

[0038]

As described above, according to the flying height measuring circuit for a magnetic head slider and the flying height measuring method applied thereto according to the present invention, the flying height of the magnetic head slider can be easily increased inside the magnetic disk device. It is possible to measure the amount or the fluctuation amount of the flying height.

Further, according to the flying height measuring circuit of the magnetic head slider and the flying height measuring method applied to the magnetic head slider according to the present invention, flying height measurement and monitoring operation can be performed for each arbitrary sector. The prediction can be performed with high accuracy, and a highly reliable magnetic disk device can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main part of a magnetic disk device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a main part of a magnetic head slider flying height measuring circuit in the magnetic disk device according to the first embodiment of the present invention.

FIG. 3 is a data structure diagram of a servo area in the magnetic disk device according to the first embodiment of the present invention.

FIG. 4 is a flowchart of a flying height monitoring process in the magnetic disk device according to the first embodiment of the present invention.

FIG. 5 is a diagram comparing the detection sensitivities of the magnetic disk device according to the first embodiment of the present invention and the conventional magnetic disk device with respect to changes in the flying height.

[Explanation of symbols]

1 magnetic disk 2 Magnetic head slider 3 spindle motor 4 Spindle motor driver 5 actuators 6 Voice coil motor driver 7 User data processing circuit 8 Servo data processing circuit 9 Switch circuit section 10 Flying height measurement circuit 11 preamplifier 12 Hard disk controller 13 Servo controller 21 fixed gain amplifier 22 A / D conversion circuit 23 Filter operation circuit 24 Differentiator circuit 25 Amplitude calculation circuit 26 Flying height calculation circuit 27 Reference amplitude value 30 servo areas 31 Flying height measurement signal 32, 37 Gap signal 33 AGC signal 34 Erase signal 35 address code 36 burst signal

Claims (4)

[Claims] 1. A magnetic disk device comprising a magnetic disk driven to rotate and a magnetic head slider floating above the magnetic disk, wherein a reproduction signal waveform read by the magnetic head slider is differentiated. A flying height measuring circuit for measuring a flying height or a floating fluctuation amount of the magnetic head slider based on the differentiated amplitude value of the reproduced signal waveform. 2. A signal used for measuring the flying height is previously recorded in a track servo data area in the flying height measuring circuit, and is recorded with a phase aligned between adjacent tracks. 1. The magnetic disk device according to 1. 3. The flying height measuring circuit measures the flying height or flying fluctuation amount of the magnetic head slider for each arbitrary sector, accumulates the measured data, and prepares a reference value and the measured data prepared in advance. If it exceeds a predetermined threshold value, it is determined that the flying height or flying fluctuation amount of the magnetic head slider is abnormal,
3. The magnetic disk device according to claim 1, which starts a predetermined processing operation. 4. A signal used for measuring the flying height recorded in advance in the data area for track servo,
Means for reproducing with a magnetic head slider, means for differentiating the reproduced signal waveform, means for obtaining the amplitude value of the differentiated reproduced signal waveform, and the amplitude value of the differentiated reproduced signal waveform, in advance, 3. A flying height measuring circuit for a magnetic head slider, comprising means for comparing the flying height of the magnetic head slider with the reference amplitude value prepared in 1.