Method of estimating life of head, method of inspecting recording medium, method of evaluating head, and information recording/reproducing apparatus

A method of estimating life of a head that reads information recorded in a recording medium includes detecting magnitude of an impact due to a contact between the head and the recording medium; and estimating the life of the head based on the magnitude of the impact detected.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a recording medium on which information is recorded, and a head that reads information recorded in the recording medium, and more particularly, to a method of estimating life of the head and the recording medium.

2. Description of the Related Art

When an information recording and reproducing apparatus (hereinafter, “magnetic disk apparatus”), which uses a magnetic disk as a recording medium to record information (data), reads information from the magnetic disk, it is common to use a magnetic head that uses giant magneto resistive effect from a giant-magneto-resistive (GMR) element or a ferromagnetic tunneling effect from a tunneling-magneto-resistive (TMR) element.

The magnetic disk apparatus is used as a storage apparatus for various systems such as a computer, a personal computer, or a server to perform reading and writing of information repeatedly. However, when the magnetic head is used for a long time, the GMR element or the TMR element degrades and an output of the magnetic head gradually decreases, which may result in occurrence of a data-read error.

Conventionally, various techniques have been proposed regarding the degradation of the magnetic head using the GMR element. For example, A. J. Wakkash N. Cheng, IEEE Trans. Mag. 35-5, 2610-2712 (1999) discloses a technique to cope with the degradation of the GMR head (magnetic head), focused on temperature. In I. F. Tsu, G. a. Burg, and W. P. Wood, IEEE Trans. Mag. 37-4, 1707-1709 (2001), a technique to cope with the degradation of the GMR head (magnetic head), focused on magnetic field, has been disclosed.

In recent years, a recording density in a magnetic disk increases, and a floating amount of a magnetic head decreases to about 10 nanometers. Ideally, the magnetic disk should be flat; however, there is actually a fine undulation on the magnetic disk. When data is read from the magnetic disk with a floating amount of about 10 nanometers, the magnetic head receives an impact from a contact between the magnetic head and the magnetic disk due to the fine undulation on the magnetic disk. Even if a magnitude of the impact is small, a life (degradation) of the magnetic head is influenced by the impact.

In the above conventional techniques, however, the impact due to the contact between the magnetic disk and the magnetic head has not been considered. Therefore, the degradation of the magnetic head cannot be estimated properly.

In a conventional method of inspecting the magnetic disk, in general, the maximum value of the magnitude of the impact that a magnetic disk receives is often used. However, when the frequency of contacts increases, even if the magnitude of each impact is small, the life of the magnetic head is influenced by the impact. Therefore, in the conventional method of inspecting the magnetic disk utilizing the maximum value of the magnitude of the impact, since an accumulation of the magnitude of the impact with time is not taken into consideration, a proper inspection of the magnetic disk can not be performed.

There are various materials used for an element to read data in the magnetic head. Durability against the impact due to the contact between the magnetic disk and the magnetic head varies according to each material or a structure of the magnetic head. In the conventional techniques, however, measuring and evaluating the durability of the magnetic head including the magnitude of the impact between the magnetic disk and the magnetic head have not been considered. Accordingly, a difference in the durability of the magnetic head against the contact between the magnetic head and the magnetic disk cannot be properly evaluated.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve at least the above problems in the conventional technology.

A method of estimating life of a head that reads information recorded in a recording medium, according to one aspect of the present invention, includes detecting magnitude of an impact due to a contact between the head and the recording medium; and estimating the life of the head based on the magnitude of the impact detected.

A method of inspecting a recording medium according to another aspect of the present invention includes detecting magnitude of an impact due to a contact between a head and the recording medium; accumulating the magnitude of the impact detected; and determining whether the recording medium is good, based on the magnitude of the impact accumulated.

A method of evaluating durability of a head, according to still another aspect of the present invention, includes detecting magnitude of an impact due to a contact between the head and a recording medium; and an evaluation process including measuring an output from the head at a predetermined time interval, and calculating an evaluation value indicating the durability of the head, based on the output measured, an initial output of the head, and the magnitude of the impact detected.

An apparatus for recording information on a recording medium and reproducing information from the recording medium, according to still another aspect of the present invention, includes a head that reproduces the information recorded on the recording medium; a contact-impact detecting unit that detects magnitude of an impact due to a contact between the head and the recording medium; and a life-estimation processing unit that estimates life of the head based on the magnitude of the impact detected, and performs at least one of a first process and a second process. The first process is to notify a value indicating the life of the head estimated, and the second process is to notify that the head has reached end of the life.

An apparatus for inspecting a recording medium, according to still another aspect of the present invention, includes a rotation control unit that rotates the recording medium on which information is recorded; a head that is floating or sliding on the recording medium under rotation at a predetermined distance from a surface of the recording medium; a position control unit that moves the head to a predetermined position on the recording medium; a contact-impact detecting unit that detects magnitude of an impact due to a contact between the head and the recording medium; an accumulating unit that accumulates the magnitude of the impact detected; and a determining unit that determines whether the recording medium is good, based on the magnitude of the impact accumulated.

An apparatus for evaluating durability of a head, according to still another aspect of the present invention, includes a contact-impact detecting unit that detects magnitude of an impact due to a contact between the head and the recording medium; and an evaluation processing unit that measures an output from the head at a predetermined time interval, and calculates an evaluation value indicating the durability of the head, based on the output measured, an initial output of the head, and the magnitude of the impact detected.

A computer-readable recording medium according to still another aspect of the present invention stores a program that makes a computer execute the above method of estimating life of a head according to the present invention.

A computer-readable recording medium according to still another aspect of the present invention stores a program that makes a computer execute the above method of inspecting a recording medium according to the present invention.

A computer-readable recording medium according to still another aspect of the present invention stores a program that makes a computer execute the above method of evaluating durability of a head according to the present invention.

DETAILED DESCRIPTION

Exemplary embodiments of the present invention will be explained below in detail with reference to the accompanying drawings. However, the present invention is not limited to these embodiments.

According to the embodiments of the present invention, a case that a magnetic disk that records information thereon using magnetism is used as a recording medium, a magnetic head that includes a GMR element to utilize a giant magneto resistive effect is used as a head (for reading data) that reproduces information form the magnetic disk, and magnitude of an impact due to contact between the magnetic head and the magnetic disk is detected by an acoustic emission (AE) signal or a piezoelectric output signal from a piezoelectric element will be explained as an example. However, a recording medium, a head, and detection of magnitude of an impact are not limited to the above. For example, a magnetic head that includes a TMR element to utilize a ferromagnetic tunneling effect may be used as the head, and a head different from the magnetic head may be used. Such a constitution may be employed that the magnitude of an impact may be detected based on the number of contacts of the recording medium and the head, and any means or method which allows detection of the magnitude of an impact due to contact between the recording medium and the head can be used.

FIG. 1is a graph of a relationship between an AE signal, an output change amount of a magnetic head, and time. InFIG. 1, one vertical axis indicates an accumulated value of AE signals (∫AEdt), the other vertical axis indicates an output change amount of a magnetic head (which, when an initial output V0of the magnetic head at time of 0 is defined as 100%, indicates a ratio of decrease in output V of the magnetic head: −ΔV/V0), and a horizontal axis indicates Time, where a solid line indicates an accumulated value of AE signals, and plot of □ indicates an output change amount of the magnetic head to a magnetic head output at a start time of operation. As shown inFIG. 1, an accumulated value of AE signals increases according to time elapsing and an output change amount increases due to lowering of an output V of the magnetic head. That is,FIG. 1is a graph of such a fact that an impact due to contact between the magnetic head and the magnetic disk is a factor for lowering an output of the magnetic head.

Here, as “(−ΔV/V0) ∞ ∫AEdt”, “(−ΔV/V0)/∫AEdt” is defined as an output degradation coefficient. Measurement results to one magnetic head are shown inFIG. 1, but a tendency similar to that inFIG. 1can be obtained even regarding measurement results of AE signals to a plurality of magnetic heads and outputs thereof.

FIG. 2is a graph of a relationship between the output change amount of the magnetic head and the AE signal. InFIG. 2, a vertical axis indicates an output change amount of a magnetic head (−ΔV/V0) and a horizontal axis indicates an accumulated value of AE signals (∫AEdt), where a solid line L1indicates a measurement result of a magnetic head No.1, a solid line L2indicates a measurement result of a magnetic head No.2, a solid line L3indicates a measurement result of a magnetic head No.3, and a solid line L4indicates a measurement result of a magnetic head No.4.FIG. 2is a graph of such a fact that output degradation coefficients are different according to differences of magnetic heads. That is, such a fact that output degradation coefficients of a plurality of magnetic heads do not take a fixed value is shown inFIG. 2.

In general, it has been known that a magnetic head degrades due to heat. Therefore, the inventors have focused on a temperature of a magnetic head (a temperature of a GMR element which is an element to read data for a magnetic head).FIG. 3is a graph of a relationship between a temperature and an output degradation coefficient of the magnetic head. InFIG. 3, a vertical axis indicates an output degradation coefficient ((−ΔV/V0)/∫AEdt), and a horizontal axis indicates an absolute temperature of the magnetic head (Tgmr), where the output change amount is represented by a single logarithm. Plot of “⋄” has been obtained by increasing and accelerating a value of current flowing in a magnetic head for reading, and plot of “♦” has been obtained by increasing and accelerating a value of current flowing in a magnetic head for writing. The respective plots are values of individual magnetic heads. A relationship between the output degradation coefficient and the absolute temperature of the magnetic head Tgmr can be represented by
(−ΔV/Vo)/∫AEdt=a×exp(b×Tgmr)   (1)
where, “a” and “b” are constants.

Eq. (1) represents that, even if an impact received by the magnetic head is fine, increase in frequency of impact causes degradation of an output of the magnetic head. In other words, unless all impacts received by the magnetic head are considered, a life of the magnetic head can not be estimated properly. Eq. (1) represents that a sensitivity of output degradation to the output degradation coefficient, i.e., the impact is an exponential function of a temperature of the magnetic head.

Assuming that the temperature of the magnetic head is fixed, an output change amount “−ΔV/V0” can be obtained from Eq. (1), as
−ΔV/Vo=a×exp(b×Tgmr)×∫AEdt(2)

Considering a temperature change of the magnetic head, the output change amount “−ΔV/V0” can be obtained from Eq. (1), as
∫(−ΔV/Vo)dt=∫(a×exp(b×Tgmr)×AE)dt(3)

When an allowable value (a threshold for determining the end of life) of the output change amount of the magnetic head and an absolute temperature of the magnetic head are set in advance, the end of the life of the magnetic head (the output change amount) can be estimated by measuring magnitude of an impact due to contact between a magnetic head and magnetic disk (Eq. (2)).

By setting the allowable value for the output change amount of the magnetic head in advance and measuring the magnitude of an impact due to contact between a magnetic head and a magnetic disk and a temperature of the magnetic head, the end of life of the magnetic head including the temperature change of the magnetic head can be estimated according to Eq. (3).

FIG. 4is a graph of a relationship between a temperature of the magnetic head and the output degradation coefficient with an approximate Eq. different from Eq. (1), where the temperature of the magnetic head and the output degradation coefficient are represented by double logarithm. Plot of “⋄” has been obtained by increasing and accelerating a value of current flowing in a magnetic head for reading, and plot of “♦” has been obtained by increasing and accelerating a value of current flowing in a magnetic head for writing. The respective plots are values of individual magnetic heads. InFIG. 4, output degradation coefficients are distributed substantially on a straight line. A relationship between the output degradation coefficient and the absolute temperature Tgmr of the magnetic head can be represented by
(−ΔV/ΔVo)/∫AEdt=a·Tgmrb(4)
where, “a” and “b” are constants.

Like Eq. (1), Eq. (4) represents that, even if magnitude of an impact received by the magnetic head is fine, increase in frequency of impact causes degradation of an output of the magnetic head and the output degradation coefficient is a function of the temperature of the magnetic head.

Regarding the output change amount “−ΔV/V0”, the following Eq. (5) can be obtained from Eq. (4).
∫(−ΔV/Vo)dt=∫(AE×a×Tgmrb)dt(5)

By setting the allowable value of the output change amount of the magnetic head and the absolute temperature of the magnetic head in advance, measuring magnitude of an impact due to contact between a magnetic head and a magnetic disk, or by setting the allowable value of the output change value of the magnetic head in advance and measuring magnitude of an impact due to contact between the magnetic head and the magnetic disk and temperature of the magnetic head, the end of life of the magnetic head can be estimated according to Eq. (5).

FIG. 5is a graph of a relationship between a temperature of a magnetic head and an output degradation coefficient with an approximate equation different from Eq. (1) and Eq. (4), where a vertical axis represents the output degradation coefficient with a natural logarithm and a horizontal axis represents a function of a reciprocal number of an absolute temperature of a magnetic head. Plot of “⋄” has been obtained by increasing and accelerating a value of current flowing in a magnetic head for reading, and plot of “♦” has been obtained by increasing and accelerating a value of current flowing in a magnetic head for writing. The respective plots are values of individual magnetic heads. A relationship between the output degradation coefficient and the absolute temperature Tgmr of the magnetic head can be represented by
ln((−ΔV/Vo)/∫AEdt)=a−b×(1/Tgmr)   (6)
where, “a” and “b” are constants. Similarly, Eq. (6) represents that, even if an impact received by the magnetic head is fine, increase in frequency of impact causes degradation of an output of the magnetic head and the output degradation coefficient is a function of the temperature of the magnetic head.

Regarding the output change amount “−ΔV/V0”, the following Eq. (7) can be obtained from Eq. (6).
−ΔV/Vo=∫(AE×exp(a−b×(1/Tgmr))dt(7)

By setting the allowable vale of the output change amount of the magnetic head and the absolute temperature of the magnetic head in advance, measuring strength of impact due to contact between a magnetic head and a magnetic disk, or by setting the allowable value of the output change amount of the magnetic head in advance and measuring magnitude of an impact due to contact between the magnetic head and the magnetic disk and temperature of the magnetic head, the end of life of the magnetic head can be estimated according to Eq. (7).

In the head life estimating method according to the present invention, from a viewpoint that an output degradation rate of a magnetic head is due to magnitude of an impact due to contact between the magnetic head and the magnetic disk received by a magnetic head and a temperature of the magnetic head, a life of the magnetic head is estimated based on the magnitude of an impact due to contact between the magnetic head and the magnetic disk and the temperature of the magnetic head.

Each of Eqs. (1), (4), and (6) shows that the output degradation coefficient is the function of the temperature of the magnetic head and, even if an impact due to contact between a magnetic head and a magnetic disk is fine, increase in frequency of impact causes degradation of an output of the magnetic head. Since a magnetic disk with many undulations imparts many impacts on a magnetic head, the impacts cause degradation of the magnetic head.

In general, when inspection about goodness and badness of a magnetic disk is performed, a piezoelectric output signal from a piezoelectric element is used as magnitude of an impact due to contact between a magnetic disk and a magnetic head, and the maximum value of the piezoelectric output signal in a one turn of a truck on the magnetic disk is used. However, as shown in Eqs. (1), (4), and (6), even if the magnitude of an impact is fine, increase in frequency of occurrences of impact affects the end of life of the magnetic head. Therefore, in an inspecting method using the maximum value of the piezoelectric output signal, since an effect of accumulation of strengths of impacts along a time axis is not considered, a proper inspection about goodness and badness of a magnetic disk can not be performed.

When a magnetic disk is inspected, since strengths of impacts over a long time can not be accumulated, an average value (a plane average value) of strengths of impacts of the magnetic disk is used. Here, the previous Eq. (1) is applied to the magnetic disk and the piezoelectric output signal is used as the magnitude of an impact instead of the AE signal. When a piezoelectric output signal is represented as PZT, an initial output of the magnetic head to the magnetic disk is represented as V0, an allowable output of the magnetic head after degradation is represented as V, and a temperature of the magnetic head is represented as Tgmr, a degradation coefficient can be represented by
(−ΔV/Vo)/∫PZTdt=a×exp(b×Tgmr)   (8)

When a usable time of a magnetic head to the magnetic disk is represented as L, and an average value of piezoelectric output signals is represented as PZTave, an accumulated value ∫PZTdt of the piezoelectric output signal can be represented by
∫PZTdt=PZTave×L(9)

The usable time L can be represented from Eqs. (8) and (9), as
L=(−ΔV/Vo)/(PZTave×(a×exp(b×Tgmr)))   (10)

The average value PZTave of the piezoelectric output signals can be represented by
PZTave=(−ΔV/Vo)/(L×a×exp(b×Tgmr))   (11)

The usable time L can be represented from Eqs. (4) and (9), as
L=(−ΔV/Vo)/(PZTave×a×Tgmrb)   (12)

The average value PZTave of the piezoelectric output signals can be represented by
PZTave=(−ΔV/Vo)/(L×a×Tgmrb)   (13)

The usable time L can be represented from Eqs. (6) and (9), by
L=(−ΔV/Vo)/(PZTave×exp(a−b×(1/Tgmr)))   (14)

The average value PZTave of the piezoelectric output signals can be represented by
PZTave=(−ΔV/Vo)/(L×exp(a−b×(1/Tgmr))   (15)

By determining the temperature Tgmr, the usable time L, and an allowable value of the output change amount “−ΔV/V0” that are usage conditions for a magnetic head, the average value PZTave of the piezoelectric output signals is determined according to Eqs. (11), (13), and (15). Accordingly, when an average value of piezoelectric output signals corresponding to strengths of impacts due to contact between a magnetic head and a magnetic disk to be inspected, which is obtained when the magnetic head is moved from an outer periphery of the magnetic disk to an inner periphery thereof during inspection, is equal to or less than an average value PZTave of piezoelectric output signals which are calculated using Eq. (11), (13), or (15), it can be determined that the usable time L can be satisfied.

In the recording medium inspecting method according to the present invention, considering that the output degradation rate of the magnetic head is caused by the magnitude of an impact due to contact between the magnetic head and a magnetic disk that is a recording medium received by the magnetic head and the temperature of the magnetic head, such a constitution is employed that, when the magnitude of an impact from the magnetic disk to the magnetic head due to contact between the magnetic disk and the magnetic head is equal to or less than a predetermined value, the magnetic head can satisfy a desired usable time, so that the recording medium can be determined as goodness.

As a material for the GMR element for the magnetic head, there are various kinds of materials such as InSb, InAs, GaAs, or InP, and output degradation amounts due to magnitude of an impact due to contact between a magnetic disk and a magnetic head are different according to materials to be used. When a magnetic head is developed or a magnetic head used in a magnetic disk apparatus is selected, it is necessary to evaluate a degree of influence of magnitude of an impact due to contact between a magnetic disk and a magnetic head.

The left-hand side (the output degradation coefficient “(−ΔV/V0)/∫AEdt”) of Eqs. (1), (4), and (6) represents durability of output degradation of a magnetic head to an AE signal, and the right-hand side represents that the output degradation coefficient is the function of the temperature of the magnetic head. Assuming that the temperature of the magnetic head is fixed, the constants “a” and “b” in Eqs. (1), (4), and (6) become coefficients determining material of a GMR element or a structure of an element. That is, with temperatures of different GMR elements (temperatures of different magnetic heads) a fixed to a predetermined value, by measuring output degradation coefficients of the magnetic heads and comparing the output degradation coefficients measured, differences in durability to impacts due to contacts of the magnetic heads and a magnetic disk can be evaluated.

In the head evaluating method according to the present invention, considering that the output degradation coefficient is the function of the temperature of the magnetic head, such a constitution is employed that durability to magnitude of an impact due to contact between the magnetic head and the magnetic head is evaluated based on the output degradation coefficient measured while the temperature of the magnetic head is kept at any fixed value or the magnetic head is kept at a plurality of level temperatures.

FIG. 6is a block diagram of a magnetic disk apparatus according to a first embodiment of the present invention. A magnetic disk apparatus1shown inFIG. 6is controlled by a host5which is an upper apparatus such as a personal computer or a server using the magnetic disk apparatus1as a storage device.

The magnetic disk apparatus1is provided with a disk enclosure (DE)10and a reading and writing processor30. The DE10includes a magnetic disk11that records information (data) from the host5therein; a head gimbal assembly (HGA)12including a writing head121that records information into the magnetic disk11, a reading head122that is constituted of a GMR element for reading data stored in the magnetic disk11, a contact impact detector123that detects magnitude of an impact due to contact between the magnetic disk11and the reading head122as an AE signal, and a temperature detector124that detects a temperature of the reading head; a head amplifier13that controls a writing current supplied to the writing head121and amplifies magnetization waveform of the reading head122, a voice coil motor (VCM)14that controls a position of the reading head122or the writing head121: and a DC motor (DCM)15that rotates the magnetic disk11. The reading and writing processor30includes a read channel circuit31that performs predetermined coding processing on data recorded in the magnetic disk11and performs predetermined decoding processing on data read from the magnetic disk11; a hard disk controller32that performs processing regarding error correction on data; a data buffer33that stores data recorded in the magnetic disk11and data read from the magnetic disk11, a micro controller unit (MCU)34that produces control information for controlling the DCM15, the VCM14, and the head amplifier13, a serve controller (SVC) that controls the DCM15and the VCM14based on the control information produced by the MCU34, and a life estimation processor36that estimates the end of life of the reading head122based on magnitude of an impact detected by the contact impact detector123and a temperature of the magnetic disk11measured by the temperature detector124.

FIG. 7is a block diagram of the life estimation processor36shown inFIG. 6. The life estimation processor36is provided with a signal converter361that converts a high frequency AE signal outputted from the contact impact detector123into a low frequency signal, an accumulating unit362that performs a predetermined arithmetic operation using the temperature of the reading head122detected by the temperature detector124and the low frequency AE signal converted by the signal converter361to calculate output change amounts of the reading head122and accumulate the output change amounts calculated, a life estimating unit363that estimates the end of life of the reading head122based on the output change amounts accumulated by the accumulating unit362and the predetermined allowable value for the reading head122, and a storage unit364that is constituted of a non-volatile memory for storing the output change amounts accumulated by the accumulating unit362.

The magnetic disk apparatus1floats the writing head121and the reading head122on the rotating magnetic disk11, so that the magnetic disk11is magnetized by the writing head121at a time of writing and a magnetism signal is read from magnetization of the magnetic disk11by the reading head122to reproduce data recorded in the magnetic disk11at a time of reading.

Tracks on the magnetic disk11are classified to servo information indicating a position of the writing head121or the reading head122, and a data section in which data is stored. A servo signal read by the reading head122is decoded into position information by the read channel circuit31, and the MCU34controls the VCM14via the SVC35such that the writing head121or the reading head122is positioned on a track accurately based on the position information.

When receives writing instruction from the host5, the hard disk controller32stores the writing instruction and data inputted from the host5into the data buffer33. The hard disk controller32calculates a physical track position on the magnetic disk11from a logical block address (LBA) included in the writing instruction. The hard disk controller32outputs address information which is the calculated physical track position to the MCU34.

The MCU34outputs head position control information that moves the head to a position corresponding to a track number of the address information to the SVC35. The SVC35determines a current value for controlling the VCM14to move the VCM14and position the writing head121on a desired track on the magnetic disk11based on the head position control information.

On the other hand, the hard disk controller32reads data stored in the data buffer33to calculate error correction code (ECC). The hard disk controller32outputs user data, address information, or the calculated ECC to the read channel circuit31.

The read channel circuit31produces writing data prepared by adding information for performing phase synchronization, output fixing, or the like to the data, the address information, or the ECC from the hard disk controller32to perform predetermined coding processing on the produced writing data, thereby producing a write signal recorded on the magnetic disk11. The read channel circuit31outputs the writing signal to the head amplifier13.

The head amplifier13changes a direction of a writing current flowing in the writing head121based on a bit of the writing signal to change a magnetization direction of the magnetic disk11and record data inputted from the host5on the magnetic disk11.

When receives a reading instruction from the host5, the hard disk controller32calculates a physical track position on the magnetic disk11from a logical address included in the reading instruction. The hard disk controller32outputs address information that is the calculated physical track position into the MCU34.

The MCU34outputs head position control information moving the head to a position corresponding to a track number included in the address information to the SVC35. The SVC35determines a current value for controlling the VCM14to move the VCM14and position the reading head122on a desired track on the magnetic disk11based on the head position control information.

The head amplifier13amplifies a magnetization waveform read from the magnetic disk11via the reading head122to produce a reading signal. The head amplifier13outputs the reading signal to the read channel circuit31.

The read channel circuit31performs a predetermined decoding processing on the user data, the address information, and the ECC based on phase synchronization or the like to convert the same to NRZ (non-return to zero) data. The read channel circuit31outputs data and ECC in the NRZ data to the hard disk controller32.

The hard disk controller32performs ECC arithmetic operation processing on the data and the ECC to correct data error and stores the data with the corrected data error in the data buffer33to output data stored in the data buffer33to the host5at a predetermined timing.

Thus, the magnetic disk apparatus1is controlled according to an instruction from the host5to perform writing of data on the magnetic disk11or perform reading of data written in the magnetic disk11.

An operation performed for estimating a life of the reading head122by the magnetic disk apparatus1will be explained with reference to a flowchart inFIG. 8. It is assumed that “0” is stored as an initial value for the accumulated value in the storage unit364at a start time of life estimation.

The contact impact detector123detects magnitude of an impact due to contact between the reading head122and the magnetic disk11as a high frequency AE signal (Step S100). The contact impact detector123outputs the detected AE signal to the signal converter361.

The signal converter361converts the high frequency AE signal to a low frequency AE signal (Step S110). Specifically, the signal converter361performs an amplitude-demodulating process, a detection process that detects an envelope, a root-mean-square (RMS) conversion process, or the like on the AE signal to convert the high frequency AE signal to the low frequency AE signal. The signal converter361outputs the converted AE signal to the accumulating unit362.

When receives the AE signal outputted from the signal converter361, the accumulating unit362requested the temperature detector124to detect a temperature of the reading head122. The temperature detector124detects a temperature of the reading head122(Step S120).

Specifically, the temperature detector124measures a resistance value of a reading element in the reading head122. When a reference temperature is represented as Ta, a reference resistance value of the reading element in the reading head122at the reference temperature Ta is represented as Ra, and the temperature of the reading element in the reading head122is represented as Tread, a resistance R of the reading element measured is expressed as the following Eq. (16).
R=Ra(1+α(Tread−Ta))   (16)
where, α is a temperature coefficient of a resistor. The temperature Tread of the reading element in the reading head122is expressed according to Eq. (16), by
Tread=(((R/Ra)−1)/α)+Ta(17)

The temperature detector124calculates the temperature of the reading element in the reading head122using Eq. (17) and notifies the calculated temperature of the reading element to the accumulating unit362as a temperature of the reading head122.

The reference temperature Ta is an ambient temperature of the reading head122or a temperature inside the disk enclosure10, and the reference resistance Ra is a resistance value when the temperature of the reading element in the reading head122is the reference temperature Ta. The temperature detector124measures the reference temperature Ta and the reference resistance Ra of the reading element at the reference temperature Ta during non-operation of the magnetic disk apparatus1at least one time.

However, since the reference resistance value Ra may change moderately in the long run, it is preferable that the resistance value of the reading head122is measured during non-operation of the magnetic disk apparatus1(while current is not caused to flow in the reading head122and the writing head121, or while current is not caused to flow in the writing head121and the temperature Tread of the reading element in the reading head122can be regarded as equal to the reference temperature Ta) at predetermined time intervals and the latest measurement value is used as the reference resistance value Ra.

The accumulating unit362calculates an output change amount of the reading head122based on the AE signal outputted from the signal converter361and the temperature of the reading head122detected by the temperature detector124(Step S130). When the AE signal outputted from the signal converter361is represented as AE1, the absolute temperature of the reading head122detected by the temperature detector124is represented as Tgmr1, and the accumulated value stored in the storage unit364is represented as Y, Eq. (4) can be expressed by
ΔV/Vo≈Y−AE1×a×exp(b×Tgmr1)   (18)
The accumulating unit362calculates an output change amount of the reading head122using Eq. (18). That is, the accumulating unit362multiplies the exponential function of the absolute temperature of the reading head122by a value proportional to the AE signal converted into the low frequency that indicates magnitude of an impact to calculate the output change amount of the reading head122. The output change amount calculated using Eq. (18) is an estimated value of a life of the reading head122based on the AE signal and the temperature of the reading head122. The accumulating unit362stores the calculated output change amount in the storage unit364and outputs the same to the life estimating unit363.

The life estimating unit363compares the output change amount calculated by the accumulating unit362and a predetermined allowable value of the output change amount of the reading head122with each other to determine whether the reading head122has reached the end of life (Step S140). As the result of comparison, when the output change amount is equal to or more than the allowable value, the life estimating unit363determines that the reading head122has reached the end of life and notifies such a fact to the host5(Step S150). As the comparison result, when the output change amount is smaller than the allowable value, the life estimating unit363determines that the reading head122has not reached the end of life yet, namely, it is still usable.

Thus, according to the first embodiment, considering that the output degradation rate of the reading head122is caused by magnitude of an impact due to contact between the reading head122and the magnetic disk11received by the reading head122and the temperature of the reading head122, since such a constitution is employed that the life of the reading head122is estimated by detecting strengths of impacts due to contact between the reading head122and the magnetic disk11and temperatures of the reading head122and multiplying the exponential functions of the absolute temperatures of the heading head122by the values proportional to the strengths of impacts to accumulate the multiplied values, even if a floating amount of the reading head122is small and contact between the reading head122and the magnetic disk11frequently occurs, or an output change occurs due to a temporary environmental change, accumulative degradation influence degree from a start time of use of the reading head122can be measured properly so that the life of the reading head122can be estimated properly.

Furthermore, according to the first embodiment, since the signal converter361converts magnitude of an impact due to contact between the reading head122and the magnetic disk11to a low frequency signal, even if high frequency signals detecting strengths of impacts due to contact between the reading head122and the magnetic disk11are sampled at sparse intervals, the strengths of impacts due to contact can be accumulated properly and the life of the head can be estimated considering the strengths of impacts.

Moreover, according to the first embodiment, since it notifies the host5that the reading head122has reached the end of life when the life estimating unit363determines that the reading head122has reached the end of life, such a drawback can be prevented that reading error frequently occurs due to the end of life of the reading head122and the entire system is influenced by the reading error.

Furthermore, according to the first embodiment, since the accumulated value is stored in the storage unit364, even if the information recording and reproducing apparatus is stopped and an operation thereof is then restarted, the life of the reading head122can be estimated properly considering the magnitude of an impact due to contact between the reading head122and the magnetic disk11and the temperatures of the reading head122that are measured continuously from an initial operation of the apparatus.

Moreover, according to the first embodiment, though the HGA12is provided with the contact impact detector123, the contact impact detector123may be constituted to detect magnitude of an impact due to contact between the magnetic disk11and the reading head122. For example, the contact impact detector123may be provided at an arm portion of the VCM14near to the HGA12.

Furthermore, according to the first embodiment, such a constitution is employed that the output change amount calculated by the accumulating unit362is stored in the storage unit364and the output change amount stored in the storage unit364is used, when a new output change amount is calculated. However, such a constitution may be employed that the accumulating unit362also holds the output change amount and it calculates a new output change amount using the output change amount in a normal operation but the output change amount stored in the storage unit364is used only when calculation of another output change amount is restarted after the magnetic disk apparatus1is put in a stopped state.

Moreover, according to the first embodiment, though the output change amount is calculated using Eq. (3), it may be calculated using Eq. (5) or Eq. (7), and the absolute temperature Tgmr of the reading head122may be set in advance assuming that the temperature of the reading head122is fixed. In that case, the temperature detector124shown inFIG. 6is removed and the previous Eq. (2) may be used instead.

Furthermore, according to the first embodiment, when the accumulated value, namely, the output change amount is equal to or more than the predetermined allowable value, the life estimating unit363determines that the reading head122has ended its life and notifies such a fact to the host5. However, such a constitution may be employed that on reception of a request from the host5, the life estimating unit363notifies the output change amount calculated by the accumulating unit362to the host5. Thereby, it is made possible to monitor the state of the information recording and reproducing apparatus via the host5, so that an operation efficiency of a system using the information recording and reproducing apparatus can be prevented from lowering due to reading error of data caused by the end of life of the reading head122.

In general, respective constituent units in the information recording and reproducing apparatus are often controlled integrally by a CPU. InFIG. 6, the DCM15, the VCM14, and the head amplifier13are controlled by the MCU34. The respective functions realized by the contact impact detector123, the temperature detector124, the signal converter361, the accumulating unit362, and the life estimating unit363according to the first embodiment are realized by a software (a program), so that they may be performed by the MCU34or the CPU.

Second Embodiment

FIG. 9is a block diagram of a magnetic disk inspecting apparatus that is a recording medium inspecting apparatus according to a second embodiment of the present invention. The magnetic disk inspecting apparatus shown inFIG. 9includes a control unit37that integrally controls respective constituent units of the magnetic disk inspecting apparatus, a DCM15athat rotates a magnetic disk11ato be inspected, a VCM14athat controls a position of an inspecting head125, a HGA12ahaving a contact impact detector123athat detects magnitude of an impact due to contact between the inspecting head125and the magnetic disk11aas a piezoelectric output signal, and an inspection processor36athat makes determination about goodness and badness of the magnetic disk11a.

FIG. 10is a block diagram of the inspection processor36ashown inFIG. 9. The inspection processor36ais provided with a signal converter361athat converts a high frequency piezoelectric output signal outputted from the contact impact detector123ato a low frequency signal, an accumulating unit362athat accumulates low frequency piezoelectric output signals converted by the signal converter361a, and a determining unit365that makes determination about goodness or badness of the magnetic disk11abased on the accumulated value of the piezoelectric output signals accumulated by the accumulating unit362a.

An operation of the magnetic disk inspecting apparatus will be explained with reference to a flowchart shown inFIG. 11. The determining unit365is preliminarily set with a determination reference value calculated from Eq. (11), (13), or (15) using the use temperature, the life time (usable guarantee time), and the allowable value of the output change amount of the magnetic head used in combination with the magnetic disk11ato be inspected.

When receives an inspection start instruction, the control unit37controls the DCM15aand the VCM14ato rotate the magnetic disk11aand start movement of the inspecting head125(Steps S200and S210). The control unit37controls the VCM14asuch that the inspecting head125moves to a predetermined radius position of the magnetic disk11afrom an outer periphery of the magnetic disk11ato an inner periphery thereof or from the inner periphery to the outer periphery.

The control unit37notifies reception of the inspection start instruction to the inspection processor36aand the inspection processor36aperforms an initial setting processing. The initial setting processing includes setting an initial value required for the signal converter361ato convert a high frequency piezoelectric output signal detected by the contact impact detector123ato a low frequency signal, setting of an initial value “0” into the accumulated value in the accumulating unit362a, measurement start of a sampling time for performing accumulation, and the like.

The contact impact detector123adetects magnitude of an impact due to contact between the inspecting head125and the magnetic disk11aas a piezoelectric output signal (Step S220). The contact impact detector123aoutputs the detected piezoelectric output signal to the signal converter361a.

The signal converter361aconverts a high frequency piezoelectric output signal to a low frequency piezoelectric output signal (Step S230). Specifically, the signal converter361aperforms an amplitude-demodulating process, a detection process that detects an envelope, an RMS converting processing, or the like on the piezoelectric output signal to convert the high frequency piezoelectric output signal to the low frequency piezoelectric output signal. The signal converter361aoutputs the converted piezoelectric output signal to the accumulating unit362a.

The accumulating unit362aaccumulates a low frequency piezoelectric output signal outputted from the signal converter361ato the previous accumulated signals for each sampling time (Steps S240and S250). Specifically, the piezoelectric output signal outputted from the signal converter361ais added to the accumulated value to calculate a new accumulated value and hold the calculated accumulated value.

The accumulating unit362arepeats a processing that adds a low frequency piezoelectric output signal obtained by converting a high frequency piezoelectric output signal detected by the contact impact detector123ain the signal converter361ato the accumulated value to calculate a new calculated value for each sampling time until the accumulating unit362areceives a notification of measurement termination (Steps S240to S260). When movement of the inspecting head125to the predetermined radius position of the magnetic disk11ais terminated, the notification of measurement termination is notified to the accumulating unit362aby the control unit37. After issuing the notification of measurement termination, the control unit37controls the DCM15ato stop rotation of the magnetic disk11a. When receiving the notification of measurement termination, the accumulating unit362aoutputs the accumulated value to the determining unit365.

The determining unit365makes determination about goodness or badness of the magnetic disk11abased on the accumulated value outputted from the accumulating unit362aand the determination reference value (Step S270). Specifically, the determining unit365calculates a value of a piezoelectric output signal on a plane average of the magnetic disk11afrom the accumulated value, and compares the calculated value and the determination reference value with each other. When the calculated value is equal to or less than the determination reference value, the determining unit365determines that the magnetic disk11ais good and outputs the determination result indicating that the magnetic disk11ais good (Step S280).

When the calculated value exceeds the determination reference value, the determining unit365determines that the measured magnetic disk11ais bad and outputs the determination result indicating that the magnetic disk11ais bad (Step S290).

Thus, according to the second embodiment, since such a constitution is employed that strengths of impacts due to contact between the magnetic disk11aand the head125are detected, the strengths of impacts detected are accumulated and a plane average of the strengths of impacts is calculated, and when a value of the plane average of the strengths of impacts calculated is smaller than the predetermined allowable value, the magnetic disk11ais determined to be good, the magnetic disk11acan be inspected considering that the magnetic disk11ais used under such an environment that contact between the head125and the magnetic disk11afrequently occurs due to reduction in floating amount of the head.

According to the second embodiment, since the signal converter361aconverts magnitude of an impact due to contact between the magnetic disk11aand the head125to a low frequency signal, even if high frequency signals detecting strengths of impacts due to contact between the magnetic disk11aand the head25are sampled at sparse intervals, the strengths of impacts due to contact can be accumulated properly and the magnetic disk11acan be inspected considering the strengths of impacts.

In general, the control unit37that controls the DCM15aand the VCM14ais often constituted of a CPU or the like. The respective functions of the contact impact detector123a, the signal converter361a, the accumulating unit362a, and the determining unit365according to the second embodiment are realized by a software (a program) and they may be implemented by a CPU.

Third Embodiment

FIG. 12is a block diagram of a magnetic-head evaluating apparatus according to a third embodiment of the present invention. The magnetic-head evaluating apparatus shown inFIG. 12includes a control unit37athat integrally controls respective constituent units of the magnetic-head evaluating apparatus and adjusts a temperature of the reading head element127, a HGA12bhaving a writing head element126that is constituted of an element for a magnetic head writing information in the magnetic disk11, the reading head element127to be evaluated that is constituted of an element for a magnetic head reading information from the magnetic disk11, a contact impact detector123bthat detects magnitude of an impact due to contact between the reading head element127and the magnetic disk11as an AE signal, and a temperature detector124athat detects a temperature of the reading head element127, a head amplifier13that controls a current supplied to the writing head element126and amplifies magnetization waveform of the reading head element127, and an accumulating processor38that calculates an output change amount of the reading head element127and an accumulated value of the AE signals based on the AE signals detected by the contact impact detector123band the reading signals amplified by the head amplifier13.

FIG. 13is a block diagram of the evaluation processor38shown inFIG. 12. The evaluation processor38is provided with a signal converter381that converts high frequency AE signals outputted from the contact impact detector123bto low frequency signals, an accumulating unit382that accumulates the low frequency AE signals converted by the signal converter381, and an evaluation value calculating unit383that calculates an output change amount based on read signals outputted from the head amplifier13and the accumulated value of the AE signals accumulated by the accumulating unit382. A function for temperature control that controls a temperature of the reading head element127to a fixed value is realized by the temperature detector124a, the head amplifier13, and the control unit37a.

An operation of the magnetic-head evaluating apparatus will be explained with a flowchart shown inFIG. 14. On reception of a start instruction (Step S300), the control unit37instructs the temperature detector124ato measure a reference temperature and a reference resistance. The temperature detector124ameasures the reference temperature and the reference resistance (Step S310). The reference temperature is an ambient temperature of the reading head element127or a temperature inside the magnetic-head evaluating apparatus. The reference resistance is a resistant value obtained when no current flows in the writing head element126and the reading head element127.

The control unit37asets the temperature of the reading head element127to an evaluation temperature (Step S320). Start instruction includes such evaluation conditions as an evaluation temperature of the reading head element127, a measurement time of an output degradation amount of the reading head element127, and an evaluation time. The control unit37acontrols a writing current flowing in the writing head element126via the head amplifier13such that the temperature of the reading head element127detected by the temperature detector124areaches the evaluation temperature. The control unit37amonitors the temperature of the reading head element127detected by the temperature detector124aduring evaluation time and controls a writing current flowing in the writing head element126via the head amplifier13such that the temperature of the reading head element127always maintains the evaluation temperature. Since the operation of the temperature detector124afor detecting a temperature of the reading head element127is the same as the operation explained regarding Step S120according to the first embodiment, explanation thereof will be omitted.

The control unit37acontrols the VCM14bto move the reading head element127to a predetermined track on the magnetic disk11and controls the DCM15bto rotate the magnetic disk11. The evaluation value calculating unit383measures an output of the reading head element127(Step S330). As an output of the reading head element127, a read signal obtained by amplifying magnetization waveform that the reading head element127has read from the magnetic disk11by the head amplifier13may be used. The evaluation value calculating unit383holds the measured output of the reading head element127as an initial output.

The control unit37acontrols the VCM14bto move the reading head element127to a tack different from a track applied for measuring the output of the reading head element127. This is because a track (a track for output measurement) applied for measuring an output of the reading head element127is made different from a track (a track for AE detection) that gives an impact to the reading head element127by contact between the reading head element127and the magnetic disk11in view of such a fact that the magnetic disk11wears due to contact between the magnetic disk11and the reading head element127. Hereinafter, when an output of the reading head element127is measured, the control unit37amoves the reading head element127to the track for output measurement, and when an impact is imparted on the reading head element127, the control unit37amoves the reading head element127to the track for AE detection.

Since it becomes difficult to detect an AE signal according to advance of wearing of the magnetic disk11, the control unit37areduces a floating amount of the reading head element127using a pressure reduction simultaneously, so that the number of contacts of the magnetic disk11and the reading head element127can be increased.

The contact impact detector123bdetects magnitude of an impact due to contact between the reading head element127and the magnetic head as an AE signal (Step S340). The contact impact detector123boutputs the detected AE signal to the signal converter381.

The signal converter381converts high frequency AE signals to low frequency AE signals (Step S350). The signal converter381outputs the converted AE signals to the accumulating unit382. The accumulating unit382accumulates the low frequency AE signals outputted from the signal converter381(Step S360). The contact impact detector123bdetects magnitude of an impact due to contact between the reading head element127and the magnetic disk11as an AE signal, the signal converter381converts the AE signal detected by the contact impact detector123bto a low frequency signal, and the accumulating unit382repeats an operation for accumulating AE signals converted by the signal converter381until the measurement time expires (Steps S340to S370).

When the measurement time expires, the evaluation value calculating unit383measures an output of the reading head element127(Step S380). The evaluation value calculating unit383calculates an evaluation value based on the measured output of the reading head element127, an initial output thereof, and the accumulated value of AE signals accumulated by the accumulating unit382and outputs the same (Step S390). The evaluation value is the output change amount of the reading head element127, the output degradation coefficient, the accumulated value of the AE signals, or the like.

The accumulating unit382accumulates AE signals which have been converted to low frequency ones by the signal converter381, and the evaluation value calculating unit383repeats an operation for calculating an evaluation value for each measurement time until the evaluation time expires or elapses (Steps S340to S400). Further, such a constitution may be employed that, while changing the setting temperature of the reading head element127, the accumulating unit382accumulates AE signals that have been converted to low frequency ones by the signal converter381and the evaluation value calculating unit383repeats an operation for calculating an evaluation value for each measurement time until the evaluation time expires or elapses (Steps S340to S400).

Thus, according to the third embodiment, from a view point that the output degradation coefficient is the function of the temperature of the reading head element127, since the temperature of the reading head element127is fixed, the output degradation coefficient is calculated from the magnitude of an impact due to a contact between the reading head element127and the magnetic disk11, and an output and an initial output of the reading head element127measured, and the calculated output degradation coefficient is used as the evaluation value, durability of the head, which is made of different kinds of materials or have different structures, to magnitude of an impact due to contact between the heads and a recording medium can be evaluated properly.

Furthermore, according to the third embodiment, since the signal converter381converts magnitude of an impact due to contact between the reading head element127and the magnetic disk11that has been detected by the contact impact detector123bto a low frequency signal, even if high frequency signals detecting strengths of impacts due to contact between the reading head element127and the magnetic disk11are sampled at sparse intervals, the strengths of impacts due to contact can be accumulated properly and the evaluation value can be calculated.

Moreover, according to the third embodiment, though the HGA12bis provided with the contact impact detector123b, the contact impact detector123bmay be constituted to detect magnitude of an impact due to contact between the magnetic disk11and the reading head element127. For example, the contact impact detector123bmay be provided at an arm portion of the VCM14bnear to the HGA12b.

In general, the control unit37athat controls the head amplifier13, the DCM15band the VCM14bis often constituted of a CPU or the like. The respective functions of the contact impact detector123b, the temperature detector124a, the signal converter381, the accumulating unit382, and the evaluation value calculating unit383according to the third embodiment are realized by a software (a program) and they may be implemented by a CPU.

According to the present invention, since magnitude of an impact due to contact between the head and the recording medium is detected and a life of the head is estimated based on the magnitude of an impact detected, a life estimating method of a head can be obtained that can estimate a life of a head properly even if a floating amount of the head is reduced and contact between a head and a recording medium frequency occurs.

Furthermore, according to the present invention, since strengths of impacts due to contacts of the head and the recording medium is accumulated, a life estimating method of a head can be obtained that can estimate a life of a head considering all the strengths of impacts due to contacts of a head and a recording medium.

Moreover, according to the present invention, since a temperature of the head is detected and the life of a head is estimated based on the temperature of head detected and the magnitude of an impact due to contact between the head and the recording medium, a life estimating method of a head can be obtained that can estimate a life of a head properly considering not only the magnitude of an impact due to contact between a head and a recording medium but also a temperature of the head.

Furthermore, according to the present invention, since the temperature of the head is detected and the strengths of impacts due to contacts of the head and the recording medium are accumulated, a life estimating method of a head can be obtained that can estimate a life of a head considering all the strengths of impacts due to contacts of a head and a recording medium and the temperatures of the head.

Moreover, according to the present invention, since an exponential function or an exponentiation function of the absolute temperature of the head is multiplied by a value proportional to the magnitude of an impact due to contact between the head and the recording medium, a life estimating method of a head can be obtained that can estimate a life of a head considering all the strengths of impacts due to contacts of a head and a recording medium and the temperatures of the head.

Furthermore, according to the present invention, since the magnitude of an impact due to contact between the head and the recording medium is converted to the low frequency signal, a life estimating method of a head can be obtained that, even if high frequency signals detecting strengths of impacts due to contact between a head and a recording medium are sampled at sparse intervals, accumulates the strengths of impacts due to contact properly to estimate a life of a head considering the strengths of impacts.

Moreover, according to the present invention, since the accumulated value of the strengths of impacts due to contact between the head and the recording medium is stored, a life estimating method of a head can be obtained that, even if use of a head is interrupted, can accumulate strengths of impacts due to contact between a head and a recording medium continuously from a start time of use of the head to estimate a life of the head.

Furthermore, according to the present invention, since strengths of impacts due to contact between a recording medium and a head are detected and the strengths of impacts detected are accumulated, a recording medium inspecting method can be obtained that can determine whether a recording medium is good or bad considering all strengths of impacts due to contact between a head and the recording medium.

Moreover, according to the present invention, since magnitude of an impact due to contact between a head and a recording medium is detected and an evaluation value indicating durability of the head using the magnitude of an impact detected is calculated, a head evaluating method can be obtained that can evaluate the durability of the head, which is made of different kinds of materials or have different structures, to magnitude of an impact due to contact between the heads and a recording medium properly.

Furthermore, according to the present invention, since magnitude of an impact due to contact between a head and a recording medium is detected and a life of the head is estimated based on the magnitude of an impact detected, an information recording and reproducing apparatus can be obtained that, even if contact between the head and the recording medium frequently occurs due to that a floating amount of the head becomes small, can estimate a life of the head properly.