Storage apparatus, storage control circuit, and head-position-displacement measuring method

A measurement recording unit causes the head to move across a predetermined amount, at least more than one track during one lap of track, with a predetermined radial position and a track position of the magnetic disk being taken as recording start points, thereby writing measurement data while drawing a spiral path. A measurement reading unit causes the measurement data recorded in a spiral manner to be read while gradually shifting a read-beginning point within a predetermined scanning range from an inner perimeter side including the recording start points to an outer perimeter side. A position-displacement detecting unit finds a distribution of amplitudes of a read-back signal within a read scanning range and detects, in a distribution of evaluation values, an amount of position displacement of a read head and a write head on the storage medium in a radial direction for storage.

This application is a priority based on prior application No. JP 2007-035957, filed Feb. 16, 2007, in Japan.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a storage apparatus, storage control circuit, and head-position-displacement measuring method for detecting a head position displacement of a write head and a read head provided to a head and correcting an amount of position displacement of the read head at the time of reading a storage medium. In particular, the present invention relates to a storage apparatus, storage control circuit, and head-position-displacement measuring method for measuring a head position displacement targeted for a storage medium provided to a non-magnetic area between tracks.

2. Description of the Related Arts

In magnetic disk apparatus in recent years, a combined-type head structure has been adopted in which a highly-sensitive read head using, for example, tunnel magnetoresistance effect (TMR), is independent from a write head. In the head having such a configuration, a position displacement of the write head and the read head occurring in a head manufacturing process cannot be completely eliminated, and therefore paths through which the write head and the read head pass at the time of recording on a certain track will be different. Therefore, it is required that such a displacement amount be measured in advance in, for example, a manufacturing inspection process, for storage, and then a correction be made by that displacement amount from a radial position at the time of recording data on a target track to read-back the data on the target track. In recent years, a space between adjacent tracks has been on the order of 200 nm. If a position displacement of the write head and the read head is several μm, a position displacement correction corresponding to several tracks has to be required. This tendency becomes a more important problem as the space between tracks is narrowed more with the advance of high density. Also in recent years, in magnetic disk apparatus, the tide of downsizing is significant and, accordingly, a disk medium capable of high-density recording has been demanded. However, in improving the recording density of magnetic disk s, there is a problem of how to prevent interference from an adjacent recording bit. Under the recognition of such a problem, a technology called discrete-track recording has been conventionally suggested, in which, against interference of a magnetic disk medium in a radial direction, the magnetic disk medium is physically sectioned for each track to reduce interference from an adjacent track. Furthermore, under the recognition of the same problem in which interference from an adjacent recording bit is prevented to address an increase in recording density, a technology called patterned media has also been conventionally suggested in which a magnetic disk medium is physically sectioned also in a perimeter direction, that is, patterning in units of recording bits is performed, thereby reducing interference from an adjacent bit. Therefore, it has been demanded that, also for storage media using technologies, such as discrete tracks and patterned media, a position displacement correction of the write head and the read head be accurately performed to achieve high-density recording.

FIG. 1linearly depicts one track length of a recording medium in a process of measuring a head position displacement, in which M number of servo sectors correspond to one cycle of track. To correct a position displacement of a write head202and a read head204provided to a combined-type head200, first with the write head202being positioned at a track204-N at a certain radial position by using a head position signal obtained through servo-sector reading by the read head204, a measurement signal of one cycle of track is recorded on a measurement pattern206as shown. At this time, since a position displacement is present between the read head204and the write head202, the read head204takes a path208that matches with a track204-N, but the write head202takes a path210at a position shifted from the track204-N, the position where the measurement pattern206is written. The amount of position displacement is detected by, after writing the measurement pattern206, reading a read position in a radial direction at which the read head204is positioned while gradually shifting the read position of the read head204from the position where the measurement pattern206is written, and finding, for example, a profile (distribution) of amplitudes of a read-back signal, thereby obtainingFIG. 2A.

InFIG. 2A, a profile (signal distribution) can be obtained in which the amplitude of the read-back signal is low at a write position212of the measurement pattern, the amplitude of the read-back signal is increased when the measurement pattern is read while gradually shifting the read position and, after reaching its peak point214, the amplitude is again decreased. An offset value218to the peak point214at which the amplitude of the read-back signal is maximum in the profile216of the read-back signal amplitude216is detected as an amount of position displacement of the read head and the write head. Here, the value of the amplitude ofFIG. 2Arepresents an average value of amplitudes of the read-back signal read over one track. Amplitudes of the read-back signal of the peak214and a ½ peak point220are average values of the read-back signal amplitudes222and224read over one track as depicted inFIG. 2B. For example, a method has been suggested in which, by using this position displacement detection method, an area for measuring a track displacement is provided on the storage medium to measure changes with time in position displacement of the write head and the read head (JP 09-045025). However, in such a position displacement detection method, it is impossible to support discrete tracks and patterned media that may possibly be positioned at a place where no magnetic substance is placed. For example, as depicted inFIG. 3, in the case of discrete tracks, a non-magnetic area228is present on both sides of a track formed of a magnetic area226. If a path210of the write head202when the read head204is positioned on the track204-N is just on the magnetic area226, a profile when the read head204is offset to position displacement detection to search the measurement pattern206is similar to that ofFIG. 2A. However, as depicted inFIG. 4, when the path210of the write head202is on the non-magnetic area228, the measurement pattern206is not accurately recorded, and a profile of amplitudes of the read-back signal when the measurement pattern206is read while gradually shifting the read position of the read head204is such as a profile216-1ofFIG. 5A, thereby making it difficult to specify an offset value of a peak point214-1where the amplitude of the read-back signal is at maximum. Here,FIG. 5Brepresents amplitudes of the read-back signal at read positions of the peak point214-1and the ½ peak point220-1as read-back signal amplitudes222-1and224-1read over one track. To solve these problems, a storage medium and a magnetic storage apparatus have also been suggested in which an area in which magnetic substances are successively formed in a radial direction of the medium is provided between a servo sector and a data sector of a storage medium (JP 2005-166115 and JP 2005-166116).

However, when the area in which magnetic substances are successively formed in the radial direction of the medium is provided between the servo sector and the data sector as in JP 2005-166115 is used for a special area for position displacement correction measurement of the write head and the read head, user data cannot be written in that area, thereby decreasing the recording capacity by that amount. Moreover, in order to accurately measure the amount of position displacement correction, a measurement area that is long to some extent, for example, one cycle of track, is required so as to average read-back signals of the measurement pattern to remove noise, thereby causing user data format efficiency to deteriorate.

SUMMARY OF THE INVENTION

According to the present invention to provide a storage apparatus, storage control circuit, and a head-position-displacement measuring method of accurately measuring a position displacement of a write head and a read head without providing a special area even in a storage medium in which a magnetic substance is sectioned in a radial direction.

The present invention provides a storage apparatus. The storage apparatus according to the present invention includes:

a storage medium with a configuration of having a plurality of tracks formed of a magnetic-storable magnetic substance, the tracks being sectioned by a non-magnetic substance that does not allow magnetic recording;

a combined-type head having a read head for reading magnetic storage information recorded on the tracks and a write head for writing magnetic storage information on the tracks;

a measurement data recording unit that causes the head to move across a predetermined amount at least equal to or more than one track during one lap of track, with a predetermined radial position and a track position of the storage medium being taken as a recoding start point, thereby writing measurement data in the storage medium while drawing a spiral path;

a measurement data reading unit that causes the head to move, while scanning read-beginning points within a predetermined scanning range from an inner perimeter side including the recording start point of the measurement data recording unit to an outer perimeter side, across the predetermined amount of the measurement data recording unit for each of the read-beginning points, thereby reading the measurement data from the storage medium while drawing a spiral path; and

a head-position-displacement detecting unit that finds a distribution of evaluation values within the predetermined scanning range from a measurement data read-back signal obtained by the measurement data reading unit and detects, in the distribution of evaluation values, an amount of position displacement of the read head and the write head on the storage medium in a radial direction for storage.

Here, the measurement data recording unit previously sets a target shift amount obtained by dividing a track width by the number of servo sectors for forming in a track perimeter direction at predetermined spacing and, after starting writing from the recording start point, causes the magnetic head to move in a radial direction by the target shift amount upon each servo-sector detection, thereby writing the measurement data in the storage medium while causing the magnetic head to move across at least one track during one lap of track.

The measurement data reading unit causes, after starting reading from a read-beginning point from which scanning is performed within the predetermined scanning range, the magnetic head to move in the radial direction by the target shift amount upon each servo-sector detection, thereby reading the measurement data from the storage medium while causing the magnetic head to move across at least one track during one lap of track.

The head position displacement detecting unit detects amplitudes of a read-back signal obtained from the measurement data reading unit as the evaluation values, and detects the amount of position displacement from a peak value in a distribution of the amplitudes. In this case, the head-position-displacement detecting unit detects, as the amplitudes of the read-back signal, an average value or an accumulated value of the amplitudes of the read-back signal obtained by reading one spiral path.

The head-position-displacement detecting unit may detect error rates of a read-back signal obtained by the measurement data reading unit as the evaluation values, and detect the amount of position displacement from a bottom peak value in the distribution of the error rates.

In the storage apparatus according to the present invention, the amount of position displacement is detected and stored for each of all track positions of the storage medium by the measurement data recording unit, the measurement data reading unit, and the head-position-displacement detecting unit.

In the storage apparatus according to the present invention, the amount of position displacement may be detected and stored at a plurality of measurement positions on the storage medium in a radial direction by the measurement data recording unit, the measurement data reading unit, and the head-position-displacement detecting unit, and an amount of position displacement at each position other than the measurement positions may be found through an interpolating calculation from amounts of position displacement at measurement positions on both sides.

The present invention provides a storage control circuit of a storage apparatus. The present invention is characterized by the storage control circuit of the storage apparatus provided with

a storage medium with a configuration of having a plurality of tracks formed of a magnetic-storable magnetic substance, the tracks being sectioned by a non-magnetic substance that does not allow magnetic recording, and

a head having a read head for reading magnetic storage information recorded on the tracks and a write head for writing magnetic storage information on the tracks, the storage control circuit including:

a measurement data recording unit that causes the head to move across a predetermined amount at least more than one track during one lap of track, with a predetermined radial position and a track position of the storage medium being taken as a recoding start point, thereby writing measurement data in the storage medium while drawing a spiral path;

a measurement data reading unit that causes the head to move, while scanning read-beginning points within a predetermined scanning range from an inner perimeter side including the recording start points of the measurement data recording unit to an outer perimeter side, across the predetermined amount of the measurement data recording unit for each of the read-beginning points, thereby reading the measurement data from the storage medium while drawing a spiral path; and

a head-position-displacement detecting unit that finds a distribution of evaluation values within the predetermined scanning range from a measurement data read-back signal obtained by the measurement data reading unit and detects, in the distribution of evaluation values, an amount of position displacement of the read head and the write head on the storage medium in a radial direction for storage.

The present invention provides a head-position-displacement measuring method of a storage apparatus. The present invention is characterized by the head-position-displacement measuring method of the storage apparatus provided with

a storage medium with a configuration of having a plurality of tracks formed of a magnetic-storable magnetic substance, the tracks being sectioned by a non-magnetic substance that does not allow magnetic recording, and

a head having a read head for reading magnetic storage information recorded on the tracks and a write head for writing magnetic storage information on the tracks, the method including:

a measurement data recording step of causing the head to move across a predetermined amount at least equal to or more than one track during one lap of track, with a predetermined radial position and a track position of the storage medium being taken as a recoding start point, thereby writing measurement data in the storage medium while drawing a spiral path;

a measurement data reading step of causing the head to move, while scanning read-beginning points within a predetermined scanning range from an inner perimeter side including the recording start point in the measurement data recording step to an outer perimeter side, across the predetermined amount in the measurement data recording step for each of the read-beginning point, thereby reading the measurement data from the storage medium while drawing a spiral path; and

a head-position-displacement detecting step of finding a distribution of evaluation values within the predetermined scanning range from a measurement data read-back signal obtained by the measurement data reading unit and detecting, in the distribution of evaluation values, an amount of position displacement of the read head and the write head on the storage medium in a radial direction for storage.

According to the present invention, even in the case of a storage medium in which a magnetic substance is sectioned in a radial direction, such as discrete tracks or a pattered medium, after recording a measurement pattern with the path of the write head being changed on a spiral, the measurement pattern is read while gradually changing the read-beginning point within the predetermined scanning range in the radial direction, with the path of the read head being changed in a spiral manner similar to that at the time of recording. Therefore, the measurement pattern is always recorded and read through the magnetic area. Thus, a position displacement of the write head and the read head can be accurately measured without providing a special area for detection of head position displacement. The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description with reference to the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 6A and 6Bare block diagrams of a magnetic disk apparatus representing one embodiment of a storage apparatus to which a head-position-displacement measuring process according to the present invention. InFIGS. 6A and 6B, a magnetic disk apparatus10known as a hard disk drive (HDD) is configured of a control board12and a disk enclosure14. The disk enclosure12is provided with a spindle motor16. The spindle motor16has a rotational shaft into which magnetic disks20-1and20-2are inserted to be rotated at a constant speed, for example, 4200 rpm. The magnetic disks20-1and20-2according to the present embodiment use a discrete-track medium or a patterned medium having a configuration in which a plurality of tracks formed of a magnetic substance are sectioned by a non-magnetic substance that does not allow magnetic recording. The disk enclosure14is provided with a voice coil motor18. The voice coil motor18has heads22-1to22-4mounted at the tip of an arm of a head actuator to position the heads with respect to medium recording surfaces of the magnetic disks20-1and20-2. The heads22-1to22-4are combined-type heads each having a write head and a read head being integrated together. As the write head, a longitudinal-magnetic-recording-type write head or a vertical-magnetic-recording-type write head is used. In the case of the vertical-magnetic-recording-type write head, as the magnetic disks20-1and20-2, vertical storage media provided with a recording layer and a soft-magnetic protective layer are used. As a read head, a GMR element or a TMR element is used. The heads22-1to22-4are signal-line-connected to a head IC24. The head IC24selects either one of the heads for writing or reading with a head select signal based on a write command or a read command from a host11as an upper-level apparatus. Also, the head IC24is provided with a write amplifier in a write system and a preamplifier in a read system. The control board12is provided with an MPU26. A bus28for the MPU26is provided with a memory30that stores a control program and control data using a RAM and a non-volatile memory32that stores a control program using an FROM or the like. Also, the bus28for the MPU26is provided with a host interface control unit34, a buffer memory control unit36that controls a buffer memory38, a hard disk controller40that functions as a formatter, a read channel42that functions as a write modulating unit and a read demodulating unit, and a motor-driving control unit44that controls the voice coil motor18and the spindle motor16. Furthermore, the MPU26, the memory30, the non-volatile memory32, the host-interface control unit34, the buffer-memory control unit36, the hard disk controller40, and the read channel42form a storage control circuit15. The storage control circuit15is achieved by one LSI circuit. The magnetic disk apparatus10performs a recording process and a reading process based on a command from the host11. Here, a normal operation in the magnetic disk apparatus is described as follows. When a write command and write data from the host11are received at the host-interface control unit34, the write command is decoded at the MPU26, and the received write data is stored in the buffer memory38as required and is then converted at the hard disk controller40to a predetermined data format. Also, an ECC code is added through an ECC encoding process. After scrambling, RLL code transformation, and further write compensation are performed in a write modulation system in the read channel42, writing is performed from, for example, a write head of the head22-1selected from the write amplifier via the head IC24to the magnetic disk20-1. At this time, a head positioning signal is given from the MPU26to the motor-driving control unit44. From the voice coil motor18, after seeking of a target track indicated by the command with the head, on-track control is performed. On the other hand, when a read command from the host is received at the host-interface control unit34, the read command is decoded at the MPU26. After a read-back signal read from the read head selected through head selection of the head IC24is amplified by the preamplifier, the read-back signal is input to a read demodulation system in the read channel42. Read data is demodulated through partial response maximum-likelihood detection (PRML) or the like. After an ECC decoding process is performed at the hard disk controller40to correct errors, the read data is buffered to the buffer memory38, and the read data is transferred from the host-interface control unit34to the host. At the time of a read process, in on-track following control after seeking the target track, a position correction control is performed such that the position displacement of the read head is corrected with the amount of read head position displacement from the control table52and the read head is positioned at a track position from which a maximum read amplitude can be obtained. The magnetic disk apparatus10according to the present embodiment performs a head position displacement measuring process of measuring the amount of position displacement of the write head and the read head provided to the heads22-1to22-4by using testing equipment or the like in the stage where assembling the apparatus is completed and storing the amount in the control table52. With the magnetic disk apparatus10being connected, the host11as the testing equipment downloads measurement firmware (program) for measuring a head position displacement to the memory30. The MPU26executes the measurement firmware downloaded to the memory30, thereby achieving the functions of the measurement recording unit46, the measurement reading unit48, and the position displacement detecting unit50to execute a process of detecting the amount of head position displacement and storing the amount in the control table52. The measurement recording unit46causes each of the heads22-1to22-4to move across a predetermined amount at least equal to or more than one track in a radial direction during one lap of track, with a predetermined radial position and a track position (for example, servo sector with an index=0) on a storage medium surface of each of the magnetic disks20-1and20-2being taken as a recording start point, thereby writes measurement data while drawing a path in a spiral manner. The measurement reading unit48causes, for each of the heads22-1to22-4, within a predetermined scanning range from an inner perimeter side including the recording start point of the measurement recording unit46to an outer perimeter side, the track to move in a radial direction by a predetermined amount equal to the amount in the measurement recording unit46for each read-beginning point while sequentially shifting the read-beginning point in a radial direction, thereby reading a measurement pattern written in the magnetic disks20-1and20-2as measurement data while drawing a spiral path. The position displacement detecting unit50finds a profile, which is a distribution of evaluation values, such as, for example, amplitudes of a read-back signal or error rates, obtained from a read-back signal in the predetermined scanning range in which the read-beginning point is set, the profile being found from the read-back signal through reading the measurement pattern obtained by the measurement reading unit48. From this profile of the evaluation values, the amount of position displacement of the read head and the write head in the radial direction on the storage medium surface is detected, and is stored in the control table52. In such detection of head position displacement, a measurement process is performed while sequentially selecting one of four heads22-1to22-4, with all tracks or a plurality of predetermined tracks on the storage medium surface of a corresponding one of the magnetic disks20-1and20-2for each head being taken as target tracks. Here, when measurement of the amount of head position displacement is performed on part of the tracks on the storage medium surface, a position displacement of tracks not to be measured is calculated through interpolation calculation for the measured positionally-displaced head, and is then stored in the control table52or, interpolation calculation is performed every time a head position displacement is corrected, as described below. After the process of measuring the head position displacement is finished, the measurement firmware downloaded from the host11to the memory30is deleted. Therefore, in the MPU26, the functions of the measurement recording unit46, the measurement reading unit48, and the position displacement detecting unit50are deleted. With the stop and end process of the apparatus, the control table52in the memory30with the detected amount of head position displacement is written and stored in a non-volatile manner in the most-outer system area on a medium recording surface of, for example, the magnetic disk20-1corresponding to the head22-1. Then, when power is turned on with the apparatus connected to the host11of the user, the magnetic disk apparatus10is activated. At the time of an initial process at activation, the control table52is read by the head22-1from the system area of the storage medium surface of the magnetic disk20-1, and is disposed on the memory30as depicted. In the MPU26, in a read process at the time of receiving a read command from the host11, when the target track is sought by the head22-1for on-track following control, the amount of head position displacement corresponding to the target track is read from the control table52of the memory32. The VCM18is then driven for position displacement correction so as to eliminate the amount of head position displacement. With this, a positioning control is performed on the head so that the head is placed at a position where the read-back signal is maximum with respect to the recording pattern of the target track or a position where an error rate is minimum.

FIG. 7is a drawing for describing an internal structure of the magnetic disk apparatus according to the present embodiment. InFIG. 7, the magnetic disk apparatus according to the present embodiment has disposed on a base54the magnetic disks20-1and20-2rotating at a predetermined speed by the spindle motor16. For the magnetic disks20-1and20-2, an actuator56rotatably supported by a shaft unit58is disposed. The actuator56has the head22-1disposed at its arm tip, and also has a coil provided on an opposite side of the arm and rotatably disposed in a yoke60vertical disposed to be fixed to the base54to have a permanent magnet inserted therein. The magnetic disks20-1and20-2rotated by the spindle motor16, as their storage medium surfaces being extracted to be shown in an enlarged manner to the outside, have the configuration of a discrete track62or a patterned medium68. The discrete track62has a track portion as a magnetic area64. On both sides of a track as this magnetic area64, non-magnetic areas66are disposed. On the other hand, in the case of the patterned media68, magnetic areas70are disposed in a track boundary portion and an area sectioning in a track direction and non-magnetic areas72are disposed taking charge in a track direction and a track width direction.

FIG. 8is a drawing for describing a state of head position displacement when the head is moved with respect to the magnetic disk in the present embodiment. InFIG. 8, to the magnetic disk20, as depicted inFIG. 7, the actuator56is rotatably provided about the shaft unit58, and the head22is mounted at the tip of the actuator56. The head22is provided with a write head74and a read head76, and both are positionally displaced in a track radial direction due to an error in manufacturing process. The head22provided with the write head74and the read head76having a position displacement is moved in a radial direction with respect to the storage medium surface of the magnetic disk20by the actuator56, a yaw angle θ=0 is formed at the center position at which the axial direction of the actuator56corresponds to a track direction. At this position of θ=0, the position displacement of the write head74and the read head76with respect to the track radial direction (not including an error at the time of manufacturing process) is minimum. On the other hand, at the position where a yaw angle θmax or +θmax at which the head74is moved by the actuator56to the position of a head22-11on the most outer side or the position of a head22-12on the most inner side, the position displacement of the write head74and the read head76with respect to the track radial direction (not including an error at the time of manufacturing process) is maximum. Therefore, in measuring the amount of head position displacement according to the present embodiment, the amount of head position displacement is measured at two positions, that is, at least the position of the most-outer head22-11and the position of the most-inner head22-12, and at positions therebetween, the amount has to be found through an interpolating calculation. Here, the amount of most-outer head position displacement and the amount of most-inner head position take values varied in opposite directions, that is, plus side and minus side, with respect to the amount of position displacement of the head at the center position of the yaw angle θ=0.

FIG. 9is a drawing for describing the control table52ofFIGS. 6A and 6Bthat stores the position-displacement measurement results according to the present embodiment. InFIG. 9, the control table52has set therein head numbers, cylinder addresses, and amounts of position displacement. The head numbers are set as HH01 to HH04 corresponding to the four heads22-1to22-4ofFIGS. 6A and 6B. The cylinder addresses correspond to track addresses at which the heads22-1to22-4are positioned, and when the total number of tracks is taken as n, the cylinder addresses are as CC1 to CCn. In the present embodiment, as the amounts of head position displacement of the target tracks each specified by the head number and the cylinder address, OFF1 to OFF4n are obtained through a head position displacement measuring process, and are then stored in the control table52as depicted in the drawing. As a matter of course, as for values of the amount of position displacement stored in the control table52, after the values measured at a plurality of track positions in the radial direction including the most outer and most inner positions are registered, as for the positions therebetween, the amount of displacement found through the interpolating calculation may be stored as a measurement value on both sides, and the amount of displacement for all tracks may be measured to be stored.

FIGS. 10A and 10Bare drawings for describing head paths at the time of normal recording/reading and at the time of recording/reading for head position displacement measurement in the present embodiment.FIG. 10Adepicts a head path at the time of normal recording/reading. For example, when data is written in a track78-N, a servo sector set at predetermined spacing in a track direction is read by the read head to demodulate a position signal, and the position of the track78-N is sought for on-track, thereby performing data recording or reading on the storage medium surface while drawing a circular head path80along the track78-N.

FIG. 10Bdepicts a read path at the time of head position measurement according to the present embodiment. In the present embodiment, with the track78-N of the magnetic disk20being sought as the target track for on-track, a servo sector having a sector number=0 with which an index can be obtained is taken as a recording or read-beginning point85-1. A control is performed such that, while the magnetic disk20is rotated once, the head is moved across, for example, an inner track78-(N+1), thereby drawing a head path82in a spiral manner from a start point85-1of the track78-N to an end point85-1of a track78-(N+1).

FIG. 11is a drawing for describing a process of recording a measurement pattern to the storage medium in the present embodiment. InFIG. 11, when a discrete track is taken as a storage medium by way of example, and three tracks, that is, tracks78-N,78-(N+1),78-(N+2) are taken out for one disk rotation. The magnetic area64is disposed in a track recording area, whilst the non-magnetic area66is disposed at a track boundary portion. Here, although the non-magnetic area66is sectioned herein, this may be successive non-magnetic areas. Here, the magnetic disk has formed thereon servo sectors at predetermined spacing in a track direction of the storage medium surface. The number of servo sector is M, for example. Therefore, inFIG. 11, a track for one rotation from sector number=0 to sector number=M−1 of the servo sectors is shown. For head position measurement of such a storage medium, a measurement pattern92is first written with the track78-N as a target track. Writing of the measurement pattern92is performed in a manner such that, with the target track78-N being sought with the read head76provided to the head22for on-track, when the sector number=0 of the servo sector being read by the read head76is detected, reaching to a read-beginning point84-1is determined, thereby starting writing the measurement pattern92by the write head74from a recording start point86-1. Then, from the read-beginning point84-1to the sector (M−1) for track one rotation, the head22is shifted by one M-th of one track width in a radial direction, that is, in a track78-(N+1) direction. With this, the head path82in a spiral manner depicted inFIG. 10B, that is, in the case of linearization inFIG. 11, a read path88represented by a straight line from a read-beginning point84-1to a read-finishing point84-2for the read head76is obtained. At the same time, for the write head74, a straight-line recording path90from a recording start point86-1to a recording end point86-2is obtained. The measurement pattern92is recorded in a straight-line manner, actually, in a spiral manner, along a recoding path90by the write head74from the track78-N through the track78-(N+1) toward the track78-(N+2). In recording of this measurement pattern92, in the present embodiment, since this is the case of a discrete track, the non-magnetic area66is disposed at each boundary portion of the track area. With the recording pattern92being recorded in a spiral manner so as to go across a track pitch at one rotation in the track direction. Therefore, even if the non-magnetic area66is present at a track boundary portion, the measurement pattern92can be reliably recorded so as to always go over the magnetic area64during one cycle of track.

FIG. 12is a drawing for describing a process of reading the measurement pattern from the storage medium in the present embodiment. In a manner as depicted inFIG. 11, reading the measurement pattern92recorded in a spiral manner from the track78-N to the track78-(N+1), with a read-beginning point84of the read head76at the time of recording being taken as a center, a scanning range94with predetermined offset values +P and −P are set in a radial direction. Then, as for the scanning range94, scanning is performed in a spiral manner in a track direction while scanning in which the read-beginning point of the read head76is gradually moved in a predetermined direction, the measurement pattern92is read. Specifically, the read-beginning point84(−P) that is offset by −P with respect to the read-beginning point84at the time of recording is sought with the read head76for on-track. With this state, reading is started when the sector number=0 of the servo sector is detected. Then, reading is performed while shifting the point to a plus side by one M-th of one track width every time a servo sector is detected, thereby moving the read head76along the reading path88(−P). That is, as inFIG. 10B, the read head76is moved along the head path80in a spiral manner. A read-back signal obtained through movement of the read head76along the reading path88(−P) is sampled to store a sample value for one cycle of track in the memory30. Then, the read head76is moved in a spiral manner at each operation start point while gradually shifting from the read-beginning point84(−P) to a plus side at predetermined spacing to the read-beginning point84(+P), thereby sampling amplitudes of the read-back signal for one cycle of track of the measurement pattern92and storing the results in the memory30. In this manner, when the reading process through sequential scanning of the scanning range94is finished, a profile96representing a signal distribution of, as signal evaluation values, amplitudes of the read-back signal with respect to the read positions is generated as shown inFIG. 13A. The profile96represents values as depicted inFIG. 13B, found as average values or accumulation values of sampled values for one cycle, in an exemplary case of the read-back signal amplitude104at the peak and the read-back signal amplitude106at ½ peak obtained through a measurement-pattern reading process. The profile96of the amplitudes of the read-back signal with respect to the read position ofFIG. 13Arepresents values obtained, as depicted by a recording path inFIG. 12, through movement of the read head76along a plurality of spiral paths with the scanning range94being taken as a read-beginning point. Among these, read along the recording path90passing the center of the measurement pattern92is performed. Therefore, although the read-back signal amplitude is small on sector0and sector M−1 sides as depicted in the read-back signal amplitude104ofFIG. 13B, sufficient amplitude values can be obtained as depicted in the read-back signal amplitude104at the center portion where the measurement pattern is present in the magnetic area64, thereby allowing a read-back peak value101to be accurately found as for the profile96obtained as average values or accumulation values. As long as the peak point101of the profile96is detected, an offset value102from write position98to the peak point101at the time of the measurement record inFIG. 11can be accurately detected as the amount of displacement of the write head74and the read head76on the track78-N in the radial direction. Here, as for the scanning range94, +P and −P values can be defined based on a maximum value of position displacement of the write head and the read head, the value that can be assumed in head manufacturing process.

FIG. 14is a flowchart of a procedure of measuring a head position displacement according to the present embodiment, and is described as follows with reference toFIGS. 6A and 6B. InFIG. 14, at step S1, measurement firmware is downloaded from the host11for use in testing equipment to the memory30of the magnetic disk device10, and is executed by the MPU26. With this, the functions of the measurement recording unit46, the measurement reading processing unit48, the position-displacement detecting unit50provided to the MPU26become effective. Then at step S2, a measurement track position is extracted as a target track position X. Specifically, from the control table52disposed in the memory30, a head number and a cylinder address are sequentially extracted. At this stage, the control table52has set therein only the head number and the cylinder address depicted inFIG. 9, and the area of the amount of position displacement is blank. Next according to the measurement recording unit46at step S3, as shown inFIG. 11, the target track position X is sought with the head for22on-track, and the head is moved across tracks during one cycle of track, thereby writing the measurement pattern in a spiral manner. Next at step S4, as depicted inFIG. 12, the scanning range94is set in the radial direction to the measurement pattern92written in a spiral manner, and the head is sequentially moved to go across one track for one cycle of track, thereby reading the measurement pattern with a head path in a spiral manner. Then at step S5, the position-displacement detecting unit50finds the profile96of the amplitudes of read-back signal with respect to the read position as depicted inFIG. 13A, for example. The offset value102is then found from the read position of the peak101in the profile96, and is stored as a corresponding amount of position displacement in the control table ofFIG. 9. In detecting the peak point101of the profile96inFIG. 13Aat step S5, when the peak point101is difficult to specify from the waveform of the profile96, read positions of points108and110crossing A/2, which are each a half amplitude of an amplitude A of the peak101, are found, and these ½ read positions of the two read positions are found as offset values102of the peak point101. Then at step S6, it is checked whether all measurement tracks set in the control table52have been processed. If not yet processed, the procedure returns to step S2, extracting the next measurement track as a target track X and repeating a similar process. If it is determined at step S6that all measurement tracks have been processed, the control table52is stored in a system area of the magnetic disk at step S7. Here, if the non-volatile memory32has a sufficient capacity, the control table52may be stored in the non-volatile memory32. Then at step S8, the measurement firmware not required any longer due to the end of the head position displacement measurement is deleted from the memory30. With this, a series of processes ends. Here, it is possible to hand over the magnetic disk apparatus10to the user while keeping the measurement firmware stored in the magnetic disk without deleting the measurement firmware as at step S8. In such a case, if a fault occurs due to the amount of head position displacement while the user is using the magnetic disk apparatus10, it is possible to execute the installed measurement firmware and newly create the control table52for the amount of head position displacement on the user side.

FIG. 15is a flowchart depicting details of the measurement recording process at step S3ofFIG. 14, and is described with reference toFIG. 11as follows. InFIG. 15, in the measurement recording process, the target track position X is obtained at step S1. Then at step S2, the target track position X is sought. This target track position X is in a state where, for example, the read head76is positioned with the track78-N ofFIG. 11being positioned at a track center passing through the read-beginning point84-1. Then at step S3, a servo sector counter m and a target shift amount δ are reset at 0. At step S4, it is determined whether reaching to the measurement recording start point has been achieved. Specifically, inFIG. 11, this is when, in the on-track state where the read head76of the head22is positioned at the track center of the track78-N, a servo sector number=0 is detected and reaching to the read-beginning point84-1is achieved. At this time, the positionally-displaced write head74is positioned at the recording start point84-1on the track78-(N+1) side. If it is determined in step S4that reaching to the measurement recording start point has been achieved, the procedure goes to step S5, in which a recording signal is recorded by the head74on the medium recording surface to write the measurement pattern92. When recording of the measurement pattern92is started, it is then checked at step S6whether the next servo sector has been detected. Upon detection of the next servo sector, the procedure goes to step S7, where the servo sector counter m is counted-up by one, and the target shift amount δ is increased by an amount obtained by dividing a track pitch Tp by the number of servo sectors M (Tp/M). Next at step S8, the target track position X is increased by the target shift amount δ updated in step S7, thereby shifting the head22to the track78-(N+1) side. Then at step S10, it is determined whether the value of m of the servo sector counter has been reached the number of servo sectors M. If not reached, the procedure repeats the processes from step S5. With such repetition of processes at steps S5to S9, the head22is sequentially moved in an inner radial direction by the target shift amount δ every time a servo sector is detected, thereby achieving movement by one track pitch in one cycle of rotation. As a result, as depicted inFIG. 10B, the measurement pattern92can be recorded along the head path82in a spiral manner. If the value of m of the servo sector counter m at step S9reaches the number of servo sectors M, the series of measurement recording processes ends.

FIG. 16is a flowchart depicting details of the measurement reading process at step S4ofFIG. 14, and is described as follows with reference toFIG. 7. InFIG. 16, in the measurement reading process, at step S1, an offset W is set at an initial value −P, thereby W=−P. This gives an offset to the read-beginning point84(−P) in the scanning range94for reading measurement inFIG. 12. Then at step S2, X=X+W is sought as the target track position X. That is, the position though which the scanning start point84(−P) in the scanning range94ofFIG. 12goes is sought with the head. Then at step S4, the servo sector counter m and the target shift amount δ are reset to zero. Then at step S5, sector numbers of the servo sectors are monitored to check whether reaching to the read-beginning point84(−P) where sector number=0 has been reached. If reaching to the read-beginning point is determined, the procedure goes to step S5for reading the measurement pattern by the read head76. Then at step S6, it is checked whether a servo sector has been detected. If a servo sector is detected, at step S7, the servo sector counter m is counted-up by one and, at the same time, the target shift amount δ is increased by the amount obtained by dividing the track pitch Tp by the number of servo sectors M (Tp/M). Then at step S8, the target track position is updated to X=X+δ. These processes at steps S5to S8are repeated until the servo sector counter m reaches the number of servo sectors M at step S9. These processes at steps S5to S9are identical to the processes at steps S5to S9in the measurement recording process depicted inFIG. 15. As a result, as depicted inFIG. 10B, the head path82can be drawn in a spiral manner moved by one track from a track passing though the read-beginning point. As a result, inFIG. 12, the recording pattern92is read by moving the read head76along the reading path88(−P), and the sampled values of the amplitudes of the read-back signal from servo sector=0 to M−1 are stored in the memory. Then at step S10, as a signal evaluation value from the read-back signal obtained through scanning of one cycle of track in a spiral manner, an average value or an accumulated value of the amplitudes of the read-back signal for one cycle of track as depicted inFIG. 13B, for example, is calculated. Then at step S11, after the offset W is updated to a value obtained by adding a shift amount δp, the procedure goes to step S12where, if the offset W does not exceed offset value+P on the opposite side of the scanning range, the procedure returns to step S2, obtaining and seeking a target track value X at the next read-beginning point in the scanning range92, reading the measurement pattern as for the track-like range in a spiral manner similarly, and then calculating signal evaluation values. Here, the shift amount δp represents a step width at the time of scanning the scanning range92, and a value that can achieve a sufficient accuracy for head position displacement correction can be specified. If the offset W exceeds the offset value+P representing a limit value on the opposite side of the scanning range94, the procedure returns to step S12, the procedure returns to the main routine ofFIG. 14. At step S5, from a profile of the evaluation values, for example, a profile of the amplitudes of the read-back signal, a head position displacement is detected for table registration. Also, the present invention relates to a program for head position displacement measurement executed on the MPU26provided with a magnetic disk apparatus. The program according to the present embodiment includes the contents as depicted in flowcharts inFIGS. 14 to 16. Furthermore, the present invention provides a storage medium having stored therein a measuring program executed on an MPU of a magnetic disk apparatus for head position displacement measurement. Here, the storage medium includes a simple storage medium, such as a CD-ROM, floppy disk (RR), DVD disk, magneto-optical disk, or IC card, and a storage medium, such as a hard disk drive, provided internal or external to a computer system, as well as a database that holds a data program through a line or the like, other computer systems and their database, and further a transmission medium on a line. Still further, in the above embodiment, an exemplary case has been described in which, at the time of measurement recording and measurement reading, the head is moved in a radial direction by at least one track during one cycle of track, recording the measurement pattern and reading the measurement pattern drawing a head path in a spiral manner. Alternatively, with the amount of movement of the head in the radial direction in one cycle of track being taken as one track width or more, recording and reading the measurement pattern may be performed with a head path diagonally going across a plurality of tracks. Still further, the present invention includes appropriate modifications without impairing objects and advantages of the present invention, and is not restricted by numerical values mentioned in the above embodiment.