JP2011108342A - Disk drive, and read/write offset measurement method - Google Patents

Abstract

The measurement time of a read / write offset is shortened.
An HDD according to an embodiment of the present invention determines a relationship between read amplitude of measurement data and measurement data of a position error signal, thereby indicating a center position of a write element. Determine the radial position. The HDD calculates the read / write offset based on the difference between the disk radius position and the measurement data center position when writing the measurement data. In this following, the radial position of the read element 121 changes on the measurement data. The HDC / MPU 23 measures the reading amplitude of the measurement data and the position error signal while moving the read element 121, thereby acquiring a large value of the reading amplitude of the measurement data at different radial positions in a short time. it can.
[Selection] Figure 3

Description

  The present invention relates to a disk drive and a read / write offset measurement method thereof, and more particularly to efficiency improvement of read / write offset measurement.

  As a disk drive, an apparatus using a disk of various modes such as an optical disk, a magneto-optical disk, or a flexible magnetic disk is known. Among them, hard disk drives (HDDs) are widely used as computer storage devices, and are used in many devices such as moving image recording / playback devices and car navigation systems.

  A magnetic disk used in the HDD has a plurality of data tracks and a plurality of servo tracks formed concentrically. Each servo track is composed of a plurality of servo sectors having address information. Each data track is composed of a plurality of data sectors including user data. Data sectors are recorded between servo sectors spaced apart in the circumferential direction.

  The HDD has a swinging actuator, and a head slider is supported by the actuator. The HDD reads servo sector address information with a head slider and controls the actuator according to the address information (servo control). As a result, the HDD can move (seek) the head slider to a desired radial position (target data track) and further position (following) the head slider. The head slider positioned on the target data track performs data writing or data reading to the target data sector in the track.

  In the data reading process, a signal read from the magnetic disk by the head slider is subjected to predetermined signal processing such as waveform shaping and decoding processing by a signal processing circuit and transmitted to the host. The transfer data from the host is similarly processed by the signal processing circuit and then written on the magnetic disk by the head slider.

  As described above, the head slider positioning control is performed by servo data on the magnetic disk. The servo sector is composed of a cylinder ID, a sector number, a burst pattern, and the like. The cylinder ID indicates a track address, and the sector number indicates a sector address in the track. The burst pattern has relative position information of the magnetic head with respect to the track.

  The head element portion on the head slider has a write element for writing data and a read element for reading data. There is known a head element portion in which the disk radial position of the read element and the radial position of the write element differ on the magnetic disk. The distance between these elements in the disk radial direction (center-to-center distance) is referred to as read / write offset in this specification.

  Head positioning uses servo data read by the read element. Therefore, in order to position the write element at a predetermined position in writing data, the HDD needs to know the read / write offset. The read / write offset varies according to the radial position. For this reason, it is necessary to measure the read / write offset that varies depending on the radial position in HDD test manufacturing (see, for example, Patent Document 1).

  FIG. 11 schematically shows the read / write offset that changes depending on the radial position on the magnetic disk. In FIG. 11, the angle θ is an angle between a virtual line connecting the swing center of the actuator and the write element 122 and the track tangential direction. A region where the angle θ is smaller than 0 is an inner peripheral region, and a region larger than 0 is an outer peripheral side region. The angle φ is an angle between a virtual line connecting the write element 122 and the read element 121 and a virtual line connecting the swing center of the actuator and the write element 122.

  The read / write offset is a function having the angle θ as a variable, and can be represented by z × sin (φ + θ). z and φ are constants. In the configuration example of FIG. 11, the read / write offset increases as the head slider moves toward the outer periphery. The change depending on the radial position of the read / write offset is not limited to this example.

  FIG. 12 is a diagram for explaining a conventional read / write / offset measurement method. In the conventional measurement, the read element is positioned at a predetermined radial position, and the measurement data string is written by the write element. Typically, the measurement data string is written over the entire magnetic disk. In FIG. 12, the measurement data written in the track n is shown. Further, the read position is indicated by a black circle by the read element. The test device estimates the RW offset and moves the read element closer to the measurement data.

  The test apparatus maintains the target radial position of the read element constant, performs following for one or more rotations of the magnetic disk, reads the measurement data, and measures the amplitude. The test apparatus further changes the target radius position in small steps, and similarly measures the read amplitude of the measurement data string while performing the following. In the example shown in the figure, the following and the reading amplitude of the measurement data are measured at a radial position of 9.

  As shown in FIG. 13, the readout amplitude shows the largest value at the center of the measurement data, and decreases as the distance from the center increases. The test apparatus calculates the read / write offset from the target radius position showing the largest amplitude value and the target radius position in writing the measurement data.

JP 2008-210483 A

  As described with reference to FIG. 12, in the conventional read / write offset measurement, the read amplitude is measured while following is performed at a fixed target radial position at each of a plurality of different radial positions. Therefore, for the measurement of the read / write offset, a time longer than the total time of the following time at each target radial position (in the example of FIG. 12, the following time at the radial position of 9) is required.

  As described above, since the read / write offset varies depending on the radial position, the measurement data is written at a plurality of radial positions on the magnetic disk, and the read / write offset is measured by reading the measurement data. It is necessary. As the recording density of the magnetic disk increases, the number of data tracks increases, and the required measurement points increase accordingly.

  Therefore, a technique that can shorten the measurement time by more efficiently measuring the read / write offset is desired.

  One embodiment of the present invention is a method for measuring a read / write offset between a read element and a write element. In this method, measurement data is written by the write element. In order to read the measurement data by the read element, a seek process is performed to move the read element to a target radius position. After the seek process is completed, the following process by the read element is started. The following process of the read element passing on the measurement data track is performed while changing the target radius position of the read element. In the following process, the measurement data and servo data are read. The read / write offset is determined using the data for measurement and the data obtained by the reading of the servo data. Thereby, the measurement time can be shortened by performing the measurement of the read / write offset more efficiently.

  Preferably, a rough search process of the center position of the measurement data is performed before the following process. The rough search process performs the following steps. The following process of the read element passing over the measurement data is performed while changing the target radius position in a change width larger than the change width of the target radial position in the following process. In the following process in the rough search process, the measurement data and servo data are read. A center position of the measurement data is determined based on the data obtained by the reading of the measurement data and the servo data in the rough search process. In accordance with the measurement result of the rough search process, a change range of the target radius position in the following after the rough search process is determined. As a result, the read / write offset can be measured more efficiently and accurately.

  Preferably, the target position in the seek process is the center position determined in the rough search process. As a result, the read / write offset can be measured more accurately.

  Preferably, the target radius position at the start of the following process and the target radius position at the end of the following process are the same. Thereby, it is possible to smoothly shift from the rough search to the next fine search.

  Preferably, the error handling function is turned off before starting the following process. Thereby, an actual position signal can be acquired appropriately.

  Preferably, in the following process, the target radial position vibrates in the disk radial direction. Thereby, more accurate measurement can be performed.

  In a preferred configuration, the target radius position at the start of the following process and the target radius position at the end of the following process are the same, and the following is completed by one rotation of the disk. Thereby, an efficient and accurate measurement can be performed.

  Another aspect of the present invention is a disk drive that measures a read / write offset between a read element and a write element. The disk drive includes a disk, a write element for writing measurement data to the disk, a read element for reading the measurement data and servo data, and reading the measurement data by the read element in a seek process. Therefore, a moving mechanism for moving the read element to a target radial position and a controller are provided. The controller performs the following process of the read element passing over the measurement data while changing the target radius position of the read element after the seek process is completed, and the measurement data in the following process Using the data obtained by reading the servo data with the read element, the read / write offset is determined. Thereby, the measurement time can be shortened by performing the measurement of the read / write offset more efficiently.

  According to the present invention, the measurement time of the read / write offset can be shortened.

It is a block diagram which shows the structure of HDD concerning this embodiment. It is a figure explaining the principle of the read-write-offset measurement concerning this embodiment. In this embodiment, it is a figure which shows typically the data for a measurement, and the locus | trajectory of a read element. In this embodiment, it is a figure which shows the change of the gain value (VGA gain value) of the variable gain amplifier corresponding to a read element locus. 6 is a timing chart for explaining timing control in read processing of read / write offset measurement data according to the present embodiment. It is a block diagram explaining timing control in the reading process of the read / write offset measurement data of the present embodiment. In this embodiment, it is a figure which shows typically the measurement data which show the relationship between a VGA value and a position signal value, and the approximate function fitted to the measurement data. It is a flowchart explaining the two-stage VGA measuring method which concerns on this embodiment. It is a flowchart explaining the more specific example of a two-stage VGA measurement to this embodiment. In a more specific example of the two-stage VGA measurement in this embodiment, a measurement result obtained by the first VGA measurement and a method for determining a target radius position range (search range) in the next measurement from the measurement result It is a figure explaining. In the prior art, the read / write offset that changes depending on the radial position on the magnetic disk is schematically shown. It is a figure explaining the method of the conventional read / write offset measurement. It is a figure which shows typically the relationship between the reading position of measurement data, and a read signal amplitude in the conventional read / write offset measurement.

  Embodiments to which the present invention is applied will be described below. For clarity of explanation, the following description and drawings are omitted and simplified as appropriate. Moreover, in each drawing, the same code | symbol is attached | subjected to the same element and the duplication description is abbreviate | omitted as needed for clarification of description. In the following, an embodiment of the present invention will be described in a hard disk drive (HDD) which is an example of a disk drive.

  The present embodiment is characterized by measuring a read / write offset, which is a distance between a read element and a write element. The head element portion formed on the head slider has a read element and a write element. The read / write offset is a distance in the disk radial direction between the read element and the write element.

  The read / write offset measurement of this embodiment is particularly useful for an HDD having a head element portion with a large read / write offset. An HDD that writes servo data by self-servo write (SSW) processing has a head slider with a large read / write offset, and the read / write offset measurement of this embodiment can be performed on such an HDD. It is particularly useful.

  The read / write offset varies according to the disk radial position. As described with reference to FIG. 11, this is due to a change in the angle (skew angle) between the imaginary line connecting the actuator, the oscillation center, and the element center and the track tangential direction. In an HDD that performs SSW processing, generally, a read element is always located on the outer peripheral side or the inner peripheral side of the write element on a disk. The read / write offset measurement of this embodiment can be applied to an HDD in which the read / write offset is 0 at a specific disk radial position. The present invention can also be applied to an HDD in which servo data is written by a servo track writer.

  The method of the present embodiment can be applied to, for example, read / write offset measurement in the initial processing of SSW and read / write offset measurement in a test process after servo writing. The method of this embodiment has an effect of shortening the time for measuring the read / write offset, and is particularly useful for measuring the read / write offset of each head slider in the test process. When the HDD as a product has a read / write / offset measurement function, the method of this embodiment can be applied to the measurement.

  In the following, as a preferred embodiment of the present invention, details of the read / write offset measurement in the HDD test process will be described. In a preferred configuration, the HDD control circuit performs a read / write offset measurement in response to a command from the host. First, the overall configuration of the HDD configuration will be described.

  As shown in FIG. 1, the HDD 1 has a magnetic disk 11 that is a disk for storing data in an enclosure 10. A spindle motor (SPM) 14 rotates the magnetic disk 11 at a predetermined angular velocity. Corresponding to each recording surface of the magnetic disk 11, a head slider 12 for accessing the magnetic disk 11 is provided.

  Each head slider 12 includes a slider that flies over the magnetic disk, and a head element unit that is fixed to the slider and converts between a magnetic signal and an electric signal. Each head slider 12 is fixed to the tip of the actuator 16. The actuator 16 is connected to a voice coil motor (VCM) 15 and moves in the radial direction on the magnetic disk 11 rotating the head slider 12 by swinging about a swing shaft.

  A ramp 17 is fixed in the enclosure 10 near the outer peripheral edge of the magnetic disk 11. The actuator 16 stops on the ramp 17 outside the magnetic disk 11 when the HDD 1 is powered off or idle. The present invention can be applied to a CSS (Contact Start and Stop) type HDD in which the actuator 16 lands and stops in a predetermined area on the magnetic disk 11.

  Circuit elements are mounted on the circuit board 20 fixed to the outside of the enclosure 10. The motor driver unit 22 drives the SPM 14 and the VCM 15 according to control data from the HDC / MPU 23. The RAM 24 functions as a buffer that temporarily stores read data and write data. The arm electronic circuit (AE) 13 in the enclosure 10 selects the head slider 12 that accesses the magnetic disk 11 from among the plurality of head sliders 12, amplifies the reproduction signal, and reads / writes the channel. (RW channel) 21. Further, the recording signal from the RW channel 21 is sent to the selected head slider 12. The present invention can be applied to an HDD having only one head slider 12.

  In the read process, the RW channel 21 amplifies the read signal supplied from the AE 13 to a constant amplitude by a variable gain amplifier (VGA), extracts data from the acquired read signal, and performs a decoding process. Do. The data to be read includes user data and servo data. The decoded read user data and servo data are transferred to the HDC / MPU 23. In the write process, the RW channel 21 code-modulates the write data transferred from the HDC / MPU 23, converts the code-modulated write data into a write signal, and supplies the write signal to the AE 13.

  The HDC / MPU 23 as a controller controls read / write processing, management of command execution order, positioning control (servo control) of the head slider 12 (actuator 16) using servo data, and interface control with the host 51. Necessary processing related to data processing, such as defect management, error handling processing when an error occurs, and overall control of the HDD 1 are executed. In particular, the HDC / MPU 23 of this embodiment performs read / write offset measurement of each head slider 12. All or part of the processing performed by the HDC / MPU 23 may be performed by a test device that is an external device. Also in this configuration, the HDD is configured including the test apparatus.

  The principle of the read / write offset measurement of this embodiment will be described. As shown in FIG. 2, the HDC / MPU 23 positions the read element 121 in the head element unit 120 on the head slider 12 at a predetermined target radius position, and writes measurement data by the write element 122. The read element 121 is positioned at a certain target radius position. While the read element 121 follows the target radial position, the write element 122 writes measurement data in the data area. In a preferred configuration, the write element 122 writes measurement data to all one data track. That is, measurement data is written between all servo sectors.

  When the measurement data is written, the HDC / MPU 23 controls the VCM 15 via the motor driver unit 22 and moves the read element 121 to a specific disk radial position (target radial position) near the measurement data track. (seek). After the seek is completed, the HDC / MPU 23 performs following while changing the target radius position. During the following, the HDC / MPU 23 reads the measurement data by the read element 121 to measure the amplitude, and reads the servo sector to measure the position error signal. The position error signal is a position signal indicating the radial position of the read element 121 on each servo sector.

  The HDC / MPU 23 determines the relationship between the read amplitude of the measurement data and the measurement data of the position error signal, thereby determining the disk radius position indicating the center position of the measurement data (write element 122). To do. The HDC / MPU 23 holds a disk radius position when writing measurement data. Therefore, the HDC / MPU 23 can calculate the read / write offset at the measured disk radial position based on the difference between the disk radial positions.

  In the read / write offset measurement of the present embodiment, the radial position of the read element 121 changes on the measurement data during following. The HDC / MPU 23 measures the reading amplitude of the measurement data and the position error signal while moving the read element 121, thereby acquiring a large value of the reading amplitude of the measurement data at different radial positions in a short time. it can. This shortens the read / write offset time.

  FIG. 3 is a diagram schematically showing the measurement data and the locus of the read element 121. In FIG. 3, the measurement data (DATA) and servo sector (SERVO) of the entire track are shown. In FIG. 3, the upper side is the outer peripheral side and the lower side is the inner peripheral side. The measurement data is designated as track n. The read element 121 moves from the left to the right in the figure (the disk rotation direction is from right to left). FIG. 3 is a schematic diagram, and the actual number of servo sectors in the HDD is several hundred. Note that the center position of the data track does not always coincide with the center of the servo track. The measurement data has the same or different format as the user data. Any format can be used as long as the clearance can be measured with the measurement data.

  In FIG. 3, the circle indicates the position of the read element 121. In the example of FIG. 3, the read element 121 starts reading from the center of the measurement data, moves to the outer peripheral side, then moves to the inner peripheral side, and further moves to the outer peripheral side to be the center of the measurement data. Return. FIG. 4 shows changes in the VGA gain value corresponding to the read element locus in FIG. The X axis is a servo sector (position in the circumferential direction). The VGA gain corresponds to the reciprocal of the amplitude of the read signal from the read element 121. Therefore, the radius position that decreases as the read signal amplitude increases and the VGA gain shows the smallest value is the center radius position of the measurement data (write element 122).

  The VGA is incorporated in the RW channel 12, and the HDC / MPU 23 acquires the VGA gain value from the RW channel 12. When the AE 13 or the RW channel 21 can directly measure the read signal amplitude, the HDC / MPU 23 may acquire those amplitude values. Further, the HDC / MPU 23 may use other data (value) representing the position in the measurement data.

  As shown in FIG. 3, in order to accurately measure the center position of the measurement data, it is preferable that the read element 121 sweeps from the inner peripheral end to the outer peripheral end of the measurement data. In other words. It is preferable that the center position of the read element 121 reaches the outer peripheral end and the inner peripheral end of the measurement data in the following. Therefore, it is preferable that the range of the target radial position that changes in the following includes these positions. Hereinafter, a range in which the target radius position changes is referred to as a target range.

  In this way, the HDC / MPU 23 performs off-track sweep on the measurement data by the read element 121. In the preferred example of FIG. 3, the read element 121 (its target radial position) reciprocates within the target range. Specifically, the HDC / MPU 23 starts following from the center of the target range, shakes the target radial position in the disk radial direction, and then returns the target radial position to the center position that is the initial position. The read element 121 moves so as to follow the target radial position, but the actual radial position and the target radial position generally do not match.

  In order to read the measurement data from the outer peripheral end to the inner peripheral end, the read element 121 needs to move only in one direction from the inner periphery to the outer periphery. That is, the HDC / MPU 23 only needs to change the target radius position in one direction (from the inner circumference side to the outer circumference side or from the outer circumference side to the inner circumference side) from end to end of the target radius position range. This trajectory is preferred when the reliability of the measured value is sufficient. As a result, the measurement time can be shortened, or the change step of the target radius position (difference between successive target radius positions) in the same measurement time can be reduced.

  A plurality of sample values can be obtained for the same target radial position by swinging (vibrating) the target radial position (read element 121) of the read element 121 in and out of the target range (read element movement range). Thereby, the reliability of a measurement result can be improved. In order to shorten the measurement time, the change of the target radius position (read element position) is preferably one cycle. In the example of FIG. 3, the change of the target radius position (read element position) ends one cycle.

  If the change in the target radial position of the read element 121 is large, the actual position of the read element 121 cannot follow the target radial position. Therefore, it is important that the step of the target radius position is a small value. In a preferred configuration, the step value is not more than the minimum value that can be changed as a function of the HDD 1 or less than the next smallest value. For example, when the target radius position can be specified in units of 1 PES, the step specified by the HDC / MPU 23 is 1 PES or less or 2 PES or less.

  In order to reduce the change step amount of the target radius position, the measurement point (disk rotational speed) read from the start to the end of the measurement is increased. For example, if the target radius position is changed by one cycle during one and a half revolutions of the disk, the change step amount of the target radius position (read element position) is larger than the method of changing the disk radial position for one cycle with one disk revolution. Can be small.

  From the viewpoint of measurement reliability, measurement time reduction, and positioning of the head slider 12 during following, as shown in the example of FIG. 3, the HDC / MPU 23 sets the target radial position at one rotation of the magnetic disk 11. It is preferable to change the vibration by one cycle. From the point of control simplicity, the HDC / MPU 23 changes the target radius position starting from the center of the target range. After swinging in and out, the target radius position returns to the same value as the initial position.

  In a preferred configuration, the HDC / MPU 23 has a function of designating a target radius position for each servo sector. Thereby, accurate position control of the read element 121 can be performed. The HDC / MPU 23 may be configured so that the target radius position can be specified only once in a plurality of sectors, as long as necessary position control can be performed in reading the measurement data. In a sector in which the target radius position cannot be specified, for example, the previous value is used. Further, although it is preferable to measure the read amplitude of the measurement data between each servo sector, a configuration in which measurement is performed only once in a plurality of sectors may be employed.

  In the following while swinging the read element 121, the HDC / MPU 23 preferably turns off the function of handling a servo read error. In the measurement of the read / write offset, it is necessary to acquire actual data of both the read amplitude and the position signal. The servo error handling function ignores position signals that deviate from the specified conditions. Therefore, the HDC / MPU 23 turns off the servo error handling function before starting the following after the seek is completed.

  With reference to the timing chart of FIG. 5 and the block diagram of FIG. 6, timing control in read processing of read / write offset measurement data will be described. FIG. 5 is an example of the timing chart, and FIG. 6 is a block diagram schematically showing components related to the measurement data reading process and signals and data therebetween.

  The servo gate signal is a signal for controlling the read timing of the servo sector. While the servo gate signal is HIGH (while the servo gate is open), the RW channel 21 and the HDC / MPU 23 process a servo data read signal from the read element 121. The read gate signal is a signal for controlling the reading timing of the measurement data. While the read gate signal is HIGH (while the read gate is open), the RW channel 21 and the HDC / MPU 23 process the measurement data read signal from the read element 121.

  The HDC / MPU 23 controls the read gate signal based on the servo gate signal. For example, the HDC / MPU 23 sets the read gate signal to HIGH after a specified time has elapsed since the trailing edge of the servo gate signal of the immediately preceding servo sector. In addition, the read gate signal is set to LOW after the specified time has elapsed. The HDC / MPU 23 sets the servo gate signal to HIGH after a specified time has elapsed from the trailing edge of the previous servo gate signal.

  The HDC / MPU 23 cannot read the measurement data during seeking. After the seek to the initial target radius position is completed, the HDC / MPU 23 reads the measurement data by controlling the read gate signal under the following control. Specifically, when the seek to the initial target position is completed, the HDC / MPU 23 starts following.

  After a predetermined time (predetermined number of servo sectors) has elapsed from the completion of the seek, the HDC / MPU 23 sets the read gate signal to HIGH and starts reading data for read / write offset measurement. The HDC / MPU 23 may start reading measurement data from a servo sector having a predetermined servo sector number (for example, number 0) after completion of seeking.

  When the HDC / MPU 23 starts the measurement data reading process, the HDC / MPU 23 acquires the position signal of each servo sector and the reading amplitude value (VGA value in this example) of the measurement data between the servo sectors from the RW channel 21. It is stored in the memory area of the RAM 24. The HDC / MPU 23 only needs to acquire one VGA value between servo sectors. The HDC / MPU 23 designates a target radius position for each servo sector.

  In this example, the target radius position shows a change of one cycle in one rotation of the magnetic disk. Accordingly, the change step amount of the target radius position is a value obtained by dividing the target change range (width) by the number of servo sectors in one track. The fraction is rounded down, for example. In the example of FIG. 5, the target radius position changes for each servo sector, and the change amount is also constant. In actual processing, the amount of change in the target radius position in each servo sector is determined by the width and the number of sectors, so it is not always constant, and the amount of change may be zero depending on the servo sector.

  With the above measurement, the HDC / MPU 23 determines the position signal values of all servo sectors in one rotation of the disk and the VGA values (read amplitude values) of measurement data for all sectors (meaning areas between servo sectors). Equivalent). The HDC / MPU 23 applies an approximate expression to the acquired value and calculates the center position of the measurement data. FIG. 7 is a diagram schematically showing measurement data indicating the relationship between the VGA value and the position signal value and an approximate function fitted to the measurement data. The relationship between the VGA value and the position signal value can be approximated by a quadratic function.

  The HDC / MPU 23 calculates a position signal value indicating the minimum value of the fitted approximation function, and determines that the disk radial position indicated by the position signal value is the center position of the measurement data (write element 122). For calculating the radius position of the VGA minimum value (maximum amplitude value), it is preferable to use an approximate function, but the radius position of the VGA minimum value may be determined by other methods. In fitting approximate functions, it is preferable to use a widely known statistical method such as deleting unnecessary data or calculating an average value.

  In order to make the VGA measurement in the read / write offset measurement more accurate, it is preferable to change the position of the read element 121 in a narrow range in the vicinity of the radial position indicating the VGA minimum value. However, it is necessary to avoid that the radial position indicating the VGA minimum value is not included in the target position range by reducing the swing width of the read element position. In a preferred configuration, the HDC / MPU 23 performs a multi-stage search for the VGA minimum position (light element center position).

  The HDC / MPU 23 performs measurement in a wide search range (target radius position range), and determines (estimates) the radial position of the VGA minimum value from the measurement result. Next, the HDC / MPU 23 performs VGA measurement in a narrower search range including the estimated radius position, and determines the radius position of the VGA minimum value from the measurement result. Thus, by performing rough search and fine search, more accurate search can be performed in a short measurement time. Further, the VGA minimum radius position can be specified more accurately by repeatedly performing VGA measurement while narrowing the search range.

  A two-stage VGA measurement method will be described with reference to the flowchart of FIG. The HDC / MPU 23 moves the read element 121 to the target radius position of the first measurement (seek) (S11). The target radius position can be calculated from the read element position in writing the measurement data and an approximate expression set in advance. The HDC / MPU 23 starts following at the target radius position.

  The HDC / MPU 23 measures the VGA and the position signal (disk radial position) while performing the following while changing the target radial position (S12). The search range at this time (the touch width of the target radius position) is a wide search range, and is preferably larger than the width of the measurement data.

  The HDC / MPU 23 determines a position signal value (disk radius position) indicating the VGA minimum value from the obtained measurement result (S13). Preferably, the HDC / MPU 23 uses an approximate function to determine the VGA minimum value and the position signal position corresponding thereto. The data used for this determination is data obtained by excluding data determined as noise from the measurement data.

  The HDC / MPU 23 determines a search range for the next measurement (S14). The HDC / MPU 23 preferably determines the center of the search range from the measurement result of the rough search. VGA measurement in a fine search can be performed more appropriately than using the same center position. Preferably, the center position is a position signal value indicating a VGA minimum value, and this configuration will be described below. The width of the search range may be calculated from a predetermined value (a preset value), or from the determined VGA minimum value or its position signal value. The width of the search range (change width of the target radius position) is a value smaller than the width of the search range in the previous VGA measurement.

  The HDC / MPU 23 moves the read element 121 (head slider 12) using the disk radius position of the minimum VGA value determined in the previous VGA measurement as the target position (seek) (S15). After the seek is completed, the HDC / MPU 23 measures the VGA and the position signal (disk radius position) while performing the following while changing the target radius position (S16). As described above, the read element movement range at this time is narrower than the previous measurement. The HDC / MPU 23 determines a position signal value (disk radius position) indicating the VGA minimum value from the obtained measurement result (S17). The HDC / MPU 23 calculates a read / write offset from the position signal and the read element position in the measurement data writing (S18).

  As described above, when the VGA measurement is performed a plurality of times while reducing the search range, the target radius position is preferably returned to the initial position after the measurement as described with reference to FIG. 3 in one VGA measurement. . Thereby, the transition to the next VGA measurement can be performed smoothly. Depending on the design, the search range in different VGA measurements may always be the same. However, as described above, more accurate VGA measurement can be performed by determining the search range from the radial position indicating the VGA minimum value obtained by the previous measurement. This is particularly useful when making many VGA measurements (more than two measurements).

  Next, a more specific example of the two-stage VGA measurement will be described. The flowchart of FIG. 9 shows the flow of this processing, and FIG. 10 explains the measurement result obtained by the first VGA measurement and the method for determining the target radius position range (search range) in the next measurement from the measurement result. It is a figure to do. As shown in FIG. 9, the HDC / MPU 23 moves the read element 121 to the target radius position for the first measurement (seek) (S31). The seek target is the center position of the measurement data.

  The HDC / MPU 23 measures the VGA and the read element radial position while swinging the read element 121 (S32). In this example, the distance between servo tracks is 256 PES, and the swing width is ± 120 PES. The HDC / MPU 23 divides the VGA measurement values into a plurality of groups every 4 PESs, and deletes groups in which σ exceeds 10 (S33). The HDC / MPU 23 searches for the minimum VGA value from the measurement data from which unnecessary data has been removed (S34).

  The HDC / MPU 23 takes the average value of VGA and PES in each group in the data grouped for each 4 PES. Further, data of the minimum value + 60% is collected when the difference between the maximum value and the minimum value of the average VGA in each group where σ is 10 or less is 100% (S35). FIG. 10 shows the measurement data by the rough search and the 60% range. The HDC / MPU 23 calculates the amplitude of the target radius position in the next VGA measurement from the collected data (S36). The HDC / MPU 23 performs quadratic function fitting (X is the radial position and Y is the VGA) on the collected data to obtain a VGA profile (S37). The HDC / MPU 23 calculates the derivative of the fitted quadratic function and calculates a position signal value indicating the VGA minimum value (S38). Thus, the first rough search is completed.

  Next, the HDC / MPU 23 starts a fine search. The HDC / MPU 23 moves the read element 121 to the radius position of the VGA minimum value calculated in step S38 (seek) (S39). The HDC / MPU 23 measures the VGA and the read element radial position while swinging the read element 121 (S40). The swing width is the value calculated in step S36. The HDC / MPU 23 divides the VGA measurement values into a plurality of groups every 4 PESs, and deletes groups in which σ exceeds 10 (S41). The HDC / MPU 23 searches for the minimum VGA value from the measurement data from which unnecessary data is removed (S42).

  The HDC / MPU 23 collects data of the minimum value + 60% when the difference between the maximum value and the minimum value of the average VGA in each group where σ is 10 or less is 100% (S43). The HDC / MPU 23 performs quadratic function fitting (X is the radial position and Y is the VGA) on the collected data to obtain a VGA profile (S44). The HDC / MPU 23 calculates the differential of the fitted quadratic function to calculate a position signal value indicating the VGA minimum value (S45). The HDC / MPU 23 calculates a read / write offset value from the calculated position signal and the radial position of the read element 121 in writing the measurement data. The second VGA measurement is the same as the process excluding step S36 in the first measurement. When performing VGA measurement three times or more, the amplitude of the next measurement is also calculated in the second measurement. Only in the last VGA measurement this step is omitted.

  As mentioned above, although this invention was demonstrated taking preferable embodiment as an example, this invention is not limited to said embodiment. A person skilled in the art can easily change, add, and convert each element of the above-described embodiment within the scope of the present invention. The present invention is not limited to the HDD, but can be applied to other types of disk drives. As long as the center position of the measurement data can be determined, a value different from the measurement amplitude may be used.

DESCRIPTION OF SYMBOLS 1 Hard disk drive, 10 Enclosure, 11 Magnetic disk 12 Head slider, 14 Spindle motor, 15 Voice coil motor 16 Actuator, 17 Lamp, 20 Circuit board 21 Read / write channel, 22 Motor driver unit 120 Head element part, 121 Read element, 122 Write element

Claims (14)

A method for measuring a read / write offset between a read element and a write element,
Write measurement data with the light element,
In order to read the measurement data by the read element, a seek process is performed to move the read element to a target radial position,
After the seek process is completed, the follow process by the read element is started,
While changing the target radius position of the read element, performing the following process of the read element that passes on the measurement data track,
In the following processing, the measurement data is read and the servo data is read,
Using the measurement data and the data obtained by the reading of the servo data, the read / write offset is determined.
Read / write offset measurement method. Before the following process, a rough search process of the center position of the measurement data is performed,
The rough search process is
While changing the target radius position in a change width larger than the change width of the target radius position in the following processing, performing the following processing of the read element that passes over the measurement data,
In the following process in the rough search process, the measurement data is read and the servo data is read,
The center position of the measurement data is determined by the data obtained by the reading of the measurement data and the servo data in the rough search process,
According to the measurement result of the rough search process, a change range of the target radius position in the following after the rough search process is determined.
The read / write offset measuring method according to claim 1. The target position in the seek process is the center position determined in the rough search process.
The read / write offset measuring method according to claim 2. The target radius position at the start of the following process is the same as the target radius position at the end of the following process.
The read / write offset measuring method according to claim 2. Before starting the following process, turn off the error handling function.
The read / write offset measuring method according to claim 1. In the following process, the target radius position is oscillating in the disk radial direction.
The read / write offset measuring method according to claim 1. The target radius position at the start of the following process is the same as the target radius position at the end of the following process,
The following is completed with one rotation of the disc.
The read / write offset measuring method according to claim 1. A disk drive for measuring a read / write offset between a read element and a write element,
A disc,
A write element for writing measurement data to the disk;
A read element for reading the measurement data and servo data;
In a seek process, in order to read the measurement data by the read element, a moving mechanism that moves the read element to a target radial position;
After the seek process is completed, the following process of the read element passing over the measurement data is performed while changing the target radial position of the read element, and the measurement data and servo data in the following process are Using the data obtained by reading by the read element, to determine the read / write offset,
A controller,
Disk drive with. The controller performs a rough search process of the center position of the measurement data before the following process,
The rough search process is
While changing the target radius position in a change width larger than the change width of the target radius position in the following processing, performing the following processing of the read element that passes over the measurement data,
In the following process in the rough search process, the measurement data is read and the servo data is read,
The center position of the measurement data is determined by the data obtained by the reading of the measurement data and the servo data in the rough search process,
According to the measurement result of the rough search process, a change range of the target radius position in the following after the rough search process is determined.
The disk drive according to claim 8. The target position in the seek process is the center position determined in the rough search process.
The disk drive of claim 9. The target radius position at the start of the following process is the same as the target radius position at the end of the following process.
The disk drive of claim 9. The controller turns off the error handling function before starting the following process.
The disk drive according to claim 8. In the following process, the target radius position is oscillating in the disk radial direction.
The disk drive according to claim 8. The target radius position at the start of the following process is the same as the target radius position at the end of the following process,
The following is completed with one rotation of the disc.
The disk drive according to claim 8.

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